Knockdown of Indy/CeNac2 extends Caenorhabditis elegans life span by inducing AMPK/aak-2

Reducing the expression of the Indy (Acronym for ‘I''m Not Dead, Yet’) gene in lower organisms promotes longevity and leads to a phenotype that resembles various aspects of caloric restriction. In C. elegans, the available data on life span extension is controversial. Therefore, the aim of this study was to determine the role of the C. elegans INDY homolog CeNAC2 in life span regulation and to delineate possible molecular mechanisms. siRNA against Indy/CeNAC2 was used to reduce expression of Indy/CeNAC2. Mean life span was assessed in four independent experiments, as well as whole body fat content and AMPK activation. Moreover, the effect of Indy/CeNAC2 knockdown in C. elegans with inactivating variants of AMPK (TG38) was studied. Knockdown of Indy/CeNAC2 increased life span by 22 ± 3% compared to control siRNA treated C. elegans, together with a decrease in whole body fat content by ~50%. Indy/CeNAC2 reduction also increased the activation of the intracellular energy sensor AMPK/aak2. In worms without functional AMPK/aak2, life span was not extended when Indy/CeNAC2 was reduced. Inhibition of glycolysis with deoxyglucose, an intervention known to increase AMPK/aak2 activity and life span, did not promote longevity when Indy/CeNAC2 was knocked down. Together, these data indicate that reducing the expression of Indy/CeNAC2 increases life span in C. elegans, an effect mediated at least in part by AMPK/aak2.     

Conditional tradeoffs between aging and organismal performance of Indy long-lived mutant flies

Alterations that extend the life span of animals and yeast typically involve decreases in metabolic rate, growth, physical activity, and/or early-life fecundity. This negative correlation between life span and the ability to assimilate and process energy, to move, grow, and reproduce, raises questions about the potential utility of life span extension. Tradeoffs between early-life fitness and longevity are central to theories of the evolution of aging, which suggests there is necessarily a price to be paid for reducing the rate of aging. It is not yet clear whether life span can be extended without undesirable effects on metabolism and fecundity. Here, we report that the long-lived Indy mutation in Drosophila causes a decrease in the slope of the mortality curve consistent with a slowing in the rate of aging without a concomitant reduction in resting metabolic rate, flight velocity, or age-specific fecundity under normal rearing conditions. However, Indy mutants on a decreased-calorie diet have reduced fecundity, suggesting that a tradeoff between longevity and this aspect of performance is conditional, i.e., the tradeoff can occur in a stressful environment while being absent in a more favorable environment. These results provide evidence that there do exist mechanisms, albeit conditional, that can extend life span without significant reduction in fecundity, metabolic rate, or locomotion.     

Mitochondrial transporters of the SLC25 family and associated diseases: a review

To date, 14 inherited diseases (including phenotypes) associated to mitochondrial transporters of the SLC25 family have been well characterized biochemically and genetically. They are rare metabolic disorders caused by mutations in the SLC25 nuclear genes that encode mitochondrial carriers, a superfamily of 53 proteins in humans that shuttle a variety of solutes across the mitochondrial membrane. Mitochondrial carriers vary considerably in the nature and size of the substrates they transport, the modes of transport and driving forces. However, their substrate translocation mechanism at the molecular level is thought to be basically the same. Herein, the main structural and functional properties of the SLC25 mitochondrial carriers and the known carrier-related diseases are presented. Two of these disorders, ADP/ATP carrier deficiency and phosphate carrier deficiency, are caused by defects of the two mitochondrial carriers that provide mitochondria with ADP and phosphate, the substrates of oxidative phosphorylation; these disorders therefore are characterized by defective energy production by mitochondria. The mutations of SLC25 carrier genes involved in other cellular functions cause carnitine/acylcarnitine carrier deficiency, HHH syndrome, aspartate/glutamate isoform 1 and 2 deficiencies, congenital Amish microcephaly, neuropathy with bilateral striatal necrosis, congenital sideroblastic anemia, neonatal epileptic encephalopathy, and citrate carrier deficiency; these disorders are characterized by specific metabolic dysfunctions depending on the role of the defective carrier in intermediary metabolism.     

Patterns of metabolic activity during aging of the wild type and longevity mutants of Caenorhabditis elegans

At least three mechanisms determine life span in Caenorhabditis elegans. An insulin-like signaling pathway regulates dauer diapause, reproduction and longevity. Reduction-or loss-of-function mutations in this pathway can extend longevity substantially, suggesting that the wild-type alleles shorten life span. The mutations extend life span by activating components of a dauer longevity assurance program in adult life, resulting in altered metabolism and enhanced stress resistance. The Clock (Clk) genes regulate many temporal processes, including life span. Mutation in the Clk genes clk-1 and gro-1 mildly affect energy production, but repress energy consumption dramatically, thereby reducing the rate of anabolic metabolism and lengthening life span. Dietary restriction, either imposed by mutation or by the culture medium increases longevity and uncovers a third mechanism of life span determination. Dietary restriction likely elicits the longevity assurance program. There is still uncertainty as to whether these pathways converge on daf-16 to activate downstream longevity effector genes such as ctl-1 and sod-3. There is overwhelming evidence that the interplay between reactive oxygen species (ROS) and the capacity to resist oxidative stress controls the aging process and longevity. It is as yet not clear whether metabolic homeostasis collapses with age as a direct result of ROS-derived damage or is selectively repressed by longevity-determining genes. The dramatic decline of protein turnover during senescence results in the accumulation of altered enzymes and in a gradual decline of metabolic performance eventually followed by fatal failure of the system.     

A new role for caveolae as metabolic platforms.

The plasma membrane of cells functions as a barrier to the environment. Caveolae are minute invaginations of the membrane that selectively carry out the exchange of information and materials with the environment, by functioning as organizers of signal transduction and through endocytosis. Recent findings of uptake of different metabolites and of lipid metabolism occurring in caveolae, point to a new general function of caveolae. As gateways for the uptake of nutrients across the plasma membrane, and as platforms for the metabolic conversion of nutrients, especially in adipocytes, caveolae are now emerging as active centers for many aspects of intermediary metabolism, with implications for our understanding of obesity, diabetes and other metabolic disorders.     

Dietary restriction in the nematode Caenorhabditis elegans

The first observation of the positive effect of reduced food intake on mammalian life span was made 70 years ago. In the decades that followed, researchers successfully applied this method to increase the life span of a very wide range of animals. The nematode Caenorhabditis elegans is an excellent model organism for studying the aging process. However, relatively little effort has been made to study the effects of dietary restriction in C. elegans. In this review we discuss the difficulties of subjecting C. elegans to dietary restriction, the effects of dietary restriction on metabolism and stress defense, and the potential role of different signaling pathways in DR-induced life extension. Recent experiments suggest that the TOR (target of rapamycin) pathway, rather than insulin-like signaling, might be involved in mediating the life-extending effect of dietary restriction.     

Characterization of a life-extending mutation in age-2, a new aging gene in Caenorhabditis elegans

We have generated a life-extending mutation, yw23, in Caenorhabditis elegans. The mutation is in what appears to be a new aging gene, which we have designated age-2. When homozygous, yw23 produces an increase of mean and maximum life span of about 20% over that of the wild-type strain, N2. Strain HG23 [age-2(yw23)] was obtained by screening for longer life spans among 430 lines of nematodes two generations after exposure to the mutagen ethylmethanesulfonate. Strain HG231 [age-2(yw23)] was obtained after a single out-crossing of HG23 to N2. When compared with N2, HG231 exhibits normal motility, slightly higher swimming rates, reduced fertility (especially at higher temperatures), somewhat longer development times, and a slightly larger size at the time of first egg laying. A Gompertz analysis suggests that HG231 extends life span by reducing the initial mortality rate. In genetic crosses, yw23 complements other known aging mutants in C. elegans genes-age-1, daf-2, spe-26, clk-1, clk-2, clk-3, and gro-1. A double-mutant strain, HG284, combining mutations in age-1 and age-2, lives longer than animals with individual mutations in either age-1 or age-2, and exhibits a longer life span at 25 degrees C than at 20 degrees C.     

A flagellar K(+)-dependent Na(+)/Ca(2+) exchanger keeps Ca(2+) low in sea urchin spermatozoa

The metabolism, flagellar beating, and acrosome reaction of spermatozoa are regulated by ion flux across the plasma membrane. As is true of most cells, swimming sperm maintain intracellular Ca(2+) concentrations at submicromolar levels. Here we describe a K(+)-dependent Na(+)/Ca(2+) exchanger (suNCKX) from sea urchin sperm. The suNCKX is phylogenetically related to other NCKXs, which use high relative intracellular K(+), and high relative extracellular Na(+), to couple the efflux of 1 Ca(2+) and 1 K(+) to the influx of 4 Na(+). The 652-aa suNCKX shares structural topology with other NCKX proteins, and has two protein kinase A sites and a His-rich region in its cytoplasmic loop. The suNCKX is encoded by a single gene, which is highly expressed in testes. The suNCKX activity of whole sperm shows Na(+) and K(+) dependence, and like other NCKXs can run in reverse exchange mode. An inhibitor blocks the suNCKX activity and sperm motility. suNCKX localizes to the plasma membrane over the sperm flagellum. The suNCKX may play a major role in keeping Ca(2+) low in swimming sperm.     

Decreased concentration of plasma leptin in periparturient dairy cows is caused by negative energy balance.

Dairy cows suffer from an intense energy deficit at parturition due to the onset of copious milk synthesis and depressed appetite. Despite this deficit, maternal metabolism is almost completely devoted to the support of mammary metabolism. Evidence from rodents suggests that, during periods of nutritional insufficiency, a reduction in plasma leptin serves to co-ordinate energy metabolism. As an initial step to determine if leptin plays this role in periparturient dairy cows, changes in the plasma concentration of leptin were measured during the period from 35 days before to 56 days after parturition. The plasma concentration of leptin was reduced by approximately 50% after parturition and remained depressed during lactation despite a gradual improvement in energy balance; corresponding changes occurred in the abundance of leptin mRNA in white adipose tissue. To determine whether negative energy balance caused this reduction in circulating leptin, cows were either milked or not milked after parturition. Absence of milk removal eliminated the energy deficit of early lactation, and doubled the plasma concentration of leptin. The plasma concentration of leptin was positively correlated with plasma concentrations of insulin and glucose, and negatively correlated with plasma concentrations of growth hormone and non-esterified fatty acids. In conclusion, the energy deficit of periparturient cows causes a sustained reduction in plasma leptin. This reduction could benefit early lactating dairy cows by promoting a faster increase in feed intake and by diverting energy from non-vital functions such as reproduction.     

AMPK and the neuroendocrine regulation of appetite and energy expenditure

This review highlights recent advances in the hormonal control of hypothalamic AMPK activity and the impact on appetite and energy metabolism. AMPK is an intracellular energy sensor that switches off ATP-consuming pathways and switches on ATP-producing pathways such as glucose uptake and fatty acid oxidation. In this regard, it is well positioned to respond to dynamic changes in metabolic state and nutritional over- or under-supply. Within the hypothalamus, AMPK responds to peripheral hormones that convey metabolic information based on increased plasma concentrations. For example, negative energy balance increases plasma ghrelin concentrations, increases hypothalamic AMPK and drives food intake. Conversely, plasma leptin concentrations are secreted in proportion to adipose levels and leptin suppresses hypothalamic AMPK activity and restricts food intake. This review explains that hypothalamic AMPK mediates neuroendocrine feedback control of energy metabolism. A current working model suggests that endocrine feedback influences hypothalamic AMPK via a number of mechanisms designed to shift an organism from negative to neutral energy balance. These mechanisms include (1) ghrelin stimulation of AMPK in NPY/AgRP in the arcuate nucleus (2) ghrelin stimulation of AMPK in the ventromedial hypothalamic nucleus, (3) a novel ghrelin-stimulated AMPK-dependent presynaptic mechanism that sustains AgRP neuron firing via a local synaptic memory system, (4) adiponectin stimulation of hypothalamic AMPK and (5) hypothalamic AMPK control of energy expenditure by thyroid hormone or leptin. The number of diverse mechanisms ensures hypothalamic AMPK drives the shift from negative to neutral energy balance and underscores the fundamental importance of hypothalamic AMPK to maintain neutral energy balance.     

Promiscuous archaeal ATP synthase concurrently coupled to Na+ and H+ translocation

ATP synthases are the primary source of ATP in all living cells. To catalyze ATP synthesis, these membrane-associated complexes use a rotary mechanism powered by the transmembrane diffusion of ions down a concentration gradient. ATP synthases are assumed to be driven either by H(+) or Na(+), reflecting distinct structural motifs in their membrane domains, and distinct metabolisms of the host organisms. Here, we study the methanogenic archaeon Methanosarcina acetivorans using assays of ATP hydrolysis and ion transport in inverted membrane vesicles, and experimentally demonstrate that the rotary mechanism of its ATP synthase is coupled to the concurrent translocation of both H(+) and Na(+) across the membrane under physiological conditions. Using free-energy molecular simulations, we explain this unprecedented observation in terms of the ion selectivity of the binding sites in the membrane rotor, which appears to have been tuned via amino acid substitutions so that ATP synthesis in M. acetivorans can be driven by the H(+) and Na(+) gradients resulting from methanogenesis. We propose that this promiscuity is a molecular mechanism of adaptation to life at the thermodynamic limit.     

Energy expenditure of rhesus monkeys subjected to 11 years of dietary restriction

Dietary restriction (DR) is currently the only paradigm that has consistently extended maximal life span and reduced the onset of age-related chronic diseases in all of the nonprimate species tested. Although it is controversial, some investigators have suggested that the underlying mechanisms may be mediated by adaptations in energy expenditure. We evaluated the extent to which DR alters energy metabolism in a unique cohort of rhesus monkeys submitted to DR for 11 yr. Total energy expenditure (doubly labeled water), resting energy expenditure (REE; indirect calorimetry), and nonbasal energy expenditure (calculated by difference) were measured in DR (n = 12) and control (n = 11) animals. Body composition was determined by dual energy x-ray absorptiometry. Both fat mass and fat-free mass were lower in the restricted animals (56 and 12%, respectively). DR induced a 17% lower total energy expenditure that was attributable to a 20% decrease in REE without changes in the nonbasal energy expenditure. Adjusted for fat-free mass, REE was 13% lower with DR (-250 kJ/d). Taken together with a reanalysis of previous DR experiments published in humans, rodents, and monkeys, these results suggest that DR may lower REE independent of the DR-induced changes in body composition. Whether this reduction in REE contributes to the life-extending properties of DR warrants further analysis, but it suggests that the long-standing debate regarding DR effects on metabolic rates may derive from the lack of consensus on how to adjust for body size and composition.     

Dietary restriction-induced life extension: a broadly based biological phenomenon

It is concluded that dietary restriction will extend the life of all species in the Animalia Kingdom, including the human species. This conclusion is based on the fact that hormesis is a component of the life-extending action and the other anti-aging effects of dietary restriction. It is also concluded that given the currently available database, it is not possible to predict the quantitative effect of dietary restriction on the human life span.     

WNK4 regulates activity of the epithelial Na+ channel in vitro and in vivo

Homeostasis of intravascular volume, Na(+), Cl(-), and K(+) is interdependent and determined by the coordinated activities of structurally diverse mediators in the distal nephron and the distal colon. The behavior of these flux pathways is regulated by the renin-angiotensin-aldosterone system; however, the mechanisms that allow independent modulation of individual elements have been obscure. Previous work has shown that mutations in WNK4 cause pseudohypoaldosteronism type II (PHAII), a disease featuring hypertension with hyperkalemia, due to altered activity of specific Na-Cl cotransporters, K(+) channels, and paracellular Cl(-) flux mediators of the distal nephron. By coexpression studies in Xenopus oocytes, we now demonstrate that WNK4 also inhibits the epithelial Na(+) channel (ENaC), the major mediator of aldosterone-sensitive Na(+) (re)absorption, via a mechanism that is independent of WNK4's kinase activity. This inhibition requires intact C termini in ENaC beta- and gamma-subunits, which contain PY motifs used to target ENaC for clearance from the plasma membrane. Importantly, PHAII-causing mutations eliminate WNK4's inhibition of ENaC, thereby paralleling other effects of PHAII to increase sodium balance. The relevance of these findings in vivo was studied in mice harboring PHAII-mutant WNK4. The colonic epithelium of these mice demonstrates markedly increased amiloride-sensitive Na(+) flux compared with wild-type littermates. These studies identify ENaC as a previously unrecognized downstream target of WNK4 and demonstrate a functional role for WNK4 in the regulation of colonic Na(+) absorption. These findings support a key role for WNK4 in coordinating the activities of diverse flux pathways to achieve integrated fluid and electrolyte homeostasis.     

Mitochondria in Neutrophil Apoptosis

Central in the regulation of the short life span of neutrophils are their mitochondria. These organelles hardly contribute to the energy status of neutrophils but play a vital role in the apoptotic process. Not only do the mitochondria contain cytotoxic proteins that are released during apoptosis and contribute to caspase activation, but they also act as sensors of the metabolic and redox state of the cell and as scavengers of free Ca2+. The balance of the expression and activity of the proapoptotic and antiapoptotic members of the Bcl-2 family of proteins determines the life span of neutrophils, because these proteins are essential for the formation of a permeability transition pore in the mitochondria and also seem to control the release of Ca2+ from the endoplasmic reticulum and thereby mitochondrial energy metabolism.     

Acetaldehyde binds to liver cell membranes without affecting membrane function

Acetaldehyde is a major metabolic product of ethanol and is found in high concentrations in the serum during alcohol abuse. The effects of acetaldehyde on isolated rat liver cells and on purified hepatocyte plasma membrane vesicles have been studied. In concentrations of 0-10 millimolar acetaldehyde has been shown to have no detectable effect on either hepatocyte metabolism or gross membrane function and is therefore unlikely to act as a direct metabolic poison. Acetaldehyde, however, is shown to bind to hepatocyte membranes via intermediary Schiff's base formation. The adduction of acetaldehyde to liver cell plasma membranes may have an effect on membrane structure. These findings are consistent with the hypothesis that any injurious effect of acetaldehyde on the liver may be mediated via the immune system rather than being a direct effect on cell metabolism.     

非酒精性脂肪性肝病与肠道菌群的关系

非酒精性脂肪性肝病(non-alcoholic fatty liver disease,NAFLD)是一种多病因导致的临床病理综合征,已成为最常见的慢性肝病之一,目前NAFLD完整的生理机制尚不完全清楚,近年来提出肠道菌群通过调控能量代谢、增加内源性乙醇、调节胆汁酸及胆碱代谢,破坏免疫平衡引发机体低度炎症等途径促进NAFLD的发生、发展,本文就肠道菌群与NAFLD的相关机制做一概述。     

饮食热量限制延缓衰老作用的研究进展

本文综述热量限制延缓衰老及其机制.无论是整体动物还是器官组织或细胞水平的研究均提示热量限制能延缓衰老,但其机制至今不明.目前有能量代谢理论、氧化应激理论、神经内分泌假说和细胞凋亡抑制等几种解释,并得到一定的实验研究支持,但没有一种理论能完全阐明热量限制延缓衰老的现象,在将实验研究结果推广于临床前仍有许多工作要做.     

MCT8: from gene to disease and therapeutic approach

Thyroid hormone metabolism and action are largely intracellular processes that require transport of the hormone across the plasma membrane by different transporters. Two of these, MCT8 and MCT10, are close members of the monocarboxylate transporter family. MCT8 is expressed in a variety of tissues, including liver, kidney, thyroid and brain. The MCT8 gene is located on the X chromosome, and mutations in MCT8 result in severe psychomotor retardation and low serum T4 and high T3 levels in affected males. The psychomotor retardation is thought to be caused by impaired neuronal T3 uptake during brain development. The abnormal thyroid hormone levels appear to result from an increased T4 to T3 conversion in the kidney as well as altered hormone secretion from the thyroid gland. Options for therapy aim at early treatment with T3 analogues, neuronal uptake of which does not require MCT8.