Unbiased gene expression analysis of the delayed fracture healing observed in Zucker diabetic fatty rats.

Aims: Impaired fracture repair in patients with type 2 diabetes mellitus (T2DM) is not fully understood. In this study, we aimed to characterize the local changes in gene expression (GE) associated with diabetic fracture. We used an unbiased approach to compare GE in the fracture callus of Zucker diabetic fatty (ZDF) rats relative to wild-type (WT) littermates at three weeks following femoral osteotomy.

Vitamin D receptor expression in mature osteoclasts reduces bone loss due to low dietary calcium intake in male mice.

Mature osteoclasts express the vitamin D receptor (VDR) and are able to respond to active vitamin D (1α, 25-dihydroxyvitamin D; 1,25(OH)D) by regulating cell maturation and activity. However, the in vivo consequences of vitamin D signalling directly within functionally mature osteoclasts is only partially understood. To investigate the in vivo role of VDR in mature osteoclasts, conditional deletion of the VDR under control of the cathepsin K promoter (Ctsk/Vdr), was assessed in 6 and 12-week-old mice, either under normal dietary conditions (NormCaP) or when fed a low calcium (0.

Vitamin D supplementation improves bone mineralisation independent of dietary phosphate in male X-linked hypophosphatemic (Hyp) mice.

The disorder of X-linked hypophosphatemia (XLH), results in the supressed renal production of active 1α,25-dihydroxyvitamin D (1,25(OH)D) due to elevated fibroblast growth factor-23 (FGF23) levels. While adequate 25(OH)D levels are generally associated with improved mineralisation of the skeleton independent of circulating 1,25(OH)D levels, it is unclear whether raising 25(OH)D to sufficiently high levels through dietary vitamin D administration contributes to improving bone mineralisation in the murine homolog for XLH, Hyp mice. Three-week-old male Hyp mice were fed one of four diets containing either 1000 IU (C) or 20,000 IU (D) vitamin D3/kg diet with either 0.

Absence of vitamin D receptor in mature osteoclasts results in altered osteoclastic activity and bone loss.

Mature osteoclasts express the vitamin D receptor (VDR) and are able to synthesise and respond to 1,25(OH)D via CYP27B1 enzyme activity. Whether vitamin D signalling within osteoclasts is necessary for the regulation of osteoclastic bone resorption in an in vivo setting is unclear. To determine the requirement for the VDR- and CYP27B1-mediated activity in mature osteoclasts, conditional deletion mouse models were created whereby either Vdr or Cyp27b1 gene was inactivated by breeding either Vdr or Cyp27b1 mice with Cathepsin K-Cre transgenic mice (Cstk) to generate Ctsk/Vdr and Ctsk/Cyp27b1 mice respectively.

Both ligand and VDR expression levels critically determine the effect of 1α,25-dihydroxyvitamin-D on osteoblast differentiation.

Previous studies have shown that 1α,25-dihydroxyvitamin D (1,25D) through vitamin D receptor (VDR) signalling has both catabolic and anabolic effects on osteoblast differentiation. However, the mechanism of these differential effects by 1,25D is not fully understood. In this study, mice with three different genetic backgrounds, representing a normal VDR level (wild-type, WT), VDR over-expression specifically in mature osteoblasts (ObVDR-B6) and global VDR knockout (VDRKO), were utilised to generate primary osteoblast-like cultures to further elucidate the effects of 1,25D on osteoblast differentiation.

Evidence for altered osteoclastogenesis in splenocyte cultures from VDR knockout mice.

The indirect action of 1α,25(OH)-vitamin-D (1,25D) on the osteoclast through stromal signalling is well established. The role of vitamin D in osteoclasts through direct 1,25D-VDR signalling is less well known. We showed previously that local 1,25D synthesis in osteoclasts modified osteoclastogenesis and osteoclastic resorptive activity.

Evidence for altered osteoclastogenesis in splenocyte cultures from Cyp27b1 knockout mice.

The association between increased serum 25-hydroxyvitamin D (25D) and reduced osteoclastic bone resorption is well known. Previously, we have demonstrated that mechanism by which this occurs, may include the conversion of 25D to 1,25-dihydroxyvitamin D (1,25D) by osteoclasts, catalysed by the CYP27B1 enzyme. Local 1,25D synthesis in osteoclasts was shown to regulate osteoclastogenesis and moderating resorptive activity.