Background: Hypertrophic cardiomyopathy (HCM) is a complex myocardial disorder (prevalence of 1:500) with no well-established disease-modifying therapy so far. Therefore, the aim of our study was to unravel the role of oxidative stress and protein quality control system (PQS) in the pathophysiology of acquired HCM.

Methods: We used left ventricle (LV) tissue obtained during heart transplantation surgery from end-stage heart failure patients with hypertrophic cardiomyopathy and compared them to non-failing human hearts from donor groups (controls). Western blot analysis, immunofluorescence confocal microscopy and enzyme-linked immunosorbent assays were used to measure autophagy, oxidative stress, inflammation, stress signaling pathways, and apoptosis. In addition, the cellular mechanical performance was assessed in single skinned cardiomyocytes.

Results: We observed increased titin-based stiffness (F_passive) in human HCM compared to non-failing hearts, and reduced after the antioxidant treatment. Titin as a main determinant of cardiomyocyte stiffness was observed to be S-glutathionylated and highly ubiquitinated in HCM patients. This was associated with a shift in the balance of reduced and oxidized forms of glutathione (GSH and GSSG, respectively) and a significant reduction in GSH level in HCM. HSP27 and α-ß crystallin were upregulated and both were S-glutathionylated in HCM. HSP70 protein levels were comparable in both HCM and control groups, however, S-glutathionylated in HCM myocytes. Administration of HSPs in vitro significantly reduced F_passive of HCM myocytes. We detected high levels of the phosphorylated monomeric superoxide anion-generating eNOS, decreased NO bioavailability, decreased sGC activity, and high levels of 3-Nitrotyrosin in HCM compared to non-failing hearts. Many signal transduction pathways that are involved in autophagy, apoptosis, cardiac contractility, and growth such as MAPK, AKT, GSK-3ß, mTOR, FOXO, JNK, and ERK1/2 were altered in HCM compared to donors. The apoptotic and pro-apoptotic factors cathepsin, procaspase 3, procaspase 9 and caspase 12, but not caspase 9, were elevated in HCM hearts and associated with increased proinflammatory cytokines (IL-6, IL-18, ICAM, VCAM1, TLR2 and TLR4) and oxidative stress (3-nitrotyrosine and H2O2).

Conclusion: Here we revealed stress signaling and impaired PQS as potential mechanisms underlying the initiation and progression of the HCM phenotype. Our data suggest that targeting the PQS and reducing oxidative stress can be a viable therapeutic approach to attenuate the severity of cardiac dysfunction in HCM and prevent its progression.