Nogo-C regulates post myocardial infarction fibrosis through the interaction with ER Ca2+ leakage channel Sec61α in mouse hearts

Cardiac fibrosis is an independent risk factor for heart failure and even the leading cause of death in myocardial infarction patients. However, molecular mechanisms associated with the pathogenesis of cardiac fibrosis following myocardial infarction are not yet fully understood. Nogo-C protein ubiquitously expresses in tissues including in the heart. Our previous study found that Nogo-C regulated cardiomyocyte apoptosis during myocardial infarction. In the present study, we found that Nogo-C was upregulated in fibrotic hearts after myocardial infarction and in Ang II- or TGF-beta 1-stimulated cardiac fibroblasts. Overexpression of Nogo-C in cardiac fibroblasts increased expression of profibrogenic proteins, while knockdown of Nogo-C inhibited the fibrotic responses of cardiac fibroblasts to Ang II- or TGF-beta 1 stimulation. Functionally, Nogo-C deficiency suppressed pro-fibrogenic proteins in post-myocardial infarction hearts and ameliorated post-myocardial infarction cardiac function. Mechanistically, we found that Nogo-C increased intracellular Ca2+ concentration and buffering Ca2+ totally abolished Nogo-C-induced fibrotic responses. Moreover, overexpression of Nogo-C caused increased Sec61 alpha, the Ca2+ leakage channel on endoplasmic reticulum membrane. Nogo-C interacted with Sec61 alpha on endoplasmic reticulum and stabilized Sec61 alpha protein by inhibiting its ubiquitination. Inhibition or knockdown of Sec61 alpha blocked Nogo-C-induced increase of cytosolic Ca2+ concentration and inhibited Nogo-C-and TGF-beta 1-induced fibrotic responses in cardiac fibroblasts, suggesting that Nogo-C regulates cardiac fibrosis through interacting with Sec61 alpha to mediate the Ca2+ leakage from endoplasmic reticulum. Thus, our results reveal a novel mechanism underlying cardiac fibrosis following myocardial infarction, and provide a therapeutic strategy for cardiac remodeling related heart diseases.