Reducing endogenous insulin is linked with protection against hepatic steatosis in mice

E4orf1 improves adipose tissue-specific metabolic risk factors and indicators of cognition function in a mouse model of Alzheimer's disease

OBJECTIVE

Obesity, impaired glycemic control, and hepatic steatosis often coexist and are risk factors for developing dementia, and Alzheimer's disease (AD). We hypothesized that a therapeutic agent that improves glycemic control and steatosis may attenuate obesity-associated progression of dementia. We previously identified that adenoviral protein E4orf1 improves glycemic control and reduces hepatic steatosis despite obesity in mice. Here, we determined if this metabolic improvement by E4orf1 will ameliorate cognitive decline in a transgenic mouse model of AD.

METHODS

Fourteen- to twenty-month-old APP/PS1/E4orf1 and APP/PS1 (control) mice were fed a high-fat diet. Cognition was determined by Morris Water Maze (MWM). Systemic glycemic control and metabolic signaling changes in adipose tissue, liver, and brain were determined.

RESULTS

Compared to control, E4orf1 expression significantly improved glucose clearance, reduced endogenous insulin requirement and lowered body-fat, enhanced glucose and lipid metabolism in adipose tissue, and reduced de novo lipogenesis in the liver. In the brain, E4orf1 mice displayed significantly greater expression of genes involved in neurogenesis and amyloid-beta degradation and performed better in MWM testing.

CONCLUSION

This study opens-up the possibility of addressing glycemic control and steatosis for attenuating obesity-related cognitive decline. It also underscores the potential of E4orf1 for the purpose, which needs further investigations.

E4orf1 Prevents Progression of Fatty Liver Disease in Mice on High Fat Diet

Non-alcoholic fatty liver disease (NAFLD) covers a broad spectrum of liver diseases ranging from steatosis to cirrhosis. There are limited data on prevention of hepatic steatosis or its progression to liver disease. Here, we tested if either transgenic (Tg) doxycycline-induced expression in adipose tissue of E4orf1 (E4), an adenoviral protein, or dietary fat restriction attenuated hepatic steatosis or its progression in mice. Twelve to fourteen-week-old TgE4 mice (E4 group) and control mice were exposed to a 60% (Kcal) high fat diet (HFD) for 20 weeks, while another group of mice on HFD for 10 weeks were switched to a chow diet (chow group) for another 10 weeks. Glycemic control was determined at weeks 10 and 20. Tissues were collected for gene and protein analysis at sacrifice. Compared to control, diet reversal significantly reduced body weight in the chow group, whereas E4 expression attenuated weight gain, despite HFD. E4 mice evinced significantly improved glucose clearance, lower endogenous insulin secretion, reduced serum triglycerides, attenuated hepatic steatosis and inflammation. Interestingly, in spite of weight loss and lower liver fat, chow mice showed significant upregulation of hepatic genes involved in lipid metabolism. Despite HFD, E4 prevents hepatic lipid accumulation and progression of hepatic steatosis, while diet reversal maintains hepatic health, but is unable to improve molecular changes.

TRIM24 is an insulin-responsive regulator of P-bodies

Insulin is a potent inducer of mRNA transcription and translation, contributing to metabolic regulation. Insulin has also been suggested to regulate mRNA stability through the processing body (P-body) molecular machinery. However, whether and how insulin regulates mRNA stability via P-bodies is not clear. Here we show that the E3-ligase TRIM24 is a critical factor linking insulin signalling to P-bodies. Upon insulin stimulation, protein kinase B (PKB, also known as Akt) phosphorylates TRIM24 and stimulates its shuttling from the nucleus into the cytoplasm. TRIM24 interacts with several critical components of P-bodies in the cytoplasm, promoting their polyubiquitylation, which consequently stabilises Pparγ mRNA. Inactivation of TRIM24 E3-ligase activity or prevention of its phosphorylation via knockin mutations in mice promotes hepatic Pparγ degradation via P-bodies. Consequently, both knockin mutations alleviate hepatosteatosis in mice fed on a high-fat diet. Our results demonstrate the critical role of TRIM24 in linking insulin signalling to P-bodies and have therapeutic implications for the treatment of hepatosteatosis.

Anti-Obesity and Anti-Hyperglycemic Effects of Meretrix lusoria Protamex Hydrolysate in ob/ob Mice

Meretrix lusoria (M. lusoria) is an economically important shellfish which is widely distributed in South Eastern Asia that contains bioactive peptides, proteins, and enzymes. In the present study, the extracted meat content of M. lusoria was enzymatic hydrolyzed using four different commercial proteases (neutrase, protamex, alcalase, and flavourzyme). Among the enzymatic hydrolysates, M. lusoria protamex hydrolysate (MLPH) fraction with MW ≤ 1 kDa exhibited the highest free radical scavenging ability. The MLPH fraction was further purified and an amino acid sequence (KDLEL, 617.35 Da) was identified by LC-MS/MS analysis. The purpose of this study was to investigate the anti-obesity and anti-hyperglycemic effects of MLPH containing antioxidant peptides using ob/ob mice. Treatment with MLPH for 6 weeks reduced body and organ weight and ameliorated the effects of hepatic steatosis and epididymal fat, including a constructive effect on hepatic and serum marker parameters. Moreover, hepatic antioxidant enzyme activities were upregulated and impaired glucose tolerance was improved in obese control mice. In addition, MLPH treatment markedly suppressed mRNA expression related to lipogenesis and hyperglycemia through activation of AMPK phosphorylation. These findings suggest that MLPH has anti-obesity and anti-hyperglycemic potential and could be effectively applied as a functional food ingredient or pharmaceutical.

E4orf1-induced reduction in endogenous insulin level is independent of pancreas endocrine function

BACKGROUND

Obesity is often associated with hyperinsulinemia due to insulin resistance. In mice models of hyperinsulinemia, adenovirus-derived E4orf1 protein promotes glucose disposal via insulin-independent pathway, and reduces insulin response to glucose load, described as its "Insulin Sparing Action". This is likely because less insulin is needed for disposing glucose in presence of E4orf1, however, there are other potential possibilities. This study determined if E4orf1 reduces insulin response to glucose load because it a) suppresses the ability of pancreatic β-cells to secret insulin, or b) upregulates glucagon production by the pancreas.

METHODS

C57BL/6J wild type (control) and transgenic C57BL/6J (E4orf1) mice that express E4orf1 protein in adipose tissue upon doxycycline feeding, were used. Post-doxycycline feeding, insulin and glucagon secretion in response to glibenclamide or phenylephrine were compared between the two groups. The pancreases were examined for histological changes.

RESULTS

In response to glibenclamide, E4orf1 mice secreted more insulin and exhibited lower blood glucose compared to control (47.4 ± 4.4 vs 27.4 ± 3.7 mg/dl, p < 0.003), but showed no difference in glucagon secretion. Post-phenylephrine injection, no differences were observed between the two groups for glucagon or insulin, except E4orf1 mice had a lower blood glucose rise after 10-min of injection compared to the control (39.7 ± 4.7 vs. 58.3 ± 7.5 mg/dl, p < 0.05). E4orf1 mice had significantly larger pancreatic islets and higher number of islets per mm² tissue area. Neither the size nor the number of islets met the criteria of hypertrophy or hyperplasia.

CONCLUSIONS/INTERPRETATION

E4orf1 retains and may enhance the ability of the pancreases to secret insulin in response to insulin secretagogue. Glucagon does not seem to play a role in the Insulin Sparing Action of E4orf1. Overall, the histology studies support better pancreatic islet health in presence of E4orf1, compared to that in control mice. The "insulin-independent" role of E4orf1 has potential therapeutic implications in addressing hyperinsulinemia in obesity.

White adipocyte-targeted dual gene silencing of FABP4/5 for anti-obesity, anti-inflammation and reversal of insulin resistance: Efficacy and comparison of administration routes

Obesity is a serious health problem with tremendous economic and social consequences, which is associated with metabolic diseases and cancer. Currently available anti-obesity drugs acting in the gastrointestinal tract, or the central nervous system have shown limited efficacy in the reduction of obesity, accompanied by severe side effects. Therefore, a novel therapeutic delivery targeting adipocytes and normalizing excess fat transport and accumulation is necessary to maximize efficacy and reduce side effects for long-term treatment. Fatty acid binding protein 4 (FABP4) is an adipokine that coordinates lipid transport in mature adipocyte and its inhibition in obesity model showed weight loss and normalized insulin response. Reduction of FABP4 level in adipocytes was compensated by fatty acid binding protein 5 (FABP5), which resulted in reduction of recovery of obesity and co-morbidities related to obesity by FABP4 knock-down alone. In this study, we developed a non-viral gene delivery system, sh (FABP4/5)/ATS9R, that silences FABP4 and FABP5 simultaneously with oligopeptide (ATS9R) that can selectively target mature adipocyte. For future clinical application to increase patient compliance, sh (FABP4/5)/ATS9R was administered subcutaneously and intraperitoneally to obese animal model and both routes demonstrated startling dual gene efficacy in visceral adipose tissues. Furthermore, dual gene silencing efficiently alleviated obesity, improved insulin sensitivity and restored hepatic metabolism in high fat diet-induced type 2 diabetes mouse model. Targeted-dual gene silencing of sh (FABP4/5)/ATS9R in adipose tissues demonstrated synergistic effects to overcome obesity and obesity-induced metabolic diseases and beneficial effects against liraglutide, providing a great potential for future translational research.

Antidiabetic E4orf1 protein prevents hepatic steatosis and reduces markers of aging-related cellular damage in high fat fed older mice

INTRODUCTION

Older age is associated with greater prevalence of hyperinsulinemia, type 2 diabetes, and fatty liver disease. These metabolic conditions and aging are bidirectionally linked to mitochondrial dysfunction and telomere attrition. Although effectively addressing these conditions is important for influencing the health and the lifespan, it is particularly challenging in older age. We reported that E4orf1, a protein derived from human adenovirus Ad36, reduces hyperinsulinemia, improves glucose clearance, and protects against hepatic steatosis in younger mice exposed to high fat diet (HFD). Here, we tested if E4orf1 will improve glycemic control, liver fat accumulation, mitochondrial integrity, and reduce telomere attrition in older mice.

RESEARCH DESIGN AND METHODS

We used 9-month-old mice that inducibly expressed E4orf1 in adipose tissue and non-E4orf1 expressing control mice. Mice were maintained on a 60% (kcal) HFD for 20 weeks and glycemic control was determined by intraperitoneal glucose tolerance test at week 20. Following 20 weeks of HF-feeding, mice were sacrificed and liver tissues collected to determine the expression of aging genes using qRT-PCR based RT² Profiler PCR array.

RESULTS

Compared with the control mice, E4orf1 significantly improved glycemic control and reduced hepatic steatosis and fibrosis. Additionally, E4orf1 maintained markers of mitochondrial integrity and telomere attrition.

CONCLUSION

E4orf1 has the potential to improve glycemic control in older mice, and the improvement persists even after longer term exposure. E4orf1 expression also maintains mitochondrial integrity and telomere attrition, thus delaying age-associated diseases. This provides strong evidence for therapeutic utility of E4orf1 in improving age-associated metabolic and cellular changes that occur with aging in humans.

Non-alcoholic fatty liver disease: molecular and cellular interplays of the lipid metabolism in a steatotic liver

INTRODUCTION

Non-alcoholic fatty liver disease (NAFLD) affects ~25% of world population and cases have increased in recent decades. These anomalies have several etiologies; however, obesity and metabolic dysfunctions are the most relevant causes. Despite being considered a public health problem, no effective therapeutic approach to treat NAFLD is available. For that, a deep understanding of metabolic routes that support hepatic diseases is needed.

AREAS COVERED

This review covers aspects of the onset of NAFLD. Thereby, biochemistry routes as well as cellular and metabolic effects of the gut microbiota in body's homeostasis and epigenetics are contextualized.

EXPERT OPINION

Recently, the development of biological sciences has generated innovative knowledge, bringing new insights and perspectives to clarify the systems biology of liver diseases. A detailed comprehension of epigenetics mechanisms will offer possibilities to develop new therapeutic and diagnostic strategies for NAFLD. Different epigenetic processes have been reported that are modulated by the environment such as gut microbiota, suggesting strong interplays between cellular behavior and pathology. Thus, a more complete description of such mechanisms in hepatic diseases will help to clarify how to control the establishment of fatty liver, and precisely describe molecular interplays that potentially control NAFLD.

E4orf1, an Adeno-viral protein, attenuates renal lipid accumulation in high fat fed mice: A novel approach to reduce a key risk factor for chronic kidney disease

Obesity and hyperlipidemia are independent risk factors of chronic kidney disease (CKD). In mice, diet induced obesity accelerates lipogenesis, lipid accumulation, and injury in kidneys. Expression of adenoviral protein, E4orf1, improves glucose clearance and reduces endogenous insulin secretion to glucose challenge in mice. Therefore, in this pilot study, we examined, if enhanced glycemic control in HFD fed E4orf1 transgenic (E4orf1-Tg) mice, will reduce renal lipogenesis and lipid accumulation. In two separate experiments, E4orf1-Tg mice were fed 60% (kcal) high-fat diet (HFD) supplemented with doxycycline for 10-weeks or 20-weeks along with wild-type (C57BL6/J) or E4orf1-non-transgenic (E4orf1-non-Tg) control mice, respectively. Protein expression of Fatty Acid Synthase (FAS) and Acetyl-CoA Carboxylase (ACC), accumulation of triglyceride (TG) along with mRNA levels of lipid metabolism and injury markers were determined in kidneys. Renal expression of FAS and ACC, and TG content was significantly reduced in E4orf1-Tg mice compared to controls. E4orf1-Tg mice show significant increase in genes involved in mitochondrial fatty acid oxidation and oxidative stress compared to wild-type mice after 10-weeks of HFD. However, mice exposed to 20-weeks of HFD, show no difference in gene expression. E4orf1 expression reduces lipid synthesis and accumulation in kidneys despite HFD, which may be due to attenuation of hyperinsulinemia by E4orf1.