Thyroid hormone induces cerebellar astrocytes and C6 glioma cells to secrete mitogenic growth factors

In this study, the effect of thyroid hormone (triiodothyronine, T-3) on the secretion of mitogenic growth factors in astrocytes and C6 glioma cells wa s examined. The proliferating activity of T-3 could be due, at least in par t, to the astrocyte secretion of acidic and basic fibroblast growth factor (aFGF and bFGF), tumor necrosis factor-beta, and transforming growth factor -beta. In contrast, the conditioned medium (CM) of T-3-treated C6 cells was mitogenic to this cell line only after hyaluronidase digestion, suggesting the impairment of growth factor mitogenic activity by hyaluronic acid. Fur thermore, the presence of bFGF was significantly greater in the CM of both T-3-treated astrocytes and T-3-treated C6 cells than in the corresponding c ontrol CM. These data show that T-3 induces cerebellar astrocytes to secret e mitogenic growth factors, predominantly bFGF, that could influence astroc yte and neuronal proliferation via autocrine and paracrine pathways.