Background
Chronic obstructive pulmonary disease (COPD) is characterized by emphysema and/or obstructive bronchiolitis. Deficiency in vitamin D3 (VD3), which regulates gene expression through binding to vitamin D receptor (VDR), is associated with high risks of COPD susceptibility. Alveolar macrophages (AM), which are generated during early ontogeny and maintained in alveoli by self-renewal in response to cytokine GM-CSF, are positively correlated with severity of emphysema. However, whether and how VD3, VDR and AM interact to contribute to COPD pathogenesis at the molecular and cellular levels are largely unknown.
Methods
We used systems biology approaches to analyze gene expression in mouse macrophages from different tissues to identify key transcription factors (TF) for AM and infer COPD disease genes. We used RNA-seq and ChIP-seq to identify genes that are regulated by VD3 in AM. We used VDR-deficient (Vdr-/-) mice to investigate the role of VD3-VDR axis in the pathogenesis of COPD and characterized the transcriptional and functional alterations of Vdr-/- AM. Findings: We find that VDR is a key TF for AM and a COPD disease gene. VDR is highly expressed in AM and in response to VD3 inhibits GM-CSF-induced AM proliferation. In Vdr-/- AM, genes involved in proliferation and immune response are upregulated. Consistently, Vdr-/- mice progressively accumulate AM and concomitantly develop emphysema without apparent infiltration of immune cells into the lung tissue. Intratracheal transfer of Vdr-/- AM into wildtype mice readily induces emphysema. The production of reactive oxygen species at basal level and in response to heme or lipopolysaccharide is elevated in Vdr-/- AM and suppressed by VD3 in wildtype AM. Interpretation: These