Abstract Body: Background: Deposition of misfolded protein aggregates observed in diverse cardiac disease models leads to proteotoxic cardiomyopathy. In earlier studies, we confirmed mutations in α-B-Crystallin, specifically Arg120Gly (CryAB^R120G), develop proteotoxic cardiomyopathy. Cardiomyocyte-specific CryAB^R120G overexpression leads to cardiac dysfunction resulting from the accumulation of toxic pre-amyloid oligomers and protein aggregation. In the event of proteotoxic insult, the chaperone proteins function to prevent the accumulation of protein aggregates. One of the multitasking chaperone proteins in the heart is Sigmar1, whose role in proteotoxic cardiomyopathy and protein aggregation remains unknown.
Hypothesis: We hypothesize that Sigmar1 plays an essential role in protein aggregate clearance, and the absence of Sigmar1 in CryAB^R120G mice aggravates pathological cardiac remodeling.
Methods and Result: We measured Sigmar1 expression level in CryAB^R120G hearts and found a significant reduction in endogenous Sigmar1 protein and transcript levels in CryAB^R120G hearts. Co-immunoprecipitation and yeast-two-hybrid assays demonstrated a direct interaction between Sigmar1 and CryAB. Therefore, we evaluated Sigmar1’s function in the proteotoxic model of heart failure. We ablated Sigmar1 in CryAB^R120G, expressing myocytes both in vitro by using Sigmar1 siRNA and in vivo by crossing Sigmar1 knockout with CryAB^R120G (CryAB^R120GxSigmar1^-/-). Both in vitro and in vivo studies displayed a dramatic increase in protein aggregate size and content in CryAB^R120GxSigmar1^-/- heart, assessed by immunostaining and electron microscopy. Echocardiography showed age-dependent aggravation of cardiac contractile dysfunction, and Masson’s Trichrome staining showed increased cardiac fibrosis in the CryAB^R120GxSigmar1^-/- hearts compared to CryAB^R120G hearts.
Conclusion: Overall, we found that Sigmar1 directly interacts with CryAB and plays a vital role in the degradation of protein aggregates where the absence of Sigmar1 causes increased protein aggregate size and content in CryAB^R120G mice, leading to aggravated pathology with ventricular dysfunction, increased interstitial fibrosis, and cardiac hypertrophy.