Sex Differences Of RyR2 Expression And Phosphorylation In Heart Failure

Abstract

Sex differences in the expression and phosphorylation of Ca handling proteins could underlie sex differences in contractile function and ventricular arrhythmias in heart failure (HF). We previously showed down-regulation of cardiac RyR (RyR2) and increased CaMKII- & PKA -dependent phosphorylation of RyR2 associated with increased CaMKII-dependent SR Ca leak in our arrhythmogenic rabbit model of HF. Here, we assessed sex differences in RyR2 expression and phosphorylation in HF. We found total RyR2 protein expression in control F was 27% lower (vs control M, n=3,3, p<0.05); but with HF, both M & F exhibited a down-regulation of RyR2 vs control M (41% and 49%, respectively, n=4,4, p<0.05). Phosphorylation of RyR2 at the serine-2809 (PKA- & CaMKII-) and serine-2815 (CaMKII) sites was increased in both HF-M & HF-F (73% & 43%, and 67% & 135%, respectively, vs control M, n=4,4,4,4, p<0.05). Moreover, CaMKII and PKA backphosphorylation (-P) of RyR2 were assessed in immunoprecipitated RyR2 proteins with specific RyR2 antibody. CaMKII-P of RyR2 was significantly increased with HF in both sexes vs control M (71% and 87%, respectively, n=5,5,5,5, p<0.05), while PKA-P of RyR2 was increased (by 228%) only in HF-F (p < 0.001). HF-M (but not HF-F) exhibited increased global expression of CaMKIIδ (cardiac isoform) by 141% (vs control M, n=4,4,4,4, p<0.05), but co-immunoprecipitated CaMKIIδ with RyR2 antibody was increased in both HF-M & HF-F (vs control M, 38% and 43%, respectively, n=3,3,3,3, p<0.05). In contrast, co-immunoprecipitated PKA with RyR2 was increased in only HF-F (26%, p< 0.001), while global expression of PKA was unchanged in both sexes. Thus, there are sex differences in RyR2 hyperphosphorylation with HF. HF-F have increased co-localized CaMKIIδ and PKA with RyR2, while HF-M have increased global CaMKIIδ and increased co-localized CaMKIIδ (but not PKA) with RyR2.