Controlled induction of paired helical filaments of the Alzheimer type in cultured human neurons, by glutamate and aspartate

Abstract

One characteristic histopathological feature of brains of patients with Senile Dementia of the Alzheimer Type (SDAT) is a neuronal change known as neurofibrillary degeneration. Ultrastructurally, this degeneration presents as aggregates of Paired Helical Filaments (PHFs). We have reported (De Boni and Crapper 1978) that brain affected with SDAT contains a factor which induces PHFs similar to those occurring in Alzheimer's disease, in human CNS neurons in vitro. We now report that PHFs may be induced in cultured, fetal human spinal cord lesions by factors other than extracts from brain affected by SDAT. Specifically, ultrastructural analyses have shown that PHFs closely similar to those found in SDAT are induced by the excitotoxic aminoacids, glutamate (Glu) and aspartate (Asp). PHFs were found with Glu and Asp in combination at 1.1 and 0.45 mM, respectively and by Glu alone at 2.2 mM, when added to the culture medium. Cultures grown and maintained in MEM Eagle medium without Glu and Asp were invariably composed of tightly packed neuropil with abundant synaptic contacts, were free of vacuolated somata or processes and did not exhibit the presence of PHFs. In contrast, cultures exposed to Glu and Asp invariably responded with the presence of vacuolated neuronal somata and degenerating neuronal processes containing intermediate filaments, frequently paired into PHFs. These induced PHFs are composed of intermediate filaments morphologically identical (diameter 10 ± 0.9 nm, n = 55) to neurofilaments. While the induced PHFs exhibit a range of periodicities (50–540 nm) with an overall mean period of 140 ± 68 nm (n = 245), approximately 4% are morphologically closely similar (mean period 76 ± 10 nm, n = 10) to those in SDAT. We conclude that the PHFs in this unique laboratory model most probably arise secondary to post-translational modifications of neurofilaments.