Dysregulation of the IL-13 Receptor System. A Novel Pathomechanism in Pulmonary Arterial Hypertension

Abstract

Idiopathic pulmonary arterial hypertension (IPAH) is characterized by medial hypertrophy due to pulmonary artery smooth muscle cell (paSMC) hyperplasia. Inflammation is proposed to play a role in vessel remodeling associated with IPAH. IL-13 is emerging as a regulator of tissue remodeling; however, the contribution of the IL-13 system to IPAH has not been assessed. The objective of this study was to assess the possible contribution of the IL-13 system to IPAH. Expression and localization of IL-13, and IL-13 receptors IL-4R, IL-13Rα1, and IL-13Rα2 were assessed by real-time reverse transcription-polymerase chain reaction, immunohistochemistry, and flow cytometry in lung tissue, paSMC, and microdissected vascular lesions from patients with IPAH, and in lung tissue from rodents with hypoxia- or monocrotaline-induced pulmonary hypertension. A whole-genome microarray analysis was used to study IL-13-regulated genes in paSMC. Pulmonary expression of the IL-13 decoy receptor IL-13Rα2 was up-regulated relative to that of the IL-13 signaling receptors IL-4R and IL-13Rα1 in patients with IPAH and in two animal models of IPAH. IL-13, signaling via STAT3 and STAT6, suppressed proliferation of paSMC by promoting G(0)/G(1) arrest. Whole-genome microarrays revealed that IL-13 suppressed endothelin-1 production by paSMC, suggesting that IL-13 controlled paSMC growth by regulating endothelin production. Ectopic expression of the il13ra2 gene resulted in partial loss of paSMC growth control by IL-13 and blunted IL-13 suppression of endothelin-1 production by paSMC, whereas small-interfering RNA knockdown of il13ra2 gene expression had the opposite effects. The IL-13 system is a novel regulator of paSMC growth. Dysregulation of IL-13 receptor expression in IPAH may partially underlie smooth muscle hypertrophy associated with pathological vascular remodeling in IPAH.