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

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

Obesity is known to induce inhibition of glucose uptake, reduction of lipid metabolism, and progressive loss of skeletal muscle function, which are all associated with mitochondrial dysfunction in skeletal muscle. Mitochondria are dynamic organelles that regulate cellular metabolism and bioenergetics, including ATP production via oxidative phosphorylation. Due to these critical roles of mitochondria, mitochondrial dysfunction results in various diseases such as obesity and type 2 diabetes. Obesity is associated with impairment of mitochondrial function (e.g., decrease in O₂ respiration and increase in oxidative stress) in skeletal muscle. The balance between mitochondrial fusion and fission is critical to maintain mitochondrial homeostasis in skeletal muscle. Obesity impairs mitochondrial dynamics, leading to an unbalance between fusion and fission by favorably shifting fission or reducing fusion proteins. Mitophagy is the catabolic process of damaged or unnecessary mitochondria. Obesity reduces mitochondrial biogenesis in skeletal muscle and increases accumulation of dysfunctional cellular organelles, suggesting that mitophagy does not work properly in obesity. Mitochondrial dysfunction and oxidative stress are reported to trigger apoptosis, and mitochondrial apoptosis is induced by obesity in skeletal muscle. It is well known that exercise is the most effective intervention to protect against obesity. Although the cellular and molecular mechanisms by which exercise protects against obesity-induced mitochondrial dysfunction in skeletal muscle are not clearly elucidated, exercise training attenuates mitochondrial dysfunction, allows mitochondria to maintain the balance between mitochondrial dynamics and mitophagy, and reduces apoptotic signaling in obese skeletal muscle.
Adenosine Triphosphate ; Apoptosis ; Energy Metabolism ; Glucose ; Homeostasis ; Lipid Metabolism ; Metabolism ; Mitochondria ; Mitochondrial Degradation ; Mitochondrial Dynamics ; Muscle, Skeletal* ; Obesity ; Organelle Biogenesis ; Organelles ; Oxidative Phosphorylation ; Oxidative Stress ; Respiration

Brain aging is an inevitable process characterized by structural and functional changes and is a major risk factor for neurodegenerative diseases. Most brain aging studies are focused on neurons and less on astrocytes which are the most abundant cells in the brain known to be in charge of various functions including the maintenance of brain physical formation, ion homeostasis, and secretion of various extracellular matrix proteins. Altered mitochondrial dynamics, defective mitophagy or mitochondrial damages are causative factors of mitochondrial dysfunction, which is linked to age-related disorders. Etoposide is an anti-cancer reagent which can induce DNA stress and cellular senescence of cancer cell lines. In this study, we investigated whether etoposide induces senescence and functional alterations in cultured rat astrocytes. Senescence-associated β-galactosidase (SA-β-gal) activity was used as a cellular senescence marker. The results indicated that etoposide-treated astrocytes showed cellular senescence phenotypes including increased SA-β-gal-positive cells number, increased nuclear size and increased senescence-associated secretory phenotypes (SASP) such as IL-6. We also observed a decreased expression of cell cycle markers, including Phospho-Histone H3/Histone H3 and CDK2, and dysregulation of cellular functions based on wound-healing, neuronal protection, and phagocytosis assays. Finally, mitochondrial dysfunction was noted through the determination of mitochondrial membrane potential using tetramethylrhodamine methyl ester (TMRM) and the measurement of mitochondrial oxygen consumption rate (OCR). These data suggest that etoposide can induce cellular senescence and mitochondrial dysfunction in astrocytes which may have implications in brain aging and neurodegenerative conditions.
Aging ; Animals ; Astrocytes ; Brain ; Cell Aging ; Cell Cycle ; Cell Line ; DNA ; Etoposide ; Extracellular Matrix Proteins ; Homeostasis ; Interleukin-6 ; Membrane Potential, Mitochondrial ; Mitochondria ; Mitochondrial Degradation ; Mitochondrial Dynamics ; Neurodegenerative Diseases ; Neurons ; Neuroprotection ; Oxygen Consumption ; Phagocytosis ; Phenotype ; Rats ; Risk Factors ; Wound Healing

BACKGROUND: Recent studies show that mitophagy, the autophagy-dependent turnover of mitochondria, mediates pulmonary epithelial cell death in response to cigarette smoke extract (CSE) exposure and contributes to the development of emphysema in vivo during chronic cigarette smoke (CS) exposure, although the underlying mechanisms remain unclear. METHODS: In this study, we investigated the role of mitophagy in the regulation of CSE-exposed lung bronchial epithelial cell (Beas-2B) death. We also investigated the role of a phosphodiesterase 4 inhibitor, roflumilast, in CSE-induced mitophagy-dependent cell death. RESULTS: Our results demonstrated that CSE induces mitophagy in Beas-2B cells through mitochondrial dysfunction and increased the expression levels of the mitophagy regulator protein, PTEN-induced putative kinase-1 (PINK1), and the mitochondrial fission protein, dynamin-1-like protein (DRP1). CSE-induced epithelial cell death was significantly increased in Beas-2B cells exposed to CSE but was decreased by small interfering RNA-dependent knockdown of DRP1. Treatment with roflumilast in Beas-2B cells inhibited CSE-induced mitochondrial dysfunction and mitophagy by inhibiting the expression of phospho-DRP1 and -PINK1. Roflumilast protected against cell death and increased cell viability, as determined by the lactate dehydrogenase release test and the MTT assay, respectively, in Beas-2B cells exposed to CSE. CONCLUSION: These findings suggest that roflumilast plays a protective role in CS-induced mitophagy-dependent cell death.
Cell Death* ; Cell Survival ; Cyclic Nucleotide Phosphodiesterases, Type 4* ; Emphysema ; Epithelial Cells* ; L-Lactate Dehydrogenase ; Lung ; Mitochondria ; Mitochondrial Degradation ; Mitochondrial Dynamics ; Pulmonary Disease, Chronic Obstructive ; Smoke* ; Tobacco Products* ; Tobacco Use

Autophagy is a physiological process which delivers the mutant cytoplasmic proteins and dysfunctional subcellular organs into lysosomes for degradation to generate fuel in the deficiency conditions. It is mainly classified into macroautophagy, microautophagy and chaperon-mediated autophagy (CMA), as well as the selective autophagy such as mitophagy and aggrephagy. This review mainly introduces the key molecular markers of macroautophagy, CMA and mitophagy.
Autophagy ; Humans ; Lysosomes ; Mitochondrial Degradation ; Molecular Chaperones

Erythropoiesis ; physiology ; Humans ; Mitochondria ; physiology ; Mitochondrial Degradation

Mitochondria are small organelles that produce the majority of cellular energy as ATP. Mitochondrial dysfunction has been implicated in the pathogenesis of Parkinson's disease (PD), and rare familial forms of PD provide valuable insight into the pathogenic mechanism underlying mitochondrial impairment, even though the majority of PD cases are sporadic. The regulation of mitochondria is crucial for the maintenance of energy-demanding neuronal functions in the brain. Mitochondrial biogenesis and mitophagic degradation are the major regulatory pathways that preserve optimal mitochondrial content, structure and function. In this mini-review, we provide an overview of the mitochondrial quality control mechanisms, emphasizing regulatory molecules in mitophagy and biogenesis that specifically interact with the protein products of three major recessive familial PD genes, PINK1, Parkin and DJ-1.
Adenosine Triphosphate ; Brain ; Homeostasis* ; Mitochondria ; Mitochondrial Degradation ; Neurons ; Organelles ; Parkinson Disease* ; Quality Control ; Organelle Biogenesis

Mitophagy is a process during which the cell selectively removes the mitochondria via the mechanism of autophagy. It is crucial to the functional completeness of the whole mitochondrial network and determines cell survival and death. On the one hand, the damaged mitochondria releases pro-apoptotic factors which induce cell apoptosis; on the other hand, the damaged mitochondria eliminates itself via autophagy, which helps to maintain cell viability. Mitophagy is of vital importance for the development and function of the nervous system. Neural cells rely on autophagy to control protein quality and eliminate the damaged mitochondria, and under normal circumstances, mitophagy can protect the neural cells. Mutations in genes related to mitophagy may cause the development and progression of neurodegenerative diseases. An understanding of the role of mitophagy in nervous system diseases may provide new theoretical bases for clinical treatment. This article reviews the research advances in the relationship between mitophagy and different types of nervous system diseases.
Apoptosis ; Autophagy ; physiology ; Humans ; Mitochondrial Degradation ; Nervous System Diseases ; etiology ; Neurodegenerative Diseases ; etiology

Mitochondria play a key role in various cell processes including ATP production, Ca homeostasis, reactive oxygen species (ROS) generation, and apoptosis. The selective removal of impaired mitochondria by autophagosome is known as mitophagy. Cerebral ischemia is a common form of stroke caused by insufficient blood supply to the brain. Emerging evidence suggests that mitophagy plays important roles in the pathophysiological process of cerebral ischemia. This review focuses on the relationship between ischemic brain injury and mitophagy. Based on the latest research, it describes how the signaling pathways of mitophagy appear to be involved in cerebral ischemia.
Animals ; Brain Ischemia ; metabolism ; pathology ; Humans ; Mitochondrial Degradation ; Reactive Oxygen Species ; metabolism ; Stroke ; metabolism ; pathology