Mitochondrial dysfunction and endoplasmic reticulum (ER) stress are considered the key determinants of insulin resistance. Impaired mitochondrial function in obese animals was shown to induce the ER stress response, resulting in reduced adiponectin synthesis in adipocytes. The expression of inducible nitric oxide synthase (iNOS) is increased in adipose tissues in genetic and dietary models of obesity. In this study, we examined whether activation of iNOS is responsible for palmitate-induced mitochondrial dysfunction, ER stress, and decreased adiponectin synthesis in 3T3L1 adipocytes. As expected, palmitate increased the expression levels of iNOS and ER stress response markers, and decreased mitochondrial contents. Treatment with iNOS inhibitor increased adiponectin synthesis and reversed the palmitate-induced ER stress response. However, the iNOS inhibitor did not affect the palmitate-induced decrease in mitochondrial contents. Chemicals that inhibit mitochondrial function increased iNOS expression and the ER stress response, whereas measures that increase mitochondrial biogenesis (rosiglitazone and adenoviral overexpression of nuclear respiratory factor-1) reversed them. Inhibition of mitochondrial biogenesis prevented the rosiglitazone-induced decrease in iNOS expression and increase in adiponectin synthesis. These results suggest that palmitate-induced mitochondrial dysfunction is the primary event that leads to iNOS induction, ER stress, and decreased adiponectin synthesis in cultured adipocytes.
3T3-L1 Cells ; *Adipocytes/drug effects/metabolism ; Adiponectin/biosynthesis ; Adipose Tissue/metabolism ; Animals ; Endoplasmic Reticulum Stress/drug effects ; Insulin Resistance/genetics ; Mice ; Mitochondria/drug effects/*metabolism/pathology ; Mitochondrial Turnover/drug effects/genetics ; *Nitric Oxide Synthase Type II/genetics/metabolism ; Nuclear Respiratory Factor 1 ; Obesity/genetics/metabolism ; Palmitic Acid/pharmacology ; Thiazolidinediones/pharmacology

BACKGROUNDMitochondrial dysfunction has been reported to be one of the contributing factors of sepsis-associated encephalopathy (SAE). Mitochondrial biogenesis controls mitochondrial homeostasis and responds to changes in cellular energy demand. In addition, it is enhanced or decreased due to mitochondrial dysfunction during SAE. The aim of this study was to explore the changes of mitochondrial biogenesis of astrocytes under septic conditions.

METHODSLipopolysaccharide (LPS; 50 ng/ml) and interferon-γ (IFN-γ; 200 U/ml) were incubated with astrocytes to model the effects of a septic insult on astrocytes in vitro. The mitochondrial ultrastructure and volume density were evaluated by transmission electron microscopy. Intracellular adenosine triphosphate (ATP) levels were detected by the firefly luciferase system. The expression of protein markers of mitochondrial biogenesis and the binding ability of mitochondrial transcription factor A (TFAM) were determined by western blot and electrophoretic mobility shift assays, respectively. The mitochondrial DNA (mtDNA) content was detected by real-time polymerase chain reaction.

RESULTSThe number of mildly damaged mitochondria was found to be significantly greater after treatment for 6 hours, as compared with at 0 hour (P < 0.05). The mitochondrial volume density was significantly elevated at 24 hours, as compared with at 0 hour (P < 0.05). The ATP levels at 6 hours, 12 hours, and 24 hours were significantly greater than those at 0 hour (P < 0.05). The protein markers of mitochondrial biogenesis were significantly increased at 6 hours and 12 hours, as compared with at 0 hour (P < 0.05). The TFAM binding activity was not significantly changed among the four time points analyzed. The mtDNA contents were significantly increased at 12 hours and 24 hours, as compared with at 0 hour (P < 0.05).

CONCLUSIONSUnder septic conditions, mitochondrial biogenesis of astrocytes increased to meet the high-energy demand and to promote mitochondrial recovery. Furthermore, the TFAM-DNA binding ability was not sensitive to sepsis-induced injury.

Animals ; Astrocytes ; drug effects ; metabolism ; Blotting, Western ; Cells, Cultured ; DNA, Mitochondrial ; genetics ; Electrophoretic Mobility Shift Assay ; Interferon-gamma ; pharmacology ; Lipopolysaccharides ; pharmacology ; Microscopy, Electron, Transmission ; Mitochondrial Turnover ; drug effects ; physiology ; Nitric Oxide ; metabolism ; Rats ; Reactive Nitrogen Species ; metabolism ; Sepsis ; metabolism ; Tumor Necrosis Factor-alpha ; metabolism