Decreased IRS-2 and Increased SREBP-1c Lead to Mixed Insulin Resistance and Sensitivity in Livers of Lipodystrophic and ob/ob Mice

Regulation of hepatic lipogenesis by asymmetric arginine methylation

BACKGROUND AND AIMS

Hepatic lipogenesis is elevated in nutrient abundant conditions to convert the excess carbohydrate into triacylglycerol (TAG). Fatty acyl moiety of TAG is eventually transported into adipose tissues by very low density lipoprotein, leading to the accumulation of TAG as a preferred storage form of excess energy. Disruption of the balance between TAG clearance and synthesis leads to the accumulation of lipids in the liver, leading to the progression of non-alcoholic fatty liver disease (NAFLD) including non-alcoholic steatohepatitis. Protein arginine methyltransferase (PRMT) 6 has been linked to the various metabolic processes including hepatic gluconeogenesis, muscle atrophy and lipodystrophy in mouse models. However, the role of PRMT6 in the control of hepatic lipogenesis has not been elucidated to date.

METHODS

We assessed the interaction between PRMT6 and LXR alpha by using co-immunoprecipitation assay. The specific arginine residue of LXR alpha that is methylated by PRMT6 was assessed by LC-MS/MS assay and the functional consequences of LXR alpha methylation was explored by mSREBP-1c luciferase assay. The effect of PRMT6 on hepatic lipogenesis was assessed by adenovirus-mediated ectopic expression of PRMT6 or knockdown of PRMT6 via shRNA in hepatocytes. Finally, the role of PRMT6 in hepatic lipid metabolism in vivo was explored by either ectopic expression of LXR alpha mutant that is defective in PRMT6-mediated arginine methylation or knockdown of PRMT6 in liver.

RESULTS

We found that promoter activity of sterol regulatory element binding protein (SREBP) 1c is robustly activated by PRMT6. Interestingly, we demonstrated that PRMT6 binds to LXR alpha, a transcription factor for SREBP-1c, via its LXXLL motif, leading to the asymmetric dimethylation of an arginine residue and activation of this protein. Indeed, ectopic expression of PRMT6 in hepatocytes led to the enhanced expression of LXR alpha target genes in the lipogenic pathway. Conversely, genetic or pharmacological inhibition of PRMT6 diminished expression of lipogenic genes and the lipid accumulation in primary hepatocytes. Mechanistically, we found that asymmetric dimethylation of LXR alpha led to the dissociation of small heterodimer partner (SHP), a transcriptional co-inhibitor of this factor, resulting in the activation of LXR alpha-mediated transcriptional process. Finally, we showed that disruption of asymmetric dimethylation of LXR alpha in the liver led to the diminished expression of genes in the lipogenesis, resulting in the reduced hepatic lipid accumulation in high fat diet-fed mice in vivo.

CONCLUSIONS

We showed that PRMT6 modulates LXR alpha activity by conferring asymmetric dimethylation of arginine 253, thus blocking SHP-mediated inhibition and promoting hepatic lipid accumulation. These results suggest that PRMT6 is critical in the control of lipid homeostasis by regulation of LXR alpha-mediated lipogenesis in the liver.

Rabson-Mendenhall Syndrome: Analysis of the Clinical Characteristics and Gene Mutations in 42 Patients

Aims

Rabson-Mendenhall syndrome (RMS) is a rare autosomal, recessive disorder characterized by severe insulin resistance due to mutations in the insulin receptor (INSR) gene. This study aims to analyze the clinical features and gene mutations in RMS, which have not been extensively studied.

Methods

PubMed, Embase, the China National Knowledge Infrastructure, and Wanfang were searched for "Rabson-Mendenhall syndrome" or "Black acanthosis hirsutism insulin resistance syndrome."

Results

A total of 42 cases from 33 articles were included. The body mass index ranged from 18.50 to 20.00 kg/m2 with an average of 16.00 kg/m2. There were no overweight (25.00∼29.90 kg/m2) or obese (≥30.00 kg/m2) patients. Acanthosis was present in 29 cases (29/42, 69.05%); growth retardation in 25 cases (25/42, 59.52%); dental anomalies including absence of teeth, crowding, and malocclusion in 23 cases (23/42, 54.76%); and hirsutism in 17 cases (17/42, 40.48%). The average glycosylated hemoglobin was 9.35%, and the average fasting blood-glucose was 8.44 mmol/L; the mean fasting insulin was 349.96 μIU/mL, and the average fasting C-peptide was 6.00 ng/mL. Diabetes was reported in 25 cases (25/33, 75.76%) all of which were diagnosed before 23 years old. All 42 patients had recorded gene mutations, with 22 patients (22/42, 52.38%) having ≥ 2 mutations and 20 cases (20/42, 47.62%) having only 1 mutation. No statistical differences were found in clinical features and laboratory parameters between patients with different mutations.

Conclusion

The study indicates that RMS should be considered in young patients with hyperinsulinemia, hyperglycemia with low weight, acanthosis nigricans, growth retardation, dental anomalies, and hirsutism.

Modification of lipoprotein metabolism and function driving atherogenesis in diabetes

Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease, characterized by raised blood glucose levels and impaired lipid metabolism resulting from insulin resistance and relative insulin deficiency. In diabetes, the peculiar plasma lipoprotein phenotype, consisting in higher levels of apolipoprotein B-containing lipoproteins, hypertriglyceridemia, low levels of HDL cholesterol, elevated number of small, dense LDL, and increased non-HDL cholesterol, results from an increased synthesis and impaired clearance of triglyceride rich lipoproteins. This condition accelerates the development of the atherosclerotic cardiovascular disease (ASCVD), the most common cause of death in T2DM patients. Here, we review the alteration of structure, functions, and distribution of circulating lipoproteins and the pathophysiological mechanisms that induce these modifications in T2DM. The review analyzes the influence of diabetes-associated metabolic imbalances throughout the entire process of the atherosclerotic plaque formation, from lipoprotein synthesis to potential plaque destabilization. Addressing the different pathophysiological mechanisms, we suggest improved approaches for assessing the risk of adverse cardiovascular events and clinical strategies to reduce cardiovascular risk in T2DM and cardiometabolic diseases.

Discovery of Novel Binders to Sterol Regulatory Element-Binding Protein-1 by High-Throughput Screening

Sterol regulatory element-binding protein-1 (SREBP-1) is a transcription factor that regulates the expression of genes related to fatty acid biosynthesis. Its high expression and activation in obesity and associated metabolic diseases make it a potential therapeutic target. However, the role of SREBP-1 in the development and exacerbation of these diseases remains unclear, partly because of the impossibility of inhibiting its function because of the lack of specific inhibitors. Here, we aimed to identify small-molecule compounds that directly bind to SREBP-1 using the recombinant N-terminal region of SREBP-1a, which is required for its transcriptional activity. A high-throughput screening campaign was conducted using a thermal shift assay and surface plasmon resonance assay to evaluate the compound affinity and specificity, which resulted in the identification of two compounds. Future analysis of their structure-activity relationships may lead to the development of specific SREBP-1 inhibitors, thereby potentially validating SREBP-1 as a therapeutic target for obesity and resultant atherosclerotic diseases.

Hepatic selective insulin resistance at the intersection of insulin signaling and metabolic dysfunction-associated steatotic liver disease

Insulin resistance (IR) is a major pathogenic factor in the progression of MASLD. In the liver, insulin suppresses gluconeogenesis and enhances de novo lipogenesis (DNL). During IR, there is a defect in insulin-mediated suppression of gluconeogenesis, but an unrestrained increase in hepatic lipogenesis persists. The mechanism of increased hepatic steatosis in IR is unclear and remains controversial. The key discrepancy is whether insulin retains its ability to directly regulate hepatic lipogenesis. Blocking insulin/IRS/AKT signaling reduces liver lipid deposition in IR, suggesting insulin can still regulate lipid metabolism; hepatic glucose metabolism that bypasses insulin's action may contribute to lipogenesis; and due to peripheral IR, other tissues are likely to impact liver lipid deposition. We here review the current understanding of insulin's action in governing different aspects of hepatic lipid metabolism under normal and IR states, with the purpose of highlighting the essential issues that remain unsettled.

Gkongensin A, an HSP90β inhibitor, improves hyperlipidemia, hepatic steatosis, and insulin resistance

The prevalence of obesity and its primary associated comorbidities, such as type 2 diabetes and fatty liver disease, has reached epidemic proportions, with no successful treatment available at present. Heat shock protein 90 (HSP90), a crucial chaperone, plays a key role in de novo lipogenesis (DNL) by stabilizing and maintaining sterol regulatory element binding protein (SREBP) activity. Kongensin A (KA), derived from Croton kongensis, inhibits RIP3-mediated necrosis, showing promise as an anti-necrotic and anti-inflammatory agent. It is not yet clear if KA, acting as an HSP90 inhibitor, can enhance hyperlipidemia, hepatic steatosis, and insulin resistance in obese individuals by controlling lipid metabolism. In this study, we first found that KA can potentially decrease lipid content at the cellular level. C57BL/6J mice were given a high-fat diet (HFD) and received KA and lovastatin through oral administration for 7 weeks. KA improved hyperlipidemia, fatty liver, and insulin resistance, as well as reduced body weight in diet-induced obese (DIO) mice, with no significant alteration in food intake. In vitro, KA suppressed DNL and reduced the amounts of mSREBPs. KA promoted mSREBP degradation via the FBW7-mediated ubiquitin-proteasome pathway. KA decreased the level of p-Akt Ser308, and p-GSK3β Ser9 by inhibiting the interaction between HSP90β and Akt. Overall, KA enhanced hyperlipidemia, hepatic steatosis, and insulin resistance by blocking SREBP activity, thereby impacting the FBW7-controlled ubiquitin-proteasome pathway.

Diabetes mellitus with severe insulin resistance in a young male patient with a heterozygous pathogenic IRS1 frameshift variant

We present the case of a young male patient (height, 158.1 cm [+3.3 standard deviation (SD)]; weight, 63.7 kg [body mass index, 25.5]) with diabetes mellitus and severe insulin resistance associated with a heterozygous pathogenic insulin receptor substrate 1 (IRS1) frameshift mutation. The patient also had severe acanthosis nigricans. Notably, the patient's father was undergoing treatment with high doses of insulin for diabetes mellitus, and had been experiencing angina pectoris. Laboratory data showed a fasting plasma glucose level of 88 mg/dL, hemoglobin A1C (HbA1c) of 7.4%, fasting insulin level of 43.1 µg/mL, and a homeostasis model assessment-insulin resistance (HOMA-IR) score of 9.36, indicating hyperinsulinism. Oral glucose tolerance test revealed a diabetic pattern and insulin hypersecretion. In addition, the patient had hyperlipidemia. Genetic studies revealed a heterozygous frameshift variant of IRS1 [NM_005544.3:c.1791dupG:p.(His598Alafs*13)] in the patient and his father, which can impair the binding and activation of phosphoinositide 3 (PI-3) kinase and defectively mediate the translocation of glucose transporter type 4 (GLUT4) in adipose tissues, possibly leading to glucose intolerance. Therefore, this variant may be disease causing. After confirming IRS1 mutation, metformin was administered, and physical exercise and dietary management were initiated; metformin was well tolerated, and optimal glycemic control was maintained.

Mechanism of Obesity-Related Lipotoxicity and Clinical Perspective

The link between cellular exposure to fatty acid species and toxicity phenotypes remains poorly understood. However, structural characterization and functional profiling of human plasma free fatty acids (FFAs) analysis has revealed that FFAs are located either in the toxic cluster or in the cluster that is transcriptionally responsive to lipotoxic stress and creates genetic risk factors. Genome-wide short hairpin RNA screen has identified more than 350 genes modulating lipotoxicity. Hypertrophic adipocytes in obese adipose are both unable to expand further to store excess lipids in the diet and are resistant to the antilipolytic action of insulin. In addition to lipolysis, the inability of packaging the excess lipids into lipid droplets causes circulating fatty acids to reach toxic levels in non-adipose tissues. Deleterious effects of accumulated lipid in non-adipose tissues are known as lipotoxicity. Although triglycerides serve a storage function for long-chain non-esterified fatty acid and their products such as ceramide and diacylglycerols (DAGs), overloading of palmitic acid fraction of saturated fatty acids (SFAs) raises ceramide levels. The excess DAG and ceramide load create harmful effects on multiple organs and systems, inducing chronic inflammation in obesity. Thus, lipotoxic inflammation results in β cells death and pancreatic islets dysfunction. Endoplasmic reticulum stress stimuli induce lipolysis by activating cyclic adenosine monophosphate (cAMP)/protein kinase A (PKA) and extracellular signal-regulated kinase (Erk) 1/2 signaling in adipocytes. However, palmitic acid-induced endoplasmic reticulum stress-c-Jun N-terminal kinase (JNK)-autophagy axis in hypertrophic adipocytes is a pro-survival mechanism against endoplasmic reticulum stress and cell death induced by SFAs. Endoplasmic reticulum-localized acyl-coenzyme A (CoA): glycerol-3-phosphate acyltransferase (GPAT) enzymes are mediators of lipotoxicity, and inhibiting these enzymes has therapeutic potential for lipotoxicity. Lipotoxicity increases the number of autophagosomes, which engulf palmitic acid, and thus suppress the autophagic turnover. Fatty acid desaturation promotes palmitate detoxification and storages into triglycerides. As therapeutic targets of glucolipotoxicity, in addition to caloric restriction and exercise, there are four different pharmacological approaches, which consist of metformin, glucagon-like peptide 1 (GLP-1) receptor agonists, peroxisome proliferator-activated receptor-gamma (PPARγ) ligands thiazolidinediones, and chaperones are still used in clinical practice. Furthermore, induction of the brown fat-like phenotype with the mixture of eicosapentanoic acid and docosahexaenoic acid appears as a potential therapeutic application for treatment of lipotoxicity.

Nonalcoholic Fatty Liver Disease and Staging of Hepatic Fibrosis

Nonalcoholic fatty liver disease (NAFLD) is in parallel with the obesity epidemic, and it is the most common cause of liver diseases. The patients with severe insulin-resistant diabetes having high body mass index (BMI), high-grade adipose tissue insulin resistance, and high hepatocellular triacylglycerols (triglycerides; TAG) content develop hepatic fibrosis within a 5-year follow-up. Insulin resistance with the deficiency of insulin receptor substrate-2 (IRS-2)-associated phosphatidylinositol 3-kinase (PI3K) activity causes an increase in intracellular fatty acid-derived metabolites such as diacylglycerol (DAG), fatty acyl CoA, or ceramides. Lipotoxicity-related mechanism of NAFLD could be explained still best by the "double-hit" hypothesis. Insulin resistance is the major mechanism in the development and progression of NAFLD/nonalcoholic steatohepatitis (NASH). Metabolic oxidative stress, autophagy, and inflammation induce NASH progression. In the "first hit" the hepatic concentrations of diacylglycerol increase with an increase in saturated liver fat content in human NAFLD. Activities of mitochondrial respiratory chain complexes are decreased in the liver tissue of patients with NASH. Hepatocyte lipoapoptosis is a critical feature of NASH. In the "second hit," reduced glutathione levels due to oxidative stress lead to the overactivation of c-Jun N-terminal kinase (JNK)/c-Jun signaling that induces cell death in the steatotic liver. Accumulation of toxic levels of reactive oxygen species (ROS) is caused at least by two ineffectual cyclical pathways. First is the endoplasmic reticulum (ER) oxidoreductin (Ero1)-protein disulfide isomerase oxidation cycle through the downstream of the inner membrane mitochondrial oxidative metabolism and the second is the Kelch like-ECH-associated protein 1 (Keap1)-nuclear factor (erythroid-derived 2)-like 2 (Nrf2) pathways. In clinical practice, on ultrasonographic examination, the elevation of transaminases, γ-glutamyltransferase, and the aspartate transaminase to platelet ratio index indicates NAFLD. Fibrosis-4 index, NAFLD fibrosis score, and cytokeratin18 are used for grading steatosis, staging fibrosis, and discriminating the NASH from simple steatosis, respectively. In addition to ultrasonography, "controlled attenuation parameter," "magnetic resonance imaging proton-density fat fraction," "ultrasound-based elastography," "magnetic resonance elastography," "acoustic radiation force impulse elastography imaging," "two-dimensional shear-wave elastography with supersonic imagine," and "vibration-controlled transient elastography" are recommended as combined tests with serum markers in the clinical evaluation of NAFLD. However, to confirm the diagnosis of NAFLD, a liver biopsy is the gold standard. Insulin resistance-associated hyperinsulinemia directly accelerates fibrogenesis during NAFLD development. Although hepatocyte lipoapoptosis is a key driving force of fibrosis progression, hepatic stellate cells and extracellular matrix cells are major fibrogenic effectors. Thereby, these are pharmacological targets of therapies in developing hepatic fibrosis. Nonpharmacological management of NAFLD mainly consists of two alternatives: lifestyle modification and metabolic surgery. Many pharmacological agents that are thought to be effective in the treatment of NAFLD have been tried, but due to lack of ability to attenuate NAFLD, or adverse effects during the phase trials, the vast majority could not be licensed.

A common variant that alters SUN1 degradation associates with hepatic steatosis and metabolic traits in multiple cohorts

BACKGROUND & AIMS

Non-alcoholic fatty liver disease (NAFLD), and its progressive form steatohepatitis (NASH), represent a genetically and phenotypically diverse entity for which there is no approved therapy, making it imperative to define the spectrum of pathways contributing to its pathogenesis. Rare variants in genes encoding nuclear envelope proteins cause lipodystrophy with early-onset NAFLD/NASH; we hypothesized that common variants in nuclear envelope-related genes might also contribute to hepatic steatosis and NAFLD.

METHODS

Using hepatic steatosis as the outcome of interest, we performed an association meta-analysis of nuclear envelope-related coding variants in three large discovery cohorts (N >120,000 participants), followed by phenotype association studies in large validation cohorts (N >600,000) and functional testing of the top steatosis-associated variant in cell culture.

RESULTS

A common protein-coding variant, rs6461378 (SUN1 H118Y), was the top steatosis-associated variant in our association meta-analysis (p <0.001). In ancestrally distinct validation cohorts, rs6461378 associated with histologic NAFLD and with NAFLD-related metabolic traits including increased serum fatty acids, type 2 diabetes, hypertension, cardiovascular disease, and decreased HDL. SUN1 H118Y was subject to increased proteasomal degradation relative to wild-type SUN1 in cells, and SUN1 H118Y-expressing cells exhibited insulin resistance and increased lipid accumulation.

CONCLUSIONS

Collectively, these data support a potential causal role for the common SUN1 variant rs6461378 in NAFLD and metabolic disease.

IMPACT AND IMPLICATIONS

Non-alcoholic fatty liver disease (NAFLD), with an estimated global prevalence of nearly 30%, is a growing cause of morbidity and mortality for which there is no approved pharmacologic therapy. Our data provide a rationale for broadening current concepts of NAFLD genetics and pathophysiology to include the nuclear envelope, and particularly Sad1 and UNC84 domain containing 1 (SUN1), as novel contributors to this common liver disease. Furthermore, if future studies confirm causality of the common SUN1 H118Y variant, it has the potential to become a broadly relevant therapeutic target in NAFLD and metabolic disease.

15-keto-PGE2 alleviates nonalcoholic steatohepatitis through its covalent modification of NF-κB factors

15-keto-PGE2 is one of the eicosanoids with anti-inflammatory properties. In this study, we demonstrated that 15-keto-PGE2 post-translationally modified the nuclear factor κ-light-chain-enhancer of activated B cells (NF-κB) subunits p105/p50 and p65 at Cys59 and Cys120 sites, respectively, hence inhibiting the activation of NF-κB signaling in macrophages. In mice fed a high-fat and high-sucrose diet (HFHSD), 15-keto-PGE2 treatment reduced pro-inflammatory cytokines and fasting glucose levels. In mice with non-alcoholic steatohepatitis (NASH) induced by a prolonged HFHSD, 15-keto-PGE2 treatment significantly decreased liver inflammation, lowered serum levels of alanine transaminase (ALT) and aspartate transferase (AST), and inhibited macrophage infiltration. It also reduced lipid droplet size and downregulated key regulators of lipogenesis. These findings highlight the potential of 15-keto-PGE2, through NF-κB modification, in preventing the development and progression of steatohepatitis, emphasizing the significance of endogenous lipid mediators in the inflammatory response.

The effect of heat-killed Lactobacillus brevis SBL88 on improving selective hepatic insulin resistance in non-alcoholic fatty liver disease mice without altering the gut microbiota

BACKGROUND AND AIM

There have been several reports that some probiotics improve non-alcoholic fatty liver disease (NAFLD); however, many studies have involved cocktail therapies. We evaluated whether heat-killed Lactobacillus brevis SBL88 (L. brevis SBL88) monotherapy improves the clinical features of NAFLD.

METHODS

The NAFLD model was induced in mice fed a high-fat diet (HFD) (HFD mice) or HFD + 1% heat-killed L. brevis SBL88 (SBL mice) for 16 weeks. Histopathological liver findings were analyzed. To evaluate the gut microbiota, a modified terminal restriction fragment length polymorphism analysis of the feces was performed. RNA sequencing in the liver was performed with Ion Proton™. To investigate the direct effects of heat-killed L. brevis SBL88, an in vitro study was performed.

RESULTS

Histopathological findings revealed that fat droplets in the liver were significantly reduced in SBL mice; however, terminal restriction fragment length polymorphism did not show alterations in the gut microbiota between HFD mice and SBL mice. RNA sequencing and pathway analysis revealed that the regulation of lipid and insulin metabolism was affected. The mRNA expression of insulin receptor substrate 2 (IRS-2) was significantly higher in SBL mice, whereas the expression of IRS-1 was not significantly different. Phospho-IRS-2 expression was also significantly increased in SBL mice. In addition, an in vitro study revealed significant alterations in IRS-2 and forkhead box protein O1 expression levels.

CONCLUSION

SBL mice exhibited partially improved selective hepatic insulin resistance. Our data suggest that heat-killed L. brevis SBL88 could attenuate the clinical features of NAFLD that are not mediated by alterations in the gut microbiota.

Antidiabetic Effect of Fermented Mesembryanthemum crystallinum L. in db/db Mice Involves Regulation of PI3K-Akt Pathway

Type 2 diabetes (T2D) is a serious health issue with increasing incidences worldwide. However, current medications have limitations due to side effects such as decreased appetite, stomach pain, diarrhea, and extreme tiredness. Here, we report the effect of fermented ice plant (FMC) in the T2M mouse model of db/db mice. FMC showed a greater inhibition of lipid accumulation compared to unfermented ice plant extract. Two-week oral administration with FMC inhibited body weight gain, lowered fasting blood glucose, and improved glucose tolerance. Serum parameters related to T2D including insulin, glycosylated hemoglobin, adiponectin, and cholesterols were improved as well. Histological analysis confirmed the protective effect of FMC on pancreas and liver destruction. FMC treatment significantly increased the expression and phosphorylation of IRS-1, PI3K, and AKT. Additionally, AMP-activated protein kinase phosphorylation and nuclear factor erythroid 2-related factor 2 were also increased in the liver tissues of db/db mice treated with FMC. Overall, our results indicate the anti-diabetic effect of FMC; therefore, we suggest that FMC may be useful as a therapeutic agent for T2D.

Liver acts as a metabolic gate for the traumatic brain injury pathology: Protective action of thyroid hormone

Clinical evidence indicates that injury to the brain elicits systemic metabolic disturbances that contributes to the brain pathology. Since dietary fructose is metabolized in the liver, we explored mechanisms by which traumatic brain injury (TBI) and dietary fructose influence liver function and their possible repercussions to brain. Consumption of fructose contributed to the detrimental effects of TBI on liver operation, in terms of glucose and lipid metabolism, de novo lipogenesis, lipid peroxidation. Thyroid hormone (T4) is metabolized in the liver and found that T4 supply improved lipid metabolism by reducing de novo lipogenesis, lipid accumulation, lipogenic enzymes (ACC, AceCS1, FAS), lipid peroxidation in liver in response to fructose and fructose-TBI. T4 supply also helped to normalize glucose metabolism and improve insulin sensitivity. Furthermore, T4 counteracted elevations of the pro-inflammatory cytokines, Tnfα and Mcp-1 after TBI and/or fructose intake in liver and circulation. T4 also exerted an effect on isolated primary hepatocytes by potentiating phosphorylation of AMPKα and AKT substrate, AS160, leading to increased glucose uptake. In addition, T4 restored the metabolism of DHA in the liver disrupted by TBI and fructose, adding important information to optimize the action of DHA in therapeutics. The overall evidence seems to indicate that the liver works as a gate for the regulation of the effects of brain injury and foods on brain pathologies.

Adiposity is associated with widespread transcriptional changes and downregulation of longevity pathways in aged skeletal muscle

BACKGROUND

Amongst healthy older people, a number of correlates of impaired skeletal muscle mass and function have been defined. Although the prevalence of obesity is increasing markedly in this age group, information is sparse about the particular impacts of obesity on ageing skeletal muscle or the molecular mechanisms that underlie this and associated disease risk.

METHODS

Here, we examined genome-wide transcriptional changes using RNA sequencing in muscle biopsies from 40 older community-dwelling men from the Hertfordshire Sarcopenia Study with regard to obesity (body mass index [BMI] >30 kg/m2 , n = 7), overweight (BMI 25-30, n = 19), normal weight (BMI < 25, n = 14), and per cent and total fat mass. In addition, we used EPIC DNA methylation array data to investigate correlations between DNA methylation and gene expression in aged skeletal muscle tissue and investigated the relationship between genes within altered regulatory pathways and muscle histological parameters.

RESULTS

Individuals with obesity demonstrated a prominent modified transcriptional signature in muscle tissue, with a total of 542 differentially expressed genes associated with obesity (false discovery rate ≤0.05), of which 425 genes were upregulated when compared with normal weight. Upregulated genes were enriched in immune response (P = 3.18 × 10-41 ) and inflammation (leucocyte activation, P = 1.47 × 10-41 ; tumour necrosis factor, P = 2.75 × 10-15 ) signalling pathways and downregulated genes enriched in longevity (P = 1.5 × 10-3 ) and AMP-activated protein kinase (AMPK) (P = 4.5 × 10-3 ) signalling pathways. Furthermore, differentially expressed genes in both longevity and AMPK signalling pathways were associated with a change in DNA methylation, with a total of 256 and 360 significant cytosine-phosphate-guanine-gene correlations identified, respectively. Similar changes in the muscle transcriptome were observed with respect to per cent fat mass and total fat mass. Obesity was further associated with a significant increase in type II fast-fibre area (P = 0.026), of which key regulatory genes within both longevity and AMPK pathways were significantly associated.

CONCLUSIONS

We provide for the first time a global transcriptomic profile of skeletal muscle in older people with and without obesity, demonstrating modulation of key genes and pathways implicated in the regulation of muscle function, changes in DNA methylation associated with such pathways and associations between genes within the modified pathways implicated in muscle regulation and changes in muscle fibre type.

Increased let-7d-5p in non-alcoholic fatty liver promotes insulin resistance and is a potential blood biomarker for diagnosis

BACKGROUND AND AIMS

The molecular mechanisms driving non-alcoholic fatty liver disease (NAFLD) are poorly understood; however, microRNAs might play a key role in these processes. We hypothesize that let-7d-5p could contribute to the pathophysiology of NAFLD and serve as a potential diagnostic biomarker.

METHODS

We evaluated let-7d-5p levels and its targets in liver biopsies from a cross-sectional study including patients with NAFLD and healthy donors, and from a mouse model of NAFLD. Moreover, the induction of let-7d-5p expression by fatty acids was evaluated in vitro. Further, we overexpressed let-7d-5p in vitro to corroborate the results observed in vivo. Circulating let-7d-5p and its potential as a NAFLD biomarker was determined in isolated extracellular vesicles from human plasma by RT-qPCR.

RESULTS

Our results demonstrate that hepatic let-7d-5p was significantly up-regulated in patients with steatosis, and this increase correlated with obesity and a decreased expression of AKT serine/threonine kinase (AKT), insulin-like growth factor 1 (IGF1), IGF-I receptor (IGF1R) and insulin receptor (INSR). These alterations were corroborated in a NAFLD mouse model. In vitro, fatty acids increased let-7d-5p expression, and its overexpression decreased AKT, IGF-IR and IR protein expression. Furthermore, let-7d-5p hindered AKT phosphorylation in vitro after insulin stimulation. Finally, circulating let-7d-5p significantly decreased in steatosis patients and receiver operating characteristic (ROC) analyses confirmed its utility as a diagnostic biomarker.

CONCLUSIONS

Our results highlight the emerging role of let-7d-5p as a potential therapeutic target for NAFLD since its overexpression impairs hepatic insulin signalling, and also, as a novel non-invasive biomarker for NAFLD diagnosis.

Uncoupling hepatic insulin resistance - hepatic inflammation to improve insulin sensitivity and to prevent impaired metabolism-associated fatty liver disease in type 2 diabetes

Diabetes mellitus is a metabolic disease clinically-characterized as acute and chronic hyperglycemia. It is emerging as one of the common conditions associated with incident liver disease in the US. The mechanism by which diabetes drives liver disease has become an intense topic of discussion and a highly sought-after therapeutic target. Insulin resistance (IR) appears early in the progression of type 2 diabetes (T2D), particularly in obese individuals. One of the co-morbid conditions of obesity-associated diabetes that is on the rise globally is referred to as non-alcoholic fatty liver disease (NAFLD). IR is one of a number of known and suspected mechanism that underlie the progression of NAFLD which concurrently exhibits hepatic inflammation, particularly enriched in cells of the innate arm of the immune system. In this review we focus on the known mechanisms that are suspected to play a role in the cause-effect relationship between hepatic IR and hepatic inflammation and its role in the progression of T2D-associated NAFLD. Uncoupling hepatic IR/hepatic inflammation may break an intra-hepatic vicious cycle, facilitating the attenuation or prevention of NAFLD with a concurrent restoration of physiologic glycemic control. As part of this review, we therefore also assess the potential of a number of existing and emerging therapeutic interventions that can target both conditions simultaneously as treatment options to break this cycle.

Insight into the role of PCSK9 in glucose metabolism

Diabetes mellitus (DM) is strongly associated with an increased risk of atherosclerotic cardiovascular disease (ASCVD). Proprotein convertase subtilisin/kexin type 9 (PCSK9) was recently identified as an important regulator of circulating low-density lipoprotein-cholesterol (LDL-C) levels via degradation of the LDL receptor, proving to be a valid target to improve lipoprotein profiles and cardiovascular outcomes in patients with ASCVD. Beyond LDL receptor processing and cholesterol homeostasis, the PCSK9 protein has recently been verified to be associated with glucose metabolism. Importantly, clinical trials suggest that treatment with PCSK9 inhibitors for patients with DM is more effective. Hence, in this review, we summarize the current findings derived from experimental, preclinical, and clinical studies regarding the association between PCSK9 and glucose metabolism, including the relationship of PCSK9 genetic mutations to glucose metabolism and diabetes, the link between plasma PCSK9 concentrations and glucose metabolic parameters, the effects of glucose-lowering drugs on plasma PCSK9 levels and the impacts of PCSK9 inhibitors on cardiovascular outcomes of patients with DM. Clinically, exploring this field may improve our understanding regarding the roles of PCSK9 in glucose metabolism and may offer an in-depth interpretation of how PCSK9 inhibitors exert effects on the treatment of patients with DM.

Patulin alleviates hepatic lipid accumulation by regulating lipogenesis and mitochondrial respiration

AIMS

The aim of this study is to evaluate the effects of patulin on hepatic lipid metabolism and mitochondrial oxidative function and elucidate the underlying molecular mechanisms.

MAIN METHODS

The effects of patulin on hepatic lipid accumulation were evaluated in free fatty acid-treated AML12 or HepG2 cells through oil red O staining, triglyceride assay, real-time polymerase chain reaction, and western blotting. Alteration of mitochondrial oxidative capacity by patulin treatment was determined using Seahorse analysis to measure the oxygen consumption rate.

KEY FINDINGS

The increased amounts of lipid droplets induced by free fatty acids were significantly reduced by patulin treatment. Patulin markedly activated the CaMKII/AMP-activated protein kinase (AMPK)/proliferator-activated receptor-γ coactivator (PGC)-1α signaling pathway in hepatocytes, reduced the expression of sterol regulatory element binding protein 1c (SREBP-1c) and lipogenic genes, and increased the expression of genes related to mitochondrial fatty acid oxidation. In addition, patulin treatment enhanced the mitochondrial consumption rate and increased the expression of mitochondrial oxidative phosphorylation proteins in HepG2 hepatocytes. The effects of patulin on anti-lipid accumulation; SREBP-1c, PGC-1α, and carnitine palmitoyltransferase 1 expression; and mitochondrial oxidative capacity were significantly prevented by compound C, an AMPK inhibitor.

SIGNIFICANCE

Patulin is a potent inducer of the AMPK pathway, and AMPK-mediated mitochondrial activation is required for the efficacy of patulin to inhibit hepatic lipid accumulation. This study is the first to report that patulin is a promising bioactive compound that prevents the development and worsening of fatty liver diseases, including non-alcoholic fatty liver disease, by improving mitochondrial quality and lipid metabolism.

Dysregulation of Lipid and Glucose Metabolism in Nonalcoholic Fatty Liver Disease

Non-Alcoholic Fatty Liver Disease (NAFLD) is a highly prevalent condition affecting approximately a quarter of the global population. It is associated with increased morbidity, mortality, economic burden, and healthcare costs. The disease is characterized by the accumulation of lipids in the liver, known as steatosis, which can progress to more severe stages such as steatohepatitis, fibrosis, cirrhosis, and even hepatocellular carcinoma (HCC). This review focuses on the mechanisms that contribute to the development of diet-induced steatosis in an insulin-resistant liver. Specifically, it discusses the existing literature on carbon flux through glycolysis, ketogenesis, TCA (Tricarboxylic Acid Cycle), and fatty acid synthesis pathways in NAFLD, as well as the altered canonical insulin signaling and genetic predispositions that lead to the accumulation of diet-induced hepatic fat. Finally, the review discusses the current therapeutic efforts that aim to ameliorate various pathologies associated with NAFLD.

An adipocentric perspective on the development and progression of non-alcoholic fatty liver disease

Alongside the liver, white adipose tissue (WAT) is critical in regulating systemic energy homeostasis. Although each organ has its specialised functions, they must work coordinately to regulate whole-body metabolism. Adipose tissues and the liver are relatively resilient and can adapt to an energy surplus by facilitating triglyceride (TG) storage up to a certain threshold level without significant metabolic disturbances. However, lipid storage in WAT beyond a "personalised" adiposity threshold becomes dysfunctional, leading to metabolic inflexibility, progressive inflammation, and aberrant adipokine secretion. Moreover, the failure of adipose tissue to store and mobilise lipids results in systemic knock-on lipid overload, particularly in the liver. Factors contributing to hepatic lipid overload include lipids released from WAT, dietary fat intake, and enhanced de novo lipogenesis. In contrast, extrahepatic mechanisms counteracting toxic hepatic lipid overload entail coordinated compensation through oxidation of surplus fatty acids in brown adipose tissue and storage of fatty acids as TGs in WAT. Failure of these integrated homeostatic mechanisms leads to quantitative increases and qualitative alterations to the lipidome of the liver. Initially, hepatocytes preferentially accumulate TG species leading to a relatively "benign" non-alcoholic fatty liver. However, with time, inflammatory responses ensue, progressing into more severe conditions such as non-alcoholic steatohepatitis, cirrhosis, and hepatocellular carcinoma, in some individuals (often without an early prognostic clue). Herein, we highlight the pathogenic importance of obesity-induced "adipose tissue failure", resulting in decreased adipose tissue functionality (i.e. fat storage capacity and metabolic flexibility), in the development and progression of NAFL/NASH.

Advances in the Diagnosis and Treatment of Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease that affects approximately one-quarter of the global adult population, posing a significant threat to human health with wide-ranging social and economic implications. The main characteristic of NAFLD is considered that the excessive fat is accumulated and deposited in hepatocytes without excess alcohol intake or some other pathological causes. NAFLD is a progressive disease, ranging from steatosis to non-alcoholic steatohepatitis (NASH), cirrhosis, hepatocellular carcinoma, liver transplantation, and death. Therefore, NAFLD will probably emerge as the leading cause of end-stage liver disease in the coming decades. Unlike other highly prevalent diseases, NAFLD has received little attention from the global public health community. Liver biopsy is currently considered the gold standard for the diagnosis and staging of NAFLD because of the absence of noninvasive and specific biomarkers. Due to the complex pathophysiological mechanisms of NAFLD and the heterogeneity of the disease phenotype, no specific pharmacological therapies have been approved for NAFLD at present, although several drugs are in advanced stages of development. This review summarizes the current evidence on the pathogenesis, diagnosis and treatment of NAFLD.

Gestational Exercise Antagonises the Impact of Maternal High-Fat High-Sucrose Diet on Liver Mitochondrial Alterations and Quality Control Signalling in Male Offspring

Maternal high-caloric nutrition and related gestational diabetes mellitus (GDM) are relevant modulators of the intrauterine environment, increasing the risk of liver metabolic alterations in mothers and offspring. In contrast, as a non-pharmacological approach against metabolic disorders, exercise is highly recommended in GDM treatment. We analysed whether gestational exercise (GE) protects mothers from diet-induced GDM metabolic consequences and mitigates liver mitochondrial deleterious alterations in their 6-week-old male offspring. Female Sprague Dawley rats were fed with control or high-fat high-sucrose (HFHS) diet and kept sedentary or submitted to GE. Male offspring were sedentary and fed with control diet. Sedentary HFHS mothers and their offspring showed impaired hepatic mitochondrial biogenesis and morphological evidence of mitochondrial remodelling. In contrast, GE-related beneficial effects were demonstrated by upregulation of mitochondrial biogenesis signalling markers and mitochondrial fusion proteins and downregulation of mitochondrial fission protein. Alterations in miR-34a, miR-130b, and miR-494, associated with epigenetic regulation of mitochondrial biogenesis, suggested that GE is a more critical modulator of intergenerational changes in miRs expression than the maternal diet. Our data showed that GE positively modulated the altered hepatic mitochondrial biogenesis and dynamics markers and quality control signalling associated with maternal HFHS-diet-related GDM in mothers and offspring.

Tilianin Protects against Nonalcoholic Fatty Liver Disease in Early Obesity Mice

Non-alcoholic fatty liver disease (NAFLD) has emerged as one of the most frequent types of liver disease in pediatric populations with obesity. Tilianin has multiple biological activities including anti-inflammatory and antioxidant. Here, we aim to explore the functions and possible mechanisms of tilianin on NAFLD in obese children. A high-fat high-carbohydrate (HFHC) diet was used to feed 21-d-old mice. Tilianin was administered at a dose of 10 or 20 mg/kg daily. HFHC-fed mice gained weight, increased liver index. The liver showed hepatocyte ballooning, inflammatory infiltration, and steatosis. Elevated levels of alanine aminotransferase (ALT), aspartate aminotransferase (AST), gamma-glutamyl transpeptidase (GGT), low-density lipoprotein cholesterol (LDL-C) and total cholesterol (TC) and reduced the high-density lipoprotein cholesterol (HDL-C) level were found in HFHC-fed mice. Administration of tilianin significantly reduced these impairments. We further evaluated proteins related to lipid metabolism and observed that LXRα, SREBP-1c, FAS and ACC1 expression were blunted following tilianin administration. In addition, tilianin suppressed reactive oxygen species (ROS) overproduction and lipid peroxide 4-Hydroxynonenal expression, ascribed to its oxidative stress-modulating capacity. Tilianin also reversed the increase in F4/80 expression and proinflammatory cytokine levels. Of note, tilianin administration resulted in decreased protein levels of active caspase-1 and NOD-like receptor protein 3 (NLRP3) in HFHC-fed mice. Our study suggests that tilianin may ameliorate NAFLD in early obese mice by modulating lipids metabolism, oxidative stress, and inflammation, which may in part involve inhibiting NLRP3 inflammasome activation.

The role of pioglitazone in the fight against insulin resistance, atherosclerosis, cardiovascular disease, and non-alcoholic fatty liver disease

Modern strategies for the treatment of type 2 diabetes mellitus involve the use of pathogenetically based approaches aimed at achieving optimal glycemic control and its long-term retention. Timely and rational use of 9 classes of hypoglycemic drugs, including as part of combination therapy, makes it possible to achieve significant success in diabetes therapy. One of the fundamental principles in the treatment of type 2 diabetes mellitus is the effect on insulin resistance. For this purpose, two groups of drugs are used: biguanides and thiazolidinediones (glitazones). The action of glitazones is directly related to an increase in the sensitivity of insulin-dependent tissues to insulin and a pronounced decrease in hyperinsulinemia in patients with type 2 diabetes. Of particular interest are the pathways of insulin signal transduction, the mechanisms of insulin resistance, and the possibilities of pathogenetic therapy with thiazolidinediones. Pioglitazone is currently the only available member of the thiazolidinedione class in the world, allowing to expand the management of diabetes mellitus by reducing insulin resistance in muscle and adipose tissue and glucose production by the liver. Its use can have a number of pleiotropic effects, including on cardiovascular diseases and non-alcoholic fatty liver disease, which expands the priorities for choosing hypoglycemic therapy in patients with type 2 diabetes at various stages of therapy.

A diet-induced murine model for non-alcoholic fatty liver disease with obesity and insulin resistance that rapidly develops steatohepatitis and fibrosis

Non-alcoholic fatty liver disease (NAFLD) has become the leading cause of chronic liver disease worldwide. Patients with NAFLD often suffer steatohepatitis, which can progress to cirrhosis and hepatocellular carcinoma. The presence of visceral obesity or type 2 diabetes mellitus (T2DM) is a major risk factor and potential therapeutic target for NAFLD. The establishment of animal models with these metabolic comorbidities and with the rapid progression of the disease is needed for developing treatments for NAFLD but remains to be archived. In the present study, KK-A^y mice, widely used as T2DM models, or C57BL6 mice were fed a high-fat, high-fructose, and high-cholesterol diet supplemented with cholic acid (NAFLD diet). The KK-A^y mice fed a NAFLD diet exhibited remarkable obesity and insulin resistance. A prominent accumulation of triglycerides and cholesterol in the liver was observed at 4 weeks. These mice developed steatohepatitis at 4 weeks and fibrosis at 12 weeks. In contrast, C57BL6 mice fed a NAFLD diet remained lean, although they still developed steatohepatitis and fibrosis. In summary, we established a diet-induced murine NAFLD model with the rapid development of steatohepatitis and fibrosis, bearing obesity and insulin resistance. This model could be useful as preclinical models for drug development of NAFLD.

Regulation of lipid droplet (LD) formation in hepatocytes via regulation of SREBP1c by non-coding RNAs

Introduction

Increased de novo lipogenesis (DNL) is one of the key factors contributing to fat accumulation and non-alcoholic fatty liver disease (NAFLD). Among the critical transcription factors (TFs) regulating DNL is mTOR and its downstream lipogenic TF, SREBP1c. In recent years, it has been established that non-coding RNAs (ncRNAs) play role in both biological processes and disease pathogenesis. Our group has previously characterized microRNAs that can target and regulate the expression of both mTOR and SREBP1c. Accordingly, this study aimed to broaden our understanding of the role of ncRNAs in regulating the mTOR/SREBP1c axis to elucidate the role of the non-coding transcriptome in DNL and lipid droplet (LD) formation. Hence, short ncRNA, miR-615-5p, and long non-coding RNA (lncRNA), H19, were chosen as they were previously proven to target mTOR by our group and in the published literature, respectively.

Methodology

Huh-7 cells were treated with 800 μM oleic acid (OA) to promote LD formation. Transfection of miR-615-5p mimics or H19 over-expression vectors was performed, followed by the measurement of their downstream targets, mTOR and SREBP, on the mRNA level by quantitative real-time PCR (qRT-PCR), and on the protein level by Western blot. To determine the functional impact of miR-615-5p and H19 on LD formation and triglyceride (TG) accumulation, post-transfection LDs were stained, imaged, and characterized, and TGs were extracted and quantified.

Results

miR-615-5p was able to reduce mTOR and SREBP1c significantly on both the mRNA and protein levels compared to control cells, while H19 caused a reduction of both targets on the protein level only. Both miR-615-5p and H19 were able to significantly reduce the LD count and total area, as well as TG levels compared to control cells.

Conclusion

To conclude, this study shows, for the first time, the impact of miR-615-5p and H19 on the mTOR/SREBP1c axis, and thus, their functional impact on LDs and TG accumulation. These findings might pave the way for using ncRNAs as potential therapeutic targets in the management of fatty liver.

Ceramide de novo synthesis in non-alcoholic fatty liver disease: Pathogenic mechanisms and therapeutic perspectives

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease, and its advanced form non-alcoholic steatohepatitis (NASH) may progress to cirrhosis and hepatocellular carcinoma. Ceramides have been shown to exacerbate NAFLD development through enhancing insulin resistance, reactive oxygen species production, liver steatosis, lipotoxicity and hepatocyte apoptosis, and eventually causing hepatic inflammation and fibrosis. Emerging evidence indicates that ceramide production in NAFLD is predominantly attributed to activation of the de novo synthesis pathway of ceramides in hepatocytes. More importantly, pharmacological modulation of ceramide de novo synthesis in preclinical studies seems efficacious for the treatment of NAFLD. In this review, we provide an overview of the pathogenic mechanisms of ceramides in NAFLD, discuss recent advances and challenges in pharmacological interventions targeting ceramide de novo synthesis, and propose some research directions in the field.

Effects of Amino Acids Supplementation on Lipid and Glucose Metabolism in HepG2 Cells

Non-alcoholic fatty liver disease and type 2 diabetes are representing symptoms of metabolic syndrome, which is often accompanied with hepatic fat accumulation and insulin resistance. Since liver is the major site of glucose and lipid metabolism, this study aimed to understand the effects of SCAAs and BCAAs supplementations on glucose and lipid metabolism in HepG2 cells. These cells were pretreated with SAMe, betaine, taurine, and BCAA for 24 h, followed by treatments of a high concentration of glucose (50 mM) or palmitic acid (PA, 0.5 mM) for 48 h to simulate high-glucose and high-fat environments. Pretreatment of BCAA and SCAAs inhibited the fat accumulation. At the transcriptional level, glucose and PA treatment led to significant increase of mRNA gluconeogenic enzyme. The mRNA expression level of GLUT2 was decreased by 20% in the SAMe-treated group and inhibited glucose synthesis by reducing the level of gluconeogenic enzyme. After SAMe or BCAA pretreatment, the mRNA expression of lipogenic enzymes was decreased. The PPAR-γ expression was increased after BCAA pretreatment, but SAMe not only downregulated the expression of PPAR-γ, but also inhibited the expression of ChREBP approximately 20% and SREBP-1c decreased by about 15%. Taken together, the effect of SAMe on glucose and lipid metabolism is significant especially on inhibiting hepatic lipogenesis and gluconeogenesis under the metabolic syndrome environment.

Trends in insulin resistance: insights into mechanisms and therapeutic strategy

The centenary of insulin discovery represents an important opportunity to transform diabetes from a fatal diagnosis into a medically manageable chronic condition. Insulin is a key peptide hormone and mediates the systemic glucose metabolism in different tissues. Insulin resistance (IR) is a disordered biological response for insulin stimulation through the disruption of different molecular pathways in target tissues. Acquired conditions and genetic factors have been implicated in IR. Recent genetic and biochemical studies suggest that the dysregulated metabolic mediators released by adipose tissue including adipokines, cytokines, chemokines, excess lipids and toxic lipid metabolites promote IR in other tissues. IR is associated with several groups of abnormal syndromes that include obesity, diabetes, metabolic dysfunction-associated fatty liver disease (MAFLD), cardiovascular disease, polycystic ovary syndrome (PCOS), and other abnormalities. Although no medication is specifically approved to treat IR, we summarized the lifestyle changes and pharmacological medications that have been used as efficient intervention to improve insulin sensitivity. Ultimately, the systematic discussion of complex mechanism will help to identify potential new targets and treat the closely associated metabolic syndrome of IR.

Chlorogenic acid improves anti-lipogenic activity of metformin by positive regulating of AMPK signaling in HepG2 cells

Metformin improves lipid profile, however, combination therapy is developing to increase its effectiveness and reduce the deleterious effects of metformin. Chlorogenic acid (CGA) has exhibited lipid-lowering effects. This study aimed to investigate the combined effect of metformin and CGA on lipid accumulation, as well as to elucidate the engaged mechanism in HepG2 cells. To find the non-lethal doses of metformin and CGA, MTT assay was performed. High Glucose (HG) at 33 mM was used to induce lipogenesis in HepG2 cells. Following treatment with different concentrations of metformin and CGA, total lipid content (Oil Red O-staining), triglyceride level, the genes expression of SREBP-1c and FAS, and phosphorylation of AMPK and ACC were measured. Both Metformin and CGA decreased HG-induced lipid accumulation individually, by decreasing total lipid content and triglyceride level. The lowest effective doses of metformin and CGA were 0.25 mM and 5 μM, respectively, which significantly reduced SREBP-1c and FAS genes expression. The combination of these concentrations reinforced these effects. The phosphorylation of AMPK and ACC were more increased by metformin in combination with CGA than both individually. Our findings suggest that CGA synergistically enhances metformin lipid reducing action via the regulating of involved factors in fatty acid synthesis. Therefore, co-administration of metformin with CGA may have further medical value in treating lipid metabolism disorders.

The regulation of HBP1, SIRT1, and SREBP-1c genes and the related microRNAs in non-alcoholic fatty liver rats: The association with the folic acid anti-steatosis

Folic acid is one of the vital micronutrients that contribute to the genetic stability and other biological activities. In addition, microRNAs regulate gene expression through a multittude of pathways. Our current work aimd to explore the possible ameliorative potency of folic acid and its association with the hepatic miR-21, -34a, and -122 expression as well as their targeted genes, HBP1, SIRT1, and SREBP-1c in rats with non-alcoholic fatty liver disease (NAFL). A total of 50 Wistar rats were randomly divided into two groups, a control group (n = 10) and NAFL group (n = 40). Rats in NAFL group were fed a high-fat diet (HFD) containing 20% fats for 14 weeks. The NAFL group was further subdivided into four groups (n = 10/group), one untreated and three orally folic acid-treated groups (25, 50, and 75 μg/Kg b.wt). NAFL characteristics was evaluated in rats in addition to the miR-21, -34a, and -122 profile as well as the transcriptional levels of HBP1, SIRT1, and SREBP-1c genes. NAFL rats exhibited the classic traits of fatty liver disease profile and dysregulation in the pattern of miR-21, -34a, and -122 expression as well as their targeted genes (HBP1, SIRT1, and SREBP-1c, respectively) in the liver. Additionally, NAFL rats had altered levels of TNF-α and adiponectin. These alterations were significantly ameliorated in a dose-dependent pattern following the folic acid treatments. In conclusions, the anti-steatotic, insulin-sensitizing, glucose-lowering and lipotropic potencies of folic acid in NAFL rats may be linked to the epigenetic modulation of the hepatic microRNAs (miR-21, -34a, and -122) and the expression of their target genes (HBP1, SIRT1, and SREBP-1c).

Hepatic IRF3 fuels dysglycemia in obesity through direct regulation of Ppp2r1b

Inflammation has profound but poorly understood effects on metabolism, especially in the context of obesity and nonalcoholic fatty liver disease (NAFLD). Here, we report that hepatic interferon regulatory factor 3 (IRF3) is a direct transcriptional regulator of glucose homeostasis through induction of Ppp2r1b, a component of serine/threonine phosphatase PP2A, and subsequent suppression of glucose production. Global ablation of IRF3 in mice on a high-fat diet protected against both steatosis and dysglycemia, whereas hepatocyte-specific loss of IRF3 affects only dysglycemia. Integration of the IRF3-dependent transcriptome and cistrome in mouse hepatocytes identifies Ppp2r1b as a direct IRF3 target responsible for mediating its metabolic actions on glucose homeostasis. IRF3-mediated induction of Ppp2r1b amplified PP2A activity, with subsequent dephosphorylation of AMPKα and AKT. Furthermore, suppression of hepatic Irf3 expression with antisense oligonucleotides reversed obesity-induced insulin resistance and restored glucose homeostasis in obese mice. Obese humans with NAFLD displayed enhanced activation of liver IRF3, with reversion after bariatric surgery. Hepatic PPP2R1B expression correlated with HgbA1C and was elevated in obese humans with impaired fasting glucose. We therefore identify the hepatic IRF3-PPP2R1B axis as a causal link between obesity-induced inflammation and dysglycemia and suggest an approach for limiting the metabolic dysfunction accompanying obesity-associated NAFLD.

Potential role of microRNAs in selective hepatic insulin resistance: From paradox to the paradigm

The paradoxical action of insulin on hepatic glucose metabolism and lipid metabolism in the insulin-resistant state has been of much research interest in recent years. Generally, insulin resistance would promote hepatic gluconeogenesis and demote hepatic de novo lipogenesis. The underlying major drivers of these mechanisms were insulin-dependent, via FOXO-1-mediated gluconeogenesis and SREBP1c-mediated lipogenesis. However, insulin-resistant mouse models have shown high glucose levels as well as excess lipid accumulation. As suggested, the inert insulin resistance causes the activation of the FOXO-1 pathway promoting gluconeogenesis. However, it does not affect the SREBP1c pathway; therefore, cells continue de novo lipogenesis. Many hypotheses were suggested for this paradoxical action occurring in insulin-resistant rodent models. A "downstream branch point" in the insulin-mediated pathway was suggested to act differentially on the FOXO-1 and SREBP1c pathways. MicroRNAs have been widely studied for their action of pathway mediation via suppressing the intermediate protein expressions. Many in vitro studies have postulated the roles of hepato-specific expressions of miRNAs on insulin cascade. Thus, miRNA would play a pivotal role in selective hepatic insulin resistance. As observed, there were confirmations and contradictions between the outcomes of gene knockout studies conducted on selective hepatic insulin resistance and hepato-specific miRNA expression studies. Furthermore, these studies had evaluated only the effect of miRNAs on glucose metabolism and few on hepatic de novo lipogenesis, limiting the ability to conclude their role in selective hepatic insulin resistance. Future studies conducted on the role of miRNAs on selective hepatic insulin resistance warrant the understanding of this paradoxical action of insulin.

Changes of LRP6/β-catenin pathway in adipose tissue of rats with intrauterine growth restriction with catch-up growth

To investigate the expression of low-density lipoprotein receptor-related protein 6 (LRP6)/β-catenin pathway related proteins in adipose tissue of rats with intrauterine growth restriction with catch-up growth SD rats were randomly divided into nutrition-restriction rats and normal feed rats during pregnancy. CG-IUGR model was established by reducing the number of offspring in the nutrition-restriction rats (CG-IUGR group); while the rats in the control group were offspring of the normal feed pregnant rats. In order to exclude the interference of gender, male offspring mice were selected in both the CG-IUGR group and the control group in the following studies. The CG-IUGR group and the control group were subjected to glucose tolerance test at 12 weeks of age, and the perirenal adipose tissue samples were taken to observe the adipose structure by HE staining. Expression of LRP6, β-catenin and insulin receptor substrate 1 (IRS-1) in adipocytes were examined by confocal microscopy. Protein expression of LRP6, β-catenin and IRS-1 were measured by Western blotting. Blood glucose level and the area under the cure of CG-IUGR group were significantly higher than that of control group (both <0.05). Adipocyte size in the CG-IUGR group was significantly larger than that of control group, and the expression of LRP6, β-catenin and IRS-1 protein in adipose tissue of the CG-IUGR group was significantly lower than that of control group (all <0.05). : The expression of LRP6/β-catenin pathway related proteins is reduced in the adipose tissue in CG-IUGR rats, probably contributing to the insulin resistance in these rats.

An antisense transcript transcribed from Irs2 locus contributes to the pathogenesis of hepatic steatosis in insulin resistance

During insulin resistance, lipid uptake by the liver is promoted by peroxisome proliferator-activated protein (PPAR) γ upregulation, leading to hepatic steatosis. Insulin, however, does not directly regulate adipogenic gene expression in liver, and the mechanisms for its upregulation in obesity remain unclear. Here, we show that the Irs2 locus, a critical regulator of insulin actions, encodes an antisense transcript, ASIrs2, whose expression increases in obesity or after refeeding in liver, reciprocal to that of Irs2. ASIrs2 regulates hepatic Pparg expression, and its suppression ameliorates steatosis in obese mice. The human ortholog AL162497.1, whose expression is correlated with that of hepatic PPARG and the severity of non-alcoholic steatohepatitis (NASH), shows genomic organization similar to that of ASIrs2. We also identified HARS2 as a potential binding protein for ASIrs2, functioning as a regulator of Pparg. Collectively, our data reveal a functional duality of the Irs2 gene locus, where reciprocal changes of Irs2 and ASIrs2 in obesity cause insulin resistance and steatosis.

SREBP-1c and lipogenesis in the liver: an update1

Sterol Regulatory Element Binding Protein-1c is a transcription factor that controls the synthesis of lipids from glucose in the liver, a process which is of utmost importance for the storage of energy. Discovered in the early nineties by B. Spiegelman and by M. Brown and J. Goldstein, it has generated more than 5000 studies in order to elucidate its mechanism of activation and its role in physiology and pathology. Synthetized as a precursor found in the membranes of the endoplasmic reticulum, it has to be exported to the Golgi and cleaved by a mechanism called regulated intramembrane proteolysis. We reviewed in 2002 its main characteristics, its activation process and its role in the regulation of hepatic glycolytic and lipogenic genes. We particularly emphasized that Sterol Regulatory Element Binding Protein-1c is the mediator of insulin effects on these genes. In the present review, we would like to update these informations and focus on the response to insulin and to another actor in Sterol Regulatory Element Binding Protein-1c activation, the endoplasmic reticulum stress.

Exploring regulatory network of metabolism through liver research

In recent years, the techniques in molecular biology have been dramatically advanced, and consequently the landscape of metabolism research has undergone a remarkable change. One of the emerging pictures as the fruits of these advancements is one depicting the regulation of systemic metabolism through inter-organ networks involving multiple tissues, either via humoral factors, which are secreted from one tissue and conveyed to their remote target tissues, or through neuronal networks which are integrated by the central nervous system. In addition, the progress in high-throughput research tools enabled detailed characterization and deeper understanding of the nature of human genome, which has attracted much attention to the importance of various non-coding RNAs species. These non-coding RNAs are often co-expressed and co-regulated with adjacent protein coding genes, adding higher levels of complexities by them functioning together as a system and often influencing biologically important pathways in a cooperative manner. Here in this review several examples of these regulatory network systems are presented, illustrating the significance of them in systemic metabolism, with a possible future research direction also being proposed.

The Interactions of Insulin and Vitamin A Signaling Systems for the Regulation of Hepatic Glucose and Lipid Metabolism

The pandemics of obesity and type 2 diabetes have become a concern of public health. Nutrition plays a key role in these concerns. Insulin as an anabolic hormonal was discovered exactly 100 years ago due to its activity in controlling blood glucose level. Vitamin A (VA), a lipophilic micronutrient, has been shown to regulate glucose and fat metabolism. VA's physiological roles are mainly mediated by its metabolite, retinoic acid (RA), which activates retinoic acid receptors (RARs) and retinoid X receptors (RXRs), which are two transcription factors. The VA status and activations of RARs and RXRs by RA and synthetic agonists have shown to affect the glucose and lipid metabolism in animal models. Both insulin and RA signaling systems regulate the expression levels of genes involved in the regulation of hepatic glucose and lipid metabolism. Interactions of insulin and RA signaling systems have been observed. This review is aimed at summarizing the history of diabetes, insulin and VA signaling systems; the effects of VA status and activation of RARs and RXRs on metabolism and RAR and RXR phosphorylation; and possible interactions of insulin and RA in the regulation of hepatic genes for glucose and lipid metabolism. In addition, some future research perspectives for understanding of nutrient and hormone interactions are provided.

Storage and Utilization of Glycogen by Mouse Liver during Adaptation to Nutritional Changes Are GLP-1 and PASK Dependent

Glucagon-like peptide 1 (GLP-1) and PAS kinase (PASK) control glucose and energy homeostasis according to nutritional status. Thus, both glucose availability and GLP-1 lead to hepatic glycogen synthesis or degradation. We used a murine model to discover whether PASK mediates the effect of exendin-4 (GLP-1 analogue) in the adaptation of hepatic glycogen metabolism to nutritional status. The results indicate that both exendin-4 and fasting block the Pask expression, and PASK deficiency disrupts the physiological levels of blood GLP1 and the expression of hepatic GLP1 receptors after fasting. Under a non-fasted state, exendin-4 treatment blocks AKT activation, whereby Glucokinase and Sterol Regulatory Element-Binding Protein-1c (Srebp1c) expressions were inhibited. Furthermore, the expression of certain lipogenic genes was impaired, while increasing Glucose Transporter 2 (GLUT2) and Glycogen Synthase (GYS). Moreover, exendin-4 treatment under fasted conditions avoided Glucose 6-Phosphatase (G6pase) expression, while maintaining high GYS and its activation state. These results lead to an abnormal glycogen accumulation in the liver under fasting, both in PASK-deficient mice and in exendin-4 treated wild-type mice. In short, exendin-4 and PASK both regulate glucose transport and glycogen storage, and some of the exendin-4 effects could therefore be due to the blocking of the Pask expression.

Sex-specific effects of in vitro fertilization on adult metabolic outcomes and hepatic transcriptome and proteome in mouse

Although in vitro fertilization (IVF) is associated with adverse perinatal outcomes, there is increasing concern about the long-term and sex-specific health implications. Augmenting our IVF mouse model to longitudinally investigate metabolic outcomes in offspring from optimal neonatal litter sizes, we found sex-specific metabolic outcomes in IVF offspring. IVF-conceived females had higher body weight and cholesterol levels compared to naturally conceived females, whereas IVF-conceived males had higher levels of triglycerides and insulin, and increased body fat composition. Through adult liver transcriptomics and proteomics, we identified sexually dimorphic dysregulation of the sterol regulatory element-binding protein (SREBP) pathways that are associated with the sex-specific phenotypes. We also found that global loss of DNA methylation in placenta was linked to higher cholesterol levels in IVF-conceived females. Our findings indicate that IVF procedures have long-lasting sex-specific effects on metabolic health of offspring and lay the foundation to utilize the placenta as a predictor of long-term outcomes.

High-fat diet accelerate hepatic fatty acids synthesis in offspring male rats induced by perinatal exposure to nonylphenol

BACKGROUND

Low dose of NP exposure can alter adipose tissue formation, and the intake of high-fat diet (HFD) can also lead to the fatty liver disease. We investigated the combined effect of NP and HFD on the first offspring of rats, and whether this effect can be passed to the next generation and the possible mechanisms involved.

METHODS

Pregnant rats had access to be treated with 5 μg/kg/day NP and normal diet. The first generation rats were given normal diet and HFD on postnatal day 21, respectively. Then the second generation rats started to only receive normal diet without NP or HFD. Body weight, organ coefficient of liver tissues, lipid profile, biochemical indexes and the expression of genes involved in lipid metabolism, as well as liver histopathology were investigated in male offspring of rats.

RESULTS

NP and HFD interaction had significant effect on the birth weight, body weight and liver tissue organ coefficient of first generation male rats. And HFD aggravated abnormal lipid metabolism, even abnormal liver function and liver histopathological damage of first generation male rats produced by the NP. And this effect can be passed on to the second generation rats. HFD also accelerated the mRNA level of fatty acid synthesis genes such as Lpl, Fas, Srebp-1 and Ppar-γ of first generation rats induced by perinatal exposure to NP, even passed on to the second generation of male rats. NP and HFD resulted in synergistical decrease of the protein expression level of ERα in liver tissue in F2 male rats.

CONCLUSION

HFD and NP synergistically accelerated synthesis of fatty acids in liver of male offspring rats through reducing the expression of ERα, which induced abnormal lipid metabolism, abnormal liver function and hepatic steatosis. Moreover, all of these damage passed on to the next generation rats.

Role of Insulin Resistance in MAFLD

Many studies have reported that metabolic dysfunction is closely involved in the complex mechanism underlying the development of non-alcoholic fatty liver disease (NAFLD), which has prompted a movement to consider renaming NAFLD as metabolic dysfunction-associated fatty liver disease (MAFLD). Metabolic dysfunction in this context encompasses obesity, type 2 diabetes mellitus, hypertension, dyslipidemia, and metabolic syndrome, with insulin resistance as the common underlying pathophysiology. Imbalance between energy intake and expenditure results in insulin resistance in various tissues and alteration of the gut microbiota, resulting in fat accumulation in the liver. The role of genetics has also been revealed in hepatic fat accumulation and fibrosis. In the process of fat accumulation in the liver, intracellular damage as well as hepatic insulin resistance further potentiates inflammation, fibrosis, and carcinogenesis. Increased lipogenic substrate supply from other tissues, hepatic zonation of Irs1, and other factors, including ER stress, play crucial roles in increased hepatic de novo lipogenesis in MAFLD with hepatic insulin resistance. Herein, we provide an overview of the factors contributing to and the role of systemic and local insulin resistance in the development and progression of MAFLD.

Lingonberry Improves Non-Alcoholic Fatty Liver Disease by Reducing Hepatic Lipid Accumulation, Oxidative Stress and Inflammatory Response

Non-alcoholic fatty liver disease (NAFLD) is the most common chronic liver disease globally and there is a pressing need for effective treatment. Lipotoxicity and oxidative stress are the important mediators in NAFLD pathogenesis. Lingonberry (Vaccinium vitis-idaea L.) is rich in anthocyanins that have antioxidant and anti-inflammatory properties. The present study investigated the effect of lingonberry supplementation on liver injury in C57BL/6J male mice fed a high-fat diet (HFD) for 12 weeks. Mice fed HFD displayed liver injury with steatosis, increased lipid peroxidation and inflammatory cytokine expression in the liver as compared to mice fed a control diet. Lingonberry supplementation for 12 weeks alleviated HFD-induced liver injury, attenuated hepatic lipid accumulation, and inflammatory cytokine expression. Lingonberry supplementation inhibited the expression of sterol regulatory element-binding protein-1c (SREBP-1c) and acetyl-CoA carboxylase-1 (AAC-1) as well as activated AMP-activated protein kinase (AMPK) in the liver. It also decreased HFD-induced hepatic oxidative stress and aggregation of inflammatory foci. This was associated with a restoration of nuclear factor erythroid 2-related factor 2 (Nrf2) and glutathione level in the liver. These results suggest that lingonberry supplementation can protect against HFD-induced liver injury partly through attenuation of hepatic lipid accumulation, oxidative stress, and inflammatory response.

S-Allylmercaptocysteine improves alcoholic liver disease partly through a direct modulation of insulin receptor signaling

Alcoholic liver disease (ALD) causes insulin resistance, lipid metabolism dysfunction, and inflammation. We investigated the protective effects and direct regulating target of S-allylmercaptocysteine (SAMC) from aged garlic on liver cell injury. A chronic ethanol-fed ALD in vivo model (the NIAAA model) was used to test the protective functions of SAMC. It was observed that SAMC (300 mg/kg, by gavage method) effectively ameliorated ALD-induced body weight reduction, steatosis, insulin resistance, and inflammation without affecting the health status of the control mice, as demonstrated by histological, biochemical, and molecular biology assays. By using biophysical assays and molecular docking, we demonstrated that SAMC directly targeted insulin receptor (INSR) protein on the cell membrane and then restored downstream IRS-1/AKT/GSK3β signaling. Liver-specific knock-down in mice and siRNA-mediated knock-down in AML-12 cells of Insr significantly impaired SAMC (250 μmol/L in cells)-mediated protection. Restoration of the IRS-1/AKT signaling partly recovered hepatic injury and further contributed to SAMC's beneficial effects. Continuous administration of AKT agonist and recombinant IGF-1 in combination with SAMC showed hepato-protection in the mice model. Long-term (90-day) administration of SAMC had no obvious adverse effect on healthy mice. We conclude that SAMC is an effective and safe hepato-protective complimentary agent against ALD partly through the direct binding of INSR and partial regulation of the IRS-1/AKT/GSK3β pathway.

Roles of Ceramides in Non-Alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease is one of the most common chronic liver diseases, ranging from simple steatosis to steatohepatitis, fibrosis, and cirrhosis. Its prevalence is rapidly increasing and presently affects around 25% of the general population of Western countries, due to the obesity epidemic. Liver fat accumulation induces the synthesis of specific lipid species and particularly ceramides, a sphingolipid. In turn, ceramides have deleterious effects on hepatic metabolism, a phenomenon called lipotoxicity. We review here the evidence showing the role of ceramides in non-alcoholic fatty liver disease and the mechanisms underlying their effects.

Free fatty acid processing diverges in human pathologic insulin resistance conditions

BACKGROUNDPostreceptor insulin resistance (IR) is associated with hyperglycemia and hepatic steatosis. However, receptor-level IR (e.g., insulin receptor pathogenic variants, INSR) causes hyperglycemia without steatosis. We examined 4 pathologic conditions of IR in humans to examine pathways controlling lipid metabolism and gluconeogenesis.METHODSCross-sectional study of severe receptor IR (INSR, n = 7) versus postreceptor IR that was severe (lipodystrophy, n = 14), moderate (type 2 diabetes, n = 9), or mild (obesity, n = 8). Lipolysis (glycerol turnover), hepatic glucose production (HGP), gluconeogenesis (deuterium incorporation from body water into glucose), hepatic triglyceride (magnetic resonance spectroscopy), and hepatic fat oxidation (plasma β-hydroxybutyrate) were measured.RESULTSLipolysis was 2- to 3-fold higher in INSR versus all other groups, and HGP was 2-fold higher in INSR and lipodystrophy versus type 2 diabetes and obesity (P < 0.001), suggesting severe adipose and hepatic IR. INSR subjects had a higher contribution of gluconeogenesis to HGP, approximately 77%, versus 52% to 59% in other groups (P = 0.0001). Despite high lipolysis, INSR subjects had low hepatic triglycerides (0.5% [interquartile range 0.1%-0.5%]), in contrast to lipodystrophy (10.6% [interquartile range 2.8%-17.1%], P < 0.0001). β-hydroxybutyrate was 2- to 7-fold higher in INSR versus all other groups (P < 0.0001), consistent with higher hepatic fat oxidation.CONCLUSIONThese data support a key pathogenic role of adipose tissue IR to increase glycerol and FFA availability to the liver in both receptor and postreceptor IR. However, the fate of FFA diverges in these populations. In receptor-level IR, FFA oxidation drives gluconeogenesis rather than being reesterified to triglyceride. In contrast, in postreceptor IR, FFA contributes to both gluconeogenesis and hepatic steatosis.TRIAL REGISTRATIONClinicalTrials.gov NCT01778556, NCT00001987, and NCT02457897.FUNDINGNational Institute of Diabetes and Digestive and Kidney Diseases, US Department of Agriculture/Agricultural Research Service 58-3092-5-001.