The nuclear form of HO-1 serves potentially as a transcriptional regulator

evels of ROS, we examined the ATP MG-516 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 21937737 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 functions. In primary mouse adipocytes, PHB1 decreases insulin-stimulated oxidation of glucose and fatty acid, implying that PHB1 may play a role in promoting fat accumulation. Indeed, our results showed the incremental mRNA and protein expression of PHBs in a time course manner using real-time PCR and immunoblotting, which is consistent with Prohibitins Are Required for Adipogenesis the prior observations that intracellular expression of PHBs is increased and extracellular secretion of PHBs is decreased during 3T3-L1 adipocyte differentiation upon genetic and proteomic approaches. In addition, we observed that the PHBs expression was mainly induced by insulin and IBMX rather than glucocorticoid among the three components ” in adipogenic induction cocktail. Insulin is known to act through the insulinlike growth factor 1 receptor. Stimulation of the IGF- 7 Prohibitins Are Required for Adipogenesis 1 receptor regulates cMyc, which is reported to be a transcription factor of PHB. IBMX, a cyclic adenosine monophosphate phosphodiesterase inhibitor, prevents the inactivation of the intracellular cAMP, and therefore enhances expression of C/EBPb, a critical transcription factor at the early stage of adipogenic program. Taken together, we postulate that the induction of PHBs is probably initiated via IGF1, cMyc and/or cAMP molecules. Interestingly, we further observed that the expression of PHBs in WAT from obese mice is not more than that from lean ones. In fact, the decrease of the genes, that are characteristic of mature adipocytes and transcription factors critical to the maintenance o