D mGluR5 antagonism increases autophagy and prevents disease progression in the zQ175 mouse model of Huntington's disease

Huntington's disease (HD) is a neurodegenerative disease caused by an expansion in the huntingtin protein (also called Htt) that induces neuronal cell death with age. We found that the treatment of 12-month-old symptomatic heterozygous and homozygous zQ175 huntingtin knockin mice for 12 weeks with CTEP, a negative allosteric modulator of metabotropic glutamate receptor 5 (mGluR5), reduced the size and number of huntingtin aggregates, attenuated caspase-3 activity, and reduced both neuronal apoptosis and neuronal loss in brain tissue. Both motor and cognitive impairments were improved in CTEP-treated zQ175 mice. The reduction in huntingtin protein aggregate burden by CTEP correlated with the activation of an autophagy pathway mediated by the kinase GSK3., the transcription factor ZBTB16, and the autophagy factor ATG14. Inhibition of mGluR5 with CTEP also reduced the inhibitory phosphorylation of the autophagosome biogenesis-related kinase ULK1, increased the phosphorylation of the autophagy factor ATG13, and increased the abundance of the autophagy-related protein Beclin1 in homozygous zQ175 mice. The findings suggest that mGluR5 antagonism may activate autophagy through convergent mechanisms to promote the clearance of mutant huntingtin aggregates and might be therapeutic in HD patients.