2 Neurofibromin-Deficient Schwann Cells Have Increased Lysophosphatidic Acid Dependent Survival and Migration – Implications for Increased Neurofibroma Formation and Growth During Pregnancy.

Abstract

Background: During pregnancy, neurofibromas often enlarge or develop for the first time in females with neurofibromatosis type 1 (NF1). Lysophosphatidic acid (LPA) is a prototypic lysophospholipid that has been implicated in tumor progression. LPA modulates cell migration and survival of Schwann cells (SCs), and interestingly, LPA is made in increasing concentrations throughout pregnancy. SCs are the tumorigenic cells in the development of neurofibromas in NF1. Given the temporal nature of LPA production and neurofibroma formation during pregnancy, we hypothesized that LPA may be a candidate molecule that promotes Schwann cell (SC) migration and survival and potentially plays a role in the increase in neurofibroma formation during pregnancy. Purpose: To define the potential role of LPA on the biochemical and cellular functions of Nf1−/− SCs. Methods: Murine SCs were isolated from WT and Nf1−/− dorsal root ganglia at embryonic day 13.5 and cultured in media containing glial growth factor. To measure SC motility, confluent SC monolayers were wounded and wound closure was monitored by time lapse microscopy following LPA stimulation. Flow cytometry (FACS) was used to quantitate the relative amount of filamentous actin per SC after LPA stimulation. LPA-dependent survival was measured by FACS using Annexin V/PI staining, and PI-3K activity was assessed by measuring Akt phosphorylation. Ras and small RhoGTPase effectors were evaluated by Western blot. Results: LPA preferentially promoted Ras-mediated Nf1−/− SC survival, migration, and F-actin reorganization and polymerization in Nf1−/− SCs as compared with WT SCs. LPA induced hyperactivation of Ras and its downstream effectors, Akt and Rac1. Addition of LY0294002, a potent PI-3K inhibitor, significantly reduced SC survival and migration in both WT and Nf1−/− cultures. Conclusions: We demonstrate that there is a gain in functions of LPA-mediated migration and survival of Nf1−/− SCs, which is dependent on the Ras/PI-3K signaling axis. As Ras is an intractable molecular target, inhibition of the PI-3K pathway may be a potential therapy for neurofibroma development and progression in NF1 patients. Furthermore, LPA is a candidate phospholipid that modulates excessive cell survival and invasiveness of Nf1−/− Schwann cells that potentially may contribute to neurofibroma development and progression in pregnant women with NF1.