L-plastin levels are associated with mortality during cardiomyopathy syndrome in farmed Atlantic salmon (Salmo salar L.)

Cardiomyopathy syndrome (CMS) is a severe infectious cardiac disease affecting Atlantic salmon (Salmo salar L.). The disease is chief cause of sudden death in Norwegian fish farms and poses serious economical and fish welfare challenges to all salmon-producing countries. Although urgently needed, there are currently no treatments or effective preventive tools available. To achieve this, an in-depth understanding of the biological mechanisms leading to CMS is first required. Proteomic-based blood plasma analysis of inflammatory and immune response proteins recently identified L-plastin as an acute response protein in salmon. Here, we investigated whether L-plastin is associated with piscine myocarditis virus (PMCV) infection and mortality during CMS. By comparing heart and blood plasma samples from surviving and deceased fish from a confirmed CMS outbreak site, we observed that L-plastin expression was elevated in cardiac tissue while circulating free L-plastin levels were reduced in deceased fish. Interestingly, a higher molecular weight band positive for L-plastin was detected in plasma from deceased fish and correlated with L-plastin expression in the heart. In addition, cardiac L-plastin levels correlated with cardiac histopathological changes, mononuclear cell infiltration and necrosis of cardiomyocytes in the heart. Our findings set the base for further investigation of L-plastin as a potential biomarker for mortality risk during PMCV infection and for understanding the course of CMS in farmed salmon.