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. Methods. Zucker rats, WT and homozygous for leptin receptor mutation (ZDF), were fed a moderately high-fat diet to induce T2DM only in the ZDF animals. At ten weeks of age, open femoral fractures were simulated using a unilateral osteotomy stabilized with an external fixator. At three weeks post-surgery, the fractured femur from each animal was retrieved for analysis. Callus formation and the extent of healing were assessed by radiograph and histology. Bone tissue was processed for total RNA extraction and messenger RNA (mRNA) sequencing (mRNA-Seq). Results. Radiographs and histology demonstrated impaired fracture healing in ZDF rats with incomplete bony bridge formation and an influx of intramedullary inflammatory tissue. In comparison, near-complete bridging between cortices was observed in Sham WT animals. Of 13,160 genes, mRNA-Seq analysis identified 13 that were differentially expressed in ZDF rat callus, using a false discovery rate (FDR) threshold of 10%. Seven genes were upregulated with high confidence (FDR = 0.05) in ZDF fracture callus, most with known roles in inflammation. Conclusion. These findings suggest that elevated or prolonged inflammation contributes to delayed fracture healing in T2DM. The identified genes may be used as biomarkers to monitor and treat delayed fracture healing in diabetic patients. Cite this article: Bone Joint Res 2023;12(10):657–666

The increased incidence of type 2 Diabetes Mellitus is associated with an impaired skeletal structure and a higher prevalence of bone fractures. Sclerostin is a negative regulator of bone formation produced by osteocytes and there is recent evidence that its expression in serum is elevated in diabetic patients compared to control subjects. In this study, we test whether hyperglycemia affects serum and bone sclerostin levels in a rat model of type 2 Diabetes as well as sclerostin production by osteoblasts in culture. We used Zucker diabetic fatty (ZDF) male rats (n=6) that spontaneously develop obesity and frank diabetes around 8–9 weeks of age and Zucker lean rats as controls (n=6) to examine sclerostin expression in serum at 9, 11 and 13 weeks using a specific ELISA. Sclerostin expression in bone tibiae was examined at 12 weeks using immunocytochemistry. Rat osteoblast-like cells UMR-106 were cultured in the presence of increasing concentrations of glucose (5, 11, 22 and 44 mM) during 48 hours and sclerostin mRNA expression and release in the supernatant determined by quantitative PCR and ELISA, respectively. Our results show that serum sclerostin levels are higher in the diabetic rats compared to lean rats at 9 weeks (+ 140%, p<0.01). Our preliminary results using immunocytochemistry for sclerostin did not show any major difference in sclerostin expression in tibiae of diabetic rats compared to lean ones, although we observed many osteocytic empty lacunae in cortical bone from diabetic rats. Glucose dose-dependent stimulated sclerostin mRNA and protein production in mature UMR106 cells while it had no effect on osteocalcin expression. Altogether, our data suggest that sclerostin production by mature osteoblasts is increased by hyperglycemia in vitro and enhanced in serum of diabetic rats. Furthers studies are required to determine whether sclerostin could contribute to the deleterious effect of Diabetes on bone

Objectives

The goals of this study were: 1) to determine if high-fat diet (HFD) feeding in female mice would negatively impact biomechanical and histologic consequences on the Achilles tendon and quadriceps muscle; and 2) to investigate whether exercise and branched-chain amino acid (BCAA) supplementation would affect these parameters or attenuate any negative consequences resulting from HFD consumption.