Protective Effect of Transforming Growth Factor- 1 on -AmyIoid Neurotoxicity in Rat H ippocampal Neurons

Neurodegeneration associated with Alzheimer’s disease is believed to involve toxicity to 3-amyloid (Af3) and related peptides. Treatment of cultured rat hippocampal neurons with A 1-40(1 p.M) or the active fragment A 25-35 (1 jiM) for 5 days led to a -40-50% decrease in neuronal viability. The hydrophilic antioxidant ascorbic acid (300 jiM) and the lipophilic antioxidant 2-mercaptoethanol (1 0 jiM) both protected significantly against A neurotoxicity. Despite the protective effects of these antioxidants, both acute and chronic treatments with Af3 25-35 did not increase production of superoxide anions, as monitored with the fluorescent probe hydroethidine. Similarly, overexpression of Cu/Zn-superoxide dismutase using adenovirus-mediated gene transfer did not protect against A 3 neurotoxicity. A 3 neurotoxicity, however, was prevented in cultures infected with a recombinant, replication-defective adenovirus overexpressing the Ca2 binding protein calbindin D28k. Transforming growth factor31 (TGF-pl) has been shown to protect neurons against both Ca2 and free radical-mediated neuronal degeneration. We found that Af3 neurotoxicity was significantly attenuated by single treatments with TGF31 (0.1-10 ng/ml) and prevented by repetitive treatments (1 0 ng/ml/day). The protective effects of TGF-(31 were associated with a preservation of mitochondrial potential and function, as determined with rhodamine-1 23-based microfluorimetry. Because both increased oxidative stress and pathophysiological Ca2 fluxes can impair mitochondrial function, preservation of mitochondrial potential by TGF1 could be directly associated with its protection against Af3 neurotoxicity. The ability of TGF-f31 to increase the expression of the anti-apoptotic proteins Bcl-2 and Bcl-xL is discussed in this context.