Sitagliptin improves functional recovery via GLP-1R-induced anti-apoptosis and facilitation of axonal regeneration after spinal cord injury

Axon growth and neuronal apoptosis are considered to be crucial therapeutic targets against spinal cord injury (SCI). Growing evidences have reported stimulation of glucagon-like peptide-1 (GLP-1)/GLP-1 receptor (GLP-1R) signalling axis provides neuroprotection in experimental models of neurodegeneration disease. Endogenous GLP-1 is rapidly degraded by dipeptidyl peptidase-IV (DPP4), resulting in blocking of GLP-1/GLP1R signalling process. Sitagliptin, a highly selective inhibitor of DPP4, has approved to have beneficial effects on diseases in which neurons damaged. However, the roles and the underlying mechanisms of sitagliptin in SCI repairing remain unclear. In this study, we used a rat model of SCI and PC12 cells/primary cortical neurons to explore the mechanism of sitagliptin underlying SCI recovery. We discovered the expression of GLP-1R decreased in the SCI model. Administration of sitagliptin significantly increased GLP-1R protein level, alleviated neuronal apoptosis, enhanced axon regeneration and improved functional recovery following SCI. Nevertheless, treatment with exendin9-39, a GLP-1R inhibitor, remarkably reversed the protective effect of sitagliptin. Additionally, we detected the AMPK/PGC-1 alpha signalling pathway was activated by sitagliptin stimulating GLP-1R. Taken together, sitagliptin may be a potential agent for axon regrowth and locomotor functional repair via GLP-1R-induced AMPK/ PGC-1 alpha signalling pathway after SCI.