Suppression Of Hepatic Glucose Production Research Articles

Food perception promotes phosphorylation of MFFS131 and mitochondrial fragmentation in liver.

Liver mitochondria play a central role in metabolic adaptations to changing nutritional states, yet their dynamic regulation upon anticipated changes in nutrient availability has remained unaddressed. Here, we found that sensory food perception rapidly induced mitochondrial fragmentation in the liver through protein kinase B/AKT (AKT)-dependent phosphorylation of serine 131 of the mitochondrial fission factor (MFFS131). This response was mediated by activation of hypothalamic pro-opiomelanocortin (POMC)-expressing neurons. A nonphosphorylatable MFFS131G knock-in mutation abrogated AKT-induced mitochondrial fragmentation in vitro. In vivo, MFFS131G knock-in mice displayed altered liver mitochondrial dynamics and impaired insulin-stimulated suppression of hepatic glucose production. Thus, rapid activation of a hypothalamus-liver axis can adapt mitochondrial function to anticipated changes of nutritional state in control of hepatic glucose metabolism.

Estimating insulin sensitivity and β-cell function from the oral glucose tolerance test: validation of a new insulin sensitivity and secretion (ISS) model.

Efficient and accurate methods to estimate insulin sensitivity (SI) and β-cell function (BCF) are of great importance for studying the pathogenesis and treatment effectiveness of type 2 diabetes (T2D). Existing methods range in sensitivity, input data, and technical requirements. Oral glucose tolerance tests (OGTTs) are preferred because they are simpler and more physiological than intravenous methods. However, current analytical methods for OGTT-derived SI and BCF also range in complexity; the oral minimal models require mathematical expertise for deconvolution and fitting differential equations, and simple algebraic surrogate indices (e.g., Matsuda index, insulinogenic index) may produce unphysiological values. We developed a new insulin secretion and sensitivity (ISS) model for clinical research that provides precise and accurate estimates of SI and BCF from a standard OGTT, focusing on effectiveness, ease of implementation, and pragmatism. This model was developed by fitting a pair of differential equations to glucose and insulin without need of deconvolution or C-peptide data. This model is derived from a published model for longitudinal simulation of T2D progression that represents glucose-insulin homeostasis, including postchallenge suppression of hepatic glucose production and first- and second-phase insulin secretion. The ISS model was evaluated in three diverse cohorts across the lifespan. The new model had a strong correlation with gold-standard estimates from intravenous glucose tolerance tests and insulin clamps. The ISS model has broad applicability among diverse populations because it balances performance, fidelity, and complexity to provide a reliable phenotype of T2D risk.NEW & NOTEWORTHY The pathogenesis of type 2 diabetes (T2D) is determined by a balance between insulin sensitivity (SI) and β-cell function (BCF), which can be determined by gold standard direct measurements or estimated by fitting differential equation models to oral glucose tolerance tests (OGTTs). We propose and validate a new differential equation model that is simpler to use than current models and requires less data while maintaining good correlation and agreement with gold standards. Matlab and Python code is freely available.

GPAT1 Activity and Abundant Palmitic Acid Impair Insulin Suppression of Hepatic Glucose Production in Primary Mouse Hepatocytes

BackgroundGlycerol-3-phosphate acyltransferase (GPAT) activity is correlated with obesity and insulin resistance in mice and humans. However, insulin resistance exists in people with normal body weight, and individuals with obesity may be metabolically healthy, implying the presence of complex pathophysiologic mechanisms underpinning insulin resistance. ObjectiveWe asked what conditions related to GPAT1 must be met concurrently for hepatic insulin resistance to occur. MethodsMouse hepatocytes were overexpressed with GPATs via adenoviral infection or exposed to high or low concentrations of glucose. Glucose production by the cells and phosphatidic acid (PA) content in the cells were assayed, GPAT activity was measured, relative messenger RNA expressions of sterol-regulatory element-binding protein 1c (SREBP1c), carbohydrate response element-binding protein (ChREBP), and GPAT1 were analyzed, and insulin signaling transduction was examined. ResultsOverexpressing GPAT1 in mouse hepatocytes impaired insulin’s suppression of glucose production, together with an increase in both N-ethylmaleimide-resistant GPAT activity and the content of di-16:0 PA. Akt-mediated insulin signaling was inhibited in hepatocytes that overexpressed GPAT1. When the cells were exposed to high-glucose concentrations, insulin suppression of glucose production was impaired, and adding palmitic acid exacerbated this impairment. High-glucose exposure increased the expression of SREBP1c, ChREBP, and GPAT1 by ∼2-, 5-, and 5.7-fold, respectively. The addition of 200 mM palmitic acid or linoleic acid to the culture media did not change the upregulation of expression of these genes by high glucose. High-glucose exposure increased di-16:0 PA content in the cells, and adding palmitic acid further increased di-16:0 PA content. The effect was specific to palmitic acid because linoleic acid did not show these effects. ConclusionThese data demonstrate that high-GPAT1 activity, whether induced by glucose exposure or acquired by transfection, and abundant palmitic acid can impair insulin’s ability to suppress hepatic glucose production in primary mouse hepatocytes.

THU047 Growth Hormone (GH) Signaling In Hepatocytes Controls Hepatic Insulin Sensitivity And Nutrient Disposition

Abstract Disclosure: M. del Rio-Moreno: None. M. Vazquez-Borrego: None. J. Cordoba-Chacon: None. O.P. McGuinness: None. R.D. Kineman: None. It is commonly accepted that GH reduces the actions of insulin. However, we reported plasma GH levels within a physiological range are negatively associated with insulin-mediated glucose uptake, but positively associated with insulin-mediated suppression of hepatic glucose production (HGP) [Cordoba-Chacon J. et al. 2014. AJP Endocrinol Metab]. These findings suggest that GH may promote insulin’s actions on the liver. To determine the direct contribution of GH signaling on hepatic insulin sensitivity, hyperinsulinemic-euglycemic clamps were performed with stable isotope tracers in chow-fed adult-onset, hepatocyte-specific GHR knockdown (aHepGHRkd) mice. aHepGHRkd mice show reduced IGF1 and increased GH levels [Cordoba-Chacon J. et al 2015, Diabetes] which indirectly impacts systemic insulin sensitivity and substrate flux to the liver. To normalize plasma IGF1 and GH levels, aHepGHRkd mice were co-treated with adeno-associated virus (AAV) that express IGF1 or a constitutively active form of STAT5b (STAT5bCA). These AAVs have a thyroxin binding globulin promoter, leading to hepatocyte-specific expression. Under both basal and clamped conditions, aHepGHRkd mice exhibited hyperinsulinemia, that was normalized by AAV-mediated IGF1 and STAT5bCA expression. Interestingly, glucose disappearance (Rd), tissue-specific glucose uptake, or HGP (gluconeogenesis and glycogenolysis) did not differ across all groups. However, higher insulin tone in aHepGHRkd mice was required to achieve the same level of Rd and suppression of HGP in the steady-state, which was indicative of systemic and hepatic insulin resistance. These observations are consistent with our previous findings that GH reduces tissue-specific glucose uptake but promotes insulin-mediated control of HGP. In contrast, aHepGHRkd mice exhibited an increased rate of hepatic de novo lipogenesis, and an increase in plasma levels of newly formed triglyceride and triglyceride-bound palmitate, that was normalized by IGF1 and STAT5bCA expression. Taken together, these results indicate loss of hepatocyte GH signaling leads to pathway selective hepatic insulin resistance. This pathway selective hepatic insulin resistance has also been reported in mouse models due to altered substrate delivery to the liver as consequence of excess dietary intake and/or increased adipose tissue lipolysis. However, chow-fed aHepGHRkd mice show hyperinsulinemia that was sufficient to normalize systemic glucose uptake and suppress WAT lipolysis, as noted by normal plasma NEFA levels under both basal and clamped conditions. Therefore, changes in substrate delivery to the liver cannot readily explain the changes observed, suggesting hepatocyte GHR-signaling plays a direct role in partitioning of hepatic nutrients in response to insulin. Presentation: Thursday, June 15, 2023

Hepatic sialic acid synthesis modulates glucose homeostasis in both liver and skeletal muscle

ObjectiveSialic acid is a terminal monosaccharide of glycans in glycoproteins and glycolipids, and its derivation from glucose is regulated by the rate-limiting enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase (GNE). Although the glycans on key endogenous hepatic proteins governing glucose metabolism are sialylated, how sialic acid synthesis and sialylation in the liver influence glucose homeostasis is unknown. Studies were designed to fill this knowledge gap. MethodsTo decrease the production of sialic acid and sialylation in hepatocytes, a hepatocyte-specific GNE knockdown mouse model was generated, and systemic glucose metabolism, hepatic insulin signaling and glucagon signaling were evaluated in vivo or in primary hepatocytes. Peripheral insulin sensitivity was also assessed. Furthermore, the mechanisms by which sialylation in the liver influences hepatic insulin signaling and glucagon signaling and peripheral insulin sensitivity were identified. ResultsLiver GNE deletion in mice caused an impairment of insulin suppression of hepatic glucose production. This was due to a decrease in the sialylation of hepatic insulin receptors (IR) and a decline in IR abundance due to exaggerated degradation through the Eph receptor B4. Hepatic GNE deficiency also caused a blunting of hepatic glucagon receptor (GCGR) function which was related to a decline in its sialylation and affinity for glucagon. An accompanying upregulation of hepatic FGF21 production caused an enhancement of skeletal muscle glucose disposal that led to an overall increase in glucose tolerance and insulin sensitivity. ConclusionThese collective observations reveal that hepatic sialic acid synthesis and sialylation modulate glucose homeostasis in both the liver and skeletal muscle. By interrogating how hepatic sialic acid synthesis influences glucose control mechanisms in the liver, a new metabolic cycle has been identified in which a key constituent of glycans generated from glucose modulates the systemic control of its precursor.

1648-P: Triagonism Targeting GCGR/GLP-1/GIP-1 Receptors Improves Insulin Sensitivity in Obese Mice

Glucagon is best known as the primary counter-regulatory hormone against insulin action. Glucagon secretion is likewise elevated in Diabetes and thus it is often implicated as a diabetogenic hormone. However, emerging data from our group and others have uncovered that Glucagon receptor (GCGR) agonism improves insulin sensitivity in both lean and obese mice. Mechanistically, this improvement is associated with enhanced AKT phosphorylation and mTOR signaling in the liver. Novel, single-molecule, triagonists targeting GCG/GLP-1/GIP receptors (GGG) have recently been described to exert stronger anti-obesity effects than dual or single agonism in obese mice. Thus, we evaluated the effect of these agonists on insulin sensitivity using hyperinsulinemic euglycemic clamp. Diet-induced obese (DIO) mice were randomly assigned to 4d treatment (10 nmole/kg subcutaneous injection) of vehicle, GGG, GCGR agonism (IUB288), GLP-1R agonism (Semaglutide), or a long-acting GIP-1R agonist (GIP-FA 085). On the fourth day, mice were fasted for 5 hours, continuously infused with 1.2mU/kg/min insulin, and blood glucose levels clamped around 80-100 mg/dL. Under these conditions Semaglutide and GGG treatments stimulated the greatest glucose infusion rate (p<0.0001) and significantly improved insulin-mediated suppression of Endo Ra (p<0.01). Smaller, but significant, enhancement was also observed in the IUB288-treated mice. Moreover, [14C]-2GDp uptake into brown adipose tissue was improved in GGG, Semaglutide, and IUB288 treated mice compared to Vehicle treated mice. Importantly, these improvements in insulin sensitivity and glucose dynamics were body-weight independent. Therefore, GCGR and GLP-1R signaling combine in GGG triagonism to improve insulin sensitivity mainly via suppression of hepatic glucose production. Disclosure T.Kim: None. S.Nason: None. J.Antipenko: None. K.M.Habegger: Consultant; Glyscend Inc., Research Support; Eli Lilly and Company, Novo Nordisk, Glyscend Inc., Stock/Shareholder; Glyscend Inc. Funding Eli Lilly and Company

Direct and systemic actions of growth hormone receptor (GHR)-signaling on hepatic glycolysis, de novo lipogenesis and insulin sensitivity, associated with steatosis

BackgroundEvidence is accumulating that growth hormone (GH) protects against the development of steatosis and progression of non-alcoholic fatty liver disease (NAFLD). GH may control steatosis indirectly by altering systemic insulin sensitivity and substrate delivery to the liver and/or by the direct actions of GH on hepatocyte function. ApproachTo better define the hepatocyte-specific role of GH receptor (GHR) signaling on regulating steatosis, we used a mouse model with adult-onset, hepatocyte-specific GHR knockdown (aHepGHRkd). To prevent the reduction in circulating insulin-like growth factor 1 (IGF1) and the subsequent increase in GH observed after aHepGHRkd, subsets of aHepGHRkd mice were treated with adeno-associated viral vectors (AAV) driving hepatocyte-specific expression of IGF1 or a constitutively active form of STAT5b (STAT5bCA). The impact of hepatocyte-specific modulation of GHR, IGF1 and STAT5b on carbohydrate and lipid metabolism was studied across multiple nutritional states and in the context of hyperinsulinemic:euglycemic clamps. ResultsChow-fed male aHepGHRkd mice developed steatosis associated with an increase in hepatic glucokinase (GCK) and ketohexokinase (KHK) expression and de novo lipogenesis (DNL) rate, in the post-absorptive state and in response to refeeding after an overnight fast. The aHepGHRkd-associated increase in hepatic KHK, but not GCK and steatosis, was dependent on hepatocyte expression of carbohydrate response element binding protein (ChREBP), in re-fed mice. Interestingly, under clamp conditions, aHepGHRkd also increased the rate of DNL and expression of GCK and KHK, but impaired insulin-mediated suppression of hepatic glucose production, without altering plasma NEFA levels. These effects were normalized with AAV-mediated hepatocyte expression of IGF1 or STAT5bCA. Comparison of the impact of AAV-mediated hepatocyte IGF1 versus STAT5bCA in aHepGHRkd mice across multiple nutritional states, indicated the restorative actions of IGF1 are indirect, by improving systemic insulin sensitivity, independent of changes in the liver transcriptome. In contrast, the actions of STAT5b are due to the combined effects of raising IGF1 and direct alterations in the hepatocyte gene program that may involve suppression of BCL6 and FOXO1 activity. However, the direct and IGF1-dependent actions of STAT5b cannot fully account for enhanced GCK activity and lipogenic gene expression observed after aHepGHRkd, suggesting other GHR-mediated signals are involved. ConclusionThese studies demonstrate hepatocyte GHR-signaling controls hepatic glycolysis, DNL, steatosis and hepatic insulin sensitivity indirectly (via IGF1) and directly (via STAT5b). The relative contribution of these indirect and direct actions of GH on hepatocytes is modified by insulin and nutrient availability. These results improve our understanding of the physiologic actions of GH on regulating adult metabolism to protect against NAFLD progression.

Hepatic Phospholipid Remodeling Modulates Insulin Sensitivity and Systemic Metabolism.

The liver plays a central role in regulating glucose and lipid metabolism. Aberrant insulin action in the liver is a major driver of selective insulin resistance, in which insulin fails to suppress glucose production but continues to activate lipogenesis in the liver, resulting in hyperglycemia and hypertriglyceridemia. The underlying mechanisms of selective insulin resistance are not fully understood. Here It is shown that hepatic membrane phospholipid composition controlled by lysophosphatidylcholine acyltransferase 3 (LPCAT3) regulates insulin signaling and systemic glucose and lipid metabolism. Hyperinsulinemia induced by high-fat diet (HFD) feeding augments hepatic Lpcat3 expression and membrane unsaturation. Loss of Lpcat3 in the liver improves insulin resistance and blunts lipogenesis in both HFD-fed and genetic ob/ob mouse models. Mechanistically, Lpcat3 deficiency directly facilitates insulin receptor endocytosis, signal transduction, and hepatic glucose production suppression and indirectly enhances fibroblast growth factor 21 (FGF21) secretion, energy expenditure, and glucose uptake in adipose tissue. These findings identify hepatic LPCAT3 and membrane phospholipid composition as a novel regulator of insulin sensitivity and provide insights into the pathogenesis of selective insulin resistance.

Sanhuang xiexin decoction synergizes insulin/PI3K-Akt/FoxO signaling pathway to inhibit hepatic glucose production and alleviate T2DM.

Sanhuang Xiexin Decoction (SHXXD) is a classic prescription for the treatment of diabetes. Excessive hepatic glucose production (HGP) is a major determinant of the occurrence and development of diabetes. Inhibition of HGP can significantly improve type 2 diabetes mellitus (T2DM). To investigate the mechanism by which SHXXD inhibits HGP. First, a mouse model of T2DM was established through high-fat diet (HFD) feeding combined with streptozotocin (STZ) injection to determine the pharmacodynamic effect of SHXXD in T2DM mice. Then, the possible pathways induced by SHXXD in the treatment of T2DM were predicted by network pharmacology combined with transcriptomics (including target prediction, network analysis and enrichment analysis). Finally, the specific mechanism of SHXXD was elucidated by in vitro experiments. In vivo experiments showed that SHXXD reduced fasting blood glucose and alleviated weight loss in T2DM mice. Improved glucose clearance rates and insulin sensitivity improve dyslipidemia, liver tissue structural abnormalities and inflammatory cell infiltration as well as increase glycogen storage in T2DM mice. The results of network pharmacology and transcriptome analysis showed that SHXXD contained 378 compounds and 2625 targets. In total, 292 intersection targets were identified between the differentially expressed genes (DEGs) of the liver tissue insulin resistance (IR) related dataset GSE23343. KEGG enrichment analysis showed that the insulin/PI3K-Akt/FoxO signaling pathway may be related to SHXXD-mediated improvements in T2DM. In vitro experimental results showed that SHXXD increased glucose consumption by HepG2-IR cells and improved their insulin sensitivity. RT‒qPCR and Western blotting results showed that SHXXD inhibited hepatic gluconeogenesis through the insulin/PI3K-Akt/FoxO signaling pathway by promoting IGFIR, PIK3R1 and AKT2 expression and subsequently inhibiting PEPCK and FBP1 expression via phosphorylation of Foxo1. In addition, PI3K/Akt deactivated p-GSK3β through phosphorylation, thereby promoting GS expression and increasing glycogen synthesis. SHXXD can target the liver to cooperate with the insulin/PI3K-Akt/FoxO signaling pathway to inhibit HGP to alleviate T2DM.

Liver Glucose-6 Phosphatase Activity is Inhibited by Refeeding in Rats

This study was conducted to determine whether inhibition of hepatic glucose-6 phosphatase is involved in the mechanism of suppression of hepatic glucose production during the postprandial period. We studied the time course of changes in the enzyme activity by refeeding food-deprived rats with nonpurified diet. The Vmax of the enzyme, assayed in homogenates from livers freeze-clamped in situ in anesthetized 48-h unfed rats (12.3 ± 0.15 U/g wet liver, mean ± SEM, n = 6) was progressively decreased upon refeeding: 11.1 ± 0.5, 8.5 ± 0.4 and 7.9 ± 0.5 U/g, in rats refed for 90, 180 (P < 0.01) and 360 min (P < 0.01), respectively. The Km of the enzyme was not affected by refeeding. No inhibition of the enzyme was observed in microsomes purified from these homogenates, suggesting a metabolite-induced inhibition mechanism. To assess the role of insulin in the inhibition, we assayed the glucose-6 phosphatase activity in similarly processed liver homogenates from food-deprived rats perfused with insulin at physiological and supraphysiological concentrations, whereas plasma glucose was maintained at the basal level by adapted glucose perfusion (euglycemic clamps). No inhibition of glucose-6 phosphatase was found under these conditions, suggesting that insulin cannot by itself account for the inhibition observed in the refeeding experiments. These data constitute the first demonstration of the inhibition of glucose-6 phosphatase activity during the postprandial period.

The Mechanisms of Neochlorogenic Acid (3-Caffeoylquinic Acid) in Improving glucose and Lipid Metabolism in Rats with Insulin Resistance Induced by A High Fat-High Fructose Diet

This study investigated the effects and the mechanism of actions of neochlorogenic acid (3-caffeoylquinic acid; 3-CQA) on glucose and lipid metabolism in rats fed a high fat-high fructose diet (HFFD). Male rats were fed HFFD (40 % lard and 20 % fructose) for 16 weeks. At the 10th week, the HFFD rats were split into 3 groups: HFFD receiving distilled water (HFFD control group), HFFD receiving 3-CQA 50 mg/kg and HFFD receiving metformin 200 mg/kg once daily for a further 6 weeks. At the end of treatment, fasting blood glucose (FBG), oral glucose-tolerance test (OGTT), lipid profile, insulin, leptin, adiponectin, markers of oxidative stress, and hepatic triglyceride content were measured. Liver, adipose tissue, and skeletal muscle were collected for histological, gene and protein examinations. Compared to the HFFD control group, the 3-CQA group exhibited significantly reduced FBG, insulin and leptin levels, and improved OGTT. Serum adiponectin increased and lipid profiles were normalized. Hepatic triglyceride was reduced with a decrease in lipid droplets in liver histological sections. Levels of serum SOD and CAT activity, and MDA were reversed by 3-CQA treatment. Moreover, 3-CQA significantly reduced the expression of adipocyte pro-inflammatory cytokine genes (MCP-1, TNF-α, and IL-6), hepatic lipogenic genes (SREBP1c, FAS, and GPAT), and hepatic gluconeogenic genes (PEPCK and G6Pase). Additionally, 3-CQA increased expression of muscle GLUT4 gene, and of GLUT4 protein with increased p-AKT and p-AMPK in skeletal muscle. In conclusion, 3-CQA improves glucose and lipid metabolism plausibly by decreasing oxidative stress and inflammation-induced insulin resistance, downregulating the expression of lipogenic and gluconeogenic genes, and enhancing insulin signaling in HFFD-induced insulin-resistant rats. HIGHLIGHTS Neochlorogenic acid (3-CQA) improves glucose and lipid metabolism by decreasing insulin resistance Neochlorogenic acid (3-CQA) deceases insulin resistance due to its activities in ameliorating obesity, oxidative stress, and adipose tissue inflammation The beneficial effects of Neochlorogenic acid (3-CQA) to improve glucose and lipid homeostasis may be mediated via suppression of hepatic glucose production and lipogenesis, and activation of muscle glucose uptake and AKT and AMPK pathways GRAPHICAL ABSTRACT

OR24-6 Liver-Specific Inhibition of Sialic Acid Biosynthesis Improves Systemic Glucose Homeostasis in Mice

Abstract Glycosylation is an important posttranslational modification that modulates protein expression and function. Sialic acid is the most abundant terminal monosaccharide of N-linked glycosylation in mammalian cells, and its biosynthesis is controlled by the rate-limited enzyme UDP-GlcNAc 2-epimerase/ManNac kinase (GNE). There is a positive association between the abundance of terminally sialylated plasma glycoproteins and the risk of type 2 diabetes (T2DM). The majority of glycosylated plasma proteins are liver-derived, and key hepatic receptors involved in glucose metabolism, such as the insulin receptor (IR) and glucagon receptor (GCGR), are terminally sialylated. Whether and how protein sialylation in the liver influences glucose homeostasis is unknown. To address this question we generated floxed GNE mice and at 4 weeks of age injected males with either AAV8 encoding a liver-specific targeted Cre recombinase or GFP, to yield mice lacking or normally expressing GNE in liver (GNELKO and GNELWT, respectively). Two weeks post AAV8 injection, GNELKO showed a &amp;gt;98% loss of GNE protein selectively in liver and drastic reductions in the sialylation of liver and plasma proteins detected by glycan-specific lectin-based analyses. Whereas body weights/body composition and plasma lipids were unaltered, GNELKO had lower fasting serum glucose and greater glucose tolerance and insulin sensitivity compared to GNELWT; serum insulin or glucose-stimulated insulin secretion were unchanged. In GNELKO mice hyperinsulinemic-euglycemic clamps displayed a loss of insulin suppression of hepatic glucose production, hepatic IRa and IRb subunit expression and Akt and GSK phosphorylation were decreased, and liver glycogen content was lowered &amp;gt;85%. However, there was also evidence of markedly impaired GCGR function in GNELKO mice, with serum glucagon levels raised 18-fold and attenuation of hepatic cAMP production, CREB phosphorylation and gluconeogenesis in response to glucagon. Regarding extrahepatic mechanisms, GNELKO mice displayed enhanced peripheral glucose disposal, and this was associated with increased IRb, Akt and GSK phosphorylation in skeletal muscle, and with serum FGF21 levels elevated by 406%. In additional studies, when invoked following 12 weeks of high fat diet feeding, liver GNE silencing caused dramatic improvements in glucose tolerance and insulin sensitivity. To evaluate the relevance of these findings to humans, liver GNE transcript levels were queried in a publicly available cohort, and they were higher in T2DM patients compared to non-diabetic controls in two independent cohorts (n= 54 and n=9 for Cohort I and n=4 and n=4 for Cohort II, respectively). Collectively these observations reveal that protein sialylation in the liver has dramatic impact on both insulin and glucagon action in the liver, and on peripheral glucose disposal. Further interrogation of the modulation of glucose control mechanisms by protein sialylation may lead to novel approaches to combatting glucose intolerance in T2DM and other conditions. Presentation: Monday, June 13, 2022 12:15 p.m. - 12:30 p.m.

Coronarin A modulated hepatic glycogen synthesis and gluconeogenesis via inhibiting mTORC1/S6K1 signaling and ameliorated glucose homeostasis of diabetic mice.

Promotion of hepatic glycogen synthesis and inhibition of hepatic glucose production are effective strategies for controlling hyperglycemia in type 2 diabetes mellitus (T2DM), but agents with both properties were limited. Herein we report coronarin A, a natural compound isolated from rhizomes of Hedychium gardnerianum, which simultaneously stimulates glycogen synthesis and suppresses gluconeogenesis in rat primary hepatocytes. We showed that coronarin A (3, 10 μM) dose-dependently stimulated glycogen synthesis accompanied by increased Akt and GSK3β phosphorylation in rat primary hepatocytes. Pretreatment with Akt inhibitor MK-2206 (2 μM) or PI3K inhibitor LY294002 (10 μM) blocked coronarin A-induced glycogen synthesis. Meanwhile, coronarin A (10 μM) significantly suppressed gluconeogenesis accompanied by increased phosphorylation of MEK, ERK1/2, β-catenin and increased the gene expression of TCF7L2 in rat primary hepatocytes. Pretreatment with β-catenin inhibitor IWR-1-endo (10 μM) or ERK inhibitor SCH772984 (1 μM) abolished the coronarin A-suppressed gluconeogenesis. More importantly, we revealed that coronarin A activated PI3K/Akt/GSK3β and ERK/Wnt/β-catenin signaling via regulation of a key upstream molecule IRS1. Coronarin A (10, 30 μM) decreased the phosphorylation of mTOR and S6K1, the downstream target of mTORC1, which further inhibited the serine phosphorylation of IRS1, and subsequently increased the tyrosine phosphorylation of IRS1. In type 2 diabetic ob/ob mice, chronic administration of coronarin A significantly reduced the non-fasting and fasting blood glucose levels and improved glucose tolerance, accompanied by the inhibited hepatic mTOR/S6K1 signaling and activated IRS1 along with enhanced PI3K/Akt/GSK3β and ERK/Wnt/β-catenin pathways. These results demonstrate the anti-hyperglycemic effect of coronarin A with a novel mechanism by inhibiting mTORC1/S6K1 to increase IRS1 activity, and highlighted coronarin A as a valuable lead compound for the treatment of T2DM.

Bone morphogenetic protein-9 maybe an important factor which improves insulin resistance in PCOS

Background Polycystic ovary syndrome (PCOS) is closely related to insulin resistance (IR). Bone morphogenetic protein-9 (BMP-9) plays an important role in maintaining glucose homeostasis, but an association between BMP-9 and PCOS has not been reported. Here, we report the changes in BMP-9 and the influence of this protein on IR in PCOS. Methods 57 PCOS patients were selected (among them 25 received interventional treatment with exenatide (EX) for 3 months, and 32 received no treatment). 22 normal control individuals and 30 IR patients were also recruited. We evaluated IR with the euglycaemic-hyperinsulinaemic clamp (EHC) technique. IR and the glucose metabolism rate were assessed by EHC and [3-3H]glucose tracer experiments. We determined the protein expression levels of BMP-9, p-AKT (protein kinase B) and androgen receptor in the ovaries and liver by Western blotting. Results We found that circulating BMP-9 levels were significantly decreased in PCOS with IR patients. Circulating BMP-9 levels and p-AKT levels were decreased in HFD and PCOS rats and increased after MF and EX treatment. The glucose infusion rate, glucose disappearance rate and suppression of hepatic glucose production decreased in the HFD and PCOS groups, the opposite results were found for HGP. AR protein expression levels increased in the HFD and PCOS groups and decreased in the MF and EX groups. Conclusions Our study results suggest that BMP-9 is an independent factor that influences IR in PCOS patients. The decrease in BMP-9 levels in the liver and ovaries may be involved in IR through the PI3K/AKT signaling pathway in PCOS rats.

192-OR: T-Type Calcium Channel Cav3.2 in GABAergic Neurons Regulates Rhythmic Glucose Metabolism

Systemic insulin sensitivity shows a diurnal rhythm with a peak upon waking. The GABAergic (γ-aminobutyric acid-producing) neurons in the suprachiasmatic nucleus (SCN) (SCNGABA neurons) were reported to control the diurnal rhythm of insulin-mediated suppression of hepatic glucose production in mice in earlier work1. SCNGABA neural firing activity displays a diurnal rhythm, with the intrinsic ionic mechanism underlying this temporal pattern not completely understood. Here we provided evidence supporting a role of the T type voltage-gated calcium ion channel subunit 3.2 (Cav3.2) in SCNGABA neurons in regulating rhythmic neural firing and glucose homeostasis. We found that Cav3.2 global knockout (Cav3.2KO) mice displayed disrupted diurnal rhythm of blood glucose levels. Selective deletion of Cav3.2 in the SCNGABA neurons abolished the oscillatory firing activity of SCNGABA neurons and led to glucose intolerance. Furthermore, our real-time calcium imaging data in freely moving mice showed that SCN GABA neuronal activity displayed a circadian rhythm pattern in WT control mice but not Cav3.2KO mice or mice with Cav3.2 selectively deleted in the SCNGABA neurons. These findings provide insights into how the calcium ion channel regulates the central circadian clock and glucose metabolism, with implications in the extended dawn phenomenon in type 2 diabetes. Keywords: Type 2 diabetes, calcium channel, Cav3.2, GABA neurons, circadian rhythm Reference: 1 Ding, G. et al. REV-ERB in GABAergic neurons controls diurnal hepatic insulin sensitivity. Nature 592, 763-767, doi:10.1038/s41586-021-03358-w (2021) . Disclosure P. Xu: None. W. Zhou: None. Z. Sun: None. Y. He: None. Funding NIH (P20 GM135002)

1311-P: Glucokinase in AGRP Neurons Is Required for Normal Insulin Secretion and Action in Female Mice

Discrete brain areas, including hypothalamic nuclei, have been implicated in glucose homeostasis. Some contain molecular machinery capable of detecting changes in blood glucose such as glucokinase (GK) , a low affinity hexokinase important for pancreatic beta cell glucose-sensing. A subset of arcuate nucleus AGRP neurons express GK. We created GKAGRP knockout (KO) mice by crossing AGRP Cre with GK floxed mice, hypothesizing that they would display impaired gluco-regulation. Despite established sex differences in metabolic neurocircuitry, female mice are not always studied. In pilots, we found impaired glucose handling in i.p. glucose tolerance tests in older GKAGRP KO females, but not younger female, nor male mice. Here, we perform detailed phenotyping, using sequential euglycemic (with stable glucose isotope tracers) and hyperglycemic clamp studies in conscious, free moving, 19-23 week old female mice with implanted carotid artery and jugular vein catheters. As shown below, we found that GKAGRP KO females were insulin resistant with a lower dextrose infusion rate and reduced suppression of hepatic glucose production during euglycemic clamps. They also displayed reduced insulin secretory responses during hyperglycemic clamps. Our data support a sexually-dimorphic central gluco-regulatory role for AGRP neurons which requires the presence of GK to facilitate normal insulin release and action. Disclosure M.Josipovic: Research Support; Novo Nordisk A/S. E.O.Staricoff: Research Support; Novo Nordisk A/S. C.H.Riches: Research Support; Novo Nordisk. L.Sheppard: None. M.Evans: Advisory Panel; Pila Pharma, Zucara Therapeutics, Other Relationship; Abbott Diabetes, Dexcom, Inc., Medtronic, Novo Nordisk, Research Support; AstraZeneca, Sanofi, Speaker’s Bureau; Lilly Diabetes. Funding European Union’s Innovative Medicines Initiative 2 Joint Undertaking (grant agreement 777460) also supported by EFPIA, T1D Exchange, JDRF, International Diabetes Federation (IDF) , The Leona M. and Harry B. Helmsley Charitable Trust, Wellcome Trust, Medical Research Council UK and Gates Cambridge Trust.

Let-7 underlies metformin-induced inhibition of hepatic glucose production

SignificanceA clear mechanistic understanding of metformin's antidiabetic effects is lacking. This is because suprapharmacological concentrations of metformin have been used in most studies. Using mouse models and human primary hepatocytes, we show that metformin, at clinically relevant doses, suppresses hepatic glucose production by activating a conserved regulatory pathway encompassing let-7, TET3, and a fetal isoform of hepatocyte nuclear factor 4 alpha (HNF4α). We demonstrate that metformin no longer has potent antidiabetic actions in a liver-specific let-7 loss-of-function mouse model and that hepatic delivery of let-7 ameliorates hyperglycemia and improves glucose homeostasis. Our results thus reveal an important role of the hepatic let-7/TET3/HNF4α axis in mediating the therapeutic effects of metformin and suggest that targeting this axis may be a potential therapeutic for diabetes.

Functionally selective signaling and broad metabolic benefits by novel insulin receptor partial agonists

Insulin analogs have been developed to treat diabetes with focus primarily on improving the time action profile without affecting ligand-receptor interaction or functional selectivity. As a result, inherent liabilities (e.g. hypoglycemia) of injectable insulin continue to limit the true therapeutic potential of related agents. Insulin dimers were synthesized to investigate whether partial agonism of the insulin receptor (IR) tyrosine kinase is achievable, and to explore the potential for tissue-selective systemic insulin pharmacology. The insulin dimers induced distinct IR conformational changes compared to native monomeric insulin and substrate phosphorylation assays demonstrated partial agonism. Structurally distinct dimers with differences in conjugation sites and linkers were prepared to deliver desirable IR partial agonist (IRPA). Systemic infusions of a B29-B29 dimer in vivo revealed sharp differences compared to native insulin. Suppression of hepatic glucose production and lipolysis were like that attained with regular insulin, albeit with a distinctly shallower dose-response. In contrast, there was highly attenuated stimulation of glucose uptake into muscle. Mechanistic studies indicated that IRPAs exploit tissue differences in receptor density and have additional distinctions pertaining to drug clearance and distribution. The hepato-adipose selective action of IRPAs is a potentially safer approach for treatment of diabetes.

Expressing the Human Cholesteryl Ester Transfer Protein Minigene Improves Diet-Induced Fatty Liver and Insulin Resistance in Female Mice.

Mounting evidence has shown that CETP has important physiological roles in adapting to chronic nutrient excess, specifically, to protect against diet-induced insulin resistance. However, the underlying mechanisms for the protective roles of CETP in metabolism are not yet clear. Mice naturally lack CETP expression. We used transgenic mice with a human CETP minigene (huCETP) controlled by its natural flanking region to further understand CETP-related physiology in response to obesity. Female huCETP mice and their wild-type littermates were fed a high-fat diet for 6 months. Blood lipid profile and liver lipid metabolism were studied. Insulin sensitivity was analyzed with euglycemic-hyperinsulinemic clamp studies combined with 3H-glucose tracer techniques. While high-fat diet feeding induced obesity for huCETP mice and their wild-type littermates lacking CETP expression, insulin sensitivity was higher for female huCETP mice than for their wild-type littermates. There was no difference in insulin sensitivity for male huCETP mice vs. littermates. The increased insulin sensitivity in females was largely caused by the better insulin-mediated suppression of hepatic glucose production. In huCETP females, CETP in the circulation decreased HDL-cholesterol content and increased liver cholesterol uptake and liver cholesterol and oxysterol contents, which was associated with the upregulation of LXR target genes in long-chain polyunsaturated fatty acid biosynthesis and PPARα target genes in fatty acid β-oxidation in the liver. The upregulated fatty acid β-oxidation may account for the improved fatty liver and liver insulin action in female huCETP mice. This study provides further evidence that CETP has beneficial physiological roles in the metabolic adaptation to nutrient excess by promoting liver fatty acid oxidation and hepatic insulin sensitivity, particularly for females.

HDL functionality in type 1 and type 2 diabetes: new insights.

Purpose of reviewTo critically appraise new insights into HDL structure and function in type 1 diabetes (T1DM) and type 2 diabetes (T2DM).Recent findingsIn young T1DM patients with early renal impairment and a high inflammatory score, both HDL antioxidative activity and endothelial vasodilatory function were impaired, revealing a critical link between HDL dysfunction, subclinical vascular damage, systemic inflammation and end organ damage. HDL may inhibit development of T2DM by attenuating endoplasmic reticulum (ER) stress and apoptotic loss of pancreatic β-cells, an effect due in part to ABC transporter-mediated efflux of specific oxysterols with downstream activation of the hedghehog signalling receptor, Smoothened. The apoM-sphingosine-1-phosphate complex is critical to HDL antidiabetic activity, encompassing protection against insulin resistance, promotion of insulin secretion, enhanced β-cell survival and inhibition of hepatic glucose production. Structure-function studies of HDL in hyperglycemic, dyslipidemic T2DM patients revealed both gain and loss of lipidomic and proteomic components. Such changes attenuated both the optimal protective effects of HDL on mitochondrial function and its capacity to inhibit endothelial cell apoptosis. Distinct structural components associated with individual HDL functions.SummaryExtensive evidence indicates that both the proteome and lipidome of HDL are altered in T1DM and T2DM, with impairment of multiple functions.