Cell-cycle arrest at G2/M and proliferation inhibition by adenovirus-expressed mitofusin-2 gene in human colorectal cancer cell lines

The mitochondrial fusion-associated protein MFN2 can be used as a novel prognostic molecule for clear cell renal cell carcinoma

BACKGROUND

Mitofusin 2 (MFN2) plays an important role in many tumors, but how its role in renal clear cell carcinoma needs further research.

METHODS

In this study, we analyzed the expression of MFN2 in renal clear cell carcinoma tissues and normal kidney tissues through the Cancer Genome Atlas (TCGA) database and our clinical samples.Enrichment analysis was performed to determine MFN2-related pathways and biological functions. The correlation of MFN2 expression with immune cells was analyzed.The correlation of the expression of methylation and the methylation sites of MFN2 were analyzed by UALCAN and TCGA databases. Univariate / multivariate COX risk regression and Kaplan-Meier methods were used to determine the prognostic value of MFN2.Nomograms were drawn to predict overall survival (OS) at 1,3, and 5 years. We investigated the role of MFN2 in renal cancer cells using CCK 8, clone formation, wound healing assay, and methylase qPCR experiments.

RESULTS

MFN2 is poorly expressed in renal clear cell carcinoma compared to normal kidney tissue,and is significantly negatively associated with TNM stage, histological grade and pathological stage.MFN2 was directly associated with OS after multivariate Cox regression analysis.MFN2 shows a hypomethylation state and shows a positive correlation with multiple methylation sites.Signaling pathways through functional enrichment to B-cell receptors and oxidative stress-induced senescence.Moreover, the low expression of MFN2 was positively correlated with the degree of immune cell infiltration in a variety of immune cells.In vitro experiments showed that overexpression of MFN2 significantly inhibited the proliferation and migration of renal clear cells and promoted methylation.

CONCLUSIONS

In conclusion, MFN2 can be used as a novel prognostic marker for renal clear cell carcinoma and requires further investigation of its role in tumor development.

Mitochondrial Dynamics and Cristae Shape Changes During Metabolic Reprogramming

Significance: The architecture of the mitochondrial network and cristae critically impact cell differentiation and identity. Cells undergoing metabolic reprogramming to aerobic glycolysis (Warburg effect), such as immune cells, stem cells, and cancer cells, go through controlled modifications in mitochondrial architecture, which is critical for achieving the resulting cellular phenotype. Recent Advances: Recent studies in immunometabolism have shown that the manipulation of mitochondrial network dynamics and cristae shape directly affects T cell phenotype and macrophage polarization through altering energy metabolism. Similar manipulations also alter the specific metabolic phenotypes that accompany somatic reprogramming, stem cell differentiation, and cancer cells. The modulation of oxidative phosphorylation activity, accompanied by changes in metabolite signaling, reactive oxygen species generation, and adenosine triphosphate levels, is the shared underlying mechanism. Critical Issues: The plasticity of mitochondrial architecture is particularly vital for metabolic reprogramming. Consequently, failure to adapt the appropriate mitochondrial morphology often compromises the differentiation and identity of the cell. Immune, stem, and tumor cells exhibit striking similarities in their coordination of mitochondrial morphology with metabolic pathways. However, although many general unifying principles can be observed, their validity is not absolute, and the mechanistic links thus need to be further explored. Future Directions: Better knowledge of the molecular mechanisms involved and their relationships to both mitochondrial network and cristae morphology will not only further deepen our understanding of energy metabolism but may also contribute to improved therapeutic manipulation of cell viability, differentiation, proliferation, and identity in many different cell types. Antioxid. Redox Signal. 39, 684-707.

Mitochondrial remodeling in colorectal cancer initiation, progression, metastasis, and therapy: A review

Colorectal cancer (CRC) is a major health concern with multifactorial pathophysiology representing intense therapeutic challenges. It is well known that deregulation of spatiotemporally-controlled signaling pathways and their metabolic reprogramming effects play a pivotal role in the development and progression of CRC. As such, the mitochondrial role in CRC initiation gained a lot of attention recently, as it is considered the powerhouse that regulates the bioenergetics in CRC. In addition, the crosstalk between microRNAs (miRNAs) and mitochondrial dysfunction has become a newfangled passion for deciphering CRC molecular mechanisms. This review sheds light on the relationship between different signaling pathways involved in metabolic reprogramming and their therapeutic targets, alterations in mitochondrial DNA content, mitochondrial biogenesis, and mitophagy, and the role of polymorphisms in mitochondrial genes as well as miRNAs regulating mitochondrial proteins in CRC initiation, progression, metastasis, and resistance to various therapies.

Exploring Core Genes by Comparative Transcriptomics Analysis for Early Diagnosis, Prognosis, and Therapies of Colorectal Cancer

Colorectal cancer (CRC) is one of the most common cancers with a high mortality rate. Early diagnosis and therapies for CRC may reduce the mortality rate. However, so far, no researchers have yet investigated core genes (CGs) rigorously for early diagnosis, prognosis, and therapies of CRC. Therefore, an attempt was made in this study to explore CRC-related CGs for early diagnosis, prognosis, and therapies. At first, we identified 252 common differentially expressed genes (cDEGs) between CRC and control samples based on three gene-expression datasets. Then, we identified ten cDEGs (AURKA, TOP2A, CDK1, PTTG1, CDKN3, CDC20, MAD2L1, CKS2, MELK, and TPX2) as the CGs, highlighting their mechanisms in CRC progression. The enrichment analysis of CGs with GO terms and KEGG pathways revealed some crucial biological processes, molecular functions, and signaling pathways that are associated with CRC progression. The survival probability curves and box-plot analyses with the expressions of CGs in different stages of CRC indicated their strong prognostic performance from the earlier stage of the disease. Then, we detected CGs-guided seven candidate drugs (Manzamine A, Cardidigin, Staurosporine, Sitosterol, Benzo[a]pyrene, Nocardiopsis sp., and Riccardin D) by molecular docking. Finally, the binding stability of four top-ranked complexes (TPX2 vs. Manzamine A, CDC20 vs. Cardidigin, MELK vs. Staurosporine, and CDK1 vs. Riccardin D) was investigated by using 100 ns molecular dynamics simulation studies, and their stable performance was observed. Therefore, the output of this study may play a vital role in developing a proper treatment plan at the earlier stages of CRC.

Mitochondrial Control in Inflammatory Gastrointestinal Diseases

Mitochondria play a central role in the pathophysiology of inflammatory bowel disease (IBD) and colorectal cancer (CRC). The maintenance of mitochondrial function is necessary for a stable immune system. Mitochondrial dysfunction in the gastrointestinal system leads to the excessive activation of multiple inflammatory signaling pathways, leading to IBD and increased severity of CRC. In this review, we focus on the mitochondria and inflammatory signaling pathways and its related gastrointestinal diseases.

Prognostic impact of mitofusin 2 expression in colon cancer

BACKGROUND

Mitofusin 2 (MFN2) is involved in several biological processes, including cancer. MFN2 is downregulated in some types of cancer and inhibits cancer cell proliferation, migration, and invasion. However, the relationship between MFN2 and colon cancer remains unknown.

METHODS

In this study, MFN2 expression was investigated using The Cancer Genome Atlas (TCGA) and the Human Protein Atlas (HPA), and the associations between prognostic factors and survival outcomes were assessed via univariate and multivariate analyses. Functional enrichment analyses based on Kyoto Encyclopedia of Genes and Genomes (KEGG) resource and Gene Set Enrichment Analysis (GSEA) were carried out.

RESULTS

MFN2 was downregulated in colon cancer tissues compared with paracancerous colon tissues (P<0.001), and low MFN2 expression was associated with an advanced tumor stage (stage IV vs. stage I, P=0.03; stage I-III vs. stage IV, P=0.003). MFN2 immunohistochemistry (IHC) staining was medium to high in colon normal tissues, but MFN2 IHC staining was faint or not identified in colorectal cancer (CRC) tumor tissues. MFN2 expression was either low or non-existent in colon cancer distinct cell clusters, according to differential gene analysis. Univariate analysis revealed that MFN2 expression in colon cancer patients was significantly associated with the stage [odds ratio (OR) =0.29 for stage IV vs. stage I, P=0.001], T-stage (OR =0.20 for T4 vs. T1, P=0.033), and distant metastasis (OR =0.31 for M1 vs. M0, P=0.000). Furthermore, Kaplan-Meier survival analysis revealed that patients with colon cancer and high MFN2 expression have a better prognosis than those with low MFN2 expression (P=0.002). MFN2 (hazard ratio =0.95, 95% confidence interval: 0.92-0.99, P=0.007) was an independent predictor of colon cancer according to univariate and multivariate Cox models. Finally, GSEA results showed that the KEGG GALACTOSE METABOLISM, APOPTOSIS, and VEGF SIGNALING pathways were activated in the high MFN2 mRNA expression group, whereas the KEGG RIBOSOME pathway was inhibited in the low MFN2 expression group.

CONCLUSIONS

Our research revealed MFN2 to be a promising predictive biomarker and therapeutic target for colon cancer.

Mitofusin-2 in cancer: Friend or foe?

Cancer is a category of disorders characterized by excessive cell proliferation with the ability to infiltrate or disseminate to other organs of the body. Mitochondrial dysfunction, as one of the most prominent hallmarks of cancer cells, has been related to the onset and development of various cancers. Mitofusin 2 (MFN2) is a major mediator of mitochondrial fusion, endoplasmic reticulum (ER)-mitochondria interaction, mitophagy and axonal transport of mitochondria. Available data have shown that MFN2, which its alterations have been associated with mitochondrial dysfunction, could affect cancer initiation and progression. In fact, it showed that MFN2 may have a double-edged sword effect on cancer fate. Precisely, it demonstrated that MFN2, as a tumor suppressor, induces cancer cell apoptosis and inhibits cell proliferation via Ca²⁺ and Bax-mediated apoptosis and increases P21 and p27 levels, respectively. It also could suppress cell survival via inhibiting PI3K/Akt, Ras-ERK1/2-cyclin D1 and mTORC2/Akt signaling pathways. On the other hand, MFN2, as an oncogene, could increase cancer invasion via snail-mediated epithelial-mesenchymal transition (EMT) and in vivo tumorigenesis. While remarkable progress has been achieved in recent decades, further exploration is required to elucidate whether MFN2 could be a friend or it's an enemy. This study aimed to highlight the different functions of MFN2 in various cancers.

Post-translational modifications on mitochondrial metabolic enzymes in cancer

Mitochondrion is the powerhouse of the cell. The research of nearly a century has expanded our understanding of mitochondrion, far beyond the view that mitochondrion is an important energy generator of cells. During the initiation, growth and survival of tumor cells, significant mitochondrial metabolic changes have taken place in the important enzymes of respiratory chain and tricarboxylic acid cycle, mitochondrial biogenesis and dynamics, oxidative stress regulation and molecular signaling. Therefore, mitochondrial metabolic proteins are the key mediators of tumorigenesis. Post-translational modification is the molecular switch that regulates protein function. Understanding how these mitochondria-related post-translational modification function during tumorigenesis will bring new ideas for the next generation of cancer treatment.

Mitofusin-2 Promotes the Epithelial-Mesenchymal Transition-Induced Cervical Cancer Progression

High expression of mitofusin-2 (MFN2), a mitochondrial fusion protein, has been frequently associated with poor prognosis of patients with cervical cancer. Here, we aimed to identify the function of MFN2 in cervical cancer to understand its influence on disease prognosis. To this end, from cervical adenocarcinoma, we performed an MTT assay and quantitative RT-PCR (qRT-PCR) analysis to assess the effects of MFN2 on the proliferation and of HeLa cells. Then, colony-formation ability and tumorigenesis were evaluated using a tumor xenograft mouse model. The migration ability related to MFN2 was also measured using a wound healing assay. Consequently, epithelial-mesenchymal transition (EMT) of MFN2-knockdowned HeLa cells originating from adenocarcinoma. markers related to MFN2 were assessed by qRT-PCR. Clinical data were analyzed using cBioPortal and The Cancer Genome Atlas. We found that MFN2 knockdown reduced the proliferation, colony formation ability, migration, and in vivo tumorigenesis of HeLa cells. Primarily, migration of MFN2-knockdowned HeLa cells decreased through the suppression of EMT. Thus, we concluded that MFN2 facilitates cancer progression and in vivo tumorigenesis in HeLa cells. These findings suggest that MFN2 could be a novel target to regulate the EMT program and tumorigenic potential in HeLa cells and might serve as a therapeutic target for cervical cancer. Taken together, this study is expected to contribute to the treatment of patients with cervical cancer.

CircTHBS1 facilitates the progression of interstitial cystitis depending on the regulation of miR-139-5p/MFN2 axis

Circular RNA (circRNA) have been found to play an important role in the progression of many diseases, including interstitial cystitis (IC). However, the role of circTHBS1 in IC progression is still unclear. Exploring the role and potential molecular mechanism of circTHBS1 in the development of IC. The enzyme-linked immunosorbent assay was used to assess the levels of inflammatory cytokines. The expression levels of circTHBS1, microRNA (miR)-139-5p, and mitofusin 2 (MFN2) were evaluated using quantitative real-time PCR. Cell proliferation and migration were determined using MTT assay, Edu staining, and transwell assay. The protein levels of epithelial-mesenchymal transition (EMT) markers and MFN2 were examined using western blot analysis. The relationship between miR-139-5p and circTHBS1 or MFN2 was confirmed using the dual-luciferase reporter assay and RIP assay. CircTHBS1 was highly repressed in IC tissues and cells, and its expression was positively correlated with the inflammatory response of IC patients. CircTHBS1 could promote the proliferation, migration, EMT process, and inflammation of IC cells, while its knockdown had an opposite effect. CircTHBS1 could serve as a sponge of miR-139-5p, and miR-139-5p could participate in the regulation of circTHBS1 on IC cell progression. In addition, miR-139-5p could target MFN2, and it could inhibit the progression of IC cells by targeting MFN2. Furthermore, circTHBS1 sponged miR-139-5p to positively regulate MFN2. CircTHBS1 promoted IC cell proliferation, migration, EMT process, and inflammation by regulating the miR-139-5p/MFN2 axis indicating that circTHBS1 might be a potential target for IC treatment.

PINK1-induced phosphorylation of mitofusin 2 at serine 442 causes its proteasomal degradation and promotes cell proliferation in lung cancer and pulmonary arterial hypertension

Impaired mitochondrial fusion, due in part to decreased mitofusin 2 (Mfn2) expression, contributes to unrestricted cell proliferation and apoptosis-resistance in hyperproliferative diseases like pulmonary arterial hypertension (PAH) and non-small cell lung cancer (NSCLC). We hypothesized that Mfn2 levels are reduced due to increased proteasomal degradation of Mfn2 triggered by its phosphorylation at serine 442 (S442) and investigated the potential kinase mediators. Mfn2 expression was decreased and Mfn2 S442 phosphorylation was increased in pulmonary artery smooth muscle cells from PAH patients and in NSCLC cells. Mfn2 phosphorylation was mediated by PINK1 and protein kinase A (PKA), although only PINK1 expression was increased in these diseases. We designed a S442 phosphorylation deficient Mfn2 construct (PD-Mfn2) and a S442 constitutively phosphorylated Mfn2 construct (CP-Mfn2). The effects of these modified Mfn2 constructs on Mfn2 expression and biological function were compared with those of the wildtype Mfn2 construct (WT-Mfn2). WT-Mfn2 increased Mfn2 expression and mitochondrial fusion in both PAH and NSCLC cells resulting in increased apoptosis and decreased cell proliferation. Compared to WT-Mfn2, PD-Mfn2 caused greater Mfn2 expression, suppression of proliferation, apoptosis induction, and cell cycle arrest. Conversely, CP-Mfn2 caused only a small increase in Mfn2 expression and did not restore mitochondrial fusion, inhibit cell proliferation, or induce apoptosis. Silencing PINK1 or PKA, or proteasome blockade using MG132, increased Mfn2 expression, enhanced mitochondrial fusion and induced apoptosis. In a xenotransplantation NSCLC model, PD-Mfn2 gene therapy caused greater tumor regression than did therapy with WT-Mfn2. Mfn2 deficiency in PAH and NSCLC reflects proteasomal degradation triggered by Mfn2-S442 phosphorylation by PINK1 and/or PKA. Inhibiting Mfn2 phosphorylation has potential therapeutic benefit in PAH and lung cancer.

Oxygen sensing, mitochondrial biology and experimental therapeutics for pulmonary hypertension and cancer

The homeostatic oxygen sensing system (HOSS) optimizes systemic oxygen delivery. Specialized tissues utilize a conserved mitochondrial sensor, often involving NDUFS2 in complex I of the mitochondrial electron transport chain, as a site of pO₂-responsive production of reactive oxygen species (ROS). These ROS are converted to a diffusible signaling molecule, hydrogen peroxide (H₂O₂), by superoxide dismutase (SOD2). H₂O₂ exits the mitochondria and regulates ion channels and enzymes, altering plasma membrane potential, intracellular Ca²⁺ and Ca²⁺-sensitization and controlling acute, adaptive, responses to hypoxia that involve changes in ventilation, vascular tone and neurotransmitter release. Subversion of this O₂-sensing pathway creates a pseudohypoxic state that promotes disease progression in pulmonary arterial hypertension (PAH) and cancer. Pseudohypoxia is a state in which biochemical changes, normally associated with hypoxia, occur despite normal pO₂. Epigenetic silencing of SOD2 by DNA methylation alters H₂O₂ production, activating hypoxia-inducible factor 1α, thereby disrupting mitochondrial metabolism and dynamics, accelerating cell proliferation and inhibiting apoptosis. Other epigenetic mechanisms, including dysregulation of microRNAs (miR), increase pyruvate dehydrogenase kinase and pyruvate kinase muscle isoform 2 expression in both diseases, favoring uncoupled aerobic glycolysis. This Warburg metabolic shift also accelerates cell proliferation and impairs apoptosis. Disordered mitochondrial dynamics, usually increased mitotic fission and impaired fusion, promotes disease progression in PAH and cancer. Epigenetic upregulation of dynamin-related protein 1 (Drp1) and its binding partners, MiD49 and MiD51, contributes to the pathogenesis of PAH and cancer. Finally, dysregulation of intramitochondrial Ca²⁺, resulting from impaired mitochondrial calcium uniporter complex (MCUC) function, links abnormal mitochondrial metabolism and dynamics. MiR-mediated decreases in MCUC function reduce intramitochondrial Ca²⁺, promoting Warburg metabolism, whilst increasing cytosolic Ca²⁺, promoting fission. Epigenetically disordered mitochondrial O₂-sensing, metabolism, dynamics, and Ca²⁺ homeostasis offer new therapeutic targets for PAH and cancer. Promoting glucose oxidation, restoring the fission/fusion balance, and restoring mitochondrial calcium regulation are promising experimental therapeutic strategies.

Mitochondrial Dynamics Related Genes -MFN1, MFN2 and DRP1 Polymorphisms are Associated with Risk of Lung Cancer

Purpose

This study aimed to evaluate the associations between mitochondrial dynamics related genes -MFN1, MFN2 and DRP1 polymorphisms and risk of lung cancer.

Methods

Six polymorphisms of MFN1, MFN2 and DRP1 were genotyped in 600 cases and 600 controls using a MassARRAY platform.

Results

The MFN1 rs13098637-C and DRP1 rs879255689-A alleles were associated with an increased risk of lung cancer (p_rs13098637=0.004, p_rs879255689=0.005), while MFN2 rs4240897-A and rs2236058-G were related to a decreased risk of disease (p<0.001). The rs13098637-TC/CC and rs879255689-GA/AA were determined as risk genotypes for lung cancer (p_rs13098637=0.014, p_rs879255689=0.013), whereas the rs4240897-GA/AA and rs2236058-GG were identified as protective genotypes against lung cancer risk (p<0.001). Genetic model analysis showed that rs13098637 was correlated with an elevated risk of lung cancer in dominant and log-additive models (p_dominant=0.007, p_log-additive=0.004). Moreover, rs879255689 was associated with an increased risk of disease in all three models (p_dominant=0.014, p_recessive=0.028, p_log-additive=0.005). In contrast, rs4240897 and rs2236058 were related to reduced risk of disease in all three models (rs4240897: p_all<0.001; rs2236058: p_dominant=0.008, p_recessive<0.001, p_log-additive<0.001). In addition, these associations were related to the smoking status and pathological type of lung cancer patients.

Conclusion

These results shed new light on the association between mitochondrial dynamics related genes and risk of lung cancer.

Mitochondrial Fusion Protein Mfn2 and Its Role in Heart Failure

Mitofusin 2 (Mfn2) is a transmembrane GTPase located on the mitochondrial outer membrane that contributes to mitochondrial network regulation. It is an essential multifunctional protein that participates in various biological processes under physical and pathological conditions, including mitochondrial fusion, reticulum–mitochondria contacts, mitochondrial quality control, and apoptosis. Mfn2 dysfunctions have been found to contribute to cardiovascular diseases, such as ischemia-reperfusion injury, heart failure, and dilated cardiomyopathy. Here, this review mainly focuses on what is known about the structure and function of Mfn2 and its crucial role in heart failure.

Mitofusin-2 is a novel anti-angiogenic factor in pancreatic cancer

Background

Aberrant expression of mitofusin-2 (MFN2) has been found to be associated with vascular endothelial growth factor A (VEGFA)-mediated angiogenesis in human umbilical vein endothelial cells (HUVECs). This study aimed to investigate the expression of MFN2 in pancreatic cancer (PC) and the role of MFN2 in vascular endothelial cell growth and angiogenesis.

Methods

Protein and mRNA expression of MFN2 and VEGFA were measured. The CCK-8 assay, tube formation assay, flow cytometry, and transmission electron microscopy were used to examine the effects of MFN2 overexpression on HUVEC growth, angiogenesis, and apoptosis. Western blot and immunocytochemical staining were conducted to measure alterations in cell cycle and apoptosis regulators and vascular endothelial growth factor receptor 2 (VEGFR2), angiopoietin-1 gene (ANGPT1), and tissue inhibitor of metalloproteinase 1 (TIMP1) expression in HUVECs.

Results

The results showed that MFN2 levels were significantly decreased in tumor tissues. Contrasting results were observed for VEGFA mRNA levels. MFN2 overexpression inhibited cell growth while promoting the formation of apoptotic bodies in HUVECs. Additionally, MFN2 overexpression enhanced the protein expression of p21 and p27 while attenuating the expression of proliferating cell nuclear antigen, VEGFA, VEGFR2, ANGPT1, and TIPM1 in HUVECs.

Conclusions

In conclusion, MFN2 expression negatively correlates with VEGFA expression in PC and inhibits endothelial cell growth and angiogenesis.

ANT2-Mediated ATP Import into Mitochondria Protects against Hypoxia Lethal Injury

Following a prolonged exposure to hypoxia–reoxygenation, a partial disruption of the ER-mitochondria tethering by mitofusin 2 (MFN2) knock-down decreases the Ca²⁺ transfer between the two organelles limits mitochondrial Ca²⁺ overload and prevents the Ca²⁺-dependent opening of the mitochondrial permeability transition pore, i.e., limits cardiomyocyte cell death. The impact of the metabolic changes resulting from the alteration of this Ca²⁺crosstalk on the tolerance to hypoxia–reoxygenation injury remains partial and fragmented between different field of expertise. >In this study, we report that MFN2 loss of function results in a metabolic switch driven by major modifications in energy production by mitochondria. During hypoxia, mitochondria maintain their ATP concentration and, concomitantly, the inner membrane potential by importing cytosolic ATP into mitochondria through an overexpressed ANT2 protein and by decreasing the expression and activity of the ATP hydrolase via IF1. This adaptation further blunts the detrimental hyperpolarisation of the inner mitochondrial membrane (IMM) upon re-oxygenation. These metabolic changes play an important role to attenuate cell death during a prolonged hypoxia–reoxygenation challenge.

Role of Mitofusins and Mitophagy in Life or Death Decisions

Mitochondria entail an incredible dynamism in their morphology, impacting death signaling and selective elimination of the damaged organelles. In turn, by recycling the superfluous or malfunctioning mitochondria, mostly prevalent during aging, mitophagy contributes to maintain a healthy mitochondrial network. Mitofusins locate at the outer mitochondrial membrane and control the plastic behavior of mitochondria, by mediating fusion events. Besides deciding on mitochondrial interconnectivity, mitofusin 2 regulates physical contacts between mitochondria and the endoplasmic reticulum, but also serves as a decisive docking platform for mitophagy and apoptosis effectors. Thus, mitofusins integrate multiple bidirectional inputs from and into mitochondria and ensure proper energetic and metabolic cellular performance. Here, we review the role of mitofusins and mitophagy at the cross-road between life and apoptotic death decisions. Furthermore, we highlight the impact of this interplay on disease, focusing on how mitofusin 2 and mitophagy affect non-alcoholic fatty liver disease.

Interplay of mitochondrial fission-fusion with cell cycle regulation: Possible impacts on stem cell and organismal aging

Declining mitochondrial function and homeostasis is a hallmark of aging. It is appreciated that the role of mitochondria is much more complex than generating reactive oxygen species to cause aging-related tissue damage. More recent literature describes that the ability of mitochondria to undergo fission or fusion events with each other impacts aging processes. A dynamic balance of mitochondrial fission and fusion events is required to sustain critical cellular functions including cell cycle. Specifically, cell cycle regulators modulate molecular activities of the mitochondrial fission (and fusion) machinery towards regulating cell cycle progression. In this review, we discus literature leading to our understanding on how shifts in the dynamic balance of mitochondrial fission and fusion can modulate progression through, exit from, and re-entry to the cell cycle or in undergoing senescence. Importantly, core regulators of mitochondrial fission or fusion are emerging as crucial stem cell regulators. We discuss the implication of such regulation in stem cells in the context of aging, given that aberrations in adult stem cells promote aging. We also propose a few hypotheses that may provide direction for further understanding about the roles of mitochondrial fission-fusion dynamics in aging biology.

The mystery of mitochondria-ER contact sites in physiology and pathology: A cancer perspective

Mitochondria-associated membranes (MAM), physical platforms that enable communication between mitochondria and the endoplasmic reticulum (ER), are enriched with many proteins and enzymes involved in several crucial cellular processes, such as calcium (Ca²⁺) homeostasis, lipid synthesis and trafficking, autophagy and reactive oxygen species (ROS) production. Accumulating studies indicate that tumor suppressors and oncogenes are present at these intimate contacts between mitochondria and the ER, where they influence Ca²⁺ flux between mitochondria and the ER or affect lipid homeostasis at MAM, consequently impacting cell metabolism and cell fate. Understanding these fundamental roles of mitochondria-ER contact sites as important domains for tumor suppressors and oncogenes can support the search for new and more precise anticancer therapies. In the present review, we summarize the current understanding of basic MAM biology, composition and function and discuss the possible role of MAM-resident oncogenes and tumor suppressors.

Mitofusin 2 in Mature Adipocytes Controls Adiposity and Body Weight

We found that exposure of adult animals to caloriedense foods rapidly abolished expression of mitofusin 2 (Mfn2), a gene promoting mitochondrial fusion and mitochondrion-endoplasmic reticulum interactions, in white and brown fat. Mfn2 mRN was also robustly lower in obese human subjects compared with lean controls. Adipocyte-specific knockdown of Mfn2 in adult mice led to increased food intake, adiposity, and impaired glucose metabolism on standard chow as well as on a diet with high calorie content. The body weight and adiposity of mature adipocyte-specific Mfn2 knockout mice on a standard diet were similar to those of control mice on a high-fat diet. The transcriptional profile of the adipose tissue in adipocyte-specific Mfn2 knockout mice was consistent with adipocyte proliferation, increased lipogenesis at the tissue level, and decreased glucose utilization at the systemic level. These observations suggest a possible crucial role for mitochondrial dynamics in adipocytes in initiating systemic metabolic dysregulation.

Mancini et al. find that the mitochondrial fusion protein Mfn2 is lower in adipose tissue of mice on a high-fat diet and that of obese humans and that this protein in the fat is important for systemic control of metabolism.

Mitochondrial division inhibitor (mdivi-1) decreases oxidative metabolism in cancer

Background

Previous studies suggested that mdivi-1 (mitochondrial division inhibitor), a putative inhibitor of dynamin-related protein (DRP1), decreased cancer cell proliferation through inducing mitochondrial fusion and altering oxygen consumption. However, the metabolic reprogramming underlying the DRP1 inhibition is still unclear in cancer cells.

Methods

To better understand the metabolic effect of DRP1 inhibition, [U-¹³C]glucose isotope tracing was employed to assess mdivi-1 effects in several cancer cell lines, DRP1-WT (wild-type) and DRP1-KO (knockout) H460 lung cancer cells and mouse embryonic fibroblasts (MEFs).

Results

Mitochondrial staining confirmed that mdivi-1 treatment and DRP1 deficiency induced mitochondrial fusion. Surprisingly, metabolic isotope tracing found that mdivi-1 decreased mitochondrial oxidative metabolism in the lung cancer cell lines H460, A549 and the colon cancer cell line HCT116. [U-¹³C]glucose tracing studies also showed that the TCA cycle intermediates had significantly lower enrichment in mdivi-1-treated cells. In comparison, DRP1-WT and DRP1-KO H460 cells had similar oxidative metabolism, which was decreased by mdivi-1 treatment. Furthermore, mdivi-1-mediated effects on oxidative metabolism were independent of mitochondrial fusion.

Conclusions

Our data suggest that, in cancer cells, mdivi-1, a putative inhibitor of DRP1, decreases oxidative metabolism to impair cell proliferation.

Deficient Endoplasmic Reticulum-Mitochondrial Phosphatidylserine Transfer Causes Liver Disease

Non-alcoholic fatty liver is the most common liver disease worldwide. Here, we show that the mitochondrial protein mitofusin 2 (Mfn2) protects against liver disease. Reduced Mfn2 expression was detected in liver biopsies from patients with non-alcoholic steatohepatitis (NASH). Moreover, reduced Mfn2 levels were detected in mouse models of steatosis or NASH, and its re-expression in a NASH mouse model ameliorated the disease. Liver-specific ablation of Mfn2 in mice provoked inflammation, triglyceride accumulation, fibrosis, and liver cancer. We demonstrate that Mfn2 binds phosphatidylserine (PS) and can specifically extract PS into membrane domains, favoring PS transfer to mitochondria and mitochondrial phosphatidylethanolamine (PE) synthesis. Consequently, hepatic Mfn2 deficiency reduces PS transfer and phospholipid synthesis, leading to endoplasmic reticulum (ER) stress and the development of a NASH-like phenotype and liver cancer. Ablation of Mfn2 in liver reveals that disruption of ER-mitochondrial PS transfer is a new mechanism involved in the development of liver disease.

Interorganellar calcium signaling in the regulation of cell metabolism: A cancer perspective

Organelles were originally considered to be individual cellular compartments with a defined organization and function. However, recent studies revealed that organelles deeply communicate within each other via Ca²⁺ exchange. This communication, mediated by specialized membrane regions in close apposition between two organelles, regulate cellular functions, including metabolism and cell fate decisions. Advances in microscopy techniques, molecular biology and biochemistry have increased our understanding of these interorganelle platforms. Research findings suggest that interorganellar Ca²⁺ signaling, which is altered in cancer, influences tumorigenesis and tumor progression by controlling cell death programs and metabolism. Here, we summarize the available data on the existence and composition of interorganelle platforms connecting the endoplasmic reticulum with mitochondria, the plasma membrane, or endolysosomes. Finally, we provide a timely overview of the potential function of interorganellar Ca²⁺ signaling in maintaining cellular homeostasis.

Dysregulated Mitochondrial Dynamics and Metabolism in Obesity, Diabetes, and Cancer

Metabolism describes the life-sustaining chemical reactions in organisms that provide both energy and building blocks for cellular survival and proliferation. Dysregulated metabolism leads to many life-threatening diseases including obesity, diabetes, and cancer. Mitochondria, subcellular organelles, contain the central energy-producing metabolic pathway, the tricarboxylic acid (TCA) cycle. Also, mitochondria exist in a dynamic network orchestrated by extracellular nutrient levels and intracellular energy needs. Upon stimulation, mitochondria undergo consistent interchange through fusion (small to big) and fission (big to small) processes. Mitochondrial fusion is primarily controlled by three GTPases, mitofusin 1 (Mfn1), Mfn2, and optic atrophy 1 (Opa1), while mitochondrial fission is primarily regulated by GTPase dynamin-related protein 1 (Drp1). Dysregulated activity of these GTPases results in disrupted mitochondrial dynamics and cellular metabolism. This review will update the metabolic roles of these GTPases in obesity, diabetes, and cancer.

Mitofusin-2 acts as biomarker for predicting poor prognosis in hepatitis B virus related hepatocellular carcinoma

OBJECTIVE

To investigate the expression of Mitofusin-2 (MFN2) in HCC tissues and its role in the development of HCC.

METHODS

A total of 107 HCC specimens were collected for tissue microarray analysis and immunohistochemistry (IHC) analysis. The relationship between MFN2 expression and clinical features of patients with HCC was analyzed.

RESULTS

Expression level of MFN2 in HCC tissues was 0.92 ± 0.78, significantly lower than that of matched paracancerous liver tissues (1.25 ± 0.75). Patients with low expression of MFN2 had significantly higher rates of cirrhosis than those with high expression of MFN2 (P = 0.049). Kaplan-Meier survival analysis showed that HCC patients with low expression of MFN2 had a worse prognosis in overall survival than HCC patients with high expression of MFN2 (P = 0.027). Patients with high expression of MFN2 had a better prognosis in disease-free survival compared with HCC patients with low expression of MFN2 (P = 0.047). Vascular invasion and MFN2 expression were shown to be prognostic variables for overall survival in patients with HCC. Multivariate analysis showed that vascular invasion (P < 0.001) and MFN2 expression (P = 0.045) were independent prognostic factors for overall survival. Vascular invasion (P < 0.001) and MFN2 expression (P = 0.042) were independent risk factors associated with disease-free survival.

CONCLUSION

Our data revealed that MFN2 expression was decreased in HCC samples. High MFN2 expression was correlated with longer survival times in patients with HCC and served as an independent factor for better outcomes. Our study therefore provides a promising biomarker for the prognostic prediction of HCC and a potential therapeutic target for the disease.

Shenqi Fuzheng Injection Reverses Cisplatin Resistance through Mitofusin-2-Mediated Cell Cycle Arrest and Apoptosis in A549/DDP Cells

The goal of this evaluation was to examine the mechanisms of Shenqi Fuzheng injection (SFI), an extract made from the plants Radix Astragali and Radix Codonopsis, in the process of chemotherapy sensitivity in non-small-cell lung cancer (NSCLC) cells. We investigated the expression of mitofusin-2 (Mfn2), a mitochondrial GTPase that may be related to chemoresistance, and found that Mfn2 expression was lower in human cisplatin-resistant lung carcinoma A549/DDP cells than in cisplatin-susceptible A549 cells. Chemosensitivity to cisplatin was restored in A549/DDP cells following supplementation in conjunction with SFI treatment, the effect of which we evaluated via cell cycle, apoptosis, and cell signaling analysis. We found that the combined use of A549/DDP cells with SFI and cisplatin enhanced cell cycle arrested in the G₂/M phase, which was accompanied by upregulation of p53 and p21 protein expression and induced mitochondrial apoptosis in conjunction with the upregulation of Bax and the downregulation of Bcl-2 protein expression. Moreover, cell cycle arrest and mitochondrial apoptosis coincided with the upregulation of Mfn2 expression, which, in turn, was related to the increased mitochondrial membrane permeabilization and elevated reactive oxygen species. In summary, our findings suggest that the effect of SFI in increasing chemotherapy sensitivity in cisplatin resistance of NSCLCs occurs through cell cycle arrest and the initiation of mitochondrial apoptosis involved in the upregulation of Mfn2 expression.

In vivo and in vitro effects of hyperplasia suppressor gene on the proliferation and apoptosis of lung adenocarcinoma A549 cells

Lung adenocarcinoma is the most common subtype of non-small cell lung cancer (NSCLC). Hyperplasia suppressor gene (HSG) has been reported to inhibit cell proliferation, migration, and remodeling in cardiovascular diseases. However, there lacks systematic researches on the effect of HSG on the apoptosis and proliferation of lung adenocarcinoma A549 cells and data of in vivo experiments. The present study aims to investigate the effects of HSG gene silencing on proliferation and apoptosis of lung adenocarcinoma A549 cells. The human lung adenocarcinoma A549 cell was selected to construct adenovirus vector. Reverse transcription-quantitative PCR (RT-qPCR) and Western blot analysis were conducted to detect expressions of HSG and apoptosis related-proteins. Cell Counting Kit (CCK)-8 assay was performed to assess A549 cell proliferation and flow cytometry to analyze cell cycle and apoptosis rate. The BALB/C nude mice were collected to establish xenograft model. Silenced HSG showed decreased mRNA and protein expressions of HSG, and elevated A549 cell survival rates at the time point of 24, 48, and 72 h. The ratio of cells at G₀/G₁ phase and apoptosis rate decreased and the ratio of cells at S- and G₂/M phases increased following the silencing of HSG. There were decreases of B cell lymphoma-2 (Bcl-2)-associated X protein (Bax), Caspase-3, and Caspase-8 expressions but increases in Bcl-2 induced by silenced HSG. As for the xenograft in nude mice, tumor volume increased, and apoptosis index (AI) decreased after HSG silencing. These results indicate that HSG gene silencing may promote the proliferation of A549 cells and inhibit the apoptosis. HSG may be a promising target for the treatment of lung adenocarcinoma.

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.

Mitochondrial Dynamics in Type 2 Diabetes and Cancer

Mitochondria are bioenergetic, biosynthetic, and signaling organelles that control various aspects of cellular and organism homeostasis. Quality control mechanisms are in place to ensure maximal mitochondrial function and metabolic homeostasis at the cellular level. Dysregulation of these pathways is a common theme in human disease. In this mini-review, we discuss how alterations of the mitochondrial network influences mitochondrial function, focusing on the molecular regulators of mitochondrial dynamics (organelle's shape and localization). We highlight similarities and critical differences in the mitochondrial network of cancer and type 2 diabetes, which may be relevant for treatment of these diseases.

Mitofusins, from Mitochondria to Metabolism

Mitochondrial architecture is involved in several functions crucial for cell viability, proliferation, senescence, and signaling. In particular, mitochondrial dynamics, through the balance between fusion and fission events, represents a central mechanism for bioenergetic adaptation to metabolic needs of the cell. As key regulators of mitochondrial dynamics, the fusogenic mitofusins have recently been linked to mitochondrial biogenesis and respiratory functions, impacting on cell fate and organism homeostasis. Here we review the implication of mitofusins in the regulation of mitochondrial metabolism, and their consequence on energy homeostasis at the cellular and physiological level, highlighting their crucial role in metabolic disorders, cancer, and aging.

Mitochondrial Fragmentation Due to Inhibition of Fusion Increases Cyclin B through Mitochondrial Superoxide Radicals

During the cell cycle, mitochondria undergo regulated changes in morphology. Two particularly interesting events are first, mitochondrial hyperfusion during the G₁-S transition and second, fragmentation during entry into mitosis. The mitochondria remain fragmented between late G₂- and mitotic exit. This mitotic mitochondrial fragmentation constitutes a checkpoint in some cell types, of which little is known. We bypass the ‘mitotic mitochondrial fragmentation’ checkpoint by inducing fragmented mitochondrial morphology and then measure the effect on cell cycle progression. Using Drosophila larval hemocytes, Drosophila S2R⁺ cell and cells in the pouch region of wing imaginal disc of Drosophila larvae we show that inhibiting mitochondrial fusion, thereby increasing fragmentation, causes cellular hyperproliferation and an increase in mitotic index. However, mitochondrial fragmentation due to over-expression of the mitochondrial fission machinery does not cause these changes. Our experiments suggest that the inhibition of mitochondrial fusion increases superoxide radical content and leads to the upregulation of cyclin B that culminates in the observed changes in the cell cycle. We provide evidence for the importance of mitochondrial superoxide in this process. Our results provide an insight into the need for mitofusin-degradation during mitosis and also help in understanding the mechanism by which mitofusins may function as tumor suppressors.

Alterations in cell cycle dynamics in human endothelium cell culture infected with influenza virus

The cell cycle of endothelium EAhy 926 cell culture infected with influenza virus has been studied. Cytometric analysis of cell culture synchronized by contact inhibition revealed the elongation of the S phase of the cell cycle in EAhy 926 cells under the influence of influenza virus. This result was shown in an EAhy 926 culture infected with influenza virus and treated with nocodazole. Comparison of a lung carcinoma A549 cell line in which influenza virus causes G₀/G₁ arrest and of an endothelial EAhy 926 cell line in which the same infection leads to S-phase elongation allows it to be suggested that different effects of influenza virus on cell cycle dynamics depend on the origin of infected cells.

Lentivirus vector-mediated mitofusin-2 overexpression in rat ovary changes endocrine function and promotes follicular development in vivo

The aim of the present study was to evaluate the expression and effect of rat mitofusin-2 (rMfn2) in the ovaries and other organs in rats. Rat models were developed by the intraovarian microinjection of an rMfn2-overexpressing lentiviral vector. Lenti-green fluorescent protein (GFP)-rMfn2 was microinjected into rat ovaries at a dosage of 2×10⁶ tuberculin units virosome (n=25) and lenti-GFP was microinjected as a control (n=25). The expression of rMfn2 in the ovaries and other tissues was observed by fluorescence microscopy on days 7, 15, 30, 45 and 60 after the microinjection (n=5/day from each group). The serum levels of estradiol (E₂), progesterone (P), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were determined by radioimmunoassay. Western blotting was used for the quantitative analysis of the expression of rMfn2 and the progesterone receptor (PR), estradiol receptor (ER), luteinizing hormone receptor (LHR) and follicle-stimulating hormone receptor (FSHR). The expression of rMfn2 was detected on day 7 after infection, increased with time and was maintained efficiently until day 60. In addition, rMfn2 was highly expressed in the fallopian tubes, uterus, cardiac muscle, liver and kidney, but expressed at a low level in adipose tissue. The serum levels of E₂ and P in the model group were significantly increased compared with those in the control group, whereas the FSH and LH levels showed no significant difference between groups. The expression levels of the ER and PR in the model group were higher than those in the control group; however, no significant difference was observed between groups for the expression levels of LHR and FSHR. These findings suggest that the intraovarian microinjection of lenti-GFP-rMfn2 resulted in a significant time-dependent overexpression of rMfn2 in various organs, and that rMfn2 overexpression in rat ovaries changed the endocrine function and promoted follicular development.