Nerve growth factor increases the mitogenicity of certain growth factors for cultured human keratinocytes: A comparison with epidermal growth factor

Abstract

Newborn foreskin and adult skin keratinocytes (KTs) were cultured in 24-well plates using keratinocyte basal medium (KBM) either alone or supplemented with epidermal growth factor (EGF) or nerve growth factor (NGF), plus one of the following: insulin (INS), insulin-like growth factors (IGF)-1 or -2, transforming growth factor alpha (TGF alpha), basic fibroblast growth factor (bFGF). Culture was maintained until one group of cells reached about 30,000 cells/well, when cells were stained with crystal violet and the extracted dye used to quantify cell numbers. In some cases, cells were subjected to the hexosaminidase assay for enumeration. In KBM alone, EGF, IGF-1, IGF-2 and TGF alpha were mitogenic to newborn KTs. In addition, NGF increased the growth of adult KTs, possibly by mechanisms involving synergy with autocrine growth factors. EGF augmented the growth of newborn cells in the presence of each of the growth factors except TGF alpha, but adult cells exhibited only additive effects. In the presence of IGF-1 or IGF-2, NGF stimulated the growth of both newborn and adult cells by as much as 150% above purely additive increases in cell numbers. NGF amplifies the effects of most neurotrophic factors that are also KT mitogens and may therefore be significant in psoriatic lesions, where many of these factors are overexpressed, and in wound healing, in promoting KT growth.