Neuronal Fc-epsilon receptor I contributes to antigen-evoked pruritus in a murine model of ocular allergy

Rootstocks and drought stress impact the composition and functionality of grapevine rhizosphere bacterial microbiota

The microbiota, a component of the plant holobiont, plays an active role in the response to biotic and abiotic stresses. Nowadays, with recurrent drought and global warming, a growing challenge in viticulture is being addressed by different practices, including the use of adapted rootstocks. However, the relationships between these practices, abiotic stress and the composition and functions of the rhizosphere microbiota remain to be deciphered. This study aimed to unravel the impact of five rootstocks, water management and the combination of both on the rhizosphere bacterial microbiota in grapevines using shotgun metagenomics approach. The results showed that drought impacted the diversity, composition and functionality of the rhizosphere bacterial community. The genera Mycolicibacterium, Mycobacterium and Rhodococcus, and the bacterial functions, including DNA damage repair, fatty acid synthesis, sugar and amino acid transport, oxidative stress reduction, toxin synthesis and detoxification of exogenous compounds were significantly enriched under drought conditions. Rootstocks also significantly affected the rhizosphere bacterial richness but its influence on diversity and functionality compared to water management was weaker. Some taxa and function could be linked to water managements applied. The interaction between rootstocks and water management further influenced the rhizosphere composition, especially under drought conditions, where distinct clustering was observed for specific rootstocks. The results highlight the importance of conducting multifactorial studies to better understand their impact on shaping functional rhizosphere bacterial communities. This study paves the way for future research on beneficial bacterial inoculation and genetic engineering of rootstock to cope with drought stress.

Sensory neuronal control of skin barrier immunity

Peripheral sensory neurons recognize diverse noxious stimuli, including microbial products and allergens traditionally thought to be targets of the mammalian immune system. Activation of sensory neurons by these stimuli leads to pain and itch responses as well as the release of neuropeptides that interact with their cognate receptors expressed on immune cells, such as dendritic cells (DCs). Neuronal control of immune cell function through neuropeptide release not only affects local inflammatory responses but can impact adaptive immune responses through downstream effects on T cell priming. Numerous neuropeptide receptors are expressed by DCs but only a few have been characterized, presenting opportunities for further investigation of the pathways by which cutaneous neuroimmune interactions modulate host immunity.

Nicotine Decreases Nerve Regeneration and Pain Behaviors via PTEN and Downstream Inflammation-Related Pathway in Two Rat Nerve Injury Models

Neuropathic pain is stubborn and associated with the peripheral nerve regeneration process. Nicotine has been found to reduce pain, but whether it is involved in the regulation of nerve regeneration and the underlying mechanism are unknown. In this study, we examined the mechanical allodynia thermal hyperalgesia together with the peripheral nerve regeneration after nicotine exposure in two rat neuropathic pain models. In the spinal nerve ligation model, in which anatomic nerve regeneration can be easily observed, nicotine reduced anatomic measures of regeneration as well as expression of regeneration marker growth-associated protein 43 (GAP43). In the tibial nerve crush model, nicotine treatment significantly suppressed GAP43 expression and functional reinnervation as measured by myelinated action potential and electromyography of gastrocnemius. In both models, nicotine treatment reduced macrophage density in the sensory ganglia and peripheral nerve. These effects of nicotine were reversed by the selective α7 nicotinic acetylcholine receptor (nAChR) blocker methyllycaconitine. In addition, nicotine significantly elevated expression of PTEN (the phosphatase and tensin homolog deleted on chromosome 10), a key player in both regeneration and pain. Pharmacological interference of PTEN could regulate GAP43 expression, pain-related behaviors, and macrophage infiltration in a nicotine-treated nerve crush model. Our results reveal that nicotine and its α7-nAChR regulate both peripheral nerve regeneration process and pain though PTEN and the downstream inflammation-related pathway.

Neuronal C-Reactive Protein/FcγRI Positive Feedback Proinflammatory Signaling Contributes to Nerve Injury Induced Neuropathic Pain

Neuropathic pain is difficult to treat in clinical practice, and the underlying mechanisms are insufficiently elucidated. Previous studies have demonstrated that the neuronal Fc-gamma-receptor type I (FcγRI) of the dorsal root ganglion (DRG) mediates antigen-specific pain. However, the mechanisms of neuronal FcγRI in neuropathic pain remain to be explored. Here, it is found that the activation of FcγRI-related signals in primary neurons induces neuropathic pain in a rat model. This work first reveals that sciatic nerve injury persistently activates neuronal FcγRI-related signaling in the DRG, and conditional knockout (CKO) of the FcγRI-encoding gene Fcgr1 in rat DRG neurons significantly alleviates neuropathic pain after nerve injury. C-reactive protein (CRP) is increased in the DRG after nerve injury, and CRP protein of the DRG evokes pain by activating neuronal FcγRI-related signals. Furthermore, microinjection of naive IgG into the DRG alleviates neuropathic pain by suppressing the activation of neuronal FcγRI. These results indicate that the activation of neuronal CRP/FcγRI-related signaling plays an important role in the development of neuropathic pain in chronic constriction injury (CCI) rats. The findings may provide novel insights into the neuroimmune responses after peripheral nerve injury and suggest potential therapeutic targets for neuropathic pain.

Biopolymers in Mucoadhesive Eye Drops for Treatment of Dry Eye and Allergic Conditions: Application and Perspectives

Dry eye syndrome and allergic conjunctivitis are the most common inflammatory disorders of the eye surface. Although eye drops are the most usual prescribed dosage form, they are characterized by low ocular availability due to numerous barrier mechanisms of the eye. The use of biopolymers in liquid ophthalmic preparations has numerous advantages, such as increasing the viscosity of the tear film, exhibiting bioadhesive properties, and resisting the drainage system, leading to prolonged retention of the preparation at the site of application, and improvement of the therapeutic effect. Some mucoadhesive polymers are multifunctional excipients, so they act by different mechanisms on increasing the permeability of the cornea. Additionally, many hydrophilic biopolymers can also represent the active substances in artificial tear preparations, due to their lubrication and moisturizing effect. With the modification of conventional ophthalmic preparations, there is a need for development of new methods for their characterization. Numerous methods for the assessment of mucoadhesiveness have been suggested by the literature. This review gives an overview related to the development of mucoadhesive liquid ophthalmic formulations for the treatment of dry eye and allergic conditions.

Astrocytic phosphatase and tensin homolog deleted on chromosome 10 regulates neuropathic pain by facilitating 3-hydroxy-3-methylglutaryl-CoA reductase-dependent cholesterol biosynthesis

ABSTRACT

Recent studies have noted the role of the phosphatase and tensin homolog deleted on chromosome 10 (PTEN) in developing neuropathic pain, but the underlying mechanisms are obscure. We found that PTEN was mainly expressed in astrocytes in the rat spinal cord and dramatically downregulated after chronic constriction injury (CCI). Intrathecal injection of a PTEN inhibitor induced pain-related behaviors in naive rats. By contrast, administration of a PTEN protector effectively mitigated CCI-induced pain. Adeno-associated virus-mediated overexpression of astrocytic PTEN in the spinal cord reduced glial activation and neuroinflammation and subsequently alleviated pain-related behaviors. Importantly, astrocyte-specific PTEN knockout ( Pten conditional knockout , Pten CKO) mice showed nociceptive sensitization and glial activation. Proteomic analysis revealed that PTEN overexpression upregulated at least 7 enzymes in the cholesterol biosynthesis pathway and the total cholesterol level in the spinal cord of CCI rats. Furthermore, PTEN directly interacted with enzymes, including 3-hydroxy-3-methylglutaryl-CoA reductase, in the cholesterol biosynthesis pathway. Astrocytic 3-hydroxy-3-methylglutaryl-CoA reductase overexpression alleviated both CCI-induced pain and mechanical allodynia in Pten CKO mice. Finally, cholesterol replenishment attenuated CCI-induced pain and suppressed spinal glial activation. Taken together, these findings imply that spinal astrocytic PTEN plays a beneficial role in CCI-induced pain by regulating cholesterol biosynthesis, and an increased level of PTEN may accelerate cholesterol biosynthesis and reduce glial activation, thereby alleviating neuropathic pain. Recovery of PTEN or cholesterol might be an effective therapeutic strategy for neuropathic pain.

Ambient ozone, and urban PM2.5 co-exposure, aggravate allergic asthma via transient receptor potential vanilloid 1-mediated neurogenic inflammation

Allergic asthma is the most common pulmonary inflammatory disease, and epidemiological studies have revealed that PM_2.5 or ambient ozone (O₃) exposure contribute to the higher prevalence of allergic asthma. Current experimental evidence focus principally on the pathogenic effect of exposure to a single air pollutant, ignoring the possible synergistic effect of combined exposure to a mix of these pollutants, which is a more realistic scenario. In this study, allergic mice and a nociceptor antagonist were used to explore the mechanisms of co-exposure to these two important air pollutants. Compared with exposure to either PM_2.5 or O₃, combined exposure to both greatly aggravated allergic asthma in a dose dependent manner, including increased airway hyperresponsiveness, goblet cell metaplasia, more severe airway inflammation and higher oxidative stress levels. In addition, co-exposure in the allergic mice resulted in elevation of the expression of transient receptor potential vanilloid 1 (TRPV1), and of the production of substance P (SP), which exacerbated lung inflammation by neurogenic inflammation. TRPV1 antagonist (capsazepine, CPZ) treatment for the co-exposed allergic mice, markedly attenuated TRPV1 expression and SP release, and reduced airway inflammation and oxidative damage, further alleviating airway hyperresponsiveness. We conclude that neuro-immune interactions might be involved in PM_2.5 and O₃ co-exposure aggravated allergic asthma.

Total IgE in tears accurately reflects the severity and predicts the prognosis of seasonal allergic conjunctivitis

Background

Although immunoglobulin E (IgE) increases significantly in tears and serum during seasonal allergic conjunctivitis (SAC), it is unclear whether tear total IgE can reflect the severity and prognosis of SAC more accurately than serum total IgE. We aimed to investigate the usefulness of measuring the total IgE in tears to evaluate the severity and determine the treatment of SAC.

Methods

This prospective, nonrandomized study involved 55 patients with SAC and 10 age‐ and sex‐matched healthy controls. Serum and tears were collected before and after treatment to analyze the total IgE. SAC patients received the same topical anti‐allergy treatment and were followed‐up every 2 weeks for 1 month. The relationship of tear and serum total IgE concentrations with pollen concentrations and symptom severity before and after treatment was assessed.

Results

The total IgE concentration in tears was higher in SAC patients than in healthy participants with significant correlations between tear and serum total IgE concentrations. The total IgE concentration in tears, but not in serum, correlated with the pollen concentration and severity of ocular symptoms and reactions in SAC. Treatment‐associated improvements in symptoms and reactions in SAC correlated with decreased concentrations of the tear total IgE. Patients with disease recurrence following treatment demonstrated significantly higher tear total IgE concentrations than patients with no recurrence.

Conclusion

The total tear IgE level can indicate the severity and predict the prognosis of SAC more accurately than the serum total IgE.

Neuronal FcεRIα directly mediates ocular itch via IgE-immune complex in a mouse model of allergic conjunctivitis

Background

Classical understanding of allergic conjunctivitis (ACJ) suggests that ocular itch results from a mast cell-dependent inflammatory process. However, treatments that target inflammatory mediators or immune cells are often unsatisfying in relieving the stubborn itch symptom. This suggests that additional mechanisms are responsible for ocular itch in ACJ. In this study, we aim to determine the role of neuronal FcεRIa in allergic ocular itch.

Methods

Calcium imaging was applied to observe the effect of IgE-immune complex in trigeminal neurons. Genomic FcεRIa knockout mice and adeno-associated virus (AAV) mediated sensory neuron FcεRIa knockdown mice were used in conjunction with behavioral tests to determine ocular itch. In addition, immunohistochemistry, Western blot and quantitative RT-PCR were used for in vitro experiments.

Results

We found that FcεRIα was expressed in a subpopulation of conjunctiva sensory neurons. IgE-IC directly activated trigeminal neurons and evoked acute ocular itch without detectible conjunctival inflammation. These effects were attenuated in both a global FcεRIa-knockout mice and after sensory neuronal-specific FcεRIa-knockdown in the mouse trigeminal ganglion. In an ovalbumin (OVA) induced murine ACJ model, FcεRIα was found upregulated in conjunctiva-innervating CGRP+ sensory neurons. Sensory neuronal-specific knockdown of FcεRIa significantly alleviated ocular itch in the ACJ mice without affecting the immune cell infiltration and mast cell activation in conjunctiva. Although FcεRIα mRNA expression was not increased by IgE in dissociated trigeminal ganglion neurons, FcεRIα protein level was enhanced by IgE in a cycloheximide-resistance manner, with concordant enhancement of neuronal responses to IgE-IC. In addition, incremental sensitization gradually enhanced the expression of FcεRIα in small-sized trigeminal neurons and aggravated OVA induced ocular itch.

Conclusions

Our study demonstrates that FcεRIα in pruriceptive neurons directly mediates IgE-IC evoked itch and plays an important role in ocular itch in a mouse model of ACJ. These findings reveal another axis of neuroimmune interaction in allergic itch condition independent to the classical IgE-mast cell pathway, and might suggest novel therapeutic strategies for the treatment of pruritus in ACJ and other immune-related disorders.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02417-x.

Nociceptor neurons promote IgE class switch in B cells

Nociceptors, the high-threshold primary sensory neurons that trigger pain, interact with immune cells in the periphery to modulate innate immune responses. Whether they also participate in adaptive and humoral immunity is, however, not known. In this study, we probed if nociceptors have a role in distinct airway and skin models of allergic inflammation. In both models, the genetic ablation and pharmacological silencing of nociceptors substantially reduced inflammatory cell infiltration to the affected tissue. Moreover, we also found a profound and specific deficit in IgE production in these models of allergic inflammation. Mechanistically, we discovered that the nociceptor-released neuropeptide Substance P help triggered the formation of antibody secreting cells and their release of IgE. Our findings suggest that nociceptors, in addition to their contributions to innate immunity, play a key role in modulating the adaptive immune response, particularly B cell antibody class switching to IgE.

Effects of CMYA1 overexpression on cardiac structure and function in mice

CMYA1 (cardiomyopathy-associated protein 1, also termed Xin) localizes to the intercalated disks (ICDs) of the myocardium and functions to maintain ICD structural integrity and support signal transduction among cardiomyocytes. Our previous study showed that CMYA1 overexpression impairs the function of gap junction intercellular communication processes. Successful model generation was verified based on PCR, western blot analysis, immunohistochemistry, and immunofluorescence analysis. Myocardial CMYA1 expression was confirmed at both the mRNA and the protein levels in the CMYA1-OE transgenic mice. Masson's trichrome staining and electron microscopy revealed myocardial fibrosis and uneven bead width or the interruption of ICDs in the hearts of the CMYA1-OE transgenic mice. Furthermore, the Cx43 protein level was reduced in the CMYA1-OE mice, and co-immunoprecipitation assays of heart tissue protein extracts revealed a physical interaction between CMYA1 and Cx43. Electrocardiogram analysis enabled the detection of an obvious ventricular bigeminy for the CMYA1-OE mice. In summary, analysis of our mouse model indicates that elevated CMYA1 levels may induce myocardial fibrosis, impair ICDs, and downregulate the expression of Cx43. The observed ventricular bigeminy in the CMYA1-OE mice may be mediated by the reduced Cx43 protein level.

Autoimmune regulation of chronic pain

Chronic pain is an unpleasant and debilitating condition that is often poorly managed by existing therapeutics. Reciprocal interactions between the nervous system and the immune system have been recognized as playing an essential role in the initiation and maintenance of pain. In this review, we discuss how neuroimmune signaling can contribute to peripheral and central sensitization and promote chronic pain through various autoimmune mechanisms. These pathogenic autoimmune mechanisms involve the production and release of autoreactive antibodies from B cells. Autoantibodies-ie, antibodies that recognize self-antigens-have been identified as potential molecules that can modulate the function of nociceptive neurons and thereby induce persistent pain. Autoantibodies can influence neuronal excitability by activating the complement pathway; by directly signaling at sensory neurons expressing Fc gamma receptors, the receptors for the Fc fragment of immunoglobulin G immune complexes; or by binding and disrupting ion channels expressed by nociceptors. Using examples primarily from rheumatoid arthritis, complex regional pain syndrome, and channelopathies from potassium channel complex autoimmunity, we suggest that autoantibody signaling at the central nervous system has therapeutic implications for designing novel disease-modifying treatments for chronic pain.

FcεR1-expressing nociceptors trigger allergic airway inflammation

BACKGROUND

Lung nociceptor neurons amplify immune cell activity and mucus metaplasia in response to an inhaled allergen challenge in sensitized mice.

OBJECTIVE

We sought to identify the cellular mechanisms by which these sensory neurons are activated subsequent to allergen exposure.

METHODS

We used calcium microscopy and electrophysiologic recording to assess whether vagal neurons directly respond to the model allergen ovalbumin (OVA). Next, we generated the first nociceptor-specific FcεR1γ knockdown (TRPV1^Cre::FcεR1γ^fl/fl) mice to assess whether this targeted invalidation would affect the severity of allergic inflammation in response to allergen challenges.

RESULTS

Lung-innervating jugular nodose complex ganglion neurons express the high-affinity IgE receptor FcεR1, the levels of which increase in OVA-sensitized mice. FcεR1γ-expressing vagal nociceptor neurons respond directly to OVA complexed with IgE with depolarization, action potential firing, calcium influx, and neuropeptide release. Activation of vagal neurons by IgE-allergen immune complexes, through the release of substance P from their peripheral terminals, directly amplifies T_H2 cell influx and polarization in the airways. Allergic airway inflammation is decreased in TRPV1^Cre::FcεR1γ^fl/fl mice and in FcεR1α^-/- mice into which bone marrow has been transplanted. Finally, increased in vivo circulating levels of IgE following allergen sensitization enhances the responsiveness of FcεR1 to immune complexes in both mouse jugular nodose complex ganglion neurons and human induced pluripotent stem cell-derived nociceptors.

CONCLUSIONS

Allergen sensitization triggers a feedforward inflammatory loop between IgE-producing plasma cells, FcεR1-expressing vagal sensory neurons, and T_H2 cells, which helps to both initiate and amplify allergic airway inflammation. These data highlight a novel target for reducing allergy, namely, FcεR1γ expressed by nociceptors.

Relevance of IgE, allergy and eye rubbing in the pathogenesis and management of Keratoconus

Keratoconus (KC) is an ectatic disease of the cornea characterized by localized thinning and protrusion causing irregular astigmatism, which can lead to significant visual impairment. KC has often been associated with allergy and/or atopy, which are immune-mediated inflammatory reactions primarily driven by IgE. A higher proportion of KC patients were reported to have history or suffer from systemic and/or ocular allergy with elevated allergen-specific IgE and/or total serum IgE. Eye rubbing, one of the risk factors for worsening of the disease and developing related complications in KC, is associated with IgE driven conditions. The current review enumerates and contextualizes the evidence related to IgE in mediating KC pathogenesis, including aberrant extra-cellular matrix remodeling. This review also discusses clinical strategies directed at modulating IgE-mediated responses in the management of KC, and the emerging academic and plausible clinical relevance of assessing serum and tear IgE (allergen-specific and total) status in improving the understanding of disease pathobiology, treatment planning, and prognosis.

Fcγ Receptor I-Coupled Signaling in Peripheral Nociceptors Mediates Joint Pain in a Rat Model of Rheumatoid Arthritis

OBJECTIVE

Rheumatoid arthritis (RA) is often accompanied by joint pain and inflammation. Previous studies have demonstrated that functional Fcγ receptor I (FcγRI) is expressed in dorsal root ganglion (DRG) neurons and might contribute to pain in rodent models of antigen-induced arthritis (AIA). This study was undertaken to elucidate the roles of nociceptive neuronal FcγRI-coupled signaling in the development of joint pain in AIA.

METHODS

RNA sequencing was used to investigate the transcriptome profile changes in the DRG in a rat model of AIA. A primary sensory neuron-specific Fcgr1a conditional-knockout (CKO) rat was established by crossing rats carrying a loxP-flanked Fcgr1a with a Pirt-specific Cre line. Behavioral, morphologic, and molecular studies were conducted to evaluate the differences between wild-type (WT) and CKO rats after AIA.

RESULTS

We first showed that AIA induced a transcriptome profile change in the DRG, involving a number of key proteins downstream of the FcγRI-related signaling pathway. Compared to the WT rats, both the IgG immune complex-induced acute pain and AIA-induced pain were alleviated in CKO rats. Moreover, the AIA-induced activation of FcγRI-related signaling in DRGs was significantly reduced in CKO rats. In addition, CKO rats showed attenuated joint swelling after AIA.

CONCLUSION

These results indicate that activation of FcγRI-coupled signaling in DRG neurons plays an important role in the development of joint pain in AIA. Our findings may provide novel insights into the interactions between the peripheral nervous system and the immune system in pathologic conditions and might suggest potential biotargets for the treatment of pain in RA.

Neurite outgrowth inhibitory levels of organophosphates induce tissue transglutaminase activity in differentiating N2a cells: evidence for covalent adduct formation

Organophosphate compounds (OPs) induce both acute and delayed neurotoxic effects, the latter of which is believed to involve their interaction with proteins other than acetylcholinesterase. However, few OP-binding proteins have been identified that may have a direct role in OP-induced delayed neurotoxicity. Given their ability to disrupt Ca²⁺ homeostasis, a key aim of the current work was to investigate the effects of sub-lethal neurite outgrowth inhibitory levels of OPs on the Ca²⁺-dependent enzyme tissue transglutaminase (TG2). At 1-10 µM, the OPs phenyl saligenin phosphate (PSP) and chlorpyrifos oxon (CPO) had no effect cell viability but induced concentration-dependent decreases in neurite outgrowth in differentiating N2a neuroblastoma cells. The activity of TG2 increased in cell lysates of differentiating cells exposed for 24 h to PSP and chlorpyrifos oxon CPO (10 µM), as determined by biotin-cadaverine incorporation assays. Exposure to both OPs (3 and/or 10 µM) also enhanced in situ incorporation of the membrane permeable substrate biotin-X-cadaverine, as indicated by Western blot analysis of treated cell lysates probed with ExtrAvidin peroxidase and fluorescence microscopy of cell monolayers incubated with FITC-streptavidin. Both OPs (10 µM) stimulated the activity of human and mouse recombinant TG2 and covalent labelling of TG2 with dansylamine-labelled PSP was demonstrated by fluorescence imaging following SDS-PAGE. A number of TG2 substrates were tentatively identified by mass spectrometry, including cytoskeletal proteins, chaperones and proteins involved protein synthesis and gene regulation. We propose that the elevated TG2 activity observed is due to the formation of a novel covalent adduct between TG2 and OPs.

Profiling of how nociceptor neurons detect danger - new and old foes

The host evolves redundant mechanisms to preserve physiological processing and homeostasis. These functions range from sensing internal and external threats, creating a memory of the insult and generating reflexes, which aim to resolve inflammation. Impairment in such functioning leads to chronic inflammatory diseases. By interacting through a common language of ligands and receptors, the immune and sensory nervous systems work in concert to accomplish such protective functions. Whilst this bidirectional communication helps to protect from danger, it can contribute to disease pathophysiology. Thus, the somatosensory nervous system is anatomically positioned within primary and secondary lymphoid tissues and mucosa to modulate immunity directly. Upstream of this interplay, neurons detect danger, which prompts the release of neuropeptides initiating (i) defensive reflexes (ranging from withdrawal response to coughing) and (ii) chemotaxis, adhesion and local infiltration of immune cells. The resulting outcome of such neuro-immune interplay is still ill-defined, but consensual findings start to emerge and support neuropeptides not only as blockers of T_H 1-mediated immunity but also as drivers of T_H 2 immune responses. However, the modalities detected by nociceptors revealed broader than mechanical pressure and temperature sensing and include signals as various as cytokines and pathogens to immunoglobulins and even microRNAs. Along these lines, we aggregated various dorsal root ganglion sensory neuron expression profiling datasets supporting such wide-ranging sensing capabilities to help identifying new danger detection modalities of these cells. Thus, revealing unexpected aspects of nociceptor neuron biology might prompt the identification of novel drivers of immunity, means to resolve inflammation and strategies to safeguard homeostasis.

CCL2/CCR2 signaling elicits itch- and pain-like behavior in a murine model of allergic contact dermatitis

Spontaneous itch and pain are the most common symptoms in various skin diseases, including allergic contact dermatitis (ACD). The chemokine (C-C motif) ligand 2 (CCL2, also referred to as monocyte chemoattractant protein 1 (MCP-1)) and its receptor CCR2 are involved in the pathophysiology of ACD, but little is known of the role of CCL2/CCR2 for the itch- and pain-behaviors accompanying the murine model of this disorder, termed contact hypersensitivity (CHS). C57BL/6 mice previously sensitized to the hapten, squaric acid dibutyl ester, applied to the abdomen were subsequently challenged twice with the hapten delivered to either the cheek or to the hairy skin of the hind paw resulting in CHS at that site. By 24 h after the 2nd challenge to the hind paw CCL2 and CCR2 mRNA, protein, and signaling activity were upregulated in the dorsal root ganglion (DRG). Calcium imaging and whole-cell current-clamp recordings revealed that CCL2 directly acted on its neuronal receptor, CCR2 to activate a subset of small-diameter, nociceptive-like DRG neurons retrogradely labeled from the CHS site. Intradermal injection of CCL2 into the site of CHS on the cheek evoked site-directed itch- and pain-like behaviors which could be attenuated by prior delivery of an antagonist of CCR2. In contrast, CCL2 failed to elicit either type of behavior in control mice. Results are consistent with the hypothesis that CHS upregulates CCL2/CCR2 signaling in a subpopulation of cutaneous small diameter DRG neurons and that CCL2 can activate these neurons through neuronal CCR2 to elicit itch- and pain-behavior. Targeting the CCL2/CCR2 signaling might be beneficial for the treatment of the itch and pain sensations accompanying ACD in humans.

Neuropathic symptoms of the ocular surface: dryness, pain, and itch

PURPOSE OF REVIEW

This review aims to describe the recent findings on epidemiology, pathophysiology, and management of neuropathic symptoms of the ocular surface, with a focus on potential similarities between sensations of dry eye, pain and itch.

RECENT FINDINGS

A narrative review of the literature was undertaken. Key references from research in dry eye, neuropathic symptoms of the ocular surface, ocular pain and itch, as well as general references on itch and pain neurobiology were included. Recent findings suggest aspects of dry eye, chronic ocular pain and itch symptomatology are driven by neuropathic pain mechanisms involving peripheral and central sensitization processes.

SUMMARY

Ocular dryness, pain, and itch are prevalent complaints with several of shared features. Multiple lines of evidence suggest that peripheral and central neuronal sensitization processes are involved in generating and maintaining ocular sensory symptoms. Research is warranted on the epidemiology of ocular sensations, molecular mechanisms involved in nociception and pruriception in the eye, electrophysiological alterations in animal models of eye conditions, and therapeutic modalities that can alleviate unpleasant ocular sensations.