Mouse Model Of Insulin Resistance Research Articles

A short peptide of the C-terminal class Y helices of apolipoprotein A-I has preserved functions in cholesterol efflux and in vivo metabolic control

Apolipoprotein A-I (ApoA-I) of high-density lipoprotein (HDL) induces glucose uptake by muscle tissues and stimulates pancreatic insulin secretion, and also facilitates cholesterol transport in circulation, and is explored for anti-diabetic and anti-atherosclerotic treatments. As the better alternative to complex protein–lipid formulations it was recently established that the C-terminal region of the ApoA-I protein singly improves the metabolic control and prevents formation of atherosclerotic plaques. Additional investigations of peptides based on the ApoA-I structure may lead to novel anti-diabetic drugs. We here investigate a short peptide (33mer, RG33) that corresponds to the two last helical segments (aa 209–241) of the ApoA-I structure (so-called class Y-helices which forms amphipathic helices) for stability and solubility in serum, for in vitro cholesterol efflux capability, and for providing in vivo glucose control in an insulin resistant mouse model. The RG33 peptide efficiently solubilizes lipid-vesicles, and promotes the efflux of cholesterol from cultured macrophages. The efflux capacity is significantly increased in the presence of lipids compared to non-lipidated RG33. Finally, acute treatment with the RG33 peptide significantly improves the glucose clearance capacity of insulin resistant mice. The impact of the RG33 peptide on glucose control and cholesterol transport, as well as the physicochemical properties, makes it a good candidate for translational exploration of its therapeutic potential in diabetes treatment.

Cold Press Pomegranate Seed Oil Attenuates Dietary-Obesity Induced Hepatic Steatosis and Fibrosis through Antioxidant and Mitochondrial Pathways in Obese Mice.

Aim: Obesity is associated with metabolic syndrome, hypertension, dyslipidemia, nonalcoholic fatty liver disease (NAFLD), and type 2 diabetes. In this study, we investigated whether the dietary supplementation of pomegranate seed oil (PSO) exerted a protective effect on liver lipid uptake, fibrosis, and mitochondrial function in a mouse model of obesity and insulin resistance. Method: In this in vivo study, eight-week-old C57BL/6J male mice were fed with a high fat diet (HFD) for 24 weeks and then were divided into three groups as follows: group (1) Lean; group (n = 6) (2) HF diet; group (n = 6) (3) HF diet treated with PSO (40 mL/kg food) (n = 6) for eight additional weeks starting at 24 weeks. Physiological parameters, lipid droplet accumulation, inflammatory biomarkers, antioxidant biomarkers, mitochondrial biogenesis, insulin sensitivity, and hepatic fibrosis were determined to examine whether PSO intervention prevents obesity-associated metabolic syndrome. Results: The PSO group displayed an increase in oxygen consumption, as well as a decrease in fasting glucose and blood pressure (p < 0.05) when compared to the HFD-fed mice group. PSO increased both the activity and expression of hepatic HO-1, downregulated inflammatory adipokines, and decreased hepatic fibrosis. PSO increased the levels of thermogenic genes, mitochondrial signaling, and lipid metabolism through increases in Mfn2, OPA-1, PRDM 16, and PGC1α. Furthermore, PSO upregulated obesity-mediated hepatic insulin receptor phosphorylation Tyr-972, p-IRB tyr1146, and pAMPK, thereby decreasing insulin resistance. Conclusions: These results indicated that PSO decreased obesity-mediated insulin resistance and the progression of hepatic fibrosis through an improved liver signaling, as manifested by increased insulin receptor phosphorylation and thermogenic genes. Furthermore, our findings indicate a potential therapeutic role for PSO in the prevention of obesity-associated NAFLD, NASH, and other metabolic disorders.

The anti-insulin resistance effect of scutellarin may be related to antioxidant stress and AMPKα activation in diabetic mice

AimsScutellarein (Sc), a natural compound and an active ingredient of Erigeronbrevis-capus (Vant.), shows anti-obesity, anti-inflammation and lipid-lowering properties in our previous study. However, no previous in vivo and vitro has been conducted to assess the effects of Sc in insulin resistance (IR). This study investigated the effects of Sc on IR and oxidative stress and explored the underlying mechanisms of action in vivo and vitro. Material and methodA well-established mouse model of IR, induced by high-fat diet (HFD) feeding, was applied in this study. The effects of Sc were evaluated on obesity, glycometabolism disorder and oxidative stress. The anti-IR effect was assessed using blood glucose, serum insulin, HOMA index, intraperitoneal glucose tolerance tests (IPGTT), intraperitoneal insulin tolerance tests (IPITT), and glucose-regulating enzyme activity. The insulin signaling pathways and AMPKα expressions were tested by Western blot. The primary culture of hepatocytes was prepared and used for confirming the above signaling pathways. ResultsObesity, IR and oxidative stress developed in HFD mice. Administration of Sc at a dose of 50mg/kg for 16 weeks effectively attenuated these changes. Further studies revealed the antagonistic effect of Sc on IR was a result of the activation of the insulin signaling pathway and AMPKα. The primary hepatocyte test, stimulated by high glucose, further confirmed that SC exerts anti-IR through the above signaling pathway and key protein. ConclusionThese results suggested that Sc possesses not only an important novel anti-IR effect but also an anti-oxidative stress effect. These favorable effects were causally associated with weight loss and the improved glycometabolism. The underlying mechanisms might associated with the activation of the insulin signaling pathway and AMPKα. Our study promotes the understanding of the pharmacological actions of Sc, and plays a role for Sc in the effective treatment of diabetes mellitus.

RIPK2 Dictates Insulin Responses to Tyrosine Kinase Inhibitors in Obese Male Mice.

Tyrosine kinase inhibitors (TKIs) used in cancer are also being investigated in diabetes. TKIs can improve blood glucose control in diabetic cancer patients, but the specific kinases that alter blood glucose or insulin are not clear. We sought to define the role of Receptor Interacting Serine/Threonine Kinase 2 (RIPK2) in mouse models of insulin resistance. We tested the TKI gefitinib, which inhibits RIPK2 activity, in wild-type (WT), Nod1-/-, Nod2-/-, and Ripk2-/- mice fed an obesogenic high-fat diet. Gefitinib lowered blood glucose during a glucose tolerance test (GTT) in a nucleotide-binding oligomerization domain (NOD)-RIPK2-independent manner in all obese mice. However, gefitinib lowered glucose-stimulated insulin secretion only in obese Ripk2-/- mice. Gefitinib had no effect on insulin secretion in obese WT, Nod1-/-, or Nod2-/- mice. Hence, genetic deletion of Ripk2 promoted the insulin-sensitizing potential of gefitinib, since this TKI lowered both blood glucose and insulin only in Ripk2-/- mice. Gefitinib did not alter the inflammatory profile of pancreas, adipose, liver, or muscle tissues in obese Ripk2-/- mice compared with obese WT mice. We also tested imatinib, a TKI that does not inhibit RIPK2 activity, in obese WT mice. Imatinib lowered blood glucose during a GTT, consistent with TKIs lowering blood glucose independently of RIPK2. However, imatinib increased glucose-stimulated insulin secretion during the glucose challenge. These data show that multiple TKIs lower blood glucose, where actions of TKIs on RIPK2 dictate divergent insulin responses, independent of tissue inflammation. Our data show that RIPK2 limits the insulin sensitizing effect of gefitinib, whereas imatinib increased insulin secretion.

GPx3 dysregulation impacts adipose tissue insulin receptor expression and sensitivity

Insulin receptor signaling is crucial for white adipose tissue (WAT) function. Consequently, lack of insulin receptor (IR) in WAT results in a diabetes-like phenotype. Yet, causes for IR downregulation in WAT of patients with diabetes are not well understood. By using multiple mouse models of obesity and insulin resistance, we identify a common downregulation of IR with a reduction of mRNA expression of selenoproteins Txnrd3, Sephs2, and Gpx3 in gonadal adipose tissue. Consistently, GPX3 is also decreased in adipose tissue of insulin-resistant and obese patients. Inducing Gpx3 expression via selenite treatment enhances IR expression via activation of the transcription factor Sp1 in 3T3-L1 preadipocytes and improves adipocyte differentiation and function. Feeding mice a selenium-enriched high-fat diet alleviates diet-induced insulin resistance with increased insulin sensitivity, decreased tissue inflammation, and elevated IR expression in WAT. Again, IR expression correlated positively with Gpx3 expression, a phenotype that is also conserved in humans. Consequently, decreasing GPx3 using siRNA technique reduced IR expression and insulin sensitivity in 3T3-L1 preadipocytes. Overall, our data identify GPx3 as a potentially novel regulator of IR expression and insulin sensitivity in adipose tissue.

Dapagliflozin exerts positive effects on beta cells, decreases glucagon and does not alter beta- to alpha-cell transdifferentiation in mouse models of diabetes and insulin resistance

Loss of beta cell identity and subsequent transdifferentiation of beta-to-alpha cells is implicated in the pathogenesis of diabetes. In addition, sodium-glucose transport protein 2 (SGLT2) inhibition has been linked to altered alpha-cell function. To investigate these phenomenon, lineage tracing of beta-cells was examined following 10–12 days dapagliflozin (1 or 5 mg/kg, once daily, as appropriate) treatment in multiple low-dose streptozotocin (STZ), high fat fed (HFF) or hydrocortisone (HC) transgenic Ins1Cre/+/Rosa26-eYFP mouse models of diabetes and insulin resistance. As anticipated, STZ, HFF and HC treated mice developed characteristic features of insulin deficiency or resistance. Dapagliflozin elicited differing beneficial effects depending on the aetiology of syndrome studied. The SGLT2 inhibitor efficiently promoted (P < 0.001) weight loss in HFF and STZ mice, whilst in HC mice it reduced (P < 0.001) energy intake, without an impact on body weight. Despite lacking significant effects on glycaemia, 1 mg/kg dapagliflozin consistently decreased both plasma and pancreatic glucagon. This was associated with increased pancreatic insulin in STZ and HFF mice. In STZ and HFF mice, beta cell proliferation and Pdx1 expression were enhanced by dapagliflozin, with a further increase in overall glucagon staining in HFF islets. Islet, beta- and alpha-cell areas were increased in dapagliflozin treated HC mice, which appeared to be linked to decreased alpha- and beta-cell apoptosis. Although the diabetes-like syndromes induced clear alterations in islet cell transdifferentiation, treatment with dapagliflozin (1 mg/kg) had no significant impact on this process, with 5 mg/kg marginally decreasing loss of beta-cells identity in STZ mice. These data suggest that SGLT2 inhibitors have positive effects on beta cells and decrease plasma and pancreatic glucagon, independent of changes in ambient glucose levels. Our combined data indicate that SGLT2 inhibitors do not directly induce hyperglucagonaemia.

Myeloid‐Specific STAT4 Deletion Improves Glucose Homeostasis in Diet‐Induced Obesity

The signal transducer and activator of transcription 4 (STAT4) is activated in response to IL‐12 and stimulates expression of genes necessary for T helper 1 cell differentiation. Recent evidence has suggested that STAT4 is involved in an inflammatory cascade leading to atherosclerosis and insulin resistance in mouse models. However, the role of STAT4 in myeloid cell functions has not been studied. IL‐12 and STAT4 is expressed in the pancreatic beta cell and therefore changes in activity could lead to altered glucose homeostasis as typically seen in type 2 diabetes (T2D). For this reason, elucidation of cell‐specific roles of STAT4 on glucose homeostasis is critical for treatment and prevention of T2D. Previous studies have shown that global STAT4 deletion significantly improves insulin signaling and glucose tolerance in high fat fed C57Bl6 mice. This study was undertaken to determine the role of myeloid specific STAT4 deletions on glucose homeostasis and islet function. We developed a novel mouse model with targeted deletion of STAT4 in myeloid cells. Here we show that high fat fed C57Bl6 mice with macrophage specific STAT4 deletion (STAT4 LysmCre) display improved glucose metabolism compared to control mice. After 16‐weeks, control mice gained an average of 24.5 grams while the STAT4 LysmCre cohort gained an average of 20 grams, indicating only moderate differences in weight gain. However, STAT4 LysmCre mice showed an improved glucose tolerance compared to control mice [AUCGlucose 68780±2820 vs. 56025±6687 (mg/dl)*min]. These results may suggest that STAT4 signaling in myeloid cells plays a key role in glucose homeostasis during high fat feeding. Further studies in progress will explore the role of myeloid STAT4 deletion on pancreatic beta cell function.Support or Funding InformationThis research is being funded by NIH grant 5R01HL142129‐02

Hydrophilic Astaxanthin: PEGylated Astaxanthin Fights Diabetes by Enhancing the Solubility and Oral Absorbability

To develop hydrophilic astaxanthin with significantly enhanced solubility and stability, astaxanthin polyethylene glycol succinate (APGS) was synthesized by esterification of an astaxanthin succinate diester with polyethylene glycol 1000. The chemical structure of the hydrophilic derivative was confirmed by 1H nuclear magnetic resonance and mass spectra. APGS showed better solubility than free astaxanthin in water and enhanced bioavailability compared to that of free astaxanthin. Additionally, testing the effects on diabetes and inflammation in a high-fat- and high-sucrose-diet-induced insulin-resistant mouse model demonstrated its benefits, suggesting that APGS maintains the health-promoting properties of astaxanthin. These results suggest that APGS could be a better source of hydrophilic astaxanthin.

Swimming Exercise Protects against Insulin Resistance via Regulating Oxidative Stress through Nox4 and AKT Signaling in High-Fat Diet-Fed Mice.

Nonpharmaceutical therapies such as exercise training and diet intervention are widely used for the treatment of insulin resistance (IR). Although the skeletal muscle is the major peripheral tissue of glucose metabolism under insulin stimulation, the mechanism underlying muscle IR is poorly understood. Using a high-fat diet-induced IR mouse model, we here show that NADPH oxidase 4 (Nox4) upregulation mediates the production of reactive oxygen species (ROS) that causes metabolic syndrome featuring IR. The Nox4 expression level was markedly elevated in IR mice, and Nox4 overexpression was sufficient to trigger IR. Conversely, downregulation of Nox4 expression through exercise training prevented diet-induced IR by reducing the production of ROS and enhancing the AKT signaling pathway. Thus, this study indicates that exercise might improve IR through a reduction of Nox4-induced ROS in the skeletal muscle and enhancement of AKT signal transduction.

Icosabutate Exerts Beneficial Effects Upon Insulin Sensitivity, Hepatic Inflammation, Lipotoxicity, and Fibrosis in Mice.

Icosabutate is a structurally engineered eicosapentaenoic acid derivative under development for nonalcoholic steatohepatitis (NASH). In this study, we investigated the absorption and distribution properties of icosabutate in relation to liver targeting and used rodents to evaluate the effects of icosabutate on glucose metabolism, insulin resistance, as well as hepatic steatosis, inflammation, lipotoxicity, and fibrosis. The absorption, tissue distribution, and excretion of icosabutate was investigated in rats along with its effects in mouse models of insulin resistance (ob/ob) and metabolic inflammation/NASH (high‐fat/cholesterol‐fed APOE*3Leiden.CETP mice) and efficacy was compared with synthetic peroxisome proliferator‐activated receptor α (PPAR‐α) (fenofibrate) and/or PPAR‐γ/(α) (pioglitazone and rosiglitazone) agonists. Icosabutate was absorbed almost entirely through the portal vein, resulting in rapid hepatic accumulation. Icosabutate demonstrated potent insulin‐sensitizing effects in ob/ob mice, and unlike fenofibrate or pioglitazone, it significantly reduced plasma alanine aminotransferase. In high‐fat/cholesterol‐fed APOE*3Leiden.CETP mice, icosabutate, but not rosiglitazone, reduced microvesicular steatosis and hepatocellular hypertrophy. Although both rosiglitazone and icosabutate reduced hepatic inflammation, only icosabutate elicited antifibrotic effects in association with decreased hepatic concentrations of multiple lipotoxic lipid species and an oxidative stress marker. Hepatic gene‐expression analysis confirmed the changes in lipid metabolism, inflammatory and fibrogenic response, and energy metabolism, and revealed the involved upstream regulators. In conclusion, icosabutate selectively targets the liver through the portal vein and demonstrates broad beneficial effects following insulin sensitivity, hepatic microvesicular steatosis, inflammation, lipotoxicity, oxidative stress, and fibrosis. Icosabutate therefore offers a promising approach to the treatment of both dysregulated glucose/lipid metabolism and inflammatory disorders of the liver, including NASH.

Photobiomodulation therapy decreases free fatty acid generation and release in adipocytes to ameliorate insulin resistance in type 2 diabetes

Excessive circulating free fatty acids (FFA) cause insulin resistance in peripheral tissues by inhibiting the proximal insulin signaling pathway. White adipose tissue (WAT) is a primary source of FFA generation and release through triglyceride (TG) hydrolysis. Thus, reducing excessive lipolysis in adipocytes ameliorates whole-body insulin resistance in type 2 diabetes. Here, we found that a noninvasive photobiomodulation therapy (PBMT), decreased FFA generation and release in WATs from high-fat diet (HFD)-fed mice and diabetic db/db mice. Meanwhile, plasma FFA and TG levels were reduced in two mouse models after PBMT. PBMT promoted mitochondrial reactive oxygen species (ROS) generation, which inhibited phosphatase and tensin homologue (PTEN) and promoted protein kinase B (AKT) activation. Photoactivation of AKT inhibited the transcriptional activity of Forkhead box transcription factor O1 (FoxO1), reducing expression of lipolytic enzymes and FFA generation and release. Eliminating ROS elimination or inhibiting AKT blocked the effects of the laser therapy in vivo and in vitro. Taken together, PBMT suppresses FFA generation and release in insulin-resistant adipocytes, contributing to improvement of insulin resistance in mouse models of type 2 diabetes.

Central Sfrp5 regulates hepatic glucose flux and VLDL-triglyceride secretion

ObjectiveSecreted frizzled-related protein 5 (Sfrp5) has been shown to be associated with energy homeostasis and insulin resistance in mouse models of obesity and diabetes. However, its central role in glucose and lipid metabolism is unknown. MethodsHFD-fed rats received ICV infusions of vehicle or Sfrp5 during a pancreatic euglycemic clamp procedure. To delineate the pathway(s) by which ICV Sfrp5 modulates HGP and VLDL-TG secretion, we inhibited the hypothalamic KATP channel using glibenclamide, the DVC NMDA receptor with MK801, and selectively transected the hepatic branch of the vagal nerve while centrally infusing Sfrp5. ResultsICV Sfrp5 in HFD-fed rats significantly increased the glucose infusion required to maintain euglycemia due to HGP inhibition during the clamp procedure; moreover, hepatic PEPCK and G6Pase expression was decreased, and InsR and Akt phosphorylation was increased in the liver. ICV Sfrp5 also decreased circulating triglyceride levels via inhibiting hepatic VLDL-TG secretion. These changes were accompanied by the inhibition of enzymes related to lipogenesis in the liver. ICV Sfrp5 significantly increased insulin-stimulated phosphorylation of InsR and Akt in the hypothalamus of HFD-fed rats, and insulin-stimulated immunodetectable PIP3 levels were higher in Sfrp5 group than in control group both in vitro and vivo. The glucose- and lipid-lowering effects of ICV Sfrp5 were eliminated by NMDA receptor or DVC KATP channel inhibition or HVAG. ConclusionsThe present study demonstrates that central Sfrp5 signaling activates a previously unappreciated InsR-Akt-PI3k-KATP channel pathway in the hypothalamus and brain-hepatic vagus neurocircuitry to decrease HGP and VLDL-TG secretion.

2-Aminoadipic acid (2-AAA) as a potential biomarker for insulin resistance in childhood obesity

Insulin resistance is an important clinical feature of metabolic syndrome, which includes obesity and type 2 diabetes. Increased adipose energy storage in obesity promote insulin resistance and other metabolic adverse effects. To identify a new link between adipocyte and insulin resistance, we performed targeted metabolite profiling of differentiated adipocytes and studied the association between adipogenic metabolites and insulin resistance. We found a correlation between 2-aminoadipic acid (2-AAA) and adipogenic differentiation. Also, circulatory 2-AAA was positively associated with obesity-related factors (fat mass, fat percent, waist circumference, BMI, BMI z-score, triglycerides, insulin, and HOMA-IR) at baseline and after 2 years in the children cohort study. Of these factors, increased BMI z-score and HOMA-IR were the primary independent factors associated with higher 2-AAA levels, and the baseline 2-AAA level was an indicator of the BMI z-score after 2 years. To validate the relationship between 2-AAA and obesity-related factors, we analyzed changes in 2-AAA levels following obesity intervention programs in two independent studies. In both studies, changes in 2-AAA levels during the intervention period were positively correlated with changes in the BMI z-score and HOMA-IR after adjusting for confounders. Moreover, the 2-AAA levels were increased in cell and mouse models of obesity-related insulin resistance. Excess 2-AAA levels led to impaired insulin signaling in insulin-sensitive cells (liver, skeletal muscle and adipose cells) and caused abnormal gluconeogenesis. Our results demonstrate that 2-AAA is associated with adipogenesis and insulin resistance. In this regard, 2-AAA could be a potential biomarker of obesity and obesity-related metabolic disorders.

Exercise Reduces Insulin Resistance in Type 2 Diabetes Mellitus via Mediating the lncRNA MALAT1/MicroRNA-382-3p/Resistin Axis

Insulin resistance (IR) is the primary pathological mechanism underlying type 2 diabetes mellitus (T2DM). Here, the study aimed to ascertain whether and how exercise mediates IR in T2DM. An in vivo mouse model of high-fat diet-induced IR and an in vitro high-glucose-induced IR model were constructed. High long non-coding RNA (lncRNA) metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) expression was detected in T2MD and was positively correlated with HOMA-IR and resistin levels. Then, short hairpin RNA targeting MALAT1 (sh-MALAT1) or pcDNA-MALAT1 was delivered into human umbilical vein endothelial cells (HUVECs) to knock down or upregulate its expression, respectively. Silencing of MALAT1 resulted in reduced levels of resistin, Ang II, tumor necrosis factor alpha (TNF-α), interleukin-6 (IL-6), soluble intercellular adhesion molecule-1 (sICAM-1), soluble vascular cell adhesion molecule-1 (sVCAM-1), endothelin-1 (ET-1), and p-insulin receptor substrate-1 (p-IRS)/ISR-1, and decreased cell migration, as well as enhanced glucose uptake and levels of nitric oxide (NO) and p-Akt/Akt. In the IR mouse model, exercise was observed to downregulate MALAT1 to reduce resistin, whereby exercise reduced homeostatic model assessment-insulin resistance (HOMA-IR). Besides, exercise also elevated microRNA-382-3p (miR-382-3p) expression in the serum of IR mice. Dual-luciferase reporter and RNA binding protein immunoprecipitation (RIP) assays identified that MALAT1 could bind to miR-382-3p to upregulate resistin. Collectively, the key observations of the study provide evidence that inhibition of MALAT1 elevates miR-382-3p to repress resistin, which consequently underlies the mechanism of exercise protecting against IR, highlighting a direction for T2DM therapy development.

Antioxidants protect against diabetes by improving glucose homeostasis in mouse models of inducible insulin resistance and obesity

Aims/hypothesisIn the context of diabetes, the health benefit of antioxidant treatment has been widely debated. In this study, we investigated the effect of antioxidant treatment during the development of insulin resistance and hyperphagia in obesity and partial lipodystrophy.MethodsWe studied the role of antioxidants in the regulation of insulin resistance using the tamoxifen-inducible fat-specific insulin receptor knockout (iFIRKO) mouse model, which allowed us to analyse the antioxidant’s effect in a time-resolved manner. In addition, leptin-deficient ob/ob mice were used as a hyperphagic, chronically obese and diabetic mouse model to validate the beneficial effect of antioxidants on metabolism.ResultsAcute induction of insulin receptor knockout in adipocytes changed the substrate preference to fat before induction of a diabetic phenotype including hyperinsulinaemia and hyperglycaemia. In healthy chow-fed animals as well as in morbidly obese mice, this diabetic phase could be reversed within a few weeks. Furthermore, after the induction of insulin receptor knockout in mature adipocytes, iFIRKO mice were protected from subsequent obesity development through high-fat diet feeding. By genetic tracing we show that the persistent fat mass loss in mice after insulin receptor knockout in adipocytes is not caused by the depletion of adipocytes. Treatment of iFIRKO mice with antioxidants postponed and reduced hyperglycaemia by increasing insulin sensitivity. In ob/ob mice, antioxidants rescued both hyperglycaemia and hyperphagia.Conclusions/interpretationWe conclude that fat mass reduction through insulin resistance in adipocytes is not reversible. Furthermore, it seems unlikely that adipocytes undergo apoptosis during the process of extreme lipolysis, as a consequence of insulin resistance. Antioxidants have a beneficial health effect not only during the acute phase of diabetes development, but also in a temporary fashion once chronic obesity and diabetes have been established.

Aged garlic extract ameliorates fatty liver and insulin resistance and improves the gut microbiota profile in a mouse model of insulin resistance.

Aged garlic extract (AGE) produced by the aging process has various beneficial pharmacological effects. In this study, the effects of AGE on fatty liver, insulin resistance and intestinal microbiota were compared between ddY-H mice, an insulin resistance mouse, and ddY-L mice, normal mice. Mice were fed an AGE-supplemented diet (4% w/w) for 7 weeks. The administration of AGE had no effect on the body weight and dietary intake of both types of mice. In the ddY-H mice, the serum levels of glucose and insulin were increased and glucose tolerance was impaired; however, the administration of AGE ameliorated these abnormal conditions. AGE did not have these effects in ddY-L mice. Triglyceride (TG) accumulation in the liver and fat absorption from the digestive tract were increased in the ddY-H mice; however, the administration of AGE reduced this increase. On the other hand, AGE exerted no such effects in the ddY-L mice. In addition, the gut microbiota has been shown to be closely associated with obesity, diabetes, dyslipidemia and non-alcoholic fatty liver disease in human and animal models. The bacterial composition of the gut microbiota in the feces of the ddY-H mice did not differ from that of the ddY-L mice at 5 weeks of age; however, it was altered in the mice at 9 and 12 weeks of age even when the mice were fed a standard diet. In the ddY-H mice, the relative presence of Lactobacillales was increased, while that of Bifidobacterium, Clostridium cluster XVIII and Prevotella was decreased. The alteration of the bacterial composition in the ddY-H mice was reversed by the administration of AGE; however, this effect of AGE was not observed in the ddY-L mice. On the whole, the findings of this study indicate that AGE improves abnormal fat accumulation and insulin resistance, and also alters the intestinal flora in ddY-H mice, suggesting the possibility that these effects of AGE may be related.

26-LB: Systemic Inhibition of MicroRNA-451 Impairs Renal Autophagy Process in a Mouse Model of Insulin Resistance and Early Diabetic Nephropathy

Diabetic nephropathy (DN) is a severe complication of diabetes mellitus and a common cause of end stage renal disease (ESRD). Novel effective therapies are needed to combat disease progression. Several studies suggest a renal protective role of microRNA-451 (miR-451) in ameliorating progression of DN. However, the role of miR-451 in DN is not understood. Defects in the autophagy process has been associated with DN. The current study aimed to elucidate the role of miR-451 in the development of DN in a mouse model of insulin resistance. Male TALLYHO/Jng mice were placed on a high-fat diet (60% kCal) and divided into two treatment groups. Mice were injected (intraperitoneal) once a week for 8-weeks with locked nucleic acid (LNA) miR-451 inhibitor or LNA-scramble (2mg/kg/bw; n=8/treatment). Mice were humanely euthanized after 12 weeks and kidneys harvested. LNA-miR-451 inhibitor significantly reduced renal expression of miR-451 by 6-fold. Collagen deposition was higher in inhibitor treated mice, as revealed by Masson’s Trichrome. Period Acid Schiff did not reveal significant glomerular damage between the two groups. Kidney weight (normalized to body weight) was significantly higher in the inhibitor treated mice. Western blotting analyses of cortex homogenates revealed increased expression of markers of renal injury, KIM1 and NGAL (p&amp;lt;0.05), in inhibitor treated mice. The expression of fibrotic signaling molecules mTOR, AMPKα, and TGF-β was significantly higher in the inhibitor treated group. The expression of autophagy markers SQSTM1/p62 and Beclin-1 was higher and lower, respectively, in inhibitor treated mice (p&amp;lt;0.05). The findings of this study suggest that reduced expression of miR-451 in DN impairs autophagy response in the kidney possibly via hyperactivation of the mTOR-signaling pathway. miR-451 may confer protection against DN by targeting key components of the autophagy process in the diabetic kidney. Disclosure M.B. Fluitt: None. N. Shivapurkar: None. L. Li: None. C.M. Ecelbarger: None. Funding American Diabetes Association (1-18-PMF-002 to M.B.F.); National Institutes of Health (TL1TR001431)

1861-P: Pioglitazone Modulates Hepatic Pyruvate Dehydrogenase and TCA Cycle Flux

Background: The insulin sensitizing actions of the antidiabetic drug Pioglitazone (PIO) have classically been ascribed to the reversal of ectopic lipid accumulation. We recently demonstrated acute, direct metabolic effects of PIO in hepatocytes, linking the suppression of hepatic glucose production to an inhibition of mitochondrial pyruvate metabolism. As the relevance of this mechanism in vivo is unclear, we studied the effects of PIO on hepatic pyruvate metabolism in a mouse model of insulin resistance. Methods: Eight-week-old male ob/ob mice were placed on a regular diet (10% kcal fat) with (n=10) or without (n=10) 300 mg/kg PIO for four weeks before study during euglycemic-hyperinsulinemic clamp (5 mU/kg min). Endogenous glucose production (EGP), hepatic glycogen synthesis and anabolic/oxidative pyruvate flux ratio (PC/PDH) were determined from [3-3H] glucose infusion and 13C NMR isotopomer analysis using [2,3-13C] pyruvate. Livers were freeze-clamped in situ for pyruvate dehydrogenase (PDH), metabolite and protein analysis. Results: PIO treatment lowered EGP by 62% (4.6 ± 1.0 vs. 12.1 ± 1.7 mg/kg min; P&amp;lt;0.01) and increased glycogen synthesis 10-fold (19.7 ± 4.8 vs. 1.9 ± 0.8 μ mol/kg liver min; P&amp;lt;0.005), whereas PC/PDH remained unchanged. PIO also suppressed liver PDH activation (14.6 ± 3.4 vs. 29.6 ± 4.3 µmol/kg liver min; P&amp;lt;0.05), as well as acetylcarnitine (140 ± 18 vs. 297 ± 40) and acetyl-CoA (17.7 ± 2.4 vs. 47.8 ± 8.8 µmol/kg liver) concentrations (P&amp;lt;0.01), whilst liver PDK4 protein expression was increased 46% compared to controls (P&amp;lt;0.05). Conclusions: Inhibition of PDH activation by Pioglitazone curtails mitochondrial acetyl-CoA delivery, relieving allosteric stimulation of pyruvate carboxylase and gluconeogenesis. Parallel reductions in PDH flux and EGP reconcile an unchanged PC/PDH ratio, suggesting an overall slowing of TCA cycle flux with PIO. These novel data highlight the therapeutic relevance of hepatic mitochondrial metabolism in the treatment of type 2 diabetes and liver disease. Disclosure C. Shannon: None. M. Ragavan: None. R.A. DeFronzo: Advisory Panel; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Elcelyx Therapeutics, Inc., Intarcia Therapeutics, Inc., Janssen Pharmaceuticals, Inc., Novo Nordisk Inc. Research Support; Self; AstraZeneca, Boehringer Ingelheim Pharmaceuticals, Inc., Janssen Pharmaceuticals, Inc., Merck &amp; Co., Inc. Speaker's Bureau; Self; AstraZeneca, Novo Nordisk Inc. M. Merritt: None. L. Norton: None. Funding University of Florida’s Southeast Center for Integrated Metabolomics (U24DK097209); National Institutes of Health

1874-P: A Novel Role for SerpinB1 in the Regulation of Insulin Signaling in Hepatocytes

Compensatory expansion of β cell mass has been pursued as a potential therapeutic strategy to cure diabetes. We previously identified SerpinB1 as a hepatocyte-derived circulating factor that contributes to adaptive beta cell expansion in the liver-specific insulin receptor knockout (LIRKO) mouse. To understand how SerpinB1 is regulated and secreted, we began by first investigating the mechanism(s) and signaling pathways that modulate the gene and protein expression of SerpinB1 in hepatocytes. Hepatic SerpinB1 expression was elevated in insulin resistant mouse models such as db/db and ob/ob, and circulating interleukin-6 (IL-6) levels were higher in these mice. Indeed, IL-6 induced SerpinB1 expression in HepG2 cells and human primary hepatocytes via the JAK/STAT3 pathway, indicating an important role for this cytokine in inducing the expression of the protease inhibitor in insulin resistant states. Conversely, silencing of SERPINB1 gene in hepatocytes decreased INSR gene and protein expression with a consequent alteration of expression of several downstream signaling genes related to gluconeogenesis and cell proliferation in hepatocytes. Ribosomal protein S3 (RPS3), identified as a binding partner of SerpinB1 in HepG2 cells, exhibited reduced expression in db/db and ob/ob mice liver along with reduced insulin receptor (IR) expression. Silencing of RPS3 gene in HepG2 cells, phenocopied the effects of SerpinB1 gene silencing, and decreased IR protein expression with consequent alterations in downstream signaling proteins. Additional studies are required to examine the precise regulation of IR expression by SerpinB1 and how the latter is secreted from insulin resistant hepatocytes. These results indicate that SerpinB1 expression is upregulated in insulin resistance by IL-6 and the SerpinB1/RPS3 complex plays a role in regulating insulin signaling in hepatocytes. Disclosure K. Orime: None. D.F. De Jesus: None. U. Jhala: None. R. Kulkarni: None.

31-OR: Skeletal Muscle Drp1 Maintains Metabolic Homeostasis through Preserving Mitochondrial Complex II Function

Dynamin-related protein 1 (Drp1) is a primary mediator of mitochondrial fission, the process of dividing an individual mitochondrion into two organelles. We have previously shown that Drp1 expression is reduced in muscle of dysglycemic men compared to healthy normoglycemic men at rest and during exercise. Moreover, our laboratory has observed mitochondrial fission incompetence in several mouse models of skeletal muscle insulin resistance. To determine whether mitochondrial fission incompetence alters muscle metabolism and insulin action, we generated two mouse models with muscle-selective conventional and inducible deletion alleles of Drp1 (mDrp1KO and miDrp1KO respectively). Muscle deletion of Drp1 reduced fatty acid oxidation, promoted the accumulation of myocellular lipids, elevated the respiratory exchange ratio (RER) assessed by indirect calorimetry, and impaired insulin action. Examination of mitochondria from mDrp1KOmuscle using transmission electron microscopy revealed a notably elongated morphology compared to Controlf/f. Moreover, real time respirometry revealed an impairment in mitochondrial complex II activity that was a likely consequence of defective SDH assembly. Complex II assembly factor SDHAF2, required for flavination of the SDHA subunit and complex II activity, was markedly reduced in both Drp1 deletion mouse models and in Drp1 knockdown (KD) myotubes. Using immunoprecipitation approaches in mouse muscle and murine myotubes, we determined that SDHAF2 associates with Drp1, and that this relationship is critical for the translocation of SDHAF2 protein into mitochondria during fission. Pharmacological inhibition of complex II recapitulated the impairment in lipid oxidation and insulin action seen in mDrp1KO and Drp1KD cells. Our findings indicate that Drp1 is critical for fatty acid oxidation and the maintenance of insulin action by controlling the assembly and function of mitochondrial complex II. Disclosure Z. Zhou: None. A.L. Hevener: None. Funding National Institute of Diabetes and Digestive and Kidney Diseases (R01DK109724)