Mitochondrial DNA alterations underlie an irreversible shift to aerobic glycolysis in fumarate hydratase-deficient renal cancer

Functional implications of fumarate-induced cysteine succination

Mutations in metabolic enzymes are associated with hereditary and sporadic forms of cancer. For example, loss-of-function mutations affecting fumarate hydratase (FH), the tricarboxylic acid (TCA) cycle enzyme, result in the accumulation of millimolar levels of fumarate that cause an aggressive form of kidney cancer. A distinct feature of fumarate is its ability to spontaneously react with thiol groups of cysteines in a chemical reaction termed succination. Although succination of a few proteins has been causally implicated in the molecular features of FH-deficient cancers, the stoichiometry, wider functional consequences, and contribution of succination to disease development remain largely unexplored. We discuss the functional implications of fumarate-induced succination in FH-deficient cells, the available methodologies, and the current challenges in studying this post-translational modification.

Tricarboxylic Acid Cycle Relationships with Non-Metabolic Processes: A Short Story with DNA Repair and Its Consequences on Cancer Therapy Resistance

Metabolic changes involving the tricarboxylic acid (TCA) cycle have been linked to different non-metabolic cell processes. Among them, apart from cancer and immunity, emerges the DNA damage response (DDR) and specifically DNA damage repair. The oncometabolites succinate, fumarate and 2-hydroxyglutarate (2HG) increase reactive oxygen species levels and create pseudohypoxia conditions that induce DNA damage and/or inhibit DNA repair. Additionally, by influencing DDR modulation, they establish direct relationships with DNA repair on at least four different pathways. The AlkB pathway deals with the removal of N-alkylation DNA and RNA damage that is inhibited by fumarate and 2HG. The MGMT pathway acts in the removal of O-alkylation DNA damage, and it is inhibited by the silencing of the MGMT gene promoter by 2HG and succinate. The other two pathways deal with the repair of double-strand breaks (DSBs) but with opposite effects: the FH pathway, which uses fumarate to help with the repair of this damage, and the chromatin remodeling pathway, in which oncometabolites inhibit its repair by impairing the homologous recombination repair (HRR) system. Since oncometabolites inhibit DNA repair, their removal from tumor cells will not always generate a positive response in cancer therapy. In fact, their presence contributes to longer survival and/or sensitization against tumor therapy in some cancer patients.

Rewiring of RNA methylation by the oncometabolite fumarate in renal cell carcinoma

Metabolic reprogramming is a hallmark of cancer that facilitates changes in many adaptive biological processes. Mutations in the tricarboxylic acid cycle enzyme fumarate hydratase (FH) lead to fumarate accumulation and cause hereditary leiomyomatosis and renal cell cancer (HLRCC). HLRCC is a rare, inherited disease characterized by the development of non-cancerous smooth muscle tumors of the uterus and skin, and an increased risk of an aggressive form of kidney cancer. Fumarate has been shown to inhibit 2-oxoglutarate-dependent dioxygenases (2OGDDs) involved in the hydroxylation of HIF1α, as well as in DNA and histone demethylation. However, the link between fumarate accumulation and changes in RNA post-transcriptional modifications has not been defined. Here, we determine the consequences of fumarate accumulation on the activity of different members of the 2OGDD family targeting RNA modifications. By evaluating multiple RNA modifications in patient-derived HLRCC cell lines, we show that mutation of FH selectively affects the levels of N6-methyladenosine (m6A), while the levels of 5-formylcytosine (f5C) in mitochondrial tRNA are unaffected. This supports the hypothesis of a differential impact of fumarate accumulation on distinct RNA demethylases. The observation that metabolites modulate specific subsets of RNA-modifying enzymes offers new insights into the intersection between metabolism and the epitranscriptome.

Oxidative stress and metabolism meet epigenetic modulation in physical exercise

Physical exercise is established as an important factor of health and generally is recommended for its positive effects on several tissues, organs, and systems. These positive effects come from metabolic adaptations that also include oxidative eustress, in which physical activity increases ROS production and antioxidant mechanisms, although this depends on the intensity of the exercise. Muscle metabolism through mechanisms such as aerobic and anaerobic glycolysis, tricarboxylic acid cycle, and oxidative lipid metabolism can produce metabolites and co-factors which directly impact the epigenetic machinery. In this review, we clearly reinforce the evidence that exercise regulates several epigenetic mechanisms and explain how these mechanisms can be regulated by metabolic products and co-factors produced during exercise. In fact, recent evidence has demonstrated the importance of epigenetics in the gene expression changes implicated in metabolic adaptation after exercise. Importantly, intermediates of the metabolism generated by continuous, acute, moderate, or strenuous exercise control the activity of epigenetic enzymes, therefore turning on or turning off the gene expression of specific programs which can lead to physiological adaptations after exercise.

Factors influencing the detection rate of fumarate peak in 1H MR spectroscopy of fumarate hydratase-deficient renal cell carcinoma at 3 T MRI

AIM

To identify factors that may be associated with fumarate detection rate in 1H-magnetic resonance spectroscopy (MRS) in fumarate hydratase-deficient renal cell carcinoma (FH-RCC).

MATERIALS AND MEHODS

Between February 2018 and March 2022, 16 FH-RCC patients with 30 lesions underwent 1H-MRS. Detection results were classified as having a detected fumarate peak (n=12), undetected peak (n=10), or technical failure (n=8). Factors including tumour size, tumour location, treatment history, and metastasis status were collected and analysed. A Bayesian logistic regression model was applied to evaluate the association between these factors and the detection result.

RESULTS

Bayesian analysis demonstrated significant associations between fumarate detection results and the following factors: long-axis diameter (odds ratio [OR] of 1.64; 95% confidence interval [CI] of 1.07-2.53), short-axis diameter (OR of 1.90; 95% CI of 1.19-3.06), voxel size (OR of 2.85; 95% CI of 1.70-4.75), treatment history (OR of 0.35; 95% CI of 0.21-0.58), non-metastatic state (OR of 2.45; 95% CI of 1.48-4.06), and lymph node metastasis (OR of 0.35; 95% CI of 0.21-0.58). Technical failure results were associated with factors such as treatment history (OR of 2.59; 95% CI of 1.37-4.66), non-metastatic state (OR of 0.36; 95% CI of 0.19-0.66), and lymph node metastasis (OR of 2.61; 95% CI of 1.39-4.74).

CONCLUSION

Tumour size, treatment history, and metastasis character were associated with the detection of abnormal fumarate accumulation. This finding will serve as a reference for interpreting 1H-MRS results and for selecting suitable scenarios to evaluate FH-RCC.

MYC-driven increases in mitochondrial DNA copy number occur early and persist throughout prostatic cancer progression

Increased mitochondrial function may render some cancers vulnerable to mitochondrial inhibitors. Since mitochondrial function is regulated partly by mitochondrial DNA copy number (mtDNAcn), accurate measurements of mtDNAcn could help reveal which cancers are driven by increased mitochondrial function and may be candidates for mitochondrial inhibition. However, prior studies have employed bulk macrodissections that fail to account for cell type-specific or tumor cell heterogeneity in mtDNAcn. These studies have often produced unclear results, particularly in prostate cancer. Herein, we developed a multiplex in situ method to spatially quantify cell type-specific mtDNAcn. We show that mtDNAcn is increased in luminal cells of high-grade prostatic intraepithelial neoplasia (HGPIN), is increased in prostatic adenocarcinomas (PCa), and is further elevated in metastatic castration-resistant prostate cancer. Increased PCa mtDNAcn was validated by 2 orthogonal methods and is accompanied by increases in mtRNAs and enzymatic activity. Mechanistically, MYC inhibition in prostate cancer cells decreases mtDNA replication and expression of several mtDNA replication genes, and MYC activation in the mouse prostate leads to increased mtDNA levels in the neoplastic prostate cells. Our in situ approach also revealed elevated mtDNAcn in precancerous lesions of the pancreas and colon/rectum, demonstrating generalization across cancer types using clinical tissue samples.

Cryptic splice mutation in the fumarate hydratase gene in patients with clinical manifestations of Hereditary Leiomyomatosis and Renal Cell Cancer

Hereditary leiomyomatosis and renal cell carcinoma (HLRCC) is an autosomal dominant condition characterized by the development of cutaneous and uterine leiomyomas and risk for development of an aggressive form of papillary renal cell cancer. HLRCC is caused by germline inactivating pathogenic variants in the fumarate hydratase (FH) gene, which encodes the enzyme that catalyzes the interconversion of fumarate and L-malate. We utilized enzyme and protein mobility assays to evaluate the FH enzyme in a cohort of patients who showed clinical manifestations of HLRCC but were negative for known pathogenic FH gene variants. FH enzyme activity and protein levels were decreased by 50% or greater in three family members, despite normal FH mRNA expression levels as measured by quantitative PCR. Direct Nanopore RNA sequencing demonstrated 57 base pairs of retained intron sequence between exons 9 and 10 of polyadenylated FH mRNA in these patients, resulting in a truncated FH protein. Genomic sequencing revealed a heterozygous intronic alteration of the FH gene (chr1: 241498239 T/C) resulting in formation of a splice acceptor site near a polypyrimidine tract, and a uterine fibroid obtained from a patient showed loss of heterozygosity at this site. The same intronic FH variant was identified in an unrelated patient who also showed a clinical phenotype of HLRCC. These data demonstrate that careful clinical assessment as well as biochemical characterization of FH enzyme activity, protein expression, direct RNA sequencing, and genomic DNA sequencing of patient-derived cells can identify pathogenic variants outside of the protein coding regions of the FH gene.

Fumarate hydratase (FH) and cancer: a paradigm of oncometabolism

Fumarate hydratase (FH) is an enzyme of the Tricarboxylic Acid (TCA) cycle whose mutations lead to hereditary and sporadic forms of cancer. Although more than twenty years have passed since its discovery as the leading cause of the cancer syndrome Hereditary leiomyomatosis and Renal Cell Carcinoma (HLRCC), it is still unclear how the loss of FH causes cancer in a tissue-specific manner and with such aggressive behaviour. It has been shown that FH loss, via the accumulation of FH substrate fumarate, activates a series of oncogenic cascades whose contribution to transformation is still under investigation. In this review, we will summarise these recent findings in an integrated fashion and put forward the case that understanding the biology of FH and how its mutations promote transformation will be vital to establish novel paradigms of oncometabolism.

Targetable NOTCH1 rearrangements in reninoma

Reninomas are exceedingly rare renin-secreting kidney tumours that derive from juxtaglomerular cells, specialised smooth muscle cells that reside at the vascular inlet of glomeruli. They are the central component of the juxtaglomerular apparatus which controls systemic blood pressure through the secretion of renin. We assess somatic changes in reninoma and find structural variants that generate canonical activating rearrangements of, NOTCH1 whilst removing its negative regulator, NRARP. Accordingly, in single reninoma nuclei we observe excessive renin and NOTCH1 signalling mRNAs, with a concomitant non-excess of NRARP expression. Re-analysis of previously published reninoma bulk transcriptomes further corroborates our observation of dysregulated Notch pathway signalling in reninoma. Our findings reveal NOTCH1 rearrangements in reninoma, therapeutically targetable through existing NOTCH1 inhibitors, and indicate that unscheduled Notch signalling may be a disease-defining feature of reninoma.

FH Variant Pathogenicity Promotes Purine Salvage Pathway Dependence in Kidney Cancer

Fumarate accumulation due to loss of fumarate hydratase (FH) drives cellular transformation. Germline FH alterations lead to hereditary leiomyomatosis and renal cell cancer (HLRCC) where patients are predisposed to an aggressive form of kidney cancer. There is an unmet need to classify FH variants by cancer-associated risk. We quantified catalytic efficiencies of 74 variants of uncertain significance. Over half were enzymatically inactive, which is strong evidence of pathogenicity. We next generated a panel of HLRCC cell lines expressing FH variants with a range of catalytic activities, then correlated fumarate levels with metabolic features. We found that fumarate accumulation blocks de novo purine biosynthesis, rendering FH-deficient cells reliant on purine salvage for proliferation. Genetic or pharmacologic inhibition of the purine salvage pathway reduced HLRCC tumor growth in vivo. These findings suggest the pathogenicity of patient-associated FH variants and reveal purine salvage as a targetable vulnerability in FH-deficient tumors.

SIGNIFICANCE

This study functionally characterizes patient-associated FH variants with unknown significance for pathogenicity. This study also reveals nucleotide salvage pathways as a targetable feature of FH-deficient cancers, which are shown to be sensitive to the purine salvage pathway inhibitor 6-mercaptopurine. This presents a new rapidly translatable treatment strategy for FH-deficient cancers. This article is featured in Selected Articles from This Issue, p. 1949.

Mitochondrial Metabolism: A New Dimension of Personalized Oncology

Energy is needed by cancer cells to stay alive and communicate with their surroundings. The primary organelles for cellular metabolism and energy synthesis are mitochondria. Researchers recently proved that cancer cells can steal immune cells' mitochondria using nanoscale tubes. This finding demonstrates the dependence of cancer cells on normal cells for their living and function. It also denotes the importance of mitochondria in cancer cells' biology. Emerging evidence has demonstrated how mitochondria are essential for cancer cells to survive in the harsh tumor microenvironments, evade the immune system, obtain more aggressive features, and resist treatments. For instance, functional mitochondria can improve cancer resistance against radiotherapy by scavenging the released reactive oxygen species. Therefore, targeting mitochondria can potentially enhance oncological outcomes, according to this notion. The tumors' responses to anticancer treatments vary, ranging from a complete response to even cancer progression during treatment. Therefore, personalized cancer treatment is of crucial importance. So far, personalized cancer treatment has been based on genomic analysis. Evidence shows that tumors with high mitochondrial content are more resistant to treatment. This paper illustrates how mitochondrial metabolism can participate in cancer resistance to chemotherapy, immunotherapy, and radiotherapy. Pretreatment evaluation of mitochondrial metabolism can provide additional information to genomic analysis and can help to improve personalized oncological treatments. This article outlines the importance of mitochondrial metabolism in cancer biology and personalized treatments.

Mitochondrial-Encoded Complex I Impairment Induces a Targetable Dependency on Aerobic Fermentation in Hürthle Cell Carcinoma of the Thyroid

A metabolic hallmark of cancer identified by Warburg is the increased consumption of glucose and secretion of lactate, even in the presence of oxygen. Although many tumors exhibit increased glycolytic activity, most forms of cancer rely on mitochondrial respiration for tumor growth. We report here that Hürthle cell carcinoma of the thyroid (HTC) models harboring mitochondrial DNA-encoded defects in complex I of the mitochondrial electron transport chain exhibit impaired respiration and alterations in glucose metabolism. CRISPR-Cas9 pooled screening identified glycolytic enzymes as selectively essential in complex I-mutant HTC cells. We demonstrate in cultured cells and a patient-derived xenograft model that small-molecule inhibitors of lactate dehydrogenase selectively induce an ATP crisis and cell death in HTC. This work demonstrates that complex I loss exposes fermentation as a therapeutic target in HTC and has implications for other tumors bearing mutations that irreversibly damage mitochondrial respiration.

SIGNIFICANCE

HTC is enriched in somatic mtDNA mutations predicted to affect complex I of the electron transport chain (ETC). We demonstrate that these mutations impair respiration and induce a therapeutically tractable reliance on aerobic fermentation for cell survival. This work provides a rationale for targeting fermentation in cancers harboring irreversible genetically encoded ETC defects. See related article by Gopal et al., p. 1904. This article is highlighted in the In This Issue feature, p. 1749.

FOXA2 controls the anti-oxidant response in FH-deficient cells

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is a cancer syndrome caused by inactivating germline mutations in fumarate hydratase (FH) and subsequent accumulation of fumarate. Fumarate accumulation leads to profound epigenetic changes and the activation of an anti-oxidant response via nuclear translocation of the transcription factor NRF2. The extent to which chromatin remodeling shapes this anti-oxidant response is currently unknown. Here, we explored the effects of FH loss on the chromatin landscape to identify transcription factor networks involved in the remodeled chromatin landscape of FH-deficient cells. We identify FOXA2 as a key transcription factor that regulates anti-oxidant response genes and subsequent metabolic rewiring cooperating without direct interaction with the anti-oxidant regulator NRF2. The identification of FOXA2 as an anti-oxidant regulator provides additional insights into the molecular mechanisms behind cell responses to fumarate accumulation and potentially provides further avenues for therapeutic intervention for HLRCC.

The Pleiotropic Effects of Fumarate: From Mitochondrial Respiration to Epigenetic Rewiring and DNA Repair Mechanisms

Tumor onset and its progression are strictly linked to its metabolic rewiring on the basis of the Warburg effect. In this context, fumarate emerged as a putative oncometabolite mediating cancer progression. Fumarate accumulation is usually driven by fumarate hydratase (FH) loss of function, the enzyme responsible for the reversible conversion of fumarate into malate. Fumarate accumulation acts as a double edge sword: on one hand it takes part in the metabolic rewiring of cancer cells, while on the other it also plays a crucial role in chromatin architecture reorganization. The latter is achieved by competing with a-ketoglutarate-dependent enzymes, eventually altering the cellular methylome profile, which in turn leads to its transcriptome modeling. Furthermore, in recent years, it has emerged that FH has an ability to recruit DNA double strand breaks. The accumulation of fumarate into damaged sites might also determine the DNA repair pathway in charge for the seizure of the lesion, eventually affecting the mutational state of the cells. In this work, we aimed to review the current knowledge on the role of fumarate as an oncometabolite orchestrating the cellular epigenetic landscape and DNA repair machinery.

Research progress on the interaction between oxidative stress and platelets: Another avenue for cancer?

Oxidative stress (OS) is a chemical imbalance between an oxidant and an antioxidant, causing damage to redox signaling and control or causing molecular damage. Unbalanced oxidative metabolism can produce excessive reactive oxygen species (ROS). These excess ROS can cause drastic changes in platelet metabolism and further affect platelet function. It will also lead to an increase in platelet procoagulant phenotype and cell apoptosis, which will increase the risk of thrombosis. The creation of ROS and subsequent platelet activation, adhesion, and recruitment are then further encouraged in an auto-amplifying loop by ROS produced from platelets. Meanwhile, cancer cells produce a higher concentration of ROS due to their fast metabolism and high proliferation rate. However, excessive ROS can result in damage to and modification of cellular macromolecules. The formation of cancer and its progression is strongly associated with oxidative stress and the resulting oxidative damage. In addition, platelets are an important part of the tumor microenvironment, and there is a significant cross-communication between platelets and cancer cells. Cancer cells alter the activation status of platelets, their RNA spectrum, proteome, and other properties. The "cloaking" of cancer cells by platelets providing physical protection，avoiding destruction from shear stress and the attack of immune cells, promoting tumor cell invasion.We explored the vicious circle interaction between ROS, platelets, and cancer in this review, and we believe that ROS can play a stimulative role in tumor growth and metastasis through platelets.

On the Role of Glycolysis in Early Tumorigenesis-Permissive and Executioner Effects

Reprogramming energy production from mitochondrial respiration to glycolysis is now considered a hallmark of cancer. When tumors grow beyond a certain size they give rise to changes in their microenvironment (e.g., hypoxia, mechanical stress) that are conducive to the upregulation of glycolysis. Over the years, however, it has become clear that glycolysis can also associate with the earliest steps of tumorigenesis. Thus, many of the oncoproteins most commonly involved in tumor initiation and progression upregulate glycolysis. Moreover, in recent years, considerable evidence has been reported suggesting that upregulated glycolysis itself, through its enzymes and/or metabolites, may play a causative role in tumorigenesis, either by acting itself as an oncogenic stimulus or by facilitating the appearance of oncogenic mutations. In fact, several changes induced by upregulated glycolysis have been shown to be involved in tumor initiation and early tumorigenesis: glycolysis-induced chromatin remodeling, inhibition of premature senescence and induction of proliferation, effects on DNA repair, O-linked N-acetylglucosamine modification of target proteins, antiapoptotic effects, induction of epithelial-mesenchymal transition or autophagy, and induction of angiogenesis. In this article we summarize the evidence that upregulated glycolysis is involved in tumor initiation and, in the following, we propose a mechanistic model aimed at explaining how upregulated glycolysis may play such a role.

Metabolic reprogramming and interventions in endometrial carcinoma

Cancer cells are usually featured by metabolic adaptations that facilitate their growth, invasion, and metastasis. Thus, reprogramming of intracellular energy metabolism is currently one of the hotspots in the field of cancer research. Whereas aerobic glycolysis (known as the Warburg effect) has long been considered a dominant form of energy metabolism in cancer cells, emerging evidence indicates that other metabolic forms, especially oxidative phosphorylation (OXPHOS), may play a critical role at least in some types of cancer. Of note, women with metabolic syndromes (MetS), including obesity, hyperglycemia, dyslipidemia, and hypertension, have an increased risk of developing endometrial carcinoma (EC), suggesting a close link between metabolism and EC. Interestingly, the metabolic preferences vary among EC cell types, particularly cancer stem cells and chemotherapy-resistant cells. Currently, it is commonly accepted that glycolysis is the main energy provider in EC cells, while OXPHOS is reduced or impaired. Moreover, agents specifically targeting the glycolysis and/or OXPHOS pathways can inhibit tumor cell growth and promote chemosensitization. For example, metformin and weight control not only reduce the incidence of EC but also improve the prognosis of EC patients. In this review, we comprehensively overview the current in-depth understanding of the relationship between metabolism and EC and provide up-to-date insights into the development of novel therapies targeting energy metabolism for auxiliary treatment in combination with chemotherapy for EC, especially those resistant to conventional chemotherapy.

MYC-driven increases in mitochondrial DNA copy number occur early and persist throughout prostatic cancer progression

Increased mitochondrial function may render some cancers vulnerable to mitochondrial inhibitors. Since mitochondrial function is regulated partly by mitochondrial DNA copy number (mtDNAcn), accurate measurements of mtDNAcn could help reveal which cancers are driven by increased mitochondrial function and may be candidates for mitochondrial inhibition. However, prior studies have employed bulk macrodissections that fail to account for cell type-specific or tumor cell heterogeneity in mtDNAcn. These studies have often produced unclear results, particularly in prostate cancer. Herein, we developed a multiplex in situ method to spatially quantify cell type specific mtDNAcn. We show that mtDNAcn is increased in luminal cells of high-grade prostatic intraepithelial neoplasia (HGPIN), is increased in prostatic adenocarcinomas (PCa), and is further elevated in metastatic castration-resistant prostate cancer. Increased PCa mtDNAcn was validated by two orthogonal methods and is accompanied by increases in mtRNAs and enzymatic activity. Mechanistically, MYC inhibition in prostate cancer cells decreases mtDNA replication and expression of several mtDNA replication genes, and MYC activation in the mouse prostate leads to increased mtDNA levels in the neoplastic prostate cells. Our in situ approach also revealed elevated mtDNAcn in precancerous lesions of the pancreas and colon/rectum, demonstrating generalization across cancer types using clinical tissue samples.

Mitochondrial redox adaptations enable alternative aspartate synthesis in SDH-deficient cells

The oxidative tricarboxylic acid (TCA) cycle is a central mitochondrial pathway integrating catabolic conversions of NAD +to NADH and anabolic production of aspartate, a key amino acid for cell proliferation. Several TCA cycle components are implicated in tumorigenesis, including loss-of-function mutations in subunits of succinate dehydrogenase (SDH), also known as complex II of the electron transport chain (ETC), but mechanistic understanding of how proliferating cells tolerate the metabolic defects of SDH loss is still lacking. Here, we identify that SDH supports human cell proliferation through aspartate synthesis but, unlike other ETC impairments, the effects of SDH inhibition are not ameliorated by electron acceptor supplementation. Interestingly, we find aspartate production and cell proliferation are restored to SDH-impaired cells by concomitant inhibition of ETC complex I (CI). We determine that the benefits of CI inhibition in this context depend on decreasing mitochondrial NAD+/NADH, which drives SDH-independent aspartate production through pyruvate carboxylation and reductive carboxylation of glutamine. We also find that genetic loss or restoration of SDH selects for cells with concordant CI activity, establishing distinct modalities of mitochondrial metabolism for maintaining aspartate synthesis. These data therefore identify a metabolically beneficial mechanism for CI loss in proliferating cells and reveal how compartmentalized redox changes can impact cellular fitness.

Macrophage fumarate hydratase restrains mtRNA-mediated interferon production

Metabolic rewiring underlies the effector functions of macrophages1-3, but the mechanisms involved remain incompletely defined. Here, using unbiased metabolomics and stable isotope-assisted tracing, we show that an inflammatory aspartate-argininosuccinate shunt is induced following lipopolysaccharide stimulation. The shunt, supported by increased argininosuccinate synthase (ASS1) expression, also leads to increased cytosolic fumarate levels and fumarate-mediated protein succination. Pharmacological inhibition and genetic ablation of the tricarboxylic acid cycle enzyme fumarate hydratase (FH) further increases intracellular fumarate levels. Mitochondrial respiration is also suppressed and mitochondrial membrane potential increased. RNA sequencing and proteomics analyses demonstrate that there are strong inflammatory effects resulting from FH inhibition. Notably, acute FH inhibition suppresses interleukin-10 expression, which leads to increased tumour necrosis factor secretion, an effect recapitulated by fumarate esters. Moreover, FH inhibition, but not fumarate esters, increases interferon-β production through mechanisms that are driven by mitochondrial RNA (mtRNA) release and activation of the RNA sensors TLR7, RIG-I and MDA5. This effect is recapitulated endogenously when FH is suppressed following prolonged lipopolysaccharide stimulation. Furthermore, cells from patients with systemic lupus erythematosus also exhibit FH suppression, which indicates a potential pathogenic role for this process in human disease. We therefore identify a protective role for FH in maintaining appropriate macrophage cytokine and interferon responses.

Fumarate induces vesicular release of mtDNA to drive innate immunity

Mutations in fumarate hydratase (FH) cause hereditary leiomyomatosis and renal cell carcinoma1. Loss of FH in the kidney elicits several oncogenic signalling cascades through the accumulation of the oncometabolite fumarate2. However, although the long-term consequences of FH loss have been described, the acute response has not so far been investigated. Here we generated an inducible mouse model to study the chronology of FH loss in the kidney. We show that loss of FH leads to early alterations of mitochondrial morphology and the release of mitochondrial DNA (mtDNA) into the cytosol, where it triggers the activation of the cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING)-TANK-binding kinase 1 (TBK1) pathway and stimulates an inflammatory response that is also partially dependent on retinoic-acid-inducible gene I (RIG-I). Mechanistically, we show that this phenotype is mediated by fumarate and occurs selectively through mitochondrial-derived vesicles in a manner that depends on sorting nexin 9 (SNX9). These results reveal that increased levels of intracellular fumarate induce a remodelling of the mitochondrial network and the generation of mitochondrial-derived vesicles, which allows the release of mtDNAin the cytosol and subsequent activation of the innate immune response.

Morphologic Characteristics and Mutational Analysis of Fumarate Hydratase Deficient Kidney and Smooth Muscle Tumors

OBJECTIVES

Fumarate hydratase (FH)-deficient tumors can occur due to germline or somatic mutations and have distinctive morphologic features. The aims of this study are to refine morphologic criteria and identify mutations in FH-deficient smooth muscle tumors (SMTs).

METHODS

The morphology of SMTs and kidney tumors submitted to a national reference laboratory for FH immunohistochemistry (IHC) was reviewed by two gynecologic and two genitourinary pathologists, respectively. Fisher exact test was used for analysis. Fourteen SMTs were sequenced using the Illumina TruSight Oncology 500 Assay.

RESULTS

Twenty-two kidney tumors (5 FH deficient) and 51 SMTs (27 FH deficient) were reviewed. FH-deficient kidney tumors exclusively showed cord-like growth, rhabdoid change, and absence of coagulative tumor necrosis and psammoma bodies. FH-deficient SMTs were significantly more likely to have staghorn vessels, eosinophilic cytoplasmic inclusions, schwannoma-like areas, or hereditary leiomyomatosis and renal cell cancer-like nuclei (P < .05 for each). Seven of 14 sequenced SMTs showed mutations of the FH gene and no other driver mutations.

CONCLUSIONS

FH-deficient SMTs submitted for FH immunohistochemistry (IHC) showed distinct morphology. Although FH IHC is used for screening of FH-deficient tumors, FH mutations were identified in only 50% of FH-deficient SMTs. This highlights the need for additional exploration of mechanisms of FH protein loss in tumors lacking FH mutations.

Mitochondrial dysfunction-targeted nanosystems for precise tumor therapeutics

Mitochondria play critical roles in the regulation of the proliferation and apoptosis of cancerous cells. Targeted induction of mitochondrial dysfunction in cancer cells by multifunctional nanosystems for cancer treatment has attracted increasing attention in the past few years. Numerous therapeutic nanosystems have been designed for precise tumor therapy by inducing mitochondrial dysfunction, including reducing adenosine triphosphate, breaking redox homeostasis, inhibiting glycolysis, regulating proteins, membrane potential depolarization, mtDNA damage, mitophagy dysregulation and so on. Understanding the mechanisms of mitochondrial dysfunction would be helpful for efficient treatment of diseases and accelerating the translation of these therapeutic strategies into the clinic. Then, various strategies to construct mitochondria-targeted nanosystems and induce mitochondrial dysfunction are summarized, and the recent research progress regarding precise tumor therapeutics is highlighted. Finally, the major challenges and an outlook in this rapidly developing field are discussed. This review is expected to inspire further development of novel mitochondrial dysfunction-based strategies for precise treatments of cancer and other human diseases.

Spectrum of germline and somatic mitochondrial DNA variants in Tuberous Sclerosis Complex

Tuberous Sclerosis Complex (TSC) is caused by loss of function variants in either TSC1 or TSC2 and is characterized by broad phenotypic heterogeneity. Currently, there is limited knowledge regarding the role of the mitochondrial genome (mtDNA) in TSC pathogenesis. In this study, we aimed to determine the prevalence and spectrum of germline and somatic mtDNA variants in TSC and identify potential disease modifiers. Analysis of mtDNA amplicon massively parallel sequencing (aMPS) data, off-target mtDNA from whole-exome sequencing (WES), and/or qPCR, revealed mtDNA alterations in 270 diverse tissues (139 TSC-associated tumors and 131 normal tissue samples) from 199 patients and six healthy individuals. Correlation of clinical features to mtDNA variants and haplogroup analysis was done in 102 buccal swabs (age: 20-71 years). No correlation was found between clinical features and either mtDNA variants or haplogroups. No pathogenic variants were identified in the buccal swab samples. Using in silico analysis, we identified three predicted pathogenic variants in tumor samples: MT-ND4 (m.11742G>A, p. Cys328Tyr, VAF: 43%, kidney angiomyolipoma), MT-CYB (m.14775T>C, p. Leu10Pro, VAF: 43%, LAM abdominal tumor) and MT-CYB (m.15555C>T, p. Pro270Leu, VAF: 7%, renal cell carcinoma). Large deletions of the mitochondrial genome were not detected. Analysis of tumors from 23 patients with corresponding normal tissue did not reveal any recurrent tumor-associated somatic variants. The mtDNA/gDNA ratio between tumors and corresponding normal tissue was also unchanged. Overall, our findings demonstrate that the mitochondrial genome is highly stable across tissues and within TSC-associated tumors.

Wild-type IDH1 Knockout Leads to G0/G1 Arrest, Impairs Cancer Cell Proliferation, Altering Glycolysis, and the TCA Cycle in Colon Cancer

The isocitrate dehydrogenase (IDH), which participates in the TCA cycle, is an important key enzyme in regulating cell metabolism. The effect of the metabolic IDH enzyme on cancer pathogenesis has recently been shown in different types of cancer. However, the role of wild-type (wt) IDH1 in the development of colon cancer is still unknown. Our study investigated the role of the IDH1 enzyme in key hallmarks of colon cancer using various methods such as wound healing, cell cycle, colony formation ability, invasion, and apoptosis analysis. Furthermore, cell metabolism was investigated by pyruvate analysis, dinitrosalicylic acid, and HPLC methods. In addition, CRISPR/Cas9 tool was utilized to knockout the IDH1 gene in colon adenocarcinoma cells (SW620). Further studies were performed in two isogenic IDH1 KO clones. Our findings in both clones suggest that IDH1 KO results in G0/G1 arrest, and reduces proliferation by approximately twofold compared to IDH1 WT cells. In addition, the invasion, migration, and colony formation abilities of IDH1 KO clones were significantly decreased accompanied by significant morphological changes. In the context of metabolism, intracellular glucose, pyruvate, αKG, and malate levels were decreased, while the intracellular citrate level was increased in IDH1 KO clones as compared to IDH1 WT cells. Our results reveal that wt IDH1 knockout leads to a decrease in the aggressive features of colon cancer cells. In conclusion, we reported that wt IDH1 has an effective role in colon cancer progression and could be a potential therapeutic target.

Mitochondria and G-quadruplex evolution: an intertwined relationship

G-quadruplexes (G4s) are non-canonical structures formed in guanine (G)-rich sequences through stacked G tetrads by Hoogsteen hydrogen bonding. Several studies have demonstrated the existence of G4s in the genome of various organisms, including humans, and have proposed that G4s have a regulatory role in various cellular functions. However, little is known regarding the dissemination of G4s in mitochondria. In this review, we report the observation that the number of potential G4-forming sequences in the mitochondrial genome increases with the evolutionary complexity of different species, suggesting that G4s have a beneficial role in higher-order organisms. We also discuss the possible function of G4s in mitochondrial (mt)DNA and long noncoding (lnc)RNA and their role in various biological processes.

Kidney tumors associated with germline mutations of FH and SDHB show a CpG island methylator phenotype (CIMP)

Germline mutations within the Krebs cycle enzyme genes fumarate hydratase (FH) or succinate dehydrogenase (SDHB, SDHC, SDHD) are associated with an increased risk of aggressive and early metastasizing variants of renal cell carcinoma (RCC). These RCCs express significantly increased levels of intracellular fumarate or succinate that inhibit 2-oxoglutarate-dependent dioxygenases, such as the TET enzymes that regulate DNA methylation. This study evaluated the genome-wide methylation profiles of 34 RCCs from patients with RCC susceptibility syndromes and 11 associated normal samples using the Illumina HumanMethylation450 BeadChip. All the HLRCC (FH mutated) and SDHB-RCC (SDHB mutated) tumors demonstrated a distinct CpG island methylator phenotype (CIMP). HLRCC tumors demonstrated an extensive and relatively uniform level of hypermethylation that showed some correlation with tumor size. SDHB-RCC demonstrated a lesser and more varied pattern of hypermethylation that overlapped in part with the HLRCC hypermethylation. Combined methylation and mRNA expression analysis of the HLRCC tumors demonstrated hypermethylation and transcription downregulation of genes associated with the HIF pathway, HIF3A and CITED4, the WNT pathway, SFRP1, and epithelial-to-mesenchymal transition and MYC expression, OVOL1. These observations were confirmed in the TCGA CIMP-RCC tumors. A selected panel of probes could identify the CIMP tumors and differentiate between HLRCC and SDHB-RCC tumors. This panel accurately detected all CIMP-RCC tumors within the TCGA RCC cohort, identifying them as HLRCC -like, and could potentially be used to create a liquid biopsy-based screening tool. The CIMP signature in these aggressive tumors could provide both a useful biomarker for diagnosis and a target for novel therapies.

Tumorigenesis Mechanisms Found in Hereditary Renal Cell Carcinoma: A Review

Renal cell carcinoma is a heterogenous cancer composed of an increasing number of unique subtypes each with their own cellular and tumor behavior. The study of hereditary renal cell carcinoma, which composes just 5% of all types of tumor cases, has allowed for the elucidation of subtype-specific tumorigenesis mechanisms that can also be applied to their sporadic counterparts. This review will focus on the major forms of hereditary renal cell carcinoma and the genetic alterations contributing to their tumorigenesis, including von Hippel Lindau syndrome, Hereditary Papillary Renal Cell Carcinoma, Succinate Dehydrogenase-Deficient Renal Cell Carcinoma, Hereditary Leiomyomatosis and Renal Cell Carcinoma, BRCA Associated Protein 1 Tumor Predisposition Syndrome, Tuberous Sclerosis, Birt-Hogg-Dubé Syndrome and Translocation RCC. The mechanisms for tumorigenesis described in this review are beginning to be exploited via the utilization of novel targets to treat renal cell carcinoma in a subtype-specific fashion.

Epidemiology of Renal Cell Carcinoma: 2022 Update

CONTEXT

International variations in the rates of kidney cancer (KC) are considerable. An understanding of the risk factors for KC development is necessary to generate opportunities to reduce its incidence through prevention and surveillance.

OBJECTIVE

To retrieve and summarize global incidence and mortality rates of KC and risk factors associated with its development, and to describe known familial syndromes and genetic alterations that represent biologic risk factors.

EVIDENCE ACQUISITION

A systematic review was conducted via Medline (PubMed) and Scopus to include meta-analyses, reviews, and original studies regarding renal cell carcinoma, epidemiology, and risk factors.

EVIDENCE SYNTHESIS

Our narrative review provides a detailed analysis of KC incidence and mortality, with significant variations across time, geography, and sex. In particular, while KC incidence has continued to increase, mortality models have leveled off. Among the many risk factors, hypertension, obesity, and smoking are the most well established. The emergence of new genetic data coupled with observational data allows for integrated management and surveillance strategies for KC care.

CONCLUSIONS

KC incidence and mortality rates vary significantly by geography, sex, and age. Associations of the development of KC with modifiable and fixed risk factors such as obesity, hypertension, smoking, and chronic kidney disease (CKD)/end-stage kidney disease (ESKD) are well described. Recent advances in the genetic characterization of these cancers have led to a better understanding of the germline and somatic mutations that predispose patients to KC development, with potential for identification of therapeutic targets that may improve outcomes for these at-risk patients.

PATIENT SUMMARY

We reviewed evidence on the occurrence of kidney cancer (KC) around the world. Currently, the main avoidable causes are smoking, obesity, and high blood pressure. Although other risk factors also contribute, prevention and treatment of these three factors provide the best opportunities to reduce the risk of developing KC at present.

Geometric Constraints Regulate Energy Metabolism and Cellular Contractility in Vascular Smooth Muscle Cells by Coordinating Mitochondrial DNA Methylation

Vascular smooth muscle cells (SMCs) can adapt to changes in cellular geometric cues; however, the underlying mechanisms remain elusive. Using 2D micropatterned substrates to engineer cell geometry, it is found that in comparison with an elongated geometry, a square-shaped geometry causes the nuclear-to-cytoplasmic redistribution of DNA methyltransferase 1 (DNMT1), hypermethylation of mitochondrial DNA (mtDNA), repression of mtDNA gene transcription, and impairment of mitochondrial function. Using irregularly arranged versus circumferentially aligned vascular grafts to control cell geometry in 3D growth, it is demonstrated that cell geometry, mtDNA methylation, and vessel contractility are closely related. DNMT1 redistribution is found to be dependent on the phosphoinositide 3-kinase and protein kinase B (AKT) signaling pathways. Cell elongation activates cytosolic phospholipase A2, a nuclear mechanosensor that, when inhibited, hinders AKT phosphorylation, DNMT1 nuclear accumulation, and energy production. The findings of this study provide insights into the effects of cell geometry on SMC function and its potential implications in the optimization of vascular grafts.

HIRA loss transforms FH-deficient cells

Fumarate hydratase (FH) is a mitochondrial enzyme that catalyzes the reversible hydration of fumarate to malate in the tricarboxylic acid (TCA) cycle. Germline mutations of FH lead to hereditary leiomyomatosis and renal cell carcinoma (HLRCC), a cancer syndrome characterized by a highly aggressive form of renal cancer. Although HLRCC tumors metastasize rapidly, FH-deficient mice develop premalignant cysts in the kidneys, rather than carcinomas. How Fh1-deficient cells overcome these tumor-suppressive events during transformation is unknown. Here, we perform a genome-wide CRISPR-Cas9 screen to identify genes that, when ablated, enhance the proliferation of Fh1-deficient cells. We found that the depletion of the histone cell cycle regulator (HIRA) enhances proliferation and invasion of Fh1-deficient cells in vitro and in vivo. Mechanistically, Hira loss activates MYC and its target genes, increasing nucleotide metabolism specifically in Fh1-deficient cells, independent of its histone chaperone activity. These results are instrumental for understanding mechanisms of tumorigenesis in HLRCC and the development of targeted treatments for patients.

Conditional Covalent Lethality Driven by Oncometabolite Accumulation

Hereditary leiomyomatosis and renal cell carcinoma (HLRCC) is a cancer predisposition syndrome driven by mutation of the tumor suppressor fumarate hydratase (FH). Inactivation of FH causes accumulation of the electrophilic oncometabolite fumarate. In the absence of methods for reactivation, tumor suppressors can be targeted via identification of synthetic lethal interactions using genetic screens. Inspired by recent advances in chemoproteomic target identification, here, we test the hypothesis that the electrophilicity of the HLRCC metabolome may produce unique susceptibilities to covalent small molecules, a phenomenon we term conditional covalent lethality. Screening a panel of chemically diverse electrophiles, we identified a covalent ligand, MP-1, that exhibits FH-dependent cytotoxicity. Synthesis and structure-activity profiling identified key molecular determinants underlying the molecule's effects. Chemoproteomic profiling of cysteine reactivity together with clickable probes validated the ability of MP-1 to engage an array of functional cysteines, including one lying in the Zn-finger domain of the tRNA methyltransferase enzyme TRMT1. TRMT1 overexpression rescues tRNA methylation from inhibition by MP-1 and partially attenuates the covalent ligand's cytotoxicity. Our studies highlight the potential for covalent metabolites and small molecules to synergistically produce novel synthetic lethal interactions and raise the possibility of applying phenotypic screening with chemoproteomic target identification to identify new functional oncometabolite targets.

Genomic and Metabolic Hallmarks of SDH- and FH-deficient Renal Cell Carcinomas

BACKGROUND

Succinate dehydrogenase-deficient and fumarate hydratase-deficient renal cell carcinomas (SDHRCC and FHRCC) are rare kidney cancers driven by loss of TCA cycle enzymes.

OBJECTIVE

To define and compare the genomic and metabolomic hallmarks of SDHRCC and FHRCC.

DESIGN, SETTING, AND PARTICIPANTS

We analyzed SDHRCC and FHRCC tumors with either immunohistochemical evidence of loss of protein expression or genomically confirmed biallelic inactivation of SDHA/B/C/D/AF2 or FH.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Somatic alterations were identified using clinical pipelines, with allele-specific copy number alterations (CNAs) identified using FACETS. Mass spectrometry-based metabolomic profiling was performed on available SDHRCC and FHRCC tumors.

RESULTS AND LIMITATIONS

Tumors were analyzed for 42 patients (25 FHRCC, 17 SDHRCC). In the germline analysis, 16/17 SDHRCCs harbored a germline alteration in SDHB, whereas only 17/22 FHRCCs had pathogenic germline FH variants. SDHRCCs had a lower mutation burden (p = 0.02) and CNA burden (p = 0.0002) than FHRCCs. All SDHRCCs presented with deletion of chromosome 1p (overlapping SDHB), whereas FHRCCs demonstrated high but not ubiquitous loss of 1q (FH locus). Both SDHRCCs and FHRCCs exhibited significant idiopathic accumulation of the metabolite guanine. FHRCC tumors had elevated levels of urea cycle metabolites (argininosuccinate, citrulline, and fumarate), whereas SDHRCC tumors had elevation of numerous acylcarnitines. These characteristic metabolic changes allowed identification of a previously unrecognized SDH-deficient RCC.

CONCLUSIONS

Despite sharing similar genetic etiology, SDHRCC and FHRCC represent distinct molecular entities with unique genetic and metabolic abnormalities.

PATIENT SUMMARY

Kidney cancers driven by loss of the gene encoding either the succinate dehydrogenase or fumarate hydratase enzyme are rare. We sought to define and compare the genetic and metabolic features of these cancer entities.

Mitochondrial quality control in diabetic cardiomyopathy: from molecular mechanisms to therapeutic strategies

In diabetic cardiomyopathy (DCM), a major diabetic complication, the myocardium is structurally and functionally altered without evidence of coronary artery disease, hypertension or valvular disease. Although numerous anti-diabetic drugs have been applied clinically, specific medicines to prevent DCM progression are unavailable, so the prognosis of DCM remains poor. Mitochondrial ATP production maintains the energetic requirements of cardiomyocytes, whereas mitochondrial dysfunction can induce or aggravate DCM by promoting oxidative stress, dysregulated calcium homeostasis, metabolic reprogramming, abnormal intracellular signaling and mitochondrial apoptosis in cardiomyocytes. In response to mitochondrial dysfunction, the mitochondrial quality control (MQC) system (including mitochondrial fission, fusion, and mitophagy) is activated to repair damaged mitochondria. Physiological mitochondrial fission fragments the network to isolate damaged mitochondria. Mitophagy then allows dysfunctional mitochondria to be engulfed by autophagosomes and degraded in lysosomes. However, abnormal MQC results in excessive mitochondrial fission, impaired mitochondrial fusion and delayed mitophagy, causing fragmented mitochondria to accumulate in cardiomyocytes. In this review, we summarize the molecular mechanisms of MQC and discuss how pathological MQC contributes to DCM development. We then present promising therapeutic approaches to improve MQC and prevent DCM progression.

Dual specificity phosphatase 1 attenuates inflammation-induced cardiomyopathy by improving mitophagy and mitochondrial metabolism

Objectives

Methods

Results

Conclusion

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DUSP1 overexpression alleviates LPS-mediated myocardial inflammation.

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DUSP1 improves lipopolysaccharide-disrupted mitochondrial function.

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DUSP1 restores FUN14 domain-containing 1 (FUNDC1)-dependent mitophagy in SCM.

Mitochondrial DNA mutations in aging and cancer

Advancing age is a major risk factor for malignant transformation and the development of cancer. As such, over 50% of neoplasms occur in individuals over the age of 70. The pathologies of both ageing and cancer have been characterized by respective groups of molecular hallmarks, and while some features are divergent between the two pathologies, several are shared. Perturbed mitochondrial function is one such common hallmark, and this observation therefore suggests that mitochondrial alterations may be of significance in age‐related cancer development. There is now considerable evidence documenting the accumulation of somatic mitochondrial DNA (mtDNA) mutations in ageing human postmitotic and replicative tissues. Similarly, mutations of the mitochondrial genome have been reported in human cancers for decades. The plethora of functions in which mitochondria partake, such as oxidative phosphorylation, redox balance, apoptosis and numerous biosynthetic pathways, manifests a variety of ways in which alterations in mtDNA may contribute to tumour growth. However, the specific mechanisms by which mtDNA mutations contribute to tumour progression remain elusive and often contradictory. This review aims to consolidate current knowledge and describe future direction within the field.

Mitonuclear genotype remodels the metabolic and microenvironmental landscape of Hürthle cell carcinoma

Hürthle cell carcinomas (HCCs) display two exceptional genotypes: near-homoplasmic mutation of mitochondrial DNA (mtDNA) and genome-wide loss of heterozygosity (gLOH). To understand the phenotypic consequences of these genetic alterations, we analyzed genomic, metabolomic, and immunophenotypic data of HCC and other thyroid cancers. Both mtDNA mutations and profound depletion of citrate pools are common in HCC and other thyroid malignancies, suggesting that thyroid cancers are broadly equipped to survive tricarboxylic acid cycle impairment, whereas metabolites in the reduced form of NADH-dependent lysine degradation pathway were elevated exclusively in HCC. The presence of gLOH was not associated with metabolic phenotypes but rather with reduced immune infiltration, indicating that gLOH confers a selective advantage partially through immunosuppression. Unsupervised multimodal clustering revealed four clusters of HCC with distinct clinical, metabolomic, and microenvironmental phenotypes but overlapping genotypes. These findings chart the metabolic and microenvironmental landscape of HCC and shed light on the interaction between genotype, metabolism, and the microenvironment in cancer.

Empagliflozin attenuates cardiac microvascular ischemia/reperfusion through activating the AMPKα1/ULK1/FUNDC1/mitophagy pathway

Mitophagy preserves microvascular structure and function during myocardial ischemia/reperfusion (I/R) injury. Empagliflozin, an anti-diabetes drug, may also protect mitochondria. We explored whether empagliflozin could reduce cardiac microvascular I/R injury by enhancing mitophagy. In mice, I/R injury induced luminal stenosis, microvessel wall damage, erythrocyte accumulation and perfusion defects in the myocardial microcirculation. Additionally, I/R triggered endothelial hyperpermeability and myocardial neutrophil infiltration, which upregulated adhesive factors and endothelin-1 but downregulated vascular endothelial cadherin and endothelial nitric oxide synthase in heart tissue. In vitro, I/R impaired the endothelial barrier function and integrity of cardiac microvascular endothelial cells (CMECs), while empagliflozin preserved CMEC homeostasis and thus maintained cardiac microvascular structure and function. I/R activated mitochondrial fission, oxidative stress and apoptotic signaling in CMECs, whereas empagliflozin normalized mitochondrial fission and fusion, neutralized supraphysiologic reactive oxygen species concentrations and suppressed mitochondrial apoptosis. Empagliflozin exerted these protective effects by activating FUNDC1-dependent mitophagy through the AMPKα1/ULK1 pathway. Both in vitro and in vivo, genetic ablation of AMPKα1 or FUNDC1 abolished the beneficial effects of empagliflozin on the myocardial microvasculature and CMECs. Taken together, the preservation of mitochondrial function through an activation of the AMPKα1/ULK1/FUNDC1/mitophagy pathway is the working mechanism of empagliflozin in attenuating cardiac microvascular I/R injury.

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Empagliflozin reduces I/R-induced microvascular damage.

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Empagliflozin suppresses I/R-induced endothelial cell damage.

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Empagliflozin activates FUNDC1-dependent mitophagy through the AMPKα1/ULK1 pathway.

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Ablation of FUNDC1 or AMPKα1 abolishes the protective effects of empagliflozin against I/R-induced microvascular damage.

Personalized Management of Pheochromocytoma and Paraganglioma

Pheochromocytomas/paragangliomas are characterized by a unique molecular landscape that allows their assignment to clusters based on underlying genetic alterations. With around 30% to 35% of Caucasian patients (a lower percentage in the Chinese population) showing germline mutations in susceptibility genes, pheochromocytomas/paragangliomas have the highest rate of heritability among all tumors. A further 35% to 40% of Caucasian patients (a higher percentage in the Chinese population) are affected by somatic driver mutations. Thus, around 70% of all patients with pheochromocytoma/paraganglioma can be assigned to 1 of 3 main molecular clusters with different phenotypes and clinical behavior. Krebs cycle/VHL/EPAS1-related cluster 1 tumors tend to a noradrenergic biochemical phenotype and require very close follow-up due to the risk of metastasis and recurrence. In contrast, kinase signaling-related cluster 2 tumors are characterized by an adrenergic phenotype and episodic symptoms, with generally a less aggressive course. The clinical correlates of patients with Wnt signaling-related cluster 3 tumors are currently poorly described, but aggressive behavior seems likely. In this review, we explore and explain why cluster-specific (personalized) management of pheochromocytoma/paraganglioma is essential to ascertain clinical behavior and prognosis, guide individual diagnostic procedures (biochemical interpretation, choice of the most sensitive imaging modalities), and provide personalized management and follow-up. Although cluster-specific therapy of inoperable/metastatic disease has not yet entered routine clinical practice, we suggest that informed personalized genetic-driven treatment should be implemented as a logical next step. This review amalgamates published guidelines and expert views within each cluster for a coherent individualized patient management plan.

Hypermethylation of mitochondrial DNA facilitates bone metastasis of renal cell carcinoma

Kidney cancers including clear cell carcinoma (RCC) are identified with very vulnerable mitochondria DNA (mtDNA) and frequent epigenetic aberrations. Bone metastasis from RCC is prevalent and destructive. Bone marrow contains a quite hypoxic microenvironment that usually insitigate 50% of hypermethylation events in conferring a selective advantage for tumor growth. We hypothesized that hypermethylation of mtDNA in RCC cells would significantly contribute to bone metastatic tumor progression. Methylation-specific polymerase chain reaction assay (MSP) was adopted to measure the methylation status of D-loop region of mtDNA in 15 pairs of bone metastatic and primary RCC as well as tumor adjescent normal kidney tissues. mtDNA copy number was examined by the real-time quantitative polymerase chain reaction (qPCR). Western blotting analysis was used to measure the accumulation of several DNA methyltransferases (DNMTs) in the mitochondria and nucleus fractions of bone metastatic RCC cells. mRNA expression of mitochondria encoded genes was examined by RT-PCR. Reactive oxygen species (ROS), mitochondrial membrane potential and ATP content were measured using in vitro cells treated with de-methylation drug 5-Azacytidine (5-Aza). Non-invasive bioluminescent imaging was performed to monitor tumor occurrence in skeleton in mice. Our results showed that the D-loop region in bone metastatic tumor cells was markedly hypermethylated than those in primary RCC tumor cells, that is associated with a decreased mtDNA copy number and accumulation of DNMT1 in the mitochondria. The bone-tropism tumor colonization and progression of RCC cells was significantly suppressed by demethylating the D-loop region of mtDNA and reducing the intracellular level of ROS and ATP by 5-Aza treatment. In conclusion, our study provided a direct association between hypermethylation of mtDNA in RCC with bone metastastic tumor growth.

Monitoring and Modulating mtDNA G-Quadruplex Dynamics Reveal Its Close Relationship to Cell Glycolysis

The mitochondrial DNA G-quadruplex (mtDNA G4) is a potential regulatory element for the regulation of mitochondrial functions; however, its relevance and specific roles in diseases remain largely unknown. Here, we engineered a set of chemical probes, including MitoISCH, an mtDNA G4-specific fluorescent probe, together with MitoPDS, a mitochondria-targeted G4-stabilizing agent, to thoroughly investigate mtDNA G4s. Using MitoISCH to monitor previously intractable dynamics of mtDNA G4s, we surprisingly found that their formation was prevalent only in endothelial and cancer cells that rely on glycolysis for energy production. Consistent with this, promotion of mtDNA G4 folding by MitoPDS in turn caused glycolysis-related gene activation and glycolysis enhancement. Remarkably, this close relationship among mtDNA G4s, glycolysis, and cancer cells further allowed MitoISCH to accumulate in tumors and label them in vivo. Our work reveals an unprecedented link between mtDNA G4s and cell glycolysis, suggesting that mtDNA G4s may be a novel cancer biomarker and therapeutic target deserving further exploration.

Emerging Role of TCA Cycle-Related Enzymes in Human Diseases

The tricarboxylic acid (TCA) cycle is the main source of cellular energy and participates in many metabolic pathways in cells. Recent reports indicate that dysfunction of TCA cycle-related enzymes causes human diseases, such as neurometabolic disorders and tumors, have attracted increasing interest in their unexplained roles. The diseases which develop as a consequence of loss or dysfunction of TCA cycle-related enzymes are distinct, suggesting that each enzyme has a unique function. This review aims to provide a comprehensive overview of the relationship between each TCA cycle-related enzyme and human diseases. We also discuss their functions in the context of both mitochondrial and extra-mitochondrial (or cytoplasmic) enzymes.

Fumarate hydratase-deficient renal cell carcinoma: A tumor with diverse morphology including cannibalism, lymphocytic emperipolesis, and defective autophagy

We report the clinicopathological findings of the first series of 3 patients from Brazil with fumarate hydratase-deficient renal cell carcinoma. The clinicopathological findings disclosed a very aggressive tumor. All 3 patients had solitary tumor at the left side, metastasis and advanced stage at the time of diagnosis; were females with a median age of 40 years; had a history of uterine leiomyomas; and, at follow-up two patients are deceased and one patient alive. The microscopic findings of these 3 patients are in accordance with the literature disclosing a variety of morphologic features being papillary arrangement, eosinophilic cytoplasm, and prominent nucleoli surrounded by clear halo the constant and most frequent findings. Previously not reported in this tumor, we describe presence of cannibalism, lymphocytic emperipolesis, and cytoplasmic vacuoles with eosinophilic inclusions associated with overexpression of p62 in immunohistochemistry which is considered to be evidence of defective autophagy. Lymphocytic emperipolesis was a more frequent finding than cannibalism and immunohistochemistry for p62 was overexpressed only in the 2 patients disclosing cytoplasmic vacuoles with eosinophilic inclusions. The presence, frequency and significance of these novel findings should be checked in large series of this rare and aggressive tumor aiming to associate with clinical behavior and eventually influence the strategy of treatment.

Pathogenic mitochondrial dysfunction and metabolic abnormalities

Herein we trace links between biochemical pathways, pathogenesis, and metabolic diseases to set the stage for new therapeutic advances. Cellular and acellular microorganisms including bacteria and viruses are primary pathogenic drivers that cause disease. Missing from this statement are subcellular compartments, importantly mitochondria, which can be pathogenic by themselves, also serving as key metabolic disease intermediaries. The breakdown of food molecules provides chemical energy to power cellular processes, with mitochondria as powerhouses and ATP as the principal energy carrying molecule. Most animal cell ATP is produced by mitochondrial synthase; its central role in metabolism has been known for >80 years. Metabolic disorders involving many organ systems are prevalent in all age groups. Progressive pathogenic mitochondrial dysfunction is a hallmark of genetic mitochondrial diseases, the most common phenotypic expression of inherited metabolic disorders. Confluent genetic, metabolic, and mitochondrial axes surface in diabetes, heart failure, neurodegenerative disease, and even in the ongoing coronavirus pandemic.

The yeast mitochondrial succinylome: Implications for regulation of mitochondrial nucleoids

Acylation modifications, such as the succinylation of lysine, are post-translational modifications and a powerful means of regulating protein activity. Some acylations occur nonenzymatically, driven by an increase in the concentration of acyl group donors. Lysine succinylation has a profound effect on the corresponding site within the protein, as it dramatically changes the charge of the residue. In eukaryotes, it predominantly affects mitochondrial proteins because the donor of succinate, succinyl-CoA, is primarily generated in the tricarboxylic acid cycle. Although numerous succinylated mitochondrial proteins have been identified in Saccharomyces cerevisiae, a more detailed characterization of the yeast mitochondrial succinylome is still lacking. Here, we performed a proteomic MS analysis of purified yeast mitochondria and detected 314 succinylated mitochondrial proteins with 1763 novel succinylation sites. The mitochondrial nucleoid, a complex of mitochondrial DNA and mitochondrial proteins, is one of the structures whose protein components are affected by succinylation. We found that Abf2p, the principal component of mitochondrial nucleoids responsible for compacting mitochondrial DNA in S. cerevisiae, can be succinylated in vivo on at least thirteen lysine residues. Abf2p succinylation in vitro inhibits its DNA-binding activity and reduces its sensitivity to digestion by the ATP-dependent ScLon protease. We conclude that changes in the metabolic state of a cell resulting in an increase in the concentration of tricarboxylic acid intermediates may affect mitochondrial functions.

[FH-deficient renal cell carcinoma expands the spectrum of renal papillary tumors]

Fumarate hydratase (FH)-deficient renal cell carcinoma (RCC) is a distinct entity, which shows a biallelic inactivation of the FH gene that consequently leads to FH protein expression and function loss, respectively. This alteration leads to an accumulation of the oncometabolite fumarate in the citrate cycle and various disorders of the cell balance and DNA processing. FH-deficient RCC often shows a morphologically overlapping spectrum with papillary renal cell carcinoma (type 2), whereby a typical mixture of growth patterns including tubulo-cystic, cribriform, and/or solid differentiation can be observed. A characteristic but non-specific morphological feature is prominent eosinophilic, virus-inclusion body-like nucleoli with perinucleolar halos. Tumoral immunohistochemical loss of FH expression supports the diagnosis but may be preserved in rare cases. Most FH-deficient RCCs show very aggressive biological behavior and are often metastasized at the time of diagnosis. The initial description encompassed RCC in association with the hereditary leiomyomatosis and renal cell carcinoma (HLRCC) syndrome, which also includes cutaneous and uterine leiomyomas. However, current data also show an increasing proportion of sporadic cases, so that a distinction (hereditary vs. sporadic) seems appropriate. So far, few but promising data on effective systemic therapeutic options have been reported. In summary, precise diagnosis is of great importance due to the frequent aggressive biological behavior, potential need to deviate from the therapeutic standard, and the possible indicator of a hereditary disease.

Increased presence of nuclear DNAJA3 and upregulation of cytosolic STAT1 and of nucleic acid sensors trigger innate immunity in the ClpP-null mouse

Mitochondrial dysfunction may activate innate immunity, e.g. upon abnormal handling of mitochondrial DNA in TFAM mutants or in altered mitophagy. Recent reports showed that also deletion of mitochondrial matrix peptidase ClpP in mice triggers transcriptional upregulation of inflammatory factors. Here, we studied ClpP-null mouse brain at two ages and mouse embryonal fibroblasts, to identify which signaling pathways are responsible, employing mass spectrometry, subcellular fractionation, immunoblots, and reverse transcriptase polymerase chain reaction. Several mitochondrial unfolded protein response factors showed accumulation and altered migration in blue-native gels, prominently the co-chaperone DNAJA3. Its mitochondrial dysregulation increased also its extra-mitochondrial abundance in the nucleus, a relevant observation given that DNAJA3 modulates innate immunity. Similar observations were made for STAT1, a putative DNAJA3 interactor. Elevated expression was observed not only for the transcription factors Stat1/2, but also for two interferon-stimulated genes (Ifi44, Gbp3). Inflammatory responses were strongest for the RLR pattern recognition receptors (Ddx58, Ifih1, Oasl2, Trim25) and several cytosolic nucleic acid sensors (Ifit1, Ifit3, Oas1b, Ifi204, Mnda). The consistent dysregulation of these factors from an early age might influence also human Perrault syndrome, where ClpP loss-of-function leads to early infertility and deafness, with subsequent widespread neurodegeneration.

Mitochondrial Heteroplasmy Shifting as a Potential Biomarker of Cancer Progression

Cancer is a serious health problem with a high mortality rate worldwide. Given the relevance of mitochondria in numerous physiological and pathological mechanisms, such as adenosine triphosphate (ATP) synthesis, apoptosis, metabolism, cancer progression and drug resistance, mitochondrial genome (mtDNA) analysis has become of great interest in the study of human diseases, including cancer. To date, a high number of variants and mutations have been identified in different types of tumors, which coexist with normal alleles, a phenomenon named heteroplasmy. This mechanism is considered an intermediate state between the fixation or elimination of the acquired mutations. It is suggested that mutations, which confer adaptive advantages to tumor growth and invasion, are enriched in malignant cells. Notably, many recent studies have reported a heteroplasmy-shifting phenomenon as a potential shaper in tumor progression and treatment response, and we suggest that each cancer type also has a unique mitochondrial heteroplasmy-shifting profile. So far, a plethora of data evidencing correlations among heteroplasmy and cancer-related phenotypes are available, but still, not authentic demonstrations, and whether the heteroplasmy or the variation in mtDNA copy number (mtCNV) in cancer are cause or consequence remained unknown. Further studies are needed to support these findings and decipher their clinical implications and impact in the field of drug discovery aimed at treating human cancer.

Adhesion-mediated mechanosignaling forces mitohormesis

Mitochondria control eukaryotic cell fate by producing the energy needed to support life and the signals required to execute programed cell death. The biochemical milieu is known to affect mitochondrial function and contribute to the dysfunctional mitochondrial phenotypes implicated in cancer and the morbidities of aging. However, the physical characteristics of the extracellular matrix are also altered in cancerous and aging tissues. Here, we demonstrate that cells sense the physical properties of the extracellular matrix and activate a mitochondrial stress response that adaptively tunes mitochondrial function via solute carrier family 9 member A1-dependent ion exchange and heat shock factor 1-dependent transcription. Overall, our data indicate that adhesion-mediated mechanosignaling may play an unappreciated role in the altered mitochondrial functions observed in aging and cancer.

Kidney cancer: from genes to therapy

Renal cell carcinoma incidence is rising worldwide with increasing subtype stratification by the World Health Organization. Each subtype has unique genetic alterations, cell biology changes and clinical findings. Such genetic alterations offer the potential for individualized therapeutic approaches that are rapidly progressing. This review highlights the most common subtypes of renal cell carcinoma, including both hereditary and sporadic forms, with a focus on genetic changes, clinical findings and ongoing clinical trials.