The calpain/ABCA1 pathway drives mast cell- initiated vascular leakage and inflammation in the skin.

Cutaneous mast cells (MCs) initiate local and systemic immune responses. To reach this end, activated MCs immediately release an arsenal of pro-inflammatory proteases. In this study, we evaluated the role of the cysteine protease, calpain in MC function. Calpain activity and protein were confirmed in the supernatants of MCs activated via either the FceR or the MrgprB2. In vivo, extracellular calpain induces vascular leakage in a MC- dependent manner. We then investigated the mechanism of calpain release. In vitro and in vivo studies suggest that the cholesterol transporter, the ATP- binding cassette A1 transporter (ABCA1) externalizes calpain. To investigate the role of the ABCA1 in MC biology, we generated mice lacking the Abca1 specifically on connective tissue MCs (Mcpt5-Cre⁺Abca1^fl/fl mice). In vitro, Abca1-deficient MCs accumulate intracellular cholesterol, have reduced calpain release and reduced pro-inflammatory cytokines levels. In vivo, in the MC903-induced atopic dermatitis model, Mcpt5-Cre⁺Abca1^fl/fl mice have reduced inflammation and a fewer MCs in affected skin compared to littermate controls. Corroborating this finding, global ABCA1 blockade with FDA-approved glyburide similarly reduced inflammation induced by MC903. Collectively, these data suggest that targeting the calpain/ABCA1 pathway may open new therapeutic avenues for MC -mediated inflammation in the skin.