Abstract Body: Background: Deposition of misfolded protein aggregates in the myocardium disrupts cardiac function and causes proteotoxic cardiomyopathy. In earlier studies, cardiomyocyte-specific overexpression of mutated α-B-Crystallin, specifically Arg120Gly (CryABR120G) 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 molecular chaperone proteins in the heart is Sigmar1, whose role in proteotoxic cardiomyopathy and protein aggregation remains unknown.
Hypothesis: We hypothesize that Sigmar1 plays an important role in protein aggregate clearance and modulating Sigmar1 level in CryABR120G mice alters cardiac function and pathological remodeling.
Methods and Results: We found significant reduction in endogenous Sigmar1 protein and transcript levels in CryABR120G hearts. Co-immunoprecipitation and yeast-two-hybrid assays showed direct interaction between Sigmar1 and CryAB. To evaluate Sigmar1’s role in cardiac proteotoxicity, we developed and characterized cardiac-specific inducible Sigmar1 overexpressing transgenic (Sigmar1TG) mouse. Sigmar1TG mice display no phenotype at the basal level. mice We crossed Sigmar1TG with CryABR120G mice (CryABR120GxSigmar1TG) and evaluated cardiac function and histopathological alterations. M-mode echocardiography showed improved cardiac function in CryABR120GxSigmar1TG mice. Picro Sirius Red staining and immunostaining for CryAB demonstrated decreased collagen content and decreased aggregate size respectively in CryABR120GxSigmar1TG hearts. Conversely, ablating Sigmar1 in CryABR120G (CryABR120GxSigmar1-/-) demonstrated aggravated cardiac function with increased collagen content and aggregate size.
Conclusion: Overall, we found that Sigmar1 directly interacts with CryAB and plays a vital role in regulating cardiac function and histopathological remodeling in CryABR120G mice where overexpressing Sigmar1 levels mediates protection by decreasing the aggregate size and collagen content, whereas ablating Sigmar1 aggravates the pathology in CryABR120G hearts.