Identification and immune regulation of 25-hydroxyvitamin D-1-α-hydroxylase in murine macrophages

Abstract

SUMMARYReceptors for 1,25(OH) 2 vitaminD 3 are found in most immune cells and important immunological effects have been described in vitro, reflected by its capacity to prevent autoimmunity and to prolong graft survival. The aim of this study was to examine the presence and nature of the enzyme responsible for final activation of the molecule, 1-a -hydroxylase, in murine macrophages and to analyse its regulation and possible role in the immune system. Peritoneal macrophages from C57Bl/6 mice were incubated with lipopolysaccharide (LPS; 100 m g/ml), interferon-gamma (IFN-g; 500 U/ml) or a combination of both. By quantitative reverse transcriptase-polymerase chain reaction, using primers based on the murine renal cDNA sequence, low levels of 1-a -hydroxylase mRNA were detected in freshly isolated cells (18^7 Â 10 26 copies/b -actin copies). Analysis of the cDNA sequence of the gene revealed identical coding sequences for the macrophage and renal enzymes. mRNA levels rose three-fold with LPS (NS), but a six-fold increase was seen after IFN-g stimulation (P , 0´05). Combining LPS and IFN-g did not result in a major additional increase, but addition of cyclosporin A further increased levels 2´5-fold both in IFN-g-and combination-stimulated cells (P , 0´05). Time course analysis revealed that upregulation of 1-a -hydroxylase was a late phenomenon, preceded by the up-regulation of activating macrophage products such as IL-1 and tumour necrosis factor-alpha. Finally, a defect in 1-ahydroxylase up-regulation by immune stimuli was found in autoimmune non-obese diabetic mice. In conclusion, we propose that the up-regulation of 1-a -hydroxylase in activated macrophages, resulting in the synthesis of 1,25(OH) 2 D 3 , might be a negative feedback loop in inflammation. A defect in this system might be an additional element in tipping the balance towards autoimmunity.

Berry meals and risk factors associated with metabolic syndrome

“…However, in our study, inflammation marker hs-CRP did not change statistically significantly, although there was a slight decrease in both the groups. This might be due to smaller vitamin D intake in berry group as even slight deficiency has a negative influence on inflammation (Overbergh et al, 2000). Also, low intake of vitamin D might have had negative effect on plasma glucose (Pittas et al, 2007).…”

Vitamin D and diabetes

“…The proximal renal tubule is the principal site of 1α-hydroxylation, although high levels of 1α-hydroxylase mRNA have also been found in human keratinocytes [15], dendritic cells [16] and macrophages [17]. This extra-renal production of 1,25(OH) 2 D 3 is regulated in a completely different manner.…”

“…This extra-renal production of 1,25(OH) 2 D 3 is regulated in a completely different manner. For example, production in macrophages is resistant to stimulation by parathyroid hormone but may be directly stimulated by immune stimuli such as IFN-γ and lipopolysaccharide [17].…”

“…Immune cells -activated macrophages and dendritic cells in particularcontain the enzyme 1α-hydroxylase, which is necessary for the final activating step in the conversion of vitamin D 3 to the metabolically active molecule, and are therefore able to synthesise and secrete 1,25(OH) 2 D 3 [17,68]. The 1α-hydroxylase present in immune cells is identical to the renal enzyme, but regulation of its expression and activity is different.…”

“…The 1α-hydroxylase present in immune cells is identical to the renal enzyme, but regulation of its expression and activity is different. Whereas the renal enzyme is principally under the control of calcaemic and bone signals (such as para- [17]. A unique feature of 1,25(OH) 2 D 3 as an immunomodulator is that not only does it interact with T cells, but it also -more importantly-targets the central cell in the immune cascade, the antigen-presenting cell (for reviews see [69,70]) (Fig.…”