Submitted to: Society for Experimental Biology Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 1/31/2008
Publication Date: 4/5/2008
Citation: Nelson, C.D., Beitz, D.C., Reinhardt, T.A., Lippolis, J.D. 2008. Toll-like receptor signaling increases production of 1,25-dihydroxyvitamin D3 in bovine macrophages [abstract). Experimental Biology 2008. p. 188.
Technical Abstract: Activation of macrophages can occur through Toll-like receptor (TLR) recognition of pathogen associated molecular patterns (PAMP). Recently, it has been discovered that TLR signaling can increase 1alpha-hydroxylase (Cyp27B1) expression in human and mouse macrophages. The enzymatic activity of 1alpha-hydroxylase produces the steroid hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) from its precursor 25-hydroxyvitamin D3 (25(OH)D3. Thus, we hypothesized that TLR recognition of PAMP can increase Cyp27B1 expression and conversion of 25(OH)D3 to 1,25(OH)2D3 in bovine macrophages. We supplemented bovine monocyte derived macrophages (BMDM) with 25(OH)D3 and stimulated them with ligands for TLR2 and TLR4. Quantitative real-time PCR was used to measure changes in Cyp27B1 and 24-hydroxylase (Cyp24A1) mRNA expression. Stimulation of BMDM with TLR2 and TLR4 ligands in the presence of 25(OH)D3 resulted in increased Cyp27B1 and Cyp24A1 mRNA expression. Conversion of 25(OH)D3 to 1,25(OH)2D3 in BMDM was demonstrated by increased expression of Cyp24A1, which is dependent on binding of the vitamin D receptor/1,25(OH)2D3 complex to the Cyp24A1 promoter. In conclusion, our results show that an autocrine vitamin D signaling pathway is present in bovine macrophages. Future studies will focus on the impact of vitamin D on the bovine immune system at the cellular and molecular level.