Expanded ataxin-3 expression impairs mitochondrial complex II activity. The activities of complexes I, II, III and IV of the mitochondrial respiratory chain were determined spectrophotometrically in (A) mitochondrial extracts from undifferentiated and NGF-differentiated PC6-3 ataxin-3 Q28 and Q108 cell lines, (B) isolated brain mitochondria of 4-5 months wild-type or MJD homozygous transgenic mice, and (C) human lymphoblastic cell lines derived from MJD patients (JMMA, JMJW) or control individuals. Graph shows the mean ± SEM of 4-9 independent measurements of the mitochondrial complexes activities. The activities of mitochondrial complexes were normalised for citrate synthase activity. Statistical analysis: t p<0.05, compared to NGF-differentiated PC6-3 Ataxin-3 Q28 (Student's t-test).