Induction of apoptosis in porcine thyroid follicles by transforming growthfactor beta 1 and epidermal growth factor

For thyroid cells in culture DNA fragmentation and morphological changes re lated to apoptosis were first described in dog thyroid cells after deprivat ion of serum, epidermal growth factor or thyrotropin. With intact porcine t hyroid follicles in three-dimensional culture, the effect of deprivation of growth factors and of incubation with transforming growth factor beta 1 (T GF-beta 1), epidermal growth factor (EGF), thyrotropin (TSH) or insulin-lik e growth factor I (IGF-I) on the incidence of apoptosis was studied. Thyroi d follicles were embedded in growth factor-depleted Matrigel and cultured i n serum-free medium with or without growth factors for 7 days followed by i ncubation for 4, 24 and 72 h with TGF-beta 1 (2 or 5 ng/mL). The percentage of apoptotic cells was determined by direct counting in electron-microscop y. Approximately 1% of apoptotic bodies could be detected in unstimulated f ollicles. This was unchanged in the presence of TSH (1 mU/mL) or IGF (10 ng /mL) but significantly increased up to 3.99 +/- 1.24% with 2 ng/mL of EGE A fter incubation with TGF-beta apoptosis increased dose-dependently to 4.05 +/- 0.67% with 2 ng/mL TGF-beta 1 and 5.16 +/- 1.75% with 5 ng/mL TGF-beta 1. The incidence of necrotic cells remained constant at about 1 to 2%. Prei ncubation of follicles with 2 ng/mL of EGF followed by incubation with 5 ng /mL TGF-beta 1 increased the rate of apoptic bodies up to 13.19 +/- 1.9%. W e conclude that growth factor depletion in thyroid follicles in three-dimen sional culture does not lead to apoptosis. TGF-beta 1, however, induces apo ptosis even in quiescent thyroid follicular cells and is significantly more pronounced in growing thyroid cells. EGF, which is a dedifferentiating gro wth factor for thyroid cells, also induces apoptosis. As EGF enhances TGF-b eta 1 mRNA and protein in thyroid follicular cells, the induction of apopto sis by EGF might also be due to TGF-beta 1. (C) Societe francaise de biochi mie et biologie moleculaire / Elsevier, Paris.