AMPK-associated signaling to bridge the gap between fuel metabolism and hepatocyte viability

The adenosine monophosphate-activated protein kinase (AMPK) and p70 ribosomal S6 kinase-1 pathway may serve as a key signaling flow that regulates energy metabolism; thus, this pathway becomes an attractive target for the treatment of liver diseases that result from metabolic derangements. In addition, AMPK emerges as a kinase that controls the redox-state and mitochondrial function, whose activity may be modulated by antioxidants. A close link exists between fuel metabolism and mitochondrial biogenesis. The relationship between fuel metabolism and cell survival strongly implies the existence of a shared signaling network, by which hepatocytes respond to challenges of external stimuli. The AMPK pathway may belong to this network. A series of drugs and therapeutic candidates enable hepatocytes to protect mitochondria from radical stress and increase cell viability, which may be associated with the activation of AMPK, liver kinase B1, and other molecules or components. Consequently, the components downstream of AMPK may contribute to stabilizing mitochondrial membrane potential for hepatocyte survival. In this review, we discuss the role of the AMPK pathway in hepatic energy metabolism and hepatocyte viability. This information may help identify ways to prevent and/or treat hepatic diseases caused by the metabolic syndrome. Moreover, clinical drugs and experimental therapeutic candidates that directly or indirectly modulate the AMPK pathway in distinct manners are discussed here with particular emphasis on their effects on fuel metabolism and mitochondrial function.     

Liver enzymes,metabolomics and genome-wide association studies:From systems biology to the personalized medicine

For several decades,serum levels of alanine(ALT) and aspartate(AST) aminotransferases have been regarded as markers of liver injury,including a wide range of etiologies from viral hepatitis to fatty liver.The increasing worldwide prevalence of metabolic syndrome and cardiovascular disease revealed that transaminases are strong predictors of type 2 diabetes,coronary heart disease,atherothrombotic risk profile,and overall risk of metabolic disease.Therefore,it is plausible to suggest that aminotransferases are surrogate biomarkers of "liver metabolic functioning" beyond the classical concept of liver cellular damage,as their enzymatic activity might actually reflect key aspects of the physiology and pathophysiology of the liver function.In this study,we summarize the background information and recent findings on the biological role of ALT and AST,and review the knowledge gained from the application of genome-wide approaches and "omics" technologies that uncovered new concepts on the role of aminotransferases in human diseases and systemic regulation of metabolic functions.Prediction of biomolecular interactions between the candidate genes recently discovered to be associated with plasma concentrations of liver enzymes showed interesting interconnectivity nodes,which suggest that regulation of aminotransferase activity is a complex and highly regulated trait.Finally,links between aminotransferase genes and metabolites are explored to understand the genetic contributions to the metabolic diversity.     

Role of sirtuins in ischemia-reperfusion injury

Ischemia-reperfusion injury(IRI)remains an unresolved and complicated situation in clinical practice,especially in the case of organ transplantation.Several factors contribute to its complexity;the depletion of energy during ischemia and the induction of oxidative stress during reperfusion initiate a cascade of pathways that lead to cell death and finally to severe organ injury.Recently,the sirtuin family of nicotinamide adenine dinucleotide-dependent deacetylases has gained increasing attention from researchers,due to their involvement in the modulation of a wide variety of cellular functions.There are seven mammalian sirtuins and,among them,the nuclear/cytoplasmic sirtuin 1(SIRT1)and the mitochondrial sirtuin 3(SIRT3)are ubiquitously expressed in many tissue types.Sirtuins are known to play major roles in protecting against cellular stress and in controlling metabolic pathways,which are key processes during IRI.In this review,we mainly focus on SIRT1 and SIRT3 and examine their role in modulating pathways against energy depletion during ischemia and their involvement in oxidative stress,apoptosis,microcirculatory stress and inflammation during reperfusion.We present evidence of the beneficial effects of sirtuins against IRI and emphasize the importance of developing new strategies by enhancing their action.     

Obesity and colorectal cancer:Role of adipokines in tumor initiation and progression

Obesity-associated diseases account for a large portion of public health challenges.Among obesity-related disorders,a direct and independent relationship has been ascertained for colorectal cancer(CRC).The evidence that adipocyte hypertrophy and excessive adipose tissue accumulation(mainly visceral)can promote pathogenic adipocyte and adipose tissue-related diseases,has led to formulate the concept of"adiposopathy",defined as adipocyte and adipose tissue dysfunction that contributes to metabolic syndrome.Adipose tissue can,indeed,be regarded as an important and highly active player of the innate immune response,in which cytokine/adipokine secretion is responsible for a paracrine loop between adipocytes and macrophages,thus contributing to the systemic chronic low-grade inflammation associated with visceral obesity,which represents a favorable niche for tumor development.The adipocyte itself participates as a central mediator of this inflammatory response in obese individuals by secreting hormones,growth factors and proinflammatory cytokines,which are of particular relevance for the pathogenesis of CRC.Among adipocyte-secreted hormones,the most relevant to colorectal tumorigenesis are adiponectin,leptin,resistin and ghrelin.All these molecules have been involved in cell growth and proliferation,as well as tumor angiogenesis and it has been demonstrated that their expression changes from normal colonic mucosa to adenoma and adenocarcinoma,suggesting their involvement in multistep colorectal carcinogenesis.These findings have led to the hypothesis that an unfavorable adipokine profile,with a reduction of those with an anti-inflammatory and anti-cancerous activity,might serve as a prognostic factor in CRC patients and that adipokines or their analogues/antagonists might become useful agents in the management or chemoprevention of CRC.     

Interplay between post-translational cyclooxygenase-2 modifications and the metabolic and proteomic profile in a colorectal cancer cohort

BACKGROUND Colorectal cancer(CRC) is the second most common cause of cancer death worldwide. It is broadly described that cyclooxygenase-2(COX-2) is mainly overexpressed in CRC but less is known regarding post-translational modifications of this enzyme that may regulate its activity, intracellular localization and stability. Since metabolic and proteomic profile analysis is essential for cancer prognosis and diagnosis, our hypothesis is that the analysis of correlations between these specific parameters and COX-2 state in tumors of a high number of CRC patients could be useful for the understanding of the basis of this cancer in humans.AIM To analyze COX-2 regulation in colorectal cancer and to perform a detailed analysis of their metabolic and proteomic profile.METHODS Biopsies from both healthy and pathological colorectal tissues were taken under informed consent from patients during standard colonoscopy procedure in the University Hospital of Bellvitge(Barcelona, Spain) and Germans Trias i Pujol University Hospital(Campus Can Ruti)(Barcelona, Spain). Western blot analysis was used to determine COX-2 levels. Deglycosylation assays were performed in both cells and tumor samples incubating each sample with peptide N-glycosidase F(PNGase F). Prostaglandin E2(PGE2) levels were determined using a specific ELISA. 1 H high resolution magic angle spinning(HRMAS) analysis was performed using a Bruker AVIII 500 MHz spectrometer and proteomic analysis was performed in a nano-liquid chromatography-tandem mass spectrometer(nano LC-MS/MS) using a QExactive HF orbitrap MS.RESULTS Our data show that COX-2 has a differential expression profile in tumor tissue of CRC patients vs the adjacent non-tumor area, which correspond to a glycosylated and less active state of the protein. This fact was associated to a lesser PGE2 production in tumors. These results were corroborated in vitro performing deglycosylation assays in HT29 cell line where COX-2 protein profile was modified after PNGase F incubation, showing higher PGE2 levels. Moreover,HRMAS analysis indicated that tumor tissue has altered metabolic features vs non-tumor counterparts, presenting increased levels of certain metabolites such as taurine and phosphocholine and lower levels of lactate. In proteomic experiments, we detected an enlarged number of proteins in tumors that are mainly implicated in basic biological functions like mitochondrial activity,DNA/RNA processing, vesicular trafficking, metabolism, cytoskeleton and splicing.CONCLUSION In our colorectal cancer cohort, tumor tissue presents a differential COX-2 expression pattern with lower enzymatic activity that can be related to an altered metabolic and proteomic profile.     

Non-alcoholic fatty liver disease and psoriasis: So far,so near

Psoriasis is a chronic inflammatory immune-mediated skin diseases which is frequently associated to comorbidities. Non-alcoholic fatty liver disease(NAFLD) is defined as an excessive accumulation of triglycerides in hepatocytes and includes a wide spectrum of liver conditions ranging from relatively benign steatosis to non-alcoholic steatohepatitis with fatty infiltration and lobular inflammation and to cirrhosis and endstage liver disease. Actually, psoriasis is considered a systemic diseases associated to comorbidities, as metabolic syndrome and NAFLD is seen the hepatic manifestation of the metabolic syndrome. The possible link between psoriasis, obesity and metabolic syndrome, which are known risk factors for NAFLD has beenrecently documented focusing in the crucial role of the adipose tissue in the development of the inflammatory background sharing by the above entities. According to recent data, patients with psoriasis show a greater prevalence of NAFLD and metabolic syndrome than the general population. Moreover, patients with NAFLD and psoriasis are at higher risk of severe liver fibrosis than those with NAFLD and without psoriasis. The link between these pathological conditions appears to be a chronic low-grade inflammatory status. The aim of this review is to focus on the multiple aspects linking NAFLD and psoriasis, only apparently far diseases.     

New techniques in the tissue diagnosis of gastrointestinal neuromuscular diseases

Gastrointestinal neuromuscular diseases are a clinically heterogeneous group of disorders of children and adults in which symptoms are presumed or proven to arise as a result of neuromuscular （including interstitial cell of Cajal） dysfunction. Common to most of these diseases are symptoms of impaired motor activity which manifest as slowed or obstructed transit with or without evidence of transient or persistent radiological visceral dilatation. A variety of histopathological techniques and allied investigations are being increasingly applied to tissue biopsies from such patients. This review outlines some of the more recent advances in this field, particularly in the most contentious area of small bowel disease manifesting as intestinal pseudo-obstruction.     

Role of the tissue microenvironment as a therapeutic target in hepatocellular carcinoma

Hepatocellular carcinoma is difficult to treat,primarilybecause the underlying molecular mechanisms drivingclinical outcome are still poorly understood.Growingevidence suggests that the tissue microenvironmenthas a role in the biological behavior of the tumor.Themain clinical issue is to identify the best target fortherapeutic approaches.Here,we discuss the hypothesis that the entire tissue microenvironment might beconsidered as a biological target.However,the tissuemicroenvironment consists of several cellular and biochemical components,each of which displays a distinctbiological activity.We discuss the major components ofthis environment and consider how they may interactto promote tumor/host crosstalk.     

Somatic mtDNA mutations and aging--facts and fancies

Mitochondria play a critical role in the life of the cell as they control their metabolic rate, energy production and cell death. Mitochondria have long been appreciated as causative to aging. The age-associated respiratory chain deficiency is typically unevenly distributed and affects only a subset of cells in various human tissues, such as heart, skeletal muscle, colonic crypts and neurons. Studies of mtDNA mutator mice has provided the first direct evidence that accelerating the mtDNA mutation rate can result in premature aging, consistent with the view that loss of mitochondrial function is a major causal factor in aging. New, controversial data have arisen from the studies on molecular mechanisms that drive premature aging in mtDNA mutator mice. Our results suggest that the accumulation of high levels of mtDNA point mutations, causing amino acid substitutions, combined with their clonal expansion is probably the main driving force behind premature aging in mtDNA mutator mice.     

Mitochondrial biogenesis and fragmentation as regulators of protein degradation in striated muscles

Mitochondria are dynamic organelles which adapt their morphology by fusion and fission events to the bioenergetic requirements of the cell. Cardiac and skeletal muscles are tissues with high energy demand and mitochondrial plasticity plays a key role in the homeostasis of these cells. Indeed, alterations in mitochondrial morphology, distribution and function are common features in catabolic conditions. Moreover, dysregulation of mitochondrial dynamics affects the signaling pathways that regulate muscle mass. This review discusses the recent findings of the role of mitochondrial fusion/fission and mitophagy in the control of proteolytic pathways. This article is part of a special issue entitled "Focus on Cardiac Metabolism".     

Molecular mechanisms mediating mitochondrial dynamics and mitophagy and their functional roles in the cardiovascular system

Mitochondria are essential organelles that produce the cellular energy source, ATP. Dysfunctional mitochondria are involved in the pathophysiology of heart disease, which is associated with reduced levels of ATP and excessive production of reactive oxygen species. Mitochondria are dynamic organelles that change their morphology through fission and fusion in order to maintain their function. Fusion connects neighboring depolarized mitochondria and mixes their contents to maintain membrane potential. In contrast, fission segregates damaged mitochondria from intact ones, where the damaged part of mitochondria is subjected to mitophagy whereas the intact part to fusion. It is generally believed that mitochondrial fusion is beneficial for the heart, especially under stress conditions, because it consolidates the mitochondria's ability to supply energy. However, both excessive fusion and insufficient fission disrupt the mitochondrial quality control mechanism and potentiate cell death. In this review, we discuss the role of mitochondrial dynamics and mitophagy in the heart and the cardiomyocytes therein, with a focus on their roles in cardiovascular disease. This article is part of a Special Issue entitled "Mitochondria: From Basic Mitochondrial Biology to Cardiovascular Disease".     

Mitochondrial dysfunction in metabolism and ageing: shared mechanisms and outcomes?

Mitochondria are key in the metabolism of aerobic organisms and in ageing progression and age-related diseases. Mitochondria are essential for obtaining ATP from glucose and fatty acids but also in many other essential functions in cells including aminoacids metabolism, pyridine synthesis, phospholipid modifications and calcium regulation. On the other hand, the activity of mitochondria is also the principal source of reactive oxygen species in cells. Ageing and chronic age-related diseases are associated with the deregulation of cell metabolism and dysfunction of mitochondria. Cell metabolism is controlled by three major nutritional sensors: mTOR, AMPK and Sirtuins. These factors control mitochondrial biogenesis and dynamics by regulating fusion, fission and turnover through mito- and autophagy. A complex interaction between the activity of these nutritional sensors, mitochondrial biogenesis rate and dynamics exists and affect ageing, age-related diseases including metabolic disease. Further, mitochondria maintain a constant communication with nucleus modulating gene expression and modifying epigenetics. In this review we highlight the importance of mitochondria in ageing and the repercussion in the progression of age-related diseases and metabolic disease.     

Characterization of the role of nitric oxide and its clinical applications

Nitric oxide (NO) has long been known as endothelium-derived relaxing factor. It is a vasodilator, modulating vascular tone, blood pressure and hemodynamics, a role exploited by nitrate donor therapy for angina, heart failure, pulmonary hypertension and erectile dysfunction. In addition, its powerful antioxidant, anti-inflammatory and antithrombotic actions are antiatherogenic with antiatherothrombotic impact. NO signaling modulates skeletal muscle and myocardial contractility and metabolism and is intimately linked with insulin signaling. Vascular and muscle NO signaling coordinate skeletal muscle and myocardial energy demand with supply and are critical for both carbohydrate and fatty acid total-body homeostasis. NO signaling in mitochondria underlies much of NO's metabolic effect, which, at low physiologic levels, links cellular energy demand with mitochondrial energy supply, while beneficially affecting mitochondrial oxidative stress and calcium handling. Mitochondria are also the site for the life-threatening deleterious effects arising from inflammation-related excessive NO levels. NO-deficient states are characterized by cell senescence, oxidative stress, inflammation, endothelial dysfunction, vascular disease, insulin resistance and type 2 diabetes mellitus. NO-enriching therapy would be expected to be of benefit not only for its hemodynamic but also for its metabolic impact. In contrast, strategies are needed to curtail excessive NO in states such as septic shock.     

Mitochondrial adenine nucleotide transport and cardioprotection

Mitochondria are highly metabolically active cell organelles that not only act as the powerhouse of the cell by supplying energy through ATP production, but also play a destructive role by initiating cell death pathways. Growing evidence recognizes that mitochondrial dysfunction is one of the major causes of cardiovascular disease. Under de-energized conditions, slowing of adenine nucleotide transport in and out of the mitochondria significantly attenuates myocardial ischemia-reperfusion injury. The purpose of this review is to elaborate on and update the mechanistic pathways which may explain how altered adenine nucleotide transport can influence cardiovascular function. This article is part of a Special Issue entitled "Local Signaling in Myocytes".     

Mitochondrial Biogenesis and Fragmentation as Regulators of Muscle Protein Degradation

Mitochondria form a dynamic network that rapidly adapts to cellular energy demand. This adaptation is particularly important in skeletal muscle because of its high metabolic rate. Indeed, muscle energy level is one of the cellular checkpoints that lead either to sustained protein synthesis and growth or protein breakdown and atrophy. Mitochondrial function is affected by changes in shape, number, and localization. The dynamics that control the mitochondrial network, such as biogenesis and fusion, or fragmentation and fission, ultimately affect the signaling pathways that regulate muscle mass. Regular exercise and healthy muscles are important players in the metabolic control of human body. Indeed, a sedentary lifestyle is detrimental for muscle function and is one of the major causes of metabolic disorders such as obesity and diabetes. This article reviews the rapid progress made in the past few years regarding the role of mitochondria in the control of proteolytic systems and in the loss of muscle mass and function.     

线粒体动力学和线粒体自噬与心血管疾病的研究进展

线粒体是一种动态的细胞器,通过响应各种代谢和环境的信号,分裂和融合改变其形态和结构,从而维持细胞的正常功能.它们短暂而快速的形态变化对于细胞周期、免疫、凋亡和线粒体质量控制等许多复杂的细胞过程至关重要.线粒体自噬与线粒体质量控制密切相关,通过将受损的功能障碍的线粒体转运到溶酶体进行降解,促进心肌细胞受损线粒体的更新,并...     

Emerging mitochondrial signaling mechanisms in physiology,aging processes,and as drug targets

Advances in research on mitochondria have elucidated their importance in cell survival and cell death regulation in addition to their function in energy production. Mitochondria are further implicated in various metabolic and aging-related diseases, which are now assumed to be caused by misregulation of physiological systems rather than pure accumulation of oxidative damage. Thus, the signaling mechanisms within mitochondria and between the organelle and its environment have gained interest as potential drug targets. Emerging mitochondrial signaling systems with potential for exploiting them for therapeutic intervention include, among others, the NAD⁺-dependent protein deacetylases of the Sirtuin family, the redox enzyme p66^Shc, and enzymes of the cyclic adenosine monophosphate (cAMP) signaling pathways. Here, we discuss functions of these signaling systems in mitochondria, their roles in aging processes and disease, and their potential to serve as therapeutic targets.     

Impact of high glucose and transforming growth factor-β on bioenergetic profiles in podocytes

Diabetic nephropathy is the most common cause of chronic renal failure in industrialized countries. Depletion of podocytes plays an important role in the progression of diabetic glomerulopathy. Various factors in the diabetic milieu lead to serious podocyte stress driving the cells toward cell cycle arrest (p27(Kip1)), hypertrophy, detachment, and apoptosis. Mitochondria are responsible for oxidative phosphorylation and energy supply in podocytes. Recent studies indicated that mitochondrial dysfunction is a key factor in diabetic nephropathy. In the present study, we investigated metabolic profiles of podocytes under diabetic conditions. We examined oxygen consumption rates (OCRs) and oxidative phosphorylation complex activities in murine podocytes. Cells were exposed to high glucose for 48 hours, cultured for 10 passages under high-glucose conditions (30 mmol/L), or incubated with transforming growth factor-β (5 ng/mL) for 24 hours. After prolonged exposure to high glucose, podocytes showed a significantly increased OCR at baseline and also a higher OCR after addition of oligomycin, indicating significant changes in mitochondrial energy metabolism. Higher OCRs after inhibition of respiration by rotenone also indicated changes in nonmitochondrial respiration. Podocytes stimulated with a proapoptotic concentration of transforming growth factor-β displayed similar bioenergetic profiles, even with decreased citrate synthase activity. In all tested conditions, we found a higher cellular nicotinamide adenine dinucleotide content and changes in activities of respiratory chain complexes. In summary, we provide for the first time evidence that key factors of the diabetic milieu induce changes in glucose metabolism and mitochondrial function in podocytes.