Metabolic Inflexibility Impairs Insulin Secretion And Results In MODY-like Diabetes In Triple FoxO-deficient Mice
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ABSTRACT: Pancreatic b-cell failure in type 2 diabetes is associated with functional abnormalities of insulin secretion and deficits of b-cell mass. It’s unclear how one begets the other. We have shown that loss of b-cell mass can be ascribed to impaired FoxO1 function in different models of diabetes. Here we show that ablation of the three FoxO genes (1, 3a, and 4) in mature b-cells results in early-onset, maturity onset diabetes of the young (MODY)-like diabetes, with signature abnormalities of the MODY networks of Hnf4a, Hnf1a, and Pdx1. Transcriptome and functional analyses reveal that FoxO-deficient b-cells are metabolically inflexible, i.e., they preferentially utilize lipids rather than carbohydrates as source of acetyl-CoA for mitochondrial oxidative phosphorylation. This results in impaired ATP generation, and reduced Ca2+-dependent insulin secretion. When viewed in the context of prior data illustrating a role of FoxO1 in b-cell dedifferentiation, the present findings define a seamless FoxO-dependent mechanism linking the twin abnormalities of b-cell function in diabetes. We used microarrays to detail the change of gene expression in pancreatic beta cells after knocking out FoxO1,3 and 4.
Project description:Pancreatic b-cell failure in type 2 diabetes is associated with functional abnormalities of insulin secretion and deficits of b-cell mass. It’s unclear how one begets the other. We have shown that loss of b-cell mass can be ascribed to impaired FoxO1 function in different models of diabetes. Here we show that ablation of the three FoxO genes (1, 3a, and 4) in mature b-cells results in early-onset, maturity onset diabetes of the young (MODY)-like diabetes, with signature abnormalities of the MODY networks of Hnf4a, Hnf1a, and Pdx1. Transcriptome and functional analyses reveal that FoxO-deficient b-cells are metabolically inflexible, i.e., they preferentially utilize lipids rather than carbohydrates as source of acetyl-CoA for mitochondrial oxidative phosphorylation. This results in impaired ATP generation, and reduced Ca2+-dependent insulin secretion. When viewed in the context of prior data illustrating a role of FoxO1 in b-cell dedifferentiation, the present findings define a seamless FoxO-dependent mechanism linking the twin abnormalities of b-cell function in diabetes. We used microarrays to detail the change of gene expression in pancreatic beta cells after knocking out FoxO1,3 and 4. Primary islets were isolated from pancretic beta cell- specific triple FoxO(1,3, and 4) KO and their littermates control (WT) mice. Gene expression was analyzed by microarray.
Project description:Pancreatic beta-cell dysfunction contributes to onset and progression of type 2 diabetes. In this state beta-cells become metabolically inflexible, losing the ability to select between carbohydrates and lipids as substrates for mitochondrial oxidation. These changes lead to beta-cell dedifferentiation. We have proposed that FoxO proteins are activated through deacetylation-dependent nuclear translocation to forestall the progression of these abnormalities. However, how deacetylated FoxO exert their actions remains unclear. To address this question, we analyzed islet function in mice homozygous for knock-in alleles encoding deacetylated FoxO1 (6KR). Islets expressing 6KR mutant FoxO1 have enhanced insulin secretion in vivo and ex vivo, and decreased fatty acid oxidation ex vivo. Remarkably, the gene expression signature associated with FoxO1 deacetylation differs from wild-type by only ~2% of the > 4,000 genes regulated in response to re-feeding. But this narrow swath includes key genes required for beta-cell identity, lipid metabolism, and mitochondrial fatty acid and solute transport. The data support the notion that deacetylated FoxO1 protects beta-cell function by limiting mitochondrial lipid utilization, and raise the possibility that inhibition of fatty acid oxidation in β-cells is beneficial to diabetes treatment.
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:Mutations in several transcription factors lead to a subtype of type 2 diabetes called maturity-onset diabetes of the young (MODY), which are characterized by autosomal dominant inheritance, an early age of disease onset, and development of marked hyperglycemia with a progressive impairment in insulin secretion (Shih and Stoffel, 2002). The most frequent form of MODY is caused by mutations in the gene encoding hepatocyte nuclear factor-1a (HNF-1a, TCF1). Mutant mice with loss of Tcf1 function as well as transgenic mice expressing a naturally occurring dominant-negative form of human TCF1(P291fsinsC) in pancreatic beta cells develop progressive hyperglycemia due to impaired glucose-stimulated insulin secretion (Hagenfeldt-Johansson et al., 2001; Yamagata et al., 2002). Importantly, these mice exhibit a progressive reduction in beta cell number, proliferation rate, and pancreatic insulin content. These data indicate that Tcf-1 target genes are also required for maintenance of normal beta cell mass. In this study we sought to identify target genes of Tcf-1 that may be responsible of mediating beta cell growth by comparing gene expression profiles of Tcf-1 knock-out and wild-type littermates in isolated pancreatic islets.
Project description:Insulin deficiency and uncontrolled diabetes lead to a catabolic state with decreased muscle strength, contributing to disease-related morbidity. FoxO transcription factors are suppressed by insulin and thus are key mediators of insulin action. To study their role in diabetic muscle wasting, we created mice with muscle-specific triple knockout of FoxO1/3/4 and induced diabetes in these M-FoxO-TKO mice with streptozotocin (STZ). Muscle mass and myofiber area were decreased 20-30% in STZ-Diabetes mice due to increased ubiquitin-proteasome degradation and autophagy alterations, characterized by increased LC3-containing vesicles, and elevated levels of phosphorylated ULK1 and LC3-II. Both the muscle loss and markers of increased degradation/autophagy were completely prevented in STZ FoxO-TKO mice. Transcriptomic analyses revealed FoxO-dependent increases in ubiquitin-mediated proteolysis pathways in STZ-Diabetes, including regulation of Fbxo32 (Atrogin1), Trim63 (MuRF1), Bnip3L, and Gabarapl. These same genes were increased 1.4- to 3.3-fold in muscle from humans with type 1 diabetes after short-term insulin deprivation. Thus, FoxO-regulated genes play a rate-limiting role in increased protein degradation and muscle atrophy in insulin-deficient diabetes.
Project description:Insulin resistance not compensated by secretion reduces energy storage, but little is known about its effect upon energy expenditure (EE). Insulin receptor substrates Irs1 and Irs2 mediate signaling in all tissues, resulting in the inhibition of FoxO transcription factors. We found that hepatic disruption of Irs1 and Irs2 (LDKO mice) attenuated high-fat diet (HFD)-induced obesity and increased whole-body EE in a FoxO1-dependent manner. Hepatic disruption of Fst (follistatin), a FoxO1-regulated hepatokine, normalized EE in LDKO mice and restored adipose mass during HFD consumption. Moreover, hepatic Fst disruption alone increased fat mass accumulation, whereas hepatic overexpression of Fst attenuated high HFD-induced obesity. Excess circulating Fst in overexpressing mice neutralized Mstn (myostatin), activating mTORC1-promoted pathways of nutrient uptake and EE in skeletal muscle. Similar to Fst overexpression, direct activation of muscle mTORC1 also reduced adipose mass. We conclude that Fst-promoted EE in muscle attenuates obesity during hepatic insulin resistance.
Project description:A strong association of the gain-of-function mutation in the TALK-1 K+ channel (p.L114P) with maturity-onset diabetes of the young (MODY) was recently reported in two distinct families. TALK-1 is a key regulator of β-cell electrical activity and glucose-stimulated insulin secretion (GSIS). KCNK16, the gene that encodes TALK-1, is the most abundant and β-cell–restricted K+ channel transcript and KCNK16 locus is strongly associated to type-2 diabetes. To investigate the impact of TALK-1-L114P on glucose homeostasis and confirm its association with MODY, a mouse model containing the TALK-1-L114P mutation was generated. Heterozygous and homozygous TALK-1-L114P mice exhibit increased neonatal lethality in the C57BL/6J and the CD-1(ICR) genetic background, respectively. Lethality is likely a result of severe hyperglycemia observed in the homozygous TALK-1-L114P neonates due to lack of GSIS and can be reduced with insulin treatment. TALK-1-L114P drastically increases whole-cell β-cell K+ currents resulting in blunted glucose-stimulated Ca2+ entry and a complete loss of glucose-induced Ca2+ oscillations. Thus, adult TALK-1-L114P mice have reduced GSIS and plasma insulin levels, which significantly impairs glucose homeostasis. Taken together, this study shows that the MODY-associated TALK-1-L114P mutation disrupts glucose homeostasis in adult mice resembling a MODY phenotype and causes neonatal lethality by altering islet hormone secretion during development. These data strongly suggest that TALK-1 is an islet-restricted target for the treatment for diabetes
Project description:Expanding beta cell mass is a critical goal in the fight against diabetes. CDK4, an extensively characterized cell cycle activator, is required to establish and maintain beta cell number. Beta cell failure in the IRS2-deletion mouse type 2 diabetes model is in part due to loss of CDK4 regulator Cyclin D2. We set out to determine whether replacement of endogenous CDK4 with the inhibitor-resistant mutant CDK4-R24C rescued the loss of beta cell mass in Irs2-deficient mice. Surprisingly, not only beta cell mass but also beta cell dedifferentiation was effectively rescued, despite no improvement in whole body insulin sensitivity. Ex vivo studies in primary islet cells revealed a novel mechanism in which CDK4 intervened downstream in the insulin signaling pathway to prevent FOXO1-mediated transcriptional repression of critical beta cell transcription factor Pdx1. FOXO1 inhibition was not related to E2F1 activity, to FOXO1 phosphorylation, or even to FOXO1 subcellular localization, but rather was related to deacetylation and reduced FOXO1 abundance. Taken together, these results demonstrate a novel differentiation-promoting activity of the classical cell cycle activator CDK4 and support the concept that beta cell mass can be expanded without compromising function.
Project description:Insulin integrates hepatic glucose and lipid metabolism, directing nutrients to storage as glycogen and triglyceride. In type 2 diabetes, levels of the former are low and the latter are exaggerated, posing a pathophysiologic and therapeutic conundrum. A branching model1 of insulin signaling, with FoxO1 presiding over glucose production2-5 and Srebp–1c regulating lipogenesis,6-8 provides a potential explanation. Here we illustrate an alternative mechanism that integrates glucose production and lipogenesis under the unifying control of FoxO. Liver–specific ablation of three FoxOs (L–FoxO1,3,4) prevents the induction of glucose–6–phosphatase and the repression of glucokinase during fasting, thus increasing lipogenesis at the expense of glucose production. We document a similar pattern in the early phases of diet-induced insulin resistance, and propose that FoxOs are required to enable the liver to direct nutritionally derived carbons to glucose vs. lipid metabolism. Our data underscore the heterogeneity of hepatic insulin resistance during progression from the metabolic syndrome to overt diabetes, and the conceptual challenge of designing therapies that curtail glucose production without promoting hepatic lipid accumulation. We used microarrays to detail the change of gene expression in liver after knocking out FoxO1,3 and 4. Liver tissue samples were collected from hepatocyte- specific triple FoxO(1,3, and 4) KO and their littermates control (WT) mice after fasting (22 h) or refeeding (4 h). Gene expression was analyzed by microarray. Mice were on a mixed background of C57BL/6J and 129.