Insulin resistance mediates high-fat diet-induced pulmonary fibrosis and airway hyperresponsiveness through the TGF-β1 pathway

Park et al. Experimental & Molecular Medicine (2019) 51:59 https://doi.org/10.1038/s12276-019-0258-7 ARTICLE Experimental & Molecular Medicine Open Access Insulin resistance mediates high-fat dietinduced pulmonary fibrosis and airway hyperresponsiveness through the TGF-β1 pathway 1234567890():,; 1234567890():,; 1234567890():,; 1234567890():,; Yoon Hee Park1, Eun Yi Oh1, Heejae Han1, Misuk Yang1, Hye Jung Park2, Kyung Hee Park1,3, Jae-Hyun Lee1,3 and Jung-Won Park 1,3 Abstract Prior studies have reported the presence of lung fibrosis and enhanced airway hyperresponsiveness (AHR) in mice with high-fat-diet (HFD)-induced obesity. This study evaluated the role of TGF-β1 in HFD-induced AHR and lung fibrosis in a murine model. We generated HFD-induced obesity mice and performed glucose and insulin tolerance tests. HFD mice with or without ovalbumin sensitization and challenge were also treated with an anti-TGF-β1 neutralizing antibody. AHR to methacholine, inflammatory cells in the bronchoalveolar lavage fluid (BALF), and histological features were evaluated. Insulin was intranasally administered to normal diet (ND) mice, and in vitro insulin stimulation of BEAS-2b cells was performed. HFD-induced obesity mice had increased insulin resistance, enhanced AHR, peribronchial and perivascular fibrosis, and increased numbers of macrophages in the BALF. However, they did not have meaningful eosinophilic or neutrophilic inflammation in the lungs compared with ND mice. The HFD enhanced TGF-β1 expression in the bronchial epithelium, but we found no differences in the expression of interleukin (IL)−4 or IL-5 in lung homogenates. Administration of the anti-TGF-β1 antibody attenuated HFD-induced AHR and lung fibrosis. It also attenuated goblet cell hyperplasia, but did not affect the AHR and inflammatory cell infiltration induced by OVA challenge. The intranasal administration of insulin enhanced TGF-β1 expression in the bronchial epithelium and lung fibrosis. Stimulating BEAS-2b cells with insulin also increased TGF-β1 production by 24 h. We concluded that HFDinduced obesity-associated insulin resistance enhances TGF-β1 expression in the bronchial epithelium, which may play an important role in the development of lung fibrosis and AHR in obesity. Introduction In the last decade, the number of diagnosed asthma patients has increased to over 300 million people worldwide1. Recent studies have demonstrated that obesity is an important causative factor of asthma, and that the risk of asthma is doubled in obese patients compared with normal weight patients2,3. Furthermore, a decrease in body Correspondence: Jung-Won Park () 1 Institute for Allergy, Yonsei University College of Medicine, Seoul, Korea 2 Department of Internal Medicine and Gangnam Severance Hospital, Yonsei University College of Medicine, Seoul, Korea Full list of author information is available at the end of the article. weight improves asthma outcomes4. As the proportion of people with obesity is steadily increasing, the burden of obesity on asthma is also becoming increasingly important5. Obesity-associated asthma differs from none obesity-associated asthma in several ways, specifically, patients with obesity-associated asthma struggle with poor asthma control and are frequently resistant to conventional treatments6,7. However, the mechanism underlying the association between obesity and asthma remains controversial. Obesity itself is associated with increases in the levels of various systemic proinflammatory mediators, such as C- © The Author(s) 2019 Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Official journal of the Korean Society for Biochemistry and Molecular Biology Park et al. Experimental & Molecular Medicine (2019) 51:59 reactive protein (CRP), leptin, and interleukin (IL)−68–10. High-fat-diet (HFD)-induced obesity may also induce increased levels of IL-1β, tumor necrosis factor (TNF)-α, IL-17, and transforming growth factor (TGF)-β in lung tissue11–14. We previously demonstrated that a HFD is significantly associated with AHR and lung fibrosis in mice with TNF-α-producing macrophages, but not with enhanced accumulation of eosinophils or neutrophils in the lung tissue, and the enhancement in AHR was eliminated by treating the obese mice with exercise4,8,11. The association between AHR and lung fibrosis without allergic inflammation in HFD-induced obesity indicates a causal relationship between airway remodeling and the development of AHR in this model. TGF-β, an adipokine, has diverse roles in the maintenance of cellular homeostasis, lung development, and physiology15. TGF-β stimulates the production of connective tissue by fibroblasts, and enhanced expression of TGF-β in the lungs may induce tissue dysfunctions, such as the lung fibrosis and airway remodeling seen in asthma and chronic bronchitis15–17. TGF-β can be secreted by epithelial cells, fibroblasts, eosinophils, mast cells, and Treg cells17. Several cytokines and chemokines related to allergic inflammation, such as IL-13, adenosine, VEGF, and CCR2, stimulate the production of TGF-β1 from these cells18. However, in addition to the TGF-β1 pathway, other mechanisms, such as the IL-13 and periostin pathway, also engage in the development of subepithelial fibrosis in the lungs and airway remodeling of asthma19. Recent studies have shown that TGF-β1 expression is also enhanced by HFD-induced obesity in mice12,13,20 and Drosophila21. Furthermore, insulin resistance is a critical problem in obesity and is associated with proinflammatory reactions involving various immune cells and cytokines22. Some studies have reported that TGF-β is associated with insulin resistance21,23, and that blocking TGF-β signaling protects against the development of HFD-induced obesity and diabetes in mice24. In vitro experiments have demonstrated that cells from insulinresistant subjects and bronchial cells treated with insulin exhibit increased TGF-β activation and subsequently increased lung fibrosis25,26. These findings suggest that TGF-β1 might be the connection between airway remodeling and AHR in obesity-associated asthma16. However, the role of TGF-β1 may be complicated as some investigators have also (...truncated)