Vitamin D3-Deficient Diet Promotes Pulmonary Fibrosis Development in Murine Model of Hypersensitivity Pneumonitis

Although vitamin D3 (VD3) deficiency has been recognized as a harmful agent in several respiratory diseases, the present study is the first one to investigate its influence on the development of hypersensitivity pneumonitis (HP). This research was conducted in a murine model of HP, wherein pulmonary fibrosis was induced by antigen of <i>Pantoea agglomerans</i>. VD3 deficiency was provoked by diet with 10-times less cholecalciferol than feed given to VD3-sufficient mice. Before and after 14 and 28 days of nebulization, lung function was evaluated. Moreover, at indicated time points, lungs were collected and subjected to histological assessment, flow cytometry, gene expression assays, and ELISA. The performed research showed a higher sensitivity of VD3-deficient mice to fibrosis response to <i>P. agglomerans</i> antigen, which was strongly associated with enhanced epithelial-to-mesenchymal transition, the signs of which were over-expression of EMT-transcription factors (<i>Snail2</i>, <i>Zeb1</i>, <i>Zeb2</i>) and mesenchymal cell markers (<i>Cdh2</i>/N-cadherin, <i>Acta2</i>/SMA, <i>Fn1</i>/Fibronectin, <i>Vim</i>/Vimentin). Indicated negative changes in VD3-deficient mice with developed HP were supported by deepening calcitriol deficiency and worsening respiratory functions, including the frequency of breathing, minute volume, total cycle times, expiratory and inspiratory time. Moreover, typical for VD3-deficient mice with HP, there was also an increased influx of immune cells into the lungs (especially neutrophils, macrophages, dendritic cells and lymphocytes Tc), a disturbed cytokine profile with over-production of growth factors favoring fibrosis (FGF2 and TGFβ), and lowered synthesis of several cytokines (IL1β, IL6, IL12, IL4 IL10, IL13). The present study reveals that VD3 deficiency promotes the development of pulmonary fibrosis in the murine model of HP.