VDR haploinsufficiency impacts body composition and skeletal acquisition in a gender-specific manner

Abstract

The vitamin D receptor (VDR) is crucial for virtually all of vitamin D's actions and is thought to be ubiquitously expressed. We hypothesized that disruption of one allele of the VDR gene would impact bone development and would have metabolic consequences. Body composition and bone mass (BMD) in VDR heterozygous (VDR HET) mice were compared to those obtained in male and female VDR KO and WT mice at 8 weeks of age. Male mice were also evaluated at 16 weeks, and bone marrow mesenchymal stem cell (MSC) differentiation was evaluated in VDR female mice. Additionally, female VDR HET and WT mice received intermittent PTH treatment or vehicle (VH) for 4 weeks. BMD was determined at baseline and after treatment. MRI was done in vivo at the end of treatment; μCT and bone histomorphometry were performed after killing the animals. VDR HET male mice had normal skeletal development until 16 weeks of age but showed significantly less gain in fat mass than WT mice. In contrast, female VDR HET mice showed decreased total-body BMD at age 8 weeks but had a normal skeletal response to PTH. MSC differentiation was also impaired in VDR HET female mice. Thus, female VDR HET mice show early impairment in bone acquisition, while male VDR HET mice exhibit a lean phenotype. Our results indicate that the VDR HET mouse is a useful model for studying the metabolic and skeletal impact of decreased vitamin D sensitivity.

Fig. 1

a Total-body (left) and femur BMD (right) in VDR WT, HET, and KO male mice at 8 weeks of age. b Total-body (left) and femur BMD (right) in VDR WT, HET, and KO male mice at 8 and 16 weeks of age. c Total-body fat mass content (left) and fat mass gain (right) during an 8-week interval in VDR WT, HET, and KO mice. *Values significantly smaller in KO than in HET and WT mice, P < 0.05; **values significantly greater in WT than in HET and KO mice, P < 0.05; ⁺values significantly smaller in KO than in HET mice

Fig. 2

Total-body (left) and femur (right) BMD in 8-week-old VDR WT, HET, and KO female mice. *Values significantly smaller in KO mice than in WT and HET mice; ⁺values higher in WT than in HET mice, P < 0.05

Fig. 3

μCT analysis showing bone volume (BV/TV) (left) and trabecular separation (right) in VDR WT and HET mice at 16 weeks of age

Fig. 4

Effect of a single-allele mutation on osteoblast differentiation. The number of ALP⁺ colonies at day 14 is decreased in VDR HET female mice, and further impairment is verified in VDR KO mice. Subsequent evaluation of mineralization activity by von Kossa (a) and alizarin red (b) shows the same defect pattern in the tree genotype

Fig. 5

a BMD in total body (left) and total-body bone mass gain (right) in VDR WT and HET female mice at age 12 weeks and after 4 weeks of treatment with vehicle (VH) or parathyroid hormone (PTH). b BMD in femur (left) and femoral bone mass gain (right) in VDR WT and HET female mice at age 12 weeks and after 4 weeks of treatment with VH or PTH. *Basal BMD (12 weeks, T1) values in WT female mice smaller than after VH treatment (16 weeks); **basal BMD (12 weeks, T1) values in WT female mice smaller than after PTH treatment; ⁺basal BMD (12 weeks, T1) values in HET female mice smaller than after PTH treatment, P < 0.05

Fig. 6

μCT images of lumbar vertebra cancellous bone (L5) (a), distal femur cancellous bone (b), and femur cortical bone (c) in WT female mice treated with vehicle (WT VH) or PTH (WT PTH) and heterozygous female mice treated with vehicle (HET VH) or PTH (HET PTH)

Fig. 7

Body fat content (a) and femoral fat content (b) assessed by MRI in WT female mice treated with vehicle (WT VH) or PTH (WT PTH) and heterozygous female mice treated with vehicle (HET VH) and PTH (HET PTH)