CGRP regulates the dysfunction of peri-implant angiogenesis and osseointegration in streptozotocin-induced diabetic rats

Diabetes is a chronic systematic disease which results in neuropathy and dysfunctional bone metabolism and microcirculation. Calcitonin gene related peptide (CGRP) is an important neuropeptide that is involved in bone formation and vascular response. This study aimed to elucidate the role of CGRP in diabetic peri-implant angiogenesis and osteogenesis, which is yet to be reported. In vivo, we injected streptozotocin into SD rats to establish an experimental diabetes model. We then implanted 1 mm x 5 mm Ti implants into rat tibiae and injected lentivirus into the bone marrow cavity to overexpress or silence the peri-implant CGRP expression. We also applied overexpression lentivirus and silencing short hair RNA (shRNA) in rat bone marrow mesenchymal stem cells (BMSCs) to investigate the biological effects of CGRP in vitro. Through the investigation of diabetic neurons, blood, and peri-implant bone, we could observe that diabetes led to decreased synthesis and expression of CGRP, and high CGRP expression were only seen in peri-implant tissues in the early-to-middle phase of diabetic bone integration. Microfil perfusion followed by micro-CT analysis showed that the overexpression of CGRP enhanced peri-implant angiogenesis via increased vessel volume and thickness. Regarding osteogenesis, CGRP was found to improve the impaired osseointegration, as observed through micro-CT reconstruction and H&E staining. Similarly, overCGRP alleviated the hyperglycemia-triggered decrease in mineralization, and rescued ALP activity and the mRNA and protein expression of VEGF-A, ALP, and OPN. CGRP also attenuated the high glucose-induced production of reactive oxygen species (ROS). Our results demonstrate the potential promotive role of CGRP in early-to-middle phase of osseointegration, as CGRP could regulate the diabetes-induced dysfunctions in peri-implant angiogenesis and osseointegration. Our study provides a new insight into the diabetic peri-implant vasculature and the potential positive effect of CGRP on diabetic peri-implant vessels and bone.