Targeting endoplasmic reticulum stress in metabolic disease

Protective roles of thrombomodulin in cisplatin-induced nephrotoxicity through the inhibition of oxidative and endoplasmic reticulum stress

Cisplatin is an effective chemotherapeutic agent widely used for the treatment of various solid tumors. However, cisplatin has an important limitation in its use; currently, there is no method to ameliorate cisplatin-induced acute kidney injury (AKI). Thrombomodulin (TM) is well known not only for its role as a cofactor in the clinically important natural anticoagulation pathway but also for its anti-inflammatory properties. Here, we investigated the effects of TM in cisplatin-induced AKI. In mice intraperitoneally injected with 15 mg/kg cisplatin, TM (10 mg/kg) or PBS was administered intravenously at 24 h after cisplatin injection. TM significantly attenuated cisplatin-induced nephrotoxicity with the suppressed elevation of blood urea nitrogen and serum creatinine, and reduced histological damages. Actually, TM treatment significantly alleviated oxidative stress-induced apoptosis by reducing reactive oxygen species (ROS) levels in cisplatin-treated renal proximal tubular epithelial cells (RPTECs) in vitro. Furthermore, TM clarified cisplatin-induced apoptosis by reducing caspase-3 levels. In addition, TM attenuated the endoplasmic reticulum (ER) stress signaling pathway in both renal tissues and RPTECs to protect the kidneys from cisplatin-induced AKI. These findings suggest that TM is a potential protectant against cisplatin-induced nephrotoxicity through suppressing ROS generation and ER stress in response to cisplatin.

Isoliquiritigenin pretreatment regulates ER stress and attenuates cisplatin-induced nephrotoxicity in male Wistar rats

Cisplatin (CP) is a chemotherapeutic drug used to treat solid tumors. However, studies have revealed its nephrotoxic effect. Oxidative stress, endoplasmic reticulum (ER) stress, and mitochondrial dysfunction are involved in CP-induced renal damage. Thus, preconditioning (hormetic effect) of ER stress is a strategy to prevent CP-induced renal damage. On the other hand, isoliquiritigenin (IsoLQ) is recognized as a flavonoid with antioxidant properties and an inducer of ER stress. Therefore, we evaluated the ER stress-inducing capacity of IsoLQ and its possible protective effect against CP-induced nephrotoxicity in adult male Wistar rats. The findings reflected that IsoLQ pretreatment might decrease renal damage by reducing plasma creatinine and blood urea nitrogen levels in animals with CP-induced nephrotoxicity. These may be associated with IsoLQ activating ER stress and unfolded protein response (UPR). We found increased messenger RNA levels of the ER stress marker glucose-related protein 78 kDa (GRP78). In addition, we also found that pretreatment with IsoLQ reduced the levels of CCAAT/enhancer-binding protein-homologous protein (CHOP) and X-box-binding protein 1 (XBP1) in the renal cortex, reflecting that IsoLQ can regulate the UPR and activation of the apoptotic pathway. Moreover, this preconditioning with IsoLQ of ER stress had oxidative stress-regulatory effects, as it restored the activity of glutathione peroxidase and glutathione reductase enzymes. Finally, IsoLQ modifies the protein expression of mitofusin 2 (Mfn-2) and voltage-dependent anion channel (VDAC). In conclusion, these data suggest that IsoLQ pretreatment has a nephroprotective effect; it could functionally regulate the ER and mitochondria and reduce CP-induced renal damage by attenuating hormesis-mediated ER stress.

A review: Mechanism and prospect of gastrodin in prevention and treatment of T2DM and COVID-19

Gastrodin is an extract from the dried tuber of the Chinese herb Gastrodia elata (Tian ma), with anti-inflammatory, antioxidant, and antiviral properties. Recent studies have shown that, compared to commonly used diabetes drugs, gastrodin has antidiabetic effects in multiple ways, with characteristics of low cost, high safety, less side effects, protection of β-cell function, relieving insulin resistance and alleviating multiple complications. In addition, it is confirmed that gastrodin can protect the function of lung and other organs, enhance antiviral activity via upregulating the type I interferon (IFN-I), and inhibit angiotensin II (AngII), a key factor in "cytokine storm" caused by COVID-19. Therefore, we reviewed the effect and mechanism of gastrodin on type 2 diabetes mellitus (T2DM), and speculated other potential mechanisms of gastrodin in alleviating insulin resistance from insulin signal pathway, inflammation, mitochondrial and endoplasmic reticulum and its potential in the prevention and treatment of COVID-19. We hope to provide new direction and treatment strategy for basic research and clinical work: gastrodin is considered as a drug for the prevention and treatment of diabetes and COVID-19.

Research progress in nucleus-targeted tumor therapy

The nucleus is considered the most important organelle in the cell as it plays a central role in controlling cell reproduction, metabolism, and the cell cycle. The successful delivery of drugs into the nucleus can achieve excellent therapeutic effects, which reveals the potential of nucleus-targeted therapy in precision medicine. However, the transportation of therapeutics into the nucleus remains a significant challenge due to various biological barriers. Herein, we summarize the recent progress in the nucleus-targeted drug delivery system (NDDS). The structures of the nucleus and nuclear envelope are first described in order to understand the mechanisms by which drugs cross the nuclear envelope. Then, various drug delivery strategies based on the mechanisms and their applications are discussed. Finally, the challenges and solutions in the field of nucleus-targeted drug delivery are raised for developing a more efficient NDDS and promoting its clinical transformation.

Therapeutic potential of endoplasmic reticulum stress inhibitors in the treatment of diabetic peripheral neuropathy

Endoplasmic stress response, the unfolded protein response (UPR), is a homeostatic signaling pathway comprising transmembrane sensors that get activated upon alterations in ER luminal environment. Studies suggest a relation between activated UPR pathways and several disease states such as Parkinson, Alzheimer, inflammatory bowel disease, tumor growth, and metabolic syndrome. Diabetic peripheral neuropathy (DPN), a common microvascular complication of diabetes-related chronic hyperglycemia, causes chronic pain, loss of sensation, foot ulcers, amputations, allodynia, hyperalgesia, paresthesia, and spontaneous pain. Factors like disrupted calcium signaling, dyslipidemia, hyperglycemia, inflammation, insulin signaling, and oxidative stress disturb the UPR sensor levels manifesting as DPN. We discuss new effective therapeutic alternatives for DPN that can be developed by targeting UPR pathways like synthetic ER stress inhibitors like 4-PhenylButyric acid (4-PBA), Sephin 1, Salubrinal and natural ER stress inhibitors like Tauroursodeoxycholic acid (TUDCA), Cordycepin, Proanthocyanidins, Crocin, Purple Rice extract and cyanidin and Caffeic Acid Phenethyl Ester (CAPE).

Interplay between calcium and endoplasmic reticulum stress

Cellular homeostasis is crucial for the healthy functioning of the organism. Disruption of cellular homeostasis activates endoplasmic reticulum (ER) stress coping responses including the unfolded protein response (UPR). There are three ER resident stress sensors responsible for UPR activation - IRE1α, PERK and ATF6. Ca²⁺ signaling plays an important role in stress responses including the UPR and the ER is the main Ca²⁺ storage organelle and a source of Ca²⁺ for cell signaling. The ER contains many proteins involved in Ca²⁺ import/export/ storage, Ca²⁺ movement between different cellular organelles and ER Ca²⁺ stores refilling. Here we focus on selected aspects of ER Ca²⁺ homeostasis and its role in activation of the ER stress coping responses.

Antioxidants affect endoplasmic reticulum stress-related diseases

The endoplasmic reticulum (ER) is a complex multifunctional organelle that maintains cell homeostasis. Intrinsic and extrinsic factors alter ER functions, including the rate of protein folding that triggers the accumulation of misfolded proteins and alters homeostasis, thus generating stress in the ER, which activates the unfolded protein response (UPR) pathway to promote cell survival and restore their homeostasis; however, if the damage is not corrected, it could also trigger cell death. In addition, ER stress and oxidative stress are closely related because excessive production of reactive oxygen species (ROS), a well-known inducer of ER stress, promotes the accumulation of misfolded proteins; at the same time, the ER stress enhances ROS production, generating a pathological cycle. Furthermore, it has been described that the dysregulation of the UPR contributes to the progression of various diseases, so the use of compounds capable of regulating ER stress, such as antioxidants, has been used in several experimental models of diseases to alleviate the damage induced by the maladaptive signaling of the UPR, the mechanism of action of antioxidants generally is dose-dependent, and it is specific in each tissue and pathology, could decrease or enhance specific proteins of the UPR to have beneficial or detrimental effects.

Cellular stress modulates severity of the inflammatory response in lungs via cell surface BiP

Inflammation is a central pathogenic feature of the acute respiratory distress syndrome (ARDS) in COVID-19. Previous pathologies such as diabetes, autoimmune or cardiovascular diseases become risk factors for the severe hyperinflammatory syndrome. A common feature among these risk factors is the subclinical presence of cellular stress, a finding that has gained attention after the discovery that BiP (GRP78), a master regulator of stress, participates in the SARS-CoV-2 recognition. Here, we show that BiP serum levels are higher in COVID-19 patients who present certain risk factors. Moreover, early during the infection, BiP levels predict severe pneumonia, supporting the use of BiP as a prognosis biomarker. Using a mouse model of pulmonary inflammation, we observed increased levels of cell surface BiP (cs-BiP) in leukocytes during inflammation. This corresponds with a higher number of neutrophiles, which show naturally high levels of cs-BiP, whereas alveolar macrophages show a higher than usual exposure of BiP in their cell surface. The modulation of cellular stress with the use of a clinically approved drug, 4-PBA, resulted in the amelioration of the lung hyperinflammatory response, supporting the anti-stress therapy as a valid therapeutic strategy for patients developing ARDS. Finally, we identified stress-modulated proteins that shed light into the mechanism underlying the cellular stress-inflammation network in lungs.

Bromocriptine-QR Therapy Reduces Sympathetic Tone and Ameliorates a Pro-Oxidative/Pro-Inflammatory Phenotype in Peripheral Blood Mononuclear Cells and Plasma of Type 2 Diabetes Subjects

Bromocriptine-QR is a sympatholytic dopamine D2 agonist for the treatment of type 2 diabetes that has demonstrated rapid (within 1 year) substantial reductions in adverse cardiovascular events in this population by as yet incompletely delineated mechanisms. However, a chronic state of elevated sympathetic nervous system activity and central hypodopaminergic function has been demonstrated to potentiate an immune system pro-oxidative/pro-inflammatory condition and this immune phenotype is known to contribute significantly to the advancement of cardiovascular disease (CVD). Therefore, the possibility exists that bromocriptine-QR therapy may reduce adverse cardiovascular events in type 2 diabetes subjects via attenuation of this underlying chronic pro-oxidative/pro-inflammatory state. The present study was undertaken to assess the impact of bromocriptine-QR on a wide range of immune pro-oxidative/pro-inflammatory biochemical pathways and genes known to be operative in the genesis and progression of CVD. Inflammatory peripheral blood mononuclear cell biology is both a significant contributor to cardiovascular disease and also a marker of the body’s systemic pro-inflammatory status. Therefore, this study investigated the effects of 4-month circadian-timed (within 2 h of waking in the morning) bromocriptine-QR therapy (3.2 mg/day) in type 2 diabetes subjects whose glycemia was not optimally controlled on the glucagon-like peptide 1 receptor agonist on (i) gene expression status (via qPCR) of a wide array of mononuclear cell pro-oxidative/pro-inflammatory genes known to participate in the genesis and progression of CVD (OXR1, NRF2, NQO1, SOD1, SOD2, CAT, GSR, GPX1, GPX4, GCH1, HMOX1, BiP, EIF2α, ATF4, PERK, XBP1, ATF6, CHOP, GSK3β, NFkB, TXNIP, PIN1, BECN1, TLR2, TLR4, TLR10, MAPK8, NLRP3, CCR2, GCR, L-selectin, VCAM1, ICAM1) and (ii) humoral measures of sympathetic tone (norepinephrine and normetanephrine), whole-body oxidative stress (nitrotyrosine, TBARS), and pro-inflammatory factors (IL-1β, IL-6, IL-18, MCP-1, prolactin, C-reactive protein [CRP]). Relative to pre-treatment status, 4 months of bromocriptine-QR therapy resulted in significant reductions of mRNA levels in PBMC endoplasmic reticulum stress-unfolded protein response effectors [GRP78/BiP (34%), EIF2α (32%), ATF4 (29%), XBP1 (25%), PIN1 (14%), BECN1 (23%)], oxidative stress response proteins [OXR1 (31%), NRF2 (32%), NQO1 (39%), SOD1 (52%), CAT (26%), GPX1 (33%), GPX4 (31%), GCH1 (30%), HMOX1 (40%)], mRNA levels of TLR pro-inflammatory pathway proteins [TLR2 (46%), TLR4 (20%), GSK3β (19%), NFkB (33%), TXNIP (18%), NLRP3 (32%), CCR2 (24%), GCR (28%)], mRNA levels of pro-inflammatory cellular receptor proteins CCR2 and GCR by 24% and 28%, and adhesion molecule proteins L-selectin (35%) and VCAM1 (24%). Relative to baseline, bromocriptine-QR therapy also significantly reduced plasma levels of norepinephrine and normetanephrine by 33% and 22%, respectively, plasma pro-oxidative markers nitrotyrosine and TBARS by 13% and 10%, respectively, and pro-inflammatory factors IL-18, MCP1, IL-1β, prolactin, and CRP by 21%,13%, 12%, 42%, and 45%, respectively. These findings suggest a unique role for circadian-timed bromocriptine-QR sympatholytic dopamine agonist therapy in reducing systemic low-grade sterile inflammation to thereby reduce cardiovascular disease risk.

Covalent inhibition of endoplasmic reticulum chaperone GRP78 disconnects the transduction of ER stress signals to inflammation and lipid accumulation in diet-induced obese mice

Targeting endoplasmic reticulum (ER) stress, inflammation, and metabolic dysfunctions may halt the pathogenesis of obesity and thereby reduce the prevalence of diabetes, cardiovascular disesases, and cancers. The present study was designed to elucidate the mechnaisms by which plant-derived celastrol ameliorated inflammation and lipid accumulation in obesity. The mouse model of diet-induced obesity was induced by feeding high-fat diet for 3 months and subsequently intervented with celastrol for 21 days. Hepatic and adipose tissues were analyzed for lipid accumulation, macrophage activation, and biomarker expression. As result, celastrol effectively reduced body weight, suppressed ER stress, inflammation, and lipogenesis while promoted hepatic lipolysis. RNA-sequencing revealed that celastrol-loaded nanomicelles restored the expression of 49 genes that regulate ER stress, inflammation, and lipid metabolism. On the other hand, celastrol-PEG4-alkyne was synthesized for identifying celastrol-bound proteins in RAW264.7 macrophages. ER chaperone GRP78 (78 kDa glucose-regulated protein) was identified by proteomics approach for celastrol binding to the residue Cys⁴¹. Upon binding and conjugation, celastrol diminished the chaperone activity of GRP78 by 130-fold and reduced ER stress in palmitate-challenged cells, while celastrol analog lacking quinone methide failed to exhibit antiobesity effects. Thus, covalent GRP78 inhibition may induce the reprograming of ER signaling, inflammation, and metabolism against diet-induced obesity.

Regulation and functions of membrane lipids: Insights from Caenorhabditis elegans

The Caenorhabditis elegans plasma membrane is composed of glycerophospholipids and sphingolipids with a small cholesterol. The C. elegans obtain the majority of the membrane lipids by modifying fatty acids present in the bacterial diet. The metabolic pathways of membrane lipid biosynthesis are well conserved across the animal kingdom. In C. elegans CDP-DAG and Kennedy pathway produce glycerophospholipids. Meanwhile, the sphingolipids are synthesized through a different pathway. They have evolved remarkably diverse mechanisms to maintain membrane lipid homeostasis. For instance, the lipid bilayer stress operates to accomplish homeostasis during any perturbance in the lipid composition. Meanwhile, the PAQR-2/IGLR-2 complex works with FLD-1 to balance unsaturated to saturated fatty acids to maintain membrane fluidity. The loss of membrane lipid homeostasis is observed in many human genetic and metabolic disorders. Since C. elegans conserved such genes and pathways, it can be used as a model organism.

ER Stress in Cardiometabolic Diseases: From Molecular Mechanisms to Therapeutics

The endoplasmic reticulum (ER) hosts linear polypeptides and fosters natural folding of proteins through ER-residing chaperones and enzymes. Failure of the ER to align and compose proper protein architecture leads to accumulation of misfolded/unfolded proteins in the ER lumen, which disturbs ER homeostasis to provoke ER stress. Presence of ER stress initiates the cytoprotective unfolded protein response (UPR) to restore ER homeostasis or instigates a rather maladaptive UPR to promote cell death. Although a wide array of cellular processes such as persistent autophagy, dysregulated mitophagy, and secretion of proinflammatory cytokines may contribute to the onset and progression of cardiometabolic diseases, it is well perceived that ER stress also evokes the onset and development of cardiometabolic diseases, particularly cardiovascular diseases (CVDs), diabetes mellitus, obesity, and chronic kidney disease (CKD). Meanwhile, these pathological conditions further aggravate ER stress, creating a rather vicious cycle. Here in this review, we aimed at summarizing and updating the available information on ER stress in CVDs, diabetes mellitus, obesity, and CKD, hoping to offer novel insights for the management of these cardiometabolic comorbidities through regulation of ER stress.

Insulin Resistance and Diabetes Mellitus in Alzheimer's Disease

Type 2 diabetes mellitus is a progressive disease that is characterized by the appearance of insulin resistance. The term insulin resistance is very wide and could affect different proteins involved in insulin signaling, as well as other mechanisms. In this review, we have analyzed the main molecular mechanisms that could be involved in the connection between type 2 diabetes and neurodegeneration, in general, and more specifically with the appearance of Alzheimer's disease. We have studied, in more detail, the different processes involved, such as inflammation, endoplasmic reticulum stress, autophagy, and mitochondrial dysfunction.

Dysbiosis of the Saliva Microbiome in Patients With Polycystic Ovary Syndrome

Significant differences in salivary microbiota communities between polycystic ovary syndrome (PCOS) patients and healthy controls have been reported, and interestingly, some salivary microbiota exhibit diurnal oscillation in healthy people. However, whether the diurnal oscillation of salivary microbiota is present in PCOS patients is unknown. In this study, we describe the differences in the saliva microbiome between the PCOS group and the control group at different time points over 24 h. 16S rRNA gene amplicon sequencing was performed on salivary and fecal samples from 10 PCOS patients and 10 healthy controls, and salivary samples were collected at 6-h intervals over 24 h (Zeitgeber (ZT)0, ZT6, ZT12, and ZT18). Among the salivary samples, those from the PCOS group showed significant differences from those of the control group at each time point. Differences were evident in taxa level and metabolic pathways. Interestingly, we found that PCOS disrupted the diurnal rhythm of the salivary microbiota abundance, as determined in the group of healthy women. In addition, no similar changes were found in PCOS patients and controls between the oral and fecal microbiota, including differential microbiota at the phylum level. In this study, significant differences in the composition of the salivary microbiota between PCOS and healthy women were detected at different time points. We also showed that the diurnal rhythm of relative abundance of the salivary microbiota was disrupted in patients with PCOS, which might be related to development of oral-related diseases and systematic metabolic disorders.

Protective effects of pterostilbene against hepatic damage, redox imbalance, mitochondrial dysfunction, and endoplasmic reticulum stress in weanling piglets

This investigation evaluated the potential of natural antioxidants, pterostilbene (PT) and its parent compound resveratrol (RSV), to alleviate hepatic damage, redox imbalance, mitochondrial dysfunction, and endoplasmic reticulum (ER) stress in early-weaned piglets. A total of 144 suckling piglets were randomly assigned to four treatments (six replicates per group, n = 6): 1) sow reared, 2) early weaned and fed a basal diet, 3) early weaned and fed the basal diet supplemented with 300 mg/kg PT, or with 4) 300 mg/kg RSV. Early weaning increased plasma alanine aminotransferase (P = 0.004) and aspartate aminotransferase (P = 0.009) activities and hepatic apoptotic rate (P = 0.001) in piglets compared with the sow-reared piglets. Early weaning decreased hepatic adenosine triphosphate (ATP; P = 0.006) content and mitochondrial complexes III (P = 0.019) and IV activities (P = 0.038), but it increased superoxide anion accumulation (P = 0.026) and the expression levels of ER stress markers, such as glucose-regulated protein 78 (P < 0.001), CCAAT/enhancer-binding protein-homologous protein (P = 0.001), and activating transcription factor (ATF) 4 (P = 0.006). PT was superior to RSV at mitigating liver injury and oxidative stress after early weaning, as indicated by decreases in the number of apoptotic cells (P = 0.036) and the levels of superoxide anion (P = 0.002) and 8-hydroxy-2 deoxyguanosine (P < 0.001). PT increased mitochondrial deoxyribonucleic acid content (P = 0.031) and the activities of citrate synthase (P = 0.005), complexes I (P = 0.004) and III (P = 0.011), and ATP synthase (P = 0.041), which may contribute to the mitigation of hepatic ATP deficit (P = 0.017) in the PT-treated weaned piglets. PT also prevented increases in the ER stress marker and ATF 6 expression levels and in the phosphorylation of inositol-requiring enzyme 1 alpha caused by early weaning (P < 0.05). PT increased sirtuin 1 activity (P = 0.031) in the liver of early-weaned piglets than those in the early-weaned piglets fed a basal diet. In conclusion, PT supplementation alleviates liver injury in weanling piglets probably by inhibiting mitochondrial dysfunction and ER stress.

Reduction in endoplasmic reticulum stress activates beige adipocytes differentiation and alleviates high fat diet-induced metabolic phenotypes

Endoplasmic reticulum (ER) stress is closely associated with various metabolic diseases, such as obesity and diabetes. Development of beige/brite adipocytes increases thermogenesis and helps to reduce obesity. Although the relationship between ER stress and white adipocytes has been studied considerably, the possible role of ER stress and the unfolded protein response (UPR) induction in beige adipocytes differentiation remain to be investigated. In this study we investigated how ER stress affected beige adipocytes differentiation both in vitro and in vivo. Phosphorylation of eIF2α was transiently decreased in the early phase (day 2), whereas it was induced at the late phase with concomitant induction of C/EBP homologous protein (CHOP) during beige adipocytes differentiation. Forced expression of CHOP inhibited the expression of beige adipocytes markers, including Ucp1, Cox8b, Cidea, Prdm16, and Pgc-1α, following the induction of beige adipocytes differentiation. When ER stress was reduced by the chemical chaperone tauroursodeoxycholic acid (TUDCA), the expression of the beige adipocytes marker uncoupling protein 1 (UCP1) was significantly enhanced in inguinal white adipose tissue (iWAT) and high fat diet (HFD)-induced abnormal metabolic phenotype was improved. In summary, we found that ER stress and the UPR induction were closely involved in beige adipogenesis. These results suggest that modulating ER stress could be a potential therapeutic intervention against metabolic dysfunctions via activation of iWAT browning.

ER stress-induced upregulation of NNMT contributes to alcohol-related fatty liver development

BACKGROUND & AIMS

N-nicotinamide methyltransferase (NNMT) is emerging as an important enzyme in the regulation of metabolism. NNMT is highly expressed in the liver. However, the exact regulatory mechanism(s) underlying NNMT expression remains unclear and its potential involvement in alcohol-related liver disease (ALD) is completely unknown.

METHODS

Both traditional Lieber-De Carli and the NIAAA mouse models of ALD were employed. A small-scale chemical screening assay and a chromatin immunoprecipitation assay were performed. NNMT inhibition was achieved via both genetic (adenoviral short hairpin RNA delivery) and pharmacological approaches.

RESULTS

Chronic alcohol consumption induces endoplasmic reticulum (ER) stress and upregulates NNMT expression in the liver. ER stress inducers upregulated NNMT expression in both AML12 hepatocytes and mice. PERK-ATF4 pathway activation is the main contributor to ER stress-mediated NNMT upregulation in the liver. Alcohol consumption fails to upregulate NNMT in liver-specific Atf4 knockout mice. Both adenoviral NNMT knockdown and NNMT inhibitor administration prevented fatty liver development in response to chronic alcohol feeding; this was also associated with the downregulation of an array of genes involved in de novo lipogenesis, including Srebf1, Acaca, Acacb and Fasn. Further investigations revealed that activation of the lipogenic pathway by NNMT was independent of its NAD⁺-enhancing action; however, increased cellular NAD⁺, resulting from NNMT inhibition, was associated with marked liver AMPK activation.

CONCLUSIONS

ER stress, specifically PERK-ATF4 pathway activation, is mechanistically involved in hepatic NNMT upregulation in response to chronic alcohol exposure. Overexpression of NNMT in the liver plays an important role in the pathogenesis of ALD.

LAY SUMMARY

In this study, we show that nicotinamide methyltransferase (NNMT) - the enzyme that catalyzes nicotinamide degradation - is a pathological regulator of alcohol-related fatty liver development. NNMT inhibition protects against alcohol-induced fatty liver development and is associated with suppressed de novo lipogenic activity and enhanced AMPK activation. Thus, our data suggest that NNMT may be a potential therapeutic target for the treatment of alcohol-related liver disease.

Isoliquiritigenin Pretreatment Induces Endoplasmic Reticulum Stress-Mediated Hormesis and Attenuates Cisplatin-Induced Oxidative Stress and Damage in LLC-PK1 Cells

Isoliquiritigenin (IsoLQ) is a flavonoid with antioxidant properties and inducer of endoplasmic reticulum (ER) stress. In vitro and in vivo studies show that ER stress-mediated hormesis is cytoprotective; therefore, natural antioxidants and ER stress inducers have been used to prevent renal injury. Oxidative stress and ER stress are some of the mechanisms of damage involved in cisplatin (CP)-induced nephrotoxicity. This study aims to explore whether IsoLQ pretreatment induces ER stress and produces hormesis to protect against CP-induced nephrotoxicity in Lilly Laboratories Cell-Porcine Kidney 1 (LLC-PK1) cells. During the first stage of this study, both IsoLQ protective concentration and pretreatment time against CP-induced toxicity were determined by cell viability. At the second stage, the effect of IsoLQ pretreatment on cell viability, ER stress, and oxidative stress were evaluated. IsoLQ pretreatment in CP-treated cells induces expression of glucose-related proteins 78 and 94 kDa (GRP78 and GRP94, respectively), attenuates CP-induced cell death, decreases reactive oxygen species (ROS) production, and prevents the decrease in glutathione/glutathione disulfide (GSH/GSSG) ratio, free thiols levels, and glutathione reductase (GR) activity. These data suggest that IsoLQ pretreatment has a moderately protective effect on CP-induced toxicity in LLC-PK1 cells, through ER stress-mediated hormesis, as well as by the antioxidant properties of IsoLQ.

Administration of mulberry leaves maintains pancreatic β-cell mass in obese/type 2 diabetes mellitus mouse model

BACKGROUND

Type 2 diabetes mellitus is characterized by insulin resistance and pancreatic β-cell dysfunction. A decrease in β-cell mass, which occurs during the progression of Type 2 diabetes mellitus, contributes to impaired insulin secretion. Mulberry leaves contain various nutritional components that exert anti-diabetic and anti-atherogenic effects. The present study analyzed the effects of mulberry leaf intake on pancreatic β-cells to clarify the mechanisms underlying its anti-diabetic function.

METHODS

Mulberry leaves (Morus alba L.) were dried at 180 °C for 8 s in a hot-air mill and fed to obesity/Type 2 diabetes mellitus db/db mouse models at 5% (w/w) as part of a normal diet from 7 to 10, 15, or 20 weeks of age. An intraperitoneal glucose tolerance test was then performed on the mice. To evaluate the β-cell mass, the pancreas was subjected to immunohistological analysis with an anti-insulin antibody. A TUNEL assay and immunohistological analysis with a proliferation marker was also performed. Expression levels of endoplasmic reticulum stress-responsible genes and proliferation markers were assessed by quantitative RT-PCR.

RESULTS

Intake of mulberry leaves maintained the β-cell function of db/db mice. Moreover, oral administration of mulberry leaves significantly decreased cell death by reducing endoplasmic reticulum stress in the pancreas. Mulberry leaves significantly increased proliferation of β-cells and the expression of pancreatic duodenal homeobox1 mRNA in the pancreas.

CONCLUSION

Considered together, these results indicate that dietary mulberry leaf administration can maintain insulin levels and pancreatic β-cell mass, at least in part, by suppressing endoplasmic reticulum stress in Type 2 diabetes mellitus mouse models.

HDAC inhibitors rescue multiple disease-causing CFTR variants

Understanding the role of the epigenome in protein-misfolding diseases remains a challenge in light of genetic diversity found in the world-wide population revealed by human genome sequencing efforts and the highly variable response of the disease population to therapeutics. An ever-growing body of evidence has shown that histone deacetylase (HDAC) inhibitors (HDACi) can have significant benefit in correcting protein-misfolding diseases that occur in response to both familial and somatic mutation. Cystic fibrosis (CF) is a familial autosomal recessive disease, caused by genetic diversity in the CF transmembrane conductance regulator (CFTR) gene, a cyclic Adenosine MonoPhosphate (cAMP)-dependent chloride channel expressed at the apical plasma membrane of epithelial cells in multiple tissues. The potential utility of HDACi in correcting the phenylalanine 508 deletion (F508del) CFTR variant as well as the over 2000 CF-associated variants remains controversial. To address this concern, we examined the impact of US Food and Drug Administration-approved HDACi on the trafficking and function of a panel of CFTR variants. Our data reveal that panobinostat (LBH-589) and romidepsin (FK-228) provide functional correction of Class II and III CFTR variants, restoring cell surface chloride channel activity in primary human bronchial epithelial cells. We further demonstrate a synergistic effect of these HDACi with Vx809, which can significantly restore channel activity for multiple CFTR variants. These data suggest that HDACi can serve to level the cellular playing field for correcting CF-causing mutations, a leveling effect that might also extend to other protein-misfolding diseases.

Does perturbation in the mitochondrial protein folding pave the way for neurodegeneration diseases?

Mitochondria, which are cell compartments that are widely present in eukaryotic cells, have been shown to be involved in a variety of synthetic, metabolic, and signaling processes, thereby playing a vital role in cells. The mitochondrial unfolded protein response (mtUPR) is a response in which mitochondria reverse the signal to the nucleus and maintain mitochondrial protein homeostasis when unfolded and misfolded proteins continue to accumulate. Multiple neurodegeneration diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), and familial amyotrophic lateral sclerosis (fALS), are public health challenges. Every year, countless efforts are expended trying to clarify the pathogenesis and treatment of neurological disorders, which are associated with mitochondrial dysfunction to some extent. Numerous studies have shown that mtUPR is involved in and plays an important role in the pathogenesis of neurological disorders, but the exact mechanism of the disorders is still unclear. Further study of the process of mtUPR in neurological disorders can help us more accurately understand their pathogenesis in order to provide new therapeutic targets. In this paper, we briefly review mtUPR signaling in Caenorhabditis elegans (C. elegans) and mammals and summarize the role of mtUPR in neurodegeneration diseases, including AD, PD and fALS.

4-Phenylbutyric Acid Reduces Endoplasmic Reticulum Stress in Chondrocytes That Is Caused by Loss of the Protein Disulfide Isomerase ERp57

Objective

The integrity of cartilage depends on the correct synthesis of extracellular matrix (ECM) components. In case of insufficient folding of proteins in the endoplasmic reticulum (ER) of chondrocytes, ECM proteins aggregate, ER stress evolves, and the unfolded protein response (UPR) is initiated. By this mechanism, chondrocytes relieve the stress condition or initiate cell death by apoptosis. Especially persistent ER stress has emerged as a pathogenic mechanism in cartilage diseases, such as chondrodysplasias and osteoarthritis. As pharmacological intervention is not available yet, it is of great interest to understand cartilage ER stress in detail and to develop therapeutics to intervene.

Methods

ERp57-deficient chondrocytes were generated by CRISPR/Cas9-induced KO. ER stress and autophagy were studied on mRNA and protein level as well as by transmission electron microscopy (TEM) in chondrocyte micromass or cartilage explant cultures of ERp57 KO mice. Thapsigargin (Tg), an inhibitor of the ER-residing Ca²⁺-ATPase, and 4-Phenylbutyric acid (4-PBA), a small molecular chemical chaperone, were applied to induce or inhibit ER stress.

Results

Our data reveal that the loss of the protein disulfide isomerase ERp57 is sufficient to induce ER stress in chondrocytes. 4-PBA efficiently diffuses into cartilage explant cultures and diminishes excessive ER stress in chondrocytes dose dependently, no matter if it is induced by ERp57 KO or stimulation with Tg.

Conclusion

ER-stress-related diseases have different sources; therefore, various targets for therapeutic treatment exist. In the future, 4-PBA may be used alone or in combination with other drugs for the treatment of ER-stress-related skeletal disorders in patients.

Impact of hepatitis C virus and alcohol, alone and combined, on the unfolded protein response in primary human hepatocytes

Hepatitis C virus (HCV) infection and alcohol abuse are leading causes of chronic liver disease and frequently coexist in patients. The unfolded protein response (UPR), a cellular stress response ranging along a spectrum from cytoprotection to apoptosis commitment, has emerged as a major contributor to human diseases including liver injuries. However, the literature contains conflicting reports as to whether HCV and ethanol activate the UPR and which UPR genes are involved. Here we have used primary human hepatocytes (PHH) to reassess this issue and address combined impacts. In this physiologically relevant model, either stressor activated a chronic complete UPR. However, the levels of UPR gene induction were only modest in the case of HCV infection. Moreover, when combined to the strong stressor thapsigargin, ethanol exacerbated the activation of pro-apoptotic genes whereas HCV tended to limit the induction of key UPR genes. The UPR resulting from HCV plus ethanol was comparable to that induced by ethanol alone with the notable exception of three pro-survival genes the expressions of which were selectively enhanced by HCV. Interestingly, HCV genome replication was maintained at similar levels in PHH exposed to ethanol. In conclusion, while both HCV and alcohol activate the hepatocellular UPR, only HCV manipulates UPR signalling in the direction of a cytoprotective response, which appears as a viral strategy to spare its own replication.

Perilipin 5 Protects against Cellular Oxidative Stress by Enhancing Mitochondrial Function in HepG2 Cells

: Non-alcoholic fatty liver disease (NAFLD) is one of the most common liver diseases worldwide. Reactive oxygen species (ROS), as potent oxidants in cells, have been shown to promote the development of NAFLD. Previous studies reported that for ROS-induced cellular oxidative stress, promoting lipid droplet (LD) accumulation is associated with the cellular antioxidation process. However, the regulatory role of LDs in relieving cellular oxidative stress is poorly understood. Here, we showed that Perilipin 5 (PLIN5), a key LD protein related to mitochondria-LD contact, reduced ROS levels and improved mitochondrial function in HepG2 cells. Both mRNA and protein levels of PLIN5 were significantly increased in cells with hydrogen peroxide or lipopolysaccharide (LPS) treatment (p < 0.05). Additionally, the overexpression of PLIN5 promoted LD formation and mitochondria-LD contact, reduced cellular ROS levels and up-regulated mitochondrial function-related genes such as COX and CS. Knockdown PLIN5, meanwhile, showed opposite effects. Furthermore, we identified that cellular oxidative stress up-regulated PLIN5 expression via the JNK-p38-ATF pathway. This study shows that the up-regulation of PLIN5 is a kind of survival strategy for cells in response to stress. PLIN5 can be a potential therapeutic target in NAFLD.

Endoplasmic reticulum stress: A master regulator of metabolic syndrome

Endoplasmic reticulum (ER) stress, a change in the ER homeostasis, leads to initiation of the unfolded protein response (UPR). The primary functions of the UPR are to restore the ER's physiological activity and coordinate the apoptotic and adaptive responses. Pathophysiological conditions that augment ER stress include hypoxia, misfolded and/or mutated protein accumulation, and high glucose. Prolonged ER stress is a critical factor in the pathogenesis of metabolic syndrome including type 2 diabetes mellitus, cardiovascular diseases, atherosclerosis, obesity, and fatty liver disease. UPR is a complex homeostatic pathway between newly synthesized proteins and their maturation, although the regulatory mechanisms contributing to the UPR and the possible therapeutic strategies are yet to be clarified. Therefore, a comprehensive understanding of the underlying molecular mechanisms is necessary to develop therapeutic interventions targeting ER stress response. In this review, we discuss the role of ER stress and UPR signaling in the pathogenesis of metabolic syndrome, highlighting the main functions of UPR components. We have emphasized the use of novel small molecular chemical chaperones, considered as modulators of ER stress. The initial studies with these chemical chaperones are promising, but detailed studies are required to define their efficacy and adverse effects during therapeutic use in humans.

Lipid storage droplet protein 5 reduces sodium palmitate‑induced lipotoxicity in human normal liver cells by regulating lipid metabolism‑related factors

Lipid storage droplet protein 5 (LSDP5) is specifically expressed in tissues with high oxidative metabolism such as liver and heart. The present study aimed to explored the role of LSDP5 in sodium palmitate-induced lipotoxicity in LO2 normal human liver cells. LO2 cells were treated with various concentrations of sodium palmitate (25, 50, 75, 100, 125 and 150 µmol/l) for 12, 24 and 48 h, and cell viability was determined by Cell Counting Kit-8. Subsequently, LO2 cells were exposed to 100 µmol/l sodium palmitate for 48 h to induce lipotoxicity (Model). Lipotoxicity Model LO2 cells were also transfected with pCMV5-LSDP5 overexpression vector, and reactive oxygen species (ROS) production, mitochondrial membrane potential (MMP) and apoptotic rates were measured. The contents of non-esterified fatty acid (NEFA), malondialdehyde (MDA) and superoxide dismutase (SOD) were also measured. The expression levels of LSDP5, and apoptosis-, mitochondrial-, lipid metabolism-related factors were detected using reverse transcription-quantitative polymerase chain reaction and western blot assays. The results indicated that sodium palmitate exposure inhibited cell viability and induced lipotoxicity in LO2 cells. LSDP5 overexpression decreased ROS and apoptotic rates, and reduced NEFA and MDA content. LSDP5 transfection rescued the loss of MMP and elevated SOD content in lipotoxicity Model LO2 cells. In addition, LSDP5 upregulated the expression levels of B-cell lymphoma-2, acetyl-CoA carboxylase1/2 and fatty acid synthase (Fas), whereas the expression levels of activated-caspase-3, Bcl-2-associated X protein, cytochrome c, cytochrome c oxidase subunits IV, carnitine palmitoyltransferase 1a and peroxisome proliferator-activated receptors α levels were downregulated. LSDP5 may produce a protective effect on sodium palmitate-induced lipotoxicity in LO2 cells by regulating lipid metabolism-related factors.

Effects of apoptosis on liver aging

As an irreversible and perennial process, aging is accompanied by functional and morphological declines in organs. Generally, aging liver exhibits a decline in volume and hepatic blood flow. Even with a preeminent regenerative capacity to restore its functions after liver cell loss, its biosynthesis and metabolism abilities decline, and these are difficult to restore to previous standards. Apoptosis is a programmed death process via intrinsic and extrinsic pathways, in which Bcl-2 family proteins and apoptosis-related genes, such as p21 and p53, are involved. Apoptosis inflicts both favorable and adverse influences on liver aging. Apoptosis eliminates transformed abnormal cells but promotes age-related liver diseases, such as nonalcoholic fatty liver disease, liver fibrosis, cirrhosis, and liver cancer. We summarize the roles of apoptosis in liver aging and age-related liver diseases.

Genetic Disorders of the Extracellular Matrix

Mutations in the genes for extracellular matrix (ECM) components cause a wide range of genetic connective tissues disorders throughout the body. The elucidation of mutations and their correlation with pathology has been instrumental in understanding the roles of many ECM components. The pathological consequences of ECM protein mutations depend on its tissue distribution, tissue function, and on the nature of the mutation. The prevalent paradigm for the molecular pathology has been that there are two global mechanisms. First, mutations that reduce the production of ECM proteins impair matrix integrity largely due to quantitative ECM defects. Second, mutations altering protein structure may reduce protein secretion but also introduce dominant negative effects in ECM formation, structure and/or stability. Recent studies show that endoplasmic reticulum (ER) stress, caused by mutant misfolded ECM proteins, makes a significant contribution to the pathophysiology. This suggests that targeting ER‐stress may offer a new therapeutic strategy in a range of ECM disorders caused by protein misfolding mutations. Anat Rec, 2019. © 2019 The Authors. The Anatomical Record published by Wiley Periodicals, Inc. on behalf of American Association of Anatomists.

Effects of metformin on metabolism of white and brown adipose tissue in obese C57BL/6J mice

BACKGROUND

To investigate effects of metformin on the regulation of proteins of white adipose tissue (WAT) and brown adipose tissue (BAT) in obesity and explore the underlying mechanisms on energy metabolism.

METHODS

C57BL/6J mice were fed with normal diet (ND, n = 6) or high-fat diet (HFD, n = 12) for 22 weeks. HFD-induced obese mice were treated with metformin (MET, n = 6). After treatment for 8 weeks, oral glucose tolerance test (OGTT) and hyperinsulinemic-euglycemic clamp were performed to evaluate the improvement of glucose tolerance and insulin sensitivity. Protein expressions of WAT and BAT in mice among ND, HFD, and MET group were identified and quantified with isobaric tag for relative and absolute quantification (iTRAQ) coupled with 2D LC-MS/MS. The results were analyzed by MASCOT, Scaffold and IPA.

RESULTS

The glucose infusion rate in MET group was increased significantly compared with HFD group. We identified 4388 and 3486 proteins in WAT and BAT, respectively. As compared MET to HFD, differential expressed proteins in WAT and BAT were mainly assigned to the pathways of EIF2 signaling and mitochondrial dysfunction, respectively. In the pathways, CPT1a in WAT, CPT1b and CPT2 in BAT were down-regulated by metformin significantly.

CONCLUSIONS

Metformin improved the body weight and insulin sensitivity of obese mice. Meanwhile, metformin might ameliorate endoplasmic reticulum stress in WAT, and affect fatty acid metabolism in WAT and BAT. CPT1 might be a potential target of metformin in WAT and BAT.

Matrine attenuates endoplasmic reticulum stress and mitochondrion dysfunction in nonalcoholic fatty liver disease by regulating SERCA pathway

Background

Endoplasmic reticulum (ER) stress, which can promote lipid metabolism disorders and steatohepatitis, contributes significantly to the pathogenesis of nonalcoholic fatty liver disease (NAFLD). Calcium (Ca²⁺) homeostasis is considered to play a key role in ER stress. Matrine (Mat) has been applied for the treatment of hepatitis B, but its effect on NAFLD is still unknown, and there is no unified view of Mat on the regulation of ER stress in the previous literature.

Methods

The pharmacological effects were studied in high-fat-diet or methionine–choline-deficient diet induced C57BL/6J mice models and in palmitic acid (PA) induced L02 human liver cell model. Calcium fluorescence experiments, computational virtual docking analysis and biochemical assays were used in identifying the locus of Mat.

Results

The results showed that Mat-treated mice were more resistant to steatosis in the liver than vehicle-treated mice and that Mat significantly reduced hepatic inflammation, lipid peroxides. The beneficial effect of Mat was associated with suppressing ER stress and restoring mitochondrial dysfunction. Additionally, Mat decreased the PA-induced lipid accumulation, ER stress and cytosolic calcium level ([Ca²⁺]_c) in hepatocyte cell lines in low and middle dose. However, the high dose Mat did not show satisfactory results in cell model. Calcium fluorescence experiments showed that Mat was able to regulate [Ca²⁺]_c. By computational virtual docking analysis and biochemical assays, Mat was shown to influence [Ca²⁺]_c via direct inhibition of SERCA.

Conclusions

The results showed that the bi-directional regulation of Mat to endoplasmic reticulum at different doses was based on the inhibition of SERCA. In addition, the results also provide a theoretical basis for Mat as a potential therapeutic strategy in NAFLD/NASH.

Electronic supplementary material

The online version of this article (10.1186/s12967-018-1685-2) contains supplementary material, which is available to authorized users.

Cyclosporine A binding to COX-2 reveals a novel signaling pathway that activates the IRE1α unfolded protein response sensor

Cyclosporine, a widely used immunosuppressant in organ transplantation and in treatment of various autoimmune diseases, activates the unfolded protein response (UPR), an ER stress coping response. In this study we discovered a new and unanticipated cyclosporine-dependent signaling pathway, with cyclosporine triggering direct activation of the UPR. COX-2 binds to and activates IRE1α, leading to IRE1α splicing of XBP1 mRNA. Molecular interaction and modeling analyses identified a novel interaction site for cyclosporine with COX-2 which caused enhancement of COX-2 enzymatic activity required for activation of the IRE1α branch of the UPR. Cyclosporine-dependent activation of COX-2 and IRE1α in mice indicated that cyclosporine-COX-2-IRE1α signaling pathway was functional in vivo. These findings identify COX-2 as a new IRE1α binding partner and regulator of the IRE1α branch of the UPR pathway, and establishes the mechanism underlying cytotoxicity associated with chronic cyclosporine exposure.

Phospholipid Remodeling in Physiology and Disease

Phospholipids are major constituents of biological membranes. The fatty acyl chain composition of phospholipids determines the biophysical properties of membranes and thereby affects their impact on biological processes. The composition of fatty acyl chains is also actively regulated through a deacylation and reacylation pathway called Lands' cycle. Recent studies of mouse genetic models have demonstrated that lysophosphatidylcholine acyltransferases (LPCATs), which catalyze the incorporation of fatty acyl chains into the sn-2 site of phosphatidylcholine, play important roles in pathophysiology. Two LPCAT family members, LPCAT1 and LPCAT3, have been particularly well studied. LPCAT1 is crucial for proper lung function due to its role in pulmonary surfactant biosynthesis. LPCAT3 maintains systemic lipid homeostasis by regulating lipid absorption in intestine, lipoprotein secretion, and de novo lipogenesis in liver. Mounting evidence also suggests that changes in LPCAT activity may be potentially involved in pathological conditions, including nonalcoholic fatty liver disease, atherosclerosis, viral infections, and cancer. Pharmacological manipulation of LPCAT activity and membrane phospholipid composition may provide new therapeutic options for these conditions.

Binding Analysis of the Inositol-Requiring Enzyme 1 Kinase Domain

Inositol-requiring enzyme 1 (IRE1) is an orchestrator of the unfolded protein response (UPR), the cellular response to endoplasmic reticulum (ER) stress that plays a crucial role in tumor development. IRE1 signaling is the most evolutionary conserved branch of the UPR. Under ER stress, the IRE1 luminal domain undergoes a conformational change to multimerize, resulting in trans-autophosphorylation and activation of the cytosolic kinase and endoribonuclease domain. Adenosine triphosphate-competitive inhibitors that bind to the IRE1 kinase site can modulate the activity of the RNase domain through an allosteric relationship between the IRE1 kinase and RNase domains. The current study aims at the investigation of available structural data of the IRE1 kinase domain and provides insights into the design of novel kinase inhibitors. To this end, a detailed analysis of IRE1 kinase active site and investigation of suitable structures for virtual screening studies were performed. The results indicate in silico target fishing as an appropriate strategy for the identification of novel IRE1 kinase binders, further validating the robustness of the in silico protocol. Importantly, the study highlights the kinase-inhibiting RNase attenuator (KIRA)-bound protein data bank 4U6R structure as the best protein structure to perform virtual screening to develop diverse and more potent KIRA-like IRE1 kinase inhibitors that are capable of allosterically affecting the RNase activity.

The Effect of Chronic Inflammation and Oxidative and Endoplasmic Reticulum Stress in the Course of Metabolic Syndrome and Its Therapy

Metabolic syndrome (MetS) is highly associated with a modern lifestyle. The prevalence of MetS has reached epidemic proportion and is still rising. The main cause of MetS and finally type 2 diabetes occurrence is excessive nutrient intake, lack of physical activity, and inflammatory cytokines secretion. These factors lead to redistribution of body fat and oxidative and endoplasmic reticulum (ER) stress occurrence, resulting in insulin resistance, increase adipocyte differentiation, and much elevated levels of proinflammatory cytokines. Cellular therapies, especially mesenchymal stem cell (MSC) transplantation, seem to be promising in the MetS and type 2 diabetes treatments, due to their immunomodulatory effect and multipotent capacity; adipose-derived stem cells (ASCs) play a crucial role in MSC-based cellular therapies. In this review, we focused on etiopathology of MetS, especially on the crosstalk between chronic inflammation, oxidative stress, and ER stress and their effect on MetS-related disease occurrence, as well as future perspectives of cellular therapies. We also provide an overview of therapeutic approaches that target endoplasmic reticulum and oxidative stress.

Molybdate Attenuates Lipid Accumulation in the Livers of Mice Fed a Diet Deficient in Methionine and Choline

Both lipid accumulation and oxidative stress are major pathologic contributors to the development of hepatic steatosis. Treatment with molybdate reduces hepatic levels of lipids in diabetic rats. Potential activities of molybdate as an antioxidant have also been demonstrated in various animal models. In the present study, we evaluated the effects of sodium molybdate dihydrate (SM) on hepatic steatosis and associated disturbances in a widely used mouse model of the metabolic disease. Male C57Bl/6 mice at 10 weeks of age were fed a diet deficient in methionine and choline (MCD) and bottled water containing SM for four weeks. The SM treatment markedly attenuated MCD-induced accumulation of lipids, mainly triglycerides, in the liver. Lipid catabolic autophagic pathways were activated by SM in the MCD-fed mouse livers, as evidenced by a decreased level of p62 expression. MCD-induced oxidative damage, such as lipid and protein oxidation, was also alleviated by SM in the liver. However, the level of MCD-induced hepatocellular damage was not affected by SM. Taken together, these findings suggest that molybdate can be used in the treatment and prevention of hepatic steatosis without inducing adverse effects in the liver. To the best of our knowledge, this is the first experimental study to investigate the effects of molybdate in non-alcoholic fatty liver disease, and also the first that demonstrates molybdate-induced autophagy.

Pien Tze Huang ameliorates liver injury by inhibiting the PERK/eIF2α signaling pathway in alcohol and high-fat diet rats

OBJECTIVE

To explore whether Pien Tze Huang (PTH) exerts a hepatoprotective effect via inhibiting the PERK/eIF2ɑ signaling pathway using an experimental animal model of alcoholic and high-fat diet rats.

METHODS

A liver injury rat model was established and treated with PTH. Pathological changes in the liver were evaluated by hematoxylin and eosin staining. Hepatic biochemical indexes were detected using an automatic biochemical analyzer. The level of Hcy in serum samples was analyzed using an ELISA. Levels of mRNAs related to ER stress signaling were measured by real-time quantitative-PCR, and protein expression levels were measured by Western blot analysis.

RESULTS

PTH ameliorated the defects in hepatic function, hepatic pathology and the impairment in lipid metabolism observed in the alcoholic and high-fat diet rats. Moreover, PTH reduced the serum Hcy level and inhibited the PERK/eIF2ɑ pathway in response to ER stress.

CONCLUSIONS

These results suggest that the administration of PTH ameliorated the severity of alcoholic and high-fat diet rats possibly by inhibiting the Hcy-induced PERK/eIF2α pathway.

Personalized therapy when tackling nonalcoholic fatty liver disease: a focus on sex, genes, and drugs

INTRODUCTION

Nonalcoholic fatty liver disease (NAFLD) is the most frequent liver disease in the world. It describes a term for a group of hepatic diseases including steatosis, fibrosis, and cirrhosis that can finally lead to hepatocellular carcinoma. There are many factors influencing NAFLD initiation and progression, such as obesity, dyslipidemia, insulin resistance, genetic factors, and hormonal changes. However, there is also lean-NAFLD which is not associated with obesity. NAFLD is considered to be a sexually dimorphic disease. In most cases, men have a higher prevalence for the disease compared to premenopausal women. Areas covered: In this review, we first summarize the NAFLD disease epidemiology, pathology, and diagnosis. We describe NAFLD progression with the focus on sexual and genetic differences for disease development and pharmacological treatment. Personalized treatment for multifactorial NAFLD is discussed in consideration of different factors, including genetics, gender and sex. Expert opinion: The livers of female and male NAFLD patients have different metabolic capacities which influence the metabolism of all drugs applied to such patients. This aspect is not yet sufficiently taken into account. The liver computational models might quicken the pace toward assessing personalized disease progression and treatment options.

Endoplasmic Reticulum Stress in Metabolic Disorders

Metabolic disorders have become among the most serious threats to human health, leading to severe chronic diseases such as obesity, type 2 diabetes, and non-alcoholic fatty liver disease, as well as cardiovascular diseases. Interestingly, despite the fact that each of these diseases has different physiological and clinical symptoms, they appear to share certain pathological traits such as intracellular stress and inflammation induced by metabolic disturbance stemmed from over nutrition frequently aggravated by a modern, sedentary life style. These modern ways of living inundate cells and organs with saturating levels of sugar and fat, leading to glycotoxicity and lipotoxicity that induce intracellular stress signaling ranging from oxidative to ER stress response to cope with the metabolic insults (Mukherjee, et al., 2015). In this review, we discuss the roles played by cellular stress and its responses in shaping metabolic disorders. We have summarized here current mechanistic insights explaining the pathogenesis of these disorders. These are followed by a discussion of the latest therapies targeting the stress response pathways.

Increased expression of CHOP and LC3B in newborn rats with bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) seriously affects the health and prognosis of children, but the efficacy of treatments is poor. The present study aimed to examine the effects of C/EBP homologous protein (CHOP), activating transcription factor 4 (ATF4) and microtubule‑associated protein light chain 3β (LC3B), and the interaction between CHOP and LC3B, in newborn rats with BPD. At 1, 7, 14 and 21 days, the rats in the model [fraction of inspired oxygen (FiO2)=80‑85%] and control groups (FiO2=21%) were randomly sacrificed, and lung samples were collected. Alveolar development was evaluated according to the radial alveolar count (RAC) and alveolar septum thickness. Ultrastructural changes were observed by transmission electron microscopy (TEM), the expression levels of CHOP, ATF4 and LC3B were determined by immunohistochemistry, and western blot and reverse transcription‑quantitative polymerase chain reaction analyses. The co‑localization of CHOP and LC3B in lung tissues was determined by immunofluorescence. The results showed that, compared with the control group, alveolarization arrest was present in the model group. The TEM observations revealed that, at 14 days, type II alveolar epithelial cell (AECII) lamellar bodies were damaged, with an apparent dilation of the endoplasmic reticulum (ER) and autophagy in cells within the model group. Between days 7 and 14, the protein levels of ATF4, CHOP and LC3B were significantly increased in the model group. The mRNA levels of CHOP and LC3B were lower at days 7‑21. CHOP and LC3B were co‑localized in the cells of the lung tissues at day 14 in the model group. Pearson's correlation analysis showed that the protein levels of CHOP and LC3B‑II were positively correlated in the model groups. As in previous studies, the present study demonstrated that BPD damaged the AECII cells, which exhibited detached and sparse microvilli and the vacuolization of lamellar bodies. In addition, it was found that the ER was dilated, with autophagosomes containing ER and other organelles in AECII cells; the expression levels of CHOP and LC3B‑II were upregulated. CHOP and LC3B‑II may have joint involvement in the occurrence and development of BPD.

The Endoplasmic Reticulum Stress Response in Neuroprogressive Diseases: Emerging Pathophysiological Role and Translational Implications

The endoplasmic reticulum (ER) is the main cellular organelle involved in protein synthesis, assembly and secretion. Accumulating evidence shows that across several neurodegenerative and neuroprogressive diseases, ER stress ensues, which is accompanied by over-activation of the unfolded protein response (UPR). Although the UPR could initially serve adaptive purposes in conditions associated with higher cellular demands and after exposure to a range of pathophysiological insults, over time the UPR may become detrimental, thus contributing to neuroprogression. Herein, we propose that immune-inflammatory, neuro-oxidative, neuro-nitrosative, as well as mitochondrial pathways may reciprocally interact with aberrations in UPR pathways. Furthermore, ER stress may contribute to a deregulation in calcium homoeostasis. The common denominator of these pathways is a decrease in neuronal resilience, synaptic dysfunction and even cell death. This review also discusses how mechanisms related to ER stress could be explored as a source for novel therapeutic targets for neurodegenerative and neuroprogressive diseases. The design of randomised controlled trials testing compounds that target aberrant UPR-related pathways within the emerging framework of precision psychiatry is warranted.

Targeting the Endoplasmic Reticulum Unfolded Protein Response to Counteract the Oxidative Stress-Induced Endothelial Dysfunction

In endothelial cells, the tight control of the redox environment is essential for the maintenance of vascular homeostasis. The imbalance between ROS production and antioxidant response can induce endothelial dysfunction, the initial event of many cardiovascular diseases. Recent studies have revealed that the endoplasmic reticulum could be a new player in the promotion of the pro- or antioxidative pathways and that in such a modulation, the unfolded protein response (UPR) pathways play an essential role. The UPR consists of a set of conserved signalling pathways evolved to restore the proteostasis during protein misfolding within the endoplasmic reticulum. Although the first outcome of the UPR pathways is the promotion of an adaptive response, the persistent activation of UPR leads to increased oxidative stress and cell death. This molecular switch has been correlated to the onset or to the exacerbation of the endothelial dysfunction in cardiovascular diseases. In this review, we highlight the multiple chances of the UPR to induce or ameliorate oxidative disturbances and propose the UPR pathways as a new therapeutic target for the clinical management of endothelial dysfunction.

Tauroursodeoxycholic Acid Protects Nucleus Pulposus Cells from Compression-Induced Apoptosis and Necroptosis via Inhibiting Endoplasmic Reticulum Stress

Tauroursodeoxycholic acid (TUDCA) is a kind of hydrophilic bile acid, which could protect cells from death via inhibiting endoplasmic reticulum (ER) stress. However, the role of TUDCA in compression-induced intervertebral disc degeneration (IVDD) has not been elucidated. Here, we used a previously described device to mimic in vivo compression conditions. NP cells treated with DMSO or TUDCA were exposed to compression. Then, cell viability, morphology, and apoptosis were detected. Furthermore, apoptosis-related proteins and necroptosis markers were detected too. To investigate the specific cytoprotective mechanisms of TUDCA in IVDD, we detected the ER morphology by electron microscopy. In addition, the ER stress of nucleus pulposus (NP) cells was quantitatively evaluated by analyzing the level of ER-stress-associated proteins. Our results revealed that TUDCA could protect NP cells from excessive compression-induced death by reducing the apoptosis and necroptosis. In addition, ER stress is involved in pathogenesis of IVDD induced by excessive compression and plays a detrimental role. TUDCA exerts its protective functions by inhibiting ER stress. In conclusion, TUDCA could protect NP cells from compression-induced death, which suggested that treatment by TUDCA may be a potential method to retard IVDD.

Proteomic analyses of brain tumor cell lines amidst the unfolded protein response

Brain tumors such as high grade gliomas are among the deadliest forms of human cancers. The tumor environment is subject to a number of cellular stressors such as hypoxia and glucose deprivation. The persistence of the stressors activates the unfolded proteins response (UPR) and results in global alterations in transcriptional and translational activity of the cell. Although the UPR is known to effect tumorigenesis in some epithelial cancers, relatively little is known about the role of the UPR in brain tumors. Here, we evaluated the changes at the molecular level under homeostatic and stress conditions in two glioma cell lines of differing tumor grade. Using mass spectrometry analysis, we identified proteins unique to each condition (unstressed/stressed) and within each cell line (U87MG and UPN933). Comparing the two, we find differences between both the conditions and cell lines indicating a unique profile for each. Finally, we used our proteomic data to identify the predominant pathways within these cells under unstressed and stressed conditions. Numerous predominant pathways are the same in both cell lines, but there are differences in biological and molecular classifications of the identified proteins, including signaling mechanisms, following UPR induction; we see that relatively minimal proteomic alterations can lead to signaling changes that ultimately promote cell survival.

Understanding the Unfolded Protein Response in the Pathogenesis of Asthma

Asthma is a heterogeneous, chronic inflammatory disease of the airways. It is a complex disease with different clinical phenotypes and results in a substantial socioeconomic burden globally. Poor understanding of pathogenic mechanisms of the disease hinders the investigation into novel therapeutics. Emerging evidence of the unfolded protein response (UPR) in the endoplasmic reticulum (ER) has demonstrated previously unknown functions of this response in asthma development. A worsening of asthmatic condition can be brought on by stimuli such as oxidative stress, pathogenic infections, and allergen exposure. All of which can induce ER stress and activate UPR leading to activation of different inflammatory responses and dysregulate the innate immune functions in the airways. The UPR as a central regulator of asthma pathogenesis may explain several unknown mechanism of the disease onset, which leads us in new directions for future asthma treatments. In this review, we summarize and discuss the causes and impact of ER–UPR in driving the pathogenesis of asthma and highlight its importance in clinical implications.

Expression of ATF6 as a marker of pre-cancerous atypical change in ulcerative colitis-associated colorectal cancer: a potential role in the management of dysplasia

BACKGROUND

Diagnosis of low-grade dysplasia (LGD) is important in the management of ulcerative colitis (UC), but it is often difficult to distinguish LGD from inflammatory regenerative epithelium. The unfolded protein response (UPR) is activated in inflammatory bowel disease and malignancies. We aimed to identify a UPR-related gene that is involved in the development of non-UC and UC-associated colorectal cancer (CRC), and to investigate whether the target gene is useful for the diagnosis of LGD.

METHODS

Using our microarray gene expression database of 152 CRCs, we identified activating transcription factor 6 (ATF6) as a target gene. Immunohistochemistry (IHC) of ATF6 were analyzed in 137 surgically resected CRCs, 95 endoscopically resected adenomas and pTis cancers, and 136 samples from 51 UC patients (93 colitis without neoplasia, 31 dysplasia, and 12 UC-associated CRC). The diagnostic accuracy of ATF6 and p53 as markers of LGD was assessed.

RESULTS

ATF6 expression was detectable in all CRCs but not in normal colonic mucosa, was elevated with increase in cellular atypia (adenoma with moderate atypia < severe atypia < pTis CRC, p < 0.001), and higher in dysplasia and CRC than in non-neoplastic colitis (p < 0.001). Notably, the difference between colitis and LGD was significant. Compared to p53-IHC, ATF6-IHC had better diagnostic accuracy for distinguishing LGD from background inflammatory mucosa (sensitivity 70.8 vs. 16.7%, specificity 78.5 vs.71.0%, respectively).

CONCLUSIONS

ATF6 was expressed in lesions undergoing pre-cancerous atypical change in both non-UC and UC-associated CRC and may be used to distinguish LGD from inflammatory regenerative epithelium in UC patients.

Transcription Factor C/EBP Homologous Protein in Health and Diseases

C/EBP homologous protein (CHOP), known also as DNA damage-inducible transcript 3 and as growth arrest and DNA damage-inducible protein 153 (GADD153), is induced in response to certain stressors. CHOP is universally acknowledged as a main conduit to endoplasmic reticulum stress-induced apoptosis. Ongoing research established the existence of CHOP-mediated apoptosis signaling networks, for which novel downstream targets are still being determined. However, there are studies that contradict this notion and assert that apoptosis is not the only mechanism by which CHOP plays in the development of pathologies. In this review, insights into the roles of CHOP in pathophysiology are summarized at the molecular and cellular levels. We further focus on the newest advances that implicate CHOP in human diseases including cancer, diabetes, neurodegenerative disorders, and notably, fibrosis.

Dissecting the Role of Disturbed ER-Golgi Trafficking in Antivirals and Alcohol Abuse-Induced Pathogenesis of Liver Disorders

Antiviral drugs and alcohol abuse-induced organelle stresses have been linked to many disorders and the underlying molecular mechanisms are under intense investigations. This brief review communicates emerging evidence and research trends on how certain antivirals and alcohol affect ER-Golgi trafficking, which potentially impacts the function and integrity of the Golgi apparatus contributing to endoplasmic reticulum stress and cellular injury.