Abstract 1606: A Novel Cardiac-Specific Isoform of the Cell Cycle-Related Kinase Provides Cardioprotection during Myocardial Ischemia

Abstract

Since heart failure (HF) is characterized by the decreased activity of pro-survival signaling pathways, we reasoned that examining genomic changes in a clinically relevant model of HF would uncover novel genes involved in protecting the heart that were downregulated in HF. Accordingly, we examined a genomic profile by DNA microarray in a primate model of myocardial infarction (MI) followed by three weeks pacing to develop HF, and compared to sham animals (n=5/group). In this array, the transcript of the gene encoding the cell cycle-related kinase (CCRK), for which no function is known in adult heart, was down-regulated by 50% in HF versus sham (P<0.05), which was confirmed by quantitative PCR. Upon sequencing, the cardiac CCRK (cCCRK) showed a conservation of the N-terminal kinase domain, but differed in its C-terminal half from the “generic” CCRK cloned in other tissues, due to alternative splicing. Although the “generic” CCRK phosphorylated its substrate, the cyclin-dependent kinase 2, and doubled the number of myocytes in the S phase of the cell cycle, these effects were not observed with cCCRK (P<0.05 between groups). Rather, overexpression of cCCRK in cardiac myocytes induced a 36% increase in protein/DNA ratio and a 50% decrease in apoptosis upon chelerythrine treatment (both, P<0.05 vs. LacZ). A tetracycline (Tet)-dependent transgenic (TG) mouse model with cardiac-specific overexpression of cCCRK was generated, which showed a 3-fold increase in cCCRK abundance compared to wild type (WT) mice (P<0.01 vs. WT) upon Tet removal. Both WT and TG mice (n=3/group) underwent 45 min no-flow ischemia of the left anterior descending artery and 24h reperfusion, followed by measurement of the area-at-risk (AAR) and infarct size (IS). The AAR/left ventricular mass was similar in WT and TG. However, IS/AAR was reduced (P<0.01) by more than 50% in TG (29±3%) compared with WT (61±5%). Therefore, a variant of CCRK is expressed in the heart, which is down-regulated in HF, which promotes cell growth and survival, when overexpressed in vitro , and which provides major protection against myocardial ischemia when overexpressed in vivo . Thus, CCRK is a novel mechanism for cardioprotection in ischemia, and may be a new approach to HF treatment. This research has received full or partial funding support from the American Heart Association, AHA National Center.