α2B-adrenoceptor deficiency leads to postnatal respiratory failure in mice

Abstract

α2-Adrenoceptors belong to the family of adrenergic receptors, which regulate the neuronal release of norepinephrine as part of a negative feedback loop. Among the α2-adrenoceptors, the α2B-subtype may also influence developmental signaling pathways involved in angiogenesis of the placenta. Thus, the aim of the present study was to determine whether α2B-adrenoceptors are also involved in other developmental processes beyond placental angiogenesis. Ablation of α2B-adrenoceptors led to lethality of mutant mice during the first hours after birth. Despite normal breathing and drinking behavior, mutant mice developed cyanosis, which could be traced back to a defect in lung morphology with significantly reduced alveolar volume and thickened interalveolar septi. In α2B-deficient lungs and in isolated alveolar type II cells, expression of sonic hedgehog (SHH) was significantly increased, resulting in mesenchymal proliferation. In vitro α 2B-adrenoreceptor stimulation suppressed expression of sonic hedgehog and the cell cycle genes cyclin D1 and Ki67. In vivo inhibition of enhanced SHH signaling by the smoothened antagonist cyclopamine partially rescued perinatal lethality, lung morphology, and altered gene expression in mutant mice. Thus, α2B-adrenoceptors in lung epithelia play an important role in suppressing sonic hedgehog-mediated proliferation of mesenchymal cells and thus prevent respiratory failure. © 2010 by The American Society for Biochemistry and Molecular Biology, Inc.