Mechanisms of Airway Smooth Muscle Hypertrophy

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DESCRIPTION (provided by applicant): Increased airway smooth muscle mass, due either to hypertrophy or hyperplasia, is present in patients with asthma. While the biochemical pathways regulating cell proliferation have been well studied, little is known about the biochemical pathways regulating airway smooth muscle protein synthesis, cell size or the accumulation of contractile apparatus proteins. Recent data from cell culture models and patients with asthma suggest that airway smooth muscle contractile protein expression may be regulated in a post- transcriptional manner. In this revised application, we propose that airway smooth muscle hypertrophy requires the activation of specific translational control pathways. To test this, we will study 1) a cell culture model of hypertrophy in which primary human bronchial smooth muscle cells are treated with transforming growth factor (TGF)-beta; 2) two mouse models of asthma; and 3) biopsy samples from human asthmatics. We propose three Specific Aims: Specific Aim 1. Determine the contributions of contractile apparatus transcription and translation in the development of human airway smooth muscle hypertrophy. We hypothesize that: 1) TGFbeta promotes airway smooth muscle hypertrophy by increasing both gene transcription and translational efficiency; and 2) murine airway remodeling is characterized in part by smooth muscle hypertrophy. Specific Aim 2. Examine the contribution of cap-dependent protein synthesis to human airway smooth muscle hypertrophy. We hypothesize that: 1) 4E-BP phosphorylation, which increases the availability of elF4E for elF4F complex formation, is required for TGFbeta-induced airway smooth muscle hypertrophy; 2) elF4E phosphorylation by MAP kinase signal integrating kinase (MNK)-1 is required for airway smooth muscle hypertrophy; and 3) airway remodeling is characterized in part by increased phosphorylation of airway smooth muscle 4E-BP and elF4E. Specific Aim 3. Examine the contribution of cap-independent protein synthesis to human airway smooth muscle hypertrophy. We hypothesize that: 1) p70 ribosomal S6 kinase (S6 kinase) is neither required nor sufficient for airway smooth muscle hypertrophy; 2) GSK3beta phosphorylation and inactivation is required and sufficient for airway smooth muscle hypertrophy; and 3) airway remodeling is characterized in part by increased phosphorylation of airway smooth muscle GSK3beta. Understanding biochemical mechanisms of airway remodeling in asthma will lead to improvements in the treatment of this disease.