Accepted

The aim of the present study was to investigate the effects of microRNA (miR)‑142‑3p on neuropathic pain caused by sciatic nerve injury in chronic compression injury (CCI) rats, and further investigate its mechanism. Rat experiments were divided into four parts in the study. In the first part, the rats were divided into the Sham and CCI groups. The expression of miR‑142‑3p, AC9 and cAMP were detected. In the second part, the rats were divided into the Sham, CCI, miR‑142‑3p mimic, mimic‑negative control (NC), miR‑142‑3p small interfering RNA (siRNA) and siRNA‑NC groups. The expression of cAMP and the levels of AMPK pathway‑related proteins were detected. In the third part, the rats were randomly divided into Sham, CCI, AC9 mimic, mi‑NC, AC9 siRNA and si‑NC groups. Double luciferase reporter assay was used to analyse the targeting relationship between miR‑142‑3p and AC9. In the fourth part, the rats were divided into the Sham, CCI, miR‑142‑3p siRNA, AC9 mimic, miR‑142‑3p siRNA + AC9 siRNA, cAMP activator (Forskolin) and miR‑142‑3p siRNA + cAMP inhibitor groups. The expression of miR‑142‑3p was significantly increased while AC9 and cAMP expression significantly decreased in CCI rats. However, AC9 overexpression significantly increased the levels of cAMP protein. Luciferase reporter assay also proved that AC9 is the target gene of miR‑142‑3p. Moreover, miR‑142‑3p silencing was found to reduce neuropathic pain in CCI rats by upregulating the expression of AC9. It was also found that cAMP activation can relieve neuropathic pain and promote the expression of AMPK‑related proteins in CCI rats. Silencing miR‑142‑3p can target AC9 to reduce the expression of inflammatory factors and neuropathic pain in CCI rats by increasing the expression of cAMP/AMPK pathway‑related proteins.

The nerve growth factor (NGF) and brain-derived neurotrophic factor (BDNF) are trophic factors required by distinct population of sensory neurons during development of the nervous system. Neurons that fail to receive appropriate trophic support are lost during this period of naturally occurring cell death. In the last decade, our understanding of the signalling pathways regulating neuronal death following NGF deprivation has advanced substantially. However, the signaling mechanisms promoting BDNF-deprivation induced sensory neuron degeneration are largely unknown. Using a well-established culture model of dorsal root ganglion (DRG), we have examined degeneration mechanisms triggered upon BDNF withdrawal in sensory neurons. Our results indicate differences and similarities between the molecular signalling pathways behind NGF and BDNF deprivation-induced death. For instance, we observed that the inhibition of Trk receptors (K252a), PKC (Gö6976), protein translation (cycloheximide) or caspases (zVAD-fmk) provides protection from NGF deprivation-induced death but not from degeneration evoked by BDNF-withdrawal. Interestingly, degeneration of BDNF-dependent sensory neurons requires BAX and appears to rely on reactive oxygen species generation rather than caspases to induce degeneration. These results highlight the complexity and divergence of mechanisms regulating developmental sensory neuron death. The elimination of neuronal cells generated in excess during embryonic stages characterizes the maturation of the nervous system. Here we address the developmental cell death mechanisms of BDNF-dependent dorsal root ganglion neurons , comparing and contrast them with those deployed in NGF-dependent sensory neurons. We observe several important differences between the molecular signalling pathways behind NGF and BDNF deprivation-induced death. Significantly, degeneration of BDNF-dependent sensory neurons requires BAX but not caspase activation, instead reactive oxygen species generation appears to play a key role in degeneration. This work highlights the complexity of cell death mechanisms in distinct embryonic sensory neuron populations.