The regulation of mitochondrial morphology: intricate mechanisms and dynamic machinery

The antiviral sirtuin 3 bridges protein acetylation to mitochondrial integrity and metabolism during human cytomegalovirus infection

Regulation of mitochondrial structure and function is a central component of infection with viruses, including human cytomegalovirus (HCMV), as a virus means to modulate cellular metabolism and immune responses. Here, we link the activity of the mitochondrial deacetylase SIRT3 and global mitochondrial acetylation status to host antiviral responses via regulation of both mitochondrial structural integrity and metabolism during HCMV infection. We establish that SIRT3 deacetylase activity is necessary for suppressing virus production, and that SIRT3 maintains mitochondrial pH and membrane potential during infection. By defining the temporal dynamics of SIRT3-substrate interactions during infection, and overlaying acetylome and proteome information, we find altered SIRT3 associations with the mitochondrial fusion factor OPA1 and acetyl-CoA acyltransferase 2 (ACAA2), concomitant with changes in their acetylation levels. Using mutagenesis, microscopy, and virology assays, we determine OPA1 regulates mitochondrial morphology of infected cells and inhibits HCMV production. OPA1 acetylation status modulates these functions, and we establish K834 as a site regulated by SIRT3. Control of SIRT3 protein levels or enzymatic activity is sufficient for regulating mitochondrial filamentous structure. Lastly, we establish a virus restriction function for ACAA2, an enzyme involved in fatty acid beta-oxidation. Altogether, we highlight SIRT3 activity as a regulatory hub for mitochondrial acetylation and morphology during HCMV infection and point to global acetylation as a reflection of mitochondrial health.

Given their functions in cellular metabolism and immune responses, mitochondria are targeted and disrupted by numerous prevalent viral pathogens, including human cytomegalovirus (HCMV). To characterize mechanisms underlying mitochondrial regulation during HCMV infection in human fibroblasts, this study integrates enzyme-substrate interaction studies, mass spectrometry quantification of protein abundance and acetylation, mutagenesis, microscopy, and virology assays. These analyses establish a link between the mitochondrial acetylation status and mitochondrial structure and metabolism during HCMV infection. We demonstrate that the mitochondrial deacetylase SIRT3 acts in host defense by modulating proteins that regulate mitochondrial structure and fatty acid oxidation. SIRT3 helps to maintain mitochondrial integrity through several mechanisms, including regulation of mitochondrial pH, membrane potential, and the balance between mitochondrial fission and fusion. As excess mitochondrial acetylation is detrimental to mitochondrial metabolism, the virus-induced alterations in SIRT3 functions and mitochondrial acetylation may be linked to known HCMV pathologies, such as the metabolic syndrome and cardiac hypertrophy.

Differential ROS-Mediated Phosphorylation of Drp1 in Mitochondrial Fragmentation Induced by Distinct Cell Death Conditions in Cerebellar Granule Neurons

Reactive oxygen species (ROS) production has been associated with neuronal death. ROS are also involved in mitochondrial fission, which is mediated by Dynamin-related protein 1 (Drp1). The regulation of mitochondrial fragmentation mediated by Drp1 and its relationship to mitochondrial ROS (mtROS) in neuronal death have not been completely clarified. The aim of this study is to evaluate the role of mtROS in cell death and their involvement in the activation of Drp1 and mitochondrial fission in a model of cell death of cultured cerebellar granule neurons (CGN). Neuronal death of CGN induced by potassium deprivation (K5) and staurosporine (ST) triggers mitochondrial ROS production and mitochondrial fragmentation. K5 condition evoked an increase of Drp1 phosphorylation at Ser616, but ST treatment led to a decrease of Drp1 phosphorylation. Moreover, the death of CGN induced by both K5 and ST was markedly reduced in the presence of MitoTEMPO; however, mitochondrial morphology was not recovered. Here, we show that the mitochondria are the initial source of ROS involved in the neuronal death of CGN and that mitochondrial fragmentation is a common event in cell death; however, this process is not mediated by Drp1 phosphorylation at Ser616.

Mitochondrial DNA Copy Number in Human Blastocyst: A Novel Biomarker for the Prediction of Implantation Potential

The relationship between mitochondrial DNA (mtDNA) copy number and the outcome of embryo transfer is under debate. Our aim was to explore the relationship between mtDNA copy number in human blastocysts and embryonic development to determine whether mtDNA represents a novel biomarker for the prediction of implantation potential. A total of 246 blastocysts were analyzed by next-generation sequencing. There was no correlation between mtDNA copy number and maternal age in all blastocyst groups and euploid blastocyst groups. Additionally, the mtDNA copy number was not significantly higher in aneuploid blastocysts. Subsequently, no relationship was observed between mtDNA copy number and blastocyst quality. The assessment of clinical pregnancy outcome after the transfer of euploid blastocysts to the uterus indicated that the mtDNA copy number was significantly lower in the clinical pregnancy group than in those who failed implantation. The cut-off value of mtDNA copy number was 320.5, which was a highly predictive value. Blastocysts with an increased mtDNA copy number had lower implantation potential, and mtDNA copy number was largely equal in terms of maternal age, chromosome ploidy, and quality of blastocysts.

Mitochondrial DNA Content May Not Be a Reliable Screening Biomarker for Live Birth After Single Euploid Blastocyst Transfer

An increasing number of studies have related the mitochondrial DNA (mtDNA) content to embryo viability and transfer outcomes. However, previous studies have focused more on the relationship between mtDNA and embryo implantation, few studies have studied the effect of the mtDNA content on live birth. In the study, we investigated whether mtDNA content is a reliable screening biomarker for live birth after single blastocyst transfer. A total of 233 couples with 316 blastocyst stage embryos undergoing in vitro fertilization treatment and pre-implantation genetic testing analysis were included in the study. All embryos were chromosomally normal and had undergone single-embryo transfers. There was no significant difference observed in the blastocyst mtDNA content among the live birth, miscarriage and non-implanted groups (p=0.999), and the mtDNA content in blastocysts from the miscarriage and live birth groups was similar [median (interquartile range), 1.00*10⁸(7.59*10⁷- 1.39*10⁸) vs 1.01*10⁸ (7.37*10⁷- 1.32*10⁸)]. Similarly, no significant association was observed between mtDNA content and embryo implantation potential (p=0.965). After adjusting for multiple confounders in a logistic regression analysis with generalized estimating equations, no associations between mtDNA content and live birth were observed in all blastocysts, Day-5 and Day-6 blastocysts (p=0.567, p=0.673, p=0.165, respectively). The live birth rate was not significantly different between blastocysts with an elevated mtDNA content and blastocysts with a normal mtDNA content (26.7% vs 33.6% p=0.780). Additionally, there was no linear correlation between the mtDNA content and maternal age (p=0.570). In conclusion, the mtDNA content does not seem to be a potential biomarker for embryo transfer outcomes (i.e., implantation and live birth) based on the existing testing tools. Embryos with an elevated mtDNA content also have development potential for successful live birth.

TNFα induces mitochondrial fragmentation and biogenesis in human airway smooth muscle

In human airway smooth muscle (hASM), mitochondrial volume density is greater in asthmatic patients compared with normal controls. There is also an increase in mitochondrial fragmentation in hASM of moderate asthmatics associated with an increase in dynamin-related protein 1 (Drp1) and a decrease in mitofusin 2 (Mfn2) expression, mitochondrial fission, and fusion proteins, respectively. Proinflammatory cytokines such TNFα contribute to hASM hyperreactivity and cell proliferation associated with asthma. However, the involvement of proinflammatory cytokines in mitochondrial remodeling is not clearly established. In nonasthmatic hASM cells, mitochondria were labeled using MitoTracker Red and imaged in three dimensions using a confocal microscope. After 24-h TNFα exposure, mitochondria in hASM cells were more fragmented, evidenced by decreased form factor and aspect ratio and increased sphericity. Associated with increased mitochondrial fragmentation, Drp1 expression increased while Mfn2 expression was reduced. TNFα also increased mitochondrial biogenesis in hASM cells reflected by increased peroxisome proliferator-activated receptor-γ coactivator 1α expression and increased mitochondrial DNA copy number. Associated with mitochondrial biogenesis, TNFα exposure also increased mitochondrial volume density and porin expression, resulting in an increase in maximum O2 consumption rate. However, when normalized for mitochondrial volume density, O2 consumption rate per mitochondrion was reduced by TNFα exposure. Associated with mitochondrial fragmentation and biogenesis, TNFα also increased hASM cell proliferation, an effect mimicked by siRNA knockdown of Mfn2 expression and mitigated by Mfn2 overexpression. The results of this study support our hypothesis that in hASM cells exposed to TNFα mitochondria are more fragmented, with an increase in mitochondrial biogenesis and mitochondrial volume density resulting in reduced O2 consumption rate per mitochondrion.

Calycosin induces apoptosis via p38‑MAPK pathway‑mediated activation of the mitochondrial apoptotic pathway in human osteosarcoma 143B cells

Previous studies have demonstrated that calycosin is a natural phytoestrogen with a similar structure to estrogen, which can inhibit cell proliferation and induce apoptosis in a variety of tumors. Calycosin exerts potential pharmacological effects on osteosarcoma cells by inducing apoptosis. The aim of the present study was to elucidate the specific molecular mechanism of calycosin-induced apoptosis in osteosarcoma cells. Cell proliferation was determined by an MTT assay. Annexin V/PI and JC-1 staining were used to detect apoptosis and mitochondrial dysfunction, respectively, by flow cytometry. Western blot analysis was used to detect the expression of caspases or mitochondrial proteins. The results revealed that calycosin reduced the cell viability of human osteosarcoma 143B cells, induced apoptosis and increased the loss of mitochondrial membrane potential (MMP). In addition, calycosin increased the expression of the proapoptotic antiapoptotic proteins cleaved caspase-3, cleaved caspase-9, cleaved poly(ADP-ribose) polymerase and Bcl-2-associated X protein (Bax), and decreased the expression of the antiapoptotic proapoptotic protein B-cell lymphoma-2 (Bcl-2), thus altering the Bax/Bcl-2 ratio. In addition, the expression levels of cytochrome c were markedly decreased in the mitochondria and increased in the cytoplasm following calycosin treatment. Furthermore, calycosin treatment induced p38-mitogen-activated protein kinase (MAPK) phosphorylation, whereas the p38-MAPK inhibitor BIRB 796 markedly reversed cell viability, apoptosis and loss of MMP in 143B cells. These results suggested that calycosin inhibited osteosarcoma 143B cell growth via p38-MAPK regulation of mitochondrial-dependent intrinsic apoptotic pathways.

A Synthetic Epoxydocosapentaenoic Acid Analogue Ameliorates Cardiac Ischemia/Reperfusion Injury: The Involvement of the Sirtuin 3-NLRP3 Pathway

While survival rates have markedly improved following cardiac ischemia-reperfusion (IR) injury, the resulting heart damage remains an important issue. Preserving mitochondrial quality and limiting NLRP3 inflammasome activation is an approach to limit IR injury, in which the mitochondrial deacetylase sirtuin 3 (SIRT3) has a role. Recent data demonstrate cytochrome P450 (CYP450)-derived epoxy metabolites, epoxydocosapentaenoic acids (EDPs), of docosahexaenoic acid (DHA), attenuate cardiac IR injury. EDPs undergo rapid removal and inactivation by enzymatic and non-enzymatic processes. The current study hypothesizes that the cardioprotective effects of the synthetic EDP surrogates AS-27, SA-26 and AA-4 against IR injury involve activation of SIRT3. Isolated hearts from wild type (WT) mice were perfused in the Langendorff mode with vehicle, AS-27, SA-26 or AA-4. Improved postischemic functional recovery, maintained cardiac ATP levels, reduced oxidative stress and attenuation of NLRP3 activation were observed in hearts perfused with the analogue SA-26. Assessment of cardiac mitochondria demonstrated SA-26 preserved SIRT3 activity and reduced acetylation of manganese superoxide dismutase (MnSOD) suggesting enhanced antioxidant capacity. Together, these data demonstrate that the cardioprotective effects of the EDP analogue SA-26 against IR injury involve preservation of mitochondrial SIRT3 activity, which attenuates a detrimental innate NLRP3 inflammasome response.

Impact of Up- and Downregulation of Metabolites and Mitochondrial Content on pH and Color of the Longissimus Muscle from Normal-pH and Dark-Cutting Beef

Limited knowledge is currently available on the biochemical basis for the development of dark-cutting beef. The objective of this research was to determine the metabolite profile and mitochondrial content differences between normal-pH and dark-cutting beef. A gas chromatography-mass spectrometer-based nontargeted metabolomic approach indicated downregulation of glycolytic metabolites, including glucose-1- and 6-phosphate and upregulation of tricarboxylic substrates such as malic and fumaric acids occurred in dark-cutting beef when compared to normal-pH beef. Neurotransmitters such as 4-aminobutyric acid and succinate semialdehyde were upregulated in dark-cutting beef than normal-pH beef. Immunohistochemistry indicated a more oxidative fiber type in dark-cutting beef than normal-pH beef. In support, the mitochondrial protein and DNA content were greater in dark-cutting beef. This increased mitochondrial content, in part, could influence oxygen consumption and myoglobin oxygenation/appearance of dark-cutting beef. The current results demonstrate that the more tricarboxylic metabolites and mitochondrial content in dark-cutting beef impact muscle pH and color.

Targeting mitochondria in melanoma: Interplay between MAPK signaling pathway and mitochondrial dynamics

Melanoma is a malignant proliferative disease originated in melanocytes, characterized by high metastatic activity and by the activation of oncogenes, such as B-RAF (40-60% of cases). Recent studies have shown that vemurafenib (a MAPK inhibitor) promoted disturbance of mitochondrial bioenergetics, although underlying mechanisms are not fully comprehended. Here we showed that MAPK inhibition by vemurafenib in B-RAF^V600E-mutated human melanoma culminated in the inhibition of DRP1 phosphorylation, associated to a large mitochondrial network remodeling to the hyperfused phenotype, and increased oxidative phosphorylation capacity. Such alterations may be associated to melanoma resistance to vemurafenib, since the impairment of oxidative phosphorylation increased the vemurafenib cytotoxicity. These results point to the potential of mitochondrial dynamics as a targetable pathway in melanoma.

Tubeimoside‑1 induces apoptosis in human glioma U251 cells by suppressing PI3K/Akt‑mediated signaling pathways

Tubeimoside-1 (TBMS1), a traditional Chinese herb extracted from Bolbostemma paniculatum (Maxim.), induces apoptosis in a number of human cancer cell lines. TBMS1 has been reported to induce apoptosis in human glioma cells, however the mechanism remains to be elucidated. The present study explored TBMS1-induced PI3K/Akt-related pathways in human glioma cells. The human glioma U251 and the human astrocyte (HA) cell lines were treated with various concentrations of TBMS1. MTT assays were conducted to analyze cell viability. Cell cycle distribution and the rate of apoptosis were assessed using flow cytometry. BrdU incorporation and Hoechst 33342 staining were performed to analyze the cell cycle and apoptosis, respectively. Western blotting was performed to investigate protein expression levels. The results demonstrated that TBMS1 reduced cell viability in human glioma cells U251 by suppressing Akt phosphorylation. Subsequently, TBMS1 inhibited DNA synthesis and induced G2/M phase arrest by targeting the PI3K/Akt/p21 and the cyclin-dependent kinase 1/cyclin B1 signaling cascades. In addition, TBMS1 triggered apoptosis via the PI3K/Akt-mediated Bcl-2 signaling pathway. These results demonstrated that TBMS1 prevented the progression of gliomas via the PI3K/Akt-dependent pathway, which provided a theoretical basis for in vivo studies to use TBMS1 as potential therapy for the prevention of cancer.

Mechanisms and roles of mitochondrial localisation and dynamics in neuronal function

Neurons are highly polarised, complex and incredibly energy intensive cells, and their demand for ATP during neuronal transmission is primarily met by oxidative phosphorylation by mitochondria. Thus, maintaining the health and efficient function of mitochondria is vital for neuronal integrity, viability and synaptic activity. Mitochondria do not exist in isolation, but constantly undergo cycles of fusion and fission, and are actively transported around the neuron to sites of high energy demand. Intriguingly, axonal and dendritic mitochondria exhibit different morphologies. In axons mitochondria are small and sparse whereas in dendrites they are larger and more densely packed. The transport mechanisms and mitochondrial dynamics that underlie these differences, and their functional implications, have been the focus of concerted investigation. Moreover, it is now clear that deficiencies in mitochondrial dynamics can be a primary factor in many neurodegenerative diseases. Here, we review the role that mitochondrial dynamics play in neuronal function, how these processes support synaptic transmission and how mitochondrial dysfunction is implicated in neurodegenerative disease.

BHRF1, a BCL2 viral homolog, disturbs mitochondrial dynamics and stimulates mitophagy to dampen type I IFN induction

Mitochondria respond to many cellular functions and act as central hubs in innate immunity against viruses. This response is notably due to their role in the activation of interferon (IFN) signaling pathways through the activity of MAVS (mitochondrial antiviral signaling protein) present at the mitochondrial surface. Here, we report that the BHRF1 protein, a BCL2 homolog encoded by Epstein-Barr virus (EBV), inhibits IFNB/IFN-β induction by targeting the mitochondria. Indeed, we have demonstrated that BHRF1 expression modifies mitochondrial dynamics and stimulates DNM1L/Drp1-mediated mitochondrial fission. Concomitantly, we have shown that BHRF1 is pro-autophagic because it stimulates the autophagic flux by interacting with BECN1/Beclin 1. In response to the BHRF1-induced mitochondrial fission and macroautophagy/autophagy stimulation, BHRF1 drives mitochondrial network reorganization to form juxtanuclear mitochondrial aggregates known as mito-aggresomes. Mitophagy is a cellular process, which can specifically sequester and degrade mitochondria. Our confocal studies uncovered that numerous mitochondria are present in autophagosomes and acidic compartments using BHRF1-expressing cells. Moreover, mito-aggresome formation allows the induction of mitophagy and the accumulation of PINK1 at the mitochondria. As BHRF1 modulates the mitochondrial fate, we explored the effect of BHRF1 on innate immunity and showed that BHRF1 expression could prevent IFNB induction. Indeed, BHRF1 inhibits the IFNB promoter activation and blocks the nuclear translocation of IRF3 (interferon regulatory factor 3). Thus, we concluded that BHRF1 can counteract innate immunity activation by inducing fission of the mitochondria to facilitate their sequestration in mitophagosomes for degradation.Abbreviations: 3-MA: 3-methyladenine; ACTB: actin beta; BCL2: BCL2 apoptosis regulator; CARD: caspase recruitment domain; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; CI: compaction index; CQ: chloroquine; DAPI: 4',6-diamidino-2-phenylindole, dihydrochloride; DDX58/RIG-I: DExD/H-box helicase 58; DNM1L/Drp1: dynamin 1 like; EBSS: Earle's balanced salt solution; EBV: Epstein-Barr virus; ER: endoplasmic reticulum; EV: empty vector; GFP: green fluorescent protein; HEK: human embryonic kidney; IFN: interferon; IgG: immunoglobulin G; IRF3: interferon regulatory factor 3; LDHA: lactate dehydrogenase A; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MAVS: mitochondrial antiviral signaling protein; MMP: mitochondrial membrane potential; MOM: mitochondrial outer membrane; PINK1: PTEN induced kinase 1; RFP: red fluorescent protein; ROS: reactive oxygen species; SQSTM1/p62: sequestosome 1; STING1: stimulator of interferon response cGAMP interactor 1; TOMM20: translocase of outer mitochondrial membrane 20; VDAC: voltage dependent anion channel.

Perturbations in Mitochondrial Dynamics Are Closely Involved in the Progression of Alcoholic Liver Disease

BACKGROUND

Mitochondria play a fundamental role in the pathogenesis of alcoholic liver disease (ALD). The preservation of functional mitochondria during toxic alcohol insults is essential for cell survival and is maintained by key processes known as mitochondrial dynamics, including fragmentation and fusion, which are regulated by mitochondria-shaping proteins (MSP). We have shown mitochondrial dynamics to be distorted by alcohol in cellular and animal models, but the effect in humans remains unknown.

METHODS

Hepatic gene expression of the main MSP involved in the mitochondrial fusion and fragmentation pathways was evaluated in patients with alcoholic hepatitis (AH) by DNA microarray (n = 15) and Reverse Transcription Polymerase Chain Reaction (n = 32). The activation of dynamin-1-like protein (Drp1) was also investigated in mitochondria isolated from liver biopsies of ALD patients (n = 8). The effects of alcohol on mitochondrial dynamics and on MSP protein expression were studied in human precision-cut liver slices (PCLS) exposed for 24 hours to increasing doses of ethanol (EtOH; 50 to 250 mM).

RESULTS

A profound hyperactivation of the fragmentation pathway was observed in AH patients, with a significant increase in the expression of Drp1 and its adapters/receptors. The translocation of Drp1 to the mitochondria was also induced in patients with severe ALD and was affected in the PCLS with short-term exposure to EtOH but only mildly. The fusion pathway was not altered in ALD, and this was confirmed in the PCLS model.

CONCLUSIONS

The present study reveals the role of mitochondrial dynamics in human ALD, confirming our previous observations in animal and cell culture models of ALD. Taken together, we show that alcohol has a significant impact on the fragmentation pathway, and we confirm Drp1 as a potential therapeutic target in severe ALD.

Sustained Ultrastructural Changes in Rat Hippocampal Formation After Repeated Electroconvulsive Seizures

BACKGROUND

Electroconvulsive therapy (ECT) is a highly effective and fast-acting treatment for depression used in the clinic. Its mechanism of therapeutic action remains uncertain. Previous studies have focused on documenting neuroplasticity in the early phase following electroconvulsive seizures (ECS), an animal model of ECT. Here, we investigate whether changes in synaptic plasticity and nonneuronal plasticity (vascular and mitochondria) are sustained 3 months after repeated ECS trials.

METHODS

ECS or sham treatment was given daily for 1 day or 10 days to a genetic animal model of depression: the Flinders Sensitive and Resistant Line rats. Stereological principles were employed to quantify numbers of synapses and mitochondria as well as length of microvessels in the hippocampus 24 hours after a single ECS. Three months after 10 ECS treatments (1 per day for 10 days) and sham-treatment, brain-derived neurotrophic factor and vascular endothelial growth factor protein levels were quantified with immunohistochemistry.

RESULTS

A single ECS treatment significantly increased the volume of hippocampal CA1-stratum radiatum, the total length of microvessels, mitochondria number, and synapse number. Observed changes were sustained as shown in the multiple ECS treatment group analyzed 3 months after the last of 10 ECS treatments.

CONCLUSION

A single ECS caused rapid effects of synaptic plasticity and nonneuronal plasticity, while repeated ECS induced long-lasting changes in the efficacy of synaptic plasticity and nonneuronal plasticity at least up to 3 months after ECS.

The ubiquitous role of mitochondria in Parkinson and other neurodegenerative diseases

Orderly mitochondrial life cycle, plays a key role in the pathology of neurodegenerative diseases. Mitochondria are ubiquitous in neurons as they respond to an ever-changing demand for energy supply. Mitochondria constantly change in shape and location, feature of their dynamic nature, which facilitates a quality control mechanism. Biological studies in mitochondria dynamics are unveiling the mechanisms of fission and fusion, which essentially arrange morphology and motility of these organelles. Control of mitochondrial network homeostasis is a critical factor for the proper function of neurons. Disease-related genes have been reported to be implicated in mitochondrial dysfunction. Increasing evidence implicate mitochondrial perturbation in neuronal diseases, such as AD, PD, HD, and ALS. The intricacy involved in neurodegenerative diseases and the dynamic nature of mitochondria point to the idea that, despite progress toward detecting the biology underlying mitochondrial disorders, its link to these diseases is difficult to be identified in the laboratory. Considering the need to model signaling pathways, both in spatial and temporal level, there is a challenge to use a multiscale modeling framework, which is essential for understanding the dynamics of a complex biological system. The use of computational models in order to represent both a qualitative and a quantitative structure of mitochondrial homeostasis, allows to perform simulation experiments so as to monitor the conformational changes, as well as the intersection of form and function.

Insulin resistance is improved in high-fat fed mice by photobiomodulation therapy at 630 nm

Photobiomodulation therapy (PBMT) in the infrared spectrum exerts positive effects on glucose metabolism, but the use of PBMT at the red spectrum has not been assessed. Male Swiss albino mice were divided into low-fat control and high-fat diet (HFD) for 12 weeks and were treated with red (630 nm) PBMT or no treatment (Sham) during weeks 9 to 12. PBMT was delivered at 31.19 J/cm² , 60 J total dose per day for 20 days. In HFD-fed mice, PBMT improved glucose tolerance, insulin resistance and fasting hyperinsulinemia. PBMT also reduced adiposity and inflammatory infiltrate in adipose tissue. Phosphorylation of Akt in epididymal adipose tissue and rectus femoralis muscle was improved by PBMT. In epididymal fat PBMT reversed the reduced phosphorylation of AS160 and the reduced Glut4 content. In addition, PBMT reversed the alterations caused by HFD in rectus femoralis muscle on proteins involved in mitochondrial dynamics and β-oxidation. In conclusion, PBMT at red spectrum improved insulin resistance and glucose metabolism in HFD-fed mice.

Update on the association between alpha-synuclein and tau with mitochondrial dysfunction: Implications for Parkinson's disease

The critical role of mitochondrial dysfunction in the pathological mechanisms of neurodegenerative disorders, particularly Parkinson's disease (PD), is well established. Compelling evidence indicates that Parkinson's proteins (e.g., α-synuclein, Parkin, PINK1, DJ-1, and LRRK2) are associated with mitochondrial dysfunction and oxidative stress in PD. Significantly, there is a possible central role of alpha-synuclein (α-Syn) in the occurrence of mitochondrial dysfunction and oxidative stress by the mediation of different signaling pathways. Also, tau, traditionally considered as the main component of neurofibrillary tangles, aggregates and amplifies the neurotoxic effects on mitochondria by interacting with α-Syn. Moreover, oxidative stress caused by mitochondrial dysfunction favors assembly of both α-Syn and tau and also plays a key role in the formation of protein aggregates. In this review, we provide an overview of the relationship between these two pathological proteins and mitochondrial dysfunction in PD, and also summarize the underlying mechanisms in the interplay of α-Syn aggregation and phosphorylated tau targeting the mitochondria, to find new strategies to prevent PD processing.

Tuning mitochondrial structure and function to criticality by fluctuation-driven mechanotransduction

Cells in vascular walls are exposed to blood pressure variability (BPV)-induced cycle-by-cycle fluctuations in mechanical forces which vary considerably with pathology. For example, BPV is elevated in hypertension but reduced under anesthesia. We hypothesized that the extent of mechanical fluctuations applied to vascular smooth muscle cells (VSMCs) regulates mitochondrial network structure near the percolation transition, which also influences ATP and reactive oxygen species (ROS) production. We stretched VSMCs in culture with cycle-by-cycle variability in area strain ranging from no variability (0%), as in standard laboratory conditions, through abnormally small (6%) and physiological (25%) to pathologically high (50%) variability mimicking hypertension, superimposed on 0.1 mean area strain. To explore how oxidative stress and ATP-dependent metabolism affect mitochondria, experiments were repeated in the presence of hydrogen peroxide and AMP-PNP, an ATP analog and competitive inhibitor of ATPases. Physiological 25% variability maintained activated mitochondrial cluster structure at percolation with a power law distribution and exponent matching the theoretical value in 2 dimensions. The 25% variability also maximized ATP and minimized cellular and mitochondrial ROS production via selective control of fission and fusion proteins (mitofusins, OPA1 and DRP1) as well as through stretch-sensitive regulation of the ATP synthase and VDAC1, the channel that releases ATP into the cytosol. Furthermore, pathologically low or high variability moved mitochondria away from percolation which reduced the effectiveness of the electron transport chain by lowering ATP and increasing ROS productions. We conclude that normal BPV is required for maintaining optimal mitochondrial structure and function in VSMCs.

Cardiac mitochondrial function depends on BUD23 mediated ribosome programming

Efficient mitochondrial function is required in tissues with high energy demand such as the heart, and mitochondrial dysfunction is associated with cardiovascular disease. Expression of mitochondrial proteins is tightly regulated in response to internal and external stimuli. Here we identify a novel mechanism regulating mitochondrial content and function, through BUD23-dependent ribosome generation. BUD23 was required for ribosome maturation, normal 18S/28S stoichiometry and modulated the translation of mitochondrial transcripts in human A549 cells. Deletion of Bud23 in murine cardiomyocytes reduced mitochondrial content and function, leading to severe cardiomyopathy and death. We discovered that BUD23 selectively promotes ribosomal interaction with low GC-content 5'UTRs. Taken together we identify a critical role for BUD23 in bioenergetics gene expression, by promoting efficient translation of mRNA transcripts with low 5'UTR GC content. BUD23 emerges as essential to mouse development, and to postnatal cardiac function.

Mitochondrial Quality Control: Role in Cardiac Models of Lethal Ischemia-Reperfusion Injury

The current standard of care for acute myocardial infarction or 'heart attack' is timely restoration of blood flow to the ischemic region of the heart. While reperfusion is essential for the salvage of ischemic myocardium, re-introduction of blood flow paradoxically kills (rather than rescues) a population of previously ischemic cardiomyocytes-a phenomenon referred to as 'lethal myocardial ischemia-reperfusion (IR) injury'. There is long-standing and exhaustive evidence that mitochondria are at the nexus of lethal IR injury. However, during the past decade, the paradigm of mitochondria as mediators of IR-induced cardiomyocyte death has been expanded to include the highly orchestrated process of mitochondrial quality control. Our aims in this review are to: (1) briefly summarize the current understanding of the pathogenesis of IR injury, and (2) incorporating landmark data from a broad spectrum of models (including immortalized cells, primary cardiomyocytes and intact hearts), provide a critical discussion of the emerging concept that mitochondrial dynamics and mitophagy (the components of mitochondrial quality control) may contribute to the pathogenesis of cardiomyocyte death in the setting of ischemia-reperfusion.

Endoplasmic Reticulum Stress and Mitochondrial Function in Airway Smooth Muscle

Inflammatory airway diseases such as asthma affect more than 300 million people world-wide. Inflammation triggers pathophysiology via such as tumor necrosis factor α (TNFα) and interleukins (e.g., IL-13). Hypercontraction of airway smooth muscle (ASM) and ASM cell proliferation are major contributors to the exaggerated airway narrowing that occurs during agonist stimulation. An emergent theme in this context is the role of inflammation-induced endoplasmic reticulum (ER) stress and altered mitochondrial function including an increase in the formation of reactive oxygen species (ROS). This may establish a vicious cycle as excess ROS generation leads to further ER stress. Yet, it is unclear whether inflammation-induced ROS is the major mechanism leading to ER stress or the consequence of ER stress. In various diseases, inflammation leads to an increase in mitochondrial fission (fragmentation), associated with reduced levels of mitochondrial fusion proteins, such as mitofusin 2 (Mfn2). Mitochondrial fragmentation may be a homeostatic response since it is generally coupled with mitochondrial biogenesis and mitochondrial volume density thereby reducing demand on individual mitochondrion. ER stress is triggered by the accumulation of unfolded proteins, which induces a homeostatic response to alter protein balance via effects on protein synthesis and degradation. In addition, the ER stress response promotes protein folding via increased expression of molecular chaperone proteins. Reduced Mfn2 and altered mitochondrial dynamics may not only be downstream to ER stress but also upstream such that a reduction in Mfn2 triggers further ER stress. In this review, we summarize the current understanding of the link between inflammation-induced ER stress and mitochondrial function and the role played in the pathophysiology of inflammatory airway diseases.

Patient-specific neural progenitor cells derived from induced pluripotent stem cells offer a promise of good models for mitochondrial disease

Mitochondria are the primary generators of ATP in eukaryotic cells through the process of oxidative phosphorylation. Mitochondria are also involved in several other important cellular functions including regulation of intracellular Ca²⁺, cell signaling and apoptosis. Mitochondrial dysfunction causes disease and since it is not possible to perform repeated studies in humans, models are essential to enable us to investigate the mechanisms involved. Recently, the discovery of induced pluripotent stem cells (iPSCs), made by reprogramming adult somatic cells (Takahashi and Yamanaka 2006; Yamanaka and Blau 2010), has provided a unique opportunity for studying aspects of disease mechanisms in patient-specific cells and tissues. Reprogramming cells to neuronal lineage such as neural progenitor cells (NPCs) generated from the neural induction of reprogrammed iPSCs can thus provide a useful model for investigating neurological disease mechanisms including those caused by mitochondrial dysfunction. In addition, NPCs display a huge clinical potential in drug screening and therapeutics.

MiD51 Is Important for Maintaining Mitochondrial Health in Pancreatic Islet and MIN6 Cells

Background: Mitochondrial dynamics are important for glucose-stimulated insulin secretion in pancreatic beta cells. The mitochondrial elongation factor MiD51 has been proposed to act as an anchor that recruits Drp1 from the cytosol to the outer mitochondrial membrane. Whether MiD51 promotes mitochondrial fusion by inactivation of Drp1 is a controversial issue. Since both the underlying mechanism and the effects on mitochondrial function remain unknown, this study was conducted to investigate the role of MiD51 in beta cells. Methods: Overexpression and downregulation of MiD51 in mouse insulinoma 6 (MIN6) and mouse islet cells was achieved using the pcDNA expression vector and specific siRNA, respectively. Expression of genes regulating mitochondrial dynamics and autophagy was analyzed by quantitative Real-Time PCR, glucose-stimulated insulin secretion by ELISA, and cellular oxygen consumption rate by optode sensor technology. Mitochondrial membrane potential and morphology were visualized after TMRE and MitoTracker Green staining, respectively. Immunofluorescence analyses were examined by confocal microscopy. Results: MiD51 is expressed in insulin-positive mouse and human pancreatic islet and MIN6 cells. Overexpression of MiD51 resulted in mitochondrial fragmentation and cluster formation in MIN6 cells. Mitochondrial membrane potential, glucose-induced oxygen consumption rate and glucose-stimulated insulin secretion were reduced in MIN6 cells with high MiD51 expression. LC3 expression remained unchanged. Downregulation of MiD51 resulted in inhomogeneity of the mitochondrial network in MIN6 cells with hyperelongated and fragmented mitochondria. Mitochondrial membrane potential, maximal and glucose-induced oxygen consumption rate and insulin secretion were diminished in MIN6 cells with low MiD51 expression. Furthermore, reduced Mfn2 and Parkin expression was observed. Based on MiD51 overexpression and downregulation, changes in the mitochondrial network structure similar to those in MIN6 cells were also observed in mouse islet cells. Conclusion: We have demonstrated that MiD51 plays a pivotal role in regulating mitochondrial function and hence insulin secretion in MIN6 cells. We propose that this anchor protein of Drp1 is important to maintain a homogeneous mitochondrial network and to avoid morphologies such as hyperelongation and clustering which are inaccessible for degradation by autophagy. Assuming that insulin granule degradation frequently suppresses autophagy in beta cells, MiD51 could be a key element maintaining mitochondrial health.

Optimization of ultrastructural preservation of human brain for transmission electron microscopy after long post-mortem intervals

Electron microscopy (EM) provides the necessary resolution to visualize the finer structures of nervous tissue morphology, which is important to understand healthy and pathological conditions in the brain. However, for the interpretation of the micrographs the tissue preservation is crucial. The quality of the tissue structure is mostly influenced by the post mortem interval (PMI), the time of death until the preservation of the tissue. Therefore, the aim of this study was to optimize the preparation-procedure for the human frontal lobe to preserve the ultrastructure as well as possible despite the long PMIs. Combining chemical pre- and post-fixation with cryo-fixation and cryo-substitution ("hybrid freezing"), it was possible to improve the preservation of the neuronal profiles of human brain samples compared to the "standard" epoxy resin embedding method. In conclusion short PMIs are generally desirable but up to a PMI of 16 h the ultrastructure can be preserved on an acceptable level with a high contrast using the "hybrid freezing" protocol described here.

Mitochondria-hubs for regulating cellular biochemistry: emerging concepts and networks

Mitochondria are iconic structures in biochemistry and cell biology, traditionally referred to as the powerhouse of the cell due to a central role in energy production. However, modern-day mitochondria are recognized as key players in eukaryotic cell biology and are known to regulate crucial cellular processes, including calcium signalling, cell metabolism and cell death, to name a few. In this review, we will discuss foundational knowledge in mitochondrial biology and provide snapshots of recent advances that showcase how mitochondrial function regulates other cellular responses.

Arabidopsis DGD1 SUPPRESSOR1 Is a Subunit of the Mitochondrial Contact Site and Cristae Organizing System and Affects Mitochondrial Biogenesis

Mitochondrial and plastid biogenesis requires the biosynthesis and assembly of proteins, nucleic acids, and lipids. In Arabidopsis (Arabidopsis thaliana), the mitochondrial outer membrane protein DGD1 SUPPRESSOR1 (DGS1) is part of a large multi-subunit protein complex that contains the mitochondrial contact site and cristae organizing system 60-kD subunit, the translocase of outer mitochondrial membrane 40-kD subunit (TOM40), the TOM20s, and the Rieske FeS protein. A point mutation in DGS1, dgs1-1, altered the stability and protease accessibility of this complex. This altered mitochondrial biogenesis, mitochondrial size, lipid content and composition, protein import, and respiratory capacity. Whole plant physiology was affected in the dgs1-1 mutant as evidenced by tolerance to imposed drought stress and altered transcriptional responses of markers of mitochondrial retrograde signaling. Putative orthologs of Arabidopsis DGS1 are conserved in eukaryotes, including the Nuclear Control of ATP Synthase2 (NCA2) protein in yeast (Saccharomyces cerevisiae), but lost in Metazoa. The genes encoding DGS1 and NCA2 are part of a similar coexpression network including genes encoding proteins involved in mitochondrial fission, morphology, and lipid homeostasis. Thus, DGS1 links mitochondrial protein and lipid import with cellular lipid homeostasis and whole plant stress responses.

Dynamin-1-Like Protein Inhibition Drives Megamitochondria Formation as an Adaptive Response in Alcohol-Induced Hepatotoxicity

Despite the growing global burden of alcoholic liver diseases, therapeutic options are limited, and novel targets are urgently needed. Accumulating evidence suggests that mitochondria adapt in response to ethanol and formation of megamitochondria in the livers of patients is recognized as a hallmark of alcoholic liver diseases. The processes involved in ethanol-induced hepatic mitochondrial changes, the impact on mitochondria-shaping proteins, and the significance of megamitochondria formation remain unknown. In this study, we investigated the mitochondrial and cellular response to alcohol in hepatoma cell line VL-17A. The mitochondrial architecture rapidly changed after 3 or 14 days of ethanol exposure with double-pronged presentation of hyperfragmentation and megamitochondria, and cell growth was inhibited. Dynamin-1-like protein (Drp1) was identified as the main mediator driving these mitochondrial alterations, and its genetic inactivation was determined to foster megamitochondria development, preserving the capacity of the cells to grow despite alcohol toxicity. The role of Drp1 in mediating megamitochondria formation in mice with liver-specific inactivation of Drp1 was further confirmed. Finally, when these mice were fed with ethanol, the presentation of hepatic megamitochondria was exacerbated compared with wild type fed with the same diet. Ethanol-induced toxicity was also reduced. Our study demonstrates that megamitochondria formation is mediated by Drp1, and this phenomenon is a beneficial adaptive response during alcohol-induced hepatotoxicity.

Mitochondrial presequence import: Multiple regulatory knobs fine-tune mitochondrial biogenesis and homeostasis

Mitochondria are pivotal organelles for cellular signaling and metabolism, and their dysfunction leads to severe cellular stress. About 60-70% of the mitochondrial proteome consists of preproteins synthesized in the cytosol with an amino-terminal cleavable presequence targeting signal. The TIM23 complex transports presequence signals towards the mitochondrial matrix. Ultimately, the mature protein segments are either transported into the matrix or sorted to the inner membrane. To ensure accurate preprotein import into distinct mitochondrial sub-compartments, the TIM23 machinery adopts specific functional conformations and interacts with different partner complexes. Regulatory subunits modulate the translocase dynamics, tailoring the import reaction to the incoming preprotein. The mitochondrial membrane potential and the ATP generated via oxidative phosphorylation are key energy sources in driving the presequence import pathway. Thus, mitochondrial dysfunctions have rapid repercussions on biogenesis. Cellular mechanisms exploit the presequence import pathway to monitor mitochondrial dysfunctions and mount transcriptional and proteostatic responses to restore functionality.

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.

Mitochondrial Assays Using Cardiac Stem Cells

Ischemic heart disease is the leading cause of death worldwide. Stem cell therapy to repair and regenerate the infarcted myocardium is a promising approach to address this unmet medical need. However, the poor survival of transplanted cells in the hostile ischemic myocardium has been a major hurdle in achieving an effective cell therapy against myocardial infarction. As such, novel strategies to promote the survival of transplanted cells are highly sought after. Mitochondria are intimately involved in cell survival and have been the main organelles being targeted for cytoprotection. Mitochondrial morphology is linked to mitochondrial function and cell viability. Therefore, quantitative methodologies to obtain reliable and reproducible results of mitochondrial morphology and function are essential for identifying and developing new cytoprotective strategies to enhance the survival of stem cells post-transplantation. Here, we describe methods for assessing mitochondrial morphology, mitochondrial membrane potential, and mitochondrial reactive oxygen species production.

UCP2-dependent improvement of mitochondrial dynamics protects against acute kidney injury

Acute kidney injury (AKI) is a public health concern, with high morbidity and mortality rates in hospitalized patients and because survivors have an increased risk of progression to chronic kidney disease. Mitochondrial damage is the critical driver of AKI-associated dysfunction and loss of tubular epithelial cells; however, the pathways that mediate these events are poorly defined. Here, in murine ischemia/reperfusion (I/R)-induced AKI, we determined that mitochondrial damage is associated with the level of renal uncoupling protein 2 (UCP2). In hypoxia-damaged proximal tubular cells, a disruption of mitochondrial dynamics demonstrated by mitochondrial fragmentation and disturbance between fusion and fission was clearly indicated. Ucp2-deficient mice (knockout mice) with I/R injury experienced more severe AKI and mitochondrial fragmentation than wild-type mice. Moreover, genetic or pharmacological treatment increased UCP2 expression, improved renal function, reduced tubular injury and limited mitochondrial fission. In cultured proximal tubular epithelial cells, hypoxia-induced mitochondrial fission was exacerbated in cells with UCP2 deletion, whereas an increase in UCP2 ameliorated the hypoxia-induced disturbance of the balance between mitochondrial fusion and fission. Furthermore, results following modulation of UCP2 suggested it has a role in preserving mitochondrial integrity by preventing loss of membrane potential and reducing subsequent mitophagy. Taken together, our results indicate that UCP2 is protective against AKI and suggest that enhancing UCP2 to improve mitochondrial dynamics has potential as a strategy for improving outcomes of renal injury. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

How Dengue Virus Circumvents Innate Immunity

In the battle between a virus and its host, innate immunity serves as the first line of defense protecting the host against pathogens. The antiviral actions start with the recognition of pathogen-associated molecular patterns derived from the virus, then ultimately turning on particular transcription factors to generate antiviral interferons (IFNs) or proinflammatory cytokines via fine-tuned signaling cascades. With dengue virus (DENV) infection, its viral RNA is recognized by the host RNA sensors, mainly retinoic acid inducible gene-I (RIG-I)-like receptors (RLRs) and toll-like receptors. DENV infection also activates the cyclic GMP-AMP synthase–stimulator of interferon genes (cGAS–STING)-mediated DNA-sensing pathway despite the absence of a DNA stage in the DENV lifecycle. In the last decade, DENV has been considered a weak IFN-inducing pathogen with the evidence that DENV has evolved multiple strategies antagonizing the host IFN system. DENV passively escapes from innate immunity surveillance and also actively subverts the innate immune system at multiple steps. DENV targets both RNA-triggered RLR–mitochondrial antiviral signaling protein (RLR–MAVS) and DNA-triggered cGAS–STING signaling to reduce IFN production in infected cells. It also blocks IFN action by inhibiting IFN regulatory factor- and signal transducer and activator of transcription-mediated signaling. This review explores the current understanding of how DENV escapes the control of the innate immune system by modifying viral RNA and viral protein and by post-translational modification of cellular factors. The roles of the DNA-sensing pathway in DENV infection, and how mitochondrial dynamics participates in innate immunity are also discussed.

A Critical Role of Mitochondria in BDNF-Associated Synaptic Plasticity After One-Week Vortioxetine Treatment

BACKGROUND

Preclinical studies have indicated that antidepressant effect of vortioxetine involves increased synaptic plasticity and promotion of spine maturation. Mitochondria dysfunction may contribute to the pathophysiological basis of major depressive disorder. Taking into consideration that vortioxetine increases spine number and dendritic branching in hippocampus CA1 faster than fluoxetine, we hypothesize that new spines induced by vortioxetine can rapidly form functional synapses by mitochondrial support, accompanied by increased brain-derived neurotrophic factor signaling.

METHODS

Rats were treated for 1 week with vortioxetine or fluoxetine at pharmacologically relevant doses. Number of synapses and mitochondria in hippocampus CA1 were quantified by electron microscopy. Brain-derived neurotrophic factor protein levels were visualized with immunohistochemistry. Gene and protein expression of synapse and mitochondria-related markers were investigated with real-time quantitative polymerase chain reaction and immunoblotting.

RESULTS

Vortioxetine increased number of synapses and mitochondria significantly, whereas fluoxetine had no effect after 1-week dosing. BDNF levels in hippocampus DG and CA1 were significantly higher after vortioxetine treatment. Gene expression levels of Rac1 after vortioxetine treatment were significantly increased. There was a tendency towards increased gene expression levels of Drp1 and protein levels of Rac1. However, both gene and protein levels of c-Fos were significantly decreased. Furthermore, there was a significant positive correlation between BDNF levels and mitochondria and synapse numbers.

CONCLUSION

Our results imply that mitochondria play a critical role in synaptic plasticity accompanied by increased BDNF levels. Rapid changes in BDNF levels and synaptic/mitochondria plasticity of hippocampus following vortioxetine compared with fluoxetine may be ascribed to vortioxetine's modulation of serotonin receptors.

Mechanisms of mitochondrial toxicity of the kinase inhibitors ponatinib, regorafenib and sorafenib in human hepatic HepG2 cells

Previous studies have shown that certain kinase inhibitors are mitochondrial toxicants. In the current investigation, we determined the mechanisms of mitochondrial impairment by the kinase inhibitors ponatinib, regorafenib, and sorafenib in more detail. In HepG2 cells cultured in galactose and exposed for 24 h, all three kinase inhibitors investigated depleted the cellular ATP pools at lower concentrations than cytotoxicity occurred, compatible with mitochondrial toxicity. The kinase inhibitors impaired the activity of different complexes of the respiratory chain in HepG2 cells exposed to the toxicants for 24 h and in isolated mouse liver mitochondria exposed acutely. As a consequence, they increased mitochondrial production of ROS in HepG2 cells in a time- and concentration-dependent fashion and decreased the mitochondrial membrane potential concentration-dependently. In HepG2 cells exposed for 24 h, they induced mitochondrial fragmentation, lysosome content and mitophagy as well as mitochondrial release of cytochrome c, leading to apoptosis and/or necrosis. In conclusion, the kinase inhibitors ponatinib, regorafenib, and sorafenib impaired the function of the respiratory chain, which was associated with increased ROS production and a drop in the mitochondrial membrane potential. Despite activation of defense measures such as mitochondrial fission and mitophagy, some cells were liquidated concentration-dependently by apoptosis or necrosis. Mitochondrial dysfunction may represent a toxicological mechanism of hepatotoxicity associated with certain kinase inhibitors.

Translational approaches to restoring mitochondrial function in Parkinson's disease

There is strong evidence of a key role for mitochondrial dysfunction in both sporadic and all forms of familial Parkinson's disease (PD). However, none of the clinical trials carried out with putative mitochondrial rescue agents have been successful. Firm establishment of a wet biomarker or a reliable readout from imaging studies detecting mitochondrial dysfunction and reflecting disease progression is also awaited. We will provide an overview of our current knowledge about mitochondrial dysfunction in PD and related drug screens. We will also summarise previously undertaken mitochondrial wet biomarker studies and relevant imaging studies with particular focus on 31P-MRI spectroscopy. We will conclude with an overview of clinical trials which tested putative mitochondrial rescue agents in PD patients.

Mitochondria Are Critical for BDNF-Mediated Synaptic and Vascular Plasticity of Hippocampus following Repeated Electroconvulsive Seizures

BACKGROUND

Electroconvulsive therapy is a fast-acting and efficient treatment of depression used in the clinic. The underlying mechanism of its therapeutic effect is still unclear. However, recovery of synaptic connections and synaptic remodeling is thought to play a critical role for the clinical efficacy obtained from a rapid antidepressant response. Here, we investigated the relationship between synaptic changes and concomitant nonneuronal changes in microvasculature and mitochondria and its relationship to brain-derived neurotrophic factor level changes after repeated electroconvulsive seizures, an animal model of electroconvulsive therapy.

METHODS

Electroconvulsive seizures or sham treatment was given daily for 10 days to rats displaying a genetically driven phenotype modelling clinical depression: the Flinders Sensitive and Resistant Line rats. Stereological principles were employed to quantify numbers of synapses and mitochondria, and the length of microvessels in the hippocampus. The brain-derived neurotrophic factor protein levels were quantified with immunohistochemistry.

RESULTS

In untreated controls, a lower number of synapses and mitochondria was accompanied by shorter microvessels of the hippocampus in "depressive" phenotype (Flinders Sensitive Line) compared with the "nondepressed" phenotype (Flinders Resistant Line). Electroconvulsive seizure administration significantly increased the number of synapses and mitochondria, and length of microvessels both in Flinders Sensitive Line-electroconvulsive seizures and Flinders Resistant Line-electroconvulsive seizures rats. In addition, the amount of brain-derived neurotrophic factor protein was significantly increased in Flinders Sensitive Line and Flinders Resistant Line rats after electroconvulsive seizures. Furthermore, there was a significant positive correlation between brain-derived neurotrophic factor level and mitochondria/synapses.

CONCLUSION

Our results indicate that rapid and efficient therapeutic effect of electroconvulsive seizures may be related to synaptic plasticity, accompanied by brain-derived neurotrophic factor protein level elevation and mitochondrial and vascular support.

The therapeutic potential of a calorie-restricted ketogenic diet for the management of Leber hereditary optic neuropathy

Leber hereditary optic neuropathy (LHON) is a maternally inherited, bilateral, sequential optic neuropathy that usually affects young males. LHON arises from a defect in complex I of the oxidative phosphorylation chain that generates increased reactive oxygen species and causes a decline in cellular ATP production. There exists no cure at present for LHON. Asymptomatic LHON mutation carriers show signs of increased mitochondrial biogenesis that may compensate for the compromise in complex I activity. Partial recovery in LHON is associated with a wider optic disc diameter and a younger age at disease onset, which may allow for greater mitochondrial bioenergetic capacity. Rescuing a mitochondrial bioenergetic deficit soon after disease onset may improve the chances of recovery and reduce visual loss in the second eye. We here propose that a calorie-restricted ketogenic diet has the potential to enhance mitochondrial bioenergetic capacity and should be explored as a potential therapeutic option for treating LHON.

Hyperglycemia exacerbates downregulation of dynamin-like protein 1 in ischemic cerebral injury

Ischemic stroke is one of the leading causes of adult disability and death. Hyperglycemia is associated with an increased risk of stroke and poor outcomes after brain injury. Dynamin-like protein I (DLP-1) regulates mitochondrial fission and promotes mitochondrial dynamics. Neurodegenerative diseases are associated with mitochondrial dysfunction, and the downregulation of DLP-1 has been previously identified in a stroke animal model. Here, we investigated the changes in DLP-1 protein expression in an animal model of focal cerebral ischemia with induced hyperglycemia. Streptozotocin (40 mg/kg) was intraperitoneally injected into male rats to induce hyperglycemia, and middle cerebral artery occlusion (MCAO) was surgically induced 4 weeks after streptozotocin treatment. Brain tissue was isolated 24 hours after MCAO, and cerebral cortex samples were used for this study. Proteomics revealed a decrease in DLP-1 expression in MCAO animals when compared with controls, and this downregulation was more prominent in MCAO animals with hyperglycemia. Reverse-transcription polymerase chain reaction and Western blot analyses confirmed that DLP-1 was significantly downregulated in MCAO-injured animals with hyperglycemia compared to those without hyperglycemia. The decrease in DLP-1 indicates mitochondrial morphological changes and dysfunction. Together, these results suggest that the severe decrease of DLP-1 seen after brain injury under hyperglycemic conditions may exacerbate the damage to the brain.

Improvement of obesity-linked skeletal muscle insulin resistance by strength and endurance training

Obesity-linked insulin resistance is mainly due to fatty acid overload in non-adipose tissues, particularly skeletal muscle and liver, where it results in high production of reactive oxygen species and mitochondrial dysfunction. Accumulating evidence indicates that resistance and endurance training alone and in combination can counteract the harmful effects of obesity increasing insulin sensitivity, thus preventing diabetes. This review focuses the mechanisms underlying the exercise role in opposing skeletal muscle insulin resistance-linked metabolic dysfunction. It is apparent that exercise acts through two mechanisms: (1) it stimulates glucose transport by activating an insulin-independent pathway and (2) it protects against mitochondrial dysfunction-induced insulin resistance by increasing muscle antioxidant defenses and mitochondrial biogenesis. However, antioxidant supplementation combined with endurance training increases glucose transport in insulin-resistant skeletal muscle in an additive fashion only when antioxidants that are able to increase the expression of antioxidant enzymes and/or the activity of components of the insulin signaling pathway are used.

Regulation of Mitochondrial Structure and Dynamics by the Cytoskeleton and Mechanical Factors

Mitochondria supply cells with energy in the form of ATP, guide apoptosis, and contribute to calcium buffering and reactive oxygen species production. To support these diverse functions, mitochondria form an extensive network with smaller clusters that are able to move along microtubules aided by motor proteins. Mitochondria are also associated with the actin network, which is involved in cellular responses to various mechanical factors. In this review, we discuss mitochondrial structure and function in relation to the cytoskeleton and various mechanical factors influencing cell functions. We first summarize the morphological features of mitochondria with an emphasis on fission and fusion as well as how network properties govern function. We then review the relationship between the mitochondria and the cytoskeletal structures, including mechanical interactions. We also discuss how stretch and its dynamic pattern affect mitochondrial structure and function. Finally, we present preliminary data on how extracellular matrix stiffness influences mitochondrial morphology and ATP generation. We conclude by discussing the more general role that mitochondria may play in mechanobiology and how the mechanosensitivity of mitochondria may contribute to the development of several diseases and aging.

A novel ADOA-associated OPA1 mutation alters the mitochondrial function, membrane potential, ROS production and apoptosis

Autosomal dominant optic atrophy (ADOA) is a dominantly inherited optic neuropathy, affecting the specific loss of retinal ganglion cells (RGCs). The majority of affected cases of ADOA are associated with mutations in OPA1 gene. Our previous investigation identified the c.1198C > G (p.P400A) mutation in the OPA1 in a large Han Chinese family with ADOA. In this report, we performed a functional characterization using lymphoblostoid cell lines derived from affected members of this family and control subjects. Mutant cell lines exhibited the aberrant mitochondrial morphology. A ~24.6% decrease in the mitochondrial DNA (mtDNA) copy number was observed in mutant cell lines, as compared with controls. Western blotting analysis revealed the variable reductions (~45.7%) in four mtDNA-encoded polypeptides in mutant cell lines. The impaired mitochondrial translation caused defects in respiratory capacity. Furthermore, defects in mitochondrial ATP synthesis and mitochondrial membrane potential (ΔΨm) were observed in mutant cell lines. These abnormalities resulted in the accumulation of oxidative damage and increasing of apoptosis in the mutant cell lines, as compared with controls. All those alterations may cause the primary degeneration of RGCs and subsequent visual loss. These data provided the direct evidence for c.1198C > G mutation leading to ADOA. Our findings may provide new insights into the understanding of pathophysiology of ADOA.

Human trypsin inhibitor reduces the apoptosis of lipopolysaccharide‑induced human kidney‑2 cells by promoting mitochondrial fusion

Imbalance in mitochondrial fusion/fission is one of the mechanisms leading to sepsis‑induced mitochondrial dysfunction and cell apoptosis. The present study examined the effects of human trypsin inhibitor (UTI), a well‑known antioxidant and anti‑inflammatory substance, on mitochondrial dynamics and cell apoptosis in lipopolysaccharide (LPS)‑induced human kidney‑2 (HK‑2) cells. The HK‑2 cells were incubated for 24 h either with LPS (800 ng/ml) or LPS (800 ng/ml) mixed with UTI (250 U/ml). Cell viability was assessed using a3‑(4,5‑dimethyl‑2‑thiazolyl)‑2, 5‑diphenyl‑2‑H‑tetrazolium bromide assay. Oxidative activities (estimated by maleic dialdehyde and superoxide dismutase), levels of inflammatory cytokines interleukin (IL)‑6 and tumor necrosis factor (TNF)‑α, and levels of ATP were measured using an enzyme‑linked immunosorbent assay. The expression levels of the mitochondrial fission protein, death‑associated protein kinase 2 (DAPK‑2), mitofusin (Mfn)1 and Mfn2 mitochondrial fusion proteins, and apoptotic and anti‑apoptotic biomarkers, including cytochrome c, caspase‑3, caspase‑9, B‑cell lymphoma (Bcl)‑2, Bcl‑extra large and poly ADP‑ribose polymerase (PARP), were assessed using western blot analyses. The changes in mitochondrial membrane potential were analyzed following JC‑1 staining. Annexin V/propidium iodide assays were used to evaluate cell apoptosis. The results showed that the balance of mitochondrial dynamics was towards mitochondrial fusion in the UTI group, as a reduced expression of DAPK2, and increased expression levels of Mfn1 and Mfn2 were detected (P<0.05, vs. LPS group). In addition, adecline in the levels of the inflammatory cytokines, TNF‑α and IL‑6, and the oxidative activities, reflected by an increase in SOD and a decrease in MDA (P<0.05, vs. LPS group) were observed. Cell apoptosis was inhibited following co‑treatment with UTI (P<0.05, vs. LPS group). It was concluded that UTI may protect mitochondrial functions by promoting mitochondrial fusion and limiting mitochondrial fission, thus reducing the apoptosis of LPS‑induced HK‑2 cells.

Mitochondrial Heterogeneity: Evaluating Mitochondrial Subpopulation Dynamics in Stem Cells

Although traditionally viewed as the “powerhouse” of the cell, an accruing body of evidence in the rapidly growing field of mitochondrial biology supports additional roles of mitochondria as key participants in a multitude of cellular functions. While it has been well established that mitochondria in different tissues have distinctive ultrastructural features consistent with differential bioenergetic demands, recent and emerging technical advances in flow cytometry, imaging, and “-omics”-based bioinformatics have only just begun to explore the complex and divergent properties of mitochondria within tissues and cell types. Moreover, contemporary studies evaluating the role of mitochondria in pluripotent stem cells, cellular reprogramming, and differentiation point to a potential importance of mitochondrial subpopulations and heterogeneity in the field of stem cell biology. This review assesses the current literature regarding mitochondrial subpopulations within cell and tissue types and evaluates the current understanding of how mitochondrial diversity and heterogeneity might impact cell fate specification in pluripotent stem cells.

Mitochondrial dynamics and cancer

Cancer is among the leading causes of death worldwide, and the number of new cases continues to rise. Despite recent advances in diagnosis and therapeutic strategies, millions of cancer-related deaths occur, indicating the need for better therapies and diagnostic strategies. Mitochondria and metabolic alterations have been recognized as important for cancer progression. However, a more precise understanding of how to manipulate mitochondria-related processes for cancer therapy remains to be established. Mitochondria are highly dynamic organelles which continually fuse and divide in response to diverse stimuli. Participation in the aforementioned processes requires a precise regulation at many levels that allows the cell to couple mitochondrial activity to nutrient availability, biosynthetic demands, proliferation rates, and external stimuli. The many functions of these organelles are intimately linked to their morphology. Recent evidence suggests an important link between mitochondrial morphology and disease, including neurodegenerative, inflammatory diseases and cancer. Here, we review recent advances in the understanding of mitochondrial dynamics with a special focus on its relationship to tumor progression.

Connecting mitochondrial dynamics and life-or-death events via Bcl-2 family proteins

The morphology of a population of mitochondria is the result of several interacting dynamical phenomena, including fission, fusion, movement, elimination and biogenesis. Each of these phenomena is controlled by underlying molecular machinery, and when defective can cause disease. New understanding of the relationships between form and function of mitochondria in health and disease is beginning to be unraveled on several fronts. Studies in mammals and model organisms have revealed that mitochondrial morphology, dynamics and function appear to be subject to regulation by the same proteins that regulate apoptotic cell death. One protein family that influences mitochondrial dynamics in both healthy and dying cells is the Bcl-2 protein family. Connecting mitochondrial dynamics with life-death pathway forks may arise from the intersection of Bcl-2 family proteins with the proteins and lipids that determine mitochondrial shape and function. Bcl-2 family proteins also have multifaceted influences on cells and mitochondria, including calcium handling, autophagy and energetics, as well as the subcellular localization of mitochondrial organelles to neuronal synapses. The remarkable range of physical or functional interactions by Bcl-2 family proteins is challenging to assimilate into a cohesive understanding. Most of their effects may be distinct from their direct roles in apoptotic cell death and are particularly apparent in the nervous system. Dual roles in mitochondrial dynamics and cell death extend beyond BCL-2 family proteins. In this review, we discuss many processes that govern mitochondrial structure and function in health and disease, and how Bcl-2 family proteins integrate into some of these processes.

Activation of Sirtuin 3 by Silybin Attenuates Mitochondrial Dysfunction in Cisplatin-induced Acute Kidney Injury

Silybin is a secondary metabolite isolated from the seeds of blessed milk thistle (Silybum marianum) that has anti-inflammatory, antioxidative, antifibrotic, and antitumor properties. Here, we showed that silybin protected against cisplatin-induced acute kidney injury (AKI) by improving mitochondrial function through the regulation of sirtuin 3 (SIRT3) expression. Male SV129 and SIRT3 knockout (KO) mice were administered a single intraperitoneal (i.p.) injection of cisplatin with or without treatment with silybin. Moreover, cultured HK2 cells were used to evaluate mitochondrial morphology and function. Our data suggested that silybin enhanced SIRT3 expression after cisplatin administration both in vivo and in vitro. Silybin treatment improved mitochondrial function and bioenergetics in wild-type, but not SIRT3-defective, cells and mice. Moreover, we demonstrated that silybin markedly attenuated cisplatin-induced AKI and tubular cell apoptosis and improved cell regeneration in a SIRT3-dependent manner. Collectively, these results suggest that silybin is a pharmacological activator of SIRT3 capable of protecting against cisplatin-induced tubular cell apoptosis and AKI by improving mitochondrial function. Thus, silybin could serve as a potential clinical renoprotective adjuvant treatment in cisplatin chemotherapy.

Skeletal muscle insulin resistance: role of mitochondria and other ROS sources

At present, obesity is one of the most important public health problems in the world because it causes several diseases and reduces life expectancy. Although it is well known that insulin resistance plays a pivotal role in the development of type 2 diabetes mellitus (the more frequent disease in obese people) the link between obesity and insulin resistance is yet a matter of debate. One of the most deleterious effects of obesity is the deposition of lipids in non-adipose tissues when the capacity of adipose tissue is overwhelmed. During the last decade, reduced mitochondrial function has been considered as an important contributor to 'toxic' lipid metabolite accumulation and consequent insulin resistance. More recent reports suggest that mitochondrial dysfunction is not an early event in the development of insulin resistance, but rather a complication of the hyperlipidemia-induced reactive oxygen species (ROS) production in skeletal muscle, which might promote mitochondrial alterations, lipid accumulation and inhibition of insulin action. Here, we review the literature dealing with the mitochondria-centered mechanisms proposed to explain the onset of obesity-linked IR in skeletal muscle. We conclude that the different pathways leading to insulin resistance may act synergistically because ROS production by mitochondria and other sources can result in mitochondrial dysfunction, which in turn can further increase ROS production leading to the establishment of a harmful positive feedback loop.

Mitochondrial Perturbation in Alzheimer's Disease and Diabetes

Mitochondria are well-known cellular organelles that play a vital role in cellular bioenergetics, heme biosynthesis, thermogenesis, calcium homeostasis, lipid catabolism, and other metabolic activities. Given the extensive role of mitochondria in cell function, mitochondrial dysfunction plays a part in many diseases, including diabetes and Alzheimer's disease (AD). In most cases, there is overwhelming evidence that impaired mitochondrial function is a causative factor in these diseases. Studying mitochondrial function in diseased cells vs healthy cells may reveal the modified mechanisms and molecular components involved in specific disease states. In this chapter, we provide a concise overview of the major recent findings on mitochondrial abnormalities and their link to synaptic dysfunction relevant to neurodegeneration and cognitive decline in AD and diabetes. Our increased understanding of the role of mitochondrial perturbation indicates that the development of specific small molecules targeting aberrant mitochondrial function could provide therapeutic benefits for the brain in combating aging-related dementia and neurodegenerative diseases by powering up brain energy and improving synaptic function and transmission.