Vitamin D and the intestine: Review and update

Abstract

The central role of vitamin D in calcium homeostasis is to increase calcium absorption from the intestine. This article describes the early work that served as the foundation for the initial model of vitamin D mediated calcium absorption. In addition, other research related to the role of vitamin D in the intestine, including those which have challenged the traditional model and the crucial role of specific calcium transport proteins, are reviewed. More recent work identifying novel targets of 1,25(OH)₂D₃ action in the intestine and highlighting the importance of 1,25(OH)₂D₃ action across the proximal/distal and crypt/villus axes in the intestine is summarized.

Keywords: 1,25-dihydroxyvitamin D3; Calbindin-D; Crypt, SLC30A10; Intestine; Plasma membrane calcium pump PMCA1b; Transient receptor potential vanilloid type-6; Villus.

Fig. 1.

VDR and 1,25(OH)₂D₃ induced Cyp24a1 are present in epithelial cells in villi and crypts. A. Isolation of intestinal epithelial cells from crypts (left panel) and villi (right panel). Duodenum from 3 month old mice was washed in cold phosphate buffered saline (PBS). Minced duodenal tissue was incubated in 3 mM EDTA in PBS with gentle shaking. Crypt epithelium was depleted of contaminating villi by passage through 70 μm filters. Villus epithelium was trapped on the 70 μm filters. B. Western blot analysis of VDR protein in intestinal epithelial cells from crypts and villi prepared from 3 month old VDR KO and WT mice. Anti-VDR (D-6) from Santa Cruz Biotechnology was used to detect mouse VDR (mVDR). VDR was recognized as a single band at approximately 48 kDa. Anti-β actin (also from Santa Cruz Biotechnology) was used as a control. C. qRT-PCR analysis of Cyp24a1 in epithelial cells from villi and crypts from WT 3 month old C57BL/6 mice injected ip with vehicle (0.1 ml; 9:1 mix of propylene glycol and ethanol) (WT + Veh) or 1,25(OH)₂D₃ (1ng/g body weight; 48, 24, and 6h prior to being euthanized). Relative quantitation of Cyp24a1 was performed using real time qPCR (Taqman analysis) using Taqman Gene Expression probes (Applied Biosystems). qPCR reactions were performed in triplicate and normalized to GAPDH. The 2^-ΔΔCt method was used to calculate relative gene expression. Data represent the results of three separate experiments. ** p < 0.01 compared to WT + Veh.

Fig. 2.

RNA-seq results reveal that villus and crypt-like human enteroids exhibit a differential response to 1,25(OH)₂D₃ treatment. A. Venn diagram indicating genes significantly upregulated at least 1.5 fold upon 1,25(OH)₂D₃ treatment in villus (differentiated) and crypt-like (undifferentiated) human enteroids and overlap of genes. The crypt and villus compartments both show upregulation of TRPV6, CYP24A1 and SLC30A10 upon 1,25(OH)₂D₃ treatment (100 nM for 24 h). The villus compartment shows sole upregulation of S100G upon 1,25(OH)₂D₃ treatment. B, C. Expression count of CYP24A1 and TRPV6 after 1,25(OH)₂D₃ treatment (lanes 2 and 4) increased in both crypt and villus-like compartments. Data is from enteroids from 5 patients (3 females and 2 males).