As we showed in HD patients' fibroblasts, we also found that chymotrypsin-like, PGPH, and trypsin-like proteasome activities were relatively decreasded in HD model striatal neurons, compared to the control striatal neurons, at both pre-differentiation (Seo and Isacson, unpublished data) and the neuronal post-differentiation stage. Here, CTRL is linked to Huntington disease.