Involvement of oxygen-regulated protein 150 in AMP-activated protein kinase-mediated alleviation of lipid-induced endoplasmic reticulum stress

HYOU1 promotes cell proliferation, migration, and invasion via the PI3K/AKT/FOXO1 feedback loop in bladder cancer

BACKGROUND

Hypoxia up-regulated 1 (HYOU1) was identified as a proto-oncogene and involved in tumorigenesis and progression in several cancer. Nonetheless, the biological function and mechanism of HYOU1 in bladder cancer (BCa) remian unclear.

METHODS

The HYOU1 level in BCa tissues and cells was examined using RT-qPCR and western blot methods. The relationship between HYOU1 expression and clinicopathologic characteristics of BCa was analyzed. The biological role of HYOU1 on BCa cell proliferation, apoptosis, migration and invasion were analyzed via counting kit-8 (CCK-8), flow cytometry, wound healing and Transwell assays, respectively. The association between HYOU1 and the PI3K/AKT/Forkhead box O1 (FOXO1) signalling was assessed via western blot assay, meanwhile the the association of FOXO1 with HYOU1 was also investigated.

RESULTS

HYOU1 was up-regulated in BCa tissues and cell lines, and the high level of HYOU1 was associated with bladder cancer histological grade and pathologic stage. Moreover, patients with high expression of HYOU1 showed poor overall survival from Kaplan-Meier Plotter. HYOU1 depletion impeded cell proliferation, migration and invasion, and induced cell apoptosis, while HYOU1 overexpression promoted cell proliferation, migration and invasion. Mechanically, our results showed that HYOU1 knockdown repressed PI3K/AKT/FOXO1 pathway and HYOU1 was negative regulated by FOXO1 in BCa. Significantly, we confirmed that the HYOU1/PI3K-AKT/FOXO1 negative feedback loop was involved in BCa cell proliferation, migration and invasion.

CONCLUSION

These findings revealed that HYOU1 acted as a pro-oncogene on BCa progression, and it will be a possible target for BCa treatment.

The dynamic effect of genetic variation on the in vivo ER stress transcriptional response in different tissues

The genetic regulation of gene expression varies greatly across tissue-type and individuals and can be strongly influenced by the environment. Many variants, under healthy control conditions, may be silent or even have the opposite effect under diseased stress conditions. This study uses an in vivo mouse model to investigate how the effect of genetic variation changes with cellular stress across different tissues. Endoplasmic reticulum stress occurs when misfolded proteins accumulate in the endoplasmic reticulum. This triggers the unfolded protein response, a large transcriptional response which attempts to restore homeostasis. This transcriptional response, despite being a conserved, basic cellular process, is highly variable across different genetic backgrounds, making it an ideal system to study the dynamic effects of genetic variation. In this study, we sought to better understand how genetic variation alters expression across tissues, in the presence and absence of endoplasmic reticulum stress. The use of different mouse strains and their F1s allow us to also identify context-specific cis- and trans- regulatory variation underlying variable transcriptional responses. We found hundreds of genes that respond to endoplasmic reticulum stress in a tissue- and/or genotype-dependent manner. The majority of the regulatory effects we identified were acting in cis-, which in turn, contribute to the variable endoplasmic reticulum stress- and tissue-specific transcriptional response. This study demonstrates the need for incorporating environmental stressors across multiple different tissues in future studies to better elucidate the effect of any particular genetic factor in basic biological pathways, like the endoplasmic reticulum stress response.

The PPARβ/δ-AMPK Connection in the Treatment of Insulin Resistance

The current treatment options for type 2 diabetes mellitus do not adequately control the disease in many patients. Consequently, there is a need for new drugs to prevent and treat type 2 diabetes mellitus. Among the new potential pharmacological strategies, activators of peroxisome proliferator-activated receptor (PPAR)β/δ show promise. Remarkably, most of the antidiabetic effects of PPARβ/δ agonists involve AMP-activated protein kinase (AMPK) activation. This review summarizes the recent mechanistic insights into the antidiabetic effects of the PPARβ/δ-AMPK pathway, including the upregulation of glucose uptake, muscle remodeling, enhanced fatty acid oxidation, and autophagy, as well as the inhibition of endoplasmic reticulum stress and inflammation. A better understanding of the mechanisms underlying the effects resulting from the PPARβ/δ-AMPK pathway may provide the basis for the development of new therapies in the prevention and treatment of insulin resistance and type 2 diabetes mellitus.

Heat stress promotes lipid accumulation by inhibiting the AMPK-PGC-1α signaling pathway in 3T3-L1 preadipocytes

Heat stress (HS) results in health problems in animals. This study was conducted to investigate the effect and the underlying mechanism of HS on the proliferation and differentiation process of 3T3-L1 preadipocytes. 3T3-L1 preadipocytes were treated at 37 °C or 41.5 °C. HS up-regulated the mRNA and protein expression level of heat shock protein 70 (HSP70). Furthermore, the proliferation of 3T3-L1 preadipocytes were significantly inhibited after HS treatment for 2 days. A large number of accumulated lipid droplets were observed under the microscope after HS treatment for 8 days. Notably, the result of oil red O staining showed that the number of lipid droplets increased significantly and the differentiation ability of the cells was enhanced after HS. Moreover, after 2 and 8 d of differentiation, HS increased the transcription levels of fat synthesis genes including peroxisome proliferators activated receptor γ (PPARγ), fatty acid binding protein 2 (AP2), fatty acid synthase (FAS) and CCAAT enhancer binding protein α (CEBPα) genes, while decreasing the transcription levels of lipid decomposition genes including ATGL and HSL genes. In addition, HS reduced the expression of AMPK and PGC-1α, as well as the dephosphorylation of AMPK. 5-Aminoimidazole-4-carboxamide ribonucleotide (AICAR) can eliminate HS induced lipogenesis by activating AMPK. These results indicated that HS inhibited the proliferation of 3T3-L1 preadipocytes and promoted lipid accumulation by inhibiting the AMPK-PGC-1α signaling pathway in 3T3-L1 preadipocytes. This work lays a theoretical foundation for improving the effect of HS on meat quality of livestock and provides a new direction for the prevention of obesity caused by HS.

Effects of Edible Insect Tenebrio molitor Larva Fermentation Extract as a Substitute Protein on Hepatosteatogenesis and Proteomic Changes in Obese Mice Induced by High-Fat Diet

Mealworms (Tenebrio molitor larva) are an edible insect and a protein-rich food; however, research on mealworms as a substitute protein is insufficient. In this study, mealworm fermentation extract (TMP) was assessed as a replacement for soy protein (SP) in a control diet (CON) or a high-fat diet (HFD) of mice for 12 weeks. TMP substitution reduced body weight, body weight gain, body fat mass (perirenal and mesenteric), fat size, glucose intolerance, and insulin resistance compared to the HFD-SP group. TMP alleviated hepatic steatosis (lipid contents and lipid droplets) in high-fat-fed mice and down-regulated the PPARγ, CD36, and DGAT2 gene levels. Proteomic analysis showed that a HFD for 12 weeks up-regulated 20 proteins and down-regulated 17 proteins in mice fed SP. On the other hand, TMP reversed the protein profiles. TMP significantly down-regulated KHK, GLO1, ATP5H, SOD, and DDAH1 and up-regulated DLD, Mup1, CPS1, Ces3b, PDI, and HYOU1 compared to the HFD-SP group. These proteins are involved in the glucose, lipid, and amino acid metabolism, as well as in oxidative stress and endoplasmic reticulum stress. Thus, substituting SP for TMP helped improve HFD-induced obesity, steatosis, and insulin resistance in mice. These results suggest that TMP is a potential substitute for commonly used protein sources.

Effects of fenofibrate and its combination with lovastatin on the expression of genes involved in skeletal muscle atrophy, including FoxO1 and its targets

Fibrates and statins have been widely used to reduce triglyceride and cholesterol levels, respectively. Besides its lipid-lowering effect, the side effect of muscle atrophy after fibrate administration to humans has been demonstrated in some studies. Combination therapy with fibrates and statins also increases the risk of rhabdomyolysis. FoxO1, a member of the FoxO forkhead type transcription factor family, is markedly upregulated in skeletal muscle in energy-deprived states and induces muscle atrophy via the expression of E3-ubiquitine ligases. In this study, we investigated the changes in FoxO1 and its targets in murine skeletal muscle with fenofibrate treatment. High doses of fenofibrate (greater than 0.5% (wt/wt)) over one week increased the expression of FoxO1 and its targets in the skeletal muscles of mice and decreased skeletal muscle weight. These fenofibrate-induced changes were diminished in the PPARα knockout mice. When the effect of combination treatment with fenofibrate and lovastatin was investigated, a significant increase in FoxO1 protein levels was observed despite the lack of deterioration of muscle atrophy. Collectively, our findings suggest that a high dose of fenofibrate over one week causes skeletal muscle atrophy via enhancement of FoxO1, and combination treatment with fenofibrate and lovastatin may further increase FoxO1 protein level.

Endogenous metabolite, kynurenic acid, attenuates nonalcoholic fatty liver disease via AMPK/autophagy- and AMPK/ORP150-mediated signaling

Endoplasmic reticulum (ER) stress plays a causative role in the development of nonalcoholic fatty liver disease (NAFLD). Kynurenic acid (KA) is a tryptophan metabolite that has been shown to exert anti-inflammatory effects in macrophages and endothelial cells. However, the role of KA in ER stress-associated development of NAFLD has not been fully explored. In the current study, we observed decreased KA levels in the serum of obese subjects. Treated hepatocytes with KA attenuated palmitate-induced lipid accumulation and downregulated lipogenesis-associated genes as well as ER stress markers in a dose-dependent manner. Furthermore, KA augmented AMP-activated protein kinase (AMPK) phosphorylation, oxygen-regulated protein 150 (ORP150) expression, and autophagy markers. The small interfering RNA-mediated suppression of AMPK and ORP150, or 3-methyladenine also abrogated the effects of KA on ER stress and lipid accumulation in hepatocytes. In accordance with in vitro observations, KA administration to mice fed a high-fat diet ameliorated hepatic lipid accumulation and decreased the expression of lipogenic genes as well as ER stress. Moreover, KA treatment increased hepatic AMPK phosphorylation, ORP150 expression, and autophagy related markers in mouse livers. Knockdown of AMPK using in vivo transfection mitigated the effects of KA on hepatic steatosis and ER stress as well as autophagy and ORP150 expression. These results suggest that KA ameliorates hepatic steatosis via the AMPK/autophagy- and AMPK/ORP150-mediated suppression of ER stress. In sum, KA might be used as a promising therapeutic agent for treatment of NAFLD.

Resveratrol Alleviates Endoplasmic Reticulum Stress-Associated Hepatic Steatosis and Injury in Mice Challenged with Tunicamycin

SCOPE

Endoplasmic reticulum (ER) stress is widely recognized as a critical factor linked to lipid metabolic disorders in nonalcoholic fatty liver disease. However, its pathogenesis remains elusive, and therapeutic options are limited. This study investigates the potential of resveratrol (RSV) to alleviate hepatic steatosis and injury in a tunicamycin (TM)-induced murine ER stress model and provides detailed evidence.

METHODS AND RESULTS

Male C57BL/6J mice were orally administered either RSV or vehicle for 2 weeks before the TM challenge. Results indicated that TM induced ER morphological damage and severe unfolded protein reaction (UPR), accompanied by increases in lipid accumulation, oxidative damage, and inflammatory response. Administering RSV decreased the expression of ER stress markers, partially normalized the active levels of UPR sensors, and facilitated sirtuin 1 activity in the liver under ER stress. Notably, the TM-induced hepatic steatosis was also alleviated by RSV, possibly by regulating the expression pattern of genes involving lipid oxidation and delivery. Consistently, RSV attenuated the TM-induced increases in lipid peroxidation, hepatocyte apoptosis, and the overactivation of inflammatory signals.

CONCLUSION

RSV may have an auxiliary therapeutic potential to prevent the development of steatosis and its progression to steatohepatitis in the liver by alleviating severe ER stress.

Bisphenol-A exposure worsens hepatic steatosis in ovariectomized mice fed on a high-fat diet: Role of endoplasmic reticulum stress and fibrogenic pathways

AIMS

Bisphenol (BP)-A exposure can impair glucose and lipid metabolism. However, it is unclear whether this endocrine disruptor (ED) modulates these processes in postmenopause, a period with organic changes that increase the risk for metabolic diseases. Herein, we evaluated the effects of BPA exposure on adiposity, glucose homeostasis and hepatic steatosis in ovariectomized (OVX) mice fed on a high-fat diet (HFD).

MAIN METHODS

Adult Swiss female mice were OVX and submitted to a normolipidic diet or HFD and drinking water without [control (OVX CTL) and OVX HFD groups, respectively] or with 1 μg/mL BPA (OVX CBPA and OVX HBPA groups, respectively), for 3 months.

KEY FINDINGS

OVX HFD females displayed increased adiposity, glucose intolerance, insulin resistance and moderate hepatic steatosis. This effect was associated with a high hepatic expression of genes involved in lipogenesis (Srebf1 and Scd1), β-oxidation (Cpt1a) and endoplasmic reticulum (ER) stress (Hspa5 and Hyou1). BPA did not alter adiposity or glucose homeostasis disruptions induced by HFD. However, this ED triggered severe steatosis, exacerbating hepatic fat and collagen depositions in OVX HBPA, in association with a reduction in Mttp mRNA, and up-regulation of genes involved in β-oxidation (Acox1 and Acadvl), mitochondrial uncoupling (Ucp2), ER stress (Hyou1 and Atf6) and chronic liver injury (Tgfb1and Casp8). Furthermore, BPA caused mild steatosis in OVX CBPA females, increasing the hepatic total lipids and mRNAs for Srebf1, Scd1, Hspa5, Hyou1 and Atf6.

SIGNIFICANCE

BPA aggravated hepatic steatosis in OVX mice. Especially when combined with a HFD, BPA caused NAFLD progression, which was partly mediated by chronic ER stress and the TGF-β1 pathway.

Decreased Metabolic Flexibility in Skeletal Muscle of Rat Fed with a High-Fat Diet Is Recovered by Individual CLA Isomer Supplementation via Converging Protective Mechanisms

Energy balance, mitochondrial dysfunction, obesity, and insulin resistance are disrupted by metabolic inflexibility while therapeutic interventions are associated with improved glucose/lipid metabolism in skeletal muscle. Conjugated linoleic acid mixture (CLA) exhibited anti-obesity and anti-diabetic effects; however, the modulatory ability of its isomers (cis9, trans11, C9; trans10, cis12, C10) on the metabolic flexibility in skeletal muscle remains to be demonstrated. Metabolic inflexibility was induced in rat by four weeks of feeding with a high-fat diet (HFD). At the end of this period, the beneficial effects of C9 or C10 on body lipid content, energy expenditure, pro-inflammatory cytokines, glucose metabolism, and mitochondrial efficiency were examined. Moreover, oxidative stress markers, fatty acids, palmitoyletanolamide (PEA), and oleyletanolamide (OEA) contents along with peroxisome proliferator-activated receptors-alpha (PPARα), AKT, and adenosine monophosphate-activated protein kinase (AMPK) expression were evaluated in skeletal muscle to investigate the underlying biochemical mechanisms. The presented results indicate that C9 intake reduced mitochondrial efficiency and oxidative stress and increased PEA and OEA levels more efficiently than C10 while the anti-inflammatory activity of C10, and its regulatory efficacy on glucose homeostasis are associated with modulation of the PPARα/AMPK/pAKT signaling pathway. Our results support the idea that the dissimilar efficacy of C9 and C10 against the HFD-induced metabolic inflexibility may be consequential to their ability to activate different molecular pathways.

SIRT1 attenuates endoplasmic reticulum stress and apoptosis in rat models of COPD

The present study aimed to investigate the protective role of sirtuin 1 (SIRT1) and oxygen regulated protein 150 (ORP150) in a rat COPD model by inducing changes in ER stress and apoptosis. We separated 48 Sprague Dawley (SD) rats into four groups randomly: the control group, resveratrol group, COPD group and the resveratrol intervention group. Rats were challenged with cigarette smoke and lipopolysaccharide with resveratrol (a selective activator of SIRT1). The lung functions of the rats were measured and recorded. The expression levels of SIRT1 and ORP150 in lung tissues were examined by western blot and RTq PCR. The expression levels of the ER stress apoptosis-associated protein were determined .The apoptotic level of lung tissues was analyzed. The results suggest that SIRT1 attenuated apoptosis and ER stress in the lung tissues of rats with COPD. During this process, a positive correlation was identified between SIRT1 and ORP150.

The endoplasmic reticulum chaperone PfGRP170 is essential for asexual development and is linked to stress response in malaria parasites

The vast majority of malaria mortality is attributed to one parasite species: Plasmodium falciparum. Asexual replication of the parasite within the red blood cell is responsible for the pathology of the disease. In Plasmodium, the endoplasmic reticulum (ER) is a central hub for protein folding and trafficking as well as stress response pathways. In this study, we tested the role of an uncharacterised ER protein, PfGRP170, in regulating these key functions by generating conditional mutants. Our data show that PfGRP170 localises to the ER and is essential for asexual growth, specifically required for proper development of schizonts. PfGRP170 is essential for surviving heat shock, suggesting a critical role in cellular stress response. The data demonstrate that PfGRP170 interacts with the Plasmodium orthologue of the ER chaperone, BiP. Finally, we found that loss of PfGRP170 function leads to the activation of the Plasmodium eIF2α kinase, PK4, suggesting a specific role for this protein in this parasite stress response pathway.

Understanding the role of glucose regulated protein 170 (GRP170) as a nucleotide exchange factor through molecular simulations

Glucose Regulated Protein 170 (GRP170), also called Oxygen Regulated Protein 150 (ORP150), is a major molecular chaperone resident in the endoplasmic reticulum (ER). It belongs to the heat shock protein (HSP70) super family and can be induced by conditions such as hypoxia, ischemia and interferences in calcium homeostasis. It was recently reported that GRP170 may act as a nucleotide exchange factor (NEF) for GRP78 or binding immunoglobulin protein (BiP), and the ER canonical HSP70. However, little is known about the mechanism underlying its NEF activity. In this study, two homology models of GRP170 were constructed based on the X-ray crystal structures of ADP and ATP bound HSP110, a cytosolic homolog of GRP170, in order to characterize the differences in the binding modes of both ligands. It was observed that the differences in the binding modes of ADP and ATP led to a conformation change in the substrate binding domain which could potentially influence the binding of its substrates such as BiP. Our findings help understand the effect of nucleotide binding on the function of this chaperone protein as a NEF as well as the structural differences between GRP170 and its family members.

AMPK alleviates endoplasmic reticulum stress by inducing the ER-chaperone ORP150 via FOXO1 to protect human bronchial cells from apoptosis

Chronic obstructive pulmonary disease (COPD), is characterized by inflammation of airways accompanied by a progressive destruction of lung parenchyma. This process is initiated in most cases by cigarette smoking. In this study we investigated the role of AMP activated protein kinase (AMPK) in cigarette smoke extract (CSE)-induced airway epithelial cell apoptosis as a consequence of endoplasmic reticulum stress (ER stress). Exposure of human bronchial epithelial cells (HBEpC) to CSE resulted in apoptosis as detected using Annexin V-PI flow cytometry. However, co-treatment with N1-(β-d-ribofuranosyl)-5-aminoimidazole-4-carboxamide (AICAR), a pharmacological activator of AMPK, significantly increased cell protection against ER stress-induced apoptosis by upregulating the 150 kDa oxygen-regulated protein (ORP150), which functions as an ER-associated chaperone, with concomitant elevation of FOXO1, a critical transcription factor regulating ORP150 expression. Lentiviral silencing of AMPK or FOXO1 using short hairpin (sh) RNA resulted in a significant decrease of ORP150 and an elevation of CCAAT/enhancer-binding protein-homologous protein (CHOP) resulting in ER stress and apoptosis of HBEpC. Together, our results strongly suggest that AMPK can activate ORP150 through FOXO1 pathway and confer protection against ER stress-induced apoptosis of airway epithelial cells following exposure to CSE. Thus, AMPK may serve as a likely therapeutic target for clinical and sub-clinical interventions in COPD.

Astragaloside IV attenuates free fatty acid-induced ER stress and lipid accumulation in hepatocytes via AMPK activation

Although the pathogenesis of non-alcoholic fatty liver disease (NAFLD) is not completely understood, the increased influx of free fatty acids (FFAs) into the liver and the FFA-induced hepatic endoplasmic reticulum (ER) stress are two crucial pathogenic processes in the initiation and development of NAFLD. In this study we investigated the effects of astragaloside IV (AS-IV), a bioactive compound purified from Astragali Radix, on FFA-induced lipid accumulation in hepatocytes and elucidated the underlying mechanisms. Human HepG2 cells and primary murine hepatocytes were exposed to FFAs (1 mmol/L, oleate/palmitate, 2:1 ratio) with or without AS-IV for 24 h. Exposure to FFAs induced marked lipid accumulation in hepatocytes, whereas co-treatment with AS-IV (100 μg/mL) significantly attenuated this phenomenon. Notably, AS-IV (50-200 μg/mL) concentration-dependently enhanced the phosphorylation of AMPK, acetyl-CoA carboxylase (ACC) and SREBP-1c, inhibited the accumulation and nuclear translocation of mature SREBP-1 and subsequently decreased the mRNA levels of lipogenic genes including acc1, fas and scd1. AS-IV treatment also concentration-dependently attenuated FFA-induced hepatic ER stress evidenced by the reduction of the key markers, GRP78, CHOP and p-PERK. Pretreated the cells with the AMPK inhibitor compound C (20 μmol/L) greatly diminished these beneficial effects of AS-IV. Our results demonstrate that AS-IV attenuates FFA-induced ER stress and lipid accumulation in an AMPK-dependent manner in hepatocytes, which supports its use as promising therapeutics for hepatic steatosis.

Effects of the new thiazolidine derivative LPSF/GQ-02 on hepatic lipid metabolism pathways in non-alcoholic fatty liver disease (NAFLD)

Non-alcoholic fatty liver disease (NAFLD) is considered the most common manifestation of metabolic syndrome. One of its most important features is the accumulation of triglycerides in the hepatocyte cells. Thiazolidinediones (TZDs) act as insulin sensitizers and are used to treat patients with type 2 diabetes and other conditions that are resistant to insulin, such as hepatic steatosis. Controversially, TZDs are also associated with the development of cardiovascular events and liver problems. For this reason, new therapeutic strategies are necessary to improve liver function in patients with chronic liver diseases. The aim of the present study was to evaluate the effects of LPSF/GQ-02 on the liver lipid metabolism in a murine model of NAFLD. Eighty male LDLR-/- mice were divided into 3 groups: 1-fed with a high-fat diet (HFD); 2-HFD+Pioglitazone (20mg/kg/day); 3-HFD+LPSF/GQ-02 (30mg/kg/day). The experiments lasted 12 weeks and drugs were administered daily by gavage in the final four weeks. The liver was processed for optical microscopy, Oil Red O, immunohistochemistry, immunofluorescence and western blot analysis. LPSF/GQ-02 effectively decreased fat accumulation, increased the hepatic levels of p-AMPK, FoxO1, ATGL, p-ACC and PPARα, and reduced the expression of LXRα, SREBP-1c and ACC. These results suggest that LPSF/GQ-02 acts directly on the hepatic lipid metabolism through the activation of the PPAR-α/AMPK/FoxO1/ATGL lipolytic pathway, and the inhibition of the AMPK/LXR/SREBP-1c/ACC/FAS lipogenic pathway.

Unfolding the Role of Large Heat Shock Proteins: New Insights and Therapeutic Implications

Heat shock proteins (HSPs) of eukaryotes are evolutionarily conserved molecules present in all the major intracellular organelles. They mainly function as molecular chaperones and participate in maintenance of protein homeostasis in physiological state and under stressful conditions. Despite their relative abundance, the large HSPs, i.e., Hsp110 and glucose-regulated protein 170 (Grp170), have received less attention compared to other conventional HSPs. These proteins are distantly related to the Hsp70 and belong to Hsp70 superfamily. Increased sizes of Hsp110 and Grp170, due to the presence of a loop structure, result in their exceptional capability in binding to polypeptide substrates or non-protein ligands, such as pathogen-associated molecules. These interactions that occur in the extracellular environment during tissue injury or microbial infection may lead to amplification of an immune response engaging both innate and adaptive immune components. Here, we review the current advances in understanding these large HSPs as molecular chaperones in proteostasis control and immune modulation as well as their therapeutic implications in treatment of cancer and neurodegeneration. Given their unique immunoregulatory activities, we also discuss the emerging evidence of their potential involvement in inflammatory and immune-related diseases.

Polyunsaturated Fatty Acids Attenuate Diet Induced Obesity and Insulin Resistance, Modulating Mitochondrial Respiratory Uncoupling in Rat Skeletal Muscle

Objectives

Omega (ω)-3 polyunsaturated fatty acids (PUFA) are dietary compounds able to attenuate insulin resistance. Anyway, the precise actions of ω-3PUFAs in skeletal muscle are overlooked. We hypothesized that PUFAs, modulating mitochondrial function and efficiency, would ameliorate pro-inflammatory and pro-oxidant signs of nutritionally induced obesity.

Study Design

To this aim, rats were fed a control diet (CD) or isocaloric high fat diets containing either ω-3 PUFA (FD) or lard (LD) for 6 weeks.

Results

FD rats showed lower weight, lipid gain and energy efficiency compared to LD-fed animals, showing higher energy expenditure and O₂ consumption/CO₂ production. Serum lipid profile and pro-inflammatory parameters in FD-fed animals were reduced compared to LD. Accordingly, FD rats exhibited a higher glucose tolerance revealed by an improved glucose and insulin tolerance tests compared to LD, accompanied by a restoration of insulin signalling in skeletal muscle. PUFAs increased lipid oxidation and reduced energy efficiency in subsarcolemmal mitochondria, and increase AMPK activation, reducing both endoplasmic reticulum and oxidative stress. Increased mitochondrial respiration was related to an increased mitochondriogenesis in FD skeletal muscle, as shown by the increase in PGC1-α and -β.

Conclusions

our data strengthened the association of high dietary ω3-PUFA intake with reduced mitochondrial energy efficiency in the skeletal muscle.

C1q/TNF-Related Protein 9 (CTRP9) attenuates hepatic steatosis via the autophagy-mediated inhibition of endoplasmic reticulum stress

C1q/TNF-Related Protein (CTRP) 9, the closest paralog of adiponectin, has been reported to protect against diet-induced obesity and non-alcoholic fatty liver disease (NAFLD). However, the underlying mechanism has not been fully elucidated. We explored the protective effect of CTRP9 against hepatic steatosis and apoptosis, and identified the mechanisms through autophagy and endoplasmic reticulum (ER) stress using in vitro and in vivo experiments. Treating HepG2 cells with human recombinant CTRP9 significantly ameliorated palmitate- or tunicamycin-induced dysregulation of lipid metabolism, caspase 3 activity and chromatin condensation, which lead to reduction of hepatic triglyceride (TG) accumulation. CTRP9 treatment induced autophagy markers including LC3 conversion, P62 degradation, Beclin1 and ATG7 through AMPK phosphorylation in human primary hepatocytes. Furthermore, CTRP9 decreased palmitate- or tunicamycin-induced ER stress markers, such as eIF2α, CHOP and IRE-1, in HepG2 cells. Compound C, an AMPK inhibitor, and 3 methyladenine (3 MA), an autophagy inhibitor, canceled the effects of CTRP9 on ER stress, apoptosis and hepatic steatosis. In the livers of HFD-fed mice, adenovirus-mediated CTRP9 overexpression significantly induced AMPK phosphorylation and autophagy, whereas suppressed ER stress markers. In addition, both SREBP1-mediated lipogenic gene expression and apoptosis were significantly attenuated, which result in improvement in hepatic steatosis by overexpression of CTRP9. These results demonstrate that CTRP9 alleviates hepatic steatosis through relief of ER stress via the AMPK-mediated induction of autophagy.

Hypercholesterolemia aggravates myocardial ischemia reperfusion injury via activating endoplasmic reticulum stress-mediated apoptosis

The effect of hypercholesterolemia on myocardial ischemia reperfusion injury (MIRI) is in controversy and the underlying mechanism is still not well understood. In the present study, we firstly detected the effects of hypercholesterolemia on MIRI and the role of endoplasmic reticulum (ER) stress-mediated apoptosis pathway in this process. The infarct size was determined by TTC staining, and apoptosis was measured by the TUNEL method. The marker proteins of ER stress response and ER stress-mediated apoptosis pathway were detected by Western blot. The results showed that high cholesterol diet-induced hypercholesterolemia significantly increased the myocardial infarct size, the release of myocardium enzyme and the ratio of apoptosis, but did not affect the recovery of cardiac function. Moreover, hypercholesterolemia also remarkably up-regulated the expressions of ER stress markers (glucose-regulated protein 78 and calreticulin) and critical molecules in ER stress-mediated apoptosis pathway (CHOP, caspase 12, phospho-JNK). In conclusion, our study demonstrated that hypercholesterolemia enhanced myocardial vulnerability/sensitivity to ischemia reperfusion injury involved in aggravation the ER stress and activation of ER stress-mediated apoptosis pathway and it gave us a new insight into the underlying mechanisms associated with hypercholesterolemia-induced exaggerated MIRI and also provided a novel target for preventing MIRI in the presence of hypercholesterolemia.

Targeting endoplasmic reticulum stress in insulin resistance

The endoplasmic reticulum (ER) is involved in the development of insulin resistance and progression to type 2 diabetes mellitus (T2DM). Disruption of ER homeostasis leads to ER stress, which activates the unfolded protein response (UPR). This response is linked to different processes involved in the development of insulin resistance (IR) and T2DM, including inflammation, lipid accumulation, insulin biosynthesis, and β-cell apoptosis. Understanding the mechanisms by which disruption of ER homeostasis leads to IR and its progression to T2DM may offer new pharmacological targets for the treatment and prevention of these diseases. Here, we examine ER stress, the UPR, and downstream pathways in insulin sensitive tissues, and in IR, and offer insights towards therapeutic strategies.

Effect of different doses of quercetin on pancreatic pathology in rats with hypertriglyceridemia related acute pancreatitis

AIM: To investigate the effect of different doses of quercetin on the pancreatic pathology in rats with cerulein-induced acute pancreatitis (AP) associated with hypertriglyceridemia (HTG).

METHODS: Seventy-two male SD rats were randomly divided into 12 groups: HTG group (n = 6, fed a high-fat diet for 2 wk: 77% normal chow + 3% cholesterol + 20% lard), HTG + AP group (n = 6, after 2 wk of a high-fat diet, AP was induced by peritoneal injection of 50 μg/kg cerulein twice at 1-h interval), HTG + AP + quercetin groups [n = 24, divided into 4 groups (6 rats each), quercetin (50, 100, 150, 200 mg/kg) was administered to rats by peritoneal injection after AP induction], normal blood lipid group (n = 6, fed normal chow for 2 wk), normal blood lipid + AP group (n = 6, after 2 wk of normal chow, AP was induced by peritoneal injection of 50 μg/kg cerulein twice at 1-h interval), normal blood lipid + AP + quercetin groups [n = 24, divided into 4 groups (6 rats each), quercetin (50, 100, 150, 200 mg/kg) was administered to rats by peritoneal injection after AP induction]. All rats were sacrificed 9 h after AP induction. Plasma levels of amylase were tested and the pathological changes of pancreatic tissues were observed.

RESULTS: After two weeks of a high-fat diet, serum levels of triglyceride and total cholesterol were much higher than those in rats given normal chow (P < 0.001). Compared with the normal blood lipid + AP group, plasma level of amylase was significantly higher (23670.00 U/L ± 2053.13 U/L vs 13136.00 U/L ± 3536.95 U/L) and pancreatic tissue injury was significantly more serious in the HTG + AP group (9.75 ± 0.94 vs 5.92 ± 1.32) (P = 0.022; P < 0.001). Quercetin intervention groups showed significantly lower levels of amylase and less serious pancreatic tissue injury; the effect was dose-dependent. This protective effect of quercetin was more obvious in the HTG + AP group than in the AP group (HTG + AP + 100, 150, 200 mg/kg quercetin group vs HTG + AP group total histopathological scores: P < 0.001 for all; normal blood lipid + AP + 100, 150, 200 mg/kg quercetin group vs normal blood lipid + AP group total histopathological scores: P = 0.084, P = 0.003, P < 0.001), particularly in acinar necrosis and inflammatory infiltration (HTG + AP + 100, 150, 200 mg/kg quercetin group vs HTG + AP group necrosis score: P < 0.001 for all; inflammatory infiltration: P = 0.008, P = 0.006, P = 0.001).

CONCLUSION: Quercetin could significantly ameliorate the pancreatic pathology in rats with HTG related AP, especially acinar necrosis and inflammatory infiltration. The protective effect is dose-dependent.

WITHDRAWN: Hypercholesterolemia aggravates myocardial ischemia reperfusion injury via activating endoplasmic reticulum stress-mediated apoptosis

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The Endoplasmic Reticulum Chaperone GRP170: From Immunobiology to Cancer Therapeutics

Glucose-regulated protein 170 (GRP170) is the largest member of glucose-regulated protein family that resides in the endoplasmic reticulum (ER). As a component of the ER chaperone network, GRP170 assists in protein folding, assembly, and transportation of secretory or transmembrane proteins. The well documented cytoprotective activity of intracellular GRP170 due to its intrinsic chaperoning property has been shown to provide a survival benefit in cancer cells during tumor progression or metastasis. Accumulating evidence shows that extracellular GRP170 displays a superior capacity in delivering tumor antigens to specialized antigen-presenting cells for cross-presentation, resulting in generation of an anti-tumor immune response dependent on cytotoxic CD8⁺ T cells. This unique feature of GRP170 provides a molecular basis for using GRP170 as an immunostimulatory adjuvant to develop a recombinant vaccine for therapeutic immunization against cancers. This review summarizes the latest findings in understanding the biological effects of GRP170 on cell functions and tumor progression. The immunomodulating activities of GRP170 during interactions with the innate and adaptive arms of the immune system as well as its therapeutic applications in cancer immunotherapy will be discussed.

Resveratrol exerts an anti-apoptotic effect on human bronchial epithelial cells undergoing cigarette smoke exposure

Cigarette smoke can cause endoplasmic reticulum stress and induce apoptosis, both of which are important pathogenic factors contributing to chronic obstructive pulmonary disease. The aim of the present study was to produce a cigarette smoke extract (CSE)-induced apoptosis human bronchial epithelial cell (HBEpC) model, to investigate the protective effects of resveratrol (RES). The role of oxygen-regulated protein 150 (ORP150) in the RES-induced activation of Sirtuin 1 (SIRT1) was additionally studied. Cultured HBEpCs were initially treated with CSE to induce apoptosis, followed by an incubation either with or without RES. Numerous techniques were used to evaluate the outcomes of the present study, including cell counting kit-8 assay, quantitative polymerase chain reaction, western blotting, Hoechst 33342 staining and AnnexinV-PI flow cytometry apoptosis analyses, and gene knockdown. It was identified that 24 h 2% CSE incubation induced apoptosis in HBEpC, accompanied by an overexpression of the apoptosis molecular markers CCAAT-enhancer-binding protein homologous protein, caspase 4 and caspase 3. Pre-treatment of the cells with RES markedly alleviated the severity of apoptosis, as confirmed by apoptosis analyses and the expression levels of the apoptosis molecular markers. SIRT1 was shown to be overexpressed following RES treatment. However, following the gene knockdown of ORP150, the anti-apoptotic effects of RES were significantly attenuated. The results of the present study demonstrate that RES may have a protective effect against CSE-induced apoptosis, and a molecular pathway involving SIRT1 and ORP150 may be associated with the anti-apoptotic functions of RES in HBEpC.

PPARβ/δ prevents endoplasmic reticulum stress-associated inflammation and insulin resistance in skeletal muscle cells through an AMPK-dependent mechanism

AIM/HYPOTHESIS

Endoplasmic reticulum (ER) stress, which is involved in the link between inflammation and insulin resistance, contributes to the development of type 2 diabetes mellitus. In this study, we assessed whether peroxisome proliferator-activated receptor (PPAR)β/δ prevented ER stress-associated inflammation and insulin resistance in skeletal muscle cells.

METHODS

Studies were conducted in mouse C2C12 myotubes, in the human myogenic cell line LHCN-M2 and in skeletal muscle from wild-type and PPARβ/δ-deficient mice and mice exposed to a high-fat diet.

RESULTS

The PPARβ/δ agonist GW501516 prevented lipid-induced ER stress in mouse and human myotubes and in skeletal muscle of mice fed a high-fat diet. PPARβ/δ activation also prevented thapsigargin- and tunicamycin-induced ER stress in human and murine skeletal muscle cells. In agreement with this, PPARβ/δ activation prevented ER stress-associated inflammation and insulin resistance, and glucose-intolerant PPARβ/δ-deficient mice showed increased phosphorylated levels of inositol-requiring 1 transmembrane kinase/endonuclease-1α in skeletal muscle. Our findings demonstrate that PPARβ/δ activation prevents ER stress through the activation of AMP-activated protein kinase (AMPK), and the subsequent inhibition of extracellular-signal-regulated kinase (ERK)1/2 due to the inhibitory crosstalk between AMPK and ERK1/2, since overexpression of a dominant negative AMPK construct (K45R) reversed the effects attained by PPARβ/δ activation.

CONCLUSIONS/INTERPRETATION

Overall, these findings indicate that PPARβ/δ prevents ER stress, inflammation and insulin resistance in skeletal muscle cells by activating AMPK.

Modulation of Kaposi's sarcoma-associated herpesvirus interleukin-6 function by hypoxia-upregulated protein 1

Kaposi's sarcoma-associated herpesvirus (KSHV, also called human herpesvirus 8) is linked to the development of Kaposi's sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman's disease (MCD). KSHV expresses several proteins that modulate host cell signaling pathways. One of these proteins is viral interleukin-6 (vIL-6), which is a homolog of human IL-6 (hIL-6). vIL-6 is able to prevent apoptosis and promote proinflammatory signaling, angiogenesis, and cell proliferation. Although it can be secreted, vIL-6 is mainly an intracellular protein that is retained in the endoplasmic reticulum (ER). We performed affinity purification and mass spectrometry to identify novel vIL-6 binding partners and found that a cellular ER chaperone, hypoxia-upregulated protein 1 (HYOU1), interacts with vIL-6. Immunohistochemical staining reveals that both PEL and KS tumor tissues express significant amounts of HYOU1. We also show that HYOU1 increases endogenous vIL-6 protein levels and that HYOU1 facilitates vIL-6-induced JAK/STAT signaling, migration, and survival in endothelial cells. Furthermore, our data suggest that HYOU1 also modulates vIL-6's ability to induce CCL2, a chemokine involved in cell migration. Finally, we investigated the impact of HYOU1 on cellular hIL-6 signaling. Collectively, our data indicate that HYOU1 is important for vIL-6 function and may play a role in the pathogenesis of KSHV-associated cancers.

IMPORTANCE

KSHV vIL-6 is detectable in all KSHV-associated malignancies and promotes tumorigenesis and inflammation. We identified a cellular protein, called hypoxia-upregulated protein 1 (HYOU1), that interacts with KSHV vIL-6 and is present in KSHV-infected tumors. Our data suggest that HYOU1 facilitates the vIL-6-induced signaling, migration, and survival of endothelial cells.

Anthocyanin increases adiponectin secretion and protects against diabetes-related endothelial dysfunction

Adiponectin is an adipose tissue-secreted adipokine with beneficial effects on the cardiovascular system. In this study, we evaluated a potential role for adiponectin in the protective effects of anthocyanin on diabetes-related endothelial dysfunction. We treated db/db mice on a normal diet with anthocyanin cyanidin-3-O-β-glucoside (C3G; 2 g/kg diet) for 8 wk. Endothelium-dependent and -independent relaxations of the aorta were then evaluated. Adiponectin expression and secretion were also measured. C3G treatment restores endothelium-dependent relaxation of the aorta in db/db mice, whereas diabetic mice treated with an anti-adiponectin antibody do not respond. C3G treatment induces adiponectin expression and secretion in cultured 3T3 adipocytes through transcription factor forkhead box O1 (Foxo1). Silencing Foxo1 expression prevented C3G-stimulated induction of adiponectin expression. In contrast, overexpression of Foxo1-ADA promoted adiponectin expression in adipocytes. C3G activates Foxo1 by increasing its deacetylation via silent mating type information regulation 2 homolog 1 (Sirt1). Furthermore, purified anthocyanin supplementation significantly improved flow-mediated dilation (FMD) and increased serum adiponectin concentrations in patients with type 2 diabetes. Changes in adiponectin concentrations positively correlated with FMD in the anthocyanin group. Mechanistically, adiponectin activates cAMP-PKA-eNOS signaling pathways in human aortic endothelial cells, increasing endothelial nitric oxide bioavailability. These results demonstrate that adipocyte-derived adiponectin is required for anthocyanin C3G-mediated improvement of endothelial function in diabetes.

Metformin Protects Endothelial Function in Diet-Induced Obese Mice by Inhibition of Endoplasmic Reticulum Stress Through 5′ Adenosine Monophosphate–Activated Protein Kinase–Peroxisome Proliferator–Activated Receptor δ Pathway

Objective—

5′ Adenosine monophosphate–activated protein kinase (AMPK) interacts with peroxisome proliferator–activated receptor δ (PPARδ) to induce gene expression synergistically, whereas the activation of AMPK inhibits endoplasmic reticulum (ER) stress. Whether the vascular benefits of antidiabetic drug metformin (AMPK activator) in diabetes mellitus and obesity is mediated by PPARδ remains unknown. We aim to investigate whether PPARδ is crucial for metformin in ameliorating ER stress and endothelial dysfunction induced by high-fat diet.

Approach and Results—

Acetylcholine-induced endothelium-dependent relaxation in aortae was measured on wire myograph. ER stress markers were determined by Western blotting. Superoxide production in mouse aortae and NO generation in mouse aortic endothelial cells were assessed by fluorescence imaging. Endothelium-dependent relaxation was impaired and ER stress markers and superoxide level were elevated in aortae from high-fat diet–induced obese mice compared with lean mice. These effects of high-fat diet were reversed by oral treatment with metformin in diet-induced obese PPARδ wild-type mice but not in diet-induced obese PPARδ knockout littermates. Metformin and PPARδ agonist GW1516 reversed tunicamycin (ER stress inducer)-induced ER stress, oxidative stress, and impairment of endothelium-dependent relaxation in mouse aortae as well as NO production in mouse aortic endothelial cells. Effects of metformin were abolished by cotreatment of GSK0660 (PPARδ antagonist), whereas effects of GW1516 were unaffected by compound C (AMPK inhibitor).

Conclusions—

Metformin restores endothelial function through inhibiting ER stress and oxidative stress and increasing NO bioavailability on activation of AMPK/PPARδ pathway in obese diabetic mice.

Alterations of pancreatic islet structure, metabolism and gene expression in diet-induced obese C57BL/6J mice

The reduction of functional β cell mass is a key feature of type 2 diabetes. Here, we studied metabolic functions and islet gene expression profiles of C57BL/6J mice with naturally occurring nicotinamide nucleotide transhydrogenase (NNT) deletion mutation, a widely used model of diet-induced obesity and diabetes. On high fat diet (HF), the mice developed obesity and hyperinsulinemia, while blood glucose levels were only mildly elevated indicating a substantial capacity to compensate for insulin resistance. The basal serum insulin levels were elevated in HF mice, but insulin secretion in response to glucose load was significantly blunted. Hyperinsulinemia in HF fed mice was associated with an increase in islet mass and size along with higher BrdU incorporation to β cells. The temporal profiles of glucose-stimulated insulin secretion (GSIS) of isolated islets were comparable in HF and normal chow fed mice. Islets isolated from HF fed mice had elevated basal oxygen consumption per islet but failed to increase oxygen consumption further in response to glucose or carbonyl cyanide-4-trifluoromethoxyphenylhydrazone (FCCP). To obtain an unbiased assessment of metabolic pathways in islets, we performed microarray analysis comparing gene expression in islets from HF to normal chow-fed mice. A few genes, for example, those genes involved in the protection against oxidative stress (hypoxia upregulated protein 1) and Pgc1α were up-regulated in HF islets. In contrast, several genes in extracellular matrix and other pathways were suppressed in HF islets. These results indicate that islets from C57BL/6J mice with NNT deletion mutation develop structural, metabolic and gene expression features consistent with compensation and decompensation in response to HF diet.

Rutaecarpine analogues reduce lipid accumulation in adipocytes via inhibiting adipogenesis/lipogenesis with AMPK activation and UPR suppression

Obesity is characterized by expansion of adipose tissue, which results from an increase in adipocyte number (adipogenesis) and adipocyte size (lipogenesis). A reversal of these processes has been suggested to be a potential antiobetic therapy. Rutaecarpine (Rut) and its novel analogues (R17 and R18) were identified to exert potent effect in reducing lipid accumulation during adipocyte differentiation in 3T3-L1 adipocytes with little cytotoxicity. All three compounds reduced lipid accumulation in a dose-dependent manner, while R17 and R18 exhibited much more potent inhibitory effects compared to that of Rut. Further studies showed that R17 suppressed both adipogenesis and lipogenesis during all stages of adipocyte differentiation as indicated by the reduced protein and mRNA levels of key regulators of adipogenesis/lipogenesis, including PPARγ, C/EBPα, SREBP-1c, ACC, FAS, and SCD-1. We next examined the effect of R17 on the UPR pathway and the results showed that the UPR markers (PERK, eIF2α, IRE1α, and spliced XBP1 mRNA) were all significantly reduced by R17. Further studies revealed that R17 persistently activated AMPK during differentiation, suggesting that the AMPK may be an upstream mechanism for the effect of R17 on adipogenesis and lipogenesis via the adipogenic/lipogenic markers and the UPR pathway. Finally, studies in fast/refeeding mice demonstrated that R17 administration was able to reduce epididymal fat mass and the levels of plasma TG and FFA in vivo. Our results suggest that rutaecarpine analogues may have therapeutic potential for obesity and related metabolic disorders. The mechanism involves the suppression of adipogenic/lipogenic proteins and the suppression of the UPR pathway possibly via the AMPK.

High molecular weight stress proteins: Identification, cloning and utilisation in cancer immunotherapy

Although the large stress/heat shock proteins (HSPs), i.e. Hsp110 and Grp170, were identified over 30 years ago, these abundant and highly conserved molecules have received much less attention compared to other conventional HSPs. Large stress proteins act as molecular chaperones with exceptional protein-holding capability and prevent the aggregation of proteins induced by thermal stress. The chaperoning properties of Hsp110 and Grp170 are integral to the ability of these molecules to modulate immune functions and are essential for developing large chaperone complex vaccines for cancer immunotherapy. The potent anti-tumour activity of the Hsp110/Grp170-tumour protein antigen complexes demonstrated in preclinical studies has led to a phase I clinical trial through the National Cancer Institute's rapid access to intervention development (RAID) programme that is presently underway. Here we review aspects of the structure and function of these large stress proteins, their roles as molecular chaperones in the biology of cell stress, and prospects for their use in immune regulation and cancer immunotherapy. Lastly, we will discuss the recently revealed immunosuppressive activity of scavenger receptor A that binds to Hsp110 and Grp170, as well as the feasibility of targeting this receptor to promote T-cell activation and anti-tumour immunity induced by large HSP vaccines and other immunotherapies.

Oleate prevents saturated-fatty-acid-induced ER stress, inflammation and insulin resistance in skeletal muscle cells through an AMPK-dependent mechanism

AIMS/HYPOTHESIS

Although the substitution of saturated fatty acids with oleate has been recommended in the management of type 2 diabetes mellitus, the mechanisms by which oleate improves insulin resistance in skeletal muscle cells are not completely known. Here, we examined whether oleate, through activation of AMP-activated protein kinase (AMPK), prevented palmitate-induced endoplasmic reticulum (ER) stress, which is involved in the link between lipid-induced inflammation and insulin resistance.

METHODS

Studies were conducted in mouse C2C12 myotubes and in the human myogenic cell line LHCN-M2. To analyse the involvement of AMPK, activators and inhibitors of this kinase and overexpression of a dominant negative AMPK construct (K45R) were used.

RESULTS

Palmitate increased the levels of ER stress markers, whereas oleate did not. In palmitate-exposed cells incubated with a lower concentration of oleate, the effects of palmitate were prevented. The induction of ER stress markers by palmitate was prevented by the presence of the AMPK activators AICAR and A-769662. Moreover, the ability of oleate to prevent palmitate-induced ER stress and inflammation (nuclear factor-kappa B [NF-κB] DNA-binding activity and expression and secretion of IL6) as well as insulin-stimulated Akt phosphorylation and 2-deoxyglucose uptake was reversed in the presence of the AMPK inhibitor compound C or by overexpression of a dominant negative AMPK construct. Finally, palmitate reduced phospho-AMPK levels, whereas this was not observed in oleate-exposed cells or in palmitate-exposed cells supplemented with oleate.

CONCLUSIONS/INTERPRETATION

Overall, these findings indicate that oleate prevents ER stress, inflammation and insulin resistance in palmitate-exposed skeletal muscle cells by activating AMPK.

Role of AMPK activation in oxidative cell damage: Implications for alcohol-induced liver disease

Chronic alcohol consumption is a well-known risk factor for liver disease. Progression of alcohol-induced liver disease (ALD) is a multifactorial process that involves a number of genetic, nutritional and environmental factors. Experimental and clinical studies increasingly show that oxidative damage induced by ethanol contributes in many ways to the pathogenesis of alcohol hepatoxicity. Oxidative stress appears to activate AMP-activated protein kinase (AMPK) signaling system, which has emerged in recent years as a kinase that controls the redox-state and mitochondrial function. This review focuses on the most recent insights concerning the activation of AMPK by reactive oxygen species (ROS), and describes recent evidences supporting the hypothesis that AMPK signaling pathways play an important role in promoting cell viability under conditions of oxidative stress, such as during alcohol exposure. We suggest that AMPK activation by ROS can promote cell survival by inducing autophagy, mitochondrial biogenesis and expression of genes involved in antioxidant defense. Hence, increased intracellular concentrations of ROS may represent a general mechanism for enhancement of AMPK-mediated cellular adaptation, including maintenance of redox homeostasis. On the other hand, AMPK inhibition in the liver by ethanol appears to play a key role in the development of steatosis induced by chronic alcohol consumption. Although more studies are needed to assess the functions of AMPK during oxidative stress, AMPK may be a possible therapeutic target in the particular case of alcohol-induced liver disease.

Piperonal prevents high-fat diet-induced hepatic steatosis and insulin resistance in mice via activation of adiponectin/AMPK pathway

OBJECTIVE

Piperonal is an important flavor additive with antibacterial and anxiolytic properties. We investigated the effects and possible mechanisms of piperonal protection against high-fat diet (HFD)-induced hepatic steatosis and insulin resistance.

METHODS

C57BL/6 J mice were fed with a normal diet (ND; based on the AIN-76 rodent diet), HFD (20% fat and 1% cholesterol), or piperonal-supplemented diet (POD; HFD supplemented with 0.05% piperonal) for 10 weeks.

RESULTS

Piperonal supplementation reduced hepatic lipid concentrations, liver dysfunction and plasma levels of insulin and glucose in HFD-fed mice. Piperonal significantly enhanced mRNA expression and secretion of adiponectin in 3T3-L1 adipocytes. Dietary piperonal significantly increased circulating adiponectin levels and hepatic AMP-activated protein kinase (AMPK) activation in HFD-fed mice; these were associated with the suppression of sterol regulatory element binding protein-1c and activation of glucose transporter-2 translocation in the livers. Piperonal also significantly reduced the expression of endoplasmic reticulum (ER) stress markers in the livers of HFD-fed mice.

CONCLUSIONS

Piperonal may activate the adiponectin/AMPK pathway in the livers of mice. The activated adiponectin/AMPK axis may inhibit p70S6 kinase signaling and the ER stress response, with protective effects on hepatic steatosis and insulin resistance.

Aberrant endoplasmic reticulum stress in vascular smooth muscle increases vascular contractility and blood pressure in mice deficient of AMP-activated protein kinase-α2 in vivo

OBJECTIVE

The endoplasmic reticulum (ER) plays a critical role in ensuring proper folding of newly synthesized proteins. Aberrant ER stress is reported to play a causal role in cardiovascular diseases. However, the effects of ER stress on vascular smooth muscle contractility and blood pressure remain unknown. The aim of this study was to investigate whether aberrant ER stress causes abnormal vasoconstriction and consequent high blood pressure in mice.

METHODS AND RESULTS

ER stress markers, vascular smooth muscle contractility, and blood pressure were monitored in mice. Incubation of isolated aortic rings with tunicamycin or MG132, 2 structurally unrelated ER stress inducers, significantly increased both phenylephrine-induced vasoconstriction and the phosphorylation of myosin light chain (Thr18/Ser19), both of which were abrogated by pretreatment with chemical chaperones or 5-Aminoimidazole-4-carboxamide ribonucleotide and metformin, 2 potent activators for the AMP-activated protein kinase. Consistently, administration of tauroursodeoxycholic acid or 4-phenyl butyric acid, 2 structurally unrelated chemical chaperones, in AMP-activated protein kinase-α2 knockout mice lowered blood pressure and abolished abnormal vasoconstrictor response of AMP-activated protein kinase-α2 knockout mice to phenylephrine. Consistently, tunicamycin (0.01 μg/g per day) infusion markedly increased both systolic and diastolic blood pressure, both of which were ablated by coadministration of 4-phenyl butyric acid. Furthermore, 4-phenyl butyric acid or tauroursodeoxycholic acid, which suppressed angiotensin II infusion-induced ER stress markers in vivo, markedly lowered blood pressure in angiotensin II-infused mice in vivo.

CONCLUSIONS

We conclude that ER stress increases vascular smooth muscle contractility resulting in high blood pressure, and AMP-activated protein kinase activation mitigates high blood pressure through the suppression of ER stress in vivo.

BRSK2 is regulated by ER stress in protein level and involved in ER stress-induced apoptosis

The accumulation of unfolded protein in lumen of the endoplasmic reticulum (ER) triggers a cell stress response called ER stress, which induces the transcriptional up-regulation of a number of proteins, including molecular chaperones and folding enzymes, the global inhibition of protein synthesis, and the activation of apoptotic pathways. The molecular mechanism underlying the apoptotic response has remained largely elusive. AMP activated protein kinase (AMPK) has been implicated in ER stress-induced apoptosis through its role in attenuating ER stress. BRSK2 (brain selective kinase 2, also known as SAD-A) is a serine/threonine kinase of the AMPK family. Here, we demonstrate that the BRSK2 protein levels are significantly down-regulated in response to ER stress in PANC-1 and HeLa cells. Furthermore, we also observed that ER stress induces endogenous BRSK2 to localize to the ER. Importantly, knockdown of endogenous BRSK2 expression enhances ER stress-mediated apoptosis in cells while over express BRSK2 in wild type or kinase-dead type both reduce the apoptosis. BRSK2 knockdown increases the transcription of CHOP and the levels of cleaved caspase-3 in cells in response to ER stress while over expression of BRSK2 decrease CHOP mRNA and levels of cleaved caspase-3. Taken together, our findings demonstrate ER stress may reduce BRSK2 protein and change BRSK2 subcellular localization, which in turn alleviate ER stress-induced apoptosis.

Fenofibrate lowers lipid accumulation in myotubes by modulating the PPARα/AMPK/FoxO1/ATGL pathway

Fenofibrate, a fibric acid derivative, is known to possess lipid-lowering effects. Although fenofibrate may activate peroxisome proliferator-activated receptor (PPAR)α and regulate the transcription of several genes, the underlying mechanisms are poorly understood. In this study, we demonstrated that incubation of C2C12 myotubes with fenofibrate increased adipose triglyceride lipase (ATGL) expression and suppressed fatty acid synthase (FAS) level, thereby decreasing intracellular triglyceride accumulation when cells were incubated at high-glucose condition. Fenofibrate increased the phosphorylation of AMP-activated protein kinase (AMPK), which subsequently increased fatty acid β-oxidation. AMPK phosphorylation was reduced by pretreatment with GW9662 (a PPARα inhibitor), suggesting that AMPK may be a downstream effector of PPARα. Pretreatment with compound C (an AMPK inhibitor) or GW9662 blocked fenofibrate-induced ATGL expression and the lipid-lowering effect. Our results suggest that AMPK is as an upstream regulator of ATGL. With further exploration, we demonstrated that fenofibrate stimulated FoxO1 translocation from the cytosol to nuclei by immunefluorescence assay, chromatin immuneprecipitation assay, and reporter assay. Furthermore, oral administration of fenofibrate ameliorated the body weight, visceral fat and serum biochemical indexes in db/db mice. Taken together, our results suggest that the lipid-lowering effect of fenofibrate was achieved by activating PPARα and AMPK signaling pathway that resulted in increasing ATGL expression, lipolysis, and fatty acid β-oxidation.

Endoplasmic reticulum stress and the on site function of resident PTP1B

Growing evidence links the stress at the endoplasmic reticulum (ER) to pathologies such as diabetes mellitus, obesity, liver, heart, renal and neurodegenerative diseases, endothelial dysfunction, atherosclerosis, and cancer. Therefore, identification of molecular pathways beyond ER stress and their appropriate modulation might alleviate the stress, and direct toward novel tools to fight this disturbance. An interesting resident of the ER membrane is protein tyrosine phosphatase 1B (PTP1B), an enzyme that negatively regulates insulin and leptin signaling, contributing to insulin and leptin resistance. Recently, new functions of PTP1B have been established linked to ER stress response. This review evaluates the novel data on ER stressors, discusses the mechanisms beyond PTP1B function in the ER stress response, and emphasizes the potential therapeutic exploitation of PTP1B to relieve ER stress.

SIRT1 attenuates palmitate-induced endoplasmic reticulum stress and insulin resistance in HepG2 cells via induction of oxygen-regulated protein 150

Endoplasmic reticulum (ER) stress has been implicated in the pathology of type 2 diabetes mellitus (T2DM). Although SIRT1 has a therapeutic effect on T2DM, the mechanisms by which SIRT1 ameliorates insulin resistance (IR) remain unclear. In this study, we investigated the impact of SIRT1 on palmitate-induced ER stress in HepG2 cells and its underlying signal pathway. Treatment with resveratrol, a SIRT1 activator significantly inhibited palmitate-induced ER stress, leading to the protection against palmitate-induced ER stress and insulin resistance. Resveratrol and SIRT1 overexpression induced the expression of oxygen-regulated protein (ORP) 150 in HepG2 cells. Forkhead box O1 (FOXO1) was involved in the regulation of ORP150 expression because suppression of FOXO1 inhibited the induction of ORP150 by SIRT1. Our results indicate a novel mechanism by which SIRT1 regulates ER stress by overexpression of ORP150, and suggest that SIRT1 ameliorates palmitate-induced insulin resistance in HepG2 cells via regulation of ER stress.

Purple sweet potato color attenuates domoic acid-induced cognitive deficits by promoting estrogen receptor-α-mediated mitochondrial biogenesis signaling in mice

Recent findings suggest that endoplasmic reticulum stress may be involved in the pathogenesis of domoic acid-induced neurodegeneration. Purple sweet potato color, a class of naturally occurring anthocyanins, has beneficial health and biological effects. Recent studies have also shown that anthocyanins have estrogenic activity and can enhance estrogen receptor-α expression. In this study, we evaluated the effect of purple sweet potato color on cognitive deficits induced by hippocampal mitochondrial dysfunction in domoic acid-treated mice and explored the potential mechanisms underlying this effect. Our results showed that the oral administration of purple sweet potato color to domoic acid-treated mice significantly improved their behavioral performance in a step-through passive avoidance task and a Morris water maze task. These improvements were mediated, at least in part, by a stimulation of estrogen receptor-α-mediated mitochondrial biogenesis signaling and by decreases in the expression of p47phox and gp91phox. Decreases in reactive oxygen species and protein carbonylation were also observed, along with a blockade of the endoplasmic reticulum stress pathway. Furthermore, purple sweet potato color significantly suppressed endoplasmic reticulum stress-induced apoptosis, which prevented neuron loss and restored the expression of memory-related proteins. However, knockdown of estrogen receptor-α using short hairpin RNA only partially blocked the neuroprotective effects of purple sweet potato color in the hippocampus of mice cotreated with purple sweet potato color and domoic acid, indicating that purple sweet potato color acts through multiple pathways. These results suggest that purple sweet potato color could be a possible candidate for the prevention and treatment of cognitive deficits in excitotoxic and other brain disorders.

Nutritional stress in eukaryotic cells: oxidative species and regulation of survival in time of scarceness

The survival response to glucose limitation in eukaryotic cells involves different signaling pathways highly conserved from yeasts to mammals. Upon nutritional restriction, a network driven by kinases such as the AMP dependent protein kinase (AMPK/Snf1), the Target of Rapamycin kinase (TOR), the Protein kinases A (PKA) or B (PKB/Akt) control stress defenses, cell cycle regulators, pro and anti apoptotic proteins, respiratory complexes, etc. In this work we review the state of the art in this scenario of kinase pathways, i.e. their principal effectors and links, both in yeasts and mammals. We also focus in downstream actors such as sirtuins and the Forkhead box class O transcription factors. Besides, we particularly analyze the participation of these kinases on the balance of Reactive Oxygen Species and their role in the regulation of survival during glucose deprivation. Key results on yeast stationary phase survival and the contribution of such genetics studies are discussed.