Down regulation of the dopamine biosynthesis pathway in the PC12 model of Huntington's disease. A: qRT-PCR was performed on samples from Q 23 and Q74 cells for 0, 1 and 5 days. All values are expressed as relative mRNA levels compared to expression levels of uninduced cells. SPR: Sepiapterin reductase, GCH1: GTP cyclohydroxylase 1, TH: Tyrosine hydroxylase, DDC: Dopa decarboxylase, DBH: Dopamine β-hydroxylase. * Significant differences between the day 1 and 5 days; * P < 0.05, **P < 0.005, ***P < 0.0005 student's t-test. Significant differences between Q23 on day 1 and Q74 on day 1; + P < 0.05, ++P < 0.005 student's t-test. B: Confocal microscopic images of Q23 and Q74 PC12 cells after 5 days of induction. Green represents huntingtin-GFP and red represents TH immunohistochemistry. In Q23 cells, both huntingtin and TH show a diffuse staining, while in Q74 cells, large aggregates are visible and a clear reduction of TH fluorescence. Scale bar = 25 μm. C: Western blot analysis on whole cell lysates of Q23 and Q74 cells with TH and β-actin as loading control. A clear reduction in TH level can be seen in the 5 day Q74 samples. D: HPLC measurements in whole cell lysates of Q23 and Q74 cells after 0, 1 and 5 days of huntingtin expression show a significant reduction in dopamine levels in the 5 day Q74 samples. (* P < 0.05, student's t-test).