Gender-Dependent Alteration of Ca(2+) and TNFα Signaling in db/db Mice, an Obesity-Linked Type 2 Diabetic Model

Cardiovascular complications are the primary death cause in type 2 diabetes, where inflammation can play a role. We, and others, have previously shown that, in diabetic cardiomyopathy, cardiac dysfunction is associated with Ca(2+) mishandling. It is possible that diabetic cardiomyopathy differently affects men and women, as the latter present higher risk to develop heart failure and a higher plasmatic level of the pro-inflammatory cytokine, tumor necrosis factor alpha (TNFα), than men. However, the gender-dependent regulation of Ca(2+) signaling in diabetes and its relationship with TNFα signaling are still unclear. Here, we analyzed TNFα signaling pathway and its role in Ca(2+) signaling dysfunction in male and female rodent models of type 2 diabetes linked to obesity (db/db mice) using confocal microscopy in freshly isolated cardiomyocytes. TNFα increased [Ca(2+)](i) transient amplitude and accelerated its decay without affecting SR Ca(2+) load or Ca(2+) spark frequency in cells from control mice. All TNFα effects on Ca(2+) handling were prevented by the inhibition of the ceramidase and the phospholipase A2 (PLA2). While the plasmatic level of TNFα was similar in male and female db/db mice, only male db/db hearts over-expressed both TNFα converting enzyme (TACE) and the protective TNFα receptors 2 (TNF-R2). TNFα receptor 1 (TNF-R1) expression, involved in negative inotropic response of TNFα, was unchanged in both male and female db/db mice compared to controls. We found that male db/db mice cardiomyocytes presented a decrease in [Ca(2+)](i) transient amplitude associated to a drop of sarcoplasmic reticulum Ca(2+) load, not seen in female db/db mice. Interestingly, sustained incubation with TNFα did not restored Ca(2+) signaling alteration observed in male db/db mice but still induces an increase in Ca(2+) spark frequency as seen in control littermates. In cardiomyocytes from female db/db mice, TNFα had no visible effects on Ca(2+) handling. In conclusion, our study shows that the alteration of Ca(2+) signaling and TNFα, seen in db/db mice, is gender specific presenting an increase in TNFα cardio-protective pathway in male mice.