Basic mechanisms of itch.

Pruritus (or itch) is an unpleasant sensation leading to a desire to scratch. In the epidermis, there are selective C or Aδ epidermal nerve endings that are pruriceptors. At their other ends, peripheral neurons form synapses with spinal neurons and interneurons. Many areas in the central nervous system are involved in itch processing. Although itch does not occur solely because of parasitic, allergic, or immunologic diseases, it is usually the consequence of neuroimmune interactions. Histamine is involved in a minority of itchy conditions, and many other mediators play a role: cytokines (eg, IL-4, IL-13, IL-31, IL-33, and thymic stromal lymphopoietin), neurotransmitters (eg, substance P, calcitonin gene-related peptide, vasoactive intestinal peptide, neuropeptide Y, NBNP, endothelin 1, and gastrin-releasing peptide), and neurotrophins (eg, nerve growth factor and brain-derived neurotrophic factor). Moreover, ion channels such as voltage-gated sodium channels, transient receptor potential vanilloid 1, transient receptor ankyrin, and transient receptor potential cation channel subfamily M (melastatin) member 8 play a crucial role. The main markers of nonhistaminergic pruriceptors are PAR-2 and MrgprX2. A notable phenomenon is the sensitization to pruritus, in which regardless of the initial cause of pruritus, there is an increased responsiveness of peripheral and central pruriceptive neurons to their normal or subthreshold afferent input in the context of chronic itch.

Do Merkel complexes initiate mechanical itch?

Itch is a common sensation which is amenable to disabling patients' life under pathological and chronic conditions. Shared assertion easily limits itch to chemical itch, without considering mechanical itch and alloknesis, its pathological counterpart. However, in recent years, our understanding of the mechanical itch pathway, particularly in the central nervous system, has been enhanced. In addition, Merkel complexes, conventionally considered as tactile end organs only responsible for light touch perception due to Piezo2 expressed by both Merkel cells and SA1 Aß-fibres - low threshold mechanical receptors (LTMRs) -, have recently been identified as modulators of mechanical itch. However, the tactile end organs responsible for initiating mechanical itch remain unexplored. The consensus is that some LTMRs, either SA1 Aß- or A∂- and C-, are cutaneous initiators of mechanical itch, even though they are not self-sufficient to finely detect and encode light mechanical stimuli into sensory perceptions, which depend on the entire hosting tactile end organ. Consequently, to enlighten our understanding of mechanical itch initiation, this article discusses the opportunity to consider Merkel complexes as potential tactile end organs responsible for initiating mechanical itch, under both healthy and pathological conditions. Their unsuspected modulatory abilities indeed show that they are tuned to detect and encode light mechanical stimuli leading to mechanical itch, especially as they host not only SA1 Aß-LTMRs but also A∂- and C-fibres.

New human in vitro co-culture model of keratinocytes and sensory neurons like cells releasing substance P with an evaluation of the expression of ZIKV entry receptors: A potent opportunity to test Zika virus entry and to study Zika virus' infection in neurons?

During the course of acute ZIKV infection, pruritus is a cardinal symptom widely documented in the literature. Its frequent association with dysesthesia and several dysautonomic manifestations, suggests a pathophysiological mechanism involving the peripheral nervous system. The aim of this study was to develop a functional human model to potentially able to be infected by ZIKV: by demonstrating the functionality on a new human model of co-culture of keratinocyte and sensory neuron derived from induced pluripotent stem cells using a classical method of capsaicin induction and SP release, and verify the presence of ZIKV entry receptor in these cells. Depending of cellular type, receptors of the TAMs family, TIMs (TIM1, TIM3 and TIM4) and DC-SIGN and RIG1 were present/detected. The cells incubations with capsaicin resulted in an increase of the substance P. Hence, this study demonstrated the possibility to obtain co-cultures of human keratinocytes and human sensory neurons that release substance P in the same way than previously published in animal models which can be used as a model of neurogenic skin inflammation. The demonstration of the expression of ZIKV entry receptors in these cells allows to considerate the potent possibility that ZIKV is able to infect cells.

Anatomical contacts between sensory neurons and epidermal cells: an unrecognized anatomical network for neuro-immuno-cutaneous crosstalk.

Sensory neurons innervating the skin are conventionally thought to be the sole transducers of touch, temperature, pain and itch. However, recent studies have shown that keratinocytes - like Merkel cells - act as sensory transducers, whether for innocuous or noxious mechanical, thermal or chemical stimuli, and communicate with intraepidermal free nerve endings via chemical synaptic contacts. This paradigm shift leads to consideration of the whole epidermis as a sensory epithelium. Sensory neurons additionally function as an efferent system. Through the release of neuropeptides in intimate neuroepidermal contact areas, they contribute to epidermal homeostasis and to the pathogenesis of inflammatory skin diseases. To counteract the dogma regarding neurocutaneous interactions, seen exclusively from the perspective of soluble and spreading mediators, this review highlights the essential contribution of the unrecognized anatomical contacts between sensory neurons and epidermal cells (keratinocytes, melanocytes, Langerhans cells and Merkel cells), which take part in the reciprocal dialogue between the skin, nervous system and immune system.

Keratinocytes Communicate with Sensory Neurons via Synaptic-like Contacts.

OBJECTIVE: Pain, temperature, and itch are conventionally thought to be exclusively transduced by the intraepidermal nerve endings. Although recent studies have shown that epidermal keratinocytes also participate in sensory transduction, the mechanism underlying keratinocyte communication with intraepidermal nerve endings remains poorly understood. We sought to demonstrate the synaptic character of the contacts between keratinocytes and sensory neurons and their involvement in sensory communication between keratinocytes and sensory neurons. METHODS: Contacts were explored by morphological, molecular, and functional approaches in cocultures of epidermal keratinocytes and sensory neurons. To interrogate whether structures observed in vitro were also present in the human epidermis, in situ correlative light electron microscopy was performed on human skin biopsies. RESULTS: Epidermal keratinocytes dialogue with sensory neurons through en passant synaptic-like contacts. These contacts have the ultrastructural features and molecular hallmarks of chemical synaptic-like contacts: narrow intercellular cleft, keratinocyte synaptic vesicles expressing synaptophysin and synaptotagmin 1, and sensory information transmitted from keratinocytes to sensory neurons through SNARE-mediated (syntaxin1) vesicle release. INTERPRETATION: By providing selective communication between keratinocytes and sensory neurons, synaptic-like contacts are the hubs of a 2-site receptor. The permanent epidermal turnover, implying a specific en passant structure and high plasticity, may have delayed their identification, thereby contributing to the long-held concept of nerve endings passing freely between keratinocytes. The discovery of keratinocyte-sensory neuron synaptic-like contacts may call for a reassessment of basic assumptions in cutaneous sensory perception and sheds new light on the pathophysiology of pain and itch as well as the physiology of touch. ANN NEUROL 2020;88:1205-1219.

Intra-epidermal nerve endings progress within keratinocyte cytoplasmic tunnels in normal human skin.

Intra-epidermal nerve endings, responsible for cutaneous perception of temperature, pain and itch, are conventionally described as passing freely between keratinocytes, from the basal to the granular layers of the epidermis. However, the recent discovery of keratinocyte contribution to cutaneous nociception implies that their anatomical relationships are much more intimate than what has been described so far. By studying human skin biopsies in confocal laser scanning microscopy, we show that intra-epidermal nerve endings are not only closely apposed to keratinocytes, but can also be enwrapped by keratinocyte cytoplasms over their entire circumference and thus progress within keratinocyte tunnels. As keratinocytes must activate intra-epidermal nerve endings to transduce nociceptive information, these findings may help understanding the interactions between the keratinocytes and nervous system. The discovery of these nerve portions progressing in keratinocyte tunnels is a strong argument to consider that contacts between epidermal keratinocytes and intra-epidermal nerve endings are not incidental and argue for the existence of specific and rapid paracrine communication from keratinocytes to sensory neurons.

Cutaneous nociception: Role of keratinocytes.

Recent years have brought an enhanced understanding of keratinocyte contribution to cutaneous nociception. While intra-epidermal nerve endings were classically considered as the exclusive transducers of cutaneous noxious stimuli, it has now been demonstrated that epidermal keratinocytes can initiate nociceptive responses, like Merkel cells do for the innocuous mechanotransduction. In the light of recent in vivo findings, this article outlines this paradigm shift that points to a not yet considered population of sensory epidermal cells.

What about physical contacts between epidermal keratinocytes and sensory neurons?

Recent studies have demonstrated that keratinocytes closely participate in sensory transduction, and therefore, intra-epidermal free nerve endings are not exclusive transducers of pain. This discovery implies the existence of close afferent communication from keratinocytes to sensory neurons. Although reciprocal interactions between keratinocytes and intra-epidermal free nerve endings via soluble mediators are well established, little attention has been paid to physical contacts between keratinocytes and intra-epidermal free nerve endings. This review proposes to consider the ultrastructural and functional knowledge of these contacts, in both human skin biopsies and keratinocyte-sensory neuron cocultures to speculate on the possible existence of synaptic contacts.

Innervation of the Male Breast: Psychological and Physiological Consequences.

Breasts, including the nipple and areola, have two functions: lactation and as an erogenous area. Male breasts are much less studied that those of women. In men, breasts have only an erotic function. Because there is dense and very well organized innervation of the nipple-areola complex in men, nipple erection occurs frequently and via different mechanisms from penile erection. Although it seems to be less important for men than for women and it is poorly studied, the erotic value of breast stimulation is notable. Consequently, there is a need to include this aspect in sexological and andrological studies and to preserve breasts and their innervation or to reconstruct them in cases of surgical intervention.

Pathophysiological Study of Sensitive Skin.

Sensitive skin is a clinical syndrome characterized by the occurrence of unpleasant sensations, such as pruritus, burning or pain, in response to various factors, including skincare products, water, cold, heat, or other physical and/or chemical factors. Although these symptoms suggest inflammation and the activation of peripheral innervation, the pathophysiogeny of sensitive skin remains unknown. We systematically analysed cutaneous biopsies from 50 healthy women with non-sensitive or sensitive skin and demonstrated that the intraepidermal nerve fibre density, especially that of peptidergic C-fibres, was lower in the sensitive skin group. These fibres are involved in pain, itching and temperature perception, and their degeneration may promote allodynia and similar symptoms. These results suggest that the pathophysiology of skin sensitivity resembles that of neuropathic pruritus within the context of small fibre neuropathy, and that environmental factors may alter skin innervation.

Breast implant-associated anaplastic large-cell lymphoma can be a diagnostic challenge for pathologists.

BACKGROUND: Primary anaplastic large-cell lymphoma (ALCL) occurring in women with breast implants is very rare. It is usually described as tumor cells infiltrating the periprosthetic capsule. These are most often revealed by a periprosthetic recurrent isolated effusion (seroma cavity), occurring late after implantation of the prosthesis. ALCL is more rarely a tumor or periprosthetic capsular contracture. CASE: We report a 66-year-old woman, initially diagnosed by cytological examination of breast effusion, in whom ALCL appeared two and a half months after the removal of a ruptured implant. Repeated biopsies of the periprosthetic capsule performed in parallel showed fibrous tissue, without tumor proliferation. Only meticulous histological examination of the total capsulectomy identified tumor cells as a thin and discontinuous layer along the inner surface of the capsule without capsular invasion. CONCLUSION: Awareness of the histological pattern of this new clinical entity is important. A total capsulectomy with a good sampling for microscopic examination should be conducted for any suspicion of breast implant-associated ALCL. Cytology-histology correlation is essential.

Transfer of the palmaris brevis motor branch to the thenar motor branch: A cadaveric preliminary study.

OBJECTIVE: High median nerve injuries can lead to poor distal recovery, especially poor functioning of median innervated thenar muscles involved in thumb opposition and palmar abduction. The palmaris brevis (PB) is a small subcutaneous muscle innervated by ulnar nerve. Innervation of the PB is in most of cases provided by the ulnar digital nerve to the little finger. The purpose of this study is to assess the feasibility of transferring the PB motor branch (PBMB) to the median nerve thenar motor branch (TMB), in order to allow for early restoration of thumb palmar abduction and opposition, through a preliminary cadaveric study. METHODS: Twenty-five cadaver upper limbs were dissected under magnification. The length of the PBMB and TMB, and their origin were recorded. Nerve transfer from PBMB to TMB was conducted, and evaluated on 2 parameters: surgical feasibility, and distance from the coaptation site to the recipient nerve muscle entry point. The PBMB and TMB were harvested, fixated in formalin, then embedded in paraffin. They were sectioned transversely, and stained with a combination of hematoxylin-eosin and Luxol fast blue. Myelinated axons were counted in each specimen and the donor-to-recipient axon ratio was recorded. RESULTS: The PBMB was constant and originated from the ulnar digital nerve of the little finger in all cases. The transfer from PBMB to TMB was feasible in all cases. Mean myelinated axon counts of PBMB and TMB were 253±142 and 356±198, respectively (p=0.06). The donor-to-recipient axon ratio was 1:1.41. The mean distance from coaptation of the PBMB to the recipient thenar muscles was 23.1±3.0mm. CONCLUSIONS: Based on our results, PBMB to TMB transfer is feasible. The PBMB has the advantage over other distal nerve transfer donors to be constant and superficial, allowing for an easier harvest. Moreover, this procedure does not sacrifice any intrinsic function of the hand, and the proximity of the PBMB with the carpal tunnel allows for a single incision procedure. Therefore, early restoration of the median innervated thenar muscles may be feasible by the PBMB to TMB transfer in cases of high median nerve lesions. LEVEL OF EVIDENCE: IV.

Identification of a novel population in high-grade oligodendroglial tumors not deleted on 1p/19q using array CGH.

Oligodendroglial tumors (ODTs) are primary tumors of the central nervous system that show recurrent codeletion of whole chromosome arms 1p and 19q. Non-1p/19q-deleted high-grade ODTs can present other genetic aberrations, CDKN2A deletion (9p21.3), EGFR amplification (7p11.2) and/or chromosome 10 loss, which are associated with a poor prognosis. The identification of these abnormalities allowed drafting a histo-molecular classification. The aim of this study was to precisely identify, using array CGH, the genomic hallmarks of these tumors, particularly those that are not deleted on 1p/19q. We studied 14 formalin-fixed paraffin-embedded high-grade ODTs using pangenomic oligonucleotide array CGH with an average resolution of 22.3 kb. The 1p/19q codeletion was found in five anaplastic oligodendrogliomas. The three genomic aberrations carrying a poor prognosis were found, most often associated, in five out of nine tumors not deleted on 1p/19q. In addition, four recurrent copy number alterations, involving genes that participate to cell growth and cycle, were found to be strongly associated in five tumors not deleted on 1p/19q: gain or amplification at 1q32.1 (MDM4, PIK3C2B genes), 12q14.1 (CDK4 gene), 12q14.3-q15 (MDM2 gene) and homozygous deletion at 22q13.1 (APOBEC3B gene). MDM2, MDM4, CDK4 and PIK3C2B are known for potentially being amplified or overexpressed in high-grade gliomas. However, the involvement of APOBEC3B, coding for mRNA edition enzyme, is described here for the first time. Our results show a strong association between these four alterations. Therefore, this can open a perspective for a novel subgroup in high-grade ODTs not deleted on 1p/19q.

[A silent-growing and fast-killing melanoma in a teenager]. / Un mélanome de progression insidieuse et rapidement fatale chez une adolescente.

Malignant melanoma is a relatively rare but potentially aggressive tumor in children and adolescents. We report the case of a metastatic malignant melanoma in a 17-year-old girl, first diagnosed on cytological features of a fine-needle lymph node aspiration and then histologically confirmed by both examination of the metastatic adenopathy and a clinically harmless skin lesion of the scalp, which harbored focal microscopic pattern of melanoma. A fluorescent in situ hybridization study revealed that both metastatic and primary cutaneous tumours contained the same and pejorative chromosomal aberration consisting in CCND1 amplification (11q13). This observation raises actual limits and challenges in the fields of diagnosis and treatment of fast-killing melanomas.

Merkel Cells Are Multimodal Sensory Cells: A Review of Study Methods.

Merkel cells (MCs) are rare multimodal epidermal sensory cells. Due to their interactions with slowly adapting type 1 (SA1) Aß low-threshold mechanoreceptor (Aß-LTMRs) afferents neurons to form Merkel complexes, they are considered to be part of the main tactile terminal organ involved in the light touch sensation. This function has been explored over time by ex vivo, in vivo, in vitro, and in silico approaches. Ex vivo studies have made it possible to characterize the topography, morphology, and cellular environment of these cells. The interactions of MCs with surrounding cells continue to be studied by ex vivo but also in vitro approaches. Indeed, in vitro models have improved the understanding of communication of MCs with other cells present in the skin at the cellular and molecular levels. As for in vivo methods, the sensory role of MC complexes can be demonstrated by observing physiological or pathological behavior after genetic modification in mouse models. In silico models are emerging and aim to elucidate the sensory coding mechanisms of these complexes. The different methods to study MC complexes presented in this review may allow the investigation of their involvement in other physiological and pathophysiological mechanisms, despite the difficulties in exploring these cells, in particular due to their rarity.

Gastric cancer cell death analyzed by live cell imaging of spheroids.

Gastric cancer (GC) is the third cause of cancer-related mortality worldwide and is often diagnosed at advanced stages of the disease. This makes the development of more comprehensive models and efficient treatments crucial. One option is based on repurposing already marketed drugs as adjuvants to chemotherapy. Accordingly, we have previously developed the combination of docetaxel and the cholesterol-lowering drug, lovastatin, as a powerful trigger of HGT-1 human GC cells' apoptosis using 2D cultures. Because 3D models, known as spheroids, are getting recognized as possibly better suited than 2Ds in toxicological research, we aimed to investigate the efficacy of this drug combination with such a model. We established monocellular spheroids from two human (GC) cell lines, HGT-1 and AGS, and bicellular spheroids from these cells mixed with cancer-associated fibroblasts. With these, we surveyed drug-induced cytotoxicity with MTT assays. In addition, we used the Incucyte live imaging and analysis system to follow spheroid growth and apoptosis. Taken together, our results showed that the lovastatin + docetaxel combination was an efficient strategy to eliminate GC cells grown in 2D or 3D cultures, lending further support in favor of repurposing lovastatin as an adjuvant to taxane-based anticancer treatment.

Sensitive Skin Syndrome: A Low-Noise Small-Fiber Neuropathy Related to Environmental Factors?

Background and Objectives: Patients frequently complain of mild, transient, unpleasant skin sensations that cannot be diagnosed as common neuropathies. Dermatologists have termed these symptoms "sensitive skin syndrome." This narrative review was performed for a better knowledge by other specialists. Databases and Data Treatment: Publications on pain in sensitive skin syndrome were obtained from PubMed. Results: There is a growing body of data supporting the concept that sensitive skin is a type of small-fiber neuropathy. The arguments are based on clinical data, a decrease in intra-epidermal nerve fiber density, quantitative sensory testing abnormalities and an association with irritable bowel syndrome and sensitive eyes. Sensitive skin is triggered by environmental factors. Sensitive skin is a frequent condition, with a lifetime prevalence of ~50% according to self-reports. Conclusions: Mild levels of skin pain or itch are frequently experienced by patients, who rarely report them. There is a need for a better knowledge of sensitive skin because it can be the first level of small-fiber neuropathies.