title: An RGS4-mediated phenotypic switch of bronchial smooth muscle cells promotes fixed airway obstruction in asthma.
abstract: In severe asthma, bronchodilator- and steroid-insensitive airflow obstruction develops through unknown mechanisms characterized by increased lung airway smooth muscle (ASM) mass and stiffness. We explored the role of a Regulator of G-protein Signaling protein (RGS4) in the ASM hyperplasia and reduced contractile capacity characteristic of advanced asthma. Using immunocytochemical staining, ASM expression of RGS4 was determined in endobronchial biopsies from healthy subjects and those from subjects with mild, moderate and severe asthma. Cell proliferation assays, agonist-induced calcium mobilization and bronchoconstriction were determined in cultured human ASM cells and in human precision cut lung slices. Using gain- and loss-of-function approaches, the precise role of RGS proteins was determined in stimulating human ASM proliferation and inhibiting bronchoconstriction. RGS4 expression was restricted to a subpopulation of ASM and was specifically upregulated by mitogens, which induced a hyperproliferative and hypocontractile ASM phenotype similar to that observed in recalcitrant asthma. RGS4 expression was markedly increased in bronchial smooth muscle of patients with severe asthma, and expression correlated significantly with reduced pulmonary function. Whereas RGS4 inhibited G protein-coupled receptor (GPCR)-mediated bronchoconstriction, unexpectedly RGS4 was required for PDGF-induced proliferation and sustained activation of PI3K, a mitogenic signaling molecule that regulates ASM proliferation. These studies indicate that increased RGS4 expression promotes a phenotypic switch of ASM, evoking irreversible airway obstruction in subjects with severe asthma.
authors.affiliation: Airways Biology Initiative, Pulmonary, Allergy and Critical Care Division, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Gautam
authors.initials: G
authors.lastname: Damera
authors.forename: Kirk M
authors.initials: KM
authors.lastname: Druey
authors.forename: Philip R
authors.initials: PR
authors.lastname: Cooper
authors.forename: Vera P
authors.initials: VP
authors.lastname: Krymskaya
authors.forename: Roy J
authors.initials: RJ
authors.lastname: Soberman
authors.forename: Yassine
authors.initials: Y
authors.lastname: Amrani
authors.forename: Toshinori
authors.initials: T
authors.lastname: Hoshi
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Brightling
authors.forename: Reynold A
authors.initials: RA
authors.lastname: Panettieri
mesh_terms: D000402:Airway Obstruction / Q000150:complications / Q000473:pathology* / Q000503:physiopathology; D001249:Asthma / Q000150:complications* / Q000473:pathology* / Q000503:physiopathology; D001980:Bronchi / Q000473:pathology*; D016084:Bronchoconstriction / Q000187:drug effects; D002217:Carbachol / Q000494:pharmacology; D049109:Cell Proliferation / Q000187:drug effects; D056966:Excitation Contraction Coupling / Q000187:drug effects; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D008297:Male; D008875:Middle Aged; D008934:Mitogens / Q000494:pharmacology; D008954:Models, Biological; D032389:Myocytes, Smooth Muscle / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology*; D010641:Phenotype; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D020710:RGS Proteins / Q000378:metabolism*; D013183:Sputum / Q000187:drug effects / Q000378:metabolism
chemical_list: D008934:Mitogens; D010982:Platelet-Derived Growth Factor; D020710:RGS Proteins; C098799:RGS4 protein; D002217:Carbachol; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt