Endurance exercise training increases APPL1 expression and improves insulin signaling in the hepatic tissue of diet-induced obese mice, independently of weight loss

Hepatic insulin resistance is the major contributor to fasting hyperglycemia in type 2 diabetes. The protein kinase Akt plays a central role in the suppression of gluconeogenesis involving forkhead box O1 (Foxo1) and peroxisome proliferator-activated receptor gamma co-activator 1 alpha (PGC-1a), and in the control of glycogen synthesis involving the glycogen synthase kinase beta (GSK3 beta) in the liver. It has been demonstrated that endosomal adaptor protein APPL1 interacts with Akt and blocks the association of Akt with its endogenous inhibitor, tribbles-related protein 3 (TRB3), improving the action of insulin in the liver. Here, we demonstrated that chronic exercise increased the basal levels and insulin-induced Akt serine phosphorylation in the liver of diet-induced obese mice. Endurance training was able to increase APPL1 expression and the interaction between APPL1 and Akt. Conversely, training reduced both TRB3 expression and TRB3 and Akt association. The positive effects of exercise on insulin action are reinforced by our findings that showed that trained mice presented an increase in Foxo1 phosphorylation and Foxo1/PGC-1a association, which was accompanied by a reduction in gluconeogenic gene expressions (PEPCK and G6Pase). Finally, exercised animals demonstrated increased at basal and insulin-induced GSK3 beta phosphorylation levels and glycogen content at 24?h after the last session of exercise. Our findings demonstrate that exercise increases insulin action, at least in part, through the enhancement of APPL1 and the reduction of TRB3 expression in the liver of obese mice, independently of weight loss. J. Cell. Physiol. 227: 29172926, 2012. (C) 2011 Wiley Periodicals, Inc.

Does Lithium Prevent Alzheimer's Disease?

Lithium salts have a well-established role in the treatment of major affective disorders. More recently, experimental and clinical studies have provided evidence that lithium may also exert neuroprotective effects. In animal and cell culture models, lithium has been shown to increase neuronal viability through a combination of mechanisms that includes the inhibition of apoptosis, regulation of autophagy, increased mitochondrial function, and synthesis of neurotrophic factors. In humans, lithium treatment has been associated with humoral and structural evidence of neuroprotection, such as increased expression of anti-apoptotic genes, inhibition of cellular oxidative stress, synthesis of brain-derived neurotrophic factor (BDNF), cortical thickening, increased grey matter density, and hippocampal enlargement. Recent studies addressing the inhibition of glycogen synthase kinase-3 beta (GSK3B) by lithium have further suggested the modification of biological cascades that pertain to the pathophysiology of Alzheimer's disease (AD). A recent placebo-controlled clinical trial in patients with amnestic mild cognitive impairment (MCI) showed that long-term lithium treatment may actually slow the progression of cognitive and functional deficits, and also attenuate Tau hyperphosphorylation in the MCI-AD continuum. Therefore, lithium treatment may yield disease-modifying effects in AD, both by the specific modification of its pathophysiology via inhibition of overactive GSK3B, and by the unspecific provision of neurotrophic and neuroprotective support. Although the clinical evidence available so far is promising, further experimentation and replication of the evidence in large scale clinical trials is still required to assess the benefit of lithium in the treatment or prevention of cognitive decline in the elderly.

Different approaches, one target: understanding cellular mechanisms of Parkinson's and Alzheimer's diseases

Neurodegenerative disorders are undoubtedly an increasing problem in the health sciences, given the increase of life expectancy and occasional vicious life style. Despite the fact that the mechanisms of such diseases are far from being completely understood, a large number of studies; that derive from both the basic science and clinical approaches have contributed substantial data in that direction. In this review, it is discussed several frontiers of basic research on Parkinson's and Alzheimer's diseases, in which research groups from three departments of the Institute of Biomedical Sciences of the University of Sao Paulo have been involved in a multidisciplinary effort. The main focus of the review involves the animal models that have been developed to study cellular and molecular aspects of those neurodegenerative diseases, including oxidative stress, insulin signaling and proteomic analyses, among others. We anticipate that this review will help the group determine future directions of joint research in the field and, more importantly, set the level of cooperation we plan to develop in collaboration with colleagues of the Nucleus for Applied Neuroscience Research that are mostly involved with clinical research in the same field.

Early and late neurodegeneration and memory disruption after intracerebroventricular streptozotocin

Glucose metabolism and insulin signaling disruptions in the brain have been proposed as a likely etiology of Alzheimer's disease. The aim of the present study was to investigate the time course of cognitive impairments induced by intracerebroventricular injection of streptozotocin (STZ) in rats and correlate them with the ensuing neurodegenerative process. Early and late effects of STZ were evaluated by using the reference and working memory versions of the Morris' water maze task and the evaluation of neurodegenerative markers by immunoblotting and the Fluoro-jade C histochemistry. The results revealed different types of behavioral and neurodegenerative responses, with distinct time courses. We observed an early disruption on the working memory as early as 3 h after STZ injections, which was followed by degenerative processes in the hippocampus at 1 and 15 days after STZ injections. Memory disruption increases over time and culminates with significant changes in amyloid-beta peptide and hyperphosphorylated Tau protein levels in distinct brain structures. These findings add information on the Alzheimer's disease-like STZ animal model and on the mechanisms underlying neurodegenerative processes. (C) 2012 Elsevier Inc. All rights reserved.

Cardiac tissue-restricted deletion of plakoglobin results in progressive cardiomyopathy and activation of {beta}-catenin signaling

Mutations in the plakoglobin (JUP) gene have been identified in arrhythmogenic right ventricular cardiomyopathy (ARVC) patients. However, the mechanisms underlying plakoglobin dysfunction involved in the pathogenesis of ARVC remain poorly understood. Plakoglobin is a component of both desmosomes and adherens junctions located at the intercalated disc (ICD) of cardiomyocytes, where it functions to link cadherins to the cytoskeleton. In addition, plakoglobin functions as a signaling protein via its ability to modulate the Wnt/beta-catenin signaling pathway. To investigate the role of plakoglobin in ARVC, we generated an inducible cardiorestricted knockout (CKO) of the plakoglobin gene in mice. Plakoglobin CKO mice exhibited progressive loss of cardiac myocytes, extensive inflammatory infiltration, fibrous tissue replacement, and cardiac dysfunction similar to those of ARVC patients. Desmosomal proteins from the ICD were decreased, consistent with altered desmosome ultrastructure in plakoglobin CKO hearts. Despite gap junction remodeling, plakoglobin CKO hearts were refractory to induced arrhythmias. Ablation of plakoglobin caused increase beta-catenin stabilization associated with activated AKT and inhibition of glycogen synthase kinase 3beta. Finally, beta-catenin/TCF transcriptional activity may contribute to the cardiac hypertrophy response in plakoglobin CKO mice. This novel model of ARVC demonstrates for the first time how plakoglobin affects beta-catenin activity in the heart and its implications for disease pathogenesis.

Epidemiological and genetic study of exertional rhabdomyolysis in a Warmblood horse family in Switzerland

REASONS FOR PERFORMING STUDY: Exertional rhabdomyolysis (ER) and its familial basis in Warmblood horses is incompletely understood. OBJECTIVES: To describe the case details, clinical signs and management of ER-affected Warmblood horses from a family with a high prevalence of ER, to determine if histopathological signs of polysaccharide storage myopathy (PSSM) and the glycogen synthase (GYS1) mutation are associated with ER in this family, and to investigate potential risk factors for development of ER. METHODS: A family consisting of a sire with ER and 71 of his descendants was investigated. History of episodes of ER, husbandry, feeding and use was assessed by interviewing horse owners using a standardised questionnaire. All horses were genotyped for GYS1. In 10 ER-affected horses, muscle histopathology was evaluated. RESULTS: Signs of ER were reported in 39% of horses and 51% of the entire family possessed the GYS1 mutation. Horses possessing the GYS1 mutation had a 7.1-times increased risk for developing ER compared to those with the normal genotype (95% confidence interval [CI] 2.37-21.23, P = 0.0005). All muscle samples from horses in the family with ER showed polysaccharide accumulation typical for PSSM, amylase-resistant in 9/10 cases. There was evidence (odds ratio 5.6, CI 1.00-31.32, P = 0.05) that fat or oil feeding improved clinical signs of ER. No other effects of environmental factors associated with clinical signs of ER were identified. CONCLUSION AND POTENTIAL RELEVANCE: PSSM associated with the GYS1 mutation is one identifiable cause of ER in Warmblood horses. Signs of ER are not always manifest in GYS1 positive horses and there are also other causes for ER in Warmblood horses. Breeding animals with the GYS1 mutation results in a high prevalence of ER due to its dominant mode of inheritance.

Hsp90 transcriptionally and post-translationally regulates the expression of NDRG1 and maintains the stability of its modifying kinase GSK3beta

N-myc downstream-regulated gene 1 (NRDG1) is a stress-induced protein whose putative function is suppression of tumor metastasis. A recent proteonomic study showed NDRG1 interacts with the molecular chaperone heat shock protein 90 (Hsp90). From their reported association, we investigated if NDRG1 is dependent on Hsp90 for its stability and is therefore a yet unidentified Hsp90 client protein. Here, we demonstrate that endogenous NDRG1 and Hsp90 physically associate in hepatocellular cancer cell lines. However, geldanamycin (GA)-mediated inhibition of Hsp90 did not disrupt their interaction or result in NDRG1 protein destabilization. On the contrary, inhibition of Hsp90 led to a transcriptional increase of NDRG1 protein which was associated with cell growth arrest. We also observed that GA inhibited the phosphorylation of NDRG1 by targeting its regulating kinases, serum- and glucocorticoid-induced kinase 1 (SGK1) and glycogen synthase kinase 3 beta (GSK3beta). We demonstrate that in the presence of GA, GSK3beta protein and activity were decreased thus indicating that Hsp90 is necessary for GSK3beta stability. Taken together, our data demonstrate that NDRG1 is not a classic client protein but interacts with Hsp90 and is still dually regulated by Hsp90 at a transcriptional and post-translational level. Finally, we suggest for the first time GSK3beta as a new client protein of Hsp90.

Evolutionarily conserved role of calcineurin in phosphodegron-dependent degradation of phosphodiesterase 4D.

Calcineurin is a widely expressed and highly conserved Ser/Thr phosphatase. Calcineurin is inhibited by the immunosuppressant drug cyclosporine A (CsA) or tacrolimus (FK506). The critical role of CsA/FK506 as an immunosuppressant following transplantation surgery provides a strong incentive to understand the phosphatase calcineurin. Here we uncover a novel regulatory pathway for cyclic AMP (cAMP) signaling by the phosphatase calcineurin which is also evolutionarily conserved in Caenorhabditis elegans. We found that calcineurin binds directly to and inhibits the proteosomal degradation of cAMP-hydrolyzing phosphodiesterase 4D (PDE4D). We show that ubiquitin conjugation and proteosomal degradation of PDE4D are controlled by a cullin 1-containing E(3) ubiquitin ligase complex upon dual phosphorylation by casein kinase 1 (CK1) and glycogen synthase kinase 3beta (GSK3beta) in a phosphodegron motif. Our findings identify a novel signaling process governing G-protein-coupled cAMP signal transduction-opposing actions of the phosphatase calcineurin and the CK1/GSK3beta protein kinases on the phosphodegron-dependent degradation of PDE4D. This novel signaling system also provides unique functional insights into the complications elicited by CsA in transplant patients.

A study in the molecular and cellular functions of GSK3beta in prostate adenocarcinoma

Kinases are part of a complex network of signaling pathways that enable a cell to respond to changes in environmental conditions in a regulated and coordinated way. For example, Glycogen Synthase Kinase 3 beta (GSK3β) modulates conformational changes, protein-protein interaction, protein degradation, and activation of unique domains in proteins that transduce signals from the extracellular milieu to the nucleus. ^ In this project, I investigated the expression and function that GSK3β exhibits in prostate cells. The capacity of GSK3β to regulate two transcription factors (JUN and CREB), which are known to be inversely utilized in prostate tumor cells, was measured. JUN/AP1 is constitutively activated in PC-3 cells; whereas, CREB/CRE activity is ∼20 fold less than the former. GSK3β overexpression obliterates JUN/AP1 activity. With respect to CREB GSK3β increases CREB/CRE activity. Cellular levels of active GSK3β can determine whether JUN or CREB is preferentially active in the PC-3s. Theoretically, in response to a particular cellular context or stimulus, a cell may coordinate JUN and CREB function by regulating GSK3β.^ A comparison of various prostate cell lines showed that active GSK3β is less expressed in normal prostate epithelial cells than in tumor cells. Differentially expressed active (GSK3β) may correlate with progression of prostate carcinoma. If a known marker associated with carcinoma of the prostate could be shown to be regulated by GSK3β then, further study of GSK3β may lead to a better understanding of both possible prevention of the disease and improved therapy for advanced stages. ^ The androgen receptor (AR) is an intriguing phosphoprotein whose regulation is potentially determined by a variety of kinases. One of these is (GSK3β) I found that (GSK3β) is a regulator of the androgen receptor in both the unliganded and liganded states. It can inhibit AR function as measured by reporter assays. Also, GSK3β associates with the AR at the DNA binding domain because deletion constructs expressing either the n-terminus or the c-terminus (both having the DBD in common) immunoprecipitated with GSK3β. Increased understanding of how GSK3β functions in prostate cancer would provide clues into how (1) certain signal pathways are coordinated and (2) the androgen receptor may be regulated. ^

Physiogenomic Analysis of Weight Loss Induced by Dietary Carbohydrate Restriction

ABSTRACT : BACKGROUND : Diets that restrict carbohydrate (CHO) have proven to be a successful dietary treatment of obesity for many people, but the degree of weight loss varies across individuals. The extent to which genetic factors associate with the magnitude of weight loss induced by CHO restriction is unknown. We examined associations among polymorphisms in candidate genes and weight loss in order to understand the physiological factors influencing body weight responses to CHO restriction. METHODS : We screened for genetic associations with weight loss in 86 healthy adults who were instructed to restrict CHO to a level that induced a small level of ketosis (CHO ~10% of total energy). A total of 27 single nucleotide polymorphisms (SNPs) were selected from 15 candidate genes involved in fat digestion/metabolism, intracellular glucose metabolism, lipoprotein remodeling, and appetite regulation. Multiple linear regression was used to rank the SNPs according to probability of association, and the most significant associations were analyzed in greater detail. RESULTS : Mean weight loss was 6.4 kg. SNPs in the gastric lipase (LIPF), hepatic glycogen synthase (GYS2), cholesteryl ester transfer protein (CETP) and galanin (GAL) genes were significantly associated with weight loss. CONCLUSION : A strong association between weight loss induced by dietary CHO restriction and variability in genes regulating fat digestion, hepatic glucose metabolism, intravascular lipoprotein remodeling, and appetite were detected. These discoveries could provide clues to important physiologic adaptations underlying the body mass response to CHO restriction.

The regulation of mTORC2 kinase activity and complex integrity

Growth factor signaling promotes anabolic processes via activation of the PI3K-Akt kinase cascade. Deregulation of the growth factor-dependent PI3K-Akt pathway was implicated in tumorigenesis. Akt is an essential serine/threonine protein kinase that controls multiple physiological functions such as cell growth, proliferation, and survival to maintain cellular homeostasis. Recently, the mammalian Target of Rapamycin Complex 2 (mTORC2) was identified as the main Akt Ser-473 kinase, and Ser-473 phosphorylation is required for Akt hyperactivation. However, the detailed mechanism of mTORC2 regulation in response to growth factor stimulation or cellular stresses is not well understood. In the first project, we studied the regulation of the mTORC2-Akt signaling under ER stress. We identified the inactivation of mTORC2 by glycogen synthase kinase-3β (GSK-3β). Under ER stress, the essential mTORC2 component, rictor, is phosphorylated by GSK-3β at Ser-1235. This phosphorylation event results in the inhibition of mTORC2 kinase activity by interrupting Akt binding to mTORC2. Blocking rictor Ser-1235 phosphorylation can attenuate the negative impacts of GSK-3β on mTORC2/Akt signaling and tumor growth. Thus, our work demonstrated that GSK-3β-mediated rictor Ser-1235 phosphorylation in response to ER stress interferes with Akt signaling by inhibiting mTORC2 kinase activity. In the second project, I investigated the regulation of the mTORC2 integrity. We found that basal mTOR kinase activity depends on ATP level, which is tightly regulated by cell metabolism. The ATP-sensitive mTOR kinase is required for SIN1 protein phosphorylation and stabilization. SIN1 is an indispensable subunit of mTORC2 and is required for the complex assembly and mTORC2 kinase activity. Our findings reveal that mTOR-mediated phosphorylation of SIN1 is critical for maintaining complex integrity by preventing SIN1 from lysosomal degradation. In sum, our findings verify two distinct mTORC2 regulatory mechanisms via its components rictor and SIN1. First, GSK-3β-mediated rictor Ser-1235 phosphorylation results in mTORC2 inactivation by interfering its substrate binding ability. Second, mTOR-mediated Ser-260 phosphorylation of SIN1 preserves its complex integrity. Thus, these two projects provide novel insights into the regulation of mTORC2.

13C NMR study of the effects of leptin treatment on kinetics of hepatic intermediary metabolism

The recent discovery of leptin receptors in peripheral tissue raises questions about which of leptin’s biological actions arise from direct effects of the hormone on extraneural tissues and what intracellular mechanisms are responsible for leptin’s effects on carbohydrate and lipid metabolism. The present study is focused on the action of leptin on hepatic metabolism. Nondestructive 13C NMR methodology was used to follow the kinetics of intermediary metabolism by monitoring flux of 13C-labeled substrate through several multistep pathways. In perfused liver from either ob/ob or lean mice, we found that acute treatment with leptin in vitro modulates pathways controlling carbohydrate flux into 13C-labeled glycogen, thereby rapidly enhancing synthesis by an insulin-independent mechanism. Acute treatment of ob/ob liver also caused a rapid stimulation of long-chain fatty acid synthesis from 13C-labeled acetyl-CoA by the de novo synthesis route. Chronic leptin treatment in vivo induced homeostatic changes that resulted in a tripling of the rate of glycogen synthesis via the gluconeogenic pathway from [2-13C]pyruvate in ob/ob mouse liver perfused in the absence of the hormone. Consistent with the 13C NMR results, leptin treatment of the ob/ob mouse in vivo resulted in significantly increased hepatic glycogen synthase activity. Chronic treatment with leptin in vivo exerted the opposite effect of acute treatment in vitro and markedly decreased hepatic de novo synthesis of fatty acids in ob/ob mouse liver. In agreement with the 13C NMR findings, activities of hepatic acetyl-CoA carboxylase and fatty acid synthase were significantly reduced by chronic treatment of the ob/ob mouse with leptin. Our data represent a demonstration of direct effects of leptin in the regulation of metabolism in the intact functioning liver.

Metabotropic glutamate receptor-initiated translocation of protein kinase p90rsk to polyribosomes: A possible factor regulating synaptic protein synthesis

Maintenance of lasting synaptic efficacy changes requires protein synthesis. We report here a mechanism that might influence translation control at the level of the single synapse. Stimulation of metabotropic glutamate receptors in hippocampal slices induces a rapid protein kinase C-dependent translocation of multifunction kinase p90rsk to polyribosomes; concomitantly, there is enhanced phosphorylation of at least six polyribosome binding proteins. Among the polyribosome bound proteins are the p90rsk-activating kinase ERK-2 and a known p90rsk substrate, glycogen synthase kinase 3β, which regulates translation efficiency via eukaryotic initiation factor 2B. Thus metabotropic glutamate receptor stimulation could induce synaptic activity-dependent translation via translocation of p90rsk to ribosomes.

The Ras/Rac1/Cdc42/SEK/JNK/c-Jun Cascade Is a Key Pathway by Which Agonists Stimulate DNA Synthesis in Primary Cultures of Rat Hepatocytes

The ability of signaling via the JNK (c-Jun NH2-terminal kinase)/stress-activated protein kinase cascade to stimulate or inhibit DNA synthesis in primary cultures of adult rat hepatocytes was examined. Treatment of hepatocytes with media containing hyperosmotic glucose (75 mM final), tumor necrosis factor α (TNFα, 1 ng/ml final), and hepatocyte growth factor (HGF, 1 ng/ml final) caused activation of JNK1. Glucose, TNFα, or HGF treatments increased phosphorylation of c-Jun at serine 63 in the transactivation domain and stimulated hepatocyte DNA synthesis. Infection of hepatocytes with poly-l-lysine–coated adenoviruses coupled to constructs to express either dominant negatives Ras N17, Rac1 N17, Cdc42 N17, SEK1−, or JNK1− blunted the abilities of glucose, TNFα, or HGF to increase JNK1 activity, to increase phosphorylation of c-Jun at serine 63, and to stimulate DNA synthesis. Furthermore, infection of hepatocytes by a recombinant adenovirus expressing a dominant-negative c-Jun mutant (TAM67) also blunted the abilities of glucose, TNFα, and HGF to stimulate DNA synthesis. These data demonstrate that multiple agonists stimulate DNA synthesis in primary cultures of hepatocytes via a Ras/Rac1/Cdc42/SEK/JNK/c-Jun pathway. Glucose and HGF treatments reduced glycogen synthase kinase 3 (GSK3) activity and increased c-Jun DNA binding. Co-infection of hepatocytes with recombinant adenoviruses to express dominant- negative forms of PI3 kinase (p110α/p110γ) increased basal GSK3 activity, blocked the abilities of glucose and HGF treatments to inhibit GSK3 activity, and reduced basal c-Jun DNA binding. However, expression of dominant-negative PI3 kinase (p110α/p110γ) neither significantly blunted the abilities of glucose and HGF treatments to increase c-Jun DNA binding, nor inhibited the ability of these agonists to stimulate DNA synthesis. These data suggest that signaling by the JNK/stress-activated protein kinase cascade, rather than by the PI3 kinase cascade, plays the pivotal role in the ability of agonists to stimulate DNA synthesis in primary cultures of rat hepatocytes.

Exercise-induced changes in expression and activity of proteins involved in insulin signal transduction in skeletal muscle: Differential effects on insulin-receptor substrates 1 and 2

Level of physical activity is linked to improved glucose homeostasis. We determined whether exercise alters the expression and/or activity of proteins involved in insulin-signal transduction in skeletal muscle. Wistar rats swam 6 h per day for 1 or 5 days. Epitrochlearis muscles were excised 16 h after the last exercise bout, and were incubated with or without insulin (120 nM). Insulin-stimulated glucose transport increased 30% and 50% after 1 and 5 days of exercise, respectively. Glycogen content increased 2- and 4-fold after 1 and 5 days of exercise, with no change in glycogen synthase expression. Protein expression of the glucose transporter GLUT4 and the insulin receptor increased 2-fold after 1 day, with no further change after 5 days of exercise. Insulin-stimulated receptor tyrosine phosphorylation increased 2-fold after 5 days of exercise. Insulin-stimulated tyrosine phosphorylation of insulin-receptor substrate (IRS) 1 and associated phosphatidylinositol (PI) 3-kinase activity increased 2.5- and 3.5-fold after 1 and 5 days of exercise, despite reduced (50%) IRS-1 protein content after 5 days of exercise. After 1 day of exercise, IRS-2 protein expression increased 2.6-fold and basal and insulin-stimulated IRS-2 associated PI 3-kinase activity increased 2.8-fold and 9-fold, respectively. In contrast to IRS-1, IRS-2 expression and associated PI 3-kinase activity normalized to sedentary levels after 5 days of exercise. Insulin-stimulated Akt phosphorylation increased 5-fold after 5 days of exercise. In conclusion, increased insulin-stimulated glucose transport after exercise is not limited to increased GLUT4 expression. Exercise leads to increased expression and function of several proteins involved in insulin-signal transduction. Furthermore, the differential response of IRS-1 and IRS-2 to exercise suggests that these molecules have specialized, rather than redundant, roles in insulin signaling in skeletal muscle.