Interplay between mitochondria and cellular calcium signalling

Influence of Tau on Neurotoxicity and Cerebral Vasculature Impairment Associated with Alzheimer's Disease

Alzheimer's disease is a fatal chronic neurodegenerative condition marked by a gradual decline in cognitive abilities and impaired vascular function within the central nervous system. This affliction initiates its insidious progression with the accumulation of two aberrant protein entities including Aβ plaques and neurofibrillary tangles. These chronic elements target distinct brain regions, steadily erasing the functionality of the hippocampus and triggering the erosion of memory and neuronal integrity. Several assumptions are anticipated for AD as genetic alterations, the occurrence of Aβ plaques, altered processing of amyloid precursor protein, mitochondrial damage, and discrepancy of neurotropic factors. In addition to Aβ oligomers, the deposition of tau hyper-phosphorylates also plays an indispensable part in AD etiology. The brain comprises a complex network of capillaries that is crucial for maintaining proper function. Tau is expressed in cerebral blood vessels, where it helps to regulate blood flow and sustain the blood-brain barrier's integrity. In AD, tau pathology can disrupt cerebral blood supply and deteriorate the BBB, leading to neuronal neurodegeneration. Neuroinflammation, deficits in the microvasculature and endothelial functions, and Aβ deposition are characteristically detected in the initial phases of AD. These variations trigger neuronal malfunction and cognitive impairment. Intracellular tau accumulation in microglia and astrocytes triggers deleterious effects on the integrity of endothelium and cerebral blood supply resulting in further advancement of the ailment and cerebral instability. In this review, we will discuss the impact of tau on neurovascular impairment, mitochondrial dysfunction, oxidative stress, and the role of hyperphosphorylated tau in neuron excitotoxicity and inflammation.

GLP-1/Sigma/RAGE receptors: An evolving picture of Alzheimer's disease pathology and treatment

According to the facts and figures 2023stated that 6.7 million Americans over the age of 65 have Alzheimer's disease (AD). The scenario of AD has reached up to the maximum, of 4.1 million individuals, 2/3rd are female patients, and approximately 1 in 9 adults over the age of 65 have dementia with AD dementia. The fact that there are now no viable treatments for AD indicates that the underlying disease mechanisms are not fully understood. The progressive neurodegenerative disease, AD is characterized by amyloid plaques and neurofibrillary tangles (NFTs) of abnormally hyperphosphorylated tau protein and senile plaques (SPs), which are brought on by the buildup of amyloid beta (Aβ). Numerous attempts have been made to produce compounds that interfere with these characteristics because of significant research efforts into the primary pathogenic hallmark of this disorder. Here, we summarize several research that highlights interesting therapy strategies and the neuroprotective effects of GLP-1, Sigma, and, AGE-RAGE receptors in pre-clinical and clinical AD models.

The Constrained Disorder Principle Accounts for the Variability That Characterizes Breathing: A Method for Treating Chronic Respiratory Diseases and Improving Mechanical Ventilation

Variability characterizes breathing, cellular respiration, and the underlying quantum effects. Variability serves as a mechanism for coping with changing environments; however, this hypothesis does not explain why many of the variable phenomena of respiration manifest randomness. According to the constrained disorder principle (CDP), living organisms are defined by their inherent disorder bounded by variable boundaries. The present paper describes the mechanisms of breathing and cellular respiration, focusing on their inherent variability. It defines how the CDP accounts for the variability and randomness in breathing and respiration. It also provides a scheme for the potential role of respiration variability in the energy balance in biological systems. The paper describes the option of using CDP-based artificial intelligence platforms to augment the respiratory process's efficiency, correct malfunctions, and treat disorders associated with the respiratory system.

Astrocytic mitochondrial frataxin-A promising target for ischemic brain injury

In the ischemic brain, hypoxia leads to mitochondrial dysfunction, insufficient energy production, and astrocyte activation. Yet, most studies investigating mitochondrial dysfunction in cerebral ischemia have focused exclusively on neurons. This review will highlight the importance of the morphological, molecular, and functional heterogeneity of astrocytes in their role in brain injuries and explore how activated astrocytes exhibit calcium imbalance, reactive oxygen species overproduction, and apoptosis. In addition, special focus will be given to the role of the mitochondrial protein frataxin in activated astrocytes during ischemia and its putative role in the pharmacological management of cerebral ischemia.

The Imbalance of Astrocytic Mitochondrial Dynamics Following Blast-Induced Traumatic Brain Injury

Mild blast-induced traumatic brain injury (bTBI) is a modality of injury that has been of major concern considering a large number of military personnel exposed to explosive blast waves. bTBI results from the propagation of high-pressure static blast forces and their subsequent energy transmission within brain tissue. Exposure to this overpressure energy causes a diffuse injury that leads to acute cell damage and, if chronic, leads to detrimental long-term cognitive deficits. The literature presents a neuro-centric approach to the role of mitochondria dynamics dysfunction in bTBI, and changes in astrocyte-specific mitochondrial dynamics have not been characterized. The balance between fission and fusion events is known as mitochondrial dynamics. As a result of fission and fusion, the mitochondrial structure is constantly altering its shape to respond to physiological stimuli or stress, which in turn affects mitochondrial function. Astrocytic mitochondria are recognized to play an essential role in overall brain metabolism, synaptic transmission, and neuron protection. Mitochondria are vulnerable to injury insults, leading to the increase in mitochondrial fission, a mechanism controlled by the GTPase dynamin-related protein (Drp1) and the phosphorylation of Drp1 at serine 616 (p-Drp1^s616). This site is critical to mediate the Drp1 translocation to mitochondria to promote fission events and consequently leads to fragmentation. An increase in mitochondrial fragmentation could have negative consequences, such as promoting an excessive generation of reactive oxygen species or triggering cytochrome c release. The aim of the present study was to characterize the unique pattern of astrocytic mitochondrial dynamics by exploring the role of DRP1 with a combination of in vitro and in vivo bTBI models. Differential remodeling of the astrocytic mitochondrial network was observed, corresponding with increases in p-Drp1^S616 four hours and seven days post-injury. Further, results showed a time-dependent reactive astrocyte phenotype transition in the rat hippocampus. This discovery can lead to innovative therapeutics targets to help prevent the secondary injury cascade after blast injury that involves mitochondria dysfunction.

Comparative transcriptomics analyses of chemosensory genes of antenna in male red swamp crayfish Procambarus clarkii

The red swamp crayfish, Procambarus clarkii, is a globally invasive species and has caused huge damage to aquaculture, biodiversity, and ecology worldwide. Antenna-expressed receptors are important for P. clarkii to detect chemosensory cues for mate attraction. In this study, we tested the behavior of male P. clarkii to the conditioned water from female P. clarkii during the mating and non-mating periods, and performed RNA sequencing to investigate the chemosensory-related genes of the antenna of male P. clarkii. The results of the behavioral assay have shown that for the female-conditioned water, male P. clarkii within the mating period can be significantly attracted, but not during the non-mating period. This suggested that the expressions of chemosensory-related genes in the antenna of male P. clarkii may change significantly with mating seasonal variation. Antenna transcriptomes found that a total of 59,218 unigenes with an average length of 1,056.41 bp, and 4,889 differentially expressed unigenes (DEGs), among which 2,128 were upregulated, while 2,761 were downregulated were obtained. A total of 12 upregulated and nine downregulated DEGs were associated with chemical reception, including four ionotropic receptors (IRs) or ionotropic glutamate receptors (iGluRs), eight G-protein-coupled receptors (GPCRs), five transient receptor potential channels (TRP channels), one sodium–calcium exchanger, one isomerase, and two uncharacterized proteins (chemosensory proteins-like, CSPs). CSPs were preliminarily classified as pheromone receptors in the antenna of male P. clarkii. Furthermore, the calcium transduction-related pathways may play an important role in the sex pheromone reception of the male P. clarkii’s antenna. The results of quantitative real-time reverse transcriptase PCR (RT-qPCR) showed that the trends of expression of eight selected unigenes were consistent with RNA-Seq results. Our results provide more comprehensive data for chemical communication mechanisms after P. clarkii enter the mating period and eventually would develop better control strategies in further.

Fully Reversible Ratiometric Nanosensors for Continuously Quantifying Mitochondrial Glutathione Concentration in Living Cells

Mitochondrial glutathione (mGSH) is both the cause of the oxidative damage and a mechanism for maintaining the redox homeostasis in mitochondria. To effectively measure mGSH dynamics in living cells, we have developed a new FRET-based nanosensor by immobilizing rhodamine B into dendritic mesoporous silica nanoparticles and installing GSH probes and mitochondria-targeting motifs onto the surface of nanoparticles. The result shows that these nanosensors show efficient FRET and a full reversibility and rapid response (<10 s) to GSH in the range of 0.5-20 mM, due to their unique nanostructure and well-overlapped spectra. The excellent photostability and low cytotoxicity make them an effective means for monitoring mGSH concentration in real time. When the mGSH nanosensors are used for quantitatively measuring mGSH variations under glucose deprivation stimulation in HeLa cells, they successfully prove themselves a useful tool for mitochondrial redox activity studies.

Mitohormesis and mitochondrial dynamics in the regulation of stem cell fate

The ability of stem cells for self-renewing, differentiation, and regeneration of injured tissues is believed to occur via the hormetic modulation of nuclear/mitochondrial signal transductions. The evidence now indicates that in damaged tissues, the mitochondria set off the alarm under oxidative stress conditions, hence they are the central regulators of stem cell fate decisions. This review aimed to provide an update to a broader concept of stem cell fate in stress conditions of damaged tissues, and insights for the mitochondrial hormesis (mitohormesis), including the integrated stress response (ISR), mitochondrial dynamics, mitochondria uncoupling, unfolded protein response, and mitokines, with implications for the control of stem cells programing in a successful clinical cell therapy.

Glutamate Metabolism in Mitochondria is Closely Related to Alzheimer's Disease

Glutamate is the main excitatory neurotransmitter in the brain, and its excitatory neurotoxicity is closely related to the occurrence and development of Alzheimer's disease. However, increasing evidence shows that in the process of Alzheimer's disease, glutamate is not only limited to its excitotoxicity as a neurotransmitter but also related to the disorder of its metabolic balance. The balance of glutamate metabolism in the brain is an important determinant of central nervous system health, and the maintenance of this balance is closely related to glutamate uptake, glutamate circulation, intracellular mitochondrial transport, and mitochondrial metabolism. In this paper, we intend to elaborate the key role of mitochondrial glutamate metabolism in the pathogenesis of Alzheimer's disease and review glutamate metabolism in mitochondria as a potential target in the treatment of Alzheimer's disease.

Impact of Tau on Neurovascular Pathology in Alzheimer's Disease

Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the most prevalent cause of dementia. The main cerebral histological hallmarks are represented by parenchymal insoluble deposits of amyloid beta (Aβ plaques) and neurofibrillary tangles (NFT), intracellular filamentous inclusions of tau, a microtubule-associated protein. It is well-established that cerebrovascular dysfunction is an early feature of AD pathology, but the detrimental mechanisms leading to blood vessel impairment and the associated neurovascular deregulation are not fully understood. In 90% of AD cases, Aβ deposition around the brain vasculature, known as cerebral amyloid angiopathy (CAA), alters blood brain barrier (BBB) essential functions. While the effects of vascular Aβ accumulation are better documented, the scientific community has only recently started to consider the impact of tau on neurovascular pathology in AD. Emerging compelling evidence points to transmission of neuronal tau to different brain cells, including astrocytes, as well as to the release of tau into brain interstitial fluids, which may lead to perivascular neurofibrillar tau accumulation and toxicity, affecting vessel architecture, cerebral blood flow (CBF), and vascular permeability. BBB integrity and functionality may therefore be impacted by pathological tau, consequentially accelerating the progression of the disease. Tau aggregates have also been shown to induce mitochondrial damage: it is known that tau impairs mitochondrial localization, distribution and dynamics, alters ATP and reactive oxygen species production, and compromises oxidative phosphorylation systems. In light of this previous knowledge, we postulate that tau can initiate neurovascular pathology in AD through mitochondrial dysregulation. In this review, we will explore the literature investigating tau pathology contribution to the malfunction of the brain vasculature and neurovascular unit, and its association with mitochondrial alterations and caspase activation, in cellular, animal, and human studies of AD and tauopathies.

Association of particulate matter air pollution with leukocyte mitochondrial DNA copy number

BACKGROUND

Ambient particulate matter (PM) has been associated with mitochondrial damage and dysfunction caused by excessive oxidative stress, but the associations between long-term PM exposure and leukocyte mitochondrial DNA copy number (mtDNAcn), a biomarker of mitochondrial dysfunction due to oxidative stress, are less studied.

OBJECTIVES

To investigate the associations between short-, intermediate- and long-term exposure (1-, 3- and 12-months) to different size fractions of PM (PM2.5, PM2.5-10 and PM10) and leukocyte mtDNAcn in a cross-sectional study.

METHODS

The associations between each of the PM exposure metrics with z scores of log-transformed mtDNAcn were examined using generalized linear regression models in 2758 female participants from the Nurses' Health Study (NHS). Monthly exposures to PM were estimated from spatio-temporal prediction models matched to each participants' address history. Potential effect modification by selected covariates was examined using multiplicative interaction terms and subgroup analyses.

RESULTS

In single-size fraction models, increases in all size fractions of PM were associated with decreases in mtDNAcn, although only models with longer averages of PM2.5 reached statistical significance. For example, an interquartile range (IQR) increase in 12-month average ambient PM2.5 (5.5 μg/m3) was associated with a 0.07 [95% confidence interval (95% CI): -0.13, -0.01; p-value = 0.02] decrease in mtDNAcn z score in both basic- and multivariable-adjusted models. Associations for PM2.5 were stronger after controlling for PM2.5-10 in two size-fraction models.

CONCLUSIONS

Our study suggests that long-term exposure to ambient PM2.5 is associated with decreased mtDNAcn in healthy women.

The Functions of Mitochondrial 2',3'-Cyclic Nucleotide-3'-Phosphodiesterase and Prospects for Its Future

2′,3′-cyclic nucleotide-3′-phosphodiesterase (CNPase) is a myelin-associated enzyme that catalyzes the phosphodiester hydrolysis of 2’,3’-cyclic nucleotides to 2’-nucleotides. However, its presence is also found in unmyelinated cells and other cellular structures. Understanding of its specific physiological functions, particularly in unmyelinated cells, is still incomplete. This review concentrates on the role of mitochondrial CNPase (mtCNPase), independent of myelin. mtCNPase is able to regulate the functioning of the mitochondrial permeability transition pore (mPTP), and thus is involved in the mechanisms of cell death, both apoptosis and necrosis. Its participation in the development of various diseases and pathological conditions, such as aging, heart disease and alcohol dependence, is also reviewed. As such, mtCNPase can be considered as a potential target for the development of therapeutic strategies in the treatment of mitochondria-related diseases.

Total flavones of Dracocephalum moldavica L. protect astrocytes against H2O2-induced apoptosis through a mitochondria-dependent pathway

BACKGROUND

The active components of Dracocephalum moldavica L. (TFDM) can inhibit myocardial ischemia by inhibiting oxidative stress. However, the effects of TFDM on astrocytes have not been investigated in vitro. The current study aimed to explore whether TFDM protects astrocytes against H₂O₂-induced apoptosis through a mitochondria-dependent pathway.

METHODS

The human glioma cell line U87 was used to investigate the ability of TFDM to protect astrocytes against H₂O₂-induced apoptosis. The cell counting kit-8 assay and flow cytometry were used to detect cell viability, apoptosis, MMP, Ca²⁺ influx and reactive oxygen species (ROS). Lactate dehydrogenase (LDH) and malonic dialdehyde (MDA) levels were measured by ELISA. In addition, protein and mRNA expression changes were detected by Western blotting and qRT-PCR.

RESULTS

TFDM (0.78~200 μg/ml) had limited cytotoxic effects on the viability of U87 cells. Compared with the model group (treated with H2O2 only), cells treated with medium- and high-dose TFDM exhibited reduced MDA concentrations (P < 0.05) and ROS production (P < 0.05) and decreased MMP (P < 0.05) and reduced apoptosis (P < 0.05). The percentage of annexin V-FITC-stained cells was markedly suppressed by TFDM, confirming its anti-apoptotic properties. WB results showed that protein expression of Bcl-2-associated X protein (BAX), Caspase-3, Caspase-9, Caspase-12, and B-cell leukemia/lymphoma 2 (Bcl2) was reduced in the TFDM group compared with that in the model group (P < 0.05) and that expression of these proteins was normalized by TFDM treatment in a dose-dependent manner. According to RT-qPCR results, TFDM pretreatment resulted in reduced mRNA expression of BAX, Caspase-9, Caspase-12, p38MAPK, and CaMKII and increased mRNA expression of mTOR compared with the model group.

CONCLUSIONS

The current study revealed the protective effects of TFDM on U87 cells under oxidative stress conditions through the inhibition of a mitochondria-dependent pathway that is associated with the CaMKII/P38MAPK/ERK1/2 and PI3K/AKT/mTOR pathways.

The role of mitochondria in shaping odor responses in Drosophila melanogaster olfactory sensory neurons

Insects detect volatile chemosignals with olfactory sensory neurons (OSNs) that express olfactory receptors. Among them, the most sensitive receptors are the odorant receptors (ORs), which form cation channels passing also Ca²⁺. Here, we investigate if and how odor-induced Ca²⁺ signals in Drosophila melanogaster OSNs are controlled by intracellular Ca²⁺ stores, especially by mitochondria. Using an open antenna preparation that allows observation and pharmacological manipulation of OSNs we performed Ca²⁺ imaging to determine the role of Ca²⁺ influx and efflux pathways in OSN mitochondria. The results indicate that mitochondria participate in shaping the OR responses. The major players of this modulation are the mitochondrial Ca²⁺ uniporter and the mitochondrial permeability transition pore. Intriguingly, OR-induced Ca²⁺ signals were only mildly affected by modulating the Ca²⁺ management of the endoplasmic reticulum.

Mitochondrial dynamics and metabolism in induced pluripotency

Somatic cells can be reprogrammed to pluripotency by either ectopic expression of defined factors or exposure to chemical cocktails. During reprogramming, somatic cells undergo dramatic changes in a wide range of cellular processes, such as metabolism, mitochondrial morphology and function, cell signaling pathways or immortalization. Regulation of these processes during cell reprograming lead to the acquisition of a pluripotent state, which enables indefinite propagation by symmetrical self-renewal without losing the ability of reprogrammed cells to differentiate into all cell types of the adult. In this review, recent data from different laboratories showing how these processes are controlled during the phenotypic transformation of a somatic cell into a pluripotent stem cell will be discussed.

Oxidative stress pathways in pancreatic β-cells and insulin-sensitive cells and tissues: importance to cell metabolism, function, and dysfunction

It is now accepted that nutrient abundance in the blood, especially glucose, leads to the generation of reactive oxygen species (ROS), ultimately leading to increased oxidative stress in a variety of tissues. In the absence of an appropriate compensatory response from antioxidant mechanisms, the cell, or indeed the tissue, becomes overwhelmed by oxidative stress, leading to the activation of intracellular stress-associated pathways. Activation of the same or similar pathways also appears to play a role in mediating insulin resistance, impaired insulin secretion, and late diabetic complications. The ability of antioxidants to protect against the oxidative stress induced by hyperglycemia and elevated free fatty acid (FFA) levels in vitro suggests a causative role of oxidative stress in mediating the latter clinical conditions. In this review, we describe common biochemical processes associated with oxidative stress driven by hyperglycemia and/or elevated FFA and the resulting clinical outcomes: β-cell dysfunction and peripheral tissue insulin resistance.

Insulin resistance and diabetes in hyperthyroidism: a possible role for oxygen and nitrogen reactive species

In addition to insulin, glycemic control involves thyroid hormones. However, an excess of thyroid hormone can disturb the blood glucose equilibrium, leading to alterations of carbohydrate metabolism and, eventually, diabetes. Indeed, experimental and clinical hyperthyroidism is often accompanied by abnormal glucose tolerance. A common characteristic of hyperthyroidism and type 2 diabetes is the altered mitochondrial efficiency caused by the enhanced production of reactive oxygen and nitrogen species. It is known that an excess of thyroid hormone leads to increased oxidant production and mitochondrial oxidative damage. It can be hypothesised that these species represent the link between hyperthyroidism and development of insulin resistance and diabetes, even though direct evidence of this relationship is lacking. In this review, we examine the literature concerning the effects of insulin and thyroid hormones on glucose metabolism and discuss alterations of glucose metabolism in hyperthyroid conditions and the cellular and molecular mechanisms that may underline them.

Role of Astrocytic Mitochondria in Limiting Ischemic Brain Injury?

Until recently, astrocyte processes were thought to be too small to contain mitochondria. However, it is now clear that mitochondria are found throughout fine astrocyte processes and are mobile with neuronal activity resulting in positioning near synapses. In this review, we discuss evidence that astrocytic mitochondria confer selective resiliency to astrocytes during ischemic insults and the functional significance of these mitochondria for normal brain function.

The Effects of Sodium Selenite on Mitochondrial DNA Copy Number and Reactive Oxygen Species Levels of In Vitro Matured Mouse Oocytes

Objective

The aim of present study is to determine the effects of supplementation of oocyte maturation medium with sodium selenite (SS) on oocyte mitochondrial DNA (mtDNA) copy number and reactive oxygen species (ROS) levels.

Materials and Methods

In this experimental study germinal vesicle (GV), metaphase I (MI), and metaphase II (MII) stage oocytes were recovered from 6-8 week old female mice after superovulation. Some of the GV oocytes were cultured and matured in the presence and absence of SS. Then in vivo and in vitro matured (IVM) oocytes were subjected to mitochondria staining by MitoTracker green, ROS analysis, and mtDNA copy number determination using absolute real-time polymerase chain reaction (PCR).

Results

The maturation rate of GV oocytes to the MII stage significantly increased in the SS supplemented group (79.25%) compared to the control group (72.46%, P<0.05). The intensity of mitochondrial staining was not different among the studied groups, whereas the mitochondria distribution in the cytoplasm of the IVM oocytes showed some aggregation pattern. The in vivo obtained MII oocytes had lower ROS levels and higher mtDNA copy numbers than IVM-MII oocytes (P<0.05). The SS supplemented group had significantly lower ROS levels and higher mtDNA copy numbers than the non-treated group (P<0.05).

Conclusion

SS increased oocyte mtDNA copy number by decreasing oxidative stress. SS had an association with better oocyte developmental competence.

Prolonged environment-induced hyperthermia alters autophagy in oxidative skeletal muscle in Sus scrofa

Prolonged heat stress represents a continuing threat to human health and agricultural production. Despite the broad, negative impact of prolonged hyperthermia little is known about underlying pathological mechanisms leading to negative health outcomes, which has limited the development of etiological interventions and left clinicians and producers with only cooling and rehydration strategies. The purpose of this investigation was to determine the extent to which prolonged environment-induced hyperthermia altered autophagy in oxidative skeletal muscle in a large animal model, serving the dual purpose of accurately modeling human physiology as well as agricultural production. We hypothesized that prolonged hyperthermia would induce autophagy in skeletal muscle, independent of the accompanying caloric restriction. To test this hypothesis pigs were treated as follows: thermoneutral (20 °C), heat stress (35 °C), or were held under thermoneutral conditions but pair-fed to the heat stress group for seven days. Upon euthanasia the red portion of the semitendinosus was collected. We found that prolonged hyperthermic exposure increased oxidative stress without a corresponding change in antioxidant enzyme activities. Hyperthermia prevented initiation of autophagy despite increased markers of nucleation, elongation and autophagosome formation. However, p62 relative protein abundance, which is inversely correlated with autophagic degradation, was strongly increased suggesting suppressed degradation of autophagosomes. Markers of mitophagy and mitochondrial abundance were largely similar between groups. These data indicate that faulty autophagy plays a key role in hyperthermic muscle dysfunction.

Pneumolysin induced mitochondrial dysfunction leads to release of mitochondrial DNA

Streptococcus pneumoniae (S.pn.) is the most common bacterial pathogen causing community acquired pneumonia. The pore-forming toxin pneumolysin (PLY) is the major virulence factor of S.pn. and supposed to affect alveolar epithelial cells thereby activating the immune system by liberation of danger-associated molecular patterns (DAMP). To test this hypothesis, we established a novel live-cell imaging based assay to analyse mitochondrial function and associated release of mitochondrial DNA (mtDNA) as DAMP in real-time. We first revealed that bacterially released PLY caused significant changes of the cellular ATP homeostasis and led to morphologic alterations of mitochondria in human alveolar epithelial cells in vitro and, by use of spectral live-tissue imaging, in human alveoli. This was accompanied by strong mitochondrial calcium influx and loss of mitochondrial membrane potential resulting in opening of the mitochondrial permeability transition pore and mtDNA release without activation of intrinsic apoptosis. Moreover, our data indicate cellular mtDNA liberation via microvesicles, which may contribute to S.pn. related pro-inflammatory immune activation in the human alveolar compartment.

Imaging Mitochondrial Calcium Fluxes with Fluorescent Probes and Single- or Two-Photon Confocal Microscopy

The concentration of calcium ions in the mitochondria has been shown to affect its function, modulating respiratory activity at low levels and causing lethal damage at high concentrations. The rhodamine series of dyes can be used to measure mitochondrial calcium concentration, but the reliability of measurements depends upon correct partitioning of the dye within to the mitochondria. Methods are described to aid verification and quantification of the mitochondrial calcium concentration using single- or two-photon confocal microscopy. The method of linear unmixing to separate fluorescent signals based on either differing excitation or emission spectra is outlined and for the purposes of illustration is applied to the separation of rhod-2 signals originating from the dye within the mitochondria and nucleoli.

Transient increases in intracellular calcium and reactive oxygen species levels in TCam-2 cells exposed to microgravity

The effects of microgravity on functions of the human body are well described, including alterations in the male and female reproductive systems. In the present study, TCam-2 cells, which are considered a good model of mitotically active male germ cells, were used to investigate intracellular signalling and cell metabolism during exposure to simulated microgravity, a condition that affects cell shape and cytoskeletal architecture. After a 24 hour exposure to simulated microgravity, TCam-2 cells showed 1) a decreased proliferation rate and a delay in cell cycle progression, 2) increased anaerobic metabolism accompanied by increased levels of intracellular Ca²⁺, reactive oxygen species and superoxide anion and modifications in mitochondrial morphology. Interestingly, all these events were transient and were no longer evident after 48 hours of exposure. The presence of antioxidants prevented not only the effects described above but also the modifications in cytoskeletal architecture and the activation of the autophagy process induced by simulated microgravity. In conclusion, in the TCam-2 cell model, simulated microgravity activated the oxidative machinery, triggering transient macroscopic cell events, such as a reduction in the proliferation rate, changes in cytoskeleton-driven shape and autophagy activation.

Regulation of mitochondrial dynamics in astrocytes: Mechanisms, consequences, and unknowns

Astrocytes are the major glial cell in the central nervous system. These polarized cells possess numerous processes that ensheath the vasculature and contact synapses. Astrocytes play important roles in synaptic signaling, neurotransmitter synthesis and recycling, control of nutrient uptake, and control of local blood flow. Many of these processes depend on local metabolism and/or energy utilization. While astrocytes respond to increases in neuronal activity and metabolic demand by upregulating glycolysis and glycogenolysis, astrocytes also possess significant capacity for oxidative (mitochondrial) metabolism. Mitochondria mediate energy supply and metabolism, cellular survival, ionic homeostasis, and proliferation. These organelles are dynamic structures undergoing extensive fission and fusion, directed movement along cytoskeletal tracts, and degradation. While many of the mechanisms underlying the dynamics of these organelles and their physiologic roles have been characterized in neurons and other cells, the roles that mitochondrial dynamics play in glial physiology is less well understood. Recent work from several laboratories has demonstrated that mitochondria are present within the fine processes of astrocytes, that their movement is regulated, and that they contribute to local Ca²⁺ signaling within the astrocyte. They likely play a role in local ATP production and metabolism, particularly that of glutamate. Here we will review these and other findings describing the mechanism by which mitochondrial dynamics are regulated in astrocytes, how mitochondrial dynamics might influence astrocyte and brain metabolism, and draw parallels to mitochondrial dynamics in neurons. Additionally, we present new analyses of the size, distribution, and dynamics of mitochondria in astrocytes performed using in vivo using 2-photon microscopy.

Inseparable tandem: evolution chooses ATP and Ca2+ to control life, death and cellular signalling

From the very dawn of biological evolution, ATP was selected as a multipurpose energy-storing molecule. Metabolism of ATP required intracellular free Ca(2+) to be set at exceedingly low concentrations, which in turn provided the background for the role of Ca(2+) as a universal signalling molecule. The early-eukaryote life forms also evolved functional compartmentalization and vesicle trafficking, which used Ca(2+) as a universal signalling ion; similarly, Ca(2+) is needed for regulation of ciliary and flagellar beat, amoeboid movement, intracellular transport, as well as of numerous metabolic processes. Thus, during evolution, exploitation of atmospheric oxygen and increasingly efficient ATP production via oxidative phosphorylation by bacterial endosymbionts were a first step for the emergence of complex eukaryotic cells. Simultaneously, Ca(2+) started to be exploited for short-range signalling, despite restrictions by the preset phosphate-based energy metabolism, when both phosphates and Ca(2+) interfere with each other because of the low solubility of calcium phosphates. The need to keep cytosolic Ca(2+) low forced cells to restrict Ca(2+) signals in space and time and to develop energetically favourable Ca(2+) signalling and Ca(2+) microdomains. These steps in tandem dominated further evolution. The ATP molecule (often released by Ca(2+)-regulated exocytosis) rapidly grew to be the universal chemical messenger for intercellular communication; ATP effects are mediated by an extended family of purinoceptors often linked to Ca(2+) signalling. Similar to atmospheric oxygen, Ca(2+) must have been reverted from a deleterious agent to a most useful (intra- and extracellular) signalling molecule. Invention of intracellular trafficking further increased the role for Ca(2+) homeostasis that became critical for regulation of cell survival and cell death. Several mutually interdependent effects of Ca(2+) and ATP have been exploited in evolution, thus turning an originally unholy alliance into a fascinating success story.This article is part of the themed issue 'Evolution brings Ca(2+) and ATP together to control life and death'.

Emerging evidence for potential role of Ca2+-ATPase-mediated calcium accumulation in symbiosomes of infected root nodule cells

Symbiosomes are organelle-like compartments responsible for nitrogen fixation in infected nodule cells of legumes, which are formed as a result of symbiotic association of soil bacteria rhizobia with certain plant root cells. They are virtually the only source of reduced nitrogen in the Earth's biosphere, and consequently, are of great importance. It has been proven that the functioning of symbiosomes depends to a large extent on the transport of various metabolites and ions - most likely including Ca2+ - across the symbiosome membrane (SM). Although it has been well established that this cation is involved in the regulation of a broad spectrum of processes in cells of living organisms, its role in the functioning of symbiosomes remains obscure. This is despite available data indicating both its transport through the SM and accumulation within these compartments. This review summarises the results obtained in the course of studies on the given aspects of calcium behaviour in symbiosomes, and on this basis gives a possible explanation of the proper functional role in them of Ca2+.

Joint Analysis of Nuclear and Mitochondrial Variants in Age-Related Macular Degeneration Identifies Novel Loci TRPM1 and ABHD2/RLBP1

Purpose

Presently, 52 independent nuclear single nucleotide polymorphisms (nSNPs) have been associated with age-related macular degeneration (AMD) but their effects do not explain all its variance. Genetic interactions between the nuclear and mitochondrial (mt) genome may unearth additional genetic loci previously unassociated with AMD risk.

Methods

Joint effects of nSNPs and selected mtSNPs were analyzed by two degree of freedom (2df) joint tests of association in the International AMD Genomics Consortium (IAMDGC) dataset (17,832 controls and 16,144 advanced AMD cases of European ancestry). Subjects were genotyped on the Illumina HumanCoreExome array. After imputation using MINIMAC and the 1000 Genomes Project Phase I reference panel, pairwise linkage disequilibrium pruning, and quality control, 3.9 million nSNPs were analyzed for interaction with mtSNPs chosen based on association in this dataset or publications: A4917G, T5004C, G12771A, and C16069T.

Results

Novel locus TRPM1 was identified with genome-wide significant joint effects (P < 5.0 × 10⁻⁸) of two intronic TRPM1 nSNPs and AMD-associated nonsynonymous MT-ND2 mtSNP A4917G. Stratified analysis by mt allele identified an association only in 4917A (major allele) carriers (P = 4.4 × 10⁻⁹, odds ratio [OR] = 0.90, 95% confidence interval [CI] = 0.87–0.93). Intronic and intergenic ABHD2/RLBP1 nSNPs demonstrated genome-wide significant joint effects (2df joint test P values from 1.8 × 10⁻⁸ to 4.9 × 10⁻⁸) and nominally statistically significant interaction effects with MT-ND5 synonymous mtSNP G12771A. Although a positive association was detected in both strata, the association was stronger in 12771A subjects (P = 0.0020, OR = 2.17, 95% CI = 1.34–3.60).

Conclusions

These results show that joint tests of main effects and gene–gene interaction reveal associations at some novel loci that were missed when considering main effects alone.

Role of Melatonin in Reducing Amphetamine-Induced Degeneration in Substantia Nigra of Rats via Calpain and Calpastatin Interaction

Excessive intracellular calcium levels induce calpain activation, thereby triggering the cell death cascade. Several lines of evidence have demonstrated the neuroprotective role of the overexpression of calpain inhibitor, calpastatin. In this study, amphetamine-induced degeneration in the substantia nigra of rats was determined by evaluating the decrease in the levels of tyrosine hydroxylase phosphorylation. Amphetamine significantly decreased calpastatin levels but increased calpain levels. An induction in calpain activity was demonstrated by an increase in the formation of calpain spectrin breakdown products. The deleterious effects of amphetamine exposure were diminished in rats by pretreatment with melatonin. In addition, the effect of melatonin on calpastatin expression was investigated in human neuroblastoma SH-SY5Y cells. Melatonin was able to increase the calpastatin levels, and this effect could be blocked by luzindole, a melatonin receptor antagonist. These results demonstrate the neuroprotective ability of melatonin and its role in inducing calpastatin expression via a receptor-dependent pathway.

Mitochondrial Dynamics: In Cell Reprogramming as It Is in Cancer

Somatic cells can be reprogrammed into a pluripotent cellular state similar to that of embryonic stem cells. Given the significant physiological differences between the somatic and pluripotent cells, cell reprogramming is associated with a profound reorganization of the somatic phenotype at all levels. The remodeling of mitochondrial morphology is one of these dramatic changes that somatic cells have to undertake during cell reprogramming. Somatic cells transform their tubular and interconnected mitochondrial network to the fragmented and isolated organelles found in pluripotent stem cells early during cell reprogramming. Accordingly, mitochondrial fission, the process whereby the mitochondria divide, plays an important role in the cell reprogramming process. Here, we present an overview of the importance of mitochondrial fission in both cell reprogramming and cellular transformation.

Silver Nanoparticles Against Salmonella enterica Serotype Typhimurium: Role of Inner Membrane Dysfunction

The evolution of antibiotics-resistant bacteria is considered a major concern. To explore promising antibacterial materials and clarify their unknown mechanisms, the mode of action of silver nanoparticles (AgNPs) against Salmonella enterica serotype typhimurium was investigated. We investigated the effect of AgNPs on the bacterial membrane. The N-phenyl-1-naphthylamine assay showed that the permeability of the outer membrane was not changed by treatment with AgNPs. The O-nitrophenyl-β-D-galactopyranoside assay showed that the inner membrane permeability increased as AgNPs concentration increased. Our results showed that AgNPs affected the inner membrane without outer membrane damage. Generally, antibiotic-induced reactive oxygen species (ROS) and changes in the Ca²⁺ gradient are known to contribute to bacterial cell death. Likewise, we detected that AgNPs induced the accumulation of ROS and intracellular Ca²⁺ depending on its concentration, using 2',7'-dichlorodihydrofluorescein and Fura-2AM, respectively. At higher concentrations, no relationship between oxidative stress and bactericidal effects of AgNPs was confirmed through a cell viability assay and intracellular Ca²⁺ assay with antioxidant N-acetylcysteine. In this study, the inner membrane disruption followed by membrane dysfunction played a key role in the antibacterial activity of AgNPs against S. typhimurium. Contrary to the expected results, ROS do not influence growth inhibition of AgNPs.

Simultaneous Measurement of Mitochondrial Calcium and Mitochondrial Membrane Potential in Live Cells by Fluorescent Microscopy

Apart from their essential role in generating ATP, mitochondria also act as local calcium (Ca²⁺) buffers to tightly regulate intracellular Ca²⁺ concentration. To do this, mitochondria utilize the electrochemical potential across their inner membrane (ΔΨm) to sequester Ca²⁺. The influx of Ca²⁺ into the mitochondria stimulates three rate-limiting dehydrogenases of the citric acid cycle, increasing electron transfer through the oxidative phosphorylation (OXPHOS) complexes. This stimulation maintains ΔΨm, which is temporarily dissipated as the positive calcium ions cross the mitochondrial inner membrane into the mitochondrial matrix. We describe here a method for simultaneously measuring mitochondria Ca²⁺ uptake and ΔΨm in live cells using confocal microscopy. By permeabilizing the cells, mitochondrial Ca²⁺ can be measured using the fluorescent Ca²⁺ indicator Fluo-4, AM, with measurement of ΔΨm using the fluorescent dye tetramethylrhodamine, methyl ester, perchlorate (TMRM). The benefit of this system is that there is very little spectral overlap between the fluorescent dyes, allowing accurate measurement of mitochondrial Ca²⁺ and ΔΨm simultaneously. Using the sequential addition of Ca²⁺ aliquots, mitochondrial Ca²⁺ uptake can be monitored, and the concentration at which Ca²⁺ induces mitochondrial membrane permeability transition and the loss of ΔΨm determined.

Physical Exercise and Brain Mitochondrial Fitness: The Possible Role Against Alzheimer's Disease

Exercise is one of the most effective strategies to maintain a healthy body and mind, with particular beneficial effects of exercise on promoting brain plasticity, increasing cognition and reducing the risk of cognitive decline and dementia in later life. Moreover, the beneficial effects resulting from increased physical activity occur at different levels of cellular organization, mitochondria being preferential target organelles. The relevance of this review article relies on the need to integrate the current knowledge of proposed mechanisms, focus mitochondria, to explain the protective effects of exercise that might underlie neuroplasticity and seeks to synthesize these data in the context of exploring exercise as a feasible intervention to delay cognitive impairment associated with neurodegenerative conditions, particularly Alzheimer disease.

Impaired Cellular Bioenergetics Causes Mitochondrial Calcium Handling Defects in MT-ND5 Mutant Cybrids

Mutations in mitochondrial DNA (mtDNA) can cause mitochondrial disease, a group of metabolic disorders that affect both children and adults. Interestingly, individual mtDNA mutations can cause very different clinical symptoms, however the factors that determine these phenotypes remain obscure. Defects in mitochondrial oxidative phosphorylation can disrupt cell signaling pathways, which may shape these disease phenotypes. In particular, mitochondria participate closely in cellular calcium signaling, with profound impact on cell function. Here, we examined the effects of a homoplasmic m.13565C>T mutation in MT-ND5 on cellular calcium handling using transmitochondrial cybrids (ND5 mutant cybrids). We found that the oxidation of NADH and mitochondrial membrane potential (Δψ_m) were significantly reduced in ND5 mutant cybrids. These metabolic defects were associated with a significant decrease in calcium uptake by ND5 mutant mitochondria in response to a calcium transient. Inhibition of glycolysis with 2-deoxy-D-glucose did not affect cytosolic calcium levels in control cybrids, but caused an increase in cytosolic calcium in ND5 mutant cybrids. This suggests that glycolytically-generated ATP is required not only to maintain Δψ_m in ND5 mutant mitochondria but is also critical for regulating cellular calcium homeostasis. We conclude that the m.13565C>T mutation in MT-ND5 causes defects in both mitochondrial oxidative metabolism and mitochondrial calcium sequestration. This disruption of mitochondrial calcium handling, which leads to defects in cellular calcium homeostasis, may be an important contributor to mitochondrial disease pathogenesis.

Reciprocal Regulation of Mitochondrial Dynamics and Calcium Signaling in Astrocyte Processes

We recently showed that inhibition of neuronal activity, glutamate uptake, or reversed-Na(+)/Ca(2+)-exchange with TTX, TFB-TBOA, or YM-244769, respectively, increases mitochondrial mobility in astrocytic processes. In the present study, we examined the interrelationships between mitochondrial mobility and Ca(2+) signaling in astrocyte processes in organotypic cultures of rat hippocampus. All of the treatments that increase mitochondrial mobility decreased basal Ca(2+). As recently reported, we observed spontaneous Ca(2+) spikes with half-lives of ∼1 s that spread ∼6 μm and are almost abolished by a TRPA1 channel antagonist. Virtually all of these Ca(2+) spikes overlap mitochondria (98%), and 62% of mitochondria are overlapped by these spikes. Although tetrodotoxin, TFB-TBOA, or YM-244769 increased Ca(2+) signaling, the specific effects on peak, decay time, and/or frequency were different. To more specifically manipulate mitochondrial mobility, we explored the effects of Miro motor adaptor proteins. We show that Miro1 and Miro2 are both expressed in astrocytes and that exogenous expression of Ca(2+)-insensitive Miro mutants (KK) nearly doubles the percentage of mobile mitochondria. Expression of Miro1(KK) had a modest effect on the frequency of these Ca(2+) spikes but nearly doubled the decay half-life. The mitochondrial proton ionophore, FCCP, caused a large, prolonged increase in cytosolic Ca(2+) followed by an increase in the decay time and the spread of the spontaneous Ca(2+) spikes. Photo-ablation of mitochondria in individual astrocyte processes has similar effects on Ca(2+). Together, these studies show that Ca(2+) regulates mitochondrial mobility, and mitochondria in turn regulate Ca(2+) signals in astrocyte processes.

SIGNIFICANCE STATEMENT

In neurons, the movement and positioning of mitochondria at sites of elevated activity are important for matching local energy and Ca(2+) buffering capacity. Previously, we demonstrated that mitochondria are immobilized in astrocytes in response to neuronal activity and glutamate uptake. Here, we demonstrate a mechanism by which mitochondria are immobilized in astrocytes subsequent to increases in intracellular [Ca(2+)] and provide evidence that mitochondria contribute to the compartmentalization of spontaneous Ca(2+) signals in astrocyte processes. Immobilization of mitochondria at sites of glutamate uptake in astrocyte processes provides a mechanism to coordinate increases in activity with increases in mitochondrial metabolism.

Inflammation and Oxidative Stress: The Molecular Connectivity between Insulin Resistance, Obesity, and Alzheimer's Disease

Type 2 diabetes (T2DM), Alzheimer's disease (AD), and insulin resistance are age-related conditions and increased prevalence is of public concern. Recent research has provided evidence that insulin resistance and impaired insulin signalling may be a contributory factor to the progression of diabetes, dementia, and other neurological disorders. Alzheimer's disease (AD) is the most common subtype of dementia. Reduced release (for T2DM) and decreased action of insulin are central to the development and progression of both T2DM and AD. A literature search was conducted to identify molecular commonalities between obesity, diabetes, and AD. Insulin resistance affects many tissues and organs, either through impaired insulin signalling or through aberrant changes in both glucose and lipid (cholesterol and triacylglycerol) metabolism and concentrations in the blood. Although epidemiological and biological evidence has highlighted an increased incidence of cognitive decline and AD in patients with T2DM, the common molecular basis of cell and tissue dysfunction is rapidly gaining recognition. As a cause or consequence, the chronic inflammatory response and oxidative stress associated with T2DM, amyloid-β (Aβ) protein accumulation, and mitochondrial dysfunction link T2DM and AD.

Molecular Events Linking Oxidative Stress and Inflammation to Insulin Resistance and β-Cell Dysfunction

The prevalence of diabetes mellitus (DM) is increasing worldwide, a consequence of the alarming rise in obesity and metabolic syndrome (MetS). Oxidative stress and inflammation are key physiological and pathological events linking obesity, insulin resistance, and the progression of type 2 DM (T2DM). Unresolved inflammation alongside a “glucolipotoxic” environment of the pancreatic islets, in insulin resistant pathologies, enhances the infiltration of immune cells which through secretory activity cause dysfunction of insulin-secreting β-cells and ultimately cell death. Recent molecular investigations have revealed that mechanisms responsible for insulin resistance associated with T2DM are detected in conditions such as obesity and MetS, including impaired insulin receptor (IR) signalling in insulin responsive tissues, oxidative stress, and endoplasmic reticulum (ER) stress. The aim of the present review is to describe the evidence linking oxidative stress and inflammation with impairment of insulin secretion and action, which result in the progression of T2DM and other conditions associated with metabolic dysregulation.

Enzymatic activities linked to cardiac energy metabolism of Trypanosoma evansi-infected rats and their possible functional correlations to disease pathogenesis

The aim of this study was to investigate the activities of important enzymes involved in the phosphoryl transfer network (adenylate kinase and creatine kinase (CK)), lactate dehydrogenase (LDH), respiratory chain complexes and biomarkers of cardiac function in rat experimentally infected by Trypanosoma evansi. Rat heart samples were evaluated at 5 and 15 days post-infection (PI). At 5 day PI, there was an increase in LDH and CK activities, and a decrease in respiratory chain complexes II, IV and succinate dehydrogenase activities. In addition, on day 15 PI, a decrease in the respiratory chain complex IV activity was observed. Biomarkers of cardiac function were higher in infected animals on days 5 and 15 PI. Considering the importance of the energy metabolism for heart function, it is possible that the changes in the enzymatic activities involved in the cardiac phosphotransfer network and the decrease in respiratory chain might be involved partially in the role of biomarkers of cardiac function of T. evansi-infected rats.

The impact of mitochondrial function/dysfunction on IVF and new treatment possibilities for infertility

Mitochondria play vital roles in oocyte functions and they are critical indicators of oocyte quality which is important for fertilization and development into viable offspring. Quality-compromised oocytes are correlated with infertility, developmental disorders, reduced blastocyst cell number and embryo loss in which mitochondrial dysfunctions play a significant role. Increasingly, women affected by metabolic disorders such as diabetes or obesity and oocyte aging are seeking treatment in IVF clinics to overcome the effects of adverse metabolic conditions on mitochondrial functions and new treatments have become available to restore oocyte quality. The past decade has seen enormous advances in potential therapies to restore oocyte quality and includes dietary components and transfer of mitochondria from cells with mitochondrial integrity into mitochondria-impaired oocytes. New technologies have opened up new possibilities for therapeutic advances which will increase the success rates for IVF of oocytes from women with compromised oocyte quality.

Emerging modes of PINK1 signaling: another task for MARK2

PTEN-induced kinase 1 (PINK1) acts at multiple levels to promote mitochondrial health, including regulatory influence on ATP-synthesis, protein quality control, apoptosis, mitochondrial transport, and destiny. PINK1 mutations are linked to Parkinson disease (PD) and mostly result in loss of kinase activity. But the molecular events responsible for neuronal death as well as the physiological targets and regulators of PINK1 are still a matter of debate. This review highlights the recent progress evolving the cellular functions of the cytosolic pool of PINK1 in mitochondrial trafficking and neuronal differentiation. Regulation of PINK1 signaling occurs by mitochondrial processing to truncated forms of PINK1, differentially targeted to several subcellular compartments. The first identified activating kinase of PINK1 is MAP/microtubule affinity regulating kinase 2 (MARK2), which phosphorylates T313, a frequent mutation site linked to PD. Kinases of the MARK2 family perform diverse functions in neuronal polarity, transport, migration, and neurodegeneration such as Alzheimer disease (AD). This new protein kinase signaling axis might provide a link between neurodegenerative processes in AD and PD diseases and opens novel possibilities in targeting pathological signaling processes.

Mitochondrial dynamics in aging and disease

Mitochondria are self-replicating organelles but nevertheless strongly depend on supply coded in nuclear genes. They serve many physiological demands in living cells. Supply of the cytoplasm with ATP and engagement in Ca(2+) regulation belong to the main functions of mitochondria. In large eukaryotic cells, in particular in neurons, with their long dendrites and axons, mitochondria have to move to the sites of their action. This trafficking involves several motor molecules and mechanisms to sense the sites of requirements of mitochondria. With aging and as a consequence of some diseases, mitochondrial components may be rendered dysfunctional, and mtDNA mutations arise during the course of replication and by the action of reactive oxygen species. Mutants in motor molecules engaged in trafficking and in the machinery of fusion and fission are causing severe deficiencies on the cellular level; they support neurodegeneration and, thus, cause many diseases. Frequent fusion and fission events mediate the elimination of impaired parts from mitochondria which finally will be degraded by autophagosomes. Extensive fusion provides a basis for functional complementation. Mobility of proteins and small molecules within the mitochondria is necessary to reach the functional goals of fusion and fission, although cristae and a large fraction of proteins of the respiratory complexes proved to be stable for hours after fusion and perform slow exchange of material.

Evolution and cell physiology. 2. The evolution of cell signaling: from mitochondria to Metazoa

The history of life is a history of levels-of-selection transitions. Each transition requires mechanisms that mediate conflict among the lower-level units. In the origins of multicellular eukaryotes, cell signaling is one such mechanism. The roots of cell signaling, however, may extend to the previous major transition, the origin of eukaryotes. Energy-converting protomitochondria within a larger cell allowed eukaryotes to transcend the surface-to-volume constraints inherent in the design of prokaryotes. At the same time, however, protomitochondria can selfishly allocate energy to their own replication. Metabolic signaling may have mediated this principal conflict in several ways. Variation of the protomitochondria was constrained by stoichiometry and strong metabolic demand (state 3) exerted by the protoeukaryote. Variation among protoeukaryotes was increased by the sexual stage of the life cycle, triggered by weak metabolic demand (state 4), resulting in stochastic allocation of protomitochondria to daughter cells. Coupled with selection, many selfish protomitochondria could thus be removed from the population. Hence, regulation of states 3 and 4, as, for instance, provided by the CO2/soluble adenylyl cyclase/cAMP pathway in mitochondria, was critical for conflict mediation. Subsequently, as multicellular eukaryotes evolved, metabolic signaling pathways employed by eukaryotes to mediate conflict within cells could now be co-opted into conflict mediation between cells. For example, in some fungi, the CO2/soluble adenylyl cyclase/cAMP pathway regulates the transition from yeast to forms with hyphae. In animals, this pathway regulates the maturation of sperm. While the particular features (sperm and hyphae) are distinct, both may involve between-cell conflicts that required mediation.

March separate, strike together--role of phosphorylated TAU in mitochondrial dysfunction in Alzheimer's disease

The energy demand and calcium buffering requirements of the brain are met by the high number of mitochondria in neurons and in these, especially at the synapses. Mitochondria are the major producer of reactive oxygen species (ROS); at the same time, they are damaged by ROS that are induced by abnormal protein aggregates that characterize human neurodegenerative diseases such as Alzheimer's disease (AD). Because synaptic mitochondria are long-lived, any damage exerted by these aggregates impacts severely on neuronal function. Here we review how increased TAU, a defining feature of AD and related tauopathies, impairs mitochondrial function by following the principle: 'March separate, strike together!' In the presence of amyloid-β, TAU's toxicity is augmented suggesting synergistic pathomechanisms. In order to restore mitochondrial functions in neurodegeneration as a means of therapeutic intervention it will be important to integrate the various aspects of dysfunction and get a handle on targeting distinct cell types and subcellular compartments.

Mitochondrial regulation in pluripotent stem cells

Due to their fundamental role in energy production, mitochondria have been traditionally known as the powerhouse of the cell. Recent discoveries have suggested crucial roles of mitochondria in the maintenance of pluripotency, differentiation, and reprogramming of induced pluripotent stem cells (iPSCs). While glycolytic energy production is observed at pluripotent states, an increase in mitochondrial oxidative phosphorylation is necessary for cell differentiation. Consequently, a transition from somatic mitochondrial oxidative metabolism to glycolysis seems to be required for successful reprogramming. Future research aiming to dissect the roles of mitochondria in the establishment and homeostasis of pluripotency, as well as combining cell reprogramming with gene editing technologies, may unearth novel insights into our understanding of mitochondrial diseases and aging.

Cellular and molecular mechanisms of mitochondrial function

Mitochondria are membrane bound organelles present in almost all eukaryotic cells. Responsible for orchestrating cellular energy production, they are central to the maintenance of life and the gatekeepers of cell death. Thought to have originated from symbiotic ancestors, they carry a residual genome as mtDNA encoding 13 proteins essential for respiratory chain function. Mitochondria comprise an inner and outer membrane that separate and maintain the aqueous regions, the intermembrane space and the matrix. Mitochondria contribute to many processes central to cellular function and dysfunction including calcium signalling, cell growth and differentiation, cell cycle control and cell death. Mitochondrial shape and positioning in cells is crucial and is tightly regulated by processes of fission and fusion, biogenesis and autophagy, ensuring a relatively constant mitochondrial population. Mitochondrial dysfunction is implicated in metabolic and age related disorders, neurodegenerative diseases and ischemic injury in heart and brain.

Orais and STIMs: physiological mechanisms and disease

The stromal interaction molecules STIM1 and STIM2 are Ca²⁺ sensors, mostly located in the endoplasmic reticulum, that detect changes in the intraluminal Ca²⁺ concentration and communicate this information to plasma membrane store-operated channels, including members of the Orai family, thus mediating store-operated Ca²⁺ entry (SOCE). Orai and STIM proteins are almost ubiquitously expressed in human cells, where SOCE has been reported to play a relevant functional role. The phenotype of patients bearing mutations in STIM and Orai proteins, together with models of STIM or Orai deficiency in mice, as well as other organisms such as Drosophila melanogaster, have provided compelling evidence on the relevant role of these proteins in cellular physiology and pathology. Orai1-deficient patients suffer from severe immunodeficiency, congenital myopathy, chronic pulmonary disease, anhydrotic ectodermal dysplasia and defective dental enamel calcification. STIM1-deficient patients showed similar abnormalities, as well as autoimmune disorders. This review summarizes the current evidence that identifies and explains diseases induced by disturbances in SOCE due to deficiencies or mutations in Orai and STIM proteins.

Imaging mitochondrial calcium signalling with fluorescent probes and single or two photon confocal microscopy

The concentration of calcium ions in the mitochondria has a profound impact on mitochondrial function, modulating respiratory activity at physiological concentrations, while causing lethal damage during calcium overload. The "rhod" series of calcium sensitive fluorescent dyes tend to accumulate preferentially in mitochondria, although the reliability of mitochondrial calcium measurements depends critically on the partitioning of dye within the mitochondria which can vary between preparations. Methods are described to aid verification and quantification of the mitochondrial calcium concentration using single or two photon confocal microscopy and combining the imaging with another cytosolic calcium sensing dye. The method of linear unmixing to separate fluorescent signals based on either differing excitation or emission spectra is outlined and for the purposes of illustration is applied to the separation of rhod-2 signals originating from dye within the mitochondrial and nucleoli.