Proteomic Analysis of Emodin Treatment in Neuropathic Pain Reveals Dysfunction of the Calcium Signaling Pathway

Background: Neuropathic pain (NP) is a syndrome of pain mediated by distinct pathophysiological processes, and current treatments are not fully satisfactory. Emodin is an effective component of Chinese traditional medicine and has an alleviating effect on NP, but the pharmacological mechanism is not clear. Methods: We used isobaric tags for relative and absolute quantitation (iTRAQ) technique integrated with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis to identify potential targets of emodin in a rat peripheral nerve chronic constriction injury (CCI) model. Results: A total of 177 differentially expressed proteins were identified among the sham group, CCI group, and emodin group, with a threshold of 1.2-fold change and a P value <= 0.05. Among them, 100 differentially expressed proteins (51 up-regulated and 49 down-regulated) were identified in the CCI group compared with sham group. Moreover, 108 differentially expressed proteins (65 up-regulated and 43 down-regulated) were identified in the emodin group with the CCI group as reference. The enrichment analysis of Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed an important role of calcium signaling pathway, neurotransmitter regulation, and long-term potentiation (LTP) in emodin-treated CCI model. Real-time quantitative fluorescence PCR (qRT-PCR) and Western blot analysis revealed that emodin decreased expression of calcium signaling related proteins, including calmodulin (CaM) dependent protein kinase II (CaMK II), phospholipase C beta 1 (PLC beta 1), protein kinase C (PKC), protein kinase C (PKA), and tropomyosin-related kinase B (TrkB), compared with the CCI group. Conclusion: Overall, these findings indicated that emodin might alleviate NP by regulating the calcium signaling pathway.