Methods for studying ER stress and UPR markers in human cells

Jumonji histone demethylases are therapeutic targets in small cell lung cancer

Small cell lung cancer (SCLC) is a recalcitrant cancer of neuroendocrine (NE) origin. Changes in therapeutic approaches against SCLC have been lacking over the decades. Here, we use preclinical models to identify a new therapeutic vulnerability in SCLC consisting of the targetable Jumonji lysine demethylase (KDM) family. We show that Jumonji demethylase inhibitors block malignant growth and that etoposide-resistant SCLC cell lines are particularly sensitive to Jumonji inhibition. Mechanistically, small molecule-mediated inhibition of Jumonji KDMs activates endoplasmic reticulum (ER) stress genes, upregulates ER stress signaling, and triggers apoptotic cell death. Furthermore, Jumonji inhibitors decrease protein levels of SCLC NE markers INSM1 and Secretogranin-3 and of driver transcription factors ASCL1 and NEUROD1. Genetic knockdown of KDM4A, a Jumonji demethylase highly expressed in SCLC and a known regulator of ER stress genes, induces ER stress response genes, decreases INSM1, Secretogranin-3, and NEUROD1 and inhibits proliferation of SCLC in vitro and in vivo. Lastly, we demonstrate that two different small molecule Jumonji KDM inhibitors (pan-inhibitor JIB-04 and KDM4 inhibitor SD70) block the growth of SCLC tumor xenografts in vivo. Our study highlights the translational potential of Jumonji KDM inhibitors against SCLC, a clinically feasible approach in light of recently opened clinical trials evaluating this drug class, and establishes KDM4A as a relevant target across SCLC subtypes.

Detection of ER Stress in iPSC-Derived Neurons Carrying the p.N370S Mutation in the GBA1 Gene

Endoplasmic reticulum (ER) stress is involved in the pathogenesis of many human diseases, such as cancer, type 2 diabetes, kidney disease, atherosclerosis and neurodegenerative diseases, in particular Parkinson's disease (PD). Since there is currently no treatment for PD, a better understanding of the molecular mechanisms underlying its pathogenesis, including the mechanisms of the switch from adaptation in the form of unfolded protein response (UPR) to apoptosis under ER stress conditions, may help in the search for treatment methods. Genetically encoded biosensors based on fluorescent proteins are suitable tools that facilitate the study of living cells and visualization of molecular events in real time. The combination of technologies to generate patient-specific iPSC lines and genetically encoded biosensors allows the creation of cell models with new properties. Using CRISPR-Cas9-mediated homologous recombination at the AAVS1 locus of iPSC with the genetic variant p.N370S (rs76763715) in the GBA1 gene, we created a cell model designed to study the activation conditions of the IRE1-XBP1 cascade of the UPR system. The cell lines obtained have a doxycycline-dependent expression of the genetically encoded biosensor XBP1-TagRFP, possess all the properties of human pluripotent cells, and can be used to test physical conditions and chemical compounds that affect the development of ER stress, the functioning of the UPR system, and in particular, the IRE1-XBP1 cascade.

Assessment of HDAC Inhibitor-Induced Endoplasmic Reticulum (ER) Stress

The endoplasmic reticulum (ER) is a multifunctional cell organelle which is important for the folding and processing of proteins. Different endogenous and exogenous factors can disturb the ER homeostasis, causing ER stress and activating the unfolded protein response (UPR) to remove misfolded proteins and aggregates. ER stress and the UPR are associated with several human diseases, such as diabetes, Alzheimer's or Parkinson's disease, and cancer. Histone deacetylase inhibitors (HDACi) are used to treat cancer and were shown to induce ER stress/to modulate the UPR, although the exact mechanism is not fully understood and needs further research. Several approaches to monitoring ER stress exist. Here we describe methods including qPCR, Western blot, transmission electron microscopy, and fluorescence microscopy to analyze changes in mRNA and protein expression levels as well as defects in ER structures after HDAC inhibitor-induced ER stress.

Orthogonally-tunable and ER-targeting fluorophores detect avian influenza virus early infection

Cell-based assays can monitor virus infection at a single-cell level with high sensitivity and cost-efficiency. For this purpose, it is crucial to develop molecular probes that respond selectively to physiological changes in live cells. We report stimuli-responsive light-emitters built on a T-shaped benzimidazole platform, and consecutive borylation reactions to produce a library of homologs displaying systematic changes in fluorescence quantum yield and environmental sensitivity. We find that certain fluorophores localize selectively at the endoplasmic reticulum, and interact with proteins involved in the stress signaling pathways. Notably, the mono-borylated compound responds selectively to the stress conditions by enhancing fluorescence, and detects avian influenza virus infection at the single-cell level. Our findings demonstrate the unprecedented practical utility of the stress-responsive molecular probes to differentiate cellular states for early diagnosis.

Methods to detect and distinguish the early stage of viral infection often involve complicated and time-consuming protocols. Here, the authors disclose a class of fluorescent molecules that enable fast detection of avian influenza virus infection by selectively localizing at the endoplasmic reticulum in the cell.

Induction of endoplasmic reticulum stress markers in an acromegaly model

Acromegaly is a growth hormone (GH) excess pathological condition in humans. Acromegaly is associated with somatic disfigurement and a wide range of systemic manifestations such as arthritis, neuropathy, carpal tunnel syndrome, reproductive disorders, metabolic disorders, and gastrointestinal complications. The influence of excess GH on the cellular level could aid in understanding the root causes of acromegaly-related health complications. Previously, we found that GH excess induces DNA damage to somatic cells and reduces the stem cells number and causes premature aging. In this study, an in-depth analysis of the acromegaly RNAseq data revealed the disruption of important biological cellular processes. Gene set enrichment analysis, heatmap, and enrichment analysis of acromegaly RNAseq data revealed induction of endoplasmic reticulum (ER) stress markers in various organs. Interestingly, the induction of ER stress was even more apparent than in aged zebrafish. Splicing of box-binding protein-1 (XBP1) mRNA is a hallmark of ER stress. Therefore, we quantified spliced XBP1 mRNA in different organs of our acromegaly model. Thus, our study emphasizes the importance of ER stress in GH oversecretion, which is important for understanding the health complications of acromegaly.

Linking unfolded protein response to ovarian cancer cell fusion

Background

Polyploid giant cancer cells (PGCCs) have been observed in epithelial ovarian tumors. They can resist antimitotic drugs, thus participating in tumor maintenance and recurrence. Although their origin remains unclear, PGCC formation seems to be enhanced by conditions that trigger the unfolded protein response (UPR) such as hypoxia or chemotherapeutic drugs like paclitaxel. Hypoxia has been shown to promote the formation of ovarian PGCCs by cell fusion. We thus hypothesized that the UPR could be involved in EOC cell fusion, possibly explaining the occurrence of PGCCs and the aggressiveness of EOC.

Methods

The UPR was induced in two ovarian cancer cell lines (SKOV3 and COV318). The UPR activation was assessed by Western blot and polyploidy indexes were calculated. Then, to confirm the implication of cell fusion in PGCC formation, two populations of SKOV3 cells were transfected with plasmids encoding for two distinct nuclear fluorescent proteins (GFP and mCherry) associated with different antibiotic resistance genes, and the two cell populations were mixed in co-culture. The co-culture was submitted to a double-antibiotic selection. The resulting cell population was characterized for its morphology, cyclicity, and proliferative and tumorigenic capacities, in addition to transcriptomic characterization.

Results

We demonstrated that cell fusion could be involved in the generation of ovarian PGCCs and this process was promoted by paclitaxel and the UPR activation. Double-antibiotic treatment of PGCCs led to the selection of a pure population of cells containing both GFP- and mCherry-positive nuclei. Interestingly, after 3 weeks of selection, we observed that these cells were no longer polynucleated but displayed a single nucleus positive for both fluorescent proteins, suggesting that genetic material mixing had occurred. These cells had reinitiated their normal cell cycles, acquired an increased invasive capacity, and could form ovarian tumors in ovo.

Conclusions

The UPR activation increased the in vitro formation of PGCCs by cell fusion, with the newly generated cells further acquiring new properties. The UPR modulation in ovarian cancer patients could represent an interesting therapeutic strategy to avoid the formation of PGCCs and therefore limit cancer relapse and drug resistance.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09648-4.

Induction of Paraptotic Cell Death in Breast Cancer Cells by a Novel Pyrazolo[3,4-h]quinoline Derivative through ROS Production and Endoplasmic Reticulum Stress

Chemotherapy has been a standard intervention for a variety of cancers to impede tumor growth, mainly by inducing apoptosis. However, development of resistance to this regimen has led to a growing interest and demand for drugs targeting alternative cell death modes, such as paraptosis. Here, we designed and synthesized a novel derivative of a pyrazolo[3,4-h]quinoline scaffold (YRL1091), evaluated its cytotoxic effect, and elucidated the underlying molecular mechanisms of cell death in MDA-MB-231 and MCF-7 breast cancer (BC) cells. We found that YRL1091 induced cytotoxicity in these cells with numerous cytoplasmic vacuoles, one of the distinct characteristics of paraptosis. YRL1091-treated BC cells displayed several other distinguishing features of paraptosis, excluding autophagy or apoptosis. Briefly, YRL1091-induced cell death was associated with upregulation of microtubule-associated protein 1 light chain 3B, downregulation of multifunctional adapter protein Alix, and activation of extracellular signal-regulated kinase 1/2 and c-Jun N-terminal kinase. Furthermore, the production of reactive oxygen species (ROS) and newly synthesized proteins were also observed, subsequently causing ubiquitinated protein accumulation and endoplasmic reticulum (ER) stress. Collectively, these results indicate that YRL1091 induces paraptosis in BC cells through ROS generation and ER stress. Therefore, YRL1091 can serve as a potential candidate for the development of a novel anticancer drug triggering paraptosis, which may provide benefit for the treatment of cancers resistant to conventional chemotherapy.

Toll-Like Receptor 4: A Macrophage Cell Surface Receptor Is Activated By Trimethylamine-N-Oxide

OBJECTIVE

Trimethylamine-N-Oxide (TMAO) is considered as a risk factor for atherosclerosis which further leads to inflammation during atherosclerosis. The exact mechanism(s) by which TMAO induces the inflammatory reactions remains to be determined. TMAO can cause the endoplasmic reticulum (ER) stress that triggers activation of Toll-Like Receptors (TLRs). In macrophages, this process stimulates the production of proinflammatory cytokines. This study designed to evaluate the expression level of TLR4 in TMAO-treated macrophages.

MATERIALS AND METHODS

In this experimental study, different concentrations of TMAO (37.5, 75, 150, and 300 μM) were exposed to murine macrophage (J774A.1 cell line) for 8, 18, 24, and 48 hours. The cells were also treated with 2.5 mM of 4-phenyl butyric acid as well as 2μg/ml of tunicamycin respectively as negative and positive controls for inducing ER-stress. We measured the viability of treated cells by the MTT test. Besides, the expression levels of TLR4 gene and protein were evaluated using western blotting and reverse transcription- quantitative polymerase chain reaction (RT-qPCR) analysis. One-Way ANOVA was used for statistical analysis.

RESULTS

No cell death was observed in treated cells. The cells treated with 150 and 300 μM doses of TMAO for 24 hours showed a significant elevation in the protein and/or mRNA levels of TLR4 when compared to normal control or tunicamycin-treated cells.

CONCLUSION

Our results may in part elucidate the mechanism by which TMAO induces the macrophage inflammatory reactions in response to the induction of ER stress, similar to what happens during atherosclerosis. It also provides documentation to support the direct contribution of TLR4 in TMAO-induced inflammation.

Dual Targeting of Endoplasmic Reticulum by Redox-Deubiquitination Regulation for Cancer Therapy

Background

Recently, nanocatalyst-induced endoplasmic reticulum (ER) stress for cancer therapy has been attracting considerable attention. However, cancer cells are often able to overcome ER stress-induced death by activating the unfolded protein response (UPR), making nanocatalytic monotherapy a poor defense against cancer progression.

Purpose

In this study, to improve the nanocatalytic treatment efficacy, a phase change material (PCM) was used to encapsulate the upstream ER stress initiator, iron oxide nanoparticles (Fe₃O₄ NPs), and the downstream UPR modulator, PR-619. Subsequently, the tumor-homing peptide tLyP-1 was coupled to it to form tLyP-1/PR-619/Fe₃O₄@PCM (tPF@PCM) theranostic platform.

Materials and Methods

tPF@PCM was synthesized using nanoprecipitation and resolidification methods followed by the EDC/NHS cross-linking method. The targeting capacity of tPF@PCM was evaluated in vitro and in vivo using flow cytometry and magnetic resonance imaging, respectively. The therapeutic efficacy of tPF@PCM was investigated in a renal cell carcinoma mouse model. Moreover, we explored the synergistic anti-tumor mechanism by examining the intracellular reactive oxygen species (ROS), aggregated proteins, ER stress response levels, and type of cell death.

Results

tPF@PCM had excellent tumor-targeting properties and exhibited satisfactory photothermal-enhanced tumor inhibition efficacy both in vitro and in vivo. Specifically, the phase transition temperature (45 °C) maintained using 808 nm laser irradiation significantly increased the release and catalytic activity of the peroxidase mimic Fe₃O₄ NPs. This strongly catalyzed the generation of hydroxyl radicals (•OH) via the Fenton reaction in the acidic tumor microenvironment. The redox imbalance subsequently resulted in an increase in the level of damaged proteins in the ER and initiated ER stress. Moreover, the pan-deubiquitinase inhibitor PR-619 blocked the “adaptive” UPR-mediated degradation of these damaged proteins, exacerbating the ER burden. Consequently, irremediable ER stress activated the “terminal” UPR, leading to apoptosis in cancer cells.

Conclusion

This ER stress-exacerbating strategy effectively suppresses tumorigenesis, offering novel directions for advances in the treatment of conventional therapy-resistant cancers.

Autophagy, Apoptosis, the Unfolded Protein Response, and Lung Function in Idiopathic Pulmonary Fibrosis

Autophagy, apoptosis, and the unfolded protein response (UPR) are fundamental biological processes essential for manifold cellular functions in health and disease. Idiopathic pulmonary fibrosis (IPF) is a progressive and lethal pulmonary disorder associated with aging that has limited therapies, reflecting our incomplete understanding. We conducted an observational study linking molecular markers of cell stress response pathways (UPR: BiP, XBP1; apoptosis: cleaved caspase-3; autophagy: LC3β) in lung tissues from IPF patients and correlated the expression of these protein markers to each subject's lung function measures. We hypothesized that changes in lung tissue expression of apoptosis, autophagy, and UPR markers correlate with lung function deficits in IPF. The cell stress markers BiP, XBP1, LC3β puncta, and cleaved caspase-3 were found to be elevated in IPF lungs compared to non-IPF lungs, and, further, BiP and cleaved caspase-3 co-localized in IPF lungs. Considering lung function independently, we observed that increased XBP1, BiP, and cleaved caspase-3 were each associated with reduced lung function (FEV1, FVC, TLC, RV). However, increased lung tissue expression of LC3β puncta was significantly associated with increased diffusion capacity (DLCO), an indicator of alveolar-capillary membrane function. Similarly, the co-localization of UPR (XBP1, BiP) and autophagy (LC3β puncta) markers was positively correlated with increased lung function (FEV1, FVC, TLC, DLCO). However, the presence of LC3β puncta can indicate either autophagy flux inhibition or activation. While the nature of our observational cross-sectional study design does not allow conclusions regarding causal links between increased expression of these cell stress markers, lung fibrosis, and lung function decline, it does provide some insights that are hypothesis-generating and suggests that within the milieu of active UPR, changes in autophagy flux may play an important role in determining lung function. Further research is necessary to investigate the mechanisms linking UPR and autophagy in IPF and how an imbalance in these cell stress pathways can lead to progressive fibrosis and loss of lung function. We conclude by presenting five testable hypotheses that build on the research presented here. Such an understanding could eventually lead to the development of much-needed therapies for IPF.

Stimulation of myogenesis by ascorbic acid and capsaicin

Myogenesis is a complex process regulated by several factors. This study evaluated the functional interaction between vitamin C and a high dose of capsaicin (a potential endoplasmic reticulum (ER) stress inducer) on myogenesis. After the induction of differentiation, treatment with ascorbic acid or ascorbic acid phosphate (AsAp) alone had minimal effects on myogenesis in C2C12 cells. However, treatment with capsaicin (300 μM) in undifferentiated C2C12 cells increased the expression levels of genes related to ER stress as well as oxidative stress. Myogenesis was effectively enhanced in C2C12 cells treated with a combination of capsaicin (300 μM) for one day before differentiation stimulation and AsAp for four days post-differentiation; subsequently, thick and long myotubes formed, and the expression levels of myosin heavy chain (MYH) 1/2 and Myh1, Myh4, and Myh7 increased. Considering that mild ER stress stimulates myogenesis, AsAp may elicit myogenesis through the alleviation of oxidative stress-induced negative effects in capsaicin-pretreated cells. The enhanced expression of Myh1 and Myh4 coincided with the expression of Col1a1, a type I collagen, suggesting that the fine-tuning of the myogenic cell microenvironment is responsible for efficient myogenesis. Our results indicate that vitamin C is a potential stimulator of myogenesis in cells, depending on the cell context.

Cooperative treatment effectiveness of ATR and HSP90 inhibition in Ewing's sarcoma cells

INTRODUCTION

Ewing's sarcoma is an aggressive childhood malignancy whose outcome has not substantially improved over the last two decades. In this study, combination treatments of the HSP90 inhibitor AUY922 with either the ATR inhibitor VE821 or the ATM inhibitor KU55933 were investigated for their effectiveness in Ewing's sarcoma cells.

METHODS

Effects were determined in p53 wild-type and p53 null Ewing's sarcoma cell lines by flow cytometric analyses of cell death, mitochondrial depolarization and cell-cycle distribution as well as fluorescence and transmission electron microscopy. They were molecularly characterized by gene and protein expression profiling, and by quantitative whole proteome analysis.

RESULTS

AUY922 alone induced DNA damage, apoptosis and ER stress, while reducing the abundance of DNA repair proteins. The combination of AUY922 with VE821 led to strong apoptosis induction independent of the cellular p53 status, yet based on different molecular mechanisms. p53 wild-type cells activated pro-apoptotic gene transcription and underwent mitochondria-mediated apoptosis, while p53 null cells accumulated higher levels of DNA damage, ER stress and autophagy, eventually leading to apoptosis. Impaired PI3K/AKT/mTOR signaling further contributed to the antineoplastic combination effects of AUY922 and VE821. In contrast, the combination of AUY922 with KU55933 did not produce a cooperative effect.

CONCLUSION

Our study reveals that HSP90 and ATR inhibitor combination treatment may be an effective therapeutic approach for Ewing's sarcoma irrespective of the p53 status.

Smoothened-activating lipids drive resistance to CDK4/6 inhibition in Hedgehog-associated medulloblastoma cells and preclinical models

Medulloblastoma is an aggressive pediatric brain tumor that can be driven by misactivation of the Hedgehog (HH) pathway. CDK6 is a critical effector of oncogenic HH signaling, but attempts to target the HH pathway in medulloblastoma have been encumbered by resistance to single-agent molecular therapy. We identified mechanisms of resistance to CDK6 inhibition in HH-associated medulloblastoma by performing orthogonal CRISPR and CRISPR interference screens in medulloblastoma cells treated with a CDK4/6 inhibitor and RNA-Seq of a mouse model of HH-associated medulloblastoma with genetic deletion of Cdk6. Our concordant in vitro and in vivo data revealed that decreased ribosomal protein expression underlies resistance to CDK6 inhibition in HH-associated medulloblastoma, leading to ER stress and activation of the unfolded protein response (UPR). These pathways increased the activity of enzymes producing Smoothened-activating (SMO-activating) sterol lipids that sustained oncogenic HH signaling in medulloblastoma despite cell-cycle attenuation. We consistently demonstrated that concurrent genetic deletion or pharmacological inhibition of CDK6 and HSD11ß2, an enzyme producing SMO-activating lipids, additively blocked cancer growth in multiple mouse genetic models of HH-associated medulloblastoma. Our data reveal what we believe to be a novel pathway of resistance to CDK4/6 inhibition as well as a novel combination therapy to treat the most common malignant brain tumor in children.

Flavonoids: Potential Candidates for the Treatment of Neurodegenerative Disorders

Neurodegenerative disorders, such as Parkinson's disease (PD), Alzheimer's disease (AD), Amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), are the most concerning disorders due to the lack of effective therapy and dramatic rise in affected cases. Although these disorders have diverse clinical manifestations, they all share a common cellular stress response. These cellular stress responses including neuroinflammation, oxidative stress, proteotoxicity, and endoplasmic reticulum (ER)-stress, which combats with stress conditions. Environmental stress/toxicity weakened the cellular stress response which results in cell damage. Small molecules, such as flavonoids, could reduce cellular stress and have gained much attention in recent years. Evidence has shown the potential use of flavonoids in several ways, such as antioxidants, anti-inflammatory, and anti-apoptotic, yet their mechanism is still elusive. This review provides an insight into the potential role of flavonoids against cellular stress response that prevent the pathogenesis of neurodegenerative disorders.

Inhibition of Brainstem Endoplasmic Reticulum Stress Rescues Cardiorespiratory Dysfunction in High Output Heart Failure

Recent evidence shows that chronic activation of catecholaminergic neurons of the rostral ventrolateral medulla is crucial in promoting autonomic imbalance and cardiorespiratory dysfunction in high output heart failure (HF). Brainstem endoplasmic reticulum stress (ERS) is known to promote cardiovascular dysfunction; however, no studies have addressed the potential role of brainstem ERS in cardiorespiratory dysfunction in high output HF. In this study, we assessed the presence of brainstem ERS and its potential role in cardiorespiratory dysfunction in an experimental model of HF induced by volume overload. High output HF was surgically induced via creation of an arterio-venous fistula in adult male Sprague-Dawley rats. Tauroursodeoxycholic acid (TUDCA), an inhibitor of ERS, or vehicle was administered intracerebroventricularly for 4 weeks post-HF induction. Compared with vehicle treatment, TUDCA improved cardiac autonomic balance (LF_HRV/HF_HRV ratio, 3.02±0.29 versus 1.14±0.24), reduced cardiac arrhythmia incidence (141.5±26.7 versus 35.67±12.5 events/h), and reduced abnormal respiratory patterns (Apneas: 11.83±2.26 versus 4.33±1.80 events/h). TUDCA administration (HF+Veh versus HF+TUDCA, P<0.05) attenuated cardiac hypertrophy (HW/BW 4.4±0.3 versus 4.0±0.1 mg/g) and diastolic dysfunction. Analysis of rostral ventrolateral medulla gene expression confirmed the presence of ERS, inflammation, and activation of renin-angiotensin system pathways in high output HF and showed that TUDCA treatment completely abolished ERS and ERS-related signaling. Taken together, these results support the notion that ERS plays a role in cardiorespiratory dysfunction in high output HF and more importantly that reducing brain ERS with TUDCA treatment has a potent salutary effect on cardiac function in this model.

Role of inositol to improve surfactant functions and reduce IL-6 levels: A potential adjuvant strategy for SARS-CoV-2 pneumonia?

To date, the spread of SARS-CoV-2 infection is increasing worldwide and represents a primary healthcare emergency. Although the infection can be asymptomatic, several cases develop severe pneumonia and acute respiratory distress syndrome (ARDS) characterized by high levels of pro-inflammatory cytokines, primarily interleukin (IL)-6. Based on available data, the severity of ARDS and serum levels of IL-6 are key determinants for the prognosis. In this scenario, available in vitro and in vivo data suggested that myo-inositol is able to increase the synthesis and function of the surfactant phosphatidylinositol, acting on the phosphoinositide 3-kinase (PI3K)-regulated signaling, with amelioration of both immune system and oxygenation at the bronchoalveolar level. In addition, myo-inositol has been found able to decrease the levels of IL-6 in several experimental settings, due to an effect on the inositol-requiring enzyme 1 (IRE1)-X-box-binding protein 1 (XBP1) and on the signal transducer and activator of transcription 3 (STAT3) pathways. In this scenario, treatment with myo-inositol may be able to reduce IL-6 dependent inflammatory response and improve oxygenation in patients with severe ARDS by SARS-CoV-2. In addition, the action of myo-inositol on IRE1 endonuclease activity may also inhibit the replication of SARS-CoV-2, as was reported for the respiratory syncytial virus. Since the available data are extremely limited, if this potential therapeutic approach will be considered valid in the clinical practice, the necessary future investigations should aim to identify the best dose, administration route (oral, intravenous and/or aerosol nebulization), and cluster(s) of patients which may get beneficial effects from this treatment.

Telomerase reverse transcriptase downregulation by RNA interference modulates endoplasmic reticulum stress and mitochondrial energy production

Telomerase is a cancer promoting ribonucleoprotein complex and is a potential therapeutic target for cancer. In this study, the effects of telomerase downregulation on the whole cell proteome were investigated. Understanding how the effect of downregulation on the whole proteome profile will generate a greater understanding of the possible roles played by telomerase in cancer. Downregulation was achieved by RNA interference (RNAi), targeting the telomerase reverse transcriptase (TERT) subunits of telomerase. Transfection of TERT siRNA downregulates TERT gene expression and induced downregulation of telomerase activity. Investigation of the effect of silencing TERT in telomerase was further validated through proteomic analysis by performing 2-dimension electrophoresis (2DE) coupled with MALDI-TOF/TOF. 12 protein spots in HeLa cells were reported to be significantly differentially expressed with 11 of them were upregulated and 1 downregulated. Through STRING analysis, differentially expressed proteins demonstrated strong associations with endoplasmic reticulum stress marker and mitochondrial energy production marker. In conclusions, the result exhibited novel integrated proteomic response involving endoplasmic reticulum stress and mitochondrial energy production in response to the TERT downregulation in cervical cancer cells.

A paralog-specific role of COPI vesicles in the neuronal differentiation of mouse pluripotent cells

The paralogous COPI coat subunit γ1-COP plays a unique role in promoting neurite outgrowth during the neuronal differentiation of mouse pluripotent cells.

Coat protein complex I (COPI)–coated vesicles mediate membrane trafficking between Golgi cisternae as well as retrieval of proteins from the Golgi to the endoplasmic reticulum. There are several flavors of the COPI coat defined by paralogous subunits of the protein complex coatomer. However, whether paralogous COPI proteins have specific functions is currently unknown. Here, we show that the paralogous coatomer subunits γ1-COP and γ2-COP are differentially expressed during the neuronal differentiation of mouse pluripotent cells. Moreover, through a combination of genome editing experiments, we demonstrate that whereas γ-COP paralogs are largely functionally redundant, γ1-COP specifically promotes neurite outgrowth. Our work stresses a role of the COPI pathway in neuronal polarization and provides evidence for distinct functions for coatomer paralogous subunits in this process.

Regulatory expression of bone morphogenetic protein 6 by 2,2'-dipyridyl

BACKGROUND

Expression of hepcidin, a hormone produced by hepatocytes which negatively regulates the circulating iron levels, is known to be positively regulated by BMP6, a member of transforming growth factor (TGF)-β family. Previous studies have shown that iron status is sensed by sinusoidal endothelial cells of hepatic lamina, leading to the modulation of BMP6 expression.

METHODS

ISOS-1, HUVEC, F-2, and SK-HEP1 endothelial cells were treated with either iron or 2,2'-dipyridyl (2DP), a cell-permeable iron-chelator, and expression level of Bmp6 was examined. To identify factors affecting Bmp6 transcription, stimulus screening for regulator of transcription (SSRT) was developed.

RESULTS

Treatment with iron slightly increased the expression levels of Bmp6, while 2DP unexpectedly increased Bmp6 expression in a dose-dependent manner. 2DP-induced Bmp6 expression was resistant to co-treatment with iron. 2DP-induced Bmp6 expression was also detected in HUVEC, F-2 cells, and SK-HEP1 cells. Luciferase-based reporter assays indicated that forced expression of JunB increased the transcription of Bmp6. 2DP induced phosphorylation of JunB; co-treatment with SP600125 blocked the 2DP-induced Bmp6 expression partially. JunB-induced Bmp6 transcription was not affected by mutations of putative JunB-responsive elements. Some endoplasmic reticulum stress inducers increased the expression of Bmp6. SSRT revealed pathways regulating Bmp6 transcription positively and negatively. Hepa1-6 liver cells and C2C12 myogenic cells were prone to 2DP induced Bmp6 expression.

CONCLUSIONS

The present study reveals non‑iron-regulated Bmp6 expression in endothelial cells.

GENERAL SIGNIFICANCE

Regulatory expression of Bmp6 may be important as a key step for fine tuning of BMP activity.

ER Stress Amelioration by Saxagliptin Protects the Liver Against Fructose-induced Insulin Resistance

BACKGROUND/AIM

The study is aimed to demonstrate whether saxagliptin treatment may reduce endoplasmic reticulum (ER) stress, oxidative damage, and inflammation in the liver of fructose-induced insulin resistance (IR) rats.

MATERIAL AND METHODS

Twenty-eight rats were divided as control, IR, saxagliptin treatment (ST) and IR+ST groups. IR caused by fructose (10%) administration for 10 weeks and, ST was administered for 15 d. The liver tissues were obtained from rats. ER stress markers were analyzed using Real-Time PCR. Oxidative stress was measured. The inflammation in the liver was detected by the streptavidin-biotin immunostaining method.

RESULTS

The values of total oxidant/antioxidant status were the same between control and IR rats. The numbers of IL-6, NF-κB and PPARγ immune⁺ cells showed significant changes in the liver among four groups. The increased mRNA expression levels of ER stress and apoptosis markers as GRP78, PERK, IRE1α, ATF-4 and -6, CHOP, Caspase-3, -8, -9 and -12 in IR reduced with ST.

CONCLUSION

These findings indicate that saxagliptin treatment may ameliorate IR by reducing ER stress rather than inflammation and oxidative stress in the liver.

Methods to Detect Endoplasmic Reticulum Stress and Apoptosis in Diabetic Nephropathy

A variety of pathophysiological cellular dysfunctions stress the endoplasmic reticulum (ER), promoting an accumulation of unfolded proteins in the ER lumen. The latter is sensed by intrinsic ER transmembrane proteins: IRE1α (inositol-requiring protein-1α), PERK (protein kinase RNA (PKR)-like ER kinase), and ATF6 (activating transcription factor 6) which when activated trigger the unfolded protein response (UPR), which includes an inhibition of protein translation while inducing specific transcription factors that induce genes aiming to relieve the ER stress response. Collectively, this reduces the burden of unfolded proteins within the ER, eventually restoring ER homeostasis and thus promoting cell survival and adaptation. However, under unresolvable ER stress conditions, the UPR promotes cell death. Diabetic nephropathy (dNP), a leading cause of end-stage renal disease in industrialized countries, is mechanistically closely linked with ER stress and renal cell death. Here, we describe methods (both in vivo and in vitro) for monitoring ER stress, UPR signaling, and cell death in renal cells by analyzing proteins and protein-protein interactions serving as markers of ER stress or cell death. These methods include visualization of interactions of UPR regulators by proximity ligation assay on renal tissue and cells and methods to detect cell death based on DNA fragmentation or fluorochrome substrates for caspases. We include two selected in vivo models to manipulate ER stress regulators and thus the UPR in murine models of dNP. Collectively, these analyses allow assessment of the activation of ER stress-induced signaling pathways and cell death in dNP and manipulation of the UPR in vivo, enabling researchers to probe for causality.

Application of a New Multiplexed Array for Rapid, Sensitive, Simultaneous and Quantitative Assessment of Spliced and Unspliced XBP1

Background

IRE1α-mediated unconventional splicing of XBP1 is emerging as a biomarker in several disease states and is indicative of activation of the unfolded protein response sensor IRE1. Splicing of XBP1 mRNA results in the translation of two distinct XBP1 protein isoforms (XBP1s and XBP1u) which, due to post-translational regulation, do not correlate with mRNA levels. As both XBP1 isoforms are implicated in pathogenic or disease progression mechanisms there is a need for a reliable, clinically applicable method to detect them.

Methods

A multiplexed isoform-specific XBP1 array utilising Biochip array technology (BAT™) was assessed for specificity and suitability when using cell protein lysates. The array was applied to RIPA protein lysates from several relevant pre-clinical models with an aim to quantify XBP1 isoforms in comparison with RT-PCR or immunoblot reference methods.

Results

A novel reliable, specific and sensitive XBP1 biochip was successfully utilised in pre-clinical research. Application of this biochip to detect XBP1 splicing at the protein level in relevant breast cancer models, under basal conditions as well as pharmacological inhibition and paclitaxel induction, confirmed the findings of previous studies. The biochip was also applied to non-adherent cells and used to quantify changes in the XBP1 isoforms upon activation of the NLRP3 inflammasome.

Conclusions

The XBP1 biochip enables isoform specific quantification of protein level changes upon activation and inhibition of IRE1α RNase activity, using a routine clinical methodology. As such it provides a research tool and potential clinical tool with a quantified, simultaneous, rapid output that is not available from any other published method.

Tanshinone IIA ameliorates cognitive deficits by inhibiting endoplasmic reticulum stress-induced apoptosis in APP/PS1 transgenic mice

Our previous data indicated that tanshinone IIA (tan IIA) improves learning and memory in a mouse model of Alzheimer's disease (AD) induced by streptozotocin via restoring cholinergic function, attenuating oxidative stress and blocking p38 MAPK signal pathway activation. This study aims to estimate whether tan IIA inhibits endoplasmic reticulum (ER) stress-induced apoptosis to prevent cognitive decline in APP/PS1 transgenic mice. Tan IIA (10 mg/kg and 30 mg/kg) was intraperitoneally administered to the six-month-old APP/PS1 mice for 30 consecutive days. β-amyloid (Aβ) plaques were measured by immunohistochemisty and Thioflavin S staining, apoptotic cells were observed by TUNEL, ER stress markers and apoptosis signaling proteins were investigated by western blotting and RT-PCR. Our results showed that tan IIA significantly ameliorates cognitive deficits and improves spatial learning ability of APP/PS1 mice in the nest-building test, novel object recognition test and Morris water maze test. Furthermore, tan IIA significantly reduced the deposition of Aβ plaques and neuronal apoptosis, and markedly prevented abnormal expression of glucose regulated protein 78 (GRP78), initiation factor 2α (eIF2α), inositol-requiring enzyme 1α (IRE1α), activating transcription factor 6 (ATF6), as well as suppressed the activation of C/EBP homologous protein (CHOP) and c-Jun N-terminal kinase (JNK) pathways in the parietal cortex and hippocampus. Moreover, tan IIA induced an up-regulation of the Bcl-2/Bax ratio and down-regulation of caspase-3 protein activity. Taken together, the above findings indicated that tan IIA improves learning and memory through attenuating Aβ plaques deposition and inhibiting ER stress-induced apoptosis. These results suggested that tan IIA might become a promising therapeutic candidate drug against AD.

Induction of the unfolded protein response (UPR) suppresses porcine reproductive and respiratory syndrome virus (PRRSV) replication

Replication of most RNA viruses is closely associated with the endoplasmic reticulum (ER) within permissive cells. As such, viruses often induce tremendous amounts of stress on cells during viral replication. To cope with the stress, cells initiate the unfolded protein response (UPR) to promote cellular survival. Porcine reproductive and respiratory syndrome virus (PRRSV), an economically important swine pathogen, was previously shown to induce cellular stress at late stages post-infection resulting in the formation of stress granules (SGs). Here in this study, we demonstrate that PRRSV also induces additional cellular response pathways, including the UPR. Confocal microscopy analysis demonstrated significant morphological changes in the ER of PRRSV-infected cells, indicative of pronounced ER stress. Further investigation revealed induction of all three branches of the UPR, including eukaryotic translation initiation factor 2-alpha kinase 3 (PERK), serine-threonine protein kinase/endoribonuclease (IRE1), and cyclic AMP-dependent transcription factor (ATF6). Activation of these sensors resulted in significant transcriptional upregulation of downstream UPR effectors. Additionally, UPR activation was shown to be detrimental to PRRSV replication, as treatment of cells with chemical ER stress inducers potently suppressed viral replication and RNA synthesis. Further investigation into the molecular mechanisms of UPR suppression of PRRSV replication revealed that PERK exacerbates the PRRSV-induced cytokine response. Collectively, these results demonstrate that PRRSV infection induces UPR activation through all three branches, and that UPR signaling may play a role in PRRSV pathogenesis. The results of this study further our understanding of the underlying molecular mechanisms of PRRSV replication and host-pathogen interactions.

Identification of proteins regulated by the proteasome following induction of endoplasmic reticulum stress

The endoplasmic reticulum (ER) is a major site for protein synthesis, folding and transport, lipid and steroid synthesis, regulating redox potential, as well as calcium storage. It therefore relies on delicate homeostasis, and perturbation of the ER function and induction of ER stress can lead to apoptosis. One cause of disruption of the ER homeostasis is the accumulation of misfolded proteins. To prevent this perturbation, the Endoplasmic Reticulum-Associated Degradation (ERAD) quality control machinery is recruited to remove these proteins in a three-step process: (1) extraction from the ER, (2) ubiquitination, and (3) subsequent proteasomal degradation. However, the identity of the proteins regulated by the proteasome following induction of the ER stress has remained obscure. In the present study, we investigated the role of the proteasome in the modulation of the proteome of HeLa cells after treatment with thapsigargin and tunicamycin, two drugs known to induce ER stress through accumulation of misfolded proteins. Using label-free quantitative proteomics we found that out of the proteins identified to decrease in their level following induction of ER stress, more than 64% are targeted by the proteasome. Among these proteins, key players of the Wnt signaling pathway, such as β-catenin and GSK3, as well as α-catenin which is involved in cell-cell adhesion, were identified as being modulated by the proteasome upon ER stress.

The redox regulator sulfiredoxin forms a complex with thioredoxin domain-containing 5 protein in response to ER stress in lung cancer cells

Sulfiredoxin (Srx) reduces hyperoxidized 2-cysteine-containing peroxiredoxins (Prxs) and protects cells against oxidative stress. Previous studies have shown that Srx is highly expressed in primary specimens of lung cancer patients and plays a pivotal role in lung tumorigenesis and cancer progression. However, the oncogenic mechanisms of Srx in cancer are incompletely understood. In this study, we found that Srx knockdown sensitizes lung cancer cells to endoplasmic reticulum (ER) stress-induced cell death. Through MS analysis, we determined that Srx forms a complex with the ER-resident protein thioredoxin domain-containing protein 5 (TXNDC5). Using reciprocal co-immunoprecipitation, immunofluorescence imaging, subcellular fractionation, and domain-mapping assays with site-specific mutagenesis and purified recombinant proteins, we further characterized the Srx-TXNDC5 interaction. In response to ER stress but not to oxidative stress, Srx exhibits an increased association with TXNDC5, facilitating the retention of Srx in the ER. Of note, TXNDC5 knockdown in lung cancer cells inhibited cell proliferation and repressed anchorage-independent colony formation and migration, but increased cell invasion and activation of mitogen-activated protein kinases. Using immunohistochemical staining, we demonstrate that TXNDC5 is highly expressed in patient-derived lung cancer specimens. Bioinformatics analysis of publicly available data sets revealed that those with high Srx levels have significantly shorter survival and that those with high TXNDC5 levels have longer survival. We conclude that the cellular levels of Srx and TXNDC5 may be useful as biomarkers to predict the survival of individuals with lung cancer.

Protective effects of tanshinone IIA on SH-SY5Y cells against oAβ1-42-induced apoptosis due to prevention of endoplasmic reticulum stress

Endoplasmic reticulum (ER) stress caused by β-amyloid protein (Aβ) may play an important role in the pathogenesis of Alzheimer disease (AD). Our previous data have indicated that tanshinone IIA (tan IIA) protected primary neurons from Aβ induced neurotoxicity. To further explore the neuroprotection of tan IIA, here we study the effects of tan IIA on the ER stress response in oligomeric Aβ_1-42 (oAβ_1-42)-induced SH-SY5Y cell injury. Our data showed that tan IIA pretreatment could increase cell viability and inhibit apoptosis caused by oAβ_1-42. Furthermore, tan IIA markedly suppressed ER dilation and prevented oAβ_1-42-induced abnormal expression of glucose regulated protein 78 (GRP78), initiation factor 2α (eIF2α), activating transcription factor 6 (ATF6), as well as inhibited the activation of C/EBP homologous protein (CHOP) and c-Jun N-terminal kinase (JNK) pathways. Moreover, tan IIA ameliorated oAβ_1-42-induced Bcl-2/Bax ratio reduction, prevented cytochrome c translocation into cytosol from mitochondria, reduced oAβ_1-42-induced cleavage of caspase-9 and caspase-3, suppressed caspase-3/7 activity, and increased mitochondrial membrane potential (MMP) and ATP content. Meanwhile, oAβ_1-42-induced cell apoptosis and activation of ER stress can also be attenuated by the inhibitor of ER stress 4-phenylbutyric acid (4-PBA). Taken together, these data indicated that tan IIA protects SH-SY5Y cells against oAβ_1-42-induced apoptosis through attenuating ER stress, modulating CHOP and JNK pathways, decreasing the expression of cytochrome c, cleaved caspase-9 and cleaved caspase-3, as well as increasing the ratio of Bcl-2/Bax, MMP and ATP content. Our results strongly suggested that tan IIA may be effective in treating AD associated with ER stress.

Trichostatin A induces p53-dependent endoplasmic reticulum stress in human colon cancer cells

Trichostatin A (TSA) has been demonstrated to exhibit various anticancer effects that influence cell cycle arrest, cell proliferation and apoptosis of cancer cells. A potential association between TSA and endoplasmic reticulum (ER) function has been suggested but its anticancer mechanism involving the induction of ER stress is unknown. p53 has previously been demonstrated to regulate ER function in response to stress but its role involving TSA and ER stress in cancer cells is poorly understood. The current study identified that TSA induced ER stress in wild type (WT) HCT116 human colon cancer cells. Following TSA treatment, the ER stress markers GRP78 and GRP94 significantly increased without hyperacetylation of their promoter regions. The inositol-requiring enzyme 1 α (IRE1α)/X-box binding protein 1 (XBP1) pathway was implicated due to an association of phosphorylated IRE1α and spliced XBP1 with ER stress. However, luciferase reporter assay indicated that splicing events were attenuated in HCT116 TP53(-/-) cells. Furthermore, cell viability and apoptosis were revealed to depend on p53 during TSA treatment. Cell viability increased and the apoptosis rate decreased in HCT116 TP53(-/-) cells compared with WT HCT116 cells undergoing TSA treatment. In conclusion, the current study revealed that TSA may induce ER stress via a p53-dependent mechanism in colon cancer cells. This provides information that may assist the development of treatments that exploit the anticancer function of TSA.

Improved IRE1 and PERK Pathway Sensors for Multiplex Endoplasmic Reticulum Stress Assay Reveal Stress Response to Nuclear Dyes Used for Image Segmentation

In response to a variety of insults the unfolded protein response (UPR) is a major cell program quickly engaged to promote either cell survival or if stress levels cannot be relieved, apoptosis. UPR relies on three major pathways, named from the endoplasmic reticulum (ER) resident proteins IRE1α, PERK, and ATF6 that mediate response. Current tools to measure the activation of these ER stress response pathways in mammalian cells are cumbersome and not compatible with high-throughput imaging. In this study, we present IRE1α and PERK sensors with improved sensitivity, based on the canonical events of xbp1 splicing and ATF4 translation at ORF3. These sensors can be integrated into host cell genomes through lentiviral transduction, opening the way for use in a wide array of immortalized or primary mammalian cells. We demonstrate that high-throughput single-cell analysis offers unprecedented kinetic details compared with endpoint measurement of IRE1α and PERK activity. Finally, we point out the limitations of dye-based nuclear segmentation for live cell imaging applications, as we show that these dyes induce UPR and can strongly affect both the kinetic and dynamic responses of IRE1α and PERK pathways.

Trimethylamine-N-oxide, as a risk factor for atherosclerosis, induces stress in J774A.1 murine macrophages

PURPOSE

Trimethylamine N-oxide (TMAO) is a biomarker for kidney problems. It has also been introduced as a risk factor for atherosclerosis. The classic risk factors for atherosclerosis trigger cellular and humeral immunoreaction in macrophages through induction of heat shock protein expressions and increased levels of GRP94 and HSP70 are associated with increased atherosclerosis risk. The present study evaluated the possible effect(s) of TMAO on the expression of GRP94 and HSP70 at protein levels.

METHODS

J774A.1 murine macrophages were treated with different micromolar concentrations of TMAO and 4-phenylbutyric acid (PBA), a chemical chaperone, for 8, 18, 24, and 48h intervals. Tunicamycin was also used as a control for induction of endoplasmic reticulum stress. Western blotting was used to evaluate the expression of GRP94 and HSP70 in macrophages at protein levels.

RESULT

Tunicamycin greatly increased protein levels of GRP94. Similarly, but to a lesser extent compared to tunicamycin, TMAO also increased GRP94. In 24h treated cells, only 300μM of TMAO, and in cells treated for 48h, all doses of TMAO produced a significant increase in relative HSP70 protein levels compared to the control. PBA failed to induce any changes in GRP94 or HSP70 protein levels.

CONCLUSION

GRP94 and HSP70 are stress-inducible heat shock protein, so the elevation in J774A.1 murine macrophages can clearly define cells under stress and elucidate the contribution of stress induced by TMAO that may have a part in the abnormal activation of macrophages involved in foam cell formation.

AAV delivery of GRP78/BiP promotes adaptation of human RPE cell to ER stress

Adeno associated virus (AAV)-mediated gene delivery of GRP78 (78 kDa glucose-regulated protein) attenuates the condition of endoplasmic reticulum (ER) stress and prevents apoptotic loss of photoreceptors in Retinitis pigmentosa (RP) rats. In the current study we overexpressed Grp78 with the help of AAV-2 in primary human retinal pigmented epithelium (hRPE) cell cultures and examined its effect on cell response to ER stress. The purpose of this work was studying potential stimulating effect of GRP78 on adaptation/pro-survival of hRPE cells under ER stress, as an in vitro model for RPE degeneration. To investigate the effect of Grp78 overexpression on unfolded protein response (UPR) markers under ER stress, hRPE primary cultures were transduced by recombinant virus rAAV/Grp78, and treated with ER stressor drug, tunicamycin. Expression changes of four UPR markers including GRP78, PERK, ATF6α, and GADD153/CHOP, were assessed by real-time PCR and western blotting. We found that GRP78 has a great contribution in modulation of UPR markers to favor adaptive response in ER-stressed hRPE cells. In fact, GRP78 overexpression affected adaptation and apoptotic phases of early UPR, through enhancement of two master regulators/ER stress sensors (PERK and ATF6α) and down-regulation of a key pro-apoptotic cascade activator (GADD153/CHOP). Together these findings demonstrate the promoting effect of GRP78 on adaptation/pro-survival of hRPE cells under ER stress. This protein with anti-apoptotic actions in the early UPR and important role in cell fate regulation, can be recruited as a useful candidate for future investigations of RPE degenerative diseases.

PERK and XBP1 differentially regulate CXCL10 and CCL2 production

Inflammation plays a key role in the pathogenesis of many retinal degenerative diseases related with photoreceptor dysfunction/degeneration. However the involvement of photoreceptor cells in inflammatory reactions is largely unknown as they are not considered as inflammatory cells. In this study, we assessed whether photoreceptor cells can produce CCL2 and CXCL10, two important players in inflammation during endoplasmic reticulum (ER) stress. After photoreceptor 661 W cells were treated with ER stress inducer thapsigargin (TG), induction of ER stress increased CXCL10 and CCL2 expression at both mRNA and protein levels, which was significantly blocked by an ER stress blocker 4-phenylbutyrate. ER stress contains three pathways: PERK, ATF6 and IRE1α. Knockdown of PERK attenuated TG-induced CXCL10 and CCL2 mRNA expression, associated with significant decreases in phosphorylation of NF-κB RelA and STAT3. In contrast to PERK, knockdown of XBP1, which is activated by IRE1α-mediated splicing, robustly enhanced TG-induced CXCL10 and CCL2 expression and phosphorylation of NF-κB RelA and STAT3. Blockade of NF-κB or STAT3 markedly diminished TG-induced CXCL10 and CCL2 expression. The specific roles of PERK and XBP1 in CXCL10 and CCL2 expression were further investigated by treating photoreceptor cells with advanced glycation end products (AGE) and high glucose (HG), two of the major contributors to diabetic complications. Similarly, AGE and HG induced CXCL10 and CCL2 expression in which PERK was a positive regulator while XBP1 was a negative regulator. These studies suggest that photoreceptors may be involved in retinal inflammation by expressing chemokines CXCL10 and CCL2. PERK and IRE1α/XBP1 in the unfolded protein response differentially regulate the expression of CXCL10 and CCL2 likely through modulation of ER stress-induced NF-κB RelA and STAT3 activation.

Trimethylamine-N-Oxide Treatment Induces Changes in the ATP-Binding Cassette Transporter A1 and Scavenger Receptor A1 in Murine Macrophage J774A.1 cells

BACKGROUND

Recently, trimethylamine N-oxide was introduced as a risk factor for atherosclerosis in terms of helping foam cell formation and worsening atherosclerosis complications. The present study was performed to investigate whether/how trimethylamine N-oxide is involved in regulation of ATP-binding cassette transporter A1 and scavenger receptor A1 in macrophages at both mRNA and protein levels.

METHODS

Murine macrophage J774A.1 cells were treated with micromolar concentrations of trimethylamine N-oxide and 4-phenylbutyric acid, a chemical chaperon, for different time intervals. Tunicamycin was also used as a control for induction of endoplasmic reticulum stress.

RESULTS

Similar to tunicamycin, trimethylamine N-oxide increased scavenger receptor A1 in all treatment periods, whereas ATP-binding cassette transporter A1 was only reduced 24 h post-treatment with trimethylamine N-oxide at both mRNA and protein levels. In contrast, 4-phenylbutyric acid failed to induce such changes in either scavenger receptor A1 or ATP-binding cassette transporter A1.

CONCLUSIONS

The results of this study, in agreement with previous studies, confirm the mechanistic role of trimethylamine N-oxide in the upregulation of scavenger receptor A1, which potentially can promote its proatherogenic role. The results also showed downregulation of ATP-binding cassette transporter A1 in trimethylamine N-oxide treated macrophages which may indicate another possible proatherosclerotic mechanism for foam cell formation.