Intestinal Vitamin D Receptor Is Dispensable for Maintaining Adult Bone Mass in Mice With Adequate Calcium Intake

Area of Science:

• Endocrinology
• Bone Biology
• Nutritional Science

Background:

• 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3) is vital for calcium absorption and bone mineralization.
• The role of the vitamin D receptor (VDR) in adult intestinal calcium (Ca) absorption and bone maintenance requires further elucidation.

Purpose of the Study:

• To investigate the critical role of VDR-mediated 1,25(OH)2D3 signaling in adult intestinal Ca absorption and bone homeostasis.
• To determine if VDR in the adult intestine is essential for preventing bone loss during low calcium intake.

Main Methods:

• Mice with inducible Vdr gene knockout in the whole intestine (WIK) or large intestine (LIK) were used.
• Mice were fed adequate (0.5%) or low (0.2%) calcium diets after Vdr gene recombination.
• Calcium absorption, serum 1,25(OH)2D3 levels, bone mass, and microarchitecture were assessed.

Main Results:

• On adequate calcium diets, WIK and LIK mice showed no significant differences compared to controls.
• Under low calcium conditions, control mice increased intestinal calcium absorption and prevented bone loss.
• WIK mice exhibited unaltered intestinal calcium absorption and significant bone loss, while LIK mice showed partial adaptation and milder bone loss.

Conclusions:

• Intestinal VDR signaling is essential for adult mice to prevent bone loss when dietary calcium intake is low.
• VDR in the adult intestine is dispensable for maintaining bone health when calcium intake is adequate.
• Targeting intestinal VDR may offer therapeutic strategies for calcium and bone metabolism disorders.