Inflammatory cytokines induce human bronchial smooth muscle cell proliferation via an NCX-1 dependent mechanism

Airway smooth muscle hyperplasia is a characteristic of airway remodeling in asthma and this is thought to be, at least in part, cytokine mediated. Because cytosolic free calcium ([Ca²⁺]cyt) plays an important role in smooth muscle proliferation, we chose to examine the role of [Ca²⁺]cyt, focusing on the expression of the Na⁺/Ca²⁺ exchanger 1 (NCX1) protein and its link to human airway smooth muscle proliferation. In vitro studies were done to examine the function and expression of NCX1 protein in human bronchial smooth muscle cells (HBSMC). Cells were grown in the presence/absence of the inflammatory cytokines TNF[alpha], IL-13, and IL-33 and assessed for proliferation using a colorimetric assay. Proliferation was induced in the presence of inflammatory cytokines and blocked in the presence of SN-6, a selective NCX1 inhibitor. Immunoblotting, immunocytochemistry, and quantitative PCR revealed that inflammatory cytokines upregulate NCX1 protein and mRNA expression. In vivo studies were done in mice using an ovalbumin model of asthma. NCX1 expression in asthmatic mice airway was compared with control mice. Immunoblotting revealed a substantial increase in NCX1 protein expression in asthmatic mice. We have demonstrated that NCX1 is expressed in HBSMC and that this expression is increased by cytokines associated with asthma. Moreover, cells proliferate with these cytokines, which is blocked by NCX1 inhibition. NCX1 is also expressed and upregulated in asthmatic mice airway. These data suggest that NCX1 may play an important role in airway remodeling associated with asthm