Expression of nerve growth factor in skin tissues and its effect on the proliferation of outer root sheath cells in cashmere goats

- NGF and TrkA levels in anagen were significantly higher than in catagen.
- NGF and TrkA were expressed in the epidermis, ORS, and IRS of hair follicles.
- NGF can regulate the proliferation of ORS cells through TrkA dependent pathways.

Nerve growth factor (NGF) is widely expressed in the nervous system and best understood for its neuronal function. The present study was designed to describe the characteristics of hair follicles and the expression pattern of NGF and its receptor, tyrosine kinase receptor (TrkA), in the skin of Liaoning cashmere goats during hair follicle cycling. Results of hematoxylin and eosin staining revealed that there was a high ratio of secondary to primary follicles, with more active secondary follicles during anagen phase than other phases. The results of quantitative real-time polymerase chain reaction and western blot showed that both NGF and TrkA mRNA and protein levels were persistently detected in the skin tissue during hair follicle cycling. Furthermore, NGF and TrkA mRNA and protein levels during anagen were significantly higher than that during catagen. Using immunohistochemistry, the especially high immunoreactivities of TrkA in the outer root sheath (ORS) and NGF in the internal root sheath (IRS) and ORS were observed during anagen of hair follicles. Meanwhile, NGF and TrkA immunoreactivities were also observed in the epidermis of cashmere goats at similar expression levels as hair follicles. ORS cells were isolated from secondary follicle, and NGF treatment experiments were also studied. Result show that 20 ng/mL or 100 ng/mL NGF could significantly promote the proliferation of ORS cells in vitro, but the promotion could be blocked by the addition of 20 ng/mL K252a, the inhibitor of TrkA. The present study indicates that NGF might be involved in the reconstruction and growth of hair follicles through TrkA tyrosine kinase dependent pathways.