We have recently shown that, in rat cerebellar granule cells, apoptosis triggered by KCl deprivation is associated with an amyloidogenic shift in the processing of amyloid precursor protein (APP) resulting in an increase of amyloid β‐protein (Aβ) secretion. To further investigate this issue we studied the relationship between secretion of APP metabolites (Aβ, APPs) and neuronal degeneration. We postulated that the endogenous products of the APP metabolism may modulate neuronal survival by an autocrine loop. Treatment of cerebellar granule cells with various antibodies raised against different epitopes of APPs and Aβ oppositely modulates low potassium apoptotic cell death. Antibodies specific for the N‐terminal of Aβ (4G8, 6E10, R3659) increased neuronal survival by 30% over controls. On the contrary, treatment of cultures undergoing apoptosis with the monoclonal antibody 22C11 directed against the APP N‐terminus reduced neuronal survival by 53%, suggesting that endogenous α‐APPs contribute to neuronal survival. Moreover low KCl culture medium, conditioned by cerebellar granule cells, attenuated the apoptotic process. This anti‐apoptotic effect was abolished by removal of APPs from the conditioned medium. Western blotting of APPs removed from the conditioned medium confirmed the presence of α‐APPs. These data indicate that APP cleavage products oppositely modulate neuronal survival through an autocrine loop and further strengthen an Alzheimer's disease pathogenetic scheme based on altered metabolism of APP.
1 Istituto di Neurobiologia, Consiglio Nazionale delle Ricerche, Via K. Marx 43, 00137 Rome, Italy
2 Instituto di Anatomia Umana, Universita' di Genova, Via De Toni 5 and 14, 16132 Genova, Italy
3 Dipartimento di Neuroscienze, Universita' di Genova, Via De Toni 5 and 14, 16132 Genova, Italy
4 Corresponding Author: Cinzia Galli
Acknowledgements: We wish to thank Professor S. Siminovich and Professor D. Mercanti for fruitful discussions and comments on the manuscript, and Dr M. Cozzolino for helpful advice and assistance. Polyclonal antibodies FCA3340 and FCA3542 were kindly provided by Dr Frederic Checler. The financial support of Telethon‐Italy (Grant n. E.579 to M.T. and n. E.855 to P.C.) is gratefully acknowledged. This work has also been supported by a grant MURST‐CNR Biotechnology Program L 95/95 (to P.C.)
Received 11 January 2000; accepted 17 February 2000