TOX4, an insulin receptor-independent regulator of hepatic glucose production, is activated in diabetic liver

Insulin resistance in type 2 diabetes mellitus

Insulin resistance is an integral pathophysiological feature of type 2 diabetes mellitus. Here, we review established and emerging cellular mechanisms of insulin resistance, their complex integrative features and their relevance to disease progression. While recognizing the heterogeneity of the elusive fundamental disruptions that cause insulin resistance, we endorse the view that effector mechanisms impinge on insulin receptor signalling and its relationship with plasma levels of insulin. We focus on hyperinsulinaemia and its consequences: acutely impaired but persistent insulin action, with reduced ability to lower glucose levels but preserved lipid synthesis and lipoprotein secretion. We emphasize the role of insulin sensitization as a therapeutic goal in type 2 diabetes mellitus.

Exome-wide association analysis identifies novel risk loci for alcohol-associated hepatitis

BACKGROUND AND AIMS

Alcohol-associated hepatitis (AH) is a clinically severe, acute disease that afflicts only a fraction of patients with alcohol use disorder. Genomic studies of alcohol-associated cirrhosis (AC) have identified several genes of large effect, but the genetic and environmental factors that lead to AH and AC, and their degree of genetic overlap, remain largely unknown. This study aims to identify genes and genetic variations that contribute to the development of AH.

APPROACH AND RESULTS

Exome-sequencing of patients with AH (N=784) and heavy drinking controls (N=951) identified an exome-wide significant association for AH at patalin-like phospholipase domain containing 3, as previously observed for AC in genome-wide association study, although with a much lower effect size. Single nucleotide polymorphisms (SNPs) of large effect size at inducible T cell costimulatory ligand ( ICOSLG ) (Chr 21) and TOX4/RAB2B (Chr 14) were also exome-wide significant. ICOSLG encodes a co-stimulatory signal for T-cell proliferation and cytokine secretion and induces B-cell proliferation and differentiation. TOX high mobility group box family member 4 ( TOX4 ) was previously implicated in diabetes and immune system function. Other genes previously implicated in AC did not strongly contribute to AH, and the only prominently implicated (but not exome-wide significant) gene overlapping with alcohol use disorder was alcohol dehydrogenase 1B ( ADH1B ). Polygenic signals for AH were observed in both common and rare variant analysis and identified genes with roles associated with inflammation.

CONCLUSIONS

This study has identified 2 new genes of high effect size with a previously unknown contribution to alcohol-associated liver disease and highlights both the overlap in etiology between liver diseases and the unique origins of AH.

Mannose reduces fructose metabolism and reverses MASH in human liver slices and murine models in vivo

BACKGROUND

Fibrosis drives liver-related mortality in metabolic dysfunction-associated steatohepatitis (MASH), yet we have limited medical therapies to target MASH-fibrosis progression. Here we report that mannose, a simple sugar, attenuates MASH steatosis and fibrosis in 2 robust murine models and human liver slices.

METHODS

The well-validated fat-and-tumor MASH murine model for liver steatosis and fibrosis was employed. Mannose was supplied in the drinking water at the start ("Prevention" group) or at week 6 of the 12-week MASH regimen ("Therapy" group). The in vivo antifibrotic effects of mannose supplementation were tested in a second model of carbon tetrachloride (CCl4)-induced liver fibrosis. A quantitative and automated digital pathology approach was used to comprehensively assess steatosis and fibrosis phenotypes. Mannose was also tested in vitro in human and primary mouse hepatocytes conditioned with free fatty acids alone or with fructose, and human precision-cut liver slices from patients with end-stage MASH cirrhosis.

RESULTS

Oral mannose supplementation improved liver fibrosis in vivo in both fat-and-tumor MASH and CCl4 mouse models, as well as in human precision-cut liver slice MASH samples. Mannose also reduced liver steatosis in fat-and-tumor MASH mice, and in human and mouse hepatocytes in vitro. Ketohexokinase, the main enzyme in fructolysis, was decreased with mannose in whole mouse liver, cultured hepatocytes, and human precision-cut liver slices. Removal of fructose or overexpression of ketohexokinase each abrogated the antisteatotic effects of mannose.

CONCLUSIONS

This study identifies mannose as a novel therapeutic candidate for MASH that mitigates steatosis by dampening hepatocyte ketohexokinase expression and exerts independent antifibrotic effects in 2 mouse models and human liver tissue slices.

LGR4 is a key regulator of hepatic gluconeogenesis

AIMS/HYPOTHESIS

Emerging evidence underscored the significance of leucine-rich repeat-containing G protein-coupled receptor (LGR) 4 in endocrine and metabolic disorders. Despite this, its role in LGR4 in hepatic glucose metabolism remains poorly understood. In this study we set out to test whether LGR4 regulates glucose production in liver through a specific signaling pathway.

METHODS

Hepatic glucose production and gluconeogenic gene expressions were detected after silence of LGR4 in three obese mice models. Then, whole-body LGR4-deficient (LGR4 KO) mice, liver-specific LGR4 knockout (LGR4LKO) mice, and liver-specific LGR4 overexpression (LGR4LOV) mice were generated, in which we analyzed the effects of LGR4 on hepatic glucose metabolism upon HFD feeding, among which live imaging and quantitative analysis of hepatic phosphoenolpyruvate carboxykinase (PEPCK)-luciferase activity were conducted.

RESULTS

LGR4 expression was significantly upregulated in the liver of three obese mouse models, and presented dynamic expression patterns in response to nutritional fluxes. We utilized global and liver-specific LGR4 knockouts (LGR4LKO), along with adenoviral-mediated LGR4 knockdown in mice, to show improved glucose tolerance and decreased hepatic gluconeogenesis. Specifically, the expression of rate-limiting gluconeogenic enzymes, PEPCK was significantly downregulated. Conversely, mouse model with adenovirus-mediated LGR4 overexpression (LGR4LOV) exhibited elevated gluconeogenesis and PEPCK expression and reversed the suppression observed in LGR4 knockout models. Notably, neither RANKL nor PKA signaling pathways, which were reported to take part in LGR4's function, were involved in the process of LGR4 regulating PEPCK. Instead, TopFlash reporter system and inhibitors application suggested that LGR4's influence on hepatic gluconeogenesis operates through the canonical Wnt/β-catenin/TCF7L2 signaling pathway.

CONCLUSIONS/INTERPRETATION

Overall, these findings underscore a novel mechanism by which LGR4 regulates hepatic gluconeogenesis, presenting a potential therapeutic target for diabetes management.

Increased hepatic gluconeogenesis and type 2 diabetes mellitus

Abnormally increased hepatic gluconeogenesis is a significant contributor to hyperglycemia in the fasting state in patients with type 2 diabetes mellitus (T2DM) due to insulin resistance. Metformin, the most prescribed drug for the treatment of T2DM, is believed to exert its effect mainly by reducing hepatic gluconeogenesis. Here, we discuss how increased hepatic gluconeogenesis contributes to T2DM and we review newly revealed mechanisms underlying the attenuation of gluconeogenesis by metformin. In addition, we analyze the recent findings on new determinants involved in the regulation of gluconeogenesis, which might ultimately lead to the identification of novel and targeted treatment strategies for T2DM.

Mulberry leaf ameliorate STZ induced diabetic rat by regulating hepatic glycometabolism and fatty acid β-oxidation

Introduction

Type 2 diabetes (T2D) is a metabolic disorder marked by disruptions in glucolipid metabolism, with numerous signaling pathways contributing to its progression. The liver, as the hub of glycolipid metabolism, plays a pivotal role in this context. Mulberry leaf (ML), a staple in traditional Chinese medicine, is widely utilized in the clinical management of T2D. Synthesizing existing literature with the outcomes of prior research, it has become evident that ML enhances glucose metabolism via multiple pathways.

Methods

In our study, we induced T2D in rats through a regimen of high-sugar and high-fat diet supplementation, coupled with intraperitoneal injections of streptozotocin. We subsequently administered the aqueous extract of ML to these rats and assessed its efficacy using fasting blood glucose levels and other diagnostic indicators. Further, we conducted a comprehensive analysis of the rats' liver tissues using metabolomics and proteomics to gain insights into the underlying mechanisms.

Results

Our findings indicate that ML not only significantly alleviated the symptoms in T2D rats but also demonstrated the capacity to lower blood glucose levels. This was achieved by modulating the glucose-lipid metabolism and amino-terminal pathways within the liver. ACSL5, Dlat, Pdhb, G6pc, Mdh2, Cs, and other key enzymes in metabolic pathways regulated by ML may be the core targets of ML treatment for T2D.

Discussion

Mulberry leaf ameliorate STZ induced diabetic rat by regulating hepatic glycometabolism and fatty acid β-oxidation.

Oxyberberine Inhibits Hepatic Gluconeogenesis via AMPK-Mediated Suppression of FoxO1 and CRTC2 Signaling Axes

Oxyberberine (OBB), a natural metabolite of berberine, has been shown to exhibit inhibitory effects on gluconeogenesis in our previous work. This work was designed to investigate the potential effects and underlying mechanisms of OBB on hepatic gluconeogenesis. Our work found that OBB significantly inhibited the expressions of glucose 6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), and decreased the glucose production in palmitic acid-induced HepG2 cells. Then, AMPK/Akt/FoxO1 and AMPK/CRTC2 signaling pathways were confirmed by transcriptomics and network pharmacology analyses. It was shown that AMPK activation may phosphorylate and promote nuclear exclusion of FoxO1 and CRTC2, two key regulators of hepatic gluconeogenesis transcriptional pathways, resulting in the inhibition of gluconeogenesis under OBB administration. Afterwards, AMPK/Akt/FoxO1, AMPK/CRTC2 signaling pathways were evidenced by western blot, immunoprecipitation and confocal immunofluorescence, and the targeted inhibitor (Compound C) and siRNA of AMPK were applied for further mechanism verification. Moreover, it was found that OBB treatment activated AMPK/Akt/FoxO1 and AMPK/CRTC2 signaling pathways to decrease hepatic gluconeogenesis in db/db mice. Similarly, the in vivo inhibitory effects of OBB on gluconeogenesis were also diminished by AMPK inhibition. Our work demonstrated that OBB can inhibit hepatic gluconeogenesis in vitro and in vivo, and its underlying mechanisms were associated with AMPK-mediated suppression of FoxO1 and CRTC2 signaling axes.

The role of adipose tissue dysfunction in hepatic insulin resistance and T2D

The root cause of type 2 diabetes (T2D) is insulin resistance (IR), defined by the failure of cells to respond to circulating insulin to maintain lipid and glucose homeostasis. While the causes of whole-body insulin resistance are multifactorial, a major contributing factor is dysregulation of liver and adipose tissue function. Adipose dysfunction, particularly adipose tissue-IR (adipo-IR), plays a crucial role in the development of hepatic insulin resistance and the progression of metabolic dysfunction-associated steatotic liver disease (MASLD) in the context of T2D. In this review, we will focus on molecular mechanisms of hepatic insulin resistance and its association with adipose tissue function. A deeper understanding of the pathophysiological mechanisms of the transition from a healthy state to insulin resistance, impaired glucose tolerance, and T2D may enable us to prevent and intervene in the progression to T2D.

Activation of the insulin receptor by insulin-like growth factor 2

Insulin receptor (IR) controls growth and metabolism. Insulin-like growth factor 2 (IGF2) has different binding properties on two IR isoforms, mimicking insulin's function. However, the molecular mechanism underlying IGF2-induced IR activation remains unclear. Here, we present cryo-EM structures of full-length human long isoform IR (IR-B) in both the inactive and IGF2-bound active states, and short isoform IR (IR-A) in the IGF2-bound active state. Under saturated IGF2 concentrations, both the IR-A and IR-B adopt predominantly asymmetric conformations with two or three IGF2s bound at site-1 and site-2, which differs from that insulin saturated IR forms an exclusively T-shaped symmetric conformation. IGF2 exhibits a relatively weak binding to IR site-2 compared to insulin, making it less potent in promoting full IR activation. Cell-based experiments validated the functional importance of IGF2 binding to two distinct binding sites in optimal IR signaling and trafficking. In the inactive state, the C-terminus of α-CT of IR-B contacts FnIII-2 domain of the same protomer, hindering its threading into the C-loop of IGF2, thus reducing the association rate of IGF2 with IR-B. Collectively, our studies demonstrate the activation mechanism of IR by IGF2 and reveal the molecular basis underlying the different affinity of IGF2 to IR-A and IR-B.

Maternal nutrient metabolism in the liver during pregnancy

The liver plays pivotal roles in nutrient metabolism, and correct hepatic adaptations are required in maternal nutrient metabolism during pregnancy. In this review, hepatic nutrient metabolism, including glucose metabolism, lipid and cholesterol metabolism, and protein and amino acid metabolism, is first addressed. In addition, recent progress on maternal hepatic adaptations in nutrient metabolism during pregnancy is discussed. Finally, the factors that regulate hepatic nutrient metabolism during pregnancy are highlighted, and the factors include follicle-stimulating hormone, estrogen, progesterone, insulin-like growth factor 1, prostaglandins fibroblast growth factor 21, serotonin, growth hormone, adrenocorticotropic hormone, prolactin, thyroid stimulating hormone, melatonin, adrenal hormone, leptin, glucagon-like peptide-1, insulin glucagon and thyroid hormone. Our vision is that more attention should be paid to liver nutrient metabolism during pregnancy, which will be helpful for utilizing nutrient appropriately and efficiently, and avoiding liver diseases during pregnancy.

TOX3 deficiency mitigates hyperglycemia by suppressing hepatic gluconeogenesis through FoxO1

BACKGROUND

Excessive hepatic glucose production is a hallmark that contributes to hyperglycemia in type 2 diabetes (T2D). The regulatory network governing this process remains incompletely understood. Here, we demonstrate that TOX3, a high-mobility group family member, acts as a major transcriptional driver for hepatic glucose production.

METHODS

Tox3-overexpressed and knockout mice were constructed to explore its metabolic functions. Transcriptomic and chromatin-immunoprecipitation sequencing (ChIP-seq) were used to identify downstream targets of TOX3. Both FoxO1 silencing and inhibitor approaches were used to assess the contribution of FoxO1. TOX3 expression levels were examined in the livers of mice and human subjects. Finally, Tox3 was genetically manipulated in diet-induced obese mice to evaluate its therapeutic potential.

RESULTS

Hepatic Tox3 overexpression activates the gluconeogenic program, resulting in hyperglycemia and insulin resistance in mice. Hepatocyte-specific Tox3 knockout suppresses gluconeogenesis and improves insulin sensitivity. Mechanistically, integrated hepatic transcriptomic and ChIP-seq analyses identify FoxO1 as a direct target of TOX3. TOX3 stimulates FoxO1 transcription by directly binding to and activating its promoter, whereas FoxO1 silencing abrogates TOX3-induced dysglycemia in mice. In human subjects, hepatic TOX3 expression shows a significant positive correlation with blood glucose levels under normoglycemic conditions, yet is repressed by high glucose during T2D. Importantly, hepatic Tox3 deficiency markedly protects against and ameliorates the hyperglycemia and glucose intolerance in diet-induced diabetic mice.

CONCLUSIONS

Our findings establish TOX3 as a driver for excessive gluconeogenesis through activating hepatic FoxO1 transcription. TOX3 could serve as a promising target for preventing and treating hyperglycemia in T2D.

Mannose Supplementation Curbs Liver Steatosis and Fibrosis in Murine MASH by Inhibiting Fructose Metabolism

Metabolic dysfunction-associated steatohepatitis (MASH) can progress to cirrhosis and liver cancer. There are no approved medical therapies to prevent or reverse disease progression. Fructose and its metabolism in the liver play integral roles in MASH pathogenesis and progression. Here we focus on mannose, a simple sugar, which dampens hepatic stellate cell activation and mitigates alcoholic liver disease in vitro and in vivo . In the well-validated FAT-MASH murine model, oral mannose supplementation improved both liver steatosis and fibrosis at low and high doses, whether administered either at the onset of the model ("Prevention") or at week 6 of the 12-week MASH regimen ("Reversal"). The in vivo anti-fibrotic effects of mannose supplementation were validated in a second model of carbon tetrachloride-induced liver fibrosis. In vitro human and mouse primary hepatocytes revealed that the anti-steatotic effects of mannose are dependent on the presence of fructose, which attenuates expression of ketohexokinase (KHK), the main enzyme in fructolysis. KHK is decreased with mannose supplementation in vivo and in vitro, and overexpression of KHK abrogated the anti-steatotic effects of mannose. Our study identifies mannose as a simple, novel therapeutic candidate for MASH that mitigates metabolic dysregulation and exerts anti-fibrotic effects.

FTY-720 alleviates diabetes-induced liver injury by inhibiting oxidative stress and inflammation

We aimed to investigate the protective effect of FTY-720 on liver injury and explore its potential mechanism in diabetic mice. The diabetic mouse model was induced with streptozotocin and FTY-720 was administered for 12 weeks. We assayed biocharacters and liver function and used histopathology staining to evaluate the protective effects of FTY-720 against diabetic liver injury. Levels of oxidative stress and inflammation in the liver were observed. mRNA and protein levels of essential enzymes for glucose metabolism were quantified in the liver and the protein expression of TLR4, HIF1α and NF-κB was determined. In vivo results revealed that FTY-720 significantly lowered blood glucose and lipids and improved liver function and alleviated liver fibrosis in diabetic mice. FTY-720 reduced oxidative stress and inflammation, with the increased catalase activity and reduced levels of malondialdehyde, myeloperoxidase, IL-1β, IL-6, TNF-α, TGF-β, and MCP1. Furthermore, FTY-720 modulated glucose metabolism in liver and elevated the ATP production, showing the promotion of glycogenesis and glycolysis and inhibition of gluconeogenesis. Moreover, FTY-720 inhibited the expression of TLR4 and HIF1α, contributing to restoration of liver function. In conclusion, FTY-720 ameliorates diabetes-induced liver injury and improves glucose homeostasis by inhibiting oxidative stress and inflammation and may be a promise drug for treatment of liver disease.

Metabolic switch from glycogen to lipid in the liver maintains glucose homeostasis in neonatal mice

Neonates strive to acquire energy when the continuous transplacental nutrient supply ceases at birth, whereas milk consumption takes hours to start. Using murine models, we report the metabolic switches in the first days of life, with an unexpected discovery of glucose as the universal fuel essential for neonatal life. Blood glucose quickly drops as soon as birth, but immediately rebounds even before suckling and maintains stable afterward. Meanwhile, neonatal liver undergoes drastic metabolic changes, from extensive glycogenolysis before suckling to dramatically induced fatty acid oxidation (FAO) and gluconeogenesis after milk suckling. Unexpectedly, blocking hepatic glycogenolysis only caused a transient hypoglycemia before milk suckling without causing lethality. Limiting lipid supply in milk (low-fat milk, [LFM]) using Cidea-/- mice, however, led to a chronic and severe hypoglycemia and consequently claimed neonatal lives. While fat replenishment rescued LFM-caused neonatal lethality, the rescue effects were abolished by blocking FAO or gluconeogenesis, pointing to a funneling of lipids and downstream metabolites into glucose as the essential fuel. Finally, glucose administration also rescued LFM-caused neonatal lethality, independent on FAO or gluconeogenesis. Therefore, our results show that the liver works as an energy conversion center to maintain blood glucose homeostasis in neonates, providing theoretical basis for managing infant hypoglycemia.

Unraveling the mysteries of hepatic insulin signaling: deconvoluting the nuclear targets of insulin

Over 100 years have passed since insulin was first administered to a diabetic patient. Since then great strides have been made in diabetes research. It has determined where insulin is secreted from, which organs it acts on, how it is transferred into the cell and is delivered to the nucleus, how it orchestrates the expression pattern of the genes, and how it works with each organ to maintain systemic metabolism. Any breakdown in this system leads to diabetes. Thanks to the numerous researchers who have dedicated their lives to cure diabetes, we now know that there are three major organs where insulin acts to maintain glucose/lipid metabolism: the liver, muscles, and fat. The failure of insulin action on these organs, such as insulin resistance, result in hyperglycemia and/or dyslipidemia. The primary trigger of this condition and its association among these tissues still remain to be uncovered. Among the major organs, the liver finely tunes the glucose/lipid metabolism to maintain metabolic flexibility, and plays a crucial role in glucose/lipid abnormality due to insulin resistance. Insulin resistance disrupts this tuning, and selective insulin resistance arises. The glucose metabolism loses its sensitivity to insulin, while the lipid metabolism maintains it. The clarification of its mechanism is warranted to reverse the metabolic abnormalities due to insulin resistance. This review will provide a brief historical review for the progress of the pathophysiology of diabetes since the discovery of insulin, followed by a review of the current research clarifying our understanding of selective insulin resistance.

Hepatic retinaldehyde deficiency is involved in diabetes deterioration by enhancing PCK1- and G6PC-mediated gluconeogenesis

Type 2 diabetes (T2D) is often accompanied with an induction of retinaldehyde dehydrogenase 1 (RALDH1 or ALDH1A1) expression and a consequent decrease in hepatic retinaldehyde (Rald) levels. However, the role of hepatic Rald deficiency in T2D progression remains unclear. In this study, we demonstrated that reversing T2D-mediated hepatic Rald deficiency by Rald or citral treatments, or liver-specific Raldh1 silencing substantially lowered fasting glycemia levels, inhibited hepatic glucogenesis, and downregulated phosphoenolpyruvate carboxykinase 1 (PCK1) and glucose-6-phosphatase (G6PC) expression in diabetic db/db mice. Fasting glycemia and Pck1/G6pc mRNA expression levels were strongly negatively correlated with hepatic Rald levels, indicating the involvement of hepatic Rald depletion in T2D deterioration. A similar result that liver-specific Raldh1 silencing improved glucose metabolism was also observed in high-fat diet-fed mice. In primary human hepatocytes and oleic acid-treated HepG2 cells, Rald or Rald + RALDH1 silencing resulted in decreased glucose production and downregulated PCK1/G6PC mRNA and protein expression. Mechanistically, Rald downregulated direct repeat 1-mediated PCK1 and G6PC expression by antagonizing retinoid X receptor α, as confirmed by luciferase reporter assays and molecular docking. These results highlight the link between hepatic Rald deficiency, glucose dyshomeostasis, and the progression of T2D, whilst also suggesting RALDH1 as a potential therapeutic target for T2D.

The E3 ubiquitin ligase NEDD4-1 protects against acetaminophen-induced liver injury by targeting VDAC1 for degradation

Acetaminophen (APAP) overdose is a major cause of liver injury. Neural precursor cell expressed developmentally downregulated 4-1 (NEDD4-1) is an E3 ubiquitin ligase that has been implicated in the pathogenesis of numerous liver diseases; however, its role in APAP-induced liver injury (AILI) is unclear. Thus, this study aimed to investigate the role of NEDD4-1 in the pathogenesis of AILI. We found that NEDD4-1 was dramatically downregulated in response to APAP treatment in mouse livers and isolated mouse hepatocytes. Hepatocyte-specific NEDD4-1 knockout exacerbated APAP-induced mitochondrial damage and the resultant hepatocyte necrosis and liver injury, while hepatocyte-specific NEDD4-1 overexpression mitigated these pathological events both in vivo and in vitro. Additionally, hepatocyte NEDD4-1 deficiency led to marked accumulation of voltage-dependent anion channel 1 (VDAC1) and increased VDAC1 oligomerization. Furthermore, VDAC1 knockdown alleviated AILI and weakened the exacerbation of AILI caused by hepatocyte NEDD4-1 deficiency. Mechanistically, NEDD4-1 was found to interact with the PPTY motif of VDAC1 through its WW domain and regulate K48-linked ubiquitination and degradation of VDAC1. Our present study indicates that NEDD4-1 is a suppressor of AILI and functions by regulating the degradation of VDAC1.

Hepatic Sam68 Regulates Systemic Glucose Homeostasis and Insulin Sensitivity

Hepatic glucose production (HGP) is an important component of glucose homeostasis, and deregulated HGP, particularly through gluconeogenesis, contributes to hyperglycemia and pathology of type-2 diabetes (T2D). It has been shown that the gluconeogenic gene expression is governed primarily by the transcription factor cAMP-response element (CRE)-binding protein (CREB) and its coactivator, CREB-regulated transcriptional coactivator 2 (CRTC2). Recently, we have discovered that Sam68, an adaptor protein and Src kinase substrate, potently promotes hepatic gluconeogenesis by promoting CRTC2 stability; however, the detailed mechanisms remain unclear. Here we show that in response to glucagon, Sam68 increases CREB/CRTC2 transactivity by interacting with CRTC2 in the CREB/CRTC2 complex and occupying the CRE motif of promoters, leading to gluconeogenic gene expression and glucose production. In hepatocytes, glucagon promotes Sam68 nuclear import, whereas insulin elicits its nuclear export. Furthermore, ablation of Sam68 in hepatocytes protects mice from high-fat diet (HFD)-induced hyperglycemia and significantly increased hepatic and peripheral insulin sensitivities. Thus, hepatic Sam68 potentiates CREB/CRTC2-mediated glucose production, contributes to the pathogenesis of insulin resistance, and may serve as a therapeutic target for T2D.

Secretion of miRNA-326-3p by senescent adipose exacerbates myocardial metabolism in diabetic mice

BACKGROUND

Adipose tissue homeostasis is at the heart of many metabolic syndromes such as diabetes. Previously it has been demonstrated that adipose tissues from diabetic patients are senescent but whether this contributes to diabetic cardiomyopathy (DCM) remains to be elucidated.

METHODS

The streptozotocin (STZ) type 1 diabetic mice were established as animal model, and adult mouse ventricular myocytes (AMVMs) isolated by langendorff perfusion as well as neonatal mouse ventricular myocytes (NMVMs) were used as cell models. Senescent associated β galactosidase (SA-β-gal) staining and RT-qPCR were used to identify the presence of adipose senescence in diabetic adipose tissue. Senescent adipose were removed either by surgery or by senolytic treatment. Large extracellular vesicles (LEVs) derived from adipose tissue and circulation were separated by ultracentrifugation. Cardiac systolic and diastolic function was evaluated through cardiac ultrasound. Cardiomyocytes contraction function was evaluated by the Ionoptix HTS system and live cell imaging, mitochondrial morphology and functions were evaluated by transmission electron microscope, live cell fluorescent probe and seahorse analysis. RNA-seq for AMVMs and miRNA-seq for LEVs were performed, and bioinformatic analysis combined with RT-qPCR and Western blot were used to elucidate underlying mechanism that senescent adipose derives LEVs exacerbates myocardial metabolism.

RESULTS

SA-β-gal staining and RT-qPCR identified the presence of adipose tissue senescence in STZ mice. Through surgical as well as pharmacological means we show that senescent adipose tissue participates in the pathogenesis of DCM in STZ mice by exacerbates myocardial metabolism through secretion of LEVs. Specifically, expression of miRNA-326-3p was up-regulated in LEVs isolated from senescent adipose tissue, circulation, and cardiomyocytes of STZ mice. Up-regulation of miRNA-326-3p coincided with myocardial transcriptomic changes in metabolism. Functionally, we demonstrate that miRNA-326-3p inhibited the expression of Rictor and resulted in impaired mitochondrial and contractile function in cardiomyocytes.

CONCLUSION

We demonstrate for the first time that senescent adipose derived LEVs exacerbates myocardial metabolism through up-regulated miRNA-326-3p which inhibits Rictor in cardiomyocytes. Furthermore, reducing senescence burden in adipose tissue is capable of relieving myocardial metabolism disorder in diabetes mellitus.

Estradiol (E2) Improves Glucose-Stimulated Insulin Secretion and Stabilizes GDM Progression in a Prediabetic Mouse Model

Female New Zealand obese (NZO) mice are an established model of preconceptional (pc.) prediabetes that progresses as gestational diabetes mellitus (GDM) during gestation. It is known that NZO mice show improvement in insulin sensitivity and glucose-stimulated insulin secretion (GSIS) during gestation in vivo. The latter is no longer detectable in ex vivo perifusion experiments in isolated islets of Langerhans, suggesting a modulation by extrapancreatic factors. Here, we demonstrated that plasma 17β-estradiol (E2) levels increased markedly in NZO mice during gestation. The aim of this work was to determine whether these increased E2 levels are responsible for the improvement in metabolism during gestation. To achieve this goal, we examined its effects in isolated islets and primary hepatocytes of both NZO and metabolically healthy NMRI mice. E2 increased GSIS in the islets of both strains significantly. Hepatic glucose production (HGP) failed to be decreased by insulin in NZO hepatocytes but was reduced by E2 in both strains. Hepatocytes of pregnant NZO mice showed significantly lower glucose uptake (HGU) compared with NMRI controls, whereby E2 stimulation diminished this difference. Hepatocytes of pregnant NZO showed reduced glycogen content, increased cyclic adenosine monophosphate (cAMP) levels, and reduced AKT activation. These differences were abolished after E2 stimulation. In conclusion, our data indicate that E2 stabilizes and prevents deterioration of the metabolic state of the prediabetic NZO mice. E2 particularly increases GSIS and improves hepatic glucose utilization to a lower extent.

Parathyroid hormone alleviates non-alcoholic liver steatosis via activating the hepatic cAMP/PKA/CREB pathway

Non-alcoholic fatty liver disease (NAFLD), hallmarked by liver steatosis, is becoming a global concern, but effective and safe drugs for NAFLD are still lacking at present. Parathyroid hormone (PTH), the only FDA-approved anabolic treatment for osteoporosis, is important in calcium-phosphate homeostasis. However, little is known about its potential therapeutic effects on other diseases. Here, we report that intermittent administration of PTH ameliorated non-alcoholic liver steatosis in diet-induced obese (DIO) mice and db/db mice, as well as fasting-induced hepatic steatosis. In vitro, PTH inhibits palmitic acid-induced intracellular lipid accumulation in a parathyroid hormone 1 receptor (PTH1R)-dependent manner. Mechanistically, PTH upregulates the expression of genes involved in lipid β-oxidation and suppresses the expression of genes related to lipid uptake and de novo lipogenesis by activating the cAMP/PKA/CREB pathway. Taken together, our current finding proposes a new therapeutic role of PTH on NAFLD.