Inhibition of glycogen synthase kinase-3β is sufficient for airway smooth muscle hypertrophy

We examined the role of glycogen synthase kinase-3 beta(GSK-3 beta) inhibition in airway smooth muscle hypertrophy, a structural change found in patients with severe asthma. LiCl, SB216763, and specific small interfering RNA ( siRNA) against GSK-3 beta, each of which inhibit GSK-3 beta activity or expression, increased human bronchial smooth muscle cell size, protein synthesis, and expression of the contractile proteins alpha-smooth muscle actin, myosin light chain kinase, smooth muscle myosin heavy chain, and SM22. Similar results were obtained following treatment of cells with cardiotrophin (CT)-1, a member of the interleukin-6 superfamily, and transforming growth factor (TGF)-beta, a proasthmatic cytokine. GSK-3 beta inhibition increased mRNA expression of alpha-actin and transactivation of nuclear factors of activated T cells and serum response factor. siRNA against eukaryotic translation initiation factor 2B epsilon (eIF2B epsilon) attenuated LiCl- and SB216763-induced protein synthesis and expression of alpha-actin and SM22, indicating that eIF2B is required for GSK-3 beta-mediated airway smooth muscle hypertrophy. eIF2B epsilon siRNA also blocked CT-1- but not TGF-beta-induced protein synthesis. Infection of human bronchial smooth muscle cells with pMSCV GSK-3 beta-A9, a retroviral vector encoding a constitutively active, nonphosphorylatable GSK-3 beta, blocked protein synthesis and alpha-actin expression induced by LiCl, SB216763, and CT-1- but not TGF-alpha. Finally, lungs from ovalbumin-sensitized and -challenged mice demonstrated increased alpha-actin and CT-1 mRNA expression, and airway myocytes isolated from ovalbumin-treated mice showed increased cell size and GSK-3 beta phosphorylation. These data suggest that inhibition of the GSK-3 beta/eIF2B epsilon translational control pathway contributes to airway smooth muscle hypertrophy in vitro and in vivo. On the other hand, TGF-beta-induced hypertrophy does not depend on GSK-3 beta/eIF2B signaling.