Nine autosomal dominant
spinocerebellar ataxias (SCAs) are caused by an abnormal expansion of CAG trinucleotide repeats that encodes a
polyglutamine (
polyQ) tract within different genes. Accumulation of aggregated
mutant proteins is a common feature of
polyQ diseases, leading to progressive neuronal dysfunction and degeneration. SCA type 3 (SCA3), the most common form of SCA worldwide, is characterized by a CAG triplet expansion in chromosome 14q32.1 ATXN3 gene. As accumulation of the mutated
polyQ protein is a possible initial event in the pathogenic cascade, clearance of aggregated
protein by
ubiquitin proteasome system (UPS) has been proposed to inhibit downstream detrimental events and suppress neuronal cell death. In this study, Chinese herbal medicine (CHM) extracts were studied for their
proteasome-activating,
polyQ aggregation-inhibitory and
neuroprotective effects in GFPu and ATXN3/Q 75 -GFP 293/SH-SY5Y cells. Among the 14 tested extracts, 8 displayed increased
proteasome activity, which was confirmed by
20S proteasome activity assay and analysis of ubiquitinated and fused GFP
proteins in GFPu cells. All the eight extracts displayed good aggregation-inhibitory potential when tested in ATXN3/Q 75 -GFP 293 cells. Among them,
neuroprotective effects of five selected extracts were shown by analyses of
polyQ aggregation, neurite outgrowth,
caspase 3 and
proteasome activities, and ATXN3-GFP,
ubiquitin, BCL2 and
BAX protein levels in neuronal differentiated ATXN3/Q 75 -GFP SH-SY5Y cells. Finally, enhanced
proteasome function, anti-oxidative activity and neuroprotection of
catalpol,
puerarin and
daidzein (active constituents of Rehmannia glutinosa and Pueraria lobata) were demonstrated in GFPu and/or ATXN3/Q 75 -GFP 293/SH-SY5Y cells. This study may have therapeutic implication in
polyQ-mediated disorders.