Macrophages protect against sensory axon loss in peripheral neuropathy.
Epigenomic landscape of the human dorsal root ganglion: sex differences and transcriptional regulation of nociceptive genes.
Cell states are influenced by the regulation of gene expression orchestrated by transcription factors capable of binding to accessible DNA regions. To uncover if sex differences exist in chromatin accessibility in the human dorsal root ganglion (hDRG), where nociceptive neurons innervating the body are found, we performed bulk and spatial assays for transposase-accessible chromatin technology followed by sequencing (ATAC-seq) from organ donors without a history of chronic pain. Using bulk ATAC-seq, we detected abundant sex differences in the hDRG. In women, differentially accessible regions (DARs) mapped mostly to the X chromosome, whereas in men, they mapped to autosomal genes. Hormone-responsive transcription factor binding motifs such as EGR1/3 were abundant within DARs in women, while JUN, FOS, and other activating protein 1 factor motifs were enriched in men, suggesting a higher activation state of cells compared with women. These observations were consistent with spatial ATAC-seq data. Furthermore, we validated that EGR1 expression is biased to female hDRG using RNAscope. In neurons, spatial ATAC-seq revealed higher chromatin accessibility in GABAergic, glutamatergic, and interferon-related genes in women and in Ca2+-signaling-related genes in men. Strikingly, XIST, responsible for inactivating 1 X chromosome by compacting it and maintaining at the periphery of the nucleus, was found to be highly dispersed in female neuronal nuclei. This is likely related to the higher chromatin accessibility in X in female hDRG neurons observed using both ATAC-seq approaches. We have documented baseline epigenomic sex differences in the hDRG which provide important descriptive information to test future hypotheses.
Novel insight into TRPV1-induced mitochondrial dysfunction in neuropathic pain.
Neuropathic pain remains one of the leading causes of global disability. The mechanism of neuropathic pain development and maintenance involves mitochondrial dysfunction induced-neuronal apoptosis of peripheral and central nociceptive pathways. The TRPV1 is a non-selective cation channel, which has a high Ca2+ permeability, playing an essential role in neuronal apoptosis in the spinal cord following peripheral nerve injury. However, the mechanism of how TRPV1 activation in the spinal cord induces mitochondrial dysfunction-mediate neuronal apoptosis, resulting in allodynia is unknown. Here, we found that activating the TRPV1 channel in the spinal cord using capsaicin, a TRPV1 agonist, results in mechanical and thermal hypersensitivity that were found to be mediated by neuroinflammation, elevated level of apoptosis, and a reduction in transcription of the mitochondrial complexes in the spinal cord and DRG. Moreover, during the early activation of the TRPV1 (1h, 24h, 48h following the capsaicin injection in the spinal cord) we observed a robust reduction in mitochondrial oxygen consumption in the non-phosphorylated state, ATP-linked respiration, maximal respiration, and electron transfer capacity (ETC). A more advanced experiment, wherein we controlled capsaicin, Ca2+ concentration and the exposure time in isolated spinal cord tissue (Lumbar, L1-L6), unveiled that TRPV1 activation impairing the mitochondrial function in terms of oxygen consumption, collapsing the Ψm and induction of the mitochondrial permeability transition pore (mPTP), which were reversed by the mPTP inhibitor-Cyclosporin A (CsA) during challenging the mitochondria with Ca2+ in a dose-dependent manner. More critically, injection of TRPV1 antagonist AMG9810 in the spinal cord following sciatic nerve crush reversed mechanical allodynia and modulated thermal hypersensitivity. In addition, the presence of TRPV1 antagonist-AMG9810 along with capsaicin and Ca2+ during challenging the spinal cord tissue completely prevents the early mPTP induction, the reduction in oxygen consumption and. In conclusion, our findings suggest that TRPV1 activation induces neuronal apoptosis, neuroinflammation, and mitochondrial dysfunction in the spinal cord, reflected in mechanical and thermal allodynia. Notable, the mitochondrial dysfunction following the TRPV1 activation in the spinal cord includes crucial elements that contribute to neuronal death, including mPTP induction, reduction in Ψm and oxygen consumption. Strikingly, regulating the TRPV1 following sciatic nerve injury reverses hypersensitivity probably via protection of the mitochondrial, suggesting a fundamental role for the TRPV1 pathway in mitochondrial dysfunction-mediated pain development.
Neurovascularization inhibiting dual responsive hydrogel for alleviating the progression of osteoarthritis.
Treating osteoarthritis (OA) associated pain is a challenge with the potential to significantly improve patients lives. Here, we report on a hydrogel for extracellular RNA scavenging and releasing bevacizumab to block neurovascularization at the osteochondral interface, thereby mitigating OA pain and disease progression. The hydrogel is formed by cross-linking aldehyde-phenylboronic acid-modified sodium alginate/polyethyleneimine-grafted protocatechuic acid (OSAP/PPCA) and bevacizumab sustained-release nanoparticles (BGN@Be), termed OSPPB. The dynamic Schiff base bonds and boronic ester bonds allow for injectability, self-healing, and pH/reactive oxygen species dual responsiveness. The OSPPB hydrogel can significantly inhibit angiogenesis and neurogenesis in vitro. In an in vivo OA model, intraarticular injection of OSPPB accelerates the healing process of condyles and alleviates chronic pain by inhibiting neurovascularization at the osteochondral interface. The injectable hydrogel represents a promising technique to treat OA and OA associated pain.
Divergent sex-specific pannexin-1 mechanisms in microglia and T cells underlie neuropathic pain.
Chronic pain is a leading cause of disability, affecting more women than men. Different immune cells contribute to this sexual divergence, but the mechanisms, especially in females, are not well defined. We show that pannexin-1 (Panx1) channels on microglia and T cells differentially cause mechanical allodynia, a debilitating symptom of neuropathic pain. In male rodents, Panx1 drives vascular endothelial growth factor-A (VEGF-A) release from microglia. Cell-specific knockdown of microglial Panx1 or pharmacological blockade of the VEGF receptor attenuated allodynia in nerve-injured males. In females, nerve injury increased spinal CD8 T cells and leptin levels. Leptin release from female-derived CD8 T cells was Panx1 dependent, and intrathecal leptin-neutralizing antibody injection sex-specifically reversed allodynia. Adoptive transfer of female-derived CD8 T cells caused robust allodynia, which was prevented by a leptin-neutralizing antibody or leptin small interfering RNA (siRNA) knockdown. Panx1-targeted approaches may alleviate neuropathic pain in both sexes, while T cell- and leptin-directed treatments could have sex-dependent benefits for women.
Neonatal exposure to morphine results in prolonged pain hypersensitivity during adolescence, driven by gut microbial dysbiosis and gut-brain axis-mediated inflammation.
Opioids, such as morphine, are used in the Neonatal Intensive Care Unit (NICU) for pain relief in neonates. However, the available evidence concerning the benefits and harms of opioid therapy in neonates remains limited. While previous studies have reported that neonatal morphine exposure (NME) results in long-term heightened pain sensitivity, the underlying mechanisms are not well understood. This study proposes that dysbiosis of the gut microbiome contributes to pain hypersensitivity following NME. Using an adolescent female murine model, pain sensitivity was evaluated using tail flick and hot plate assays for thermal pain and the Von Frey assay for mechanical pain. Gut microbiome composition was assessed using 16 s rRNA sequencing, while transcriptomic changes in midbrain samples were investigated using bulk RNA-sequencing. NME induced prolonged hypersensitivity to thermal and mechanical pain in adolescence, accompanied by persistent gut microbial dysbiosis and sustained systemic inflammation, characterized by elevated circulating cytokine levels (e.g., IL-1α, IL-12p70, IFN-γ, IL-10). Transplantation of the microbiome from NME adolescents recapitulated pain hypersensitivity in naïve adolescent mice, while neonatal probiotic intervention with Bifidobacterium infantis (B. infantis) reversed the hypersensitivity by preventing gut dysbiosis and associated systemic inflammation. Furthermore, transcriptomic analysis of the midbrain tissues revealed that NME upregulated several genes and key signaling pathways, including those related to immune activation and excitatory signaling, which were notably mitigated by neonatal B. infantis administration. Together, these findings highlight the critical role of the gut-brain axis in modulating pain sensitivity and suggest that targeting the gut microbiome offers a promising therapeutic strategy for managing neurobiological disorders following early opioid exposure.
Increased TRPA1 functionality in the skin of rats and cancer patients following oxaliplatin treatment.
Chemotherapy-induced peripheral neuropathy is a debilitating pathology affecting a majority of patients who are being treated with specific cytostatic compounds including oxaliplatin. Various in vitro, ex vivo and in vivo preclinical experiments indicate that transient receptor potential ankyrin 1 (TRPA1) plays a crucial role in the symptomatology of chemotherapy-induced peripheral neuropathy. However, it is unclear whether oxaliplatin also modulates the TRPA1 functionality in the skin of rodents or patients. Here, we quantified the vasodilation after topical application of the TRPA1 agonist cinnamaldehyde in a rodent model of chemotherapy-induced peripheral neuropathy (male Sprague Dawley rats, aged 6 weeks) as well as on fingers of patients suffering from chronic chemotherapy-induced peripheral neuropathy after oxaliplatin treatment. Compared to vehicle-treated rats, a cumulative dose of oxaliplatin 32 mg/kg enhanced the vasodilation after cinnamaldehyde application on rat abdominal skin. Likewise, also in patients with chronic chemotherapy-induced peripheral neuropathy after oxaliplatin, the response to cinnamaldehyde was significantly higher compared to sex- and age-matched healthy controls. Thereby, this study is the first to translate the evidence of increased TRPA1 functionality in vitro or ex vivo in rodents to in vivo conditions in human. The increased TRPA1 functionality in patients with chronic chemotherapy-induced peripheral neuropathy does not only confirm the potential of TRPA1 as target to hit to provide efficacious analgesia, it also paves the way for additional patient stratification on a molecular level and possible treatment response prediction.
A role for proprioceptors in sngception.
Proprioceptors are primary mechanosensory neurons to monitor the status of muscle contraction and/or body position (). Although proprioceptors are known as non-nociceptive mechanoreceptors, they also express the pro-nociceptive acid-sensing ion channel 3 (ASIC3) (-). To probe the role for proprioceptors in sensing acidosis (or sngception) (), we found that genetic deletion of in proprioceptors but not in nociceptors abolished acid-induced chronic hyperalgesia in mice. Chemo-optogenetically activating proprioceptors resulted in hyperalgesic priming that favored chronic pain induced by acidosis. In humans, intramuscular acidification induced acid perception but not pain. Conversely, in a spinal cord-injured patient who lost pain sensation in the right leg, proprioception and sngception were remaining somatosensory functions, associated with the spinal dorsal column. Together, evidence from both mouse and human studies suggests a role for proprioceptors in sngception.
Scratching promotes allergic inflammation and host defense via neurogenic mast cell activation.
Itch is a dominant symptom in dermatitis, and scratching promotes cutaneous inflammation, thereby worsening disease. However, the mechanisms through which scratching exacerbates inflammation and whether scratching provides benefit to the host are largely unknown. We found that scratching was required for skin inflammation in mouse models dependent on FcεRI-mediated mast cell activation. Scratching-induced inflammation required pain-sensing nociceptors, the neuropeptide substance P, and the mast cell receptor MrgprB2. Scratching also increased cutaneous inflammation and augmented host defense to superficial infection. Thus, through the activation of nociceptor-driven neuroinflammation, scratching both exacerbated allergic skin disease and provided protection from , reconciling the seemingly paradoxical role of scratching as a pathological process and evolutionary adaptation.
Trigeminal nerve microstructure is linked with neuroinflammation and brainstem activity in migraine.
Although the pathophysiology of migraine involves a complex ensemble of peripheral and central nervous system changes that remain incompletely understood, the activation and sensitization of the trigeminovascular system is believed to play a major role. However, non-invasive, in vivo neuroimaging studies investigating the underlying neural mechanisms of trigeminal system abnormalities in human migraine patients are limited. Here, we studied 60 patients with migraine (55 females, mean age ± SD: 36.28 ± 11.95 years) and 20 age-/sex-matched healthy controls (19 females, mean age ± SD: 35.45 ± 13.30 years) using ultra-high field 7 Tesla diffusion tensor imaging and functional MRI, as well as PET with the translocator protein ligand [11C]-PBR28. We evaluated MRI diffusivity measures and PET signal at the trigeminal nerve root, as well as brainstem functional MRI response to innocuous, ophthalmic trigeminal nerve territory stimulation. Patients with migraine demonstrated altered white matter microstructure at the trigeminal nerve root (n=53), including reduced fractional anisotropy, compared to healthy controls (n=18). Furthermore, in patients, lower fractional anisotropy was accompanied by 1) higher neuroinflammation (i.e. elevated [11C]-PBR28 PET signal) at the nerve root (n=36) and 2) lower functional MRI activation in an ipsilateral pontine cluster consistent with spinal trigeminal nucleus (n=51). These findings were more robust on the right side, which was consistent with the observation that right headache dominant patients demonstrated higher migraine severity compared to left headache dominant patients in our cohort. Multimodal imaging of the integrated neural mechanisms that characterize migraine underscores the importance of trigeminal system remodeling as both a key aspect of the dynamics underlying migraine pathophysiology and a target for therapeutic interventions.