Circadian Rhythms in Cardiovascular Metabolism

Energetic demand and nutrient supply fluctuate as a function of time-of-day, in alignment with sleep-wake and fasting-feeding cycles. These daily rhythms are mirrored by 24-hour oscillations in numerous cardiovascular functional parameters, including blood pressure, heart rate, and myocardial contractility. It is, therefore, not surprising that metabolic processes also fluctuate over the course of the day, to ensure temporal needs for ATP, building blocks, and metabolism-based signaling molecules are met. What has become increasingly clear is that in addition to classic signal-response coupling (termed reactionary mechanisms), cardiovascular-relevant cells use autonomous circadian clocks to temporally orchestrate metabolic pathways in preparation for predicted stimuli/stresses (termed anticipatory mechanisms). Here, we review current knowledge regarding circadian regulation of metabolism, how metabolic rhythms are synchronized with cardiovascular function, and whether circadian misalignment/disruption of metabolic processes contribute toward the pathogenesis of cardiovascular disease.

Sustained Increases in Cardiomyocyte Protein O-Linked β-N-Acetylglucosamine Levels Lead to Cardiac Hypertrophy and Reduced Mitochondrial Function Without Systolic Contractile Impairment

Background Lifestyle and metabolic diseases influence the severity and pathogenesis of cardiovascular disease through numerous mechanisms, including regulation via posttranslational modifications. A specific posttranslational modification, the addition of O-linked β-N acetylglucosamine (O-GlcNAcylation), has been implicated in molecular mechanisms of both physiological and pathologic adaptations. The current study aimed to test the hypothesis that in cardiomyocytes, sustained protein O-GlcNAcylation contributes to cardiac adaptations, and its progression to pathophysiology. Methods and Results Using a naturally occurring dominant-negative O-GlcNAcase (dnOGA) inducible cardiomyocyte-specific overexpression transgenic mouse model, we induced dnOGA in 8- to 10-week-old mouse hearts. We examined the effects of 2-week and 24-week dnOGA overexpression, which progressed to a 1.8-fold increase in protein O-GlcNAcylation. Two-week increases in protein O-GlcNAc levels did not alter heart weight or function; however, 24-week increases in protein O-GlcNAcylation led to cardiac hypertrophy, mitochondrial dysfunction, fibrosis, and diastolic dysfunction. Interestingly, systolic function was maintained in 24-week dnOGA overexpression, despite several changes in gene expression associated with cardiovascular disease. Specifically, mRNA-sequencing analysis revealed several gene signatures, including reduction of mitochondrial oxidative phosphorylation, fatty acid, and glucose metabolism pathways, and antioxidant response pathways after 24-week dnOGA overexpression. Conclusions This study indicates that moderate increases in cardiomyocyte protein O-GlcNAcylation leads to a differential response with an initial reduction of metabolic pathways (2-week), which leads to cardiac remodeling (24-week). Moreover, the mouse model showed evidence of diastolic dysfunction consistent with a heart failure with preserved ejection fraction. These findings provide insight into the adaptive versus maladaptive responses to increased O-GlcNAcylation in heart.

Cardiac fibroblast GSK-3α aggravates ischemic cardiac injury by promoting fibrosis, inflammation, and impairing angiogenesis

Myocardial infarction (MI) is the leading cause of death worldwide. Glycogen synthase kinase-3 (GSK-3) has been considered to be a promising therapeutic target for cardiovascular diseases. GSK-3 is a family of ubiquitously expressed serine/threonine kinases. GSK-3 isoforms appear to play overlapping, unique, and even opposing functions in the heart. Previously, our group identified that cardiac fibroblast (FB) GSK-3β acts as a negative regulator of fibrotic remodeling in the ischemic heart. However, the role of FB-GSK-3α in MI pathology is not defined. To determine the role of FB-GSK-3α in MI-induced adverse cardiac remodeling, GSK-3α was deleted specifically in the residential fibroblast or myofibroblast (MyoFB) using tamoxifen (TAM) inducible Tcf21 or Periostin (Postn) promoter-driven Cre recombinase, respectively. Echocardiographic analysis revealed that FB- or MyoFB-specific GSK-3α deletion prevented the development of dilative remodeling and cardiac dysfunction. Morphometrics and histology studies confirmed improvement in capillary density and a remarkable reduction in hypertrophy and fibrosis in the KO group. We harvested the hearts at 4 weeks post-MI and analyzed signature genes of adverse remodeling. Specifically, qPCR analysis was performed to examine the gene panels of inflammation (TNFα, IL-6, IL-1β), fibrosis (COL1A1, COL3A1, COMP, Fibronectin-1, Latent TGF-β binding protein 2), and hypertrophy (ANP, BNP, MYH7). These molecular markers were essentially normalized due to FB-specific GSK-3α deletion. Further molecular studies confirmed that FB-GSK-3α could regulate NF-kB activation and expression of angiogenesis-related proteins. Our findings suggest that FB-GSK-3α plays a critical role in the pathological cardiac remodeling of ischemic hearts, therefore, it could be therapeutically targeted.

GSK-3 at the heart of cardiometabolic diseases: Isoform-specific targeting is critical to therapeutic benefit

Glycogen synthase kinase-3 (GSK-3) is a family of serine/threonine kinases. The GSK-3 family has 2 isoforms, GSK-3α and GSK-3β. The GSK-3 isoforms have been shown to play overlapping as well as isoform-specific-unique roles in both, organ homeostasis and the pathogenesis of multiple diseases. In the present review, we will particularly focus on expanding the isoform-specific role of GSK-3 in the pathophysiology of cardiometabolic disorders. We will highlight recent data from our lab that demonstrated the critical role of cardiac fibroblast (CF) GSK-3α in promoting injury-induced myofibroblast transformation, adverse fibrotic remodeling, and deterioration of cardiac function. We will also discuss studies that found the exact opposite role of CF-GSK-3β in cardiac fibrosis. We will review emerging studies with inducible cardiomyocyte (CM)-specific as well as global isoform-specific GSK-3 KOs that demonstrated inhibition of both GSK-3 isoforms provides benefits against obesity-associated cardiometabolic pathologies. The underlying molecular interactions and crosstalk among GSK-3 and other signaling pathways will be discussed. We will briefly review the specificity and limitations of the available small molecule inhibitors targeting GSK-3 and their potential applications to treat metabolic disorders. Finally, we will summarize these findings and offer our perspective on envisioning GSK-3 as a therapeutic target for the management of cardiometabolic diseases.

Ponatinib Drives Cardiotoxicity by S100A8/A9-NLRP3-IL-1β Mediated Inflammation

BACKGROUND

The tyrosine kinase inhibitor ponatinib is the only treatment option for chronic myelogenous leukemia patients with T315I (gatekeeper) mutation. Pharmacovigilance analysis of Food and Drug Administration and World Health Organization datasets has revealed that ponatinib is the most cardiotoxic agent among all Food and Drug Administration-approved tyrosine kinase inhibitors in a real-world scenario. However, the mechanism of ponatinib-induced cardiotoxicity is unknown.

METHODS

The lack of well-optimized mouse models has hampered the in vivo cardio-oncology studies. Here, we show that cardiovascular comorbidity mouse models evidence a robust cardiac pathological phenotype upon ponatinib treatment. A combination of multiple in vitro and in vivo models was employed to delineate the underlying molecular mechanisms.

RESULTS

An unbiased RNA sequencing analysis identified the enrichment of dysregulated inflammatory genes, including a multifold upregulation of alarmins S100A8/A9, as a top hit in ponatinib-treated hearts. Mechanistically, we demonstrate that ponatinib activates the S100A8/A9-TLR4 (Toll-like receptor 4)-NLRP3 (NLR family pyrin domain-containing 3)-IL (interleukin)-1β signaling pathway in cardiac and systemic myeloid cells, in vitro and in vivo, thereby leading to excessive myocardial and systemic inflammation. Excessive inflammation was central to the cardiac pathology because interventions with broad-spectrum immunosuppressive glucocorticoid dexamethasone or specific inhibitors of NLRP3 (CY-09) or S100A9 (paquinimod) nearly abolished the ponatinib-induced cardiac dysfunction.

CONCLUSIONS

Taken together, these findings uncover a novel mechanism of ponatinib-induced cardiac inflammation leading to cardiac dysfunction. From a translational perspective, our results provide critical preclinical data and rationale for a clinical investigation into immunosuppressive interventions for managing ponatinib-induced cardiotoxicity.

Metabolic labeling of cardiomyocyte-derived small extracellular-vesicle (sEV) miRNAs identifies miR-208a in cardiac regulation of lung gene expression

Toxoplasma gondii uracil phosphoribosyltransferase (UPRT) converts 4‐thiouracil (4TUc) into 4‐thiouridine (4TUd), which is incorporated into nascent RNAs and can be biotinylated, then labelled with streptavidin conjugates or isolated via streptavidin‐affinity methods. Here, we generated mice that expressed T. gondii UPRT only in cardiomyocytes (^CMUPRT mice) and tested our hypothesis that CM‐derived miRNAs (^CMmiRs) are transferred into remote organs after myocardial infarction (MI) by small extracellular vesicles (sEV) that are released from the heart into the peripheral blood (^PBsEV). We found that 4TUd was incorporated with high specificity and sensitivity into RNAs isolated from the hearts and ^PBsEV of ^CMUPRT mice 6 h after 4TUc injection. In ^PBsEV, 4TUd was incorporated into CM‐specific/enriched miRs including miR‐208a, but not into miRs with other organ or tissue‐type specificities. 4TUd‐labelled miR208a was also present in lung tissues, especially lung endothelial cells (ECs), and CM‐derived miR‐208a (^CMmiR‐208a) levels peaked 12 h after experimentally induced MI in ^PBsEV and 24 h after MI in the lung. Notably, miR‐208a is expressed from intron 29 of α myosin heavy chain (αMHC), but αMHC transcripts were nearly undetectable in the lung. When ^PBsEV from mice that underwent MI (MI‐^PBsEV) or sham surgery (Sham‐^PBsEV) were injected into intact mice, the expression of Tmbim6 and NLK, which are suppressed by miR‐208a and cooperatively regulate inflammation via the NF‐κB pathway, was lower in the lungs of MI‐^PBsEV–treated animals than the lungs of animals treated with Sham‐^PBsEV or saline. In MI mice, Tmbim6 and NLK were downregulated, whereas endothelial adhesion molecules and pro‐inflammatory cells were upregulated in the lung; these changes were significantly attenuated when the mice were treated with miR‐208a antagomirs prior to MI surgery. Thus, ^CMUPRT mice enables us to track ^PBsEV‐mediated transport of ^CMmiRs and identify an miR‐208a‐mediated mechanism by which myocardial injury alters the expression of genes and inflammatory response in the lung.

Fibroblast GSK-3α Promotes Fibrosis via RAF-MEK-ERK Pathway in the Injured Heart

BACKGROUND

Heart failure is the leading cause of mortality, morbidity, and health care expenditures worldwide. Numerous studies have implicated GSK-3 (glycogen synthase kinase-3) as a promising therapeutic target for cardiovascular diseases. GSK-3 isoforms seem to play overlapping, unique and even opposing functions in the heart. Previously, we have shown that of the 2 isoforms of GSK-3, cardiac fibroblast GSK-3β acts as a negative regulator of myocardial fibrosis in the ischemic heart. However, the role of cardiac fibroblast-GSK-3α in the pathogenesis of cardiac diseases is completely unknown.

METHODS

To define the role of cardiac fibroblast-GSK-3α in myocardial fibrosis and heart failure, GSK-3α was deleted from fibroblasts or myofibroblasts with tamoxifen-inducible Tcf21- or Postn-promoter-driven Cre recombinase. Control and GSK-3α KO mice were subjected to cardiac injury and heart parameters were evaluated. The fibroblast kinome mapping was carried out to delineate molecular mechanism followed by in vivo and in vitro analysis.

RESULTS

Fibroblast-specific GSK-3α deletion restricted fibrotic remodeling and preserved function of the injured heart. We observed reductions in cell migration, collagen gel contraction, α-SMA protein levels, and expression of ECM genes in TGFβ1-treated KO fibroblasts, indicating that GSK-3α is required for myofibroblast transformation. Surprisingly, GSK-3α deletion did not affect SMAD3 activation, suggesting the profibrotic role of GSK-3α is SMAD3 independent. The molecular studies confirmed decreased ERK signaling in GSK-3α-KO CFs. Conversely, adenovirus-mediated expression of a constitutively active form of GSK-3α (Ad-GSK-3αS21A) in fibroblasts increased ERK activation and expression of fibrogenic proteins. Importantly, this effect was abolished by ERK inhibition.

CONCLUSIONS

GSK-3α-mediated MEK-ERK activation is a critical profibrotic signaling circuit in the injured heart, which operates independently of the canonical TGF-β1-SMAD3 pathway. Therefore, strategies to inhibit the GSK-3α-MEK-ERK signaling circuit could prevent adverse fibrosis in diseased hearts.

Abstract EC106: Cardiac Fibroblast GSK-3α Aggravates Ischemic Cardiac Injury By Promoting Fibrosis, Inflammation, And Impairing Angiogenesis

Background: Myocardial Infarction (MI) is the leading cause of death worldwide. Numerous studies from our lab and others have implicated Glycogen Synthase Kinase-3 (GSK-3) as a promising therapeutic target for cardiovascular diseases. GSK-3 is a family of ubiquitously expressed serine/threonine kinases. GSK-3 isoforms appear to play overlapping, unique, and even opposing functions in the heart. Previously our group has identified that cardiac fibroblast (CF) GSK-3β acts as a negative regulator of fibrotic remodeling in the ischemic heart. However, the role of CF-GSK-3α in MI-induced adverse cardiac remodeling is not defined.

Methods and Results: To determine the role of CF-GSK-3α in MI-induced adverse cardiac remodeling, GSK-3α was deleted specifically in the activated fibroblast/myofibroblast using tamoxifen (TAM)-inducible Periostin promoter-driven Cre recombinase system. At 12 weeks of age, mice were fed with TAM diet. After 1 week of TAM treatment, control (GSK-3α fl/fl Cre -/- ) and KO (GSK-3α fl/fl Cre +/- ) mice were subjected to permanent LAD ligation (MI) surgery. Echocardiographic analysis revealed that control mice developed severe systolic dysfunction and dilative cardiac remodeling post-MI. These MI-induced pathologies were remarkably prevented by myofibroblast-specific GSK-3α deletion. To further confirm the role of CF-GSK-3α in processes contributing to cardiac remodeling, we harvested the hearts at 4 weeks post-MI and analyzed signature genes of adverse remodeling. Specifically, qPCR analysis was performed to examine the gene panels of inflammation (TNFα, IL-6, IL-1β), fibrosis (COL1A1, COL3A1, COMP), and angiogenesis (VEGFR2, CD31, HIF-1α). As expected, ischemic injury induced the expression of inflammation and fibrosis-related genes in the control group. In contrast, CF-GSK-3α KO hearts did not display any of these hallmarks. Another critical feature of adverse cardiac remodeling is impaired angiogenesis. Indeed, the CF-GSK-3α KO hearts were protected from MI-induced reduction in angiogenesis-related genes. Taken together, our findings support a driving role of CF-GSK-3α in MI-induced adverse cardiac remodeling.

Conclusion: Our findings suggest a critical role of CF-GSK-3α in pathological cardiac remodeling and heart failure that could be therapeutically targeted for future clinical applications.

Abstract P1018: Bone Marrow Progenitor Cell-Derived Exosomes Activate Cardiac Fibroblasts Via Mir-21a-5p Mediated Integrin Alpha V Stabilization

Abstract: Heart failure is leading cause of death worldwide, and cardiac fibrosis is the hallmark of heart failure. We previously showed that interleukin-10 (IL10) treatment significantly reduces pressure overload-induced cardiac fibrosis. We also have demonstrated that fibroblast progenitor cells (bone marrow-prominin positive cells; FPCs) play a prominent role in developing cardiac fibrosis, yet the mechanism is largely unknown. Here, we hypothesized that pro-fibrotic miRNAs enriched in exosomes derived from IL10 KO FPCs promote fibroblast activation and cardiac fibrosis in pressure-overloaded myocardium.

Methods: Exosomes were isolated from WT and IL-10KO FPCs. Exosomal miRNAs profiling was performed using fibrosis-associated miRNA profiler kit from Qiagen. To determine the contribution of exosomal miR21 on TAC-induced fibrosis, miR21 level was reduced in FPCs-derived exosomes using miR21 silencer. Modified exosomes were injected into heart immediately after TAC surgery.

Results: FPCs were identified as CD45+/prominin-1 cells using FACS. TGFβ treatment exacerbated fibrotic genes (Col1α, fibronectin, periostin, and αSMA) expression in IL10KO FPCs compared to WT-FPCs. Pathway-based miRNA array revealed that IL10KO FPCs exosomes are enriched with miR-21a-5p and facilitated fibroblasts activation as observed by qPCR (αSMA and Col1α), western (Col1α and TGFβ levels), wound healing, and immunostaining assay (Col1α/DAPI expression) as compared to WT control. Interestingly, miR21 inhibition in IL10KO FPCs exosome using antimiR 21, reduced TGFβ-induced cardiac fibroblast activation. Target prediction database analysis revealed that Integrin Subunit Alpha V (ITGAV) is a strong regulatory target for miRNA21. At molecular level, we found that exosomal miR-21a-5p stabilizes ITGAV, which ultimately enhances fibroblast activation and cardiac fibrosis both in vitro and in vivo.

Conclusions: In conclusion, we report that FPCs derived miR21 packaged in exosomes activates cardiac fibroblasts in IL10-KO mice via miR-21a-5p/ITGAV/Col1α signaling axis and increased cardiac fibrosis. IL10 treatment significantly reduced miR21 exosomal packaging, inhibited fibroblasts activation, and reduced cardiac fibrosis following TAC.

Abstract P3060: Circulating Gut Microbial Peptides Exacerbate Cardiac Dysfunction In IL10KO Mice Following Transaortic Constriction

Background: Heart failure is the leading cause of morbidity and mortality in the USA. Recently, impaired intestinal permeability is known to augment cardiac dysfunction. Though, the cardioprotective role of IL10 is well known, its role in reducing gut dysbiosis and maintaining intestinal permeability during hypertrophic heart failure is not known. We hypothesized that IL10 maintains intestinal permeability and inhibits the release of gut microbial peptides (GMPs) which ultimately improves cardiac function.

Methods: WT & IL10KO mice were subjected to TAC or sham surgery. Heart and intestine were collected to evaluate inflammation genes expression, immune cell infiltration (flow cytometry), and intestinal permeability (WB and immunohistochemistry). Blood was collected to quantify peptidoglycan (PGN) and other bacterial metabolites (TMAO) levels. The effect of PGN on mitochondrial functions was evaluated in neonatal cardiomyocytes.

Results: Cardiac functions were significantly reduced in IL10KO mice following TAC. IL10 KO mice showed exacerbated inflammation (IL1β, IL6 and TNFα genes expression) following TAC. TAC induced leukocytes (monocyte/macrophage, T-cell and neutrophils) recruitments in the intestine in IL10KO mice. TAC mice showed gut dysbiosis (16S rRNA sequencing) in IL10KO mice. Further, IL10KO mice exhibited higher intestinal permeability as shown by increase in PV1 level and reduction in zonulin-1 (ZO-1) protein. Plasma PGN level was significantly increased in IL10KO mice following TAC. Pathway-based cardiotoxicity array showed a significant increase in uncoupler protein 2 (UCP2) and phospholamban (PLN; a calcium handling protein) genes expression in cardiomyocytes following PGN treatment. Finally, IL10 treatment restores PGN-induced decrease in mitochondrial membrane potential (TMRE assay) in cardiomyocytes.

Conclusion: Taken together, data suggest that IL-10 helps to maintain gut wall permeability and reduced gut microbial peptide circulation to the heart and thus improves cardiac function by improving mitochondrial function. Ongoing investigations using molecular approaches will provide a better understanding of gut-heart signaling and its impact on the progress of heart failure.

Abstract GS109: Ponatinib-induced Cardiotoxicity Is Driven By S100A8/A9-NLRP3-IL1β Signaling Mediated Excessive Inflammation

Background: The tyrosine kinase inhibitor (TKI) ponatinib is the oral drug for the treatment of chronic myelogenous leukemia (CML) patients with T315I (gatekeeper) mutation. Pharmacovigilance analysis of FDA and WHO datasets have revealed that ponatinib is the most cardiotoxic agent among all FDA-approved TKIs in a real-world scenario. However, the mechanism of ponatinib-induced cardiotoxicity is unknown. The cardiotoxic effects of ponatinib remained hidden in preclinical studies and were only revealed in phase 2 clinical studies and by the subsequent meta-analysis. The lack of well-optimized mouse models has hampered the in vivo cardio-oncology studies. To this end, here we aimed to investigate the hidden cardiotoxic mechanism of ponatinib and strategies to prevent the cardiotoxic manifestations.

Methods: We employed wild-type C57BL/6, cardiovascular (CV) comorbidity models e.g., transverse aortic constriction (TAC)-pressure overload (cardiac comorbidity) and high-fat diet-fed ApoE -/- (vascular comorbidity), to investigate the cardiotoxic mechanism of ponatinib. Echocardiography was performed to assess cardiac function. Comprehensive immune profiling was performed to identify ponatinib-induced immune activation using flow cytometry analysis and cytokine assay.

Results: Echocardiographic assessment of ponatinib treated high-fat diet-fed ApoE -/- and pressure overload (PO) murine model showed a significant decline in cardiac function, suggesting the key role of CV-comorbidities in ponatinib-induced cardiomyopathy. A combination of multiple in vitro and in vivo models was employed to delineate the underlying molecular mechanisms. An unbiased RNA-Seq analysis identified the enrichment of dysregulated inflammatory genes, including a multi-fold upregulation of alarmins S100A8/A9 as a top hit in ponatinib-treated hearts. Mechanistically, we demonstrate that ponatinib activates the S100A8/9-TLR4-NLRP3-IL-1β signaling pathway in cardiac and systemic myeloid cells (monocytes and neutrophils), in vitro and in vivo , thereby leading to excessive myocardial and systemic inflammation. Excessive inflammation was central to the cardiac pathology because interventions with broad-spectrum immunosuppressive glucocorticoid dexamethasone or direct NLRP3 inhibitor Cy-09 nearly abolished the ponatinib-induced cardiac dysfunction. Taken together, these findings uncover a novel mechanism of ponatinib-induced cardiac inflammation leading to cardiac dysfunction.

Conclusions: These findings uncover a novel mechanism of ponatinib-induced cardiac inflammation leading to cardiac dysfunction. Our results provide critical preclinical data and rationale for a clinical investigation into immunosuppressive interventions to mitigate ponatinib-induced cardiotoxicity.

Abstract P2077: Caspase8ap2 M6a Mrna Methylation Enhances Cardiomyocyte Apoptosis Following Myocardial Ischemia

Objective: Heart failure is the leading cause of morbidity and mortality in the United States. Cardiomyocyte death is one of the critical mediators of cardiac dysfunction following ischemic injury. However, the role of posttranscriptional regulation on cell-death-associated genes is not well explored during ischemic heart failure. N6-methyladenosine (m6A) is the most abundant and conserved chemical modification found in eukaryotic mRNA and is associated with mRNA synthesis and metabolism. We have recently shown that m6A RNA methylation regulates the angiogenic potential of endothelial cells following ischemic injury. However, the role of m6A mRNA methylation in cardiac cell death following ischemic injury is not well defined.

Methods: Cardiac function (using echocardiography) was measured at baseline and four weeks post-MI in mice. In the end, mice were euthanized, and hearts were excised for biochemical and histological analysis. Cardiac cell death was assessed in H9C2 cells and cardiomyocytes using FACs (Annexin V and PI) and TUNNEL assay. The Casp8AP2 stability were measured using actinomycin D assay. To demonstrate the molecular mechanism, METTL3 was inhibited using siRNA or shRNA.

Results: The cardiac function was significantly reduced following MI. Enhanced m6A mRNA methylation was observed in mice hearts following MI. Histological (TUNEL assay) and biochemical (WB: Caspase 8, cleaved cas8, caspase3, cleaved caspase3, Casp8AP2) analysis showed increased myocytes apoptosis in mice following MI. At the molecular level, hypoxic stress (nutrient depiviation+1%O2) induces global m6A mRNA methylation, which leads to Cas8AP2 gene stability and activation of extrinsic apoptotic pathways in cardiomyocytes in vitro. In contrast, METTL3 inhibition significantly reduced Cas8AP2 mRNA methylation, enhanced its degradation, and ultimately reduced cardiomyocyte cell death.

Conclusion: In conclusion, we have shown that increased Casp8AP2 m6A RNA methylation enhances its stability and activates caspase-3 cleavage, which eventually leads to cardiomyocyte death following myocardial ischemia. The reduction of the RNA methylation through METTL3 inhibition (methyltransferase) reduced hypoxia-induced apoptosis of cardiomyocytes.

Isoform-Specific Role of GSK-3 in High Fat Diet Induced Obesity and Glucose Intolerance

Obesity-associated metabolic disorders are rising to pandemic proportions; hence, there is an urgent need to identify underlying molecular mechanisms. Glycogen synthase kinase-3 (GSK-3) signaling is highly implicated in metabolic diseases. Furthermore, GSK-3 expression and activity are increased in Type 2 diabetes patients. However, the isoform-specific role of GSK-3 in obesity and glucose intolerance is unclear. Pharmacological GSK-3 inhibitors are not isoform-specific, and tissue-specific genetic models are of limited value to predict the clinical outcome of systemic inhibiion. To overcome these limitations, we created novel mouse models of ROSA26CreERT2-driven, tamoxifen-inducible conditional deletion of GSK-3 that allowed us to delete the gene globally in an isoform-specific and temporal manner. Isoform-specific GSK-3 KOs and littermate controls were subjected to a 16-week high-fat diet (HFD) protocol. On an HFD, GSK-3α KO mice had a significantly lower body weight and modest improvement in glucose tolerance compared to their littermate controls. In contrast, GSK-3β-deletion-mediated improved glucose tolerance was evident much earlier in the timeline and extended up to 12 weeks post-HFD. However, this protective effect weakened after chronic HFD (16 weeks) when GSK-3β KO mice had a significantly higher body weight compared to controls. Importantly, GSK-3β KO mice on a control diet maintained significant improvement in glucose tolerance even after 16 weeks. In summary, our novel mouse models allowed us to delineate the isoform-specific role of GSK-3 in obesity and glucose tolerance. From a translational perspective, our findings underscore the importance of maintaining a healthy weight in patients receiving lithium therapy, which is thought to work by GSK-3 inhibition mechanisms.

Novel Mechanisms of Exosome-Mediated Phagocytosis of Dead Cells in Injured Heart

[Figure: see text].

Mechanisms of Fibroblast Activation and Myocardial Fibrosis: Lessons Learned from FB-Specific Conditional Mouse Models

Heart failure (HF) is a leading cause of morbidity and mortality across the world. Cardiac fibrosis is associated with HF progression. Fibrosis is characterized by the excessive accumulation of extracellular matrix components. This is a physiological response to tissue injury. However, uncontrolled fibrosis leads to adverse cardiac remodeling and contributes significantly to cardiac dysfunction. Fibroblasts (FBs) are the primary drivers of myocardial fibrosis. However, until recently, FBs were thought to play a secondary role in cardiac pathophysiology. This review article will present the evolving story of fibroblast biology and fibrosis in cardiac diseases, emphasizing their recent shift from a supporting to a leading role in our understanding of the pathogenesis of cardiac diseases. Indeed, this story only became possible because of the emergence of FB-specific mouse models. This study includes an update on the advancements in the generation of FB-specific mouse models. Regarding the underlying mechanisms of myocardial fibrosis, we will focus on the pathways that have been validated using FB-specific, in vivo mouse models. These pathways include the TGF-β/SMAD3, p38 MAPK, Wnt/β-Catenin, G-protein-coupled receptor kinase (GRK), and Hippo signaling. A better understanding of the mechanisms underlying fibroblast activation and fibrosis may provide a novel therapeutic target for the management of adverse fibrotic remodeling in the diseased heart.

Abstract P317: Cardiac Fibroblast GSK3α Promotes Myocardial Fibrotic Remodeling Through GSK3α-ERK-IL11 Signaling Circuit

Background: Myocardial fibrosis contributes significantly to heart failure (HF). Fibroblasts are among the predominant cell type in the heart and are primary drivers of fibrosis. To identify the kinases involved in fibrosis, we analyzed the kinome of mouse cardiac fibroblasts (CF) isolated from normal and failing hearts. This unbiased screening revealed the critical role of the GSK-3 family-centric pathways in fibrosis. Previously we have shown that among two isoforms of GSK3, CF-GSK3β acts as a negative regulator of fibrosis in the injured heart. However, the role of CF-GSK3α in the pathogenesis of cardiac diseases is completely unknown.

Methods and Results: To define the role of CF-GSK3α in HF, we employed two novel fibroblast-specific KO mouse models. Specifically, GSK3α was deleted from fibroblasts or myofibroblasts with tamoxifen-inducible Tcf21- or periostin- promoter-driven Cre recombinase. In both models, GSK3α deletion restricted pressure overload-induced cardiac fibrosis and preserved cardiac function. We examined the effect of GSK3α deletion on myofibroblast transformation and pro-fibrotic TGFβ1-SMAD3 signaling in vitro . A significant reduction in cell migration, collagen gel contraction, and α-SMA expression in TGFβ1-treated KO CFs confirmed that GSK3α is required for myofibroblast transformation. Surprisingly, GSK3α deletion did not affect SMAD3 activation, indicating the pro-fibrotic role of GSK3α is SMAD3 independent. To further delineate the underlying mechanisms, proteins were isolated from CFs of WT and KO mice at 4 weeks post-injury, and kinome profiling was performed. The kinome analysis identified the downregulation of RAF family kinase activity in KO CFs. Moreover, mapping of significantly altered kinases against literature annotated interactions generated ERK-centric networks. Consistently, flow cytometric analysis of CFs confirmed significantly low levels of pERK in KO mice. Additionally, our in vitro studies demonstrated that GSK3α deletion prevents TGFβ1-induced ERK activation. Interestingly, IL-11, a pro-fibrotic downstream effector of TGFβ1, was remarkably reduced in KO CFs and ERK inhibition further decreased IL-11 expression. Taken together, herein, we discovered the GSK3α-ERK-IL-11 signaling as a critical pro-fibrotic pathway in the heart. Strategies to inhibit this pro-fibrotic network could prevent adverse fibrosis and HF.

Conclusion: CF-GSK3α plays a causal role in myocardial fibrosis that could be therapeutically targeted for future clinical applications.

Abstract 117: Ponatinib Mediated Cardiotoxicity Is Driven By Pro-inflammatory S100A8/A9-NLRP3-IL-1β Signaling Circuit

Background: Ponatinib is a third-generation tyrosine kinase inhibitor (TKI) for chronic myelogenous leukemia (CML) treatment. Of note, ponatinib is the only treatment option for CML patients with T315I (gatekeeper) mutation. Unexpected clinical cardiotoxicity, including fatal myocardial infarction and congestive heart failure, has hampered its clinical use. Herein, we aimed to investigate the cardiotoxic mechanism of ponatinib and strategies to prevent the cardiotoxic manifestations.

Methods: We employed wild-type C57BL/6, cardiovascular (CV) comorbidity models e.g., transverse aortic constriction (TAC)-pressure overload (cardiac comorbidity) and high-fat diet fed ApoE -/- (vascular comorbidity), to investigate the cardiotoxic mechanism of ponatinib. Echocardiography was performed to assess cardiac function. Comprehensive immune profiling was performed to identify ponatinib-induced immune dynamics using flow cytometry analysis.

Results: Echocardiographic assessment of ponatinib treated high-fat diet fed ApoE -/- and pressure overload (PO) murine model showed significant decline in cardiac function, suggesting the key role of CV-comorbidities in ponatinib-induced cardiomyopathy. An unbiased RNA-Seq analysis identified the enrichment of dysregulated inflammatory genes, including a multi-fold upregulation of alarmins S100A8/A9 as a top hit in ponatinib-treated hearts. A combination of in vitro and in vivo mechanistic analysis, identified that ponatinib activates the S100A8/9-TLR4-NLRP3-IL-1β signaling pathway in cardiac and systemic myeloid cells (monocytes and neutrophils), thereby leading to excessive myocardial and systemic inflammation. Finally, we demonstrate that ponatinib-induced excessive inflammation is central to the cardiac pathology because a broad immunosuppressive agent dexamethasone abolished the adverse cardiac remodeling and dysfunction of ponatinib treated hearts.

Conclusions: These findings uncover a novel mechanism of ponatinib-induced cardiac inflammation leading to cardiac dysfunction. Our results provide critical preclinical data and rationale for clinical investigation into immunosuppressive interventions to mitigate ponatinib-induced cardiotoxicity.

Cardiac natriuretic peptide deficiency sensitizes the heart to stress induced ventricular arrhythmias via impaired CREB signaling

AIMS

The cardiac natriuretic peptides (atrial natriuretic peptide [ANP] and B-type natriuretic peptide [BNP]) are important regulators of cardiovascular physiology, with reduced natriuretic peptide (NP) activity linked to multiple human cardiovascular diseases. We hypothesized that deficiency of either ANP or BNP would lead to similar changes in left ventricular structure and function given their shared receptor affinities.

METHODS AND RESULTS

We directly compared murine models deficient of ANP or BNP in the same genetic backgrounds (C57BL6/J) and environments. We evaluated control, ANP deficient (Nppa-/-) or BNP deficient (Nppb-/-) mice under unstressed conditions and multiple forms of pathological myocardial stress. Survival, myocardial structure, function and electrophysiology, tissue histology, and biochemical analyses were evaluated in the groups. In vitro validation of our findings was performed using human derived induced pluripotent stem cell cardiomyocytes (iPS-CM). In the unstressed state, both ANP and BNP deficient mice displayed mild ventricular hypertrophy which did not increase up to 1 year of life. NP-deficient mice exposed to acute myocardial stress secondary to thoracic aortic constriction (TAC) had similar pathological myocardial remodeling but a significant increase in sudden death. We discovered that the NP-deficient mice are more susceptible to stress induced ventricular arrhythmias using both in vivo and ex vivo models. Mechanistically, deficiency of either ANP or BNP led to reduced myocardial cGMP levels and reduced phosphorylation of the cAMP response element-binding protein (CREBS133) transcriptional regulator. Selective CREB inhibition sensitized wild type hearts to stress induced ventricular arrhythmias. ANP and BNP regulate cardiomyocyte CREBS133 phosphorylation through a cGMP-dependent protein kinase 1 (PKG1) and p38 mitogen activated protein kinase (p38 MAPK) signaling cascade.

CONCLUSIONS

Our data show that ANP and BNP act in a non-redundant fashion to maintain myocardial cGMP levels to regulate cardiomyocyte p38 MAPK and CREB activity. Cardiac natriuretic peptide deficiency leads to a reduction in CREB signaling which sensitizes the heart to stress induced ventricular arrhythmias.

TRANSLATIONAL PERSPECTIVE

Our study found that ANP or BNP deficiency leads to increased sudden death and ventricular arrhythmias after acute myocardial stress in murine models. We discovered that ANP and BNP act in a non-redundant fashion to maintain myocardial cGMP levels and uncovered a unique role for these peptides in regulating cardiomyocyte p38 MAPK and CREB signaling through a cGMP-PKG1 pathway. Importantly, this signaling pathway was conserved in human cardiomyocytes. This study provides mechanistic insight into how modulating natriuretic peptide levels in human heart failure patients reduces sudden death and mortality.

Targeting 5-HT2B Receptor Signaling Prevents Border Zone Expansion and Improves Microstructural Remodeling After Myocardial Infarction

BACKGROUND

Myocardial infarction (MI) induces an intense injury response that ultimately generates a collagen-dominated scar. Although required to prevent ventricular rupture, the fibrotic process is often sustained in a manner detrimental to optimal recovery. Cardiac myofibroblasts are the cells tasked with depositing and remodeling collagen and are a prime target to limit the fibrotic process after MI. Serotonin 2B receptor (5-HT2B) signaling has been shown to be harmful in a variety of cardiopulmonary pathologies and could play an important role in mediating scar formation after MI.

METHODS

We used 2 pharmacological antagonists to explore the effect of 5-HT2B inhibition on outcomes after MI and characterized the histological and microstructural changes involved in tissue remodeling. Inducible 5-HT2B ablation driven by Tcf21MCM and PostnMCM was used to evaluate resident cardiac fibroblast- and myofibroblast-specific contributions of 5-HT2B, respectively. RNA sequencing was used to motivate subsequent in vitro analyses to explore cardiac fibroblast phenotype.

RESULTS

5-HT2B antagonism preserved cardiac structure and function by facilitating a less fibrotic scar, indicated by decreased scar thickness and decreased border zone area. 5-HT2B antagonism resulted in collagen fiber redistribution to thinner collagen fibers that were more anisotropic, enhancing left ventricular contractility, whereas fibrotic tissue stiffness was decreased, limiting the hypertrophic response of uninjured cardiomyocytes. Using a tamoxifen-inducible Cre, we ablated 5-HT2B from Tcf21-lineage resident cardiac fibroblasts and saw similar improvements to the pharmacological approach. Tamoxifen-inducible Cre-mediated ablation of 5-HT2B after onset of injury in Postn-lineage myofibroblasts also improved cardiac outcomes. RNA sequencing and subsequent in vitro analyses corroborate a decrease in fibroblast proliferation, migration, and remodeling capabilities through alterations in Dnajb4 expression and Src phosphorylation.

CONCLUSIONS

Together, our findings illustrate that 5-HT2B expression in either cardiac fibroblasts or activated myofibroblasts directly contributes to excessive scar formation, resulting in adverse remodeling and impaired cardiac function after MI.

Impact of COVID-19 on Clinical Practices during Lockdown: A pan India Survey of Orthopaedic Surgeons

Introduction:

The social lockdown measures imposed to contain the COVID-19 pandemic, have had profound effects on the healthcare systems across the world and India has been no exception to it. The study was aimed to evaluate the impact of COVID-19 on orthopaedic practice in India during the lockdown period and assess the preparedness of orthopaedic surgeons for resuming clinical practice after the initial lockdown was lifted.

Materials and Methods:

An online survey of 35 questions was conducted to evaluate impact on (i) general orthopaedic practice (ii) hospital protocols (iii) out-patient practice (iv) surgical practice (v) personal protective equipment (PPE) use and (vi) post-lockdown preparedness.

Results:

A total number of 588 practising orthopaedic surgeons from India completed the survey. Majority (88.3%) found severe impact (>50%) on trauma surgery and non-trauma surgery with significant reduction in out -patient attendance compared to corresponding time in 2019. There were significant changes made in individual hospital protocols (91.7 %). Appropriate required PPE was available in majority of the hospitals (74.3%). No remodelling or upgrading of the existing operating theatre infrastructure was done by most surgeons (89.5%).

Conclusion:

This pan India survey of orthopaedic surgeons has indicated that COVID-19 has had a profound impact on their outpatient and surgical trauma and non-trauma practice, due to the lockdown and resulted in significant changes to hospital protocols. Preparedness to resume clinical and surgical practice was associated with anxiety in two-thirds of the respondents. Majority of the orthopaedic practitioners felt that they would continue to conduct pre-operative COVID-19 screening and use PPE even after the lockdown is over.

Clinical profile and outcomes of De novo posttransplant thrombotic microangiopathy

Thrombotic microangiopathy (TMA) after kidney transplant is rather uncommon but an important reversible cause of graft loss. This retrospective study of biopsy-proven posttransplant TMA was done to identify the important etiological factors, clinical features, and outcomes of post transplant TMA in a tertiary care referral hospital in northern India. This retrospective study was conducted among all renal transplant recipients who presented with graft dysfunction between 1989 and 2015. All the cases were looked for their etiology, clinical course, treatment modalities, and renal outcomes. The study was conducted in accord with prevailing ethical principles and reviewed by our own institutional review board. Seventeen patients out of 2000 (0.008%) transplants done during the study period had posttransplant TMA, out of which all the patients had de novo TMA, and the median time of presentation after transplantation was four months. Systemic TMA was noted in only four patients. Biopsy revealed associated rejection in five patients and associated calcineurin inhibitor (CNI) toxicity in 12 patients. Patients with TMA due to CNI toxicity were managed with CNI reduction or switching to alternate CNI or mammalian target of rapamycin inhibitors. In addition, antithymocyte globulin and plasma exchange were used in rejection-associated TMA. While four out of 12 patients (33%) in CNI-related TMA developed end-stage renal disease (ESRD), all patients in rejection-associated TMA developed ESRD. The overall one-year graft survival was 47%, whereas five- and 10-year survival was 35%. There was no significant difference in graft survival between localized and systemic TMAs (P = 0.4). Posttransplant TMA should be suspected even if there are no systemic features of hemolysis and early graft biopsy and prompt action is needed. The occurrence of TMA in the setting of rejection is associated with grave prognosis.

The BDNF rs6265 Polymorphism is a Modifier of Cardiomyocyte Contractility and Dilated Cardiomyopathy

Brain-derived neurotrophic factor (BDNF) is a neuronal growth and survival factor that harbors cardioprotective qualities that may attenuate dilated cardiomyopathy. In ~30% of the population, BDNF has a common, nonsynonymous single nucleotide polymorphism rs6265 (Val66Met), which might be correlated with increased risk of cardiovascular events. We previously showed that BDNF correlates with better cardiac function in Duchenne muscular dystrophy (DMD) patients. However, the effect of the Val66Met polymorphism on cardiac function has not been determined. The goal of the current study was to determine the effects of rs6265 on BDNF biomarker suitability and DMD cardiac functions more generally. We assessed cardiovascular and skeletal muscle function in human DMD patients segregated by polymorphic allele. We also compared echocardiographic, electrophysiologic, and cardiomyocyte contractility in C57/BL-6 wild-type mice with rs6265 polymorphism and in mdx/mTR (mDMD) mouse model of DMD. In human DMD patients, plasma BDNF levels had a positive correlation with left ventricular function, opposite to that seen in rs6265 carriers. There was also a substantial decrease in skeletal muscle function in carriers compared to the Val homozygotes. Surprisingly, the opposite was true when cardiac function of DMD carriers and non-carriers were compared. On the other hand, Val66Met wild-type mice had only subtle functional differences at baseline but significantly decreased cardiomyocyte contractility. Our results indicate that the Val66Met polymorphism alters myocyte contractility, conferring worse skeletal muscle function but better cardiac function in DMD patients. Moreover, these results suggest a mechanism for the relative preservation of cardiac tissues compared to skeletal muscle in DMD patients and underscores the complexity of BDNF signaling in response to mechanical workload.

Abstract MP151: Cardiomyocyte HIPK2 is a Critical Regulator of Purinergic Signaling Regulated Myocardial Inflammation

Objective: Heart failure (HF) is a major and growing public health problem worldwide. Recently our lab has identified HIPK2 as an essential kinase to maintain basal cardiac function. However, the role of cardiomyocytes specific HIPK2 (CM-HIPK2) in myocardial inflammation is unknown.

Methods: α-MHC promoter-driven, Cre mice were crossed with HIPK2 fl/fl mice to generate CM-HIPK2 KO. Echocardiography was performed to assess cardiac function. Immunoblotting assays were performed to determine the expression of HIPK2, CD39, CD73, and other signaling pathway . Flow cytometry and ELISA were performed to study the dynamics of inflammation.

Results: Consistent with our previous report , echocardiography confirmed an impaired cardiac function in 3 months old CM-HIPK2 KO as compared to their littermate controls. Importantly, cardiac function in the KOs starts to deteriorate at ~2.5 months of age, thus, at two months of age, the cardiac function of KO and littermate control was comparable. Comprehensive immune profiling of CM-HIPK2 KO and littermate control hearts were performed at two months of age. We observed an increased frequency of infiltrated CD45 + leukocytes, CCR2 + pro-inflammatory macrophages, Th17 + , Th9 + , CD45 + TNFα + , CD45 + IL1β + , CD45 + Ki67 + cells but diminished frequency of Myeloid-derived suppressor cells (MDSCs), TCRαβ + CTLA-4 + and TCRαβ + PD-1 + in the CM-HIPK2 KO hearts. Mechanistically, we observed a significantly reduced expression of CD39 and CD73 over HIPK2 deleted cardiomyocytes. Indeed, CD39 and CD73 are the key players of purinergic signaling regulated inflammation response. In-vitro studies with neonatal rat ventricular cardiomyocytes (NRVMs) corroborated the in-vivo findings. Specifically, adenovirus-mediated overexpression of HIPK2 significantly increased CD39 expression. Consistently, Ad-shRNA-HIPK2 expression suppressed the CD39 expression. Taken together, our findings suggest a critical role of CM-HIPK2 in purinergic signaling mediated myocardial inflammation.

Conclusions: CM-HIPK2 maintains basal cardiac function by controlling purinergic signaling regulated myocardial inflammation. Future work will explore the underlying mechanism of HIPK2 mediated regulation of CD39 and CD73.

Abstract 365: Ponatinib Triggers Cardiac Inflammation by STAT-3 Dependent Immune Checkpoint Blockade

Background: Ponatinib is a potent anticancer tyrosine kinase inhibitor (TKI) with considerable cardiotoxicity. The manifestation of cardiovascular adverse events, including fatal myocardial infarction and congestive heart failure, has hampered its clinical use. Therefore, a better understanding of the mechanism by which ponatinib exerts cardiotoxicity is urgently warranted to efficiently counteract treatment-related adversities.

Methods: Wild type C57BL/6, comorbidity mouse model ApoE -/- , and pressure overload (PO) mouse model were used to investigate the cardiotoxic mechanism of ponatinib. Echocardiography was performed to assess cardiac function. Flow cytometry analysis was performed to assess the dynamics of inflammation.

Results: We observed that high-fat diet (HFD) fed ApoE -/- mice develop cardiac dysfunction within 2 weeks of ponatinib treatment. An unbiased RNA-Seq analysis revealed significant upregulation of inflammatory genes (CCR1, CCR5, CCL6, CCL8, CCL9, CXCL4) in ponatinib treated hearts. Since ApoE -/- background, and HFD are known confounder of inflammation signal, we validated this observation in naïve C57BL/6 mice. Despite the lack of cardiac dysfunction in ponatinib treated naïve C57BL/6 mice, comprehensive immune profiling depicted upregulation of myocardial inflammation as evident by infiltrated immune cells (CD45 + TNFα + , CD45 + CD11b + F4/80 + Ly6C + CCR2 + , CD45 + Gal1 + ). Interestingly, we also demonstrated the downregulation of immune checkpoints over T cells (TCRαβ + CTLA4 + , TCRαβ + PD1 + ) in ponatinib treated hearts. Next, in the PO mouse model, ponatinib treated mice showed significant cardiac dysfunction with myocardial inflammation as reflected by increased frequencies of inflammatory parameters (TNFα + , IL1β + , IL6 + , MCP1 + , CXCL9 + ). Mechanistically, we demonstrated that ponatinib potentially suppresses PD-L1 expression over cardiomyocytes via inhibition of STAT3, subsequently leading to immune cells mediated myocardial inflammation.

Conclusions: These findings uncover a novel mechanism of ponatinib induced cardiac inflammation leading to adverse cardiac function. It also suggests that strategies to attenuate inflammation may be an effective therapy to prevent ponatinib induced cardiac adverse events.

Abstract 285: High Throughput Profiling of Gsk3α Regulated Fibroblast Kinome Reveals Raf as a Mediator of Fibrosis in Failing Heart

Background: Heart failure is the leading cause of mortality, morbidity, and healthcare expenditures worldwide. Numerous studies have implicated Glycogen Synthase Kinase-3 (GSK-3) as a promising therapeutic target for cardiovascular diseases. GSK-3 isoforms appear to play overlapping, unique, and even opposing functions in the heart. Recently our group has identified cardiac fibroblast (CF) GSK3β as a negative regulator of fibrotic remodeling in the ischemic heart. However, the role of CF-GSK3α in cardiac pathophysiology is unknown.

Methods and Results: GSK3α was deleted specifically from cardiac fibroblasts or myofibroblasts with tamoxifen-inducible TCF21- or periostin- promoter-driven Cre recombinase. At 2 months of age, WT and KO mice were subjected to cardiac injury, and heart functions were monitored by serial echocardiography. Histological analysis and morphometric studies were performed at 8 weeks post-injury. In both settings, GSK3α deletion restricted fibrotic remodeling and improved cardiac function. To investigate underlying mechanisms, we examined the effect of GSK3α deletion on myofibroblast transformation and pro-fibrotic TGFβ1-SMAD3 signaling in vitro . WT and KO mouse embryonic fibroblasts (MEFs) were treated with TGFβ1. Indeed, a significant reduction in cell migration, collagen gel contraction, and α-SMA expression in TGFβ1 treated KO MEFs confirmed that GSK3α is required for myofibroblast transformation. Surprisingly, GSK3α deletion had no effect on SMAD3 activation, indicating the pro-fibrotic role of GSK3α is SMAD3 independent. At 4 weeks post-injury, total proteins were isolated from CFs of WT and KO animals, and kinome profiling was performed by utilizing PamStation®12 high throughput microarray platform. The upstream kinase analysis identified the downregulation of RAF family kinase activity in GSK3α-KO-CFs. Moreover, mapping of significantly altered kinases against literature annotated interactions generated ERK-centric networks. These findings are consistent with previous studies that implicated ERK in fibrotic diseases across multiple organs.

Conclusion: CF-GSK3α plays a causal role in the cardiac pathophysiology that could be therapeutically targeted for future clinical applications.

A Pharmacovigilance Study of Hydroxychloroquine Cardiac Safety Profile: Potential Implication in COVID-19 Mitigation

In light of the favorable outcomes of few small, non-randomized clinical studies, the Food and Drug Administration (FDA) has issued an Emergency Use Authorization (EUA) to Hydroxychloroquine (HCQ) for hospitalized coronavirus disease 2019 (COVID-19) patients. In fact, subsequent clinical studies with COVID-19 and HCQ have reported limited efficacy and poor clinical benefits. Unfortunately, a robust clinical trial for its effectiveness is not feasible at this emergency. Additionally, HCQ was suspected of causing cardiovascular adverse reactions (CV-AEs), but it has never been directly investigated. The objective of this pharmacovigilance analysis was to determine and characterize HCQ-associated cardiovascular adverse events (CV-AEs). We performed a disproportionality analysis of HCQ-associated CV-AEs using the FDA adverse event reporting system (FAERS) database. The FAERS database, comprising more than 11,901,836 datasets and 10,668,655 patient records with drug-adverse reactions, was analyzed. The disproportionality analysis was used to calculate the reporting odds ratios (ROR) with 95% confidence intervals (CI) to predict HCQ-associated CV-AEs. HCQ was associated with higher reporting of right ventricular hypertrophy (ROR: 6.68; 95% CI: 4.02 to 11.17), left ventricular hypertrophy (ROR: 3.81; 95% CI: 2.57 to 5.66), diastolic dysfunction (ROR: 3.54; 95% CI: 2.19 to 5.71), pericarditis (ROR: 3.09; 95% CI: 2.27 to 4.23), torsades de pointes (TdP) (ROR: 3.05; 95% CI: 2.30 to 4.10), congestive cardiomyopathy (ROR: 2.98; 95% CI: 2.01 to 4.42), ejection fraction decreased (ROR: 2.41; 95% CI: 1.80 to 3.22), right ventricular failure (ROR: 2.40; 95% CI: 1.64 to 3.50), atrioventricular block complete (ROR: 2.30; 95% CI: 1.55 to 3.41) and QT prolongation (ROR: 2.09; 95% CI: 1.74 to 2.52). QT prolongation and TdP are most relevant to the COVID-19 treatment regimen of high doses for a comparatively short period and represent the most common HCQ-associated AEs. The patients receiving HCQ are at higher risk of various cardiac AEs, including QT prolongation and TdP. These findings highlight the urgent need for prospective, randomized, controlled studies to assess the risk/benefit ratio of HCQ in the COVID-19 setting before its widespread adoption as therapy.

Cardiotoxicity of the BCR-ABL1 tyrosine kinase inhibitors: Emphasis on ponatinib

The advent of tyrosine kinase inhibitors (TKIs) targeted therapy revolutionized the treatment of chronic myeloid leukemia (CML) patients. However, cardiotoxicity associated with these targeted therapies puts the cancer survivors at higher risk. Ponatinib is a third-generation TKI for the treatment of CML patients having gatekeeper mutation T315I, which is resistant to the first and second generation of TKIs, namely, imatinib, nilotinib, dasatinib, and bosutinib. Multiple unbiased screening from our lab and others have identified ponatinib as most cardiotoxic FDA approved TKI among the entire FDA approved TKI family (total 50+). Indeed, ponatinib is the only treatment option for CML patients with T315I mutation. This review focusses on the cardiovascular risks and mechanism/s associated with CML TKIs with a particular focus on ponatinib cardiotoxicity. We have summarized our recent findings with transgenic zebrafish line harboring BNP luciferase activity to demonstrate the cardiotoxic potential of ponatinib. Additionally, we will review the recent discoveries reported by our and other laboratories that ponatinib primarily exerts its cardiotoxicity via an off-target effect on cardiomyocyte prosurvival signaling pathways, AKT and ERK. Finally, we will shed light on future directions for minimizing the adverse sequelae associated with CML-TKIs.

Ponatinib-induced cardiotoxicity: delineating the signalling mechanisms and potential rescue strategies

AIMS

Tyrosine kinase inhibitors (TKIs) have revolutionized the treatment of chronic myelogenous leukaemia (CML). However, cardiotoxicity of these agents remains a serious concern. The underlying mechanism of these adverse cardiac effects is largely unknown. Delineation of the underlying mechanisms of TKIs associated cardiac dysfunction could guide potential prevention strategies, rescue approaches, and future drug design. This study aimed to determine the cardiotoxic potential of approved CML TKIs, define the associated signalling mechanism and identify potential alternatives.

METHODS AND RESULTS

In this study, we employed a zebrafish transgenic BNP reporter line that expresses luciferase under control of the nppb promoter (nppb:F-Luciferase) to assess the cardiotoxicity of all approved CML TKIs. Our in vivo screen identified ponatinib as the most cardiotoxic agent among the approved CML TKIs. Then using a combination of zebrafish and isolated neonatal rat cardiomyocytes, we delineated the signalling mechanism of ponatinib-induced cardiotoxicity by demonstrating that ponatinib inhibits cardiac prosurvival signalling pathways AKT and extra-cellular-signal-regulated kinase (ERK), and induces cardiomyocyte apoptosis. As a proof of concept, we augmented AKT and ERK signalling by administration of Neuregulin-1β (NRG-1β), and this prevented ponatinib-induced cardiomyocyte apoptosis. We also demonstrate that ponatinib-induced cardiotoxicity is not mediated by inhibition of fibroblast growth factor signalling, a well-known target of ponatinib. Finally, our comparative profiling for the cardiotoxic potential of CML approved TKIs, identified asciminib (ABL001) as a potentially much less cardiotoxic treatment option for CML patients with the T315I mutation.

CONCLUSION

Herein, we used a combination of in vivo and in vitro methods to systematically screen CML TKIs for cardiotoxicity, identify novel molecular mechanisms for TKI cardiotoxicity, and identify less cardiotoxic alternatives.

Deletion of Cardiomyocyte Glycogen Synthase Kinase-3 Beta (GSK-3β) Improves Systemic Glucose Tolerance with Maintained Heart Function in Established Obesity

Obesity is an independent risk factor for cardiovascular diseases (CVD), including heart failure. Thus, there is an urgent need to understand the molecular mechanism of obesity-associated cardiac dysfunction. We recently reported the critical role of cardiomyocyte (CM) Glycogen Synthase Kinase-3 beta (GSK-3β) in cardiac dysfunction associated with a developing obesity model (deletion of CM-GSK-3β prior to obesity). In the present study, we investigated the role of CM-GSK-3β in a clinically more relevant model of established obesity (deletion of CM-GSK-3β after established obesity). CM-GSK-3β knockout (GSK-3β^fl/flCre+/-) and controls (GSK-3β^fl/flCre-/-) mice were subjected to a high-fat diet (HFD) in order to establish obesity. After 12 weeks of HFD treatment, all mice received tamoxifen injections for five consecutive days to delete GSK-3β specifically in CMs and continued on the HFD for a total period of 55 weeks. To our complete surprise, CM-GSK-3β knockout (KO) animals exhibited a globally improved glucose tolerance and maintained normal cardiac function. Mechanistically, in stark contrast to the developing obesity model, deleting CM-GSK-3β in obese animals did not adversely affect the GSK-3αS21 phosphorylation (activity) and maintained canonical β-catenin degradation pathway and cardiac function. As several GSK-3 inhibitors are in the trial to treat various chronic conditions, including metabolic diseases, these findings have important clinical implications. Specifically, our results provide critical pre-clinical data regarding the safety of GSK-3 inhibition in obese patients.

Mouse Models of Heart Failure with Preserved or Reduced Ejection Fraction

Heart failure (HF) is a chronic, complex condition with increasing incidence worldwide, necessitating the development of novel therapeutic strategies. This has led to the current clinical strategies, which only treat symptoms of HF without addressing the underlying causes. Multiple animal models have been developed in an attempt to recreate the chronic HF phenotype that arises following a variety of myocardial injuries. Although significant strides have been made in HF research, an understanding of more specific mechanisms will require distinguishing models that resemble HF with preserved ejection fraction (HFpEF) from those with reduced ejection fraction (HFrEF). Therefore, current mouse models of HF need to be re-assessed to determine which of them most closely recapitulate the specific etiology of HF being studied. This will allow for the development of therapies targeted specifically at HFpEF or HFrEF. This review will summarize the commonly used mouse models of HF and discuss which aspect of human HF each model replicates, focusing on whether HFpEF or HFrEF is induced, to allow better investigation into pathophysiological mechanisms and treatment strategies.

Inhibition of GSK-3 to induce cardiomyocyte proliferation: a recipe for in situ cardiac regeneration

With an estimated 38 million current patients, heart failure (HF) is a leading cause of morbidity and mortality worldwide. Although the aetiology differs, HF is largely a disease of cardiomyocyte (CM) death or dysfunction. Due to the famously limited amount of regenerative capacity of the myocardium, the only viable option for advanced HF patients is cardiac transplantation; however, donor's hearts are in very short supply. Thus, novel regenerative strategies are urgently needed to reconstitute the injured hearts. Emerging data from our lab and others have elucidated that CM-specific deletion of glycogen synthase kinase (GSK)-3 family of kinases induces CM proliferation, and the degree of proliferation is amplified in the setting of cardiac stress. If this proliferation is sufficiently robust, one could induce meaningful regeneration without the need for delivering exogenous cells to the injured myocardium (i.e. cardiac regeneration in situ). Herein, we will discuss the emerging role of the GSK-3s in CM proliferation and differentiation, including their potential implications in cardiac regeneration. The underlying molecular interactions and cross-talk among signalling pathways will be discussed. We will also review the specificity and limitations of the available small molecule inhibitors targeting GSK-3 and their potential applications to stimulate the endogenous cardiac regenerative responses to repair the injured heart.

Neutrophil-Derived S100A8/A9 Amplify Granulopoiesis After Myocardial Infarction

BACKGROUND

Myocardial infarction (MI) triggers myelopoiesis, resulting in heightened production of neutrophils. However, the mechanisms that sustain their production and recruitment to the injured heart are unclear.

METHODS

Using a mouse model of the permanent ligation of the left anterior descending artery and flow cytometry, we first characterized the temporal and spatial effects of MI on different myeloid cell types. We next performed global transcriptome analysis of different cardiac cell types within the infarct to identify the drivers of the acute inflammatory response and the underlying signaling pathways. Using a combination of genetic and pharmacological strategies, we identified the sequelae of events that led to MI-induced myelopoiesis. Cardiac function was assessed by echocardiography. The association of early indexes of neutrophilia with major adverse cardiovascular events was studied in a cohort of patients with acute MI.

RESULTS

Induction of MI results in rapid recruitment of neutrophils to the infarct, where they release specific alarmins, S100A8 and S100A9. These alarmins bind to the Toll-like receptor 4 and prime the nod-like receptor family pyrin domain-containing 3 inflammasome in naïve neutrophils and promote interleukin-1β secretion. The released interleukin-1β interacts with its receptor (interleukin 1 receptor type 1) on hematopoietic stem and progenitor cells in the bone marrow and stimulates granulopoiesis in a cell-autonomous manner. Genetic or pharmacological strategies aimed at disruption of S100A8/A9 and their downstream signaling cascade suppress MI-induced granulopoiesis and improve cardiac function. Furthermore, in patients with acute coronary syndrome, higher neutrophil count on admission and after revascularization correlates positively with major adverse cardiovascular disease outcomes.

CONCLUSIONS

Our study provides novel evidence for the primary role of neutrophil-derived alarmins (S100A8/A9) in dictating the nature of the ensuing inflammatory response after myocardial injury. Therapeutic strategies aimed at disruption of S100A8/A9 signaling or their downstream mediators (eg, nod-like receptor family pyrin domain-containing 3 inflammasome, interleukin-1β) in neutrophils suppress granulopoiesis and may improve cardiac function in patients with acute coronary syndrome.

Cardiomyocyte Homeodomain-Interacting Protein Kinase 2 Maintains Basal Cardiac Function via Extracellular Signal-Regulated Kinase Signaling

BACKGROUND

Cardiac kinases play a critical role in the development of heart failure, and represent potential tractable therapeutic targets. However, only a very small fraction of the cardiac kinome has been investigated. To identify novel cardiac kinases involved in heart failure, we used an integrated transcriptomics and bioinformatics analysis and identified Homeodomain-Interacting Protein Kinase 2 (HIPK2) as a novel candidate kinase. The role of HIPK2 in cardiac biology is unknown.

METHODS

We used the Expression2Kinase algorithm for the screening of kinase targets. To determine the role of HIPK2 in the heart, we generated cardiomyocyte (CM)-specific HIPK2 knockout and heterozygous mice. Heart function was examined by echocardiography, and related cellular and molecular mechanisms were examined. Adeno-associated virus serotype 9 carrying cardiac-specific constitutively active MEK1 (TnT-MEK1-CA) was administrated to rescue cardiac dysfunction in CM-HIPK2 knockout mice.

RESULTS

To our knowledge, this is the first study to define the role of HIPK2 in cardiac biology. Using multiple HIPK2 loss-of-function mouse models, we demonstrated that reduction of HIPK2 in CMs leads to cardiac dysfunction, suggesting a causal role in heart failure. It is important to note that cardiac dysfunction in HIPK2 knockout mice developed with advancing age, but not during development. In addition, CM-HIPK2 knockout mice and CM-HIPK2 heterozygous mice exhibited a gene dose-response relationship of CM-HIPK2 on heart function. HIPK2 expression in the heart was significantly reduced in human end-stage ischemic cardiomyopathy in comparison to nonfailing myocardium, suggesting a clinical relevance of HIPK2 in cardiac biology. In vitro studies with neonatal rat ventricular CMscorroborated the in vivo findings. Specifically, adenovirus-mediated overexpression of HIPK2 suppressed the expression of heart failure markers, NPPA and NPPB, at basal condition and abolished phenylephrine-induced pathological gene expression. An array of mechanistic studies revealed impaired extracellular signal-regulated kinase 1/2 signaling in HIPK2-deficient hearts. An in vivo rescue experiment with adeno-associated virus serotype 9 TnT-MEK1-CA nearly abolished the detrimental phenotype of knockout mice, suggesting that impaired extracellular signal-regulated kinase signaling mediated apoptosis as the key factor driving the detrimental phenotype in CM-HIPK2 knockout mice hearts.

CONCLUSIONS

Taken together, these findings suggest that CM-HIPK2 is required to maintain normal cardiac function via extracellular signal-regulated kinase signaling.

Cadherin-11 blockade reduces inflammation-driven fibrotic remodeling and improves outcomes after myocardial infarction

Over one million Americans experience myocardial infarction (MI) annually, and the resulting scar and subsequent cardiac fibrosis gives rise to heart failure. A specialized cell-cell adhesion protein, cadherin-11 (CDH11), contributes to inflammation and fibrosis in rheumatoid arthritis, pulmonary fibrosis, and aortic valve calcification but has not been studied in myocardium after MI. MI was induced by ligation of the left anterior descending artery in mice with either heterozygous or homozygous knockout of CDH11, wild-type mice receiving bone marrow transplants from Cdh11-deficient animals, and wild-type mice treated with a functional blocking antibody against CDH11 (SYN0012). Flow cytometry revealed significant CDH11 expression in noncardiomyocyte cells after MI. Animals given SYN0012 had improved cardiac function, as measured by echocardiogram, reduced tissue remodeling, and altered transcription of inflammatory and proangiogenic genes. Targeting CDH11 reduced bone marrow-derived myeloid cells and increased proangiogenic cells in the heart 3 days after MI. Cardiac fibroblast and macrophage interactions increased IL-6 secretion in vitro. Our findings suggest that CDH11-expressing cells contribute to inflammation-driven fibrotic remodeling after MI and that targeting CDH11 with a blocking antibody improves outcomes by altering recruitment of bone marrow-derived cells, limiting the macrophage-induced expression of IL-6 by fibroblasts and promoting vascularization.

Abstract 738: Comparative Cardiotoxicity of Tyrosine Kinase Inhibitors Ponatinib and PF114

Background: The advent of tyrosine kinase inhibitor (TKI) targeted therapy revolutionized the treatment of chronic myelogenous leukemia (CML) patients, leading to a significant impact on remission rates and overall survival. However, cardiotoxicity associated with these targeted therapies put the cancer survivors at greater risk. Ponatinib is an example shown unexpected wide spectrum of cardiotoxic complications which limits its clinical applications. A newly designed 4 th -generation tyrosine kinase inhibitor PF114 having better target spectra in CML, could be a potential alternative to ponatinib. But the cardiotoxic potential of PF114 is not yet fully understood.

Objectives: The objectives of the present study were to compare cardiotoxicity of ponatinib with PF114.

Methods: In this study, we employed zebrafish transgenic BNP reporter line that expresses luciferase under control of the nppb promoter ( nppb : F-Luciferase) to compare cardiotoxic potential of TKIs. We also exploited NRVMs to explore cardiotoxic mechanism associated with ponatinib and PF114.

Results: We observed that increasing dose of PF114 showed minimal induction of the BNP reporter compared to ponatinib. PF114 did not reduce the ventricular fractional shortening in zebrafish as compared to ponatinib. Consistently, in cultured rat cardiomyocytes, PF114 could not reiterate the same cardiotoxic effect of ponatinib as depicted by cell viability and TUNEL assay. Mechanistically, PF114 has shown no effects on essential prosurvival AKT and ERK signaling pathway while ponatinib is known to exerts its cardiotoxic effects by their inhibition. Additionally, the allosteric tyrosine kinase inhibitor ABL001(Asciminib) in combination with PF114 depicts less pronounced cardiotoxic effects than ponatinib in similar settings.

Conclusions: This study provides further rationale to utilize zebrafish for the prediction of cardiotoxicity of anticancer drugs. The comparative cardiotoxicity of ponatinib and PF114 suggest that PF114 is a significantly less cardiotoxic analogue and safer treatment option than ponatinib for CML patients harboring BCR/ABL-T315I “gatekeeper” mutation.

Abstract 530: Cardiac Fibroblast GSK-3α Contributes to Ventricular Remodeling and Dysfunction of the Failing Heart

Background: Heart failure is the leading cause of mortality, morbidity, and healthcare expenditures worldwide. Numerous studies from our lab and others have implicated Glycogen Synthase Kinase-3 (GSK-3) as a promising therapeutic target for cardiovascular diseases. GSK-3 isoforms appear to play overlapping, unique and even opposing functions in the heart. Recently our group has identified cardiac fibroblast (CF) GSK-3β as a negative regulator of fibrotic remodeling in the ischemic heart. However, the role of CF-GSK-3α in cardiac pathophysiology is poorly understood.

Methods and Results: To determine the role of CF-GSK-3α in the pathogenesis of heart failure, GSK -3α was deleted specifically from mouse resident cardiac fibroblast or myofibroblast with tamoxifen-inducible TCF21- or periostin (Postn)- promoter-driven Cre recombinase. At 2 months of age, WT and KO mice were subjected to cardiac injury and heart functions were monitored by serial echocardiography. Histological analysis and morphometric studies were performed at 8 weeks post-injury. In TCF21-KO mice, deletion of GSK-3α from resident cardiac fibroblasts significantly restricted pressure overload-induced adverse cardiac remodeling and improved cardiac function. Consistently, in Postn-KO mice, deletion of GSK-3α from myofibroblasts remarkably reduced LV scar circumference and prevented cardiac dysfunction post-MI. To gain the mechanistic insights of observed GSK-3α mediated fibrotic remodeling, we examined the effect of GSK-3α deletion on myofibroblast transformation and profibrotic TGF-β1-SMAD3 signaling in vitro . WT and GSK-3α KO mouse embryonic fibroblasts (MEFs) were treated with TGF-β1 (10 ng/mL). Indeed, a significant reduction in cell migration, collagen gel contraction, and α-SMA expression in TGF-β1 treated GSK-3α KO MEF confirmed that GSK-3α is required for myofibroblast transformation. Surprisingly, GSK-3α deletion had no effect on TGF-β1 induced SMAD3 activation indicating the potential involvement of GSK-3α in eliciting SMAD3 independent profibrotic response.

Conclusion: These findings suggest the causal role of CF-GSK3α in the cardiac remodeling of the injured heart that could be a therapeutically targeted for the future clinical applications.

Generation of Nppa-tagBFP reporter knock-in mouse line for studying cardiac chamber specification

Nppa is a cardiac hormone which plays critical roles in regulating salt-water balance. Its expression is restricted to the atria of the healthy post-natal heart. During heart development, spatio-temporal expression of Nppa is dynamically changed within the heart and becomes restricted to the atria upon birth. In contrast to its atrial specific expression after birth, Nppa is re-expressed in the adult ventricles in response to cardiac hypertrophy. To study cardiac chamber specification during development and pathological cardiac remodeling during heart disease, we generated a novel Nppa reporter mouse line by knocking-in a tagBFP reporter cassette into 3'-UTR of the Nppa gene without disrupting the endogenous gene. Our results demonstrated dynamic tagBFP expression in the developing heart, recapitulating the spatiotemporal expression pattern of endogenous Nppa. We also found that Nppa-tagBFP is induced in the ventricle during pathological remodeling. Taken together, Nppa-tagBFP reporter knock-in mouse model described in this article will serve as a valuable tool to study cardiac chamber specification during development as well as pathological cardiac remodeling.

Cardiomyocyte-GSK-3α promotes mPTP opening and heart failure in mice with chronic pressure overload

Chronic pressure-overload (PO)- induced cardiomyopathy is one of the leading causes of left ventricular (LV) remodeling and heart failure. The role of the α isoform of glycogen synthase kinase-3 (GSK-3α) in PO-induced cardiac remodeling is unclear and its downstream molecular targets are largely unknown. To investigate the potential roles of GSK-3α, cardiomyocyte-specific GSK-3α conditional knockout (cKO) and control mice underwent trans-aortic constriction (TAC) or sham surgeries. Cardiac function in the cKOs and littermate controls declined equally up to 2 weeks of TAC. At 4 week, cKO animals retained concentric LV remodeling and showed significantly less decline in contractile function both at systole and diastole, vs. controls which remained same until the end of the study (6 wk). Histological analysis confirmed preservation of LV chamber and protection against TAC-induced cellular hypertrophy in the cKO. Consistent with attenuated hypertrophy, significantly lower level of cardiomyocyte apoptosis was observed in the cKO. Mechanistically, GSK-3α was found to regulate mitochondrial permeability transition pore (mPTP) opening and GSK-3α-deficient mitochondria showed delayed mPTP opening in response to Ca²⁺ overload. Consistently, overexpression of GSK-3α in cardiomyocytes resulted in elevated Bax expression, increased apoptosis, as well as a reduction of maximum respiration capacity and cell viability. Taken together, we show for the first time that GSK-3α regulates mPTP opening under pathological conditions, likely through Bax overexpression. Genetic ablation of cardiomyocyte GSK-3α protects against chronic PO-induced cardiomyopathy and adverse LV remodeling, and preserves contractile function. Selective inhibition of GSK-3α using isoform-specific inhibitors could be a viable therapeutic strategy to limit PO-induced heart failure.

Cardiomyocyte SMAD4-Dependent TGF-β Signaling is Essential to Maintain Adult Heart Homeostasis

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SMAD4 is the central intracellular mediator of TGF-β pathway.

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CM-specific loss of SMAD4 causes cardiac dysfunction independent of fibrotic remodeling.

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Deletion CM-SMAD4 affects CM survival.

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CM-SMAD4 loss leads to down-regulation of several ion channels’ genes, resulting in cardiac conduction abnormalities.

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CM-SMAD4 deletion alters sarcomere shortening kinetics, in parallel with reduction in cardiac myosin-binding protein C levels.

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These results demonstrate a fundamental role for CM-SMAD4–dependent TGF-β signaling in adult heart homeostasis.

The role of the transforming growth factor (TGF)-β pathway in myocardial fibrosis is well recognized. However, the precise role of this signaling axis in cardiomyocyte (CM) biology is not defined. In TGF-β signaling, SMAD4 acts as the central intracellular mediator. To investigate the role of TGF-β signaling in CM biology, the authors deleted SMAD4 in adult mouse CMs. We demonstrate that CM-SMAD4–dependent TGF-β signaling is critical for maintaining cardiac function, sarcomere kinetics, ion-channel gene expression, and cardiomyocyte survival. Thus, our findings raise a significant concern regarding the therapeutic approaches that rely on systemic inhibition of the TGF-β pathway for the management of myocardial fibrosis.

Abstract 361: Analysis of Cardiotoxic Mechanisms Associated With Tyrosine Kinase Inhibitor Ponatinib

Background: Ponatinib, a potent pan-BCR-ABL tyrosine kinase inhibitor (TKI) holds significant promise in the treatment of chronic myelogenous leukemia (CML), although the potential cardiotoxicity of this agent remains a concern. In order to overcome ponatinib associated cardiotoxicity, delineation of linked cardiotoxic mechanisms and potential rescue methods are urgently warranted.

Objectives: The objectives of the present study were to delineate the signaling mechanisms responsible for ponatinib-induced cardiotoxicity and to identify the potential rescue strategies.

Methods: In this study, we employed direct in vivo drug screening in zebrafish for the prediction of cardiotoxicity. We also exploited neonatal rat ventricular myocytes (NRVMs) to explore cardiotoxic mechanism associated with ponatinib.

Results: We observed that ponatinib leads to cardiomyocyte apoptosis, elevation in BNP level, decrease in heart rate and fractional shortening leading to cardiac dysfunction in Zebrafish. Consistently, in cultured rat cardiomyocytes, ponatinib was found most cytotoxic drug among all the approved CML TKIs. Mechanistically, ponatinib inhibits the essential prosurvival AKT and ERK signaling pathway, resulting to cardiomyocyte apoptosis. Interestingly, we evaluated the cardioprotective effects of Neuregulin-1β to limit ponatinib toxicity. Neuregulin-1β treatment significantly protects ponatinib-induced cardiotoxicity by supplementing the essential cardiomyocyte prosurvival AKT/ERK signaling pathways. Additionally, the allosteric tyrosine kinase inhibitor asciminib depicts less pronounced cardiotoxic effects than ponatinib in similar settings.

Conclusions: This study will advance our mechanistic understanding of ponatinib-induced cardiotoxicity, accelerate the discovery of cardioprotective strategies to prevent and rescue the ponatinib-induced cardiotoxicity. Furthermore, this study suggests asciminib as an alternate treatment option than ponatinib for patients suffering from CML with T315I “gatekeeper” mutation.

Abstract 114: A Role for Brain-derived Neurotrophic Factor in Duchenne Cardiomyopathy

Brain-derived neurotrophic factor (BDNF) and its receptor, tropomyosin receptor kinase B (TrkB) harbor cardioprotective qualities that may attenuate CM. In a small cohort of DMD patients we found that BDNF blood levels positively correlated with preserved ejection fraction (EF) and less fibrosis, and carriers of the common BDNF single nucleotide polymorphism rs6265 (Val66-Met) tended to exhibit earlier age of onset of fibrosis with subsequent progression to LV dysfunction, compared to non-carriers. We thus hypothesized that BDNF/TrkB signaling delays CM progression in DMD. To test this hypothesis, we administered the TrkB agonist 7,8-dihydroxyflavone (DHF) to mdx 4cv ; mTR KO mice in their drinking water for 26 weeks, beginning at 8 weeks of age. Based on echocardiography, DHF treatment preserved cardiac output compared to vehicle-treated controls. Conversely, mdx 4cv ; mTR KO mice injected intraperitoneally with the TrkB inhibitor (K252a) displayed bradycardia and PR interval prolongation, as measured by EKG, as well as acute (10-20 min) reduction in percent EF and fractional shortening, as measured by echocardiography. K252a also significantly reduced sarcomere shortening in isolated murine cardiomyocytes. BDNF might also contribute to cardiac repair. Using humanized BDNF polymorphic mice, which have the Val66-Met mutation, we found that post-myocardial infarction cardiac dysfunction was significantly exacerbated in Met/Met mice compared to Val/Val littermate controls. Finally, we evaluated the role of BDNF/TrkB in human cardiomyocytes differentiated from induced pluripotent cells obtained from DMD patients (DMD iPSC-CMs) and found that they highly express BDNF protein in lysates and supernatants. DMD iPSC-CMs also expressed a truncated version of TrkB that lacks the tyrosine kinase domain essential for canonical BDNF/TrkB signaling. Nonetheless, DMD iPSC-CMs responded to treatment with recombinant BDNF, including increased phosphorylation of GSK-3α, mTOR, AMPK, and MSK1/2. Considered together, our results indicate that BDNF plays a protective role in the dystrophic heart and might represent a novel therapeutic candidate for DMD cardiomyopathy.

Role of Preoperative Duplex Ultrasonography to Predict Functional Maturation of Wrist Radiocephalic Arteriovenous Fistula: A Study on Indian Population

Radiocephalic arteriovenous fistula (RCAVF) is the first choice for native arteriovenous fistula (AVF). Preoperative vessel assessment with ultrasonography (USG) has been reported to enhance the outcome of native AVF, but data regarding its predictive value for functional maturation of RCAVF are scanty. We aimed to determine the role of preoperative duplex USG (DUS) for prediction of functional maturity of radiocephalic fistula in the wrist. The data from 173 patients were analyzed prospectively. The estimated duplex variable included size, patency, and continuity of cephalic vein and size, peak systolic velocity, and wall calcifications in radial artery at the wrist. The subjects underwent RCAVF creation and were reviewed 6-8 weeks post procedure for adequacy of maturation. Doppler variables between successful and failed maturation groups were compared. Successful functional fistula maturation was noted in 138 (80.9%) patients. Values of radial artery diameter, cephalic vein diameter, and peak systolic velocity were >2 mm, 2.2 mm, and 32.8 cm/s, respectively, for successful maturation of RCAVF in more than 90% of cases. Vascular calcifications were detected preoperatively in 15 diabetic patients and 9 (60%) of them had fistula failure. Preoperative DUS can provide a good prediction on functional maturation of RCAVF. Vascular calcifications were associated with high risk of maturation failure in diabetics.

Late posttransplant lymphoproliferative disease: Report of a rare case and role of positron emission tomography-computed tomography

Posttransplant lymphoproliferative disease (PTLD) is an uncommon complication of immunosuppression after solid organ transplantation. Early PTLD (<1 year after transplantation) is frequently found around the allograft, whereas late PTLD (>1 year after transplantation) does not have such a preference. 18-Fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸FDG PET-CT) has clinical significance in the evaluation of PTLD. ¹⁸FDG PET-CT scan allows precise anatomic localization of FDG-avid lesions, hence helpful in staging of disease and evaluation of response to therapy. It can better characterize persistent lesions and differentiate residual tumor from fibrosis or necrosis. We present a rare case report of a perigraft PTLD developing 12 years after renal transplantation sparing the graft, in an Epstein–Barr virus-negative patient.

Chronic Neuregulin-1β Treatment Mitigates the Progression of Postmyocardial Infarction Heart Failure in the Setting of Type 1 Diabetes Mellitus by Suppressing Myocardial Apoptosis, Fibrosis, and Key Oxidant-Producing Enzymes

BACKGROUND

Type 1 diabetes mellitus (DM) patients surviving myocardial infarction (MI) have substantially higher cardiovascular morbidity and mortality compared to their nondiabetic counterparts owing to the more frequent development of subsequent heart failure (HF). Neuregulin (NRG)-1β is released from cardiac microvascular endothelial cells and acts as a paracrine factor via the ErbB family of tyrosine kinase receptors expressed in cardiac myocytes to regulate cardiac development and stress responses. Because myocardial NRG-1/ErbB signaling has been documented to be impaired during HF associated with type 1 DM, we examined whether enhancement of NRG-1β signaling via exogenous administration of recombinant NRG-1β could exert beneficial effects against post-MI HF in the type 1 diabetic heart.

METHODS AND RESULTS

Type 1 DM was induced in male Sprague Dawley rats by a single injection of streptozotocin (STZ) (65 mg/kg). Two weeks after induction of type 1 DM, rats underwent left coronary artery ligation to induce MI. STZ-diabetic rats were treated with saline or NRG-1β (100 µg/kg) twice per week for 7 weeks, starting 2 weeks before experimental MI. Residual left ventricular function was significantly greater in the NRG-1β-treated STZ-diabetic MI group compared with the vehicle-treated STZ-diabetic MI group 5 weeks after MI as assessed by high-resolution echocardiography. NRG-1β treatment of STZ-diabetic MI rats was associated with reduced myocardial fibrosis and apoptosis as well as decreased gene expression of key oxidant-producing enzymes.

CONCLUSIONS

These results suggest that recombinant NRG-1β may be a promising therapeutic for HF post-MI in the setting of type 1 DM.

Entanglement of GSK-3β, β-catenin and TGF-β1 signaling network to regulate myocardial fibrosis

Nearly every form of the heart disease is associated with myocardial fibrosis, which is characterized by the accumulation of activated cardiac fibroblasts (CFs) and excess deposition of extracellular matrix (ECM). Although, CFs are the primary mediators of myocardial fibrosis in a diseased heart, in the traditional view, activated CFs (myofibroblasts) and resulting fibrosis were simply considered the secondary consequence of the disease, not the cause. Recent studies from our lab and others have challenged this concept by demonstrating that fibroblast activation and fibrosis are not simply the secondary consequence of a diseased heart, but are crucial for mediating various myocardial disease processes. In regards to the mechanism, the vast majority of literature is focused on the direct role of canonical SMAD-2/3-mediated TGF-β signaling to govern the fibrogenic process. Herein, we will discuss the emerging role of the GSK-3β, β-catenin and TGF-β1-SMAD-3 signaling network as a critical regulator of myocardial fibrosis in the diseased heart. The underlying molecular interactions and cross-talk among signaling pathways will be discussed. We will primarily focus on recent in vivo reports demonstrating that CF-specific genetic manipulation can lead to aberrant myocardial fibrosis and sturdy cardiac phenotype. This will allow for a better understanding of the driving role of CFs in the myocardial disease process. We will also review the specificity and limitations of the currently available genetic tools used to study myocardial fibrosis and its associated mechanisms. A better understanding of the GSK-3β, β-catenin and SMAD-3 signaling network may provide a novel therapeutic target for the management of myocardial fibrosis in the diseased heart.

Abstract 98: Canonical TGF-β1 Signaling in Cardiomyocytes is Essential to Maintain Basal Cardiac Function

The role of canonical transforming growth factor-β (TGF-β) pathway is well recognized in fibroblast biology and fibrosis in diseased hearts. However, its role in cardiomyocyte (CM) biology is not clear. SMAD4 is the central intracellular mediator of canonical TGF-β signaling. Herein, we investigate the role of SMAD4 in CM-biology and cardiac pathophysiology. SMAD4 homozygous floxed ( SMAD4 fl/fl ) and heterozygous floxed ( SMAD4 fl/- ) mice were crossed with α-myosin heavy chain (Mer-Cre-Mer) to create conditional CM-specific SMAD4-KO ( SMAD4 fl/fl Cre +/- ) and SMAD4 haploinsufficiency ( SMAD4 fl/- Cre +/- ), respectively. At 10 Wks of age, mice were subjected to well established tamoxifen diet protocol for 2 Wks. Echocardiographic analysis at 4 Wks post-tamoxifen treatment reveals that CM-specific loss of SMAD4 leads to dilatative ventricular remodeling as reflected by significantly increased LVIDs. This dilatative remodeling was associated with severe ventricular dysfunction as reflected by significantly reduced ejection fraction (EF) and fractional shortening (FS). Both HW/BW and LW/BW were significantly elevated in SMAD4 KO mice, suggesting pathological hypertrophy and heart failure in KOs. Analysis of Masson trichrome stained heart sections reveals a marked increase in fibrosis in the KO hearts. Q-PCR analysis showed the re-expression of fetal gene program (ANP, BNP), further confirming pathological remodeling in the KO hearts. As the heart functions of heterozygous mice and littermate controls were comparable at baseline, we stress them with TAC surgery. Consistent with KO findings, at 4 Wks post-TAC, heterozygous mice demonstrated characteristic heart failure phenotype. Taken together, these findings suggest that SMAD4 is required to maintain basal cardiac function and to prevent adverse ventricular remodeling in a pressure-overloaded heart.