Autophagy and aging—importance of amino acid levels

Identifying non-muscle-invasive and muscle-invasive bladder cancer based on blood serum surface-enhanced Raman spectroscopy

The assessment of the muscle invasion of bladder cancer typically plays a crucial role in therapeutic decision-making and has significant impacts on the recurrence rate and survival rate. Although histopathology is sufficiently accurate and usually served as the gold standard for bladder cancer diagnosis, it is invasive, time-consuming, and requires intensive sample preparation by a well-trained pathologist to achieve an optimal diagnosis. Therefore, a fast and noninvasive method to accurately identify non-muscle-invasive bladder cancer (NMIBC) and muscle-invasive bladder cancer (MIBC) is in demand. In this study, the SERS technique combined with the PLS-LDA method based on a small amount of blood serum samples is employed to distinguish healthy volunteers, NMIBC, and MIBC patients. According to the results, the overall diagnostic accuracy is 93.3%. The diagnostic accuracies are 97.8% and 93.2% for healthy versus bladder cancer groups and NMIBC versus MIBC groups, respectively. Therefore, the proposed method has demonstrated excellent performance on accurately identifying muscle invasion of bladder cancer, which can assist timely diagnosis and proper treatment for bladder cancer patients.

Food Reduction in Avicenna's View and Related Principles in Classical Medicine

Context

Traditional Iranian medicine (TIM) is a rich and valuable school of thought that believes medications are not the only effective approach for the treatment of diseases but that nutrition is also important.

Evidence Acquisition

Our study includes two parts; the first is a book review of the Canon of Medicine by Avicenna (10th and 11th centuries), in which we focus on finding and understanding Avicenna’s point of view. In the second part, we searched for “food reduction” as a key word from 2000 to 2015 in databases such as Google Scholar, PubMed, Copernicus, DOAJ, EBSCO-CINAHL, and the Iranian search database Iranmedex for principles of food reduction in classical medicine.

Results

The main methods of treatment in traditional medicine include changes in lifestyle, especially diet, the use of medications, and the use of manipulation methods. For diet, the individual may be prohibited from eating or food amounts may be decreased or increased. Centuries ago, Avicenna was making use of methods of food reduction as an important therapeutic approach in the treatment of diseases. According to him, food reduction, to the extent that it does not cause energy loss helps to cure disease. Avicenna has proposed food reduction as an aid to treating a variety of ailments such as headaches and reflux.

Conclusions

Today, a variety of basic and clinical research has shown that food reduction or calorie restriction to a standard level can effectively prevent and treat a variety of diseases such as neoplasms, diabetes, and kidney disease. Practical principles explained by traditional Iranian medicine, in particular Avicenna, could open important and quite uncomplicated strategies for the prevention and treatment of diseases.

Autophagy and leucine promote chronological longevity and respiration proficiency during calorie restriction in yeast

We have previously shown that autophagy is required for chronological longevity in the budding yeast Saccharomyces cerevisiae. Here we examine the requirements for autophagy during extension of chronological life span (CLS) by calorie restriction (CR). We find that autophagy is upregulated by two CR interventions that extend CLS: water wash CR and low glucose CR. Autophagy is required for full extension of CLS during water wash CR under all growth conditions tested. In contrast, autophagy was not uniformly required for full extension of CLS during low glucose CR, depending on the atg allele and strain genetic background. Leucine status influenced CLS during CR. Eliminating the leucine requirement in yeast strains or adding supplemental leucine to growth media extended CLS during CR. In addition, we observed that both water wash and low glucose CR promote mitochondrial respiration proficiency during aging of autophagy-deficient yeast. In general, the extension of CLS by water wash or low glucose CR was inversely related to respiration deficiency in autophagy-deficient cells. Also, autophagy is required for full extension of CLS under non-CR conditions in buffered media, suggesting that extension of CLS during CR is not solely due to reduced medium acidity. Thus, our findings show that autophagy is: (1) induced by CR, (2) required for full extension of CLS by CR in most cases (depending on atg allele, strain, and leucine availability) and, (3) promotes mitochondrial respiration proficiency during aging under CR conditions.

Metabolomic profiling in colorectal cancer: opportunities for personalized medicine

Colorectal cancer (CRC) is one of the most common types of cancer in the world, with high prevalence and mortality. Understanding the alterations of cancer metabolism and identifying reliable biomarkers would facilitate the development of novel technologies of CRC screening and early diagnosis, as well as new approaches to providing personalized medicine. Metabolomics, as an emerging molecular phenotyping approach, provides a clinical platform technology with an unprecedented amount of metabolic readout information, which is ideal for theranostic biomarker discovery. Metabolic signatures can link the unique pathophysiological states of patients to personalized health monitoring and intervention strategies. This article presents an overview of the metabolomic studies of CRC with a focus on recent advances in the biomarker discovery in serum, urine, fecal water and tissue samples for cancer diagnosis. The development and application of metabolomics towards personalized medicine, including early diagnosis, cancer staging, treatment and drug discovery are also discussed.

Maintenance of mitochondrial morphology by autophagy and its role in high glucose effects on chronological lifespan of Saccharomyces cerevisiae

In Saccharomyces cerevisiae, mitochondrial morphology changes when cells are shifted between nonfermentative and fermentative carbon sources. Here, we show that cells of S. cerevisiae grown in different glucose concentrations display different mitochondrial morphologies. The morphology of mitochondria in the cells growing in 0.5% glucose was similar to that of mitochondria in respiring cells. However, the mitochondria of cells growing in higher glucose concentrations (2% and 4%) became fragmented after growth in these media, due to the production of acetic acid; however, the fragmentation was not due to intracellular acidification. From a screen of mutants involved in sensing and utilizing nutrients, cells lacking TOR1 had reduced mitochondrial fragmentation, and autophagy was found to be essential for this reduction. Mitochondrial fragmentation in cells grown in high glucose was reversible by transferring them into conditioned medium from a culture grown on 0.5% glucose. Similarly, the chronological lifespan of cells grown in high glucose medium was reduced, and this phenotype could be reversed when cells were transferred to low glucose conditioned medium. These data indicate that chronological lifespan seems correlated with mitochondrial morphology of yeast cells and that both phenotypes can be influenced by factors from conditioned medium of cultures grown in low glucose medium.

Oxidative stresses and ageing

Oxidative damage to cellular constituents has frequently been associated with aging in a wide range of organisms. The power of yeast genetics and biochemistry has provided the opportunity to analyse in some detail how reactive oxygen and nitrogen species arise in cells, how cells respond to the damage that these reactive species cause, and to begin to dissect how these species may be involved in the ageing process. This chapter reviews the major sources of reactive oxygen species that occur in yeast cells, the damage they cause and how cells sense and respond to this damage.

Morphological and biochemical studies on aging and autophagy

To maintain health in the elderly is a crucial objective for modern medicine that involves both basic and clinical researches. Autophagy is a fundamental auto-cannibalizing process that preserves cellular homeostasis and, if altered, either by excess or defect, greatly changes cell fate and can result in incapacitating human diseases. Efficient autophagy may prolong lifespan, but unfortunately this process becomes less efficient with age. The present review is focused on the close relationship between autophagy and age-related disorders in different tissues/organs and in transgenic animal models. In particular, it comments on the up to date literature on mechanisms responsible for age-related impairment of autophagy. Moreover, before discussing about these mechanisms, it is necessary to describe the metabolic autophagic regulation of autophagy and the proteins involved in this process. At the end, these data would summarize the autophagic link with aging process, as important tools in the future biogerontology scenario.

Autophagy induction by tetrahydrobiopterin deficiency

Tetrahydrobiopterin (BH₄) deficiency is a genetic disorder associated with a variety of metabolic syndromes such as phenylketonuria (PKU). In this article, the signaling pathway by which BH₄ deficiency inactivates mTORC1 leading to the activation of the autophagic pathway was studied utilizing BH₄-deficient Spr(-/-) mice generated by the knockout of the gene encoding sepiapterin reductase (SR) catalyzing BH₄ synthesis. We found that mTORC1 signaling was inactivated and autophagic pathway was activated in tissues from Spr(-/-) mice. This study demonstrates that tyrosine deficiency causes mTORC1 inactivation and subsequent activation of autophagic pathway in Spr(-/-) mice. Therapeutic tyrosine diet completely rescued dwarfism and mTORC1 inhibition but inactivated autophagic pathway in Spr(-/-) mice. Tyrosine-dependent inactivation of mTORC1 was further supported by mTORC1 inactivation in Pah(enu2) mouse model lacking phenylalanine hydroxylase (Pah). NIH3T3 cells grown under the condition of tyrosine restriction exhibited autophagy induction. However, mTORC1 activation by RhebQ64L, a positive regulator of mTORC1, inactivated autophagic pathway in NIH3T3 cells under tyrosine-deficient conditions. In addition, this study first documents mTORC1 inactivation and autophagy induction in PKU patients with BH₄ deficiency.

A microarray-based genetic screen for yeast chronological aging factors

Model organisms have played an important role in the elucidation of multiple genes and cellular processes that regulate aging. In this study we utilized the budding yeast, Saccharomyces cerevisiae, in a large-scale screen for genes that function in the regulation of chronological lifespan, which is defined by the number of days that non-dividing cells remain viable. A pooled collection of viable haploid gene deletion mutants, each tagged with unique identifying DNA “bar-code” sequences was chronologically aged in liquid culture. Viable mutants in the aging population were selected at several time points and then detected using a microarray DNA hybridization technique that quantifies abundance of the barcode tags. Multiple short- and long-lived mutants were identified using this approach. Among the confirmed short-lived mutants were those defective for autophagy, indicating a key requirement for the recycling of cellular organelles in longevity. Defects in autophagy also prevented lifespan extension induced by limitation of amino acids in the growth media. Among the confirmed long-lived mutants were those defective in the highly conserved de novo purine biosynthesis pathway (the ADE genes), which ultimately produces IMP and AMP. Blocking this pathway extended lifespan to the same degree as calorie (glucose) restriction. A recently discovered cell-extrinsic mechanism of chronological aging involving acetic acid secretion and toxicity was suppressed in a long-lived ade4Δ mutant and exacerbated by a short-lived atg16Δ autophagy mutant. The identification of multiple novel effectors of yeast chronological lifespan will greatly aid in the elucidation of mechanisms that cells and organisms utilize in slowing down the aging process.

The aging process is associated with the onset of several age-associated diseases including diabetes and cancer. In rodent model systems, the dietary regimen known as caloric restriction (CR) is known to delay or prevent these diseases and to extend lifespan. As a result, there is a great deal of interest in understanding the mechanisms by which CR functions. The budding yeast, Saccharomyces cerevisiae, has proven to be an effective model for the analysis of genes and cellular pathways that contribute to the regulation of aging. In this study we have performed a microarray-based genetic screen in yeast that identified short- and long-lived mutants from a population that contained each of the viable haploid gene deletion mutants from the yeast gene knockout collection that were pooled together. Using such an approach, we were able to identify genes from several pathways that had not been previously implicated in aging, including some that appear to contribute to the CR effect induced by restriction of either amino acids or sugar. These results are expected to provide new groundwork for future mechanistic aging studies in more complex organisms.

Autophagy and amino acid homeostasis are required for chronological longevity in Saccharomyces cerevisiae

Following cessation of growth, yeast cells remain viable in a nondividing state for a period of time known as the chronological lifespan (CLS). Autophagy is a degradative process responsible for amino acid recycling in response to nitrogen starvation and amino acid limitation. We have investigated the role of autophagy during chronological aging of yeast grown in glucose minimal media containing different supplemental essential and nonessential amino acids. Deletion of ATG1 or ATG7, both of which are required for autophagy, reduced CLS, whereas deletion of ATG11, which is required for selective targeting of cellular components to the vacuole for degradation, did not reduce CLS. The nonessential amino acids isoleucine and valine, and the essential amino acid leucine, extended CLS in autophagy-deficient as well as autophagy-competent yeast. This extension was suppressed by constitutive expression of GCN4, which encodes a transcriptional regulator of general amino acid control (GAAC). Consistent with this, GCN4 expression was reduced by isoleucine and valine. Furthermore, elimination of the leucine requirement extended CLS and prevented the effects of constitutive expression of GCN4. Interestingly, deletion of LEU3, a GAAC target gene encoding a transcriptional regulator of branched side chain amino acid synthesis, dramatically increased CLS in the absence of amino acid supplements. In general, this indicates that activation of GAAC reduces CLS whereas suppression of GAAC extends CLS in minimal medium. These findings demonstrate important roles for autophagy and amino acid homeostasis in determining CLS in yeast.

Physiological functions of autophagy

The field of autophagy research has advanced rapidly in recent years, with important discoveries made in relation to both molecular mechanisms and physiological functions. Initially, autophagy was thought to be primarily a response to starvation. Although this might be true in lower eukaryotes, this catabolic process exerts various physiological functions in higher eukaryotes. This review summarizes the physiological roles of autophagy in amino acid pool maintenance, intracellular quality control, development, cell death, tumor suppression and anti-aging.

Aberrant insulin receptor signaling and amino acid homeostasis as a major cause of oxidative stress in aging

The mechanisms leading to the increase in free radical-derived oxidative stress in "normal aging" remains obscure. Here we present our perspective on studies from different fields that reveal a previously unnoticed vicious cycle of oxidative stress. The plasma cysteine concentrations during starvation in the night and early morning hours (the postabsorptive state) decreases with age. This decrease is associated with a decrease in tissue concentrations of the cysteine derivative and quantitatively important antioxidant glutathione. The decrease in cysteine reflects changes in the autophagic protein catabolism that normally ensures free amino acid homeostasis during starvation. Autophagy is negatively regulated by the insulin receptor signaling cascade that is enhanced by oxidative stress in the absence of insulin. This synopsis of seemingly unrelated processes reveals a novel mechanism of progressive oxidative stress in which decreasing antioxidant concentrations and increasing basal (postabsorptive) insulin receptor signaling activity compromise not only the autophagic protein catabolism but also the activity of FOXO transcription factors (i.e., two functions that were found to have an impact on lifespan in several animal models of aging). In addition, the aging-related decrease in glutathione levels is likely to facilitate certain "secondary" disease-related mechanisms of oxidative stress. Studies on cysteine supplementation show therapeutic promise.

Renal ageing: changes in the cellular mechanism of energy metabolism and oxidant handling

The age-dependent changes in the kidney are often debilitating, can be life-threatening and are a significant cause of increasing health costs worldwide. Excessive fibrosis, a general lack of regenerative ability and an increase in apoptosis in cells that determine healthy renal function work together to cause chronic kidney disease. This review provides information on the molecules and mechanisms that determine the age-dependent effects in the kidney, and in particular, the effects of cellular metabolism and oxidant handling on the ageing kidney. With a better understanding of the influence of ageing on the structural and functional alterations that occur, new targeted therapies may be developed to minimize renal damage and promote health in the elderly.

Apoptosis effector mechanisms: a requiem performed in different keys

Apoptosis is the regulated form of cell death utilized by metazoans to remove unneeded, damaged, or potentially deleterious cells. Certain manifestations of apoptosis may be associated with the proteolytic activity of caspases. These changes are often held as hallmarks of apoptosis in dying cells. Consequently, many regard caspases as the central effectors or executioners of apoptosis. However, this "caspase-centric" paradigm of apoptotic cell death does not appear to be as universal as once believed. In fact, during apoptosis the efficacy of caspases may be highly dependent on the cytotoxic stimulus as well as genetic and epigenetic factors. An ever-increasing number of studies strongly suggest that there are effectors in addition to caspases, which are important in generating apoptotic signatures in dying cells. These seemingly caspase-independent effectors may represent evolutionarily redundant or failsafe mechanisms for apoptotic cell elimination. In this review, we will discuss the molecular regulation of caspases and various caspase-independent effectors of apoptosis, describe the potential context and/or limitations of these mechanisms, and explore why the understanding of these processes may have relevance in cancer where treatment is believed to engage apoptosis to destroy tumor cells.

Autophagy preceded apoptosis in oridonin-treated human breast cancer MCF-7 cells

Recent studies have shown that MCF-7 cells undergo autophagy under some conditions, such as tamoxifen treatment and starvation. In this study, we investigated autophagy in MCF-7 cells under oridonin treatment and further examined the relationship between autophagy and apoptosis. After 3-MA (the specific inhibitor of autophagy) pre-culture, MCF-7 cells were exposed to oridonin, and the growth inhibitory ratio, morphologic changes, DNA fragmentation, proteins expression, autophagic ratio and apoptotic ratio were evaluated. Oridonin inhibited the proliferation of MCF-7 cells and induced autophagy in vitro. MDC (a specific dye for autophagosome) recruitment and typical apoptotic features, including apoptotic bodies, membrane blebbing as well as nuclear condensation, were induced by oridonin. Oridonin downregulated the phosphorylation of ERK, whereas those of JNK and P38 kinase were upregulated. In the condition of oridonin treatment, 3-MA significantly reduced the autophagic level, and the apoptotic cell ratio was also declined. Furthermore, combined treatment with oridonin and 3-MA upregulated ERK phosphorylation and downregulated JNK and P38 kinases phosphorylation compared with oridonin alone treatment groups, indicating that autophagy facilitated apoptosis in oridonin-induced MCF-7 cells. In addition, 3-MA application downregulated DNA ladder and Bax expression but upregulated Bcl-2 expression, compared with oridonin alone treatment. Taken together, oridonin simultaneously induced MCF-7 cells both apoptosis and autophagy, and in this settings, inhibition of autophagy induced lowered apoptotic level, therefore, autophagy participated in upregulation of apoptosis.

Oxidative stress and aberrant signaling in aging and cognitive decline

Brain aging is associated with a progressive imbalance between antioxidant defenses and intracellular concentrations of reactive oxygen species (ROS) as exemplified by increases in products of lipid peroxidation, protein oxidation, and DNA oxidation. Oxidative conditions cause not only structural damage but also changes in the set points of redox-sensitive signaling processes including the insulin receptor signaling pathway. In the absence of insulin, the otherwise low insulin receptor signaling is strongly enhanced by oxidative conditions. Autophagic proteolysis and sirtuin activity, in turn, are downregulated by the insulin signaling pathway, and impaired autophagic activity has been associated with neurodegeneration. In genetic studies, impairment of insulin receptor signaling causes spectacular lifespan extension in nematodes, fruit flies, and mice. The predicted effects of age-related oxidative stress on sirtuins and autophagic activity and the corresponding effects of antioxidants remain to be tested experimentally. However, several correlates of aging have been shown to be ameliorated by antioxidants. Oxidative damage to mitochondrial DNA and the electron transport chain, perturbations in brain iron and calcium homeostasis, and changes in plasma cysteine homeostasis may altogether represent causes and consequences of increased oxidative stress. Aging and cognitive decline thus appear to involve changes at multiple nodes within a complex regulatory network.

Dietary restriction in Drosophila: delayed aging or experimental artefact?

Lifespan can be extended by reduction of dietary intake. This practice is referred to as dietary restriction (DR), and extension of lifespan by DR is evolutionarily conserved in taxonomically diverse organisms including yeast, invertebrates, and mammals. Although these two often-stated facts carry the implication that the mechanisms of DR are also evolutionarily conserved, extension of lifespan could be a case of evolutionary convergence, with different underlying mechanisms in different taxa. Furthermore, extension of lifespan by different methods of DR in the same organism may operate through different mechanisms. These topics remain unresolved because of the very fact that the mechanisms of DR are unknown. Given these uncertainties, it is essential that work on the mechanisms of DR is not clouded by imprecise descriptions of methods or by technical problems. Here we review the recent literature on DR in Drosophila to point out some methodological issues that can obscure mechanistic interpretations. We also indicate some experiments that could be performed to determine if DR in Drosophila operates through similar mechanisms to the process in rodents.

Lipid oxidation and autophagy in yeast

Autophagy, a process involved in the degradation and the recycling of long-lived proteins and organelles to survive nitrogen starvation, is generally non-selective. However, recent data suggest that selective forms of autophagy exist, that are able to specifically target several organelles, including mitochondria. Conversely, mitochondrial alterations could trigger autophagy. Such a selective form of autophagy might be involved in the elimination of damaged mitochondria. We reported previously that, mitochondria were early targets of rapamycin-induced autophagy. Here we report that rapamycin-induced autophagy is accompanied by the early production of reactive oxygen species and by the early oxidation of mitochondrial lipid. Inhibition of these oxidative effects by resveratrol largely impaired autophagy of both cytosolic proteins and mitochondria, and delayed subsequent cell death. These results support a role of mitochondrial oxidation events in the activation of autophagy.

Nutrient control of macroautophagy in mammalian cells

A growing number of evidences indicate a strict causality between the reduction of autophagic functionality and aging. In this context the preservation of a proper autophagic response is of paramount importance to preserve the cellular processes in aging cell. Nutrients availability, especially for amino acids, is the most physiological key regulator of macroautophagy. In mammalian cells the knowledge of the mechanism and the underlying regulation of macroautophagy has been greatly improved in recent years and we focus on the role of nutrients, in particular on their involvement in preventing cellular aging through the modulation of autophagy. This review covers the main features of macroautophagy regulation by nutrients, in particular amino acids as well as glucose and vitamins, and its mechanisms, focusing primarily on the mammalian hepatocyte, which has been extensively utilized to dissect signaling pathways underlying the regulation of macroautophagy.

C. elegans feeding defective mutants have shorter body lengths and increased autophagy

BACKGROUND

Mutations that cause feeding defects in the nematode C. elegans are known to increase life span. Here we show that feeding defective mutants also have a second general trait in common, namely that they are small.

RESULTS

Our measurements of the body lengths of a variety of feeding defective mutants, or of a variety of double mutants affecting other pathways that regulate body length in C. elegans, i.e. the DBL-1/TGFbeta, TAX-6/calcineurin and the SMA-1/betaH-spectrin pathways, indicate that food uptake acts as a separate pathway regulating body length. In early stages, before eating begins, feeding defective worms have no defect in body length or, in some cases, have only slightly smaller body length compared to wild-type. A significant difference in body length is first noticeable at later larval stages, a difference that probably correlates with increasing starvation. We also show that autophagy is induced and that the quantity of fat is decreased in starved worms.

CONCLUSION

Our results indicate that the long-term starvation seen in feeding-defective C. elegans mutants activates autophagy, and leads to depletion of fat deposits, small cell size and small body size.

Oxidative stress and ageing: is ageing a cysteine deficiency syndrome?

Reactive oxygen species (ROS) are constantly produced in biological tissues and play a role in various signalling pathways. Abnormally high ROS concentrations cause oxidative stress associated with tissue damage and dysregulation of physiological signals. There is growing evidence that oxidative stress increases with age. It has also been shown that the life span of worms, flies and mice can be significantly increased by mutations which impede the insulin receptor signalling cascade. Molecular studies revealed that the insulin-independent basal activity of the insulin receptor is increased by ROS and downregulated by certain antioxidants. Complementary clinical studies confirmed that supplementation of the glutathione precursor cysteine decreases insulin responsiveness in the fasted state. In several clinical trials, cysteine supplementation improved skeletal muscle functions, decreased the body fat/lean body mass ratio, decreased plasma levels of the inflammatory cytokine tumour necrosis factor alpha (TNF-alpha), improved immune functions, and increased plasma albumin levels. As all these parameters degenerate with age, these findings suggest: (i) that loss of youth, health and quality of life may be partly explained by a deficit in cysteine and (ii) that the dietary consumption of cysteine is generally suboptimal and everybody is likely to have a cysteine deficiency sooner or later.

Oxidative Aging and Insulin Receptor Signaling

The life span of nematodes, fruit flies, and mice can be significantly increased (and aging-related changes decreased) by mutations affecting insulin receptor signaling. This effect involves several cellular functions which are negatively regulated by the insulin receptor and thus typically expressed under fasting conditions. This involvement raises the question of whether the insulin-independent basal receptor kinase activity in the postabsorptive state can be decreased without compromising the physiologically important response to insulin in the postprandial state. Recent studies have shown that (a) the basal human insulin receptor kinase activity is increased under oxidative conditions in the absence of insulin and (b) insulin signaling in the fasted state can be decreased by cysteine supplementation. Cysteine supplementation has also been shown to improve certain aging-related parameters, suggesting that the average dietary cysteine consumption in Western countries may be suboptimal. These findings provide a conceptual framework that extends the "free radical theory of aging."

Interdependent regulation of insulin receptor kinase activity by ADP and hydrogen peroxide

Insulin signaling requires autophosphorylation of the insulin receptor kinase (IRK) domain. Using purified recombinant IRK fragments and the isolated intact insulin receptor, we show here that autophosphorylation is inhibited by ADP and that this effect is essentially reversed by hydrogen peroxide. Autophosphorylation was inhibited by hydrogen peroxide (60 microM) in the absence of ADP but enhanced in the presence of inhibitory concentrations of ADP (67 microM). Enhancement by hydrogen peroxide required direct interaction of hydrogen peroxide with the kinase domain and was not seen in insulin receptor mutants C1245A and C1308A. A similar enhancement was obtained in intact cells in the absence of insulin upon treatment with 1-(2-chloroethyl)-3-(2-hydroxyethyl)-1-nitrosourea, indicating that IRK activity can be alternatively enhanced by a shift in the thiol/disulfide redox status. Molecular modeling of the IRK domain indicated that the ATP-binding site becomes distorted after releasing the nucleotide unless the IRK domain is oxidatively derivatized at Cys1245. Recent clinical studies suggest that these effects may play a role in obesity due to the fact that cytoplasmic creatine kinase in combination with phosphocreatine normally ensures rapid removal of ADP in muscle cells but not in fat cells.

Glycogen autophagy

Glycogen autophagy, which includes the sequestration and degradation of cell glycogen in the autophagic vacuoles, is a selective process under conditions of demand for the massive hepatic production of glucose, as in the postnatal period. It represents a link between autophagy and glycogen metabolism. The formation of autophagic vacuoles in the hepatocytes of newborn animals is spatially and biochemically related to the degradation of cell glycogen. Many molecular elements and signaling pathways including the cyclic AMP/cyclic AMP-dependent protein kinase and the phosphoinositides/TOR pathways are implicated in the control of this process. These two pathways may converge on the same target to regulate glycogen autophagy.