Differences in ATP Generation Via Glycolysis and Oxidative Phosphorylation and Relationships with Sperm Motility in Mouse Species

Mouse sperm produce enough ATP to sustain motility by anaerobic glycolysis and respiration. However, previous studies indicated that an active glycolytic pathway is required to achieve normal sperm function and identified glycolysis as the main source of ATP to fuel the motility of mouse sperm. All the available evidence has been gathered from the studies performed using the laboratory mouse. However, comparative studies of closely related mouse species have revealed a wide range of variation in sperm motility and ATP production and that the laboratory mouse has comparatively low values in these traits. In this study, we compared the relative reliance on the usage of glycolysis or oxidative phosphorylation as ATP sources for sperm motility between mouse species that exhibit significantly different sperm performance parameters. We found that the sperm of species with higher oxygen consumption/lactate excretion rate ratios were able to produce higher amounts of ATP, achieving higher swimming velocities. Additionally, we show that the species with higher respiration/glycolysis ratios have a higher degree of dependence upon active oxidative phosphorylation. Moreover, we characterize for the first time two mouse species in which sperm depend on functional oxidative phosphorylation to achieve normal performance. Finally, we discuss that sexual selection could promote adaptations in sperm energetic metabolism tending to increase the usage of a more efficient pathway for the generation of ATP (and faster sperm).

Hyperglycemia Promotes Schwann Cell De-differentiation and De-myelination via Sorbitol Accumulation and Igf1 Protein Down-regulation

Diabetes mellitus (DM) is frequently accompanied by complications, such as peripheral nerve neuropathy. Schwann cells play a pivotal role in regulating peripheral nerve function and conduction velocity; however, changes in Schwann cell differentiation status in DM are not fully understood. Here, we report that Schwann cells de-differentiate into immature cells under hyperglycemic conditions as a result of sorbitol accumulation and decreased Igf1 expression in those cells. We found that de-differentiated Schwann cells could be re-differentiated in vitro into mature cells by treatment with an aldose reductase inhibitor, to reduce sorbitol levels, or with vitamin D3, to elevate Igf1 expression. In vivo DM models exhibited significantly reduced nerve function and conduction, Schwann cell de-differentiation, peripheral nerve de-myelination, and all conditions were significantly rescued by aldose reductase inhibitor or vitamin D3 administration. These findings reveal mechanisms underlying pathological changes in Schwann cells seen in DM and suggest ways to treat neurological conditions associated with this condition.

(18)F-FDG uptake on PET correlates with biological potential in early oral squamous cell carcinoma

CONCLUSION

The maximum standardized uptake value (SUVmax) of early oral squamous cell carcinoma (OSCC) may have a role as an imaging biomarker for assessment of malignant potential, including cell metabolism and angiogenesis.

OBJECTIVE

The usefulness of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) has been proven in various cancers, including OSCC. Moreover, in several carcinomas, the SUVmax of the tumor has been shown to correlate with the histological type, tumor stage, differentiation, and prognosis. Here, we investigated whether the SUVmax of early OSCC was associated with the biological features.

METHODS

Twenty-seven patients with newly diagnosed early OSCC who underwent preoperative FDG-PET and curative surgical resection were included in this study. Tumor sections were stained by immunohistochemistry for glucose transporter 1 (GLUT1), L-type amino acid transporter 1 (LAT1), CD98, microvessels (CD34), cell proliferation marker (Ki-67), and cell cycle regulator (p53). The correlation between SUVmax and clinicopathological findings or the expression level of these molecules was analyzed.

RESULTS

SUVmax of primary OSCC was significantly higher in patients with T2 stage. Moreover, patients whose tumors showed vascular invasion had a tendency to show higher SUVmax. A significant correlation was observed between SUVmax and the expression of LAT1 or microvessel density.

How does mild hypothermia affect monoclonal antibody glycosylation?

The application of mild hypothermic conditions to cell culture is a routine industrial practice used to improve recombinant protein production. However, a thorough understanding of the regulation of dynamic cellular processes at lower temperatures is necessary to enhance bioprocess design and optimization. In this study, we investigated the impact of mild hypothermia on protein glycosylation. Chinese hamster ovary (CHO) cells expressing a monoclonal antibody (mAb) were cultured at 36.5°C and with a temperature shift to 32°C during late exponential/early stationary phase. Experimental results showed higher cell viability with decreased metabolic rates. The specific antibody productivity increased by 25% at 32°C and was accompanied by a reduction in intracellular nucleotide sugar donor (NSD) concentrations and a decreased proportion of the more processed glycan structures on the mAb constant region. To better understand CHO cell metabolism at 32°C, flux balance analysis (FBA) was carried out and constrained with exometabolite data from stationary phase of cultures with or without a temperature shift. Estimated fluxomes suggested reduced fluxes of carbon species towards nucleotide and NSD synthesis and more energy was used for product formation. Expression of the glycosyltransferases that are responsible for N-linked glycan branching and elongation were significantly lower at 32°C. As a result of mild hypothermia, mAb glycosylation was shown to be affected by both NSD availability and glycosyltransferase expression. The combined experimental/FBA approach generated insight as to how product glycosylation can be impacted by changes in culture temperature. Better feeding strategies can be developed based on the understanding of the metabolic flux distribution.

Direct measurement of local dissolved oxygen concentration spatial profiles in a cell culture environment

Controlling local dissolved oxygen concentration (DO) in media is critical for cell or tissue cultures. Various biomaterials and culture methods have been developed to modulate DO. Direct measurement of local DO in cultures has not been validated as a method to test DO modulation. In the present study we developed a DO measurement system equipped with a Clark-type oxygen microelectrode manipulated with 1 μm precision in three-dimensional space to explore potential applications for tissue engineering. By determining the microelectrode tip position precisely against the bottom plane of culture dishes with rat or human cardiac cells in static monolayer culture, we successfully obtained spatial distributions of DO in the medium. Theoretical quantitative predictions fit the obtained data well. Based on analyses of the variance between samples, we found the data reflected "local" oxygen consumption in the vicinity of the microelectrode and the detection of temporal changes in oxygen consumption rates of cultured cells was limited by the diffusion rate of oxygen in the medium. This oxygen measuring system monitors local oxygen consumption and production with high spatial resolution, and can potentially be used with recently developed oxygen modulating biomaterials to design microenvironments and non-invasively monitor local DO dynamics during culture.

Reduced Ssy1-Ptr3-Ssy5 (SPS) signaling extends replicative life span by enhancing NAD+ homeostasis in Saccharomyces cerevisiae

Attenuated nutrient signaling extends the life span in yeast and higher eukaryotes; however, the mechanisms are not completely understood. Here we identify the Ssy1-Ptr3-Ssy5 (SPS) amino acid sensing pathway as a novel longevity factor. A null mutation of SSY5 (ssy5Δ) increases replicative life span (RLS) by ∼50%. Our results demonstrate that several NAD(+) homeostasis factors play key roles in this life span extension. First, expression of the putative malate-pyruvate NADH shuttle increases in ssy5Δ cells, and deleting components of this shuttle, MAE1 and OAC1, largely abolishes RLS extension. Next, we show that Stp1, a transcription factor of the SPS pathway, directly binds to the promoter of MAE1 and OAC1 to regulate their expression. Additionally, deletion of SSY5 increases nicotinamide riboside (NR) levels and phosphate-responsive (PHO) signaling activity, suggesting that ssy5Δ increases NR salvaging. This increase contributes to NAD(+) homeostasis, partially ameliorating the NAD(+) deficiency and rescuing the short life span of the npt1Δ mutant. Moreover, we observed that vacuolar phosphatase, Pho8, is partially required for ssy5Δ-mediated NR increase and RLS extension. Together, our studies present evidence that supports SPS signaling is a novel NAD(+) homeostasis factor and ssy5Δ-mediated life span extension is likely due to concomitantly increased mitochondrial and vacuolar function. Our findings may contribute to understanding the molecular basis of NAD(+) metabolism, cellular life span, and diseases associated with NAD(+) deficiency and aging.

The pivotal role of the mitochondrial amidoxime reducing component 2 in protecting human cells against apoptotic effects of the base analog N6-hydroxylaminopurine

N-Hydroxylated nucleobases and nucleosides as N-hydroxylaminopurine (HAP) or N-hydroxyadenosine (HAPR) may be generated endogenously in the course of cell metabolism by cytochrome P450, by oxidative stress or by a deviating nucleotide biosynthesis. These compounds have shown to be toxic and mutagenic for procaryotic and eucaryotic cells. For DNA replication fidelity it is therefore of great importance that organisms exhibit effective mechanisms to remove such non-canonical base analogs from DNA precursor pools. In vitro, the molybdoenzymes mitochondrial amidoxime reducing component 1 and 2 (mARC1 and mARC2) have shown to be capable of reducing N-hydroxylated base analogs and nucleoside analogs to the corresponding canonical nucleobases and nucleosides upon reconstitution with the electron transport proteins cytochrome b5 and NADH-cytochrome b5 reductase. By RNAi-mediated down-regulation of mARC in human cell lines the mARC-dependent N-reductive detoxication of HAP in cell metabolism could be demonstrated. For HAPR, on the other hand, the reduction to adenosine seems to be of less significance in the detoxication pathway of human cells as HAPR is primarily metabolized to inosine by direct dehydroxylamination catalyzed by adenosine deaminase. Furthermore, the effect of mARC knockdown on sensitivity of human cells to HAP was examined by flow cytometric quantification of apoptotic cell death and detection of poly (ADP-ribose) polymerase (PARP) cleavage. mARC2 was shown to protect HeLa cells against the apoptotic effects of the base analog, whereas the involvement of mARC1 in reductive detoxication of HAP does not seem to be pivotal.

Investigational cancer drugs targeting cell metabolism in clinical development

Introduction: Malignant cell transformation and tumor progression are associated with alterations in glycolysis, fatty acid synthesis, amino acid delivery and production of reactive oxygen species. With increased understanding of the role of metabolism in tumors, there has been interest in developing agents that target tumor specific metabolic pathways. Numerous promising agents targeting altered metabolic pathways are currently in Phase I - III clinical trials. Areas covered: This paper reviews the early phase clinical trial development of these agents and provides perspective on the future direction of this emerging field. Specifically, the authors describe novel and repurposed therapies, focusing on the effects of each agent on tumor metabolism and results from relevant Phase I and II clinical trials. Expert opinion: Metabolism modulating agents, alone and in combinations with other classes of agents, have shown efficacy in the treatment of neoplasm, which, the authors believe, will bear positive results in future studies. Because of the significant crosstalk between metabolic pathways and oncogenic signaling pathways, the authors also believe that combining metabolic modifiers with targeted agents will be an important strategy. An increased understanding of cancer metabolism, in addition to the continued study of metabolic modulators, should lead to further advances in this nascent therapeutic field in the future.

Silencing ECHS1 attenuates the proliferation and induces the autophagy of hepatocellular carcinoma via impairing cell metabolism and activating AMPK

Hepatocellular carcinoma (HCC) is among the most common cancers in the world with a low survival rate. Our previous study showed Short chain enoyl-CoA hydratase (ECHS1) could bind to HBsAg (HBs) and that ECHS1's localization in mitochondria induced HepG2 cell apoptosis. However, the role of the ECHS1 in energy metabolism and autophagy during hepatocellular carcinoma development remains undefined. We aimed to determine what ECHS1 does to energy metabolism and its effects on HCC progression. We performed CCK-8, EdU assays in hepatocellular carcinoma cell lines (HepG2 and HuH7) with stable ECHS1 knock-down. ATP and NADP+/NADPH levels were measured using an colorimetric assay. Our data demonstrated that ECHS1 silencing inhibited cell proliferation and induced autophagy. ECHS1 knockdown did not increase fatty acid synthesis, but decreased cellular ATP. This resulted in AMP-activated protein kinase (AMPK) activation and induced HCC cell autophagy. Our results showed that silencing ECHS1 to attenuate proliferation and induce autophagy may make it a novel cancer therapy target.

Imaging lipid metabolism in live Caenorhabditis elegans using fingerprint vibrations

Quantitation of lipid storage, unsaturation, and oxidation in live C. elegans has been a long-standing obstacle. The combination of hyperspectral stimulated Raman scattering imaging and multivariate analysis in the fingerprint vibration region represents a platform that allows the quantitative mapping of fat distribution, degree of fat unsaturation, lipid oxidation, and cholesterol storage in vivo in the whole worm. Our results reveal for the first time that lysosome-related organelles in intestinal cells are sites for storage of cholesterol in C. elegans.

BRCA1 and estrogen/estrogen receptor in breast cancer: where they interact?

BRCA1 mainly acts as a tumor suppressor and BRCA1 mutation correlates with increased cancer risk. Although it is well recognized that BRCA1 related tumorigenesis is mainly caused by the increased DNA damage and decreased genome stability, it is not clear that why BRCA1 related patients have higher risk for cancer development mainly in estrogen responsive tissues such as breast and ovary. Recent studies suggested that BRCA1 and E-ER (estrogen and estrogen receptor) signaling synergistically regulate the mammary epithelial cell proliferation and differentiation. In this current presentation, we reviewed the correlation between mammary gland epithelial cell transformation and the status of BRCA1 and ER. Then the mechanisms of BRCA1 and E-ER interaction at both gene transcription level and protein-protein interaction level are discussed. Furthermore, the tumorigenic mechanisms are discussed by focusing on the synergistic effect of BRCA1 and E-ER on cell metabolism, ROS management, and antioxidant activity in mammary gland epithelial cells. Also, the possibility of cell de-differentiation promoted by coordinated effect between BRCA1 mutation and E-ER signal is explored. Together, the currently available evidences suggest that BRCA1 mutation and E-ER signal together, contribute to breast tumorigenesis by providing the metabolic support for cancer cell growth and even may directly be involved in promoting the de-differentiation of cancer-prone epithelial cells.

Trafficking GRK2: Cellular and Metabolic consequences of GRK2 subcellular localization

G protein coupled receptor kinase 2 (GRK2) has a key role in cellular function by regulating different intracellular mechanisms in a kinase dependent or independent manner. In this review we have dealt with the recently discovered roles of GRK2 in the regulation of cell metabolism. In particular, we have focused on recent findings about the mitochondrial role of GRK2 in the regulation of energy metabolism. Few findings exist about this topic that all concur to identify a mitochondrial localization of GRK2, leading to the rising of the following question: is GRK2 detrimental or advantageous for mitochondrial function? By the review of available literature, a new concept arises about GRK2 role into the cell,which is that of a stress protein acutely activated by cellular stress whose specific subcellular localization, in particular mitochondrial localization, results in compensatory metabolic responses. Thus, the possibility to regulate GRK2 trafficking within the cell is a promising strategy to regulate the adaptative effects of the kinase on cell metabolism.

1H NMR detects different metabolic profiles in glioblastoma stem-like cells

The metabolic profiles of glioblastoma stem-like cells (GSCs) growing in neurospheres were examined by (1)H NMR spectroscopy. Spectra of two GSC lines, labelled 1 and 83, from tumours close to the subventricular zone of the temporal lobe were studied in detail and compared with those of neural stem/progenitor cells from the adult olfactory bulb (OB-NPCs) and of the T98G glioblastoma cell line. In both GSCs, signals from myoinositol (Myo-I), UDP-hexosamines (UDP-Hex) and glycine indicated an astrocyte/glioma metabolism. For line 1, the presence of signals from N-acetyl aspartate, GABA and creatine pointed to a neuronal fingerprint. These metabolites were almost absent from line 83 spectra, whereas lipid signals, absent from normal neural lineages, were intense in line 83 spectra and remained low in those of line 1, irrespective of apoptotic fate. Spectra of OB-NPC cells displayed strong similarities with those from line 1, with low lipid signals and clearly detectable neuronal signals. In contrast, the spectral profile of line 83 was more similar to that of T98G, displaying high lipids and nearly complete absence of the neuronal markers. A mixed neural-astrocyte metabolic phenotype with a strong neuronal fingerprint was therefore found in line 1, while an astrocytic/glioma-like metabolism prevailed in line 83. We found a signal assigned to the amide proton of N-acetyl galactosamine in GSC lines and in OB-NPC spectra, whereas it was absent from those of T98G cells. This signal may be related to a stem-cell-specific protein glycosylation pattern and is therefore suggested as a marker of cell multipotency. Other GSC lines from patients with different clinical outcomes were then examined. Unsupervised analysis of spectral data from 13 lines yielded two clusters, with six lines resembling spectral features of line 1 and seven resembling those of line 83, suggesting that distinct metabolic phenotypes may be present in GSC lines.

Histone acetyltransferase p300 promotes MKL1-mediated transactivation of catechol-O-methyltransferase gene

Previous studies have revealed that histone acetyltransferase p300 is recruited to the promoters of certain cardiac and smooth muscle specific genes to enhance the transactivation activity of myocardin, which is a master regulator in cardiovascular differentiation and development. Here, we found that the gene encoding catechol-O-methyltransferase (COMT), an important metabolic enzyme catalyzing the conversion of estrogen, is also a target gene of myocardin-related transcription factors (MRTFs). Megakaryoblastic leukemia 1 (MKL1, also named MRTF-A) and p300 could synergistically augment the expression of COMT gene, increase the metabolic rate of estrogen, and thus reduce the proliferation of MCF-7 breast cancer cells stimulated by estrogen.

Omega-3 polyunsaturated fatty acid promotes the inhibition of glycolytic enzymes and mTOR signaling by regulating the tumor suppressor LKB1

The omega-3 polyunsaturated fatty acids (ω3PUFAs) are a class of lipids biologically effective for the treatment of inflammatory disorders, cardiovascular disease and cancer. Patients consuming a high dietary intake of ω3PUFAs have shown a low incidence of metabolic disorders, including cancer. Although the effects of ω3PUFAs intake was shown to be involved in the prevention and treatment of these diseases, the underlying molecular mechanisms involved are not well understood. Here, we show that ω3PUFA, docosahexaenoic acid (DHA) enhanced the tumor suppressor function of LKB1. We observed that when LKB1 expressing cells are treated with DHA, there is an increase in LKB1 activity leading to phosphorylation of AMPK and inhibition of mTOR signaling. Abrogation of LKB1 in MCF-7 cells by siRNA reversed this phenotype. Furthermore, cellular metabolism was altered and ATP levels were reduced in response to DHA treatment, which was further attenuated in cells expressing LKB1. More importantly, in mammary epithelial cells expressing LKB1, the rate of glycolysis was decreased as a result of diminished expression of glycolytic enzymes. Functionally, these events lead to a decrease in the migration potential of these cells. Overall, our discovery shows for the first time that LKB1 function is enhanced in response to ω3PUFA treatment, thereby resulting in the regulation of cell metabolism.

From sirtuin biology to human diseases: an update

Originally rising to notoriety for their role in the regulation of aging, sirtuins are a family of NAD(+)-dependent enzymes that have been connected to a steadily growing set of biological processes. In addition to regulating aging, sirtuins play key roles in the maintenance of organismal metabolic homeostasis. These enzymes also have primarily protective functions in the development of many age-related diseases, including cancer, neurodegeneration, and cardiovascular disease. In this minireview, we provide an update on the known roles for each of the seven mammalian sirtuins in these areas.

Redox regulation of mitochondrial biogenesis

The cell renews, adapts, or expands its mitochondrial population during episodes of cell damage or periods of intensified energy demand by the induction of mitochondrial biogenesis. This bigenomic program is modulated by redox-sensitive signals that respond to physiological nitric oxide (NO), carbon monoxide (CO), and mitochondrial reactive oxygen species production. This review summarizes our current ideas about the pathways involved in the activation of mitochondrial biogenesis by the physiological gases leading to changes in the redox milieu of the cell, with an emphasis on the responses to oxidative stress and inflammation. The cell's energy supply is protected from conditions that damage mitochondria by an inducible transcriptional program of mitochondrial biogenesis that operates in large part through redox signals involving the nitric oxide synthase and the heme oxygenase-1/CO systems. These redox events stimulate the coordinated activities of several multifunctional transcription factors and coactivators also involved in the elimination of defective mitochondria and the expression of counterinflammatory and antioxidant genes, such as IL10 and SOD2, as part of a unified damage-control network. The redox-regulated mechanisms of mitochondrial biogenesis schematically outlined in the graphical abstract link mitochondrial quality control to an enhanced capacity to support the cell's metabolic needs while improving its resistance to metabolic failure and avoidance of cell death during periods of oxidative stress.

Collagen with simvastatin promotes cell metabolism in osteoblast-like SaOS-2 cells

Background:

Simvastatin (SMV) is one of the cholesterol-lowering pharmacological drugs. Recent studies demonstrate that it has a bone stimulatory effect. The present study was designed to investigate the effect of SMV along with collagen membrane on osteoblast-like SaOS-2 cells and also to standardize the dosage of SMV to be incorporated into the collagen membrane to achieve regeneration.

Materials and Methods:

SMV at doses of 0.5, 1, 1.5, and 2 mg was incorporated into the collagen membrane and cell metabolism was assessed by (3-[4,5-dimethylthiazolyl-2]-2,5-diphenyltetrazolium bromide) (MTT) assay for 24 h.

Results:

SMV enhanced cell metabolism dose dependently at 24-h time and the maximum effect was obtained at a concentration of 1.5 mg of SMV.

Conclusion:

These results indicate that collagen with 1.5 mg SMV exhibits positive effect on cell metabolism of human osteoblast-like SaOS-2 cells.

Elevated CO(2) levels cause mitochondrial dysfunction and impair cell proliferation

Elevated CO(2) concentrations (hypercapnia) occur in patients with severe lung diseases. Here, we provide evidence that high CO(2) levels decrease O(2) consumption and ATP production and impair cell proliferation independently of acidosis and hypoxia in fibroblasts (N12) and alveolar epithelial cells (A549). Cells exposed to elevated CO(2) died in galactose medium as well as when glucose-6-phosphate isomerase was knocked down, suggesting mitochondrial dysfunction. High CO(2) levels led to increased levels of microRNA-183 (miR-183), which in turn decreased expression of IDH2 (isocitrate dehydrogenase 2). The high CO(2)-induced decrease in cell proliferation was rescued by α-ketoglutarate and overexpression of IDH2, whereas proliferation decreased in normocapnic cells transfected with siRNA for IDH2. Also, overexpression of miR-183 decreased IDH2 (mRNA and protein) as well as cell proliferation under normocapnic conditions, whereas inhibition of miR-183 rescued the normal proliferation phenotype in cells exposed to elevated levels of CO(2). Accordingly, we provide evidence that high CO(2) induces miR-183, which down-regulates IDH2, thus impairing mitochondrial function and cell proliferation. These results are of relevance to patients with hypercapnia such as those with chronic obstructive pulmonary disease, asthma, cystic fibrosis, bronchopulmonary dysplasia, and muscular dystrophies.

A systemic review of PET and biology in lung cancer

Positron emission tomography imaging with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose ((18)F-FDG) has been established as a significant molecular imaging technique in the management of lung cancer. However, (18)F-FDG accumulation is not specific, therefore several other radiotracers targeting hypoxia, cell proliferation and amino acid metabolism have been developed for the imaging of human cancers. This review summarizes the current data on the correlation between the underlying molecular biology and tumor PET accumulation in lung cancer.

ESR Microscopy for Biological and Biomedical Applications

We report on electron-spin resonance microscopy (ESRM) providing sub-micron resolution (~700nm) with a high spin concentration sample, i.e. lithium phthalocyanine (LiPc) crystal. For biomedical applications of our ESRM, we have imaged samples containing rat basophilic leukemia (RBL) cells as well as cancerous tissue samples with a resolution of several microns using a water soluble spin probe, Trityl_OX063_d24. Phantom samples with the nitroxide spin label, (15)N PDT, were also imaged to demonstrate that nitroxides, which are commonly used as spin labels, may also be used for ESRM applications. ESRM tissue imaging would therefore be valuable for diagnostic or therapeutic purposes. Also, ESRM can be used to study the motility or the metabolism of cells in various environments. With further modification and/or improvement of imaging probe and spectrometer instrumentation sub-micron biological images should be obtainable, thereby providing a useful tool for various biomedical applications.

UCP3 translocates lipid hydroperoxide and mediates lipid hydroperoxide-dependent mitochondrial uncoupling

Although the literature contains many studies on the function of UCP3, its role is still being debated. It has been hypothesized that UCP3 may mediate lipid hydroperoxide (LOOH) translocation across the mitochondrial inner membrane (MIM), thus protecting the mitochondrial matrix from this very aggressive molecule. However, no experiments on mitochondria have provided evidence in support of this hypothesis. Here, using mitochondria isolated from UCP3-null mice and their wild-type littermates, we demonstrate the following. (i) In the absence of free fatty acids, proton conductance did not differ between wild-type and UCP3-null mitochondria. Addition of arachidonic acid (AA) to such mitochondria induced an increase in proton conductance, with wild-type mitochondria showing greater enhancement. In wild-type mitochondria, the uncoupling effect of AA was significantly reduced both when the release of O2* in the matrix was inhibited and when the formation of LOOH was inhibited. In UCP3-null mitochondria, however, the uncoupling effect of AA was independent of the above mechanisms. (ii) In the presence of AA, wild-type mitochondria released significantly more LOOH compared with UCP3-null mitochondria. This difference was abolished both when UCP3 was inhibited by GDP and under a condition in which there was reduced LOOH formation on the matrix side of the MIM. These data demonstrate that UCP3 is involved both in mediating the translocation of LOOH across the MIM and in LOOH-dependent mitochondrial uncoupling.

The role of polyamines in supporting growth of mammalian cells is mediated through their requirement for translation initiation and elongation

Polyamines are essential cell constituents whose depletion results in growth cessation. Here we have investigated potential mechanisms of action of polyamines in supporting mammalian cell proliferation. We demonstrate that polyamines regulate translation both at the initiation and at the elongation steps. L-alpha-difluoromethylornithine treatment resulting in polyamine depletion reduces protein synthesis via inhibition of translation initiation. N1-guanyl-diaminoheptane (GC7), a spermidine analogue that inhibits eukaryotic initiation factor 5A (eIF5A) hypusination, also caused inhibition of translation initiation. In contrast, depletion of eIF5A by short hairpin RNA inhibits translation elongation as was recently demonstrated in yeast and Drosophila. These results suggest that in addition to competing with spermidine in the hypusination reaction, GC7 also competes with spermidine at yet undefined sites required for translation initiation. Finally, we show that either polyamine depletion or GC7 treatment induced eIF2alpha phosphorylation and reduced phosphorylation of 4E-BP, thus setting the molecular basis for the observed inhibition of translation initiation.

Alteration of mammalian cell metabolism by dynamic nutrient feeding

The metabolism of hybridoma cells was controlled to reduce metabolic formation in fed-batch cultures by dynamically feeding a salt-free nutrient concentrate. For this purpose, on-line oxygen uptake rate (OUR) measurement was used to estimate the metabolic demand of hybridoma cells and to determine the feeding rate of a concentrated solution of salt-free DMEM/F12 medium supplemented with other medium components. The ratios among glucose, glutamine and other medium components in the feeding nutrient concentrate were adjusted stoichiometrically to provide balanced nutrient conditions for cell growth. Through on-line control of the feeding rate of the nutrient concentrate, both glucose and glutamine concentrations were maintained at low levels of 0.5 and 0.2 mM respectively during the growth stage. The concentrations of the other essential amino acids were also maintained without large fluctuations. The cell metabolism was altered from that observed in batch cultures resulting in a significant reduction of lactate, ammonia and alanine production. Compared to a previously reported fed-batch culture in which only glucose was maintained at a low level and only a reduced lactate production was observed, this culture has also reduced the production of other metabolites, such as ammonium and alanine. As a result, a high viable cell concentration of more than 1.0 × 10(7) cells/mL was achieved and sustained over an extended period. The results demonstrate an efficient nutrient feeding strategy for controlling cell metabolism to achieve and sustain a high viable cell concentration in fed-batch mammalian cell cultures in order to enhance the productivity.