Citrullination is linked to reduced Ca2+ sensitivity in hearts of a murine model of rheumatoid arthritis

Abstract

Aims: Cardiac contractile dysfunction is prevalent in rheumatoid arthritis (RA), with an increased risk for heart failure. A hallmark of RA has increased levels of peptidyl arginine deaminases (PAD) that convert arginine to citrulline leading to ubiquitous citrullination, including in the heart. We aimed to investigate whether PAD-dependent citrullination in the heart was linked to contractile function in a mouse model of RA during the acute inflammatory phase.

Methods: We used hearts from the collagen-induced arthritis (CIA) mice, with overt arthritis, and control mice to analyze cardiomyocyte Ca²⁺ handling and fractional shortening, the force-Ca²⁺ relationship in isolated myofibrils, the levels of PAD, protein post-translational modifications, and Ca²⁺ handling protein. Then, we used an in vitro model to investigate the role of TNF-α in the PAD-mediated citrullination of proteins in cardiomyocytes.

Results: Cardiomyocytes from CIA mice displayed larger Ca²⁺ transients than controls, whereas cell shortening was similar in the two groups. Myofibrils from CIA hearts required higher [Ca²⁺ ] to reach 50% of maximum shortening, ie Ca²⁺ sensitivity was lower. This was associated with increased PAD2 expression and α-actin citrullination. TNF-α increased PAD-mediated citrullination which was blocked by pre-treatment with the PAD inhibitor 2-chloroacetamide.

Conclusion: Using a mouse RA model we found evidence of impaired cardiac contractile function linked to reduced Ca²⁺ sensitivity, increased expression of PAD2, and citrullination of α-actin, which was triggered by TNF-α. This provides molecular and physiological evidence for acquired cardiomyopathy and a potential mechanism for RA-associated heart failure.

Keywords: Ca2+ sensitivity; PAD; citrullination; heart failure; rheumatoid arthritis.