CNTs-CaP/CS-AZ91D extracts induce CGRP production in dorsal root ganglion neurons to facilitate osteogenesis in rats

Clinical trials have proven the beneficial effect of biodegradable orthopedic composites on bone repair; however, the mechanisms underlying composite-induced bone formation have not yet been fully explored. AZ91D magnesium alloy coated with carbon nanotubes (CNTs) and calcium phosphate (CaP)/chitosan (CS) (CNTs-CaP/CS-AZ91D) is a synthetic composite consisting of magnesium alloy, CNTs and CaP/CS. Its extracts induce the production of the calcitonin gene-related peptide (CGRP), a local neuropeptide that contributes to osteogenic differentiation, in dorsal root ganglion (DRG) neurons. This study was aimed at validating the upregulation of CGRP in CNTs-CaP/CS-AZ91D extract-induced DRG neurons. Besides, bone marrow-derived mesenchymal stem cells (BMSCs) showed greater osteogenic capacity after co-culture with CNTs-CaP/CS-AZ91D extract-induced DRG neurons, and this co-culture promoted autophagy in BMSCs to facilitate osteogenic differentiation. The dysregulation of CREB1/TRIM16/JAK1/STAT3 signaling was determined in BMSCs co-cultured with CNTs-CaP/CS-AZ91D extract-induced DRG neurons. However, all these results were counteracted by the knockdown of the CGRP receptor. <i>In vivo</i> study showed accelerated osteogenesis in the femur of CNTs-CaP/CS-AZ91D-implanted rats; however, this effect was inhibited by the CGRP receptor antagonist BIBN4096BS. In summary, this study highlights the critical role of the peripheral nervous system in osteogenesis and suggests the potential of CNTs-CaP/CS-AZ91D for improving bone formation in the future.