Introduction: Heart failure with preserved ejection fraction (HFpEF) remains a major clinical challenge, particularly prevalent in aged hypertensive females. While sex-specific alterations in left ventricular (LV) remodeling have been characterized, data on the right ventricle (RV) a crucial determinant of HF outcomes are sparse. We previously reported distinct molecular and functional remodeling in the LV of hypertensive Ren-2 transgenic rats (TG) with sex-specific features. Here, we extend these findings to the RV, focusing on sex differences in myocyte function and molecular signaling.
Methods: Male and female TG rats aged 1 year were compared to age- and sex-matched wild-type (WT) controls. RV cardiomyocyte function was assessed using skinned cardiomyocyte preparations to measure passive stiffness (Fpassive) and calcium sensitivity (pCa50). Molecular profiling included Western blot analyses of titin, MyBPC (Myosin binding protein-C), cardiac troponin I (cTnI), and calcium-handling proteins (RyR2 (Ryanodine receptor 2), PLB(Phospholamban)), along with kinases (PKG (cGMP-dependent protein kinase), PKA (protein kinase A), CaMKII (Ca2+/calmodulin-dependent protein kinase II)).
Results: Female TG rats showed significantly higher RV Fpassive compared to TG males, indicating increased diastolic stiffness in females. Additionally, pCa50 of force production was markedly elevated in female TG RV myocytes, suggesting enhanced contractile responsiveness. These functional differences were associated with sex-specific molecular alterations. In female RV tissue, hypophosphorylation of titin and cTnI was more pronounced than in males, accompanied by a greater reduction in PKG activity and greater enhancement of CaMKII activity. Western blot analyses revealed reduced phosphorylation of key PKG targets (e.g., titin N2Bus, cTnI Ser23/24, and MyBPC), as well as suppressed PKG expression and downstream signaling more pronounced in female TG. Notably, PKA-mediated phosphorylation was also lower in female TG RVs. These changes parallel our previous LV findings, but exhibit greater magnitude or altered patterns in the RV. Importantly, we observed upregulation of RyR2 and increased expression of PLB in the RV of TG females compared to males and WT, pointing toward heightened intracellular calcium release and augmented Gq-coupled signaling. These molecular derangements likely contribute to the sex-specific increase in pCa50 and cardiomyocyte stiffness.
Conclusion: This study demonstrates, for the first time, that hypertensive female rats exhibit exacerbated RV stiffness and increased calcium responsiveness compared to males, linked to sex-specific dysregulation of titin phosphorylation, PKG/CaMKII signaling, and altered expression of calcium-handling proteins RyR2 and PLB. These findings provide mechanistic insights into right heart involvement in female-predominant HFpEF and highlight the importance of sex as a biological variable in RV-targeted therapeutic strategies.
