Severe Hepatic Insulin Resistance Research Articles

1338-P: Characteristics of Patients with Type 2 Diabetes without Nonalcoholic Fatty Liver Disease (NAFLD)

About 70% of patients with type 2 diabetes mellitus (T2DM) have NAFLD which is a risk factor for cirrhosis and hepatocellular carcinoma. Many factors may be associated with more severe disease (i.e., insulin resistance, obesity). However, the metabolic profile of T2DM patients spared from having NAFLD and liver fibrosis is unclear. To this end, we recruited 266 patients with a history of T2DM without a known history of NAFLD (age: 59 ± 10 years; female 58.3 %; BMI: 33.0 ± 6.3 kg/m2, A1c: 7.0 ± 1.4 %) attending the outpatient university clinics. We performed a medical history, physical exam and measured routine/metabolic laboratories, liver fat (by CAP score ≥ 274 dB/m) and fibrosis (by liver stiffness measurement or LSM ≥7.0 kPa or F≥1) by elastography. A total of 32% patients did not have NAFLD, but when compared to NAFLD patients there were no differences in terms of age, gender, or race. Those without NAFLD had a lower mean BMI ± SD (29.6 ± 5.2 vs. 34.6 ± 6.2 kg/m2) and better glycemic control (mean A1c: 6.7 ± 1.3% vs. 7.2 ± 1.4%, both p<0.05). Patients without NAFLD had lower plasma ALT levels (mean 21 ± 12 vs. 28 ± 19 U/L; p<0.05). Patients with NAFLD had more severe (hepatic) insulin resistance (IR) (HOMA-IR: 3.0 ± 2.3 vs. 4.9 ± 3.2, p<0.05), with more people having a HOMA-IR ≥3.0 (35% vs. 72%, p<0.05). In multiple regression analysis, with a 95% CI, obesity (OR 4.0, 2.3-7.1), HOMA-IR (OR 3.1, 1.0-5.7), and worse glycemic control (A1c) (OR 1.7, 1.1-2.9) accounted for most of the difference between subjects with vs. without NAFLD. In NAFLD patients, comparing those with vs. without fibrosis, obesity (OR 2.8, 1.6-4.9) and elevated aminotransferases (OR 2.1, 1.3-3.2) accounted for most of the difference among patient. Conclusion: Patients with type 2 diabetes mellitus without NAFLD are usually more insulin sensitive and have a more favorable cardiometabolic profile than those with NAFLD. This highlights the role of insulin resistance and lipotoxicity in the development of NAFLD in this population. Disclosure E.Valdez saenz: None. D.Barb: None. M.J.Gurka: None. A.Sharma: None. K.Cusi: Consultant; Poxel SA, Altimmune, Arrowhead Pharmaceuticals, Inc., AstraZeneca, 89bio, Inc., Bristol-Myers Squibb Company, Lilly, Madrigal Pharmaceuticals, Inc., Merck & Co., Inc., Medscape, Myovant, Novo Nordisk, ProSciento, Quest Diagnostics, Sagimet, Sonic Incytes, Terns, Research Support; Echosens, Inventiva, LabCorp, Zydus. E.Godinez leiva: None. R.Lomonaco: None. S.A.Marangi: None. S.Kalavalapalli: None. M.A.Gonzalez: None. X.Chi: None. A.Ortiz rocha: None. Y.Mohseni: None. Funding National Institutes of Health (R01120331-01A1)

Carboxylesterase 2a deletion provokes hepatic steatosis and insulin resistance in mice involving impaired diacylglycerol and lysophosphatidylcholine catabolism

ObjectiveHepatic triacylglycerol accumulation and insulin resistance are key features of NAFLD. However, NAFLD development and progression are rather triggered by the aberrant generation of lipid metabolites and signaling molecules including diacylglycerol (DAG) and lysophosphatidylcholine (lysoPC). Recent studies showed decreased expression of carboxylesterase 2 (CES2) in the liver of NASH patients and hepatic DAG accumulation was linked to low CES2 activity in obese individuals. The mouse genome encodes several Ces2 genes with Ces2a showing highest expression in the liver. Herein we investigated the role of mouse Ces2a and human CES2 in lipid metabolism in vivo and in vitro. MethodsLipid metabolism and insulin signaling were investigated in mice lacking Ces2a and in a human liver cell line upon pharmacological CES2 inhibition. Lipid hydrolytic activities were determined in vivo and from recombinant proteins. ResultsCes2a deficient mice (Ces2a-ko) are obese and feeding a high-fat diet (HFD) provokes severe hepatic steatosis and insulin resistance together with elevated inflammatory and fibrotic gene expression. Lipidomic analysis revealed a marked rise in DAG and lysoPC levels in the liver of Ces2a-ko mice fed HFD. Hepatic lipid accumulation in Ces2a deficiency is linked to lower DAG and lysoPC hydrolytic activities in liver microsomal preparations. Moreover, Ces2a deficiency significantly increases hepatic expression and activity of MGAT1, a PPAR gamma target gene, suggesting aberrant lipid signaling upon Ces2a deficiency. Mechanistically, we found that recombinant Ces2a and CES2 show significant hydrolytic activity towards lysoPC (and DAG) and pharmacological inhibition of CES2 in human HepG2 cells largely phenocopies the lipid metabolic changes present in Ces2a-ko mice including reduced lysoPC and DAG hydrolysis, DAG accumulation and impaired insulin signaling. ConclusionsCes2a and CES2 are critical players in hepatic lipid signaling likely via the hydrolysis of DAG and lysoPC at the ER.

SOX4 promotes beige adipocyte-mediated adaptive thermogenesis by facilitating PRDM16-PPARγ complex.

Brown and beige fat protect against cold environments and obesity by catabolizing stored energy to generate heat. This process is achieved by controlling thermogenesis-related gene expression and the development of brown/beige fat through the induction of transcription factors, most notably PPARγ. However, the cofactors that induce the expression of thermogenic genes with PPARγ are still not well understood. In this study, we explored the role of SOX4 in adaptive thermogenesis and its relationship with PPARγ. Methods: Whole transcriptome deep sequencing (RNA-seq) analysis of inguinal subcutaneous white adipose tissue (iWAT) after cold stimulation was performed to identify genes with differential expression in mice. Indirect calorimetry detected oxygen consumption rate and heat generation. mRNA levels were analyzed by qPCR assays. Proteins were detected by immunoblotting and immunofluorescence. Interaction of proteins was detected by endogenous and exogenous Co-IP. ChIP-qPCR, FAIRE assay and luciferase reporter assays were used to investigate transcriptional regulation. Results: SOX4 was identified as the main transcriptional effector of thermogenesis. Mice with either adipocyte-specific or UCP1+ cells deletion of SOX4 exhibited significant cold intolerance, decreased energy expenditure, and beige adipocyte formation, which was attributed to decreased thermogenic gene expression. In addition, these mice developed obesity on a high-fat diet, with severe hepatic steatosis, insulin resistance, and inflammation. At the cell level, loss of SOX4 from preadipocytes inhibited the development of beige adipocytes, and loss of SOX4 from mature beige adipocytes reduced the expression of thermogenesis-related genes and energy metabolism. Mechanistically, SOX4 stimulated the transcriptional activity of Ucp1 by binding to PPARγ and activating its transcriptional function. These actions of SOX4 were, at least partly, mediated by recruiting PRDM16 to PPARγ, thus forming a transcriptional complex to elevate the expression of thermogenic genes. Conclusion: SOX4, as a coactivator of PPARγ, drives the thermogenic gene expression program and thermogenesis of beige fat, promoting energy expenditure. It has important physiological significance in resisting cold and obesity.

Severe Hepatic Insulin Resistance Induces Vascular Dysfunction: Improvement by Liver-Specific Insulin Receptor Isoform A Gene Therapy in a Murine Diabetic Model.

Background: Cardiovascular dysfunction is linked to insulin-resistant states. In this paper, we analyzed whether the severe hepatic insulin resistance of an inducible liver-specific insulin receptor knockout (iLIRKO) might generate vascular insulin resistance and dysfunction, and whether insulin receptor (IR) isoforms gene therapy might revert it. Methods: We studied in vivo insulin signaling in aorta artery and heart from iLIRKO. Vascular reactivity and the mRNA levels of genes involved in vascular dysfunction were analyzed in thoracic aorta rings by qRT-PCR. Finally, iLIRKO mice were treated with hepatic-specific gene therapy to analyze vascular dysfunction improvement. Results: Our results suggest that severe hepatic insulin resistance was expanded to cardiovascular tissues. This vascular insulin resistance observed in aorta artery from iLIRKO mice correlated with a reduction in both PI3K/AKT/eNOS and p42/44 MAPK pathways, and it might be implicated in their vascular alterations characterized by endothelial dysfunction, hypercontractility and eNOS/iNOS levels’ imbalance. Finally, regarding long-term hepatic expression of IR isoforms, IRA was more efficient than IRB in the improvement of vascular dysfunction observed in iLIRKO mice. Conclusion: Severe hepatic insulin resistance is sufficient to produce cardiovascular insulin resistance and dysfunction. Long-term hepatic expression of IRA restored the vascular damage observed in iLIRKO mice.

IRhom2 Promotes Hepatic Steatosis by Activating MAP3K7-Dependent Pathway.

Nonalcoholic fatty liver disease (NAFLD) has been widely recognized as a precursor to metabolic complications. Elevated inflammation levels are predictive of NAFLD-associated metabolic disorder. Inactive rhomboid-like protein 2 (iRhom2) is regarded as a key regulator in inflammation. However, the precise mechanisms by which iRhom2-regulated inflammation promotes NAFLD progression remain to be elucidated. Here, we report that insulin resistance, hepatic steatosis, and specific macrophage inflammatory activation are significantly alleviated in iRhom2-deficient (knockout [KO]) mice, but aggravated in iRhom2 overexpressing mice. We further show that, mechanistically, in response to a high-fat diet (HFD), iRhom2 KO mice and mice with iRhom2 deficiency in myeloid cells only showed less severe hepatic steatosis and insulin resistance than controls. Inversely, transplantation of bone marrow cells from healthy mice to iRhom2 KO mice expedited the severity of insulin resistance and hepatic dyslipidemia. Of note, in response to HFD, hepatic iRhom2 binds to mitogen-activated protein kinase kinase kinase 7 (MAP3K7) to facilitate MAP3K7 phosphorylation and nuclear factor kappa B cascade activation, thereby promoting the activation of c-Jun N-terminal kinase/insulin receptor substrate 1 signaling, but disturbing AKT/glycogen synthase kinase 3β-associated insulin signaling. The iRhom2/MAP3K7 axis is essential for iRhom2-regulated liver steatosis. iRhom2 may represent a therapeutic target for the treatment of HFD-induced hepatic steatosis and insulin resistance.

FoxO1 suppresses Fgf21 during hepatic insulin resistance to impair peripheral glucose utilization and acute cold tolerance

SUMMARYFgf21 (fibroblast growth factor 21) is a regulatory hepatokine that, in pharmacologic form, powerfully promotes weight loss and glucose homeostasis. Although “Fgf21 resistance” is inferred from higher plasma Fgf21 levels in insulin-resistant mice and humans, diminished Fgf21 function is understood primarily via Fgf21 knockout mice. By contrast, we show that modestly reduced Fgf21—owing to cell-autonomous suppression by hepatic FoxO1—contributes to dysregulated metabolism in LDKO mice (Irs1L/L·Irs2L/L·CreAlb), a model of severe hepatic insulin resistance caused by deletion of hepatic Irs1 (insulin receptor substrate 1) and Irs2. Knockout of hepatic Foxo1 in LDKO mice or direct restoration of Fgf21 by adenoviral infection restored glucose utilization by BAT (brown adipose tissue) and skeletal muscle, normalized thermogenic gene expression in LDKO BAT, and corrected acute cold intolerance of LDKO mice. These studies highlight the Fgf21-dependent plasticity and importance of BAT function to metabolic health during hepatic insulin resistance.

1914-P: Prolonged (12-Hour) Glucagon Infusion Stimulates Adipocyte Lipolysis and Inflammation In Vivo in Humans

Hyperglucagonemia is a characteristic feature of T2DM and contributes to the metabolic disturbances. Although some rodent studies have suggested that glucagon stimulates lipolysis in adipocytes, the long-term effect of hyperglucagonemia on adipose tissue metabolism and glucose homeostasis in vivo in humans is unclear. The aim of the present study was to examine the effect of 12-hour glucagon infusion on hepatic glucose production (HGP) and adipocyte metabolism in healthy individuals. 8 NGT subjects (5M/3F, age=35±5, BMI = 24±1) received a 12-hour (6PM to 6AM) glucagon infusion (6ng/kg/min) with 3-3H-glucose infusion followed by subcutaneous adipose tissue biopsy at 6AM. On a different day the subjects returned for a repeat study with infusion (6PM to 6AM) of normal saline. Plasma glucagon increased from 57±3 to 219±21 pg/ml. Plasma glucose increased transiently after the start of glucagon and declined to baseline levels at 6AM. Plasma insulin levels increased significantly following glucagon compared to saline (20±7 vs. 8±3 mU/L, p<0.05) and remained elevated at 6AM. Basal HGP (3.2±0.1 vs. 2.9±0.1 mg/kg/min, p<0.01) and fasting plasma FFA concentrations (0.70±0.1 vs. 0.39±0.1 mM, p<0.01) were increased after 12-hour glucagon infusion despite increased plasma insulin levels, indicating severe hepatic and adipocyte insulin resistance. Lipolysis-related gene expression in adipose tissue biopsy were upregulated following 12-hour glucagon infusion (ATGL, 1.14±0.07 vs. 0.77±0.03; HSL, 1.17±0.03 vs. 0.9±0.13; MGL, 1.2±0.04 vs. 0.82±0.2, all p<0.05). Plasma concentration of inflammatory markers were also increased after 12-hour glucagon infusion (IL-1β, 0.65±0.05 vs. 0.49±0.05 pg/mL; TNF-α, 2.03±0.23 vs. 1.75±0.17 pg/mL, both p<0.05). Overall, these results demonstrate that prolonged physiologic hyperglucagonemia causes marked hepatic and adipocyte insulin resistances, stimulates lipolysis and increases plasma FFA, and induces adipocyte and systemic inflammation. Disclosure D. Tripathy: None. M. Fourcaudot: None. L. Norton: None. R.A. DeFronzo: None. X. Chen: None.

Ectopic lipid deposition mediates insulin resistance in adipose specific 11β-hydroxysteroid dehydrogenase type 1 transgenic mice

ContextExcessive adipose glucocorticoid action is associated with insulin resistance, but the mechanisms linking adipose glucocorticoid action to insulin resistance are still debated. We hypothesized that insulin resistance from excess glucocorticoid action may be attributed in part to increased ectopic lipid deposition in liver. MethodsWe tested this hypothesis in the adipose specific 11β-hydroxysteroid dehydrogenase-1 (HSD11B1) transgenic mouse, an established model of adipose glucocorticoid excess. Tissue specific insulin action was assessed by hyperinsulinemic-euglycemic clamps, hepatic lipid content was measured, hepatic insulin signaling was assessed by immunoblotting. The role of hepatic lipid content was further probed by administration of the functionally liver-targeted mitochondrial uncoupler, Controlled Release Mitochondrial Protonophore (CRMP). FindingsHigh fat diet fed HSD11B1 transgenic mice developed more severe hepatic insulin resistance than littermate controls (endogenous suppression of hepatic glucose production was reduced by 3.8-fold, P < 0.05); this was reflected by decreased insulin-stimulated hepatic insulin receptor kinase tyrosine phosphorylation and AKT serine phosphorylation. Hepatic insulin resistance was associated with a 53% increase (P < 0.05) in hepatic triglyceride content, a 73% increase in diacylglycerol content (P < 0.01), and a 66% increase in PKCε translocation (P < 0.05). Hepatic insulin resistance was prevented with administration of CRMP by reversal of hepatic steatosis and prevention of hepatic diacylglycerol accumulation and PKCε activation. ConclusionsThese findings are consistent with excess adipose glucocorticoid activity being a predisposing factor for the development of lipid (diacylglycerol-PKCε)-induced hepatic insulin resistance.

Evaluation and Management of Youth-Onset Type 2 Diabetes: A Position Statement by the American Diabetes Association.

Although all types of diabetes result in hyperglycemia, the pathophysiology of each type of diabetes is different. These guidelines summarize available data specific to the comprehensive care of youth with type 2 diabetes. The objective is to enrich the recognition of type 2 diabetes in youth, its risk factors, its pathophysiology, its management, and the prevention of associated complications. Glucose homeostasis is maintained by a balance between insulin secretion from the pancreatic β-cells and sensitivity to insulin in skeletal muscle, adipose tissue, and liver (1). When insulin sensitivity declines, insulin secretion must increase to maintain glucose tolerance, and, in most youth, decreased insulin sensitivity due to puberty and/or obesity is compensated by increased insulin secretion. However, when β-cells cannot secrete sufficient insulin to compensate for insulin resistance, abnormalities in glucose homeostasis ensue, potentially progressing to prediabetes and type 2 diabetes as β-cell function deteriorates further (2–9). The relationship between β-cell function and insulin sensitivity in adults and youth has been demonstrated to be a hyperbolic function and can be described mathematically as the product of insulin sensitivity and β-cell function, called the disposition index (DI) (1). The DI essentially expresses the amount of insulin being secreted relative to the degree of insulin resistance and is a constant for a given degree of glucose tolerance in any one individual. Overweight and obesity are major acquired contributors to the development of insulin resistance, particularly in the face of the physiologic insulin resistance characteristic of puberty. Robust pancreatic β-cell compensatory insulin secretion maintains normal glucose homeostasis. However, in adolescents with obesity who develop type 2 diabetes, there is severe peripheral and hepatic insulin resistance, with ∼50% lower peripheral insulin sensitivity than peers with obesity without diabetes, along with increased fasting hepatic glucose production and inadequate first- and second-phase insulin secretion, resulting …

ApoC-III Levels Correlate with Insulin Resistance and HbA1c in Familial Partial Lipodystrophy—Observations from the Broaden Study

Familial Partial Lipodystrophy (FPLD) is a rare genetic disorder with selective loss of adipose tissue from the periphery with an increase in ectopic fat leading to severe hepatic insulin resistance, and hypertriglyceridemia. ApoC-III is a secreted liver glycoprotein associated with hypertriglyceridemia and insulin resistance. We inquired the relationship between lipid and other metabolic parameters with morphometric characteristics (including those of ectopic fat deposition) and circulating apoC-III levels in a cohort of FPLD patients who were screened for enrollment into the BROADEN study, a global trial to study efficacy of volanesorsen (an antisense mRNA apoC-III inhibitor). 28 patients are included in these analyses (age range, 28 to 65, mean 45 years; M/F, 7/21; all but one Caucasian). Table 1 shows the significant relationships observed using linear regression analyses between circulating ApoC-III levels and investigated parameters. These results reiterate the tight relationship between triglyceride levels and ApoC-III levels, and further demonstrate that circulating ApoC-III levels also correlate with insulin resistance, and HbA1c as well as important left ventricle morphometric parameters. It is plausible to hypothesize that a strategy to lower apoC-III levels may have additional benefits beyond lowering triglyceride levels.Table 1: Relationship of metabolic and echocardiogram parameters in FPLDParametersR2p-valuenParametersR2p-valuenTriglycerides* vs. ApoC-III0.63&amp;lt;0.00128LV end systolic diameter vs ApoC-III0.260.02719HOMA-IR* vs. ApoC-III0.190.01928LV end systolic diameter vs Triglycerides*0.250.03119HOMA-IR* vs. Triglycerides*0.150.04228Left ventricle outflow tract dimension vs ApoC-III0.220.04519Insulin* vs. ApoC-III0.140.04528Left ventricle outflow tract dimension vs Triglycerides*0.290.01719HbA1c** vs. ApoC-III0.230.03021* Parameter log-transformed**Subjects with HbA1c&amp;lt;6.4% excluded Disclosure R. Meral: None. A. Digenio: Employee; Self; Akcea Therapeutics. A.H. Neidert: None. J. Tami: Employee; Self; Ionis Pharmaceuticals, Inc.. Stock/Shareholder; Self; Ionis Pharmaceuticals, Inc. E.A. Oral: Advisory Panel; Self; Aegerion Pharmaceuticals. Research Support; Self; Aegerion Pharmaceuticals, Akcea Therapeutics. Advisory Panel; Self; Akcea Therapeutics. Research Support; Self; Ionis Pharmaceuticals, Inc., AstraZeneca. Other Relationship; Self; Aegerion Pharmaceuticals.

Hepatic protein tyrosine phosphatase receptor gamma links obesity-induced inflammation to insulin resistance

Obesity-induced inflammation engenders insulin resistance and type 2 diabetes mellitus (T2DM) but the inflammatory effectors linking obesity to insulin resistance are incompletely understood. Here, we show that hepatic expression of Protein Tyrosine Phosphatase Receptor Gamma (PTPR-γ) is stimulated by inflammation in obese/T2DM mice and positively correlates with indices of inflammation and insulin resistance in humans. NF-κB binds to the promoter of Ptprg and is required for inflammation-induced PTPR-γ expression. PTPR-γ loss-of-function lowers glycemia and insulinemia by enhancing insulin-stimulated suppression of endogenous glucose production. These phenotypes are rescued by re-expression of Ptprg only in liver of mice lacking Ptprg globally. Hepatic PTPR-γ overexpression that mimics levels found in obesity is sufficient to cause severe hepatic and systemic insulin resistance. We propose hepatic PTPR-γ as a link between obesity-induced inflammation and insulin resistance and as potential target for treatment of T2DM.

Isoflurane and Sevoflurane Induce Severe Hepatic Insulin Resistance in a Canine Model.

IntroductionAnesthesia induces insulin resistance, which may contribute to elevated blood glucose and adverse post-operative outcomes in critically ill patients, and impair glycemic control in surgical patients with diabetes. However, little is known about the mechanisms by which anesthesia impairs insulin sensitivity. Here we investigate the effects of anesthesia on insulin sensitivity in metabolic tissues.MethodsHyperinsulinemic-euglycemic clamps were performed in 32 lean (control diet; n = 16 conscious versus n = 16 anesthetized) and 24 fat-fed (6 weeks fat-feeding; n = 16 conscious versus n = 8 anesthetized) adult male mongrel dogs in conjunction with tracer methodology to differentiate hepatic versus peripheral insulin sensitivity. Propofol was administered as an intravenous bolus (3mg/kg) to initiate anesthesia, which was then maintained with inhaled sevoflurane or isoflurane (2–3%) for the duration of the procedure.ResultsAnesthesia reduced peripheral insulin sensitivity by approximately 50% in both lean and fat-fed animals as compared to conscious animals, and insulin action at the liver was almost completely suppressed during anesthesia such that hepatic insulin sensitivity was decreased by 75.5% and; 116.2% in lean and fat-fed groups, respectively.ConclusionInhaled anesthesia induces severe hepatic insulin resistance in a canine model. Countermeasures that preserve hepatic insulin sensitivity may represent a therapeutic target that could improve surgical outcomes in both diabetic and healthy patients.

Early inflammation-associated factors blunt sterol regulatory element-binding proteins-1-mediated lipogenesis in high-fat diet-fed APPSWE /PSEN1dE9 mouse model of Alzheimer's disease.

Alzheimer's disease (AD) patients have an increased incidence of Type 2 diabetes (T2D); however, the underlying mechanisms are not well understood. Since AD is considered a multifactorial disease that affects both the central nerves system and periphery and the dysregulation of hepatic lipid and glucose metabolism play critical roles in T2D, we, therefore, aim to explore the influence of AD genotype on the liver during the progress of high-fat diet (HFD)-induced T2D. Fourteen-week-old female APPSWE /PSEN1dE9 (AD) mice and age-, gender-matched wild-type controls C57BL/6J (WT) mice were fed a HFD (45% kcal fat content) or a standard chow diet (chow, 12% kcal fat content) for 22weeks. The effects of diet and genotype were analyzed. Mouse primary hepatocytes were used to decipher the underlying mechanisms. HFD induced significantly higher body weight gain, more severe hyperglycemia, glucose intolerance and hepatic insulin resistance in AD mice than in WT mice. However, AD mice showed reduced HFD-induced hepatic steatosis, and SREBP-1-mediated lipogenic signaling was activated by HFD in WT mice but not in AD mice. In addition, 14-week-old AD mice exhibited higher expression of NF-κB p65, p-JNK and p-p38MAPK, as well as higher hepatic and serum contents of IL-6 and TNFα. In mouse primary hepatocyte cultures, IL-6 and TNFα inhibited high-glucose plus insulin-induced activation of SREBP-1-mediated lipogenic signaling and biosynthesis of non-esterified fatty acid and triglyceride. Early inflammation-associated factors most likely diminish HFD-induced hepatic lipid deposition by inhibiting SREBP-1-mediated de novo lipogenesis, thus driving substrate flux to glucose production for hyperglycemia and hepatic insulin resistance in T2D development. Alzheimer's disease (AD) is a multifactorial disease affecting both central nerves system and periphery organs. Therefore, we explored the hepatic susceptibility to high-fat diet (HFD) in AD mice. We found that AD mice were resistant to HFD-induced hepatic fat accumulation in spite of more severe obesity, hyperglycemia, glucose intolerance and hepatic insulin resistance. Mechanistically, AD mice exhibited hepatic inflammation at an early stage, which inhibited sterol regulatory element-binding proteins-1 (SREBP-1)-mediated de novo lipogenesis, and most likely drive substrate flux to glucose production for hyperglycemia and hepatic insulin resistance. Cover Image for this issue: doi: 10.1111/jnc.13306.

Dysfunction of lipid metabolism in lipodystrophic Seipin-deficient mice

Congenital generalized lipodystrophy (CGL) is characterized by a complete loss of body adipose tissue accompanying dyslipidemia, severe hepatic steatosis and insulin resistance. However, the mechanisms of dyslipidemia and hepatic steatosis are unclear. Here using the lipodystrophic Seipin-deficient mouse (Seipin−/−) model, we found Seipin−/− mice were unable to respond appropriately to a long time fasting and developed postprandial hypertriglyceridemia. Impaired very low density lipoprotein (VLDL) secretion and enhanced triglyceride-rich lipoproteins (TRL) clearance were also observed in our Seipin−/− mice. To identify the association between upregulation of hepatic LDL receptor and enhanced TRL clearance, we crossed Seipin−/− mice with Ldlr−/− mice to generate Seipin−/−Ldlr−/− mice. Seipin−/−Ldlr−/− mice displayed increased TRL clearance only after 24 h-fast rather 6 h-fast. In contrast to Seipin−/− mice, Seipin−/−Ldlr−/− mice displayed hypertriglyceridemia as observed in human CGL patients. Furthermore, in this study, we demonstrated hepatic steatosis in lipodystrophy Seipin−/− mice is a metabolic adaptation of dysfunctional adipose tissue. This study using lipodystrophic model established the importance of adipose tissue in energy homeostasis and lipid metabolism.

Insulin receptor isoform A confers a higher proliferative capability to pancreatic beta cells enabling glucose availability and IGF-I signaling

The main compensatory response to insulin resistance is the pancreatic beta cell hyperplasia to account for increased insulin secretion. In fact, in a previous work we proposed a liver–pancreas endocrine axis with IGF-I (insulin-like growth factor type I) secreted by the liver acting on IRA insulin receptor in beta cells from iLIRKO mice (inducible Liver Insulin Receptor KnockOut) that showed a high IRA/IRB ratio. However, the role of insulin receptor isoforms in the IGF-I-induced beta cell proliferation as well as the underlying molecular mechanisms remain poorly understood. For this purpose, we have used four immortalized mouse beta cell lines: bearing IR (IRLoxP), lacking IR (IRKO), expressing exclusively IRA (IRA), or alternatively expressing IRB (IRB). Pancreatic beta cell proliferation studies showed that IRA cells are more sensitive than those expressing IRB to the mitogenic response induced by IGF-I, acting through the pathway IRA/IRS-1/2/αp85/Akt/mTORC1/p70S6K. More importantly, IRA beta cells, but not IRB, showed an increased glucose uptake as compared with IRLoxP cells, this effect being likely owing to an enhanced association between Glut-1 and Glut-2 with IRA. Overall, our results strongly suggest a prevalent role of IRA in glucose availability and IGF-I-induced beta cell proliferation mainly through mTORC1. These results could explain, at least partially, the role played by the liver-secreted IGF-I in the compensatory beta cell hyperplasia observed in response to severe hepatic insulin resistance in iLIRKO mice.

Integrin α1-null Mice Exhibit Improved Fatty Liver When Fed a High Fat Diet Despite Severe Hepatic Insulin Resistance

Hepatic insulin resistance is associated with increased collagen. Integrin α1β1 is a collagen-binding receptor expressed on hepatocytes. Here, we show that expression of the α1 subunit is increased in hepatocytes isolated from high fat (HF)-fed mice. To determine whether the integrin α1 subunit protects against impairments in hepatic glucose metabolism, we analyzed glucose tolerance and insulin sensitivity in HF-fed integrin α1-null (itga1(-/-)) and wild-type (itga1(+/+)) littermates. Using the insulin clamp, we found that insulin-stimulated hepatic glucose production was suppressed by ∼50% in HF-fed itga1(+/+) mice. In contrast, it was not suppressed in HF-fed itga1(-/-) mice, indicating severe hepatic insulin resistance. This was associated with decreased hepatic insulin signaling in HF-fed itga1(-/-) mice. Interestingly, hepatic triglyceride and diglyceride contents were normalized to chow-fed levels in HF-fed itga1(-/-) mice. This indicates that hepatic steatosis is dissociated from insulin resistance in HF-fed itga1(-/-) mice. The decrease in hepatic lipid accumulation in HF-fed itga1(-/-) mice was associated with altered free fatty acid metabolism. These studies establish a role for integrin signaling in facilitating hepatic insulin action while promoting lipid accumulation in mice challenged with a HF diet.

The Suprachiasmatic Nucleus Controls Circadian Energy Metabolism and Hepatic Insulin Sensitivity

Disturbances in the circadian system are associated with the development of type 2 diabetes mellitus. Here, we studied the direct contribution of the suprachiasmatic nucleus (SCN), the central pacemaker in the circadian system, in the development of insulin resistance. Exclusive bilateral SCN lesions in male C57Bl/6J mice, as verified by immunochemistry, showed a small but significant increase in body weight (+17%), which was accounted for by an increase in fat mass. In contrast, mice with collateral damage to the ventromedial hypothalamus and paraventricular nucleus showed severe obesity and insulin resistance. Mice with exclusive SCN ablation revealed a loss of circadian rhythm in activity, oxygen consumption, and food intake. Hyperinsulinemic–euglycemic clamp analysis 8 weeks after lesioning showed that the glucose infusion rate was significantly lower in SCN lesioned mice compared with sham-operated mice (−63%). Although insulin potently inhibited endogenous glucose production (−84%), this was greatly reduced in SCN lesioned mice (−7%), indicating severe hepatic insulin resistance. Our data show that SCN malfunctioning plays an important role in the disturbance of energy balance and suggest that an absence of central clock activity, in a genetically intact animal, may lead to the development of insulin resistance.

Prediabetes: A Prevalent and Treatable, but Often Unrecognized, Clinical Condition

Type 2 diabetes mellitus (T2DM) affects more than 8% of the United States population.1 The onset of T2DM is gradual, with most individuals progressing through a state of pre-diabetes which is defined as impaired fasting glucose (IFG; plasma glucose of 100–125 mg/dl or 5.6–6.9 mmol/l) and/or impaired glucose tolerance (IGT; plasma glucose of 140–199 mg/dl or 7.8–11.0 mmol/l 2h after an oral load of 75g dextrose) and/or hemoglobin A1C 5.7–6.4%.2 According to a study of a nationally representative sample (n =1,547), an estimated 35% of the United States population suffers from pre-diabetes: 19% have IFG only, 5% have IGT only, and 10% have both IFG and IGT.3 Although individuals can spend years in a pre-diabetic state, an expert American Diabetes Association (ADA) panel estimated that up to 70% will eventually progress to T2DM.4 However, not all individuals with pre-diabetes progress at the same rate. A meta-analysis of prospective cohort studies showed that the annual incidence of diabetes in people with IGT, IFG, or both was 6.1%, 7.0%, and 14.0% respectively.5 The diagnosis of pre-diabetes presents healthcare providers with an opportunity to identify patients at increased risk for T2DM and to implement interventions that can delay or prevent T2DM and its complications.4 Unfortunately, this opportunity is often unrecognized, as an analysis of a nationally representative sample of patients with pre-diabetes (n=584) concluded that only 31.7%, 33.4%, 25.9% had been counseled about exercise, diet, or both, respectively by a doctor or health professional.3 Possible reasons for not counseling patients include lack of reimbursement, lack of resources, lack of time, and lack of skill.6, 7 However, individuals who have been counseled by their health-care provider to adopt a healthy lifestyle reported greater adherence to weight control and diet modification and had lower low density lipoprotein (LDL) cholesterol, lower body mass index (BMI), and higher high density lipoprotein (HDL) cholesterol.8 Still, it is unclear whether counseling sessions by a primary care provider in the outpatient setting are correlated with improvements in fasting plasma glucose in patients with pre-diabetes compared to similar patients who have not been counseled. While there is some evidence to suggest lifestyle counseling may be associated with self-reported changes in lifestyle behavior in overweight and obese adults with pre-diabetes and diabetes,9 other data suggest that lifestyle intervention programs that have been implemented in the outpatient healthcare setting have had an insignificant impact on fasting plasma glucose.6 Nevertheless, according to ADA guidelines there is clear evidence to support providing medical nutrition therapy as needed to patients with pre-diabetes.10 Given the high prevalence of pre-diabetes, it is important to understand the basic underlying pathophysiology and how lifestyle interventions can be implemented in the clinical setting to reduce a patient’s risk for developing T2DM.

Alcohol, insulin resistance and the liver–brain axis

Chronic alcohol exposure inhibits insulin and insulin-like growth factor signaling in the liver and brain by impairing the signaling cascade at multiple levels. These alterations produced by alcohol cause severe hepatic and central nervous system insulin resistance as the cells fail to adequately transmit signals downstream through Erk/mitogen-activated protein kinase (MAPK), which is needed for DNA synthesis and liver regeneration, and phosphatidylinositol 3-kinase (PI3K), which promotes growth, survival, cell motility, glucose utilization, plasticity, and energy metabolism. The robust inhibition of insulin signaling in liver and brain is augmented by additional factors involving the activation of phosphatases such as phosphatase and tensin homologue (PTEN), which further impairs insulin signaling through PI3K/Akt. Thus, intact insulin signaling is important for neuronal survival. Chronic alcohol consumption produces steatohepatitis, which also promotes hepatic insulin resistance, oxidative stress and injury, with the attendant increased generation of "toxic lipids" such as ceramides that increase insulin resistance. The PI3K/Akt signaling cascade is altered by direct interaction with ceramides as well as through PTEN upregulation as a downstream target gene of enhanced p53 transcriptional activity. Cytotoxic ceramides transferred from the liver to the blood can enter the brain due to their lipid-soluble nature, and thereby exert neurodegenerative effects via a liver-brain axis. We postulate that the neurotoxic and neurodegenerative effects of liver-derived ceramides activate pro-inflammatory cytokines and increase lipid adducts and insulin resistance in the brain to impair cognitive and motor function. These observations are discussed in the context of insulin sensitizers as potential cytoprotective agents against liver and brain injury induced by alcohol.

Apolipoprotein CIII overexpressing mice are predisposed to diet‐induced hepatic steatosis and hepatic insulin resistance

Nonalcoholic fatty liver disease (NAFLD) and insulin resistance have recently been found to be associated with increased plasma concentrations of apolipoprotein CIII (APOC3) in humans carrying single nucleotide polymorphisms within the insulin response element of the APOC3 gene. To examine whether increased expression of APOC3 would predispose mice to NAFLD and hepatic insulin resistance, human APOC3 overexpressing (ApoC3Tg) mice were metabolically phenotyped following either a regular chow or high-fat diet (HFD). After HFD feeding, ApoC3Tg mice had increased hepatic triglyceride accumulation, which was associated with cellular ballooning and inflammatory changes. ApoC3Tg mice also manifested severe hepatic insulin resistance assessed by a hyperinsulinemic-euglycemic clamp, which could mostly be attributed to increased hepatic diacylglycerol content, protein kinase C-ε activation, and decreased insulin-stimulated Akt2 activity. Increased hepatic triglyceride content in the HFD-fed ApoC3Tg mice could be attributed to a ≍70% increase in hepatic triglyceride uptake and ≍50% reduction hepatic triglyceride secretion. Conclusion: These data demonstrate that increase plasma APOC3 concentrations predispose mice to diet-induced NAFLD and hepatic insulin resistance. (Hepatology 2011;54:1650-1660)