Hepatic insulin sensitivity is improved in high-fat diet-fed Park2 knockout mice in association with increased hepatic AMPK activation and reduced steatosis

MiR-181c-5p Regulates Lung Adenocarcinoma Progression via Targeting PRKN

Accumulating evidence indicates that microRNAs (miRNAs) have a vital effect on lung adenocarcinoma. However, the contributions and possible mechanisms of miR-181c-5p to lung adenocarcinoma remain largely unclear. Our objective is to clarify the potential mechanism by which miR-181c-5p regulates lung adenocarcinoma progression. RT-qPCR was performed to determine the levels of miR-181c-5p in lung adenocarcinoma tissues and cells. CCK-8 and Transwell assays were conducted to evaluate the viability, migration, and invasion of H460 cells, respectively. The putative target association between miR-181c-5p and the Parkin gene (PRKN) was predicted using miRDB and confirmed by dual-luciferase reporter assay. MiR-181c-5p expression was found to be up-regulated in both lung adenocarcinoma tissues and cells. Suppression of miR-181c-5p resulted in the inhibition of viability, migration, and invasion in lung adenocarcinoma cells. PRKN level was negatively related to miR-181c-5p expression and mediated with the miR-181c-5p's functions on lung adenocarcinoma progression. MiR-181c-5p regulates lung adenocarcinoma progression via targeting PRKN, indicating miR-181c-5p is expected to be a diagnostic and predictive marker for lung adenocarcinoma, providing new insights into the development of treatment strategies for lung adenocarcinoma.

G-protein coupled receptor 19 (GPR19) knockout mice display sex-dependent metabolic dysfunction

G-protein coupled receptors (GPCRs) mediate signal transduction from the cellular surface to intracellular metabolic pathways. While the function of many GPCRs has been delineated previously, a significant number require further characterization to elucidate their cellular function. G-protein coupled receptor 19 (GPR19) is a poorly characterized class A GPCR which has been implicated in the regulation of circadian rhythm, tumor metastasis, and mitochondrial homeostasis. In this report, we use a novel knockout (KO) mouse model to examine the role of GPR19 in whole-body metabolic regulation. We show that loss of GPR19 promotes increased energy expenditure and decreased activity in both male and female mice. However, only male GPR19 KO mice display glucose intolerance in response to a high fat diet. Loss of GPR19 expression in male mice, but not female mice, resulted in diet-induced hepatomegaly, which was associated with decreased expression of key fatty acid oxidation genes in male GPR19 KO livers. Overall, our data suggest that loss of GPR19 impacts whole-body energy metabolism in diet-induced obese mice in a sex-dependent manner.

Dysregulation of Lipid and Glucose Homeostasis in Hepatocyte-Specific SLC25A34 Knockout Mice

Nonalcoholic fatty liver disease (NAFLD) is an epidemic affecting 30% of the US population. It is characterized by insulin resistance, and by defective lipid metabolism and mitochondrial dysfunction in the liver. SLC25A34 is a major repressive target of miR-122, a miR that has a central role in NAFLD and liver cancer. However, little is known about the function of SLC25A34. To investigate SLC25A34 in vitro, mitochondrial respiration and bioenergetics were examined using hepatocytes depleted of Slc25a34 or overexpressing Slc25a34. To test the function of SLC25A34 in vivo, a hepatocyte-specific knockout mouse was generated, and loss of SLC25A34 was assessed in mice maintained on a chow diet and a fast-food diet (FFD), a model for NAFLD. Hepatocytes depleted of Slc25a34 displayed increased mitochondrial biogenesis, lipid synthesis, and ADP/ATP ratio; Slc25a34 overexpression had the opposite effect. In the knockout model on chow diet, SLC25A34 loss modestly affected liver function (altered glucose metabolism was the most pronounced defect). RNA-sequencing revealed changes in metabolic processes, especially fatty acid metabolism. After 2 months on FFD, knockouts had a more severe phenotype, with increased lipid content and impaired glucose tolerance, which was attenuated after longer FFD feeding (6 months). This work thus presents a novel model for studying SLC25A34 in vivo in which SLC25A34 plays a role in mitochondrial respiration and bioenergetics during NAFLD.

Dietary Antioxidant Anthocyanins Mitigate Type II Diabetes through Improving the Disorder of Glycometabolism and Insulin Resistance

Insulin resistance (IR) is one of the pathological reasons for type II diabetes mellitus (T2DM). Therefore, it is important to prevent the body from developing T2DM by improving IR and maintaining glucose homeostasis. Anthocyanins (ACNs) are water-soluble pigments and are widely distributed in natural products. This article summarizes research on the bioavailability and metabolism of ACNs. Moreover, we further elaborate on how ACNs reduce IR and hyperglycemia during the development of T2DM based on studies over the past 20 years. Many studies have demonstrated that ACNs are small molecules that target the pancreatic, liver, muscle, and adipose tissues, preventing IR and hyperglycemia. However, the molecular mechanisms are still unclear. Therefore, we envision whether the molecular mechanism of reducing T2DM by ACNs could be more deeply investigated.

Sodium nitroprusside protects HFD induced gut dysfunction via activating AMPKα/SIRT1 signaling

Background

Activation of Adenosine 5′-monophosphate-activated protein kinase/Sirtuin1 (AMPK/SIRT1) exerts an effect in alleviating obesity and gut damage. Sodium nitroprusside (SNP), a nitric oxide (NO) donor, has been reported to activate AMPK. This study was to investigate the effect of SNP on HFD induced gut dysfunction and the mechanism.

Methods

SNP was applied on lipopolysaccharide (LPS) stimulated Caco-2 cell monolayers which mimicked intestinal epithelial barrier dysfunction and HFD-fed mice which were complicated by gut dysfunction. Then AMPKα/SIRT1 pathway and gut barrier indicators were investigated.

Results

SNP rescued the loss of tight junction proteins ZO-1 and occludin, the inhibition of AMPKα/SIRT1 in LPS stimulated Caco-2 cell monolayers, and the effects were not shown when AMPKa1 was knocked-down by siRNA. SNP also alleviated HFD induced obesity and gut dysfunction in mice, as indicated by the decreasing of intestinal permeability, the increasing expression of ZO-1 and occludin, the decreasing levels of pro-inflammatory cytokine IL-6, and the repairing of gut microbiota dysbiosis. These effects were complicated by the increased colonic NO content and the activated AMPKα/SIRT1 signaling.

Conclusions

The results may imply that SNP, as a NO donor, alleviates HFD induced gut dysfunction probably by activating the AMPKα/SIRT1 signaling pathway.

Comparing prophylactic effect of exercise and metformin on cognitive brain functions in rats with type 3 diabetes mellitus

Introduction

Type 2 diabetes mellitus (DM) and Alzheimer's disease (AD) are two major medical conditions that constitute a significant financial burden on most healthcare systems. Due to AD sharing "insulin resistance" mechanistic features with DM, some scientists have proposed "type 3 DM" terminology for it. This study aims to compare the prophylactic effect of exercise and metformin on cognitive brain functions in rats with type 3 DM.

Material and methods

Two groups of rats were included in the study: the control group (n = 15) and the streptozotocin-induced type 2 diabetic group (n = 45). The diabetic group was subdivided into three equal subgroups: a sedentary non-treated diabetic group, an exercised group, and a metformin-treated group. We estimated step-down avoidance task latency, serum glucose, insulin, free fatty acids (FFA), cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and triglycerides (TG), brain Aβ-42 and glucose, histological changes by toluidine blue, and immunohistochemistry for brain Aβ-42 and tau-positive cells.

Results

Serum glucose, FFA, TG, cholesterol, LDL, brain Aβ-42, brain glucose, the number of hippocampal dark and degenerated cells, and brain Aβ-42 and tau-positive cells, were all significantly lower. In contrast, serum insulin and HDL, the number of hippocampal granular cells, and latency of the step-down avoidance task were significantly higher in exercised and metformin-treated groups compared to the diabetic group. There were significantly higher values of serum insulin and brain/plasma glucose ratio and number of brain tau-positive cells in the metformin-treated group than in the exercised group.

Conclusions

We can conclude that exercise can be as effective as metformin regarding prophylaxis against the deleterious effects of type 3 DM on cognitive brain functions.

Hepatic insulin sensitivity is improved in high-fat diet-fed Park2 knockout mice in association with increased hepatic AMPK activation and reduced steatosis

Park2 is an E3 ubiquitin ligase known for its role in mitochondrial quality control via the mitophagy pathway. Park2 KO mice are protected from diet‐induced obesity and hepatic insulin sensitivity is improved in high‐fat diet (HFD)‐fed Park2 KO mice even under body weight‐matched conditions. In order to better understand the cellular mechanism by which Park2 KO mice are protected from diet‐induced hepatic insulin resistance, we determined changes in multiple pathways commonly associated with the pathogenesis of insulin resistance, namely levels of bioactive lipid species, activation of the endoplasmic reticulum (ER) stress response and changes in cytokine levels and signaling. We report for the first time that whole‐body insulin sensitivity is unchanged in regular chow (RC)‐fed Park2 KO mice, and that liver diacylglycerol levels are reduced and very‐long‐chain ceramides are increased in Park2 KO mice fed HFD for 1 week. Hepatic transcriptional markers of the ER stress response were reduced and plasma tumor necrosis factor‐α (TNFα), interleukin‐6 and −10 (IL6, IL10) were significantly increased in HFD‐fed Park2 KO mice; however, there were no detectable differences in hepatic inflammatory signaling pathways between groups. Interestingly, hepatic adenylate charge was reduced in HFD‐fed Park2 KO liver and was associated increased activation of AMPK. These data suggest that negative energy balance that contributed to protection from obesity during chronic HFD manifested at the level of the hepatocyte during short‐term HFD feeding and contributed to the improved hepatic insulin sensitivity.

Liver-specific Prkn knockout mice are more susceptible to diet-induced hepatic steatosis and insulin resistance

Objective

PARKIN is an E3 ubiquitin ligase that regulates mitochondrial quality control through a process called mitophagy. Recent human and rodent studies suggest that loss of hepatic mitophagy may occur during the pathogenesis of obesity-associated fatty liver and contribute to changes in mitochondrial metabolism associated with this disease. Whole-body Prkn knockout mice are paradoxically protected against diet-induced hepatic steatosis; however, liver-specific effects of Prkn deficiency cannot be discerned in this model due to pleotropic effects of germline Prkn deletion on energy balance and subsequent protection against diet-induced obesity. We therefore generated the first liver-specific Prkn knockout mouse strain (LKO) to directly address the role of hepatic Prkn.

Methods

Littermate control (WT) and LKO mice were fed regular chow (RC) or high-fat diet (HFD) and changes in body weight and composition were measured over time. Liver mitochondrial content was assessed using multiple, complementary techniques, and mitochondrial respiratory capacity was assessed using Oroboros O₂K platform. Liver fat was measured biochemically and assessed histologically, while global changes in hepatic gene expression were measured by RNA-seq. Whole-body and tissue-specific insulin resistance were assessed by hyperinsulinemic-euglycemic clamp with isotopic tracers.

Results

Liver-specific deletion of Prkn had no effect on body weight or adiposity during RC or HFD feeding; however, hepatic steatosis was increased by 45% in HFD-fed LKO compared with WT mice (P < 0.05). While there were no differences in mitochondrial content between genotypes on either diet, mitochondrial respiratory capacity and efficiency in the liver were significantly reduced in LKO mice. Gene enrichment analyses from liver RNA-seq results suggested significant changes in pathways related to lipid metabolism and fibrosis in HFD-fed Prkn knockout mice. Finally, whole-body insulin sensitivity was reduced by 35% in HFD-fed LKO mice (P < 0.05), which was primarily due to increased hepatic insulin resistance (60% of whole-body effect; P = 0.11).

Conclusions

These data demonstrate that PARKIN contributes to mitochondrial homeostasis in the liver and plays a protective role against the pathogenesis of hepatic steatosis and insulin resistance.

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Mitochondrial respiratory capacity is reduced in liver-specific Prkn knockout mice.

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Liver-specific Prkn knockout mice develop more severe steatosis during high-fat diet feeding.

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Pathogenesis of NAFLD, including insulin resistance and markers of fibrosis, is enhanced in liver-specific Prkn knockout mice.

Mitophagy in the Pathogenesis of Liver Diseases

Autophagy is a catabolic process involving vacuolar sequestration of intracellular components and their targeting to lysosomes for degradation, thus supporting nutrient recycling and energy regeneration. Accumulating evidence indicates that in addition to being a bulk, nonselective degradation mechanism, autophagy may selectively eliminate damaged mitochondria to promote mitochondrial turnover, a process termed “mitophagy”. Mitophagy sequesters dysfunctional mitochondria via ubiquitination and cargo receptor recognition and has emerged as an important event in the regulation of liver physiology. Recent studies have shown that mitophagy may participate in the pathogenesis of various liver diseases, such as liver injury, liver steatosis/fatty liver disease, hepatocellular carcinoma, viral hepatitis, and hepatic fibrosis. This review summarizes the current knowledge on the molecular regulations and functions of mitophagy in liver physiology and the roles of mitophagy in the development of liver-related diseases. Furthermore, the therapeutic implications of targeting hepatic mitophagy to design a new strategy to cure liver diseases are discussed.