Inter-organ proteomic analysis reveals insights into the molecular mechanisms underlying the anti-diabetic effects of cis-9, trans-11-conjugated linoleic acid in ob/ob mice

cis‐9, trans‐11‐Conjugated linoleic acid (c9 t11 CLA) exerts anti‐diabetic effects by improving systemic insulin sensitivity and inflammation. Levels of CLA in beef can be increased by feeding cattle on pasture. This study aimed to explore the efficacy of a CLA‐rich diet (0.6% w/w c9 t11 CLA), presented as beef enriched with CLA or beef supplemented with synthetic CLA (c9 t11 CLA), for 28 days on molecular biomarkers of the metabolic syndrome, and adipose, hepatic, and skeletal muscle proteome in male ob/ob mice. Despite equal weight gain, CLA‐fed mice had lower plasma glucose, insulin, non‐esterified fatty acid, triacylglycerol and interleukin‐6, and higher adiponectin concentrations than controls. c9 t11 CLA induced differential regulation of redox status across all tissues, and decreased hepatic and muscle endoplasmic reticulum stress. CLA also modulated mechanistic links between the actin cytoskeleton, insulin signalling, glucose transport and inflammation in the adipose tissue. In the liver and muscle, c9 t11 CLA improved metabolic flexibility through co‐ordination between carbohydrate and energy metabolism. c9 t11 CLA may ameliorate systemic insulin sensitivity in obesity‐induced diabetes by altering cellular stress and redox status, and modulating nutrient handling in key insulin‐sensitive tissues through complex biochemical interplay among representative proteomic signatures.     

The chloride anion as a signalling effector

The specific role of the chloride anion (Cl^?) as a signalling effector or second messenger has been increasingly recognized in recent years. It could represent a key factor in the regulation of cellular homeostasis. Changes in intracellular Cl^? concentration affect diverse cellular functions such as gene and protein expression and activities, post‐translational modifications of proteins, cellular volume, cell cycle, cell proliferation and differentiation, membrane potential, reactive oxygen species levels, and intracellular/extracellular pH. Cl^? also modulates functions in different organelles, including endosomes, phagosomes, lysosomes, endoplasmic reticulum, and mitochondria. A better knowledge of Cl^? signalling could help in understanding the molecular and metabolic changes seen in pathologies with altered Cl^? transport or under physiological conditions. Here we review relevant evidence supporting the role of Cl^? as a signalling effector.     

Methionine metabolism and methyltransferases in the regulation of aging and lifespan extension across species

Methionine restriction (MetR) extends lifespan across different species and exerts beneficial effects on metabolic health and inflammatory responses. In contrast, certain cancer cells exhibit methionine auxotrophy that can be exploited for therapeutic treatment, as decreasing dietary methionine selectively suppresses tumor growth. Thus, MetR represents an intervention that can extend lifespan with a complementary effect of delaying tumor growth. Beyond its function in protein synthesis, methionine feeds into complex metabolic pathways including the methionine cycle, the transsulfuration pathway, and polyamine biosynthesis. Manipulation of each of these branches extends lifespan; however, the interplay between MetR and these branches during regulation of lifespan is not well understood. In addition, a potential mechanism linking the activity of methionine metabolism and lifespan is regulation of production of the methyl donor S‐adenosylmethionine, which, after transferring its methyl group, is converted to S‐adenosylhomocysteine. Methylation regulates a wide range of processes, including those thought to be responsible for lifespan extension by MetR. Although the exact mechanisms of lifespan extension by MetR or methionine metabolism reprogramming are unknown, it may act via reducing the rate of translation, modifying gene expression, inducing a hormetic response, modulating autophagy, or inducing mitochondrial function, antioxidant defense, or other metabolic processes. Here, we review the mechanisms of lifespan extension by MetR and different branches of methionine metabolism in different species and the potential for exploiting the regulation of methyltransferases to delay aging.     

PKB and the mitochondria: AKTing on apoptosis

Cellular homeostasis depends upon the strict regulation of responses to external stimuli, such as signalling cascades triggered by nutrients and growth factors, and upon cellular metabolism. One of the major molecules coordinating complex signalling pathways is protein kinase B (PKB), a serine/threonine kinase also known as Akt. The number of substrates known to be phosphorylated by PKB and its interacting partners, as well as our broad understanding of how PKB is implicated in responses to growth factors, metabolic pathways, proliferation, and cell death via apoptosis is constantly increasing. Activated by the insulin/growth factor-phosphatidylinositol 3-kinase (PI3K) cascade, PKB triggers events that promote cell survival and prevent apoptosis. It is also now widely accepted that mitochondria are not just suppliers of ATP, but that they participate in regulatory and signalling events, responding to multiple physiological inputs and genetic stresses, and regulate both cell proliferation and death. Thus, mitochondria are recognized as important players in apoptotic events and it is logical to predict some form of interplay with PKB. In this review, we will summarize mechanisms by which PKB mediates its anti-apoptotic activities in cells and survey recent developments in understanding mitochondrial dynamics and their role during apoptosis.     

CLPP deficiency protects against metabolic syndrome but hinders adaptive thermogenesis

Mitochondria are fundamental for cellular metabolism as they are both a source and a target of nutrient intermediates originating from converging metabolic pathways, and their role in the regulation of systemic metabolism is increasingly recognized. Thus, maintenance of mitochondrial homeostasis is indispensable for a functional energy metabolism of the whole organism. Here, we report that loss of the mitochondrial matrix protease CLPP results in a lean phenotype with improved glucose homeostasis. Whole‐body CLPP‐deficient mice are protected from diet‐induced obesity and insulin resistance, which was not present in mouse models with either liver‐ or muscle‐specific depletion of CLPP. However, CLPP ablation also leads to a decline in brown adipocytes function leaving mice unable to cope with a cold‐induced stress due to non‐functional adaptive thermogenesis. These results demonstrate a critical role for CLPP in different metabolic stress conditions such as high‐fat diet feeding and cold exposure providing tools to understand pathologies with deregulated Clpp expression and novel insights into therapeutic approaches against metabolic dysfunctions linked to mitochondrial diseases.     

Novel insights into the osmotic stress response of yeast

Response to hyperosmolarity in the baker's yeast Saccharomyces cerevisiae has attracted a great deal of attention of molecular and cellular biologists in recent years, from both the fundamental scientific and applied viewpoint. Indeed the underlying molecular mechanisms form a clear demonstration of the intricate interplay of (environmental) signalling events, regulation of gene expression and control of metabolism that is pivotal to any living cell. In this article we briefly review the cellular response to conditions of hyperosmolarity, with focus on the high-osmolarity glycerol mitogen-activated protein kinase pathway as the major signalling route governing cellular adaptations. Special attention will be paid to the recent finding that in the yeast cell also major structural changes occur in order to ensure maintenance of cell integrity. The intriguing role of glycerol in growth of yeast under (osmotic) stress conditions is highlighted.     

Methionine supplementation stimulates mitochondrial respiration

Mitochondria play essential metabolic functions in eukaryotes. Although their major role is the generation of energy in the form of ATP, they are also involved in maintenance of cellular redox state, conversion and biosynthesis of metabolites and signal transduction. Most mitochondrial functions are conserved in eukaryotic systems and mitochondrial dysfunctions trigger several human diseases.By using multi-omics approach, we investigate the effect of methionine supplementation on yeast cellular metabolism, considering its role in the regulation of key cellular processes. Methionine supplementation induces an up-regulation of proteins related to mitochondrial functions such as TCA cycle, electron transport chain and respiration, combined with an enhancement of mitochondrial pyruvate uptake and TCA cycle activity. This metabolic signature is more noticeable in cells lacking Snf1/AMPK, the conserved signalling regulator of energy homeostasis. Remarkably, snf1Δ cells strongly depend on mitochondrial respiration and suppression of pyruvate transport is detrimental for this mutant in methionine condition, indicating that respiration mostly relies on pyruvate flux into mitochondrial pathways.These data provide new insights into the regulation of mitochondrial metabolism and extends our understanding on the role of methionine in regulating energy signalling pathways.     

Tumour glycolysis: the many faces of HIF

We present a model for tumour metabolism that incorporates both microenvironmental (extracellular) and oncogenic (intracellular) influences. We explore the effects of the interaction between the hypoxic microenvironment and intracellular signalling on the glycolytic response of tumour tissue, finding that the glycolytic state is dependent on a delicately balanced interplay between the cellular hypoxic response, mediated by hypoxia-inducible factor-1α (HIF-1α), and growth-factor signalling cascades, which are frequently mutated in cancers. Our findings demonstrate the importance of considering both environmental and intracellular regulation when interpreting tumour metabolism for diagnostic or prognostic purposes. To illustrate this, we demonstrate the potential impact of this multi-factorial regulation on the kinetics of radiolabelled glucose analogues, used in positron emission tomography (PET).     

Plant sugars are crucial players in the oxidative challenge during abiotic stress: extending the traditional concept

Plants suffering from abiotic stress are commonly facing an enhanced accumulation of reactive oxygen species (ROS) with damaging as well as signalling effects at organellar and cellular levels. The outcome of an environmental challenge highly depends on the delicate balance between ROS production and scavenging by both enzymatic and metabolic antioxidants. However, this traditional classification is in need of renewal and reform, as it is becoming increasingly clear that soluble sugars such as disaccharides, raffinose family oligosaccharides and fructans – next to their associated metabolic enzymes – are strongly related to stress‐induced ROS accumulation in plants. Therefore, this review aims at extending the current concept of antioxidants functioning during abiotic stress, with special focus on the emanate role of sugars as true ROS scavengers. Examples are given based on their cellular location, as different organelles seem to exploit distinct mechanisms. Moreover, the vacuole comes into the picture as important player in the ROS signalling network of plants. Elucidating the interplay between the mechanisms controlling ROS signalling during abiotic stress will facilitate the development of strategies to enhance crop tolerance to stressful environmental conditions.     

Is metabolic rate a universal ‘pacemaker’ for biological processes?

A common, long‐held belief is that metabolic rate drives the rates of various biological, ecological and evolutionary processes. Although this metabolic pacemaker view (as assumed by the recent, influential ‘metabolic theory of ecology’) may be true in at least some situations (e.g. those involving moderate temperature effects or physiological processes closely linked to metabolism, such as heartbeat and breathing rate), it suffers from several major limitations, including: (i) it is supported chiefly by indirect, correlational evidence (e.g. similarities between the body‐size and temperature scaling of metabolic rate and that of other biological processes, which are not always observed) – direct, mechanistic or experimental support is scarce and much needed; (ii) it is contradicted by abundant evidence showing that various intrinsic and extrinsic factors (e.g. hormonal action and temperature changes) can dissociate the rates of metabolism, growth, development and other biological processes; (iii) there are many examples where metabolic rate appears to respond to, rather than drive the rates of various other biological processes (e.g. ontogenetic growth, food intake and locomotor activity); (iv) there are additional examples where metabolic rate appears to be unrelated to the rate of a biological process (e.g. ageing, circadian rhythms, and molecular evolution); and (v) the theoretical foundation for the metabolic pacemaker view focuses only on the energetic control of biological processes, while ignoring the importance of informational control, as mediated by various genetic, cellular, and neuroendocrine regulatory systems. I argue that a comprehensive understanding of the pace of life must include how biological activities depend on both energy and information and their environmentally sensitive interaction. This conclusion is supported by extensive evidence showing that hormones and other regulatory factors and signalling systems coordinate the processes of growth, metabolism and food intake in adaptive ways that are responsive to an organism's internal and external conditions. Metabolic rate does not merely dictate growth rate, but is coadjusted with it. Energy and information use are intimately intertwined in living systems: biological signalling pathways both control and respond to the energetic state of an organism. This review also reveals that we have much to learn about the temporal structure of the pace of life. Are its component processes highly integrated and synchronized, or are they loosely connected and often discordant? And what causes the level of coordination that we see? These questions are of great theoretical and practical importance.     

Quantification of mRNA and protein and integration with protein turnover in a bacterium

Biological function and cellular responses to environmental perturbations are regulated by a complex interplay of DNA, RNA, proteins and metabolites inside cells. To understand these central processes in living systems at the molecular level, we integrated experimentally determined abundance data for mRNA, proteins, as well as individual protein half‐lives from the genome‐reduced bacterium Mycoplasma pneumoniae. We provide a fine‐grained, quantitative analysis of basic intracellular processes under various external conditions. Proteome composition changes in response to cellular perturbations reveal specific stress response strategies. The regulation of gene expression is largely decoupled from protein dynamics and translation efficiency has a higher regulatory impact on protein abundance than protein turnover. Stochastic simulations using in vivo data show how low translation efficiency and long protein half‐lives effectively reduce biological noise in gene expression. Protein abundances are regulated in functional units, such as complexes or pathways, and reflect cellular lifestyles. Our study provides a detailed integrative analysis of average cellular protein abundances and the dynamic interplay of mRNA and proteins, the central biomolecules of a cell.     

Autophagy in obesity and atherosclerosis: Interrelationships between cholesterol homeostasis,lipoprotein metabolism and autophagy in macrophages and other systems

The incidence of diseases characterized by a dysregulation of lipid metabolism such as obesity, diabetes and atherosclerosis is rising at alarming rates, driving research to uncover new therapies to manage dyslipidemias and resolve the metabolic syndrome conundrum. Autophagy and lipid homeostasis – both ancient cellular pathways – have seemingly co-evolved to share common regulatory elements, and autophagy has emerged as a prominent mechanism involved in the regulation of lipid metabolism. This review highlights recent findings on the role of autophagy in the regulation of cellular cholesterol homeostasis and lipoprotein metabolism, with special emphasis on macrophages. From modulation of inflammation to regulation of cellular cholesterol levels, a protective role for autophagy in atherosclerosis is emerging. The manipulation of autophagic activity represents a new possible therapeutic approach for the treatment complex metabolic disorders such as obesity and the metabolic syndrome.     

The interplay between host cellular and gut microbial metabolism in NAFLD development and prevention

Metabolism regulation centred on insulin resistance is increasingly important in nonalcoholic fatty liver disease (NAFLD). This review focuses on the interactions between the host cellular and gut microbial metabolism during the development of NAFLD. The cellular metabolism of essential nutrients, such as glucose, lipids and amino acids, is reconstructed with inflammation, immune mechanisms and oxidative stress, and these alterations modify the intestinal, hepatic and systemic environments, and regulate the composition and activity of gut microbes. Microbial metabolites, such as short-chain fatty acids, secondary bile acids, protein fermentation products, choline and ethanol and bacterial toxicants, such as lipopolysaccharides, peptidoglycans and bacterial DNA, play vital roles in NAFLD. The microbe–metabolite relationship is crucial for the modulation of intestinal microbial composition and metabolic activity. The intestinal microbiota and their metabolites participate in epithelial cell metabolism via a series of cell receptors and signalling pathways and remodel the metabolism of various cells in the liver via the gut–liver axis. Microbial metabolic manipulation is a promising strategy for NAFLD prevention, but larger-sampled clinical trials are required for future application.     

Energetic adaptations: Metabolic control of endocytic membrane traffic

Endocytic membrane traffic controls the access of myriad cell surface proteins to the extracellular milieu, and thus gates nutrient uptake, ion homeostasis, signaling, adhesion and migration. Coordination of the regulation of endocytic membrane traffic with a cell's metabolic needs represents an important facet of maintenance of homeostasis under variable conditions of nutrient availability and metabolic demand. Many studies have revealed intimate regulation of endocytic membrane traffic by metabolic cues, from the specific control of certain receptors or transporters, to broader adaptation or remodeling of the endocytic membrane network. We examine how metabolic sensors such as AMP‐activated protein kinase, mechanistic target of rapamycin complex 1 and hypoxia inducible factor 1 determine sufficiency of various metabolites, and in turn modulate cellular functions that includes control of endocytic membrane traffic. We also examine how certain metabolites can directly control endocytic traffic proteins, such as the regulation of specific protein glycosylation by limiting levels of uridine diphosphate N‐acetylglucosamine (UDP‐GlcNAc) produced by the hexosamine biosynthetic pathway. From these ideas emerge a growing appreciation that endocytic membrane traffic is orchestrated by many intrinsic signals derived from cell metabolism, allowing alignment of the functions of cell surface proteins with cellular metabolic requirements. Endocytic membrane traffic determines how cells interact with their environment, thus defining many aspects of nutrient uptake and energy consumption. We examine how intrinsic signals that reflect metabolic status of a cell regulate endocytic traffic of specific proteins, and, in some cases, exert broad control of endocytic membrane traffic phenomena. Hence, endocytic traffic is versatile and adaptable and can be modulated to meet the changing metabolic requirements of a cell.