Airway smooth muscle hyperplasia and hypertrophy correlate with glycogen synthase kinase-3β phosphorylation in a mouse model of asthma

Bentley JK, Deng H, Linn MJ, Lei J, Dokshin GA, Fingar DC, Bitar KN, Henderson WR Jr, Hershenson MB. Airway smooth muscle hyperplasia and hypertrophy correlate with glycogen synthase kinase-3 beta phosphorylation in a mouse model of asthma. Am J Physiol Lung Cell Mol Physiol 296: L176-L184, 2009. First published November 14, 2008; doi:10.1152/ajplung.90376.2008.-Increased airway smooth muscle (ASM) mass, a characteristic finding in asthma, may be caused by hyperplasia or hypertrophy. Cell growth requires increased translation of contractile apparatus mRNA, which is controlled, in part, by glycogen synthase kinase (GSK)-3 beta, a constitutively active kinase that inhibits eukaryotic initiation factor-2 activity and binding of methionyl tRNA to the ribosome. Phosphorylation of GSK-3 beta inactivates it, enhancing translation. We sought to quantify the contributions of hyperplasia and hypertrophy to increased ASM mass in ovalbumin (OVA)- sensitized and - challenged BALB/c mice and the role of GSK-3 beta in this process. Immunofluorescent probes, confocal microscopy, and stereological methods were used to analyze the number and volume of cells expressing alpha-smooth muscle actin and phospho-Ser(9) GSK-3 beta (pGSK). OVA treatment caused a 3-fold increase in ASM fractional unit volume or volume density (Vv) (PBS, 0.006 +/- 0.0003; OVA, 0.014 +/- 0.001), a 1.5-fold increase in ASM number per unit volume (Nv), and a 59% increase in volume per cell (Vv/Nv) ( PBS, 824 +/- 76 mu m(3); OVA, 1,310 +/- 183 mu m(3)). In OVA-treated mice, there was a 12-fold increase in the Vv of pGSK (+) ASM, a 1.5-fold increase in the Nv of pGSK (+) ASM, and a 1.6-fold increase in Vv/Nv. Lung homogenates from OVA-treated mice showed increased GSK-3 beta phosphorylation and lower GSK-3 beta activity. Both hyperplasia and hypertrophy are responsible for increased ASM mass in OVA-treated mice. Phosphorylation and inactivation of GSK-3 beta are associated with ASM hypertrophy, suggesting that this kinase may play a role in asthmatic airway remodeling.