Abstract 17456: Inositol 1,4,5-Trisphosphate Receptors (ITP3Rs) and Activation of Cardiac Fibroblasts in Ischemia/Reperfusion Injury

Abstract

Introduction: Inositol 1,4,5-trisphosphate receptors (ITP3Rs) are Ca 2+ release channels on the endoplasmic reticulum (ER). The role of ITP3Rs in cardiomyocytes has been previously investigated for hypertrophy and arrhythmias, however, the exact function in the activation of cardiac fibroblasts (FBs) is yet to be determined. The main goal of this project is to investigate the mechanisms linking FB ITP3Rs to post-ischemia/reperfusion (I/R) cardiac fibrosis. Hypothesis: We hypothesize that ITP3Rs activate FB via a direct transcriptional regulation of αSMA and other genes involved in myoFB activation. Indeed, myoFB differentiation and persistence is regulated by a balance between pro-and anti-apoptotic signaling pathways. Methods: We generated myoFB-specific ITP3Rs KO mice (ITP3R KO ) and isolated FBs as well as cardiomyocytes via collagenase digestion and performed immunoprecipitation (IP) assays showing that ITP3Rs bind p53 upregulated modulator of apoptosis (PUMA). Cytosolic levels of Cytochrome C (Cyt C) were assessed in myoFB isolated from areas remote from injury and scar areas 7 d after I/R. After having immunoprecipitated for ITP3R1 we blotted the isolated FBs for PUMA and, vice versa. PUMA levels were measured in cytosol, ER, and mitochondria of FBs isolated from regions remote from injury and scar areas 7 d post I/R. Results: Our data show reduced levels of cytosolic Cyt C following I/R, which was prevented by IP3Rs ablation, providing an explanation for the persistence of myoFBs in remote areas. We found that the mitochondrial expression of PUMA was significantly decreased - while ER levels were markedly increased - in myoFBs isolated from areas remote from I/R injury, indicating a sequestration of PUMA by ITP3Rs; this phenotype was rescued by ITP3Rs ablation. Instead, in myoFBs isolated from the scar areas, mitochondrial PUMA levels were increased both in ITP3R fl/fl and ITP3R KO mice, and no sequestration was observed, consistent with the absence of ITP3R upregulation. Conclusions: Using a specific Cre/lox KO model, we provide the first assessment of functional contribution of ITP3R to post-I/R activation of cardiac FBs and understanding the molecular mechanisms underlying excessive reactive fibrosis in the heart.