Transforming growth factor-β inhibits apoptosis induced by β-amyloid peptide fragment 25-35 in cultured neuronal cells

Previously, we demonstrated that transforming growth factor-beta (TGF-beta) pretreatment protects neuroblastoma cell lines, human hNT neurons, and primary rat embryo hippocampal neurons (REHIPs) from degeneration caused by incubation with beta-amyloid peptide (A beta). Here we present evidence suggesting that TGF-beta interferes with an apoptotic pathway induced by A beta. TGF-beta pretreatment decreases the amount of DNA laddering seen following A beta treatment in neuroblastoma cells, while in REHIPs, TGF-beta decreases the number of positive cells detected in situ by Klenow labelling following A beta treatment. RT-PCR shows that in REHIPs, A beta decreases mRNA expression of Bcl-2, as well as the ratio of Bcl-x(L)/Bcl-x(S), with little effect on Bar expression. These changes are expected to promote apoptosis. When REHIPs are incubated with TGF-beta before addition of A beta, the Bcl-x(L)/Bcl-x(S) ratio and Bcl-2 levels are increased compared to cells treated with A beta alone. Again there is little effect on Bar expression. Western blotting and immunohistochemistry experiments also show that TGF-beta maintains increased levels of Bcl-2 and Bcl-x(L) protein in REHIPs even in the presence of A beta. This pattern of gene expression should function to decrease apoptosis. Similarly, RT-PCR analysis of mRNA prepared from hNT cells shows that TGF-beta pretreatment before addition of A beta maintains a higher level of Bcl-2 expression and an increased Bcl-x(L)/Bcl-x(S) ratio as compared to cells treated with A beta alone. In neuronal cell types treated with A beta, TGF-beta appears to regulate expression of genes in the Bcl-2 family to favor an anti-apoptotic pathway. (C) 1998 Elsevier Science B.V. All rights reserved.