A receptor for eating mitochondria

A novel ND1 mitochondrial DNA mutation is maternally inherited in growth hormone transgenesis in amago salmon (Oncorhynchus masou ishikawae)

Growth hormone (GH) transgenesis can be used to manipulate the growth performance of fish and mammals. In this study, homozygous and hemizygous GH-transgenic amago salmon (Oncorhynchus masou ishikawae) derived from a single female exhibited hypoglycemia. Proteomic and signal network analyses using iTRAQ indicated a decreased NAD⁺/NADH ratio in transgenic fish, indicative of reduced mitochondrial ND1 function and ROS levels. Mitochondrial DNA sequencing revealed that approximately 28% of the deletion mutations in the GH homozygous- and hemizygous-female-derived mitochondrial DNA occurred in ND1. These fish also displayed decreased ROS levels. Our results indicate that GH transgenesis in amago salmon may induce specific deletion mutations that are maternally inherited over generations and alter energy production.

Mitophagy in Cardiomyocytes and in Platelets: A Major Mechanism of Cardioprotection Against Ischemia/Reperfusion Injury

Mitophagy, a process that selectively removes damaged organelles by autolysosomal degradation, is an early cellular response to ischemia. Mitophagy is activated in both cardiomyocytes and platelets during ischemia/reperfusion (I/R) and heart disease conditions. We focus on the molecular regulation of mitophagy and highlight the role of mitophagy in cardioprotection.

Thymoquinone induces caspase-independent, autophagic cell death in CPT-11-resistant lovo colon cancer via mitochondrial dysfunction and activation of JNK and p38

Chemotherapy causes unwanted side effects and chemoresistance, limiting its effectiveness. Therefore, phytochemicals are now used as alternative treatments. Thymoquinone (TQ) is used to treat different cancers, including colon cancer. The irinotecan-resistant (CPT-11-R) LoVo colon cancer cell line was previously constructed by stepwise CPT-11 challenges to untreated parental LoVo cells. TQ dose-dependently increased the total cell death index and activated apoptosis at 2 μM, which then diminished at increasing doses. The possibility of autophagic cell death was then investigated. TQ caused mitochondrial outer membrane permeability (MOMP) and activated autophagic cell death. JNK and p38 inhibitors (SP600125 and SB203580, respectively) reversed TQ autophagic cell death. TQ was also found to activate apoptosis before autophagy, and the direction of cell death was switched toward autophagic cell death at initiation of autophagosome formation. Therefore, TQ resulted in caspase-independent, autophagic cell death via MOMP and activation of JNK and p38 in CPT-11-R LoVo colon cancer cells.

Neurodegenerative disorders: dysregulation of a carefully maintained balance?

The aggregation of misfolded proteins has long been regarded as a pathological event in neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease and Huntington's disease. However, the exact molecular mechanisms that govern protein metabolism that may lead to toxicity remain largely unclear. Originally targeted as the causative agent, it has since become evident that aggregation formation may not be necessary for disease progression and studies show that they may even serve functional and protective roles. Although the focus has since shifted to the toxicity of intermediate protein species preceding aggregation formation, many questions remain: Is the blame for the neural destruction to be put on one event alone, or rather on a state of cellular disequilibrium resulting from multiple events? If the cause is multifactorial, then what triggers the toxic cascade and how can this be targeted therapeutically? In order to understand the origin of toxicity, the exact underlying mechanism and impact of each contributing process must be assessed. Therefore, the structural properties, mechanism of formation, cytotoxic and/or protective effects, as well as the clinical impact of protein intermediates and aggregates will be reviewed here with the goal to establish a neurodegenerative disease model aimed at improving current therapeutics, which may ultimately contribute towards improved treatment modalities.

Quality control system response to stochastic growth of amyloid fibrils

We introduce a stochastic model describing aggregation of misfolded proteins and degradation by the protein quality control system in a single cell. Aggregate growth is contrasted by the cell quality control system, that attacks them at different stages of the growth process, with an efficiency that decreases with their size. Model parameters are estimated from experimental data. Two qualitatively different behaviors emerge: a homeostatic state, where the quality control system is stable and aggregates of large sizes are not formed, and an oscillatory state, where the quality control system periodically breaks down, allowing for formation of large aggregates. We discuss how these periodic breakdowns may constitute a mechanism for the development of neurodegenerative diseases.

Mitophagy and mitochondrial morphology in human melanoma-derived cells post exposure to simulated sunlight

PURPOSE

To assess changes in mitochondrial morphology and mitophagy induced by simulated sunlight irradiation (SSI) and how these changes are modulated by mitochondrial activity and energy source.

MATERIALS AND METHODS

Human malignant amelanotic melanoma A375 cells were pre-treated with either a mitochondrial activity enhancer, uncoupler or were either melanin or glutamine supplemented/starved for 4 hours pre-exposure to sunlight. A Q-Sun Solar Simulator (Q-Lab, Homestead, FL, USA) was employed to expose cells to simulated sunlight. Confocal microscopy imaging of A375 cells co-loaded with mitochondria and lysosome-specific fluorescent dyes was used to identify these organelles and predict mitophagic events.

RESULTS

SSI induces pronounced changes in mitochondrial dynamics and mitophagy in exposed skin cells compared to control and these effects were modified by both glutamine and melanin.

CONCLUSIONS

Mitochondrial dynamics and rate of mitophagy in melanoma cells are sensitive to even short bursts of environmentally relevant SSI. Mitochondrial dynamics, and its modulation, may also play a role in mitophagy regulation, cell survival and proliferation post SSI.

Not just fat: the structure and function of the lipid droplet

Lipid droplets (LDs) are independent organelles that are composed of a lipid ester core and a surface phospholipid monolayer. Recent studies have revealed many new proteins, functions, and phenomena associated with LDs. In addition, a number of diseases related to LDs are beginning to be understood at the molecular level. It is now clear that LDs are not an inert store of excess lipids but are dynamically engaged in various cellular functions, some of which are not directly related to lipid metabolism. Compared to conventional membrane organelles, there are still many uncertainties concerning the molecular architecture of LDs and how each function is placed in a structural context. Recent findings and remaining questions are discussed.

Autophagy and the degradation of mitochondria

The cellular process of macromolecular degradation known as macroautophagy has long been known to play a role in the elimination of mitochondria. Over the past decade, much progress has been made in the development of systems by which the nature and mechanism of mitochondria degradation may be studied. Recent findings imply that the degradation of mitochondria via autophagy may be more specific and more tightly regulated than originally thought, and have led to designation of this specific type of autophagy as "mitophagy". In this review we provide a brief history of the development of mitophagy models and their associated discoveries.