TNNI3K, a cardiac-specific kinase, promotes physiological cardiac hypertrophy in transgenic mice

Expression Levels of the Tnni3k Gene in the Heart Are Highly Associated with Cardiac and Glucose Metabolism-Related Phenotypes and Functional Pathways

BACKGROUND

Troponin-I interacting kinase encoded by the TNNI3K gene is expressed in nuclei and Z-discs of cardiomyocytes. Mutations in TNNI3K were identified in patients with cardiac conduction diseases, arrhythmias, and cardiomyopathy.

METHODS

We performed cardiac gene expression, whole genome sequencing (WGS), and cardiac function analysis in 40 strains of BXD recombinant inbred mice derived from C57BL/6J (B6) and DBA/2J (D2) strains. Expression quantitative trait loci (eQTLs) mapping and gene enrichment analysis was performed, followed by validation of candidate Tnni3k-regulatory genes.

RESULTS

WGS identified compound splicing and missense T659I Tnni3k variants in the D2 parent and some BXD strains (D allele) and these strains had significantly lower Tnni3k expression than those carrying wild-type Tnni3k (B allele). Expression levels of Tnni3k significantly correlated with multiple cardiac (heart rate, wall thickness, PR duration, and T amplitude) and metabolic (glucose levels and insulin resistance) phenotypes in BXDs. A significant cis-eQTL on chromosome 3 was identified for the regulation of Tnni3k expression. Furthermore, Tnni3k-correlated genes were primarily involved in cardiac and glucose metabolism-related functions and pathways. Genes Nodal, Gnas, Nfkb1, Bmpr2, Bmp7, Smad7, Acvr1b, Acvr2b, Chrd, Tgfb3, Irs1, and Ppp1cb were differentially expressed between the B and D alleles.

CONCLUSIONS

Compound splicing and T659I Tnni3k variants reduce cardiac Tnni3k expression and Tnni3k levels are associated with cardiac and glucose metabolism-related phenotypes.

Genetic Burden of TNNI3K in Diagnostic Testing of Patients With Dilated Cardiomyopathy and Supraventricular Arrhythmias

BACKGROUND

Genetic variants in TNNI3K (troponin-I interacting kinase) have previously been associated with dilated cardiomyopathy (DCM), cardiac conduction disease, and supraventricular tachycardias. However, the link between TNNI3K variants and these cardiac phenotypes shows a lack of consensus concerning phenotype and protein function.

METHODS

We describe a systematic retrospective study of a cohort of patients undergoing genetic testing for cardiac arrhythmias and cardiomyopathy including TNNI3K. We further performed burden testing of TNNI3K in the UK Biobank. For 2 novel TNNI3K variants, we tested cosegregation. TNNI3K kinase function was estimated by TNNI3K autophosphorylation assays.

RESULTS

We demonstrate enrichment of rare coding TNNI3K variants in DCM patients in the Amsterdam cohort. In the UK Biobank, we observed an association between TNNI3K missense (but not loss-of-function) variants and DCM and atrial fibrillation. Furthermore, we demonstrate genetic segregation for 2 rare variants, TNNI3K-p.Ile512Thr and TNNI3K-p.His592Tyr, with phenotypes consisting of DCM, cardiac conduction disease, and supraventricular tachycardia, together with increased autophosphorylation. In contrast, TNNI3K-p.Arg556_Asn590del, a likely benign variant, demonstrated depleted autophosphorylation.

CONCLUSIONS

Our findings demonstrate an increased burden of rare coding TNNI3K variants in cardiac patients with DCM. Furthermore, we present 2 novel likely pathogenic TNNI3K variants with increased autophosphorylation, suggesting that enhanced autophosphorylation is likely to drive pathogenicity.

Embryonic Hyperglycemia Disrupts Myocardial Growth, Morphological Development, and Cellular Organization: An In Vivo Experimental Study

Hyperglycemia during gestation can disrupt fetal heart development and increase postnatal cardiovascular disease risk. It is therefore imperative to identify early biomarkers of hyperglycemia during gestation-induced fetal heart damage and elucidate the underlying molecular pathomechanisms. Clinical investigations of diabetic adults with heart dysfunction and transgenic mouse studies have revealed that overexpression or increased expression of TNNI3K, a heart-specific kinase that binds troponin cardiac I, may contribute to abnormal cardiac remodeling, ventricular hypertrophy, and heart failure. Optimal heart function also depends on the precise organization of contractile and excitable tissues conferred by intercellular occlusive, adherent, and communicating junctions. The current study evaluated changes in embryonic heart development and the expression levels of sarcomeric proteins (troponin I, desmin, and TNNI3K), junctional proteins, glucose transporter-1, and Ki-67 under fetal hyperglycemia. Stage 22HH Gallus domesticus embryos were randomly divided into two groups: a hyperglycemia (HG) group, in which individual embryos were injected with 30 mmol/L glucose solution every 24 h for 10 days, and a no-treatment (NT) control group, in which individual embryos were injected with physiological saline every 24 h for 10 days (stage 36HH). Embryonic blood glucose, height, and weight, as well as heart size, were measured periodically during treatment, followed by histopathological analysis and estimation of sarcomeric and junctional protein expression by western blotting and immunostaining. Hyperglycemic embryos demonstrated delayed heart maturation, with histopathological analysis revealing reduced left and right ventricular wall thickness (−39% and −35% vs. NT). Immunoexpression levels of TNNI3K and troponin 1 increased (by 37% and 39%, respectively), and desmin immunofluorescence reduced (by 23%). Embryo-fetal hyperglycemia may trigger an increase in the expression levels of TNNI3K and troponin I, as well as dysfunction of occlusive and adherent junctions, ultimately inducing abnormal cardiac remodeling.

Knockout of Cardiac Troponin I-Interacting Kinase leads to cardiac dysfunction and remodeling

Cardiac troponin I-interacting kinase (TNNI3K) is a cardiac-specific kinase that has been identified as a diagnostic marker and a therapeutic target in cardiovascular diseases. However, the biological function of TNNI3K in cardiac dysfunction and remodeling remain elusive. In the present study, a Tnni3k cardiomyocyte-specific knockout (Tnni3k-cKO) mouse model was established. Echocardiography was used to evaluate cardiac function in mice. Heart failure markers were detected using enzyme-linked immunosorbent assay. Hematoxylin and eosin staining, wheat germ agglutinin staining, Masson's trichrome staining, Sirius red staining, and TUNEL staining were used to assess histopathological changes, cardiac hypertrophy, collagen deposition, and myocardial apoptosis, respectively. Expression levels of TNNI3K, apoptosis-related proteins, and p38 mitogen-activated protein kinase were measured using Western blot analysis. Compared to wild-type controls, cardiac dysfunction and cardiac remodeling of Tnni3k-cKO mice increased gradually with age. Tnni3k-cKO mice exhibited cardiac hypertrophy, cardiac fibrosis, and cardiomyocyte apoptosis. Upregulation of cleaved caspase-3 in Tnni3k-cKO mice appeared to be related to phosphorylation and activation of the p38 mitogen-activated protein kinase signaling pathway. In conclusion, this study shows that TNNI3K is essential for cardiac development and function, providing new insights into the development of novel therapeutic strategies for cardiac diseases.

Angiopoietin 2 as a Novel Potential Biomarker for Acute Aortic Dissection

Biomarker-assisted diagnosis of acute aortic dissection (AAD) is important for initiation of treatment and improved survival. However, identification of biomarkers for AAD in blood is a challenging task. The present study aims to find the potential AAD biomarkers using a transcriptomic strategy. Arrays based genome-wide gene expression profiling were performed using ascending aortic tissues which were collected from AAD patients and healthy donors. The differentially expressed genes were validated using quantitative reverse transcriptase PCR (qRT-PCR) and western blot. The plasma levels of a potential biomarker, angiopoietin 2 (ANGPT2) were determined in case-control cohort (77 AAD patients and 82 healthy controls) by enzyme linked immunosorbent assay. Receiver operating characteristic curve (ROC) was used to evaluate the diagnostic power of ANGPT2 for AAD. Transcriptome data demonstrated that a total of 18 genes were significantly up-regulated and 28 genes were significantly down-regulated among AAD tissues (foldchange>3.0, p < 0.01). By bioinformatic analysis, we identified ANGPT2 as a candidate biomarker for blood-based detection of AAD. The qRT-PCR and protein expression demonstrated that ANGPT2 increased 2.4- and 4.2 folds, respectively in aortic tissue of AAD patients. Immunohistochemical staining demonstrated that ANGPT2 was markedly increased in intima of the aortic wall in AAD. Furthermore, ANGPT2 was significantly elevated in AAD patients as compared with controls (median 1625 vs. 383 pg/ml, p < 1E-6). ROC curve analysis showed that ANGPT2 was highly predictive of a diagnosis of type A AAD (area under curve 0.93, p < 1E-6). Sensitivity and specificity were 81 and 90%, respectively at the cutoff value of 833 pg/ml. In conclusion, ANGPT2 could be a promising biomarker for diagnosis of AAD; however, more studies are still needed to verify its specificity in diagnosing of AAD.

A Novel Missense Mutation in TNNI3K Causes Recessively Inherited Cardiac Conduction Disease in a Consanguineous Pakistani Family

Cardiac conduction disease (CCD), which causes altered electrical impulse propagation in the heart, is a life-threatening condition with high morbidity and mortality. It exhibits genetic and clinical heterogeneity with diverse pathomechanisms, but in most cases, it disrupts the synchronous activity of impulse-generating nodes and impulse-conduction underlying the normal heartbeat. In this study, we investigated a consanguineous Pakistani family comprised of four patients with CCD. We applied whole exome sequencing (WES) and co-segregation analysis, which identified a novel homozygous missense mutation (c.1531T>C;(p.Ser511Pro)) in the highly conserved kinase domain of the cardiac troponin I-interacting kinase (TNNI3K) encoding gene. The behaviors of mutant and native TNNI3K were compared by performing all-atom long-term molecular dynamics simulations, which revealed changes at the protein surface and in the hydrogen bond network. Furthermore, intra and intermolecular interaction analyses revealed that p.Ser511Pro causes structural variation in the ATP-binding pocket and the homodimer interface. These findings suggest p.Ser511Pro to be a pathogenic variant. Our study provides insights into how the variant perturbs the TNNI3K structure-function relationship, leading to a disease state. This is the first report of a recessive mutation in TNNI3K and the first mutation in this gene identified in the Pakistani population.

The Diverse Roles of TNNI3K in Cardiac Disease and Potential for Treatment

In the two decades since the discovery of TNNI3K it has been implicated in multiple cardiac phenotypes and physiological processes. TNNI3K is an understudied kinase, which is mainly expressed in the heart. Human genetic variants in TNNI3K are associated with supraventricular arrhythmias, conduction disease, and cardiomyopathy. Furthermore, studies in mice implicate the gene in cardiac hypertrophy, cardiac regeneration, and recovery after ischemia/reperfusion injury. Several new papers on TNNI3K have been published since the last overview, broadening the clinical perspective of TNNI3K variants and our understanding of the underlying molecular biology. We here provide an overview of the role of TNNI3K in cardiomyopathy and arrhythmia covering both a clinical perspective and basic science advancements. In addition, we review the potential of TNNI3K as a target for clinical treatments in different cardiac diseases.

Silencing Cardiac Troponin I-Interacting Kinase Reduces Lipopolysaccharide-Induced Sepsis-Induced Myocardial Dysfunction in Rat by Regulating Apoptosis-Related Proteins

The aim of this study was to investigate the effect of cardiac troponin I-interacting kinase (TNNI3K) on sepsis-induced myocardial dysfunction (SIMD) and further explore the underlying molecular mechanisms. In this study, a lipopolysaccharide- (LPS-) induced myocardial injury model was used. qRT-PCR was performed to detect the mRNA expression of TNNI3K. Western blot was conducted to quantitatively detect the expression of TNNI3K and apoptosis-related proteins (Bcl-2, Bax, and caspase-3). ELISA was performed to detect the content of lactate dehydrogenase (LDH) and creatine kinase (CK). TUNEL assay was used to detect the apoptosis of H9C2 cells. In LPS-induced H9C2 cells, TNNI3K was up regulated. Besides, the CK activity, the content of LDH, and the apoptosis of H9C2 cells were significantly increased after treatment with LPS. Silencing TNNI3K decreased the LDH release activity and CK activity and inhibited apoptosis of H9C2 cell. Further research illustrated that si-TNNI3K promoted the protein expression of Bcl-2 and decreased the protein expression of Bax and cleaved caspase-3. The study concluded that TNNI3K was upregulated in LPS-induced H9C2 cells. Importantly, functional research findings indicated that silencing TNNI3K alleviated LPS-induced H9C2 cell injury by regulating apoptosis-related proteins.

MiR-223-3p in Cardiovascular Diseases: A Biomarker and Potential Therapeutic Target

Cardiovascular diseases, involving vasculopathy, cardiac dysfunction, or circulatory disturbance, have become the major cause of death globally and brought heavy social burdens. The complexity and diversity of the pathogenic factors add difficulties to diagnosis and treatment, as well as lead to poor prognosis of these diseases. MicroRNAs are short non-coding RNAs to modulate gene expression through directly binding to the 3′-untranslated regions of mRNAs of target genes and thereby to downregulate the protein levels post-transcriptionally. The multiple regulatory effects of microRNAs have been investigated extensively in cardiovascular diseases. MiR-223-3p, expressed in multiple cells such as macrophages, platelets, hepatocytes, and cardiomyocytes to modulate their cellular activities through targeting a variety of genes, is involved in the pathological progression of many cardiovascular diseases. It participates in regulation of several crucial signaling pathways such as phosphatidylinositol 3-kinase/protein kinase B, insulin-like growth factor 1, nuclear factor kappa B, mitogen-activated protein kinase, NOD-like receptor family pyrin domain containing 3 inflammasome, and ribosomal protein S6 kinase B1/hypoxia inducible factor 1 α pathways to affect cell proliferation, migration, apoptosis, hypertrophy, and polarization, as well as electrophysiology, resulting in dysfunction of cardiovascular system. Here, in this review, we will discuss the role of miR-223-3p in cardiovascular diseases, involving its verified targets, influenced signaling pathways, and regulation of cell function. In addition, the potential of miR-223-3p as therapeutic target and biomarker for diagnosis and prediction of cardiovascular diseases will be further discussed, providing clues for clinicians.

Identification of a nonsense mutation in TNNI3K associated with cardiac conduction disease

BACKGROUND

Cardiac conduction disease (CCD) is a common cardiovascular disease which can lead to life-threatening conditions. The importance of heredity in CCD has been realized in recent years. Several causal genes have been found to be implicated in CCD such as SCN5A, TRPM4, SCN1B, TNNI3K, LMNA, and NKX2.5. To date, only four genetic mutations in TNNI3K have been identified related to CCD.

METHODS

Whole-exome sequencing (WES) was carried out in order to identify the underlying disease-causing mutation in a Chinese family with CCD. The potential mutations were confirmed by Sanger sequencing. Real-time qPCR was used to detect the level of TNNI3K mRNA expression.

RESULTS

A nonsense mutation in TNNI3K (NM_015978.2: g.170891C > T, c.1441C > T) was identified in this family and validated by Sanger sequencing. Real-time qPCR confirmed that the level of TNNI3K mRNA expression was decreased compared with the controls.

CONCLUSIONS

This study found the first nonsense TNNI3K mutation associated with CCD in a Chinese family. TNNI3K harboring the mutation (c.1441C > T) implicated a loss-of-function pathogenic mechanism with an autosomal dominant inheritance pattern. This research enriches the phenotypic spectrum of TNNI3K mutations, casting a new light upon the genotype-phenotype correlations between TNNI3K mutations and CCD and indicating the importance of TNNI3K screening in CCD patients.

3D-QSAR Assisted Design of Novel 7-Deazapurine Derivatives as TNNI3K Kinase Inhibitors Using Molecular Docking and Molecular Dynamics Simulation

Background:

Cardiac troponin I-interacting kinase (TNNI3K) is a cardiac-specific kinase that belongs to MAPKKK family. It is a dual-function kinase with tyrosine and serine/threonine kinase activity. Over-expression of TNNI3K results in various cardiovascular diseases such as cardiomyopathy, ischemia/reperfusion injury, heart failure, etc. Since, it is a cardiac-specific kinase and expressed only in heart tissue, it is an ideal molecular target to treat cardiac diseases. The main objective of the work is to study and understand the structure-activity relationship of the reported deazapurine derivatives and to use the 3D-QSAR and docking results to design potent and novel TNNI3K inhibitors of this series.

Methods:

In the present study, we have used molecular docking 3D QSAR, and molecular dynamics simulation to understand the structure-activity correlation of reported TNNI3K inhibitors and to design novel compounds of deazapurine derivatives with increased activity.

Results:

Both CoMFA (q2=0.669, NOC=5, r2=0.944) and CoMSIA (q2=0.783, NOC=5, r2=0.965) have resulted in satisfactory models. The models were validated using external test set, Leave-out- Five, bootstrapping, progressive scrambling, and rm2 metrics calculations. The validation procedures showed the developed models were robust and reliable. The docking results and the contour maps analysis helped in the better understanding of the structure-activity relationship.

Conclusion:

This is the first report on 3D-QSAR modeling studies of TNNI3K inhibitors. Both docking and MD results were consistent and showed good correlation with the previous experimental data. Based on the information obtained from contour maps, 31 novel TNNI3K inhibitors were designed. These designed compounds showed higher activity than the existing dataset compounds.

Supraventricular tachycardias, conduction disease, and cardiomyopathy in 3 families with the same rare variant in TNNI3K (p.Glu768Lys)

BACKGROUND

Rare genetic variants in TNNI3K encoding troponin-I interacting kinase have been linked to a distinct syndrome consisting primarily of supraventricular tachycardias and variably expressed conduction disturbance and dilated cardiomyopathy in 2 families.

OBJECTIVE

The purpose of this study was to identify new genetic variants associated with inherited supraventricular tachycardias, cardiac conduction disease, and cardiomyopathy.

METHODS

We conducted next generation sequencing in 3 independent multigenerational families with atrial/junctional tachycardia with or without conduction disturbance, dilated cardiomyopathy, and sudden death. We also assessed the effect of identified variant on protein autophosphorylation.

RESULTS

In this study, we uncovered the same ultra-rare genetic variant in TNNI3K (c.2302G>A, p.Glu768Lys), which co-segregated with disease features in all affected individuals (n = 23) from all 3 families. TNNI3K harboring the TNNI3K-p.Glu768Lys variant displayed enhanced kinase activity, in line with expectations from previous mouse studies that demonstrated increased conduction indices and procardiomyopathic effects with increased levels of Tnni3k.

CONCLUSION

This study corroborates further the causal link between rare genetic variation in TNNI3K and this distinct complex phenotype, and points to enhanced kinase activity of TNNI3K as the underlying pathobiological mechanism.

Troponin through the looking-glass: emerging roles beyond regulation of striated muscle contraction

Troponin is a heterotrimeric Ca²⁺-binding protein that has a well-established role in regulating striated muscle contraction. However, mounting evidence points to novel cellular functions of troponin, with profound implications in cancer, cardiomyopathy pathogenesis and skeletal muscle aging. Here, we highlight the non-canonical roles and aberrant expression patterns of troponin beyond the sarcomeric milieu. Utilizing bioinformatics tools and online databases, we also provide pathway, subcellular localization, and protein-protein/DNA interaction analyses that support a role for troponin in multiple subcellular compartments. This emerging knowledge challenges the conventional view of troponin as a sarcomere-specific protein exclusively involved in muscle contraction and may transform the way we think about sarcomeric proteins, particularly in the context of human disease and aging.

Overexpression of miR-223 Tips the Balance of Pro- and Anti-hypertrophic Signaling Cascades toward Physiologic Cardiac Hypertrophy

MicroRNAs (miRNAs) have been extensively examined in pathological cardiac hypertrophy. However, few studies focused on profiling the miRNA alterations in physiological hypertrophic hearts. In this study we generated a transgenic mouse model with cardiac-specific overexpression of miR-223. Our results showed that elevation of miR-223 caused physiological cardiac hypertrophy with enhanced cardiac function but no fibrosis. Using the next generation RNA sequencing, we observed that most of dys-regulated genes (e.g. Atf3/5, Egr1/3, Sfrp2, Itgb1, Ndrg4, Akip1, Postn, Rxfp1, and Egln3) in miR-223-transgenic hearts were associated with cell growth, but they were not directly targeted by miR-223. Interestingly, these dys-regulated genes are known to regulate the Akt signaling pathway. We further identified that miR-223 directly interacted with 3'-UTRs of FBXW7 and Acvr2a, two negative regulators of the Akt signaling. However, we also validated that miR-223 directly inhibited the expression of IGF-1R and β1-integrin, two positive regulators of the Akt signaling. Lastly, Western blotting did reveal that Akt was activated in miR-223-overexpressing hearts. Adenovirus-mediated overexpression of miR-223 in neonatal rat cardiomyocytes induced cell hypertrophy, which was blocked by the addition of MK2206, a specific inhibitor of Akt Taken together, these data represent the first piece of work showing that miR-223 tips the balance of promotion and inactivation of Akt signaling cascades toward activation of Akt, a key regulator of physiological cardiac hypertrophy. Thus, our study suggests that the ultimate phenotype outcome of a miRNA may be decided by the secondary net effects of the whole target network rather than by several primary direct targets in an organ/tissue.

Small molecule and peptide therapies for chronic heart failure: a patent review (2011 - 2014)

INTRODUCTION

Chronic heart failure (CHF) is the long-term inability of the heart to meet circulatory demands under normal conditions. Effects of CHF can include increased blood volume, increased vascular resistance and compromised contractility leading to fluid retention, dyspnea and fatigue. Current standard of care for chronic systolic heart failure is directed towards managing hypoperfusion through the renin-angiotensin-aldosterone and sympathetic nervous systems. Treatment may also involve reversal of maladaptive cardiac remodeling and prevention of life-threatening arrhythmias.

AREAS COVERED

This review highlights small molecule and peptidic agents for the treatment of CHF with patents published between 2011 and 2014. Targets are subdivided into inotropic agents, ventricular remodeling, diuretics and the renin-angiotensin-aldosterone system.

EXPERT OPINION

CHF represents a large, unmet medical need where improved therapies are needed. The renin-angiotensin-aldosterone system pathway continues to be a major source of new therapies for CHF with new inotropic therapies emerging. Promising initial clinical results for a few approaches combined with the expectation of additional clinical results in the near future make this an exciting time in the pursuit of new treatments for CHF.

TNNI3K in cardiovascular disease and prospects for therapy

Cardiovascular diseases are an important cause of morbidity and mortality worldwide and the global burden of these diseases continues to grow. Therefore new therapies are urgently needed. The role of protein kinases in disease, including cardiac disease, is long recognized, making kinases important therapeutic targets. We here review the knowledge gathered in the last decade about troponin I-interacting kinase (TNNI3K), a kinase with cardiac-restricted expression that has been implicated in various cardiac phenotypes and diseases including heart failure, cardiomyopathy, ischemia/reperfusion injury and conduction of the cardiac electrical impulse.

MicroRNA-221 inhibits autophagy and promotes heart failure by modulating the p27/CDK2/mTOR axis

MicroRNAs have emerged as crucial regulators of cardiac homeostasis and remodeling in various cardiovascular diseases. We previously demonstrated that miR-221 regulated cardiac hypertrophy in vitro. In the present study, we demonstrated that the cardiac-specific overexpression of miR-221 in mice evoked cardiac dysfunction and heart failure. The lipidated form of microtubule-associated protein 1 light chain 3 was significantly decreased and sequestosome 1 was accumulated in cardiac tissues of transgenic (TG) mice, indicating that autophagy was impaired. Overexpression of miR-221 in vitro reduced autophagic flux through inhibiting autophagic vesicle formation. Furthermore, mammalian target of rapamycin (mTOR) was activated by miR-221, both in vivo and in vitro. The inactivation of mTOR abolished the miR-221-induced inhibition of autophagy and cardiac remodeling. Our previous study has demonstrated that cyclin-dependent kinase (CDK) inhibitor p27 was a direct target of miR-221 in cardiomyocytes. Consistently, the expression of p27 was markedly suppressed in the myocardia of TG mice. Knockdown of p27 by siRNAs was sufficient to mimic the effects of miR-221 overexpression on mTOR activation and autophagy inhibition, whereas overexpression of p27 rescued miR-221-induced autophagic flux impairment. Inhibition of CDK2 restored the impaired autophagic flux and rescued the cardiac remodeling induced by either p27 knockdown or miR-221 overexpression. These findings reveal that miR-221 is an important regulator of autophagy balance and cardiac remodeling by modulating the p27/CDK2/mTOR axis, and implicate miR-221 as a therapeutic target in heart failure.

Inhibition of the cardiomyocyte-specific troponin I-interacting kinase limits oxidative stress, injury, and adverse remodeling due to ischemic heart disease

Ischemia–reperfusion injury is strongly associated with increased oxidative stress, mitochondrial dysfunction, and cell death. These processes are diminished in an animal model of ischemia–reperfusion by the genetic loss or pharmacological inhibition of troponin I–interacting kinase.

Inhibition of the cardiomyocyte-specific kinase TNNI3K limits oxidative stress, injury, and adverse remodeling in the ischemic heart

Percutaneous coronary intervention is first-line therapy for acute coronary syndromes (ACS) but can promote cardiomyocyte death and cardiac dysfunction via reperfusion injury, a phenomenon driven in large part by oxidative stress. Therapies to limit this progression have proven elusive, with no major classes of new agents since the development of anti-platelets/anti-thrombotics. We report that cardiac troponin I-interacting kinase (TNNI3K), a cardiomyocyte-specific kinase, promotes ischemia/reperfusion injury, oxidative stress, and myocyte death. TNNI3K-mediated injury occurs through increased mitochondrial superoxide production and impaired mitochondrial function and is largely dependent on p38 mitogen-activated protein kinase (MAPK) activation. We developed a series of small-molecule TNNI3K inhibitors that reduce mitochondrial-derived superoxide generation, p38 activation, and infarct size when delivered at reperfusion to mimic clinical intervention. TNNI3K inhibition also preserves cardiac function and limits chronic adverse remodeling. Our findings demonstrate that TNNI3K modulates reperfusion injury in the ischemic heart and is a tractable therapeutic target for ACS. Pharmacologic TNNI3K inhibition would be cardiac-selective, preventing potential adverse effects of systemic kinase inhibition.

TNNI3K mutation in familial syndrome of conduction system disease, atrial tachyarrhythmia and dilated cardiomyopathy

Locus mapping has uncovered diverse etiologies for familial atrial fibrillation (AF), dilated cardiomyopathy (DCM), and mixed cardiac phenotype syndromes, yet the molecular basis for these disorders remains idiopathic in most cases. Whole-exome sequencing (WES) provides a powerful new tool for familial disease gene discovery. Here, synergistic application of these genomic strategies identified the pathogenic mutation in a familial syndrome of atrial tachyarrhythmia, conduction system disease (CSD), and DCM vulnerability. Seven members of a three-generation family exhibited the variably expressed phenotype, three of whom manifested CSD and clinically significant arrhythmia in childhood. Genome-wide linkage analysis mapped two equally plausible loci to chromosomes 1p3 and 13q12. Variants from WES of two affected cousins were filtered for rare, predicted-deleterious, positional variants, revealing an unreported heterozygous missense mutation disrupting the highly conserved kinase domain in TNNI3K. The G526D substitution in troponin I interacting kinase, with the most deleterious SIFT and Polyphen2 scores possible, resulted in abnormal peptide aggregation in vitro and in silico docking models predicted altered yet energetically favorable wild-type mutant dimerization. Ventricular tissue from a mutation carrier displayed histopathological hallmarks of DCM and reduced TNNI3K protein staining with unique amorphous nuclear and sarcoplasmic inclusions. In conclusion, mutation of TNNI3K, encoding a heart-specific kinase previously shown to modulate cardiac conduction and myocardial function in mice, underlies a familial syndrome of electrical and myopathic heart disease. The identified substitution causes a TNNI3K aggregation defect and protein deficiency, implicating a dominant-negative loss of function disease mechanism.

Troponin I-interacting protein kinase: a novel cardiac-specific kinase, emerging as a molecular target for the treatment of cardiac disease

Coronary artery disease is the leading cause of death and disability worldwide. In patients with acute coronary syndromes, timely and effective myocardial reperfusion by percutaneous coronary intervention is the primary treatment of choice to minimize the ischemic injury and limit the size of the myocardial infarction (MI). However, reperfusion can itself promote cardiomyocyte death, which leads to cardiac dysfunction via reperfusion injury. The molecular mechanisms of ischemia-reperfusion (IR) injury are not completely understood and new drug targets are needed. Recently, we reported that cardiac troponin I-interacting protein kinase (TNNI3K), a cardiomyocyte-specific kinase, promotes IR injury via profound oxidative stress, thereby promoting cardiomyocyte death. By using novel genetic animal models and newly developed small-molecule TNNI3K inhibitors, we demonstrated that TNNI3K-mediated IR injury occurs through impaired mitochondrial function and is in part dependent on p38 MAPK. Here we discuss the emerging role of TNNI3K as a promising new drug target to limit IR-induced myocardial injury. We will also examine the underlying mechanisms that drive the profoundly reduced infarct size in mice in whichTNNI3Kis specifically deleted in cardiomyocytes. Because TNNI3K is a cardiac-specific kinase, it could be an ideal molecular target, as inhibiting it would have little or no effect on other organ systems, a serious problem associated with the use of kinase inhibitors targeting kinases that are more widely expressed.