Vitamin D deficiency and a defective signalling has been reported in Crohn’s disease (CD) patients. Vitamin D signals through the vitamin D receptor (VDR) which is a member of the nuclear receptor family of transcription factors that play an immunoregulatory role in the gut. We have previously demonstrated that a single-nucleotide polymorphism (SNP) in the VDR gene can modify the expression of this protein in peripheral blood mononuclear cells of CD patients. We aim to analyse the modulation of the VDR protein in human intestinal fibroblasts.
We used intestinal fibroblasts isolated from intestinal tissue of the non-damaged mucosa and the damaged mucosa of CD patients. Control cells were obtained from the non-damaged intestine of patients with colorectal cancer. Fibroblasts were treated with 1,25 Vitamin D3 (100 nM) for 24 h. VDR protein levels were determined by western blot and VDR, CYP24A1, COL1A1 and αSMA gene expression by qPCR. Statistical significance was measured by t-test.
VDR protein levels were significantly lower in fibroblasts obtained from the damaged intestine of CD patients than that obtained from controls (Figure 1A). In fibroblasts from CD patients, we detected lower VDR protein levels in those obtained from damaged mucosa than in those from the non-damaged. Treatment of these cells with vitamin D3 significantly increased VDR protein expression in all cases, but VDR protein levels were much lower in fibroblasts from damaged intestine (Figure 1B). The mRNA expression of VDR and its target, CPY24A1, was significantly lower in fibroblasts from the damaged tissue than in fibroblasts from the non-damaged. In contrast, the mRNA expression of collagen 1a1 and αSMA was higher in fibroblast from damaged intestine. When compared fibroblasts obtained from the non-damaged intestine of CD with control fibroblasts, the mRNA expression of CYP24A1 was significantly lower in cells from CD patients, suggesting that factors other than local inflammation may be involved (Figure 1C).
Local inflammation, and probably genetic factors, are involved in the decrease in VDR protein levels detected in fibroblasts from CD patients.