Insulin Receptor Knockout Mice Research Articles

Insulin receptor orchestrates kidney antibacterial defenses

Urinary tract infection (UTI) commonly afflicts people with diabetes. This augmented infection risk is partly due to deregulated insulin receptor (IR) signaling in the kidney collecting duct. The collecting duct is composed of intercalated cells (ICs) and principal cells (PCs). Evidence suggests that ICs contribute to UTI defenses. Here, we interrogate how IR deletion in ICs impacts antibacterial defenses against uropathogenic Escherichia coli. We also explore how IR deletion affects immune responses in neighboring PCs with intact IR expression. To accomplish this objective, we profile the transcriptomes of IC and PC populations enriched from kidneys of wild-type and IC-specific IR knock-out mice that have increased UTI susceptibility. Transcriptomic analysis demonstrates that IR deletion suppresses IC-integrated stress responses and innate immune defenses. To define how IR shapes these immune defenses, we employ murine and human kidney cultures. When challenged with bacteria, murine ICs and human kidney cells with deregulated IR signaling cannot engage central components of the integrated stress response-including activating transcriptional factor 4 (ATF4). Silencing ATF4 impairs NFkB activation and promotes infection. In turn, NFkB silencing augments infection and suppresses antimicrobial peptide expression. In diabetic mice and people with diabetes, collecting duct cells show reduced IR expression, impaired integrated stress response engagement, and compromised immunity. Collectively, these translational data illustrate how IR orchestrates collecting duct antibacterial responses and the communication between ICs and PCs.

Autocrine insulin-like growth factor 2 signaling as a potential target in the associated development of pulmonary emphysema and cancer in smokers

BackgroundTobacco smoking causes pulmonary inflammation, resulting in emphysema, an independent risk factor for lung cancer. Induction of insulin-like growth factor 2 (IGF2) in response to lung injury by tobacco carcinogens, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol and polycyclic aromatic hydrocarbon benzo[a]pyrene in combination (NB), is critical for the proliferation of alveolar type 2 cells (AT2s) for lung repair. However, persistent IGF2 overexpression during NB-induced severe injury results in hyperproliferation of AT2s without coordinated AT2-to-AT1 differentiation, disrupting alveolar repair, which leads to the concurrent development of emphysema and lung cancer. The current study aims to verify the role of IGF2 signaling in the associated development of emphysema and cancer and develop effective pharmaceuticals for the diseases using animal models that recapitulate the characteristics of these chronic diseases.MethodsThe pathogenesis of pulmonary emphysema and cancer was analyzed by lung function testing, histological evaluation, in situ zymography, dihydroethidium staining, and immunofluorescence and immunohistochemistry analyses utilizing mouse models of emphysema and cancer established by moderate exposure to NB for up to seven months.ResultsModerate NB exposure induced IGF2 expression in AT2s during the development of pulmonary emphysema and lung cancer in mice. Using AT2-specific insulin receptor knockout mice, we verified the causative role of sustained IGF2 signaling activation in AT2s in emphysema development. IGF2-targeting strategies, including voltage-dependent calcium channel blocker (CCB) and a neutralizing antibody, significantly suppressed the NB-induced development of emphysema and lung cancer. A publicly available database revealed an inverse correlation between the use of calcium channel blockers and a COPD diagnosis.ConclusionsOur work confirms sustained IGF2 signaling activation in AT2s couples impaired lung repair to the concurrent development of emphysema and cancer in mice. Additionally, CCB and IGF2-specific neutralizing antibodies are effective pharmaceuticals for the two diseases.

SAT038 Dietary Trans-10,cis-12 Conjugated Linoleic Acid Regulates Glucose Levels In Mice With Severe Insulin Resistance: Potential Effects On The Liver Via HNF4α And FOX01

Abstract Disclosure: S.M. Lee: None. J.T. Muratalla: None. C.W. Liew: None. J. Cordoba-Chacon: None. Plasma trans-10 cis-12-conjugated linoleic acid CLA (t10c12-CLA) is inversely associated with increased risk of diabetes in humans. In mice, it is well-known that t10c12-CLA induces whole-body insulin resistance due to severe lipodystrophy (loss of whole-body adipose tissue). However, t10c12-CLA-fed mice show normal glucose levels and, t10c12-CLA improved glucose clearance in models with preexisting insulin resistance: Zucker fatty/diabetic rats, obese and insulin resistant Ldlr-/- mice, and diet-induced obese and insulin resistant male mice. In this study, we assessed whether supplementation of t10c12-CLA in a low-fat diet reduces glucose levels in adipocyte-specific insulin receptor knockout (IRFKO) mice, which is a mouse model of congenital lipodystrophy. In addition to lipodystrophy, IRFKO mice show liver steatosis and increased blood glucose levels that are consequences of whole-body insulin resistance and increased hepatic gluconeogenesis. Briefly, 5-6-week-old male and female control and IRFKO mice were fed with a low-fat diet supplemented with 0.8% t10c12-CLA for 5 weeks. In IRFKO mice, dietary t10c12-CLA did not reduce adipose tissue mass. However, dietary t10c12-CLA increased liver steatosis and plasma insulin levels. Surprisingly, dietary t10c12-CLA reduced glucose levels in both male and female IRFKO mice. Also, dietary t10c12-CLA reduced food intake and polydipsia, which were increased in IRFKO mice due to lipodystrophy and hyperglycemia, respectively. A transcriptomic analysis (RNA-seq) of livers of control and IRFKO male mice fed with a t10c12-CLA diet showed that t10c12-CLA reduced the expression of the key gluconeogenic and mitochondrial fatty oxidation genes. Previous studies have suggested that t10c12-CLA reduces the expression of Forkhead box 01 (Fox01) and Hepatocyte nuclear factor 4 alpha (HNF4α). Of note, the livers of t10c12-CLA-fed control and IRFKO male mice showed a downregulation of positive targets of FoxO1 and HNF4α. In addition, livers of t10c12-CLA-fed mice showed reduced total FOXO1 protein levels, and increased phosphorylation of FOXO1 in t10c12-CLA-fed IRFKO mice. These findings suggest that t10c12-CLA could be directly acting on the liver to alter HNF4α and FOXO1-dependent regulation of hepatic fatty acid oxidation and glucose production. These actions may explain why t10c12-CLA-fed mice do not show increased glucose levels and is potentially linked to the inverse association between t10c12-CLA levels and diabetes risk. Presentation: Saturday, June 17, 2023

Endothelial Insulin Resistance Exacerbates Experimental Periodontitis

Epidemiological studies suggest that the severity of periodontitis is higher in people with diabetes than in healthy individuals. Insulin resistance might play a crucial role in the pathogenesis of multiple diabetic complications and is reportedly induced in the gingiva of rodents with type 2 diabetes; however, the molecular mechanisms underlying the pathogenesis of diabetes-related periodontitis remain unclear. Therefore, we aimed to investigate whether endothelial insulin resistance in the gingiva may contribute to the pathogenesis of periodontitis as well as elucidate its underlying molecular mechanisms. We demonstrated that insulin treatment downregulated lipopolysaccharide (LPS)–induced or tumor necrosis factor α (TNFα)–induced VCAM1 expression in endothelial cells (ECs) via the PI3K/Akt activating pathway, resulting in reduced cellular adhesion between ECs and leukocytes. Hyperglycemia-induced selective insulin resistance in ECs diminished the effect of insulin on LPS- or TNFα-stimulated VCAM1 expression. Vascular endothelial cell–specific insulin receptor knockout (VEIRKO) mice exhibited selective inhibition of the PI3K/Akt pathway in the gingiva and advanced experimental periodontitis-induced alveolar bone loss via upregulation of Vcam1, Tnfα, Mcp-1, Rankl, and neutrophil migration into the gingiva compared with that in the wild-type (WT) mice despite being free from diabetes. We also observed that insulin-mediated activation of FoxO1, a downstream target of Akt, was suppressed in the gingiva of VEIRKO and high-fat diet (HFD)–fed mice, hyperglycemia-treated ECs, and primary ECs from VEIRKO. Further analysis using ECs transfected with intact and mutated FoxO1, with mutations at 3 insulin-mediated phosphorylation sites (T24A, S256D, S316A), suggested that insulin-mediated regulation of VCAM1 expression and cellular adhesion of ECs with leukocytes was attenuated by mutated FoxO1 overexpression. These results suggest that insulin resistance in ECs may contribute to the progression of periodontitis via dysregulated VCAM1 expression and cellular adhesion with leukocytes, resulting from reduced activation of the PI3K/Akt/FoxO1 axis.

1594-P: Interorgan Insulin-Leptin Signal Cross Talk Originating in the Liver Enhances Survival under Food-Shortage Conditions

The liver can store energy and distribute it to other tissues/organs, according to the energy states involving hepatic insulin action. In addition, we and others have shown that the liver transmits metabolic information to other organs, via neuronal and humoral mechanisms. Herein, we demonstrate a novel form of inter-organ crosstalk originating in the liver, which links hepatic insulin action with hypothalamic leptin signaling and promotes survival during food shortage. We first observed that tamoxifen-inducible liver insulin receptor (IR) knockout (iLIRKO) mice ate more and consumed less oxygen with decreased hypothalamic leptin action, thereby gaining body weight. Circulating soluble leptin receptor (sLepR) levels were elevated in iLIRKO mice. We then produced tamoxifen-inducible liver leptin receptor (LepR) and IR double-knockout (iLLepRIRKO) mice. In iLLepRIRKO mice, sLepR elevations were not seen. Moreover, increased body weights, hyperphagia and decreased whole-body oxygen consumption seen in iLIRKO mice were reversed, indicating the importance of hepatic sLepR production in the liver-hypothalamus crosstalk. Human hepatic lepr and circulating sLepR levels also correlated negatively with hepatic insulin action indices. Additionally, we restricted food intake in wild type mice. Food restriction decreased hepatic insulin action and whole-body oxygen consumption with increased circulating sLepR. We furthermore performed food restriction in tamoxifen-inducible liver LepR knockout (iLLepRKO) mice. Notably, in iLLepRKO mice, the decreases in basal metabolic rates were blunted and mortality was markedly increased during food restriction. Collectively, the liver translates metabolic cues regarding energy-deficient status, which is reflected by decreased hepatic insulin action, into sLepR, thereby suppressing energy dissipation. This novel inter-organ crosstalk may assure survival of individuals facing food shortages in nature. Disclosure K.Takahashi: Speaker's Bureau; Taisho Pharmaceutical Holdings Co., Ltd. T.Yamada: Speaker's Bureau; MSD, Mitsubishi Tanabe Pharma Corporation, Eli Lilly Japan K.K., Boehringer Ingelheim Japan, Inc., Novo Nordisk, Sumitomo Dainippon Pharma Co., Ltd., Taisho Pharmaceutical Holdings Co., Ltd., Abbott Japan Co., Ltd. H.Katagiri: None. Funding Japan Society for the Promotion of Science (21K08522, 22H03126, 20H05694); Japan Science and Technology Agency (JPMJPS2023)

Increased serum extracellular vesicle miR-144-3p and miR-486a-3p in a mouse model of adipose tissue regeneration promote hepatocyte proliferation by targeting Txnip.

Adipose-derived stem cells are expected to be applied to regenerative medicine for various incurable diseases including liver cirrhosis. Although microRNAs contained in extracellular vesicles (EV-miRNAs) have been implicated in their regenerative effects, the precise mechanism has not been fully elucidated. Tamoxifen-inducible adipocyte-specific insulin receptor knockout (iFIRKO) mice are known to exhibit acute adipose tissue regeneration with increased numbers of adipose stem and progenitor cells (ASPCs). Because adipose tissue is the major source of circulating EV-miRNAs, we investigated alterations in serum EV-miRNAs in iFIRKO mice. A comprehensive analysis using miRNA sequencing on serum EVs revealed that most EV-miRNAs were decreased due to the loss of mature adipocytes, but there were 19 EV-miRNAs that were increased in the serum of iFIRKO mice. Among them, miR-144-3p and miR-486a-3p were found to be increased in the liver as well as serum EVs. While the expression levels of pri-miR-144-3p and pri-miR-486a-3p were not increased in the liver, they were elevated in the adipose tissue, suggesting that these miRNAs may be delivered from ASPCs increased in the adipose tissue to the liver via EVs. Increased hepatocyte proliferation was observed in the liver of iFIRKO mice, and we found that both miR-144-3p and miR-486a-3p have a function to promote hepatocyte proliferation by suppressing Txnip expression as a target gene. miR-144-3p and miR-486a-3p can be candidate therapeutic tools for conditions requiring hepatocyte proliferation, such as liver cirrhosis, and our current study suggests that examining EV-miRNAs secreted in vivo may lead to the discovery of miRNAs involved in regenerative medicine that have not been identified by in vitro analysis.

Inter-organ insulin-leptin signal crosstalk from the liver enhances survival during food shortages

Crosstalk among organs/tissues is important for regulating systemic metabolism. Here, we demonstrate inter-organ crosstalk between hepatic insulin and hypothalamic leptin actions, which maintains survival during food shortages. In inducible liver insulin receptor knockout mice, body weight is increased with hyperphagia and decreased energy expenditure, accompanied by increased circulating leptin receptor (LepR) and decreased hypothalamic leptin actions. Additional hepatic LepR deficiency reverses these metabolic phenotypes. Thus, decreased hepatic insulin action suppresses hypothalamic leptin action with increased liver-derived soluble LepR. Human hepatic and circulating LepR levels also correlate negatively with hepatic insulin action indices. In mice, food restriction decreases hepatic insulin action and energy expenditure with increased circulating LepR. Hepatic LepR deficiency increases mortality with enhanced energy expenditure during food restriction. The liver translates metabolic cues regarding energy-deficient status, which is reflected by decreased hepatic insulin action, into soluble LepR, thereby suppressing energy dissipation and assuring survival during food shortages.

Chronic hyperinsulinemia promotes human hepatocyte senescence

ObjectiveCellular senescence, an irreversible proliferative cell arrest, is caused by excessive intracellular or extracellular stress/damage. Increased senescent cells have been identified in multiple tissues in different metabolic and other aging-related diseases. Recently, several human and mouse studies emphasized the involvement of senescence in development and progression of NAFLD. Hyperinsulinemia, seen in obesity, metabolic syndrome, and other conditions of insulin resistance, has been linked to senescence in adipocytes and neurons. Here, we investigate the possible direct role of chronic hyperinsulinemia in the development of senescence in human hepatocytes. MethodsUsing fluorescence microscopy, immunoblotting, and gene expression, we tested senescence markers in human hepatocytes subjected to chronic hyperinsulinemia in vitro and validated the data in vivo by using liver-specific insulin receptor knockout (LIRKO) mice. The consequences of hyperinsulinemia were also studied in senescent hepatocytes following doxorubicin as a model of stress-induced senescence. Furthermore, the effects of senolytic agents in insulin- and doxorubicin-treated cells were analyzed. ResultsResults showed that exposing the hepatocytes to prolonged hyperinsulinemia promotes the onset of senescence by increasing the expression of p53 and p21. It also further enhanced the senescent phenotype in already senescent hepatocytes. Addition of insulin signaling pathway inhibitors prevented the increase in cell senescence, supporting the direct contribution of insulin. Furthermore, LIRKO mice, in which insulin signaling in the liver is abolished due to deletion of the insulin receptor gene, showed no differences in senescence compared to their wild-type counterparts despite having marked hyperinsulinemia indicating these are receptor-mediated effects. In contrast, the persistent hyperinsulinemia in LIRKO mice enhanced senescence in white adipose tissue. In vitro, senolytic agents dasatinib and quercetin reduced the prosenescent effects of hyperinsulinemia in hepatocytes. ConclusionOur findings demonstrate a direct link between chronic hyperinsulinemia and hepatocyte senescence. This effect can be blocked by reducing the levels of insulin receptors or administration of senolytic drugs, such as dasatinib and quercetin.

1353-P: Activation of Brown Adipose Tissue by Low-Protein Diet Ameliorates Hyperglycemia in Lipodystrophic Diabetic Mice Model

Long-term ad libitum dietary restriction such as low-protein diet (LPD) improves metabolic health and extends the life span of mice and possibly humans. However, most studies conducted thus far have focused on the preventive, but not therapeutic, potential of LPDs. Previously we shown that LPD (5.1% kcal from protein) was able to improve postprandial blood glucose values of the lipodystrophic IRFKO (adipose-specific insulin receptor knockout) mice after 14 days with strong activation of interscapular brown adipose tissue (iBAT) and increase energy expenditure. To determine whether iBAT activation was responsible for the hyperglycemia normalization after the LPD treatment, we surgically denervated iBAT of IRFKO mice before LPD treatment. Blood glucose were measured twice a week for up to 4 weeks, at the end of the monitoring mice were subjected to indirect calorimetry assessment (Promethion, Sable Systems) . Our data showed that surgical denervation of iBAT abolished the hyperglycemia normalization effect of LPD in the IRFKO mice. Morphologically, surgical denervation also prevented the ‘browning’ effect of LPD on the whitening iBAT observed in IRFKO mice. In line with the morphological data, LPD failed to induce thermogenic markers including UCP1 and BMP8b in denervated iBAT. In contrast, iBAT denervation has lesser effects on the LPD-induced energy expenditure and circulating FGF21 level, possibly due to compensation by beige fat formation in the inguinal WAT. Together, our data confirms that hyperglycemia normalization caused by LPD on IRFKO is iBAT activation dependent. Our observation suggests that blood glucose could be utilized to fuel LPD-induced iBAT activation as a mechanism for amino acid homeostasis. Further experimentation needs to be done in order to narrow down the mechanism driving this phenomenon. Taken together, our data suggest that short-term LPD could be a potential strategy for the treatment of metabolic syndrome. Disclosure M.D.Munoz: None. A.Zamudio: None. M.A.Mccann: None. C.Liew: None. Funding NIH RDK109015A1

1336-P: FoxO1-ATGL-Sirt1-FoxO1 Feed Forward Signaling Mediates Effects on Hepatic Gene Expression and Glucose Homeostasis in LIRKO Mice

FoxO1 is a major target of insulin action and regulates expression of ATGL and its inhibitor, G0S2, in the liver (Cell Rep 15:349, 2016) . Here, we asked whether ATGL mediates effects of FoxO1 in liver-specific insulin receptor knockout (LIRKO) mice. Studies in LIRKO and IR/FoxO1 double knockout (LIRFKO) mice show ATGL expression is increased and G0S2 is suppressed in a FoxO1-dependent fashion when insulin signaling is disrupted in the liver. ATGL knockdown (KD) reduces high plasma glucose and insulin concentrations, HOMA-IR and fatty acid oxidation, and improves glucose tolerance in LIRKO mice. Hyperinsulinemic-euglycemic clamp studies show ATGL KD improves insulin sensitivity due to effects on both HGP and glucose utilization, reflecting changes in WAT lipolysis, BAT metabolism and hepatic gene expression. The expression of FoxO1-regulated gluconeogenic genes (PEPCK, G6Pase, PCO, PGC-1α) , hepatokines (e.g., follistatin) and IGFBP-1 is increased in LIRKO mice and reduced by ATGL KD, reflecting changes in acetylation of FoxO1 and its co-activator, PGC-1α (decreased in LIRKO, increased by ATGL KD) . Rictor acetylation, which promotes activation of Akt and phosphorylation of FoxO1, also is increased by ATGL KD in LIRKO mice and isolated hepatocytes. Since ATGL promotes activation of Sirt1 (Mol Cell 77:810, 2020) and Sirt1 deacetylates FoxO1, PGC-1α and rictor, these studies suggest FoxO1 promotes increased ATGL and Sirt1 activity, and that Sirt1 activation enhances the effects of FoxO1 on gene expression and glucose homeostasis in a feed forward fashion (FoxO1 -> ATGL -> Sirt1 -> FoxO1) . Targeting the FoxO1/ATGL/Sirt1 pathway may provide a useful strategy for improving glucose homeostasis when insulin signaling is impaired in the liver. Disclosure I.O-sullivan: None. S.Bhattacharyya: None. C.Liew: None. S.M.Lee: None. J.Cordoba-chacon: None. R.J.Perry: None. G.I.Shulman: Advisory Panel; 89bio, Inc., AstraZeneca, Equator Therapeutics, Inc., Janssen Research & Development, LLC, Merck & Co., Inc., Consultant; DiCerna Pharmaceuticals, Inc., Novo Nordisk, Other Relationship; Generian Pharmaceuticals, iMetabolic Biopharma Corporation, Maze Therapeutics, The Liver Company, Stock/Shareholder; Levels Health, Inc. . T.Unterman: None. Funding Department of Veterans Affairs (5I01BX001968)

Insulin regulates arginine-stimulated insulin secretion in humans

AimsInsulin potentiates glucose-stimulated insulin secretion. These effects are attenuated in beta cell–specific insulin receptor knockout mice and insulin resistant humans. This investigation examines whether short duration insulin exposure regulates beta cell responsiveness to arginine, a non-glucose secretagogue, in healthy humans. Materials and methodsArginine-stimulated insulin secretion was studied in 10 healthy humans. In each subject arginine was administered as a bolus followed by continuous infusion on two occasions one month apart, after sham/saline or hyperinsulinemic-isoglycemic clamp, respectively providing low and high insulin pre-exposure conditions. Arginine-stimulated insulin secretion was measured by C-peptide deconvolution, and by a selective immunogenic (DAKO) assay for direct measurement of endogenous but not exogenous insulin. ResultsPre-exposure to exogenous insulin augmented arginine-stimulated insulin secretion. The effect was seen acutely following arginine bolus (endogenous DAKO insulin incremental AUC240-255min 311.6 ± 208.1 (post-insulin exposure) versus 120.6 ± 42.2 μU/ml•min (sham/saline) (t-test P = 0.021)), as well as in response to continuous arginine infusion (DAKO insulin incremental AUC260-290min 1095.3 ± 592.1 (sham/saline) versus 564.8 ± 207.1 μU/ml•min (high insulin)(P = 0.009)). Findings were similar when beta cell response was assessed using C-peptide, insulin secretion rates by deconvolution, and the C-peptide to glucose ratio. ConclusionsWe demonstrate a physiologic role of insulin in regulation of the beta cell secretory response to arginine.

Pericyte Insulin Receptors Modulate Retinal Vascular Remodeling and Endothelial Angiopoietin Signaling.

Pericytes regulate vascular development, stability, and quiescence; their dysfunction contributes to diabetic retinopathy. To explore the role of insulin receptors in pericyte biology, we created pericyte insulin receptor knockout mice (PIRKO) by crossing PDGFRβ-Cre mice with insulin receptor (Insr) floxed mice. Their neonatal retinal vasculature exhibited perivenous hypervascularity with venular dilatation, plus increased angiogenic sprouting in superficial and deep layers. Pericyte coverage of capillaries was unaltered in perivenous and periarterial plexi, and no differences in vascular regression or endothelial proliferation were apparent. Isolated brain pericytes from PIRKO had decreased angiopoietin-1 mRNA, whereas retinal and lung angiopoietin-2 mRNA was increased. Endothelial phospho-Tie2 staining was diminished and FoxO1 was more frequently nuclear localized in the perivenous plexus of PIRKO, in keeping with reduced angiopoietin-Tie2 signaling. Silencing of Insr in human brain pericytes led to reduced insulin-stimulated angiopoietin-1 secretion, and conditioned media from these cells was less able to induce Tie2 phosphorylation in human endothelial cells. Hence, insulin signaling in pericytes promotes angiopoietin-1 secretion and endothelial Tie2 signaling and perturbation of this leads to excessive vascular sprouting and venous plexus abnormalities. This phenotype mimics elements of diabetic retinopathy, and future work should evaluate pericyte insulin signaling in this disease.

The Roles of the IGF Axis in the Regulation of the Metabolism: Interaction and Difference between Insulin Receptor Signaling and IGF-I Receptor Signaling.

It has been well established that insulin-like growth factors (IGFs) mainly mediate long-term actions in cell fates, whereas insulin predominantly exerts its role on metabolic activity. Indeed, insulin mediates multiple anabolic biological activities in glucose and amino acid transport, lipid and protein synthesis, the induction of glycogen, the inhibition of gluconeogenesis, lipolysis, and protein degradation. The interactions and differences between insulin receptor signaling and IGF-I receptor signaling in the metabolism and the cell fates are quite complicated. Because of the overlapping actions of IGF-I singling with insulin signaling, it has been difficult to distinguish the role of both signaling mechanisms on the metabolism. Furthermore, comprehensive information on the IGF-I function in respective tissues remains insufficient. Therefore, we need to clarify the precise roles of IGF-I signaling on the metabolism separate from those of insulin signaling. This review focuses on the metabolic roles of IGFs in the respective tissues, especially in terms of comparison with those of insulin, by overviewing the metabolic phenotypes of tissue-specific IGF-I and insulin receptor knockout mice, as well as those in mice treated with the dual insulin receptor/IGF-I receptor inhibitor OSI-906.

1180-P: Short-Term Low-Protein Diet Ameliorates Metabolic Dysfunction in Diabetic Lipodystrophic Mice

Long-term ad libitum dietary restriction such as low-protein diet (LPD) improves metabolic health and extend the life spans of mice and possibly human. However, most studies conducted thus far have mainly focused on preventive rather than the treatment potential of LP diets. To determine whether dietary protein or caloric restriction could be used to treat preexisting metabolic symptoms, particularly in a more severely affected mouse model, we subjected hyperglycemic lipodystrophic IRFKO (adipose-specific insulin receptor knockout) mice to LPD (5.1% kcal from protein). Interestingly, postprandial blood glucose (BG) values of the IRFKO mice began to improve 10 days after the introduction of LPD. The IRFKO mice became normoglycemic 2 weeks after the onset of the LPD treatment. Activation of adaptive thermogenesis in brown (BAT) and beige adipose tissues promotes energy expenditure (EE) and utilization of BG and triglyceride (TG). A LPD has been previously shown to promote EE via the sympathetic nervous system (SNS). Consistent with previous study, we observed that a LPD acutely and sustainably upregulates EE in both the WT and IRFKO mice. This is likely due to LPD dramatically improves BAT functions by transforming the whitened unilocular lipid droplet BAT in the IRFKO mice into normal looking brown multi-locular lipid droplet BAT within 1 week of LPD treatment. This is further supported by significant increase in thermogenic markers expression in the BAT after LPD. Besides thermogenic markers, we also observed a time-dependent regulation of gene markers for fatty acid transport, oxidation and glucose metabolism in BAT after LPD. Together with changes in blood chemistry in the IRFKO mice, we think that glucose and lipid-lowering effects of LPD is the consequence of continuous activation of EE leading to utilization and depletion of systemic thermogenic fuels. Taken together, our data suggest that short-term LPD could be a potential strategy for the treatment of metabolic syndrome. Disclosure M. D. Munoz: None. M. A. Mccann: None. P. Kim: None. C. Liew: None.

High-Fat Diet Accelerates Pathological Progression and Intestinal Inflammation in a Type 2 Diabetes Rodent Model

Insulin signaling lowers postprandial glucose by stimulating cell surface translocation of the insulin sensitive glucose transporter 4 (GLUT4). In order to better understand how insulin resistance contributes to the pathophysiological progression of type 2 diabetes, we generated human GLUT4 promoter-driven insulin receptor knockout (GIRKO) mice and characterized their metabolic features relative to control mice. Although the role of insulin resistance in diabetes is beyond dispute, our previous studies showed that GIRKO mice fed normal chow diet (NCD) had an unexpectedly low rate of frank diabetes despite severe insulin resistance in muscle, fat, and brain.In the current study, we first sought to determine whether GIRKO mice would respond to high-fat diet (HFD) challenge with worsened glycemic outcome compared to control mice on HFD. Secondly, we sought to determine whether HFD-induced pathologies in GIRKO mice were caused by adaptations in the gastrointestinal (GI) tract and microbiome. We discovered that after beginning the HFD-feeding regimen, GIRKO mice rapidly developed hyperinsulinemia and hyperglycemia without excessive adiposity gain. Furthermore, GIRKO mice displayed dyslipidemia via increased hepatic lipid accumulation and serum lipid content. We used indirect calorimetry to characterize the metabolic features of single-housed mice. HFD-fed GIRKO mice had comparatively lower respiratory exchange ratio (RER), indicating relatively greater lipid metabolism compared to control mice on HFD. Despite having increased circulating incretins, GIRKO mice had impaired oral glucose tolerance and limited glucose-lowering benefit from Exendin-4 (Ex-4) injections. Since HFD promotes inflammation in the gastrointestinal (GI) tract, we performed gene expression analysis and pathway analysis of duodenal mRNAs to investigate whether inflammatory response, glucose transport, and lipid transport were altered in HFD-fed GIRKO mice. Among the top pathways discovered in pathway analysis were those involved with inflammatory signaling, carbohydrate transport, and xenobiotic metabolism, which supports that HFD-fed GIRKO mice have increased GI tract inflammation which may promote impaired glucose homeostasis.In conclusion, our studies suggest that HFD increased intestinal inflammation and exacerbated insulin resistance, which catalyzed the pathological progression of diabetes. Future studies are necessary to identify the molecular and cellular signaling pathways which culminate in frank diabetes, which may lead to therapeutic targets for regulating glucose homeostasis in the context of insulin resistance.

1734-P: High Dietary Fat Intake Exacerbates Insulin Resistance in a Type 2 Diabetes Genetic Mouse Model

GLUT4, an insulin-sensitive glucose transporter, plays a major role of postprandial glucose disposal. We previously reported that human GLUT4 promoter-driven insulin receptor knockout (GIRKO) mice have reduced insulin signaling in central and peripheral tissues and develop hyperglycemia, albeit at a lower rate in an age-dependent manner on normal chow diet. Long-term high fat diet (HFD) feeding is well established for causing adiposity gain, increased inflammation, and insulin resistance. We hypothesized that HFD feeding will exacerbate the insulin resistance and result in rapid progression to overt diabetes in GIRKO mice. To test this, we examined the physiological response of euglycemic GIRKO mice to HFD in a time course study. We used indirect calorimetry analysis and found that GIRKO mice showed differences in energy partitioning shortly after HFD feeding started. The majority of GIRKO mice cohorts had 5-fold higher circulating insulin and 1.5-fold elevated blood glucose after 1 month of HFD feeding. In addition to the hyperglycemia and hyperinsulinemia, GIRKO mice also exhibited impaired glucose tolerance and islet hyperplasia, suggesting extreme insulin resistance exceeded the compensatory increase of insulin production. After 3 months on HFD, GIRKO mice had increased relative liver size, elevated hepatic triglycerides, and reduced hepatic glycogen, demonstrating impaired hepatic insulin signaling to stimulate glycogen synthesis and inhibit gluconeogenesis. We also confirmed the increase of key hepatic gluconeogenic gene expression, which likely contributed to hyperglycemia. The rapid progression of metabolic defects of GIRKO mice on HFD is not due to excessive weight or adiposity gain. In conclusion, our studies of HFD-fed GIRKO mouse will offer insights in the role of the dietary contribution to diabetes disease progression without the confounding factor of increased adiposity. Disclosure A. Reilly: None. S. Yan: None. A.J. Loncharich: None. H. Ren: None. Funding Indiana University Diabetes and Obesity Research Training Program (T32DK064466); National Institute of Diabetes and Digestive and Kidney Diseases (R01DK120772, R00DK098294); Indiana Diabetes Center (P30DK097512); Indiana Clinical and Translational Sciences Institute (UL1TR002529)

214-LB: Brain Mitochondrial Function and Cognition Are Impaired in Brain Insulin Receptor Knockout Mice

Insulin resistance has been linked to cognitive dysfunction and increased risk for Alzheimer’s disease and other dementias. It is unclear if cognitive decline during insulin resistance is due to systemic or brain-specific insulin resistance. Previous studies demonstrated that brain mitochondrial function is reduced concurrent to diminished insulin signaling in high fat-fed mice. However, it remains to be determined whether insulin signaling in the brain directly impacts brain mitochondrial function and cognition. Therefore, we developed a tamoxifen inducible brain-specific insulin receptor knockout (BIRKO) mouse by breeding C57/BL6J mice with a floxed insulin receptor gene with mice that express a tamoxifen-inducible Nestin-Cre. These BIRKO mice were used to identify if brain insulin signaling is required for maintenance of brain mitochondrial function and cognition. Four weeks after tamoxifen administration, we confirmed using western blotting that the insulin receptor was completely absent in all regions of the brain, but not the muscle, heart, liver, kidney, or adipose from the BIRKO mice. Spatial learning was reduced (P<0.05; n=8 so far) and short-term memory trended to be reduced (P=0.18; n=8 so far) in BIRKO mice compared to controls. Further, ATP production rate was reduced (64 vs. 42 pmols/s/mg tissue; P<0.005; n=9) and reactive oxygen species production was increased (33 vs. 58 pmols/s/g tissue; P<0.005; n=9) in isolated mitochondria from the cerebrum in BIRKO mice versus controls. These changes were not accompanied by altered body weight, fat mass or lean body mass. Because the clearly pronounced mitochondrial deficits in the brain of BIRKO mice are accompanied by cognitive decline, our results suggest a link between cognition and brain mitochondrial function. Thus, these novel and important findings warrant further studies to provide molecular insights into the mechanisms governing the link of brain insulin resistance to Alzheimer’s disease and other dementias. Disclosure M.W. Pataky: None. G. Ruegsegger: None. K. Klaus: None. P. Starski: None. K. Nair: None. Funding National Institutes of Health (T32DK07352)

Parental metabolic syndrome epigenetically reprograms offspring hepatic lipid metabolism in mice.

The prevalence of nonalcoholic fatty liver disease (NAFLD) is increasing worldwide. Although gene-environment interactions have been implicated in the etiology of several disorders, the impact of paternal and/or maternal metabolic syndrome on the clinical phenotypes of offspring and the underlying genetic and epigenetic contributors of NAFLD have not been fully explored. To this end, we used the liver-specific insulin receptor knockout (LIRKO) mouse, a unique nondietary model manifesting 3 hallmarks that confer high risk for the development of NAFLD: hyperglycemia, insulin resistance, and dyslipidemia. We report that parental metabolic syndrome epigenetically reprograms members of the TGF-β family, including neuronal regeneration-related protein (NREP) and growth differentiation factor 15 (GDF15). NREP and GDF15 modulate the expression of several genes involved in the regulation of hepatic lipid metabolism. In particular, NREP downregulation increases the protein abundance of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) and ATP-citrate lyase (ACLY) in a TGF-β receptor/PI3K/protein kinase B-dependent manner, to regulate hepatic acetyl-CoA and cholesterol synthesis. Reduced hepatic expression of NREP in patients with NAFLD and substantial correlations between low serum NREP levels and the presence of steatosis and nonalcoholic steatohepatitis highlight the clinical translational relevance of our findings in the context of recent preclinical trials implicating ACLY in NAFLD progression.

Postnatal knockout of beta cell insulin receptor impaired insulin secretion in male mice exposed to high-fat diet stress

The presence of insulin receptor (IR) on insulin-secreting beta cells suggests an autocrine regulatory role for insulin in its own signalling. Congenital beta cell-specific IR knockout (βIRKO) mouse studies have demonstrated the development of age-dependent glucose intolerance. We investigated the role of beta cell IR signalling specifically during postnatal life following undisturbed prenatal pancreatic development and maturation. We utilized a tamoxifen-inducible mouse insulin 1 promoter (MIP) driven Cre recombinase IR knockout mouse model (MIP-βIRKO) to achieve partial knockout of IR in islets and determine the functional role of beta cell IR in adult mice fed a control normal diet (ND) or 60% high-fat diet (HFD). At 24 weeks of age, MIP-βIRKO ND mice maintained glucose tolerance, insulin release, and unchanged beta cell mass when compared to control ND mice. In contrast, 24-week-old MIP-βIRKO mice demonstrated significant glucose intolerance and lower insulin release after 18 weeks of HFD feeding. A reduction in beta cell soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein expression, phosphorylated AktS473 and P70S6K1T389, and glucose transporter 2 (GLUT2) expression were also identified in MIP-βIRKO HFD islets. Overall, the postnatal knockout of beta cell IR in HFD-fed mice resulted in decreased expression of beta cell glucose-sensing and exocytotic proteins and a reduction in intracellular signalling. These findings highlight that IR expression in the adult islet is required to maintain beta cell function under hyperglycemic stress.

Identification of two microRNA nodes as potential cooperative modulators of liver metabolism.

AimHepatic insulin resistance is a hallmark of type 2 diabetes and non‐alcoholic fatty liver disease. Dysregulation of microRNA (miRNA) expression in insulin‐resistant livers might coordinate impaired hepatic metabolic function. Here, we aimed to discover miRNAs and their downstream targets involved in hepatic insulin resistance.MethodsWe determined miRNA expression profiles by small RNA sequencing of two mouse models of impaired hepatic insulin action: high‐fat diet‐induced obesity and liver‐specific insulin receptor knockout. Conversely, we assessed the hepatic miRNA expression profile after treatment with the antidiabetic hormone, fibroblast growth factor 21 (FGF21). Ontology analysis of predicted miRNA gene targets was performed to identify regulated gene pathways. Target enrichment analysis and miRNA mimic overexpression in vitro were used to identify unified protein targets of nodes of regulated miRNAs.ResultsWe identified an array of miRNA species regulated by impaired liver insulin action or after fibroblast growth factor 21 treatment. Ontology analysis of predicted miRNA gene targets identified pathways controlling hepatic energy metabolism and insulin sensitivity. We identified a node of two miRNAs downregulated in the livers of liver‐specific insulin receptor knockout mice, miR‐883b and miR‐205, which positively regulate the expression of transcription factor zinc finger E‐box‐binding homeobox 1 (ZBED1). We found another node of two miRNAs upregulated in the livers of fibroblast growth factor 21‐treated mice, miR‐155‐3p and miR‐1968‐5p, which canonically downregulates the caveola component, polymerase I and transcript release factor (PTRF), a gene previously implicated in hepatic energy metabolism.ConclusionsThis study identifies two nodes of coregulated miRNAs that might coordinately control hepatic energy metabolism in states of insulin resistance.