Cardiac Over-Expression of Creatine Kinase Differentially Affects Cardiomyocyte Function in Ischemic and Non-Ischemic Heart Failure

Abstract

The role of creatine kinase (CK), the primary cardiac energy reserve reaction, in heart failure (HF) remains controversial. We hypothesized CK role may be HF model/condition dependent, and tested if overexpressing myofibrillar or mitochondrial CK (CK-M and CK-mito) differently impacts function in myocytes from mice subjected to myocardial infarction (MI, 8 wk in vivo LAD ligation, with viable and necrotic regions) or transverse aortic constriction (8 wk TAC, non-ischemic stress uniformly affecting all myocytes). Using the β1/β2-agonist isoproterenol (2.5nM, ISO) as energetic stress, we superfused wild-type (WT), CK-M and CK-mito myocytes from control (CON), MI and TAC mice. After ISO, in CON WT, CK-M or CK-mito myocytes sarcomere fractional shortening (FS) and Ca2+ transients increased by ∼310% and ∼125%, respectively. WT MI myocytes displayed similar basal and ISO-stimulated values, attesting that MI myocytes are likely from remote heart regions, thus healthy and functionally competent. Neither CK-M nor CK-mito overexpression further improved function in these cells. Conversely, WT-TAC myocytes showed a significant decline in ISO response: FS=184%, Ca2+ transients=36%, rescued by CK-M or CK-mito overexpression (FS ∼320%, Ca2+ transients ∼110%). Since oxidative stress is a hallmark of HF and an ISO infusion sequela, we exposed myocytes to H2O2 (50μM). CON WT and CK-M myocytes developed irreversible arrhythmia after ∼410 sec; however, in CON CK-mito this interval was prolonged (600sec, p=.04). In MI myocytes, CK-M and CK-mito were equipotent (both ∼665 vs 462sec for WT, p=.05), while in TAC cells CK-M countered H2O2 effects (621sec vs 366 for WT, p=.03; CK-mito=494sec). Overexpressing CK-M or CK-mito in vivo improves function and Ca2+ handling of stressed TAC myocytes. Interestingly, overexpressing either CK isoform shields CON, TAC and MI myocytes against oxidative stress with mechanisms that remain to be determined.