Major urinary protein 1 interacts with cannabinoid receptor type 1 in fatty acid-induced hepatic insulin resistance in a mouse hepatocyte model

Contrasting effects of whole-body and hepatocyte-specific deletion of the RNA polymerase III repressor Maf1 in the mouse

MAF1 is a nutrient-sensitive, TORC1-regulated repressor of RNA polymerase III (Pol III). MAF1 downregulation leads to increased lipogenesis in Drosophila melanogaster, Caenorhabditis elegans, and mice. However, Maf1 -/- mice are lean as increased lipogenesis is counterbalanced by futile pre-tRNA synthesis and degradation, resulting in increased energy expenditure. We compared Chow-fed Maf1 -/- mice with Chow- or High Fat (HF)-fed Maf1 hep-/- mice that lack MAF1 specifically in hepatocytes. Unlike Maf1 -/- mice, Maf1 hep-/- mice become heavier and fattier than control mice with old age and much earlier under a HF diet. Liver ChIPseq, RNAseq and proteomics analyses indicate increased Pol III occupancy at Pol III genes, very few differences in mRNA accumulation, and protein accumulation changes consistent with increased lipogenesis. Futile pre-tRNA synthesis and degradation in the liver, as likely occurs in Maf1 hep-/- mice, thus seems insufficient to counteract increased lipogenesis. Indeed, RNAseq and metabolite profiling indicate that liver phenotypes of Maf1 -/- mice are strongly influenced by systemic inter-organ communication. Among common changes in the three phenotypically distinct cohorts, Angiogenin downregulation is likely linked to increased Pol III occupancy of tRNA genes in the Angiogenin promoter.

Transcriptomic survey of key reproductive and metabolic tissues in mouse models of polycystic ovary syndrome

Excessive androgen production and obesity are key to polycystic ovary syndrome (PCOS) pathogenesis. Prenatal androgenized (PNA), peripubertal androgenized, and overexpression of nerve growth factor in theca cells (17NF) are commonly used PCOS-like mouse models and diet-induced maternal obesity model is often included for comparsion. To reveal the molecular features of these models, we have performed transcriptome survey of the hypothalamus, adipose tissue, ovary and metaphase II (MII) oocytes. The largest number of differentially expressed genes (DEGs) is found in the ovaries of 17NF and in the adipose tissues of peripubertal androgenized models. In contrast, hypothalamus is most affected in PNA and maternal obesity models suggesting fetal programming effects. The Ms4a6e gene, membrane-spanning 4-domains subfamily A member 6E, a DEG identified in the adipose tissue in all mouse models is also differently expressed in adipose tissue of women with PCOS, highlighting a conserved disease function. Our comprehensive transcriptomic profiling of key target tissues involved in PCOS pathology highlights the effects of developmental windows for androgen exposure and maternal obesity, and provides unique resource to investigate molecular mechanisms underlying PCOS pathogenesis.

Comparative Proteomic Analysis of Liver Tissues and Serum in db/db Mice

Background and Aims: Non-alcoholic fatty liver disease (NAFLD) affects one-quarter of individuals worldwide. Liver biopsy, as the current reliable method for NAFLD evaluation, causes low patient acceptance because of the nature of invasive sampling. Therefore, sensitive non-invasive serum biomarkers are urgently needed. Results: The serum gene ontology (GO) classification and Kyoto encyclopedia of genes and genomes (KEGG) analysis revealed the DEPs enriched in pathways including JAK-STAT and FoxO. GO analysis indicated that serum DEPs were mainly involved in the cellular process, metabolic process, response to stimulus, and biological regulation. Hepatic proteomic KEGG analysis revealed the DEPs were mainly enriched in the PPAR signaling pathway, retinol metabolism, glycine, serine, and threonine metabolism, fatty acid elongation, biosynthesis of unsaturated fatty acids, glutathione metabolism, and steroid hormone biosynthesis. GO analysis revealed that DEPs predominantly participated in cellular, biological regulation, multicellular organismal, localization, signaling, multi-organism, and immune system processes. Protein-protein interaction (PPI) implied diverse clusters of the DEPs. Besides, the paralleled changes of the common upregulated and downregulated DEPs existed in both the liver and serum were validated in the mRNA expression of NRP1, MUP3, SERPINA1E, ALPL, and ALDOB as observed in our proteomic screening. Methods: We conducted hepatic and serum proteomic analysis based on the leptin-receptor-deficient mouse (db/db), a well-established diabetic mouse model with overt obesity and NAFLD. The results show differentially expressed proteins (DEPs) in hepatic and serum proteomic analysis. A parallel reaction monitor (PRM) confirmed the authenticity of the selected DEPs. Conclusion: These results are supposed to offer sensitive non-invasive serum biomarkers for diabetes and NAFLD.

The major urinary protein gene cluster knockout mouse as a novel model for translational metabolism research

Scientific evidence suggests that not only murine scent communication is regulated by major urinary proteins, but that their expression may also vary in response to metabolism via a yet unknown mechanism. Major urinary proteins are expressed mainly in the liver, showing a sexually dimorphic pattern with substantially higher expression in males. Here, we investigate the metabolic implications of a major urinary protein knockout in twelve-week-old male and female C57BL/6N mice during ad libitum feeding. Despite both sexes of major urinary protein knockout mice displayed numerically increased body weight and visceral adipose tissue proportions compared to sex-matched wildtype mice, the main genotype-specific metabolic differences were observed exclusively in males. Male major urinary protein knockout mice exhibited plasma and hepatic lipid accumulation accompanied by a hepatic transcriptome indicating an activation of lipogenesis. These findings match the higher major urinary protein expression in male compared to female wildtype mice, suggesting a more distinct reduction in energy requirements in male compared to female major urinary protein knockout mice. The observed sex-specific anabolic phenotype confirms a role of major urinary protein in metabolism and, since major urinary proteins are not expressed in humans, suggests the major urinary protein knockout mouse as a potential alternative model for translational metabolism research which needs to be further elucidated.

Adipose MDM2 regulates systemic insulin sensitivity

The intimate association between obesity and type II diabetes urges for a deeper understanding of adipocyte function. We and others have previously delineated a role for the tumor suppressor p53 in adipocyte biology. Here, we show that mice haploinsufficient for MDM2, a key regulator of p53, in their adipose stores suffer from overt obesity, glucose intolerance, and hepatic steatosis. These mice had decreased levels of circulating palmitoleic acid [non-esterified fatty acid (NEFA) 16:1] concomitant with impaired visceral adipose tissue expression of Scd1 and Ffar4. A similar decrease in Scd and Ffar4 expression was found in in vitro differentiated adipocytes with perturbed MDM2 expression. Lowered MDM2 levels led to nuclear exclusion of the transcriptional cofactors, MORC2 and LIPIN1, and thereby possibly hampered adipocyte function by antagonizing LIPIN1-mediated PPARγ coactivation. Collectively, these data argue for a hitherto unknown interplay between MDM2 and MORC2/LIPIN1 involved in balancing adipocyte function.

Proteomic Analysis of Niemann-Pick Type C Hepatocytes Reveals Potential Therapeutic Targets for Liver Damage

Niemann-Pick type C disease (NPCD) is a lysosomal storage disorder caused by mutations in the NPC1 gene. The most affected tissues are the central nervous system and liver, and while significant efforts have been made to understand its neurological component, the pathophysiology of the liver damage remains unclear. In this study, hepatocytes derived from wild type and Npc1^-/- mice were analyzed by mass spectrometry (MS)-based proteomics in conjunction with bioinformatic analysis. We identified 3832 proteins: 416 proteins had a p-value smaller than 0.05, of which 37% (n = 155) were considered differentially expressed proteins (DEPs), 149 of them were considered upregulated, and 6 were considered downregulated. We focused the analysis on pathways related to NPC pathogenic mechanisms, finding that the most significant changes in expression levels occur in proteins that function in the pathways of liver damage, lipid metabolism, and inflammation. Moreover, in the group of DEPs, 30% (n = 47) were identified as lysosomal proteins and 7% (n = 10) were identified as mitochondrial proteins. Importantly, we found that lysosomal DEPs, including CTSB/D/Z, LIPA, DPP7 and GLMP, and mitocondrial DEPs, AKR1B10, and VAT1 had been connected with liver fibrosis, damage, and steatosis in previous studies, validiting our dataset. Our study found potential therapeutic targets for the treatment of liver damage in NPCD.

Cannabinoid receptor type 1 antagonist inhibits progression of obesity-associated nonalcoholic steatohepatitis in a mouse model by remodulating immune system disturbances

SCOPE

This study investigated whether AM251, a cannabinoid receptor type 1 (CB1) antagonist, ameliorates hepatic levels of metabolic abnormalities and inflammatory responses in a murine nonalcoholic steatohepatitis (NASH) model via reversal of disturbances in the immune system.

METHODS AND RESULTS

Fifteen-week-old male obese db/db mice were randomly assigned to the following two groups: no treatment and treatment with AM251 at 5 mg/kg for 15 days. C57BL/6J-Lean mice were utilized as the control group. Plasma parameters, liver histopathology, and hepatic status were measured. For the in vitro study, macrophage-derived RAW264.7 cells were cultured with AM251 or CB1 small interfering RNA (siRNA) before challenge with arachidonyl-2'-chloroethylamide (ACEA) or a high concentration of fatty acids (HFFAs). The db/db mice exhibited an increase in CB1 levels, lipid droplet accumulation, mitogen-activated protein kinase-related inflammatory responses, and macrophage and neutrophil infiltration in the liver tissues. Flow cytometry analysis revealed an elevation in macrophages and T helper cells, plus a decrease in natural killer T cells and regulatory T cells in the liver tissues of the db/db mice; treatment with 5 mg/kg AM251 reversed these changes. Moreover, in vitro experiments revealed that administration of 3.3 μM AM251 or CB1 siRNA prevented 1 mM HFFA- and 1 μΜ ACEA-induced inflammatory cytokine protein expression in the RAW264.7 cells.

CONCLUSION

These findings suggested that a blockade caused by CB1 reduced obesity-associated NASH progression via correction of immune system dysregulations and elevated inflammatory responses in the liver tissues.

Mitophagy in Hepatic Insulin Resistance: Therapeutic Potential and Concerns

Metabolic syndrome, characterized by central obesity, hypertension, and hyperlipidemia, increases the morbidity and mortality of cardiovascular disease, type 2 diabetes, nonalcoholic fatty liver disease, and other metabolic diseases. It is well known that insulin resistance, especially hepatic insulin resistance, is a risk factor for metabolic syndrome. Current research has shown that hepatic fatty acid accumulation can cause hepatic insulin resistance through increased gluconeogenesis, lipogenesis, chronic inflammation, oxidative stress and endoplasmic reticulum stress, and impaired insulin signal pathway. Mitochondria are the major sites of fatty acid β-oxidation, which is the major degradation mechanism of fatty acids. Mitochondrial dysfunction has been shown to be involved in the development of hepatic fatty acid–induced hepatic insulin resistance. Mitochondrial autophagy (mitophagy), a catabolic process, selectively degrades damaged mitochondria to reverse mitochondrial dysfunction and preserve mitochondrial dynamics and function. Therefore, mitophagy can promote mitochondrial fatty acid oxidation to inhibit hepatic fatty acid accumulation and improve hepatic insulin resistance. Here, we review advances in our understanding of the relationship between mitophagy and hepatic insulin resistance. Additionally, we also highlight the potential value of mitophagy in the treatment of hepatic insulin resistance and metabolic syndrome.

Cyp1b1 deletion and retinol deficiency coordinately suppress mouse liver lipogenic genes and hepcidin expression during post-natal development

Cyp1b1 deletion and gestational vitamin A deficiency (GVAD) redirect adult liver gene expression. A matched sufficient pre- and post-natal diet, which has high carbohydrate and normal iron content (LF12), increased inflammatory gene expression markers in adult livers that were suppressed by GVAD and Cyp1b1 deletion. At birth on the LF12 diet, Cyp1b1 deletion and GVAD each suppress liver expression of the iron suppressor, hepcidin (Hepc), while increasing stellate cell activation markers and suppressing post-natal increases in lipogenesis. Hepc was less suppressed in Cyp1b1-/- pups with a standard breeder diet, but was restored by iron supplementation of the LF12 diet.

CONCLUSIONS

The LF12 diet delivered low post-natal iron and attenuated Hepc. Hepc decreases in Cyp1b1-/- and GVAD mice resulted in stellate activation and lipogenesis suppression. Endothelial BMP6, a Hepc stimulant, is a potential coordinator and Cyp1b1 target. These neonatal changes in Cyp1b1-/- mice link to diminished adult obesity and liver inflammation.

Albiflorin Granule significantly decreased the cholesterol gallstone formation by the regulation of insulin transduction signal

OBJECTIVE

To study the mechanism of insulin resistance in the cholesterol gallstone formation from insulin signal transduction pathway so as to reveal the possible mechanism and the effective role of Albiflorin Granule on preventing the cholesterol gallstones.

METHODS

Serum triglycerides (TG), free fatty acid (FFA), and total cholesterol (TC) from different groups were measured and liver cells InsR, PKB, IKK-β protein expression levels were detected by western blotting.

RESULTS

Albiflorin significantly decreased the cholesterol gallstone formation rate, increased glucose infusion rate in gallstone guinea pigs and improved insulin resistance. Compared with the normal group, insulin receptor and PKB protein expression in GS group were significantly reduced. IKK-β protein in the GS group increased significantly and Albiflorin could reduce IKK-β protein expression in guinea pig liver cells.

CONCLUSIONS

The model of insulin resistance in cholesterol gallstone guinea pig was successfully established, which plays an important role in the cholesterol gallstone formation. All aspects of insulin signaling pathway are involved in gallstone formation. Albiflorin can regulate various aspects of insulin signal transduction pathway to prevent the formation of gallbladder.

Casein glycomacropeptide-derived peptide IPPKKNQDKTE ameliorates high glucose-induced insulin resistance in HepG2 cells via activation of AMPK signaling

SCOPE

Recently, casein glycomacropeptide (GMP)-derived peptide was found to possess potent antioxidant and anti-inflammatory activities. In this study, the improvement effects and underlying molecular mechanisms of GMP-derived peptide on hepatic insulin resistance were investigated.

METHODS AND RESULTS

The peptide IPPKKNQDKTE was identified from GMP papain hydrolysates by LC-ESI-MS/MS. Effects of IPPKKNQDKTE on glucose metabolism and expression levels of the hepatic insulin signaling proteins in high glucose-induced insulin-resistant HepG2 cells were evaluated. Results showed that IPPKKNQDKTE dose-dependently increased glucose uptake and intracellular glycogen in insulin-resistant HepG2 cells without affecting cell viability. IPPKKNQDKTE increased the phosphorylation of Akt and GSK3β and decreased the expression levels of p-GS, G6Pase and PEPCK. These IPPKKNQDKTE-mediated protection effects were reversed by PI3K/Akt inhibitor LY294002, showing the mediatory role of PI3K/Akt. Moreover, treatment with IPPKKNQDKTE reduced IRS-1 Ser307 phosphorylation and increased phosphorylation of AMPK. Knockdown AMPK using siRNA in HepG2 cells increased Ser307 phosphorylation of IRS-1 and reduced Akt phosphorylation in IPPKKNQDKTE-treated insulin-resistant cells.

CONCLUSION

IPPKKNQDKTE prevents high glucose-induced insulin resistance in HepG2 cells by modulating the IRS-1/PI3K/Akt signaling pathway through AMPK activation, indicating that IPPKKNQDKTE plays a potential role in the prevention and treatment of hepatic insulin resistance and type 2 diabetes.

Cannabinoid receptor type 1 mediates high-fat diet-induced insulin resistance by increasing forkhead box O1 activity in a mouse model of obesity

Hepatic glucose production is promoted by forkhead box O1 (FoxO1) under conditions of insulin resistance. The overactivity of cannabinoid receptor type 1 (CB1R) partly causes increased liver fat deposits and metabolic dysfunction in obese rodents by decreasing mitochondrial function. The aim of the present study was to investigate the role of FoxO1 in CB1R-mediated insulin resistance through the dysregulation of mitochondrial function in the livers of mice with high-fat diet (HFD)-induced obesity. For this purpose, male C57BL/6 mice were randomly assigned to groups and either fed a standard diet (STD), a HFD, or a HFD with 1-week treatment of the CB1R inverse agonist, AM251, at 1 or 5 mg/kg. For in vitro experiments, AML12 hepatocytes were incubated with FoxO1 siRNA prior to challenge with arachidonyl-2'-chloroethylamide (ACEA) or a high concentration of free fatty acids (HFFA). Plasma parameters were analyzed using colorimetric methods. Liver histopathology and hepatic status markers were examined. The HFD-fed mice exhibited an increase in CB1R levels in the liver. Moreover, in response to increased hepatic oxidative stress, the HFD-fed mice also displayed hepatic mitochondrial dysfunction, as indicated by the decreased mRNA levels of carnitine palmitoyltransferase-1 (CPT-1), mitochondrial transcription factor A (TFAM), nuclear respiratory factor-1 (NRF-1) and citrate synthase. On the contrary, these effects in the HFD-fed mice were reversed by treatment with 5 mg/kg AM251. The administration of AM251 suppressed the induction of FoxO1, phosphoenolpyruvate carboxykinase (PEPCK) and glucose 6-phosphatase (G6Pase) expression in the livers of the mice fed a HFD by enhancing the phosphorylation of insulin signaling cascades thus, further lowering the high level of the homeostatic model assessment of insulin resistance (HOMA‑IR) index. In our in vitro experiments, transfection with FoxO1 siRNA prevented the HFFA- and ACEA-induced decrease in the gene expression of mitochondrial biogenesis-related factors, and abrogated the HFFA- and ACEA-induced increase in PEPCK and G6Pase expression. Taken together, our findings suggest that the anti-insulin resistance effect of AM251, which leads to an improvement of mitochondrial function in hepatic steatosis, is mediated through FoxO1.