Vitamin D and type II sodium-dependent phosphate cotransporters.
Level 5 - mechanism / opinion, no new human data
Narrative review summarizing in vitro cell culture and knockout mouse experiments without clinical trial data.
PubMed 23652552 · doi:10.1159/000346786
What was done
This narrative review summarizes findings from cell culture models (human renal epithelial cells) and transgenic animal models (VDR-null mice). The authors examined how 1,25-dihydroxyvitamin D [1,25(OH)2D3], parathyroid hormone (PTH), fibroblast growth factor 23 (FGF23), and Klotho regulate renal (NaPi-IIa, NaPi-IIc / Npt2a, Npt2c) and intestinal (NaPi-IIb / Npt2b) type II sodium-phosphate cotransporter expression and activity.
What was found
The abstract reports no numerical values, effect sizes, or sample sizes. Directional mechanistic findings include: - Functional vitamin D receptor-responsive elements were identified in human renal NaPi-IIa and NaPi-IIc genes. - Suckling VDR-null mice exhibited hypophosphatemia driven by elevated PTH; a high-calcium rescue diet lowered PTH and normalized renal Npt2a and Npt2c levels. - FGF23 reduced renal Pi transport and 1α-hydroxylase via a VDR-independent mechanism. - FGF23 induction of 24-hydroxylase, suppression of serum 1,25(OH)2D3, and downregulation of intestinal Npt2b required the VDR. - 1,25(OH)2D3 increased Klotho expression, which inhibited renal NaPi-IIa.
Why it matters
This synthesis clarifies the molecular pathways linking vitamin D, PTH, and FGF23/Klotho signaling to phosphate cotransporter regulation in the gut and kidney.
Limits
The findings derive entirely from in vitro and transgenic mouse models, which may not fully reflect human clinical physiology. The abstract provides no quantitative data, error estimates, or human outcome measures.
Cited by
- supports High levels of vitamin D increase the intestinal absorption of both dietary calcium and phosphorus.