Figure 3. Acetylation of Mutant Htt at K444 Leads to Neuroprotection.

(A) Lentiviral expression of acetylation-resistant Htt (lenti-Htt571-72Q-KR) in primary corticostriatal cultures leads to increased toxicity compared to acetylated Htt (lenti-Htt571-72Q), as determined by caspase 3/7 activation. At least three independent experiments were performed; *p < 0.01.

(B) Protection from Htt toxicity by CBP requires acetylation of Htt at K444. Rat primary corticostriatal neurons were transfected with Htt590-97Q or Htt590-97Q-KR together with CBP-HAT or vector, and toxicity scored for at least 150 neurons per sample. Results of three independent experiments are expressed as means + SEM (p = 0.001).

(C) Acetylation of mutant Htt is protective in vivo in C. elegans. In animals expressing acetylated mutant Htt (Htt564-150Q) and CBP-HAT, the intact GFP-expressing ASH neuron (arrow, left upper panel) takes up the red fluorescent dye DiD (left middle and lower panels); no degeneration is detected. In contrast, in most animals expressing acetylation-resistant mutant Htt (Htt564-150Q-KR) and CBP-HAT, ASH neurons are GFP positive (arrow, right upper panel) and DiD negative (right middle and lower panels); neurodegeneration increases with K444R mutation. Consistent with previous studies, the ASI neurons (arrowheads) express less Htt protein, are less consistently affected by polyglutamine toxicity, and, hence, were not scored.

(D) Affected ASH neurons were scored and compared for Htt564-150Q + CBP and Htt564-150Q-KR + CBP. Average percentage degenerated ± SEM is shown for multiple independent strains (p = 0.0012, see Experimental Procedures for details).