TRANSFORMING-GROWTH-FACTOR-BETA INHIBITS APOPTOSIS INDUCED BY BETA-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 neuron s, and primary rat embryo hippocampal neurons (REHIPs) from degenerati on caused by incubation with beta-amyloid peptide (A beta). Here we pr esent evidence suggesting that TGF-beta interferes with an apoptotic p athway induced by A beta. TGF-beta pretreatment decreases the amount o f DNA laddering seen following A beta treatment in neuroblastoma cells , while in REHIPs, TGF-beta decreases the number of positive cells det ected in situ by Klenow labelling following A beta treatment. RT-PCR s hows that in REHIPs, A beta decreases mRNA expression of Bcl-2, as wel l as the ratio of Bcl-x(L)/Bcl-x(S), with little effect on Bar express ion. 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 ev en in the presence of A beta. This pattern of gene expression should f unction to decrease apoptosis. Similarly, RT-PCR analysis of mRNA prep ared from hNT cells shows that TGF-beta pretreatment before addition o f 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 alon e. In neuronal cell types treated with A beta, TGF-beta appears to reg ulate expression of genes in the Bcl-2 family to favor an anti-apoptot ic pathway. (C) 1998 Elsevier Science B.V. All rights reserved.