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.

State-of-the-art methodologies used in preclinical studies to assess left ventricular diastolic and systolic function in mice, pitfalls and troubleshooting

“…Myocardial infarction (MI) or transverse aortic constriction (TAC), induced by permanent ligation of coronary artery or banding of ascending aorta to induce pressure overload respectively, represent established models of HFrEF ( 10 – 15 ). In absence of a direct myocardial injury, the impaired contractile performance of the heart has also been described in models of rheumatoid arthritis where chronic inflammation was associated with systolic dysfunction ( 16 ) while the acute phase of rheumatoid arthritis is characterized by impaired myofibrils cross-bridges formation in response to elevated intracellular Ca 2+ ( 17 ). Several transgenic models have been used to identify important causes of heart failure or its progression and to identify putative targets for therapy ( 8 , 9 ).…”