Mitochondrial regulation of cell cycle and proliferation

Exogenous H2S modulates mitochondrial fusion-fission to inhibit vascular smooth muscle cell proliferation in a hyperglycemic state

Aim

Vascular smooth muscle cell (VSMC) proliferation in response to hyperglycemia is an important process in the development of arterial vessel hyperplasia. The shape change of mitochondria is dynamic and closely related to fission and fusion. Hydrogen sulfide (H₂S) was confirmed to have anti-oxidative, anti-inflammatory and anti-proliferative effects. However, little it is known about its effects on mitochondrial morphology induced by hyperglycemia. The aim of the study is to demonstrate that H₂S inhibits VSMC proliferation through regulating mitochondrial fission.

Methods and results

We observe lower H₂S levels as well as higher proliferative protein expression levels for proliferative cell nuclear antigen (PCNA) and cyclin D1 and higher mitochondrial fusion–fission protein expression levels for dynamin-related protein 1 (Drp 1) in human kidney arteries and in db/db mouse aorta. Exogenous H₂S (100 μM NaHS) inhibits vascular smooth muscle cells of human pulmonary aorta(HPASMC) proliferation and migration in response to high glucose using the BrdU and scratch wound repair assays, decreases proliferative protein (PCNA and cyclin D1) expression, and reduces ROS production in the cytoplasm and mitochondria. When HPASMCs proliferate with a high glucose treatment, the mitochondria become small spheres with a short rod-shaped structure, whereas NaHS, a mitochondrial division inhibitor and siDrp prevent VSMC proliferation and maintain mitochondria as stationary and randomly dispersed with fixed structures.

Conclusion

Exogenous H₂S aids in inhibiting mitochondrial fragmentation and affects proliferation in db/db mice and HPASMCs by decreasing Drp 1 expression.

Electronic supplementary material

The online version of this article (doi:10.1186/s13578-016-0102-x) contains supplementary material, which is available to authorized users.

Diallyl trisulfide induces osteosarcoma cell apoptosis through reactive oxygen species-mediated downregulation of the PI3K/Akt pathway

Diallyl trisulfide (DATS) is a natural organosulfur compound isolated from garlic, and has been reported to possess anticancer activities. However, the cancer growth inhibitory effects and molecular mechanisms in human osteosarcoma cells have not been well studied. The present study demonstrated that DATS significantly reduced cell viability in a dose- and time-dependent manner in MG63 and MNNG/HOS cells. DATS-induced G0/G1 phase arrest was found to correlate with a decrease in cyclin D1 in concomitance with an increase in p21 and p27. DATS induced a marked increase in reactive oxygen species (ROS) levels and collapse of mitochondrial membrane potential (Δψm) in the osteosarcoma cells. DATS induced apoptosis in the MG63 and MNNG/HOS cells via inhibition of the PI3K/Akt signaling pathway and through the mitochondrial apoptotic pathway. The efficiency of DATS basically approached the efficacy of LY294002, a specific PI3K inhibitor. However, N-acetylcysteine (NAC), a general ROS scavenger, completely blocked the DATS-induced ROS increase, inhibition of the PI3K/Akt pathway and cell apoptosis. Overall, DATS has the potential to be developed as a new anticancer drug. The mechanisms of action involve the ROS-mediated downregulation of the PI3K/Akt pathway.

Activation of transient receptor potential vanilloid 1 accelerates re-endothelialization and inhibits neointimal formation after vascular injury

OBJECTIVE

Transient receptor potential vanilloid 1 (TRPV1) is an important regulator of endothelial function, but the effects of TRPV1 on endothelial recovery and neointimal formation after vascular injury remain elusive. We tested the effects of activating TRPV1 using capsaicin on re-endothelialization and neointimal formation after wire-induced injury of the carotid artery in mice.

METHODS

The human umbilical vein endothelial cells (HUVECs) were treated with the TRPV1 agonist capsaicin, its antagonist capsazepine, intracellular calcium chelator BAPTA, or mitofusin 2 (Mfn2)-specific short interfering RNA (siRNA). The migration, proliferation, mitochondrial morphology, membrane potential, and adenosine triphosphate production were measured. The carotid artery wire injury procedure was performed in male TRPV1 knockout mice and C57BL/6J wild-type (WT) mice that were then treated with or without Mfn2 siRNA. The re-endothelialization and neointimal formation were evaluated.

RESULTS

Capsaicin significantly enhanced the migration and proliferation of HUVECs. Both capsazepine and BAPTA abolished capsaicin-induced migration and proliferation of HUVECs. In addition, capsaicin stimulated the formation of reticular mitochondria, augmented mitochondrial membrane potential, increased adenosine triphosphate production, and upregulated Mfn2. However, these effects were attenuated by knockdown of Mfn2 with specific siRNA. Dietary capsaicin markedly accelerated re-endothelialization and inhibited neointimal formation in WT mice but not in TRPV1 knockout mice. Moreover, Mfn2 siRNA also attenuated capsaicin-induced enhancement of endothelial recovery and suppression of neointimal hyperplasia in WT mice.

CONCLUSIONS

Activation of TRPV1 with capsaicin attenuates neointimal formation by accelerating re-endothelialization through upregulation of Mfn2.

Mitochondrial DNA copy number in whole blood and glioma risk: A case control study

Alterations in mitochondrial DNA (mtDNA) copy number are observed in human gliomas. However, whether variations in mtDNA copy number in whole blood play any role in glioma carcinogenesis is still largely unknown. In current study with 395 glioma patients and 425 healthy controls, we intended to investigate the association between mtDNA copy number in whole blood and glioma risk. Overall, we found that levels of mtDNA copy number were significantly higher in glioma cases than healthy controls (mean: 1.48 vs. 1.32, P < 0.01). In both cases and controls, levels of mtDNA copy number were inversely correlated with age (P < 0.01, respectively). And in cases, newly diagnosed, glioblastoma (GBM), and high grade glioma patients had significantly lower mtDNA copy number than their counterparts (P = 0.02, P < 0.01, and P = 0.04, respectively). In the multivariate analysis, elevated mtDNA copy number levels were associated with a 1.63-fold increased risk of glioma (adjusted odds ratio (OR) = 1.63, 95% confidence interval (CI) = 1.23-2.14). In further quartile analysis, study subjects who had highest levels of mtNDA copy number had 1.75-fold increased risk of gliomas (adjOR = 1.75, 95%CI = 1.18-2.61). In brief, our findings support the role of mtDNA copy number in the glioma carcinogenesis. © 2016 Wiley Periodicals, Inc.

A ratiometric two-photon probe for quantitative imaging of mitochondrial pH values

Mitochondrial pH (pHmito) is known to be alkaline (near 8.0) and has emerged as a potential factor for mitochondrial function and disorder. We have developed a ratiometric two-photon probe (CMP1) for quantitative analysis of pHmito in live cells and tissues. This probe is designed to function by controlling the intramolecular charge transfer from 2-naphthol, having an ideal pKa value (7.86 ± 0.05) in the cells to monitor pHmito. This transition results in a marked yellow to red emission color change in response to pH alterations from 6.0 to 9.0. CMP1 exhibits easy loading, selective and robust staining ability of mitochondria, low cytotoxicity, and bright two-photon excited fluorescence in situ, thereby allowing quantitative imaging of the pHmito in live cells and tissues. The ratiometric TPM imaging clearly reveals that subcellular distribution of the pHmito values is heterogeneous, with the pHmito values in the perinuclear region being higher than those at the periphery of the cells. The changes of pHmito values on carbonyl cyanide m-chlorophenyl hydrazone (CCCP) treatment and autophagic processes were also investigated along with their morphological alterations at specific subcellular positions. We also used CMP1 to visualize the pHmito values of Parkinson's disease model astrocytes as well as living hippocampal tissues. Our results demonstrate that CMP1 will be useful as a quantitative imaging probe to study pHmito in biomedical research.

Measured Effects of Wnt3a on Proliferation of HEK293T Cells Depend on the Applied Assay

The Wnt signaling pathway has been associated with many essential cell processes. This study aims to examine the effects of Wnt signaling on proliferation of cultured HEK293T cells. Cells were incubated with Wnt3a, and the activation of the Wnt pathway was followed by analysis of the level of the β-catenin protein and of the expression levels of the target genes MYC and CCND1. The level of β-catenin protein increased up to fourfold. While the mRNA levels of c-Myc and cyclin D1 increased slightly, the protein levels increased up to a factor of 1.5. Remarkably, MTT and BrdU assays showed different results when measuring the proliferation rate of Wnt3a stimulated HEK293T cells. In the BrdU assays an increase of the proliferation rate could be detected, which correlated to the applied Wnt3a concentration. Oppositely, this correlation could not be shown in the MTT assays. The MTT results, which are based on the mitochondrial activity, were confirmed by analysis of the succinate dehydrogenase complex by immunofluorescence and by western blotting. Taken together, our study shows that Wnt3a activates proliferation of HEK293 cells. These effects can be detected by measuring DNA synthesis rather than by measuring changes of mitochondrial activity.

Axin is expressed in mitochondria and suppresses mitochondrial ATP synthesis in HeLa cells

Many recent studies have revealed that axin is involved in numerous cellular functions beyond the negative regulation of β-catenin-dependent Wnt signaling. Previously, an association of ectopic axin with mitochondria was observed. In an effort to investigate the relationship between axin and mitochondria, we found that axin expression suppressed cellular ATP production, which was more apparent as axin expression levels increased. Also, mitochondrial expression of axin was observed using two axin-expressing HeLa cell models: doxycycline-inducible ectopic axin expression (HeLa-axin) and axin expression enhanced by long-term treatment with XAV939 (HeLa-XAV). In biochemical analysis, axin is associated with oxidative phosphorylation (OXPHOS) complex IV and is involved in defects in the assembly of complex IV-containing supercomplexes. Functionally, axin expression reduced the activity of OXPHOS complex IV and the oxygen consumption rate (OCR), suggesting axin-mediated mitochondrial dysfunction. Subsequent studies using various inhibitors of Wnt signaling showed that the reduction in cellular ATP levels was weaker in cases of ICAT protein expression and treatment with iCRT3 or NSC668036 compared with XAV939 treatment, suggesting that XAV939 treatment affects ATP synthesis in addition to suppressing Wnt signaling activity. Axin-mediated regulation of mitochondrial function may be an additional mechanism to Wnt signaling for regulation of cell growth.

Tauroursodeoxycholic acid increases neural stem cell pool and neuronal conversion by regulating mitochondria-cell cycle retrograde signaling

The low survival and differentiation rates of stem cells after either transplantation or neural injury have been a major concern of stem cell-based therapy. Thus, further understanding long-term survival and differentiation of stem cells may uncover new targets for discovery and development of novel therapeutic approaches. We have previously described the impact of mitochondrial apoptosis-related events in modulating neural stem cell (NSC) fate. In addition, the endogenous bile acid, tauroursodeoxycholic acid (TUDCA) was shown to be neuroprotective in several animal models of neurodegenerative disorders by acting as an anti-apoptotic and anti-oxidant molecule at the mitochondrial level. Here, we hypothesize that TUDCA might also play a role on NSC fate decision. We found that TUDCA prevents mitochondrial apoptotic events typical of early-stage mouse NSC differentiation, preserves mitochondrial integrity and function, while enhancing self-renewal potential and accelerating cell cycle exit of NSCs. Interestingly, TUDCA prevention of mitochondrial alterations interfered with NSC differentiation potential by favoring neuronal rather than astroglial conversion. Finally, inhibition of mitochondrial reactive oxygen species (mtROS) scavenger and adenosine triphosphate (ATP) synthase revealed that the effect of TUDCA is dependent on mtROS and ATP regulation levels. Collectively, these data underline the importance of mitochondrial stress control of NSC fate decision and support a new role for TUDCA in this process.

The Expression of a Novel Mitochondrially-Encoded Gene in Gonadic Precursors May Drive Paternal Inheritance of Mitochondria

Mitochondria have an active role in germ line development, and their inheritance dynamics are relevant to this process. Recently, a novel protein (RPHM21) was shown to be encoded in sperm by the male-transmitted mtDNA of Ruditapes philippinarum, a species with Doubly Uniparental Inheritance (DUI) of mitochondria. In silico analyses suggested a viral origin of RPHM21, and we hypothesized that the endogenization of a viral element provided sperm mitochondria of R. philippinarum with the ability to invade male germ line, thus being transmitted to the progeny. In this work we investigated the dynamics of germ line development in relation to mitochondrial transcription and expression patterns using qPCR and specific antibodies targeting the germ line marker VASPH (R. philippinarum VASA homolog), and RPHM21. Based on the experimental results we conclude that both targets are localized in the primordial germ cells (PGCs) of males, but while VASPH is detected in all PGCs, RPHM21 appears to be expressed only in a subpopulation of them. Since it has been predicted that RPHM21 might have a role in cell proliferation and migration, we here suggest that PGCs expressing it might gain advantage over others and undertake spermatogenesis, accounting for RPHM21 presence in all spermatozoa. Understanding how foreign sequence endogenization and co-option can modify the biology of an organism is of particular importance to assess the impact of such events on evolution.

Mitochondria: A Therapeutic Target for Parkinson's Disease?

Parkinson’s disease (PD) is one of the most common neurodegenerative disorders. The exact causes of neuronal damage are unknown, but mounting evidence indicates that mitochondrial-mediated pathways contribute to the underlying mechanisms of dopaminergic neuronal cell death both in PD patients and in PD animal models. Mitochondria are organized in a highly dynamic tubular network that is continuously reshaped by opposing processes of fusion and fission. Defects in either fusion or fission, leading to mitochondrial fragmentation, limit mitochondrial motility, decrease energy production and increase oxidative stress, thereby promoting cell dysfunction and death. Thus, the regulation of mitochondrial dynamics processes, such as fusion, fission and mitophagy, represents important mechanisms controlling neuronal cell fate. In this review, we summarize some of the recent evidence supporting that impairment of mitochondrial dynamics, mitophagy and mitochondrial import occurs in cellular and animal PD models and disruption of these processes is a contributing mechanism to cell death in dopaminergic neurons. We also summarize mitochondria-targeting therapeutics in models of PD, proposing that modulation of mitochondrial impairment might be beneficial for drug development toward treatment of PD.

Impaired mitochondrial function in HepG2 cells treated with hydroxy-cobalamin[c-lactam]: A cell model for idiosyncratic toxicity

The vitamin B12 analog hydroxy-cobalamin[c-lactam] (HCCL) impairs mitochondrial protein synthesis and the function of the electron transport chain. Our goal was to establish an in vitro model for mitochondrial dysfunction in human hepatoma cells (HepG2), which can be used to investigate hepatotoxicity of idiosyncratic mitochondrial toxicants. For that, HepG2 cells were treated with HCCL, which inhibits the function of methylmalonyl-CoA mutase and impairs mitochondrial protein synthesis. Secondary, cells were incubated with propionate that served as source of propionyl-CoA, a percursor of methylmalonyl-CoA. Dose-finding experiments were conducted to evaluate the optimal dose and treatment time of HCCL and propionate for experiments on mitochondrial function. 50 μM HCCL was cytotoxic after exposure of HepG2 cells for 2d and 10 and 50 μM HCCL enhanced the cytotoxicity of 100 or 1000 μM propionate. Co-treatment with HCCL (10 μM) and propionate (1000 μM) dissipated the mitochondrial membrane potential and impaired the activity of enzyme complex IV of the electron transport chain. Treatment with HCCL decreased the mRNA content of mitochondrially encoded proteins, whereas the mtDNA content remained unchanged. We observed mitochondrial ROS accumulation and decreased mitochondrial SOD2 expression. Moreover, electron microscopy showed mitochondrial swelling. Finally, HepG2 cells pretreated with a non-cytotoxic combination of HCCL (10 μM) and propionate (100 μM) were more sensitive to the mitochondrial toxicants dronedarone, benzbromarone, and ketoconazole than untreated cells. In conclusion, we established and characterized a cell model, which could be used for testing drugs with idiosyncratic mitochondrial toxicity.

Metabolic Plasticity in Cancer Cells: Reconnecting Mitochondrial Function to Cancer Control

Anomalous increase in glycolytic activity defines one of the key metabolic alterations in cancer cells. A realization of this feature has led to critical advancements in cancer detection techniques such as positron emission tomography (PET) as well as a number of therapeutic avenues targeting the key glycolytic steps within a cancer cell. A normal healthy cell's survival relies on a sensitive balance between the primordial glycolysis and a more regulated mitochondrial bioenergetics. The salient difference between these two bioenergetics pathways is that oxygen availability is an obligatory requirement for mitochondrial pathway while glycolysis can function without oxygen. Early observations that some cancer cells up-regulate glycolytic activity even in the presence of oxygen (aerobic glycolysis) led to a hypothesis that such an altered cancer cell metabolism stems from inherent mitochondrial dysfunction. While a general validity of this hypothesis is still being debated, a number of recent research efforts have yielded clarity on the physiological origins of this aerobic glycolysis phenotype in cancer cells. Building on these recent studies, we present a generalized scheme of cancer cell metabolism and propose a novel hypothesis that might rationalize new avenues of cancer intervention.

Giving microbes their due – animal life in a microbially dominant world

The new technology of next-generation sequencing is changing our perceptions of the form and function of the biological world. The emerging data reveal an array of microbes that is more vast and more central to all biological processes than previously appreciated. Further, evidence is accumulating that the alliances of microbes with one another and with constituents of the macrobiological world are critical for the health of the biosphere. This contribution summarizes the basic arguments as to why, when considering the biochemical adaptations of animals, we should integrate the roles of their microbial partners.

Oxidative stress and mitochondrial dysfunction play a role in myelodysplastic syndrome development, diagnosis, and prognosis: A pilot study

The imbalance between reactive oxygen species (ROS) production and their elimination by antioxidants leads to oxidative stress. Depending on their concentration, ROS can trigger apoptosis or stimulate cell proliferation. We hypothesized that oxidative stress and mitochondrial dysfunction may participate not only in apoptosis detected in some myelodysplastic syndrome (MDS) patients, but also in increasing proliferation in other patients. We investigated the involvement of oxidative stress and mitochondrial dysfunction in MDS pathogenesis, as well as assessed their diagnostic and prognostic values. Intracellular peroxides, superoxide, superoxide/peroxides ratio, reduced glutathione (GSH), and mitochondrial membrane potential (Δψ(mit)) levels were analyzed in bone marrow cells from 27 MDS patients and 12 controls, by flow cytometry. We observed that all bone marrow cell types from MDS patients had increased intracellular peroxide levels and decreased GSH content, compared with control cells. Moreover, oxidative stress levels were MDS subtype- and risk group-dependent. Low-risk patients had the highest ROS levels, which can be related with their high apoptosis; and intermediate-2-risk patients had high Δψ(mit) that may be associated with their proliferative potential. GSH levels were negatively correlated with transfusion dependency, and peroxide levels were positively correlated with serum ferritin level. GSH content proved to be an accurate parameter to discriminate patients from controls. Finally, patients with high ROS or low GSH levels, as well as high superoxide/peroxides ratio had lower overall survival. Our results suggest that oxidative stress and mitochondrial dysfunction are involved in MDS development, and that oxidative stress parameters may constitute novel diagnosis and/or prognosis biomarkers for MDS.

Extensive temporal transcriptome and microRNA analyses identify molecular mechanisms underlying mitochondrial dysfunction induced by multi-walled carbon nanotubes in human lung cells

Understanding toxicity pathways of engineered nanomaterials (ENM) has recently been brought forward as a key step in twenty-first century ENM risk assessment. Molecular mechanisms linked to phenotypic end points is a step towards the development of toxicity tests based on key events, which may allow for grouping of ENM according to their modes of action. This study identified molecular mechanisms underlying mitochondrial dysfunction in human bronchial epithelial BEAS 2B cells following exposure to one of the most studied multi-walled carbon nanotubes (Mitsui MWCNT-7). Asbestos was used as a positive control and a non-carcinogenic glass wool material was included as a negative fibre control. Decreased mitochondrial membrane potential (MMP↓) was observed for MWCNTs at a biologically relevant dose (0.25 μg/cm(2)) and for asbestos at 2 μg/cm(2), but not for glass wool. Extensive temporal transcriptomic and microRNA expression analyses identified a 330-gene signature (including 26 genes with known mitochondrial function) related to MWCNT- and asbestos-induced MMP↓. Forty-nine of the MMP↓-associated genes showed highly similar expression patterns over time (six time points) and the majority was found to be regulated by two transcription factors strongly involved in mitochondrial homeostasis, APP and NRF1. In addition, four miRNAs were correlated with MMP↓ and one of them, miR-1275, was found to negatively correlate with a large part of the MMP↓-associated genes. Cellular processes such as gluconeogenesis, mitochondrial LC-fatty acid β-oxidation and spindle microtubule function were enriched among the MMP↓-associated genes and miRNAs. These results are expected to be useful in the identification of key events in ENM-related toxicity pathways for the development of molecular screening techniques.

Non-thermal plasma activates human keratinocytes by stimulation of antioxidant and phase II pathways

Non-thermal atmospheric pressure plasma provides a novel therapeutic opportunity to control redox-based processes, e.g. wound healing, cancer, and inflammatory diseases. By spatial and time-resolved delivery of reactive oxygen and nitrogen species, it allows stimulation or inhibition of cellular processes in biological systems. Our data show that both gene and protein expression is highly affected by non-thermal plasma. Nuclear factor erythroid-related factor 2 (NRF2) and phase II enzyme pathway components were found to act as key controllers orchestrating the cellular response in keratinocytes. Additionally, glutathione metabolism, which is a marker for NRF2-related signaling events, was affected. Among the most robustly increased genes and proteins, heme oxygenase 1, NADPH-quinone oxidoreductase 1, and growth factors were found. The roles of NRF2 targets, investigated by siRNA silencing, revealed that NRF2 acts as an important switch for sensing oxidative stress events. Moreover, the influence of non-thermal plasma on the NRF2 pathway prepares cells against exogenic noxae and increases their resilience against oxidative species. Via paracrine mechanisms, distant cells benefit from cell-cell communication. The finding that non-thermal plasma triggers hormesis-like processes in keratinocytes facilitates the understanding of plasma-tissue interaction and its clinical application.

Tuning of peroxiredoxin catalysis for various physiological roles

Peroxiredoxins (Prxs) make up an ancient family of enzymes that are the predominant peroxidases for nearly all organisms and play essential roles in reducing hydrogen peroxide, organic hydroperoxides, and peroxynitrite. Even between distantly related organisms, the core protein fold and key catalytic residues related to its cysteine-based catalytic mechanism have been retained. Given that these enzymes appeared early in biology, Prxs have experienced more than 1 billion years of optimization for specific ecological niches. Although their basic enzymatic function remains the same, Prxs have diversified and are involved in roles such as protecting DNA against mutation, defending pathogens against host immune responses, suppressing tumor formation, and--for eukaryotes--helping regulate peroxide signaling via hyperoxidation of their catalytic Cys residues. Here, we review the current understanding of the physiological roles of Prxs by analyzing knockout and knockdown studies from ∼25 different species. We also review what is known about the structural basis for the sensitivity of some eukaryotic Prxs to inactivation by hyperoxidation. In considering the physiological relevance of hyperoxidation, we explore the distribution across species of sulfiredoxin (Srx), the enzyme responsible for rescuing hyperoxidized Prxs. We unexpectedly find that among eukaryotes appearing to have a "sensitive" Prx isoform, some do not contain Srx. Also, as Prxs are suggested to be promising targets for drug design, we discuss the rationale behind recently proposed strategies for their selective inhibition.

Systematic characterization of cell cycle phase-dependent protein dynamics and pathway activities by high-content microscopy-assisted cell cycle phenotyping

Cell cycle progression is coordinated with metabolism, signaling and other complex cellular functions. The investigation of cellular processes in a cell cycle stage-dependent manner is often the subject of modern molecular and cell biological research. Cell cycle synchronization and immunostaining of cell cycle markers facilitate such analysis, but are limited in use due to unphysiological experimental stress, cell type dependence and often low flexibility. Here, we describe high-content microscopy-assisted cell cycle phenotyping (hiMAC), which integrates high-resolution cell cycle profiling of asynchronous cell populations with immunofluorescence microscopy. hiMAC is compatible with cell types from any species and allows for statistically powerful, unbiased, simultaneous analysis of protein interactions, modifications and subcellular localization at all cell cycle stages within a single sample. For illustration, we provide a hiMAC analysis pipeline tailored to study DNA damage response and genomic instability using a 3–4-day protocol, which can be adjusted to any other cell cycle stage-dependent analysis.

Interaction between endoplasmic/sarcoplasmic reticulum stress (ER/SR stress), mitochondrial signaling and Ca(2+) regulation in airway smooth muscle (ASM)

Airway inflammation is a key aspect of diseases such as asthma. Several inflammatory cytokines (e.g., TNFα and IL-13) increase cytosolic Ca(2+) ([Ca(2+)]cyt) responses to agonist stimulation and Ca(2+) sensitivity of force generation, thereby enhancing airway smooth muscle (ASM) contractility (hyper-reactive state). Inflammation also induces ASM proliferation and remodeling (synthetic state). In normal ASM, the transient elevation of [Ca(2+)]cyt induced by agonists leads to a transient increase in mitochondrial Ca(2+) ([Ca(2+)]mito) that may be important in matching ATP production with ATP consumption. In human ASM (hASM) exposed to TNFα and IL-13, the transient increase in [Ca(2+)]mito is blunted despite enhanced [Ca(2+)]cyt responses. We also found that TNFα and IL-13 induce reactive oxidant species (ROS) formation and endoplasmic/sarcoplasmic reticulum (ER/SR) stress (unfolded protein response) in hASM. ER/SR stress in hASM is associated with disruption of mitochondrial coupling with the ER/SR membrane, which relates to reduced mitofusin 2 (Mfn2) expression. Thus, in hASM it appears that TNFα and IL-13 result in ROS formation leading to ER/SR stress, reduced Mfn2 expression, disruption of mitochondrion-ER/SR coupling, decreased mitochondrial Ca(2+) buffering, mitochondrial fragmentation, and increased cell proliferation.

Cell cycle arrest and cell survival induce reverse trends of cardiolipin remodeling

Cell survival from the arrested state can be a cause of the cancer recurrence. Transition from the arrest state to the growth state is highly regulated by mitochondrial activity, which is related to the lipid compositions of the mitochondrial membrane. Cardiolipin is a critical phospholipid for the mitochondrial integrity and functions. We examined the changes of cardiolipin species by LC-MS in the transition between cell cycle arrest and cell reviving in HT1080 fibrosarcoma cells. We have identified 41 cardiolipin species by MS/MS and semi-quantitated them to analyze the detailed changes of cardiolipin species. The mass spectra of cardiolipin with the same carbon number form an envelope, and the C64, C66, C68, C70 C72 and C74 envelopes in HT1080 cells show a normal distribution in the full scan mass spectrum. The cardiolipin quantity in a cell decreases while entering the cell cycle arrest, but maintains at a similar level through cell survival. While cells awakening from the arrested state and preparing itself for replication, the groups with short acyl chains, such as C64, C66 and C68 show a decrease of cardiolipin percentage, but the groups with long acyl chains, such as C70 and C72 display an increase of cardiolipin percentage. Interestingly, the trends of the cardiolipin species changes during the arresting state are completely opposite to cell growing state. Our results indicate that the cardiolipin species shift from the short chain to long chain cardiolipin during the transition from cell cycle arrest to cell progression.

Minireview: DNA replication in plant mitochondria

Higher plant mitochondrial genomes exhibit much greater structural complexity compared to most other organisms. Unlike well-characterized metazoan mitochondrial DNA (mtDNA) replication, an understanding of the mechanism(s) and proteins involved in plant mtDNA replication remains unclear. Several plant mtDNA replication proteins, including DNA polymerases, DNA primase/helicase, and accessory proteins have been identified. Mitochondrial dynamics, genome structure, and the complexity of dual-targeted and dual-function proteins that provide at least partial redundancy suggest that plants have a unique model for maintaining and replicating mtDNA when compared to the replication mechanism utilized by most metazoan organisms.

Vitexicarpin induces apoptosis in human prostate carcinoma PC-3 cells through G2/M phase arrest

Vitexicarpin (3', 5-dihydroxy-3, 4', 6, 7-tetramethoxyflavone), a polymethoxyflavone isolated from Viticis Fructus (Vitex rotundifolia Linne fil.), has long been used as an anti-inflammatory herb in traditional Chinese medicine. It has also been reported that vitexicarpin can inhibit the growth of various cancer cells. However, there is no report elucidating its effect on human prostate carcinoma cells. The aim of the present study was to examine the apoptotic induction activity of vitexicarpin on PC-3 cells and molecular mechanisms involved. MTT studies showed that vitexicarpin dose-dependently inhibited growth of PC-3 cells with an IC50~28.8 μM. Hoechst 33258 staining further revealed that vitexicarpin induced apoptotic cell death. The effect of vitexicarpin on PC-3 cells apoptosis was tested using prodium iodide (PI)/Annexin V-FITC double staining and flow cytometry. The results indicated that vitexicarpin induction of apoptotic cell death in PC-3 cells was accompanied by cell cycle arrest in the G2/M phase. Furthermore, our study demonstrated that vitexicarpin induction of PC-3 cell apoptosis was associated with upregulation of the proapoptotic protein Bax, and downregulation of antiapoptotic protein Bcl-2, release of Cytochrome c from mitochondria and decrease in mitochondrial membrane potential. Our findings suggested that vitexicarpin may become a potential leading drug in the therapy of prostate carcinoma.

Mitochondrial translocation of p53 modulates neuronal fate by preventing differentiation-induced mitochondrial stress

AIMS

Apoptosis regulatory proteins, such as p53, play a pivotal role in neural differentiation, through mechanisms independent of cell death. In addition, p53 has been identified as an important regulator of mitochondrial survival response, maintaining mitochondrial DNA (mtDNA) integrity and oxidative protection. The aim of this study was to determine the role of mitochondrial p53 in organelle damage and neural differentiation.

RESULTS

Our results show that mitochondrial apoptotic events such as reactive oxygen species production, mitochondrial membrane permeabilization, and cytochrome c release are typical of early-stage mouse neural stem cell differentiation, which occurs 3-18 h after induction of differentiation, with no evidence of cell death. In addition, decreased mtDNA content, lipidated LC3 (LC3-II), colocalization of mitochondria and LC3-II puncta, and mitochondria-associated Parkin are consistent with activation of mitophagy. Importantly, at early stages of neural differentiation, p53 was actively translocated to mitochondria and attenuated mitochondrial oxidative stress, cytochrome c release, and mitophagy. Forced mitochondrial translocation of p53 increased neurogenic potential and neurite outgrowth.

INNOVATION AND CONCLUSION

In conclusion, our results reveal a novel role for mitochondrial p53, which modulates mitochondrial damage and apoptosis-related events in the context of neural differentiation, thus enhancing neuronal fate.

De novo comparative transcriptome analysis of Acremonium chrysogenum: high-yield and wild-type strains of cephalosporin C producer

β-lactam antibiotics are widely used in clinic. Filamentous fungus Acremonium chrysogenum is an important industrial fungus for the production of CPC, one of the major precursors of β-lactam antibiotics. Although its fermentation yield has been bred significantly over the past decades, little is known regarding molecular changes between the industrial strain and the wild type strain. This limits the possibility to improve CPC production further by molecular breeding. Comparative transcriptome is a powerful tool to understand the molecular mechanisms of CPC industrial high yield producer compared to wild type. A total of 57 million clean sequencing reads with an average length of 100 bp were generated from Illumina sequencing platform. 22,878 sequences were assembled. Among the assembled unigenes, 9502 were annotated and 1989 annotated sequences were assigned to 121 pathways by searching against the Kyoto Encyclopedia of Genes and Genomes pathway (KEGG) database. Furthermore, we compared the transcriptome differences between a high-yield and a wild-type strain during fermentation. A total of 4329 unigenes with significantly different transcription level were identified, among which 1737 were up-regulated and 2592 were down-regulated. 24 pathways were subsequently determined which involve glycerolipid metabolism, galactose metabolism, and pyrimidine metabolism. We also examined the transcription levels of 18 identified genes, including 11 up-regulated genes and 7 down-regulated genes using reverse transcription quantitative -PCR (RT-qPCR). The results of RT-qPCR were consistent with the Illumina sequencing. In this study, the Illumina sequencing provides the most comprehensive sequences for gene expression profile of Acremonium chrysogenum and allows de novo transcriptome assembly while lacking genome information. Comparative analysis of RNA-seq data reveals the complexity of the transcriptome in the fermentation of different yield strains. This is an important public information platform which could be used to accelerate the research to improve CPC production in Acremonium chrysogenum.

Mitochondrial function and mitochondrial DNA maintenance with advancing age

We review the impact of mitochondrial DNA (mtDNA) maintenance and mitochondrial function on the aging process. Mitochondrial function and mtDNA integrity are closely related. In order to create a protective barrier against reactive oxygen and nitrogen species (RONS) attacks and ensure mtDNA integrity, multiple cellular mtDNA copies are packaged together with various proteins in nucleoids. Regulation of antioxidant and RONS balance, DNA base excision repair, and selective degradation of damaged mtDNA copies preserves normal mtDNA quantities. Oxidative damage to mtDNA molecules does not substantially contribute to increased mtDNA mutation frequency; rather, mtDNA replication errors of DNA PolG are the main source of mtDNA mutations. Mitochondrial turnover is the major contributor to maintenance of mtDNA and functionally active mitochondria. Mitochondrial turnover involves mitochondrial biogenesis, mitochondrial dynamics, and selective autophagic removal of dysfunctional mitochondria (i.e., mitophagy). All of these processes exhibit decreased activity during aging and fall under greater nuclear genome control, possibly coincident with the emergence of nuclear genome instability. We suggest that the age-dependent accumulation of mutated mtDNA copies and dysfunctional mitochondria is associated primarily with decreased cellular autophagic and mitophagic activity.

Fus1/Tusc2 is a novel regulator of mitochondrial calcium handling, Ca2+-coupled mitochondrial processes, and Ca2+-dependent NFAT and NF-κB pathways in CD4+ T cells

AIMS

Fus1 has been established as mitochondrial tumor suppressor, immunomodulator, and antioxidant protein, but molecular mechanism of these activities remained to be identified. Based on putative calcium-binding and myristoyl-binding domains that we identified in Fus1, we explored our hypothesis that Fus1 regulates mitochondrial calcium handling and calcium-coupled processes.

RESULTS

Fus1 loss resulted in reduced rate of mitochondrial calcium uptake in calcium-loaded epithelial cells, splenocytes, and activated CD4(+) T cells. The reduced rate of mitochondrial calcium uptake in Fus1-deficient cells correlated with cytosolic calcium increase and dysregulation of calcium-coupled mitochondrial parameters, such as reactive oxygen species production, ΔμH(+), mitochondrial permeability transition pore opening, and GSH content. Inhibition of calcium efflux via mitochondria, Na(+)/Ca(2+) exchanger significantly improved the mitochondrial calcium uptake in Fus1(-/-) cells. Ex vivo analysis of activated CD4(+) T cells showed Fus1-dependent changes in calcium-regulated processes, such as surface expression of CD4 and PD1/PD-L1, proliferation, and Th polarization. Fus1(-/-) T cells showed increased basal expression of calcium-dependent NF-κB and NFAT targets but were unable to fully activate these pathways after stimulation.

INNOVATION

Our results establish Fus1 as one of the few identified regulators of mitochondrial calcium handling. Our data support the idea that alterations in mitochondrial calcium dynamics could lead to the disruption of metabolic coupling in mitochondria that, in turn, may result in multiple cellular and systemic abnormalities.

CONCLUSION

Our findings suggest that Fus1 achieves its protective role in inflammation, autoimmunity, and cancer via the regulation of mitochondrial calcium and calcium-coupled parameters.

To breathe or not to breathe: the haematopoietic stem/progenitor cells dilemma

Adult haematopoietic stem/progenitor cells (HSPCs) constitute the lifespan reserve for the generation of all the cellular lineages in the blood. Although massive progress in identifying the cluster of master genes controlling self-renewal and multipotency has been achieved in the past decade, some aspects of the physiology of HSPCs still need to be clarified. In particular, there is growing interest in the metabolic profile of HSPCs in view of their emerging role as determinants of cell fate. Indeed, stem cells and progenitors have distinct metabolic profiles, and the transition from stem to progenitor cell corresponds to a critical metabolic change, from glycolysis to oxidative phosphorylation. In this review, we summarize evidence, reported in the literature and provided by our group, highlighting the peculiar ability of HSPCs to adapt their mitochondrial oxidative/bioenergetic metabolism to survive in the hypoxic microenvironment of the endoblastic niche and to exploit redox signalling in controlling the balance between quiescence versus active cycling and differentiation. Especial prominence is given to the interplay between hypoxia inducible factor-1, globins and NADPH oxidases in managing the mitochondrial dioxygen-related metabolism and biogenesis in HSPCs under different ambient conditions. A mechanistic model is proposed whereby 'mitochondrial differentiation' is a prerequisite in uncommitted stem cells, paving the way for growth/differentiation factor-dependent processes. Advancing the understanding of stem cell metabolism will, hopefully, help to (i) improve efforts to maintain, expand and manipulate HSPCs ex vivo and realize their potential therapeutic benefits in regenerative medicine; (ii) reprogramme somatic cells to generate stem cells; and (iii) eliminate, selectively, malignant stem cells.

LINKED ARTICLES

This article is part of a themed section on Emerging Therapeutic Aspects in Oncology. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.169.issue-8.

How to analyze mitochondrial morphology in healthy cells and apoptotic cells in Caenorhabditis elegans

Mitochondria constantly undergo fusion and fission events. A proper balance of fusion and fission is essential in healthy cells, as disrupting this balance is associated with several neurodegenerative diseases. Mitochondrial fission has also been shown to play an important role during apoptosis. Hence, the machineries that control mitochondrial morphology have both nonapoptotic and apoptotic functions. Seminal work in yeast has identified some of the key components of these machineries. However, the list is certainly not complete and new factors that are specific to metazoans are being identified every year. In this review, we describe methodologies to test whether a particular candidate gene plays a role in the control of mitochondrial morphology in healthy cells and apoptotic cells using Caenorhabditis elegans.

Modulation of mitochondrial functions by the indirect antioxidant sulforaphane: a seemingly contradictory dual role and an integrative hypothesis

The chemotherapeutic isothiocyanate sulforaphane (SFN) was early linked to anticarcinogenic and antiproliferative activities. Soon after, this compound, derived from cruciferous vegetables, became an excellent and useful trial for anti-cancer research in experimental models including growth tumor, metastasis, and angiogenesis. Many subsequent reports showed modifications in mitochondrial signaling, functionality, and integrity induced by SFN. When cytoprotective effects were found in toxic and ischemic insult models, seemingly contradictory behaviors of SFN were discovered: SFN was inducing deleterious changes in cancer cell mitochondria that eventually would carry the cell to death via apoptosis and also was protecting noncancer cell mitochondria against oxidative challenge, which prevented cell death. In both cases, SFN exhibited effects on mitochondrial redox balance and phase II enzyme expression, mitochondrial membrane potential, expression of the family of B cell lymphoma 2 homologs, regulation of proapoptotic proteins released from mitochondria, activation/inactivation of caspases, mitochondrial respiratory complex activities, oxygen consumption and bioenergetics, mitochondrial permeability transition pore opening, and modulation of some kinase pathways. With the ultimate findings related to the induction of mitochondrial biogenesis by SFN, it could be considered that SFN has effects on mitochondrial dynamics that explain some divergent points. In this review, we list the reports involving effects on mitochondrial modulation by SFN in anti-cancer models as well as in cytoprotective models against oxidative damage. We also attempt to integrate the data into a mechanism explaining the various effects of SFN on mitochondrial function in only one concept, taking into account mitochondrial biogenesis and dynamics and making a comparison with the theory of reactive oxygen species threshold of cell death. Our interest is to achieve a complete view of cancer and protective therapies based on SFN that can be extended to other chemotherapeutic compounds with similar characteristics. The work needed to test this hypothesis is quite extensive.

Sulforaphane induces reactive oxygen species-mediated mitotic arrest and subsequent apoptosis in human bladder cancer 5637 cells

The present study was undertaken to determine whether sulforaphane-derived reactive oxygen species (ROS) might cause growth arrest and apoptosis in human bladder cancer 5637 cells. Our results show that the reduced viability of 5637 cells by sulforaphane is due to mitotic arrest, but not the G2 phase. The sulforaphane-induced mitotic arrest correlated with an induction of cyclin B1 and phosphorylation of Cdk1, as well as a concomitant increased complex between cyclin B1 and Cdk1. Sulforaphane-induced apoptosis was associated with the activation of caspase-8 and -9, the initiators caspases of the extrinsic and intrinsic apoptotic pathways, respectively, and activation of effector caspase-3 and cleavage of poly (ADP-ribose) polymerase. However, blockage of caspase activation inhibited apoptosis and abrogated growth inhibition in sulforaphane-treated 5637 cells. This study further investigated the roles of ROS with respect to mitotic arrest and the apoptotic effect of sulforaphane, and the maximum level of ROS accumulation was observed 3h after sulforaphane treatment. However, a ROS scavenger, N-acetyl-L-cysteine, notably attenuated sulforaphane-mediated apoptosis as well as mitotic arrest. Overall, these results suggest that sulforaphane induces mitotic arrest and apoptosis of 5637 cells via a ROS-dependent pathway.

α-Tocopherol administration blocks adaptive changes in cell NADH/NAD+ redox state and mitochondrial function leading to inhibition of gastric mucosa cell proliferation in rats

In experimentally induced chronic gastritis, a compensatory mucosal cell proliferation occurs with enhanced glucose oxidative metabolism linked to lipoperoxidative events. Therefore, this study was aimed at assessing the participation of cell NAD/NADH redox state and mitochondrial functions during gastric mucosa proliferation and the effects of in vivo α-tocopherol (vitamin E) administration. Glucose oxidation and oxygen consumption were tested in gastric mucosa samples obtained from rats with gastritis and from those also treated with α-tocopherol. Gastric mucosal mitochondria were isolated and structural and functional parameters were determined. Succinate oxidation, ADP phosphorylation, mitochondrial enzyme activities, and membrane lipid composition were measured. In addition, parameters indicative of cellular NAD/NADH redox state, proliferation, apoptosis, and nitric oxide (NO) metabolism were also determined. After ethanol withdrawal, the damaged gastric mucosa increased glucose and oxygen consumption, events associated with a more reduced cytoplasmic NAD/NADH ratio. Enhanced mitochondrial oxidative phosphorylation and increased mitochondrial enzyme activities occurred early, accompanied by recovery of lost mitochondrial protein and lipid composition in the gastric mucosa, events associated with increased NO production. When mitochondrial function and structural events were normalized, apoptosis was initiated as assessed by the mitochondrial Bax/Bcl2 ratio. Treatment with α-tocopherol inhibited cell proliferation and blocked enhanced glucose utilization, mitochondrial substrate oxidation, and changes in redox state, delaying the onset of these adaptive metabolic changes, whereas it inhibited cell proliferation. In conclusion, α-tocopherol could abolish damage-induced "stress" signaling by desynchronizing mitochondrial adaptive responses, including mitochondria biogenesis, and consequently NAD/NADH redox, which seems to regulate gastric mucosal cell proliferation.

The tumor microenvironment: characterization, redox considerations, and novel approaches for reactive oxygen species-targeted gene therapy

The tumor microenvironment is a complex system that involves the interaction between malignant and neighbor stromal cells embedded in a mesh of extracellular matrix (ECM) components. Stromal cells (fibroblasts, endothelial, and inflammatory cells) are co-opted at different stages to help malignant cells invade the surrounding ECM and disseminate. Malignant cells have developed adaptive mechanisms to survive under the extreme conditions of the tumor microenvironment such as restricted oxygen supply (hypoxia), nutrient deprivation, and a prooxidant state among others. These conditions could be eventually used to target drugs that will be activated specifically in this microenvironment. Preclinical studies have shown that modulating cellular/tissue redox state by different gene therapy (GT) approaches was able to control tumor growth. In this review, we describe the most relevant features of the tumor microenvironment, addressing reactive oxygen species-generating sources that promote a prooxidative microenvironment inside the tumor mass. We describe different GT approaches that promote either a decreased or exacerbated prooxidative microenvironment, and those that make use of the differential levels of ROS between cancer and normal cells to achieve tumor growth inhibition.

Hypoxic culture conditions as a solution for mesenchymal stem cell based regenerative therapy

Cell-based regenerative therapies, based on in vitro propagation of stem cells, offer tremendous hope to many individuals suffering from degenerative diseases that were previously deemed untreatable. Due to the self-renewal capacity, multilineage potential, and immunosuppressive property, mesenchymal stem cells (MSCs) are considered as an attractive source of stem cells for regenerative therapies. However, poor growth kinetics, early senescence, and genetic instability during in vitro expansion and poor engraftment after transplantation are considered to be among the major disadvantages of MSC-based regenerative therapies. A number of complex inter- and intracellular interactive signaling systems control growth, multiplication, and differentiation of MSCs in their niche. Common laboratory conditions for stem cell culture involve ambient O₂ concentration (20%) in contrast to their niche where they usually reside in 2–9% O₂. Notably, O₂ plays an important role in maintaining stem cell fate in terms of proliferation and differentiation, by regulating hypoxia-inducible factor-1 (HIF-1) mediated expression of different genes. This paper aims to describe and compare the role of normoxia (20% O₂) and hypoxia (2–9% O₂) on the biology of MSCs. Finally it is concluded that a hypoxic environment can greatly improve growth kinetics, genetic stability, and expression of chemokine receptors during in vitro expansion and eventually can increase efficiency of MSC-based regenerative therapies.

Mitochondrial bioenergetics, mass, and morphology are altered in cells of the degenerating human annulus

Back pain and intervertebral disc degeneration have a growing socioeconomic healthcare impact. Information on mitochondrial function in human intervertebral disc cells, however, is surprisingly sparse. We assessed mitochondrial bioenergetics, mass, and ultrastructure in annulus cells cultured from human discs of varying degenerative stages. Citrate synthase activity (reflecting mitochondrial mass) declined significantly with increasing Thompson grade (p < 0.0001). Both mitochondrial (p = 0.009) and non-mitochondrial (p = 0.0029) respiration showed significant changes with increasing stages of disc degeneration. No significant relationships were found for the association of respiration data with herniated or non-herniated status, or with subject age. Examination of mitochondrial ultrastructure in cultured annulus cells revealed unusual features which included mitochondrial inclusion bodies, poorly defined cristae and dark staining. Findings reported here are novel and document biochemical, metabolic, and morphologic abnormalities in mitochondria in cells from more degenerated annulus cells. Data suggest that the disc degenerative, not age, is a major factor associated with mitochondrial impairment, and also implicate oxidative stress, driven by mitochondrial dysfunction, as a major component within the degenerating disc. Findings have relevance to advancements in cell-based therapies to treat disc degeneration.

Together and apart: inhibition of DNA synthesis by connexin-43 and its relationship to transforming growth factor β

The membrane and channel protein connexin-43 (Cx43), as well as the cytokine transforming growth factor (TGF) β, suppress proliferative growth in cardiomyocytes and other cell types. Previously we showed that the inhibitory effect of Cx43 is canceled when Cx43 becomes phosphorylated at serine (S) 262 in response to mitogen stimulation. We have now asked if the TGFβ-triggered inhibition of DNA synthesis is associated with changes in Cx43 phosphorylation at S262. Conversely, we investigated if inhibition of DNA synthesis by overexpressed Cx43 is dependent on engaging TGFβ signal transduction. We report that TGFβ acutely prevented mitogen-induced Cx43 phosphorylation at S262, while chronic inhibition of TGFβ signal transduction raised baseline levels of endogenous phospho-S262-Cx43 without affecting total Cx43. Inhibition of baseline TGFβ signal transduction through (a) inhibiting TGFβ receptor I (TGFβRI) with SB431542, (b) inhibiting TGFβ receptor II (TGFβRII) by overexpressing dominant-negative (DN) TGFβRII, (c) inhibiting the downstream signaling mediator Smad2 by overexpressing DN Smad2, each separately increased baseline cardiomyocyte DNA synthesis, but could not reverse DNA synthesis inhibition by overexpressed Cx43. It is suggested that inhibition of cardiomyocyte DNA synthesis by TGFβ/TGFβRI/II/phospho-Smad2 signaling is mediated, at least in part, by reducing endogenous phospho-S262-Cx43 levels.

Paeonol inhibits hepatic fibrogenesis via disrupting nuclear factor-κB pathway in activated stellate cells: in vivo and in vitro studies

BACKGROUND AND AIMS

Hepatic fibrosis represents a major cause of morbidity and mortality worldwide. The present study was to evaluate the antifibrogenesis effect of paeonol and involved mechanisms.

METHODS

The degree of liver injury was evaluated biochemically by measuring serum and fibrotic markers and pathological examination. Cell viability was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay and trypan blue staining. Cytotoxic effects were determined using lactate dehydrogenase release assay. Cell cycle was determined using single dyeing methods of propidium iodide (PI) by flow cytometry. Apoptosis was confirmed using double-staining of annexin V/PI and Hoechst. Western blot, immunofluorescence and real-time polymerase chain reaction were used to explore the molecular mechanisms.

RESULTS

Treatment with paeonol significantly protected the liver from injury by reducing the activities of serum aspartate aminotransferase, alanine aminotransferase, improving the histological architecture of the liver, and by inhibiting activation of hepatic stellate cells (HSCs) in vivo. Interestingly, paeonol had no apparent cytotoxic effects but could markedly inhibit primary HSC proliferation and induced HSC cell cycle arrest at the G2/M checkpoint. These effects were caused by paeonol suppression of phosphorylation of cycle protein cdc2 and of CDK2. Moreover, that paeonol triggered mitochondrial apoptosis pathway and led to activation of caspase cascades in HSCs was found. Mechanistic investigations revealed that the nuclear factor-κB (NF-κB) pathway inhibition resulted in the earlier events. Furthermore, paeonol altered the expression of some marker proteins relevant to HSCs activation.

CONCLUSION

Paeonol could inhibit HSC proliferation and induce mitochondrial apoptosis via disrupting NF-κB pathway, which might be the mechanisms of paeonol reduction of liver fibrosis.

Novel roles of reactive oxygen species in the pathogenesis of acute myeloid leukemia

It has become apparent that regulation of ROS is important in cell signaling and homeostasis. Accumulation of ROS triggers oxidative stress in various cell types and contributes to the development, progression, and persistence of cancer. Recent research has demonstrated that redox dysregulation caused by ROS promotes proliferation, differentiation, genomic, and epigenetic alterations; immune evasion; and survival in leukemic cells. ROS act as signaling molecules to regulate redox-sensitive transcriptional factors, enzymes, oncogenes, and other downstream effectors. Thus, a thorough understanding the role of ROS as key mediators in leukemogenesis is likely to provide opportunities for improved pharmacological intervention. In this review, we summarize the recent findings that support a role for ROS in the pathogenesis of AML and outline innovative approaches in the implementation of redox therapies for myeloid malignancies.

Mitochondrial-targeted nitroxides disrupt mitochondrial architecture and inhibit expression of peroxiredoxin 3 and FOXM1 in malignant mesothelioma cells

Malignant mesothelioma (MM) is an intractable tumor of the peritoneal and pleural cavities primarily linked to exposure to asbestos. Recently, we described an interplay between mitochondrial-derived oxidants and expression of FOXM1, a redox-responsive transcription factor that has emerged as a promising therapeutic target in solid malignancies. Here we have investigated the effects of nitroxides targeted to mitochondria via triphenylphosphonium (TPP) moieties on mitochondrial oxidant production, expression of FOXM1 and peroxiredoxin 3 (PRX3), and cell viability in MM cells in culture. Both Mito-carboxy-proxyl (MCP) and Mito-TEMPOL (MT) caused dose-dependent increases in mitochondrial oxidant production that was accompanied by inhibition of expression of FOXM1 and PRX3 and loss of cell viability. At equivalent concentrations TPP, CP, and TEMPOL had no effect on these endpoints. Live cell ratiometric imaging with a redox-responsive green fluorescent protein targeted to mitochondria (mito-roGFP) showed that MCP and MT, but not CP, TEMPOL, or TPP, rapidly induced mitochondrial fragmentation and swelling, morphological transitions that were associated with diminished ATP levels and increased production of mitochondrial oxidants. Mdivi-1, an inhibitor of mitochondrial fission, did not rescue mitochondria from fragmentation by MCP. Immunofluorescence microscopy experiments indicate a fraction of FOXM1 coexists in the cytoplasm with mitochondrial PRX3. Our results indicate that MCP and MT inhibit FOXM1 expression and MM tumor cell viability via perturbations in redox homeostasis caused by marked disruption of mitochondrial architecture, and suggest that both compounds, either alone or in combination with thiostrepton or other agents, may provide credible therapeutic options for the management of MM.

Impairment of mitochondrial dynamics: a target for the treatment of neurological disorders?

Mitochondrial dysfunction has long been appreciated in the pathogenesis of various neurological disorders. However, the molecular basis underlying the decline in mitochondrial function is not fully understood. Mitochondria are highly dynamic organelles that frequently undergo fusion and fission. In healthy cells, the delicate balance between fusion and fission is required for maintaining normal mitochondrial and cellular function. However, under pathological conditions, the balance is disrupted, resulting in excessive mitochondrial fragmentation and mitochondrial dysfunction. The impaired fusion and fission processes can lead to apoptosis, necrosis and autophagic cell death and seem to play causal roles in the progression of acute and chronic neuronal injuries. In this article, important aspects of what is currently known about the molecular machinery regulating mitochondrial fission and fusion in mammalian cells is summarized. Special emphasis will be given to the consequences of disregulated mitochondrial morphology in the pathogenesis of neurological diseases.

Redox control of leukemia: from molecular mechanisms to therapeutic opportunities

Reactive oxygen species (ROS) play both positive and negative roles in the proliferation and survival of a cell. This dual nature has been exploited by leukemia cells to promote growth, survival, and genomic instability-some of the hallmarks of the cancer phenotype. In addition to altered ROS levels, many antioxidants are dysregulated in leukemia cells. Together, the production of ROS and the expression and activity of antioxidant enzymes make up the primary redox control of leukemia cells. By manipulating this system, leukemia cells gain proliferative and survival advantages, even in the face of therapeutic insults. Standard treatment options have improved leukemia patient survival rates in recent years, although relapse and the development of resistance are persistent challenges. Therapies targeting the redox environment show promise for these cases. This review highlights the molecular mechanisms that control the redox milieu of leukemia cells. In particular, ROS production by the mitochondrial electron transport chain, NADPH oxidase, xanthine oxidoreductase, and cytochrome P450 will be addressed. Expression and activation of antioxidant enzymes such as superoxide dismutase, catalase, heme oxygenase, glutathione, thioredoxin, and peroxiredoxin are perturbed in leukemia cells, and the functional consequences of these molecular alterations will be described. Lastly, we delve into how these pathways can be potentially exploited therapeutically to improve treatment regimens and promote better outcomes for leukemia patients.

Sulforaphane attenuates gentamicin-induced nephrotoxicity: role of mitochondrial protection

Sulforaphane (SFN), an isothiocyanate naturally occurring in Cruciferae, induces cytoprotection in several tissues. Its protective effect has been associated with its ability to induce cytoprotective enzymes through an Nrf2-dependent pathway. Gentamicin (GM) is a widely used antibiotic; nephrotoxicity is the main side effect of this compound. In this study, it was investigated if SFN is able to induce protection against GM-induced nephropathy both in renal epithelial LLC-PK1 cells in culture and in rats. SFN prevented GM-induced death and loss of mitochondrial membrane potential in LLC-PK1 cells. In addition, it attenuated GM-induced renal injury (proteinuria, increases in serum creatinine, in blood urea nitrogen, and in urinary excretion on N-acetyl-β-D-glucosaminidase, and decrease in creatinine clearance and in plasma glutathione peroxidase activity) and necrosis and apoptosis in rats. The apoptotic death was associated with enhanced active caspase-9. Caspase-8 was unchanged in all the studied groups. In addition, SFN was able to prevent GM-induced protein nitration and decrease in the activity of antioxidant enzymes catalase and glutathione peroxidase in renal cortex. In conclusion, the protective effect of SFN against GM-induced acute kidney injury could be associated with the preservation in mitochondrial function that would prevent the intrinsic apoptosis and nitrosative stress.

Mitochondria and cell signalling

Mitochondria have long been considered as crucial organelles, primarily for their roles in biosynthetic reactions such as ATP synthesis. However, it is becoming increasingly apparent that mitochondria are intimately involved in cell signalling pathways. Mitochondria perform various signalling functions, serving as platforms to initiate cell signalling, as well as acting as transducers and effectors in multiple processes. Here, we discuss the active roles that mitochondria have in cell death signalling, innate immunity and autophagy. Common themes of mitochondrial regulation emerge from these diverse but interconnected processes. These include: the outer mitochondrial membrane serving as a major signalling platform, and regulation of cell signalling through mitochondrial dynamics and by mitochondrial metabolites, including ATP and reactive oxygen species. Importantly, defects in mitochondrial control of cell signalling and in the regulation of mitochondrial homeostasis might underpin many diseases, in particular age-related pathologies.

Targeting cell cycle regulation in cancer therapy

Cell proliferation is an essential mechanism for growth, development and regeneration of eukaryotic organisms; however, it is also the cause of one of the most devastating diseases of our era: cancer. Given the relevance of the processes in which cell proliferation is involved, its regulation is of paramount importance for multicellular organisms. Cell division is orchestrated by a complex network of interactions between proteins, metabolism and microenvironment including several signaling pathways and mechanisms of control aiming to enable cell proliferation only in response to specific stimuli and under adequate conditions. Three main players have been identified in the coordinated variation of the many molecules that play a role in cell cycle: i) The cell cycle protein machinery including cyclin-dependent kinases (CDK)-cyclin complexes and related kinases, ii) The metabolic enzymes and related metabolites and iii) The reactive-oxygen species (ROS) and cellular redox status. The role of these key players and the interaction between oscillatory and non-oscillatory species have proved essential for driving the cell cycle. Moreover, cancer development has been associated to defects in all of them. Here, we provide an overview on the role of CDK-cyclin complexes, metabolic adaptations and oxidative stress in regulating progression through each cell cycle phase and transitions between them. Thus, new approaches for the design of innovative cancer therapies targeting crosstalk between cell cycle simultaneous events are proposed.

Metabolic Stress and Disorders Related to Alterations in Mitochondrial Fission or Fusion

Mitochondrial morphology and metabolism play an important role in cellular homeostasis. Recent studies have shown that the fidelity of mitochondrial morphology is important in maintaining mitochondrial shape, number, size, membrane potential, ATP synthesis, mtDNA, motility, signaling, quality control, response to cellular stress, mitophagy and apoptosis. This article provides an overview of the current state of knowledge of the fission and fusion machinery with a focus on the mechanisms underlying the regulation of the mitochondrial morphology and cellular energy state. Several lines of evidence indicate that dysregulation of mitochondrial fission or fusion is associated with mitochondrial dysfunction, which in turn impacts mitophagy and apoptosis. Metabolic disorders are also associated with dysregulation of fission or fusion and the available lines of evidence point to a bidirectional interplay between the mitochondrial fission or fusion reactions and bioenergetics. Clearly, more in-depth studies are needed to fully elucidate the mechanisms that control mitochondrial fission and fusion. It is envisioned that the outcome of such studies will improve the understanding of the molecular basis of related metabolic disorders and also facilitate the development of better therapeutics.

Endocannabinoids in neuroendopsychology: multiphasic control of mitochondrial function

The endocannabinoid system (ECS) is a construct based on the discovery of receptors that are modulated by the plant compound tetrahydrocannabinol and the subsequent identification of a family of nascent ligands, the 'endocannabinoids'. The function of the ECS is thus defined by modulation of these receptors-in particular, by two of the best-described ligands (2-arachidonyl glycerol and anandamide), and by their metabolic pathways. Endocannabinoids are released by cell stress, and promote both cell survival and death according to concentration. The ECS appears to shift the immune system towards a type 2 response, while maintaining a positive energy balance and reducing anxiety. It may therefore be important in resolution of injury and inflammation. Data suggest that the ECS could potentially modulate mitochondrial function by several different pathways; this may help explain its actions in the central nervous system. Dose-related control of mitochondrial function could therefore provide an insight into its role in health and disease, and why it might have its own pathology, and possibly, new therapeutic directions.

Mechanisms linking obesity, inflammation and altered metabolism to colon carcinogenesis

Due to its prevalence, obesity is now considered a global epidemic. It is linked to increased risk of colorectal cancer, the third most common cancer and the second leading cause of death among adults in Western countries. Obese adipose tissue differs from lean adipose tissue in its immunogenic profile, body fat distribution and metabolic profile. Obese adipose tissue releases free fatty acids, adipokines and many pro-inflammatory chemokines. These factors are known to play a key role in regulating malignant transformation and cancer progression. Obese adipose tissue is infiltrated by macrophages that participate in inflammatory pathways activated within the tissue. Adipose tissue macrophages consist of two different phenotypes. M1 macrophages reside in obese adipose tissue and produce pro-inflammatory cytokines, and M2 macrophages reside in lean adipose tissue and produce anti-inflammatory cytokines, such as interleukin-10 (IL-10). The metabolic networks that confer tumour cells with their oncogenic properties, such as increased proliferation and the ability to avoid apoptosis are still not well understood. We review the interactions between adipocytes and immune cells that may alter the metabolism towards promotion of colorectal cancer.

Mechanisms of hepatocellular toxicity associated with dronedarone--a comparison to amiodarone

Dronedarone is a new antiarrhythmic drug with an amiodarone-like benzofuran structure. Shortly after its introduction, dronedarone became implicated in causing severe liver injury. Amiodarone is a well-known mitochondrial toxicant. The aim of our study was to investigate mechanisms of hepatotoxicity of dronedarone in vitro and to compare them with amiodarone. We used isolated rat liver mitochondria, primary human hepatocytes, and the human hepatoma cell line HepG2, which were exposed acutely or up to 24h. After exposure of primary hepatocytes or HepG2 cells for 24h, dronedarone and amiodarone caused cytotoxicity and apoptosis starting at 20 and 50 µM, respectively. The cellular ATP content started to decrease at 20 µM for both drugs, suggesting mitochondrial toxicity. Inhibition of the respiratory chain required concentrations of ~10 µM and was caused by an impairment of complexes I and II for both drugs. In parallel, mitochondrial accumulation of reactive oxygen species (ROS) was observed. In isolated rat liver mitochondria, acute treatment with dronedarone decreased the mitochondrial membrane potential, inhibited complex I, and uncoupled the respiratory chain. Furthermore, in acutely treated rat liver mitochondria and in HepG2 cells exposed for 24h, dronedarone started to inhibit mitochondrial β-oxidation at 10 µM and amiodarone at 20 µM. Similar to amiodarone, dronedarone is an uncoupler and an inhibitor of the mitochondrial respiratory chain and of β-oxidation both acutely and after exposure for 24h. Inhibition of mitochondrial function leads to accumulation of ROS and fatty acids, eventually leading to apoptosis and/or necrosis of hepatocytes. Mitochondrial toxicity may be an explanation for hepatotoxicity of dronedarone in vivo.

Energy and redox homeostasis in tumor cells

Cancer cells display abnormal morphology, chromosomes, and metabolism. This review will focus on the metabolism of tumor cells integrating the available data by way of a functional approach. The first part contains a comprehensive introduction to bioenergetics, mitochondria, and the mechanisms of production and degradation of reactive oxygen species. This will be followed by a discussion on the oxidative metabolism of tumor cells including the morphology, biogenesis, and networking of mitochondria. Tumor cells overexpress proteins that favor fission, such as GTPase dynamin-related protein 1 (Drp1). The interplay between proapoptotic members of the Bcl-2 family that promotes Drp 1-dependent mitochondrial fragmentation and fusogenic antiapoptotic proteins such as Opa-1 will be presented. It will be argued that contrary to the widespread belief that in cancer cells, aerobic glycolysis completely replaces oxidative metabolism, a misrepresentation of Warburg's original results, mitochondria of tumor cells are fully viable and functional. Cancer cells also carry out oxidative metabolism and generally conform to the orthodox model of ATP production maintaining as well an intact electron transport system. Finally, data will be presented indicating that the key to tumor cell survival in an ROS rich environment depends on the overexpression of antioxidant enzymes and high levels of the nonenzymatic antioxidant scavengers.