Endogenous and pharmacological inhibition of calpain decreases migration of hypoxic pulmonary arterial smooth muscle cells (PASMCs)

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Prolonged exposure to hypoxia causes pulmonary hypertension due to contraction, proliferation and migration of PASMCs, which result from hypoxia‐induced elevations in basal intracellular calcium concentration ([Ca2+]i). Calpain, a Ca2+‐dependent cysteine protease, has two major isoforms, μ‐ and m‐calpain, that require μM and mM [Ca2+]i, respectively, for activation. Calpain is known to participate in fibroblast and endothelial cell migration and proliferation, and PASMCs exhibit increased calpain levels during hypoxia (Ma et al, JCI 2011). In this study, we hypothesized that reducing calpain activity through in vivo overexpression of calpastatin (CAST), an endogenous calpain inhibitor, or in vitro inhibition with the pharmacological agent, calpeptin, would impair migration of PASMCs. For in vivo experiments, wild type (WT) and CAST overexpressing mice were exposed to normoxia or chronic hypoxia (10% O2; 21 d). For in vitro experiments, PASMCs were isolated from WT or CAST mice before exposure to normoxia or hypoxia (4% O2; 24 h). PASMC migration was measured using a modified Boyden chamber transwell assay. For both in vitro and in vivo experiments, WT, but not CAST, PASMCs exhibited increased migration in response to hypoxia. In WT PASMCs, calpeptin prevented hypoxia‐induced migration. These results suggest that calpain activity is necessary to facilitate the migration of hypoxic PASMCs.