Regulation of energy metabolism in human cells in aging and diabetes: FoF(1), mtDNA, UCP, and ROS

Gene disruption of ribosomal protein L5 (RPL5) decreased the sensitivity of CHO-K1 cells to uncoupler carbonylcyanide-3-chlorophenylhydrazone

Protonophoric uncoupler carbonylcyanide-3-chlorophenylhydrazone (CCCP) decreases the proton motive force (ΔP) of the mitochondrial inner membrane and results in inhibition of oxidative phosphorylation. In this study, a CCCP-resistant clone was isolated from a random gene trap insertional mutant library of Chinese hamster ovary (CHO)-K1 cells which was constructed by infecting a retrovirus vector, ROSAβgeo. Although we expected the isolation of the mutants defective in nuclear genes responsible for mitochondrial functions, the disrupted gene of the isolated mutant that we named R1 cells was identified as one of the alleles for ribosomal protein 5 of large subunit (RPL5). The R1 cells express as much as 80% RPL5 protein compared with the parental CHO-K1 cells, possibly due to enhanced transcription from a remaining wild-type RPL5 allele in R1 cells. Furthermore, the protein amount is not decreased by CCCP in R1 cells, in contrast to its clear reduction by CCCP in parental cells. Since mutations of RPL5 and other ribosomal proteins are responsible for the ribosomopathies and cancer, the present mutant may be a useful cellular model of such human diseases from a viewpoint of energy metabolism as well as a tool for the study of ribosome biogenesis and extra-ribosomal function of the RPL5 protein.

Dissecting the Origin of Breast Cancer Subtype Stem Cell and the Potential Mechanism of Malignant Transformation

Background

Breast cancer is the most common incident form of cancer in women including different subtypes. Cancer stem cells (CSCs) have been confirmed to exist in breast cancer. But the research on the origin of breast cancer subtype stem cells (BCSSCs) is still inadequate.

Methods

We identified the putative origin cells of BCSSCs through comparing gene signatures between BCSSCs and normal mammary cells from multiple perspectives: common signature, expression consistency, functional similarity and shortest path length. First, the potential origin cells were ranked according to these measures separately. Then Q statistic was employed to combine all rank lists into a unique list for each subtype, to prioritize the origin cells for each BCSSC. Next, we identified origin-related gene modules through integrating functional interaction network with differentially expressed genes. Finally, transcription factors of significant gene modules were predicted by Match^TM.

Results

The results showed that Luminal A CSC was most relevant to luminal progenitor cell or mature luminal cell; luminal B and HER2 CSC were most relevant to bipotent-enriched progenitor cell; basal-like CSC was most relevant to bipotent-enriched progenitor cell or mature luminal cell. Network modules analysis revealed genes related to mitochondrial respiratory chain (MRC) were significantly dysregulated during the origin of luminal B CSC. In addition, SOX10 emerged as a key regulator of MRC.

Conclusions

Our study supports substantive evidence for the possible origin of four kinds of BCSSCs. Dysfunction of MRC may contribute to the origin of luminal B CSC. These findings may have important implications to treat and prevent breast cancer.

Nitric oxide in the normal kidney and in patients with diabetic nephropathy

Nitric oxide (NO) is a gas with biological and regulatory properties, produced from arginine by the way of nitric oxide synthases (NOS), and with a very short half-life (few seconds). A "coupled" NOS activity leads to NO generation, whereas its uncoupling produces the reactive oxygen species peroxynitrite (ONOO(-)). Uncoupling is usually due to inflammation, oxidative stress, decreased cofactor availability, or excessive NO production. Competitive inhibitors of NO production are post-translationally methylated arginine residues in proteins, which are constantly released into the circulation. NO availability is altered in many clinical conditions associated with vascular dysfunction, such as diabetes mellitus. The kidney plays an important role in body NO homeostasis. This article provides an overview of current literature, on NO production/availability, with a focus on diabetic nephropathy. In diabetes, NO availability is usually decreased (with exception of the early, hyper filtration phase of nephropathy in Type 1 diabetes), and it could constitute a factor of the generalized vasculopathy present in diabetic nephropathy. NO generation in Type 2 diabetes with nephropathy is inversely associated with the dimethyl-arginine concentrations, which are therefore important modulators of NO synthesis independently from the classic stimulatory pathways (such as the insulin effect). A disturbed NO metabolism is present in diabetes associated with nephropathy. Although modulation of NO production is not yet a common therapeutical strategy, a number of yet experimental compounds need to be tested as potential interventions to treat the vascular dysfunction and nephropathy in diabetes, as well as in other diseased states. Finally, in diabetic nephropathy NO deficiency may be associated to that of hydrogen sulfide, another interesting gaseous mediator which is increasingly investigated.

ATP synthase: from single molecule to human bioenergetics

ATP synthase (F(o)F(1)) consists of an ATP-driven motor (F(1)) and a H(+)-driven motor (F(o)), which rotate in opposite directions. F(o)F(1) reconstituted into a lipid membrane is capable of ATP synthesis driven by H(+) flux. As the basic structures of F(1) (alpha(3)beta(3)gammadeltaepsilon) and F(o) (ab(2)c(10)) are ubiquitous, stable thermophilic F(o)F(1) (TF(o)F(1)) has been used to elucidate molecular mechanisms, while human F(1)F(o) (HF(1)F(o)) has been used to study biomedical significance. Among F(1)s, only thermophilic F(1) (TF(1)) can be analyzed simultaneously by reconstitution, crystallography, mutagenesis and nanotechnology for torque-driven ATP synthesis using elastic coupling mechanisms. In contrast to the single operon of TF(o)F(1), HF(o)F(1) is encoded by both nuclear DNA with introns and mitochondrial DNA. The regulatory mechanism, tissue specificity and physiopathology of HF(o)F(1) were elucidated by proteomics, RNA interference, cytoplasts and transgenic mice. The ATP synthesized daily by HF(o)F(1) is in the order of tens of kilograms, and is primarily controlled by the brain in response to fluctuations in activity.

Peroxisome proliferator-activated receptor-gamma coactivator 1-alpha overexpression prevents endothelial apoptosis by increasing ATP/ADP translocase activity

OBJECTIVE

Fatty acids increase reactive oxygen species generation and cell apoptosis in endothelial cells. The peroxisome proliferator-activated receptor-gamma coactivator 1-alpha (PGC-1alpha) is a transcriptional coactivator that increases mitochondrial biogenesis and fatty acid oxidation in various cells. This study was undertaken to investigate the possible preventive effect of PGC-1alpha on endothelial apoptosis and its molecular mechanism.

METHODS AND RESULTS

Treatment with linoleic acid in cultured human aortic endothelial cells increased reactive oxygen species generation and cell apoptosis. These effects appeared to be mediated by increases in cytosolic fat metabolites, ie, fatty acyl CoA, diacylglycerol, and ceramide, and consequent decreases in ATP/ADP translocase activity of adenine nucleotide translocator. Adenoviral overexpression of PGC-1alpha prevented linoleic acid-induced increases in reactive oxygen species generation and cell apoptosis in human aortic endothelial cells by increasing fatty acid oxidation, decreasing diacylglycerol and ceramide, and increasing ATP/ADP translocase activity. In isolated aorta, PGC-1alpha overexpression prevented linoleic acid-induced decrease in endothelium-dependent vasorelaxation, and this effect was abolished by adenine nucleotide translocator1 shRNA.

CONCLUSIONS

PGC-1alpha regulates reactive oxygen species generation and apoptosis in endothelial cells by increasing fatty acid oxidation and enhancing ATP/ADP translocase activity. Measures to increase PGC-1alpha expression or ATP/ADP translocase activity in vascular cells may aid in the prevention or treatment of atherosclerosis.

Association of the Ser326Cys polymorphism in the OGG1 gene with type 2 DM

The association of the Ser326Cys polymorphism of the 8-oxoguanine glycosylase 1 (OGG1) gene with type 2 diabetes was examined using a Japanese population (n (M/W): 4585 (2085/2500); age: 62.6 +/- 10.9 years). HbA1c levels and frequency of diabetic subjects were significantly higher in subjects with genotypes with Cys allele than in those without (p = 0.032 and 0.037, respectively). Multiple logistic regression analysis showed that genotypes with Cys allele were significantly associated with diabetes (OR: 1.32, p = 0.0289). In subjects whose glucose tolerance was classified by FPG and 2-h PG (n = 1.634), the association was more substantial (genotypes with Cys allele vs. without, OR: 1.70, p = 0.0059; genotypes Cys/Cys vs. Ser/Ser, OR: 2.19, p = 0.0008). In subjects with genotype Ser/Ser, the insulin secretion index, HOMA-beta, increased in the subjects with glucose intolerance and decreased in the subjects with diabetes, while, in subjects with genotypes Ser/Cys + Cys/Cys, HOMA-beta decreased as the glucose tolerance progressed (p for trend = 0.010).

The alpha/beta interfaces of alpha(1)beta(1), alpha(3)beta(3), and F1: domain motions and elastic energy stored during gamma rotation

ATP synthase (F(o)F(1)) consists of F(1) (ATP-driven motor) and F(o) (H(+)-driven motor). F(1) is a complex of alpha(3)beta(3)gammadeltaepsilon subunits, and gamma is the rotating cam in alpha(3)beta(3). Thermophilic F(1) (TF(1)) is exceptional in that it can be crystallized as a beta monomer and an alpha(3)beta(3) oligomer, and it is sufficiently stable to allow alphabeta refolding and reassembly of hybrid complexes containing 1, 2, and 3 modified alpha or beta. The nucleotide-dependent open-close conversion of conformation is an inherent property of an isolated beta and energy and signals are transferred through alpha/beta interfaces. The catalytic and noncatalytic interfaces of both mitochondrial F(1) (MF(1)) and TF(1) were analyzed by an atom search within the limits of 0.40 nm across the alphabeta interfaces. Seven (plus thermophilic loop in TF(1)) contact areas are located at both the catalytic and noncatalytic interfaces on the open beta form. The number of contact areas on closed beta increased to 11 and 9, respectively, in the catalytic and noncatalytic interfaces. The interfaces in the barrel domain are immobile. The torsional elastic strain applied through the mobile areas is concentrated in hinge residues and the P-loop in beta. The notion of elastic energy in F(o)F(1) has been revised. X-ray crystallography of F(1) is a static snap shot of one state and the elastic hypotheses are still inconsistent with the structure, dyamics, and kinetics of F(o)F(1). The domain motion and elastic energy in F(o)F(1) will be elucidated by time-resolved crystallography.

Mitochondrial function and substrate availability

Carbohydrates and lipid oxidations support energy metabolism by distinct pathways exhibiting similarities and differences. Alterations of energy metabolism during sepsis are well recognized; however, failure of oxygen or substrate supply is not a prominent cause. The occurrence of a "mitochondrial cytopathy" induced by sepsis explains some of these abnormalities, which may represent a "metabolic hibernation," a potential strategy of defense during the very acute phase of the illness. Our view of the involvement of mitochondrial metabolism in cell signaling has evolved considerably. Because of the structure of the respiratory chain, the way electrons are provided (upstream or downstream of complex 1 [i.e., nicotinamide adenine dinucleotide {reduced form} or flavin adenine dinucleotide {reduced form}]) plays an important role in the regulation of several functions, including the yield of adenosine triphosphate synthesis and the production of reactive oxygen species. Moreover, the modern view of energy channeling and compartmentation in the cell may open attractive hypotheses regarding the changes in cellular energy distribution in pathologic states, such as sepsis.

Up-regulation of plasma membrane-associated redox activities in neuronal cells lacking functional mitochondria

Mitochondria-deficient cells (rho(o) cells) survive through enhanced glycolytic metabolism in the presence of pyruvate and uridine. The plasma membrane redox system (PMRS) contains several NAD(P)H-related enzymes and plays a key role in maintaining the levels of NAD(+)/NADH and reduced coenzyme Q. In this study, rho(o) cells were used to investigate how the PMRS is regulated under conditions of mitochondrial dysfunction. rho(o) cells exhibited a lower oxygen consumption rate and higher levels of lactate than parental cells, and were more sensitive to glycolysis inhibitors (2-deoxyglucose and iodoacetamide) than control cells. However, they were more resistant to H(2)O(2), consistent with increased catalase activity and decreased oxidative damage (protein carbonyls and nitrotyrosine). PM-associated redox enzyme activities were enhanced in rho(o) cells compared to those in control cells. Our data suggest that all PMRS enzymes and biomarkers tested are closely related to the ability of the PMs to maintain redox homeostasis. These results illustrate that an up-regulated PM redox activity can protect cells from oxidative stress as a result of an improved antioxidant capacity, and suggest a mechanism by which neurons adapt to conditions of impaired mitochondrial function.

The ROS production induced by a reverse-electron flux at respiratory-chain complex 1 is hampered by metformin

Mitochondrial reactive oxygen species (ROS) production was investigated in mitochondria extracted from liver of rats treated with or without metformin, a mild inhibitor of respiratory chain complex 1 used in type 2 diabetes. A high rate of ROS production, fully suppressed by rotenone, was evidenced in non-phosphorylating mitochondria in the presence of succinate as a single complex 2 substrate. This ROS production was substantially lowered by metformin pretreatment and by any decrease in membrane potential (Delta Phi(m)), redox potential (NADH/NAD), or phosphate potential, as induced by malonate, 2,4-dinitrophenol, or ATP synthesis, respectively. ROS production in the presence of glutamate-malate plus succinate was lower than in the presence of succinate alone, but higher than in the presence of glutamate-malate. Moreover, while rotenone both increased and decreased ROS production at complex 1 depending on forward (glutamate-malate) or reverse (succinate) electron flux, no ROS overproduction was evidenced in the forward direction with metformin. Therefore, we propose that reverse electron flux through complex 1 is an alternative pathway, which leads to a specific metformin-sensitive ROS production.

Respiration under control of uncoupling proteins: Clinical perspective

The term 'uncoupling protein' was originally used for the mitochondrial membrane protein UCP1, which is uniquely present in mitochondria of brown adipocytes, thermogenic cells that regulate body temperature in small rodents, hibernators and mammalian newborns. In these cells, UCP1 acts as a proton carrier activated by free fatty acids and creates a shunt between complexes of the respiratory chain and ATP-synthase resulting in a futile proton cycling and dissipation of oxidation energy as heat. Recent identification of new homologues to UCP1 expressed in brown and white adipose tissue, muscle, brain and other tissues together with the hypothesis that these novel uncoupling proteins (UCPs) may regulate thermogenesis and/or fatty acid metabolism and furthermore may protect against free radical oxygen species production have generated considerable optimism for rapid advances in the identification of new targets for pharmacological management of complex pathological syndromes such as obesity, type 2 diabetes or chronic inflammatory diseases. However, since the physiological and biochemical roles of the novel UCPs are not yet clear, the main challenge today consists first of all in providing mechanistic explanation for their functions in cellular physiology. This lively awaited information may be the basis for potential pharmacological targeting of the UCPs in future.

Caenorhabditis elegans as a screening tool for the endothelial cell-derived putative aging-related proteins detected by proteomic analysis

Endothelial cells go through progressive pathophysiologic modification as cellular senescence progresses. In vitro, endothelial cell senescence is accompanied by failure of proliferation and by perturbations in gene and protein expressions. Moreover, this cellular senescence in culture has been proposed to reflect processes that occur in the organism in vivo and free radical theory is accepted to be the most plausible explanation for this process. We have screened proteins involved in both cellular senescence and reactive oxygen species induced condition using 2-D gel analysis and found that ubiquitin carboxyl terminal hydrolase L1, peroxyredoxin 2, peroxyredoxin 4, fatty acid binding proteins (FABPs), and 5'-AMP-activated protein kinase beta-1 subunit were candidate aging-related proteins. To evaluate in vivo function of these proteins, Caenorhabditis elegans (C. elegans) knock-down system using RNA interference was applied. Aging-specific expression of lipofucsin and the lifespan of knocked-down C. elegans were observed to assess the outcome. Interestingly, the inhibition of the genes led to short lifespan and earlier accumulation of lipofucsin with increasing age when compared with the wild type. These results suggest that the above genes may be related to cellular senescence process in determining the longevity in C. elegans and that gene inactivation renders animals susceptible to oxidative stress.

Proteomic analysis of the proteins expressed by hydrogen peroxide treated cultured human dermal microvascular endothelial cells

Reactive oxygen species (ROS) have been traditionally regarded as toxic by-products of aerobic metabolism. However, ROS also act as intracellular signaling molecules and can mediate phenotypes in vascular endothelial cells, which may be physiological or pathological in nature. To clarify the molecular mechanisms of ROS signaling, we examined hydrogen peroxide (H(2)O(2))-responsive proteins in cultured human dermal microvascular endothelial cells (HMVEC) using proteomic tools. Protein expression in HMVEC was studied after they had been exposed to low- and high-levels of H(2)O(2) for various times, and intracellular ROS production was examined by flow cytometer and UV spectrophotometer. Proteins obtained from dose- and time-dependent series were separated by two-dimensional gel electrophoresis and tentatively identified by matrix-assisted laser desorption-time of flight mass spectrometry, by matching the tryptic mass maps obtained with entries in the NCBI and Swiss-Prot protein sequence database. At least 163 proteins were changed by H(2)O(2), and 60 proteins were identified. Oxidative stress triggered dramatic change in the expression of proteins in primary microvessel endothelial cells, and their mapping to cellular process provided a view of the ubiquitous cellular changes elicited by H(2)O(2). These results could provide a framework for the understanding of the mechanisms of cellular redox homeostasis and H(2)O(2) metabolism in microendothelium environment in various biological processes as well as pathological conditions.

Control and Regulatory Mechanisms Associated with Thermogenesis in Flying Insects and Birds

Most insects and birds are able to fly. The chitin made exoskeleton of insects poses them several constraints, and this is one the reasons they are in general small sized animals. On the other hand, because birds possess an endoskeleton made of bones they may grow much larger when compared to insects. The two taxa are quite different with regards to their general “design” platform, in particular with respect to their respiratory and circulatory systems. However, because they fly, they may share in common several traits, namely those associated with the control and regulatory mechanisms governing thermogenesis. High core temperatures are essential for animal flight irrespective of the taxa they belong to. Birds and insects have thus evolved mechanisms which allowed them to control and regulate high rates of heat fluxes. This article discusses possible convergent thermogenic control and regulatory mechanisms associated with flight in insects and birds.

HIV Protease Inhibitors Prevent Mitochondrial Hyperpolarization and Redox Imbalance and Decrease Endogenous Uncoupler Protein-2 Expression in Gp120-Activated Human T Lymphocytes

It has been demonstrated that HIV protease inhibitors (PIs) are able to inhibit apoptosis of both infected and uninfected T cells. It was hypothesized that the mechanisms underlying this effect are associated with a specific activity of these drugs against mitochondrial modifications occurring in the execution phase of apoptosis. In this work, we investigated the activity of PIs towards the early changes occurring in mitochondrial membrane potential in freshly isolated uninfected human T lymphocytes sensitized to CD95/Fas-induced physiological apoptosis via pre-exposure to HIV envelope protein gp120. The results obtained clearly indicate that PIs are capable of hindering early morphogenetic changes bolstering T cell apoptosis, that is, cell polarization and mitochondrial hyperpolarization. The target effect on mitochondria appeared to be characterized by a specific activity of PIs in the maintenance of their homeostasis either in intact cells or in cell-free systems, that is, isolated mitochondria. PIs seem to act as boosters of mitochondrial defense mechanisms, including modulation of endogenous uncouplers. These results add new insights in the field of PI mitochondrial toxicity mechanisms and pharmacological perspectives for the use of these drugs in the control of immune system homeostasis.

Increased reactive oxygen species production with antisense oligonucleotides directed against uncoupling protein 2 in murine endothelial cells

Uncoupling protein 2 (UCP-2) belongs to the mitochondrial anion carrier family. It is ubiquitously expressed but is most abdundant in the reticuloendothelial system. In addition to uncoupling function, UCP-2 modulates the production of reactive oxygen species (ROS) by isolated mitochondria. Using an antisense oligonucleotide strategy, we investigated whether a defect in UCP-2 expression modulates ROS in intact endothelial cells. Murine endothelial cells (CRL 2181) pretreated by antisense oligonucleotides directed against UCP-2 mRNA exhibited a significant and specific increase in membrane potential and intracellular ROS level compared with control scrambled or anti-UCP-1 and -UCP-3 antisense oligonucleotides. These specific changes induced by UCP-2 antisense oligonucleotides were correlated with a rise in extracellular superoxide anion production and oxidative stress assessed by thiobarbituric acid reactive substance values. Taken together, these data suggest a role for UCP-2 in control of ROS production and subsequent oxidation of surrounding compounds mediating oxidative stress of endothelial cells. These data also support the notion that manipulations of UCP-2 at the genetic level could control ROS metabolism at the cellular level.

Disorders of mitochondrial protein synthesis

Mitochondrial tRNA gene mutations, including heteroplasmic deletions that eliminate one or more tRNAs, as well as point mutations that may be either hetero- or homoplasmic, are associated with a wide spectrum of human diseases. These range from rare syndromic disorders to cases of commoner conditions such as sensorineural deafness or cardiomyopathy. The disease spectrum of mutations in a given gene, or even a single mutation, may vary, but some patterns are evident, for example the prominence of cardiomyopathy resulting from tRNAIle defects, or of MERFF-like disease from tRNALys defects. Molecular studies of many laboratories have reached a consensus on molecular mechanisms associated with these mutations. Although precise details vary, loss of translational function of the affected tRNA(s) seems to be the final outcome, whether by impaired pre-tRNA processing, half-life, base-modification or aminoacylation. However, a mechanistic understanding of the consequences of this for the assembly and function of the mitochondrial OXPHOS complexes and for the physiological functions of the affected tissues is still a distant prospect. This review presents some views of possible downstream consequences of specific tRNA deficiencies.

Neuronal ageing from an intraneuronal perspective: roles of endoplasmic reticulum and mitochondria

The nature of brain ageing and the age-dependent decline in cognitive functions remains poorly understood. Physiological brain ageing is characterised by mild mental dysfunctions, whereas age-dependent neurodegeneration, as illustrated by Alzheimer disease (AD), results rapidly in severe dementia. These two states of the aged brain, the physiological and the pathological, are fundamentally different as the latter stems from significant neuronal loss, whereas the former develops without significant neuronal demise. In this paper, we review the changes in neuronal Ca(2+) homeostasis that occur during brain ageing, and conclude that normal, physiological ageing is characterised mainly by a decrease of neuronal homeostatic reserve, defined as the capacity to respond effectively to functional and metabolic stressors, but does not reach the trigger required to induce neuronal death. In contrast, during neurodegenerative states, Ca(2+) homeostasis is affected early during the pathological process and result in significant neuronal demise. We also review recent evidence suggesting that the endoplasmic reticulum (ER) might play an important role in controlling the balance between healthy and pathological neuronal ageing.

Single nucleotide polymorphisms of thrifty genes for energy metabolism: evolutionary origins and prospects for intervention to prevent obesity-related diseases

The "thrifty" genotype and phenotype that save energy are detrimental to the health of people living in affluent societies. Individual differences in energy metabolism are caused primarily by single nucleotide polymorphisms (SNPs), some of which promote the development of obesity/type 2 diabetes mellitus. In this review, four major questions are addressed: (1) Why did regional differences in energy metabolism develop during evolution? (2) How do genes respond to starvation and affluence? (3) Which SNPs correspond to the hypothetical "thrifty genes"? (4) How can we cope with disease susceptibility caused by the "thrifty" SNPs? We examined mtDNA and genes for energy metabolism in people who live in several parts of Asia and the Pacific islands. We included 14 genes, and the SNP frequencies of PPAR gamma 2, LEPR, and UCP3-p and some other genes differ significantly between Mongoloids and Caucasoids. These differences in SNPs may have been caused by natural selection depending on the types of agriculture practiced in different regions. Interventions to counteract the adverse effects of "thrifty" SNPs have been partially effective.

Aging is a deprivation syndrome driven by a germ-soma conflict

Evolution through natural selection can be described as driven by a perpetual conflict of individuals competing for limited resources. Recently, I postulated that the shortage of resources godfathered the evolutionary achievements of the differentiation-apoptosis programming [Rev. Neurosci. 12 (2001) 217]. Unicellular deprivation-induced differentiation into germ cell-like spores can be regarded as the archaic reproduction events which were fueled by the remains of the fratricided cells of the apoptotic fruiting body. Evidence has been accumulated suggesting that conserved through the ages as the evolutionary legacy of the germ-soma conflict, the somatic loss of immortality during the ontogenetic segregation of primordial germ cells recapitulates the archaic fate of the fruiting body. In this heritage, somatic death is a germ cell-triggered event and has been established as evolutionary-fixed default state following asymmetric reproduction in a world of finite resources. Aging, on the other hand, is the stress resistance-dependent phenotype of the somatic resilience that counteracts the germ cell-inflicted death pathway. Thus, aging is a survival response and, in contrast to current beliefs, is antagonistically linked to death that is not imposed by group selection but enforced upon the soma by the selfish genes of the "enemy within". Environmental conditions shape the trade-off solutions as compromise between the conflicting germ-soma interests. Mechanistically, the neuroendocrine system, particularly those components that control energy balance, reproduction and stress responses, orchestrate these events. The reproductive phase is a self-limited process that moulds onset and progress of senescence with germ cell-dependent factors, e.g. gonadal hormones. These degenerate the regulatory pacemakers of the pineal-hypothalamic-pituitary network and its peripheral, e.g. thymic, gonadal and adrenal targets thereby eroding the trophic milieu. The ensuing cellular metabolic stress engenders adaptive adjustments of the glucose-fatty acid cycle, responses that are adequate and thus fitness-boosting under fuel shortage (e.g. during caloric restriction) but become detrimental under fuel abundance. In a Janus-faced capacity, the cellular stress response apparatus expresses both tolerogenic and mutagenic features of the social and asocial deprivation responses [Rev. Neurosci. 12 (2001) 217]. Mediated by the derangement of the energy-Ca(2+)-redox homeostatic triangle, a mosaic of dedifferentiation/apoptosis and mutagenic responses actuates the gradual exhaustion of functional reserves and eventually results in a multitude of aging-related diseases. This scenario reconciles programmed and stochastic features of aging and resolves the major inconsistencies of current theories by linking ultimate and proximate causes of aging. Reproduction, differentiation, apoptosis, stress response and metabolism are merged into a coherent regulatory network that stages aging as a naturally selected, germ cell-triggered and reproductive phase-modulated deprivation response.

Uncoupling proteins and thermoregulation

Energy balance in animals is a metabolic state that exists when total body energy expenditure equals dietary energy intake. Energy expenditure, or thermogenesis, can be subcategorized into groups of obligatory and facultative metabolic processes. Brown adipose tissue (BAT), through the activity of uncoupling protein 1 (UCP1), is responsible for nonshivering thermogenesis, a major component of facultative thermogenesis in newborn humans and in small mammals. UCP1, found in the mitochondrial inner membrane in BAT, uncouples energy substrate oxidation from mitochondrial ATP production and hence results in the loss of potential energy as heat. Mice that do not express UCP1 (UCP1 knockouts) are markedly cold sensitive. The recent identification of four new homologs to UCP1 expressed in BAT, muscle, white adipose tissue, brain, and other tissues has been met by tremendous scientific interest. The hypothesis that the novel UCPs may regulate thermogenesis and/or fatty acid metabolism guides investigations worldwide. Despite several hundred publications on the new UCPs, there are a number of significant controversies, and only a limited understanding of their physiological and biochemical properties has emerged. The discovery of UCP orthologs in fish, birds, insects, and even plants suggests the widespread importance of their metabolic functions. Answers to fundamental questions regarding the metabolic functions of the new UCPs are thus pending and more research is needed to elucidate their physiological functions. In this review, we discuss recent findings from mammalian studies in an effort to identify potential patterns of function for the UCPs.

Islet expression of the DNA repair enzyme 8-oxoguanosine DNA glycosylase (Ogg1) in human type 2 diabetes

BACKGROUND: It has become increasingly clear that beta-cell failure plays a critical role in the pathogenesis of type 2 diabetes. Free-radical mediated beta-cell damage has been intensively studied in type 1 diabetes, but not in human type 2 diabetes. Therefore, we studied the protein expression of the DNA repair enzyme Ogg1 in pancreases from type 2 diabetics. Ogg1 was studied because it is the major enzyme involved in repairing 7,8-dihydro-8-oxoguanosine DNA adducts, a lesion previously observed in a rat model of type 2 diabetes. Moreover, in a gene expression screen, Ogg1 was over-expressed in islets from a human type 2 diabetic. METHODS: Immunofluorescent staining of Ogg1 was performed on pancreatic specimens from healthy controls and patients with diabetes for 2-23 years. The intensity and islet area stained for Ogg1 was evaluated by semi-quantitative scoring. RESULTS: Both the intensity and the area of islet Ogg1 staining were significantly increased in islets from the type 2 diabetic subjects compared to the healthy controls. A correlation between increased Ogg1 fluorescent staining intensity and duration of diabetes was also found. Most of the staining observed was cytoplasmic, suggesting that mitochondrial Ogg1 accounts primarily for the increased Ogg1 expression. CONCLUSION: We conclude that oxidative stress related DNA damage may be a novel important factor in the pathogenesis of human type 2 diabetes. An increase of Ogg1 in islet cell mitochondria is consistent with a model in which hyperglycemia and consequent increased beta-cell oxidative metabolism lead to DNA damage and the induction of Ogg1 expression.

Uncoupling proteins--a new family of proteins with unknown function

Uncoupling proteins are inner mitochondrial membrane proteins, which dissipate the proton gradient, releasing the stored energy as heat. Five proteins have been cloned, named UCP1, UCP2, UCP3, UCP4 and UCP5/BMCP1. These proteins are structurally related but differ in tissue expression. UCP1 is expressed uniquely in the brown adipose tissue, while UCP2 is widely distributed, UCP3 is mainly restricted to skeletal muscle and UCP4 and UCP5/BMCP1 expressed in the brain. The properties and regulation of the uncoupling proteins and their exact function has been the focus of an intense research during recent years. This review briefly summarizes the actual knowledge of the properties and function of this new family of proteins. While UCP1 has a clear role in energy homeostasis, the newcomers UCP2-UCP5 may have more delicate physiological importance acting as free radical oxygen scavengers and in the regulation of ATP-dependent processes, such as secretion.

Chronic docosahexaenoic acid intake enhances expression of the gene for uncoupling protein 3 and affects pleiotropic mRNA levels in skeletal muscle of aged C57BL/6NJcl mice

Docosahexaenoic acid [DHA, 22:6(n-3)] prevents cardiovascular disease by decreasing obesity. It also prevents cancer and other geriatric diseases. We studied the chronic pleiotropic effects of DHA on transcription including that of mRNAs for uncoupling proteins (UCP). Male and female mice (9 mo old) were fed high (n-6) or high (n-3) fatty acid diets for 4 mo. Compared with controls fed high (n-6) fatty acid diets [high (n-6) group], the livers of male and female mice fed DHA [high (n-3) group] contained six- (P < 0.001) and fivefold (P < 0.001) more DHA, respectively. The high (n-3) group had less white adipose tissue [35.3% in males (P < 0.001) and 27.3% in females (P < 0.001)]. The high (n-3) group expressed more uncoupling protein 3 (UCP3) in the gastrocnemius, 108% higher (P < 0.001) and 104% higher (P < 0.001) in males and females, respectively, than those in the high (n-6) group. However, the prevention of many diseases by DHA is not explained by UCP3. Thus, the gene expression profiles of both high (n-3) and high (n-6) groups were analyzed in skeletal muscle using cDNA expression array. Of 588 genes surveyed in the array, the high (n-3) group showed 12 genes (2%) including those for glucose regulators (e.g., CD38) and tumor suppressors (e.g., CTCF) that were expressed 100-340% more than those of the high (n-6) group. Furthermore, 28 genes (4.8%), including growth factors (e.g., ErbB-2 receptor) and immune regulators (e.g., interleukin-1 beta precursor) were expressed 50-90% less in the high (n-3) group than in the high (n-6) group. These results explain in part the important pleiotropic effects of DHA, which are independent of obesity control by UCP3 suppression.

Gene therapy by mitochondrial transfer

Mitochondrial DNA (mtDNA) is highly susceptible to mutation. Novel approaches such as those involving cytoplast fusion and mitochondrial microinjection are essential for gene therapy of diseases caused by these mutations, due to the non-Mendelian genetics of these diseases. In this fusion method, mtDNA in the cytoplast is transferred into mutant cells via the formation of cybrids; once inside the cell the mtDNA complement the defect correctly and safely. The genes in cloned animals are composed of nuclear DNA (nDNA) of a mature tissue and mtDNA from an oocyte. Recent advances in transmitochondrial mice depends on the microinjection of mitochondria into the oocyte. Here we present data on in vitro gene therapy using human mtDNA, cybrid formation and microinjection.

Age-related decreases in basal limb blood flow in humans: time course, determinants and habitual exercise effects

Basal whole-limb blood flow is lower in older than in young healthy sedentary men due to a lower limb vascular conductance. In Study 1, we determined whether age-associated reductions in basal whole-leg (femoral artery) blood flow and vascular conductance are modulated by habitual physical activity by studying 89 healthy men aged 20-35 or 55-75 years (26 sedentary, 31 physically active and 32 endurance exercise trained). Femoral blood flow (duplex Doppler) and vascular conductance were approximately 20-30 % lower (P < 0.01) in the older men in all three physical activity groups. In Study 2, to determine the temporal pattern and relation to local metabolism and lean tissue mass of the age-associated reductions in femoral blood flow, we studied 142 healthy men aged 18-79 years. Femoral blood flow (r = -0.40) and vascular conductance (r = -0.51) were linearly and inversely related to age (both P < 0.001). Leg fat-free mass (r = -0.48) and estimated leg oxygen consumption (r = -0.49) declined with advancing age (both P < 0.001), and were strongly and positively related (r = 0.75; P < 0.001). The age-associated decline in femoral blood flow correlated with the corresponding reductions in leg fat-free mass and estimated leg oxygen consumption (both r = 0.47; P < 0.001). We concluded that: (1) basal whole-limb blood flow and vascular conductance decrease progressively with advancing age in healthy men; (2) reductions in both limb fat-free mass and oxygen consumption are related to the decline in whole-limb blood flow with age; and (3) habitual aerobic exercise does not appear to modulate the age-related reductions in basal limb blood flow and vascular conductance.

Glucose starvation reduces IGF-I mRNA in tumor cells: evidence for an effect on mRNA stability

The purpose of this study was to characterize the mechanisms by which glucose regulates IGF-I gene expression in rat C6 glioma cells and in rat GH3 pituitary adenoma cells. Glucose starvation for periods of 12 to 48 h decreased IGF-I mRNA levels. In contrast, there was no stimulation of IGF-I mRNA by medium glucose between 1 and 25 mM over a 24-h period. Studies with hexoses and glycolytic metabolites suggested that glucose metabolism was required to maintain IGF-I mRNA. Glucose starvation lowered IGF-I mRNA half-life in both C6 and GH3 cells. Protein synthesis inhibition lowered IGF-I mRNA by about 20% in glucose-fed C6 and GH3 cells, while potently increasing IGF-I mRNA in glucose-starved C6 cells and not altering IGF-I mRNA in glucose-starved GH3 cells. Our results suggest that in these tumor cells, IGF-I mRNA stability is reduced by glucose starvation, secondary to a deficiency in intracellular glucose metabolism. Ongoing protein synthesis is not required for this mRNA de-stabilizing effect in GH3 cells. Rather, in glucose-starved C6 cells, decreased IGF-I mRNA stability may result from the action of a labile protein.