When mitophagy dictates the outcome of cellular infection: the case of Brucella abortus

Mitochondria are at the basis of various cellular functions ranging from metabolism and redox homeostasis to inflammation and cell death regulation. Mitochondria therefore constitute an attractive target for invading pathogens to fulfil their infectious cycle. This involves the modulation to their advantage of mitochondrial metabolism and dynamics, including the controlled degradation of mitochondria through mitophagy. Mitophagy might for instance be beneficial for bacterial survival as it can clear bactericidal mitochondrial ROS produced by damaged organelle fragments from the intracellular niche. In the case of the bacterial pathogen Brucella abortus, mitophagy induction has another role in the intracellular lifecycle of the bacteria. Indeed, in our study, we showed that B. abortus triggers an iron-dependent BNIP3L-mediated mitophagy response required for proper bacterial egress and infection of neighboring cells. These results highlight the diversity of mitophagy processes that might be crucial for several stages of cellular infection.

Host cell egress of Brucella abortus requires BNIP3L-mediated mitophagy

The facultative intracellular pathogen Brucella abortus interacts with several organelles of the host cell to reach its replicative niche inside the endoplasmic reticulum. However, little is known about the interplay between the intracellular bacteria and the host cell mitochondria. Here, we showed that B. abortus triggers substantive mitochondrial network fragmentation, accompanied by mitophagy and the formation of mitochondrial Brucella-containing vacuoles during the late steps of cellular infection. Brucella-induced expression of the mitophagy receptor BNIP3L is essential for these events and relies on the iron-dependent stabilisation of the hypoxia-inducible factor 1α. Functionally, BNIP3L-mediated mitophagy appears to be advantageous for bacterial exit from the host cell as BNIP3L depletion drastically reduces the number of reinfection events. Altogether, these findings highlight the intricate link between Brucella trafficking and the mitochondria during host cell infection.

A critical role for heme synthesis and succinate in the regulation of pluripotent states transitions

Using embryonic stem cells (ESCs) in regenerative medicine or in disease modeling requires a complete understanding of these cells. Two main distinct developmental states of ESCs have been stabilized in vitro, a naïve pre-implantation stage and a primed post-implantation stage. Based on two recently published CRISPR-Cas9 knockout functional screens, we show here that the exit of the naïve state is impaired upon heme biosynthesis pathway blockade, linked in mESCs to the incapacity to activate MAPK- and TGFβ-dependent signaling pathways after succinate accumulation. In addition, heme synthesis inhibition promotes the acquisition of 2 cell-like cells in a heme-independent manner caused by a mitochondrial succinate accumulation and leakage out of the cell. We further demonstrate that extracellular succinate acts as a paracrine/autocrine signal, able to trigger the 2C-like reprogramming through the activation of its plasma membrane receptor, SUCNR1. Overall, this study unveils a new mechanism underlying the maintenance of pluripotency under the control of heme synthesis.

To eat or not to eat mitochondria? How do host cells cope with mitophagy upon bacterial infection?

Mitochondria fulfil a plethora of cellular functions ranging from energy production to regulation of inflammation and cell death control. The fundamental role of mitochondria makes them a target of choice for invading pathogens, with either an intracellular or extracellular lifestyle. Indeed, the modulation of mitochondrial functions by several bacterial pathogens has been shown to be beneficial for bacterial survival inside their host. However, so far, relatively little is known about the importance of mitochondrial recycling and degradation pathways through mitophagy in the outcome (success or failure) of bacterial infection. On the one hand, mitophagy could be considered as a defensive response triggered by the host upon infection to maintain mitochondrial homeostasis. However, on the other hand, the pathogen itself may initiate the host mitophagy to escape from mitochondrial-mediated inflammation or antibacterial oxidative stress. In this review, we will discuss the diversity of various mechanisms of mitophagy in a general context, as well as what is currently known about the different bacterial pathogens that have developed strategies to manipulate the host mitophagy.

Endogenous TOM20 Proximity Labeling: A Swiss-Knife for the Study of Mitochondrial Proteins in Human Cells

Biotin-based proximity labeling approaches, such as BioID, have demonstrated their use for the study of mitochondria proteomes in living cells. The use of genetically engineered BioID cell lines enables the detailed characterization of poorly characterized processes such as mitochondrial co-translational import. In this process, translation is coupled to the translocation of the mitochondrial proteins, alleviating the energy cost typically associated with the post-translational import relying on chaperone systems. However, the mechanisms are still unclear with only few actors identified but none that have been described in mammals yet. We thus profiled the TOM20 proxisome using BioID, assuming that some of the identified proteins could be molecular actors of the co-translational import in human cells. The obtained results showed a high enrichment of RNA binding proteins close to the TOM complex. However, for the few selected candidates, we could not demonstrate a role in the mitochondrial co-translational import process. Nonetheless, we were able to demonstrate additional uses of our BioID cell line. Indeed, the experimental approach used in this study is thus proposed for the identification of mitochondrial co-translational import effectors and for the monitoring of protein entry inside mitochondria with a potential application in the prediction of mitochondrial protein half-life.

Encapsulation of stem-cell derived β-cells: A promising approach for the treatment for type 1 diabetes mellitus

Type 1 diabetes mellitus is an auto-immune disease causing the T-cell mediated destruction of insulin-producing β-cells, resulting in chronic hyperglycemia. Current treatments such as insulin replacement therapy or the transplantation of pancreas or pancreatic islets present major disadvantages such as the constant need of drugs, as well as a shortage of donor organs. In this review, we discuss a sustainable solution to overcome these limitations combining the use of β-cells, derived from stem cells, and their encapsulation within a protective matrix. This article provides an exhaustive overview of currently investigated stem cell sources including embryonic, mesenchymal as well as induced pluripotent stem cells in combination with various up to date encapsulation methods allowing the formation of immuno-protective devices. In order to identify current limitations of this interdisciplinary therapeutic approach and to find sustainable solutions, it is essential to consider key aspects from all involved domains. This includes biological parameters such as the stem cell origin but also the different aspects of the encapsulation process, the used materials and their physico-chemical properties such as elasticity, porosity and permeability cut-off as well as the best implantation sites allowing efficient and self-autonomous control of glycemia by the transplanted encapsulated cells.

Multi-Allergen Quantification in Food Using Concatemer-Based Isotope Dilution Mass Spectrometry: A Collaborative Study

BACKGROUND

Food allergen analysis is essential for the development of a risk-based approach for allergen management and labeling. Mass spectrometry has become a method of choice for allergen analysis, even if quantification remains challenging. Moreover, harmonization is still lacking between laboratories, while interlaboratory validation of analytical methods is necessary for such harmonization.

OBJECTIVE

This collaborative study aimed to evaluate the potential of mass spectrometry for food allergen detection and quantification using a standard addition quantification strategy and a stable isotope-labeled concatemer as an internal standard.

METHODS

In-house-produced test material (cookies), blank and incurred with four allergens (egg, milk, peanut and hazelnut), allergen standards, an internal standard and the complete methodology (including sample preparation and UHPLC-MS/MS method) were provided to nine laboratories involved in the study. Method sensitivity and selectivity were evaluated with incurred test material and accuracy with spiked test material. Quantification was based on the standard addition strategy using certified reference materials as allergen protein standards and a stable isotope-labeled concatemer as an internal standard.

RESULTS

All laboratories were able to detect milk, hazelnut and peanut in the incurred cookies with sufficient sensitivity to reach the AOAC INTERNATIONAL Standard Method Performance Requirements (SMPR® 2016.002). Egg detection was more complicated due to food processing effects, yet five laboratories reached the sensitivity requirements. Recovery results were laboratory dependent. Some milk and hazelnut peptides were quantified in agreement with SMPR by all participants. Furthermore, over 90% of the received quantification results agreed with SMPR for method precision.

CONCLUSION

The encouraging results of this pioneering collaborative study represent an additional step towards harmonization among laboratories testing for allergens.

HIGHLIGHTS

In this pioneer collaborative study, food allergens were analyzed by mass spectrometry with characterized incurred and spiked test materials, calibration with certified reference material and a single stable isotope-labeled concatemer as an internal standard.

Characterization of the Proteins Secreted by Equine Muscle-Derived Mesenchymal Stem Cells Exposed to Cartilage Explants in Osteoarthritis Model

BACKGROUND

Osteoarthritis (OA) is a highly prevalent joint degenerative disease for which therapeutic treatments are limited or invasive. Cell therapy based on mesenchymal stem/stromal cells (MSCs) is therefore seen as a promising approach for this disease, in both human and horses. As the regenerative potential of MSCs is mainly conferred by paracrine function, the goal of this study was to characterize the secreted proteins of muscle-derived MSCs (mdMSCs) in an in vitro model of OA to evaluate the putative clinical interest of mdMSCs as cell therapy for joint diseases like osteoarthritis.

METHODS

An equine osteoarthritis model composed of cartilage explants exposed to pro-inflammatory cytokines was first developed. Then, the effects of mdMSC co-culture on cartilage explant were studied by measuring the glycosaminoglycan release and the NO₂^- production. To identify the underlying molecular actors, stable isotope-labeling by amino acids in cell culture based secreted protein analyses were conducted, in the presence of serum. The relative abundance of highly sequenced proteins was finally confirmed by western blot.

RESULTS

Co-culture with muscle-derived MSCs decreases the cytokine-induced glycosaminoglycan release by cartilage explants, suggesting a protecting effect of mdMSCs. Among the 52 equine proteins sequenced in the co-culture conditioned medium, the abundance of decorin and matrix metalloproteinase 3 was significantly modified, as confirmed by western blot analyses.

CONCLUSIONS

These results suggest that muscle-derived MSCs could reduce the catabolic effect of TNFα and IL-1β on cartilage explant by decreasing the secretion and activity of matrix metalloproteinase 3 and increasing the decorin secretion. mdMSCs capacity to reduce the catabolic consequences of cartilage exposure to pro-inflammatory cytokines. These effects can be explained by mdMSC-secreted bioactive such as TIMP-1 and decorin, known as an inhibitor of MMP3 and an anti-inflammatory protein, respectively.

The global downregulation of protein synthesis observed during hepatogenic maturation is associated with a decrease in TOP mRNA translation

Translational regulation is of paramount importance for proteome remodeling during stem cell differentiation at both the global and the transcript-specific levels. In this study, we characterized translational remodeling during hepatogenic differentiation of induced pluripotent stem cells (iPSCs) by polysome profiling. We demonstrate that protein synthesis increases during exit from pluripotency and is then globally repressed during later steps of hepatogenic maturation. This global downregulation of translation is accompanied by a decrease in the abundance of protein components of the translation machinery, which involves a global reduction in translational efficiency of terminal oligopyrimidine tract (TOP) mRNA encoding translation-related factors. Despite global translational repression during hepatogenic differentiation, key hepatogenic genes remain efficiently translated, and the translation of several transcripts involved in hepatospecific functions and metabolic maturation is even induced. We conclude that, during hepatogenic differentiation, a global decrease in protein synthesis is accompanied by a specific translational rewiring of hepatospecific transcripts.

Selecting processing robust markers using high resolution mass spectrometry for the detection of milk in food products

BACKGROUND

Cow's milk allergy is one of the most reported food allergies in Europe. To help patients suffering from food allergies it is important to be able to detect milk in different foods. An analytical method that is gaining interest in the field of allergen detection is Ultra-High Performance Liquid Chromatography-tandem Mass Spectrometry, where the analyte is a target peptide. When these peptide biomarkers are selected the effect of food processing should be taken into account to allow a robust detection method.

OBJECTIVE

This works aims at identifying such processing stable peptide markers for milk for the Ultra-High Performance Liquid Chromatography-tandem Mass Spectrometry based detection of food allergens in different food products.

METHODS

Milk-incurred food materials that underwent several processing techniques were produced. This was followed by establishing tryptic peptide profiles from each matrix using Ultra-High Performance Liquid Chromatography-High Resolution Mass Spectrometry .

RESULT

A careful comparison of peptide profiles/intensities and the use of specific exclusion criteria resulted in the selection of 8 peptide biomarkers suitable for application in Ultra-High Performance Liquid Chromatography-tandem Mass Spectrometry based milk detection methods. One of these markers is a α-lactalbumin specific peptide, which has been determined to be stable in different incurred materials for the first time.

CONCLUSION

To our knowledge, this is the first systematic and experimentally based approach for the selection of suitable milk peptide biomarkers robust towards multiple, often applied food processing techniques for milk. Ensuring the exact knowledge of the food processing circumstances by starting from well-defined raw material and using fully controlled settings to produce incurred test material allowed the construction of a peptide database with robust markers. These robust markers can be used for the development of a robust detection method for milk in different food matrices.

MPV17 does not control cancer cell proliferation

MPV17 is described as a mitochondrial inner membrane channel. Although its function remains elusive, mutations in the MPV17 gene result in hepato-cerebral mitochondrial DNA depletion syndrome in humans. In this study, we show that MPV17 silencing does not induce depletion in mitochondrial DNA content in cancer cells. We also show that MPV17 does not control cancer cell proliferation despite the fact that we initially observed a reduced proliferation rate in five MPV17-silenced cancer cell lines with two different shRNAs. However, shRNA-mediated MPV17 knockdown performed in this work provided misguiding results regarding the resulting proliferation phenotype and only a rescue experiment was able to shed definitive light on the implication of MPV17 in cancer cell proliferation. Our results therefore emphasize the caution that is required when scientific conclusions are drawn from a work based on lentiviral vector-based gene silencing and clearly demonstrate the need to systematically perform a rescue experiment in order to ascertain the specific nature of the experimental results.

Update on the role of Sirtuin 3 in cell differentiation: A major metabolic target that can be pharmacologically controlled

Cell differentiation is a fundamental biological event in which a precursor stem cell is turning into a specialized somatic cell. It is thus crucial for the development, tissue turnover and regeneration in mammals. Among the numerous changes taking place in a cell during a differentiation programme, the biology of mitochondria, the central organelle mainly responsible for energy homeostasis and stress adaptation, is deeply modified. These modifications are now well recognized as taking an active part to the completion of the differentiation programme. Indeed, mitochondrial biogenesis and metabolic shift are observed during cell differentiation, adapting many syntheses, calcium homeostasis, ATP and reactive oxygen species production, to the needs. These mitochondrial functions are substantially regulated by the post-translational modifications of the mitochondrial proteins among which lysine acetylation is essential. This mitoacetylome is then globally controlled by the balance between spontaneous/enzymatically-catalysed protein acetylation and the NAD⁺-dependent deacetylation mediated by Sirtuin 3. This enzyme is now considered as a major regulator of the function of the organelle. Regarding the requirement of these mitochondrial adaptations, the subsequent growing interest for this enzyme recently extended to the investigation of the mechanisms driving cell differentiation. This review summarizes the currently available information about the significance of SIRT3 in cell differentiation in physio-pathological contexts. We also suggest a control of the differentiation-activated autophagy by SIRT3, a hypothesis supported by recent findings establishing a causal link between SIRT3 and autophagy. Eventually, an update on the present pharmacological modulators of SIRT3 in a context of cell differentiation is discussed.

Hybrid Alginate@TiO2 Porous Microcapsules as a Reservoir of Animal Cells for Cell Therapy

The number of patients suffering from diseases linked with hormone deficiency (e.g., type 1 diabetes mellitus) has significantly increased in recent years. As organ transplantation presents its limits, the design of novel robust devices for cell encapsulation is of great interest. The current study reports the design of a novel hybrid alginate microcapsule reinforced by titania via a biocompatible synthesis from an aqueous stable titania precursor (TiBALDH) and a cationic polyamine (PDDAC) under mild conditions. The biocompatibility of this one-pot synthesis was confirmed by evaluation of the cytotoxicity of the precursor, additive, product, and by-product. The morphology, structure, and properties of the obtained hybrid microcapsule were characterized in detail. The microcapsule displayed mesoporous, which was a key parameter to allow the diffusion of nutrients and metabolites and to avoid the entry of immune defenders. The hybrid microcapsule also showed enhanced mechanical stability compared to the pure alginate microcapsule, making it an ideal candidate as a cell reservoir. HepG2 model cells encapsulated in the hybrid microcapsules remained intact for 43 days as highlighted by fluorescent viability probes, their oxygen consumption, and their albumin secretion. The study provides a significant progress in the conception of the robust and biocompatible reservoirs of animal cells for cell therapy.

Development of a strategy for the quantification of food allergens in several food products by mass spectrometry in a routine laboratory

Worldwide, mass spectrometry is widely used to detect and quantify food allergens, especially in complex and processed food products. Yet, the absence of a regulatory framework for the developed methods has led to a lack of harmonization between laboratories. In this study, ten allergens were analyzed in eight food products by UHPLC-MS/MS, in order to establish criteria for the retention time, variation tolerance, the ion ratio deviation, and the signal-to-noise ratio for allergen detection. The set of criteria should help laboratories to compare results and avoid false positives and negatives. Furthermore, a strategy combining standard addition and labeled peptide correction was used to quantify milk, soy, peanut, and egg allergens in eight food products. This strategy is particularly interesting for routine laboratories, which receive hundreds of samples and cannot use an external calibration curve for each sample.

Prolyl carboxypeptidase activity in the circulation and its correlation with body weight and adipose tissue in lean and obese subjects

Background

Prolyl carboxypeptidase (PRCP) is involved in the regulation of body weight, likely by hydrolysing alpha-melanocyte-stimulating hormone and apelin in the hypothalamus and in the periphery. A link between PRCP protein concentrations in plasma and metabolic disorders has been reported. In this study, we investigated the distribution of circulating PRCP activity and assessed its relation with body weight and adipose tissue in obese patients and patients who significantly lost weight.

Methods

PRCP activity was measured using reversed-phase high-performance liquid chromatography in different isolated blood fractions and primary human cells to investigate the distribution of circulating PRCP. PRCP activity was measured in serum of individuals (n = 75) categorized based on their body mass index (BMI < 25.0; 25.0–29.9; 30.0–39.9; ≥ 40.0 kg/m²) and the diagnosis of metabolic syndrome. Differences in serum PRCP activity were determined before and six months after weight loss, either by diet (n = 45) or by bariatric surgery (n = 24). Potential correlations between serum PRCP activity and several metabolic and biochemical parameters were assessed. Additionally, plasma PRCP concentrations were quantified using a sensitive ELISA in the bariatric surgery group.

Results

White blood cells and plasma contributed the most to circulating PRCP activity. Serum PRCP activity in lean subjects was 0.83 ± 0.04 U/L and increased significantly with a rising BMI (p<0.001) and decreased upon weight loss (diet, p<0.05; bariatric surgery, p<0.001). The serum PRCP activity alteration reflected body weight changes and was found to be positively correlated with several metabolic parameters, including: total, abdominal and visceral adipose tissue. Plasma PRCP concentration was found to be significantly correlated to serum PRCP activity (0.865; p<0.001). Additionally, a significant decrease (p<0.001) in plasma PRCP protein concentration (mean ± SD) before (18.2 ± 3.7 ng/mL) and 6 months after bariatric surgery (15.7 ± 2.7 ng/mL) was found.

Conclusion

Our novel findings demonstrate that white blood cells and plasma contributed the most to circulating PRCP activity. Additionally, we have shown that there were significant correlations between serum PRCP activity and various metabolic parameters, and that plasma PRCP concentration was significantly correlated to serum PRCP activity. These novel findings on PRCP activity in serum support further investigation of its in vivo role and involvement in several metabolic diseases.

Liquid chromatography coupled to tandem mass spectrometry for detecting ten allergens in complex and incurred foodstuffs

Food allergy is a considerable heath problem, as undesirable contaminations by allergens during food production are still widespread and may be dangerous for human health. To protect the population, laboratories need to develop reliable analytical methods in order to detect allergens in various food products. Currently, a large majority of allergen-related food recalls concern bakery products. It is therefore essential to detect allergens in unprocessed and processed foodstuffs. In this study, we developed a method for detecting ten allergens in complex (chocolate, ice cream) and processed (cookie, sauce) foodstuffs, based on ultra-high performance liquid chromatography coupled to tandem mass spectrometry (UHPLC-MS/MS). Using a single protocol and considering a signal-to-noise ratio higher than 10 for the most abundant multiple reaction monitoring (MRM) transition, we were able to detect target allergens at 0.5mg/kg for milk proteins, 2.5mg/kg for peanut, hazelnut, pistachio, and cashew proteins, 3mg/kg for egg proteins, and 5mg/kg for soy, almond, walnut, and pecan proteins. The ability of the method to detect 10 allergens with a single protocol in complex and incurred food products makes it an attractive alternative to the ELISA method for routine laboratories.

Mild mitochondrial uncoupling induces HSL/ATGL-independent lipolysis relying on a form of autophagy in 3T3-L1 adipocytes

Obesity is characterized by an excessive triacylglycerol accumulation in white adipocytes. Various mechanisms allowing the tight regulation of triacylglycerol storage and mobilization by lipid droplet-associated proteins as well as lipolytic enzymes have been identified. Increasing energy expenditure by inducing a mild uncoupling of mitochondria in adipocytes might represent a putative interesting anti-obesity strategy as it reduces the adipose tissue triacylglycerol content (limiting alterations caused by cell hypertrophy) by stimulating lipolysis through yet unknown mechanisms, limiting the adverse effects of adipocyte hypertrophy. Herein, the molecular mechanisms involved in lipolysis induced by a mild uncoupling of mitochondria in white 3T3-L1 adipocytes were characterized. Mitochondrial uncoupling-induced lipolysis was found to be independent from canonical pathways that involve lipolytic enzymes such as HSL and ATGL. Finally, enhanced lipolysis in response to mitochondrial uncoupling relies on a form of autophagy as lipid droplets are captured by endolysosomal vesicles. This new mechanism of triacylglycerol breakdown in adipocytes exposed to mild uncoupling provides new insights on the biology of adipocytes dealing with mitochondria forced to dissipate energy.

Highlight on Bottlenecks in Food Allergen Analysis: Detection and Quantification by Mass Spectrometry

Food laboratories have developed methods for testing allergens in foods. The efficiency of qualitative and quantitative methods is of prime importance in protecting allergic populations. Unfortunately, food laboratories encounter barriers to developing efficient methods. Bottlenecks include the lack of regulatory thresholds, delays in the emergence of reference materials and guidelines, and the need to detect processed allergens. In this study, ultra-HPLC coupled to tandem MS was used to illustrate difficulties encountered in determining method performances. We measured the major influences of both processing and matrix effects on the detection of egg, milk, soy, and peanut allergens in foodstuffs. The main goals of this work were to identify difficulties that food laboratories still encounter in detecting and quantifying allergens and to sensitize researchers to them.

Advances in ultra-high performance liquid chromatography coupled to tandem mass spectrometry for sensitive detection of several food allergens in complex and processed foodstuffs

Sensitive detection of food allergens is affected by food processing and foodstuff complexity. It is therefore a challenge to detect cross-contamination in food production that could endanger an allergic customer's life. Here we used ultra-high performance liquid chromatography coupled to tandem mass spectrometry for simultaneous detection of traces of milk (casein, whey protein), egg (yolk, white), soybean, and peanut allergens in different complex and/or heat-processed foodstuffs. The method is based on a single protocol (extraction, trypsin digestion, and purification) applicable to the different tested foodstuffs: chocolate, ice cream, tomato sauce, and processed cookies. The determined limits of quantitation, expressed in total milk, egg, peanut, or soy proteins (and not soluble proteins) per kilogram of food, are: 0.5mg/kg for milk (detection of caseins), 5mg/kg for milk (detection of whey), 2.5mg/kg for peanut, 5mg/kg for soy, 3.4mg/kg for egg (detection of egg white), and 30.8mg/kg for egg (detection of egg yolk). The main advantage is the ability of the method to detect four major food allergens simultaneously in processed and complex matrices with very high sensitivity and specificity.

Lipin-1 regulates cancer cell phenotype and is a potential target to potentiate rapamycin treatment

Lipogenesis inhibition was reported to induce apoptosis and repress proliferation of cancer cells while barely affecting normal cells. Lipins exhibit dual function as enzymes catalyzing the dephosphorylation of phosphatidic acid to diacylglycerol and as co-transcriptional regulators. Thus, they are able to regulate lipid homeostasis at several nodal points. Here, we show that lipin-1 is up-regulated in several cancer cell lines and overexpressed in 50 % of high grade prostate cancers. The proliferation of prostate and breast cancer cells, but not of non-tumorigenic cells, was repressed upon lipin-1 knock-down. Lipin-1 depletion also decreased cancer cell migration through RhoA activation. Lipin-1 silencing did not significantly affect global lipid synthesis but enhanced the cellular concentration of phosphatidic acid. In parallel, autophagy was induced while AKT and ribosomal protein S6 phosphorylation were repressed. We also observed a compensatory regulation between lipin-1 and lipin-2 and demonstrated that their co-silencing aggravates the phenotype induced by lipin-1 silencing alone. Most interestingly, lipin-1 depletion or lipins inhibition with propranolol sensitized cancer cells to rapamycin. These data indicate that lipin-1 controls main cellular processes involved in cancer progression and that its targeting, alone or in combination with other treatments, could open new avenues in anticancer therapy.

Effects of a Sublethal and Transient Stress of the Endoplasmic Reticulum on the Mitochondrial Population

Endoplasmic reticulum (ER) and mitochondria are not discrete intracellular organelles but establish close physical and functional interactions involved in several biological processes including mitochondrial bioenergetics, calcium homeostasis, lipid synthesis, and the regulation of apoptotic cell death pathways. As many cell types might face a transient and sublethal ER stress during their lifetime, it is thus likely that the adaptive UPR response might affect the mitochondrial population. The aim of this work was to study the putative effects of a non-lethal and transient endoplasmic reticulum stress on the mitochondrial population in HepG2 cells. The results show that thapsigargin and brefeldin A, used to induce a transient and sublethal ER stress, rapidly lead to the fragmentation of the mitochondrial network associated with a decrease in mitochondrial membrane potential, O2 (•-) production and less efficient respiration. These changes in mitochondrial function are transient and preceded by the phosphorylation of JNK. Inhibition of JNK activation by SP600125 prevents the decrease in O2 (•-) production and the mitochondrial network fragmentation observed in cells exposed to the ER stress but has no impact on the reduction of the mitochondrial membrane potential. In conclusion, our data show that a non-lethal and transient ER stress triggers a rapid activation of JNK without inducing apoptosis, leading to the fragmentation of the mitochondrial network and a reduction of O2 (•-) production. J. Cell. Physiol. 231: 1913-1931, 2016. © 2015 Wiley Periodicals, Inc.

Mitochondria Retrograde Signaling and the UPR mt: Where Are We in Mammals?

Mitochondrial unfolded protein response is a form of retrograde signaling that contributes to ensuring the maintenance of quality control of mitochondria, allowing functional integrity of the mitochondrial proteome. When misfolded proteins or unassembled complexes accumulate beyond the folding capacity, it leads to alteration of proteostasis, damages, and organelle/cell dysfunction. Extensively studied for the ER, it was recently reported that this kind of signaling for mitochondrion would also be able to communicate with the nucleus in response to impaired proteostasis. The mitochondrial unfolded protein response (UPR^mt) is activated in response to different types and levels of stress, especially in conditions where unfolded or misfolded mitochondrial proteins accumulate and aggregate. A specific UPR^mt could thus be initiated to boost folding and degradation capacity in response to unfolded and aggregated protein accumulation. Although first described in mammals, the UPR^mt was mainly studied in Caenorhabditis elegans, and accumulating evidence suggests that mechanisms triggered in response to a UPR^mt might be different in C. elegans and mammals. In this review, we discuss and integrate recent data from the literature to address whether the UPR^mt is relevant to mitochondrial homeostasis in mammals and to analyze the putative role of integrated stress response (ISR) activation in response to the inhibition of mtDNA expression and/or accumulation of mitochondrial mis/unfolded proteins.

Connecting Mitochondria, Metabolism, and Stem Cell Fate

As sites of cellular respiration and energy production, mitochondria play a central role in cell metabolism. Cell differentiation is associated with an increase in mitochondrial content and activity and with a metabolic shift toward increased oxidative phosphorylation activity. The opposite occurs during reprogramming of somatic cells into induced pluripotent stem cells. Studies have provided evidence of mitochondrial and metabolic changes during the differentiation of both embryonic and somatic (or adult) stem cells (SSCs), such as hematopoietic stem cells, mesenchymal stem cells, and tissue-specific progenitor cells. We thus propose to consider those mitochondrial and metabolic changes as hallmarks of differentiation processes. We review how mitochondrial biogenesis, dynamics, and function are directly involved in embryonic and SSC differentiation and how metabolic and sensing pathways connect mitochondria and metabolism with cell fate and pluripotency. Understanding the basis of the crosstalk between mitochondria and cell fate is of critical importance, given the promising application of stem cells in regenerative medicine. In addition to the development of novel strategies to improve the in vitro lineage-directed differentiation of stem cells, understanding the molecular basis of this interplay could lead to the identification of novel targets to improve the treatment of degenerative diseases.

miRNA-196b inhibits cell proliferation and induces apoptosis in HepG2 cells by targeting IGF2BP1

Background

Tumor hypoxia is one of the features of tumor microenvironment that contributes to chemoresistance. miRNAs have recently been shown to play important roles in tumorigenesis and drug resistance. Moreover, hypoxia also regulates the expression of a series of miRNAs. However, the interaction between chemoresistance, hypoxia and miRNAs has not been explored yet. The aim of this study is to understand the mechanisms activated/inhibited by miRNAs under hypoxia that induce resistance to chemotherapy-induced apoptosis.

Methods

TaqMan low-density array was used to identify changes in miRNA expression when cells were exposed to etoposide under hypoxia or normoxia. The effects of miR-196b overexpression on apoptosis and cell proliferation were studied in HepG2 cells. miR-196b target mRNAs were identified by proteomic analysis, luciferase activity assay, RT-qPCR and western blot analysis.

Results

Results showed that hypoxia down-regulated miR-196b expression that was induced by etoposide. miR-196b overexpression increased the etoposide-induced apoptosis and reversed the protection of cell death observed under hypoxia. By a proteomic approach combined with bioinformatics analyses, we identified IGF2BP1 as a potential target of miR-196b. Indeed, miR-196b overexpression decreased IGF2BP1 RNA expression and protein level. The IGF2BP1 down-regulation by either miR-196b or IGF2BP1 siRNA led to an increase in apoptosis and a decrease in cell viability and proliferation in normal culture conditions. However, IGF2BP1 silencing did not modify the chemoresistance induced by hypoxia, probably because it is not the only target of miR-196b involved in the regulation of apoptosis.

Conclusions

In conclusion, for the first time, we identified IGF2BP1 as a direct and functional target of miR-196b and showed that miR-196b overexpression reverses the chemoresistance induced by hypoxia. These results emphasize that the chemoresistance induced by hypoxia is a complex mechanism.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0349-6) contains supplementary material, which is available to authorized users.

Heat-modified citrus pectin induces apoptosis-like cell death and autophagy in HepG2 and A549 cancer cells

Cancer is still one of the leading causes of death worldwide, and finding new treatments remains a major challenge. Previous studies showed that modified forms of pectin, a complex polysaccharide present in the primary plant cell wall, possess anticancer properties. Nevertheless, the mechanism of action of modified pectin and the pathways involved are unclear. Here, we show that citrus pectin modified by heat treatment induced cell death in HepG2 and A549 cells. The induced cell death differs from classical apoptosis because no DNA cleavage was observed. In addition, Z-VAD-fmk, a pan-caspase inhibitor, did not influence the observed cell death in HepG2 cells but appeared to be partly protective in A549 cells, indicating that heat-modified citrus pectin might induce caspase-independent cell death. An increase in the abundance of the phosphatidylethanolamine-conjugated Light Chain 3 (LC3) protein and a decrease in p62 protein abundance were observed in both cell types when incubated in the presence of heat-modified citrus pectin. These results indicate the activation of autophagy. To our knowledge, this is the first time that autophagy has been revealed in cells incubated in the presence of a modified form of pectin. This autophagy activation appears to be protective, at least for A549 cells, because its inhibition with 3-methyladenine increased the observed modified pectin-induced cytotoxicity. This study confirms the potential of modified pectin to improve chemotherapeutic cancer treatments.

Taxol-induced unfolded protein response activation in breast cancer cells exposed to hypoxia: ATF4 activation regulates autophagy and inhibits apoptosis

Understanding the mechanisms responsible for the resistance against chemotherapy-induced cell death is still of great interest since the number of patients with cancer increases and relapse is commonly observed. Indeed, the development of hypoxic regions as well as UPR (unfolded protein response) activation is known to promote cancer cell adaptive responses to the stressful tumor microenvironment and resistance against anticancer therapies. Therefore, the impact of UPR combined to hypoxia on autophagy and apoptosis activation during taxol exposure was investigated in MDA-MB-231 and T47D breast cancer cells. The results showed that taxol rapidly induced UPR activation and that hypoxia modulated taxol-induced UPR activation differently according to the different UPR pathways (PERK, ATF6, and IRE1α). The putative involvement of these signaling pathways in autophagy or in apoptosis regulation in response to taxol exposure was investigated. However, while no link between the activation of these three ER stress sensors and autophagy or apoptosis regulation could be evidenced, results showed that ATF4 activation, which occurs independently of UPR activation, was involved in taxol-induced autophagy completion. In addition, an ATF4-dependent mechanism leading to cancer cell adaptation and resistance against taxol-induced cell death was evidenced. Finally, our results demonstrate that expression of ATF4, in association with hypoxia-induced genes, can be used as a biomarker of a poor prognosis for human breast cancer patients supporting the conclusion that ATF4 might play an important role in adaptation and resistance of breast cancer cells to chemotherapy in hypoxic tumors.

Mitochondria: a target for bacteria

Eukaryotic cells developed strategies to detect and eradicate infections. The innate immune system, which is the first line of defence against invading pathogens, relies on the recognition of molecular patterns conserved among pathogens. Pathogen associated molecular pattern binding to pattern recognition receptor triggers the activation of several signalling pathways leading to the establishment of a pro-inflammatory state required to control the infection. In addition, pathogens evolved to subvert those responses (with passive and active strategies) allowing their entry and persistence in the host cells and tissues. Indeed, several bacteria actively manipulate immune system or interfere with the cell fate for their own benefit. One can imagine that bacterial effectors can potentially manipulate every single organelle in the cell. However, the multiple functions fulfilled by mitochondria especially their involvement in the regulation of innate immune response, make mitochondria a target of choice for bacterial pathogens as they are not only a key component of the central metabolism through ATP production and synthesis of various biomolecules but they also take part to cell signalling through ROS production and control of calcium homeostasis as well as the control of cell survival/programmed cell death. Furthermore, considering that mitochondria derived from an ancestral bacterial endosymbiosis, it is not surprising that a special connection does exist between this organelle and bacteria. In this review, we will discuss different mitochondrial functions that are affected during bacterial infection as well as different strategies developed by bacterial pathogens to subvert functions related to calcium homeostasis, maintenance of redox status and mitochondrial morphology.

Inhibition of mitochondrial genome expression triggers the activation of CHOP-10 by a cell signaling dependent on the integrated stress response but not the mitochondrial unfolded protein response

Mitochondria-to-nucleus communication, known as retrograde signaling, is important to adjust the nuclear gene expression in response to organelle dysfunction. Among the transcription factors described to respond to mitochondrial stress, CHOP-10 is activated by respiratory chain inhibition, mitochondrial accumulation of unfolded proteins and mtDNA mutations. In this study, we show that altered/impaired expression of mtDNA induces CHOP-10 expression in a signaling pathway that depends on the eIF2α/ATF4 axis of the integrated stress response rather than on the mitochondrial unfolded protein response.

Unraveling biochemical pathways affected by mitochondrial dysfunctions using metabolomic approaches

Mitochondrial dysfunction(s) (MDs) can be defined as alterations in the mitochondria, including mitochondrial uncoupling, mitochondrial depolarization, inhibition of the mitochondrial respiratory chain, mitochondrial network fragmentation, mitochondrial or nuclear DNA mutations and the mitochondrial accumulation of protein aggregates. All these MDs are known to alter the capacity of ATP production and are observed in several pathological states/diseases, including cancer, obesity, muscle and neurological disorders. The induction of MDs can also alter the secretion of several metabolites, reactive oxygen species production and modify several cell-signalling pathways to resolve the mitochondrial dysfunction or ultimately trigger cell death. Many metabolites, such as fatty acids and derived compounds, could be secreted into the blood stream by cells suffering from mitochondrial alterations. In this review, we summarize how a mitochondrial uncoupling can modify metabolites, the signalling pathways and transcription factors involved in this process. We describe how to identify the causes or consequences of mitochondrial dysfunction using metabolomics (liquid and gas chromatography associated with mass spectrometry analysis, NMR spectroscopy) in the obesity and insulin resistance thematic.

Mitochondrial remodeling in hepatic differentiation and dedifferentiation

Mitochondrial biogenesis and metabolism have recently emerged as important actors of stemness and differentiation. On the one hand, the differentiation of stem cells is associated with an induction of mitochondrial biogenesis and a shift from glycolysis toward oxidative phosphorylations (OXPHOS). In addition, interfering with mitochondrial biogenesis or function impacts stem cell differentiation. On the other hand, some inverse changes in mitochondrial abundance and function are observed during the reprogramming of somatic cells into induced pluripotent stem cells (iPSCs). Yet although great promises in cell therapy might generate better knowledge of the mechanisms regulating the stemness and differentiation of somatic stem cells (SSCs)-which are preferred over embryonic stem cells (ESCs) and iPSCs because of ethical and safety considerations-little interest was given to the study of their mitochondria. This study provides a detailed characterization of the mitochondrial biogenesis occurring during the hepatogenic differentiation of bone marrow-mesenchymal stem cells (BM-MSCs). During the hepatogenic differentiation of BM-MSCs, an increased abundance of mitochondrial DNA (mtDNA) is observed, as well as an increased expression of several mitochondrial proteins and biogenesis regulators, concomitant with increased OXPHOS activity, capacity, and efficiency. In addition, opposite changes in mitochondrial morphology and in the abundance of several OXPHOS subunits were found during the spontaneous dedifferentiation of primary hepatocytes. These data support reverse mitochondrial changes in a different context from genetically-engineered reprogramming. They argue in favor of a mitochondrial involvement in hepatic differentiation and dedifferentiation.

Mass spectrometry-based identification of proteins interacting with nucleic acids

The identification of the regulatory proteins that control DNA transcription as well as RNA stability and translation represents a key step in the comprehension of gene expression regulation. Those proteins can be purified by DNA- or RNA-affinity chromatography, followed by identification by mass spectrometry. Although very simple in the concept, this represents a real technological challenge due to the low abundance of regulatory proteins compared to the highly abundant proteins binding to nucleic acids in a nonsequence-specific manner. Here we review the different strategies that have been set up to reach this purpose, discussing the key parameters that should be considered to increase the chances of success. Typically, two categories of biological questions can be distinguished: the identification of proteins that specifically interact with a precisely defined binding site, mostly addressed by quantitative mass spectrometry, and the identification in a non-comparative manner of the protein complexes recruited by a poorly characterized long regulatory region of nucleic acids. Finally, beside the numerous studies devoted to in vitro-assembled nucleic acid-protein complexes, the scarce data reported on proteomic analyses of in vivo-assembled complexes are described, with a special emphasis on the associated challenges.

Functional and morphological impact of ER stress on mitochondria

Over the past years, knowledge and evidence about the existence of crosstalks between cellular organelles and their potential effects on survival or cell death have been constantly growing. More recently, evidence accumulated showing an intimate relationship between endoplasmic reticulum (ER) and mitochondria. These close contacts not only establish extensive physical links allowing exchange of lipids and calcium but they can also coordinate pathways involved in cell life and death. It is now obvious that ER dysfunction/stress and unfolded protein response (UPR) as well as mitochondria play major roles in apoptosis. However, while the effects of major ER stress on cell death have been largely studied and reviewed, it becomes more and more evident that cells might regularly deal with sublethal ER stress, a condition that does not necessarily lead to cell death but might affect the function/activity of other organelles such as mitochondria. In this review, we will particularly focus on these new, interesting and intriguing metabolic and morphological events that occur during the early adaptative phase of the ER stress, before the onset of cell death, and that remain largely unknown. Relevance and implication of these mitochondrial changes in response to ER stress conditions for human diseases such as type II diabetes and Alzheimer's disease will also be considered.

PPAR agonist-induced reduction of Mcp1 in atherosclerotic plaques of obese, insulin-resistant mice depends on adiponectin-induced Irak3 expression

Synthetic peroxisome proliferator-activated receptor (PPAR) agonists are used to treat dyslipidemia and insulin resistance. In this study, we examined molecular mechanisms that explain differential effects of a PPARα agonist (fenofibrate) and a PPARγ agonist (rosiglitazone) on macrophages during obesity-induced atherogenesis. Twelve-week-old mice with combined leptin and LDL-receptor deficiency (DKO) were treated with fenofibrate, rosiglitazone or placebo for 12 weeks. Only rosiglitazone improved adipocyte function, restored insulin sensitivity, and inhibited atherosclerosis by decreasing lipid-loaded macrophages. In addition, it increased interleukin-1 receptor-associated kinase-3 (Irak3) and decreased monocyte chemoattractant protein-1 (Mcp1) expressions, indicative of a switch from M1 to M2 macrophages. The differences between fenofibrate and rosiglitazone were independent of Pparγ expression. In bone marrow-derived macrophages (BMDM), we identified the rosiglitazone-associated increase in adiponectin as cause of the increase in Irak3. Interestingly, the deletion of Irak3 in BMDM (IRAK3^−/− BMDM) resulted in activation of the canonical NFκB signaling pathway and increased Mcp1 protein secretion. Rosiglitazone could not decrease the elevated Mcp1 secretion in IRAK3^−/− BMDM directly and fenofibrate even increased the secretion, possibly due to increased mitochondrial reactive oxygen species production. Furthermore, aortic extracts of high-fat insulin-resistant LDL-receptor deficient mice, with lower adiponectin and Irak3 and higher Mcp1, showed accelerated atherosclerosis. In aggregate, our results emphasize an interaction between PPAR agonist-mediated increase in adiponectin and macrophage-associated Irak3 in the protection against atherosclerosis by PPAR agonists.

Hypoxia-induced modulation of apoptosis and BCL-2 family proteins in different cancer cell types

Hypoxia plays an important role in the resistance of tumour cells to chemotherapy. However, the exact mechanisms underlying this process are not well understood. Moreover, according to the cell lines, hypoxia differently influences cell death. The study of the effects of hypoxia on the apoptosis induced by 5 chemotherapeutic drugs in 7 cancer cell types showed that hypoxia generally inhibited the drug-induced apoptosis. In most cases, the effect of hypoxia was the same for all the drugs in one cell type. The expression profile of 93 genes involved in apoptosis as well as the protein level of BCL-2 family proteins were then investigated. In HepG2 cells that are strongly protected against cell death by hypoxia, hypoxia decreased the abundance of nearly all the pro-apoptotic BCL-2 family proteins while none of them are decreased in A549 cells that are not protected against cell death by hypoxia. In HepG2 cells, hypoxia decreased NOXA and BAD abundance and modified the electrophoretic mobility of BIM_EL. BIM and NOXA are important mediators of etoposide-induced cell death in HepG2 cells and the hypoxia-induced modification of these proteins abundance or post-translational modifications partly account for chemoresistance. Finally, the modulation of the abundance and/or of the post-translational modifications of most proteins of the BCL-2 family by hypoxia involves p53-dependent and –independent pathways and is cell type-dependent. A better understanding of these cell-to-cell variations is crucial in order to overcome hypoxia-induced resistance and to ameliorate cancer therapy.

TMEM45A is essential for hypoxia-induced chemoresistance in breast and liver cancer cells

BACKGROUND

Hypoxia is a common characteristic of solid tumors associated with reduced response to radio- and chemotherapy, therefore increasing the probability of tumor recurrence. The aim of this study was to identify new mechanisms responsible for hypoxia-induced resistance in breast cancer cells.

METHODS

MDA-MB-231 and HepG2 cells were incubated in the presence of taxol or etoposide respectively under normoxia and hypoxia and apoptosis was analysed. A whole transcriptome analysis was performed in order to identify genes whose expression profile was correlated with apoptosis. The effect of gene invalidation using siRNA was studied on drug-induced apoptosis.

RESULTS

MDA-MB-231 cells incubated in the presence of taxol were protected from apoptosis and cell death by hypoxia. We demonstrated that TMEM45A expression was associated with taxol resistance. TMEM45A expression was increased both in MDA-MB-231 human breast cancer cells and in HepG2 human hepatoma cells in conditions where protection of cells against apoptosis induced by chemotherapeutic agents was observed, i.e. under hypoxia in the presence of taxol or etoposide. Moreover, this resistance was suppressed by siRNA-mediated silencing of TMEM45A. Kaplan Meier curve showed an association between high TMEM45A expression and poor prognostic in breast cancer patients. Finally, TMEM45 is highly expressed in normal differentiated keratinocytes both in vitro and in vivo, suggesting that this protein is involved in epithelial functions.

CONCLUSION

Altogether, our results unravel a new mechanism for taxol and etoposide resistance mediated by TMEM45A. High levels of TMEM45A expression in tumors may be indicative of potential resistance to cancer therapy, making TMEM45A an interesting biomarker for resistance.

Unbiased proteomic analysis of proteins interacting with the HIV-1 5'LTR sequence: role of the transcription factor Meis

To depict the largest picture of a core promoter interactome, we developed a one-step DNA-affinity capture method coupled with an improved mass spectrometry analysis process focused on the identification of low abundance proteins. As a proof of concept, this method was developed through the analysis of 230 bp contained in the 5′long terminal repeat (LTR) of the human immunodeficiency virus 1 (HIV-1). Beside many expected interactions, many new transcriptional regulators were identified, either transcription factors (TFs) or co-regulators, which interact directly or indirectly with the HIV-1 5′LTR. Among them, the homeodomain-containing TF myeloid ectopic viral integration site was confirmed to functionally interact with a specific binding site in the HIV-1 5′LTR and to act as a transcriptional repressor, probably through recruitment of the repressive Sin3A complex. This powerful and validated DNA-affinity approach could also be used as an efficient screening tool to identify a large set of proteins that physically interact, directly or indirectly, with a DNA sequence of interest. Combined with an in silico analysis of the DNA sequence of interest, this approach provides a powerful approach to select the interacting candidates to validate functionally by classical approaches.

Mild mitochondrial uncoupling does not affect mitochondrial biogenesis but downregulates pyruvate carboxylase in adipocytes: role for triglyceride content reduction

In adipocytes, mitochondrial uncoupling is known to trigger a triglyceride loss comparable with the one induced by TNFα, a proinflammatory cytokine. However, the impact of a mitochondrial uncoupling on the abundance/composition of mitochondria and its connection with triglyceride content in adipocytes is largely unknown. In this work, the effects of a mild mitochondrial uncoupling triggered by FCCP were investigated on the mitochondrial population of 3T3-L1 adipocytes by both quantitative and qualitative approaches. We found that mild mitochondrial uncoupling does not stimulate mitochondrial biogenesis in adipocytes but induces an adaptive cell response characterized by quantitative modifications of mitochondrial protein content. Superoxide anion radical level was increased in mitochondria of both TNFα- and FCCP-treated adipocytes, whereas mitochondrial DNA copy number was significantly higher only in TNFα-treated cells. Subproteomic analysis revealed that the abundance of pyruvate carboxylase was reduced significantly in mitochondria of TNFα- and FCCP-treated adipocytes. Functional study showed that overexpression of this major enzyme of lipid metabolism is able to prevent the triglyceride content reduction in adipocytes exposed to mitochondrial uncoupling or TNFα. These results suggest a new mechanism by which the effects of mitochondrial uncoupling might limit triglyceride accumulation in adipocytes.

Crosstalk between mitochondrial (dys)function and mitochondrial abundance

A controlled regulation of mitochondrial mass through either the production (biogenesis) or the degradation (mitochondrial quality control) of the organelle represents a crucial step for proper mitochondrial and cell function. Key steps of mitochondrial biogenesis and quality control are overviewed, with an emphasis on the role of mitochondrial chaperones and proteases that keep mitochondria fully functional, provided the mitochondrial activity impairment is not excessive. In this case, the whole organelle is degraded by mitochondrial autophagy or "mitophagy." Beside the maintenance of adequate mitochondrial abundance and functions for cell homeostasis, mitochondrial biogenesis might be enhanced, through discussed signaling pathways, in response to various physiological stimuli, like contractile activity, exposure to low temperatures, caloric restriction, and stem cells differentiation. In addition, mitochondrial dysfunction might also initiate a retrograde response, enabling cell adaptation through increased mitochondrial biogenesis.

miR-212/132 expression and functions: within and beyond the neuronal compartment

During the last two decades, microRNAs (miRNAs) emerged as critical regulators of gene expression. By modulating the expression of numerous target mRNAs mainly at the post-transcriptional level, these small non-coding RNAs have been involved in most, if not all, biological processes as well as in the pathogenesis of a number of diseases. miR-132 and miR-212 are tandem miRNAs whose expression is necessary for the proper development, maturation and function of neurons and whose deregulation is associated with several neurological disorders, such as Alzheimer's disease and tauopathies (neurodegenerative diseases resulting from the pathological aggregation of tau protein in the human brain). Although their involvement in neuronal functions is the most described, evidences point towards a role of these miRNAs in many other biological processes, including inflammation and immune functions. Incidentally, miR-132 was recently classified as a ‘neurimmiR’, a class of miRNAs operating within and between the neural and immune compartments. In this review, we propose an outline of the current knowledge about miR-132 and miR-212 functions in neurons and immune cells, by describing the signalling pathways and transcription factors regulating their expression as well as their putative or demonstrated roles and validated mRNA targets.

Hypersensitivity of A8344G MERRF mutated cybrid cells to staurosporine-induced cell death is mediated by calcium-dependent activation of calpains

Mutations in the mitochondrial DNA can lead to the development of mitochondrial diseases such as Myoclonic Epilepsy with Ragged Red Fibers (MERRF) or Mitochondrial Encephalomyopathy, Lactic Acidosis and Stroke-like episodes (MELAS). We first show that human 143B-derived cybrid cells harboring either the A8344G (MERRF) or the A3243G (MELAS) mutation, are more prone to undergo apoptosis then their wild-type counterpart, when challenged with various apoptotic inducers such as staurosporine, etoposide and TRAIL. In addition, investigating the mechanisms underlying A8344G cybrid cells hypersensitivity to staurosporine-induced cell death, we found that staurosporine treatment activates caspases independently of cytochrome c release in both wild-type and mutated cells. Caspases are activated, at least partly, through the activation of calcium-dependent calpain proteases, a pathway that is more strongly activated in mutated cybrid cells than in wild-type cells exposed to staurosporine. These results suggest that calcium homeostasis perturbation induced by mitochondrial dysfunction could predispose cells to apoptosis, a process that could take part into the progressive cell degeneration observed in MERRF syndrome, and more generally in mitochondrial diseases.