This has allowed us to draw several important conclusions

hondrial biogenesis during adipogenesis, the relative contents of mitochondrial mtDNA were examined in 3T3-L1 cells upon PHB knockdown and adipocyte-differentiation induction. Our results showed that the contents of relative mtDNA were significantly increased in 3T3-L1 cells subject to adipogenic induction. The increments of mtDNA were partially suppressed upon PHB1- or PHB2- silencing in 3T3-L1 cells, whether or not subject to adipogenic induction. These results, in accordance with the observations in HeLa cells, suggest that PHBs are required in maintaining mitochondrial contents. Effects of PHB silencing on mitochondria in 3T3-L1 cells The ultrastructure of mitochondria in siRNA transfected 3T3L1 cells was examined using electron microscopy. We observed that the regular lamellar cristae in mitochondria were lost in siPHB1- or siPHB2-transfected 3T3-L1 cells, whereas siControl transfection did not affect the ultrastructure of mitochondria. To further investigate the effects of mitochondrial PHBs during adipogenesis, the mitochondrial purchase 518303-20-3 morphology of PHBsilencing 3T3-L1 cells was compared before and after adipogenic induction. MitoTracker analysis revealed that, instead of normally tubular mitochondria, about 40% of the PHB1 or PHB2 knockdown cells consisted of fragmented mitochondria either before or after the cellular adipogenesis. Actually, punctiform mitochondria have been observed in our previous study upon PHB1-knockdown in ovarian cancer cells. Because a lack of ” PHB1 or PHB2 might reduce mitochondrial membrane integrity, disrupt OXPHOS and therefore result in increased levels of ROS, we examined the ATP accumulation and ROS formation upon PHB1- or PHB2-silencing in 3T3-L1 preadipocytes. Our results showed that ROS levels were significantly increased in either PHB1- or PHB2-knockdown 3T3-L1 cells, whereas the contents of ATP were unaffected. The increase of ROS could be ablated when the cells were preincubated with PEG-catalase, a hydrogen peroxide scavenger, indicating the specificity of the DCF-DA signal for hydrogen peroxide. These results, in agreement with the effects ” of PHB deficiency on wild type C. elegans, suggest the damage of mitochondrial OXPHOS system upon PHB-silencing in 3T3-L1 cells. To further investigate the underlying mechanisms of the extra ROS generation, mitochondrial complex I activity was examined. Our data demonstrated a reduction of the complex I activity in PHB1- or PHB2-knockdown 3T3-L1 cells. This result is in accordance with the observation in the PHB1depleted endothelial cells, indicating the affection of mitochondrial electron transport in the OXPHOS system. Discussion It is well established and reviewed that mitochondrial biogenesis is essential during adipocyte differentiation; and that PHBs complexes, located in the inner membrane of mitochondria, play a crucial role in mitochondrial morphology and dynamics. A recent study provides the evidence that depletion of PHB1 or PHB2 in C. elegans significantly decreases mitochondrial membrane potential and adipose accumulation in young adults. However, studies on the effects of PHBs in mammalian adipogenesis are currently lacking. Data presented here indicate that the levels of PHBs are remarkably increased during adipogenesis in 3T3-L1 cells, and silencing of PHBs causes mitochondrial fragmentation and adipogenic reduction. Either PHB1 or PHB2-knockout mice exhibit early embryonic lethality, indicating that these proteins have fundamentally important fun