Glucocorticoids differentially regulate expression of duodenal and renal calbindin-D9k through glucocorticoid receptor-mediated pathway in mouse model

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Abstract
Dexmethasone (Dex) is a member of the glucocorticoids (GCs), and is broadly used as an anti-inflammatory medication. Continuous administration with GCs induces adverse effects and suffering in humans (i.e., osteoporosis) due to negative calcium balance derived from low re- and absorption in the duodenum and kidney. A cytosolic calcium-binding protein, calbindin-D9k (CaBP-9k), is dominantly expressed in the renal and intestinal tissues involved in calcium re- and absorption and plays an active role in calcium transport. In the present study, we employed adrenalectomized (ADX) and sham-treated (Sham) male mice to examine the effect of Dex on CaBP-9k gene expression in the duodenum and kidney. Dex significantly reduced the levels of duodenal CaBP-9k mRNA and protein, and it restored ADX-induced decrease in renal CaBP-9k protein compared with the level of Sham control. Dex treatment increased calcium and phosphate levels in the sera of both Sham and ADX mice. In a time course experiment, Dex significantly decreased duodenal CaBP-9k at the transcriptional and translational levels at 3 days, whereas it temporarily increased CaBP-9k mRNA and protein levels at 12 and 24 h. Altered CaBP-9k expression by Dex was completely reversed by mifepristone, an antagonist for the GC receptor (GR). In addition, duodenal CaBP-9k and GR were colocalized on the enterocyte (duodenocyte), supporting a role for GR in regulating CaBP-9k. In ovariectomized (OVX) and ADX female mice daily treated with Dex for 3 days, duodenal CaBP-9k was expressed at the same level as in male mice. Also, no cross-activity of progesterone and Dex on their receptors was observed. Taken together, these results indicate that mouse CaBP-9k gene may be regulated by Dex in a tissue-specific manner, and reduced duodenal CaBP-9k via the GR pathway may take part in negative calcium absorption of GC-induced osteoporosis, whereas renal CaBP-9k may not be involved in the regulation of calcium homeostasis.

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