Vitamin D Signaling Enhances Expression of Antibacterial β-Defensin Genes in Bovine Monocytes
Vitamin D contributes to immunity of cattle via an intracrine vitamin D pathway that is activated in macrophages in response to recognition of pathogens. The 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) that is produced in that pathway activates the vitamin D receptor and regulates the transcription of vitamin D-dependent genes. RNA sequence analysis of 1,25(OH)2D3-treated monocytes compared to control-treated monocytes identified bovine β-defensin 3 (DEFB3) and β-defensin 6 (DEFB6) as potential targets of the activated vitamin D receptor. The DEFB3 and DEFB6 genes encode for small antibacterial peptides and are located on bovine chromosome 27 along with DEFB1, DEFB4A, DEFB5, DEFB7, DEFB10, enteric β-defensin (EBD), lingual antimicrobial peptide (LAP), and tracheal antimicrobial peptide (TAP). The objective of this study was to evaluate the effects of 1,25(OH)2D3 on expression of the β-defensin genes in resting and stimulated monocytes. Peripheral blood monocytes from eight Holstein cows were treated with 0 or 100 ng/mL lipopolysaccharide (LPS) in combination with 0 or 10 nM 1,25(OH)2D3 and cultured for 24h. The mRNA transcripts for each of the β-defensin genes were measured with real-time PCR and normalized to ribosomal protein S9 transcript abundance. The effects of 1,25(OH)2D3 and LPS on expression of each of the β-defensin genes was analyzed with a general linear model that accounted for effects of cow and treatment. In the non-stimulated monocytes, the 1,25(OH)2D3 treatment increased DEFB3, DEFB6, DEFB7, and DEFB10 gene expression (P<0.05; 10±3, 17±8, 4±1, and 5±2 fold change ± SE, respectively). Similarly, the 1,25(OH)2D3 treatment increased DEFB3, DEFB6, DEFB7, and DEFB10 gene expression in the LPS-stimulated monocytes (P<0.05; 10±3, 60±28, 7±2, and 20±6 fold change ± SE, respectively). DEFB1, DEFB4A, DEFB5, DEFB13, EBD, LAP, and TAP were not affected by 1,25(OH)2D3 in either resting or LPS-stimulated monocytes. In addition, LPS treatment alone did not significantly increase any of the β-defensin genes evaluated in this study (P>0.05) . In conclusion, 1,25(OH)2D3 induces expression of the DEFB3, DEFB6, DEFB7, and DEFB10 genes in bovine monocytes. Upregulation of these β-defensin antimicrobial genes in response to 1,25(OH)2D3 suggests vitamin D is needed in cattle to support innate host defense mechanisms.
Keywords: Vitamin D, Innate Immunity