Immune regulation of 1alpha-hydroxylase in murine peritoneal macrophages: unravelling the IFNgamma pathway.

The activated form of vitamin D3, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), plays an important role in the immune system. Indeed, receptors for 1,25(OH)2D3 are found on most immune cells, and 1α-hydroxylase, the enzyme responsible for final activation of vitamin D3, is expressed by monocytes/macrophages, resulting in secretion of 1,25(OH)2D3 after immune stimulation. We have previously shown that in murine peritoneal macrophages 1α-hydroxylase is highly regulated by immune signals such as IFNγ and LPS. In the present study we made use of two different knock-out mouse models with disruptions in two key transcription factors in the IFNγ-signalling cascade (STAT1α and IRF1), to evaluate their role in the regulation of 1α-hydroxylase. This was performed by culturing peritoneal macrophages from these knock-out mice in the presence of IFNγ and LPS, and evaluating the impact of the absence of the respective transcription factors on 1α-hydroxylase mRNA expression by real-time RT-PCR. In addition also the mRNA expression profiles of the essential transcription factors STAT1α, IRF1 and C/EBPβ were investigated. The data confirm a crucial role for STAT1α as well as for C/EBPβ in the regulation of 1α-hydroxylase in monocytes.