Rhes Deletion Prevents Age-Dependent Selective Motor Deficits and Reduces Phosphorylation of S6K in Huntington Disease Hdh150Q(CAG) Knock-In Mice

Huntington disease (HD) is a neurodegenerative disease caused by a CAG trinucleotide repeat expansion in the huntingtin (mHTT) protein. This expansion is thought to promote striatal atrophy by a combination of cell- and non-cell-autonomous processes, but the mechanisms are unclear. Previous evidence suggests that the striatal-enriched SUMO E3-like protein Rhes could play a pathological role in HD. Rhes interacts with, and SUMOylates, mHTT and promotes toxicity and Rhes deletion ameliorates the HD phenotype in cell and severe mouse models of HD. However, the effect of Rhes on less severe knock-in models of HD remains obscure. Here, we report that a Hdh(CAG)150 knock-in murine model of HD showed diminished body weight but no changes in locomotor coordination or activity at 80 and 100 weeks of age. Conversely, Rhes deletion did not impact the body weight or behaviors but caused a significant reduction of gait, clasping, and tremor behaviors in Hdh 150Q/150Q mice. Rhes deletion did not affect the loss of striatal DARPP-32 protein levels but abrogated the hyper ribosomal protein S6 kinase beta-1 (S6K) phosphorylation, which is a substrate for a mechanistic target of rapamycin complex 1 (mTORC1) signaling, in Hdh(CAG)150 mice. Interestingly, striatal Rhes protein levels were downregulated in the striatum of Hdh(CAG)150 mice, indicating a potential compensatory mechanisms at work. Thus, Rhes deletion prevents age-dependent behavioral deficits and diminishes hyperactive mTORC1-S6K signaling in Hdh(CAG)150 knock-in mice HD striatum.