Gα13 regulates methacholine-induced contraction of bronchial smooth muscle via phosphorylation of MLC20

Reversible airway constriction is induced by an increase in airway smooth muscle contractility in response to methacholine likely as a bronchospastic stimulus. Despite the finding of Gα12 and Gα13 up-regulation in airway hyperresponsive animals, their functional role of contraction in airway smooth muscle has not been directly explored. This study investigated the differential regulatory role of Gα12/Gα13 in methacholine-induced contraction of trachea and bronchus in Gα12 or Gα13 gene knockout mice after ovalbumin sensitization and challenges. Organ bath assays and videomicroscopy revealed that Gα13 deficiency delayed methacholine-induced contractile response of bronchiolar smooth muscle, but not that of tracheal smooth muscle. In primary bronchial smooth muscle cells, knockdown of Gα13 blocked methacholine-induced phosphorylation of 20 kDa regulatory light chain of myosin II (MLC20), a prerequisite step for the contractile initiation of actin and myosin. Gα13-dependent MLC20 phosphorylation was confirmed in murine embryonic fibroblasts. After ovalbumin sensitization and challenges, wild type mice exhibited methacholine-induced bronchial contraction of lung tissue. Heterozygous absence of the Gα13 gene abrogated methacholine-induced contractions, whereas homozygous absence of the Gα12 gene failed to do so. Our findings indicate that Gα13, but not Gα12, specifically regulates cholinergic bronchial contraction in airway responsiveness via controlling phosphorylation of MLC20 by methacholine.

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