Unique Energy Metabolism Research Articles

The role of mitochondrial dynamics in the pathophysiology of endometriosis.

Endometriosis is a chronic disease of reproductive age, associated with pelvic pain and infertility. Endometriotic cells adapt to changing environments such as oxidative stress and hypoxia in order to survive. However, the underlying mechanisms remain to be fully elucidated. In this review, we summarize our current understanding of the pathogenesis of endometriosis, focusing primarily on the molecular basis of energy metabolism, redox homeostasis, and mitochondrial function, and discuss perspectives on future research directions. Papers published up to March 31, 2023 in the PubMed and Google Scholar databases were included in this narrative literature review. Mitochondria serve as a central hub sensing a multitude of physiological processes, including energy production and cellular redox homeostasis. Under hypoxia, endometriotic cells favor glycolysis and actively produce pyruvate, nicotinamide adenine dinucleotide phosphate (NADPH), and other metabolites for cell proliferation. Mitochondrial fission and fusion dynamics may regulate the phenotypic plasticity of cellular energy metabolism, that is, aerobic glycolysis or OXPHOS. Endometriotic cells have been reported to have reduced mitochondrial numbers, increased lamellar cristae, improved energy efficiency, and enhanced cell proliferation and survival. Increased mitochondrial fission and fusion turnover by hypoxic and normoxic conditions suggests an activation of mitochondrial quality control mechanisms. Recently, candidate molecules that influence mitochondrial dynamics have begun to be identified. This review suggests that unique energy metabolism and redox homeostasis driven by mitochondrial dynamics may be linked to the pathophysiology of endometriosis. However, further studies are needed to elucidate the regulatory mechanisms of mitochondrial dynamics in endometriosis.

Genetic and Physiological Probing of Cytoplasmic Bypasses for the Energy-Converting Methyltransferase Mtr in Methanosarcina acetivorans.

Methanogenesis is a unique energy metabolism carried out by members of the domain Archaea. Unlike most other methanogens, which reduce CO2 to methane with hydrogen as the electron donor, Methanosarcina acetivorans is able to grow on methylated compounds, on acetate, and on carbon monoxide (CO). These substrates are metabolized via distinct yet overlapping pathways. For the use of any single methanogenic substrate, the membrane-integral, energy-converting N5-methyl-tetrahydrosarcinapterin (H4SPT):coenzyme M (HS-CoM) methyltransferase (Mtr) is required. It was proposed that M. acetivorans can bypass the methyl transfer catalyzed by Mtr via cytoplasmic activities. To address this issue, conversion of different energy substrates by an mtr deletion mutant was analyzed. No significant methyl transfer from H4SPT to HS-CoM could be detected with CO as the electron donor. In contrast, formation of methane and CO2 in the presence of methanol or trimethylamine was indicative of an Mtr bypass in the oxidative direction. As methane thiol and dimethyl sulfide were transiently produced during methylotrophic methanogenesis in the mtr mutant, involvement in this process of methyl sulfide-dependent methyltransferases (Mts) was analyzed in a strain lacking both the Mts system and Mtr. It could be unequivocally demonstrated that the Mts system is not involved in bypassing Mtr, thereby ruling out previous proposals. Conversion of [13C]methanol indicated that in the absence of Mtr M. acetivorans provides the reducing equivalents for methyl-S-CoM reduction to methane by oxidizing (an) intracellular compound(s) to CO2 rather than disproportioning the source of methyl groups. Thus, no in vivo Mtr bypass appears to exist in M. acetivorans. IMPORTANCE Methanogenic archaea possess only a limited number of chemiosmotic coupling sites in their respiratory chains. Among them, N5-methyl-H4SPT:HS-CoM methyltransferase (Mtr) is the most widely distributed. Previous observations led to the conclusion that Methanosarcina acetivorans is able to bypass this reaction via methyl sulfide-dependent methyltransferases (Mts). However, strains lacking Mtr are not able to produce methane from CO. Also, these strains are unable to oxidize methylated substrates to CO2, in contrast to observations in the close relative Methanosarcina barkeri. The results also highlight the sole function of the Mts system in methyl sulfide metabolism. Thus, no in vivo Mtr bypass appears to exist in M. acetivorans.

Denitrification in foraminifera has an ancient origin and is complemented by associated bacteria

Benthic foraminifera are unicellular eukaryotes that inhabit sediments of aquatic environments. Several foraminifera of the order Rotaliida are known to store and use nitrate for denitrification, a unique energy metabolism among eukaryotes. The rotaliid Globobulimina spp. has been shown to encode an incomplete denitrification pathway of bacterial origin. However, the prevalence of denitrification genes in foraminifera remains unknown, and the missing denitrification pathway components are elusive. Analyzing transcriptomes and metagenomes of 10 foraminiferal species from the Peruvian oxygen minimum zone, we show that denitrification genes are highly conserved in foraminifera. We infer the last common ancestor of denitrifying foraminifera, which enables us to predict the ability to denitrify for additional foraminiferal species. Additionally, an examination of the foraminiferal microbiota reveals evidence for a stable interaction with Desulfobacteraceae, which harbor genes that complement the foraminiferal denitrification pathway. Our results provide evidence that foraminiferal denitrification is complemented by the foraminifera-associated microbiome. The interaction of foraminifera with their resident bacteria is at the basis of foraminiferal adaptation to anaerobic environments that manifested in ecological success in oxygen depleted habitats.

Bta-miR-2400 Targets SUMO1 to Affect Yak Preadipocytes Proliferation and Differentiation.

Simple SummaryYak adipose tissue may have evolved a unique energy metabolism manner that accommodates the organism’s seasonal growth rhythms. Rare reports have shown that miRNAs regulate lipid metabolism in domestic yaks. In the present study, miR-2400 is a novel bovine miRNA; gain- and loss- function of bta-miR-2400 were performed in Yak preadipocytes, and it was revealed that bta-miR-2400 regulates lipid metabolism and energy homeostasis in yak preadipocytes by directly targeting small ubiquitin like modifier 1 (SUMO1) to promote cell proliferation and inhibit differentiation. These findings will undoubtedly facilitate future studies of miRNA regulation in lipid metabolism in high-altitude animals.Yak adipose tissue may have evolved a unique energy metabolism manner to accommodate the organism’s seasonal growth rhythms. MiRNAs regulate multiple biological processes including systemic metabolism and energy homeostasis through post-transcriptional regulations. Rare reports have shown that miRNAs regulate lipid metabolism in domestic yaks. Therefore, we investigated the regulatory mechanisms of bta-miR-2400 in modulating yak preadipocytes proliferation and differentiation. We found that bta-miR-2400 was highly expressed in adipose tissue. Overexpression of bta-miR-2400 in yak preadipocytes significantly enhanced cell proliferation, increased the number of EdU fluorescence-stained cells, and promoted the expression of proliferation marker genes (CDK2, CDK4 and PCNA). Besides, overexpression of bta-miR-2400 repressed the expression of adipogenesis-related marker genes, and the content of cellular triglyceride was substantially reduced. Conversely, inhibition of bta-miR-2400 showed opposite effects compared to those of bta-miR-2400 overexpression in yak preadipocytes. Further, luciferase reporter assays revealed that SUMO1 is a target gene of bta-miR-2400, with bta-miR-2400 being able to down-regulate SUMO1 mRNA and protein expression. In conclusion, bta-miR-2400 regulates lipid metabolism and energy homeostasis in yak preadipocytes by directly targeting SUMO1 to promote cell proliferation and inhibit differentiation.

Using structural biology of methanogen enzymes to aid our understanding of methane formation

Methane is a potent greenhouse gas (28-fold more potent than carbon dioxide) and is a significant gas contributing to global climate change. Approximately a billion tons of methane are produced each year by methanogenic archaea in ruminants. These archaea possess a number of unusual traits such as isoprenoid-based lipids, unusual cell wall chemistry and a unique energy metabolism (methanogenesis) that requires six methanogen-specific cofactors. Many of the enzymes involved in these processes have no direct analogues in the host animal. To gain insights into the fundamental biology of rumen methanogens we have determined crystal structures of key enzymes with archaeal-specific traits. Over 600 enzymes were targeted for structure determination which produced approximately 200 purified soluble enzymes for crystallographic screening. More than 50 different enzymes have produced crystals and 30 structures have been solved for individual enzymes to date. The results have helped illuminate our understanding of methane formation at this critical juncture in the world’s history.

Regulation of tumor cell glycometabolism and tumor therapy

Tumor cells have unique energy metabolism phenomena, namely high glucose absorption, aerobic glycolysis and high lactic acid production, which are characterized by down-regulation of related proteins involved in oxidative metabolism in tumor cells, and up-regulation of glucose transporters and monocarboxylate transporters. Studies have shown that drugs that target tumor cell glucose metabolism have the ability to selectively kill tumor cells, bringing new hope for tumor treatment. Tumor stem cells are considered to be the root cause of tumor recurrence, metastasis and poor prognosis, and their energy metabolism characteristics have not yet been agreed. Studies have shown that reversing the energy metabolism of tumor stem cells can increase their chemosensitivity. This article reviews recent studies on tumor and tumor stem cell glucose metabolism and the opportunities and challenges of tumor treatment through targeting glucose metabolism, which might provide new ideas and opportunities for clinical tumor therapy.

NAD Metabolism in Cancer Therapeutics.

Cancer cells have a unique energy metabolism for sustaining rapid proliferation. The preference for anaerobic glycolysis under normal oxygen conditions is a unique trait of cancer metabolism and is designated as the Warburg effect. Enhanced glycolysis also supports the generation of nucleotides, amino acids, lipids, and folic acid as the building blocks for cancer cell division. Nicotinamide adenine dinucleotide (NAD) is a co-enzyme that mediates redox reactions in a number of metabolic pathways, including glycolysis. Increased NAD levels enhance glycolysis and fuel cancer cells. In fact, nicotinamide phosphoribosyltransferase (Nampt), a rate-limiting enzyme for NAD synthesis in mammalian cells, is frequently amplified in several cancer cells. In addition, Nampt-specific inhibitors significantly deplete NAD levels and subsequently suppress cancer cell proliferation through inhibition of energy production pathways, such as glycolysis, tricarboxylic acid (TCA) cycle, and oxidative phosphorylation. NAD also serves as a substrate for poly(ADP-ribose) polymerase (PARP), sirtuin, and NAD gylycohydrolase (CD38 and CD157); thus, NAD regulates DNA repair, gene expression, and stress response through these enzymes. Thus, NAD metabolism is implicated in cancer pathogenesis beyond energy metabolism and considered a promising therapeutic target for cancer treatment. In this review, we present recent findings with respect to NAD metabolism and cancer pathogenesis. We also discuss the current and future perspectives regarding the therapeutics that target NAD metabolic pathways.

PTPN11 Mutations Confer Unique Metabolic Properties and Increase Resistance to Venetoclax and Azacitidine in Acute Myelogenous Leukemia

Previous studies have demonstrated the importance of energy metabolism as it relates to numerous aspects of leukemia stem cell (LSC) biology. Specifically, in acute myelogenous leukemia (AML), it has been shown that LSCs have a unique reliance on oxidative phosphorylation (OXPHOS), and that inhibition of B-cell lymphoma 2 (BCL-2) acts to down-regulate OXPHOS and eradicate LSCs in pre-clinical models. In the clinical setting, when BCL-2 inhibitor venetoclax is combined with azacitidine, high response rates (~80%) in elderly de novo AML patients have been observed (PMID: 29339097). Nonetheless, a significant portion of these patients ultimately experience disease progression. The mechanism of resistance and characteristics of these patients is poorly understood.Our preliminary data shows that the venetoclax + azacitidine (ven/aza) regimen targets LSCs through alteration of energy metabolism. Specifically, the regimen disrupts the TCA cycle leading to decreases in ATP production and inhibition of OXPHOS. This metabolic targeting is central to ven/aza efficacy and we hypothesize that resistance and progression of AML patients is due to compensatory mechanisms that restore sufficient levels of OXPHOS (PMID:3333149). Investigation of such mechanisms led us to explore the potential activity of MCL1. Previous studies have shown MCL1 can influence venetoclax resistance, however little is known about MCL1's role in metabolism, although a report in breast cancer cells suggests MCL1 modulates OXPHOS (PMID: 28978427). In leukemia, MCL1 expression has been shown to be partially upregulated through mutations in protein tyrosine phosphatase non- receptor type 11 (PTPN11), and PTPN11 mutations have been shown to increase LSC frequency. Thus, we hypothesized that PTPN11 mutations may confer resistance to venetoclax-based regimens at least partially by up-regulation of MCL1.To test this hypothesis, we investigated the relationship between PTPN11 mutations, MCL1, and the metabolic phenotype. In comparison to specimens with a wild type allele, LSCs isolated from PTPN11 mutant patient specimens showed increased levels of OXPHOS as well as glycolysis, amino acids, and fatty acids, suggesting an ability to utilize multiple energy sources for survival. PTPN11 mutant specimens also show decreased sensitivity to venetoclax, suggesting OXPHOS is not affected by venetoclax to the same degree as PTPN11 wild type specimens (fig. 1). Furthermore, when we introduced a mutated allele of PTPN11 into a primary AML specimen we observed increased oxidative phosphorylation and glycolysis, which correlated with decreased in vitro sensitivity to venetoclax (fig. 2).To test the potential role of MCL1 in PTPN11 mutant specimens, we employed a small molecule MCL-1 inhibitor. Metabolic analysis of specimens treated with the MCL-1 inhibitor showed decreased OXPHOS in PTPN11 mutant specimens (fig 3). Further, PTPN11 mutant specimens exhibit increased sensitivity to the MCL-1 inhibitor (fig. 4).To investigate a potential mechanistic link to clinical observations, we next examined 45 older, previously untreated AML patients from our institution who received ven/aza, both in the context of the multi-institutional study NCT02203773 (N=33) and with off-label use (N=12). Of 12 variables examined, only the presence of PTPN11 predicted shorter response duration (table 1). In addition, of the 9 patients who progressed ven/aza, 2 (22%) acquired PTPN11 mutations upon progression, further suggesting PTPN11 may represent a resistance mechanism to this regimen. Notably, PTPN11 is not preferentially detected in patients who progress after regimens other than ven/aza.In conclusion, AML containing PTPN11 mutations exhibit a unique energy metabolism profile. These specimens also appear to have increased sensitivity to MCL-1 inhibitors. The presence of PTPN11 mutations represents both a novel method for predicting response to ven/aza and a potential strategy for targeting patients who progress. We propose that addition of an MCL-1 inhibitor for treatment of AML patients bearing PTPN11 or related mutations may increase therapeutic responses. DisclosuresSavona:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding; Boehringer Ingelheim: Consultancy. Fesik:Boehringer Ingelheim: Consultancy. Pollyea:Celyad: Consultancy, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Curis: Membership on an entity's Board of Directors or advisory committees; Agios: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Celgene: Membership on an entity's Board of Directors or advisory committees; AbbVie: Consultancy, Research Funding; Karyopharm: Membership on an entity's Board of Directors or advisory committees; Argenx: Consultancy, Membership on an entity's Board of Directors or advisory committees; Gilead: Consultancy.

A Novel Eukaryotic Denitrification Pathway in Foraminifera

SummaryBenthic foraminifera are unicellular eukaryotes inhabiting sediments of aquatic environments. Several species were shown to store and use nitrate for complete denitrification, a unique energy metabolism among eukaryotes. The population of benthic foraminifera reaches high densities in oxygen-depleted marine habitats where they play a key role in the marine nitrogen cycle. However, the mechanisms of denitrification in foraminifera are still unknown, and the possibility of a contribution of associated bacteria is debated. Here, we present evidence for a novel eukaryotic denitrification pathway that is encoded in foraminiferal genomes. Large-scale genome and transcriptomes analyses reveal the presence of a denitrification pathway in foraminifera species of the genus Globobulimina. This includes the enzymes nitrite reductase (NirK) and nitric oxide reductase (Nor) as well as a wide range of nitrite/nitrate transporters (Nrt). A phylogenetic reconstruction of the enzymes’ evolutionary history uncovers evidence for an ancient acquisition of the foraminiferal denitrification pathway from prokaryotes. We propose a model for denitrification in foraminifera where a common electron transport chain is used for anaerobic and aerobic respiration. The evolution of hybrid respiration in foraminifera likely contributed to their ecological success, which is well documented in palaeontological records since the Cambrian period.

Moonlighting Functions of Cysteinyl-tRNA Synthetases: Cycteine Hydropersulfide Production and Regulation of Mitochondrial Biogenesis and Bioenergetics

Hydrogen sulfide and reactive persulfide species such as cysteine hydropersulfide (CysSSH) are reportedly formed endogenously in prokaryotic and eukaryotic cells and in mammals in vivo. The chemical properties and abundance of these species suggest a pivotal role for reactive persulfides (i.e., various compounds containing -SSH) in different cellular regulatory processes. We proposed that CysSSH and related reactive sulfur species can behave as potent antioxidants and cellular protectants and may function as redox signaling intermediates. Extensive persulfide formation is now apparent in cysteine-containing proteins in Escherichia coli and mammalian cells and is thus far believed to result from post-translational modifications involving hydrogen sulfide-related chemistry. Here, we discovered moonlighting (dual) functions of cysteinyl-tRNA synthetases (CARSs), serve as the principal cysteine persulfide synthase (CPERS) in vivo. Targeted disruption of a gene encoding mitochondrial CARS (CARS2) in mice and human cells revealed that persulfides derived from CARS2 are critically involved in the mitochondrial biogenesis and energy metabolism, i.e., bioenergetics, which is known for a long time as sulfur respiration in anaerobic bacteria. Further investigating CARS-dependent persulfide production will clarify aberrant redox signaling that we may call as sulfur stress and a unique energy metabolism in mammals.

Discovery of New Class of Trypanocidal Compounds Targeting the Energy Metabolism of African Trypanosomes

Background African trypanosomes are the pathogens that cause sleeping sickness in humans and Nagana in animals. These diseases are fatal, endemic in sub-Saharan Africa and attributed to the underdevelopment of the subregion. Not less than 25,000 human lives and animals worth $1.5 billion are lost annually to the diseases. There is no vaccine and the available therapeutic options are few and with limited efficacy, prompting the search for new drug candidates. The unique energy metabolism pathway of African trypanosomes is considered a validated rational strategy towards the development of new drugs. Our previous results show that the simultaneous inhibition of the parasites’ glycerol kinase (TGK) and alternative oxidase (TAO), two key enzymes for ATP synthesis in the parasites’ resulted in trypanosomes death. However, while ascofuranone (AF) is an established TAO inhibitor, there is no known inhibitor for any TGK. The present study was aimed at the discovery of novel TGK inhibitors for co-administration with AF.Methods Protein X-ray crystallography, computational medicinal chemistry, and enzyme assay approaches was used to conduct large-scale screening of a chemical library.ResultsThe resulting hits were compounds possessing different structural scaffolds, which potently inhibited TGK up to 50 nM IC50 values. Interestingly, a number of the inhibitors caused the expected improvement in the potency of AF against trypanosome cells, causing a shift in trypanocidal activity of AF (IC50) from nanomolar to picomolar concentrations (P < 0.05). Remarkably, one of the inhibitors was identified as a dual inhibitor of TGK and TAO. The complex structures of both enzymes with the inhibitors have been determined, providing a platform for further refinement of the trypanocidal potencies by structure–activity relationship studies.Conclusion We have utilized rational design approach to identify novel trypanocidal compounds that may be used for the design of new class of anti-trypanosomal drugs for African trypanosomiasis.Disclosures All authors: No reported disclosures.

Long-chain acylcarnitine content determines the pattern of energy metabolism in cardiac mitochondria

In the heart, a nutritional state (fed or fasted) is characterized by a unique energy metabolism pattern determined by the availability of substrates. Increased availability of acylcarnitines has been associated with decreased glucose utilization; however, the effects of long-chain acylcarnitines on glucose metabolism have not been previously studied. We tested how changes in long-chain acylcarnitine content regulate the metabolism of glucose and long-chain fatty acids in cardiac mitochondria in fed and fasted states. We examined the concentrations of metabolic intermediates in plasma and cardiac tissues under fed and fasted states. The effects of substrate availability and their competition for energy production at the mitochondrial level were studied in isolated rat cardiac mitochondria. The availability of long-chain acylcarnitines in plasma reflected their content in cardiac tissue in the fed and fasted states, and acylcarnitine content in the heart was fivefold higher in fasted state compared to the fed state. In substrate competition experiments, pyruvate and fatty acid metabolites effectively competed for the energy production pathway; however, only the physiological content of acylcarnitine significantly reduced pyruvate and lactate oxidation in mitochondria. The increased availability of long-chain acylcarnitine significantly reduced glucose utilization in isolated rat heart model and in vivo. Our results demonstrate that changes in long-chain acylcarnitine contents could orchestrate the interplay between the metabolism of pyruvate-lactate and long-chain fatty acids, and thus determine the pattern of energy metabolism in cardiac mitochondria.

Selenocysteine, Pyrrolysine, and the Unique Energy Metabolism of Methanogenic Archaea

Methanogenic archaea are a group of strictly anaerobic microorganisms characterized by their strict dependence on the process of methanogenesis for energy conservation. Among the archaea, they are also the only known group synthesizing proteins containing selenocysteine or pyrrolysine. All but one of the known archaeal pyrrolysine-containing and all but two of the confirmed archaeal selenocysteine-containing protein are involved in methanogenesis. Synthesis of these proteins proceeds through suppression of translational stop codons but otherwise the two systems are fundamentally different. This paper highlights these differences and summarizes the recent developments in selenocysteine- and pyrrolysine-related research on archaea and aims to put this knowledge into the context of their unique energy metabolism.

Archaeal Protein Biogenesis: Posttranslational Modification and Degradation

The study of Archaea at the DNA and RNA levels has provided considerable insight into replication, transcription, and other information-associated events which are either unique to this remarkable group of organisms or which were later found to also occur in Bacteria and/or Eukarya. In contrast, largely due to a lack of suitable model systems and a limited number of appropriate molecular tools, considerably less was known about archaeal proteins in terms of their biogenesis, modification, trafficking, or degradation. In recent years, however, we have witnessed major advances in proteomics, successful in vitro reconstitutions, and the development of reporter systems compatible with extreme conditions. Relying on such tools, insight into different stages in the life of archaeal proteins has begun to accumulate. In this special issue of Archaea, we present a series of articles addressing the current state of understanding of selected facets of archaeal protein biogenesis and processing. An article by De Koning et al. discussing how fidelity in archaeal information processing at the DNA, RNA, and protein levels is achieved begins this special issue. Rother and Krzycki then address proteins containing the unusual animo acids, selenocysteine, and pyrrolysine, as related to the unique energy metabolism of methanogenic archaea. Soppa compares one specific posttranslational modification, acetylation, across evolutionary lines, while Botting et al. discuss the importance of lysine methylation in hyperthermophilic crenarchaeota. Questions related to protein assembly are considered when Iwasaki addresses the iron-sulfur world in hyperthermoacidophilic archaea. Protein degradation is the focus of two articles in this special issue. Makarova and Koonin rely on comparative genomic analysis to reveal functional versatility of archaeal ubiquitin-like proteins, while Humbard et al. report on the phosphorylation and methylation of Haloferax volcanii proteasomal proteins. Archaeal cell surface proteins undergo a variety of post-translational modifications. However, such proteins must first be targeted to and traverse the plasma membrane. Accordingly, Zwieb and Bhuiyan discuss the latest findings on the archaeal signal recognition particle targeting system. Storf et al. address questions related to the biogenesis of one class of membrane proteins, namely, lipoproteins. An article by Ellen et al. considers archaeal protein export and describes different cell surface structures, while a report by Jarrell et al. focuses on the S-layer glycoprotein and flagella as reporters of choice of different protein processing events. With this in mind, Peyfoon and colleagues describe the N-linked glycan decorating the S-layer glycoprotein of Sulfolobus acidocaldarius. Finally, Kaminski and Eichler consider the workings of AglD, one of the enzymes which is involved in Haloferax volcanii S-layer glycoprotein N-glycosylation. In this, the first special issue of Archaea dedicated to archaeal protein biogenesis, we have tried to give the reader a sampling of the current research scene. It is our sincere hope that the community will find interest in the articles included here. More importantly, it is our intention that the work presented will stimulate other laboratories to begin studying questions related to archaeal protein biogenesis, hopefully in time for the next installment of this special issue. Jerry Eichler Julie Maupin-Furlow Joerg Soppa

Adaptation of Energy Metabolism in Breast Cancer Brain Metastases

Brain metastases are among the most feared complications in breast cancer, as no therapy exists that prevents or eliminates breast cancer spreading to the brain. New therapeutic strategies depend on specific knowledge of tumor cell properties that allow breast cancer cell growth within the brain tissue. To provide information in this direction, we established a human breast cancer cell model for brain metastasis based on circulating tumor cells from a breast cancer patient and variants of these cells derived from bone or brain lesions in immunodeficient mice. The brain-derived cells showed an increased potential for brain metastasis in vivo and exhibited a unique protein expression profile identified by large-scale proteomic analysis. This protein profile is consistent with either a selection of predisposed cells or bioenergetic adaptation of the tumor cells to the unique energy metabolism of the brain. Increased expression of enzymes involved in glycolysis, tricarboxylic acid cycle, and oxidative phosphorylation pathways suggests that the brain metastatic cells derive energy from glucose oxidation. The cells further showed enhanced activation of the pentose phosphate pathway and the glutathione system, which can minimize production of reactive oxygen species resulting from an enhanced oxidative metabolism. These changes promoted resistance of brain metastatic cells to drugs that affect the cellular redox balance. Importantly, the metabolic alterations are associated with strongly enhanced tumor cell survival and proliferation in the brain microenvironment. Thus, our data support the hypothesis that predisposition or adaptation of the tumor cell energy metabolism is a key element in breast cancer brain metastasis, and raise the possibility of targeting the functional differentiation in breast cancer brain lesions as a novel therapeutic strategy.

Comparison of gene expression profiles between white and brown adipose tissues of rat by microarray analysis

To characterize the energy metabolism in brown adipose tissue (BAT), the differences in gene expression profiles between BAT and white adipose tissue (WAT) were analyzed using a high-density cDNA microarray. RNAs isolated from two adipose tissues were hybridized to an Agilent rat cDNA Microarray that contained about 14,500 cDNA probe sets. The expression levels of 499 cDNA/ESTs were found to be at least 5-fold higher or lower in BAT than in WAT. Consistent with our previous findings, high expression levels of genes encoding uncoupling protein 1, muscle-type carnitine palmitoyltransferase and some other proteins involved in energy metabolism in BAT were found. Most of the genes encoding mitochondrial proteins, such as subunits of ATP synthase, cytochrome c oxidase, and NADH dehydrogenase, were highly expressed, reflecting possible differences in the cellular content of mitochondria between BAT and WAT. However, the expression levels of several genes encoding mitochondrial protein, such as liver mitochondrial aldehyde dehydrogenase and dicarboxylate carrier, were remarkably lower in BAT. These results may give important clues to understand the unique energy metabolism in BAT.

Novel Energy Metabolism in Anaerobic Hyperthermophilic Archaea: A Modified Embden-Meyerhof Pathway.

Hyperthermophiles, a group of microorganisms whose optimum growth temperatures are above 80°C, have been isolated mainly from marine and continental volcanic environments. They are viewed as potential sources of extraordinarily stable biomolecules with applications in novel industrial processes. Most hyperthermophiles belong to the domain Archaea, the third domain of life, and are considered to be the most ancient of all extant life forms. Recent studies have revealed unusual energy metabolic processes in hyperthermophilic archaea, e.g. a modified Embden-Meyerhof pathway, that have not been observed so far in organisms belonging to the Bacteria and Eucarya domains. Several novel enzymes — ADP-dependent glucokinase, ADP-dependent phosphofruktokinase, glyceraldehyde-3-phosphate ferredoxin oxidoreductase, phosphoenolpyruvate synthase, pyruvate: ferredoxin oxidoreductase, and ADP-forming acetyl-CoA synthetase — have been found to be involved in the modified Embden-Meyerhof pathway of the hyperthermophilic archaeon Pyrococcus furiosus. In addition, a novel regulation site for energy metabolism and a unique mode of ATP regeneration have been postulated to exist in the pathway of P. furiosus. The metabolic design observed in this microorganism might reflect the situation at an early stage of evolution. This review focuses mainly on the unique energy metabolism and related enzymes of P. furiosus that have recently been described.

Characteristics of the aerobic respiratory chains of the microaerophiles Campylobacter jejuni and Helicobacter pylori.

The respiratory chain enzymes of microaerophilic bacteria should play a major role in their adaptation to growth at low oxygen tensions. The genes encoding the putative NADH:quinone reductases (NDH-1), the ubiquinol:cytochrome c oxidoreductases (bc1 complex) and the terminal oxidases of the microaerophiles Campylobacter jejuni and Helicobacter pylori were analysed to identify structural elements that may be required for their unique energy metabolism. The gene clusters encoding NDH-1 in both C. jejuni and H. pylori lacked nuoE and nuoF, and in their place were genes encoding two unknown proteins. The NuoG subunit in these microaerophilic bacteria appeared to have an additional Fe-S cluster that is not present in NDH-1 from other organisms; but C. jejuni and H. pylori differed from each other in a cysteine-rich segment in this subunit, which is present in some but not all NDH-1. Both organisms lacked genes orthologous to those encoding NDH-2. The subunits of the bc1 complex of both bacteria were similar, and the Rieske Fe-S and cytochrome b subunits had significant similarity to those of Paracoccus denitrificans and Rhodobacter capsulatus, well-studied bacterial bc1 complexes. The composition of the terminal oxidases of C. jejuni and H. pylori was different; both bacteria had cytochrome cbb3 oxidases, but C. jejuni also contained a bd-type quinol oxidase. The primary structures of the major subunits of the cbb3-type (terminal) oxidase of C. jejuni and H. pylori indicated that they form a separate group within the cbb3 protein family. The implications of the results for the function of the enzymes and their adaptation to microaerophilic growth are discussed.