Diabetes is a consequence of a decrease on functional β-cell mass. We have recently demonstrated that epoxypukalide (Epoxy) is a natural compound with beneficial effects on primary cultures of rat ...islets. In this study, we extend our previous investigations to test the hypothesis that Epoxy protects β-cells and improves glucose metabolism in STZ-induced diabetic mice.
We used 3-months old male mice that were treated with Epoxy at 200 μg/kg body weight. Glucose intolerance was induced by multiple intraperitoneal low-doses of streptozotocin (STZ) on 5 consecutive days. Glucose homeostasis was evaluated measuring plasma insulin levels and glucose tolerance. Histomorphometry was used to quantify the number of pancreatic β-cells per islet. β-cell proliferation was assessed by BrdU incorporation, and apoptosis by TUNEL staining. Epoxy treatment significantly improved glucose tolerance and plasma insulin levels. These metabolic changes were associated with increased β-cell numbers, as a result of a two-fold increase in β-cell proliferation and a 50% decrease in β-cell death.
Our results demonstrate that Epoxy improves whole-body glucose homeostasis by preventing pancreatic β-cell death due to STZ-induced toxicity in STZ-treated mice.
Excessive production of triglyceride-rich VLDL is attributable to hypertriglyceridemia. VLDL production is facilitated by microsomal triglyceride transfer protein (MTP) in a rate-limiting step that ...is regulated by insulin. To characterize the underlying mechanism, we studied hepatic MTP regulation by forkhead box O1 (FoxO1), a transcription factor that plays a key role in hepatic insulin signaling. In HepG2 cells, MTP expression was induced by FoxO1 and inhibited by exposure to insulin. This effect correlated with the ability of FoxO1 to bind and stimulate MTP promoter activity. Deletion or mutation of the FoxO1 target site within the MTP promoter disabled FoxO1 binding and resulted in abolition of insulin-dependent regulation of MTP expression. We generated mice that expressed a constitutively active FoxO1 transgene and found that increased FoxO1 activity was associated with enhanced MTP expression, augmented VLDL production, and elevated plasma triglyceride levels. In contrast, RNAi-mediated silencing of hepatic FoxO1 was associated with reduced MTP and VLDL production in adult mice. Furthermore, we found that hepatic FoxO1 abundance and MTP production were increased in mice with abnormal triglyceride metabolism. These data suggest that FoxO1 mediates insulin regulation of MTP production and that augmented MTP levels may be a causative factor for VLDL overproduction and hypertriglyceridemia in diabetes.
IDE is a ubiquitous metalloprotease with cytosolic and mitochondrial subcellular localization that degrades insulin and glucagon. People with T2D and diet-induced obese mice show lower hepatic IDE ...levels. We revealed a key role of IDE on the insulin-mediated repression of hepatic gluconeogenesis, but its function on glucagon-dependent activation of gluconeogenesis and mitochondrial respiration in hepatocytes remains completely unknown. Here, we aim to elucidate the role of IDE on glucagon signalling and its impact on gluconeogenesis and energy metabolism in hepatocytes. Liver homogenized and primary hepatocytes obtained from L-IDE-KO mice (deletion of IDE in liver) showed decreased expression of glucagon receptor (~60%), CREB protein (~40%), and lower phosphorylation of CREB (~50%) upon glucagon stimulation compared to controls. Similar results were found in AML12-shRNA-Ide cells, in which IDE protein levels were reduced by ~50%. Additionally, glucagon stimulation resulted in lower (~30%) cAMP levels and diminished phosphorylation of PKA substrates in AML12-shRNA-Ide. Surprisingly, these alterations in glucagon signalling paralleled with ~20-fold increases in the expression of the gluconeogenic genes G6p6 and Pck1. Of note, basal and uncoupler-stimulated respiration increased ~4-fold in AML12-shRNA-Ide in parallel with a ~2-fold increment of mitochondrial and glycolytic ATP production. Finally, similar mitochondrial phenotype was found in human hepatocytes lacking IDE (HepG2-IDE-KO cells), which exhibited higher FoxO1 levels and fragmented mitochondria. The effects on mitochondrial respiration were independent of IDE's proteolytic activity.
In summary, reduced IDE expression in hepatocytes has a deleterious effect on glucagon signalling leading to up-regulated gluconeogenesis and mitochondrial respiration. We conclude that IDE is a mechanistic link to couple hepatic gluconeogenesis with mitochondrial energy production.
Disclosure
C.M. González-Casimiro: None. P. Cámara-Torres: None. B. Merino: None. J. Santo-Domingo: None. M.A. de la Fuente: None. A. Alonso: None. I. Cozar-Castellano: None. G. Perdomo: None.
Funding
Ministerio de Ciencia e Innovación-Spain (PID2019-110496RB-C22)
Excessive endogenous glucose production contributes to fasting hyperglycemia in diabetes. This effect stems from inept insulin suppression of hepatic gluconeogenesis. To understand the underlying ...mechanisms, we studied the ability of forkhead box O6 (FoxO6) to mediate insulin action on hepatic gluconeogenesis and its contribution to glucose metabolism.
We characterized FoxO6 in glucose metabolism in cultured hepatocytes and in rodent models of dietary obesity, insulin resistance, or insulin-deficient diabetes. We determined the effect of FoxO6 on hepatic gluconeogenesis in genetically modified mice with FoxO6 gain- versus loss-of-function and in diabetic db/db mice with selective FoxO6 ablation in the liver.
FoxO6 integrates insulin signaling to hepatic gluconeogenesis. In mice, elevated FoxO6 activity in the liver augments gluconeogenesis, raising fasting blood glucose levels, and hepatic FoxO6 depletion suppresses gluconeogenesis, resulting in fasting hypoglycemia. FoxO6 stimulates gluconeogenesis, which is counteracted by insulin. Insulin inhibits FoxO6 activity via a distinct mechanism by inducing its phosphorylation and disabling its transcriptional activity, without altering its subcellular distribution in hepatocytes. FoxO6 becomes deregulated in the insulin-resistant liver, accounting for its unbridled activity in promoting gluconeogenesis and correlating with the pathogenesis of fasting hyperglycemia in diabetes. These metabolic abnormalities, along with fasting hyperglycemia, are reversible by selective inhibition of hepatic FoxO6 activity in diabetic mice.
Our data uncover a FoxO6-dependent pathway by which the liver orchestrates insulin regulation of gluconeogenesis, providing the proof-of-concept that selective FoxO6 inhibition is beneficial for curbing excessive hepatic glucose production and improving glycemic control in diabetes.
Recent studies have implicated inhibitor of kappaB kinase (IKK) in mediating fatty acid (FA)-induced insulin resistance. How IKK causes these effects is unknown. The present study addressed the role ...of nuclear factor kappaB (NFkappaB), the distal target of IKK activity, in FA-induced insulin resistance in L6 myotubes, an in vitro skeletal muscle model. A 6-h exposure of myotubes to the saturated FA palmitate reduced insulin-stimulated glucose uptake by approximately 30%, phosphatidylinositol-3 kinase and protein kinase B phosphorylation by approximately 40%, and stimulated inhibitor of kappaBalpha degradation and the nuclear translocation of NFkappaB. On the other hand, the Omega-3 polyunsaturated FA linolenate neither induced insulin resistance nor promoted nuclear localization of NFkappaB. Supporting the hypothesis that IKK acts through NFkappaB to cause insulin resistance, the IKK inhibitors acetylsalicylate and parthenolide prevented FA-induced reductions in insulin-stimulated glucose uptake and NFkappaB nuclear translocation. Most importantly, NFkappaB SN50, a cell-permeable peptide that inhibits NFkappaB nuclear translocation downstream of IKK, was sufficient to prevent palmitate-induced reductions in insulin-stimulated glucose uptake. Acetylsalicylate, but not NFkappaB SN50, prevented FA effects on phosphatidylinositol-3 kinase activity and protein kinase B phosphorylation. We conclude that FAs induce insulin resistance and activates NFkappaB in L6 cells. Furthermore, inhibition of NFkappaB activation, indirectly by preventing IKK activation or directly by inhibiting NFkappaB nuclear translocation, prevents the detrimental effects of palmitate on the metabolic actions of insulin in L6 myotubes.
Apolipoprotein A-V (apoA-V) and apoC-III are exchangeable constituents of VLDL and HDL. ApoA-V counteracts the effect of apoC-III on triglyceride (TG) metabolism with poorly defined mechanisms. To ...better understand the effects of apoA-V on TG and cholesterol metabolism, we delivered apoA-V cDNA into livers of hypertriglyceridemic APOC3 transgenic mice by adenovirus-mediated gene transfer. In response to hepatic apoA-V production, plasma TG levels were reduced significantly as a result of enhanced VLDL catabolism without alternations in VLDL production. This effect was associated with reduced apoC-III content in VLDL. Increased apoA-V production also resulted in decreased apoC-III and increased apoA-I content in HDL. Furthermore, apoA-V-enriched HDL was associated with enhanced LCAT activity and increased cholesterol efflux. This effect, along with apoE enrichment in HDL, contributed to HDL core expansion and α-HDL formation, accounting for significant increases in both the number and size of HDL particles. As a result, apoA-V-treated APOC3 transgenic mice exhibited decreased VLDL-cholesterol and increased HDL-cholesterol levels. ApoA-V-mediated reduction of apoC-III content in VLDL represents an important mechanism by which apoA-V acts to ameliorate hypertriglyceridemia in adult APOC3 transgenic mice. In addition, increased apoA-V levels accounted for cholesterol redistribution from VLDL to larger HDL particles. These data suggest that in addition to its TG-lowering effect, apoA-V plays a significant role in modulating HDL maturation and cholesterol metabolism.
Type 1 diabetes mellitus (T1DM) is due to the selective destruction of islet beta cells by immune cells. Current therapies focused on repressing the immune attack or stimulating beta cell ...regeneration still have limited clinical efficacy. Therefore, it is timely to identify innovative targets to dampen the immune process, while promoting beta cell survival and function. Liver receptor homologue-1 (LRH-1) is a nuclear receptor that represses inflammation in digestive organs, and protects pancreatic islets against apoptosis. Here, we show that BL001, a small LRH-1 agonist, impedes hyperglycemia progression and the immune-dependent inflammation of pancreas in murine models of T1DM, and beta cell apoptosis in islets of type 2 diabetic patients, while increasing beta cell mass and insulin secretion. Thus, we suggest that LRH-1 agonism favors a dialogue between immune and islet cells, which could be druggable to protect against diabetes mellitus.
No Alcoholic Fatty Liver Disease (NAFLD) is characterized by an abnormal accumulation of fat in hepatocytes, without alcohol, where overweight and obesity are determinants. Ecosonografia evaluated ...the prevalence of fatty liver in obese pediatric patients and its relation to nutritional assessment. The sample consisted of 85 children (51 females, 34 males), age 3-17. The abdominal ecosonography, BMI, waist circumference were performed; Godard Test for physical activity, history of diabetes, dyslipidemia, obesity and cardiovascular disease were questioned. Lipid profile, glucose and insulin resistance were determined. Data analyzed from descriptive and comparative tables. We obtained: mean age 9.8 ± 2.7 females and males 9.6 ± 2.7 years. The ecosonography indicated 50% and 50% fatty liver-pancreas fatty liver in children aged 3-6 years; 7-11 years 39.7% fatty liver-pancreas; 12-17yrs 31.6% fatty liver-pancreas (p > 0.05); BMI > 26 kg/m2 42.9% fatty liver-pancreas; 21 to 25 kg/m2 44.7% fatty liver; 15 to 20 kg/m2 60%fatty liver-pancreas (p> 0.05). 97.6% with high CC; 68.2% with inadequate physical activity; high frequency of history of chronic non-communicable diseases. We concluded that this population had predominantly fatty liver fatty replacement of the pancreas (HG-RGP) in the groups with higher BMI, CC and high male unrelated insulin resistance, altered lipid profile and diagnosis HG. We inferred that the anthropometric assessment of waist circumference and abdominal ecosonography indicate the presence of visceral obesity, a condition that predisposes to hepatic steatosis, pancreas and/or liver-pancreas.
No Alcoholic Fatty Liver Disease (NAFLD) is characterized by an abnormal accumulation of fat in hepatocytes, without alcohol, where overweight and obesity are determinants. Ecosonografía evaluated ...the prevalence of fatty liver in obese pediatric patients and its relation to nutritional assessment. The sample consisted of 85 children (51 females, 34 males), age 3-17. The abdominal ecosonography, BMI, waist circumference were performed; Godard Test for physical activity, history of diabetes, dyslipidemia, obesity and cardiovascular disease were questioned. Lipid profile, glucose and insulin resistance were determined. Data analyzed from descriptive and comparative tables. We obtained: mean age 9.8 ± 2.7 females and males 9.6 ± 2.7 years. The ecosonography indicated 50% and 50% fatty liver-pancreas fatty liver in children aged 3-6 years; 7-11 years 39.7% fatty liver-pancreas; 12-17yrs 31.6% fatty liver-pancreas (p> 0.05); BMI> 26kg/m2 42.9% fatty liver-pancreas; 21 to 25 kg/m2 44.7% fatty liver; 15 to 20 kg/m2 60%fatty liver-pancreas (p> 0.05). 97.6% with high CC; 68.2% with inadequate physical activity; high frequency of history of chronic non-communicable diseases. We concluded that this population had predominantly fatty liver fatty replacement of the pancreas (HG-RGP) in the groups with higher BMI, CC and high male unrelated insulin resistance, altered lipid profile and diagnosis HG. We inferred that the anthropometric assessment of waist circumference and abdominal ecosonography indicate the presence of visceral obesity, a condition that predisposes to hepatic steatosis, pancreas and / or liver-pancreas. El hígado graso no alcohólico (HGNA), se caracteriza por la acumulación anormal de grasa en los hepatocitos, sin consumo de alcohol, donde sobrepeso y obesidad son factores condicionantes. Se evaluó, por ecosonografía, la prevalencia de hígado graso en pacientes pediátricos obesos y su relación con la evaluación nutricional. Muestra conformada por 85 niños, (51 hembras, 34 varones), edad 3-17 años.Se realizó ecosonografía abdominal, IMC, circunferencia de cintura; Test Godard para actividad física, se interrogó antecedentes de diabetes, dislipidemia, obesidad y enfermedad cardiovascular. Se determinó perfil lipídico, glucosay resistencia a la insulina.Datos analizados a partir de tablas descriptivas y comparativas. Se obtuvo: edad promedio hembras 9,8±2,7 y varones 9,6±2,7 años. La ecosonografía indico 50% hígado graso y 50% hígado-páncreas graso en niños de 3-6 años; 7-11 años hígado-páncreas graso 39,7%; 12-17años 31,6% hígado-páncreas graso (p>0,05); IMC>26kg/m2 hígado-páncreas graso 42,9%; 21-25 kg/m2 44,7% hígado graso; 15-20 kg/m2 60% hígadopáncreas graso; (p>0,05). CC alta 97,6%. Un 68,2% con actividad física insuficiente; alta frecuencia de antecedentes de enfermedades crónicas no trasmisibles. Se concluye queen la población en estudiohubo predominio dehígado graso con reemplazo graso de páncreas (HG-RGP) en los grupos con mayor IMC, circunferencia de cintura y sexo masculino, sin relación entre resistencia a la insulina, alteraciones del perfil lipídico y diagnóstico de HG. Se infiere que es la evaluación antropométrica de circunferencia de cintura y la ecosonografía abdominal las que indican la presencia de obesidad visceral, que predispone a la condición de esteatosis hepática, pancreática y/o hepática-pancreática.
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