Pulmonary Macrophages Attenuate Hypoxic Pulmonary Vasoconstriction via β3AR/iNOS Pathway in Rats Exposed to Chronic Intermittent Hypoxia.

Koichi Uemura,Hisashi Nagai,Ichiro Kuwahira,Rutsuko Yamaguchi,Tatsuo Shimosawa,Lisa Wingenfeld,Sayoko Ogura,Mikiyasu Shirai,Daryl O Schwenke,Yutaka Fujii,Takashi Sonobe,Hirotsugu Tsuchimochi,Ken-Ichi Yoshida,Keiji Umetani,Tadakatsu Inagaki,Akina Nara,James T Pearson

doi:10.1371/journal.pone.0131923

Abstract

Chronic intermittent hypoxia (IH) induces activation of the sympathoadrenal system, which plays a pivotal role in attenuating hypoxic pulmonary vasoconstriction (HPV) via central β1-adrenergic receptors (AR) (brain) and peripheral β2AR (pulmonary arteries). Prolonged hypercatecholemia has been shown to upregulate β3AR. However, the relationship between IH and β3AR in the modification of HPV is unknown. It has been observed that chronic stimulation of β3AR upregulates inducible nitric oxide synthase (iNOS) in cardiomyocytes and that IH exposure causes expression of iNOS in RAW264.7 macrophages. iNOS has been shown to have the ability to dilate pulmonary vessels. Hence, we hypothesized that chronic IH activates β3AR/iNOS signaling in pulmonary macrophages, leading to the promotion of NO secretion and attenuated HPV. Sprague-Dawley rats were exposed to IH (3-min periods of 4–21% O2) for 8 h/d for 6 weeks. The urinary catecholamine concentrations of IH rats were high compared with those of controls, indicating activation of the sympathoadrenal system following chronic IH. Interestingly, chronic IH induced the migration of circulating monocytes into the lungs and the predominant increase in the number of pro-inflammatory pulmonary macrophages. In these macrophages, both β3AR and iNOS were upregulated and stimulation of the β3AR/iNOS pathway in vitro caused them to promote NO secretion. Furthermore, in vivo synchrotron radiation microangiography showed that HPV was significantly attenuated in IH rats and the attenuated HPV was fully restored by blockade of β3AR/iNOS pathway or depletion of pulmonary macrophages. These results suggest that circulating monocyte-derived pulmonary macrophages attenuate HPV via activation of β3AR/iNOS signaling in chronic IH.

Highlights

Intermittent hypoxia (IH) during sleep periods is a distinctive feature in the patients of sleep apnea syndrome (SAS) [1,2,3]
Immunofluorescent staining of pulmonary tissue performed after 6 weeks of IH exposure demonstrated that the number of pulmonary macrophages was significantly increased and the positive ratio of β3AR-expressing cells was high (Fig 1A–1D)
Western blotting and RT-PCR showed that the β3AR was expressed in both the lung tissue and BAL fluid (BALF)-derived alveolar macrophages of N rats (Fig 1F–1H), and immunohistochemistry demonstrated that the β3AR was expressed on the endothelium of the pulmonary arteries (S4A Fig)

Summary

Introduction

Intermittent hypoxia (IH) during sleep periods is a distinctive feature in the patients of sleep apnea syndrome (SAS) [1,2,3]. We hypothesized that 1) β3AR in the pulmonary macrophages may be upregulated by IH associated with sympathoadrenal activation, 2) iNOS expression in the pulmonary macrophages may be increased following stimulation of the upregulated β3AR as well as directly by IH per se, and 3) the β3AR/iNOS signaling in the pulmonary macrophages may be activated to release substantial NO in response to acute hypoxic exposure and may modify HPV To verify these hypotheses, we performed the following experiments using rats treated with chronic IH (IH rats) and rats exposed to normoxia (N rats). Using synchrotron radiation microangiography for visualizing the pulmonary microvessels in vivo, we revealed the functional contribution of β3AR/iNOS signaling in the pulmonary macrophages to modulation of HPV

Materials and Methods

Results

Discussion