Neurotransmitters, neuropeptides and their receptors interact with immune response in healthy and psoriatic skin

Sensory ASIC3 channel exacerbates psoriatic inflammation via a neurogenic pathway in female mice

Psoriasis is an immune-mediated skin disease associated with neurogenic inflammation, but the underlying molecular mechanism remains unclear. We demonstrate here that acid-sensing ion channel 3 (ASIC3) exacerbates psoriatic inflammation through a sensory neurogenic pathway. Global or nociceptor-specific Asic3 knockout (KO) in female mice alleviates imiquimod-induced psoriatic acanthosis and type 17 inflammation to the same extent as nociceptor ablation. However, ASIC3 is dispensable for IL-23-induced psoriatic inflammation that bypasses the need for nociceptors. Mechanistically, ASIC3 activation induces the activity-dependent release of calcitonin gene-related peptide (CGRP) from sensory neurons to promote neurogenic inflammation. Botulinum neurotoxin A and CGRP antagonists prevent sensory neuron-mediated exacerbation of psoriatic inflammation to similar extents as Asic3 KO. In contrast, replenishing CGRP in the skin of Asic3 KO mice restores the inflammatory response. These findings establish sensory ASIC3 as a critical constituent in psoriatic inflammation, and a promising target for neurogenic inflammation management.

Excimer light effect on neurogenic inflammation in active versus stable psoriasis lesions

Neurogenic inflammation, mediated by T helper 17 cell (Th17) and neurons that release neuropeptides such as substance P (SP), is thought to play a role in the pathogenesis of psoriasis. Excimer light is used in the treatment of psoriasis via induction of T cell apoptosis. The objective of this study is to study the effect of excimer light on active versus stable psoriasis and investigate the levels of substance P and its receptor in both groups. The study included 27 stable and 27 active psoriatic patients as well as 10 matched healthy controls. Clinical examination (in the form of local psoriasis severity index (PSI) and visual analogue scale (VAS)) was done to determine disease severity, level of itching, and quality of life. Tissue levels of SP and neurokinin-1 receptor (NK-1R) were measured by ELISA before and after 9 excimer light sessions in 43 patients. A statistically significant lower levels of PSI and VAS were reached after therapy with no significant difference between the stable and active groups. The mean tissue levels of SP before therapy were significantly higher than the control group. Lower levels of SP and NK-1 receptor were found after treatment overall and in each group. Excimer therapy can be effective for both stable and active plaque psoriasis and this effect could be partly through its role on ameliorating the neurogenic inflammation.

Electroacupuncture on Baihui (DU20) and Xuehai (SP10) acupoints alleviates psoriatic inflammation by regulating neurotransmitter substance P- Neurokinin-1 receptor signaling

Background

At present, acupuncture-related practices have been widely used to treat psoriasis. In our study, we investigated the effect and explored the mechanism of electroacupuncture (EA) on acupoints Baihui (DU20) and Xuehai (SP10) for the treatment of psoriasis.

Methods

Imiquimod-induced psoriasis-like mouse model was used in this study. Mice were treated with electroacupuncture at DU20 and SP10 (depth of 2-3 mm, frequency of 2/15 Hz, intensity of 0.5-1.0 mA, 10 min/day). The severity of psoriasis-like lesions for each group was assessed. In addition, histological analysis of the lesions were performed. The levels of inflammatory cytokines were determined using Elisa. The expression levels of Substance P (SP) and NK1R were measured using Western blotting. In addition, NK1R inhibitor was administrated to evaluate the target of electroacupuncture in our mouse model.

Results

Electroacupuncture significantly alleviated IMQ-induced skin lesions and epidermal thickness, accompanied with reduced keratinocyte proliferation, CD3+, CD4+, and CD8+ T cells infiltration. The reduced levels of inflammatory cytokines was observed after electroacupuncture treatment. In addition, electroacupuncture inhibited the expression levels of SP and NK1R. NK1R inhibitor could ameliorate lesional symptoms and suppress epidermal thickening and CD3+, CD4+, and CD8 + T cell infiltration.

Conclusions

Electroacupuncture relieved psoriasis-like inflammation and T cell infiltration. This therapeutic action was likely mediated by the modulation of Substance P and its receptor NK1R.

Molecular Mechanisms of Neurogenic Inflammation of the Skin

The skin, including the hypodermis, is the largest body organ and is in constant contact with the environment. Neurogenic inflammation is the result of the activity of nerve endings and mediators (neuropeptides secreted by nerve endings in the development of the inflammatory reaction in the skin), as well as interactions with other cells such as keratinocytes, Langerhans cells, endothelial cells and mast cells. The activation of TRPV-ion channels results in an increase in calcitonin gene-related peptide (CGRP) and substance P, induces the release of other pro-inflammatory mediators and contributes to the maintenance of cutaneous neurogenic inflammation (CNI) in diseases such as psoriasis, atopic dermatitis, prurigo and rosacea. Immune cells present in the skin (mononuclear cells, dendritic cells and mast cells) also express TRPV1, and their activation directly affects their function. The activation of TRPV1 channels mediates communication between sensory nerve endings and skin immune cells, increasing the release of inflammatory mediators (cytokines and neuropeptides). Understanding the molecular mechanisms underlying the generation, activation and modulation of neuropeptide and neurotransmitter receptors in cutaneous cells can aid in the development of effective treatments for inflammatory skin disorders.

Neural Regulation of Innate Immunity in Inflammatory Skin Diseases

As the largest barrier organ of the body, the skin is highly innervated by peripheral sensory neurons. The major function of these sensory neurons is to transmit sensations of temperature, pain, and itch to elicit protective responses. Inflammatory skin diseases are triggered by the aberrant activation of immune responses. Recently, increasing evidence has shown that the skin peripheral nervous system also acts as a regulator of immune responses, particularly innate immunity, in various skin inflammatory processes. Meanwhile, immune cells in the skin can express receptors that respond to neuropeptides/neurotransmitters, leading to crosstalk between the immune system and nervous system. Herein, we highlight recent advances of such bidirectional neuroimmune interactions in certain inflammatory skin conditions.

Immunologic aspects of migraine: A review of literature

Migraine headaches are highly prevalent, affecting 15% of the population. However, despite many studies to determine this disease's mechanism and efficient management, its pathophysiology has not been fully elucidated. There are suggested hypotheses about the possible mediating role of mast cells, immunoglobulin E, histamine, and cytokines in this disease. A higher incidence of this disease in allergic and asthma patients, reported by several studies, indicates the possible role of brain mast cells located around the brain vessels in this disease. The mast cells are more specifically within the dura and can affect the trigeminal nerve and cervical or sphenopalatine ganglion, triggering the secretion of substances that cause migraine. Neuropeptides such as calcitonin gene-related peptide (CGRP), neurokinin-A, neurotensin (NT), pituitary adenylate-cyclase-activating peptide (PACAP), and substance P (SP) trigger mast cells, and in response, they secrete pro-inflammatory and vasodilatory molecules such as interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF) as a selective result of corticotropin-releasing hormone (CRH) secretion. This stress hormone contributes to migraine or intensifies it. Blocking these pathways using immunologic agents such as CGRP antibody, anti-CGRP receptor antibody, and interleukin-1 beta (IL-1β)/interleukin 1 receptor type 1 (IL-1R1) axis-related agents may be promising as potential prophylactic migraine treatments. This review is going to summarize the immunological aspects of migraine.

The Dopamine Gene Receptors (DRD1-5) Expression Alteration in Psoriasis Patients

BACKGROUND

Psoriasis is a chronic inflammatory autoimmune disease that is considered linked to genetic and environmental factors such as stress. Since the neurotransmitter dopamine has a close association with stress configuration, it can be a candidate for relieving psoriasis representation. In addition to the CNS, immune cells can play a decisive role in regulating immune functions through dopamine synthesis and the expression of its receptors. Altered response of immune cells to dopamine as well as a distorted expression of dopamine receptors (DRs) in immune cells have been reported in some chronic inflammatory conditions.

OBJECTIVE

This study aims the evaluation of dopamine receptor (DR1-DR5) gene expression in mononuclear blood cells of psoriatic patients in comparison with normal individuals.

METHODS

We isolated peripheral mononuclear cells (PBMCs) from blood samples followed by total RNA extraction, cDNA synthesis, and real-time PCR using specific primer pairs.

RESULTS

We found that all types of DRs are expressed in the PBMCs of normal and psoriatic individuals. We also concluded that compared to controls, DR2 and DR4 were overexpressed in psoriasis patients while DR3 was low-expressed.

CONCLUSION

Increased expression of DR2 and DR4 along with decreased expression of DR3 in PBMCs of psoriasis patients not only provide new insight into the pathogenesis of psoriasis but may also be effective in designing future therapeutic strategies attributable to psoriasis.

Immunotherapy using Histobulin™ in psoriasis: A case report

There is no cure for psoriasis. A psoriasis patient was treated with Histobulin™. The patient's clinical symptoms and signs disappeared after the eighth injection and did not recur for more than 18 months. Histobulin™ was effective in the treatment of psoriasis and is suggested as a curative therapeutic for psoriasis.

There is no cure for psoriasis, and early treatment is recommended to improve skin manifestations and systemic inflammation, which can lead to comorbidities in various organs. Histobulin™ was effective and induced remission in a psoriasis patient.

Pruritus: A Sensory Symptom Generated in Cutaneous Immuno-Neuronal Crosstalk

Pruritus or itch generated in the skin is one of the most widespread symptoms associated with various dermatological and systemic (immunological) conditions. Although many details about the molecular mechanisms of the development of both acute and chronic itch were uncovered in the last 2 decades, our understanding is still incomplete and the clinical management of pruritic conditions is one of the biggest challenges in daily dermatological practice. Recent research revealed molecular interactions between pruriceptive sensory neurons and surrounding cutaneous cell types including keratinocytes, as well as resident and transient cells of innate and adaptive immunity. Especially in inflammatory conditions, these cutaneous cells can produce various mediators, which can contribute to the excitation of pruriceptive sensory fibers resulting in itch sensation. There also exists significant communication in the opposite direction: sensory neurons can release mediators that maintain an inflamed, pruritic tissue-environment. In this review, we summarize the current knowledge about the sensory transduction of pruritus detailing the local intercellular interactions that generate itch. We especially emphasize the role of various pruritic mediators in the bidirectional crosstalk between cutaneous non-neuronal cells and sensory fibers. We also list various dermatoses and immunological conditions associated with itch, and discuss the potential immune-neuronal interactions promoting the development of pruritus in the particular diseases. These data may unveil putative new targets for antipruritic pharmacological interventions.

Neuropeptide Cortistatin Regulates Dermal and Pulmonary Fibrosis in an Experimental Model of Systemic Sclerosis

INTRODUCTION

Scleroderma, or systemic sclerosis, is a complex connective tissue disorder characterized by autoimmunity, vasculopathy, and progressive fibrosis of the skin and internal organs. Because its aetiology is unknown, the identification of genes/factors involved in disease severity, differential clinical forms, and associated complications is critical for understanding its pathogenesis and designing novel treatments. Neuroendocrine mediators in the skin emerge as potential candidates. We investigated the role played by the neuropeptide cortistatin in a preclinical model of scleroderma.

METHODS

Dermal fibrosis was induced by repetitive intradermal injections of bleomycin in wild-type and cortistatin-deficient mice. The histopathological signs and expression of fibrotic markers were evaluated in the skin and lungs.

RESULTS

An inverse correlation between cortistatin levels and fibrogenic activation exists in the damaged skin and dermal fibroblasts. Bleomycin-challenged skin lesions of mice that are partially and totally deficient in cortistatin showed exacerbated histopathological signs of scleroderma, characterized by thicker and more fibrotic dermal layer, enlarged epidermis, and increased inflammatory infiltration in comparison to those of wild-type mice. Cortistatin deficiency enhanced dermal collagen deposits, connective tissue growth factor expression, loss of microvessels, and predisposition to suffer severe complications that co-occur with dermal exposition to bleomycin, including pulmonary fibrotic disease and increased mortality. Treatment with cortistatin mitigated these pathological processes.

DISCUSSION/CONCLUSION

We identify cortistatin as an endogenous break of skin inflammation and fibrosis. Deficiency in cortistatin could be a marker of poor prognosis of scleroderma and associated complications. Cortistatin-based therapies emerge as attractive candidates to treat severe forms of systemic sclerosis and to manage fibrosis-related side effects of bleomycin chemotherapy in oncologic patients.

Terrestrosin D ameliorates skin lesions in an imiquimod-induced psoriasis-like murine model by inhibiting the interaction between Substance P and Dendritic cells

BACKGROUND

Psoriasis is a psychosomatic immune skin disease with psychological factors contributing to the disease. Substance P (SP) is highly expressed in the psoriatic lesions of patients and is involved in pathological disease progression. Tribulus terrestris L. has been used as a Chinese herbal medicine for disease prevention for thousands of years. Terrestrosin D (TED) has been identified as the effective monomeric component of Tribulus terrestris L..

PURPOSE

We investigated whether TED could reverse imiquimod-induced psoriatic lesions, and then, investigated its potential mechanism of action both in vivo and in vitro.

METHODS

5% imiquimod cream was applied onto the backs of mice for 6 days to induce psoriasis-like skin lesions. The psoriatic area and severity index (PASI) was then used for scoring disease severity. Pathological changes and Ki-67 expression levels in skin lesions were measured using hematoxylin and eosin (H&E) and immunofluorescence staining after TED administration. The in vivo and in vitro expression levels of inflammatory cytokines, the ratio of DCs, and SP were measured using ProcartaPlex Mouse Cytokine panels, flow cytometry, and western blotting. Behavioral assessments were determined using the open field and elevated plus-maze (EPM) test.

RESULTS

TED decreased PASI scores, epidermal thickness, Ki-67 expression levels, the ratio of DCs in the spleen, and secretion of IL-12p70, IL-18, and TNF-α in imiquimod-induced psoriasis-like murine models. Furthermore, TED increased IL-10 secretion levels, improved behavior, and down-regulated the expression levels of SP. Additionally, TED inhibited the in vitro maturation and activation of SP-induced CD11c⁺ DCs and the release of IL-12p70 and IL-23.

CONCLUSION

TED reduced DCs maturation, down-regulated the expression levels of inflammatory factors, and improved skin lesions and behavior of psoriasis-like murine models by inhibiting the interaction between Substance P and Dendritic cells.

The hair follicle-psoriasis axis: Shared regulatory mechanisms and therapeutic targets

It has long been known that there is a special affinity of psoriasis for the scalp: Here, it occurs most frequently, lesions terminate sharply in frontal skin beyond the hair line and are difficult to treat. Yet, surprisingly, scalp psoriasis only rarely causes alopecia, even though the pilosebaceous unit clearly is affected. Here, we systematically explore the peculiar, insufficiently investigated connection between psoriasis and growing (anagen) terminal scalp hair follicles (HFs), with emphasis on shared regulatory mechanism and therapeutic targets. Interestingly, several drugs and stressors that can trigger/aggravate psoriasis can inhibit hair growth (e.g. beta-blockers, chloroquine, carbamazepine, interferon-alpha, perceived stress). Instead, several anti-psoriatic agents can stimulate hair growth (e.g. cyclosporine, glucocorticoids, dithranol, UV irradiation), while skin/HF trauma (Köbner phenomenon/depilation) favours the development of psoriatic lesions and induces anagen in "quiescent" (telogen) HFs. On this basis, we propose two interconnected working models: (a) the existence of a bidirectional "hair follicle-psoriasis axis," along which keratinocytes of anagen scalp HFs secrete signals that favour the development and maintenance of psoriatic scalp lesions and respond to signals from these lesions, and (b) that anagen induction and psoriatic lesions share molecular "switch-on" mechanisms, which invite pharmacological targeting, once identified. Therefore, we advocate a novel, cross-fertilizing and integrative approach to psoriasis and hair research that systematically characterizes the "HF-psoriasis axis," focused on identification and therapeutic targeting of selected, shared signalling pathways in the future management of both, psoriasis and hair growth disorders.

Immunomodulatory Properties of Host Defence Peptides in Skin Wound Healing

Cutaneous wound healing is a vital biological process that aids skin regeneration upon injury. Wound healing failure results from persistent inflammatory conditions observed in diabetes, or autoimmune diseases like psoriasis. Chronic wounds are incurable due to factors like poor oxygenation, aberrant function of peripheral sensory nervature, inadequate nutrients and blood tissue supply. The most significant hallmark of chronic wounds is heavily aberrant immune skin function. The immune response in humans relies on a large network of signalling molecules and their interactions. Research studies have reported on the dual role of host defence peptides (HDPs), which are also often called antimicrobial peptides (AMPs). Their duality reflects their potential for acting as antibacterial peptides, and as immunodulators that assist in modulating several biological signalling pathways related to processes such as wound healing, autoimmune disease, and others. HDPs may differentially control gene regulation and alter the behaviour of epithelial and immune cells, resulting in modulation of immune responses. In this review, we shed light on the understanding and most recent advances related to molecular mechanisms and immune modulatory features of host defence peptides in human skin wound healing. Understanding their functional role in skin immunity may further inspire topical treatments for chronic wounds.

Cutaneous Neuroimmune Interactions in Peripheral Neuropathic Pain States

Bidirectional interplay between the peripheral immune and nervous systems plays a crucial role in maintaining homeostasis and responding to noxious stimuli. This crosstalk is facilitated by a variety of cytokines, inflammatory mediators and neuropeptides. Dysregulation of this delicate physiological balance is implicated in the pathological mechanisms of various skin disorders and peripheral neuropathies. The skin is a highly complex biological structure within which peripheral sensory nerve terminals and immune cells colocalise. Herein, we provide an overview of the sensory innervation of the skin and immune cells resident to the skin. We discuss modulation of cutaneous immune response by sensory neurons and their mediators (e.g., nociceptor-derived neuropeptides), and sensory neuron regulation by cutaneous immune cells (e.g., nociceptor sensitization by immune-derived mediators). In particular, we discuss recent findings concerning neuroimmune communication in skin infections, psoriasis, allergic contact dermatitis and atopic dermatitis. We then summarize evidence of neuroimmune mechanisms in the skin in the context of peripheral neuropathic pain states, including chemotherapy-induced peripheral neuropathy, diabetic polyneuropathy, post-herpetic neuralgia, HIV-induced neuropathy, as well as entrapment and traumatic neuropathies. Finally, we highlight the future promise of emerging therapies associated with skin neuroimmune crosstalk in neuropathic pain.

Neurokinin receptors and their implications in various autoimmune diseases

Neurokinin receptors belong to the GPCRs family and are ubiquitously expressed throughout the nervous and immune systems. Neurokinin receptors in coordination with neurokinins playing an important role in many physiological processes, including smooth muscle contraction, secretion, proliferation, and nociception. They also contribute to various disease conditions such as inflammatory bowel disease, rheumatoid arthritis, multiple sclerosis, psoriasis, and cancer. Neurokinin receptors antagonist are potent and highly selective and showing success in treating chemotherapy-induced nausea and vomiting. In this review, discuss the various neurokinin receptor expression on immune cells and their importance in various inflammatory and autoimmune diseases and their therapeutic importance.

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The Neurokinin receptor is an important regulatory mechanism to control the neuronal and immune systems.

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Various neurokinin receptors (NK1R, NK2R, and NK3R) are expressed in neurons and cells of the immune system.

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Substance P (SP) controls the differentiation and function of immune cells.

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SP-NK1R receptor signaling shows substantial cross-talk between neuronal and immune systems in inflammation and autoimmunity.

Depressive-like behaviors in mice with Imiquimod-induced psoriasis

Psoriasis is not only a chronic inflammatory skin disease but also a psychosomatic disorder. Depression is one of the most common associated diseases, which aggravates psoriatic skin lesions and affects the life quality of patients. Clinical experiments establish a correlation between psoriasis and depression; however, the mechanisms yet unclear because only a few related studies are available. Therefore, to investigate whether imiquimod-induced psoriasis-like mice showed depressive-like behavior, 5% imiquimod cream was smeared on the back of mice to induce psoriasis-like skin lesions for 8 days. Consequently, the psoriasis area and severity index (PASI) score, epidermal thickness, expression of Ki67 and CD3⁺ T lymphocyte, the content of IL-12p70, IL-17A, and IL-23 in skin lesions were increased. The psoriasis-like mice presented significant changes in body mass. The sugar water preference rate, the central area distance and area time, and the content of 3,4-dihydroxyphenylaceticacid (DOPAC) and noradrenaline (NE) in the prefrontal cortex, 5-hydroxytryptamine (5-HT), adrenaline (Ad), and DOPAC in the hippocampus, and Ad and γ-aminobutyric acid (GABA) in the hypothalamus of psoriasis-like mice were significantly decreased. The results showed that after the application of imiquimod, depressive-like behaviors appeared in psoriasis-like mice, and the secretion of related neurotransmitters was disordered. Thus, these mice could be used as animal models for studying psoriasis complicated with depression symptoms.

The Role of Nociceptive Neurons in the Pathogenesis of Psoriasis

Psoriasis is a chronic inflammatory skin disease. Emerging evidence shows that neurogenic inflammation, induced by nociceptive neurons and T helper 17 cell (Th17) responses, has a fundamental role in maintaining the changes in the immune system due to psoriasis. Nociceptive neurons, specific primary sensory nerves, have a multi-faceted role in detecting noxious stimuli, maintaining homeostasis, and regulating the immunity responses in the skin. Therefore, it is critical to understand the connections and interplay between the nociceptive neurons and the immune system in psoriasis. Here, we review works on the altered innervation that occurs in psoriasis. We examine how these distinct sensory neurons and their signal transducers participate in regulating inflammation. Numerous clinical studies report the dysfunction of nociceptive neurons in psoriasis. We discuss the mechanism behind the inconsistent activation of nociceptive neurons. Moreover, we review how neuropeptides, involved in regulating Th17 responses and the role of nociceptive neurons, regulate immunity in psoriasis. Understanding how nociceptive neurons regulate immune responses enhances our knowledge of the neuroimmunity involved in the pathogenesis of psoriasis and may form the basis for new approaches to treat it.

Critical Neurotransmitters in the Neuroimmune Network

Immune cells rely on cell-cell communication to specify and fine-tune their responses. They express an extensive network of cell communication modes, including a vast repertoire of cell surface and transmembrane receptors and ligands, membrane vesicles, junctions, ligand and voltage-gated ion channels, and transporters. During a crosstalk between the nervous system and the immune system these modes of cellular communication and the downstream signal transduction events are influenced by neurotransmitters present in the local tissue environments in an autocrine or paracrine fashion. Neurotransmitters thus influence innate and adaptive immune responses. In addition, immune cells send signals to the brain through cytokines, and are present in the brain to influence neural responses. Altered communication between the nervous and immune systems is emerging as a common feature in neurodegenerative and immunopathological diseases. Here, we present the mechanistic frameworks of immunostimulatory and immunosuppressive effects critical neurotransmitters - dopamine (3,4-dihydroxyphenethylamine), serotonin (5-hydroxytryptamine), substance P (trifluoroacetate salt powder), and L-glutamate - exert on lymphocytes and non-lymphoid immune cells. Furthermore, we discuss the possible roles neurotransmitter-driven neuroimmune networks play in the pathogenesis of neurodegenerative disorders, autoimmune diseases, cancer, and outline potential clinical implications of balancing neuroimmune crosstalk by therapeutic modulation.