Schwann Cells From Human Neurofibromas Show Increased Proliferation Rates Under the Influence of Progesterone

Abstract

Neurofibromatosis type 1 (NF1) is a hereditary disease caused by mutations of the NF1 gene at 17q11.2. Loss of the NF1 gene product in Schwann cells leads to the development of benign nerve sheath tumors. These neurofibromas may occur at any time but tend to arise during periods of hormonal imbalance, suggesting that hormones influence neurofibroma growth. As steroid hormone levels rise during these times, we hypothesized that progesterone has proliferative effects on neurofibroma-derived Schwann cells. We chose specific medium conditions for selective proliferation of NF (ϩ/Ϫ) and NF (Ϫ/Ϫ) cells from human neurofibromas. Genetic characterization was not performed, but former works have shown that under the conditions used (ϩ/Ϫ) and (Ϫ/Ϫ) cells can be selected. Different progesterone concentrations were added at different days with BrdU-staining was performed to investigate proliferation rates and DAB-staining to identify a progesterone receptor. We could demonstrate that Schwann cells from human neurofibromas express progesterone receptors. These cells show elevated proliferation rates (highest in NF(Ϫ/Ϫ) cells) under progesterone, whereas normal human Schwann cells were not affected. These data suggest that progesterone plays an important role in the development of neurofibromas in NF1. (1). Thus, NF1 represents one of the most frequent hereditary diseases. The disease is characterized by typical clinical symptoms that were summarized in a "diagnostic criteria list" at a National Institutes of Health consensus conference in 1988 (2). Despite a markedly variable clinical expression, the hallmark feature of the disease is benign peripheral nerve sheath tumors termed neurofibromas. These tumors consist of a mixed cellular population that mainly consists of Schwann cells and fibroblasts but also contains a significant proportion of mast cells, perineurial, and endothelial cells (3). All NF1 patients will inevitably develop neurofibromas during their lifetime (1) but the number, size, and age of onset of these tumors are entirely unpredictable.Homozygous inactivation of the NF1 gene and subsequent loss of its gene product neurofibromin in Schwann cells has been identified as the primary step in a pathogenetic process that ultimately results in the development of neurofibromas (4,5). Many investigators (6,7) have stressed the fact that apart from mutations at NF1, various additional factors are necessary to enable neurofibroma formation. However, still very little is known about these additional factors, which might affect tumor development and growth in NF1.From a clinical view, dermal neurofibromas tend to develop in adolescence as well as during pregnancy. These are times of increased hormonal influence and it has to be postulated that steroid hormones might affect neurofibroma development.In this context, it is intriguing that progesterone-as a steroid hormone with numerous functions in the human body-has been shown to play an important role in myelin synthesis of Schwann cells. Jung-Testas et al. (8)...

What accounts for the variable responses to progesterone on Schwann cells from mice and humans—the species-specific influence or the paracrine effects from the tumor microenvironment?

“…12 There may be a differential cellular expression of progesterone receptors in humans and in mice, which could explain the observed differences in Schwann cell proliferation in each of these studies. Li et al 5 noted that they were unable to detect progesterone receptors in their xenografts, and we have also been unable to detect progesterone receptors in murine cells using western blot.…”

“…Mast cell, fibroblast and Schwann cell cultures were derived from wild type (WT) and Nf1 haploinsufficient (+/-) mice and WT, Nf1 +/-and Nf1 knock out (-/-) embryos using our established methodologies. [7][8][9] In contrast to studies reported in human cells and tissues, [4][5][6] progesterone did not show any positive impact on proliferation of Nf1 mutated murine cells. Furthermore, the addition of progesterone to the Schwann cell cultures abrogated the glial growth factor (GGF) mediated gain in Nf1 -/-Schwann cell proliferation.…”

Evolving Pattern with Age of Cutaneous Signs in Neurofibromatosis Type 1: A Cross-Sectional Study of 728 Patients

“…In histological studies, receptors of growth or steroid hormones have been described on cutaneous NF, reinforcing their potential role in NF growth [8]. In vitro progesterone was shown to induce a higher proliferation rate of NF1-derived Schwann cells in comparison with non-NF1 human Schwann cells [9,10]. …”

Clinical characteristics predicting internal neurofibromas in 357 children with neurofibromatosis-1: results from a cross-selectional study

“…Changes in steroid hormone production may affect the NF1 phenotype. Immunostaining studies have provided support for this hypothesis by identifying the progesterone receptor in neurofibromas [30]. Estrogen and progesterone increased the growth rate of MPNSTs xenografts in mice [31].…”