Abstract P280: Deletion of Cardiac Ankyrin Repeat Kinase Reduces Ischemia/Reperfusion Injury in the Heart in Vivo

Abstract

Ischemic heart disease impacts millions of Americans and can progress to heart failure. Current therapies do not address this progression and new therapeutic targets are needed. One novel potential target is cardiac ankyrin repeat kinase (CARK, also troponin I interacting kinase; TNNI3K). CARK is expressed only in the heart and is significantly up-regulated in failing human hearts. Beyond this, little is known about CARK’s biological roles. To determine CARK’s function in the injured heart we subjected transgenic (Tg) mice expressing wild-type or kinase-inactive (KI) CARK to 30 minutes of LV ischemia followed by 24 hours of reperfusion (I/R). CARK-Tg mice had significantly larger infarcts (32.2% AAR vs 16.1% in WT littermates, p<0.05) following I/R. Cardiac troponin I (cTnI) serum levels were also significantly elevated in CARK-Tg mice after 24h, consistent with increased injury. Conversely, infarct size was decreased in mice expressing KI CARK and levels of cTnI were reduced, suggesting that blocking CARK activity may protect against acute injury. To test this, we employed an inducible, cardiac-specific knockout mouse (CARK-KO). CARK-KO mice showed a significant reduction in infarct size (20.52% vs 32.9%, p=0.01) as well as cTnI levels post-I/R. To confirm these findings, wild-type mice were treated with a small molecule CARK inhibitor and then were subjected to I/R. CARK inhibition significantly reduced infarct size (10.92% vs 21.74% p<0.01) as well as serum levels of cTnI. These data indicate that loss of CARK reduces myocyte injury and death after I/R. To examine the mechanism of this effect, primary NRVM were either transduced with a CARK adenovirus or treated with one of two selective CARK inhibitors, and then subjected to oxidative stress using H2O2. CARK over-expression worsened, while CARK inhibition significantly blunted H2O2 - induced apoptosis. Taken together, these data suggest that CARK plays an adverse role in the heart’s response to ischemia, in part by increasing apoptosis. Furthermore, inhibition of CARK may protect the ischemic heart by limiting initial cell loss and thus reducing infarct size. These findings enhance understanding of CARK’s role in the heart and provide evidence for CARK as a novel therapeutic target for ischemic injury.