Hepatitis C virus NS5A protein enhances gluconeogenesis through upregulation of Akt-/JNK-PEPCK signalling pathways

LYPLAL1 enzyme activity is linked to hepatic glucose metabolism

The serine hydrolase LYPLAL1 is a poorly characterised enzyme with emerging roles in hepatic metabolism. A multitude of association studies have shown links between variants of this gene locus and metabolic conditions such as obesity and insulin resistance. However, the enzyme's function is still largely unknown. Recent biochemical studies have revealed that it may play a role in hepatic glucose metabolism and that its activity is allosterically regulated. Herein, we use a selective activity-based probe to delineate LYPLAL1's involvement in hepatic metabolism. We show that the enzyme's activity is modulated during metabolic stress, specifically pointing to a putative role in negatively regulating gluconeogenesis and upregulating glycolysis. We also determine that knock-out of the enzyme does not affect liver lipid profiles and bring forth evidence for insulin-mediated control of LYPLAL1 in HepG2 cells. Furthermore, LYPLAL1 activity appears to be largely post-translationally regulated as gene expression levels remain largely constant under insulin and glucagon treatments. Taken together these data point to an enzymatic role in regulating glucose metabolism that may be part of a feedback mechanism of signal transduction.

Oligonol ameliorates liver function and brain function in the 5 × FAD mouse model: transcriptional and cellular analysis

Alzheimer's disease (AD) is a common neurodegenerative disease worldwide and is accompanied by memory deficits, personality changes, anxiety, depression, and social difficulties. For treatment of AD, many researchers have attempted to find medicinal resources with high effectiveness and without side effects. Oligonol is a low molecular weight polypeptide derived from lychee fruit extract. We investigated the effects of oligonol in 5 × FAD transgenic AD mice, which developed severe amyloid pathology, through behavioral tests (Barnes maze, marble burying, and nestle shredding) and molecular experiments. Oligonol treatment attenuated blood glucose levels and increased the antioxidant response in the livers of 5 × FAD mice. Moreover, the behavioral score data showed improvements in anxiety, depressive behavior, and cognitive impairment following a 2-month course of orally administered oligonol. Oligonol treatment not only altered the circulating levels of cytokines and adipokines in 5 × FAD mice, but also significantly enhanced the mRNA and protein levels of antioxidant enzymes and synaptic plasticity in the brain cortex and hippocampus. Therefore, we highlight the therapeutic potential of oligonol to attenuate neuropsychiatric problems and improve memory deficits in the early stage of AD.

Crohn's Disease Pathobiont Adherent-Invasive E coli Disrupts Epithelial Mitochondrial Networks With Implications for Gut Permeability

BACKGROUND & AIMS

Adherent-invasive Escherichia coli are implicated in inflammatory bowel disease, and mitochondrial dysfunction has been observed in biopsy specimens from patients with inflammatory bowel disease. As a novel aspect of adherent-invasive E coli-epithelial interaction, we hypothesized that E coli (strain LF82) would elicit substantial disruption of epithelial mitochondrial form and function.

METHODS

Monolayers of human colon-derived epithelial cell lines were exposed to E coli-LF82 or commensal E coli and RNA sequence analysis, mitochondrial function (adenosine triphosphate synthesis) and dynamics (mitochondrial network imaging, immunoblotting for fission and fusion proteins), and epithelial permeability (transepithelial resistance, flux of fluorescein isothiocyanate-dextran and bacteria) were assessed.

RESULTS

E coli-LF82 significantly affected epithelial expression of ∼8600 genes, many relating to mitochondrial function. E coli-LF82-infected epithelia showed swollen mitochondria, reduced mitochondrial membrane potential and adenosine triphosphate, and fragmentation of the mitochondrial network: events not observed with dead E coli-LF82, medium from bacterial cultures, or control E coli. Treatment with Mitochondrial Division Inhibitor 1 (Mdivi1, inhibits dynamin-related peptide 1, guanosine triphosphatase principally responsible for mitochondrial fission) or P110 (prevents dynamin-related peptide 1 binding to mitochondrial fission 1 protein) partially reduced E coli-LF82-induced mitochondrial fragmentation in the short term. E coli-LF82-infected epithelia showed loss of the long isoform of optic atrophy factor 1, which mediates mitochondrial fusion. Mitochondrial Division Inhibitor 1 reduced the magnitude of E coli-LF82-induced increased transepithelial flux of fluorescein isothiocyanate dextran. By 8 hours after infection, increased cytosolic cytochrome C and DNA fragmentation were apparent without evidence of caspase-3 or apoptosis inducing factor activation.

CONCLUSIONS

Epithelial mitochondrial fragmentation caused by E coli-LF82 could be targeted to maintain cellular homeostasis and mitigate infection-induced loss of epithelial barrier function. Data have been deposited in NCBI's Gene Expression Omnibus and are accessible through GEO series accession numbers GSE154121 and GSE154122 (https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE154121).

The metabolic regulator small heterodimer partner contributes to the glucose and lipid homeostasis abnormalities induced by hepatitis C virus infection

BACKGROUND

Chronic hepatitis C virus (HCV) infection can predispose the host to metabolic abnormalities. The orphan nuclear receptor small heterodimer partner (SHP; NR0B2) has been identified as a key transcriptional regulatory factor of genes involved in diverse metabolic pathways. The protective effects of SHP against HCV-induced hepatic fibrosis have been reported. However, the exact mechanisms of its role on metabolism are largely unknown. We investigated the role of hepatic SHP in regulating glucose and lipid homeostasis, particularly in the metabolic stress response caused by HCV infection.

MATERIALS AND METHODS

Gluconeogenesis and lipogenesis levels and SHP expression were measured in HCV-infected cells, as well as in liver samples from HCV-infected patients and persistently HCV-infected mice.

RESULTS

We demonstrated that SHP is involved in gluconeogenesis via the acetylation of the Forkhead box O (FoxO) family transcription factor FoxO1, which is mediated by histone deacetylase 9 (HDAC9). Meanwhile, SHP regulates lipogenesis in the liver via suppressing the induction of sterol regulatory element-binding protein-1c (SREBP-1c) expression by the SUMOylation of Liver X receptor α (LXRα) at the SREBP-1c promoter. In particular, SHP can be strongly reduced upon stimulation, such as by HCV infection. The SHP expression levels were decreased in the livers from the CHC patients and persistently HCV-infected mice, and a negative correlation was observed between the SHP expression levels and gluconeogenic or lipogenic activities, emphasizing the clinical relevance of these results.

CONCLUSIONS

Our results suggest that SHP is involved in HCV-induced abnormal glucose and lipid homeostasis and that SHP could be a major target for therapeutic interventions targeting HCV-associated metabolic diseases.

The posttranslational modification of HDAC4 in cell biology: Mechanisms and potential targets

Histone deacetylase 4 (HDAC4) is a member of the HDACs family, its expression is closely related to the cell development. The cell is an independent living entity that undergoes proliferation, differentiation, senescence, apoptosis, and pathology, and each process has a strict and complex regulatory system. With deepening of its research, the expression of HDAC4 is critical in the life process. This review focuses on the posttranslational modification of HDAC4 in cell biology, providing an important target for future disease treatment.

Robust Regression Analysis of GCMS Data Reveals Differential Rewiring of Metabolic Networks in Hepatitis B and C Patients

About one in 15 of the world’s population is chronically infected with either hepatitis virus B (HBV) or C (HCV), with enormous public health consequences. The metabolic alterations caused by these infections have never been directly compared and contrasted. We investigated groups of HBV-positive, HCV-positive, and uninfected healthy controls using gas chromatography-mass spectrometry analyses of their plasma and urine. A robust regression analysis of the metabolite data was conducted to reveal correlations between metabolite pairs. Ten metabolite correlations appeared for HBV plasma and urine, with 18 for HCV plasma and urine, none of which were present in the controls. Metabolic perturbation networks were constructed, which permitted a differential view of the HBV- and HCV-infected liver. HBV hepatitis was consistent with enhanced glucose uptake, glycolysis, and pentose phosphate pathway metabolism, the latter using xylitol and producing threonic acid, which may also be imported by glucose transporters. HCV hepatitis was consistent with impaired glucose uptake, glycolysis, and pentose phosphate pathway metabolism, with the tricarboxylic acid pathway fueled by branched-chain amino acids feeding gluconeogenesis and the hepatocellular loss of glucose, which most probably contributed to hyperglycemia. It is concluded that robust regression analyses can uncover metabolic rewiring in disease states.

Hepatitis C virus induces a prediabetic state by directly impairing hepatic glucose metabolism in mice

Virus-related type 2 diabetes is commonly observed in individuals infected with the hepatitis C virus (HCV); however, the underlying molecular mechanisms remain unknown. Our aim was to unravel these mechanisms using FL-N/35 transgenic mice expressing the full HCV ORF. We observed that these mice displayed glucose intolerance and insulin resistance. We also found that Glut-2 membrane expression was reduced in FL-N/35 mice and that hepatocyte glucose uptake was perturbed, partly accounting for the HCV-induced glucose intolerance in these mice. Early steps of the hepatic insulin signaling pathway, from IRS2 to PDK1 phosphorylation, were constitutively impaired in FL-N/35 primary hepatocytes via deregulation of TNFα/SOCS3. Higher hepatic glucose production was observed in the HCV mice, despite higher fasting insulinemia, concomitant with decreased expression of hepatic gluconeogenic genes. Akt kinase activity was higher in HCV mice than in WT mice, but Akt-dependent phosphorylation of the forkhead transcription factor FoxO1 at serine 256, which triggers its nuclear exclusion, was lower in HCV mouse livers. These findings indicate an uncoupling of the canonical Akt/FoxO1 pathway in HCV protein-expressing hepatocytes. Thus, the expression of HCV proteins in the liver is sufficient to induce insulin resistance by impairing insulin signaling and glucose uptake. In conclusion, we observed a complete set of events leading to a prediabetic state in HCV-transgenic mice, providing a valuable mechanistic explanation for HCV-induced diabetes in humans.

Hepatitis C virus suppresses Hepatocyte Nuclear Factor 4 alpha, a key regulator of hepatocellular carcinoma

Hepatitis C Virus (HCV) infection presents with a disturbed lipid profile and can evolve to hepatic steatosis and hepatocellular carcinoma (HCC). Hepatocyte Nuclear Factor 4 alpha (HNF4α) is the most abundant transcription factor in the liver, a key regulator of hepatic lipid metabolism and a critical determinant of Epithelial to Mesenchymal Transition and hepatic development. We have previously shown that transient inhibition of HNF4α initiates transformation of immortalized hepatocytes through a feedback loop consisting of miR-24, IL6 receptor (IL6R), STAT3, miR-124 and miR-629, suggesting a central role of HNF4α in HCC. However, the role of HNF4α in Hepatitis C Virus (HCV)-related hepatocarcinoma has not been evaluated and remains controversial. In this study, we provide strong evidence suggesting that HCV downregulates HNF4α expression at both transcriptional and translational levels. The observed decrease of HNF4α expression correlated with the downregulation of its downstream targets, HNF1α and MTP. Ectopic overexpression of HCV proteins also exhibited an inhibitory effect on HNF4α levels. The inhibition of HNF4α expression by HCV appeared to be mediated at transcriptional level as HCV proteins suppressed HNF4α gene promoter activity. HCV also up-regulated IL6R, activated STAT3 protein phosphorylation and altered the expression of acute phase genes. Furthermore, as HCV triggered the loss of HNF4α a consequent change of miR-24, miR-629 or miR-124 was observed. Our findings demonstrated that HCV-related HCC could be mediated through HNF4α-microRNA deregulation implying a possible role of HNF4α in HCV hepatocarcinogenesis. HCV inhibition of HNF4α could be sustained to promote HCC.

D-Xylose as a sugar complement regulates blood glucose levels by suppressing phosphoenolpyruvate carboxylase (PEPCK) in streptozotocin-nicotinamide-induced diabetic rats and by enhancing glucose uptake in vitro

BACKGROUND/OBJECTIVES

Type 2 diabetes (T2D) is more frequently diagnosed and is characterized by hyperglycemia and insulin resistance. D-Xylose, a sucrase inhibitor, may be useful as a functional sugar complement to inhibit increases in blood glucose levels. The objective of this study was to investigate the anti-diabetic effects of D-xylose both in vitro and stretpozotocin (STZ)-nicotinamide (NA)-induced models in vivo.

MATERIALS/METHODS

Wistar rats were divided into the following groups: (i) normal control; (ii) diabetic control; (iii) diabetic rats supplemented with a diet where 5% of the total sucrose content in the diet was replaced with D-xylose; and (iv) diabetic rats supplemented with a diet where 10% of the total sucrose content in the diet was replaced with D-xylose. These groups were maintained for two weeks. The effects of D-xylose on blood glucose levels were examined using oral glucose tolerance test, insulin secretion assays, histology of liver and pancreas tissues, and analysis of phosphoenolpyruvate carboxylase (PEPCK) expression in liver tissues of a STZ-NA-induced experimental rat model. Levels of glucose uptake and insulin secretion by differentiated C2C12 muscle cells and INS-1 pancreatic β-cells were analyzed.

RESULTS

In vivo, D-xylose supplementation significantly reduced fasting serum glucose levels (P < 0.05), it slightly reduced the area under the glucose curve, and increased insulin levels compared to the diabetic controls. D-Xylose supplementation enhanced the regeneration of pancreas tissue and improved the arrangement of hepatocytes compared to the diabetic controls. Lower levels of PEPCK were detected in the liver tissues of D-xylose-supplemented rats (P < 0.05). In vitro, both 2-NBDG uptake by C2C12 cells and insulin secretion by INS-1 cells were increased with D-xylose supplementation in a dose-dependent manner compared to treatment with glucose alone.

CONCLUSIONS

In this study, D-xylose exerted anti-diabetic effects in vivo by regulating blood glucose levels via regeneration of damaged pancreas and liver tissues and regulation of PEPCK, a key rate-limiting enzyme in the process of gluconeogenesis. In vitro, D-xylose induced the uptake of glucose by muscle cells and the secretion of insulin cells by β-cells. These mechanistic insights will facilitate the development of highly effective strategy for T2D.

Cellular stress responses in hepatitis C virus infection: Mastering a two-edged sword

Hepatitis C virus (HCV) infection affects chronically more than 150 million humans worldwide. Chronic HCV infection causes severe liver disease and hepatocellular carcinoma. While immune response-mediated events are major players in HCV pathogenesis, the impact that viral replication has on cellular homeostasis is increasingly recognized as a necessary contributor to pathological manifestations of HCV infection such as steatosis, insulin-resistance or liver cancer. In this review, we will briefly overview the different cellular stress pathways that are induced by hepatitis C virus infection, the response that the cell promotes to attempt regaining homeostasis or to induce dysfunctional cell death, and how the virus co-opts these response mechanisms to promote both viral replication and survival of the infected cell. We will review the role of unfolded protein and oxidative stress responses as well as the role of auto- and mitophagy in HCV infection. Finally, we will discuss the recent discovery of a cellular chaperone involved in stress responses, the sigma-1 receptor, as a cellular factor required at the onset of HCV infection and the potential molecular events underlying the proviral role of this cellular factor in HCV infection.