The mammalian Ste20-like kinase 2 (Mst2) modulates stress-induced cardiac hypertrophy

Multi-Omics Analysis Revealed That TAOK1 Can Be Used as a Prognostic Marker and Target in a Variety of Tumors, Especially in Cervical Cancer

Background

Thousand and One Kinase 1 (TAOK1), a member of the MAPK kinase family, plays a crucial role in processes like microtubule dynamics, DNA damage response, and neurodevelopment. While TAOK1 is linked to tumorigenesis, its oncogenic role across cancers remains unclear. This study aims to explore the relationship between TAOK1 expression, prognosis, and immune function in various cancers.

Methods

We analyzed TAOK1 expression in multiple cancers using TCGA, GEO, CCLE, and other bioinformatics databases. The correlation between TAOK1 expression and immune cell infiltration was assessed with the ESTIMATE algorithm. We also examined associations with tumor stemness, DNA methylation, gene copy number alterations, and drug sensitivity. The oncogenic role of TAOK1 was further evaluated in vitro with SiHa and A2780 cells and in vivo with TAOK1 overexpression in SiHa cells.

Results

TAOK1 is a key prognostic biomarker in various cancers and its high expression is associated with poor prognosis. It showed a significant negative correlation with immune cell infiltration and immune checkpoints. GSEA identified its involvement in key tumour pathways, highlighting the therapeutic potential of inhibiting the TAOK1 gene. The high expression of TAOK1 is associated with DNA methylation and gene copy number variation, and in addition its upstream regulator, EP300, is closely associated with TAOK1 expression. In vitro cellular experiments demonstrated that inhibition of TAOK1 reduced the proliferation of SiHa and A2780 cells, whereas overexpression of TAOK1 in SiHa cells promoted growth. These findings were further validated in vivo by nude mouse tumourigenicity assay and human tissue immunohistochemistry.

Conclusion

TAOK1 serves as a promising prognostic biomarker and potential therapeutic target, especially for cervical cancer. These results support its clinical potential in cancer prognosis and treatment strategies.

Expression of foetal gene Pontin is essential in protecting heart against pathological remodelling and cardiomyopathy

Cardiac remodelling is a key process in the development of heart failure. Reactivation of foetal cardiac genes is often associated with cardiac remodelling. Here we study the role of Pontin (Ruvbl1), which is highly expressed in embryonic hearts, in mediating adverse remodelling in adult mouse hearts. We observe that Pontin deficiency in cardiomyocytes leads to induced apoptosis, increased hypertrophy and fibrosis, whereas Pontin overexpression improves survival, increases proliferation and reduces the hypertrophic response. Moreover, RNAseq analysis show that genes involved in cell cycle regulation, cell proliferation and cell survival/apoptosis are differentially expressed in Pontin knockout. Specifically, we detect changes in the expression of Hippo pathway components in the Pontin knockout mice. Using a cellular model we show that Pontin induces YAP activity, YAP nuclear translocation, and transcriptional activity. Our findings identify Pontin as a modulator of adverse cardiac remodelling, possibly via regulation of the Hippo pathway. This study may lead to the development of a new approach to control cardiac remodelling by targeting Pontin.

Dual inhibition of Mst1 and Mst2 exacerbates cardiac dysfunction during pressure overload stress in mice

Heart failure remains a leading cause of morbidity and mortality worldwide. The evolutionarily conserved Hippo-Yap signaling pathway regulates cardiac responses to stress and progression to heart failure. Mst1 and Mst2 are the core Hippo pathway kinases, yet their role within chronically stressed cardiomyocytes remains largely unknown. Genetic mouse models revealed that the extent of Mst1/2 inhibition elicits opposing effects on stress-induced cardiac dysfunction. Yap-TEAD1 activation, cell cycling, and hallmarks of cardiomyocyte dedifferentiation, which can impair contractile function during sustained stress, were enhanced in Mst1/2 double knockout hearts. These findings implicate a physiological function of Mst1/2 to promote cardiomyocyte maturity in the adult heart.

Circular RNAs: a small piece in the heart failure puzzle

Cardiovascular disease, specifically heart failure (HF), remains a significant concern in the realm of healthcare, necessitating the development of new treatments and biomarkers. The RNA family consists of various subgroups, including microRNAs, PIWI-interacting RNAs (piRAN) and long non-coding RNAs, which have shown potential in advancing personalized healthcare for HF patients. Recent research suggests that circular RNAs, a lesser-known subgroup of RNAs, may offer a novel set of targets and biomarkers for HF. This review will discuss the biogenesis of circular RNAs, their unique characteristics relevant to HF, their role in heart function, and their potential use as biomarkers in the bloodstream. Furthermore, future research directions in this field will be outlined. The stability of exosomal circRNAs makes them suitable as biomarkers, pathogenic regulators, and potential treatments for cardiovascular diseases such as atherosclerosis, acute coronary syndrome, ischemia/reperfusion injury, HF, and peripheral artery disease. Herein, we summarized the role of circular RNAs and their exosomal forms in HF diseases.

Obscurin Rho GEF domains are phosphorylated by MST-family kinases but do not exhibit nucleotide exchange factor activity towards Rho GTPases in vitro

Obscurin is a giant muscle protein (>800 kDa) featuring multiple signalling domains, including an SH3-DH-PH domain triplet from the Trio-subfamily of guanosine nucleotide exchange factors (GEFs). While previous research suggests that these domains can activate the small GTPases RhoA and RhoQ in cells, in vitro characterization of these interactions using biophysical techniques has been hampered by the intrinsic instability of obscurin GEF domains. To study substrate specificity, mechanism and regulation of obscurin GEF function by individual domains, we successfully optimized recombinant production of obscurin GEF domains and found that MST-family kinases phosphorylate the obscurin DH domain at Thr5798. Despite extensive testing of multiple GEF domain fragments, we did not detect any nucleotide exchange activity in vitro against 9 representative small GTPases. Bioinformatic analyses show that obscurin differs from other Trio-subfamily GEFs in several important aspects. While further research is necessary to evaluate obscurin GEF activity in vivo, our results indicate that obscurin has atypical GEF domains that, if catalytically active at all, are subject to complex regulation.

The role of the Hippo pathway in autophagy in the heart

The Hippo pathway, an evolutionarily conserved signalling mechanism, controls organ size and tumourigenesis. Increasing lines of evidence suggest that autophagy, an important mechanism of lysosome-mediated cellular degradation, is regulated by the Hippo pathway, which thereby profoundly affects cell growth and death responses in various cell types. In the heart, Mst1, an upstream component of the Hippo pathway, not only induces apoptosis but also inhibits autophagy through phosphorylation of Beclin 1. YAP/TAZ, transcription factor co-factors and the terminal effectors of the Hippo pathway, affect autophagy through transcriptional activation of TFEB, a master regulator of autophagy and lysosomal biogenesis. The cellular abundance of YAP is negatively regulated by autophagy and suppression of autophagy induces accumulation of YAP, which, in turn, acts as a feedback mechanism to induce autophagosome formation. Thus, the Hippo pathway and autophagy regulate each other, thereby profoundly affecting cardiomyocyte survival and death. This review discusses the interaction between the Hippo pathway and autophagy and its functional significance during stress conditions in the heart and the cardiomyocytes therein.

Micro RNA-411 Expression Improves Cardiac Phenotype Following Myocardial Infarction in Mice

Induction of endogenous regenerative capacity has emerged as one promising approach to repair damaged hearts following myocardial infarction (MI). Re-expression of factors that are exclusively expressed during embryonic development may reactivate the ability of adult cardiomyocytes to regenerate. Here, we identified miR-411 as a potent inducer of cardiomyocyte proliferation. Overexpression of miR-411 in the heart significantly increased cardiomyocyte proliferation and survival in a model MI. We found that miR-411 enhances the activity of YAP, the main downstream effector of the Hippo pathway, in cardiomyocytes. In conclusion, miR-411 induces cardiomyocyte regeneration and improves cardiac function post-MI likely by modulating the Hippo/YAP pathway.

Reengineering Ponatinib to Minimize Cardiovascular Toxicity

Small molecule tyrosine kinase inhibitors (TKI) have revolutionized cancer treatment and greatly improved patient survival. However, life-threatening cardiotoxicity of many TKIs has become a major concern. Ponatinib (ICLUSIG) was developed as an inhibitor of the BCR-ABL oncogene and is among the most cardiotoxic of TKIs. Consequently, use of ponatinib is restricted to the treatment of tumors carrying T315I-mutated BCR-ABL, which occurs in chronic myeloid leukemia (CML) and confers resistance to first- and second-generation inhibitors such as imatinib and nilotinib. Through parallel screening of cardiovascular toxicity and antitumor efficacy assays, we engineered safer analogs of ponatinib that retained potency against T315I BCR-ABL kinase activity and suppressed T315I mutant CML tumor growth. The new compounds were substantially less toxic in human cardiac vasculogenesis and cardiomyocyte contractility assays in vitro. The compounds showed a larger therapeutic window in vivo, leading to regression of human T315I mutant CML xenografts without cardiotoxicity. Comparison of the kinase inhibition profiles of ponatinib and the new compounds suggested that ponatinib cardiotoxicity is mediated by a few kinases, some of which were previously unassociated with cardiovascular disease. Overall, the study develops an approach using complex phenotypic assays to reduce the high risk of cardiovascular toxicity that is prevalent among small molecule oncology therapeutics.

SIGNIFICANCE

Newly developed ponatinib analogs retain antitumor efficacy but elicit significantly decreased cardiotoxicity, representing a therapeutic opportunity for safer CML treatment.

Some Insights into the Regulation of Cardiac Physiology and Pathology by the Hippo Pathway

The heart is one of the most fascinating organs in living beings. It beats up to 100,000 times a day throughout the lifespan, without resting. The heart undergoes profound anatomical, biochemical, and functional changes during life, from hypoxemic fetal stages to a completely differentiated four-chambered cardiac muscle. In the middle, many biological events occur after and intersect with each other to regulate development, organ size, and, in some cases, regeneration. Several studies have defined the essential roles of the Hippo pathway in heart physiology through the regulation of apoptosis, autophagy, cell proliferation, and differentiation. This molecular route is composed of multiple components, some of which were recently discovered, and is highly interconnected with multiple known prosurvival pathways. The Hippo cascade is evolutionarily conserved among species, and in addition to its regulatory roles, it is involved in disease by drastically changing the heart phenotype and its function when its components are mutated, absent, or constitutively activated. In this review, we report some insights into the regulation of cardiac physiology and pathology by the Hippo pathway.

The Hippo effector YAP1/TEAD1 regulates EPHA3 expression to control cell contact and motility

The EPHA3 protein tyrosine kinase, a member of the ephrin receptor family, regulates cell fate, cell motility, and cell-cell interaction. These cellular events are critical for tissue development, immunological responses, and the processes of tumorigenesis. Earlier studies revealed that signaling via the STK4-encoded MST1 serine-threonine protein kinase, a core component of the Hippo pathway, attenuated EPHA3 expression. Here, we investigated the mechanism by which MST1 regulates EPHA3. Our findings have revealed that the transcriptional regulators YAP1 and TEAD1 are crucial activators of EPHA3 transcription. Silencing YAP1 and TEAD1 suppressed the EPHA3 protein and mRNA levels. In addition, we identified putative TEAD enhancers in the distal EPHA3 promoter, where YAP1 and TEAD1 bind and promote EPHA3 expression. Furthermore, EPHA3 knockout by CRISPR/Cas9 technology reduced cell-cell interaction and cell motility. These findings demonstrate that EPHA3 is transcriptionally regulated by YAP1/TEAD1 of the Hippo pathway, suggesting that it is sensitive to cell contact-dependent interactions.

Identification of a dual TAOK1 and MAP4K5 inhibitor using a structure-based virtual screening approach

The STE20 kinase family is a complex signalling cascade that regulates cytoskeletal organisation and modulates the stress response. This signalling cascade includes various kinase mediators, such as TAOK1 and MAP4K5. The dysregulation of the STE20 kinase pathway is linked with cancer malignancy. A small-molecule inhibitor targeting the STE20 kinase pathway has therapeutic potential. In this study, a structure-based virtual screening (SBVS) approach was used to identify potential dual TAOK1 and MAP4K5 inhibitors. Enzymatic assays confirmed three potential dual inhibitors (>50% inhibition) from our virtual screening, and analysis of the TAOK1 and MAP4K5 binding sites indicated common interactions for dual inhibition. Compound 1 revealed potent inhibition of colorectal and lung cancer cell lines. Furthermore, compound 1 arrested cancer cells in the G0/G1 phase, which suggests the induction of apoptosis. Altogether, we show that the STE20 signalling mediators TAOK1 and MAP4K5 are promising targets for drug research.

Targeting the Hippo pathway in heart repair

The Hippo pathway is an evolutionarily and functionally conserved signaling pathway that controls organ size by regulating cell proliferation, apoptosis, and differentiation. Emerging evidence has shown that the Hippo pathway plays critical roles in cardiac development, homeostasis, disease, and regeneration. Targeting the Hippo pathway has tremendous potential as a therapeutic strategy for treating intractable cardiovascular diseases such as heart failure. In this review, we summarize the function of the Hippo pathway in the heart. Particularly, we highlight the posttranslational modification of Hippo pathway components, including the core kinases LATS1/2 and their downstream effectors YAP/TAZ, in different contexts, which has provided new insights and avenues in cardiac research.

Characterization of Hepatitis B Virus Integrations Identified in Hepatocellular Carcinoma Genomes

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related mortality. Almost half of HCC cases are associated with hepatitis B virus (HBV) infections, which often lead to HBV sequence integrations in the human genome. Accurate identification of HBV integration sites at a single nucleotide resolution is critical for developing a better understanding of the cancer genome landscape and of the disease itself. Here, we performed further analyses and characterization of HBV integrations identified by our recently reported VIcaller platform in recurrent or known HCC genes (such as TERT, MLL4, and CCNE1) as well as non-recurrent cancer-related genes (such as CSMD2, NKD2, and RHOU). Our pathway enrichment analysis revealed multiple pathways involving the alcohol dehydrogenase 4 gene, such as the metabolism pathways of retinol, tyrosine, and fatty acid. Further analysis of the HBV integration sites revealed distinct patterns involving the integration upper breakpoints, integrated genome lengths, and integration allele fractions between tumor and normal tissues. Our analysis also implies that the VIcaller method has diagnostic potential through discovering novel clonal integrations in cancer-related genes. In conclusion, although VIcaller is a hypothesis free virome-wide approach, it can still be applied to accurately identify genome-wide integration events of a specific candidate virus and their integration allele fractions.

Hippo pathway deletion in adult resting cardiac fibroblasts initiates a cell state transition with spontaneous and self-sustaining fibrosis

Cardiac fibroblasts (CFs) respond to injury by transitioning through multiple cell states, including resting CFs, activated CFs, and myofibroblasts. We report here that Hippo signaling cell-autonomously regulates CF fate transitions and proliferation, and non-cell-autonomously regulates both myeloid and CF activation in the heart. Conditional deletion of Hippo pathway kinases, Lats1 and Lats2, in uninjured CFs initiated a self-perpetuating fibrotic response in the adult heart that was exacerbated by myocardial infarction (MI). Single cell transcriptomics showed that uninjured Lats1/2 mutant CFs spontaneously transitioned to a myofibroblast cell state. Through gene regulatory network reconstruction, we found that Hippo-deficient myofibroblasts deployed a network of transcriptional regulators of endoplasmic reticulum (ER) stress, and the unfolded protein response (UPR) consistent with elevated secretory activity. We observed an expansion of myeloid cell heterogeneity in uninjured Lats1/2 CKO hearts with similarity to cells recovered from control hearts post-MI. Integrated genome-wide analysis of Yap chromatin occupancy revealed that Yap directly activates myofibroblast cell identity genes, the proto-oncogene Myc, and an array of genes encoding pro-inflammatory factors through enhancer-promoter looping. Our data indicate that Lats1/2 maintain the resting CF cell state through restricting the Yap-induced injury response.

Pharmacological inhibition of Hippo pathway, with the novel kinase inhibitor XMU-MP-1, protects the heart against adverse effects during pressure overload

BACKGROUND AND PURPOSE

The Hippo pathway has emerged as a potential therapeutic target to control pathological cardiac remodelling. The core components of the Hippo pathway, mammalian Ste-20 like kinase 1 (Mst1) and mammalian Ste-20 like kinase 2 (Mst2), modulate cardiac hypertrophy, apoptosis, and fibrosis. Here, we study the effects of pharmacological inhibition of Mst1/2 using a novel inhibitor XMU-MP-1 in controlling the adverse effects of pressure overload-induced hypertrophy.

EXPERIMENTAL APPROACH

We used cultured neonatal rat cardiomyocytes (NRCM) and C57Bl/6 mice with transverse aortic constriction (TAC) as in vitro and in vivo models, respectively, to test the effects of XMU-MP-1 treatment. We used luciferase reporter assays, western blots and immunofluorescence assays in vitro, with echocardiography, qRT-PCR and immunohistochemical methods in vivo.

KEY RESULTS

XMU-MP-1 treatment significantly increased activity of the Hippo pathway effector yes-associated protein and inhibited phenylephrine-induced hypertrophy in NRCM. XMU-MP-1 improved cardiomyocyte survival and reduced apoptosis following oxidative stress. In vivo, mice 3 weeks after TAC, were treated with XMU-MP-1 (1 mg·kg-1 ) every alternate day for 10 further days. XMU-MP-1-treated mice showed better cardiac contractility than vehicle-treated mice. Cardiomyocyte cross-sectional size and expression of the hypertrophic marker, brain natriuretic peptide, were reduced in XMU-MP-1-treated mice. Improved heart function in XMU-MP-1-treated mice with TAC, was accompanied by fewer TUNEL positive cardiomyocytes and lower levels of fibrosis, suggesting inhibition of cardiomyocyte apoptosis and decreased fibrosis.

CONCLUSIONS AND IMPLICATIONS

The Hippo pathway inhibitor, XMU-MP-1, reduced cellular hypertrophy and improved survival in cultured cardiomyocytes and, in vivo, preserved cardiac function following pressure overload.

The Hippo Signaling Pathway in Cardiac Development and Diseases

Heart disease continues to be the leading cause of morbidity and mortality worldwide. Cardiac malformation during development could lead to embryonic or postnatal death. However, matured heart tissue has a very limited regenerative capacity. Thus, loss of cardiomyocytes from injury or diseases in adults could lead to heart failure. The Hippo signaling pathway is a newly identified signaling cascade that modulates regenerative response by regulating cardiomyocyte proliferation in the embryonic heart, as well as in postnatal hearts after injury. In this review, we summarize recent findings highlighting the function and regulation of the Hippo signaling pathway in cardiac development and diseases.

PKC and PKN in heart disease

The protein kinase C (PKC) and closely related protein kinase N (PKN) families of serine/threonine protein kinases play crucial cellular roles. Both kinases belong to the AGC subfamily of protein kinases that also include the cAMP dependent protein kinase (PKA), protein kinase B (PKB/AKT), protein kinase G (PKG) and the ribosomal protein S6 kinase (S6K). Involvement of PKC family members in heart disease has been well documented over the years, as their activity and levels are mis-regulated in several pathological heart conditions, such as ischemia, diabetic cardiomyopathy, as well as hypertrophic or dilated cardiomyopathy. This review focuses on the regulation of PKCs and PKNs in different pathological heart conditions and on the influences that PKC/PKN activation has on several physiological processes. In addition, we discuss mechanisms by which PKCs and the closely related PKNs are activated and turned-off in hearts, how they regulate cardiac specific downstream targets and pathways, and how their inhibition by small molecules is explored as new therapeutic target to treat cardiomyopathies and heart failure.

How Hippo Signaling Pathway Modulates Cardiovascular Development and Diseases

Cardiovascular disease remains the leading cause of death around the globe. Cardiac deterioration is associated with irreversible cardiomyocyte loss. Understanding how the cardiovascular system develops and the pathological processes of cardiac disease will contribute to finding novel and preventive therapeutic methods. The canonical Hippo tumor suppressor pathway in mammalian cells is primarily composed of the MST1/2-SAV1-LATS1/2-MOB1-YAP/TAZ cascade. Continuing research on this pathway has identified other factors like RASSF1A, Nf2, MAP4Ks, and NDR1/2, further enriching our knowledge of the Hippo-YAP pathway. YAP, the core effecter of the Hippo pathway, may accumulate in the nucleus and initiate transcriptional activity if the pathway is inhibited. The role of Hippo signaling has been widely investigated in organ development and cancers. A heart of normal size and function which is critical for survival could not be generated without the proper regulation of the Hippo tumor suppressor pathway. Recent research has demonstrated a novel role of Hippo signaling in cardiovascular disease in the context of development, hypertrophy, angiogenesis, regeneration, apoptosis, and autophagy. In this review, we summarize the current knowledge of how Hippo signaling modulates pathological processes in cardiovascular disease and discuss potential molecular therapeutic targets.

Advanced glycation end products reduce the calcium transient in cardiomyocytes by increasing production of reactive oxygen species and nitric oxide

Advanced glycation end products (AGE) are central to the development of cardiovascular complications associated with diabetes mellitus. AGE may alter cellular function through cross‐linking of cellular proteins or by activating the AGE receptor (RAGE). However, the signalling molecules involved during AGE stimulation in cardiomyocytes remain unclear. Here, we investigated the effects of AGE treatment on intracellular calcium homeostasis of isolated cardiomyocytes and studied the activation of signalling molecules involved in this process. Treatment of cardiomyocytes with AGE for 24 h resulted in a dose‐dependent reduction in calcium transient amplitude, reaching a maximum 50% reduction at a dose of 1 mg·mL⁻¹. This was accompanied with a 32% reduction in sarcoplasmic reticulum calcium content but without any detectable changes in the expression of major calcium channels. Mechanistically, we observed a significant increase in the production of reactive oxygen species (ROS) in AGE‐treated cardiomyocytes and enhancement of NADPH oxidase activity. This was accompanied with activation of p38 kinase and nuclear translocation of NF‐κB, and subsequently induction of inducible NO synthase (iNOS) expression, leading to excessive nitric oxide production. Overall, our data reveal the molecular signalling that may underlie the alteration of intracellular calcium homeostasis in cardiac myocytes due to AGE stimulation. This may provide new insights into the pathophysiological mechanisms of the development of diabetic cardiomyopathy.

The Hippo pathway in tissue homeostasis and regeneration

While several organs in mammals retain partial regenerative capability following tissue damage, the underlying mechanisms remain unclear. Recently, the Hippo signaling pathway, better known for its function in organ size control, has been shown to play a pivotal role in regulating tissue homeostasis and regeneration. Upon tissue injury, the activity of YAP, the major effector of the Hippo pathway, is transiently induced, which in turn promotes expansion of tissue-resident progenitors and facilitates tissue regeneration. In this review, with a general focus on the Hippo pathway, we will discuss its major components, functions in stem cell biology, involvement in tissue regeneration in different organs, and potential strategies for developing Hippo pathway-targeted regenerative medicines.

A growing role for the Hippo signaling pathway in the heart

Heart disease is a major cause of clinical morbidity and mortality, and a significant health and economic burden worldwide. The loss of functional cardiomyocytes, often a result of myocardial infarction, leads to impaired cardiac output and ultimately heart failure. Therefore, efforts to improve cardiomyocyte viability and stimulate cardiomyocyte proliferation remain attractive therapeutic goals. Originally identified in Drosophila, the Hippo signaling pathway is highly conserved from flies to humans and regulates organ size through modulation of both cell survival and proliferation. This is particularly relevant to the heart, an organ with limited regenerative ability. Recent work has demonstrated a critical role for this signaling cascade in determining heart development, homeostasis, injury and the potential for regeneration. Here we review the function of canonical and non-canonical Hippo signaling in cardiomyocytes, with a particular focus on proliferation and survival, and how this impacts the stressed adult heart.

The Hippo Pathway: A Master Regulatory Network Important in Development and Dysregulated in Disease

The Hippo Pathway is a master regulatory network that regulates proliferation, cell growth, stemness, differentiation, and cell death. Coordination of these processes by the Hippo Pathway throughout development and in mature organisms in response to diverse external and internal cues plays a role in morphogenesis, in controlling organ size, and in maintaining organ homeostasis. Given the importance of these processes, the Hippo Pathway also plays an important role in organismal health and has been implicated in a variety of diseases including eye disease, cardiovascular disease, neurodegeneration, and cancer. This review will focus on Drosophila reports that identified the core components of the Hippo Pathway revealing specific downstream biological outputs of this complicated network. A brief description of mammalian reports will complement review of the Drosophila studies. This review will also survey upstream regulation of the core components with a focus on feedback mechanisms.

The oxoglutarate receptor 1 (OXGR1) modulates pressure overload-induced cardiac hypertrophy in mice

The G-protein-coupled receptors (GPCRs) family of proteins play essential roles in the heart, including in the regulation of cardiac hypertrophy. One member of this family, the oxoglutarate receptor 1 (OXGR1), may have a crucial role in the heart because it acts as a receptor for α-ketoglutarate, a metabolite that is elevated in heart failure patients. OXGR1 is expressed in the heart but its precise function during cardiac pathophysiological process is unknown. Here we used both in vivo and in vitro approaches to investigate the role of OXGR1 in cardiac hypertrophy. Genetic ablation of Oxgr1 in mice (OXGR1^-/-) resulted in a significant increase in hypertrophy following transverse aortic constriction (TAC). This was accompanied by reduction in contractile function as indicated by cardiac fractional shortening and ejection fraction. Conversely, adenoviral mediated overexpression of OXGR1 in neonatal rat cardiomyocytes significantly reduced phenylephrine-induced cardiomyocyte hypertrophy, a result that was consistent with the in vivo data. Using a combination of yeast two hybrid screening and phospho-antibody array analysis we identified novel interacting partner and downstream signalling pathway that might be regulated by the OXGR1. First, we found that OXGR1 forms a molecular complex with the COP9 signalosome complex subunit 5 (CSN5). Secondly, we observed that the STAT3 signalling pathway was upregulated in OXGR1^-/- hearts. Since CSN5 interacts with TYK2, a major upstream regulator of STAT3, OXGR1 might regulate the pro-hypertrophic STAT3 pathway via interaction with the CSN5-TYK2 complex. In conclusion, our study has identified OXGR1 as a novel regulator of pathological hypertrophy via the regulation of the STAT3. Identification of molecules that can specifically activate or inhibit this receptor may be very useful in the development of novel therapeutic approach for pathological cardiac hypertrophy.

Hippo Signaling in the Heart - Non-Canonical Pathways Impact Growth, Survival and Function

Initially identified inDrosophila melanogaster, the Hippo signaling pathway regulates organ size through modulation of cell proliferation, survival and differentiation. This pathway is evolutionarily conserved and canonical signaling involves a kinase cascade that phosphorylates and inhibits the downstream effector Yes-associated protein (YAP). Recent research has demonstrated a fundamental role of Hippo signaling in cardiac development, homeostasis, injury and regeneration, and remains the subject of intense investigation. However, 2 prominent members of this pathway, RASSF1A and Mst1, have been shown to influence heart function and stress responses through YAP-independent mechanisms. This review summarizes non-canonical targets of RASSF1A and Mst1 and discusses their role in the context of cardiac hypertrophy, autophagy, apoptosis and function. (Circ J 2016; 80: 1504-1510).

The plasma membrane calcium ATPase 4 signalling in cardiac fibroblasts mediates cardiomyocyte hypertrophy

The heart responds to pathological overload through myocyte hypertrophy. Here we show that this response is regulated by cardiac fibroblasts via a paracrine mechanism involving plasma membrane calcium ATPase 4 (PMCA4). Pmca4 deletion in mice, both systemically and specifically in fibroblasts, reduces the hypertrophic response to pressure overload; however, knocking out Pmca4 specifically in cardiomyocytes does not produce this effect. Mechanistically, cardiac fibroblasts lacking PMCA4 produce higher levels of secreted frizzled related protein 2 (sFRP2), which inhibits the hypertrophic response in neighbouring cardiomyocytes. Furthermore, we show that treatment with the PMCA4 inhibitor aurintricarboxylic acid (ATA) inhibits and reverses cardiac hypertrophy induced by pressure overload in mice. Our results reveal that PMCA4 regulates the development of cardiac hypertrophy and provide proof of principle for a therapeutic approach to treat this condition.

Cardiac and vascular toxicities of angiogenesis inhibitors: The other side of the coin

Angiogenesis is one of the best-described tumor hallmarks. Targeting angiogenesis is becoming a successful strategy to suppress cancer growth. Vascular endothelial growth factor (VEGF), the fulcrum of angiogenesis, contributes to vascular and cardiac homeostasis. Angiogenesis inhibitors classically associated with vascular side effects are increasingly recognized for cardiac adverse effects as reflected by several meta-analyses. A global approach to these findings is a pressing need, and future strategies involving collaboration among different medical specialties are highly encouraged.

mTORC2 regulates cardiac response to stress by inhibiting MST1

The mTOR and Hippo pathways have recently emerged as the major signaling transduction cascades regulating organ size and cellular homeostasis. However, direct crosstalk between two pathways is yet to be determined. Here, we demonstrate that mTORC2 is a direct negative regulator of the MST1 kinase, a key component of the Hippo pathway. mTORC2 phosphorylates MST1 at serine 438 in the SARAH domain, thereby reducing its homodimerization and activity. We found that Rictor/mTORC2 preserves cardiac structure and function by restraining the activity of MST1 kinase. Cardiac-specific mTORC2 disruption through Rictor deletion leads to a marked activation of MST1 that, in turn, promotes cardiac dysfunction and dilation, impairing cardiac growth and adaptation in response to pressure overload. In conclusion, our study demonstrates the existence of a direct crosstalk between mTORC2 and MST1 that is critical for cardiac cell survival and growth.