Elimination of endoplasmic reticulum stress and cardiovascular, type 2 diabetic, and other metabolic diseases

FicD regulates adaptation to the unfolded protein response in the murine liver

The unfolded protein response (UPR) is a cellular stress response that is activated when misfolded proteins accumulate in the endoplasmic reticulum (ER). Regulation of the UPR response must be adapted to the needs of the cell as prolonged UPR responses can result in disrupted cellular function and tissue damage. Previously, we discovered that the enzyme FicD (also known as Fic or HYPE) through its AMPylation and deAMPylation activity can modulate the UPR response via post-translational modification of BiP. FicD AMPylates BiP during homeostasis and deAMPylates BiP during stress. We hypothesized that FicD regulation of the UPR will play a role in mitigating the deleterious effects of UPR activation in tissues with frequent physiological stress. Here, we explore the role of FicD in the murine liver. As seen in our pancreatic studies, livers lacking FicD exhibit enhanced UPR signaling in response to short term physiologic fasting and feeding stress. However, in contrast to studies on the pancreas, livers, as a more regenerative tissue, remained remarkably resilient in the absence of FicD. The livers of FicD-/- did not show marked changes in UPR signaling or damage after either chronic high fat diet (HFD) feeding or acute pathological UPR induction. Intriguingly, FicD-/- mice showed changes in UPR induction and weight loss patterns following repeated pathological UPR induction. These findings indicate that FicD regulates UPR responses during mild physiological stress and in adaptation to repeated stresses, but there are tissue specific differences in the requirement for FicD regulation.

The Role of Endoplasmic Reticulum Stress in Metabolic Diseases

The endoplasmic reticulum (ER), the center of protein folding, also controls the cell's life-and-death signaling mechanisms. ER stress caused by unfolded or misfolded proteins leads to the activation of the unfolded protein response (UPR) in the cell. The UPR utilizes three main signaling pathways to restore disrupted ER homeostasis. These signaling pathways are protein kinase R-like endoplasmic reticulum kinase, inositol-requiring enzyme 1, and activating transcription factor 6. Studies have reported that ER stress (ERS) plays a role in the pathogenesis of metabolic disorders such as diabetes, obesity, atherosclerosis, and nonalcoholic liver disease. This review will briefly discuss the ERS response in these metabolic diseases.

Aneuploidy underlies brefeldin A-induced antifungal drug resistance in Cryptococcus neoformans

Cryptococcus neoformans is at the top of the list of "most wanted" human pathogens. Only three classes of antifungal drugs are available for the treatment of cryptococcosis. Studies on antifungal resistance mechanisms are limited to the investigation of how a particular antifungal drug induces resistance to a particular drug, and the impact of stresses other than antifungals on the development of antifungal resistance and even cross-resistance is largely unexplored. The endoplasmic reticulum (ER) is a ubiquitous subcellular organelle of eukaryotic cells. Brefeldin A (BFA) is a widely used chemical inducer of ER stress. Here, we found that both weak and strong selection by BFA caused aneuploidy formation in C. neoformans, mainly disomy of chromosome 1, chromosome 3, and chromosome 7. Disomy of chromosome 1 conferred cross-resistance to two classes of antifungal drugs: fluconazole and 5-flucytosine, as well as hypersensitivity to amphotericin B. However, drug resistance was unstable, due to the intrinsic instability of aneuploidy. We found overexpression of AFR1 on Chr1 and GEA2 on Chr3 phenocopied BFA resistance conferred by chromosome disomy. Overexpression of AFR1 also caused resistance to fluconazole and hypersensitivity to amphotericin B. Furthermore, a strain with a deletion of AFR1 failed to form chromosome 1 disomy upon BFA treatment. Transcriptome analysis indicated that chromosome 1 disomy simultaneously upregulated AFR1, ERG11, and other efflux and ERG genes. Thus, we posit that BFA has the potential to drive the rapid development of drug resistance and even cross-resistance in C. neoformans, with genome plasticity as the accomplice.

FicD regulates adaptation to the unfolded protein response in the murine liver

The unfolded protein response (UPR) is a cellular stress response that is activated when misfolded proteins accumulate in the endoplasmic reticulum (ER). The UPR elicits a signaling cascade that results in an upregulation of protein folding machinery and cell survival signals. However, prolonged UPR responses can result in elevated cellular inflammation, damage, and even cell death. Thus, regulation of the UPR response must be tuned to the needs of the cell, sensitive enough to respond to the stress but pliable enough to be stopped after the crisis has passed. Previously, we discovered that the bi-functional enzyme FicD can modulate the UPR response via post-translational modification of BiP. FicD AMPylates BiP during homeostasis and deAMPylates BiP during stress. We found this activity is important for the physiological regulation of the exocrine pancreas. Here, we explore the role of FicD in the murine liver. Like our previous studies, livers lacking FicD exhibit enhanced UPR signaling in response to short term physiologic fasting and feeding stress. However, the livers of FicD -/- did not show marked changes in UPR signaling or damage after either chronic high fat diet (HFD) feeding or acute pathological UPR induction. Intriguingly, FicD -/- mice showed changes in UPR induction and weight loss patterns following repeated pathological UPR induction. These findings show that FicD regulates UPR responses during mild physiological stress and may play a role in maintaining resiliency of tissue through adaptation to repeated ER stress.

Integrative analysis of genes reveals endoplasmic reticulum stress-related immune responses involved in dilated cardiomyopathy with fibrosis

Endoplasmic reticulum (ER) stress has been implicated in the mechanisms underlying the fibrotic process in dilated cardiomyopathy (DCM) and results in disease exacerbation; however, the molecular details of this mechanism remain unclear. Through microarray and bioinformatic analyses, we explored genetic alterations in myocardial fibrosis (MF) and identified potential biomarkers related to ER stress. We integrated two public microarray datasets, including 19 DCM and 16 control samples, and comprehensively analyzed differential expression, biological functions, molecular interactions, and immune infiltration levels. The immune cell signatures suggest that inflammatory immune imbalance may promote MF progression. Both innate and adaptive immunity are involved in MF development, and T-cell subsets account for a considerable proportion of immune infiltration. The immune subtypes were further compared, and 103 differentially expressed ER stress-related genes were identified. These genes were mainly enriched in neuronal apoptosis, protein modification, oxidative stress reaction, glycolysis and gluconeogenesis, and NOD-like receptor signaling pathways. Furthermore, the 15 highest-scoring core genes were identified. Seven hub genes (AK1, ARPC3, GSN, KPNA2, PARP1, PFKL, and PRKC) might participate in immune-related mechanisms. Our results offer a new integrative view of the pathways and interaction networks of ER stress-related genes and provide guidance for developing novel therapeutic strategies for MF.

Hydrogen Sulfide Ameliorates Angiotensin II-Induced Atrial Fibrosis Progression to Atrial Fibrillation Through Inhibition of the Warburg Effect and Endoplasmic Reticulum Stress

Atrial fibrosis is the basis for the occurrence and development of atrial fibrillation (AF) and is closely related to the Warburg effect, endoplasmic reticulum stress (ERS) and mitochondrion dysfunctions-induced cardiomyocyte apoptosis. Hydrogen sulfide (H₂S) is a gaseous signalling molecule with cardioprotective, anti-myocardial fibrosis and improved energy metabolism effects. Nevertheless, the specific mechanism by which H₂S improves the progression of atrial fibrosis to AF remains unclear. A case-control study of patients with and without AF was designed to assess changes in H₂S, the Warburg effect, and ERS in AF. The results showed that AF can significantly reduce cystathionine-γ-lyase (CSE) and 3-mercaptopyruvate thiotransferase (3-MST) expression and the H₂S level, induce cystathionine-β-synthase (CBS) expression; increase the Warburg effect, ERS and atrial fibrosis; and promote left atrial dysfunction. In addition, AngII-treated SD rats had an increased Warburg effect and ERS levels and enhanced atrial fibrosis progression to AF compared to wild-type SD rats, and these conditions were reversed by sodium hydrosulfide (NaHS), dichloroacetic acid (DCA) or 4-phenylbutyric acid (4-PBA) supplementation. Finally, low CSE levels in AngII-induced HL-1 cells were concentration- and time-dependent and associated with mitochondrial dysfunction, apoptosis, the Warburg effect and ERS, and these effects were reversed by NaHS, DCA or 4-PBA supplementation. Our research indicates that H₂S can regulate the AngII-induced Warburg effect and ERS and might be a potential therapeutic drug to inhibit atrial fibrosis progression to AF.

Lacrimal gland homeostasis is maintained by the AQP5 pathway by attenuating endoplasmic reticulum stress inflammation in the lacrimal gland of AQP5 knockout mice

Purpose

AQP5^-/- mice spontaneously exhibit dry eye symptoms. The purpose of this study was to assess the endoplasmic reticulum (ER) stress-mediated inflammation generated by a deficiency of aquaporin 5 (AQP5) in the lacrimal gland.

Methods

Hematoxylin and eosin (H&E) staining, Oil Red O staining, and transmission electron microscopy (TEM) analysis were performed to identify structural changes in lacrimal gland epithelial cells because of AQP5 deficiency. Corneal epithelial defects were assessed with sodium fluorescein staining. The expression profiles of mRNA and proteins were determined by quantitative real-time reverse transcription PCR (qRT-PCR) and western blot. Mice in the quercetin group were injected intraperitoneally with 40 mg/kg of quercetin, and the control group was injected with an equal volume of dimethyl sulfoxide (DMSO) for 4 weeks.

Results

Aqueous tear secretion fell at about 50% in 1- and 6-month-old AQP5^-/- mice compared with that of AQP5^+/+ mice. TEM showed that the ER structure was damaged. ER stress was significantly increased in the lacrimal gland of AQP5^-/- mice. Lipid droplets accumulated in the matrix and acinar cells, and changes occurred in the lipid metabolism and gene expression levels for PPARα, CPT1α, and CPT2 in the AQP5^-/- mice. Immune cell infiltration and increases in the gene expression levels of the chemokines CXCL1, CXCL2, and CCL5 were found in the lacrimal gland of AQP5^-/- mice. Quercetin partially reversed ER stress levels, inflammation, and lipid accumulation, and it inhibited tear secretion.

Conclusions

The study data indicated that a deficiency of AQP5 induced pathophysiological changes and functional decompensation of the lacrimal gland. Quercetin may improve the inflammation in the lacrimal glands of AQP5^-/- mice by regulating the ER stress levels.

Tonsil-derived mesenchymal stem cells incorporated in reactive oxygen species-releasing hydrogel promote bone formation by increasing the translocation of cell surface GRP78

Controlling the senescence of mesenchymal stem cells (MSCs) is essential for improving the efficacy of MSC-based therapies. Here, a model of MSC senescence was established by replicative subculture in tonsil-derived MSCs (TMSCs) using senescence-associated β-galactosidase, telomere-length related genes, stemness, and mitochondrial metabolism. Using transcriptomic and proteomic analyses, we identified glucose-regulated protein 78 (GRP78) as a unique MSC senescence marker. With increasing cell passage number, GRP78 gradually translocated from the cell surface and cytosol to the (peri)nuclear region of TMSCs. A gelatin-based hydrogel releasing a sustained, low level of reactive oxygen species (ROS-hydrogel) was used to improve TMSC quiescence and self-renewal. TMSCs expressing cell surface-specific GRP78 (csGRP78+), collected by magnetic sorting, showed better stem cell function and higher mitochondrial metabolism than unsorted cells. Implantation of csGRP78+ cells embedded in ROS-hydrogel in rats with calvarial defects resulted in increased bone regeneration. Thus, csGRP78 is a promising biomarker of senescent TMSCs, and the combined use of csGRP78+ cells and ROS-hydrogel improved the regenerative capacity of TMSCs by regulating GRP78 translocation.

Activity of Cytochrome p450 as a Steroidogenesis and Oxidation Catalyst of Cholesterol in Experimental Animals Exposed to Cigarette Smoke

BACKGROUND: Basically, body regulates various harmful substances, including nicotine and tar which were carried by cigarette smoke. Nicotine which accumulated in blood was transported to liver to be metabolized and excreted in kidneys. The metabolism of nicotine into a harmless substance to body is closely related to the role of cytochrome P450 enzyme. In liver, nicotine was catalyzed by cytochrome P450 to be intermediate nicotine-Δ-1 ‘(5’) - iminium ion. The elevation of cholesterol leads the P450 to discard overage cholesterol to keep cholesterol homeostasis and atheroprotection. AIM: The aim of the study was to determine the activity of cytochrome P450 to cigarette smoke exposure and to cholesterol level. MATERIALS AND METHODS: A total of 32 Rattus norvegicus male Wistar albino strain was exposed to cigarette smoke with a different number of cigarettes for 57 weeks (2, 3, and 4 cigarette/day group, with a group of control). In the 58th week, the blood of rats was collected for enzyme-linked immunosorbent assay analysis. RESULTS: Both cytochrome P450 activity and cholesterol level affected to cigarette smoke exposure (p > 0.05, 0.00 for cholesterol levels and 0.04 for p450 levels). CONCLUSIONS: Exposure of cigarette smoke significantly has an impact on increasing cholesterol levels and decreasing the activity of P450 enzyme. The elevating of cigarette number had a significant impact between the smoker and non-smoker groups.

Molecular Stressors Engender Protein Connectivity Dysfunction through Aberrant N-Glycosylation of a Chaperone

Stresses associated with disease may pathologically remodel the proteome by both increasing interaction strength and altering interaction partners, resulting in proteome-wide connectivity dysfunctions. Chaperones play an important role in these alterations, but how these changes are executed remains largely unknown. Our study unveils a specific N-glycosylation pattern used by a chaperone, Glucose-regulated protein 94 (GRP94), to alter its conformational fitness and stabilize a state most permissive for stable interactions with proteins at the plasma membrane. This "protein assembly mutation' remodels protein networks and properties of the cell. We show in cells, human specimens, and mouse xenografts that proteome connectivity is restorable by inhibition of the N-glycosylated GRP94 variant. In summary, we provide biochemical evidence for stressor-induced chaperone-mediated protein mis-assemblies and demonstrate how these alterations are actionable in disease.

Rapamycin Rescues Endoplasmic Reticulum Stress-Induced Dry Eye Syndrome in Mice

Purpose

To investigate whether rapamycin protects tear production and the ocular surface during endoplasmic reticulum (ER) stress-induced dry eye syndrome in mice.

Methods

Tunicamycin was injected intraperitoneally in BALB/c mice without or with rapamycin (TM or RM5 group). Peritoneal injection of PBS performed in vehicle group. Group without injection served as control. Blinking rate, fluorescein staining score (FSS), and phenol red thread tear production test were measured at 4 days, 1 week, and 2 weeks after treatment. Levels of inflammatory and angiogenic cytokines were measured by ELISA.

Results

Blinking rate and FSS were elevated, and tear production was decreased in TM group compared with controls (P < 0.05 for all), which was ameliorated by rapamycin at 1 and 2 weeks. Levels of inflammatory and angiogenic cytokines in the cornea and lacrimal glands were higher in the TM group than controls, and lower in the RM5 group than the TM group at 1 and 2 weeks (P < 0.05 for all).

Conclusion

Rapamycin protected tear production and the ocular surface against this dry eye syndrome by ameliorating ER stress-induced vascular damage and inflammation of lacrimal glands and the ocular surface.

Association between endoplasmic reticulum stress and risk factors of diabetic retinopathy

Diabetic retinopathy (DR) is one of the most common and challenging ocular complications of diabetes mellitus. As a chronic, progressive ocular disease that poses a serious threat to vision, DR has gradually become a leading cause of blindness worldwide. Emerging evidence points to an important role of endoplasmic reticulum (ER) stress in not only maintaining the steady-state equilibrium in the body, but also in intracellular synthesis, protein folding, and other essential functions. Recent studies have demonstrated clear associations between ER stress-related physiological functions and the pathogenesis of DR. When cells are stimulated by external stimuli, UPR pathway is activated firstly to protect it. However, long-term harmful factors can induce ER stress. which interferes with the physiological metabolism of retinal cells and participates in the occurrence of DR via the ATF6 pathway, PERK pathway and IRE1 pathway. At present, ER stress blocker is expected to become a new anti-DR therapy. Thus, understanding the relationship between ER stress and DR will help to develop new effective preventative treatments. In this review, we summarize the risk factors of DR pathogenesis induced by ER stress toward revealing potentially new therapeutic targets.

Homocysteine Induces Apoptosis of Human Umbilical Vein Endothelial Cells via Mitochondrial Dysfunction and Endoplasmic Reticulum Stress

Homocysteine- (Hcy-) induced endothelial cell apoptosis has been suggested as a cause of Hcy-dependent vascular injury, while the proposed molecular pathways underlying this process are unclear. In this study, we investigated the adverse effects of Hcy on human umbilical vein endothelial cells (HUVEC) and the underlying mechanisms. Our results demonstrated that moderate-dose Hcy treatment induced HUVEC apoptosis in a time-dependent manner. Furthermore, prolonged Hcy treatment increased the expression of NOX4 and the production of intracellular ROS but decreased the ratio of Bcl-2/Bax and mitochondrial membrane potential (MMP), resulting in the leakage of cytochrome c and activation of caspase-3. Prolonged Hcy treatment also upregulated glucose-regulated protein 78 (GRP78), activated protein kinase RNA-like ER kinase (PERK), and induced the expression of C/EBP homologous protein (CHOP) and the phosphorylation of NF-κb. The inhibition of NOX4 decreased the production of ROS and alleviated the Hcy-induced HUVEC apoptosis and ER stress. Blocking the PERK pathway partly alleviated Hcy-induced HUVEC apoptosis and the activation of NF-κb. Taken together, our results suggest that Hcy-induced mitochondrial dysfunction crucially modulated apoptosis and contributed to the activation of ER stress in HUVEC. The excessive activation of the PERK pathway partly contributed to Hcy-induced HUVEC apoptosis and the phosphorylation of NF-κb.

Novel approaches to drug discovery for the treatment of type 2 diabetes

INTRODUCTION

Type 2 diabetes mellitus (T2DM) is a chronic, complex and multifactorial metabolic disorder, which has become a serious global health problem. The side effects of known drugs and the deficiency of long-term safety data, in addition to the already determined adverse effects for the current preclinical drugs against T2DM, have largely called upon the urgent exploration of novel therapeutic and preventative strategies against this disease.

AREAS COVERED

The authors highlight the potential approaches for anti-T2DM drug discovery by focusing on: the restoration of pancreatic β-cell mass, the promotion of insulin secretion, the regulation of oxidative stress and endoplasmic reticulum (ER) stress and the modulation of autophagy.

EXPERT OPINION

T2DM is based on the gradual development of insulin resistance and β-cell dysfunction. Thus, the restoration of β-cell function is considered as one of the promising therapeutic strategies against T2DM. The stress factors, such as oxidative stress, ER stress and autophagy, play potent roles in the regulation of β-cell apoptosis, insulin secretion and sensitivity in the development of T2DM involving complicated cross-talks. Based on multiplex stress-involved regulatory networks, more and more novel potential targets have been discovered and the multi-targeted drug leads are expected to help develop more effective clinical agents for the treatment of T2DM.

ER stress and ER stress-induced apoptosis are activated in gastric SMCs in diabetic rats

AIM: To investigate the gastric muscle injury caused by endoplasmic reticulum (ER) stress in rats with diabetic gastroparesis.

METHODS: Forty rats were randomly divided into two groups: a control group and a diabetic group. Diabetes was induced by intraperitoneal injection of 60 mg/kg of streptozotocin. Gastric emptying was determined at the 4^th and 12^th week. The ultrastructural changes in gastric smooth muscle cells (SMCs) were investigated by transmission electron microscopy. TdT-mediated dUTP nick end labeling (TUNEL) assay was performed to assess apoptosis of SMCs. Expression of the ER stress marker, glucose-regulated protein 78 (GRP78), and the ER-specific apoptosis mediator, caspase-12 protein, was determined by immunohistochemistry.

RESULTS: Gastric emptying was significantly lower in the diabetic rats than in the control rats at the 12^th wk (40.71% ± 2.50%, control rats vs 54.65% ± 5.22%, diabetic rats; P < 0.05). Swollen and distended ER with an irregular shape was observed in gastric SMCs in diabetic rats. Apoptosis of gastric SMCs increased in the diabetic rats in addition to increased expression of GRP78 and caspase-12 proteins.

CONCLUSION: ER stress and ER stress-mediated apoptosis are activated in gastric SMCs in diabetic rats with gastroparesis.

PAR-4: a possible new target for age-related disease

INTRODUCTION

Apoptosis plays an important role in age-related disease, and prostate apoptosis response-4 (PAR-4) is a novel apoptosis-inducing factor that regulates apoptosis in most cells. Recent studies suggest that PAR-4 plays an important role in the progression of many age-related diseases. This review highlights the significance of PAR-4 and builds a strong case supporting its role as a possible therapeutic target in age-related disease.

AREAS COVERED

This review covers the advancements over the last 15 years with respect to PAR-4 and its significance in age-related disease. Additionally, it provides knowledge regarding the significance of PAR-4 in age-related disease as well as its role in apoptotic signaling pathways, endoplasmic reticulum (ER) stress, and other mechanisms that may induce age-related disease.

EXPERT OPINION

PAR-4 may be a potential therapeutic target that can trigger selective apoptosis in cancer cells. It is induced by ER stress and increased ER stress, and it is involved in the activity of the dopamine D2 receptor. Abnormal expression of PAR-4 may be associated with cardiovascular disease and diabetes. PAR-4 agonists and inhibitors must be identified before gene therapy can commence.

The modulation of endoplasmic reticulum stress by chemical chaperone upregulates immune negative cytokine IL-35 in apolipoprotein E-deficient mice

Interleukin (IL)-35 is a newly identified immune negative molecule which is secreted by CD4(+)Foxp3(+) T regulatory cells (Tregs) and contributes to their suppressive capacity. Early data have shown that IL-35 inhibits development of several autoimmune diseases. However, the role of IL-35 in atherosclerosis, a lipid-driven chronic inflammatory disease in arterial wall, remains to be investigated. Here, we found that IL-35 was involved in atherosclerosis in apolipoprotein E-deficient (ApoE(-/-)) mice. ApoE(-/-) mice with established atherosclerotic lesion displayed a lower level of IL-35 compared to age-matched wild type C57BL/6 mice without plaque. However, IL-35 expression increased significantly in ApoE(-/-) mice with attenuated plaque. More importantly, we found that modulation of ER stress treated by chemical chaperone, 4-Phenyl butyric acid (PBA) in vivo, mainly upregulated immune negative regulating molecule IL-35, as well as IL-10 and Foxp3, accompanied by increased Tregs. However, no obvious impact on pro-inflammatory molecules such as TNF-α, IFN-γ, IL-17 and IL-23 was observed, which provides new insight into the benefit of ER stress recovery from attenuated plaque. Our results suggest that IL-35 might have a potential value for atherosclerotic therapy.