Nociceptors are specialized sensory neurons that detect damaging or potentially damaging stimuli and are found in the dorsal root ganglia (DRG) and trigeminal ganglia. These neurons are critical for the generation of neuronal signals that ultimately create the perception of pain. Nociceptors are also primary targets for treating acute and chronic pain. Single-cell transcriptomics on mouse nociceptors has transformed our understanding of pain mechanisms. We sought to generate equivalent information for human nociceptors with the goal of identifying transcriptomic signatures of nociceptors, identifying species differences and potential drug targets. We used spatial transcriptomics to molecularly characterize transcriptomes of single DRG neurons from eight organ donors. We identified 12 clusters of human sensory neurons, 5 of which are C nociceptors, as well as 1 C low-threshold mechanoreceptors (LTMRs), 1 Aβ nociceptor, 2 Aδ, 2 Aβ, and 1 proprioceptor subtypes. By focusing on expression profiles for ion channels, G protein–coupled receptors (GPCRs), and other pharmacological targets, we provided a rich map of potential drug targets in the human DRG with direct comparison to mouse sensory neuron transcriptomes. We also compared human DRG neuronal subtypes to nonhuman primates showing conserved patterns of gene expression among many cell types but divergence among specific nociceptor subsets. Last, we identified sex differences in human DRG subpopulation transcriptomes, including a marked increase in calcitonin-related polypeptide alpha ( CALCA ) expression in female pruritogen receptor–enriched nociceptors. This comprehensive spatial characterization of human nociceptors might open the door to development of better treatments for acute and chronic pain disorders.

Injury-induced sensitization of nociceptors contributes to pain states and the development of chronic pain. Inhibiting activity-dependent mRNA translation through mechanistic target of rapamycin and mitogen-activated protein kinase (MAPK) pathways blocks the development of nociceptor sensitization. These pathways convergently signal to the eukaryotic translation initiation factor (eIF) 4F complex to regulate the sensitization of nociceptors, but the details of this process are ill defined. Here we investigated the hypothesis that phosphorylation of the 5Ј cap-binding protein eIF4E by its specific kinase MAPK interacting kinases (MNKs) 1/2 is a key factor in nociceptor sensitization and the development of chronic pain. Phosphorylation of ser209 on eIF4E regulates the translation of a subset of mRNAs. We show that pronociceptive and inflammatory factors, such as nerve growth factor (NGF), interleukin-6 (IL-6), and carrageenan, produce decreased mechanical and thermal hypersensitivity, decreased affective pain behaviors, and strongly reduced hyperalgesic priming in mice lacking eIF4E phosphorylation (eIF4E S209A ). Tests were done in both sexes, and no sex differences were found. Moreover, in patch-clamp electrophysiology and Ca 2ϩ imaging experiments on dorsal root ganglion neurons, NGF-and IL-6-induced increases in excitability were attenuated in neurons from eIF4E S209A mice. These effects were recapitulated in Mnk1/2 Ϫ/Ϫ mice and with the MNK1/2 inhibitor cercosporamide. We also find that cold hypersensitivity induced by peripheral nerve injury is reduced in eIF4E S209A and Mnk1/2 Ϫ/Ϫ mice and following cercosporamide treatment. Our findings demonstrate that the MNK1/2-eIF4E signaling axis is an important contributing factor to mechanisms of nociceptor plasticity and the development of chronic pain.

Migraine is the second leading cause for disability worldwide and the most common neurological disorder. It is also three times more common in women; reasons for this sex difference are not known. Using preclinical behavioral models of migraine, we show that application of calcitonin gene-related peptide (CGRP) to the rat dura mater produces cutaneous periorbital hypersensitivity. Surprisingly, this response was observed only in females; dural CGRP at doses from 1 pg to 3.8 g produce no responses in males. In females, dural CGRP causes priming to a pH 7.0 solution after animals recover from the initial CGRP-induced allodynia. Dural application of interleukin-6 causes acute responses in males and females but only causes priming to subthreshold dural CGRP (0.1 pg) in females. Intracisternal application of BDNF also causes similar acute hypersensitivity responses in males and females but only priming to subthreshold dural CGRP (0.1 pg) in females. Females were additionally primed to a subthreshold dose of the NO-donor sodium nitroprusside (0.1 mg/kg) following dural CGRP. Finally, the sexually dimorphic responses to dural CGRP were not specific to rats as similar female-specific hypersensitivity responses were seen in mice, where increased grimace responses were also observed. These data are the first to demonstrate that CGRP-induced headache-like behavioral responses at doses up to 3.8 g are female-specific both acutely and following central and peripheral priming. These data further implicate dural CGRP signaling in the pathophysiology of migraine and propose a model where dural CGRP-based mechanisms contribute to the sexual disparity of this female-biased disorder.Calcitonin gene-related peptide (CGRP) has long been implicated in the pathophysiology of migraine, and CGRP-based therapeutics are efficacious for the treatment of migraine in humans. However, the location of action for CGRP in migraine remains unclear. We show here that application of CGRP to the cranial meninges causes behavioral responses consistent with headache in preclinical rodent models. Surprisingly, however, these responses are only observed in females. Acute responses to meningeal CGRP are female-specific and sensitization to CGRP after two distinct stimuli are also female-specific. These data implicate the dura mater as a primary location of action for CGRP in migraine and suggest that female-specific mechanisms downstream of CGRP receptor activation contribute to the higher prevalence of migraine in women.

Nociceptors, sensory neurons in the DRG that detect damaging or potentially damaging stimuli, are key drivers of neuropathic pain. Injury to these neurons causes activation of translation regulation signaling, including the mechanistic target of rapamycin complex 1 (mTORC1) and mitogen-activated protein kinase interacting kinase (MNK) eukaryotic initiation factor (eIF) 4E pathways. This is a mechanism driving changes in excitability of nociceptors that is critical for the generation of chronic pain states; however, the mRNAs that are translated to lead to this plasticity have not been elucidated. To address this gap in knowledge, we used translating ribosome affinity purification in male and female mice to comprehensively characterize mRNA translation in Scn10a-positive nociceptors in chemotherapy-induced neuropathic pain (CIPN) caused by paclitaxel treatment. This unbiased method creates a new resource for the field, confirms many findings in the CIPN literature and also find extensive evidence for new target mechanisms that may cause CIPN. We provide evidence that an underlying mechanism of CIPN is sustained mTORC1activationdrivenbyMNK1-eIF4Esignaling.RagA,aGTPasecontrollingmTORC1activity,isidentifiedasanoveltargetofMNK1-eIF4E signaling. This demonstrates a novel translation regulation signaling circuit wherein MNK1-eIF4E activity drives mTORC1 via control of RagA translation. CIPN and RagA translation are strongly attenuated by genetic ablation of eIF4E phosphorylation, MNK1 elimination or treatment with the MNK inhibitor eFT508. We identify a novel translational circuit for the genesis of neuropathic pain caused by chemotherapy with important implications for therapeutics.

Prophylactic use of negative pressure dressings for closed laparotomy wounds significantly reduces the incidence of SSI at 30 days postoperatively.