Aims

In Huntington’s disease (HD), the mutant huntingtin (mHtt) accumulates as toxic aggregates in the brain, with deleterious effects on motor-coordination and cognitive functions. Reducing the levels of mHtt is therefore a promising therapeutic strategy. Previously we showed that selective inhibition of GSK-3 enhances mHtt clearance and improves motor and coordination abilities in the HD model of R6/2 mice. However, how GSK-3 impacts mHtt dynamics is not fully understood.

Methods

We established cell systems and primary neurons expressing mHtt, and conducted genetic and pharmacological manipulations to identify GSK-3-mediated down targets/pathways responsible for its deleterious activity toward accumulation of mHtt amounts and aggregates.

Results

GSK-3α isozyme has a prominent effect in accelerating mHtt aggregates as compared to that achieved with GSK-3α. GSK-3α reduced autophagosome biogenesis and inhibited autophagic flux. The use of deleted constructs of GSK-3α indicated that both N- and C-terminals are important for mHtt upregulation. Proteomic analysis further indicated that overexpression of GSK-3α altered cellular traffic, membrane transport, and mitochondria activity, while the use of GSK-3 inhibitor recovered expression levels of cellular structure- cell motility- and membrane transport- proteins that were sharply decrease by mHtt.

Conclusions

GSK-3α is a major player in accelerating the formation and abundance of mHtt aggregates. This involves impairment in autophagy, cellular traffic, and membrane transport. The importance of both N/C terminals of GSK-3α in this process suggests that unique protein-protein interactions are required for producing its maximal deleterious effect in boosting mHtt aggregates.