Rosiglitazone Treatment Prevents Mitochondrial Dysfunction in Mutant Huntingtin-expressing Cells: POSSIBLE ROLE OF PEROXISOME PROLIFERATOR-ACTIVATED RECEPTOR-γ (PPARγ) IN THE PATHOGENESIS OF HUNTINGTON DISEASE

Peroxisome proliferator-activated receptor-γ (PPARγ) is a member of the PPAR family of transcription factors. Synthetic PPARγ agonists are used as oral anti-hyperglycemic drugs for the treatment of non-insulin-dependent diabetes. However, emerging evidence indicates that PPARγ activators can also prevent or attenuate neurodegeneration. Given these previous findings, the focus of this report is on the potential neuroprotective role of PPARγ activation in preventing the loss of mitochondrial function in Huntington disease (HD). For these studies we used striatal cells that express wild-type (STHdhQ⁷/Q⁷) or mutant (STHdhQ¹¹¹/Q¹¹¹) huntingtin protein at physiological levels. Treatment of mutant cells with thapsigargin resulted in a significant decrease in mitochondrial calcium uptake, an increase in reactive oxygen species production, and a significant decrease in mitochondrial membrane potential. PPARγ activation by rosiglitazone prevented the mitochondrial dysfunction and oxidative stress that occurred when mutant striatal cells were challenged with pathological increases in calcium. The beneficial effects of rosiglitazone were likely mediated by activation of PPARγ, as all protective effects were prevented by the PPARγ antagonist GW9662. Additionally, the PPARγ signaling pathway was significantly impaired in the mutant striatal cells with decreases in PPARγ expression and reduced PPARγ transcriptional activity. Treatment with rosiglitazone increased mitochondrial mass levels, suggesting a role for the PPARγ pathway in mitochondrial function in striatal cells. Altogether, this evidence indicates that PPARγ activation by rosiglitazone attenuates mitochondrial dysfunction in mutant huntingtin-expressing striatal cells, and this could be an important therapeutic avenue to ameliorate the mitochondrial dysfunction that occurs in HD.