Submitted on July 8, 2008
Revised on October 21, 2008
Accepted on November 10, 2008
AIRWAY SMOOTH MUSCLE HYPERPLASIA AND HYPERTROPHY CORRELATE WITH GLYCOGEN SYNTHASE KINASE-3
PHOSPHORYLATION IN A MOUSE MODEL OF ASTHMA
J Kelley Bentley1, Huan Deng1, Marisa J Linn1, Jing Lei1, Gregoriy A Dokshin1, Diane C. Fingar1, Khalil N. Bitar1, William R Henderson, Jr.2, and Marc B Hershenson1*
1 University of Michigan
2 University of Washington
* To whom correspondence should be addressed. E-mail: mhershen{at}umich.edu.
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
, a constitutively-active kinase which inhibits eukaryotic initiation factor-2 activity and binding of methionyl tRNA to the ribosome. Phosphorylation of GSK-3 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 in this process. Immunofluorescent probes, confocal microscopy and stereological methods were used to analyze the number and volume of cells expressing 
-smooth muscle actin and phospho-Ser9 GSK-3 (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 µ3; OVA, 1310±183 µ3). In OVA-treated mice, there was a 12-fold increase in the Vv of pGSK (+) ASM, a 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 phosphorylation and lower GSK-3 activity. Both hyperplasia and hypertrophy are responsible for increased ASM mass in OVA-treated mice. Phosphorylation and inactivation of GSK-3 are associated with ASM hypertrophy, suggesting that this kinase may play a role in asthmatic airway remodeling.
