Abstract
The protein sarcospan (SSPN) is an integral member of the dystrophin-glycoprotein complex (DGC) and has been shown to be important in the heart during the development and the response to acute stress. In this study, we investigated the role of SSPN in the cardiac response to acute ischemia-reperfusion (IR) injury in SSPN-deficient (SSPN(-/-)) mice. First, the hemodynamic response of SSPN(-/-) mice was tested and was similar to SSPN(+/+) (wild-type) mice after isoproterenol injection. Using the in situ Langendorff perfusion method, SSPN(-/-) hearts were subjected to IR injury and found to have increased infarct size and arrhythmia susceptibility compared to SSPN(+/+). Ca(2+) handling was assessed in single cardiomyocytes and diastolic Ca(2+) levels were increased after acute β-AR stimulation in SSPN(+/+) but not SSPN(-/-). It was also found that SSPN(-/-) cardiomyocytes had reduced Ca(2+) SR content compared to SSPN(+/+) but similar SR Ca(2+) release. Next, we used qRT-PCR to examine gene expression of Ca(2+) handling proteins after acute IR injury. SSPN(-/-) hearts showed a significant decrease in L-type Ca(2+) channels and a significant increase in Ca(2+) release channel (RyR2) expression. Interestingly, under oxidizing conditions reminiscent of IR, SSPN(-/-) cardiomyocytes, had increased H(2)O(2)-induced reactive oxygen species production compared to SSPN(+/+). Examination of oxidative stress proteins indicated that NADPH oxidase 4 and oxidized CAMKII were increased in SSPN(-/-) hearts after acute IR injury. These results suggest that increased arrhythmia susceptibility in SSPN(-/-) hearts post-IR injury may arise from alterations in Ca(2+) handling and a reduced capacity to regulate oxidative stress pathways.