Neuropathic pain affects ∼7–10% of the global population and is notoriously resistant to conventional analgesic therapies. Elucidation of the molecular mechanisms that contribute to pain development might lead to novel treatments. Among these mechanisms, central and peripheral sensitization play prominent roles. Sensitization occurs when peripheral or central nociceptive neurons become hyperexcitable, resulting in increased responsiveness to both noxious stimuli (hyperalgesia) and non-noxious stimuli (allodynia). Peripheral sensitization arises from functional and molecular alterations in primary afferent nociceptors, often mediated by inflammatory cytokines, prostaglandins, or nerve injury. These alterations include changes in ion channel expression and function, increased peripheral synaptic transmission, and intracellular signaling cascades that amplify excitability. In contrast, central sensitization involves activity-dependent plasticity in spinal dorsal horn and supraspinal circuits, characterized by increased synaptic efficacy, receptor trafficking, intracellular signaling, and transcriptional reprogramming (Ma et al., 2024).
Recent studies have highlighted the contributions of epigenetic regulation in sustaining maladaptive gene expression changes that underpin chronic pain states. Epigenetic mechanisms, such as DNA methylation, histone modification, and non-coding RNA interactions, enable heritable changes in gene expression without altering the underlying DNA sequence (Penas and Navarro, 2018). Post-translational modifications of histones—highly conserved proteins around which DNA is wrapped to form nucleosomes—modify chromatin structure and modulate transcriptional accessibility. Acetylation by histone acetyltransferases (HATs) generally promotes gene expression by loosening chromatin, whereas histone deacetylases (HDACs) reverse this effect and can repress transcription. Notably, the balance of HAT and HDAC activity influences pain-relevant gene expression (Wang et al., 2018). In contrast, histone methylation can either activate or repress transcription, depending on the specific lysine residue modified. A well-characterized repressive modification is trimethylation of histone H3 at lysine 27 (referred to asH3K27me3), catalyzed by the polycomb complex component enhancer of zeste homolog 2 (EZH2; Jiang et al., 2023). H3K27me3 represses transcription by recruiting chromatin remodelers that condense chromatin and prevent transcription factor access. This repression can be reversed by demethylases such as JMJD3, which plays key roles in inflammation and neural plasticity. Aberrant regulation of H3K27me3 has been implicated in the development of neuropathic pain, with elevated levels observed in sensory ganglia after nerve injury (Qi et al., 2022).
In contrast to chromatin-level histone modifications, microRNAs mediate post-transcriptional regulation of pain-relevant gene expression by silencing mRNA targets through sequence-specific binding. These ∼22 nucleotide noncoding RNAs typically bind to complementary siites in the 3′ untranslated regions (UTRs) of target mRNAs, leading to transcript degradation or translational repression (O'Brien et al., 2018). MicroRNAs are critical for synaptic plasticity and neuronal function, and their dysregulation is increasingly implicated in pain pathways. For example, miR-124 downregulation is associated with enhanced neuroinflammation; the miR-183 cluster regulates mechanical pain thresholds (Peng et al., 2017); and reduced levels of miR-7a increase the expression of voltage-gated sodium channels, thereby augmenting sensory neuron excitability. In addition, miR-140 and miR-144 are downregulated after nerve injury and contribute to nociceptive sensitization (Zhao et al., 2023).
Given the established role of microRNAs in neuropathic pain, Sun et al. (2025) sought to identify additional microRNAs whose expression levels change in the trigeminal ganglia of rats after chronic constriction injury. High-throughput RNA sequencing revealed that miR-216a-3p was significantly downregulated, which was subsequently confirmed via quantitative PCR (qPCR). To assess the functional relevance of this downregulation, a synthetic miR-216a-3p agomir was administered directly into the trigeminal ganglia of injured rats, resulting in marked attenuation of both mechanical allodynia and thermal hyperalgesia. Conversely, inhibition of miR-216a-3p in naive animals was sufficient to elicit pain behaviors, confirming its role as a negative regulator of nociceptive sensitivity.
To investigate the upstream regulatory mechanism responsible for reduction in miR-216a-3p levels, Sun et al. (2025) performed chromatin immunoprecipitation and found that H3K27me3 levels at the miR-216a-3p promoter were significantly elevated in injured animals, consistent with EZH2-mediated transcriptional repression. To assess the involvement of transcriptional regulators, the authors examined SOX10, a factor known to regulate gene expression in sensory neurons. Under basal conditions, electrophoretic mobility shift and ChIP–qPCR assays demonstrated that SOX10 binds the miR-216a-3p promoter. Following injury, SOX10 binding was diminished in conjunction with increased H3K27me3 levels. Although chromatin compaction was not directly measured, the authors interpret the reduced SOX10 occupancy in the context of elevated H3K27me3 as indicative of a shift toward a repressive chromatin state that limits transcription factor access.
Sun et al. (2025) next used bioinformatic prediction tools to identify potential downstream targets of miR-216a-3p. STIM1 was predicted to contain a conserved miR-216a-3p binding site within its 3′ UTR, suggesting it as a likely target. This was supported by luciferase reporter assays, which confirmed direct targeting of STIM1 by miR-216a-3p. Western blot analysis further demonstrated that overexpression of miR-216a-3p decreased STIM1 protein levels, whereas inhibition of miR-216a-3p increased its expression.
Previous studies have linked calcium dysregulation to chronic pain (Qi et al., 2022), providing a rationale for investigating the role of calcium-regulatory pathways in injury-induced sensitization. STIM1 is a key mediator of store-operated calcium entry (SOCE), a process that replenishes cytosolic calcium when endoplasmic reticulum stores are depleted. Notably, calcium overload perturbs neuronal excitability and synaptic signaling and has been previously implicated in the pathogenesis of neuropathic pain (Hou et al., 2020). These findings support the hypothesis that upregulation of STIM1 contributes to neuropathic pain in the model used by Sun et al. (2025). In sensory neurons, loss of miR-216a-3p relieved repression of STIM1, leading to sustained intracellular calcium elevation. Importantly, Sun et al. (2025) demonstrated that elevated STIM1 levels exacerbated pain behaviors in vivo, likely via calcium-dependent enhancement of nociceptor excitability. Together, these results support a role for the H3K27me3–miR-216a-3p–STIM1 axis in injury-induced sensitization.
The study by Sun et al. (2025) provides new insights into the molecular mechanisms underlying neuropathic pain. Specifically, H3K27me3-mediated repression of miR-216a-3p led to upregulation of STIM1, which in turn was associated with increased neuronal excitability, likely as a result of elevated intracellular calcium levels. The identification of the H3K27me3-SOX10-miR-216a-3p-STIM1 axis opens new possibilities for therapeutic intervention in neuropathic pain conditions. EZH2 inhibitors, which reduce H3K27me3 levels, could potentially restore miR-216a-3p expression and alleviate pain. Similarly, microRNA-based therapies, such as miR-216a-3p mimics, may be a novel approach to pain management. However, the development of these therapies faces challenges, including delivery to specific neuronal populations and potential off-target effects due to the pleiotropic nature of microRNAs.
While the study by Sun et al. (2025) provides compelling mechanistic insight into the epigenetic mechanisms underlying neuropathic pain, several important questions remain. A key limitation is the assessment of miR-216a-3p expression at a single post-injury time point, which precludes analysis of its temporal dynamics. Thus, the observed downregulation may reflect either a transient early response or a sustained repression contributing to chronic pain. Additionally, although the authors identified miR-216a-3p as a key node in their model, other microRNAs previously implicated in neuropathic pain were not detected. This discrepancy may arise from differences in the injury models used (chronic constriction injury in trigeminal ganglia vs spared nerve injury or dorsal root ganglia), the specific anatomical region examined, or the time point of RNA collection. These factors may substantially influence the profile of dysregulated microRNAs. Future studies incorporating longitudinal sampling, comparison across multiple pain models, and validation in human nociceptor datasets will be essential to determine whether the H3K27me3–miR-216a-3p–STIM1 axis contributes to pain more generally and to clarify how it fits within the broader landscape of microRNA regulation in neuropathic pain.
By delineating the H3K27me3–SOX10–miR-216a-3p–STIM1 regulatory cascade, Sun et al. (2025) identify a mechanism through which epigenetic repression controls microRNA-mediated modulation of calcium signaling and neuronal excitability. This axis integrates histone modification and post-transcriptional gene silencing into the molecular framework of injury-induced neural plasticity, thereby refining current models of neuropathic pain pathogenesis. The data implicate transcriptionally encoded alterations, specifically, H3K27me3-driven silencing of miR-216a-3p, as a potential contributor to neuronal hyperexcitability associated with neuropathic pain. By conceptualizing neuropathic pain as a state maintained by epigenetically entrenched gene expression patterns, Sun et al. (2025) provide a mechanistically nuanced and clinically actionable paradigm for understanding and treating chronic pain.
Footnotes
Review of Sun et al.
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I would like to thank Dr. DJ Cook for his mentorship throughout my graduate training. The views expressed here are my own and do not necessarily reflect those of the original authors or the journal.
This Journal Club was mentored by DJ Cook.
The author declares no competing financial interests.
- Correspondence should be addressed to Sapphire Newman-Fogel at 19snf3{at}queensu.ca.
