Nerve growth factor and the skin

Role of neuromediators in the development of skin inflammation in patients with atopic dermatitis

Neurotransmitters such as neuropeptides and neurotrophins can have an effect on the development of a skin inflammatory reaction and itching as well as condition of nerve fibers. Goal. To assess the expression of neuropeptides and neurotrophins in the skin of patients with atopic dermatitis. Materials and methods. Expression of neuropeptides of substance P and SP-R receptor, calcitonin gene-related peptide (CGRP) and CGRP-R receptor, neurotrophin (nerve growth factor) and TrkA receptor as well as amphiregulin enhancing the growth of nerve fibers and semaphorin-3A terminating the growth of nerve fibers was determined in the skin of patients with atopic dermatitis based on the immunohistochemistry analysis method. Expression of protein PGP9.5 being a marker of nerve fibers was also determined. Results. The authors discovered penetration of nerve fibers expressing substance P and CGRP into the epidermis in patients with atopic dermatitis. Expression of the nerve growth factor and amphiregulin was discovered in epidermis but no expression of semaphorin-3A was discovered. Conclusion. Nerve fibers expressing neuropeptides such as substance P and CGRP can penetrate into the epidermis in patients with atopic dermatitis, which can maintain the inflammatory reaction and itching in such patients. Expression of the growth factors (nerve growth factor and amphiregulin) can contribute to the growth of nerve fibers and their penetration into epidermis against the background of the absence of any expression of semaphorin-3A inhibiting their growth.

Neurotrophins in healthy and diseased skin

Neurotrophins (NT) belong to a family of structurally and functionally related proteins that, depending on the tissue context and the receptors involved, promote either neuronal cell survival and differentiation or cell death. NT, and in particular NGF, were first identified as neurotrophic factors supporting the synthesis and development of sensory neurons in the central and peripheral nervous system. It is now widely accepted that NT also act as growth factors in non-neuronal cells, including the skin. In the skin, most cell types are able to secrete and/or to respond to stimulation by NT, creating a unique network of molecular signaling in the cutaneous microenvironment. Moreover, many skin diseases have been associated with an involvement of a number of neural factors including NT, but less attention has been given to the role of NT as growth factors in the development of skin pathologies. This review summarizes currently data on the expression and function of NT and their receptors in several cell types in the skin. Moreover it focuses on the role of the skin NT network in two cutaneous conditions, melanoma and psoriasis where NT are clearly involved.

Neurotrophins and their receptors stimulate melanoma cell proliferation and migration

Melanoma is a highly aggressive skin tumor that originates in the epidermis from melanocytes. As melanocytes share with the nervous system a common neuroectodermal origin and express all neurotrophins (NTs), we evaluated the expression and function of NTs and their receptors in melanoma. We report that primary and metastatic melanoma cell lines synthesize and secrete all NTs. Moreover, melanoma cells express the low-affinity (p75NTR) and the high-affinity tyrosine kinase NT receptors (Trk). The inhibition of Trk receptors by either K252a or Trk/Fc chimeras prevents proliferation, indicating that autocrine NTs are responsible for this effect. NT-3, NT-4, and nerve growth factor (NGF) induce cell migration, with a stronger effect on metastatic cell lines. Transfection with p75NTR small interfering RNA (p75NTRsiRNA) or treatment with K252a inhibits NT-induced melanoma cell migration, indicating that both the low- and high-affinity NT receptors mediate this effect. All melanoma cell lines express the p75NTR coreceptor sortilin by which proNGF stimulates migration in melanoma cells, but not in cells transfected with p75NTRsiRNA. These results indicate that NTs, through their receptors, play a critical role in the progression of melanoma.

Neurotrophin-3 involvement in the regulation of hair follicle morphogenesis

Hair follicle epithelium and nervous system share a common ectodermal origin, and some neurotrophins can modulate keratinocyte proliferation and apoptosis. It is therefore reasonable to ask whether growth factors that control neural development are also involved in the regulation of hair follicle morphogenesis. Focusing on neurotrophin-3 (NT-3) and its high-affinity-receptor [tyrosine kinase C (TrkC)], we show that hair placode keratinocytes express TrkC mRNA and immunoreactivity early during murine hair follicle morphogenesis. In later stages of hair follicle development, TrkC mRNA, TrkC-, and NT-3-immunoreactivity are seen in keratinocytes of the proximal hair bulb as well as in dermal papilla fibroblasts. Compared with the corresponding wild-type animals, early stages of hair follicle morphogenesis are significantly accelerated in newborn NT-3 overexpressing mice, whereas these are retarded in newborn heterozygous NT-3 knockout (+/-) mice. These observations suggest that NT-3 is an important growth modulator during morphogenesis and remodeling of neuroectodermal-mesenchymal interaction systems like the hair follicle.

Expression of nerve growth factor and epidermal growth factor receptors in neural nevi with nevic corpuscles

The histogenesis of "nevic corpuscles" (NCs) in neural nevi is still controversial. Recent studies have revealed that nerve growth factors (NGFs) and other growth factors [that is, epidermal growth factor (EGF)] could have various paracrine and autocrine functions on Schwann cells and melanocytes. We examined the immunohistochemical expression of NGF and EGF receptors (r) in 15 cases of neural nevi containing NCs along with 37 cases of other benign and malignant melanocytic lesions without neural differentiation (total, 52). Section were prepared from formalin-fixed and paraffin-embedded tissues. Monoclonal antibodies to NGFr and EGFr were used with the Avidin-biotin-complex (ABC) technique. We found strong reactivity for NGFr in 14 of 15 neural nevi with a predilection for NCs, but only eight of 37 were positive in the other group of melanocytic lesions without neural differentiation (four Spitz nevi, two melanomas, and two compound nevi). EGFr expression was limited mainly to NCs in four cases of neural nevi. We conclude that neural differentiation and NC formation are associated with NGFr overexpression, whereas EGFr expression is only limited. The relative paucity of NGFr expression in other type of benign and malignant melanocytic lesions supports the view that neural "differentiation" is a distinct process in certain long-standing melanocytic nevi. We postulate that NGFr overexpression may be the result of the reactivation of oncofetal genes that could become manifest in either abnormal schwannian differentiation (as seen in neural nevi), in a neoplastic context (as seen in neural and melanocytic tumors).