Hepatic NADH reductive stress underlies common variation in metabolic traits.

The cellular NADH/NAD+ ratio is fundamental to biochemistry, but the extent to which it reflects versus drives metabolic physiology in vivo is poorly understood. Here we report the in vivo application of Lactobacillus brevis (Lb)NOX1, a bacterial water-forming NADH oxidase, to assess the metabolic consequences of directly lowering the hepatic cytosolic NADH/NAD+ ratio in mice. By combining this genetic tool with metabolomics, we identify circulating α-hydroxybutyrate levels as a robust marker of an elevated hepatic cytosolic NADH/NAD+ ratio, also known as reductive stress. In humans, elevations in circulating α-hydroxybutyrate levels have previously been associated with impaired glucose tolerance2, insulin resistance3 and mitochondrial disease4, and are associated with a common genetic variant in GCKR5, which has previously been associated with many seemingly disparate metabolic traits. Using LbNOX, we demonstrate that NADH reductive stress mediates the effects of GCKR variation on many metabolic traits, including circulating triglyceride levels, glucose tolerance and FGF21 levels. Our work identifies an elevated hepatic NADH/NAD+ ratio as a latent metabolic parameter that is shaped by human genetic variation and contributes causally to key metabolic traits and diseases. Moreover, it underscores the utility of genetic tools such as LbNOX to empower studies of 'causal metabolism'.

An insulin-regulated arrestin domain protein controls hepatic glucagon action.

Glucagon signaling is essential for maintaining normoglycemia in mammals. The arrestin fold superfamily of proteins controls the trafficking, turnover, and signaling of transmembrane receptors as well as other intracellular signaling functions. Further investigation is needed to understand the in vivo functions of the arrestin domain-containing 4 (ARRDC4) protein family member and whether it is involved in mammalian glucose metabolism. Here, we show that mice with a global deletion of the ARRDC4 protein have impaired glucagon responses and gluconeogenesis at a systemic and molecular level. Mice lacking ARRDC4 exhibited lower glucose levels after fasting and could not suppress gluconeogenesis at the refed state. We also show that ARRDC4 coimmunoprecipitates with the glucagon receptor, and ARRDC4 expression is suppressed by insulin. These results define ARRDC4 as a critical regulator of glucagon signaling and glucose homeostasis and reveal a novel intersection of insulin and glucagon pathways in the liver.

Paradoxical activation of transcription factor SREBP1c and de novo lipogenesis by hepatocyte-selective ATP-citrate lyase depletion in obese mice.

Hepatic steatosis associated with high-fat diet, obesity, and type 2 diabetes is thought to be the major driver of severe liver inflammation, fibrosis, and cirrhosis. Cytosolic acetyl CoA (AcCoA), a central metabolite and substrate for de novo lipogenesis (DNL), is produced from citrate by ATP-citrate lyase (ACLY) and from acetate through AcCoA synthase short chain family member 2 (ACSS2). However, the relative contributions of these two enzymes to hepatic AcCoA pools and DNL rates in response to high-fat feeding are unknown. We report here that hepatocyte-selective depletion of either ACSS2 or ACLY caused similar 50% decreases in liver AcCoA levels in obese mice, showing that both pathways contribute to the generation of this DNL substrate. Unexpectedly however, the hepatocyte ACLY depletion in obese mice paradoxically increased total DNL flux measured by D2O incorporation into palmitate, whereas in contrast, ACSS2 depletion had no effect. The increase in liver DNL upon ACLY depletion was associated with increased expression of nuclear sterol regulatory element-binding protein 1c and of its target DNL enzymes. This upregulated DNL enzyme expression explains the increased rate of palmitate synthesis in ACLY-depleted livers. Furthermore, this increased flux through DNL may also contribute to the observed depletion of AcCoA levels because of its increased conversion to malonyl CoA and palmitate. Together, these data indicate that in fat diet-fed obese mice, hepatic DNL is not limited by its immediate substrates AcCoA or malonyl CoA but rather by activities of DNL enzymes.

Arrestin domain-containing 3 (Arrdc3) modulates insulin action and glucose metabolism in liver.

Insulin action in the liver is critical for glucose homeostasis through regulation of glycogen synthesis and glucose output. Arrestin domain-containing 3 (Arrdc3) is a member of the α-arrestin family previously linked to human obesity. Here, we show that Arrdc3 is differentially regulated by insulin in vivo in mice undergoing euglycemic-hyperinsulinemic clamps, being highly up-regulated in liver and down-regulated in muscle and fat. Mice with liver-specific knockout (KO) of the insulin receptor (IR) have a 50% reduction in Arrdc3 messenger RNA, while, conversely, mice with liver-specific KO of Arrdc3 (L-Arrdc3 KO) have increased IR protein in plasma membrane. This leads to increased hepatic insulin sensitivity with increased phosphorylation of FOXO1, reduced expression of PEPCK, and increased glucokinase expression resulting in reduced hepatic glucose production and increased hepatic glycogen accumulation. These effects are due to interaction of ARRDC3 with IR resulting in phosphorylation of ARRDC3 on a conserved tyrosine (Y382) in the carboxyl-terminal domain. Thus, Arrdc3 is an insulin target gene, and ARRDC3 protein directly interacts with IR to serve as a feedback regulator of insulin action in control of liver metabolism.

Disrupted glucose homeostasis and skeletal-muscle-specific glucose uptake in an exocyst knockout mouse model.

Skeletal muscle is responsible for the majority of glucose disposal following meals, and this is achieved by insulin-mediated trafficking of glucose transporter type 4 (GLUT4) to the cell membrane. The eight-protein exocyst trafficking complex facilitates targeted docking of membrane-bound vesicles, a process underlying the regulated delivery of fuel transporters. We previously demonstrated the role of exocyst subunit EXOC5 in insulin-stimulated GLUT4 exocytosis and glucose uptake in cultured rat skeletal myoblasts. However, the in vivo role of EXOC5 in skeletal muscle remains unclear. Using mice with inducible, skeletal-muscle-specific knockout of exocyst subunit EXOC5 (Exoc5-SMKO), we examined how muscle-specific disruption of the exocyst would affect glucose homeostasis in vivo. We found that both male and female Exoc5-SMKO mice displayed elevated fasting glucose levels. Additionally, male Exoc5-SMKO mice had impaired glucose tolerance and lower serum insulin levels. Using indirect calorimetry, we observed that male Exoc5-SMKO mice have a reduced respiratory exchange ratio during the light period and lower energy expenditure. Using the hyperinsulinemic-euglycemic clamp method, we further showed that insulin-stimulated skeletal muscle glucose uptake is reduced in Exoc5-SMKO males compared with wild-type controls. Overall, our findings indicate that EXOC5 and the exocyst are necessary for insulin-stimulated glucose uptake in skeletal muscle and regulate glucose homeostasis in vivo.

Rho/ROCK mechanosensor in adipocyte stiffness and traction force generation.

It is increasingly recognized that interaction of adipose cells with extracellular mechanophysical milieus may play a role in regulating adipogenesis and differentiated adipocyte function and such interaction can be mediated by the mechanics of adipose cells. We measured the stiffness and traction force of adipose cells and examined the role of Rho/ROCK, the upstream effector of actin cytoskeletal contractility, in affecting these mechanical properties. Cellular Young's modulus obtained from atomic force microscopy (AFM) was significantly reduced by ROCK inhibitor (Y-27632) but elevated by Rho activator (CN01), for both preadipocytes and differentiated adipocytes. Immunofluorescent imaging suggested this could be attributed to the changes in Rho/ROCK-induced stressed actin filament formation. AFM also confirmed that differentiated adipocytes had higher stiffness than preadipocytes. On the other hand, traction force microscopy (TFM) revealed differentiated adipocytes exerted lower traction forces than preadipocytes. Traction forces of both preadipocytes and adipocytes were decreased by ROCK inhibition, but not significantly altered by Rho activation. Notably, an increasing trend of traction force with respect to cell spreading area was detected, and this trend was substantially amplified by Rho activation. Such traction force-cell area correlation was an order-of-magnitude smaller for differentiated adipocytes relative to preadipocytes, potentially due to disrupted force transmission through cytoskeleton-focal adhesion linkage by lipid droplets. Our work provides new data evidencing the Rho/ROCK control in adipose cell mechanics, laying the groundwork for adipocyte mechanotransduction studies on adipogenesis and adipose tissue remodeling.

GABA-stimulated adipose-derived stem cells suppress subcutaneous adipose inflammation in obesity.

Accumulating evidence suggests that subcutaneous and visceral adipose tissues are differentially associated with metabolic disorders. In obesity, subcutaneous adipose tissue is beneficial for metabolic homeostasis because of repressed inflammation. However, the underlying mechanism remains unclear. Here, we demonstrate that γ-aminobutyric acid (GABA) sensitivity is crucial in determining fat depot-selective adipose tissue macrophage (ATM) infiltration in obesity. In diet-induced obesity, GABA reduced monocyte migration in subcutaneous inguinal adipose tissue (IAT), but not in visceral epididymal adipose tissue (EAT). Pharmacological modulation of the GABAB receptor affected the levels of ATM infiltration and adipose tissue inflammation in IAT, but not in EAT, and GABA administration ameliorated systemic insulin resistance and enhanced insulin-dependent glucose uptake in IAT, accompanied by lower inflammatory responses. Intriguingly, compared with adipose-derived stem cells (ADSCs) from EAT, IAT-ADSCs played key roles in mediating GABA responses that repressed ATM infiltration in high-fat diet-fed mice. These data suggest that selective GABA responses in IAT contribute to fat depot-selective suppression of inflammatory responses and protection from insulin resistance in obesity.

Diet-induced obesity mediated by the JNK/DIO2 signal transduction pathway.

The cJun N-terminal kinase (JNK) signaling pathway is a key mediator of metabolic stress responses caused by consuming a high-fat diet, including the development of obesity. To test the role of JNK, we examined diet-induced obesity in mice with targeted ablation of Jnk genes in the anterior pituitary gland. These mice exhibited an increase in the pituitary expression of thyroid-stimulating hormone (TSH), an increase in the blood concentration of thyroid hormone (T4), increased energy expenditure, and markedly reduced obesity compared with control mice. The increased amount of pituitary TSH was caused by reduced expression of type 2 iodothyronine deiodinase (Dio2), a gene that is required for T4-mediated negative feedback regulation of TSH expression. These data establish a molecular mechanism that accounts for the regulation of energy expenditure and the development of obesity by the JNK signaling pathway.

Sclerostin influences body composition by regulating catabolic and anabolic metabolism in adipocytes.

Sclerostin has traditionally been thought of as a local inhibitor of bone acquisition that antagonizes the profound osteoanabolic capacity of activated Wnt/ß-catenin signaling, but serum sclerostin levels in humans exhibit a correlation with impairments in several metabolic parameters. These data, together with the increased production of sclerostin in mouse models of type 2 diabetes, suggest an endocrine function. To determine whether sclerostin contributes to the coordination of whole-body metabolism, we examined body composition, glucose homeostasis, and fatty acid metabolism in Sost-/- mice as well as mice that overproduce sclerostin as a result of adeno-associated virus expression from the liver. Here, we show that in addition to dramatic increases in bone volume, Sost-/- mice exhibit a reduction in adipose tissue accumulation in association with increased insulin sensitivity. Sclerostin overproduction results in the opposite metabolic phenotype due to adipocyte hypertrophy. Additionally, Sost-/- mice and those administered a sclerostin-neutralizing antibody are resistant to obesogenic diet-induced disturbances in metabolism. This effect appears to be the result of sclerostin's effects on Wnt signaling and metabolism in white adipose tissue. Since adipocytes do not produce sclerostin, these findings suggest an unexplored endocrine function for sclerostin that facilitates communication between the skeleton and adipose tissue.

CRISPR-delivery particles targeting nuclear receptor-interacting protein 1 (Nrip1) in adipose cells to enhance energy expenditure.

RNA-guided, engineered nucleases derived from the prokaryotic adaptive immune system CRISPR-Cas represent a powerful platform for gene deletion and editing. When used as a therapeutic approach, direct delivery of Cas9 protein and single-guide RNA (sgRNA) could circumvent the safety issues associated with plasmid delivery and therefore represents an attractive tool for precision genome engineering. Gene deletion or editing in adipose tissue to enhance its energy expenditure, fatty acid oxidation, and secretion of bioactive factors through a "browning" process presents a potential therapeutic strategy to alleviate metabolic disease. Here, we developed "CRISPR-delivery particles," denoted CriPs, composed of nano-size complexes of Cas9 protein and sgRNA that are coated with an amphipathic peptide called Endo-Porter that mediates entry into cells. Efficient CRISPR-Cas9-mediated gene deletion of ectopically expressed GFP by CriPs was achieved in multiple cell types, including a macrophage cell line, primary macrophages, and primary pre-adipocytes. Significant GFP loss was also observed in peritoneal exudate cells with minimum systemic toxicity in GFP-expressing mice following intraperitoneal injection of CriPs containing Gfp-targeting sgRNA. Furthermore, disruption of a nuclear co-repressor of catabolism, the Nrip1 gene, in white adipocytes by CriPs enhanced adipocyte browning with a marked increase of uncoupling protein 1 (UCP1) expression. Of note, the CriP-mediated Nrip1 deletion did not produce detectable off-target effects. We conclude that CriPs offer an effective Cas9 and sgRNA delivery system for ablating targeted gene products in cultured cells and in vivo, providing a potential therapeutic strategy for metabolic disease.

Interleukin-6 derived from cutaneous deficiency of stearoyl-CoA desaturase- 1 may mediate metabolic organ crosstalk among skin, adipose tissue and liver.

Stearoyl-CoA desaturase 1 (SCD1), a lipogenic enzyme that adds a double bond at the delta 9 position of stearate (C18: 0) and palmitate (C16: 0), has been proven to be important in the development of obesity. Mice with skin-specific deficiency of SCD1 (SKO) display increased whole-body energy expenditure, which is protective against adiposity from a high-fat diet because it improves glucose clearance, insulin sensitivity, and hepatic steatosis. Of note, these mice also display elevated levels of the "pro-inflammatory" plasma interleukin-6 (IL-6). In whole skin of SKO mice, IL-6 mRNA levels are increased, and protein expression is evident in hair follicle cells and in keratinocytes. Recently, the well-known role of IL-6 in causing white adipose tissue lipolysis has been linked to indirectly activating the gluconeogenic enzyme pyruvate carboxylase 1 in the liver, thereby increasing hepatic glucose production. In this study, we suggest that skin-derived IL-6 leads to white adipose tissue lipolysis, which contributes to the lean phenotype of SKO mice without the incidence of meta-inflammation that is associated with IL-6 signaling.

Endoplasmic reticulum chaperone GRP78 regulates macrophage function and insulin resistance in diet-induced obesity.

Obesity-mediated inflammation is a major cause of insulin resistance, and macrophages play an important role in this process. The 78-kDa glucose-regulated protein (GRP78) is a major endoplasmic reticulum chaperone that modulates unfolded protein response (UPR), and mice with GRP78 heterozygosity were resistant to diet-induced obesity. Here, we show that mice with macrophage-selective ablation of GRP78 (Lyz- GRP78-/-) are protected from skeletal muscle insulin resistance without changes in obesity compared with wild-type mice after 9 wk of high-fat diet. GRP78-deficient macrophages demonstrated adapted UPR with up-regulation of activating transcription factor (ATF)-4 and M2-polarization markers. Diet-induced adipose tissue inflammation was reduced, and bone marrow-derived macrophages from Lyz- GRP78-/- mice demonstrated a selective increase in IL-6 expression. Serum IL-13 levels were elevated by >4-fold in Lyz- GRP78-/- mice, and IL-6 stimulated the myocyte expression of IL-13 and IL-13 receptor. Lastly, recombinant IL-13 acutely increased glucose metabolism in Lyz- GRP78-/- mice. Taken together, our data indicate that GRP78 deficiency activates UPR by increasing ATF-4, and promotes M2-polarization of macrophages with a selective increase in IL-6 secretion. Macrophage-derived IL-6 stimulates the myocyte expression of IL-13 and regulates muscle glucose metabolism in a paracrine manner. Thus, our findings identify a novel crosstalk between macrophages and skeletal muscle in the modulation of obesity-mediated insulin resistance.-Kim, J. H., Lee, E., Friedline, R. H., Suk, S., Jung, D. Y., Dagdeviren, S., Hu, X., Inashima, K., Noh, H. L., Kwon, J. Y., Nambu, A., Huh, J. R., Han, M. S., Davis, R. J., Lee, A. S., Lee, K. W., Kim, J. K. Endoplasmic reticulum chaperone GRP78 regulates macrophage function and insulin resistance in diet-induced obesity.

Myeloid-specific Acat1 ablation attenuates inflammatory responses in macrophages, improves insulin sensitivity, and suppresses diet-induced obesity.

Macrophages are phagocytes that play important roles in health and diseases. Acyl-CoA:cholesterol acyltransferase 1 (ACAT1) converts cellular cholesterol to cholesteryl esters and is expressed in many cell types. Unlike global Acat1 knockout (KO), myeloid-specific Acat1 KO ( Acat1-) does not cause overt abnormalities in mice. Here, we performed analyses in age- and sex-matched Acat1-M/-M and wild-type mice on chow or Western diet and discovered that Acat1-M/-M mice exhibit resistance to Western diet-induced obesity. On both chow and Western diets, Acat1-M/-M mice display decreased adipocyte size and increased insulin sensitivity. When fed with Western diet, Acat1-M/-M mice contain fewer infiltrating macrophages in white adipose tissue (WAT), with significantly diminished inflammatory phenotype. Without Acat1, the Ly6Chi monocytes express reduced levels of integrin-ß1, which plays a key role in the interaction between monocytes and the inflamed endothelium. Adoptive transfer experiment showed that the appearance of leukocytes from Acat1-M/-M mice to the inflamed WAT of wild-type mice is significantly diminished. Under Western diet, Acat1-M/-M causes suppression of multiple proinflammatory genes in WAT. Cell culture experiments show that in RAW 264.7 macrophages, inhibiting ACAT1 with a small-molecule ACAT1-specific inhibitor reduces inflammatory responses to lipopolysaccharide. We conclude that under Western diet, blocking ACAT1 in macrophages attenuates inflammation in WAT. Other results show that Acat1-M/-M does not compromise antiviral immune response. Our work reveals that blocking ACAT1 suppresses diet-induced obesity in part by slowing down monocyte infiltration to WAT as well as by reducing the inflammatory responses of adipose tissue macrophages.

Myeloid-specific deletion of Zfp36 protects against insulin resistance and fatty liver in diet-induced obese mice.

Obesity is associated with adipose tissue inflammation that contributes to insulin resistance. Zinc finger protein 36 (Zfp36) is an mRNA-binding protein that reduces inflammation by binding to cytokine transcripts and promoting their degradation. We hypothesized that myeloid-specific deficiency of Zfp36 would lead to increased adipose tissue inflammation and reduced insulin sensitivity in diet-induced obese mice. As expected, wild-type (Control) mice became obese and diabetic on a high-fat diet, and obese mice with myeloid-specific loss of Zfp36 [knockout (KO)] demonstrated increased adipose tissue and liver cytokine mRNA expression compared with Control mice. Unexpectedly, in glucose tolerance testing and hyperinsulinemic-euglycemic clamp studies, myeloid Zfp36 KO mice demonstrated improved insulin sensitivity compared with Control mice. Obese KO and Control mice had similar macrophage infiltration of the adipose depots and similar peripheral cytokine levels, but lean and obese KO mice demonstrated increased Kupffer cell (KC; the hepatic macrophage)-expressed Mac2 compared with lean Control mice. Insulin resistance in obese Control mice was associated with enhanced Zfp36 expression in KCs. Compared with Control mice, KO mice demonstrated increased hepatic mRNA expression of a multitude of classical (M1) inflammatory cytokines/chemokines, and this M1-inflammatory hepatic milieu was associated with enhanced nuclear localization of IKKß and the p65 subunit of NF-κB. Our data confirm the important role of innate immune cells in regulating hepatic insulin sensitivity and lipid metabolism, challenge-prevailing models in which M1 inflammatory responses predict insulin resistance, and indicate that myeloid-expressed Zfp36 modulates the response to insulin in mice.

IL-10 prevents aging-associated inflammation and insulin resistance in skeletal muscle.

Altered energy balance and insulin resistance are important characteristics of aging. Skeletal muscle is a major site of glucose disposal, and the role of aging-associated inflammation in skeletal muscle insulin resistance remains unclear. To investigate, we examined glucose metabolism in 18-mo-old transgenic mice with muscle-specific overexpression of IL-10 (MIL10) and in wild-type mice during hyperinsulinemic-euglycemic clamping. Despite similar fat mass and energy balance, MIL10 mice were protected from aging-associated insulin resistance with significant increases in glucose infusion rates, whole-body glucose turnover, and skeletal muscle glucose uptake (∼60%; P < 0.05), as compared to age-matched WT mice. This protective effect was associated with decreased muscle inflammation, but no changes in adipose tissue inflammation in aging MIL10 mice. These results demonstrate the importance of skeletal muscle inflammation in aging-mediated insulin resistance, and our findings further implicate a potential therapeutic role of anti-inflammatory cytokine in the treatment of aging-mediated insulin resistance.-Dagdeviren, S., Jung, D. Y., Friedline, R. H., Noh, H. L., Kim, J. H., Patel, P. R., Tsitsilianos, N., Inashima, K., Tran, D. A., Hu, X., Loubato, M. M., Craige, S. M., Kwon, J. Y., Lee, K. W., Kim, J. K. IL-10 prevents aging-associated inflammation and insulin resistance in skeletal muscle.

Nocturnal activation of melatonin receptor type 1 signaling modulates diurnal insulin sensitivity via regulation of PI3K activity.

Recent genetic studies have highlighted the potential involvement of melatonin receptor 1 (MT1 ) and melatonin receptor 2 (MT2 ) in the pathogenesis of type 2 diabetes. Here, we report that mice lacking MT1 (MT1 KO) tend to accumulate more fat mass than WT mice and exhibit marked systemic insulin resistance. Additional experiments revealed that the main insulin signaling pathway affected by the loss of MT1 was the activation of phosphatidylinositol-3-kinase (PI3K). Transcripts of both catalytic and regulatory subunits of PI3K were strongly downregulated within MT1 KO mice. Moreover, the suppression of nocturnal melatonin levels within WT mice, by exposing mice to constant light, resulted in impaired PI3K activity and insulin resistance during the day, similar to what was observed in MT1 KO mice. Inversely, administration of melatonin to WT mice exposed to constant light was sufficient and necessary to restore insulin-mediated PI3K activity and insulin sensitivity. Hence, our data demonstrate that the activation of MT1 signaling at night modulates insulin sensitivity during the day via the regulation of the PI3K transcription and activity. Lastly, we provide evidence that decreased expression of MTNR1A (MT1 ) in the liver of diabetic individuals is associated with poorly controlled diabetes.

Role of the hypothalamic-pituitary-thyroid axis in metabolic regulation by JNK1.

The cJun N-terminal kinase 1 (JNK1) is implicated in diet-induced obesity. Indeed, germline ablation of the murine Jnk1 gene prevents diet-induced obesity. Here we demonstrate that selective deficiency of JNK1 in the murine nervous system is sufficient to suppress diet-induced obesity. The failure to increase body mass is mediated, in part, by increased energy expenditure that is associated with activation of the hypothalamic-pituitary-thyroid axis. Disruption of thyroid hormone function prevents the effects of nervous system JNK1 deficiency on body mass. These data demonstrate that the hypothalamic-pituitary-thyroid axis represents an important target of metabolic signaling by JNK1.

Liver-specific reconstitution of CEACAM1 reverses the metabolic abnormalities caused by its global deletion in male mice.

AIMS/HYPOTHESIS: The carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) promotes insulin clearance. Mice with global null mutation (Cc1 -/-) or with liver-specific inactivation (L-SACC1) of Cc1 (also known as Ceacam1) gene display hyperinsulinaemia resulting from impaired insulin clearance, insulin resistance, steatohepatitis and obesity. Because increased lipolysis contributes to the metabolic phenotype caused by transgenic inactivation of CEACAM1 in the liver, we aimed to further investigate the primary role of hepatic CEACAM1-dependent insulin clearance in insulin and lipid homeostasis. To this end, we examined whether transgenic reconstitution of CEACAM1 in the liver of global Cc1 -/- mutant mice reverses their abnormal metabolic phenotype. METHODS: Insulin response was assessed by hyperinsulinaemic-euglycaemic clamp analysis and energy balance was analysed by indirect calorimetry. Mice were overnight-fasted and refed for 7 h to assess fatty acid synthase activity in the liver and the hypothalamus in response to insulin release during refeeding. RESULTS: Liver-based rescuing of CEACAM1 restored insulin clearance, plasma insulin level, insulin sensitivity and steatohepatitis caused by global deletion of Cc1. It also reversed the gain in body weight and total fat mass observed with Cc1 deletion, in parallel to normalising energy balance. Mechanistically, reversal of hyperphagia appeared to result from reducing fatty acid synthase activity and restoring insulin signalling in the hypothalamus. CONCLUSIONS/INTERPRETATION: Despite the potential confounding effects of deleting Cc1 from extrahepatic tissues, liver-based rescuing of CEACAM1 resulted in full normalisation of the metabolic phenotype, underscoring the key role that CEACAM1-dependent hepatic insulin clearance pathways play in regulating systemic insulin sensitivity, lipid homeostasis and energy balance.

Protein Kinase Mitogen-activated Protein Kinase Kinase Kinase Kinase 4 (MAP4K4) Promotes Obesity-induced Hyperinsulinemia.

Previous studies revealed a paradox whereby mitogen-activated protein kinase kinase kinase kinase 4 (Map4k4) acted as a negative regulator of insulin sensitivity in chronically obese mice, yet systemic deletion of Map4k4 did not improve glucose tolerance. Here, we report markedly reduced glucose-responsive plasma insulin and C-peptide levels in whole body Map4k4-depleted mice (M4K4 iKO) as well as an impaired first phase of insulin secretion from islets derived from M4K4 iKO mice ex vivo After long-term high fat diet (HFD), M4K4 iKO mice pancreata also displayed reduced ß cell mass, fewer proliferating ß cells and reduced islet-specific gene mRNA expression compared with controls, although insulin content was normal. Interestingly, the reduced plasma insulin in M4K4 iKO mice exposed to chronic (16 weeks) HFD was not observed in response to acute HFD challenge or short term treatment with the insulin receptor antagonist S961. Furthermore, the improved insulin sensitivity in obese M4K4 iKO mice was abrogated by high exogenous insulin over the course of a euglycemic clamp study, indicating that hypoinsulinemia promotes insulin sensitivity in chronically obese M4K4 iKO mice. These results demonstrate that protein kinase Map4k4 drives obesity-induced hyperinsulinemia and insulin resistance in part by promoting insulin secretion from ß cells in mice.

Increased Glucose-induced Secretion of Glucagon-like Peptide-1 in Mice Lacking the Carcinoembryonic Antigen-related Cell Adhesion Molecule 2 (CEACAM2).

Carcinoembryonic antigen-related cell adhesion molecule 2 (CEACAM2) regulates food intake as demonstrated by hyperphagia in mice with the Ceacam2 null mutation (Cc2(-/-)). This study investigated whether CEACAM2 also regulates insulin secretion. Ceacam2 deletion caused an increase in ß-cell secretory function, as assessed by hyperglycemic clamp analysis, without affecting insulin response. Although CEACAM2 is expressed in pancreatic islets predominantly in non-ß-cells, basal plasma levels of insulin, glucagon and somatostatin, islet areas, and glucose-induced insulin secretion in pooled Cc2(-/-) islets were all normal. Consistent with immunofluorescence analysis showing CEACAM2 expression in distal intestinal villi, Cc2(-/-) mice exhibited a higher release of oral glucose-mediated GLP-1, an incretin that potentiates insulin secretion in response to glucose. Compared with wild type, Cc2(-/-) mice also showed a higher insulin excursion during the oral glucose tolerance test. Pretreating with exendin(9-39), a GLP-1 receptor antagonist, suppressed the effect of Ceacam2 deletion on glucose-induced insulin secretion. Moreover, GLP-1 release into the medium of GLUTag enteroendocrine cells was increased with siRNA-mediated Ceacam2 down-regulation in parallel to an increase in Ca(2+) entry through L-type voltage-dependent Ca(2+) channels. Thus, CEACAM2 regulates insulin secretion, at least in part, by a GLP-1-mediated mechanism, independent of confounding metabolic factors.