Merkel Cells as Putative Regulatory Cells in Skin Disorders: An In Vitro Study

Merkel cells (MCs) are involved in mechanoreception, but several lines of evidence suggest that they may also participate in skin disorders through the release of neuropeptides and hormones. In addition, MC hyperplasias have been reported in inflammatory skin diseases. However, neither proliferation nor reactions to the epidermal environment have been demonstrated. We established a culture model enriched in swine MCs to analyze their proliferative capability and to discover MC survival factors and modulators of MC neuroendocrine properties. In culture, MCs reacted to bFGF by extending outgrowths. Conversely, neurotrophins failed to induce cell spreading, suggesting that they do not act as a growth factor for MCs. For the first time, we provide evidence of proliferation in culture through Ki-67 immunoreactivity. We also found that MCs reacted to histamine or activation of the proton gated/osmoreceptor TRPV4 by releasing vasoactive intestinal peptide (VIP). Since VIP is involved in many pathophysiological processes, its release suggests a putative regulatory role for MCs in skin disorders. Moreover, in contrast to mechanotransduction, neuropeptide exocytosis was Ca2+-independent, as inhibition of Ca2+ channels or culture in the absence of Ca2+ failed to decrease the amount of VIP released. We conclude that neuropeptide release and neurotransmitter exocytosis may be two distinct pathways that are differentially regulated

Intraepidermal nerve fibres are not the exclusive tranducers of nociception

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The whole epidermis as the forefront of the sensory system

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Lifting the veil on the keratinocyte contribution to cutaneous nociception

International audienceAbstract Cutaneous nociception is essential to prevent individuals from sustaining injuries. According to the conventional point of view, the responses to noxious stimuli are thought to be exclusively initiated by sensory neurons, whose activity would be at most modulated by keratinocytes. However recent studies have demonstrated that epidermal keratinocytes can also act as primary nociceptive transducers as a supplement to sensory neurons. To enlighten our understanding of cutaneous nociception, this review highlights recent and relevant findings on the cellular and molecular elements that underlie the contribution of epidermal keratinocytes as nociceptive modulators and noxious sensors, both under healthy and pathological conditions

Emergence of New Concepts in Skin Physiopathology through the Use of in vitro Human Skin Explants Models

Background: This review summarizes uses and new applications for dermatological research of in vitro culture models of human skin explants (HSEs). In the last decade, many innovations have appeared in the literature and an exponential number of studies have been recorded in various fields of application such as process culture engineering, stem cell extractions methodology, or cell-to-cell interaction studies under physiological and pathological conditions, wound-healing, and inflammation. Most studies also concerned pharmacology, cosmetology, and photobiology. However, these topics will not be considered in our review. Summary: A better understanding of the mechanisms driving intercellular relationships, at work in the maintenance of 3D tissue architectures has led to the improvement of cell culture techniques. Many papers have focused on the physiological ways that govern in vitro tissue maintenance of HSEs. The analysis of the necessary mechanical stress, intercellular and cell-matrix interactions, allows the maintenance and prolonged use of HSEs in culture for up to 15 days, regardless of the great variability of study protocols from one laboratory to another and in accordance with the objectives set. Because of their close similarities to fresh skin, HSEs are increasingly used to study skin barrier repair and wound healing physiology. Easy to use in co-culture, this model allows a better understanding of the connections and interactions between the peripheral nervous system, the skin and the immune system. The development of the concept of an integrated neuro-immuno-cutaneous system at work in skin physiology and pathology highlighted by this article represents one of the new technical challenges in the field of in vitro culture of HSE. This review of the literature also reveals the importance of using such models in pathology. As sources of stem cells, HSEs are the basis for the development of new tissue engineering models such as organoids or optical clearing tissues technology. This study identifies the main advances and cross-cutting issues in the use of HSE

Cutaneous nociception: Role of keratinocytes

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New insights into the roles of myofibroblasts and innervation during skin healing and innovative therapies to improve scar innervation

International audienceDuring the resolution phase of normal skin wound healing, there is a considerable loss of various cell types, including myofibroblasts by apoptosis. Inappropriate delay of apoptosis, and thus increased survival of myofibroblasts, may be a factor leading to pathologies and excessive scarring. Considerable data now clearly suggest that innervation plays a major role in wound healing, including the modulation of fibroblast cellular activity. An abnormal level of neuromediators is implicated not only in the development of chronic wounds but also in excessive scar formation. Understanding interactions between neuromediators and myofibroblasts, allowing normal reinnervation and having adequate levels of neuromediators during the healing process are clearly important to avoid the appearance of pathological healing or fibrosis/scarring. The aim of this review was first to discuss the mechanisms leading to normal or excessive scarring and then to present the roles of innervation during wound healing. Finally, the latest therapeutic strategies to help wound repair and reinnervation after skin damage will be introduced. Advantages and limitations in the use of neuropeptides, growth factors and biomaterials will be discussed as well as the most recent studies on electrostimulation and the potential of targeting resident skin mesenchymal stem cells

Expression of neuroserpin, a selective inhibitor of tissue-type plasminogen activator in the human skin

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The evolution and use of skin explants: potential and limitations for dermatological research.

International audienceDifferent models have been developed to understand the biology of skin or to test pharmaceutical/cosmetic products. These models can be in vitro models that possess advantages such as mono and co-culture models in 2D, which are very reproducible, or organotypic models (skin explant and reconstructed skin) that present a 3D organisation. Animal or human in vivo models allow studies that are closer to reality. In virtuo models developed on computers control all known parameters and do not require animals. The major limitations of these models are the lack of 3D structure for in vitro culture, the variability of results from organotypic models, ethical problems inherent to human and animal tests and the presence of numerous unknown parameters in in virtuo systems. Despite their limitations, skin explants seem to be an interesting model for studies. Skin explants may be kept from a few hours to 10-14 days on supports or directly in culture medium. These explants are generally cultivated at 37 °C, 5% CO(2), preferentially in serum-free conditions. Three basic techniques are used to characterise these models: histological stains, proliferation, apoptosis and cytotoxicity tests. Skin explants could be a very convenient model to study wound-healing, inflammation processes, autoimmune diseases, malignant transformation, stress, ageing, and to serve as screening tests

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

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