The Z-disc: Mechanosensor at the interface between myosin biomechanics and hypertrophic signaling

Despite over two decades of research on the etiology of hypertrophic cardiomyopathy (HCM) and the identification of >1000 mutations in sarcomeric proteins such as β-cardiac myosin (MYH7), the mechanism by which altered force at the level of the sarcomere is transduced into cellular hypertrophy is still incompletely understood. We have previously described a striking widening of the Z-disc in septal myectomy samples from patients with HCM, as well as in human induced pluripotent stem cell derived cardiomyocyte (hiPSC-CM) lines in which we CRISPR-edited two different HCM mutations in MYH7. We propose that the Z-disc is the mechano-transduction link at the interface of myosin biomechanics and hypertrophy. We performed a comparative genome and mutation-wide molecular key driver analysis. Genome-wide analysis (RNAseq) of 26 HCM myectomy samples revealed altered expression of 52 Z-disc-related genes vs. donor heart controls. In HCM hiPSC-CMs, 24 Z-disc genes were altered (single-cell RNA-seq). 14 altered Z-disc genes were shared between human samples and hiPSC-CMs. Pro-hypertrophic signaling was activated through differential expression of five modulators (GLRX3, LMCD1, MYOZ2, PAK1IP1, C10ORF7) of calcineurin. We hypothesized that widening of the Z-disc, differential expression of Z-disc genes and downstream hypertrophic signaling were due to an increase in active tension on Z-disc anchored actin by adjacent myosin molecules, which was confirmed using traction force microscopy. Our findings suggest that the Z-disc acts as a mechano-sensor at the interface between myosin biomechanics and hypertrophic signaling. To further test this hypothesis, we used a vinculin FRET-tension sensor to directly measure intracellular force at the Z-disc with different myosin perturbations. This unique combination of patient samples and CRISPR-edited hiPSC-CMs confirms the fidelity of our in vitro model in recapitulating human disease and increases the potential translation of our findings to develop new therapies.