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GPER/β-alanine Positive Interaction in the Dorsal Root Ganglion Uncovers Potential Mechanisms: Mediating Continuous Neuronal Sensitization and Neuroinflammation Responses in Neuropathic Pain

ABSTRACT: Background: The pathogenesis of neuropathic pain and the reasons for the prolonged unhealing are still unknown. Increasing evidence suggests that oestrogen sex differences play a role in pain sensitivity, but few studies focused on the role of oestrogen receptor which maybe an important molecular component contributing to peripheral pain transduction. We aimed to investigate the impact of ooestrogen receptors in nociceptive neuronal response in the dorsal root ganglion (DRG) and spinal dorsal horn using a spared nerve injury (SNI) rat model of chronic pain. Methods: We used a class of oestrogen receptors antagonists and agonists intrathecal (i.t.) administrated to male rats with SNI or normal rats to identify the main receptor. Moreover, we applied genes identified through genomic metabolic analysis to determine the key metabolism point and elucidate potential mechanisms mediating continuous neuronal sensitisation and neuroinflammation responses in neuropathic pain. The excitability of DRG neurons was detected using the patch clamp technique. Primary culture was used to extract microglia and DRG neurons, and siRNA transfection was used to silence receptor protein expression. Immunofluorescence, Western blotting, qPCR and behavioral testing were used to assess the expressions, cellular distributions, and actions of main receptor and its related signaling molecules. Results: Increasing the expression and function of G protein-coupled oestrogen receptor (GPER), but not oestrogen receptor-α (ERα) and oestrogen receptor-β (ERβ), in the DRG neuron and microglia, but not the dorsal spinal cord, contributed to SNI-induced neuronal sensitisation. Inhibiting GPER expression in the DRG alleviated SNI-induced pain behaviours and neuroinflammation by downregulating iNOS, IL-1β and IL-6 expression as well as restoring GABAα2 expression simultaneously. Additionally, the positive interaction between GPER and β-alanine, β-alanine accumulation enhances pain sensation and promotes chronic pain development. Conclusion: GPER activation in the DRG causes a positive interaction of β-alanine with iNOS, IL-1β and IL-6 expression and represses GABAα2 involved in post-SNI neuropathic pain development. Blocking GPER and eliminating β-alanine in the DRG neuron and microglia may prevent neuropathic pain development.

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE201163 | GEO | 2022/06/29

REPOSITORIES: GEO

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Project description:Peripheral nerve injury alters the expression of hundreds of proteins in dorsal root ganglia (DRG). Targeting some of these proteins has led to successful treatments for acute pain, but not for sustained postoperative neuropathic pain. The latter may require targeting multiple proteins. Since a single microRNA (miR) can affect the expression of multiple proteins, here, we describe an approach to identify chronic neuropathic pain-relevant miRs. We used two variants of the spared nerve injury (SNI): Sural-SNI and Tibial-SNI and found distinct pain phenotypes between the two. Both models induced strong mechanical allodynia, but only Sural-SNI rats maintained strong mechanical and cold allodynia, as previously reported. In contrast, we found that Tibial-SNI rats recovered from mechanical allodynia and never developed cold allodynia. Since both models involve nerve injury, we increased the probability of identifying differentially regulated miRs that correlated with the quality and magnitude of neuropathic pain and decreased the probability of detecting miRs that are solely involved in neuronal regeneration. We found seven such miRs in L3-L5 DRG. The expression of these miRs increased in Tibial-SNI. These miRs displayed a lower level of expression in Sural-SNI, with four having levels lower than those in sham animals. Bioinformatics analysis of how these miRs could affect the expression of some ion channels supports the view that, following a peripheral nerve injury, the increase of the 7 miRs may contribute to the recovery from neuropathic pain while the decrease of four of them may contribute to the development of chronic neuropathic pain. The approach used resulted in the identification of a small number of potentially neuropathic pain relevant miRs. Additional studies are required to investigate whether manipulating the expression of the identified miRs in primary sensory neurons can prevent or ameliorate chronic neuropathic pain following peripheral nerve injuries. To identify the miRs that were differentially dysregulated between Tibial-SNI and Sural-SNI, we first performed 12 microarrays in a limited number of samples (in four individual DRGs per group: Sham, Tibial-SNI and Sural-SNI; two L3-DRG and two L4-DRG). Then, miRs identified as having differential expression were corroborated with real time qRT-PCR in RNA isolated from individual DRGs (L3, L4 and L5) derived from 4 rats per group (not presented here, but in the manuscript).

Project description:Neuropathic pain is a chronic debilitating condition with a high comorbidity with depression. Clinical reports and animal studies have suggested that both the medial prefrontal cortex (mPFC) and the anterior cingulate cortex (ACC) are critically implicated in regulating the affective symptoms of neuropathic pain. Neuropathic pain induces long-term structural, functional and biochemical changes in both regions, which are thought to be regulated by multiple waves of gene transcription. However, the similarity and differences in the transcriptomic profiles changed by neuropathic pain between these regions are largely unknown. Furthermore, women are more susceptible to pain and depression than men. The molecular mechanisms underlying this sexual dimorphism remain to be explored. Here, we performed RNA sequencing and analyzed the transcriptomic profiles of the mPFC and ACC of female and male mice at 2 weeks after spared nerve injury (SNI), an early time point when the mice began to show mild depressive symptoms. Our results show that the SNI-induced transcriptomic changes in female and male mice are largely distinct. Interestingly, the female mice exhibit more robust transcriptomic changes in the ACC than male, whereas the opposite pattern occurs in the mPFC. Cell type enrichment analyses reveal that the differentially expressed genes involve genes enriched in both neurons and various types of glia. We further performed Gene Set Enrichment Analysis (GSEA), which reveal significant de-enrichment of myelin sheath development in both female and male mPFC after SNI. In the female ACC, gene sets for synaptic organization and mitochondria function are enriched, and gene sets for extracellular matrix are de-enriched after SNI, while such signatures are absent in male ACC. Collectively, these findings reveal sexual dimorphism at the transcriptional level induced by neuropathic pain, and provide novel therapeutic targets for chronic pain and its associated affective disorders.