Targeting mutant TNNT2-induced epigenetic perturbation and pathogenic signaling in left ventricular non-compaction cardiomyopathy

Background Compound mutations of TNNT2 R 141 W/+ (encoding troponin T) and MYPN S 1296 T/+ (encoding myopalladin) are associated with familial left ventricle non-compaction cardiomyopathy (LVNC). However, it remains unclear in which would be the pathogenic mutation, the underlying mechanism, and the target therapy for LVNC. Methods Knock-in C57BL/6J mice harboring mutations in orthologous genes in Tnnt2 R 154 W or/and Mypn S 1291 T and human cardiomyocytes derived from iPSC of healthy donors and LVNC patients (LVNC-hCM) were employed for disease modeling, omics analysis, mechanistic study, and drug development. Results Using knock-in mice for disease modeling, it was clarified that the orthologous mutation in Tnnt2 , but not in Mypn , led to cardiac hypertrabeculation, noncompaction, and heart failure. 3D protein structure modeling by Swiss-model found a loss of slat bridge between TNNT2(R141W) and E-257 in tropomyosin, contributing to the decreased cardiac contraction. Further mechanistic study discovered that troponin T (TNNT2) appears to function as an HDAC1 sponge in cardiomyocyte nuclei. The compromised association between nuclear TNNT2(R141W) and HDAC1 causes cardiac epigenetic perturbation and subsequentially leads to transcriptional dysregulation. The downregulation of cardiac muscular genes was concomitant with the impairment of cardiac contraction, which would be partially rescued by pan HDAC inhibitor. Besides, the upregulation of TGFβ-signaling molecules and EZH2 did contribute to cardiac growth defects, which were mitigated by TGFβR1 inhibitor (A83-01) and EZH2 inhibitor (GSK503), respectively. Simvastatin, a hit drug identified from the repurposed drug screening, can restore nuclear TNNT2(R141W)-HDAC1 association, thereby recovering cardiac epigenetic, translational profiles, growth and function in LVNC-hCM in vitro and cardiac function in LVNC mice harboring Tnnt2 R 154 W in vivo . The cardiac function was significantly improved in the proband receiving 5 mg once daily for consecutive two years. Conclusion Mutant TNNT2(R141W) diminished its nuclear HDAC1 sponge function in cardiomyocyte to induce LVNC pathogenesis through perturbating cardiac epigenetic and the gene expressions. Targeting to HDAC, TGFβ, EZH2 may rescue part of cardiac pathological signaling. Simvastatin can act as a chemical chaperone to comprehensively recover cardiac epigenetic via restoring nuclear TNNT2(R141W)-HDAC1 association.