Activation of the Hedgehog Pathway Promotes Recovery of Neurological Function After Traumatic Brain Injury by Protecting the Neurovascular Unit

Abstract

The homeostasis of the neurovascular unit (NVU) is disrupted after traumatic brain injury (TBI), and therapeutic strategies targeting the NVU would likely improve neurological outcomes after TBI. Sonic Hedgehog (Shh), which is an endogenous activator of the Hedgehog pathway, promotes brain repair in various injuries. In this study, the controlled cortical impact (CCI) was used to establish a moderate TBI model in adult male Sprague-Dawley rats (250-300 g), and the NVU was reconstructed in vitro from the blood-brain barrier (BBB) and neurons to investigate the effects of exogenous Shh protein on TBI. The modified neurological severity scores (mNSS) and Morris water maze tests were used to evaluate the effect of Shh on neurological function after TBI. The effect of Shh on the NVU in vivo was evaluated by detecting the degrees of cerebral edema and neuronal apoptosis. The integrity and permeability of the BBB, the level of inflammatory factors, and the expression of apoptotic proteins were detected to explore the effect of exogenous Shh on the NVU in vitro. The results showed that exogenous Shh reduced cerebral edema and neuronal apoptosis and promoted neurological recovery after TBI in rats. In vitro experiments showed that Shh-induced activation of the Hedgehog pathway promoted stability of the NVU by reducing damage to the tight junction structure and inhibiting the release of inflammatory factors and neuron apoptosis. Based on these results, the Shh-induced activation of the Hedgehog pathway might be a new promising treatment for TBI.

Keywords: Blood-brain barrier; Hedgehog pathway; Inflammation; Neurovascular unit; Oxygen-glucose deprivation; Traumatic brain injury.