Project description:Mice were fasted for 18 hr overnight then sacrificed or treated with 13C-U-glucose (2 g/kg ip) and sacrificed 1 hr later by decapitation and liver was immediately freeze-clamped and stored in liquid N2 and then at -80 C. Wild type (IR and IR/FoxO1 floxed) mice were sacrificed after fasting and 1 hr post-glucose treatment. Liver-specific insulin receptor knockout (LIRKO) and insulin receptor/FoxO1 double knockout (LIRFKO) mice were sacrificed 1 hr post glucose treatment.
http://www.nature.com/ncomms/2015/150512/ncomms8079/full/ncomms8079.html
Project description:FoxO proteins are major targets of insulin action. To better define the role of FoxO1 in mediating insulin effects in the liver, we generated liver-specific insulin receptor knockout (LIRKO) and IR/FoxO1 double knockout (LIRFKO) mice. Here we show that LIRKO mice are severely insulin resistant based on glucose, insulin and C-peptide levels, and glucose and insulin tolerance tests, and genetic deletion of hepatic FoxO1 reverses these effects. 13C-glucose and insulin clamp studies indicate that regulation of both hepatic glucose production (HGP) and glucose utilization is impaired in LIRKO mice, and these defects are also restored in LIRFKO mice corresponding to changes in gene expression. We conclude that (1) inhibition of FoxO1 is critical for both direct (hepatic) and indirect effects of insulin on HGP and utilization, and (2) extrahepatic effects of insulin are sufficient to maintain normal whole-body and hepatic glucose metabolism when liver FoxO1 activity is disrupted.
Research is published:
http://www.nature.com/ncomms/2015/150512/ncomms8079/full/ncomms8079.html
Project description:The effect of liver specific deletion of the insulin receptor substrate-1 (Irs1) and/or Irs2 upon gene expression in the fasted and fed liver of mice; and the effect of liver specific Foxo1 deletion in the Irs1 and Irs2 knockout liver during fasting and feeding.
Project description:Decreased skeletal muscle strength and mitochondrial dysfunction are characteristic of diabetes. Action of insulin through insulin receptor (IR) and IGF-1 receptor (IGF1R) maintain muscle mass via suppression of FoxOs, but whether FoxO activation coordinates atrophy in concert with mitochondrial dysfunction is unknown. In the absence of systemic glucose or lipid abnormalities, muscle-specific IR knockout (MIRKO) or combined IR/IGF1R knockout (MIGIRKO) impaired mitochondrial respiration, decreased ATP production, and increased ROS. These mitochondrial abnormalities were not present in muscle-specific IR/IGF1R and FoxO1/3/4 quintuple knockout mice (QKO). Although autophagy was increased when IR/IGF1R were deleted in muscle, mitophagy was not increased. Mechanistically, RNA-seq revealed that complex-I core subunits were decreased in MIGIRKO muscle, and these were reversed with FoxO knockout. Thus, insulin-deficient diabetes or loss of insulin/IGF-1 action in muscle decreases complex-I driven mitochondrial respiration and supercomplex assembly, in part by FoxO-mediated repression of Complex-I subunit expression.
Project description:We developed a novel network inference approach, Biologically Anchored Knowledge Expansion (BAKE), to analyze large volume gene expression data obtained from a mouse model of insulin resistance progression. Both genetic aspects and dietary factors, specifically high caloric high-fat high-sugar diets, contribute to the progression of insulin resistance. To mimic genetic predisposition, we used a mouse model with double heterozygous deletion of early insulin signaling pathway intermediates, insulin receptor (IR) and insulin receptor substrate 1 (IRS1) genes. These mice were fed with high-fat (Western) or low-fat (Chow) diet for 8 and 16 weeks starting at 8 weeks of age. Gene expression data was collected from adipocytes isolated from these mice. Applying BAKE analysis to the adipocyte gene expression data, we demonstrate that we can accurately discover a novel regulatory gene in the insulin signaling pathway. The mouse model of double heterozygous deletion of insulin receptor (IR) and insulin receptor substrate 1 (IRS1) was originally introduced as a polygenic model to study the development of type 2 diabetes. This mouse model, on an atherosclerosis-prone ApoE null background (IR+/- IRS1+/- ApoE-/-), also shows increased atherosclerotic lesions due to impaired insulin signaling. For our study we used female double heterozygous mice (IR+/- IRS1+/-, 'Dhet' mice or 'Dâ mice) on an ApoE null background (ApoE-/-, âEâ) fed with a Western (high-fat) diet for 8 (DW8, n=5) and 16 (DW16, n=9) weeks starting at 8 weeks of age or with a Chow (low-fat) diet (DC8, n=7; DC16, n=5). There were also ApoE null mice (ApoE-/-, 'Eâ) fed either Western diet for 8 (EW8, n=6) and 16 (EW16, n=8) weeks or Chow diet for 16 weeks (EC16, n=5) starting at 8 weeks of age.
Project description:Mediator complex function as an integrative hub for transcriptional regulation. Here we show that Mediator subunit MED23 regulate glucose and lipid metabolism via FOXO1 in liver. Here, we have generated a liver-specific Med23-knockout (LMKO) mouse and found that Med23-deletion in liver improved glucose and lipid metabolism, as well as insulin responsiveness, and prevented diet-induced obesity. Mechanistically, MED23 participated in gluconeogenesis and cholesterol synthesis by interacting with FOXO1. Disruption of this interaction by hepatic Med23-deletion impaired the Mediator and RNAP II recruitment and partially reduced the expression of the FOXO1 target genes. Remarkably, acute hepatic Med23 knockdown in db/db mice significantly improved insulin sensitivity. Overall, our data revealed Mediator MED23 as a critical regulator of glucose and lipid metabolism, suggesting novel therapeutic strategies against metabolic diseases.
Project description:Understanding mechanisms causing MAFLD (Metabolic Associated Fatty Liver Disease) and its progression to MASH (metabolic dysfunction-associated steatohepatitis) is clinically important and scientifically challenging. Hepatic insulin resistance is a common component in the progression of MAFLD in patients and experimental animals; however, hepatic steatosis caused by the HFD45% (high-fat diet) decreases during chronic hepatic IR generated by inactivation of Irs1/2 (LDKO), AKT1/2, or InsR 1-3—which is inconsistent with the expected relationship between IR and MAFLD in humans4. Here we found that complete hepatic insulin resistance promotes the fructose-enriched GAN diet-induced MAFLD, including acute inflammation and MASH in LDKO mice. Unexpectedly, fructose phosphorylation catalyzed by hepatic Khk (ketohexokinase) was not required as acute MAFLD progressed strongly in LDKOKhkL/L mice fed the GAN diet. FoxO1 activated during hepatic IR induces Fst (Follistatin) expression and secretion from the liver of LDKO mice. Inactivation of hepatic FoxO1 in LTKO mice (LDKO•FoxO1L/L) or Fst in LDKOFstKO mice prevented acute MAFLD during the GAN diet. Consistently, overexpression of hepatic Fst promoted GAN diet-induced MAFLD/MASH and hepatic carcinoma. Mechanistically, circulating Fst promoted adipose tissue IR and lipolysis, which can deliver FFA (free fatty acid) to the liver for esterification with excess Gro3P (glycerol 3-phosphate) generated by fructose metabolism, although hepatic DNL (de novo lipogenesis) decreased strongly in LDKO mice while. Since circulating FST correlates positively with both T2D and MAFLD in humans, our results suggests that hepatic FST induced by progressive hepatic IR might promote MAFLD/MASH during the consumption of sugar-sweetened food and beverages consumed frequently by people and animals with T2D.
Project description:Insulin resistance increases patient’s risk of developing type 2 diabetes (T2D), nonalcoholic steatohepatitis (NASH) and a host of other comorbidities including cardiovascular disease and cancer. At the molecular level, insulin exerts its function through the insulin receptor (IR), a transmembrane receptor tyrosine kinase. Data from human genetic studies have shown that Grb14 functions as a negative modulator of IR activity, and germline Grb14-knockout (KO) mice have improved insulin signaling in liver and muscle tissues. Here, we show that Grb14 knockdown in the liver and the heart with an AAV-shRNA (Grb14-shRNA) improves glucose homeostasis in diet-induced obese (DIO) mice. A previous report has shown that germline deletion of Grb14 in mice results in cardiac hypertrophy and decreased systolic function, effects that could severely limit the therapeutic potential of targeting Grb14. In this report, we demonstrate that there are no significant changes in hemodynamic function as measured by echocardiography in DIO Grb14 and DIO sham mice for a period of four months. While additional studies are needed to further establish efficacy and to de-risk potential negative cardiac effects in pre-clinical heart failure models, our data support inhibiting Grb14 to treat diabetes and related conditions.
Project description:To investigate the effects of acute loss of mature adipocytes in adipose tissue on the liver, we created tamoxifen-inducible adipocyte-specific insulin receptor knockout (iFIRKO) mice. We then performed comprehensive gene expression analysis on the liver of iFIRKO and control mice.