Platelet-derived growth factors and fibroblast growth factors are mitogens for rat Schwann cells.

Abstract

Abstract. Rat sciatic nerve Schwann cells in culture respond to a limited range of mitogens, including glial growth factor, transforming growth factors beta-1 and beta-2 (TGF-fll, TGF-/~2), some cell membrane-associated factors, and to agents such as cholera toxin and forskolin which raise intracellular levels of cAME These responses require the presence of FCS, which exhibits little or no mitogenic activity in the absence of other factors. However, we recently found that forskolin greatly potentiates the mitogenic signal from TGFs-/~I and/32, raising the possibility that cAMP might couple other factors to mitogenesis. We have therefore screened a range of candidate mitogens using DNA synthesis assays. Other than TGFs-fl and glial growth factor, none of the factors tested were mitogenic in the presence of 10% serum alone. With the addition of forskolin, however, porcine PDGF, human PDGF, acidic and basic FGF were potent mitogens for rat Schwann cells, stimulating DNA synthesis and increasing cell number. Cholera toxin and dibutyrylcyclicAMP, but not 1,9-dideoxyforskolin, can substitute for forskolin indicating that the mitogenic effect is mediated via adenylyl cyclase activation. Porcine PDGF gave half-maximal stimulation at 15 pM, and human PGDF an equivalent response at 1 nM. Basic FGF was half maximal at 5 pM, acidic FGF at 1 nM.The recognition of PDGFs and FGFs as mitogens for Schwann cells has many implications for the study of Schwann cell proliferation in the development and regeneration of nerves, and in Schwann cell tumorigenesis.S CHWANN cells, the glial cells of the peripheral nervous system, surround all peripheral nerve axons, and in the case of myelinated nerve fibers, elaborate the myelin sheaths necessary for fast impulse conduction. There are many important developmental and functional interactions between Schwann cells and axons. Of particular interest for this paper is the proliferation of Schwann cells in three contexts. During development, Schwann cells proliferate and migrate out along newly formed axons, surrounding them, and myelinating them in some cases (3,32). If the nerve is injured, through mechanical trauma, neurotoxins or demyelinating diseases for example, Schwann cells again proliferate to restore the integrity of the Schwann cell sheath and aid regeneration of functional nerve fibers (1, 42). Thirdly, Schwann cell tumors may arise on any peripheral nerve, as in the cases of Von Recklinghausen's neurofibromatosis, bilaterai acoustic neurofibromatosis, and spontaneous, nonhereditary acoustic neuromas (47). The origin and nature of the factors involved in these proliferative processes are poorly understood.Attempts to define the factors involved in Schwann cell proliferation have revealed positive responses by various types of Schwann cell in culture to a limited range of mitogens (38, 51), including a few polypeptide growth factors (35), molecules derived from central and peripheral nervous system membranes (13,28,37,39,43,44,49,53), and analogues of cAMP and agents, such as chole...

Notch and Schwann cell transformation

“…Similarly, abrogating Notch activity in NIH 3T3 cells promotes FGFdependent cellular transformation (Small et al, 2003). However, since FGF acts as a mitogen for rat Schwann cells (Davis and Stroobant, 1990), it is unlikely that Notch acts as a general antagonist of FGF signaling. While certain aspects of Notch's oncogenic effects can be mimicked in cultured cells, the mechanisms underlying these effects, including their cell type specificity, are largely unknown.…”

Evaluation and management of peripheral nerve injury

“…After injury, macrophages migrate into the distal stump and may be involved in initiating Schwann cell proliferation. Macrophages upregulate IL-1, which induces an increase in NGF transcription and NGF receptor density, and also secrete mitogens that trigger Schwann cell proliferation (Davis and Stroobant, 1990). Neural cell surface molecules and the extracellular matrix molecules laminin and tenascin are strongly upregulated by denervated Schwann cells and may foster axonal regeneration (Martini, 1994).…”

Mesenchymal Stem Cells and Umbilical Cord as Sources for Schwann Cell Differentiation: their Potential in Peripheral Nerve Repair

“…PDGF contributes to DNA synthesis and acts as a mitogen in Schwann cells [102]. Neuregulin, either heregulin or GGF, selectively induces Schwann cells from neural crest cells and promotes the survival and proliferation of Schwann cell progenitors [100].…”