Ca2+ handling remodelling in a porcine model of right ventricular dysfunction

Increased afterload is the primary pathophysiologic mechanism for right ventricular failure (RVF), which is the most critical determinant of survival in patients with pulmonary hypertension (PH). The cellular and molecular processes involved in the RV remodeling, including Ca2+ handling as an instrumental actor in the heart, remain incompletely understood. We gain insights into the cellular Ca2+ signaling in a large animal model of RV failure, the chronic thromboembolic pulmonary hypertension (CTEPH) piglet model, to develop specific therapy targeting RVF. CTEPH piglet model consisted of a primary left pulmonary artery ligation followed by weekly embolization in the right lower lobe leading to PH and progressive RV hypertrophy and failure. After six weeks, the piglet model replicated all the features of human CTEPH: increased pulmonary vascular resistance, mean pulmonary arterial pressure (PAP), and RV wall thickness associated with RV dysfunction as assessed by the reduced tricuspid annular plane systolic excursion (TAPSE). RV histological analyses revealed hypertrophied cardiomyocytes and aberrant fibrosis. At the cell level, RV myocytes from CTEPH piglets presented reduced L-type Ca2+ currents and CACNA1C mRNA, lower and slower [Ca2+]i transients, decreased sarcoplasmic reticulum Ca2+ content, and cell shortening to myocytes from sham piglets. This was related to reduce Sarco/Endoplasmic Reticulum Ca2+-ATPase isoform 2a (SERCA2a) protein expression. We found that store-operated Ca2+ entry is increased in hypertrophied RV myocytes, which is correlated with a de novo expression of the SR Ca2+ sensor STIM1L (long stromal interacting molecule 1). Finally, we found that Ca2+ sparks are larger and longer in RV myocytes from CTEPH piglets, whereas their frequencies and amplitude were unchanged compared to myocytes from sham. This was associated with profound disorganization of T tubules and ryanodine receptors (RyR) clustering without changes in RyR phosphorylation status. Our data highlight a cellular Ca2+ cycling remodeling that participates to the pathogenesis of RVF in CTEPH piglets.