Hsp70 and Hsp40 improve neurite outgrowth and suppress intracytoplasmic aggregate formation in cultured neuronal cells expressing mutant SOD1.

Mutations of the superoxide dismutase 1 (SOD1) gene cause familial amyotrophic lateral sclerosis (FALS). Intracytoplasmic aggregate formation consisting of mutant SOD1 is the histological hallmark of FALS. Since a previous report revealed that Hsp70 reduced aggregate formation and cell death in a cell model of FALS, here we examined the combined effects of Hsp70 and its cofactor, Hsp40, on a cell model of FALS. The combination of Hsp70 and Hsp40 reduced intracytoplasmic aggregates and markedly improved neurite outgrowth. They also prevented cell death to a relatively lesser extent. Neurite outgrowth was recognized almost exclusively in the cells without intracytoplasmic aggregates. Hsp70 and Hsp40 were upregulated in cells expressing mutant SOD1, and were colocalized with intracytoplasmic aggregates of mutant SOD1. These findings suggest that heat shock proteins (HSPs) promote neurite outgrowth by suppressing intracytoplasmic aggregate formation and restoring cellular dysfunctions. This is the first demonstration that overexpression of HSPs improved neurite outgrowth as it suppressed intracytoplasmic aggregate formation and cell death in a cultured neuronal cell model of FALS. These findings may provide a basis for the utilization of HSPs in developing a treatment for FALS. Copyright 2002 Elsevier Science B.V.