Mitochondrial retrograde signaling mediated by UCP2 inhibits cancer cell proliferation and tumorigenesis

The Role of Mitochondrial Solute Carriers SLC25 in Cancer Metabolic Reprogramming: Current Insights and Future Perspectives

Cancer cells undergo remarkable metabolic changes to meet their high energetic and biosynthetic demands. The Warburg effect is the most well-characterized metabolic alteration, driving cancer cells to catabolize glucose through aerobic glycolysis to promote proliferation. Another prominent metabolic hallmark of cancer cells is their increased reliance on glutamine to replenish tricarboxylic acid (TCA) cycle intermediates essential for ATP production, aspartate and fatty acid synthesis, and maintaining redox homeostasis. In this context, mitochondria, which are primarily used to maintain energy homeostasis and support balanced biosynthesis in normal cells, become central organelles for fulfilling the heightened biosynthetic and energetic demands of proliferating cancer cells. Mitochondrial coordination and metabolite exchange with other cellular compartments are crucial. The human SLC25 mitochondrial carrier family, comprising 53 members, plays a pivotal role in transporting TCA intermediates, amino acids, vitamins, nucleotides, and cofactors across the inner mitochondrial membrane, thereby facilitating this cross-talk. Numerous studies have demonstrated that mitochondrial carriers are altered in cancer cells, actively contributing to tumorigenesis. This review comprehensively discusses the role of SLC25 carriers in cancer pathogenesis and metabolic reprogramming based on current experimental evidence. It also highlights the research gaps that need to be addressed in future studies. Understanding the involvement of these carriers in tumorigenesis may provide valuable novel targets for drug development.

Stress-induced premature senescence in high five cell cultures: a principal factor in cell-density effects

The Baculovirus Expression Vector System (BEVS) is highly valued in vaccine development, protein engineering, and drug metabolism research due to its biosafety, operational convenience, rapid scalability, and capacity for self-assembling virus-like particles. However, increasing cell density at the time of inoculation severely compromises the production capacity of BEVS, resulting in the "cell density effect". This study aimed to explore the mechanisms of the cell density effect through time-series analysis of transcriptomes and proteomes, with the goal of overcoming or alleviating the decline in productivity caused by increased cell density. The dynamic analysis of the omics of High Five cells under different CCI (cell density at infection) conditions showed that the impact of the "cell density effect" increased over time, particularly affecting genetic information processing, error repair, protein expression regulation, and material energy metabolism. Omics analysis of the growth stage of High Five cells showed that after 36 h of culture (cell density of about 1 × 106 cells/mL), the expression of ribosome-related proteins decreased, resulting in a rapid decrease in protein synthesis capacity, which was a key indicator of cell aging. Senescence verification experiments showed that cells began to show obvious early aging characteristics after 36 h, resulting in a decrease in the host cell's ability to resist stress. Overexpression and siRNA inhibition studies showed that the ndufa12 gene was a potential regulatory target for restricting the "cell density effect". Our results suggested that stress-induced premature senescence in High Five cell cultures, resulting in reduced energy metabolism and protein synthesis capabilities, was a critical factor contributing to cell density effects, and ultimately affecting virus production. In conclusion, this study provided new insights into managing virus production limitations due to cell density effects and offered innovative strategies to mitigate the adverse effects of cellular aging in biomanufacturing technologies.

A New Strategy for Targeting UCP2 to Modulate Glycolytic Reprogramming as a Treatment for Sepsis A New Strategy for Targeting UCP2

Sepsis is a severe and life-threatening disease caused by infection, characterized by a dysregulated immune response. Unfortunately, effective treatment strategies for sepsis are still lacking. The intricate interplay between metabolism and the immune system limits the treatment options for sepsis. During sepsis, there is a profound shift in cellular energy metabolism, which triggers a metabolic reprogramming of immune cells. This metabolic alteration impairs immune responses, giving rise to excessive inflammation and immune suppression. Recent research has demonstrated that UCP2 not only serves as a critical target in sepsis but also functions as a key metabolic switch involved in immune cell-mediated inflammatory responses. However, the regulatory mechanisms underlying this modulation are complex. This article focuses on UCP2 as a target and discusses metabolic reprogramming during sepsis and the complex regulatory mechanisms between different stages of inflammation. Our research indicates that overexpression of UCP2 reduces the Warburg effect, restores mitochondrial function, and improves the prognosis of sepsis. This discovery aims to provide a promising approach to address the significant challenges associated with metabolic dysfunction and immune paralysis.

UCP2, a Member of the Mitochondrial Uncoupling Proteins: An Overview from Physiological to Pathological Roles

UCP2 is an uncoupling protein homolog to UCP1. Unlike UCP1, which participates in non-shivering thermogenesis by uncoupling oxidative phosphorylation (OXPHOS), UCP2 does not perform a canonical H+ leak, consuming the protonmotive force (Δp) through the inner mitochondrial membrane. The UCP2 biological role is elusive. It can counteract oxidative stress, acting with a "mild uncoupling" process to reduce ROS production, and, in fact, UCP2 activities are related to inflammatory processes, triggering pathological conditions. However, the Δp dissipation by UCP2 activity reduces the mitochondrial ATP production and rewires the bioenergetic metabolism of the cells. In all likelihood, UCP2 works as a carrier of metabolites with four carbon atoms (C4), reversing the anaerobic glycolysis-dependent catabolism to OXPHOS. Indeed, UCP2 can perform catalysis in dual mode: mild uncoupling of OXPHOS and metabolite C4 exchange of mitochondria. In vivo, the UCP2 features in the biology of mitochondria promote healthy ageing, increased lifespan, and can assure cerebro- and cardiovascular protection. However, the pathological conditions responsible for insulin secretion suppression are dependent on UCP2 activity. On balance, the uncertain biochemical mechanisms dependent on UCP2 do not allow us to depict the protective role in mitochondrial bioenergetics.

UCP2 and pancreatic cancer: conscious uncoupling for therapeutic effect

Pancreatic cancer has an exaggerated dependence on mitochondrial metabolism, but methods to specifically target the mitochondria without off target effects in normal tissues that rely on these organelles is a significant challenge. The mitochondrial uncoupling protein 2 (UCP2) has potential as a cancer-specific drug target, and thus, we will review the known biology of UCP2 and discuss its potential role in the pathobiology and future therapy of pancreatic cancer.

Uncoupling protein 2 modulates polarization and metabolism of human primary macrophages via glycolysis and the NF‑κB pathway

Metabolic abnormalities, particularly the M1/M2 macrophage imbalance, play a critical role in the development of various diseases, leading to severe inflammatory responses. The present study aimed to investigate the role of uncoupling protein 2 (UCP2) in regulating macrophage polarization, glycolysis, metabolic reprogramming, reactive oxygen species (ROS) and inflammation. Primary human macrophages were first polarized into M1 and M2 subtypes, and these two subtypes were infected by lentivirus-mediated UCP2 overexpression or knockdown, followed by enzyme-linked immunosorbent assay, reverse transcription-quantitative PCR, western blotting and flow cytometry to analyze the effects of UCP2 on glycolysis, oxidative phosphorylation (OXPHOS), ROS production and cytokine secretion, respectively. The results demonstrated that UCP2 expression was suppressed in M1 macrophages and increased in M2 macrophages, suggesting its regulatory role in macrophage polarization. UCP2 overexpression decreased macrophage glycolysis, increased OXPHOS, decreased ROS production, and led to the conversion of M1 polarization to M2 polarization. This process involved NF-κB signaling to regulate the secretion profile of cytokines and chemokines and affected the expression of key enzymes of glycolysis and a key factor for maintaining mitochondrial homeostasis (nuclear respiratory factor 1). UCP2 knockdown in M2 macrophages exacerbated inflammation and oxidative stress by promoting glycolysis, which was attenuated by the glycolysis inhibitor 2-deoxyglucose. These findings highlight the critical role of UCP2 in regulating macrophage polarization, metabolism, inflammation and oxidative stress through its effects on glycolysis, providing valuable insights into potential therapeutic strategies for macrophage-driven inflammatory and metabolic diseases.

Role of UCP2 in the Energy Metabolism of the Cancer Cell Line A549

The uncoupling protein UCP2 is a mitochondrial carrier for which transport activity remains controversial. The physiological contexts in which UCP2 is expressed have led to the assumption that, like UCP1, it uncouples oxidative phosphorylation and thereby reduces the generation of reactive oxygen species. Other reports have involved UCP2 in the Warburg effect, and results showing that UCP2 catalyzes the export of matrix C4 metabolites to facilitate glutamine utilization suggest that the carrier could be involved in the metabolic adaptations required for cell proliferation. We have examined the role of UCP2 in the energy metabolism of the lung adenocarcinoma cell line A549 and show that UCP2 silencing decreased the basal rate of respiration, although this inhibition was not compensated by an increase in glycolysis. Silencing did not lead to either changes in proton leakage, as determined by the rate of respiration in the absence of ATP synthesis, or changes in the rate of formation of reactive oxygen species. The decrease in energy metabolism did not alter the cellular energy charge. The decreased cell proliferation observed in UCP2-silenced cells would explain the reduced cellular ATP demand. We conclude that UCP2 does not operate as an uncoupling protein, whereas our results are consistent with its activity as a C4-metabolite carrier involved in the metabolic adaptations of proliferating cells.

UCP2 deficiency impairs podocyte autophagy in diabetic nephropathy

OBJECTIVE

Podocytes have been indicated to be a critical factor for the development of diabetic kidney disease. Podocyte loss leads to irreversible glomerular injury and proteinuria in animal models. As terminal differentiated cells, autophagy is crucial for maintaining podocyte homeostasis. Previous studies have shown that Uncoupling proteins 2 (UCP2) regulate fatty acid metabolism, mitochondrial calcium uptake and reactive oxygen species (ROS) production. This study aimed to investigate whether UCP2 promote autophagy in podocyte and further explore the regulation mechanism of UCP2.

METHODS

For podocyte-specific UCP2-KO mice, we cross bred UCP2f^l/fl mouse strain with the podocin-Cre mice. Diabetic mice were obtained by daily intraperitoneally injections of 40 mg/kg streptozotocin for 3 days. After 6 weeks, mice were scarified, and kidney tissues were analyzed by histological stain, Western blot, Immunofluorescence, and immunohistochemistry. Also, urine samples were collected for protein quantification. For in vitro study, podocytes were primary cultured from UCP2f^l/fl mouse or transfected with adeno-associated virus (AAV)-UCP2.

RESULTS

Diabetic kidney showed elevated expression of UCP2 and specific ablation of UCP2 in podocyte aggravates diabetes-induced albuminuria and glomerulopathy. UCP2 protects hyperglycemia-induced podocyte injury by promoting autophagy in vivo and in vitro. Rapamycin treatment significantly ameliorates streptozotocin (STZ)-induced podocyte injury in UCP2^-/- mice.

CONCLUSION

UCP2 expression in podocyte increased under diabetic condition and appeared to be an initial compensatory response. UCP2 deficiency in podocyte impaired autophagy and exacerbates podocyte injury and proteinuria in diabetic nephropathy.

UCP2 as a Cancer Target through Energy Metabolism and Oxidative Stress Control

Despite numerous therapies, cancer remains one of the leading causes of death worldwide due to the lack of markers for early detection and response to treatment in many patients. Technological advances in tumor screening and renewed interest in energy metabolism have allowed us to identify new cellular players in order to develop personalized treatments. Among the metabolic actors, the mitochondrial transporter uncoupling protein 2 (UCP2), whose expression is increased in many cancers, has been identified as an interesting target in tumor metabolic reprogramming. Over the past decade, a better understanding of its biochemical and physiological functions has established a role for UCP2 in (1) protecting cells from oxidative stress, (2) regulating tumor progression through changes in glycolytic, oxidative and calcium metabolism, and (3) increasing antitumor immunity in the tumor microenvironment to limit cancer development. With these pleiotropic roles, UCP2 can be considered as a potential tumor biomarker that may be interesting to target positively or negatively, depending on the type, metabolic status and stage of tumors, in combination with conventional chemotherapy or immunotherapy to control tumor development and increase response to treatment. This review provides an overview of the latest published science linking mitochondrial UCP2 activity to the tumor context.

UCP2 silencing restrains leukemia cell proliferation through glutamine metabolic remodeling

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematologic malignancy derived from early T cell progenitors. Since relapsed T-ALL is associated with a poor prognosis improving initial treatment of patients is essential to avoid resistant selection of T-ALL. During initiation, development, metastasis and even in response to chemotherapy, tumor cells face strong metabolic challenges. In this study, we identify mitochondrial UnCoupling Protein 2 (UCP2) as a tricarboxylic acid (TCA) cycle metabolite transporter controlling glutamine metabolism associated with T-ALL cell proliferation. In T-ALL cell lines, we show that UCP2 expression is controlled by glutamine metabolism and is essential for their proliferation. Our data show that T-ALL cell lines differ in their substrate dependency and their energetic metabolism (glycolysis and oxidative). Thus, while UCP2 silencing decreases cell proliferation in all leukemia cells, it also alters mitochondrial respiration of T-ALL cells relying on glutamine-dependent oxidative metabolism by rewiring their cellular metabolism to glycolysis. In this context, the function of UCP2 in the metabolite export of malate enables appropriate TCA cycle to provide building blocks such as lipids for cell growth and mitochondrial respiration. Therefore, interfering with UCP2 function can be considered as an interesting strategy to decrease metabolic efficiency and proliferation rate of leukemia cells.

Identification of UCP1 and UCP2 as Potential Prognostic Markers in Breast Cancer: A Study Based on Immunohistochemical Analysis and Bioinformatics

Background: Uncoupling protein 1 (UCP1) and UCP2 are associated with tumor metabolism and immunity. However, the prognostic value and molecular mechanisms underlying their action in breast cancer (BC) remain unclear.

Materials and methods: In TCGA-BRCA cohort, we investigated the expression characteristics of UCP mRNAs, analyzed their prognostic value by Kaplan-Meier survival analysis, their potential molecular functions by gene set enrichment analysis, and their relationship with immune infiltrating cell types using TIMER and CIBERSORT, along with the assessment of their association with mutational profiles. Kaplan-Meier survival analysis was performed for UCPs in our cohort and their association with BC thermogenesis was assessed by thermal tomography.

Results: High expression of UCP1 and UCP2 were positive prognostic markers for BC. UCP1 was associated with the impaired glucose metabolism, while UCP2 with enhanced anti-tumor immunity. High expressions of UCP1 and UCP2 were associated with CDH1 mutations. High UCP1 expression was associated with a high rate of thermogenesis in BC.

Conclusions: These results implied a key role of UCP1 and UCP2 in prognosis, metabolism, and immune infiltration in BC. Further investigation of the relevant molecular mechanisms may provide new strategies for BC treatment.

Type 2 Diabetes Mellitus Intersects With Pancreatic Cancer Diagnosis and Development

The relationship between type 2 diabetes mellitus (T2DM) and pancreatic cancer (PC) is complex. Diabetes is a known risk factor for PC, and new-onset diabetes (NOD) could be an early manifestation of PC that may be facilitate the early diagnosis of PC. Metformin offers a clear benefit of inhibiting PC, whereas insulin therapy may increase the risk of PC development. No evidence has shown that novel hypoglycemic drugs help or prevent PC. In this review, the effects of T2DM on PC development are summarized, and novel strategies for the prevention and treatment of T2DM and PC are discussed.

Molecular Insights into the Recruiting Between UCP2 and DDX5/UBAP2L in the Metabolic Plasticity of Non-Small-Cell Lung Cancer

Mitochondrial uncoupling protein 2 (UCP2) is distributed in tumor cells with a link to the support of systemic metabolic deregulation, and the downregulation of UCP2 has been unveiled as a biomarker of oncogenesis and chemoresistance in non-small-cell lung cancer (NSCLC) cells. However, the underlying mechanism of how UCP2 cooperates with other proteins in this metabolic reprogramming remains largely unsolved. We employed a combined computational and experimental strategy to explore into the recruiting of DDX5 with other proteins, and we unraveled the underlying structural mechanisms. We found that recruiting by ATP-dependent RNA helicase DDX5 (DDX5)/ubiquitin-associated protein 2-like (UBAP2L) might help UCP2 to play the pathological roles in NSCLC cells. According to the view of thermodynamics in physics, UCP2 tends to recruit DDX5 rather than UBAP2L, as shown by the ensemble-based docking, molecular dynamics simulations and molecular mechanics generalized Born surface area (MM/GBSA) approach. Cellular immunofluorescence assays further demonstrated that UCP2 associate with DDX5, and the recruiting of DDX5 with UCP2 at least partially contribute to the metabolic plasticity of NSCLCs via the AKT/mTOR pathway. Our study proposed an efficient way for detecting the protein-protein association via the experimentally validated molecular simulation. Our results shed light on the functional annotation of UCP and DDX family proteins in dysregulated metabolism, and the identification of candidate therapeutic targets for NSCLC.

The role of uncoupling protein 2 in macrophages and its impact on obesity-induced adipose tissue inflammation and insulin resistance

The development of a chronic, low-grade inflammation originating from adipose tissue in obese subjects is widely recognized to induce insulin resistance, leading to the development of type 2 diabetes. The adipose tissue microenvironment drives specific metabolic reprogramming of adipose tissue macrophages, contributing to the induction of tissue inflammation. Uncoupling protein 2 (UCP2), a mitochondrial anion carrier, is thought to separately modulate inflammatory and metabolic processes in macrophages and is up-regulated in macrophages in the context of obesity and diabetes. Here, we investigate the role of UCP2 in macrophage activation in the context of obesity-induced adipose tissue inflammation and insulin resistance. Using a myeloid-specific knockout of UCP2 (Ucp2^ΔLysM), we found that UCP2 deficiency significantly increases glycolysis and oxidative respiration, both unstimulated and after inflammatory conditions. Strikingly, fatty acid loading abolished the metabolic differences between Ucp2^ΔLysM macrophages and their floxed controls. Furthermore, Ucp2^ΔLysM macrophages show attenuated pro-inflammatory responses toward Toll-like receptor-2 and -4 stimulation. To test the relevance of macrophage-specific Ucp2 deletion in vivo, Ucp2^ΔLysM and Ucp2^fl/fl mice were rendered obese and insulin resistant through high-fat feeding. Although no differences in adipose tissue inflammation or insulin resistance was found between the two genotypes, adipose tissue macrophages isolated from diet-induced obese Ucp2^ΔLysM mice showed decreased TNFα secretion after ex vivo lipopolysaccharide stimulation compared with their Ucp2^fl/fl littermates. Together, these results demonstrate that although UCP2 regulates both metabolism and the inflammatory response of macrophages, its activity is not crucial in shaping macrophage activation in the adipose tissue during obesity-induced insulin resistance.

Mitochondria control mTORC1 activity-linked compartmentalization of eIF4E to regulate extracellular export of microRNAs

Defective intracellular trafficking and export of microRNAs (miRNAs) have been observed in growth-retarded mammalian cells having impaired mitochondrial potential and dynamics. Here, we found that uncoupling protein 2 (Ucp2)-mediated depolarization of mitochondrial membrane also results in progressive sequestration of miRNAs within polysomes and lowers their release via extracellular vesicles. Interestingly, the impaired miRNA-trafficking process in growth-retarded human cells could be reversed in the presence of Genipin, an inhibitor of Ucp2. Mitochondrial detethering of endoplasmic reticulum (ER), observed in cells with depolarized mitochondria, was found to be responsible for defective compartmentalization of translation initiation factor eIF4E to polysomes attached to ER. This caused a retarded translation process accompanied by enhanced retention of miRNAs and target mRNAs within ER-attached polysomes to restrict extracellular export of miRNAs. Reduced compartment-specific activity of the mammalian target of rapamycin complex 1 (mTORC1), the master regulator of protein synthesis, in cells with defective mitochondria or detethered ER, caused reduced phosphorylation of eIF4E-BP1 and prevented eIF4E targeting to ER-attached polysomes and miRNA export. These data suggest how mitochondrial membrane potential and dynamics, by affecting mTORC1 activity and compartmentalization, determine the subcellular localization and export of miRNAs.

UCP2 silencing in glioblastoma reduces cell proliferation and invasiveness by inhibiting p38 MAPK pathway

Uncoupling protein-2 (UCP2) is a mitochondrial inner membrane anion carrier and is emerging as a negative regulator of ROS production. Overexpression of UCP2 has been detected in various tumors, but its role in glioblastoma remains unclear. Using tissue microarrays and interrogations of public databases, we explored that the expression of UCP2 is upregulated in glioma, especially in GBM, and overexpression of UCP2 correlates with poor prognosis in glioma patients. To further reveal the role of UCP2 in glioma, UCP2-slienced cell lines (U251, U87MG and A172) by lentivirus were constructed to study how silenced UCP2 expression affects cellular functions in vitro, and tumorigenicity in vivo. RNA-Seq based genome and pathway analysis were performed to elucidate the underlying mechanisms of action of UCP2. Our results revealed that UCP2 silenced glioma cells show inhibited migration, invasiveness, clonogenicity, proliferation, promoted cell apoptosis in vitro, and weaker tumorigenicity in nude mice. Transcriptome analysis suggested a UCP2-dependent regulation of p38 MAPK (Mitogen-activated protein kinase) signaling networks, which was further validated by qRT-PCR and Western blot. Our research provides a new insight into the biological significance of UCP2 in glioma and its potential application in treatment and diagnosis.

UCP2 Deficiency Increases Colon Tumorigenesis by Promoting Lipid Synthesis and Depleting NADPH for Antioxidant Defenses

Colorectal cancer (CRC) is associated with metabolic and redox perturbation. The mitochondrial transporter uncoupling protein 2 (UCP2) controls cell proliferation in vitro through the modulation of cellular metabolism, but the underlying mechanism in tumors in vivo remains unexplored. Using murine intestinal cancer models and CRC patient samples, we find higher UCP2 protein levels in tumors compared to their non-tumoral counterparts. We reveal the tumor-suppressive role of UCP2 as its deletion enhances colon and small intestinal tumorigenesis in AOM/DSS-treated and Apc^Min/+ mice, respectively, and correlates with poor survival in the latter model. Mechanistically, UCP2 loss increases levels of oxidized glutathione and proteins in tumors. UCP2 deficiency alters glycolytic pathways while promoting phospholipid synthesis, thereby limiting the availability of NADPH for buffering oxidative stress. We show that UCP2 loss renders colon cells more prone to malignant transformation through metabolic reprogramming and perturbation of redox homeostasis and could favor worse outcomes in CRC.

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UCP2 protein expression, but not mRNA, is increased in CRC in both mice and humans

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UCP2 loss promotes AOM/DSS-induced CAC and Apc^Min-dependent intestinal cancer

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UCP2 loss-induced oxidative stress contributes to increased colon tumorigenesis

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UCP2 deficiency drives an imbalance between lipid metabolism and NADPH homeostasis

Mitochondrial spare respiratory capacity: Mechanisms, regulation, and significance in non-transformed and cancer cells

Mitochondrial metabolism must constantly adapt to stress conditions in order to maintain bioenergetic levels related to cellular functions. This absence of proper adaptation can be seen in a wide array of conditions, including cancer. Metabolic adaptation calls on mitochondrial function and draws on the mitochondrial reserve to meet increasing needs. Among mitochondrial respiratory parameters, the spare respiratory capacity (SRC) represents a particularly robust functional parameter to evaluate mitochondrial reserve. We provide an overview of potential SRC mechanisms and regulation with a focus on its particular significance in cancer cells.

The role of ectopic adipose tissue: benefit or deleterious overflow?

Ectopic adipose tissues (EAT) are present adjacent to many organs and have predominantly been described in overweight and obesity. They have been suggested to be related to fatty acid overflow and to have harmful effects. The objective of this semi-comprehensive review is to explore whether EAT may play a supportive role rather than interfering with its function, when the adjacent organ is challenged metabolically and functionally. EAT are present adhered to different tissues or organs, including lymph nodes, heart, kidney, ovaries and joints. In this review, we only focused on epicardial, perinodal, and peritumoral fat since these locations have been studied in more detail. Evidence was found that EAT volume significantly increased, associated with chronic metabolic challenges of the corresponding tissue. In vitro evidence revealed transfer of fatty acids from peritumoral and perinodal fat to the adjacent tissue. Cytokine expression in these EAT is upregulated when the adjacent tissue is challenged. In these tissues, glycolysis is enhanced, whereas fatty acid oxidation is increased. Together with more direct evidence, this shows that glucose is oxidized to a lesser degree, but used to support anabolic metabolism of the adjacent tissue. In these situations, browning occurs, resulting from upregulation of anabolic metabolism, stimulated by uncoupling proteins 1 and 2 and possibly 3. In conclusion, the evidence found is fragmented but the available data support the view that accumulation and browning of adipocytes adjacent to the investigated organs or tissues may be a normal physiological response promoting healing and (patho)physiological growth.

Single-crystal structure and intracellular localization of Zn(II)-thiosemicarbazone complex targeting mitochondrial apoptosis pathways

Tracking of drugs in cancer cells is important for basic biology research and therapeutic applications. Therefore, we designed and synthesised a Zn(II)-thiosemicarbazone complex with photoluminescent property for organelle-specific imaging and anti-cancer proliferation. The Zn(AP44eT)(NO₃)₂ coordination ratio of metal to ligand was 1:1, which was remarkably superior to 2-((3-aminopyridin-2-yl) methylene)-N, N-diethylhydrazinecarbothioamide (AP44eT·HCl) in many aspects, such as fluorescence and anti-tumour activity. Confocal fluorescence imaging showed that the Zn(AP44eT)(NO₃)₂ was aggregated in mitochondria. Moreover, Zn(AP44eT)(NO₃)₂ was more effective than the metal-free AP44eT·HCl in shortening the G2 phase in the MCF-7 cell cycle and promoting apoptosis of cancer cells. Supposedly, the effects of these complexes might be located mainly in the mitochondria and activated caspase-3 and 9 proteins.

The Warburg Effect Promotes Mitochondrial Injury Regulated by Uncoupling Protein-2 in Septic Acute Kidney Injury

BACKGROUND

Evidence implying that metabolism reprogramming plays an important role in the regulation of sepsis is increasing; however, whether it has a similar role in septic organ dysfunction remains unclear. Here, we provide evidence to support a new role of uncoupling protein-2 (UCP2)-regulated Warburg effect, i.e., aerobic glycolysis, in promoting mitochondrial injury in the kidney.

METHODS

To imitate sepsis condition, male C57BL/6 mice were operated by the cecal ligation puncture in vivo, whereas a normal human kidney cell line (HK-2) was treated with lipopolysaccharide in vitro. UCP2 small interfering RNA pretreatment was performed to knock down UCP2 expression in vitro. The glycolysis metabolite was detected by liquid chromatography/tandem mass spectrometry in vivo and detected by commercial kits in vitro. Oxidative phosphorylation level and glycolysis level were monitored by measuring the oxygen consumption rate (indicative of respiration) and extracellular acidification rate (indicative of glycolysis) in vitro. Exogenous lactate was supplied to stimulate HK-2 cells and indicators of mitochondrial dysfunction were also assessed.

RESULTS

Aerobic glycolysis is enhanced in septic tubular epithelial cells, and the glycolysis inhibitor 2-deoxyglucose can partially restore mitochondrial membrane potential and decrease the reactive oxygen species production. With the knockdown of UCP2, the aerobic glycolysis level upregulates, and mitochondrial injury increases.

CONCLUSIONS

These results provide insights on a new mechanism of metabolic regulation of mitochondrial injury and the importance of targeting aerobic glycolysis for the treatment of septic acute kidney injury.

Ectopic HOTTIP expression induces noncanonical transactivation pathways to promote growth and invasiveness in pancreatic ductal adenocarcinoma

HOXA transcript at the distal tip (HOTTIP), a long noncoding RNA, is upregulated in pancreatic ductal adenocarcinoma (PDAC), but the HOTTIP-mediated oncogenic pathway is not fully understood. We identified canonical HOTTIP-HOXA13 targets, CYP26B1, CLIC5, CHI3L1 and UCP2-responsible for cell growth and cell invasion. Genome-wide analysis revealed that 38% of HOTTIP-regulated genes contain H3K4me3 and HOTTIP enrichment at their promoters, without HOXA13 binding. HOTTIP complexes with WDR5-MLL1 to trans-activate oncogenic proteins CYB5R2, SULT1A1, KIF26A, SLC1A4, and TSC22D1 by directly inducing H3K4me3 at their promoters. The WDR5, MLL1, and H3K4me3 levels at their promoters and their expression levels are sensitive to HOTTIP expression. These results indicate the importance of the noncanonical trans-acting HOTTIP-WDR5-MLL1 pathway in the HOTTIP regulatory mechanism by promoting oncogenic protein expression. Furthermore, HOTTIP is regulated by miR-497 in PDAC cells, but HOTTIP is negatively correlated with miR-497 levels in PDAC tissues. In conclusion, HOTTIP is upregulated in PDAC due to the loss of the inhibitory miR-497; HOTTIP promotes PDAC progression through the canonical HOTTIP-HOXA13 axis. A novel noncanonical trans-acting HOTTIP-WDR5-MLL1-H3K4me3 pathway is also delineated.

Interplay Between Diabetes and Pancreatic Ductal Adenocarcinoma and Insulinoma: The Role of Aging, Genetic Factors, and Obesity

Epidemiologic analyses have shed light on an association between type 2 diabetes (T2D) and pancreatic ductal adenocarcinoma (PDAC). Recent data also suggest a potential relationship between T2D and insulinoma. Under rare circumstances, type 1 diabetes (T1D) can also be implicated in tumorigenesis. The biological mechanisms underlying such relationships are extremely complex. Some genetic factors contributing to the development of T2D are shared with pancreatic exocrine and endocrine tumors. Obesity and overweight can also contribute to the initiation and severity of T2D, while aging may influence both endocrine and exocrine tumors. Finally, pharmacological treatments of T2D may have an impact on PDAC. On the other hand, some treatments for insulinoma can trigger diabetes. In the present minireview, we discuss the cellular and molecular mechanisms that could explain these interactions. This analysis may help to define new potential therapeutic strategies.

Role of purines in regulation of metabolic reprogramming

Purines, among most influential molecules, are reported to have essential biological function by regulating various cell types. A large number of studies have led to the discovery of many biological functions of the purine nucleotides such as ATP, ADP, and adenosine, as signaling molecules that engage G protein-coupled or ligand-gated ion channel receptors. The role of purines in the regulation of cellular functions at the gene or protein level has been well documented. With the advances in multiomics, including those from metabolomic and bioinformatic analyses, metabolic reprogramming was identified as a key mechanism involved in the regulation of cellular function under physiological or pathological conditions. Recent studies suggest that purines or purine-derived products contribute to important regulatory functions in many fundamental biological and pathological processes related to metabolic reprogramming. Therefore, this review summarizes the role and potential mechanism of purines in the regulation of metabolic reprogramming. In particular, the molecular mechanisms of extracellular purine- and intracellular purine-mediated metabolic regulation in various cells during disease development are discussed. In summary, our review provides an extensive resource for studying the regulatory role of purines in metabolic reprogramming and sheds light on the utilization of the corresponding peptides or proteins for disease diagnosis and therapy.

UCP2 gene polymorphisms in obesity and diabetes, and the role of UCP2 in cancer

Mitochondria are the primary sites for ATP synthesis and free radical generation in organisms. Abnormal mitochondrial metabolism contributes to many diseases, including obesity, diabetes and cancer. UCP2 is an ion/anion transporter located in mitochondrial inner membrane, and has a crucial role in regulating oxidative stress, cellular metabolism, cell proliferation and cell death. Polymorphisms of the UCP2 gene have been associated with diabetes and obesity because UCP2 is involved in energy expenditure and insulin secretion. Moreover, UCP2 gene expression is often amplified in cancers, and increased UCP2 expression contributes to cancer growth, cancer metabolism, anti-apoptosis and drug resistance. The present review summarizes the latest findings of UCP2 with respect to obesity, diabetes and cancer.

Mitochondrial fusion exploits a therapeutic vulnerability of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) requires mitochondrial oxidative phosphorylation (OXPHOS) to fuel its growth, however, broadly inhibiting this pathway might also disrupt essential mitochondrial functions in normal tissues. PDAC cells exhibit abnormally fragmented mitochondria that are essential to its oncogenicity, but it was unclear if this mitochondrial feature was a valid therapeutic target. Here, we present evidence that normalizing the fragmented mitochondria of pancreatic cancer via the process of mitochondrial fusion reduces OXPHOS, which correlates with suppressed tumor growth and improved survival in preclinical models. Mitochondrial fusion was achieved by genetic or pharmacologic inhibition of dynamin related protein-1 (Drp1) or through overexpression of mitofusin-2 (Mfn2). Notably, we found that oral leflunomide, an FDA-approved arthritis drug, promoted a two-fold increase in Mfn2 expression in tumors and was repurposed as a chemotherapeutic agent, improving the median survival of mice with spontaneous tumors by 50% compared to vehicle. We found that the chief tumor suppressive mechanism of mitochondrial fusion was enhanced mitophagy, which proportionally reduced mitochondrial mass and ATP production. These data suggest that mitochondrial fusion is a specific and druggable regulator of pancreatic cancer growth that could be rapidly translated to the clinic.

Mitochondria in cancer: in the aspects of tumorigenesis and targeted therapy

Mitochondria play pivotal roles in most eukaryotic cells, ranging from energy production to regulation of apoptosis. As sites of cellular respiration, mitochondria experience accumulation of reactive oxygen species (ROS) due to damage in electron transport chain carriers. Mutations in mitochondrial DNA (mtDNA) as well as nuclear DNA are reported in various cancers. Mitochondria have a dual role in cancer: the development of tumors due to mutations in mitochondrial genome and the generation of ROS. Impairment in the mitochondria-regulated apoptosis pathway accelerates tumorigenesis. Numerous strategies targeting mitochondria have been developed to induce the mitochondrial (i.e. intrinsic) apoptosis pathway in cancer cells. This review elaborates the roles of mitochondria in cancer with respect to mutations and apoptosis and discusses mitochondria-targeting strategies as cancer therapies to enhance the killing of cancer cells.

Capsaicin induces cytotoxicity in human osteosarcoma MG63 cells through TRPV1-dependent and -independent pathways

An accumulating body of evidence has shown that capsaicin induces apoptosis in various tumor cells as a mechanism of its anti-tumor activity. However, the effects of capsaicin on osteosarcoma have not been studied extensively. In the current study, we explore the molecular mechanism of capsaicin-mediated tumor suppressive function in osteosarcoma. We found that capsaicin-induced apoptosis and the activation of transient receptor potential receptor vanilloid 1 (TRPV1) in a dose- and time-dependent manner in human osteosarcoma MG63 cells in vitro. Blocking TRPV1 using capsazepine attenuated the capsaicin-induced cytotoxicity, mitochondrial dysfunction, overproduction of reactive oxygen species (ROS) and decrease in superoxide dismutase (SOD) activity. In addition, the results demonstrated that capsaicin induced the activation of adenosine 5'-monophosphate-activated protein kinase (AMPK), p53 and C-jun N-terminal kinase (JNK). In addition, Compound C (antagonist of AMPK) attenuated the activation of p53, which appeared to be TRPV1 independent. Taken together, the present study suggests that capsaicin effectively causes cell death in human osteosarcoma MG63 cells via the activation of TRPV1-dependent (mitochondrial dysfunction, and overproduction of ROS and JNK) and TRPV1-independent (AMPK-p53) pathways. Thus, capsaicin may be a potential anti-osteosarcoma agent.

Bouchardatine suppresses rectal cancer in mice by disrupting its metabolic pathways via activating the SIRT1-PGC-1α-UCP2 axis

Cancer metabolism is an attractive target of the therapeutic strategy for cancer. The present study identified bouchardatine (Bou) as a potent suppressor of rectal cancer growth by cycle-arresting independent of apoptosis. In cultured HCT-116 rectal cancer cells, Bou increased glucose uptake/oxidation and capacity of mitochondrial oxidation. These effects were associated with an upregulation of uncoupling protein 2 (UCP2) and the activation of its upstream Sirtuin 1 (SIRT1)/(Liver kinase B1) LKB1- (Adenosine monophosphate-activated protein kinase) AMPK axis. The pivotal role of UCP2 in the cancer-suppressing effect was demonstrated by overexpressing UCP2 in HCT-116 cells with similar metabolic effects to those produced by Bou. Interestingly, Bou activated peroxisome proliferators activated receptor γ coactivator 1α (PGC-1α) and recruited it to the promoter of UCP2 in HCT-116 cells along with deacetylation (thus activation) by SIRT1. The requirement of SIRT1 for the cancer-suppressing effect through the PGC-1α-UCP2 was confirmed by the reciprocal responses to Bou in HCT-116 with defected and overexpressed SIRT1. Whereas knockdown, mutation or pharmacological inhibition of SIRT1 all abolished Bou-induced deacetylation/activation of PGC-1α, the opposing effects were observed after overexpressing SIRT1. In mice, administration of Bou (50 mg/kg) also suppressed the growth of rectal cancer associated with increases the UCP2 expression and mitochondria capacity in the tumor. Collectively, our findings suggest that Bou has a therapeutic potential for the treatment of rectal cancer by disrupting the metabolic path of cancer cells via activating the PGC-1α-UCP2 axis with SIRT1 as its primary target.

Glutamine regulates mitochondrial uncoupling protein 2 to promote glutaminolysis in neuroblastoma cells

Mitochondrial uncoupling protein 2 (UCP2) is highly abundant in rapidly proliferating cells that utilize aerobic glycolysis, such as stem cells, cancer cells, and cells of the immune system. However, the function of UCP2 has been a longstanding conundrum. Considering the strict regulation and unusually short life time of the protein, we propose that UCP2 acts as a "signaling protein" under nutrient shortage in cancer cells. We reveal that glutamine shortage induces the rapid and reversible downregulation of UCP2, decrease of the metabolic activity and proliferation of neuroblastoma cells, that are regulated by glutamine per se but not by glutamine metabolism. Our findings indicate a very rapid (within 1 h) metabolic adaptation that allows the cell to survive by either shifting its metabolism to the use of the alternative fuel glutamine or going into a reversible, more quiescent state. The results imply that UCP2 facilitates glutamine utilization as an energetic fuel source, thereby providing metabolic flexibility during glucose shortage. The targeting UCP2 by drugs to intervene with cancer cell metabolism may represent a new strategy for treatment of cancers resistant to other therapies.

Dichloroacetic acid upregulates apoptosis of ovarian cancer cells by regulating mitochondrial function

Background

Metabolic reprogramming is a characteristic of tumor cells and is considered a potential therapeutic target. Even under aerobic conditions, tumor cells use glycolysis to produce energy, a phenomenon called the “Warburg effect”. Pyruvate dehydrogenase kinase 1 (PDK1) is a key factor linking glycolysis and the tricarboxylic acid cycle. Dichloroacetic acid (DCA) reverses the Warburg effect by inhibition of PDK1 to switch cytoplasmic glucose metabolism to mitochondrial oxidative phosphorylation (OXPHOS).

Methods

Cell viability was examined using a standard MTT assay. Glucose consumption and l-lactate production were measured using commercial colorimetric kits, and intracellular lactate dehydrogenase (LDH) activity was evaluated using cell lysates and an LDH Quantification Kit. Real-time PCR was used to detect the expression of related genes. The production of total ROS was evaluated by staining with dichlorofluorescin diacetate.

Results

Comparison of various aspects of glucose metabolism, such as expression of key enzymes in glycolysis, lactate production, glucose consumption, mitochondrial oxygen consumption rate, and citric acid production, revealed that A2780/DDP cells were primarily dependent on glycolysis whereas A2780 cells were primarily dependent on mitochondrial OXPHOS. Mitochondrial uncoupling protein 2 (UCP2) protects against mitochondrial ROS while allowing energy metabolism to switch to glycolysis. Treatment of A2780 cells with various concentrations of DCA resulted in decreased expression of UCP2, a metabolic switch from glycolysis to mitochondrial OXPHOS, and an increase in oxidative stress induced by ROS. These effects were not observed in A2780/DDP cells with higher UCP2 expression suggesting that UCP2 might induce changes in mitochondrial functions that result in different sensitivities to DCA.

Conclusion

Our results show that a drug targeting tumor metabolic changes affects almost the entire process of glucose metabolism. Thus, it is necessary to comprehensively determine tumor metabolic functions to facilitate individualized antitumor therapy.

Mechanisms underlying UCP1 dependent and independent adipocyte thermogenesis

The growing focus on brown adipocytes has spurred an interest in their potential benefits for metabolic diseases. Brown and beige (or brite) adipocytes express high levels of uncoupling protein 1 (Ucp1) to dissipate heat instead of generating ATP. Ucp1 induction by stimuli including cold, exercise, and diet increases nonshivering thermogenesis, leading to increased energy expenditure and prevention of obesity. Recently, studies in adipocytes have indicated the existence of functional Ucp1-independent thermogenic regulators. Furthermore, substrate cycling involving creatine metabolites, cold-induced N-acyl amino acids, and oxidized lipids in white adipocytes can increase energy expenditure in the absence of Ucp1. These studies emphasize the need for a better understanding of the mechanisms governing energy expenditure in adipocytes and their potential applications in the prevention of human obesity and metabolic diseases.

Genipin induces cell death via intrinsic apoptosis pathways in human glioblastoma cells

Genipin, a compound derived from Gardenis jasminoides Ellis fruits, was demonstrated to be the specific uncoupling protein 2 (UCP2) inhibitor. UCP2 is a mitochondrial carrier protein that creates proton leaks across the inner mitochondrial membrane, thus uncoupling oxidative phosphorylation from adenosine triphosphate (ATP) synthesis. Several studies revealed that UCP2 is broadly over-expressed in leukemia, colorectal, lung, ovarian, prostate, testicular, and bladder cancers. However, the effect of genipin still needs to be elucidated in neurological malignancies. In this study, we investigated the anticancer effect of genipin in U87MG and A172 cell lines. The anticancer effect of genipin on these cell lines was measured by microculture tetrazoliumtest (MTT), Trypan blue exclusion, and colony formation assays, in the presence of various concentrations of genipin at different time intervals. We assessed apoptosis and measure intracellular reactive oxygen species (ROS) by flow cytometry. Expression of UCP2 and some of the genes involved in apoptosis was analyzed by real-time quantitative polymerase chain reaction (PCR). Results of the MTT assay showed that genipin moderately reduced metabolic activity of both cell lines in dose- and time-dependent manner. Result of Trypan blue exclusion test indicated that the viable cell count decreased in the treated group in a concentration-dependent manner. Genipin also significantly decreased colony formation ability of these cells in a concentration-dependent manner. Result of morphological changes showed that there were significant differences in cell number and morphology in treated groups as compared with the untreated groups. Flow cytometric analysis of U87MG and A172 cells with annexin V/propidium iodide staining, 48 hours after treatment with genipin, displays 22.4% and 26.1% apoptotic population, respectively, in treated cells, in comparison to 7.42% and 9.31% apoptotic cells of untreated cells. After treatment, UCP2 and B-cell lymphoma 2 (BCL ₂ ) genes are downregulated, and BCL ₂ associated X protein, BCL ₂ antagonist/killer, BCL ₂ interacting killer, and Cytochrome c genes are upregulated. Genipin treatment increased mitochondrial ROS levels and also induced apoptosis through caspase-3 upregulation. In conclusion, the antiproliferative effects of genipin on the growth of both glioblastoma cell lines have been shown in all of these assays, and genipin profoundly induced apoptosis in both cell lines via the UCP2-related mitochondrial pathway through the induction of intracellular ROS.

Integrative analysis of significant RNA-binding proteins in colorectal cancer metastasis

The aberrant expression of RNA-binding proteins (RBPs) plays a crucial role in the occurrence and progression of human cancer. However, the key functions of RBPs in the metastasis of colorectal cancer have not yet been fully elucidated. Here, we integrated multi-omics data and identified four differentially expressed RBPs (APOBEC3G, EEF1A2, EIF5AL1 and CELF3) in patients with colorectal cancer metastasis. To clarify the underlying molecular mechanisms, we systematically analyzed the genomic features and downstream regulatory relationships of the four RBPs. In a genomic level, the copy number variations of APOBEC3G, EEF1A2, and CELF3 demonstrated significantly differential distributions between metastatic and nonmetastatic patients. Besides that, combining sequence and expression information, we identified 436 putative RNA targets regulated by the four RBPs through strict multistep bioinformatics screening. For the downstream analysis, the evidence from functional enrichment analysis and public literature indicated the roles of these target genes in the carcinogenesis and progression of colorectal cancer. Furthermore, through the machine learning algorithm and statistical analysis, we obtained two gene candidates that had obvious effects on the metastasis and overall survival status of patients with colorectal cancer. In summary, our study comprehensively explored the influence of APOBEC3G, EEF1A2, EIF5AL1, and CELF3 in colorectal cancer metastasis, which may offer favorable perspectives for clinical diagnosis and therapy.

Mitochondrial Uncoupling Proteins: Subtle Regulators of Cellular Redox Signaling

SIGNIFICANCE

Mitochondria are the energetic, metabolic, redox, and information signaling centers of the cell. Substrate pressure, mitochondrial network dynamics, and cristae morphology state are integrated by the protonmotive force Δp or its potential component, ΔΨ, which are attenuated by proton backflux into the matrix, termed uncoupling. The mitochondrial uncoupling proteins (UCP1-5) play an eminent role in the regulation of each of the mentioned aspects, being involved in numerous physiological events including redox signaling. Recent Advances: UCP2 structure, including purine nucleotide and fatty acid (FA) binding sites, strongly support the FA cycling mechanism: UCP2 expels FA anions, whereas uncoupling is achieved by the membrane backflux of protonated FA. Nascent FAs, cleaved by phospholipases, are preferential. The resulting Δp dissipation decreases superoxide formation dependent on Δp. UCP-mediated antioxidant protection and its impairment are expected to play a major role in cell physiology and pathology. Moreover, UCP2-mediated aspartate, oxaloacetate, and malate antiport with phosphate is expected to alter metabolism of cancer cells.

CRITICAL ISSUES

A wide range of UCP antioxidant effects and participations in redox signaling have been reported; however, mechanisms of UCP activation are still debated. Switching off/on the UCP2 protonophoretic function might serve as redox signaling either by employing/releasing the extra capacity of cell antioxidant systems or by directly increasing/decreasing mitochondrial superoxide sources. Rapid UCP2 degradation, FA levels, elevation of purine nucleotides, decreased Mg²⁺, or increased pyruvate accumulation may initiate UCP-mediated redox signaling.

FUTURE DIRECTIONS

Issues such as UCP2 participation in glucose sensing, neuronal (synaptic) function, and immune cell activation should be elucidated. Antioxid. Redox Signal. 29, 667-714.

The histone demethylase Phf2 acts as a molecular checkpoint to prevent NAFLD progression during obesity

Aberrant histone methylation profile is reported to correlate with the development and progression of NAFLD during obesity. However, the identification of specific epigenetic modifiers involved in this process remains poorly understood. Here, we identify the histone demethylase Plant Homeodomain Finger 2 (Phf2) as a new transcriptional co-activator of the transcription factor Carbohydrate Responsive Element Binding Protein (ChREBP). By specifically erasing H3K9me2 methyl-marks on the promoter of ChREBP-regulated genes, Phf2 facilitates incorporation of metabolic precursors into mono-unsaturated fatty acids, leading to hepatosteatosis development in the absence of inflammation and insulin resistance. Moreover, the Phf2-mediated activation of the transcription factor NF-E2-related factor 2 (Nrf2) further reroutes glucose fluxes toward the pentose phosphate pathway and glutathione biosynthesis, protecting the liver from oxidative stress and fibrogenesis in response to diet-induced obesity. Overall, our findings establish a downstream epigenetic checkpoint, whereby Phf2, through facilitating H3K9me2 demethylation at specific gene promoters, protects liver from the pathogenesis progression of NAFLD.

Uncoupling protein 2 downregulation by hypoxia through repression of peroxisome proliferator-activated receptor γ promotes chemoresistance of non-small cell lung cancer

Hypoxic microenvironment is critically involved in the response of non-small cell lung cancer (NSCLC) to chemotherapy, the mechanisms of which remain largely unknown. Here, we found that NSCLC patients exhibited increased chemotherapeutic resistance when complicated by chronic obstructive pulmonary disease (COPD), a critical cause of chronic hypoxemia. The downregulation of uncoupling protein 2 (UCP2), which is attributed to hypoxia-inducible factor 1 (HIF-1)-mediated suppression of the transcriptional factor peroxisome proliferator-activated receptor γ (PPARγ), was involved in NSCLC chemoresistance, and predicted a poor survival rate of patients receiving routine chemotherapy. UCP2 suppression induced reactive oxygen species production and upregulation of the ABC transporter protein ABCG2, which leads to chemoresistance by promoting drug efflux. UCP2 downregulation also altered metabolic rates as shown by elevated glucose uptake and reduced oxygen consumption. These data suggest that UCP2 is a key mediator of hypoxia-triggered chemoresistance of NSCLCs, which can be potentially targeted in clinical treatment of chemo-refractory NSCLCs.

Metabolomics facilitates the discrimination of the specific anti-cancer effects of free- and polymer-conjugated doxorubicin in breast cancer models

Metabolomics is becoming a relevant tool for understanding the molecular mechanisms involved in the response to new drug delivery systems. The applicability of this experimental approach to cell cultures and animal models makes metabolomics a useful tool for establishing direct connections between in vitro and in vivo data, thus providing a reliable platform for the characterization of chemotherapeutic agents. Herein, we used metabolomic profiles based on nuclear magnetic resonance (NMR) spectroscopy to evaluate the biochemical pathways involved in the response to a chemotherapeutic anthracycline drug (Doxorubicin, Dox) and an N-(2-hydroxypropyl) methacrylamide (HPMA) copolymer-conjugated form (HPMA-Dox) in an in vitro cell culture model and an in vivo orthotopic breast cancer model. We also used protein expression and flow cytometry studies to obtain a better coverage of the biochemical alterations associated with the administration of these compounds. The overall analysis revealed that polymer conjugation leads to increased apoptosis, reduced glycolysis, and reduced levels of phospholipids when compared to the free chemotherapeutic drug. Our results represent a first step in the application of integrated in vitro and in vivo metabolomic studies to the evaluation of drug delivery systems.

Defects in the mitochondrial-tRNA modification enzymes MTO1 and GTPBP3 promote different metabolic reprogramming through a HIF-PPARγ-UCP2-AMPK axis

Human proteins MTO1 and GTPBP3 are thought to jointly catalyze the modification of the wobble uridine in mitochondrial tRNAs. Defects in each protein cause infantile hypertrophic cardiomyopathy with lactic acidosis. However, the underlying mechanisms are mostly unknown. Using fibroblasts from an MTO1 patient and MTO1 silenced cells, we found that the MTO1 deficiency is associated with a metabolic reprogramming mediated by inactivation of AMPK, down regulation of the uncoupling protein 2 (UCP2) and transcription factor PPARγ, and activation of the hypoxia inducible factor 1 (HIF-1). As a result, glycolysis and oxidative phosphorylation are uncoupled, while fatty acid metabolism is altered, leading to accumulation of lipid droplets in MTO1 fibroblasts. Unexpectedly, this response is different from that triggered by the GTPBP3 defect, as GTPBP3-depleted cells exhibit AMPK activation, increased levels of UCP2 and PPARγ, and inactivation of HIF-1. In addition, fatty acid oxidation and respiration are stimulated in these cells. Therefore, the HIF-PPARγ-UCP2-AMPK axis is operating differently in MTO1- and GTPBP3-defective cells, which strongly suggests that one of these proteins has an additional role, besides mitochondrial-tRNA modification. This work provides new and useful information on the molecular basis of the MTO1 and GTPBP3 defects and on putative targets for therapeutic intervention.

Aberrant proliferation and differentiation of glycogen storage disease type Ib mesenchymal stem cells

Glycogen storage disease type Ib (GSD-Ib) is caused by mutations of the glucose-6-phosphate transporter (G6PT) and characterized by disrupted glucose homeostasis, neutropenia, and neutrophil dysfunction. To investigate the role of G6PT in human adipose-derived mesenchymal stem cells (hMSCs), the G6PT gene was mutated by CRISPR/Cas9 technology and single cell-derived G6PT^-/- hMSCs were established. G6PT^-/- hMSCs have significantly increased cell proliferation but impaired adipogenesis and osteogenesis. These phenotypes are associated with two mechanisms: i) metabolic reprogramming in G6PT^-/- hMSCs causing a metabolic shift toward glycolysis rather than oxidative phosphorylation and ii) increased cyclooxygenase-2-derived prostaglandin E₂ secretion in G6PT^-/- hMSCs. This study demonstrates that G6PT is essential for proliferation and differentiation of MSCs, providing important insights into the GSD-Ib phenotypes.

The Effect of Hypoxia and Metformin on Fatty Acid Uptake, Storage, and Oxidation in L6 Differentiated Myotubes

Metabolic impairments associated with obstructive sleep apnea syndrome (OSA) are linked to tissue hypoxia, however, the explanatory molecular and endocrine mechanisms remain unknown. Using gas-permeable cultureware, we studied the chronic effects of mild and severe hypoxia on free fatty acid (FFA) uptake, storage, and oxidation in L6 myotubes under 20, 4, or 1% O₂. Additionally, the impact of metformin and the peroxisome proliferator-activated receptor (PPAR) β/δ agonist, called GW501516, were investigated. Exposure to mild and severe hypoxia reduced FFA uptake by 37 and 32%, respectively, while metformin treatment increased FFA uptake by 39% under mild hypoxia. GW501516 reduced FFA uptake under all conditions. Protein expressions of CD36 (cluster of differentiation 36) and SCL27A4 (solute carrier family 27 fatty acid transporter, member 4) were reduced by 17 and 23% under severe hypoxia. Gene expression of UCP2 (uncoupling protein 2) was reduced by severe hypoxia by 81%. Metformin increased CD36 protein levels by 28% under control conditions and SCL27A4 levels by 56% under mild hypoxia. Intracellular lipids were reduced by mild hypoxia by 18%, while in controls only, metformin administration further reduced intracellular lipids (20% O₂) by 36%. Finally, palmitate oxidation was reduced by severe hypoxia, while metformin treatment reduced non-mitochondrial O₂ consumption, palmitate oxidation, and proton leak at all O₂ levels. Hypoxia directly reduced FFA uptake and intracellular lipids uptake in myotubes, at least partially, due to the reduction in CD36 transporters. Metformin, but not GW501516, can increase FFA uptake and SCL27A4 expression under mild hypoxia. Described effects might contribute to elevated plasma FFA levels and metabolic derangements in OSA.

Mitochondrial Protein UCP2 Controls Pancreas Development

The mitochondrial carrier uncoupling protein (UCP) 2 belongs to the family of the UCPs. Despite its name, it is now accepted that UCP2 is rather a metabolite transporter than a UCP. UCP2 can regulate oxidative stress and/or energetic metabolism. In rodents, UCP2 is involved in the control of α- and β-cell mass as well as insulin and glucagon secretion. Our aim was to determine whether the effects of UCP2 observed on β-cell mass have an embryonic origin. Thus, we used Ucp2 knockout mice. We found an increased size of the pancreas in Ucp2^-/- fetuses at embryonic day 16.5, associated with a higher number of α- and β-cells. This phenotype was caused by an increase of PDX1⁺ progenitor cells. Perinatally, an increase in the proliferation of endocrine cells also participates in their expansion. Next, we analyzed the oxidative stress in the pancreata. We quantified an increased nuclear translocation of nuclear factor erythroid 2-related factor 2 (NRF2) in the mutant, suggesting an increased production of reactive oxygen species (ROS). Phosphorylation of AKT, an ROS target, was also activated in the Ucp2^-/- pancreata. Finally, administration of the antioxidant N-acetyl-l-cysteine to Ucp2^-/- pregnant mice alleviated the effect of knocking out UCP2 on pancreas development. Together, these data demonstrate that UCP2 controls pancreas development through the ROS-AKT signaling pathway.

Bile acid and cigarette smoke enhance the aggressive phenotype of esophageal adenocarcinoma cells by downregulation of the mitochondrial uncoupling protein-2

Limited information is available regarding mechanisms that link the known carcinogenic risk factors of gastro-esophageal reflux and cigarette smoking to metabolic alterations in esophageal adenocarcinoma (EAC). In the present study, we utilized a novel in-vitro model to examine whether bile acid and cigarette smoke increase the aggressiveness of EAC and whether these changes are associated with metabolic changes. EAC cells (EACC) were exposed to 10 μg/ml cigarette smoke condensate (CSC) and/or 100 μM of the oncogenic bile acid, deoxycholic acid (DCA), for 5 days. These exposure conditions were chosen given their lack of effect on proliferation or viability. DCA and CSC increased invasion, migration, and clonogenicity in EAC cells. These changes were associated with concomitant increases in ATP, ROS, and lactate production indicative of increased mitochondrial respiration as well as glycolytic activity. DCA and CSC exposure significantly decreased expression of uncoupling protein-2 (UCP2), a mitochondrial inner membrane protein implicated in regulation of the proton gradient. Knockdown of UCP2 in EACC phenocopied DCA and CSC exposure as evidenced by increased cell migration, invasion, and clonogenicity, whereas over-expression of UCP2 had an inverse effect. Furthermore, over-expression of UCP2 abrogated DCA and CSC-mediated increases in lactate and ATP production in EACC. DCA and CSC promote the aggressive phenotype of EACC with concomitant metabolic changes occurring via downregulation of UCP2. These results indicate that UCP2 is integral to the aggressive phenotype of EACC. This mechanism suggests that targeting alterations in cellular energetics may be a novel strategy for EAC therapy.

Association of insertion-deletions polymorphisms with colorectal cancer risk and clinical features

AIM

To investigate the association between 16 insertion-deletions (INDEL) polymorphisms, colorectal cancer (CRC) risk and clinical features in an admixed population.

METHODS

One hundred and forty patients with CRC and 140 cancer-free subjects were examined. Genomic DNA was extracted from peripheral blood samples. Polymorphisms and genomic ancestry distribution were assayed by Multiplex-PCR reaction, separated by capillary electrophoresis on the ABI 3130 Genetic Analyzer instrument and analyzed on GeneMapper ID v3.2. Clinicopathological data were obtained by consulting the patients’ clinical charts, intra-operative documentation, and pathology scoring.

RESULTS

Logistic regression analysis showed that polymorphism variations in IL4 gene was associated with increased CRC risk, while TYMS and UCP2 genes were associated with decreased risk. Reference to anatomical localization of tumor Del allele of NFKB1 and CASP8 were associated with more colon related incidents than rectosigmoid. In relation to the INDEL association with tumor node metastasis (TNM) stage risk, the Ins alleles of ACE, HLAG and TP53 (6 bp INDEL) were associated with higher TNM stage. Furthermore, regarding INDEL association with relapse risk, the Ins alleles of ACE, HLAG, and UGT1A1 were associated with early relapse risk, as well as the Del allele of TYMS. Regarding INDEL association with death risk before 10 years, the Ins allele of SGSM3 and UGT1A1 were associated with death risk.

CONCLUSION

The INDEL variations in ACE, UCP2, TYMS, IL4, NFKB1, CASP8, TP53, HLAG, UGT1A1, and SGSM3 were associated with CRC risk and clinical features in an admixed population. These data suggest that this cancer panel might be useful as a complementary tool for better clinical management, and more studies need to be conducted to confirm these findings.

Expression and putative role of mitochondrial transport proteins in cancer

Cancer cells undergo major changes in energy and biosynthetic metabolism. One of them is the Warburg effect, in which pyruvate is used for fermentation rather for oxidative phosphorylation. Another major one is their increased reliance on glutamine, which helps to replenish the pool of Krebs cycle metabolites used for other purposes, such as amino acid or lipid biosynthesis. Mitochondria are central to these alterations, as the biochemical pathways linking these processes run through these organelles. Two membranes, an outer and inner membrane, surround mitochondria, the latter being impermeable to most organic compounds. Therefore, a large number of transport proteins are needed to link the biochemical pathways of the cytosol and mitochondrial matrix. Since the transport steps are relatively slow, it is expected that many of these transport steps are altered when cells become cancerous. In this review, changes in expression and regulation of these transport proteins are discussed as well as the role of the transported substrates. This article is part of a Special Issue entitled Mitochondria in Cancer, edited by Giuseppe Gasparre, Rodrigue Rossignol and Pierre Sonveaux.

MUC2 mucin deficiency alters inflammatory and metabolic pathways in the mouse intestinal mucosa

The mucus layer in the intestine affects several aspects of intestinal biology, encompassing physical, chemical protection, immunomodulation and growth, thus contributing to homeostasis. Mice with genetic inactivation of the Muc2 gene, encoding the MUC2 mucin, the major protein component of mucus, exhibit altered intestinal homeostasis, which is strictly dependent on the habitat, likely due to differing complements of intestinal microbes. Our previous work established that Muc2 deficiency was linked to low chronic inflammation resulting in tumor development in the small, large intestine including the rectum. Here, we report that inactivation of Muc2 alters metabolic pathways in the normal appearing mucosa of Muc2^-/- mice. Comparative analysis of gene expression profiling of isolated intestinal epithelial cells (IECs) and the entire intestinal mucosa, encompassing IECs, immune and stromal cells underscored that more than 50% of the changes were common to both sets of data, suggesting that most alterations were IEC-specific. IEC-specific expression data highlighted perturbation of lipid absorption, processing and catabolism linked to altered Pparα signaling in IECs. Concomitantly, alterations of glucose metabolism induced expression of genes linked to de novo lipogenesis, a characteristic of tumor cells. Importantly, gene expression alterations characterizing Muc2^-/- IECs are similar to those observed when analyzing the gene expression signature of IECs along the crypt-villus axis in WT B6 mice, suggesting that Muc2^-/- IECs display a crypt-like gene expression signature. Thus, our data strongly suggest that decreased lipid metabolism, and alterations in glucose utilization characterize the crypt proliferative compartment, and may represent a molecular signature of pre-neoplastic lesions.

Non-coding RNAs: the dark side of nuclear-mitochondrial communication

Mitochondria are critical hubs for the integration of several key metabolic processes implicated in cell growth and survival. They originated from bacterial ancestors through endosymbiosis, following the transfer of more than 90% of their endosymbiont genome to the host cell nucleus. Over time, a mutually beneficial symbiotic relationship has been established, which relies on continuous and elaborate signaling mechanisms between this life-essential organelle and its host. The ability of mitochondria to signal their functional state and trigger compensatory and adaptive cellular responses has long been recognized, but the underlying molecular mechanisms involved have remained poorly understood. Recent evidence indicates that non-coding RNAs (ncRNAs) may contribute to the synchronization of a series of essential cellular and mitochondrial biological processes, acting as "messengers" between the nucleus and the mitochondria. Here, we discuss the emerging putative roles of ncRNAs in various bidirectional signaling pathways established between the host cell and its mitochondria, and how the dysregulation of these pathways may lead to aging-related diseases, including cancer, and offer new promising therapeutic avenues.