Abstract 14420: STIM and Orai Spatial Distribution in the Infarcted Mouse Heart Reveals Their Role in Fibroblast Activation

Abstract

Introduction: Heart failure (HF) remains a major source of late morbidity and mortality after myocardial infarction (MI). Calcium handling and the signaling pathways that govern the functional remodeling associated with HF are unclear. Store-operated calcium entry (SOCE) is a key factor in modulating Ca2+ signals. SOCE is mediated by the STIM protein and Orai channels. Monitoring STIM and Orai distribution is of great interest for studying cardiac remodeling after MI. This study investigated the spatial distribution of STIM and Orai in the heart after MI injury. Methods: The myocardial injury was induced in adult mice via ligation of the left anterior descending artery. MI- and sham-operated animals were euthanized, and hearts were harvested for ex-vivo analyses at 3, 7, 14, and 28 days after MI. We used western blot coupled with immunostaining to detect temporal and spatial profiling of specific STIM and Orai isoforms in different physiological zones and timepoints of MI to generate an integrative high-resolution map of STIM-Orai expression during cardiac remodeling. Results: We found that STIM1 and Orai1 proteins were upregulated from 3-day post-MI throughout day 28 post-MI, (3-4 fold times higher than controls, p<0.001). STIM1 and Orai1 were the most abundant isoforms present in the injured heart. In contrast, Orai3 expression was found to transiently increase at 3- and 7-day post-MI (1.5 fold, p>0.01), STIM2 and Orai2 expression did not change. Spatial pattern analysis revealed a marked gradient of STIM1 and Orai1 expression (decreasing from the border zone, the infarcted area, and the distal area). Co-labeling with cell-specific markers revealed that cardiac fibroblasts exhibited a high level of STIM1 and Orai1 expression. In vitro activation of cardiac fibroblasts showed a marked increase of STIM1 and Orai1 protein expression. Conclusions: Taken together, these data demonstrate that STIM1 and Orai1 expression is associated with fibroblast activation during fibrotic remodeling in the MI. Ca2+ signaling pathways that drive the expansion of fibrosis may rely on sustained STIM1 and Orai1 expression in scar formation and fibroblast activation, of which could provide future targets to exploit for treatment to prevent HF.