Overexpression of histidine-rich Ca-binding protein protects against ischemia/reperfusion-induced cardiac injury.

The histidine-rich Ca-binding protein (HRC) is a Ca-storage protein in cardiac sarcoplasmic reticulum. Recent transgenic studies revealed that this protein inhibits the maximal rates of sarcoplasmic reticulum Ca-transport, leading to cardiac dysfunction. In view of the role of sarcoplasmic reticulum Ca-cycling in myocardial ischemia/reperfusion injury, we designed this study to gain further insight into the role of HRC during ischemia/reperfusion. The transgenic mouse model with cardiac-specific overexpression of HRC was utilized and cardiac contractile parameters were assessed before and after ischemia/reperfusion injury by Langendorff perfusion. After a 20-min stabilization period, the hearts were subjected to 40 min of global ischemia, followed by 60 min of reperfusion. We found that although transgenic (TG) hearts showed depressed cardiac function (25%) compared to wild types (WTs) at baseline, they exhibited better recovery of left ventricular developed pressure (86.6+/-2.6% in TGs vs. 58.3+/-4.0% in WTs of pre-ischemic values, P<0.05) and higher rates of contraction and relaxation after ischemia/reperfusion than WTs. This improvement was accompanied by smaller infarcts (23.1+/-1.7% in TGs vs. 41.1+/-2.5% in WTs of infarct region-to-risk region ratio, P<0.05) and lower creatine kinase release. Notably, the extent of apoptotic cell death was significantly attenuated, as evidenced by decreased DNA fragmentation, upregulation of the antiapoptotic protein Bcl-2, and downregulation of the active caspases (3, 9 and 12) following ischemia/reperfusion in TG hearts, compared with WTs. Extension of these studies to an in vivo model of 30-min myocardial ischemia, via coronary artery occlusion, followed by 24-h reperfusion, showed that the infarct region-to-risk region ratio was 9+/-0.9% in TGs, compared with 20.4+/-2.9% in WTs (P<0.05). Our findings suggest that increased cardiac HRC expression protects against ischemia/reperfusion injury in the heart, resulting in improved recovery of function and reduced infarction.