Inhibition of Endoplasmic Reticulum Oxidoreductin 1 Modulates Neuronal Excitability and Nociceptive Sensitivity in Mice.

BACKGROUND: In the peripheral nervous system, nociceptors become hyperexcitable in both acute and chronic pain conditions. This phenotype can be mediated by dysregulated calcium, which occurs if the endoplasmic reticulum and mitochondria fail to buffer it appropriately. The redox enzyme endoplasmic reticulum oxidoreductin 1 (ERO1) regulates calcium transfer at endoplasmic reticulum-mitochondria contact sites (ERMCSs). This study hypothesized that inhibiting ERO1 and thereby dampening ERMCS calcium transfer might lower nociceptor hyperexcitability in sensory neurons and pain-like behaviors in mice. METHODS: C57BL/6 mice were used for histology, behavior, and cell culture experiments. Behavior included thermal tail flick, the formalin hind paw injection model of acute inflammatory pain, and hind paw incision postsurgical pain. Postmortem human dorsal root ganglia (DRGs) were used for immunohistochemistry and in vitro calcium imaging. RESULTS: This study demonstrates that the α isoform of ERO1 is expressed in mouse DRGs across multiple subtypes of mouse sensory neurons. This led us to peripherally administer an ERO1 inhibitor in mice, which acutely reversed nociception in acute inflammatory and postsurgical pain models. The hypothesis was that this may be due to reduced excitability of DRG neurons and tested ERO1 inhibition in vitro. In cultured DRGs, ERO1 inhibition dampened nociceptor excitability and mitochondrial function, suggesting that reduced calcium transfer through ERMCS could be responsible for the behavior observed in vivo . ERO1α expression was also found in human DRGs using immunohistochemistry and previously published single-cell RNA-sequencing data. Finally, the study showed that ERO1 inhibition modulates human sensory neuronal excitability in cultured post-mortem DRGs. CONCLUSIONS: This study found that ERO1 inhibition dampens mitochondrial function, sensory neuron excitability, and acute pain-like behavior in mice. Additionally, ERO1 inhibition decreases sensory neuron excitability in post-mortem human sensory neurons in vitro. The results indicate that targeting ERO1 may be a viable strategy for non-narcotic acute pain relief.