High-Throughput Microscopy Analysis of Mitochondrial Membrane Potential in 2D and 3D Models.

Recent proteomic, metabolomic, and transcriptomic studies have highlighted a connection between changes in mitochondria physiology and cellular pathophysiological mechanisms. Secondary assays to assess the function of these organelles appear fundamental to validate these -omics findings. Although mitochondrial membrane potential is widely recognized as an indicator of mitochondrial activity, high-content imaging-based approaches coupled to multiparametric to measure it have not been established yet. In this paper, we describe a methodology for the unbiased high-throughput quantification of mitochondrial membrane potential in vitro, which is suitable for 2D to 3D models. We successfully used our method to analyze mitochondrial membrane potential in monolayers of human fibroblasts, neural stem cells, spheroids, and isolated muscle fibers. Moreover, by combining automated image analysis and machine learning, we were able to discriminate melanoma cells from macrophages in co-culture and to analyze the subpopulations separately. Our data demonstrated that our method is a widely applicable strategy for large-scale profiling of mitochondrial activity.

Comparison among Neuroblastoma Stages Suggests the Involvement of Mitochondria in Tumor Progression.

Neuroblastoma (NB) is the most common extracranial tumor of early childhood and accounts for 15% of all pediatric cancer mortalities. However, the precise pathways and genes underlying its progression are unknown. Therefore, we performed a differential gene expression analysis of neuroblastoma stage 1 and stage 4 + 4S to discover biological processes associated with NB progression. From this preliminary analysis, we found that NB samples (stage 4 + 4S) are characterized by altered expression of some proteins involved in mitochondria function and mitochondria-ER contact sites (MERCS). Although further analyses remain necessary, this review may provide new hints to better understand NB molecular etiopathogenesis, by suggesting that MERCS alterations could be involved in the progression of NB.

Chronic social stress disrupts the intracellular redistribution of brain hexokinase 3 induced by shifts in peripheral glucose levels.

Chronic stress has the potential to impair health and may increase the vulnerability for psychiatric disorders. Emerging evidence suggests that specific neurometabolic dysfunctions play a role herein. In mice, chronic social defeat (CSD) stress reduces cerebral glucose uptake despite hyperglycemia. We hypothesized that this metabolic decoupling would be reflected by changes in contact sites between mitochondria and the endoplasmic reticulum, important intracellular nutrient sensors, and signaling hubs. We thus analyzed the proteome of their biochemical counterparts, mitochondria-associated membranes (MAMs) from whole brain tissue obtained from CSD and control mice. This revealed a lack of the glucose-metabolizing enzyme hexokinase 3 (HK3) in MAMs from CSD mice. In controls, HK3 protein abundance in MAMs and also in striatal synaptosomes correlated positively with peripheral blood glucose levels, but this connection was lost in CSD. We conclude that the ability of HK3 to traffic to sites of need, such as MAMs or synapses, is abolished upon CSD and surmise that this contributes to a cellular dysfunction instigated by chronic stress. KEY MESSAGES : Chronic social defeat (CSD) alters brain glucose metabolism CSD depletes hexokinase 3 (HK3) from mitochondria-associated membranes (MAMs) CSD results in loss of positive correlation between blood glucose and HK3 in MAMs and synaptosomes.

GDAP1 loss of function inhibits the mitochondrial pyruvate dehydrogenase complex by altering the actin cytoskeleton.

Charcot-Marie-Tooth (CMT) disease 4A is an autosomal-recessive polyneuropathy caused by mutations of ganglioside-induced differentiation-associated protein 1 (GDAP1), a putative glutathione transferase, which affects mitochondrial shape and alters cellular Ca2+ homeostasis. Here, we identify the underlying mechanism. We found that patient-derived motoneurons and GDAP1 knockdown SH-SY5Y cells display two phenotypes: more tubular mitochondria and a metabolism characterized by glutamine dependence and fewer cytosolic lipid droplets. GDAP1 interacts with the actin-depolymerizing protein Cofilin-1 and beta-tubulin in a redox-dependent manner, suggesting a role for actin signaling. Consistently, GDAP1 loss causes less F-actin close to mitochondria, which restricts mitochondrial localization of the fission factor dynamin-related protein 1, instigating tubularity. GDAP1 silencing also disrupts mitochondria-ER contact sites. These changes result in lower mitochondrial Ca2+ levels and inhibition of the pyruvate dehydrogenase complex, explaining the metabolic changes upon GDAP1 loss of function. Together, our findings reconcile GDAP1-associated phenotypes and implicate disrupted actin signaling in CMT4A pathophysiology.

The Interplay of Microtubules with Mitochondria-ER Contact Sites (MERCs) in Glioblastoma.

Gliomas are heterogeneous neoplasms, classified into grade I to IV according to their malignancy and the presence of specific histological/molecular hallmarks. The higher grade of glioma is known as glioblastoma (GB). Although progress has been made in surgical and radiation treatments, its clinical outcome is still unfavorable. The invasive properties of GB cells and glioma aggressiveness are linked to the reshaping of the cytoskeleton. Recent works suggest that the different susceptibility of GB cells to antitumor immune response is also associated with the extent and function of mitochondria-ER contact sites (MERCs). The presence of MERCs alterations could also explain the mitochondrial defects observed in GB models, including abnormalities of energy metabolism and disruption of apoptotic and calcium signaling. Based on this evidence, the question arises as to whether a MERCs-cytoskeleton crosstalk exists, and whether GB progression is linked to an altered cytoskeleton-MERCs interaction. To address this possibility, in this review we performed a meta-analysis to compare grade I and grade IV GB patients. From this preliminary analysis, we found that GB samples (grade IV) are characterized by altered expression of cytoskeletal and MERCs related genes. Among them, the cytoskeleton-associated protein 4 (CKAP4 or CLIMP-63) appears particularly interesting as it encodes a MERCs protein controlling the ER anchoring to microtubules (MTs). Although further in-depth analyses remain necessary, this perspective review may provide new hints to better understand GB molecular etiopathogenesis, by suggesting that cytoskeletal and MERCs alterations cooperate to exacerbate the cellular phenotype of high-grade GB and that MERCs players can be exploited as novel biomarkers/targets to enhance the current therapy for GB.

Cisplatin resistance can be curtailed by blunting Bnip3-mediated mitochondrial autophagy.

Cisplatin (CDDP) is commonly used to treat a multitude of tumors including sarcomas, ovarian and cervical cancers. Despite recent investigations allowed to improve chemotherapy effectiveness, the molecular mechanisms underlying the development of CDDP resistance remain a major goal in cancer research. Here, we show that mitochondrial morphology and autophagy are altered in different CDDP resistant cancer cell lines. In CDDP resistant osteosarcoma and ovarian carcinoma, mitochondria are fragmented and closely juxtaposed to the endoplasmic reticulum; rates of mitophagy are also increased. Specifically, levels of the mitophagy receptor BNIP3 are higher both in resistant cells and in ovarian cancer patient samples resistant to platinum-based treatments. Genetic BNIP3 silencing or pharmacological inhibition of autophagosome formation re-sensitizes these cells to CDDP. Our study identifies inhibition of BNIP3-driven mitophagy as a potential therapeutic strategy to counteract CDDP resistance in ovarian carcinoma and osteosarcoma.

Inhibition of the mitochondrial protein Opa1 curtails breast cancer growth.

BACKGROUND: Mitochondrial fusion and fission proteins have been nominated as druggable targets in cancer. Whether their inhibition is efficacious in triple negative breast cancer (TNBC) that almost invariably develops chemoresistance is unknown. METHODS: We used a combination of bioinformatics analyses of cancer genomic databases, genetic and pharmacological Optic Atrophy 1 (OPA1) inhibition, mitochondrial function and morphology measurements, micro-RNA (miRNA) profiling and formal epistatic analyses to address the role of OPA1 in TNBC proliferation, migration, and invasion in vitro and in vivo. RESULTS: We identified a signature of OPA1 upregulation in breast cancer that correlates with worse prognosis. Accordingly, OPA1 inhibition could reduce breast cancer cells proliferation, migration, and invasion in vitro and in vivo. Mechanistically, while OPA1 silencing did not reduce mitochondrial respiration, it increased levels of miRNAs of the 148/152 family known to inhibit tumor growth and invasiveness. Indeed, these miRNAs were epistatic to OPA1 in the regulation of TNBC cells growth and invasiveness. CONCLUSIONS: Our data show that targeted inhibition of the mitochondrial fusion protein OPA1 curtails TNBC growth and nominate OPA1 as a druggable target in TNBC.

Interaction Between Mitochondrial DNA Variants and Mitochondria/Endoplasmic Reticulum Contact Sites: A Perspective Review.

Mitochondria contain their own genome, mitochondrial DNA (mtDNA), essential to support their fundamental intracellular role in ATP production and other key metabolic and homeostatic pathways. Mitochondria are highly dynamic organelles that communicate with all the other cellular compartments, through sites of high physical proximity. Among all, their crosstalk with the endoplasmic reticulum (ER) appears particularly important as its derangement is tightly implicated with several human disorders. Population-specific mtDNA variants clustered in defining the haplogroups have been shown to exacerbate or mitigate these pathological conditions. The exact mechanisms of the mtDNA background-modifying effect are not completely clear and a possible explanation is the outcome of mitochondrial efficiency on retrograde signaling to the nucleus. However, the possibility that different haplogroups shape the proximity and crosstalk between mitochondria and the ER has never been proposed neither investigated. In this study, we pose and discuss this question and provide preliminary data to answer it. Besides, we also address the possibility that single, disease-causing mtDNA point mutations may act also by reshaping organelle communication. Overall, this perspective review provides a theoretical platform for future studies on the interaction between mtDNA variants and organelle contact sites.

Chlorogenic Acid Interaction with Cisplatin and Oxaliplatin: Studies in Cervical Carcinoma Cells.

The antiproliferative effect of the naturally occurring polyphenol chlorogenic acid (CGA) was evaluated in combination with either cisplatin or oxaliplatin in human cervical carcinoma cell lines that were either sensitive (A431) or resistant to cisplatin (A431Pt), in order to provide evidence to overcome drug resistance. Cytotoxicity of platinating drugs (IC50 - 10(-6) - 10(-5) M) was enhanced by 1-2 orders of magnitude by increasing incubation times (1, 4, and 24 hours) in the two cell lines. CGA treatment presented low cytotoxicity per se (IC50 ~ 10(-4) M at 24 h) if compared with platinum drugs and its activity was similar in A431Pt cells and in their sensitive A431 counterpart. The combination of the platinating drugs with CGA (10(-6) - 10(-4) M) indicated variable effects on cytotoxicity, ranging from potentiation to various degrees of antagonism (in A431 cells) and no effect (in A431Pt cells). In order to explain the different cytotoxic activity elicited by oxaliplatin and cisplatin in association with CGA, the possible presence of chemical interactions was investigated by HPLC analysis. The drug association with CGA caused evident changes in their chromatographic profile, suggesting occurrence of in vitro chemical interactions.

Effect of Quercetin on Cell Cycle and Cyclin Expression in Ovarian Carcinoma and Osteosarcoma Cell Lines.

Resistance to chemotherapeutic drugs is a major problem in cancer treatment. The search for new interventions able to overcome this resistance may involve compounds of natural origin, such as flavonoids, ubiquitously present in many foods. In the present study, the cytotoxic effects and cell cycle modulation of the flavonoid quercetin were investigated in ovarian carcinoma (SKOV3) and osteosarcoma (U2OS) human cell lines and in their cisplatin (CDDP)-resistant counterparts (SKOV3/CDDP and U2OSPt cells, respectively). Quercetin (10-50 µM) caused evident changes in the distribution of cell cycle phases in the CDDP-resistant SKOV3/CDDP ovarian cell line. The levels of cyclin D1 and cyclin B1 were determined by means of Western blot in all cell lines incubated with quercetin (50 µM) for 48 hours. The cyclin D1 expression was significantly decreased following the treatment with quercetin in SKOV3 and U2OSPt cells, but not in SKOV3/CDDP and U2OS cells. The reduction of cyclin D1 level could be linked to the G1/S phase alteration found in quercetin-treated cells. Although cyclin B1 is required for G2/M phase, and despite our observation that quercetin influenced the G2/M phase of cell cycle, the flavonoid did not affect cyclin B1 levels in all cell lines, indicating the involvement of other possible mechanisms. These results suggest that quercetin, exceeding the resistance to CDDP, might become an interesting tool to evaluate cytotoxic activity in combination with chemotherapy drugs.

Cell cycle control by natural phenols in cisplatin-resistant cell lines.

Fifteen plant polyphenols, including flavonoids, cinnamic acids, coumarins and capsaicin, were investigated for their capacity to suppress cell growth and regulate the cell cycle of in vitro human ovarian carcinoma (2008 cell line) and cervix squamous carcinoma cells (A431), and their cisplatin (CDDP)-resistant subclones (C13 and A431Pt, respectively). Evaluation of the cytotoxic effects of the polyphenols (0.01-100 µM) indicated that especially rhein and quercetin were almost equiactive in wild type and CDDP-resistant cells, indicating lack of cross-resistance with cisplatin. Capsaicin was more potent in CDDP-resistant subclones than in wild type cells. The order of their potencies is flavonoids > anthraquinones > vanilloids > coumarins > phenols, cinnamic acids. The natural phenols which were most cytotoxic (rhein, quercetin and capsaicin) were able to cause the arrest of the cancer cell cycle, suggesting that specific cell cycle regulatory proteins are possibly involved in their intracellular mechanism of action. In particular, the natural compounds were revealed to be more active in CDDP-resistant cells than in wild types, especially inducing apoptotic death.