mitochondrial proteins has been observed GW 501516 supplier during adipogenesis in a proteomic analysis. It is reported that inhibition of mitochondrial citrate export causes a significant reduction in fat accumulation in 3T3-L1 cells. In addition, DNA binding of PPARc induced by the adipogenic cocktail is completely prevented in preadipocytes treated with an inhibitor of mitochondrial respiration. In the present study, we detected a remarkable increment of mitochondrial content and PHBs in differentiated adipocytes when compared to preadipocytes. Furthermore, in the mitochondrial fraction, the concentration of PHB1 or PHB2 is much higher in adipocyte-differentiated 3T3-L1 cells, suggesting that the increase of mitochondrial PHB1 or PHB2 is beyond the increase of the mitochondrial mass during adipogenesis. The mitochondrial content is reduced in PHBdeficient 3T3-L1 cells, which may be one of the mechanisms to explain our previous findings that PHB is essential for stabilizing the mitochondrial integrity and membrane potential. Interestingly, our data demonstrate that the protein levels of PHB1 and PHB2 in nuclear fractions are slightly increased in 3T3-L1 cells upon adipocyte differentiation. The mitochondrial-nuclear communication by PHBs shuttling under cell stress or cell differentiation has been recently reported. However, the existence and influence of nuclear translocation of PHBs during 3T3-L1 cell adipogenesis remain unclear. The analysis of the native structure of PHB1 and PHB2 in yeast, nematodes and mammals has revealed that 
both proteins are present in a high molecular-weight complex in the inner membrane of mitochondria. The mitochondrial network is composed of highly interconnected tubules formed by balanced fusion and fission events. Our previous study has shown that PHB1 down-regulation resulted in a transition of mitochondrial morphology from a normal reticular network to vesicular punctiform in ovarian cancer cells. Here, we observed the loss of mitochondrial cristae and the fragmentation of mitochondrial network in either PHB1 or PHB2 knockdown 3T3L1 preadipocytes. These findings are in agreement with the reports on PHB2-deficient MEFs and PHB1- or PHB2-silencing in HeLa cells, which suggests that the fusion of mitochondrial membranes is impaired in the absence of PHBs. The abnormal mitochondrial morphology observed in the absence of PHBs may be explained by an altered processing of OPA1, a large dynamin-like GTPase that is found in the mitochondrial intermembrane space and regulates both mitochondrial fusion and cristae morphogenesis. The mechanism by which PHBs affect OPA1 processing remains to be determined. Mitochondria are described as power plants because they generate most of the cellular supply of ATP, which is used as a source of chemical energy. We have not seen significant changes in ATP levels in 3T3-L1 preadipocytes upon PHB1- or PHB2silencing. These observations are in accordance with the reports in PHB2-deficient MEFs and in PHB1- or PHB2-deficient wild-type C. elegans. Schleicher et al. has also reported that the degree of mitochondrial coupling of the respiratory chain in PHB1knockdown endothelial cells was similar to the control cells. In addition to their crucial role in energy homeostasis, mitochondria are the main site of ROS generation. Mitochondrial ROS have been proven to act as signaling molecules that impact many basic cellular functions such as cell differentiation. It has been demonstrated that mitochondrial