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.