Ca2+/calmodulin-dependent protein kinase II and protein kinase A differentially regulate sarcoplasmic reticulum Ca2+ leak in human cardiac pathology

Abstract

Background: Sarcoplasmic reticulum (SR) Ca(2+) leak through ryanodine receptor type 2 (RyR2) dysfunction is of major pathophysiological relevance in human heart failure (HF); however, mechanisms underlying progressive RyR2 dysregulation from cardiac hypertrophy to HF are still controversial.

Methods and results: We investigated healthy control myocardium (n=5) and myocardium from patients with compensated hypertrophy (n=25) and HF (n=32). In hypertrophy, Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and protein kinase A (PKA) both phosphorylated RyR2 at levels that were not different from healthy myocardium. Accordingly, inhibitors of these kinases reduced the SR Ca(2+) leak. In HF, however, the SR Ca(2+) leak was nearly doubled compared with hypertrophy, which led to reduced systolic Ca(2+) transients, a depletion of SR Ca(2+) storage and elevated diastolic Ca(2+) levels. This was accompanied by a significantly increased CaMKII-dependent phosphorylation of RyR2. In contrast, PKA-dependent RyR2 phosphorylation was not increased in HF and was independent of previous β-blocker treatment. In HF, CaMKII inhibition but not inhibition of PKA yielded a reduction of the SR Ca(2+) leak. Moreover, PKA inhibition further reduced SR Ca(2+) load and systolic Ca(2+) transients.

Conclusions: In human hypertrophy, both CaMKII and PKA functionally regulate RyR2 and may induce SR Ca(2+) leak. In the transition from hypertrophy to HF, the diastolic Ca(2+) leak increases and disturbed Ca(2+) cycling occurs. This is associated with an increase in CaMKII- but not PKA-dependent RyR2 phosphorylation. CaMKII inhibition may thus reflect a promising therapeutic target for the treatment of arrhythmias and contractile dysfunction.

Keywords: calcium–calmodulin-dependent protein kinase type 2; heart failure; hypertrophy; protein kinases; sarcoplasmic reticulum.