"Time Is out of Joint" in Pluripotent Stem Cells: How and Why

The circadian rhythm is necessary for the homeostasis and health of living organisms. Molecular clocks interconnected by transcription/translation feedback loops exist in most cells of the body. A puzzling exemption to this, otherwise, general biological hallmark is given by the cell physiology of pluripotent stem cells (PSCs) that lack circadian oscillations gradually acquired following their in vivo programmed differentiation. This process can be nicely phenocopied following in vitro commitment and reversed during the reprogramming of somatic cells to induce PSCs. The current understanding of how and why pluripotency is "time-uncoupled" is largely incomplete. A complex picture is emerging where the circadian core clockwork is negatively regulated in PSCs at the post-transcriptional/translational, epigenetic, and other-clock-interaction levels. Moreover, non-canonical functions of circadian core-work components in the balance between pluripotency identity and metabolic-driven cell reprogramming are emerging. This review selects and discusses results of relevant recent investigations providing major insights into this context.

Mitochondrial sAC-cAMP-PKA Axis Modulates the ΔΨm-Dependent Control Coefficients of the Respiratory Chain Complexes: Evidence of Respirasome Plasticity

The current view of the mitochondrial respiratory chain complexes I, III and IV foresees the occurrence of their assembly in supercomplexes, providing additional functional properties when compared with randomly colliding isolated complexes. According to the plasticity model, the two structural states of the respiratory chain may interconvert, influenced by the intracellular prevailing conditions. In previous studies, we suggested the mitochondrial membrane potential as a factor for controlling their dynamic balance. Here, we investigated if and how the cAMP/PKA-mediated signalling influences the aggregation state of the respiratory complexes. An analysis of the inhibitory titration profiles of the endogenous oxygen consumption rates in intact HepG2 cells with specific inhibitors of the respiratory complexes was performed to quantify, in the framework of the metabolic flux theory, the corresponding control coefficients. The attained results, pharmacologically inhibiting either PKA or sAC, indicated that the reversible phosphorylation of the respiratory chain complexes/supercomplexes influenced their assembly state in response to the membrane potential. This conclusion was supported by the scrutiny of the available structure of the CI/CIII2/CIV respirasome, enabling us to map several PKA-targeted serine residues exposed to the matrix side of the complexes I, III and IV at the contact interfaces of the three complexes.

The Relationship between Clock Genes, Sirtuin 1, and Mitochondrial Activity in Head and Neck Squamous Cell Cancer: Effects of Melatonin Treatment

The circadian clock is a regulatory system, with a periodicity of approximately 24 h, which generates rhythmic changes in many physiological processes, including mitochondrial activity. Increasing evidence links chronodisruption with aberrant functionality in clock gene expression, resulting in multiple diseases such as cancer. Melatonin, whose production and secretion oscillates according to the light-dark cycle, is the principal regulator of clock gene expression. In addition, the oncostatic effects of melatonin correlate with an increase in mitochondrial activity. However, the direct links between circadian clock gene expression, mitochondrial activity, and the antiproliferative effects of melatonin in cancers, including head and neck squamous cell carcinoma (HNSCC), remain largely unknown. In this study, we analyzed the effects of melatonin on HNSCC cell lines (Cal-27 and SCC9), which were treated with 500 and 1000 µM melatonin. We found that the antiproliferative effect of melatonin is not mediated by the Bmal1 clock gene. Additionally, high doses of melatonin were observed to result in resynchronization of oscillatory circadian rhythm genes (Per2 and Sirt1). Surprisingly, the resynchronizing effect of melatonin on Per2 and Sirt1 did not produce alterations in the oscillation of mitochondrial respiratory activity. These results increase our understanding of the possible antiproliferative mechanisms in melatonin in the treatment of head and neck squamous cell carcinoma and suggest that its antiproliferative effects are independent of clock genes but are directly related to mitochondrial activity.

Metabolic reprogramming in inflammatory microglia indicates a potential way of targeting inflammation in Alzheimer's disease

Microglia activation drives the pro-inflammatory activity in the early stages of Alzheimer's disease (AD). However, the mechanistic basis is elusive, and the hypothesis of targeting microglia to prevent AD onset is little explored. Here, we demonstrated that upon LPS exposure, microglia shift towards an energetic phenotype characterised by high glycolysis and high mitochondrial respiration with dysfunction. Although the activity of electron transport chain (ETC) complexes is boosted by LPS, this is mostly devoted to the generation of reactive oxygen species. We showed that by inhibiting succinate dehydrogenase (SDH) with dimethyl malonate (DMM), it is possible to modulate the LPS-induced metabolic rewiring, facilitating an anti-inflammatory phenotype. DMM improves mitochondrial function in a direct way and by reducing LPS-induced mitochondrial biogenesis. Moreover, the block of SDH with DMM inhibits the recruitment of hypoxia inducible-factor 1 α (HIF-1α), which mediates the induction of glycolysis and cytokine expression. Similar bioenergetic alterations were observed in the microglia isolated from AD mice (3xTg-AD), which present high levels of circulating LPS and brain toll-like receptor4 (TLR4). Moreover, this well-established model of AD was used to show a potential effect of SDH inhibition in vivo as DMM administration abrogated brain inflammation and modulated the microglia metabolic alterations of 3xTg-AD mice. The RNA-sequencing analysis from a public dataset confirmed the consistent transcription of genes encoding for ETC subunits in the microglia of AD mice (5xFAD). In conclusion, TLR4 activation promotes metabolic changes and the pro-inflammatory activity in microglia, and SDH might represent a promising therapeutic target to prevent AD development.

Characterization of the effect of pomegranate crude extract, and its post-harvesting preservation procedures, on redox tone, cellular growth and metabolic profile of MDA-MB-231 cell line

BACKGROUND

Pomegranate is known for its beneficial properties due to its high content in antioxidants and might constitute a natural option for preventing and treatment of different pathologies including cancer. Since mitochondria are involved in tumorigenesis through ROS production and modulation of oxidative metabolism, we investigated the biological effects of pomegranate on cellular redox state, proliferation and metabolism in the breast cancer cell line MDA-MB-231 (MDA).

METHODS

MDA were treated for 24 h with graded concentration of filtered Pomegranate juice (PJ) and tested for metabolic Flux Analysis with XFe96 Extracellular Flux Analyzer, for proliferation using the xCELLigence System Real-Time Cell Analyzer and for intracellular ROS content by Confocal Microscopy Imaging.

RESULTS

Cells-treatment with freshly prepared pomegranate juice (PJ) resulted in a significant reduction of the intracellular ROS content already at the lower concentration of PJ tested. Additionally, it enhanced mitochondria respiration, and decreased glycolysis at high concentrations, inhibiting at the same time cell proliferation. As pomegranate is a seasonal fruit, assessment of optimum storage conditions preserving its bio-active properties was investigated. Our results indicated that storage conditions under controlled atmosphere for 30 days was able to enhance mitochondrial respiration at the same extent than freshly extracted PJ. Conversely, freezing procedure, though retaining the antioxidant and cell-growth inhibitory property, elicited an opposite effect on the metabolic profile as compared with fresh extract.

CONCLUSION

Overall, the results of our study, on the one hand, confirms the preventive/therapeutic potential of PJ, as well as of its post-harvested processing, for cancer management. On the other hand, it highlights the intrinsic difficulties in attaining mechanistic insights when a multiplicity of effects is elicited by a crude mixture of bio-active compounds.

The circadian clock circuitry modulates leukemia initiating cell activity in T-cell acute lymphoblastic leukemia

BACKGROUND

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological malignancy, characterized by restricted cellular subsets with asymmetrically enriched leukemia initiating cell (LIC) activity. Nonetheless, it is still unclear which signaling programs promote LIC maintenance and progression.

METHODS

Here, we evaluated the role of the biological clock in the regulation of the molecular mechanisms and signaling pathways impacting the cellular dynamics in T-ALL through an integrated experimental approach including gene expression profiling of shRNA-modified T-ALL cell lines and Chromatin Immunoprecipitation Sequencing (ChIP-Seq) of leukemic cells. Patient-derived xenograft (PDXs) cell subsets were also genetically manipulated in order to assess the LIC activity modulated by the loss of biological clock in human T-ALL.

RESULTS

We report that the disruption of the circadian clock circuitry obtained through shRNA-mediated knockdown of CLOCK and BMAL1 genes negatively impacted the growth in vitro as well as the activity in vivo of LIC derived from PDXs after transplantation into immunodeficient recipient mice. Additionally, gene expression data integrated with ChIP-Seq profiles of leukemic cells revealed that the circadian clock directly promotes the expression of genes, such as IL20RB, crucially involved in JAK/STAT signaling, making the T-ALL cells more responsive to Interleukin 20 (IL20).

CONCLUSION

Taken together, our data support the concept that the biological clock drives the expression of IL20R prompting JAK/STAT signaling and promoting LIC activity in T-ALL and suggest that the selective targeting of circadian components could be therapeutically relevant for the treatment of T-ALL patients.

Bioenergetic profile and redox tone modulate in vitro osteogenesis of human dental pulp stem cells: new perspectives for bone regeneration and repair

BACKGROUND

Redox signaling and energy metabolism are known to be involved in controlling the balance between self-renewal and proliferation/differentiation of stem cells. In this study we investigated metabolic and redox changes occurring during in vitro human dental pulp stem cells (hDPSCs) osteoblastic (OB) differentiation and tested on them the impact of the reactive oxygen species (ROS) signaling.

METHODS

hDPSCs were isolated from dental pulp and subjected to alkaline phosphatase and alizarin red staining, q-RT-PCR, and western blotting analysis of differentiation markers to assess achievement of osteogenic/odontogenic differentiation. Moreover, a combination of metabolic flux analysis and confocal cyto-imaging was used to profile the metabolic phenotype and to evaluate the redox tone of hDPSCs.

RESULTS

In differentiating hDPSCs we observed the down-regulation of the mitochondrial respiratory chain complexes expression since the early phase of the process, confirmed by metabolic flux analysis, and a reduction of the basal intracellular peroxide level in its later phase. In addition, dampened glycolysis was observed, thereby indicating a lower energy-generating phenotype in differentiating hDPSCs. Treatment with the ROS scavenger Trolox, applied in the early-middle phases of the process, markedly delayed OB differentiation of hDPSCs assessed as ALP activity, Runx2 expression, mineralization capacity, expression of stemness and osteoblast marker genes (Nanog, Lin28, Dspp, Ocn) and activation of ERK1/2. In addition, the antioxidant partly prevented the inhibitory effect on cell metabolism observed following osteogenic induction.

CONCLUSIONS

Altogether these results provided evidence that redox signaling, likely mediated by peroxide species, influenced the stepwise osteogenic expansion/differentiation of hDPSCs and contributed to shape its accompanying metabolic phenotype changes thus improving their efficiency in bone regeneration and repair.

Regulation of mitochondrial complex III activity and assembly by TRAP1 in cancer cells

BACKGROUND

Metabolic reprogramming is an important issue in tumor biology. A recently-identified actor in this regard is the molecular chaperone TRAP1, that is considered an oncogene in several cancers for its high expression but an oncosuppressor in others with predominant oxidative metabolism. TRAP1 is mainly localized in mitochondria, where it interacts with respiratory complexes, although alternative localizations have been described, particularly on the endoplasmic reticulum, where it interacts with the translational machinery with relevant roles in protein synthesis regulation.

RESULTS

Herein we show that, inside mitochondria, TRAP1 binds the complex III core component UQCRC2 and regulates complex III activity. This decreases respiration rate during basal conditions but allows sustained oxidative phosphorylation when glucose is limiting, a condition in which the direct TRAP1-UQCRC2 binding is disrupted, but not TRAP1-complex III binding. Interestingly, several complex III components and assembly factors show an inverse correlation with survival and response to platinum-based therapy in high grade serous ovarian cancers, where TRAP1 inversely correlates with stage and grade and directly correlates with survival. Accordingly, drug-resistant ovarian cancer cells show high levels of complex III components and high sensitivity to complex III inhibitory drug antimycin A.

CONCLUSIONS

These results shed new light on the molecular mechanisms involved in TRAP1-dependent regulation of cancer cell metabolism and point out a potential novel target for metabolic therapy in ovarian cancer.

Myoglobin expression by alternative transcript in different mesenchymal stem cells compartments

BACKGROUND

The metabolic phenotype of stem cells is increasingly recognized as a hallmark of their pluripotency with mitochondrial and oxygen-related metabolism playing a not completely defined role in this context. In a previous study, we reported the ectopic expression of myoglobin (MB) in bone marrow-derived hematopoietic stem/progenitor cells. Here, we have extended the analysis to mesenchymal stem cells (MSCs) isolated from different tissues.

METHODS

MSCs were isolated from human placental membrane, mammary adipose tissue and dental pulp and subjected to RT-PCR, Western blotting and mass spectrometry to investigate the expression of MB. A combination of metabolic flux analysis and cyto-imaging was used to profile the metabolic phenotype and the mitochondria dynamics in the different MSCs.

RESULTS

As for the hematopoietic stem/progenitor cells, the expression of Mb was largely driven by an alternative transcript with the protein occurring both in the monomer and in the dimer forms as confirmed by mass spectrometry analysis. Comparing the metabolic fluxes between neonatal placental membrane-derived and adult mammary adipose tissue-derived MSCs, we showed a significantly more active bioenergetics profile in the former that correlated with a larger co-localization of myoglobin with the mitochondrial compartment. Differences in the structure of the mitochondrial network as well as in the expression of factors controlling the organelle dynamics were also observed between neonatal and adult mesenchymal stem cells. Finally, the expression of myoglobin was found to be strongly reduced following osteogenic differentiation of dental pulp-derived MSCs, while it was upregulated following reprogramming of human fibroblasts to induce pluripotent stem cells.

CONCLUSIONS

Ectopic expression of myoglobin in tissues other than muscle raises the question of understanding its function therein. Properties in addition to the canonical oxygen storage/delivery have been uncovered. Finding of Mb expressed via an alternative gene transcript in the context of different stem cells with metabolic phenotypes, its loss during differentiation and recovery in iPSCs suggest a hitherto unappreciated role of Mb in controlling the balance between aerobic metabolism and pluripotency. Understanding how Mb contributes through modulation of the mitochondrial physiology to the stem cell biology paves the way to novel perspectives in regenerative medicine as well as in cancer stem cell therapy.

On the Origin of Hemoglobin Cooperativity under Non-equilibrium Conditions

Abnormal hemoglobins can have major consequences for tissue delivery of oxygen. Correct diagnosis of hemoglobinopathies with altered oxygen affinity requires a determination of hemoglobin oxygen dissociation curve, which relates the hemoglobin oxygen saturation to the partial pressure of oxygen in the blood. Determination of the oxygen dissociation curve of human hemoglobin is typically carried out under conditions in which hemoglobin is in equilibrium with O2 at each partial pressure. However, in the human body due to the fast transit of red blood cells through tissues hemoglobin oxygen exchanges occur under non-equilibrium conditions. We describe the determination of non-equilibrium oxygen dissociation curve and show that under these conditions the true nature of hemoglobin cooperativity is revealed as emerging solely from the consecutive binding of oxygen to each one of the four subunits of hemoglobin until the entire tetramer is saturated. We call this form of cooperativity the sequential cooperativity of hemoglobin and define the simplest model that includes it as the minimalist model of hemoglobin. A single instantiation of this model accounts for ~70% of hemoglobin cooperativity under non-equilibrium conditions. The total cooperativity of hemoglobin can be viewed more correctly as the summation of two instantiations of the minimalist model (each one corresponding to a tetramer of low and high affinity for O2, respectively) in equilibrium with each other, as in the Monod-Wyman-Changeux model of hemoglobin. In addition to offering new insights on the nature of hemoglobin reaction with oxygen, the methodology described here for the determination of hemoglobin non-equilibrium oxygen dissociation curve provides a simple, fast, low-cost alternative to complex spectrophotometric methods, which is expected to be particularly valuable in regions where hemoglobinopathies are a significant public health problem, but where highly specialized laboratories capable of determining a traditional oxygen dissociation curve are not easily accessible.

The Histone Variant MacroH2A1 Impacts Circadian Gene Expression and Cell Phenotype in an In Vitro Model of Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death worldwide. A foremost risk factor for HCC is obesity/metabolic syndrome-related non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH), which is prompted by remarkable changes in transcription patterns of genes enriching metabolic, immune/inflammatory, and circadian pathways. Epigenetic mechanisms play a role in NAFLD-associated HCC, and macroH2A1, a variant of histone H2A, is involved in the pathogenesis modulating the expression of oncogenes and/or tumor suppressor genes and interacting with SIRT1, which crucially impacts the circadian clock circuitry. Hence, we aimed to appraise if and how macroH2A1 regulated the expression patterns of circadian genes in the setting of NAFLD-associated HCC. We took advantage of an in vitro model of liver cancer represented by HepG2 (human hepatocarcinoma) cells stably knocked down for macroH2A1 and conducted whole transcriptome profiling and deep phenotyping analysis. We found up-regulation of PER1 along with several deregulated circadian genes, enriching several important pathways and functions related to cancer onset and progression, such as epithelial-to-mesenchymal transition, cell cycle deregulation, and DNA damage. PER1 silencing partially mitigated the malignant phenotype induced by the loss of macroH2A1 in HCC cells. In conclusion, our findings suggest a modulatory role for the core circadian protein PER1 in liver carcinogenesis in the context of a lack of the macroH2A1 epigenetic and transcriptional landscape.

The heme synthesis-export system regulates the tricarboxylic acid cycle flux and oxidative phosphorylation

Heme is an iron-containing porphyrin of vital importance for cell energetic metabolism. High rates of heme synthesis are commonly observed in proliferating cells. Moreover, the cell-surface heme exporter feline leukemia virus subgroup C receptor 1a (FLVCR1a) is overexpressed in several tumor types. However, the reasons why heme synthesis and export are enhanced in highly proliferating cells remain unknown. Here, we illustrate a functional axis between heme synthesis and heme export: heme efflux through the plasma membrane sustains heme synthesis, and implementation of the two processes down-modulates the tricarboxylic acid (TCA) cycle flux and oxidative phosphorylation. Conversely, inhibition of heme export reduces heme synthesis and promotes the TCA cycle fueling and flux as well as oxidative phosphorylation. These data indicate that the heme synthesis-export system modulates the TCA cycle and oxidative metabolism and provide a mechanistic basis for the observation that both processes are enhanced in cells with high-energy demand.

How Cells Communicate with Each Other in the Tumor Microenvironment: Suggestions to Design Novel Therapeutic Strategies in Cancer Disease

Connexin- and pannexin (Panx)-formed hemichannels (HCs) and gap junctions (GJs) operate an interaction with the extracellular matrix and GJ intercellular communication (GJIC), and on account of this they are involved in cancer onset and progression towards invasiveness and metastatization. When we deal with cancer, it is not correct to omit the immune system, as well as neglecting its role in resisting or succumbing to formation and progression of incipient neoplasia until the formation of micrometastasis, nevertheless what really occurs in the tumor microenvironment (TME), which are the main players and which are the tumor or body allies, is still unclear. The goal of this article is to discuss how the pivotal players act, which can enhance or contrast cancer progression during two important process: "Activating Invasion and Metastasis" and the "Avoiding Immune Destruction", with a particular emphasis on the interplay among GJIC, Panx-HCs, and the purinergic system in the TME without disregarding the inflammasome and cytokines thereof derived. In particular, the complex and contrasting roles of Panx1/P2X7R signalosome in tumor facilitation and/or inhibition is discussed in regard to the early/late phases of the carcinogenesis. Finally, considering this complex interplay in the TME between cancer cells, stromal cells, immune cells, and focusing on their means of communication, we should be capable of revealing harmful messages that help the cancer growth and transform them in body allies, thus designing novel therapeutic strategies to fight cancer in a personalized manner.

TRAP1 enhances Warburg metabolism through modulation of PFK1 expression/activity and favors resistance to EGFR inhibitors in human colorectal carcinomas

Metabolic rewiring is a mechanism of adaptation to unfavorable environmental conditions and tumor progression. TRAP1 is an HSP90 molecular chaperone upregulated in human colorectal carcinomas (CRCs) and responsible for downregulation of oxidative phosphorylation (OXPHOS) and adaptation to metabolic stress. The mechanism by which TRAP1 regulates glycolytic metabolism and the relevance of this regulation in resistance to EGFR inhibitors were investigated in patient‐derived CRC spheres, human CRC cells, samples, and patients. A linear correlation was observed between TRAP1 levels and ¹⁸F‐fluoro‐2‐deoxy‐glucose (¹⁸F‐FDG) uptake upon PET scan or GLUT1 expression in human CRCs. Consistently, TRAP1 enhances GLUT1 expression, glucose uptake, and lactate production and downregulates OXPHOS in CRC patient‐derived spheroids and cell lines. Mechanistically, TRAP1 maximizes lactate production to balance low OXPHOS through the regulation of the glycolytic enzyme phosphofructokinase‐1 (PFK1); this depends on the interaction between TRAP1 and PFK1, which favors PFK1 glycolytic activity and prevents its ubiquitination/degradation. By contrast, TRAP1/PFK1 interaction is lost in conditions of enhanced OXPHOS, which results in loss of TRAP1 regulation of PFK1 activity and lactate production. Notably, TRAP1 regulation of glycolysis is involved in resistance of RAS‐wild‐type CRCs to EGFR monoclonals. Indeed, either TRAP1 upregulation or high glycolytic metabolism impairs cetuximab activity in vitro, whereas TRAP1 targeting and/or inhibition of glycolytic pathway enhances cell response to cetuximab. Finally, a linear correlation between ¹⁸F‐FDG PET uptake and poor response to cetuximab in first‐line therapy in human metastatic CRCs was observed. These results suggest that TRAP1 is a key determinant of CRC metabolic rewiring and favors resistance to EGFR inhibitors through regulation of glycolytic metabolism.

Mitochondrial calcium drives clock gene-dependent activation of pyruvate dehydrogenase and of oxidative phosphorylation

Regulation of metabolism is emerging as a major output of circadian clock circuitry in mammals. Accordingly, mitochondrial oxidative metabolism undergoes both in vivo and in vitro daily oscillatory activities. In a previous study we showed that both glycolysis and mitochondrial oxygen consumption display a similar time-resolved rhythmic activity in synchronized HepG2 cell cultures, which translates in overall bioenergetic changes as here documented by measurement of the ATP level. Treatment of synchronized cells with specific metabolic inhibitors unveiled pyruvate as a major source of reducing equivalents to the respiratory chain with its oxidation driven by the rhythmic (de)phosphorylation of pyruvate dehydrogenase. Further investigation enabled to causally link the autonomous cadenced mitochondrial respiration to a synchronous increase of the mitochondrial Ca²⁺. The rhythmic change of the mitochondrial respiration was dampened by inhibitors of the mitochondrial Ca²⁺ uniporter as well as of the ryanodine receptor Ca²⁺ channel or the ADPR cyclase, indicating that the mitochondrial Ca²⁺ influx originated from the ER store, likely at contact sites with the mitochondrial compartment. Notably, blockage of the mitochondrial Ca²⁺ influx resulted in deregulation of the expression of canonical clock genes such as BMALl1, CLOCK, NR1D1. All together our findings unveil a hitherto unexplored function of Ca²⁺-mediated signaling in time keeping the mitochondrial metabolism and in its feed-back modulation of the circadian clockwork.

Loss of Function of the Gene Encoding the Histone Methyltransferase KMT2D Leads to Deregulation of Mitochondrial Respiration

KMT2D encodes a methyltransferase responsible for histone 3 lysine 4 (H3K4) mono-/di-methylation, an epigenetic mark correlated with active transcription. Here, we tested the hypothesis that KMT2D pathogenic loss-of-function variants, which causes the Kabuki syndrome type 1, could affect the mitochondrial metabolic profile. By using Seahorse technology, we showed a significant reduction of the mitochondrial oxygen consumption rate as well as a reduction of the glycolytic flux in both Kmt2d knockout MEFs and skin fibroblasts of Kabuki patients harboring heterozygous KMT2D pathogenic variants. Mass-spectrometry analysis of intermediate metabolites confirmed alterations in the glycolytic and TCA cycle pathways. The observed metabolic phenotype was accompanied by a significant increase in the production of reactive oxygen species. Measurements of the specific activities of the mitochondrial respiratory chain complexes revealed significant inhibition of CI (NADH dehydrogenase) and CIV (cytochrome c oxidase); this result was further supported by a decrease in the protein content of both complexes. Finally, we unveiled an impaired oxidation of glucose and larger reliance on long-chain fatty acids oxidation. Altogether, our findings clearly indicate a rewiring of the mitochondrial metabolic phenotype in the KMT2D-null or loss-of-function context that might contribute to the development of Kabuki disease, and represents metabolic reprogramming as a potential new therapeutic approach.

ZSCAN4+ mouse embryonic stem cells have an oxidative and flexible metabolic profile

Cultured mouse embryonic stem cells are a heterogeneous population with diverse differentiation potential. In particular, the subpopulation marked by Zscan4 expression has high stem cell potency and shares with 2 cell stage preimplantation embryos both genetic and epigenetic mechanisms that orchestrate zygotic genome activation. Although embryonic de novo genome activation is known to rely on metabolites, a more extensive metabolic characterization is missing. Here we analyze the Zscan4⁺ mouse stem cell metabolic phenotype associated with pluripotency maintenance and cell reprogramming. We show that Zscan4⁺ cells have an oxidative and adaptable metabolism, which, on one hand, fuels a high bioenergetic demand and, on the other hand, provides intermediate metabolites for epigenetic reprogramming. Our findings enhance our understanding of the metastable Zscan4⁺ stem cell state with potential applications in regenerative medicine.

Nandrolone induces a stem cell-like phenotype in human hepatocarcinoma-derived cell line inhibiting mitochondrial respiratory activity

Nandrolone is a testosterone analogue with anabolic properties commonly abused worldwide, recently utilized also as therapeutic agent in chronic diseases, cancer included. Here we investigated the impact of nandrolone on the metabolic phenotype in HepG2 cell line. The results attained show that pharmacological dosage of nandrolone, slowing cell growth, repressed mitochondrial respiration, inhibited the respiratory chain complexes I and III and enhanced mitochondrial reactive oxygen species (ROS) production. Intriguingly, nandrolone caused a significant increase of stemness-markers in both 2D and 3D cultures, which resulted to be CxIII-ROS dependent. Notably, nandrolone negatively affected differentiation both in healthy hematopoietic and mesenchymal stem cells. Finally, nandrolone administration in mice confirmed the up-regulation of stemness-markers in liver, spleen and kidney. Our observations show, for the first time, that chronic administration of nandrolone, favoring maintenance of stem cells in different tissues would represent a precondition that, in addition to multiple hits, might enhance risk of carcinogenesis raising warnings about its abuse and therapeutic utilization.

TAp73 regulates ATP7A: possible implications for ageing-related diseases

The p53 family member p73 controls a wide range of cellular function. Deletion of p73 in mice results in increased tumorigenesis, infertility, neurological defects and altered immune system. Despite the extensive effort directed to define the molecular underlying mechanism of p73 function a clear definition of its transcriptional signature and the extent of overlap with the other p53 family members is still missing. Here we describe a novel TAp73 target, ATP7A a member of a large family of P-type ATPases implicated in human neurogenerative conditions and cancer chemoresistance. Modulation of TAp73 expression influences basal expression level of ATP7A in different cellular models and chromatin immunoprecipitation confirmed a physical direct binding of TAp73 on ATP7A genomic regions. Bioinformatic analysis of expression profile datasets of human lung cancer patients suggests a possible implication of TAp73/ATP7A axis in human cancer. These data provide a novel TAp73-dependent target which might have implications in ageing-related diseases such as cancer and neurodegeneration.

Deferasirox drives ROS-mediated differentiation and induces interferon-stimulated gene expression in human healthy haematopoietic stem/progenitor cells and in leukemia cells

Background

Administration of the iron chelator deferasirox (DFX) in transfusion-dependent patients occasionally results in haematopoiesis recovery by a mechanism remaining elusive. This study aimed to investigate at a molecular level a general mechanism underlying DFX beneficial effects on haematopoiesis, both in healthy and pathological conditions.

Methods

Human healthy haematopoietic stem/progenitor cells (HS/PCs) and three leukemia cell lines were treated with DFX. N-Acetyl cysteine (NAC) and fludarabine were added as antioxidant and STAT1 inhibitor, respectively. In vitro colony-forming assays were assessed both in healthy and in leukemia cells. Intracellular and mitochondrial reactive oxygen species (ROS) as well as mitochondrial content were assessed by cytofluorimetric and confocal microscopy analysis; mtDNA was assessed by qRT-PCR. Differentiation markers were monitored by cytofluorimetric analysis. Gene expression analysis (GEA) was performed on healthy HS/PCs, and differently expressed genes were validated in healthy and leukemia cells by qRT-PCR. STAT1 expression and phosphorylation were assessed by Western blotting. Data were compared by an unpaired Student t test or one-way ANOVA.

Results

DFX, at clinically relevant concentrations, increased the clonogenic capacity of healthy human CD34⁺ HS/PCs to form erythroid colonies. Extension of this analysis to human-derived leukemia cell lines Kasumi-1, K562 and HL60 confirmed DFX capacity to upregulate the expression of specific markers of haematopoietic commitment. Notably, the abovementioned DFX-induced effects are all prevented by the antioxidant NAC and accompanied with overproduction of mitochondria-generated reactive oxygen species (ROS) and increase of mitochondrial content and mtDNA copy number. GEA unveiled upregulation of genes linked to interferon (IFN) signalling and tracked back to hyper-phosphorylation of STAT1. Treatment of leukemic cell lines with NAC prevented the DFX-mediated phosphorylation of STAT1 as well as the expression of the IFN-stimulated genes. However, STAT1 inhibition by fludarabine was not sufficient to affect differentiation processes in leukemic cell lines.

Conclusions

These findings suggest a significant involvement of redox signalling as a major regulator of multiple DFX-orchestrated events promoting differentiation in healthy and tumour cells. The understanding of molecular mechanisms underlying the haematological response by DFX would enable to predict patient’s ability to respond to the drug, to extend treatment to other patients or to anticipate the treatment, regardless of the iron overload.

Electronic supplementary material

The online version of this article (10.1186/s13287-019-1293-y) contains supplementary material, which is available to authorized users.

Parkin Mutation Affects Clock Gene-Dependent Energy Metabolism

Growing evidence highlights a tight connection between circadian rhythms, molecular clockworks, and mitochondrial function. In particular, mitochondrial quality control and bioenergetics have been proven to undergo circadian oscillations driven by core clock genes. Parkinson’s disease (PD) is a chronic neurodegenerative disease characterized by a selective loss of dopaminergic neurons. Almost half of the autosomal recessive forms of juvenile parkinsonism have been associated with mutations in the PARK2 gene coding for parkin, shown to be involved in mitophagy-mediated mitochondrial quality control. The aim of this study was to investigate, in fibroblasts from genetic PD patients carrying parkin mutations, the interplay between mitochondrial bioenergetics and the cell autonomous circadian clock. Using two different in vitro synchronization protocols, we demonstrated that normal fibroblasts displayed rhythmic oscillations of both mitochondrial respiration and glycolytic activity. Conversely, in fibroblasts obtained from PD patients, a severe damping of the bioenergetic oscillatory patterns was observed. Analysis of the core clock genes showed deregulation of their expression patterns in PD fibroblasts, which was confirmed in induced pluripotent stem cells (iPSCs) and induced neural stem cells (iNSCs) derived thereof. The results from this study support a reciprocal interplay between the clockwork machinery and mitochondrial energy metabolism, point to a parkin-dependent mechanism of regulation, and unveil a hitherto unappreciated level of complexity in the pathophysiology of PD and eventually other neurodegenerative diseases.

Dichloroacetate Affects Mitochondrial Function and Stemness-Associated Properties in Pancreatic Cancer Cell Lines

Targeting metabolism represents a possible successful approach to treat cancer. Dichloroacetate (DCA) is a drug known to divert metabolism from anaerobic glycolysis to mitochondrial oxidative phosphorylation by stimulation of PDH. In this study, we investigated the response of two pancreatic cancer cell lines to DCA, in two-dimensional and three-dimension cell cultures, as well as in a mouse model. PANC-1 and BXPC-3 treated with DCA showed a marked decrease in cell proliferation and migration which did not correlate with enhanced apoptosis indicating a cytostatic rather than a cytotoxic effect. Despite PDH activation, DCA treatment resulted in reduced mitochondrial oxygen consumption without affecting glycolysis. Moreover, DCA caused enhancement of ROS production, mtDNA, and of the mitophagy-marker LC3B-II in both cell lines but reduced mitochondrial fusion markers only in BXPC-3. Notably, DCA downregulated the expression of the cancer stem cells markers CD24/CD44/EPCAM only in PANC-1 but inhibited spheroid formation/viability in both cell lines. In a xenograft pancreatic cancer mouse-model DCA treatment resulted in retarding cancer progression. Collectively, our results clearly indicate that the efficacy of DCA in inhibiting cancer growth mechanistically depends on the cell phenotype and on multiple off-target pathways. In this context, the novelty that DCA might affect the cancer stem cell compartment is therapeutically relevant.

From fever to immunity: A new role for IGFBP-6?

Fever is a fundamental response to infection and a hallmark of inflammatory disease, which has been conserved and shaped through millions of years of natural selection. Although fever is able to stimulate both innate and adaptive immune responses, the very nature of all the molecular thermosensors, the timing and the detailed mechanisms translating a physical trigger into a fundamental biological response are incompletely understood. Here we discuss the consequence of hyperthermic stress in dendritic cells (DCs), and how the sole physical input is sensed as an alert stimulus triggering a complex transition in a very narrow temporal window. Importantly, we review recent findings demonstrating the significant and specific changes discovered in gene expression and in the metabolic phenotype associated with hyperthermia in DCs. Furthermore, we discuss the results that support a model based on a thermally induced autocrine signalling, which rewires and sets a metabolism checkpoint linked to immune activation of dendritic cells. Importantly, in this context, we highlight the novel regulatory functions discovered for IGFBP‐6 protein: induction of chemotaxis; capacity to increase oxidative burst and degranulation of neutrophils, ability to induce metabolic changes in DCs. Finally, we discuss the role of IGFBP‐6 in autoimmune disease and how novel mechanistic insights could lead to exploit thermal stress‐related mechanisms in the context of cancer therapy.

The Circadian Clock Regulates Metabolic Phenotype Rewiring Via HKDC1 and Modulates Tumor Progression and Drug Response in Colorectal Cancer

An endogenous molecular clockwork drives various cellular pathways including metabolism and the cell cycle. Its dysregulation is able to prompt pathological phenotypes including cancer. Besides dramatic metabolic alterations, cancer cells display severe changes in the clock phenotype with likely consequences in tumor progression and treatment response. In this study, we use a comprehensive systems-driven approach to investigate the effect of clock disruption on metabolic pathways and its impact on drug response in a cellular model of colon cancer progression. We identified distinctive time-related transcriptomic and metabolic features of a primary tumor and its metastatic counterpart. A mapping of the expression data to a comprehensive genome-scale reconstruction of human metabolism allowed for the in-depth functional characterization of 24 h-oscillating transcripts and pointed to a clock-driven metabolic reprogramming in tumorigenesis. In particular, we identified a set of five clock-regulated glycolysis genes, ALDH3A2, ALDOC, HKDC1, PCK2, and PDHB with differential temporal expression patterns. These findings were validated in organoids and in primary fibroblasts isolated from normal colon and colon adenocarcinoma from the same patient. We further identified a reciprocal connection of HKDC1 to the clock in the primary tumor, which is lost in the metastatic cells. Interestingly, a disruption of the core-clock gene BMAL1 impacts on HKDC1 and leads to a time-dependent rewiring of metabolism, namely an increase in glycolytic activity, as well as changes in treatment response. This work provides novel evidence regarding the complex interplay between the circadian clock and metabolic alterations in carcinogenesis and identifies new connections between both systems with pivotal roles in cancer progression and response to therapy.

Correction: Exposure to 1.8 GHz electromagnetic fields affects morphology, DNA-related Raman spectra and mitochondrial functions in human lympho-monocytes

[This corrects the article DOI: 10.1371/journal.pone.0192894.].

Rewiring carbohydrate catabolism differentially affects survival of pancreatic cancer cell lines with diverse metabolic profiles

An increasing body of evidence suggests that targeting cellular metabolism represents a promising effective approach to treat pancreatic cancer, overcome chemoresistance and ameliorate patient's prognosis and survival. In this study, following whole-genome expression analysis, we selected two pancreatic cancer cell lines, PANC-1 and BXPC-3, hallmarked by distinct metabolic profiles with specific concern to carbohydrate metabolism. Functional comparative analysis showed that BXPC-3 displayed a marked deficit of the mitochondrial respiratory and oxidative phosphorylation activity and a higher production of reactive oxygen species and a reduced NAD⁺/NADH ratio, indicating their bioenergetic reliance on glycolysis and a different redox homeostasis as compared to PANC-1. Both cell lines were challenged to rewire their metabolism by substituting glucose with galactose as carbon source, a condition inhibiting the glycolytic flux and fostering full oxidation of the sugar carbons. The obtained data strikingly show that the mitochondrial respiration-impaired-BXPC-3 cell line was unable to sustain the metabolic adaptation required by glucose deprivation/substitution, thereby resulting in a G2\M cell cycle shift, unbalance of the redox homeostasis, apoptosis induction. Conversely, the mitochondrial respiration-competent-PANC-1 cell line did not show clear evidence of cell sufferance. Our findings provide a strong rationale to candidate metabolism as a promising target for cancer therapy. Defining the metabolic features at time of pancreatic cancer diagnosis and likely of other tumors, appears to be crucial to predict the responsiveness to therapeutic approaches or coadjuvant interventions affecting metabolism.

Targeting Endoplasmic Reticulum and/or Mitochondrial Ca2+ Fluxes as Therapeutic Strategy for HCV Infection

Chronic hepatitis C is characterized by metabolic disorders and by a microenvironment in the liver dominated by oxidative stress, inflammation and regeneration processes that can in the long term lead to liver cirrhosis and hepatocellular carcinoma. Several lines of evidence suggest that mitochondrial dysfunctions play a central role in these processes. However, how these dysfunctions are induced by the virus and whether they play a role in disease progression and neoplastic transformation remains to be determined. Most in vitro studies performed so far have shown that several of the hepatitis C virus (HCV) proteins also localize to mitochondria, but the consequences of these interactions on mitochondrial functions remain contradictory and need to be confirmed in the context of productively replicating virus and physiologically relevant in vitro and in vivo model systems. In the past decade we have been proposing a temporal sequence of events in the HCV-infected cell whereby the primary alteration is localized at the mitochondria-associated ER membranes and causes release of Ca²⁺ from the ER, followed by uptake into mitochondria. This ensues successive mitochondrial dysfunction leading to the generation of reactive oxygen and nitrogen species and a progressive metabolic adaptive response consisting in decreased oxidative phosphorylation and enhanced aerobic glycolysis and lipogenesis. Here we resume the major results provided by our group in the context of HCV-mediated alterations of the cellular inter-compartmental calcium flux homeostasis and present new evidence suggesting targeting of ER and/or mitochondrial calcium transporters as a novel therapeutic strategy.

Exposure to 1.8 GHz electromagnetic fields affects morphology, DNA-related Raman spectra and mitochondrial functions in human lympho-monocytes

Blood is a fluid connective tissue of human body, where it plays vital functions for the nutrition, defense and well-being of the organism. When circulating in peripheral districts, it is exposed to some physical stresses coming from outside the human body, as electromagnetic fields (EMFs) which can cross the skin. Such fields may interact with biomolecules possibly inducing non thermal-mediated biological effects at the cellular level. In this study, the occurrence of biochemical/biological modifications in human peripheral blood lympho-monocytes exposed in a reverberation chamber for times ranging from 1 to 20 h to EMFs at 1.8 GHz frequency and 200 V/m electric field strength was investigated. Morphological analysis of adherent cells unveiled, in some of these, appearance of an enlarged and deformed shape after EMFs exposure. Raman spectra of the nuclear compartment of cells exposed to EMFs revealed the onset of biochemical modifications, mainly consisting in the reduction of the DNA backbone-linked vibrational modes. Respirometric measurements of mitochondrial activity in intact lympho-monocytes resulted in increase of the resting oxygen consumption rate after 20 h of exposure, which was coupled to a significant increase of the FoF1-ATP synthase-related oxygen consumption. Notably, at lower time-intervals of EMFs exposure (i.e. 5 and 12 h) a large increase of the proton leak-related respiration was observed which, however, recovered at control levels after 20 h exposure. Confocal microscopy analysis of the mitochondrial membrane potential supported the respiratory activities whereas no significant variations in the mitochondrial mass/morphology was observed in EMFs-exposed lympho-monocytes. Finally, altered redox homeostasis was shown in EMFs-exposed lympho-monocytes, which progressed differently in nucleated cellular subsets. This results suggest the occurrence of adaptive mechanisms put in action, likely via redox signaling, to compensate for early impairments of the oxidative phosphorylation system caused by exposure to EMFs. Overall the data presented warn for health safety of people involved in long-term exposure to electromagnetic fields, although further studies are required to pinpoint the leukocyte cellular subset(s) selectively targeted by the EMFs action and the mechanisms by which it is achieved.

Febrile temperature reprograms by redox-mediated signaling the mitochondrial metabolic phenotype in monocyte-derived dendritic cells

Fever-like hyperthermia is known to stimulate innate and adaptive immune responses. Hyperthermia-induced immune stimulation is also accompanied with, and likely conditioned by, changes in the cell metabolism and, in particular, mitochondrial metabolism is now recognized to play a pivotal role in this context, both as energy supplier and as signaling platform. In this study we asked if challenging human monocyte-derived dendritic cells with a relatively short-time thermal shock in the fever-range, typically observed in humans, caused alterations in the mitochondrial oxidative metabolism. We found that following hyperthermic stress (3h exposure at 39°C) TNF-α-releasing dendritic cells undergo rewiring of the oxidative metabolism hallmarked by decrease of the mitochondrial respiratory activity and of the oxidative phosphorylation and increase of lactate production. Moreover, enhanced production of reactive oxygen and nitrogen species and accumulation of mitochondrial Ca²⁺ was consistently observed in hyperthermia-conditioned dendritic cells and exhibited a reciprocal interplay. The hyperthermia-induced impairment of the mitochondrial respiratory activity was (i) irreversible following re-conditioning of cells to normothermia, (ii) mimicked by exposing normothermic cells to the conditioned medium of the hyperthermia-challenged cells, (iii) largely prevented by antioxidant and inhibitors of the nitric oxide synthase and of the mitochondrial calcium porter, which also inhibited release of TNF-α. These observations combined with gene expression analysis support a model based on a thermally induced autocrine signaling, which rewires and sets a metabolism checkpoint linked to immune activation of dendritic cells.

Para-hydroxyphenylpyruvate inhibits the pro-inflammatory stimulation of macrophage preventing LPS-mediated nitro-oxidative unbalance and immunometabolic shift

Targeting metabolism is emerging as a promising therapeutic strategy for modulation of the immune response in human diseases. In the presented study we used the lipopolysaccharide (LPS)-mediated activation of RAW 264.7 macrophage-like cell line as a model to investigate changes in the metabolic phenotype and to test the effect of p-hydroxyphenylpyruvate (pHPP) on it. pHPP is an intermediate of the PHE/TYR catabolic pathway, selected as analogue of the ethyl pyruvate (EP), which proved to exhibit antioxidant and anti-inflammatory activities. The results obtained show that LPS-priming of RAW 264.7 cell line to the activated M1 state resulted in up-regulation of the inducible nitric oxide synthase (iNOS) expression and consequently of NO production and in release of the pro-inflammatory cytokine IL-6. All these effects were prevented dose dependently by mM concentrations of pHPP more efficiently than EP. Respirometric and metabolic flux analysis of LPS-treated RAW 264.7 cells unveiled a marked metabolic shift consisting in downregulation of the mitochondrial oxidative phosphorylation and upregulation of aerobic glycolysis respectively. The observed respiratory failure in LPS-treated cells was accompanied with inhibition of the respiratory chain complexes I and IV and enhanced production of reactive oxygen species. Inhibition of the respiratory activity was also observed following incubation of human neonatal fibroblasts (NHDF-neo) with sera from septic patients. pHPP prevented all the observed metabolic alteration caused by LPS on RAW 264.7 or by septic sera on NHDF-neo. Moreover, we provide evidence that pHPP is an efficient reductant of cytochrome c. On the basis of the presented results a working model, linking pathogen-associated molecular patterns (PAMPs)-mediated immune response to mitochondrial oxidative metabolism, is put forward along with suggestions for its therapeutic control.

Clock-genes and mitochondrial respiratory activity: Evidence of a reciprocal interplay

In the past few years mounting evidences have highlighted the tight correlation between circadian rhythms and metabolism. Although at the organismal level the central timekeeper is constituted by the hypothalamic suprachiasmatic nuclei practically all the peripheral tissues are equipped with autonomous oscillators made up by common molecular clockworks represented by circuits of gene expression that are organized in interconnected positive and negative feed-back loops. In this study we exploited a well-established in vitro synchronization model to investigate specifically the linkage between clock gene expression and the mitochondrial oxidative phosphorylation (OxPhos). Here we show that synchronized cells exhibit an autonomous ultradian mitochondrial respiratory activity which is abrogated by silencing the master clock gene ARNTL/BMAL1. Surprisingly, pharmacological inhibition of the mitochondrial OxPhos system resulted in dramatic deregulation of the rhythmic clock-gene expression and a similar result was attained with mtDNA depleted cells (Rho0). Our findings provide a novel level of complexity in the interlocked feedback loop controlling the interplay between cellular bioenergetics and the molecular clockwork. This article is part of a Special Issue entitled 'EBEC 2016: 19th European Bioenergetics Conference, Riva del Garda, Italy, July 2-6, 2016', edited by Prof. Paolo Bernardi.

Dichloroacetate, a selective mitochondria-targeting drug for oral squamous cell carcinoma: a metabolic perspective of treatment

Reprogramming of metabolism is a well-established property of cancer cells that is receiving growing attention as potential therapeutic target. Oral squamous cell carcinomas (OSCC) are aggressive and drugs-resistant human tumours displaying wide metabolic heterogeneity depending on their malignant genotype and stage of development. Dichloroacetate (DCA) is a specific inhibitor of the PDH-regulator PDK proved to foster mitochondrial oxidation of pyruvate. In this study we tested comparatively the effects of DCA on three different OSCC-derived cell lines, HSC-2, HSC-3, PE15. Characterization of the three cell lines unveiled for HSC-2 and HSC-3 a glycolysis-reliant metabolism whereas PE15 accomplished an efficient mitochondrial oxidative phosphorylation. DCA treatment of the three OSCC cell lines, at pharmacological concentrations, resulted in stimulation of the respiratory activity and caused a remarkably distinctive pro-apoptotic/cytostatic effect on HSC-2 and HSC-3. This was accompanied with a large remodeling of the mitochondrial network, never documented before, leading to organelle fragmentation and with enhanced production of reactive oxygen species. The data here presented indicate that the therapeutic efficacy of DCA may depend on the specific metabolic profile adopted by the cancer cells with those exhibiting a deficient mitochondrial oxidative phosphorylation resulting more sensitive to the drug treatment.

Hematopoietic stem/progenitor cells express myoglobin and neuroglobin: adaptation to hypoxia or prevention from oxidative stress?

Oxidative metabolism and redox signaling prove to play a decisional role in controlling adult hematopoietic stem/progenitor cells (HSPCs) biology. However, HSPCs reside in a hypoxic bone marrow microenvironment raising the question of how oxygen metabolism might be ensued. In this study, we provide for the first time novel functional and molecular evidences that human HSPCs express myoglobin (Mb) at level comparable with that of a muscle-derived cell line. Optical spectroscopy and oxymetry enabled to estimate an O2-sensitive heme-containing protein content of approximately 180 ng globin per 10(6) HSPC and a P50 of approximately 3 µM O2. Noticeably, expression of Mb mainly occurs through a HIF-1-induced alternative transcript (Mb-V/Mb-N = 35 ± 15, p < .01). A search for other Mb-related globins unveiled significant expression of neuroglobin (Ngb) but not of cytoglobin. Confocal microscopy immune detection of Mb in HSPCs strikingly revealed nuclear localization in cell subsets expressing high level of CD34 (nuclear/cytoplasmic Mb ratios 1.40 ± 0.02 vs. 0.85 ± 0.05, p < .01) whereas Ngb was homogeneously distributed in all the HSPC population. Dual-color fluorescence flow cytometry indicated that while the Mb content was homogeneously distributed in all the HSPC subsets that of Ngb was twofold higher in more immature HSPC. Moreover, we show that HSPCs exhibit a hypoxic nitrite reductase activity releasing NO consistent with described noncanonical functions of globins. Our finding extends the notion that Mb and Ngb can be expressed in nonmuscle and non-neural contexts, respectively, and is suggestive of a differential role of Mb in HSPC in controlling oxidative metabolism at different stages of commitment.

Protective role of amantadine in mitochondrial dysfunction and oxidative stress mediated by hepatitis C virus protein expression

Amantadine is an antiviral and antiparkinsonian drug that has been evaluated in combination therapies against hepatitis C virus (HCV) infection. Controversial results have been reported concerning its efficacy, and its mechanism of action remains unclear. Data obtained in vitro suggested a role of amantadine in inhibiting HCV p7-mediated cation conductance. In keeping with the fact that mitochondria are responsible to ionic fluxes and that HCV infection impairs mitochondrial function, we investigated a potential role of amantadine in modulating mitochondrial function. Using a well-characterized inducible cell line expressing the full-length HCV polyprotein, we found that amantadine not only prevented but also rescued HCV protein-mediated mitochondrial dysfunction. Specifically, amantadine corrected (i) overload of mitochondrial Ca²⁺; (ii) inhibition of respiratory chain activity and oxidative phosphorylation; (iii) reduction of membrane potential; and (iv) overproduction of reactive oxygen species. The effects of amantadine were observed within 15 min following drug administration and confirmed in Huh-7.5 cells transfected with an infectious HCV genome. These effects were also observed in cells expressing subgenomic HCV constructs, indicating that they are not mediated or only in part mediated by p7. Single organelle analyzes carried out on isolated mouse liver mitochondria demonstrated that amantadine induces hyperpolarization of the membrane potential. Moreover, amantadine treatment increased the calcium threshold required to trigger mitochondrial permeability transition opening. In conclusion, these results support a role of amantadine in preserving cellular bioenergetics and redox homeostasis in HCV-infected cells and unveil an effect of the drug which might be exploited for a broader therapeutic utilization.

Hepatitis C virus, mitochondria and auto/mitophagy: Exploiting a host defense mechanism

Hepatitis C virus (HCV) is the major reason for liver transplantation and the main cause of liver-related morbidity and mortality in a great number of countries. As for the other viruses, this pathogen interferes in more than one process and in more than one way with host cell biology. A mounting body of evidence points, in particular, toward the drastic alterations of mitochondrial physiology and functions that virus is able to induce, albeit the mechanisms have partly remained elusive. Role of the mitochondria in immunity and in quality control systems, as autophagy, as well as the strategies that HCV has evolved to evade and even to manipulate mitochondrial surveillance for its benefit, highlights the importance of deepening the mechanisms that modulate this virus-mitochondrion interaction, not only to intensify our knowledge of the HCV infection pathogenesis but also to design efficient antiviral strategies.

p-Hydroxyphenylpyruvate, an intermediate of the Phe/Tyr catabolism, improves mitochondrial oxidative metabolism under stressing conditions and prolongs survival in rats subjected to profound hemorrhagic shock

The aim of this study was to test the effect of a small volume administration of p-hydroxyphenylpyruvate (pHPP) in a rat model of profound hemorrhagic shock and to assess a possible metabolic mechanism of action of the compound. The results obtained show that hemorrhaged rats treated with 2–4% of the estimated blood volume of pHPP survived significantly longer (p<0.001) than rats treated with vehicle. In vitro analysis on cultured EA.hy 926 cells demonstrated that pHPP improved cell growth rate and promoted cell survival under stressing conditions. Moreover, pHPP stimulated mitochondria-related respiration under ATP-synthesizing conditions and exhibited antioxidant activity toward mitochondria-generated reactive oxygen species. The compound effects reported in the in vitro and in vivo analyses were obtained in the same millimolar concentration range. These data disclose pHPP as an efficient energetic substrates-supplier to the mitochondrial respiratory chain as well as an antioxidant supporting the view that the compound warrants further evaluation as a therapeutic agent.

Effect of resveratrol on mitochondrial function: implications in parkin-associated familiar Parkinson's disease

Mitochondrial dysfunction and oxidative stress occur in Parkinson's disease (PD), but the molecular mechanisms controlling these events are not completely understood. Peroxisome proliferator-activated receptor-gamma coactivator-1α (PGC-1α) is a transcriptional coactivator known as master regulator of mitochondrial functions and oxidative metabolism. Recent studies, including one from our group, have highlighted altered PGC-1α activity and transcriptional deregulation of its target genes in PD pathogenesis suggesting it as a new potential therapeutic target. Resveratrol, a natural polyphenolic compound proved to improve mitochondrial activity through the activation of several metabolic sensors resulting in PGC-1α activation. Here we have tested in vitro the effect of resveratrol treatment on primary fibroblast cultures from two patients with early-onset PD linked to different Park2 mutations. We show that resveratrol regulates energy homeostasis through activation of AMP-activated protein kinase (AMPK) and sirtuin 1 (SIRT1) and raise of mRNA expression of a number of PGC-1α's target genes resulting in enhanced mitochondrial oxidative function, likely related to a decrease of oxidative stress and to an increase of mitochondrial biogenesis. The functional impact of resveratrol treatment encompassed an increase of complex I and citrate synthase activities, basal oxygen consumption, and mitochondrial ATP production and a decrease in lactate content, thus supporting a switch from glycolytic to oxidative metabolism. Moreover, resveratrol treatment caused an enhanced macro-autophagic flux through activation of an LC3-independent pathway. Our results, obtained in early-onset PD fibroblasts, suggest that resveratrol may have potential clinical application in selected cases of PD-affected patients.

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.

Chronic pro-oxidative state and mitochondrial dysfunctions are more pronounced in fibroblasts from Down syndrome foeti with congenital heart defects

Trisomy of chromosome 21 is associated to congenital heart defects in ∼50% of affected newborns. Transcriptome analysis of hearts from trisomic human foeti demonstrated that genes involved in mitochondrial function are globally downregulated with respect to controls, suggesting an impairment of mitochondrial function. We investigated here the properties of mitochondria in fibroblasts from trisomic foeti with and without cardiac defects. Together with the upregulation of Hsa21 genes and the downregulation of nuclear encoded mitochondrial genes, an abnormal mitochondrial cristae morphology was observed in trisomic samples. Furthermore, impairment of mitochondrial respiratory activity, specific inhibition of complex I, enhanced reactive oxygen species production and increased levels of intra-mitochondrial calcium were demonstrated. Seemingly, mitochondrial dysfunction was more severe in fibroblasts from cardiopathic trisomic foeti that presented a more pronounced pro-oxidative state. The data suggest that an altered bioenergetic background in trisomy 21 foeti might be among the factors responsible for a more severe phenotype. Since the mitochondrial functional alterations might be rescued following pharmacological treatments, these results are of interest in the light of potential therapeutic interventions.

Targeting mitochondria in the infection strategy of the hepatitis C virus

Hepatitis C virus (HCV) infection induces a state of oxidative stress more pronounced than that observed in many other inflammatory diseases. Here, we propose a temporal sequence of events in the HCV-infected cell whereby the primary alteration consists of a release of Ca(2+) from the endoplasmic reticulum, followed by uptake into mitochondria. This ensues successive mitochondrial dysfunction leading to the generation of reactive oxygen species and a progressive metabolic adaptive response. Evidence is provided for a positive feed-back mechanism between alterations of calcium and redox homeostasis. This likely involves deregulation of the mitochondrial permeability transition and induces progressive dysfunction of cellular bioenergetics. Pathogenetic implications of the model and new opportunities for therapeutic intervention are discussed. This article is part of a Directed Issue entitled: Bioenergetic dysfunction, adaptation and therapy.

The cyclophilin inhibitor alisporivir prevents hepatitis C virus-mediated mitochondrial dysfunction

Alisporivir (Debio-025) is an analogue of cyclosporine A and represents the prototype of a new class of non-immunosuppressive cyclophilin inhibitors. In vitro and in vivo studies have shown that alisporivir inhibits hepatitis C virus (HCV) replication, and ongoing clinical trials are exploring its therapeutic potential in patients with chronic hepatitis C. Recent data suggest that the antiviral effect is mediated by inhibition of cyclophilin A, which is an essential host factor in the HCV life cycle. However, alisporivir also inhibits mitochondrial permeability transition by binding to cyclophilin D. Because HCV is known to affect mitochondrial function, we explored the effect of alisporivir on HCV protein-mediated mitochondrial dysfunction. Through the use of inducible cell lines, which allow to investigate the effects of HCV polyprotein expression independent from viral RNA replication and which recapitulate the major alterations of mitochondrial bioenergetics observed in infectious cell systems, we show that alisporivir prevents HCV protein-mediated decrease of cell respiration, collapse of mitochondrial membrane potential, overproduction of reactive oxygen species and mitochondrial calcium overload. Strikingly, some of the HCV-mediated mitochondrial dysfunctions could even be rescued by alisporivir.

CONCLUSION

These observations provide new insights into the pathogenesis of HCV-related liver disease and reveal an additional mechanism of action of alisporivir that is likely beneficial in the treatment of chronic hepatitis C.

Native LDL-induced oxidative stress in human proximal tubular cells: multiple players involved

Dyslipidemia is a well-established condition proved to accelerate the progression of chronic kidney disease leading to tubulo-interstitial injury. However, the molecular aspects of the dyslipidemia-induced renal damage have not been fully clarified and in particular the role played by low-density lipoproteins (LDLs). This study aimed to examine the effects of native non-oxidized LDL on cellular oxidative metabolism in cultured human proximal tubular cells. By means of confocal microscopy imaging combined to respirometric and enzymatic assays it is shown that purified native LDL caused a marked increase of cellular reactive oxygen species (ROS) production, which was mediated by activation of NADPH oxidase(s) and by mitochondrial dysfunction by means of a ROS-induced ROS release mechanism. The LDL-dependent mitochondrial alterations comprised inhibition of the respiratory chain activity, enhanced ROS production, uncoupling of the oxidative phosphorylation efficiency, collapse of the mtΔΨ, increased Ca²⁺ uptake and loss of cytochrome c. All the above LDL-induced effects were completely abrogated by chelating extracellular Ca²⁺ as well as by inhibition of the Ca²⁺-activated cytoplas-mic phospholipase A2, NADPH oxidase and mitochondrial permeability transition. We propose a mechanicistic model whereby the LDL-induced intracellular redox unbalance is triggered by a Ca²⁺ inward flux-dependent commencement of cPLA2 followed by activation of a lipid- and ROS-based cross-talking signalling pathway. This involves first oxidants production via the plasmamembrane NADPH oxidase and then propagates downstream to mitochondria eliciting redox- and Ca²⁺-dependent dysfunctions leading to cell-harming conditions. These findings may help to clarify the mechanism of dyslipidemia-induced renal damage and suggest new potential targets for specific therapeutic strategies to prevent oxidative stress implicated in kidney diseases.