Long-lasting Analgesia via Targeted in situ Repression of NaV1.7
Ontology highlight
ABSTRACT: Current treatments for chronic pain rely largely on opioids despite their significant side effects and risk of addiction. Genetic studies have identified in humans key targets pivotal to nociceptive processing. In particular, a hereditary loss-of-function mutation in NaV1.7, a sodium channel protein associated with signaling in nociceptive sensory afferents, leads to insensitivity to pain without other neurodevelopmental alterations. However, the high sequence and structural similarity between NaV subtypes has frustrated efforts to develop selective inhibitors. Here, we investigated targeted epigenetic repression of NaV1.7 in primary afferents via epigenome engineering approaches based on clustered regularly interspaced short palindromic repeats (CRISPR)-dCas9 and zinc finger proteins at the spinal level as a potential treatment for chronic pain. Towards this end, we first optimized the efficiency of NaV1.7 repression in vitro in Neuro2A cells, and then by the lumbar intrathecal route delivered both epigenome-engineering platforms via adeno-associated viruses (AAVs) to assess their effects in three mouse models of pain: carrageenan-induced inflammatory pain, paclitaxel-induced neuropathic pain and BzATP-induced pain. Our results demonstrate: i) effective repression of NaV1.7 in lumbar dorsal root ganglia; ii) reduced thermal hyperalgesia in the inflammatory state; iii) decreased tactile allodynia in the neuropathic state; and iv) no changes in normal motor function. We anticipate this genomically scarless and non-addictive pain prevention and amelioration approach enabling Long-lasting Analgesia via Targeted in vivo Epigenetic Repression of NaV1.7, a methodology we dub pain LATER, will have significant therapeutic potential in management of persistent pain states.
Project description:Voltage-gated sodium channels (Navs) 1.7, 1.8, and 1.9 are predominately expressed in peripheral sensory neurons and are critical for action potential propagation in nociceptors. Unexpectedly, we found that expression of SCN9A, SCN10A, SCN11A, and SCN2A, the alpha subunit of Nav1.7, Nav1.8, Nav1.9 and Nav1.2, respectively, are up-regulated in spinal dorsal horn (SDH) neurons of miR-96 knockout mice. These mice also have de-repression of CACNA2d1/2 in DRG and display heat and mechanical allodynia that could be attenuated by intrathecal or intraperitoneal injection of Nav1.7 or Nav1.8 inhibitors or Gabapentin. Moreover, Gad2::CreERT2 conditional miR-96 knockout mice phenocopied global knockout mice, implicating inhibitory neurons; nerve injury induced significant loss of miR-96 in SDH GABAergic and Glutamatergic neurons in mice which negative correlated to up-regulation of Nav1.7, Nav1.8, Nav1.9 and Scn2a, this dis-regulation of miR-96 and Navs in SDH neurons contributed to neuropathic pain which can be alleviated by intrathecal injection of Nav1.7 or Nav1.8 blockers. In conclusion, miR-96 is required to avoid allodynia through limiting the expression of VGCCs and Navs in DRG and Navs in SDH in naïve and nerve injury induced neuropathic pain mice. Our findings suggest that central nervous system penetrating Nav1.7 and Nav1.8 inhibitors may be efficacious for pain relief.
Project description:Sensitization of spinal nociceptive circuits plays a cardinal role in neuropathic pain. This sensitization depends on new gene expression that is primarily regulated via transcriptional and translational control mechanisms. The relative roles of these mechanisms in regulating gene expression in the clinically relevant chronic phase of neuropathic pain are not well understood. Here, we show that changes in gene expression in the spinal cord during the chronic phase of neuropathic pain are substantially regulated at the translational level. Downregulating spinal translation at the chronic phase alleviated pain hypersensitivity. Cell-type-specific profiling revealed that spinal inhibitory neurons exhibited greater changes in translation after peripheral nerve injury compared to excitatory neurons. Notably, increasing translation selectively in all inhibitory neurons or parvalbumin-positive (PV + ) interneurons, but not excitatory neurons, promoted mechanical pain hypersensitivity. Furthermore, increasing translation in PV + neurons decreased their intrinsic excitability and spiking activity, whereas reducing translation in spinal PV + neurons prevented the nerve injury-induced decrease in excitability. Thus, translational control mechanisms in the spinal cord, primarily in inhibitory neurons, play a critical role in mediating neuropathic pain hypersensitivity.
Project description:An insulating myelin sheath ensures saltatory conduction of mechanosensory A afferents. Myelin damage results in the electrical instability of A fibers and the ability to generate pain in response to light touch/pressure (mechanical allodynia). We have hypothesized and then established that the release of T cell epitopes of myelin basic protein (MBP) enables nociceptive circuitry in myelinated fibers. Thus, mass spectrometry analysis of the rat sciatic nerve proteome followed by bioinformatics examination of the datasets revealed a loss of MBP and activation of T-helper cell signaling in the nerves undergoing chronic constriction injury (CCI). Matrix metalloproteinase-9 (MMP-9) proteolysis resulted in the MBP digest peptides, including the MBP84-104 and MBP68-86 regions, which exhibit prominent immunogenic epitopes. Myelin-forming Schwann cells and paranodal areas accumulated MHCII, MMP-9 and the degraded MBP at the sciatic nerve injury site. Administration of the immunodominant MBP84-104 and MBP68-86 peptides but not of the control peptides in a naïve rat sciatic nerve produced robust mechanical allodynia. Allodynia was accompanied by the T cell infiltration and an increase in MHCII, IL-17A and TNF- levels at the nerve injection site and the segmental ganglia. The pro-nociceptive activity of the synthetic MBP84-104 diminished in athymic nude rats lacking T cells. SB-3CT, an antagonist of MMP-9, inhibited mechanical allodynia, neuroinflammation and spinal sensitization after CCI. Collectively, our novel data implicate, for the first time, MMP-mediated cleavage of MBP and the resulting MBP digest fragments as a major cause of neuropathic pain. Gene extression profiling of total RNAs extracted from rat sciatic nerves, dorsal root ganglion and spinal cords after MBP84-104 peptide injection
Project description:Neuropathic pain is a refractory condition that involves de novo protein synthesis in the nociceptive pathway. The mechanistic target of rapamycin (mTOR) is a master regulator of protein synthesis; however, mechanisms underlying its role in neuropathic pain remain elusive. Using spared nerve injury-induced neuropathic pain model, we found mTOR activation in large-diameter dorsal root ganglion (DRG) neurons and spinal microglia. However, selective ablation of mTOR in DRG neurons, rather than microglia, alleviated neuropathic pain. Combining transcriptomic profiling, electrophysiological recording and pharmacologic manipulations, we demonstrated that activated mTOR promoted neuropeptide Y (NPY) induction in mechanoreceptors and that NPY acted on Y2 receptors (Y2R) but not Y1R to enhance nociceptor excitability. Peripheral replenishment of NPY reversed pain alleviation upon mTOR removal, whereas Y2R antagonists prevented its function. Our findings reveal an unexpected link between mTOR and NPY in promoting nociceptor sensitization and neuropathic pain, through NPY/Y2R signaling-mediated intra-ganglionic transmission.
Project description:Nociception is protective and prevents tissue damage but can also facilitate chronic pain. If a general principle governs these two types of pain is unknown. Here, we show that both basal mechanical and neuropathic pain are controlled by microRNA-183 cluster in mice. This single cluster controls more than 80% of neuropathic pain-regulated genes and scales basal mechanical sensitivity and mechanical allodynia by regulating auxiliary voltage-gated calcium channel subunits a2d. Basal sensitivity is controlled in nociceptors and allodynia involves TrkB+ light-touch mechanoreceptors. These light-touch sensitive neurons that normally do not elicit pain produce pain during neuropathy that is reversed by gabapentin. Thus, a single miRNA cluster continuously scales acute noxious mechanical sensitivity in nociceptive neurons and suppresses neuropathic pain transduction in a specific, light-touch sensitive neuronal type recruited during mechanical allodynia.
Project description:Pain is the leading cause of disability in the developed world but remains a poorly treated condition. Specifically, post-surgical pain continues to be a frequent and undermanaged condition. Here, we investigate the analgesic potential of pharmacological NaV1.7 inhibition in a mouse model of acute post-surgical pain, based on incision of the plantar skin and underlying muscle of the hind paw. We demonstrate that local and systemic treatment with the selective NaV1.7 inhibitor μ-theraphotoxin-Pn3a is effectively anti-allodynic in this model and completely reverses mechanical hypersensitivity in the absence of motor adverse effects. In addition, the selective NaV1.7 inhibitors ProTx-II and PF-04856264 as well as the clinical candidate CNV1014802 also reduced mechanical allodynia. Interestingly, co-administration of the opioid receptor antagonist naloxone completely reversed analgesic effects of Pn3a, indicating an involvement of endogenous opioids in the analgesic activity of Pn3a. Additionally, we found super-additive antinociceptive effects of sub-therapeutic Pn3a doses not only with the opioid oxycodone but also with the GABAB receptor agonist baclofen. Transcriptomic analysis of gene expression changes in dorsal root ganglia of mice post-surgery revealed decreased expression of several pro-nociceptive genes including N- and P/Q-type voltage-gated calcium channels important for neurotransmitter release, which suggest a reactive compensatory mechanism to reduce excessive pain similar to the endogenous opioid system. In summary, these findings suggest that pain after surgery can be successfully treated with NaV1.7 inhibitors alone or in combination with baclofen or opioids, which may present a novel and safe treatment strategy for this frequent and poorly managed condition.
Project description:Maladaptive changes of nerve injury–associated genes in dorsal root ganglia (DRGs) are critical for neuropathic pain genesis. Emerging evidence supports the role of long noncoding RNAs (lncRNAs) in regulating gene transcription. Here we identified a conserved lncRNA, named nerve injury–specific lncRNA (NIS-lncRNA) for its upregulation in injured DRGs exclusively in response to nerve injury. This upregulation was triggered by nerve injury–induced increase in DRG ELF1, a transcription factor that bound to the NIS-lncRNA promoter. Blocking this upregulation attenuated nerve injury–induced CCL2 increase in injured DRGs and nociceptive hypersensitivity during the development and maintenance periods of neuropathic pain. Mimicking NIS-lncRNA upregulation elevated CCL2 expression, increased CCL2-mediated excitability in DRG neurons, and produced neuropathic pain symptoms. Mechanistically, NIS-lncRNA recruited more binding of the RNA-interacting protein FUS to the Ccl2 promoter and augmented Ccl2 transcription in injured DRGs. Thus, NIS-lncRNA participates in neuropathic pain likely by promoting FUS-triggered DRG Ccl2 expression and may be a potential target in neuropathic pain management.
Project description:Not all patients with nerve injury develop neuropathic pain. The extent of nerve damage and age at the time of injury are two of the few risk factors identified to date. In addition, preclinical studies show that neuropathic pain variance is heritable. To define such factors further, we performed a large-scale gene profiling experiment which plotted global expression changes in the rat dorsal root ganglion in three peripheral neuropathic pain models. This resulted in the discovery that the potassium channel alpha subunit KCNS1, involved in neuronal excitability, is constitutively expressed in sensory neurons and markedly downregulated following nerve injury. KCNS1 was then characterized by an unbiased network analysis as a putative pain gene, a result confirmed by single nucleotide polymorphism association studies in humans. A common amino acid changing allele, the 'valine risk allele', was significantly associated with higher pain scores in five of six independent patient cohorts assayed (total of 1359 subjects). Risk allele prevalence is high, with 18-22% of the population homozygous, and an additional 50% heterozygous. At lower levels of nerve damage (lumbar back pain with disc herniation) association with greater pain outcome in homozygote patients is P = 0.003, increasing to P = 0.0001 for higher levels of nerve injury (limb amputation). The combined P-value for pain association in all six cohorts tested is 1.14 E-08. The risk profile of this marker is additive: two copies confer the most, one intermediate and none the least risk. Relative degrees of enhanced risk vary between cohorts, but for patients with lumbar back pain, they range between 2- and 3-fold. Although work still remains to define the potential role of this protein in the pathogenic process, here we present the KCNS1 allele rs734784 as one of the first prognostic indicators of chronic pain risk. Screening for this allele could help define those individuals prone to a transition to persistent pain, and thus requiring therapeutic strategies or lifestyle changes that minimize nerve injury. Microarrays were run on mRNA extracted from adult rat L4 and L5 DRGs cells after 3,7,21,40 hours after three different sciatic nerve lesions [Spared Nerve Injury (SNI); Chronic Constriction Injury (CCI); Spinal Nerve Ligation (Ch) with Sham controls (SH)].
Project description:Beta-endorphinergic neurons in the hypothalamic arcuate nucleus (ARC) synthesize beta-endorphin (β-EP) to alleviate nociceptive behaviors, although the underlying regulatory mechanisms remain unknown. Here, we elucidated a novel epigenetic pathway driven by microRNA regulation of beta-endorphin synthesis in ARC neurons to control neuropathic pain. In pain-injured rats miR-203a-3p was the most highly upregulated miRNA in the ARC. A similar increase was identified in the cerebrospinal fluid of trigeminal neuralgia patients. Mechanistically, histone deacetylase 9 downregulation increased acetylation of histone H3 lysine-18, facilitating the binding of NR4A2 transcription factor to the miR-203a-3p gene promoter increasing miR-203a-3p expression following nerve injury. Further, increased miR-203a-3p was found to maintain neuropathic pain by targeting proprotein convertase 1, an endopeptidase necessary for the cleavage of proopiomelanocortin, the precursor of β-EP. Our findings highlight an epigenetic regulatory pathway for β-EP synthesis that contributes to neuropathic pain development and maintenance mechanisms providing for new therapeutic targets for neuropathic pain treatment.
Project description:Neuropathic pain is a prevalent and debilitating chronic disease that is characterized by activation in glial cells in various pain-related regions within the central nervous system. Recent studies have suggested a sexually dimorphic role of microglia in the maintenance of neuropathic pain in rodents. Here, we utilized RNA sequencing analysis of microglia to identify whether there is a common neuropathic microglial signature and characterize the sex differences in microglia in pain-related regions in nerve injury and chemotherapy-induced peripheral neuropathy mouse models. Whilst mechanical allodynia and behavioral changes were observed in all models, transcriptomic analysis of microglia revealed no common transcriptional changes in spinal and supraspinal regions and in different neuropathic models. However, there was a substantial change in microglial gene expression within the ipsilateral lumbar spinal cord 7-days after chronic constriction injury (CCI) of the sciatic nerve. Both sexes upregulated genes associated with inflammation, phagosome, and lysosome activation, though males revealed a prominent global transcriptional shift not observed in female mice. This study demonstrates a lack of a common neuropathic microglial signature and indicates distinct sex differences in spinal microglia, suggesting they contribute to the sex-specific pain processing following nerve injury.