Activation of peroxisome proliferator-activated receptor pathway stimulates the mitochondrial respiratory chain and can correct deficiencies in patients' cells lacking its components

Context: The mitochondrial respiratory chain (RC) disorders are the largest group of inborn errors of metabolism and still remain without treatment in most cases. Objective: We tested whether bezafibrate, a drug acting as a peroxisome proliferator-activated receptor (PPAR) agonist, could stimulate RC capacities. Design: Fibroblasts or myoblasts from controls or patients deficient in complex I (CI), complex III (CIII), or complex IV (CIV) were cultured with or without bezafibrate. Main Outcome Measures: Enzyme activities, mRNA and protein expression, and respiration rates were measured. Results: In control cells, bezafibrate increased the CI, CIII, and CIV enzyme activities (+42 to +52%), as well as RC mRNAs (+40 to +120%) and RC protein levels (+50 to +150%). Nine of 14 patient cell lines tested exhibited a significant increase in the activity of the deficient RC complex after bezafibrate treatment (+46 to +133%), and full pharmacological correction could be achieved in seven cell lines. Similar effects were obtained using a PPAR delta agonist. These changes were related to a drug-induced increase in the mutated mRNAs and RC protein levels. Finally, the molecular mechanisms by which the PPAR pathway could induce the expression of genes encoding structural subunits or ancillary proteins of the RC apparatus, leading to stimulate the activity and protein levels of RC complex, likely involved the PPAR gamma coactivator-1 alpha. Conclusions: This study suggests a rationale for a possible correction of moderate RC disorders due to mutations in nuclear genes, using existing drugs, and brings new insights into the role of PPAR in the regulation of the mitochondrial RC in human cells.