The Concerted Action of Mitochondrial Dynamics and Positioning: New Characters in Cancer Onset and Progression

Nitric oxide-dependent cell death in glioblastoma and squamous cell carcinoma via prodeath mitochondrial clustering

Besides the fission-fusion dynamics, the cellular distribution of mitochondria has recently emerged as a critical biological parameter in regulating mitochondrial function and cell survival. We previously found that mitochondrial clustering on the nuclear periphery, or monopolar perinuclear mitochondrial clustering (MPMC), accompanies the anticancer activity of air plasma-activated medium (APAM) against glioblastoma and human squamous cell carcinoma, which is closely associated with oxidant-dependent tubulin remodeling and mitochondrial fragmentation. Accordingly, this study investigated the regulatory roles of nitric oxide (NO) in the anticancer activity of APAM. Time-lapse analysis revealed a time-dependent increase in NO accompanied by MPMC. In contrast, APAM caused minimal increases in MPMC and NO levels in nontransformed cells. NO, hydroxyl radicals, and lipid peroxide levels increased near the damaged nuclear periphery, possibly within mitochondria. NO scavenging prevented tubulin remodeling, MPMC, perinuclear oxidant production, nuclear damage, and cell death. Conversely, synthetic NO donors augmented all the prodeath events and acted synergistically with APAM. Salinomycin, an emerging drug against multidrug-resistant cancers, had similar NO-dependent effects. These results suggest that APAM and salinomycin induce NO-dependent cell death, where MPMC and oxidative mitochondria play critical roles. Our findings encourage further investigations on MPMC as a potential target for NO-driven anticancer agents against drug-resistant cancers.

Ozone mediates the anticancer effect of air plasma by triggering oxidative cell death caused by H2O2 and iron

Cold atmospheric plasmas and plasma-treated solutions (PTSs) have emerged as promising approaches in cancer treatment because of their tumor-selective actions. While oxidative stress is critical for their effects, the precise mechanisms, including chemical mediators, remain obscure. Previously, we reported that air plasma-activated medium (APAM) exhibited tumor-selective anticancer activity. The fragmentation of mitochondria and their asymmetrical assembly around the peripheral regions of the damaged nucleus, namely, monopolar perinuclear mitochondrial clustering (MPMC), proceed to the effect. Subsequently, we found that APAM had a substantial amount of O3 in addition to hydrogen peroxide (H2O2), nitrile (NO2-), and nitrate (NO3-). In the present study, we investigated the possible role of O3 in the anticancer effect. For this purpose, we created a nitrogen oxide-free ozonated medium ODM. ODM exhibited potent cytotoxicity against various cancer but not nonmalignant cells. ODM also increased MPMC, hydroxyl radicals, lipid peroxides, and their shifts to perinuclear sites in cancer cells. Catalase and iron chelation prevented these events and cytotoxicity. ODM also decreases the intracellular labile irons while increasing those within mitochondria. ODM had substantial H2O2, but this oxidant failed to cause MPMC and cytotoxicity. These results show that ODM can mimic the effects of APAM, including MPMC and tumor-selective anticancer effects. The findings suggest that O3 is critical in mediating the anticancer effects of APAM by triggering oxidative cell death caused by H2O2 and iron.

Melatonin as a therapeutic agent for alleviating endothelial dysfunction in cardiovascular diseases: Emphasis on oxidative stress

The vascular endothelium is vital in maintaining cardiovascular health by regulating vascular permeability and tone, preventing thrombosis, and controlling vascular inflammation. However, when oxidative stress triggers endothelial dysfunction, it can lead to chronic cardiovascular diseases (CVDs). This happens due to oxidative stress-induced mitochondrial dysfunction, inflammatory responses, and reduced levels of nitric oxide. These factors cause damage to endothelial cells, leading to the acceleration of CVD progression. Melatonin, a natural antioxidant, has been shown to inhibit oxidative stress and stabilize endothelial function, providing cardiovascular protection. The clinical application of melatonin in the prevention and treatment of CVDs has received widespread attention. In this review, based on bibliometric studies, we first discussed the relationship between oxidative stress-induced endothelial dysfunction and CVDs, then summarized the role of melatonin in the treatment of atherosclerosis, hypertension, myocardial ischemia-reperfusion injury, and other CVDs. Finally, the potential clinical use of melatonin in the treatment of these diseases is discussed.

Key hepatoprotective roles of mitochondria in liver regeneration

Treatment of advanced liver disease using surgical modalities is possible due to the liver's innate ability to regenerate following resection. Several key cellular events in the regenerative process converge at the mitochondria, implicating their crucial roles in liver regeneration. Mitochondria enable the regenerating liver to meet massive metabolic demands by coordinating energy production to drive cellular proliferative processes and vital homeostatic functions. Mitochondria are also involved in terminating the regenerative process by mediating apoptosis. Studies have shown that attenuation of mitochondrial activity results in delayed liver regeneration, and liver failure following resection is associated with mitochondrial dysfunction. Emerging mitochondria therapy (i.e., mitotherapy) strategies involve isolating healthy donor mitochondria for transplantation into diseased organs to promote regeneration. This review highlights mitochondria's inherent role in liver regeneration.

The Therapeutic Strategies Targeting Mitochondrial Metabolism in Cardiovascular Disease

Cardiovascular disease (CVD) is a group of systemic disorders threatening human health with complex pathogenesis, among which mitochondrial energy metabolism reprogramming has a critical role. Mitochondria are cell organelles that fuel the energy essential for biochemical reactions and maintain normal physiological functions of the body. Mitochondrial metabolic disorders are extensively involved in the progression of CVD, especially for energy-demanding organs such as the heart. Therefore, elucidating the role of mitochondrial metabolism in the progression of CVD is of great significance to further understand the pathogenesis of CVD and explore preventive and therapeutic methods. In this review, we discuss the major factors of mitochondrial metabolism and their potential roles in the prevention and treatment of CVD. The current application of mitochondria-targeted therapeutic agents in the treatment of CVD and advances in mitochondria-targeted gene therapy technologies are also overviewed.

Air Plasma-Activated Medium Evokes a Death-Associated Perinuclear Mitochondrial Clustering

Intractable cancers such as osteosarcoma (OS) and oral cancer (OC) are highly refractory, recurrent, and metastatic once developed, and their prognosis is still disappointing. Tumor-targeted therapy, which eliminates cancers effectively and safely, is the current clinical choice. Since aggressive tumors are substantially resistant to multidisciplinary therapies that target apoptosis, tumor-specific activation of another cell death modality is a promising avenue for meeting this goal. Here, we report that a cold atmospheric air plasma-activated medium (APAM) can kill OS and OC by causing a unique mitochondrial clustering. This event was named monopolar perinuclear mitochondrial clustering (MPMC) based on its characteristic unipolar mitochondrial perinuclear accumulation. The APAM caused apoptotic and nonapoptotic cell death. The APAM increased mitochondrial ROS (mROS) and cell death, and the antioxidants such as N-acetylcysteine (NAC) prevented them. MPMC occurred following mitochondrial fragmentation, which coincided with nuclear damages. MPMC was accompanied by mitochondrial lipid peroxide (mLPO) accumulation and prevented by NAC, Ferrostatin-1, and Nocodazole. In contrast, the APAM induced minimal cell death, mROS generation, mLPO accumulation, and MPMC in fibroblasts. These results suggest that MPMC occurs in a tumor-specific manner via mitochondrial oxidative stress and microtubule-driven mitochondrial motility. MPMC induction might serve as a promising target for exerting tumor-specific cytotoxicity.

Ultrastructural changes in cristae of lymphoblasts in acute lymphoblastic leukemia parallel alterations in biogenesis markers

We explored the link between mitochondrial biogenesis and mitochondrial morphology using transmission electron microscopy (TEM) in lymphoblasts of pediatric acute lymphoblastic leukemia (ALL) patients and compared these characteristics between tumors and control samples. Gene expression of mitochondrial biogenesis markers was analysed in 23 ALL patients and 18 controls and TEM for morphology analysis was done in 15 ALL patients and 9 healthy controls. The area occupied by mitochondria per cell and the cristae cross-sectional area was observed to be significantly higher in patients than in controls (p-value = 0.0468 and p-value< 0.0001, respectively). The mtDNA copy numbers, TFAM, POLG, and c-myc gene expression were significantly higher in ALL patients than controls (all p-values< 0.01). Gene Expression of PGC-1α was higher in tumor samples. The analysis of the correlation between PGC-1α expression and morphology parameters i.e., both M/C ratio and cristae cross-sectional area revealed a positive trend (r = 0.3, p = 0.1). The increased area occupied by mitochondria and increased cristae area support the occurrence of cristae remodelling in ALL. These changes might reflect alterations in cristae dynamics to support the metabolic state of the cells by forming a more condensed network. Ultrastructural imaging can be useful for affirming changes occurring at a subcellular organellar level.

Mitochondria and Their Relationship with Common Genetic Abnormalities in Hematologic Malignancies

Hematologic malignancies are known to be associated with numerous cytogenetic and molecular genetic changes. In addition to morphology, immunophenotype, cytochemistry and clinical characteristics, these genetic alterations are typically required to diagnose myeloid, lymphoid, and plasma cell neoplasms. According to the current World Health Organization (WHO) Classification of Tumors of Hematopoietic and Lymphoid Tissues, numerous genetic changes are highlighted, often defining a distinct subtype of a disease, or providing prognostic information. This review highlights how these molecular changes can alter mitochondrial bioenergetics, cell death pathways, mitochondrial dynamics and potentially be related to mitochondrial genetic changes. A better understanding of these processes emphasizes potential novel therapies.

Naked mole-rat brown fat thermogenesis is diminished during hypoxia through a rapid decrease in UCP1

Naked mole-rats are among the most hypoxia-tolerant mammals. During hypoxia, their body temperature (T_b) decreases via unknown mechanisms to conserve energy. In small mammals, non-shivering thermogenesis in brown adipose tissue (BAT) is critical to T_b regulation; therefore, we hypothesize that hypoxia decreases naked mole-rat BAT thermogenesis. To test this, we measure changes in T_b during normoxia and hypoxia (7% O₂; 1-3 h). We report that interscapular thermogenesis is high in normoxia but ceases during hypoxia, and T_b decreases. Furthermore, in BAT from animals treated in hypoxia, UCP1 and mitochondrial complexes I-V protein expression rapidly decrease, while mitochondria undergo fission, and apoptosis and mitophagy are inhibited. Finally, UCP1 expression decreases in hypoxia in three other social African mole-rat species, but not a solitary species. These findings suggest that the ability to rapidly down-regulate thermogenesis to conserve oxygen in hypoxia may have evolved preferentially in social species.

Miro1 functions as an inhibitory regulator of MFN at elevated mitochondrial Ca2+ levels

Mitochondria function as an integrated network that moves along the microtubules within cells and changes the morphology through membrane fusion and fission events. Mitofusin (MFN) mediates membrane tethering and subsequent fusion of the mitochondrial outer membrane. Understanding the regulatory mechanisms of MFN function is critical to tackling the pathology related to mitochondrial network imbalance. Here, we reveal a novel inhibitory mechanism of MFN-mediated fusion by mitochondrial Rho GTPase (Miro1) in response to elevated mitochondrial Ca²⁺ concentration ([Ca²⁺ ]_m ). We showed that elevated [Ca²⁺ ]_m prevents the fusion between mitochondria forming the outer membrane tether by ectopically expressing MFN. Lowering [Ca²⁺ ]_m by treating cells with an inhibitor of mitochondrial calcium uniporter or knocking down Miro1/2 induces more fused networks. Miro1 interacts with MFN as supported by co-immunoprecipitation and protein association identified by proximity labeling proteomics. It suggests that Miro1 functions as a Ca²⁺ -sensor and inhibits MFN function at elevated [Ca²⁺ ]_m. Miro1 EF-hand mutant has a compromised inhibitory effect, which reiterates Ca²⁺ -modulated regulation. Dysregulated Ca²⁺ -handling and mitochondrial network imbalance are highly relevant in the pathology of cancers, cardiovascular, and neurodegenerative diseases. Miro1 functions as a coordinated Ca²⁺ -responder by pausing mitochondrial transport while reducing network fusion and cooperating with Drp1-mediated fission. It likely prevents the detrimental effect of Ca²⁺ _m overload and facilitates mitophagy. Our finding reveals a novel regulation of mitochondrial network dynamics responding to [Ca²⁺ ]_m through the interplay of Miro1 and MFN. Modulation of Miro1 and MFN interaction is a potential intervention to promote network homeostasis.

Combined Anticancer Effect of Plasma-Activated Infusion and Salinomycin by Targeting Autophagy and Mitochondrial Morphology

Non-thermal atmospheric pressure plasma (NTAPP)-activated liquids have emerged as new promising anticancer agents because they preferentially injure malignant cells. Here, we report plasma-activated infusion (PAI) as a novel NTAPP-based anti-neoplastic agent. PAI was prepared by irradiating helium NTAP to form a clinically approved infusion fluid. PAI dose-dependently killed malignant melanoma and osteosarcoma cell lines while showing much lower cytotoxic effects on dermal and lung fibroblasts. We found that PAI and salinomycin (Sal), an emerging anticancer stem cell agent, mutually operated as adjuvants. The combined administration of PAI and Sal was much more effective than single-agent application in reducing the growth and lung metastasis of osteosarcoma allografts with minimal adverse effects. Mechanistically, PAI explicitly induced necroptosis and increased the phosphorylation of receptor-interacting protein 1/3 rapidly and transiently. PAI also suppressed the ambient autophagic flux by activating the mammalian target of the rapamycin pathway. PAI increased the phosphorylation of Raptor, Rictor, and p70-S6 kinase, along with decreased LC3-I/II expression. In contrast, Sal promoted autophagy. Moreover, Sal exacerbated the mitochondrial network collapse caused by PAI, resulting in aberrant clustering of fragmented mitochondrial in a tumor-specific manner. Our findings suggest that combined administration of PAI and Sal is a promising approach for treating these apoptosis-resistant cancers.

Effect of Reactive Oxygen Species on the Endoplasmic Reticulum and Mitochondria during Intracellular Pathogen Infection of Mammalian Cells

Oxidative stress, particularly reactive oxygen species (ROS), are important for innate immunity against pathogens. ROS directly attack pathogens, regulate and amplify immune signals, induce autophagy and activate inflammation. In addition, production of ROS by pathogens affects the endoplasmic reticulum (ER) and mitochondria, leading to cell death. However, it is unclear how ROS regulate host defense mechanisms. This review outlines the role of ROS during intracellular pathogen infection, mechanisms of ROS production and regulation of host defense mechanisms by ROS. Finally, the interaction between microbial pathogen-induced ROS and the ER and mitochondria is described.

Mitochondrial metabolism in regulating macrophage polarization: an emerging regulator of metabolic inflammatory diseases

As a major type of immune cells with heterogeneity and plasticity, macrophages are classically divided into inflammatory (M1) and alternative/anti-inflammatory (M2) types and play a crucial role in the progress of the inflammatory diseases. Recent studies have shown that metabolism is an important determinant of macrophage phenotype. Mitochondria, one of the most important compartments involving cell metabolism, are closely associated with the regulation of cell functions. In most types of cell, mitochondrial oxidative phosphorylation (OXPHOS) is the primary mode of cellular energy production. However, mitochondrial OXPHOS is inhibited in activated M1 macrophages, rendering them unable to be converted into M2 phenotype. Thus, mitochondrial metabolism is a crucial regulator in macrophage functions. This review summarizes the roles of mitochondria in macrophage polarization and analyzes the molecular mechanisms underlying mitochondrial metabolism and function, which may provide new approaches for the treatment of metabolic inflammatory diseases.

NF-κB and mitochondria cross paths in cancer: mitochondrial metabolism and beyond

NF-κB plays a pivotal role in oncogenesis. This transcription factor is best known for promoting cancer cell survival and tumour-driving inflammation. However, several lines of evidence support a crucial role for NF-κB in governing energy homeostasis and mediating cancer metabolic reprogramming. Mitochondria are central players in many metabolic processes altered in cancer. Beyond their bioenergetic activity, several facets of mitochondria biology, including mitochondrial dynamics and oxidative stress, promote and sustain malignant transformation. Recent reports revealed an intimate connection between NF-κB pathway and the oncogenic mitochondrial functions. NF-κB can impact mitochondrial respiration and mitochondrial dynamics, and, reciprocally, mitochondria can sense stress signals and convert them into cell biological responses leading to NF-κB activation. In this review we discuss their emerging reciprocal regulation and the significance of this interplay for anticancer therapy.

TPP-related mitochondrial targeting copper (II) complex induces p53-dependent apoptosis in hepatoma cells through ROS-mediated activation of Drp1

Background

In recent years, copper complexes have gradually become the focus of potential anticancer drugs due to their available redox properties and low toxicity. In this study, a novel mitochondrion-targeting copper (II) complex, [Cu (ttpy-tpp)Br₂] Br (simplified as CTB), is first synthesized by our group. CTB with tri-phenyl-phosphine (TPP), a targeting and lipophilic group, can cross the cytoplasmic and mitochondrial membranes of tumor cells. The present study aims to investigate how CTB affects mitochondrial functions and exerts its anti-tumor activity in hepatoma cells.

Methods

Multiple molecular experiments including Flow cytometry, Western blot, Immunofluorescence, Tracker staining, Transmission Electron Microscopy and Molecular docking simulation were used to elucidate the underlying mechanisms. Human hepatoma cells were subcutaneously injected into right armpit of male nude mice for evaluating the effects of CTB in vivo.

Results

CTB induced apoptosis via collapse of mitochondrial membrane potential (MMP), ROS production, Bax mitochondrial aggregation as well as cytochrome c release, indicating that CTB-induced apoptosis was associated with mitochondrial pathway in human hepatoma cells. Mechanistic study revealed that ROS-related mitochondrial translocation of p53 was involved in CTB-mediated apoptosis. Simultaneously, elevated mitochondrial Drp1 levels were also observed, and interruption of Drp1 activation played critical role in p53-dependent apoptosis. CTB also strongly suppressed the growth of liver cancer xenografts in vivo.

Conclusion

In human hepatoma cells, CTB primarily induces mitochondrial dysfunction and promotes accumulation of ROS, leading to activation of Drp1. These stimulation signals accelerate mitochondrial accumulation of p53 and lead to the eventual apoptosis. Our research shows that CTB merits further evaluation as a chemotherapeutic agent for the treatment of Hepatocellular carcinoma (HCC).

Monitoring and Determining Mitochondrial Network Parameters in Live Lung Cancer Cells

Mitochondria are dynamic organelles that constantly fuse and divide, forming dynamic tubular networks. Abnormalities in mitochondrial dynamics and morphology are linked to diverse pathological states, including cancer. Thus, alterations in mitochondrial parameters could indicate early events of disease manifestation or progression. However, finding reliable and quantitative tools for monitoring mitochondria and determining the network parameters, particularly in live cells, has proven challenging. Here, we present a 2D confocal imaging-based approach that combines automatic mitochondrial morphology and dynamics analysis with fractal analysis in live small cell lung cancer (SCLC) cells. We chose SCLC cells as a test case since they typically have very little cytoplasm, but an abundance of smaller mitochondria compared to many of the commonly used cell types. The 2D confocal images provide a robust approach to quantitatively measure mitochondrial dynamics and morphology in live cells. Furthermore, we performed 3D reconstruction of electron microscopic images and show that the 3D reconstruction of the electron microscopic images complements this approach to yield better resolution. The data also suggest that the parameters of mitochondrial dynamics and fractal dimensions are sensitive indicators of cellular response to subtle perturbations, and hence, may serve as potential markers of drug response in lung cancer.

Mitochondria as playmakers of apoptosis, autophagy and senescence

Mitochondria are the key energy-producing organelles and cellular source of reactive species. They are responsible for managing cell life and death by a balanced homeostasis passing through a network of structures, regulated principally via fission and fusion. Herein we discuss about the most advanced findings considering mitochondria as dynamic biophysical systems playing compelling roles in the regulation of energy metabolism in both physiologic and pathologic processes controlling cell death and survival. Precisely, we focus on the mitochondrial commitment to the onset, maintenance and counteraction of apoptosis, autophagy and senescence in the bioenergetic reprogramming of cancer cells. In this context, looking for a pharmacological manipulation of cell death processes as a successful route for future targeted therapies, there is major biotechnological challenge in underlining the location, function and molecular mechanism of mitochondrial proteins. Based on the critical role of mitochondrial functions for cellular health, a better knowledge of the main molecular players in mitochondria disfunction could be decisive for the therapeutical control of degenerative diseases, including cancer.

A Bridge of Light: Toward Chinese and Western Medicine Perspectives Through Ultraweak Photon Emissions

The gap between Western medicine and traditional Chinese medicine (CM) is closely related to the diversity in culture, philosophy, and scientific developments. Although numerous studies have evaluated the efficacy of acupuncture, the gap in explanatory disease models has not been bridged so far. Developments in research of ultraweak photon emission (UPE) and organized dynamics of metabolism and its relationship with technological advances in metabolomics have created the conditions to bring the basics of the medicines of the West and East together which might open the avenue for a scientific dialogue. The paper discusses (1) the UPE in relation to Qi energy, meridians and acupuncture points in CM, (2) the biochemical explanation of photon emission of living systems in Western biomedicine, and (3) the progress in research on the large-scale organization and dynamics of the metabolic network including photon metabolism.

Autophagy inhibitors regulate TRAIL sensitivity in human malignant cells by targeting the mitochondrial network and calcium dynamics

In a variety of cancer cell types, the pharmacological and genetic blockade of autophagy increases apoptosis induced by various anticancer drugs. These observations suggest that autophagy counteracts drug-induced apoptosis. We previously reported that in human melanoma and osteosarcoma cells, autophagy inhibitors, such as 3-methyladenine and chloroquine increased the sensitivity to apoptosis induced by tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). In the present study, we report that different autophagy inhibitors regulate the mitochondrial network and calcium (Ca²⁺) dynamics in these cells. We found that compared to tumor cells, normal fibroblasts were more resistant to the cytotoxicity of TRAIL and autophagy inhibitors used either alone or in combination. Notably, TRAIL increased the autophagic flux in the tumor cells, but not in the fibroblasts. Live-cell imaging revealed that in tumor cells, TRAIL evoked modest mitochondrial fragmentation, while subtoxic concentrations of the autophagy inhibitors led to mitochondrial fusion. Co-treatment with TRAIL and subtoxic concentrations of the autophagy inhibitors resulted in severe mitochondrial fragmentation, swelling and clustering, similar to what was observed with autophagy inhibitors at toxic concentrations. The enhanced aberration of the mitochondrial network was preceded by a reduction in mitochondrial Ca²⁺ loading and store-operated Ca²⁺ entry. On the whole, the findings of this study indicate that co-treatment with TRAIL and autophagy inhibitors leads to increased mitochondrial Ca²⁺ and network dysfunction in a tumor-selective manner. Therefore, the co-administration of TRAIL and autophagy inhibitors may prove to be a promising tumor-targeting approach for the treatment of TRAIL-resistant cancer cells.

Rapid quantification of mitochondrial fractal dimension in individual cells

An improved technique for fractal characterization called the modified blanket method is introduced that can quantify surrounding fractal structures on a pixel by pixel basis without artifacts associated with scale-dependent image features such as object size. The method interprets images as topographical maps, obtaining information regarding the local surface area as a function of image resolution. Local fractal dimension (FD) can be quantified from the power law exponent derived from the surface area and image resolution relationship. We apply this technique on simulated cell images of known FD and compared the obtained values to power spectral density (PSD) analysis. Our method is sensitive to a wider FD range (2.0-4.5), having a mean error of 1.4% compared to 6% for PSD analysis. This increased sensitivity and an ability to compute regional FD properties enabled the discrimination of the differences in radiation resistant cancer cell responses that could not be detected using PSD analysis.

Calcium, mitochondria and cell metabolism: A functional triangle in bioenergetics

The versatility of mitochondrial metabolism and its fine adjustments to specific physiological or pathological conditions regulate fundamental cell pathways, ranging from proliferation to apoptosis. In particular, Ca²⁺ signalling has emerged as a key player exploited by mitochondria to tune their activity according with cell demand. The functional interaction between mitochondria and endoplasmic reticulum (ER) deeply impacts on the correct mitochondrial Ca²⁺ signal, thus modulating cell bioenergetics and functionality. Indeed, Ca²⁺ released by the ER is taken up by mitochondria where, both in the intermembrane space and in the matrix, it regulates the activity of transporters, enzymes and proteins involved in organelles' metabolism. In this review, we will briefly summarize Ca²⁺-dependent mechanisms involved in the regulation of mitochondrial activity. Moreover, we will discuss some recent reports, in which alterations in mitochondrial Ca²⁺ signalling have been associated with specific pathological conditions, such as neurodegeneration and cancer.

Salvianolic acid B renders glioma cells more sensitive to radiation via Fis-1-mediated mitochondrial dysfunction

Glioma remains the leading cause of brain tumor-related death worldwide, and radiation is a standard adjuvant therapy with proven efficacy. Salvianolic acid B (SalB), a bioactive compound isolated from Radix Salviae, has been shown to exert anti-cancer effects in many cancer cell lines, including glioma. This study aimed to investigate whether SalB could affect response to radiation in human glioma cells. We found that SalB decreased cell viability of U87 cells in a-dose-dependent manner. A subthreshold dose of SalB at 0.5 μM, which had no effect on cell viability and apoptosis, significantly increased radiation sensitivity of U87 cells in a dose- and time-dependent manner, but had no effect on sensitivity to temozolomide (TMZ). Similar results were also observed in human glioma U373 cells. In addition, SalB aggravated the radiation-induced apoptosis and mitochondrial dysfunction, as measured by mitochondrial Ca²⁺ buffering capacity and mitochondrial swelling. SalB treatment markedly promoted mitochondrial fission and differently regulated the expression of fission proteins. Furthermore, downregulation of the fission protein Fis-1 using siRNA was found to partially reversed the SalB-induced effects on cell viability, apoptosis and mitochondrial fission in U87 cells. In conclusion, our results suggest that a subthreshold dose of SalB renders glioma cells more sensitive to radiation via Fis-1-mediated mitochondrial dysfunction, and radiotherapy combined with SalB might be a novel treatment for glioma patients.

The Role of Mitochondrial H+-ATP Synthase in Cancer

Cancer cells reprogram energy metabolism by boosting aerobic glycolysis as a main pathway for the provision of metabolic energy and of precursors for anabolic purposes. Accordingly, the relative expression of the catalytic subunit of the mitochondrial H⁺-ATP synthase—the core hub of oxidative phosphorylation—is downregulated in human carcinomas when compared with its expression in normal tissues. Moreover, some prevalent carcinomas also upregulate the ATPase inhibitory factor 1 (IF1), which is the physiological inhibitor of the H⁺-ATP synthase. IF1 overexpression, both in cells in culture and in tissue-specific mouse models, is sufficient to reprogram energy metabolism to an enhanced glycolysis by limiting ATP production by the H⁺-ATP synthase. Furthermore, the IF1-mediated inhibition of the H⁺-ATP synthase promotes the production of mitochondrial ROS (mtROS). mtROS modulate signaling pathways favoring cellular proliferation and invasion, the activation of antioxidant defenses, resistance to cell death, and modulation of the tissue immune response, favoring the acquisition of several cancer traits. Consistently, IF1 expression is an independent marker of cancer prognosis. By contrast, inhibition of the H⁺-ATP synthase by α-ketoglutarate and the oncometabolite 2-hydroxyglutarate, reduces mTOR signaling, suppresses cancer cell growth, and contributes to lifespan extension in several model organisms. Hence, the H⁺-ATP synthase appears as a conserved hub in mitochondria-to-nucleus signaling controlling cell fate. Unraveling the molecular mechanisms responsible for IF1 upregulation in cancer and the signaling cascades that are modulated by the H⁺-ATP synthase are of utmost interest to decipher the metabolic and redox circuits contributing to cancer origin and progression.

Mitofusin 2: from functions to disease

Mitochondria are highly dynamic organelles whose functions are essential for cell viability. Within the cell, the mitochondrial network is continuously remodeled through the balance between fusion and fission events. Moreover, it dynamically contacts other organelles, particularly the endoplasmic reticulum, with which it enterprises an important functional relationship able to modulate several cellular pathways. Being mitochondria key bioenergetics organelles, they have to be transported to all the specific high-energy demanding sites within the cell and, when damaged, they have to be efficiently removed. Among other proteins, Mitofusin 2 represents a key player in all these mitochondrial activities (fusion, trafficking, turnover, contacts with other organelles), the balance of which results in the appropriate mitochondrial shape, function, and distribution within the cell. Here we review the structural and functional properties of Mitofusin 2, highlighting its crucial role in several cell pathways, as well as in the pathogenesis of neurodegenerative diseases, metabolic disorders, cardiomyopathies, and cancer.

Reactive Oxygen Species and Mitochondrial Dynamics: The Yin and Yang of Mitochondrial Dysfunction and Cancer Progression

Mitochondria are organelles with a highly dynamic ultrastructure maintained by a delicate equilibrium between its fission and fusion rates. Understanding the factors influencing this balance is important as perturbations to mitochondrial dynamics can result in pathological states. As a terminal site of nutrient oxidation for the cell, mitochondrial powerhouses harness energy in the form of ATP in a process driven by the electron transport chain. Contemporaneously, electrons translocated within the electron transport chain undergo spontaneous side reactions with oxygen, giving rise to superoxide and a variety of other downstream reactive oxygen species (ROS). Mitochondrially-derived ROS can mediate redox signaling or, in excess, cause cell injury and even cell death. Recent evidence suggests that mitochondrial ultrastructure is tightly coupled to ROS generation depending on the physiological status of the cell. Yet, the mechanism by which changes in mitochondrial shape modulate mitochondrial function and redox homeostasis is less clear. Aberrant mitochondrial morphology may lead to enhanced ROS formation, which, in turn, may deteriorate mitochondrial health and further exacerbate oxidative stress in a self-perpetuating vicious cycle. Here, we review the latest findings on the intricate relationship between mitochondrial dynamics and ROS production, focusing mainly on its role in malignant disease.

Highlighting the endoplasmic reticulum-mitochondria connection: Focus on Mitofusin 2

The endoplasmic reticulum (ER) and the mitochondrial network are two highly interconnected cellular structures. By proteinaceous tethers, specialized membrane domains of the ER are tightly associated with the outer membrane of mitochondria, allowing the assembly of signaling platforms where different cell functions take place or are modulated, such as lipid biosynthesis, Ca²⁺ homeostasis, inflammation, autophagy and apoptosis. The ER-mitochondria coupling is highly dynamic and contacts between the two organelles can be modified in their number, extension and thickness by different stimuli. Importantly, several pathological conditions, such as cancer, neurodegenerative diseases and metabolic syndromes show alterations in this feature, underlining the key role of ER-mitochondria crosstalk in cell physiology. In this contribution, we will focus on one of the major modulator of ER-mitochondria apposition, Mitofusin 2, discussing the structure of the protein and its debated role on organelles tethering. Moreover, we will critically describe different techniques commonly used to investigate this crucial issue, highlighting their advantages, drawbacks and limits.