SECOND MESSENGER SYSTEMS ON THE ACTIONS OF A-BETA ON HIPPOCAMPAL NEURONS

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Deposition of fibrillary beta-amyloid peptide (Abeta), the main component of amyloid plaques, is considered by most uccrent theories on Alzheimer's disease (AD) to be a key factor in the selective neuritic dystrophy and neuronal degeneration. Extracellular deposition of Abeta is thought to be one of the causes of AD pathology. The neural fibrillary tangles, cell loss, vascular damage, and dementia are presumed to follow as a direct result of this deposition. Accordingly, much of AD research focuses on understanding the molecular pathways for Abeta generation, on discovering factors affecting Abeta aggregation and deposition and on identifying the effects of Abeta at the cellular level. Most of our understanding concerning the effects of Abeta on cellular events is derived from research on cultured embryonic nerve cells, a preparation in an early stage of its maturation that cannot adequately resemble mature neurons that usually succumb to AD. In contrast, the preliminary experiments which will constitute the basis of the proposed studies, were obtained in acutely dissociated adult or aged hippocampal neurons. In these cells, intracellular second messenger- related pathways appear to mediate rapid cellular effects of Ab that may underlie some of the pathological consequences of the aggregated peptide. Acute exposure of the neurons to Abetas dramatically enhanced NMDA channel function through a modulatory pathway distinct from known effects of Abetas including elevated Ca2+ influx, liberation of free radicals, or activation of tachykinin receptors. Based on these findings, the present proposal will address the following hypothesis: intracellular second messenger pathways, including protein kinases or phosphatases, are activated by Abeta in adult or aged neurons. This project has four specific aims: 1) to identify protein kinases and phosphoprotein phosphatases activated or inhibited by Abeta; 2) to ascertain whether Abeta activates 2nd messenger systems common to other peptide receptors; 3) to determine the role and contribution of Ca2+ in the cellular and toxic actions of Abeta; and 4) to reveal the possible involvement of G-proteins and cyclic GMP in the cellular actions of Abeta. The study will use high resolution electrophysiological recordings in vitro in adult rodent CNS neurons, and in collaboration with Dr. Frautschy, it will assess the cellular damage produced by Abeta administration in vivo into the brains of mice null mutant for the intracellular Ca2+-binding proteins calbindin (CB) and parvalbumin (PV). By addressing the effects of Abeta on cellular second messenger functions in adult and aged nerve cells of the hippocampus and studying these novel actions of Abeta on cellular second messenger functions in adult and aged nerve cells of the hippocampus, and studying these novel actions on Abeta on NMDA channel activity in fully developed and aged neurons this proposal will identify intracellular second messenger pathways possibly involved in the actions of Abeta. An activation of second messenger cascades by Abeta may cause may lead, in the long run, to the neuronal dysfunction and the eventual degeneration associated with AD.