Electroacupuncture reduces calcium influx and inhibits endoplasmic reticulum stress by inhibiting the PKCδ-TRPA1 pathway to promote motor function recovery after spinal cord injury

Background: Following spinal cord injury (SCI), mechanical trauma and an inflammatory microenvironment activate the PKCδ-TRPA1 pathway, resulting in calcium overload within neurons and subsequently inducing endoplasmic reticulum (ER) stress-mediated neuronal apoptosis. The mechanisms and therapeutic potential of electroacupuncture (EA) in the treatment of SCI have yet to be fully elucidated. This study aimed to explore the causes of neuronal Ca2+ overload post-SCI and to investigate the neuroprotective and regenerative mechanisms of EA in an SCI mouse model. Methods: C57BL6 mice were randomly divided into a Sham group, an SCI group, and an SCI + EA group. The Basso Mouse Scale, motor-evoked potential, and movement videos of the mice were captured, and DeepLabCut was used to analyze the recovery of motor function. Western blotting was used to detect the protein levels of related indicators. Immunofluorescence staining was used to analyse the cellular localization and fluorescence intensity of each indicator. Hematoxylin and eosin staining and Nissl staining were used for histological evaluation. EA treatment resulted in higher BMS scores; increased ankle, knee, and hip mobility; and improved hindlimb support in the EA group. Results: PKCδ and TRPA1 protein expression was upregulated after SCI, and neuronal calcium ion overload occurred, leading to neuronal ER stress-induced apoptosis. After EA treatment, inflammatory microenvironment-related indicators were downregulated, which inhibited the activation of calcium channels by PKCδ-TRPA1, reduced ER stress-induced apoptosis caused by calcium overload in neurons, and protected neurons from secondary injury. EA increases the expression of neurotrophic factors and promotes nerve regeneration, and we found that EA treatment promotes axonal elongation by stabilizing microtubules. Conclusions: According to our findings, (i) mechanical injury and the inflammatory microenvironment after SCI activate PKCδ-TRPA1, which is important for neuronal ER stress and apoptosis caused by neuronal calcium overload. (ii) EA treatment reduces the expression of PKCδ-TRPA1 as well as the ER stress and apoptosis caused by neuronal calcium overload. (iii) EA promoted neurogenesis and axonal regeneration by promoting the secretion of neurotrophic factors and promoted axon elongation by stabilizing microtubules, thus promoting the recovery of motor function in SCI mice.