Increased melanogenesis in cultured epidermal melanocytes from patients with neurofibromatosis 1 (NF1)

Abstract

Melanocyte cultures from the normally pigmented skin of patients with neurofibromatosis 1 (NF 1) have a higher melanin content than those from the skin of healthy donors. An additional increase in the amount of melanin per cell was found in 5 out of 6 lines of melanocytes derived from café au lait macules of NF 1 patients. Omission of the tumor promoter phorbol-12-myristate-13-acetate from the culture medium brings about a comparable increase in the melanin content in all three kinds of melanocyte cultures. Cultures of NF 1 melanocytes show a higher tyrosine hydroxylase activity than those of control melanocytes, and incorporate larger amounts of dihydroxyphenylalanine than the latter. We conclude that melanogenesis in epidermis melanocytes is affected by defective alleles of the NF 1 gene. Our findings do not contradict the hypothesis that the defect underlying NF 1 impairs the inhibition of a wild-type RAS oncogene by interfering with the GTPase-activating function of the NF 1 gene product.

Neurofibromin as a regulator of melanocyte development and differentiation

“…Cultured human melanocytes from the café-au-lait macules of NF1 patients have been shown to contain a higher melanin content than non-lesional melanocytes, consistent with increased melanogenesis in these cells (Kaufmann et al, 1991). Our results show both in purified and in mixed primary cultures a higher level of melanogenic gene expression in Nf1 +/-melanocytes than wild-type cells, providing nominal experimental support to the observation of an increased constitutive level of pigmentation in affected NF1 siblings (Riccardi, 1992).…”

Partial Blindness to Submicron Topography in <b><i>NF1</i></b> Haploinsufficient Cultured Fibroblasts Indicates a New Function of Neurofibromin in Regulation of Mechanosensoric

“…in cultured melanocytes [Kaufmann et al, 1991;Kemkemer et al, 2002;Jungbauer et al, 2004] and keratinocytes [Koivunen et al, 2000]. The reduced number of cytokeratin bundles in differentiating cultured NF1 +/-keratinocytes indicates a function of neurofibromin in the organization of cytoskeleton during the formation of cellular contacts [Koivunen et al, 2000].…”

“…In vitro, NF1 haploinsufficiency influences several cellular pathways. An altered proliferation was found in mast cells [Ingram et al, 2000], melanocytes [Kaufmann et al, 1991], fibroblasts, keratinocytes, osteoblasts, astrocytes [Jouhilahti et al, 2011], and endothelial cells [Wu et al, 2006]. The upregulated cell cycle and DNA repair pathways in NF1 +/-cells may promote the loss of the wild-type allele [Pemov et al, 2010].…”

“…Cell-type specific syntheses can be changed by NF1 haploinsufficiency, e.g. the production of melanin in melanocytes [Kaufmann et al, 1991;De Schepper et al, 2005], of osteopontin in osteoblasts [Li et al, 2009], of FGF-2, PDGF and midkine in Schwann cells [Mashour et al, 2001], or of collagen in fibroblasts [Yang et al, 2006]. Some NF1 +/-cells display more variable sizes and shapes than their NF1 +/+ counterparts, when they are cultured on surfaces with high stiffness such as Schwann cells [Rosenbaum et al, 2000], keratinocytes [Koivunen et al, 2000;Korkiamäki et al, 2002] or osteoclasts [Heervä et al, 2010;Stevenson et al, 2011].…”

In vitro modeling of hyperpigmentation associated to neurofibromatosis type 1 using melanocytes derived from human embryonic stem cells

“…Just how these defects in multiple signaling pathways cause the specific alterations of pigmentation originally observed in patients is not yet clear. Early histological analyses of human melanocytes retrieved from CALMs pointed to an overall increase in their number (12), in the size of pigment granules or melanosomes (13,14), or in the cell content in melanogenic factors (15). Mouse models of the disease were difficult to generate, because homozygous Nf1 −/− mice died in utero (16) and Nf1 +/− mice manifested neither pigmentation abnormalities nor neurofibromas (17,18).…”