Dorsal Root Ganglion Neurons Research Articles

GFRα1 Promotes Axon Regeneration after Peripheral Nerve Injury by Functioning as a Ligand.

The neurotrophic factor, Glial cell line derived neurotrophi factor (GDNF), exerts a variety of biological effects through binding to its receptors, GDNF family receptor alpha-1 (GFRα1), and RET. However, the existence of cells expressing GFRα1 but not RET raises the possibility that GFRα1 can function independently from RET. Here, it is shown that GFRα1 released from repair Schwann cells (RSCs) functions as a ligand in a GDNF-RET-independent manner to promote axon regeneration after peripheral nerve injury (PNI). Local administration of GFRα1 into injured nerve promoted axon regeneration, even more when combined with GDNF blockade. GFRα1 bound to a receptor complex consisting of NCAM and integrin α7β1 of dorsal root ganglion neurons in a GDNF-RET independent manner. This is further confirmed by the Ret Y1062F knock-in mice, which cannot transmit most of GDNF-RET signaling. Finally, local administration of GFRα1 into injured sciatic nerve promoted functional recovery. These findings reveal a novel role of GFRα1 as a ligand, the molecular mechanism supporting axon regeneration by RSCs, and a novel therapy for peripheral nerve repair.

Structure-guided design of a peripherally restricted chemogenetic system.

Designer receptors exclusively activated by designer drugs (DREADDs) are chemogenetic tools for remotely controlling cellular signaling, neural activity, behavior, and physiology. Using a structure-guided approach, we provide a peripherally restricted Gi-DREADD, hydroxycarboxylic acid receptor DREADD (HCAD), whose native receptor is minimally expressed in the brain, and a chemical actuator that does not cross the blood-brain barrier (BBB). This was accomplished by combined mutagenesis, analoging via an ultra-large make-on-demand library, structural determination of the designed DREADD receptor via cryoelectron microscopy (cryo-EM), and validation of HCAD function. Expression and activation of HCAD in dorsal root ganglion (DRG) neurons inhibit action potential (AP) firing and reduce both acute and tissue-injury-induced inflammatory pain. The HCAD chemogenetic system expands the possibilities for studying numerous peripheral systems with little adverse effects on the central nervous system (CNS). The structure-guided approach used to generate HCAD also has the potential to accelerate the development of emerging chemogenetic tools for basic and translational sciences.

MiR-374 family is a key regulator of chronic primary pain onset.

Chronic primary pain conditions (CPPCs) are linked to catecholamine activation of peripheral adrenergic receptors. Yet, catecholamine-dependent epigenetic mechanisms, such as microRNA (miRNA) regulation of mRNA transcripts, remain largely unknown. We sought to identify RNA species correlated with case status in 3 pain cohorts, to validate RNAs found to be dysregulated in a mouse model of CPPC onset, and to directly test the role of adrenergic receptors in miRNA regulation. Furthermore, we tested antinociceptive effects of miR-374 overexpression. We used RNA-seq and quantitative reverse transcription polymerase chain reaction to measure RNA expression in 3 pain cohorts. Next, we validated identified RNAs with quantitative reverse transcription polymerase chain reaction in a mouse model of CPPC onset, measuring expression in plasma, peripheral (adipose, muscle, dorsal root ganglia [DRG]), and central (spinal cord) tissues. Then, we stimulated adrenergic receptors in primary adipocyte and DRG cultures to directly test regulation of microRNAs by adrenergic signaling. Furthermore, we used in vitro calcium imaging to measure the antinociceptive effects of miR-374 overexpression. We found that one miRNA family, miR-374, was downregulated in the plasma of individuals with temporomandibular disorder, fibromyalgia syndrome, or widespread pain following a motor vehicle collision. miR-374 was also downregulated in plasma, white adipose tissue, and spinal cord from mice with multisite mechanical sensitivity. miR-374 downregulation in plasma and spinal cord was female specific. Norepinephrine stimulation of primary adipocytes, but not DRG, led to decreased miR-374 expression. Furthermore, we identified tissue-specific and sex-specific changes in the expression of predicted miR-374 mRNA targets, including known (HIF1A, NUMB, TGFBR2) and new (ATXN7, CRK-II) pain targets. Finally, we demonstrated that miR-374 overexpression in DRG neurons reduced capsaicin-induced nociceptor activity. Downregulation of miR-374 occurs between adrenergic receptor activation and mechanical hypersensitivity, and its adipocyte source implicates adipose signaling in nociception. Further study of miR-374 may inform therapeutic strategies for the millions worldwide who experience CPPCs.

Protective role of TRPV1+ nociceptive neurons communication to macrophages against T. cruzi infection in mice

Chagas’ disease is a life-threatening condition caused by Trypanosoma cruzi. Patients with chronic disease may develop gastrointestinal, neurological, or associated neuro-digestive dysfunctions. CNS invasion by T. cruzi can occur in the acute phase, and its presence in the brain and cerebrospinal fluid was reported. T. cruzi induces nociceptor neuron activation and pain. Nociceptive neurons and macrophage interact in diseases, and this neuroimmune communication has a pivotal role in disease outcome. We investigated, the role of TRPV1+ neurons in experimental T. cruzi infection in mice. T. cruzi forms were observed in the DRG and spinal cord in early stages of acute infection, and intrathecal administration of T. cruzi antigens into spinal cord induced pain. Trpv1 mRNA expression was increased in the DRG of infected mice and targeting TRPV1 reduced T. cruzi-induced pain. TRPV1 nociceptor ablation increased blood parasitemia while TRPV1 knockout mice presented 50% mortality upon infection in a normally non-lethal model. TRPV1 knockout also worsened clinical outcomes (hepatomegaly and megacecum), increased plasmatic Th2 cytokines and nitrite in cardiac tissue, and reduced heart leukocyte infiltration. Conditioned media of capsaicin-stimulated DRG neurons decreased macrophage internalization of T. cruzi, and CGRP receptor antagonism in infected mice reduced pain, increased early parasitemia and promoted 18% mortality. This indicates that soluble mediators released upon nociceptor activation such as CGRP increase macrophage ability to control disease outcome. These data unveil TRPV1+ neurons release CGRP to limit macrophage internalization of T. cruzi, triggering protective mechanisms against T. cruzi infection.

Spinal Nerve Axotomy: Effects on Ih In Vivo and HCNs in DRG Neurons

In vitro experiments performed on dissociated dorsal root ganglion (DRG) neurons suggest the involvement of the hyperpolarization-activated cation current (Ih) in enhancing neuronal excitability, potentially contributing to neuropathic pain. However, the more confirmative in vivo information about how nerve injury interacts with Ih is lacking. In this study, Ih was recorded in vivo using the dynamic single-electrode voltage clamp (dSEVC) technique on L5 DRG neurons of normal rats and those seven days after spinal nerve axotomy (SNA). Compared to normal rats, SNA unexpectedly inhibited the activity of Ih channels on A-fiber DRG neurons: (a) the Ih current magnitude, density, and conductance were consistently diminished; and (b) the Ih activation velocity was slowed and the voltage for Ih activation was hyperpolarized. The half-activation voltage (V0.5) exhibited a negative shift, and the time constant for Ih activation was prolonged across all test potentials, indicating the reduced availability of Ih after SNA. To further investigate the mechanisms of SNA on Ih, the underlying HCN channels and the correlated mRNA were quantified and compared. The mRNA expression level of HCN1-4 was uniformly enhanced after SNA, which might have contributed to the increased cytoplasmic HCN1 intensity observed in both medium- and large-sized DRG neurons. This finding contradicted the functional reduction of Ih after SNA. Surprisingly, the HCN labeling pattern was altered after SNA: the labeling area of HCN1 and HCN2 at the membranous ring region of the axotomized large neurons became significantly thinner or absent. We concluded that the diminished ring immunoreactivity for HCN1 and HCN2 correlated with a reduced availability of Ih channels, elucidating the observed decrease in Ih in axotomized A-fiber neurons.

SPECIALIZED PRO-RESOLVING MEDIATOR MARESIN 1 ATTENUATES PAIN IN A MOUSE MODEL OF OSTEOARTHRITIS

We test whether the specialized pro-resolving molecule Maresin 1 (MaR1) attenuates nociceptive behaviors in mice with osteoarthritis-like pain. OA-like pain behavior was induced by intra-articular injection of monosodium iodoacetate (MIA) and treated with MaR1 (N=6) or vehicle (N=5) by intraperitoneal injection 8 weeks after injury. Mice without MIA injection were used as control (N=6). Nociceptive behaviors were examined by von Frey and dynamic weight bearing measurements. CGRP expression and activated macrophages in the dorsal root ganglion (DRG) were examined by immunofluorescence staining. The inflammatory profile in circulation was assessed by cytokine array. Calcium imaging was performed to assess the in vitro functional response of DRG neurons from animals with OA-like pain behavior to MaR1 with or without RAR Related Orphan Receptor A (RORA) inverse agonist SR3335. MaR1 attenuated knee pain behavior in treated mice (N=6) compared to non-treated mice (N=5) as shown by increased paw withdrawal threshold with a mean difference of 112.2% (95% CI [49.79, 174.6], p=0.0784) at 4 hours and 150.9% (95% CI [104.2, 197.5], p=0.0001) at 4 days post-MaR1 treatment, and increased weight bearing with a mean difference of 20.08% (95% CI [2.798, 37.37], p=0.0277) at 1 day post-MaR1 treatment. CGRP expression and activated macrophages were decreased in the DRG, and inflammatory cytokine levels in the circulation were attenuated. Calcium imaging showed MaR1 reduced the functional response of DRG neurons through RORA. Our results show that MaR1 reduces OA-like pain behavior in mice and could be a potential treatment for OA pain.

Elevated vesicular Zn2+ in dorsal root ganglion neurons expressing the transporter TMEM163 causes age-associated itchy skin in mice.

The prevalent itching condition associated with aging, historically referred to as senile pruritus, diminishes quality of life. Despite its impact, effective treatments remain elusive, largely due to an incomplete understanding of its pathological cause. In this study, we reveal a subset of dorsal root ganglion neurons enriched with Zn2+ that express the vesicular Zn2+ transporter TMEM163. These neurons form direct synapses with and modulate the activity of spinal NPY+ inhibitory interneurons. In aged mice, both the expression of TMEM163 and the concentration of vesicular Zn2+ within the central terminals of TMEM163+ primary afferents show marked elevation. Importantly, the excessive release of vesicular Zn2+ significantly dampens the activity of NPY+ neurons, triggering the disinhibition of itch-transmitting neural circuits and resulting in chronic itch. Intriguingly, chelating Zn2+ within the spinal dorsal horn effectively relieves itch in aged mice. Our study thus unveils a novel molecular mechanism underlying senile pruritus.

Dorsal root ganglia CSF1+ neuronal subtypes have different impact on macrophages and microglia after spared nerve injury.

Colony-stimulating factor 1 (CSF1) is a growth factor secreted by dorsal root ganglia (DRG) neurons important for DRG macrophages and spinal cord (SC) microglia injury-induced proliferation and activation, specifically released after spared nerve injury (SNI). In this study, we investigated if SNI-induced CSF1 expression and perineuronal rings of macrophages around mouse DRG neurons vary between L3-L5 DRG and with the neuronal type, and if the CSF1+ neuronal projections at the SC dorsal horns were associated with an increased microglial number in the corresponding laminae. Seven days after surgery, L3-L5 DRG as well as their corresponding segments at the SC level were collected, frozen, and cut. DRG sections were double-immunostained using antibodies against CSF1 and NF200, CGRP or IB4, while SC sections were immunostained using a fluorescent Nissl Stain and analyzed for CX3CR1-GFP microglia number and distribution by an in-house ImageJ Plug-in. Our results showed that SNI-induced CSF1 expression was common for all subtypes of mouse DRG neurons, being responsible for attracting more resident macrophages around them in a DRG-dependent manner, with L4 showing the stronger response and CSF1+/NF200+ neurons showing the highest incidence. Even though the total number of microglia in the SC ipsilateral dorsal horns increased after SNI, the increase at their specific laminar projection sites did not mirror the incidence of DRG neuronal subtypes among CSF1+ neurons. Taken together, these results contribute to a more comprehensive understanding of the connection between CSF1 and macrophage/microglia response after SNI and emphasize the importance of considering L3-L5 DRG individually when investigating SNI-neuropathic pain pathogenesis in mice.

Sensory neuron LKB1 mediates ovarian and reproductive function

Treatments for reproductive disorders in women consist of hormone replacement therapy, which have negative side effects that impact health, spurring the need to understand new mechanisms to employ new therapeutic strategies. Bidirectional communication between sensory neurons and the organs they innervate is an emerging area of interest in tissue physiology with a relevance in reproductive disorders. We hypothesized that the metabolic activity of sensory neurons has a profound effect on reproductive phenotypes. To investigate this phenomenon, we utilized a murine model with conditional deletion of liver kinase B1 (LKB1), a serine/threonine kinase that regulates cellular metabolism in sensory neurons (Nav1.8cre; LKB1fl/fl). LKB1 deletion in sensory neurons resulted in reduced ovarian innervation from dorsal root ganglia neurons and increased follicular turnover compared to littermate controls. Female mice with this LKB1 deletion had significantly more pups per litter compared to wild-type females. Interestingly, the LKB1 genotype of male breeders had no effect on fertility outcomes, thus indicating a female-specific role of sensory neuron metabolism in fertility. In summary, LKB1 expression in peripheral sensory neurons plays an important role in modulating fertility of female mice via ovarian sensory innervation.

Automated production of nerve repair constructs containing endothelial cell tube-like structures

Engineered neural tissue (EngNT) is a stabilised aligned cellular hydrogel that offers a potential alternative to the nerve autograft for the treatment of severe peripheral nerve injury. This work aimed to automate the production of EngNT, to improve the feasibility of scalable manufacture for clinical translation. Endothelial cells were used as the cellular component of the EngNT, with the formation of endothelial cell tube-like structures mimicking the polarised vascular structures formed early on in the natural regenerative process. Gel aspiration-ejection for the production of EngNT was automated by integrating a syringe pump with a robotic positioning system, using software coded in Python to control both devices. Having established the production method and tested mechanical properties, the EngNT containing human umbilical vein endothelial cells (EngNT-HUVEC) was characterised in terms of viability and alignment, compatibility with neurite outgrowth from rat dorsal root ganglion neurons and formation of endothelial cell networksin vitro. EngNT-HUVEC manufactured using the automated system contained viable and aligned endothelial cells, which developed into a network of multinucleated endothelial cell tube-like structures inside the constructs and an outer layer of endothelialisation. The EngNT-HUVEC constructs were made in various sizes within minutes. Constructs provided support and guidance to regenerating neuritesin vitro. This work automated the formation of EngNT, facilitating high throughput manufacture at scale. The formation of endothelial cell tube-like structures within stabilised hydrogels provides an engineered tissue with potential for use in nerve repair.

A key role of PIEZO2 mechanosensitive ion channel in adipose sensory innervation.

Compared to the well-established functions of sympathetic innervation, the role of sensory afferents in adipose tissues remains less understood. Recent work revealed the anatomical and physiological significance of adipose sensory innervation; however, its molecular underpinning remains unclear. Here, using organ-targeted single-cell RNA sequencing, we identified the mechanoreceptor PIEZO2 as one of the most prevalent receptors in fat-innervating dorsal root ganglia (DRG) neurons. We found that selective PIEZO2 deletion in fat-innervating neurons phenocopied the molecular alternations in adipose tissue caused by DRG ablation. Conversely, a gain-of-function PIEZO2 mutant shifted the adipose phenotypes in the opposite direction. These results indicate that PIEZO2 plays a major role in the sensory regulation of adipose tissues. This discovery opens new avenues for exploring mechanosensation in organs not traditionally considered mechanically active, such as the adipose tissues, and therefore sheds light on the broader significance of mechanosensation in regulating organ function and homeostasis.

HC-HA/PTX3 from Human Amniotic Membrane Induced Differential Gene Expressions in DRG Neurons: Insights into the Modulation of Pain.

Background: The biologics derived from human amniotic membranes (AMs) demonstrate potential pain-inhibitory effects in clinical settings. However, the molecular basis underlying this therapeutic effect remains elusive. HC-HA/PTX3 is a unique water-soluble regenerative matrix that is purified from human AMs. We examined whether HC-HA/PTX3 can modulate the gene networks and transcriptional signatures in the dorsal root ganglia (DRG) neurons transmitting peripheral sensory inputs to the spinal cord. Methods: We conducted bulk RNA-sequencing (RNA-seq) of mouse DRG neurons after treating them with HC-HA/PTX3 (15 µg/mL) for 10 min and 24 h in culture. Differential gene expression analysis was performed using the limma package, and Gene Ontology (GO) and protein-protein interaction (PPI) analyses were conducted to identify the networks of pain-related genes. Western blotting and in vitro calcium imaging were used to examine the protein levels and signaling of pro-opiomelanocortin (POMC) in DRG neurons. Results: Compared to the vehicle-treated group, 24 h treatment with HC-HA/PTX3 induced 2047 differentially expressed genes (DEGs), which were centered on the ATPase activity, receptor-ligand activity, and extracellular matrix pathways. Importantly, PPI analysis revealed that over 50 of these DEGs are closely related to pain and analgesia. Notably, HC-HA/PTX3 increased the expression and signaling pathway of POMC, which may affect opioid analgesia. Conclusions: HC-HA/PTX3 induced profound changes in the gene expression in DRG neurons, centered around various neurochemical mechanisms associated with pain modulation. Our findings suggest that HC-HA/PTX3 may be an important biological active component in human AMs that partly underlies its pain inhibitory effect, presenting a new strategy for pain treatment.

Membrane lipid nanodomains modulate HCN pacemaker channels in nociceptor DRG neurons

Cell membranes consist of heterogeneous lipid nanodomains that influence key cellular processes. Using FRET-based fluorescent assays and fluorescence lifetime imaging microscopy (FLIM), we find that the dimension of cholesterol-enriched ordered membrane domains (OMD) varies considerably, depending on specific cell types. Particularly, nociceptor dorsal root ganglion (DRG) neurons exhibit large OMDs. Disruption of OMDs potentiated action potential firing in nociceptor DRG neurons and facilitated the opening of native hyperpolarization-activated cyclic nucleotide-gated (HCN) pacemaker channels. This increased neuronal firing is partially due to an increased open probability and altered gating kinetics of HCN channels. The gating effect on HCN channels is likely due to a direct modulation of their voltage sensors by OMDs. In animal models of neuropathic pain, we observe reduced OMD size and a loss of HCN channel localization within OMDs. Additionally, cholesterol supplementation inhibited HCN channels and reduced neuronal hyperexcitability in pain models. These findings suggest that disturbances in lipid nanodomains play a critical role in regulating HCN channels within nociceptor DRG neurons, influencing pain modulation.

Trpv1-lineage neuron-expressing Kcnq4 channel modulates itch sensation in mice.

Voltage-gated potassium channel subfamily q member 4 (Kcnq4) is predominantly expressed by hair cells and auditory neurons and regulates the neuronal excitability in the auditory pathway. Although it is further detected in myelinated large-diameter dorsal root ganglia (DRG) neurons in the periphery, the expression and function of Kcnq4 channel in nociceptors remains unknown. Here we showed that Kcnq4 is substantially expressed by unmyelinated small-diameter DRG neurons in both human and mouse. In spite of a dispensable role in acute pain and chronic skin inflammation, Kcnq4 is specifically involved in the regulation of scratching behavior through controlling action potential firing properties, evidenced by the increased neuronal excitability in small-diameter DRG neurons isolated from Kcnq4 deficient mice. Moreover, genetic ablation of Kcnq4 in Trpv1-positive neurons exacerbates both acute and chronic itch behavior in mice. Taken together, our results uncover a functional role of Trpv1-lineage neuron-expressing Kcnq4 channel in the modulation of itch-specific neuronal excitation in the periphery.

The epidermal growth factor receptor inhibitor gefitinib enhances in vitro and in vivo sensory axon regeneration and functional recovery following transection in a mouse median nerve injury model.

The epidermal growth factor receptor (EGFR; ErbB1), a membrane bound receptor tyrosine kinase, is hypothesized to have an inhibitory influence on peripheral nerve regeneration. This study examines the impact of EGFR inhibition on nerve regeneration using the commercially available small molecule inhibitor gefitinib. In vitro assays included neurite outgrowth of cultured dorsal root ganglion (DRG) neurons from adult C57Bl/6 wildtype mice on immobilized chondroitin sulfate proteoglycans (CSPG). Following forelimb median nerve injury, EGFR expression, number of regenerated neurons (using retrograde labeling) and myelination of motor and sensory neurons were compared between mice that received either gefitinib or vehicle. Functional recovery was assessed using grip strength. EGFR expression on DRG and spinal motor neurons was confirmed. Gefitinib significantly increased neurite outgrowth in medium sized (30-50 μm) DRG neurons, resulting in longer neurites (183 ± 36 μm) compared with CSPG alone (49 ± 9 μm). After median nerve injury, significantly greater numbers of sensory neurons (638 ± 112 vs. 301 ± 81), but not motor neurons (31 ± 12 vs. 42 ± 13) regenerated in animals treated with gefitinib compared with controls. Regenerated axons in gefitinib treated animals displayed significantly greater diameter and increased g-ratio compared with controls. Grip strength recovered more quickly in animals receiving gefitinib compared with controls (27.6 vs. 19.1 g 18 days post-injury). This study provides data supporting the role of EGFR as a negative regulator of sensory but not motor neuron regeneration. Further, it demonstrates versatile potential uses of existing pharmaceuticals.

Piezo1 Regulates Stiffness-Dependent DRG Axon Regeneration via Modifying Cytoskeletal Dynamics.

Despite medical interventions, the regenerative capacity of the peripheral nervous system is limited. Dorsal root ganglion (DRG) neurons possess the capacity to detect mechanical signals from their microenvironment, but the impact and mechanism by which these signals regulate axon regrowth and even regeneration in DRG neurons remain unclear. In this study, DRG neurons from newborn rats are cultured on substrates with varying degrees of stiffness in vitro to investigate the role of mechanical signals in axon regrowth. The findings reveal that substrate stiffness plays a crucial role in regulating axon regrowth, with an optimal stiffness required for this process. In addition, the data demonstrate that Piezo1, a mechanosensitive cation channel, detects substrate stiffness at the growth cone and regulates axon regrowth through activating downstream Ca2+-CaMKII-FAK-actin cascade signaling pathway. Interestingly, knocking down Piezo1 in adult rat DRG neurons leads to enhanced axon regeneration and accelerated recovery of sensory function after sciatic nerve injury. Overall, these findings contribute to the understanding of the role of mechanical signals in axon regeneration and highlight microenvironmental stiffness as a promising therapeutic target for repairing nerve injuries.

Pharmacologically enabling the degradation of NaV1.8 channels to reduce neuropathic pain.

In phase II clinical trials, NaV1.8 channels were identified as viable targets to treat acute pain. Results were modest, however, and NaV1.8 pore blockers must be given systemically, potentially leading to adverse effects, especially during prolonged use. A local, long-lasting approach is desirable, yet local anesthetics are neither specific nor long-lasting. In lieu of a pore blocker approach, we show a pharmacological method targeting the scaffolding and degradation of NaV1.8 channels, which attenuated neuropathic pain behavior in mice. NaV1.8 channels interact with the WW domain-containing scaffold protein called Magi-1. WW domains are typically found in ubiquitin ligases, and NaV1.8 channels are susceptible to degradation by ubiquitin ligases. Here, we show NaV1.8 and MAGI-1 colocalized in human tissues. We demonstrate that a lipidated peptide derived from the NaV1.8 WW binding domain, at sub-micromolar concentrations, inhibited rodent dorsal root ganglion neuronal firing. The peptide reduced NaV1.8 channel immunoreactivity and tetrodotoxin-resistant currents in human dorsal root ganglion neurons. We found that the lipidated peptide attenuated neuropathic pain behaviors in mice for multiple weeks after a single injection. Our results reveal that the NaV1.8-targeted lipidated peptide provides local and sustained analgesia, serving as a viable alternative to NaV1.8 pore blockers.

Primary sensory neuron-derived miR-let-7b underlies stress-elicited psoriasis

Psoriasis, a chronic autoimmune skin condition with significant global morbidity, badly impairs patients’ quality of life. Stress has been identified as a prominent trigger for psoriasis, and effectively management of stress can ameliorate its pathological manifestations. However, the precise mechanisms by which stress influences psoriasis remain elusive. In this study, we found that mice subjected to chronic social defeat stress (CSDS) exhibit severer imiquimod (IMQ)-induced psoriasis with increased epidermal scaling, epidermal hyperplasia, number of epidermal ridges, itch, and skin inflammation than control mice. Mechanistic study reveals that CSDS leads to an elevated release of miR-let-7b, an endogenous ligand of Toll-like receptor 7 (TLR7), from the peripheral terminal of dorsal root ganglia (DRG) neurons into the skin. This process can stimulate skin-resident macrophages to release cytokines (such as IL-6 and TNF-a) and chemokines (such as MCP-1), subsequently promoting the recruitment of additional macrophages into the skin. Notably, the specific blockade of miR-let-7b in DRG neurons effectively relieve stress-induced exacerbations of psoriasis. Furthermore, intradermal injection of synthetic miR-let-7b can induce a psoriasis-like phenotype in wildtype mice, a phenomenon that can be countered by the application of a TLR7 antagonist. Additionally, microfluidic chamber coculture assays demonstrated that miR-let-7b released by DRG neurons activates macrophages via TLR7 expressed on these immune cells. Totally, this study found that stress-induced upregulation and release of miR-let-7b from DRG neurons stimulates macrophages to secrete more inflammatory cytokines and chemokines, thereby exacerbating skin inflammation and the psoriatic phenotype. These findings provide a potential therapeutic strategy targeting the miR-let-7b/TLR7 pathway to alleviate stress-induced exacerbation of psoriasis.

Direct Effects of the Janus Kinase Inhibitor Baricitinib on Sensory Neurons.

Therapeutically, the Janus kinase (Jak) 1/Jak2 inhibitor baricitinib reduces the pathology of rheumatoid arthritis and may also reduce pain. Here, we investigated whether baricitinib directly affects joint nociceptors. We recorded action potentials from nociceptive C- and A∂-fibers of the normal and inflamed knee joint in anesthetized rats to monitor their responses to innocuous and noxious joint rotation. In isolated and cultured dorsal root ganglion (DRG) neurons, we examined Stat3 activation using Western blots and monitored excitability using patch-clamp recordings. Intra-articular injection of baricitinib did not alter C- and A∂-fiber responses to innocuous and noxious rotations of the normal knee but reduced C-fiber responses to these stimuli in inflamed joints. Baricitinib prevented the increase in C-fiber responses to joint rotation evoked by interleukin (IL)-6 plus soluble interleukin-6 receptor (sIL-6R) but not the increase evoked by TNF. In DRG neurons, baricitinib blocked Stat3 activation by hyper-IL-6, and baricitinib or the Stat3 inhibitor Sta21 prevented induction of hyperexcitability by IL-6 plus sIL-6R. Thus, neuronal Jaks are involved in the generation of C-fiber hyperexcitability induced by inflammation and IL-6. Pain reduction by baricitinib may result, at least in part, from direct effects on joint nociceptors.

Deep RNA sequencing of human dorsal root ganglion neurons reveals somatosensory mechanisms.

Deep RNA sequencing of human dorsal root ganglion neurons reveals somatosensory mechanisms.