Behavioral, metabolic, and lipidomic characterization of the 5xFADxTg30 mouse model of Alzheimer's disease.

Alzheimer's disease (AD) is associated with both extracellular amyloid-ß (Aß) plaques and intracellular tau-containing neurofibrillary tangles (NFT). We characterized the behavioral, metabolic and lipidomic phenotype of the 5xFADxTg30 mouse model which contains overexpression of both Aß and tau. Our results independently reproduce several phenotypic traits described previously for this model, while providing additional characterization. This model develops many aspects associated with AD including frailty, decreased survival, initiation of aspects of cognitive decline and alterations to specific lipid classes and molecular lipid species in the plasma and brain. Notably, some sex-specific differences exist in this model and motor impairment with aging in this model does compromise the utility of the model for some movement-based behavioral assessments of cognitive function. These findings provide a reference for individuals interested in using this model to understand the pathology associated with elevated Aß and tau or for testing potential therapeutics for the treatment of AD.

Yap regulates skeletal muscle fatty acid oxidation and adiposity in metabolic disease.

Obesity is a major risk factor underlying the development of metabolic disease and a growing public health concern globally. Strategies to promote skeletal muscle metabolism can be effective to limit the progression of metabolic disease. Here, we demonstrate that the levels of the Hippo pathway transcriptional co-activator YAP are decreased in muscle biopsies from obese, insulin-resistant humans and mice. Targeted disruption of Yap in adult skeletal muscle resulted in incomplete oxidation of fatty acids and lipotoxicity. Integrated 'omics analysis from isolated adult muscle nuclei revealed that Yap regulates a transcriptional profile associated with metabolic substrate utilisation. In line with these findings, increasing Yap abundance in the striated muscle of obese (db/db) mice enhanced energy expenditure and attenuated adiposity. Our results demonstrate a vital role for Yap as a mediator of skeletal muscle metabolism. Strategies to enhance Yap activity in skeletal muscle warrant consideration as part of comprehensive approaches to treat metabolic disease.

Evidence against a role for NLRP3-driven islet inflammation in db/db mice.

OBJECTIVES: Type 2 diabetes (T2D) is associated with chronic, low grade inflammation. Activation of the NLRP3 inflammasome and secretion of its target interleukin-1ß (IL-1ß) have been implicated in pancreatic ß cell failure in T2D. Specific targeting of the NLRP3 inflammasome to prevent pancreatic ß cell death could allow for selective T2D treatment without compromising all IL-1ß-associated immune responses. We hypothesized that treating a mouse model of T2D with MCC950, a compound that specifically inhibits NLRP3, would prevent pancreatic ß cell death, thereby preventing the onset of T2D. METHODS: Diabetic db/db mice were treated with MCC950 via drinking water for 8 weeks from 6 to 14 weeks of age, a period over which they developed pancreatic ß cell failure. We assessed metabolic parameters such as body composition, glucose tolerance, or insulin secretion over the course of the intervention. RESULTS: MCC950 was a potent inhibitor of NLRP3-induced IL-1ß in vitro and was detected at high levels in the plasma of treated db/db mice. Treatment of pre-diabetic db/db mice with MCC950, however, did not prevent pancreatic dysfunction and full onset of the T2D pathology. When examining the NLRP3 pathway in the pancreas of db/db mice, we could not detect an activation of this pathway nor increased levels of its target IL-1ß. CONCLUSIONS: NLRP3 driven-pancreatic IL-1ß inflammation does not play a key role in the pathogenesis of the db/db murine model of T2D.

PKR is not obligatory for high-fat diet-induced obesity and its associated metabolic and inflammatory complications.

Protein kinase R (PKR) has previously been suggested to mediate many of the deleterious consequences of a high-fat diet (HFD). However, previous studies have observed substantial phenotypic variability when examining the metabolic consequences of PKR deletion. Accordingly, herein, we have re-examined the role of PKR in the development of obesity and its associated metabolic complications in vivo as well as its putative lipid-sensing role in vitro. Here we show that the deletion of PKR does not affect HFD-induced obesity, hepatic steatosis or glucose metabolism, and only modestly affects adipose tissue inflammation. Treatment with the saturated fatty acid palmitate in vitro induced comparable levels of inflammation in WT and PKR KO macrophages, demonstrating that PKR is not necessary for the sensing of pro-inflammatory lipids. These results challenge the proposed role for PKR in obesity, its associated metabolic complications and its role in lipid-induced inflammation.

Genetic manipulation of cardiac Hsp72 levels does not alter substrate metabolism but reveals insights into high-fat feeding-induced cardiac insulin resistance.

Heat shock protein 72 (Hsp72) protects cells against a variety of stressors, and multiple studies have suggested that Hsp72 plays a cardioprotective role. As skeletal muscle Hsp72 overexpression can protect against high-fat diet (HFD)-induced insulin resistance, alterations in substrate metabolism may be a mechanism by which Hsp72 is cardioprotective. We investigated the impact of transgenically overexpressing (Hsp72 Tg) or deleting Hsp72 (Hsp72 KO) on various aspects of cardiac metabolism. Mice were fed a normal chow (NC) or HFD for 12 weeks from 8 weeks of age to examine the impact of diet-induced obesity on metabolic parameters in the heart. The HFD resulted in an increase in cardiac fatty acid oxidation and a decrease in cardiac glucose oxidation and insulin-stimulated cardiac glucose clearance; however, there was no difference in Hsp72 Tg or Hsp72 KO mice in these rates compared with their respective wild-type control mice. Although HFD-induced cardiac insulin resistance was not rescued in the Hsp72 Tg mice, it was preserved in the skeletal muscle, suggesting tissue-specific effects of Hsp72 overexpression on substrate metabolism. Comparison of two different strains of mice (BALB/c vs. C57BL/6J) also identified strain-specific differences in regard to HFD-induced cardiac lipid accumulation and insulin resistance. These strain differences suggest that cardiac lipid accumulation can be dissociated from cardiac insulin resistance. Our study finds that genetic manipulation of Hsp72 does not lead to alterations in metabolic processes in cardiac tissue under resting conditions, but identifies mouse strain-specific differences in cardiac lipid accumulation and insulin-stimulated glucose clearance.

Adipose tissue inflammation in glucose metabolism.

Obesity is now recognised as a low grade, chronic inflammatory disease that is linked to a myriad of disorders including cancer, cardiovascular disease and type 2 diabetes (T2D). With respect to T2D, work in the last decade has revealed that cells of the immune system are recruited to white adipose tissue beds (WAT), where they can secrete cytokines to modulate metabolism within WAT. As many of these cytokines are known to impair insulin action, blocking the recruitment of immune cells has been purported to have therapeutic utility for the treatment of obesity-induced T2D. As inflammation is critical for host defence, and energy consuming in nature, the blockade of inflammatory processes may, however, result in unwanted complications. In this review, we outline the immunological changes that occur within the WAT with respect to systemic glucose homeostasis. In particular, we focus on the role of major immune cell types in regulating nutrient homeostasis and potential initiating stimuli for WAT inflammation.

Targeting gp130 to prevent inflammation and promote insulin action.

Obesity and type 2 diabetes are now the most prevalent metabolic diseases in the Western world and the development of new strategies to treat these metabolic diseases is most warranted. Obesity results in a state of chronic low-grade inflammation in metabolically active tissues such as the liver, adipose tissue, brain and skeletal muscle. Work in our laboratory has focussed on the role of the cytokine interleukin-6 (IL)-6 and other IL-6-like cytokines that signal through the gp130 receptor complex. We have focussed on the role of blocking IL-6 trans-signalling to prevent inflammation on the one hand, and activating membrane-bound signalling to promote insulin sensitivity on the other hand. Since the cloning of the IL-6 gene nearly 30 years ago, a pattern has emerged associating IL-6 with a number of diseases associated with inflammation including rheumatoid arthritis (RA), Crohn's disease and several cancers. Accordingly, tocilizumab, an IL-6 receptor-inhibiting monoclonal antibody, is now useful for the treatment of RA. However, this may not be the most optimal strategy to block inflammation associated with IL-6 and may result in unwanted side effects that, paradoxically, could actually promote metabolic disease.

Distinct patterns of tissue-specific lipid accumulation during the induction of insulin resistance in mice by high-fat feeding.

AIMS/HYPOTHESIS: While it is well known that diet-induced obesity causes insulin resistance, the precise mechanisms underpinning the initiation of insulin resistance are unclear. To determine factors that may cause insulin resistance, we have performed a detailed time-course study in mice fed a high-fat diet (HFD). METHODS: C57Bl/6 mice were fed chow or an HFD from 3 days to 16 weeks and glucose tolerance and tissue-specific insulin action were determined. Tissue lipid profiles were analysed by mass spectrometry and inflammatory markers were measured in adipose tissue, liver and skeletal muscle. RESULTS: Glucose intolerance developed within 3 days of the HFD and did not deteriorate further in the period to 12 weeks. Whole-body insulin resistance, measured by hyperinsulinaemic-euglycaemic clamp, was detected after 1 week of HFD and was due to hepatic insulin resistance. Adipose tissue was insulin resistant after 1 week, while skeletal muscle displayed insulin resistance at 3 weeks, coinciding with a defect in glucose disposal. Interestingly, no further deterioration in insulin sensitivity was observed in any tissue after this initial defect. Diacylglycerol content was increased in liver and muscle when insulin resistance first developed, while the onset of insulin resistance in adipose tissue was associated with increases in ceramide and sphingomyelin. Adipose tissue inflammation was only detected at 16 weeks of HFD and did not correlate with the induction of insulin resistance. CONCLUSIONS/INTERPRETATION: HFD-induced whole-body insulin resistance is initiated by impaired hepatic insulin action and exacerbated by skeletal muscle insulin resistance and is associated with the accumulation of specific bioactive lipid species.

Skeletal muscle-specific overproduction of constitutively activated c-Jun N-terminal kinase (JNK) induces insulin resistance in mice.

AIMS/HYPOTHESIS: Although skeletal muscle insulin resistance has been associated with activation of c-Jun N-terminal kinase (JNK), whether increased JNK activity causes insulin resistance in this organ is not clear. In this study we examined the metabolic consequences of isolated JNK phosphorylation in muscle tissue. METHODS: Plasmids containing genes encoding a wild-type JNK1 (WT-JNK) or a JNK1/JNKK2 fusion protein (rendering JNK constitutively active; CA-Jnk) were electroporated into one tibialis anterior (TA) muscle of C57Bl/6 mice, with the contralateral TA injected with an empty vector (CON) to serve as a within-animal control. RESULTS: Overproduction of WT-JNK resulted in a modest (~25%) increase in phosphorylation (Thr(183)/Tyr(185)) of JNK, but no differences were observed in Ser(307) phosphorylation of insulin receptor substrate 1 (IRS-1) or total IRS-1 protein, nor in insulin-stimulated glucose clearance into the TA muscle when comparing WT-JNK with CON. By contrast, overexpression of CA-Jnk, which markedly increased the phosphorylation of CA-JNK, also increased serine phosphorylation of IRS-1, markedly decreased total IRS-1 protein, and decreased insulin-stimulated phosphorylation of the insulin receptor (Tyr(1361)) and phosphorylation of Akt at (Ser(473) and Thr(308)) compared with CON. Moreover, overexpression of CA-Jnk decreased insulin-stimulated glucose clearance into the TA muscle compared with CON and these effects were observed without changes in intramuscular lipid species. CONCLUSIONS/INTERPRETATION: Constitutive activation of JNK in skeletal muscle impairs insulin signalling at the level of IRS-1 and Akt, a process which results in the disruption of normal glucose clearance into the muscle.

Deficiency of haematopoietic-cell-derived IL-10 does not exacerbate high-fat-diet-induced inflammation or insulin resistance in mice.

AIMS/HYPOTHESIS: Recent work has identified the important roles of M1 pro-inflammatory and M2 anti-inflammatory macrophages in the regulation of insulin sensitivity. Specifically, increased numbers of M2 macrophages and a decrease in M1 macrophages within the adipose tissue are associated with a state of enhanced insulin sensitivity. IL-10 is an anti-inflammatory cytokine and is a critical effector molecule of M2 macrophages. METHODS: In the present study, we examined the contribution of haematopoietic-cell-derived IL-10 to the development of obesity-induced inflammation and insulin resistance. We hypothesised that haematopoietic-cell-restricted deletion of IL-10 would exacerbate obesity-induced inflammation and insulin resistance. Lethally irradiated wild-type recipient mice receiving bone marrow from either wild-type or Il10-knockout mice were placed on either a chow or a high-fat diet for a period of 12 weeks and assessed for alterations in body composition, tissue inflammation and glucose and insulin tolerance. RESULTS: Contrary to our hypothesis, neither inflammation, as measured by the activation of pro-inflammatory stress kinases and gene expression of several pro-inflammatory cytokines in the adipose tissue and liver, nor diet-induced obesity and insulin resistance were exacerbated by the deletion of haematopoietic-cell-derived IL-10. Interestingly, however, Il10 mRNA expression and IL-10 protein production in liver and/or adipose tissue were markedly elevated in Il10-knockout bone-marrow-transplanted mice relative to wild-type bone marrow-transplanted mice. CONCLUSIONS/INTERPRETATION: These data show that deletion of IL-10 from the haematopoietic system does not potentiate high-fat diet-induced inflammation or insulin resistance.

Interleukin-6-deficient mice develop hepatic inflammation and systemic insulin resistance.

AIMS/HYPOTHESIS: The role of IL-6 in the development of obesity and hepatic insulin resistance is unclear and still the subject of controversy. We aimed to determine whether global deletion of Il6 in mice (Il6 (-/-)) results in standard chow-induced and high-fat diet (HFD)-induced obesity, hepatosteatosis, inflammation and insulin resistance. METHODS: Male, 8-week-old Il6 (-/-) and littermate control mice were fed a standard chow or HFD for 12 weeks and phenotyped accordingly. RESULTS: Il6 (-/-) mice displayed obesity, hepatosteatosis, liver inflammation and insulin resistance when compared with control mice on a standard chow diet. When fed a HFD, the Il6 (-/-) and control mice had marked, equivalent gains in body weight, fat mass and ectopic lipid deposition in the liver relative to chow-fed animals. Despite this normalisation, the greater liver inflammation, damage and insulin resistance observed in chow-fed Il6 (-/-) mice relative to control persisted when both were fed the HFD. Microarray analysis from livers of mice fed a HFD revealed that genes associated with oxidative phosphorylation, the electron transport chain and tricarboxylic acid cycle were uniformly decreased in Il6 (-/-) relative to control mice. This coincided with reduced maximal activity of the mitochondrial enzyme ß-hydroxyacyl-CoA-dehydrogenase and decreased levels of mitochondrial respiratory chain proteins. CONCLUSIONS/INTERPRETATION: Our data suggest that IL-6 deficiency exacerbates HFD-induced hepatic insulin resistance and inflammation, a process that appears to be related to defects in mitochondrial metabolism.

Is interleukin-6 receptor blockade the Holy Grail for inflammatory diseases?

Interleukin-6 (IL-6) has been linked to a myriad of diseases associated with inflammation, including rheumatoid arthritis (RA), Crohn's disease, and several types of cancer. In 2009 the US Food and Drug Administration accepted a complete-response submission for the use of Actemra (tocilizumab), the first humanized IL-6 receptor-inhibiting monoclonal antibody, for the treatment of RA. Although this treatment will certainly help in managing inflammatory disorders such as RA, we suggest that side effects of such blockade may be excess weight gain and hyperlipidemia.

The 2009 stock conference report: inflammation, obesity and metabolic disease.

Obesity is linked with many deleterious health consequences and is associated with increased risk of chronic disease including type 2 diabetes, atherosclerosis and certain forms of cancer. Recent work has highlighted the impact of obesity to activate inflammatory gene networks and suggests a causal function of inflammation in the pathogenesis of the metabolic syndrome. Since 2005, when Dr Gokhan Hotamisligil chaired the fourth Stock Conference in Istanbul, Turkey, entitled 'Obesity and Inflammation', there has been an explosion of studies investigating the relationship between obesity, inflammation and substrate metabolism. The exuberance surrounding this field of research is exemplified by the body of work that has been published in these past 4 years, including over 1400 publications. During this time, several novel mechanisms relating to cellular inflammation have been uncovered including the role of the hematopoietic system, toll-like receptor activation, endoplasmic reticulum stress and very recently T-cell activation in obesity-induced insulin resistance. These discoveries have led us to rethink cellular nutrient sensing and its role in inflammation and metabolic disease. Despite burgeoning investigation in this field, there still remain a number of unanswered questions. This review that evolved from the 2009 Stock Conference summarizes current research and identifies the deficiencies in our understanding of this topic. The overall goal of this Stock Conference was to bring together leading investigators in the field of inflammation and obesity research in the hope of fostering new ideas, thus advancing the pursuit of novel therapeutic strategies to reduce disease risk and or better treat chronic disease including type 2 diabetes, cardiovascular disease and cancer.

Brain-derived neurotrophic factor is produced by skeletal muscle cells in response to contraction and enhances fat oxidation via activation of AMP-activated protein kinase.

AIMS/HYPOTHESIS: Brain-derived neurotrophic factor (BDNF) is produced in skeletal muscle, but its functional significance is unknown. We aimed to determine the signalling processes and metabolic actions of BDNF. METHODS: We first examined whether exercise induced BDNF expression in humans. Next, C2C12 skeletal muscle cells were electrically stimulated to mimic contraction. L6 myotubes and isolated rat extensor digitorum longus muscles were treated with BDNF and phosphorylation of the proteins AMP-activated protein kinase (AMPK) (Thr(172)) and acetyl coenzyme A carboxylase beta (ACCbeta) (Ser(79)) were analysed, as was fatty acid oxidation (FAO). Finally, we electroporated a Bdnf vector into the tibialis cranialis muscle of mice. RESULTS: BDNF mRNA and protein expression were increased in human skeletal muscle after exercise, but muscle-derived BDNF appeared not to be released into the circulation. Bdnf mRNA and protein expression was increased in muscle cells that were electrically stimulated. BDNF increased phosphorylation of AMPK and ACCbeta and enhanced FAO both in vitro and ex vivo. The effect of BDNF on FAO was AMPK-dependent, since the increase in FAO was abrogated in cells infected with an AMPK dominant negative adenovirus or treated with Compound C, an inhibitor of AMPK. Electroporation of a Bdnf expression vector into the tibialis cranialis muscle resulted in increased BDNF protein production and tropomyosin-related kinase B (TrkB(Tyr706/707)) and extracellular signal-regulated protein kinase (p44/42 Thr(202)/Tyr(204)) phosphorylation in these muscles. In addition, phosphorylation of ACCbeta was markedly elevated in the Bdnf electroporated muscles. CONCLUSIONS/INTERPRETATION: These data identify BDNF as a contraction-inducible protein in skeletal muscle that is capable of enhancing lipid oxidation in skeletal muscle via activation of AMPK.

Examination of 'lipotoxicity' in skeletal muscle of high-fat fed and ob/ob mice.

Excess lipid accumulation resulting from an elevated supply of plasma fatty acids is linked to the pathogenesis of the metabolic syndrome and heart disease. The term 'lipotoxicity' was coined to describe how lipid accumulation leads to cellular dysfunction and death in non-adipose tissues including the heart, pancreas and liver. While lipotoxicity has been shown in cultured skeletal muscle cells, the degree of lipotoxicity in vivo and the functional consequences are unresolved. We studied three models of fatty acid overload in male mice: 5 h Intralipid((R)) and heparin infusion, prolonged high fat feeding (HFF) and genetic obesity induced by leptin deficiency (ob/ob mice). Markers of apoptosis, proteolysis and autophagy were assessed as readouts of lipotoxicity. The Intralipid((R)) infusion increased caspase 3 activity in skeletal muscle, demonstrating that enhancing fatty acid flux activates pro-apoptotic pathways. HFF and genetic obesity increased tissue lipid content but did not influence apoptosis. Gene array analysis revealed that HFF reduced the expression of 31 pro-apoptotic genes. Markers of autophagy (LC3beta and beclin-1 expression) were unaffected by HFF and were associated with enhanced Bcl(2) protein expression. Proteolytic activity was similarly unaffected by HFF or in ob/ob mice. Thus, contrary to our previous findings in muscle culture in vitro and in other non-adipose tissues in vivo, lipid overload did not induce apoptosis, autophagy or proteolysis in skeletal muscle. A broad transcriptional suppression of pro-apoptotic proteins may explain this resistance to lipid-induced cell death in skeletal muscle.

Hepatic lactate uptake versus leg lactate output during exercise in humans.

The exponential rise in blood lactate with exercise intensity may be influenced by hepatic lactate uptake. We compared muscle-derived lactate to the hepatic elimination during 2 h prolonged cycling (62 +/- 4% of maximal O(2) uptake, (.)Vo(2max)) followed by incremental exercise in seven healthy men. Hepatic blood flow was assessed by indocyanine green dye elimination and leg blood flow by thermodilution. During prolonged exercise, the hepatic glucose output was lower than the leg glucose uptake (3.8 +/- 0.5 vs. 6.5 +/- 0.6 mmol/min; mean +/- SE) and at an arterial lactate of 2.0 +/- 0.2 mM, the leg lactate output of 3.0 +/- 1.8 mmol/min was about fourfold higher than the hepatic lactate uptake (0.7 +/- 0.3 mmol/min). During incremental exercise, the hepatic glucose output was about one-third of the leg glucose uptake (2.0 +/- 0.4 vs. 6.2 +/- 1.3 mmol/min) and the arterial lactate reached 6.0 +/- 1.1 mM because the leg lactate output of 8.9 +/- 2.7 mmol/min was markedly higher than the lactate taken up by the liver (1.1 +/- 0.6 mmol/min). Compared with prolonged exercise, the hepatic lactate uptake increased during incremental exercise, but the relative hepatic lactate uptake decreased to about one-tenth of the lactate released by the legs. This drop in relative hepatic lactate extraction may contribute to the increase in arterial lactate during intense exercise.

Stearoyl CoA desaturase 1 is elevated in obesity but protects against fatty acid-induced skeletal muscle insulin resistance in vitro.

AIMS/HYPOTHESIS: Stearoyl CoA desaturase 1 (SCD1) is implicated in mediating obesity and insulin resistance. Paradoxically, SCD1 converts saturated fatty acids, the lipid species implicated in mediating insulin resistance, to monounsaturated fatty acids. The aim of the present study was to assess the molecular mechanisms that implicate SCD1 in the aetiology of fatty acid-induced insulin resistance. METHODS: SCD1 protein was transiently decreased or increased in rat L6 skeletal muscle myotubes using SCD1 short interfering RNA (siRNA) or liposome-mediated transfection of pcDNA3.1/Hygro-mSCD1, respectively. RESULTS: Reducing SCD1 protein resulted in marked esterification of exogenous fatty acids into diacylglycerol (DAG) and ceramide. Insulin-stimulated Akt activity and phosphorylation and 2-deoxyglucose uptake were reduced with SCD1 siRNA. Exposure of L6 myotubes to palmitate abolished insulin-stimulated glucose uptake in both control and SCD1 siRNA myotubes. Overexpression of SCD1 resulted in triacylglycerol esterification but attenuated ceramide and DAG accumulation and protected myotubes from fatty acid-induced insulin resistance. CONCLUSIONS/INTERPRETATION: SCD1 protects from cellular toxicity in L6 myotubes by preventing excessive accumulation of bioactive lipid metabolites.