Immune regulation of lα-hydroxylase in murine peritoneal macrophages:: Unravelling the IFNγ pathway

The activated form of vitamin D-3, 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3) plays an important role in the immune system. Indeed, receptors for 1.25(OH)(2)D-3 are found on most immune cells, and 1 alpha-hydroxylase, the enzyme responsible for final activation of vitamin D-3, is expressed by monocytes/macrophages, resulting in secretion of 1,25(OH)(2)D-3 after immune stimulation. We have previously shown that in murine peritoneal macrophages 1 alpha-hydroxylase is highly regulated by immune signals such as IFN-gamma 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 IFN gamma- signalling cascade (STAT1 alpha and IRF1). to evaluate their role in the regulation of 1 alpha-hydroxylase. This was performed by culturing peritoneal macrophages; from these knockout mice in the presence of IFN gamma and LPS, and evaluating the impact of the absence of the respective transcription factors on 1 alpha-hydroxylase mRNA expression by real-time RT-PCR. In addition also the mRNA expression profiles of the essential transcription factors STAT1 alpha, IRF1 and C/EBPP were investigated. The data confirm a crucial role for STAT1 alpha as well as for C/EBPP in the regulation of 1 alpha-hydroxylase in monocytes. (c) 2007 Published by Elsevier Ltd.