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The Effects of Leptin on Airway Smooth Muscle Responses

¹ Firestone Institute for Respiratory Health, St. Joseph's Healthcare, and Department of Medicine, McMaster University, Hamilton, Ontario, Canada; and ² Division of Pulmonary & Critical Care Medicine, University of Michigan, Ann Arbor, Michigan

Correspondence and requests for reprints should be addressed to Dr. Parameswaran Nair, Firestone Institute for Respiratory Health, St. Joseph's Healthcare, 50 Charlton Avenue East, Hamilton, Ontario, L8N 4A6, Canada. E-mail: parames{at}mcmaster.ca

Obesity is associated with asthma and airway hyperresponsiveness. Leptin modulates some of the proinflammatory effects observed in obesity. The objective of this study was to determine the effects of leptin on airway smooth muscle responses. The effect of leptin (0.1–100 ng/ml) on migration (toward platelet-derived growth factor [PDGF], 10 ng/ml, across collagen-coated membrane in Transwell culture plates), proliferation (by BrDU incorporation), and cytokine production (by Bioplex bead assay) of cultured human airway smooth muscle cells from nine nonasthmatic donors was assessed. Effects of leptin on the contractile responses were studied in bovine tracheal smooth muscle rings. Leptin receptor expression and activation of STAT-3, Src kinase, Suppressor of Cytokine Signaling-3 (SOCS-3), and COX were evaluated by Western blotting and PCR. PGE₂ levels in supernatant were assessed by enzyme immunoassay. Human airway smooth muscle cells express leptin receptor, which, when engaged, phosphorylated STAT-3. Leptin inhibited PDGF-induced human airway smooth muscle migration and proliferation and IL-13–induced eotaxin production. Leptin did not stimulate cytokine synthesis and did not evoke contractile responses or inhibit isoproterenol-induced relaxation of carbachol-induced contraction of bovine tracheal rings. The inhibitory effects on migration and eotaxin production are not due to activation of SOCS-3 but are partly due to increased production of PGE₂ because they were attenuated by indomethacin. In conclusion, leptin inhibited human airway smooth muscle proliferation, migration toward PDGF, and IL-13–induced eotaxin production. This is partly mediated by PGE₂ secretion from smooth muscle cells induced by leptin. The association between obesity and asthma is unlikely to be due to a direct effect of leptin on airway smooth muscle.

Key Words: leptin • airway smooth muscle • migration • proliferation • cytokines • PGE₂

CLINICAL RELEVANCE The proinflammatory effects of obesity in asthma are unlikely to be due to a direct effect of leptin on airway smooth muscle.