The first step for understanding the molecular mechanism of the antifibrotic effect of inhaling 25(OH)-vitamin D3 and 1,25(OH)2-vitamin D3 in the murine model of hypersensitivity pneumonitis

The studies revealed that VD3-deficiency triggers EMT, the signs of which were increased expression of EMT transcription factors (Snail1, Snail2, Zeb1, and Zeb2), inhibited expression of epithelial cell markers (E-cadherin and occludin), and altered expression of mesenchymal cell markers, including upregulated N-cadherin and vimentin. Pathological changes caused by VD3-deficiencies accelerated in response to SE-PA, the signs of which were: 1) upregulated expression of Snail1, Snail2, Zeb1, Zeb2, Acta2, Cdh2, Fn1, and Vim; 2) downregulated expression of Cdh1 and Ocln; 3) increased level of α-SMA, fibronectin, vimentin, and occludin; 4) decreased amount of N-cadherin; 5) increased deposition of fibers in lung tissue. All negative changes recorded on the transcriptome level in VD3-deficient mice with HP were effectively reduced by inhalations of 25(OH)-VD3 and 1,25,25(OH)2-VD3, suggesting that their antifibrotic effects are associated with EMT inhibition. Nevertheless, the beneficial impact of VD3-metabolites on the proteome level was associated with restoration of the balance in the expression of EMT molecules disturbed by cholecalciferol deficiency and SE-PA exposure; metabolites lowered the overexpressed amounts of fibronectin, vimentin, and occludin and simultaneously increased the expression of vitamin D3 metabolites downregulated N-cadherin and enhanced of vitamin D3 metabolite expression of E-cadherin.