Type 2 Diabetes-Driven Alterations in Bone Healing and Angiogenesis
Medicine and Health Sciences
INTRODUCTION: Two out of five U.S. citizens born after 2014 are expected to develop type 2 diabetes (T2D). T2D patients are at increased risk for fracture and impaired fracture healing, including: increased frequency of partial union, delayed union, or nonunion. These outcomes can in part be explained by T2D-mediated physiological and structural changes in bone; most prominently, compromised microvascular performance, which negatively impacts angiogenesis necessary for bone regeneration. Currently, to enhance bone healing in nonunion, the only FDA-approved biological treatment is the use of bone morphogenetic protein-2 (BMP-2). However, BMP-2 does not always achieve union, has adverse side effects, and may not be optimal for overcoming the T2D-specific impairments to bone healing. OBJECTIVE: In this study, we aimed to characterize the mechanisms by which T2D impairs bone healing and hypothesize that this effect is mediated by impairments in angiogenesis and endothelial cell proliferation and function. METHODS: Using Tie2-CreER;Td-Tomato mice (Tie2CreERT+), we established a high fat diet (HFD)-induced T2D mouse model to compare with low fat diet (LFD)-fed mice. Mice underwent glucose tolerance testing, insulin tolerance testing, and echoMRI to confirm the T2D-like metabolic phenotype. They were then subjected to a femoral critical-size defect surgery and were treated with either saline or BMP-2. 60 mice were allocated to each diet and experimental treatment group. Healing of the defect was assessed by X-rays. Additionally, bone marrow-derived endothelial cells (BMECs) were collected from the surgically treated mice to assess changes in endothelial colony and tube formation in vitro. Statistical analyses were performed with a two-way ANOVA and a Tukey post-hoc test. All procedures completed were approved by the Indiana University School of Medicine Institutional Animal Care and Use Committee. RESULTS: Our results showed that after 12 weeks, HFD mice acquired a T2D-like metabolic phenotype. X-ray imaging revealed that fracture healing was impaired in the HFD mice, even with the administration of BMP-2. The isolation of BMECs was confirmed by visualization of fluorescent Tie2+ cells. Unexpectedly, in vitro tube formation assays indicated that HFD improved vessel-like formation properties. BMP-2 treatment appeared to improve some vessel-like formation properties compared to control treatment. CONCLUSIONS: Further data will need to be collected to better characterize differences in bone healing and to analyze angiogenesis in the healing femurs. Still, these data are significant as they reveal the mechanisms by which T2D impairs bone healing and demonstrate the important difference between examining endothelial cells in vitro vs. in vivo. Future investigations will examine if thrombopoietin, which our group has previously shown to improve both fracture healing and angiogenesis, may be a more effective treatment than BMP-2 in this model.
Copyright 2019 all authors
Perugini, Anthony J. OMS-2; Bhatti, Fazal Ur Rehman; Dadwal, Ushashi C.; Babu, Deepa Sheik Pran; Sun, Seungyup; Awosanya, Olatundun D.; Blosser, Rachel J.; Tersey, Sarah A.; Orr, Kara S.; Randhave, Karishma R.; Li, Jiliang; Evans-Molina, Carmella; and Kacena, Melissa A., "Type 2 Diabetes-Driven Alterations in Bone Healing and Angiogenesis" (2019). MU-COM Research Day. 109.