Expression of nerve growth factor mRNA and its translation products in the anagen hair follicle

The cellular localization of NGF mRNA and its translation products have been identified in ovine hair follicles. NGF mRNA was detected in the proliferating cells of the follicle bulb and differentiating cells of the suprabulbar region, but was absent from the outer root sheath. Western analysis revealed the presence of a 73 kDa NGF prohormone in extracts of ovine flank skin, but the mature 13 kDa NGF was absent. Immunohistochemical analysis with antibodies specific to mouse NGF and a pro-NGF specific domain localized the NGF prohormone to outer root sheath cells in the upper bulb region of the follicle, adjacent to the zone of keratinization. Antibody binding was also associated with the luminal epithelium of the apocrine sweat gland and the pilary canal of the follicle at its junction with the epidermis. These observations, together with the reported presence of high- and low-affinity NGF receptors in the follicle, implicate the NGF prohormone-responsive neuronal system in the regulation of hair growth.