Gender-Dependent Alteration of Ca2+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 Ca2+ 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 (TNF alpha), than men. However, the gender-dependent regulation of Ca2+ signaling in diabetes and its relationship with TNF alpha signaling are still unclear. Here, we analyzed TNF alpha signaling pathway and its role in Ca2+ 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. TNF alpha increased [Ca2+](i) transient amplitude and accelerated its decay without affecting SR Ca2+ load or Ca2+ spark frequency in cells from control mice. All TNF alpha effects on Ca2+ handling were prevented by the inhibition of the ceramidase and the phospholipase A2 (PLA2). While the plasmatic level of TNF alpha was similar in male and female db/db mice, only male db/db hearts over-expressed both TNF alpha converting enzyme (TACE) and the protective TNF alpha receptors 2 (TNF-R2). TNF alpha receptor 1 (TNF-R1) expression, involved in negative inotropic response of TNF alpha, 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 [Ca2+](i) transient amplitude associated to a drop of sarcoplasmic reticulum Ca2+ load, not seen in female db/db mice. Interestingly, sustained incubation with TNF alpha did not restored Ca2+ signaling alteration observed in male db/db mice but still induces an increase in Ca2+ spark frequency as seen in control littermates. In cardiomyocytes from female db/db mice, TNF alpha had no visible effects on Ca2+ handling. In conclusion, our study shows that the alteration of Ca(2+)signaling and TNF alpha, seen in db/db mice, is gender specific presenting an increase in TNF alpha cardio-protective pathway in male mice.