CCN6 regulates mitochondrial function

Despite established links of CCN6, or Wnt induced signaling protein-3 (WISP3), with progressive pseudo rheumatoid dysplasia, functional characterization of CCN6 remains incomplete. In light of the documented negative correlation between accumulation of reactive oxygen species (ROS) and CCN6 expression, we investigated whether CCN6 regulates ROS accumulation through its influence on mitochondrial function. We found that CCN6 localizes to mitochondria, and depletion of CCN6 in the chondrocyte cell line C-28/I2 by using siRNA results in altered mitochondrial electron transport and respiration. Enhanced electron transport chain (ETC) activity of CCN6-depleted cells was reflected by increased mitochondrial ROS levels in association with augmented mitochondrial ATP synthesis, mitochondrial membrane potential and Ca(2+) Additionally, CCN6-depleted cells display ROS-dependent PGC1α (also known as PPARGC1A) induction, which correlates with increased mitochondrial mass and volume density, together with altered mitochondrial morphology. Interestingly, transcription factor Nrf2 (also known as NFE2L2) repressed CCN6 expression. Taken together, our results suggest that CCN6 acts as a molecular brake, which is appropriately balanced by Nrf2, in regulating mitochondrial function.