Expression of genes involved in calcium absorption in human duodenum.
BACKGROUND
The role of vitamin D metabolites in the regulation of expression of genes involved in dietary calcium absorption by the human intestine remains poorly understood despite much work in animals.


METHODS
To investigate this, we measured the expression of transcripts for two of these genes, calbindin-D9k and the basolateral membrane calcium pumping ATPase, PMCA1, in duodenal endoscopic biopsies from 40 subjects. Northern blots were hybridized with previously characterized probes, and the signal was quantified by phosphor imaging. These transcript levels were related to circulating vitamin D metabolites and also analysed according to the vitamin D receptor gene TaqI polymorphism determined in DNA from blood.


RESULTS
Plasma 1,25-dihydroxycholecalciferol correlated significantly with calbindin-D9k RNA (r = 0.4, P < 0.02) but not with PMCA1. Plasma 25-OH-cholecalciferol was not correlated with transcripts for either gene and, furthermore, the mean levels of these transcripts did not differ significantly when grouped by vitamin D receptor genotype.


CONCLUSIONS
In normal humans, 1, 25-dihydroxycholecalciferol has a small but significant relationship to duodenal expression of calbindin-D9k, but not to PMCA1 expression.
Walters
J R
JR
Imperial College School of Medicine, Hammersmith Hospital, London. jwalters@rpms.ac.uk
Howard
A
A
Lowery
L J
LJ
Mawer
E B
EB
Legon
S
S
D064026:Calbindins; D002117:Calcitriol / Q000097:blood; D002118:Calcium / Q000378:metabolism*; D004386:Duodenum / Q000378:metabolism*; D005786:Gene Expression Regulation; D005838:Genotype; D006801:Humans; D007408:Intestinal Absorption / Q000235:genetics*; D018167:Receptors, Calcitriol / Q000235:genetics; D064030:S100 Calcium Binding Protein G / Q000235:genetics
D064026:Calbindins; D018167:Receptors, Calcitriol; D064030:S100 Calcium Binding Protein G; C576506:S100G protein, human; D002117:Calcitriol; D002118:Calcium