AGGREGATION OF NEUROFILAMENTS IN NF-L TRANSFECTED NEURONAL CELLS - REGENERATION OF THE FILAMENTOUS NETWORK BY A PROTEIN-KINASE-C INHIBITOR

Cytoplasmic inclusion bodies that are accumulations of neurofilaments are the pathological hallmark of many neurodegenerative diseases and h ave been produced in transgenic mice by overexpression of mouse (NF-L and NF-M; light and medium chains, respectively) and human (NF-M and N F-H; medium and heavy chains, respectively) neurofilament subunits. Th is report describes a neuronal culture model in which human NF-L was o verexpressed to produce cytoplasmic accumulations of neurofilaments wi thin cell bodies concomitant with the collapse of the endogenous neuro filament network. Electron microscopy showed that, within accumulation s, neurofilaments retained a filamentous structure. The culture model thus provides a novel system in which the effect on neurofilament accu mulations of manipulating protein phosphorylation can be studied. Trea tment of cells containing neurofilament accumulations with bisindolylm aleimide, a specific protein kinase C inhibitor, resulted in regenerat ion of the filamentous network; this effect was not due to a change in the level of transfected NF-L expression. These findings lend support to the suggestion that an impairment in the regulation of protein pho sphorylation may lead to the accumulation of neurofilaments seen in ne urodegenerative disease.