ALTERATIONS IN NEURAL INTERMEDIATE FILAMENT ORGANIZATION - FUNCTIONALIMPLICATIONS AND THE INDUCTION OF PATHOLOGICAL-CHANGES RELATED TO MOTOR-NEURON DISEASE

The properties regulating the supramolecular organization of neural in termediate filament (NIF) networks have been investigated in cultured dorsal root ganglion (DRG) neurons, The studies described take advanta ge of the ability of endogenous NIF to incorporate purified biotinylat ed neurofilament triplet (NFT) proteins, NF-L, NF-M and NF-H, When inj ected at concentrations of 0.8-1.0 mg/ml injection buffer, each of the se proteins is incorporated without perturbing the endogenous NIF netw ork, However, at progressively higher concentrations, NF-H induces the aggregation and accumulation of NIF in the cell body. Subsequent to t he induction of these aggregates, numerous alterations in the cytoarch itecture of neurons can be detected, The latter occur in a temporal se quence which appears to begin with the fragmentation of the Golgi comp lex. At later times, accumulation of mitochondria within the proximal region of neurites, peripheralization of the nucleus, and a significan t decrease in neurite caliber become obvious, After longer time period s, the NIF aggregates are seen to react with an antibody which reveals abnormally phosphorylated NF-H, These observations demonstrate that a n imbalance in the normal stoichiometric relationships among the NFT p roteins rapidly alters the supramolecular organization of the NIF netw ork, These changes most likely reflect the normal functions of neurofi laments in cell shape and the organization and cytoplasmic distributio n of membranous organelles, interestingly, virtually all of these chan ges closely resemble those which have been reported in motor neuron di seases such as amyotrophic lateral sclerosis (ALS), These findings sug gest that cultured neurons can be used as models for more precisely de fining the relationships between the formation of NIF aggregates and t he sequence of cytopathological events which typify neurodegenerative diseases.