Characteristic alterations of cutaneous neurogenic factors in photoaged skin

Although it has been recognized that photoageing and chronological ageing differ in various morphological and biological aspects, the characteristic alterations of cutaneous neurogenic factors in photoaged skin are poorly characterized.

To characterize cutaneous neurogenic factors, including innervation, neuropeptides, nerve growth factor and interactions of mast cells, in photoaged skin.

Paired biopsy specimens were obtained from sun-exposed volar forearm skin and from sun-protected dorsal upper arm skin of 20 elderly subjects. Various cutaneous neurogenic factors, including innervation, neuropeptides, neurokinin receptor, nerve growth factor, neurogenic inflammation and morphology of mast cells, were compared in sun-exposed vs. sun-protected skin quantitatively and qualitatively.

Cutaneous neurogenic factors associated with photoageing were characterized by a significant increase in the densities of dermal and intraepidermal nerve fibres, a correlation between epidermal innervation and the severity of photodamage, increases in the number of neuropeptidergic sensory nerve fibres in the dermis and in tissue levels of sensory neuropeptides, increases in the content of nerve growth factor, reduced expression of neurokinin receptor 1 by epidermal keratinocytes and by vascular endothelial cells and a tachykinin-specific reduction of cutaneous neurogenic inflammation. Mast cells in photodamaged skin showed several characteristic morphological features, including various degrees of activation and an intimate association with fibroblasts, which were distinct from those in sun-protected skin. Furthermore, mast cells in photodamaged skin possessed larger amounts of substance P within their granules than did those in sun-protected skin.

These findings document for the first time characteristic alterations of cutaneous neurogenic factors in photodamaged skin and suggest that the cutaneous nervous system may be involved in photoageing processes.