TDAG51 is induced by homocysteine, promotes detachment-mediated programmed cell death, and contributes to the cevelopment of atherosclerosis in hyperhomocysteinemia

Endoplasmic reticulum stress and the development of endothelial dysfunction

The vascular endothelium plays a critical role in cardiovascular homeostasis, and thus identifying the underlying causes of endothelial dysfunction has important clinical implications. In this regard, the endoplasmic reticulum (ER) has recently emerged as an important regulator of metabolic processes. Dysfunction within the ER, broadly termed ER stress, evokes the unfolded protein response (UPR), an adaptive pathway that aims to restore ER homeostasis. Although the UPR is the first line of defense against ER stress, chronic activation of the UPR leads to cell dysfunction and death and has recently been implicated in the pathogenesis of endothelial dysfunction. Numerous risk factors for endothelial dysfunction can induce ER stress, which may in turn disrupt endothelial function via direct effects on endothelium-derived vasoactive substances or by activating other pathogenic cellular networks such as inflammation and oxidative stress. This review summarizes the available data linking ER stress to endothelial dysfunction.

A review about biomarkers for the investigation of vascular function and impairment in diabetes mellitus

The aim of this review was to analyze the main biomarkers of vascular function and impairment in patients with type 2 diabetes. Medline, SCOPUS, Web of Science, and Google Scholar databases were searched. We concluded that proatherogenic adhesion molecules (soluble intercellular adhesion molecule-1, soluble vascular adhesion molecule-1, and soluble E selectin) and inflammatory cytokines (high-sensitivity C-reactive protein, interleukin-6, and tumor necrosis factor-α) were elevated in type 2 diabetes mellitus. Their increased expression and release contribute to the accelerated atherogenesis typical of these patients. For these reasons, the early identification of high levels of these biomarkers will help to establish new strategies to reduce cardiovascular complications.

Regulation of PHLDA1 Expression by JAK2-ERK1/2-STAT3 Signaling Pathway

Toll-like receptor 2 (TLR2)-mediated signaling cascades and gene regulation are mainly involved in diseases, such as immunity and inflammation. In this study, microarray analysis was performed using bone marrow-derived macrophages (BMDM) and Raw 264.7 cells to identify novel proteins involved in the TLR2-mediated cellular response. We found that pleckstrin homology-like domain family, member 1 (PHLDA1) is a novel gene up-regulated by TLR2 stimulation and determined the unique signaling pathway for its expression. Treatment with TLR2 agonist Pam3 CSK4 increased mRNA, protein, and fluorescence staining of PHLDA1. Induction of PHLDA1 by TLR2 stimulation disappeared from TLR2 KO mice-derived BMDM. Among janus kinase (JAK) family members, JAK2 was involved in TLR2-stimulated PHLDA1 expression. Signal transducer and activator of transcription 3 (STAT3) also participated in PHLDA1 expression downstream of the JAK2. Interestingly, ERK1/2 was an intermediate between JAK2 and STAT3. In silico analysis revealed the presence of highly conserved γ-activated sites within mouse PHLDA1 promoter and confirmed the JAK2-STAT3 pathway is important to Pam3 CSK4 -induced PHLDA1 transcription. These findings suggest that the JAK2-ERK1/2-STAT3 pathway is an important signaling pathway for PHLDA1 expression and that these proteins may play a critical role in eliciting TLR2-mediated immune and inflammatory response.

Elevated serum homocysteine level as an independent risk factor for erectile dysfunction: a prospective pilot case-control study

Homocysteine is an amino acid that is produced from the metabolic demethylation of dietary methionine. It has gained arising attention for its association with increased risk of myocardial infarction, stroke and venous thromboembolism. Erectile dysfunction (ED), especially for vasculogenic ED, is a vascular disorder of cavernosal vascular bed. In this prospective pilot case-control study, we investigated plasma homocysteine levels in 32 ED patients and 20 healthy control men. Related patients characteristics including age, weight, height, marital status, smoking and drinking status, level of education were collected and analysed as well as penile colour Doppler ultrasound parameters. ED patients were further categorised into mild, moderate and severe ED based on 5-item of the International Index of Erectile Function. Higher homocysteine levels were observed in ED patients as compared with controls (p < .05). A multivariate logistic regression with likelihood ratio test revealed that homocysteine and penile peak systolic blood flow velocity (PSV) levels posed significant indicators for ED (chi-square of likelihood ratio = 20.42, df = 2, p < .005) as well as moderate and severe ED occurrence (chi-square of likelihood ratio = 28.50, df = 2, p < .005). The threshold value of homocysteine concentration to discriminate ED and control subjects was 12.65 μmol/L by performing receiver operating characteristic curve analyses. These data suggested that elevation of homocysteine levels was associated with an increased risk of ED.

Role of endoplasmic reticulum stress in endothelial dysfunction

AIM

Endoplasmic reticulum (ER) stress is implicated in the pathogenesis of several human disorders, including cardiovascular disease (CVD). CVD recognizes endothelial dysfunction (ED) as its pathogenetic primum movens; interestingly a large body of evidence has identified the unchecked ER stress response as a main actor in vascular damage elicited by various cardio-metabolic risk factors. In the present Review, we summarize findings from experimental studies on the ER stress-related ED, focusing on the mechanisms underlying this association.

DATA SYNTHESIS

Different noxious agents, such as hyperhomocysteinemia, hyperlipidemia, hyperglycemia and chronic inflammation, induce ED promoting an amplified ER stress response as demonstrated by several studies in animal models, as well as in human primary and immortalized endothelial cells. ER stress represents therefore a key mediator of vascular damage, operating in a setting of increased inflammatory burden and oxidative stress, thus contributing to foster a vicious pathogenic cycle.

CONCLUSIONS

Experimental studies summarized in this Review strongly suggest that an unchecked ER stress response plays a central role in the pathogenesis of ED and, consequently, CVD. Counteracting ER stress may thus represent a promising, even if largely unexplored as-yet, therapeutic approach aimed to prevent vascular damage, slowing the progression from ED to cardiovascular events.

Characterization of the metastatic phenotype of a panel of established osteosarcoma cells

Osteosarcoma (OS) is the most common bone tumor in pediatric patients. Metastasis is a major cause of mortality and morbidity. The rarity of this disease coupled with the challenges of drug development for metastatic cancers have slowed the delivery of improvements in long-term outcomes for these patients. In this study, we collected 18 OS cell lines, confirmed their expression of bone markers and complex karyotypes, and characterized their in vivo tumorgenicity and metastatic potential. Since prior reports included conflicting descriptions of the metastatic and in vivo phenotypes of these models, there was a need for a comparative assessment of metastatic phenotypes using identical procedures in the hands of a single investigative group. We expect that this single characterization will accelerate the study of this metastatic cancer. Using these models we evaluated the expression of six previously reported metastasis-related OS genes. Ezrin was the only gene consistently differentially expressed in all the pairs of high/low metatstatic OS cells. We then used a subtractive gene expression approach of the high and low human metastatic cells to identify novel genes that may be involved in OS metastasis. PHLDA1 (pleckstrin homology-like domain, family A) was identified as one of the genes more highly expressed in the high metastatic compared to low metastatic cells. Knocking down PHLDA1 with siRNA or shRNA resulted in down regulation of the activities of MAPKs (ERK1/2), c-Jun N-terminal kinases (JNK), and p38 mitogen-activated protein kinases (MAPKs). Reducing the expression of PHLDA1 also delayed OS metastasis progression in mouse xenograft models.

Association of brachial-ankle pulse wave velocity with cardiovascular risk factors in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is associated with premature atherosclerosis. Increasing arterial stiffness is closely associated with atherosclerotic cardiovascular diseases, and pulse wave velocity (PWV) is considered to be an indicator of arterial stiffness. The objective of this study was to identify the relationship between brachial-ankle pulse wave velocity (baPWV) and cardiovascular risk factors in patients with SLE. Age, body mass index (BMI), systolic blood pressure (SBP), diastolic blood pressure (DBP), fasting blood glucose (FBS), plasma lipid profile, plasma homocysteine, thiobarbituric acid reactive substances (TBARS), baPWV, ankle-brachial index (ABI), and SLE-related factors were determined in a total of 83 SLE patients (12 males and 71 females). All SLE patients were further classified into two subgroups according to baPWV value (baPWV 1400 cm/s, n 37 versus baPWV 1400 cm/s, n 46). The mean baPWV value of studied SLE patients was 1520 381 cm/s. Age, BMI, SBP, DBP, FBS, TBARS and homocysteine levels were significantly higher in SLE patients with baPWV value 1400 cm/s than in SLE patients with baPWV value 1400 cm/s. In addition, baPWV correlated significantly with age, SBP, DBP, FBS and homocysteine. Moreover, stepwise multiple regression analysis showed that age and SBP were independently associated with baPWV. The results of this study indicate a possible link between vascular stiffness measured by baPWV and cardiovascular risk factors in patients with SLE.

Endoplasmic Reticulum Stress and Associated ROS

The endoplasmic reticulum (ER) is a fascinating network of tubules through which secretory and transmembrane proteins enter unfolded and exit as either folded or misfolded proteins, after which they are directed either toward other organelles or to degradation, respectively. The ER redox environment dictates the fate of entering proteins, and the level of redox signaling mediators modulates the level of reactive oxygen species (ROS). Accumulating evidence suggests the interrelation of ER stress and ROS with redox signaling mediators such as protein disulfide isomerase (PDI)-endoplasmic reticulum oxidoreductin (ERO)-1, glutathione (GSH)/glutathione disuphide (GSSG), NADPH oxidase 4 (Nox4), NADPH-P450 reductase (NPR), and calcium. Here, we reviewed persistent ER stress and protein misfolding-initiated ROS cascades and their significant roles in the pathogenesis of multiple human disorders, including neurodegenerative diseases, diabetes mellitus, atherosclerosis, inflammation, ischemia, and kidney and liver diseases.

Up-regulation of TDAG51 is a dependent factor of LPS-induced RAW264.7 macrophages proliferation and cell cycle progression

CONTEXT

As a component of the outer membrane in Gram-negative bacteria, lipopolysaccharide (LPS)-induced proliferation and cell cycle progression of monocytes/macrophages. It has been suggested that the proapoptotic T-cell death-associated gene 51 (TDAG51) might be associated with cell proliferation and cell cycle progression; however, its role in the interaction between LPS and macrophages remains unclear.

OBJECTIVE

We attempted to elucidate the role(s) of TDAG51 played in the interaction between LPS and macrophages.

MATERIALS AND METHODS

We investigated TDAG51 expression in RAW264.7 cells stimulated with LPS and examined the effects of RNA interference-mediated TDAG51 down-regulation. We used CCK-8 assay and flow cytometry analysis to evaluate the interaction between TDAG51 and LPS-induced proliferation and cell cycle progression in RAW264.7 cells.

RESULTS

Our findings indicate that TDAG51 is up-regulated in LPS-stimulated RAW264.7 cells, the TDAG51 siRNA effectively reduced TDAG51 protein up-regulation following LPS stimulation in RAW264.7 cells, the significant changes of the proliferation and cell cycle progression of RAW264.7 cells in TDAG51 Knockdown RAW264.7 cells treated with LPS were observed.

CONCLUSION

These findings suggested that TDAG51 up-regulation is a dependent event during LPS-mediated proliferation and cell cycle progression, and which increase our understanding of the interaction mechanism between LPS and macrophages.

Homocysteine activates T cells by enhancing endoplasmic reticulum-mitochondria coupling and increasing mitochondrial respiration

Hyperhomocysteinemia (HHcy) accelerates atherosclerosis by increasing proliferation and stimulating cytokine secretion in T cells. However, whether homocysteine (Hcy)-mediated T cell activation is associated with metabolic reprogramming is unclear. Here, our in vivo and in vitro studies showed that Hcy-stimulated splenic T-cell activation in mice was accompanied by increased levels of mitochondrial reactive oxygen species (ROS) and calcium, mitochondrial mass and respiration. Inhibiting mitochondrial ROS production and calcium signals or blocking mitochondrial respiration largely blunted Hcy-induced T-cell interferon γ (IFN-γ) secretion and proliferation. Hcy also enhanced endoplasmic reticulum (ER) stress in T cells, and inhibition of ER stress with 4-phenylbutyric acid blocked Hcy-induced T-cell activation. Mechanistically, Hcy increased ER-mitochondria coupling, and uncoupling ER-mitochondria by the microtubule inhibitor nocodazole attenuated Hcy-stimulated mitochondrial reprogramming, IFN-γ secretion and proliferation in T cells, suggesting that juxtaposition of ER and mitochondria is required for Hcy-promoted mitochondrial function and T-cell activation. In conclusion, Hcy promotes T-cell activation by increasing ER-mitochondria coupling and regulating metabolic reprogramming.

The Role of Endoplasmic Reticulum Stress and Unfolded Protein Response in Atherosclerosis

Pathogenesis of atherosclerosis is a complex process involving several metabolic and signalling pathways. Accumulating evidence demonstrates that endoplasmic reticulum stress and associated apoptosis can be induced in the pathological conditions of atherosclerotic lesions and contribute to the disease progression. Notably, they may play a role in the development of vulnerable plaques that induce thrombosis and are therefore especially dangerous. Endoplasmic reticulum stress response is regulated by several signaling mechanisms that involve protein kinases and transcription factors. Some of these molecules can be regarded as potential therapeutic targets to improve treatment of atherosclerosis. In this review we will discuss the role of endoplasmic reticulum stress and apoptosis in atherosclerosis development in different cell types and summarize the current knowledge on potential therapeutic agents targeting molecules regulating these pathways and their possible use for anti-atherosclerotic therapy.

Pleckstrin homology-like domain, family A, member 1 (PHLDA1) and cancer

Pleckstrin homology-like domain, family A, member 1 (PHLDA1) encodes a member of an evolutionarily conserved pleckstrin homology-related domain protein family. It was first identified as a potential transcription factor required for Fas expression and activation-induced apoptosis in mouse T cell hybridomas. The exact molecular and biological functions of PHLDA1 remain to be elucidated. However, its expression is induced by a variety of external stimuli and there is evidence that it may function as a transcriptional activator that acts as a mediator of apoptosis, proliferation, differentiation and cell migration dependent on the cellular type and context. Recently, PHLDA1 has received attention due to its association with cancer. In the present review, the current knowledge of PHLDA1 protein structure, expression regulation and function is summarized. In addition, the current data in the literature is reviewed with regards to the role of PHLDA1 in cancer pathogenesis.

Cystathionine β-synthase regulates endothelial function via protein S-sulfhydration

Deficiencies of the human cystathionine β-synthase (CBS) enzyme are characterized by a plethora of vascular disorders and hyperhomocysteinemia. However, several clinical trials demonstrated that despite reduction in homocysteine levels, disease outcome remained unaffected, thus the mechanism of endothelial dysfunction is poorly defined. Here, we show that the loss of CBS function in endothelial cells (ECs) leads to a significant down-regulation of cellular hydrogen sulfide (H2S) by 50% and of glutathione (GSH) by 40%. Silencing CBS in ECs compromised phenotypic and signaling responses to the VEGF that were potentiated by decreased transcription of VEGF receptor (VEGFR)-2 and neuropilin (NRP)-1, the primary receptors regulating endothelial function. Transcriptional down-regulation of VEGFR-2 and NRP-1 was mediated by a lack in stability of the transcription factor specificity protein 1 (Sp1), which is a sulfhydration target of H2S at residues Cys68 and Cys755. Reinstating H2S but not GSH in CBS-silenced ECs restored Sp1 levels and its binding to the VEGFR-2 promoter and VEGFR-2, NRP-1 expression, VEGF-dependent proliferation, and migration phenotypes. Thus, our study emphasizes the importance of CBS-mediated protein S-sulfhydration in maintaining vascular health and function.-Saha, S., Chakraborty, P. K., Xiong, X., Dwivedi, S. K. D., Mustafi, S. B., Leigh, N. R., Ramchandran, R., Mukherjee, P., Bhattacharya, R. Cystathionine β-synthase regulates endothelial function via protein S-sulfhydration.

Endothelial NOTCH1 is suppressed by circulating lipids and antagonizes inflammation during atherosclerosis

Briot et al. show that inflammatory lipids deriving from a high-fat diet suppress NOTCH1 expression and signaling in adult arterial endothelium and propose that reduction of endothelial NOTCH1 is a predisposing factor in the onset of atherosclerosis.

Although much progress has been made in identifying the mechanisms that trigger endothelial activation and inflammatory cell recruitment during atherosclerosis, less is known about the intrinsic pathways that counteract these events. Here we identified NOTCH1 as an antagonist of endothelial cell (EC) activation. NOTCH1 was constitutively expressed by adult arterial endothelium, but levels were significantly reduced by high-fat diet. Furthermore, treatment of human aortic ECs (HAECs) with inflammatory lipids (oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphocholine [Ox-PAPC]) and proinflammatory cytokines (TNF and IL1β) decreased Notch1 expression and signaling in vitro through a mechanism that requires STAT3 activation. Reduction of NOTCH1 in HAECs by siRNA, in the absence of inflammatory lipids or cytokines, increased inflammatory molecules and binding of monocytes. Conversely, some of the effects mediated by Ox-PAPC were reversed by increased NOTCH1 signaling, suggesting a link between lipid-mediated inflammation and Notch1. Interestingly, reduction of NOTCH1 by Ox-PAPC in HAECs was associated with a genetic variant previously correlated to high-density lipoprotein in a human genome-wide association study. Finally, endothelial Notch1 heterozygous mice showed higher diet-induced atherosclerosis. Based on these findings, we propose that reduction of endothelial NOTCH1 is a predisposing factor in the onset of vascular inflammation and initiation of atherosclerosis.

Protein kinase R-like ER kinase and its role in endoplasmic reticulum stress-decided cell fate

Over the past few decades, understandings and evidences concerning the role of endoplasmic reticulum (ER) stress in deciding the cell fate have been constantly growing. Generally, during ER stress, the signal transductions are mainly conducted by three ER stress transducers: protein kinase R-like endoplasmic reticulum kinase (PERK), inositol-requiring kinase 1 (IRE1) and activating transcription factor 6 (ATF6). Consequently, the harmful stimuli from the ER stress transducers induce apoptosis and autophagy, which share several crosstalks and eventually decide the cell fate. The dominance of apoptosis or autophagy induced by ER stress depends on the type and degree of the stimuli. When ER stress is too severe and prolonged, apoptosis is induced to eliminate the damaged cells; however, when stimuli are mild, cell survival is promoted to maintain normal physiological functions by inducing autophagy. Although all the three pathways participate in ER stress-induced apoptosis and autophagy, PERK shows several unique characteristics by interacting with some specific downstream effectors. Notably, there are some preliminary findings on PERK-dependent mechanisms switching autophagy and apoptosis. In this review, we particularly focused on the novel, intriguing and complicated role of PERK in ER stress-decided cell fate, and also discussed more roles of PERK in restoring cellular homeostasis. However, more in-depth knowledge of PERK in the future would facilitate our understanding about many human diseases and benefit in searching for new molecular therapeutic targets.

Homocysteine-Induced Endothelial Dysfunction

This review discussed and in particular emphasis the potential cellular pathways and the biological processes involved that lead to homocysteine-induced endothelial dysfunction, in particular in the impaired endothelial dependent dilatation aspect. Hyperhomocysteinemia is an independent cardiovascular risk factor that has been associated with atherosclerotic vascular diseases and ischemic heart attacks. The potential mechanisms by which elevated plasma homocysteine level leads to reduction in nitric oxide bioavailability include the disruptive uncoupling of nitric oxide synthase activity and quenching of nitric oxide by oxidative stress, the enzymatic inhibition by asymmetric dimethylarginine, endoplasmic reticulum stress with eventual endothelial cell apoptosis, and chronic inflammation/prothrombotic conditions. Homocysteine-induced endothelial dysfunction presumably affecting the bioavailability of the potent vasodilator ‘nitric oxide', and such dysfunction can easily be monitor by flow-mediated dilation method using ultrasound. Understanding the mechanisms by which plasma homocysteine alter endothelial nitric oxide production is therefore essential in the comprehension of homocysteine-induced impairment of endothelial dependent dilatation, and its association of cardiovascular risk and its pathophysiology.

Downregulated expression of PHLDA1 protein is associated with a malignant phenotype of cholangiocarcinoma

Cholangiocarcinoma is one of the most aggressive types of malignancy, and is associated with poor patient prognosis. Recent findings suggest that a decrease in pleckstrin homology-like domain family A, member 1 (PHLDA1) expression is significant in the induction of cell migration and tumor invasion. The clinicopathological significance of the expression of PHLDA1, and its potential correlation with the expression of CD133 in cholangiocarcinoma have remained to be elucidated. In the present study, PHLDA1 protein expression was investigated by immunohistochemical analysis of 218 cholangiocarcinoma tissue samples, as well as 30 para-neoplastic and 20 normal bile ducts. The expression status of PHLDA1 and CD133 was determined, and these results were analyzed against the age, gender, tumor location and size, histological grade, clinical stage and overall mean survival time of the patients. The expression of PHLDA1 protein was markedly decreased in 35.3% of cholangiocarcinomas, compared with that of the para-neoplastic and normal cholangiocytes. Carcinomas with loss of expression of PHLDA1 were significantly correlated with the tumor site (P=0.001), histological grade (P=0.020) and clinical stage (P=0.0001), but not with age (P=0.085), gender (P=0.456) or size (P=0.413), respectively. Kaplan-Meier survival analysis indicated that the loss of expression of PHLDA1 was significantly correlated with the overall survival time (Log rank=193.861; P=0.0001). Furthermore, the expression of PHLDA1 was found to be inversely correlated with the expression of CD133 (γ=-0.142; P=0.036). These findings suggested that the decreased expression of PHLDA1 may be significant in the carcinogenesis and progression of cholangiocarcinoma, and may represent a novel adjunct marker of disease prognosis.

Gene Expression Analyses during Spontaneous Reversal of Cardiomyopathy in Mice with Repressed Nuclear CUG-BP, Elav-Like Family (CELF) Activity in Heart Muscle

CUG-BP, Elav-like family (CELF) proteins regulate cell type- and developmental stage-specific alternative splicing in the heart. Repression of CELF-mediated splicing activity via expression of a nuclear dominant negative CELF protein in heart muscle was previously shown to induce dysregulation of alternative splicing, cardiac dysfunction, cardiac hypertrophy, and dilated cardiomyopathy in MHC-CELFΔ transgenic mice. A “mild” line of MHC-CELFΔ mice that expresses a lower level of the dominant negative protein exhibits cardiac dysfunction and myopathy at a young age, but spontaneously recovers normal cardiac function and heart size with age despite the persistence of splicing defects. To the best of our knowledge, this was the first example of a genetically induced cardiomyopathy that spontaneously recovers without intervention. In this study, we explored the basis for this recovery. We examined whether a transcriptional program regulated by serum response factor (SRF) that is dysregulated in juvenile MHC-CELFΔ mice is restored in the mild line with age, and evaluated global changes in gene expression by microarray analyses. We found that differences in gene expression between the mild line and wild type hearts are greatly reduced in older animals, including a partial recovery of SRF target gene expression. We did not find evidence of a new compensatory pathway being activated in the mild line with age, and propose that recovery may occur due to developmental stage-specific compatibility of CELF-dependent splice variants with the cellular environment of the cardiomyocyte.

Endoplasmic reticulum stress and endothelial dysfunction

Prolonged perturbation of the endoplasmic reticulum (ER) leads to ER stress and unfolded protein response (UPR) and contributes to the pathogenesis of various chronic disorders. This review focuses on the role of ER stress and UPR in endothelial cells and the relevance of these processes to vascular diseases. Chronic activation of ER stress and UPR pathways in endothelial cells leads to increased oxidative stress and inflammation and often results in cell death. Because endothelial cells play a pivotal role in maintaining vascular homeostasis, various pathological conditions interfering with this homeostasis including homocysteinemia, hyperlipidemia, high glucose, insulin resistance, disturbed blood flow, and oxidative stress can lead to endothelial dysfunction in part through the activation of ER stress. We discuss recently discovered aspects of the role of ER stress/UPR in those pathological conditions. We also summarize recent findings implicating ER stress and UPR in systemic hypertension as well as pulmonary arterial hypertension. Finally, this review will highlight a novel role of UPR mediators in the process of angiogenesis.

Role of endoplasmic reticulum stress in atherosclerosis and diabetic macrovascular complications

Age-related changes in endoplasmic reticulum (ER) are associated with stress of this cell organelle. Unfolded protein response (UPR) is a normal physiological reaction of a cell in order to prevent accumulation of unfolded and misfolded proteins in the ER and improve the normal ER function. However, in pathologic conditions such as atherosclerosis, obesity, and diabetes, ER function becomes impaired, leading to the development of ER stress. In chronic ER stress, defective posttranslational protein folding results in deposits of aberrantly folded proteins in the ER and the induction of cell apoptosis mediated by UPR sensors C/EBPα-homologous protein (CHOP) and inositol requiring protein-1 (IRE1). Since ER stress and ER-induced cell death play a nonredundant role in the pathogenesis of atherosclerosis and diabetic macrovascular complications, pharmaceutical targeting of ER stress components and pathways may be beneficial in the treatment and prevention of cardiovascular pathology.

Rapamycin induces apoptosis when autophagy is inhibited in T-47D mammary cells and both processes are regulated by Phlda1

Autophagy is an evolutionarily conserved lysosomal degradation pathway and plays a critical role in the homeostatic process of recycling proteins and organelles. Functional relationships have been described between apoptosis and autophagy. Perturbations in the apoptotic machinery have been reported to induce autophagic cell deaths. Inhibition of autophagy in cancer cells has resulted in cell deaths that manifested hallmarks of apoptosis. However, the molecular relationships and the circumstances of which molecular pathways dictate the choice between apoptosis and autophagy are currently unknown. This study aims to identify specific gene expression of rapamycin-induced autophagy and the effects of rapamycin when the autophagy process is inhibited. In this study, we have demonstrated that rapamycin is capable of inducing autophagy in T-47D breast carcinoma cells. However, when the autophagy process was inhibited by 3-MA, the effects of rapamycin became apoptotic. The Phlda1 gene was found to be up-regulated in both autophagy and apoptosis and silencing this gene was found to reduce both activities, strongly suggests that Phlda1 mediates and positively regulates both autophagy and apoptosis pathways.

4-Phenylbutyrate inhibits tunicamycin-induced acute kidney injury via CHOP/GADD153 repression

Different forms of acute kidney injury (AKI) have been associated with endoplasmic reticulum (ER) stress; these include AKI caused by acetaminophen, antibiotics, cisplatin, and radiocontrast. Tunicamycin (TM) is a nucleoside antibiotic known to induce ER stress and is a commonly used inducer of AKI. 4-phenylbutyrate (4-PBA) is an FDA approved substance used in children who suffer from urea cycle disorders. 4-PBA acts as an ER stress inhibitor by aiding in protein folding at the molecular level and preventing misfolded protein aggregation. The main objective of this study was to determine if 4-PBA could protect from AKI induced by ER stress, as typified by the TM-model, and what mechanism(s) of 4-PBA's action were responsible for protection. C57BL/6 mice were treated with saline, TM or TM plus 4-PBA. 4-PBA partially protected the anatomic segment most susceptible to damage, the outer medullary stripe, from TM-induced AKI. In vitro work showed that 4-PBA protected human proximal tubular cells from apoptosis and TM-induced CHOP expression, an ER stress inducible proapoptotic gene. Further, immunofluorescent staining in the animal model found similar protection by 4-PBA from CHOP nuclear translocation in the tubular epithelium of the medulla. This was accompanied by a reduction in apoptosis and GRP78 expression. CHOP(-/-) mice were protected from TM-induced AKI. The protective effects of 4-PBA extended to the ultrastructural integrity of proximal tubule cells in the outer medulla. When taken together, these results indicate that 4-PBA acts as an ER stress inhibitor, to partially protect the kidney from TM-induced AKI through the repression of ER stress-induced CHOP expression.

TDAG51 deficiency promotes oxidative stress-induced apoptosis through the generation of reactive oxygen species in mouse embryonic fibroblasts

Apoptosis has an important role in maintaining tissue homeostasis in cellular stress responses such as inflammation, endoplasmic reticulum stress, and oxidative stress. T-cell death-associated gene 51 (TDAG51) is a member of the pleckstrin homology-like domain family and was first identified as a pro-apoptotic gene in T-cell receptor-mediated cell death. However, its pro-apoptotic function remains controversial. In this study, we investigated the role of TDAG51 in oxidative stress-induced apoptotic cell death in mouse embryonic fibroblasts (MEFs). TDAG51 expression was highly increased by oxidative stress responses. In response to oxidative stress, the production of intracellular reactive oxygen species was significantly enhanced in TDAG51-deficient MEFs, resulting in the activation of caspase-3. Thus, TDAG51 deficiency promotes apoptotic cell death in MEFs, and these results indicate that TDAG51 has a protective role in oxidative stress-induced cell death in MEFs.

The effect of donor variation and senescence on endothelial differentiation of human mesenchymal stromal cells

Application of autologous cells is considered for a broad range of regenerative therapies because it is not surrounded by the immunological and ethical issues of allo- or xenogenic cells. However, isolation, expansion, and application of autologous cells do suffer from variability in therapeutic efficacy due to donor to donor differences and due to prolonged culture. One important source of autologous cells is mesenchymal stromal cells (MSCs), which can differentiate toward endothelial-like cells, thus making them an ideal candidate as cell source for tissue vascularization. Here we screened MSCs from 20 donors for their endothelial differentiation capacity and correlated it with the gene expression profile of the whole genome in the undifferentiated state. Cells of all donors were able to form tubes on Matrigel and induced the expression of endothelial genes, although with quantitative differences. In addition, we analyzed the effect of prolonged in vitro expansion on the multipotency of human MSCs and found that endothelial differentiation is only mildly sensitive to expansion-induced loss of differentiation as compared to osteogenic and adipogenic differentiation. Our results show the robustness of the endothelial differentiation protocol and the gene expression data give insight in the differences in endothelial differentiation between donors.

Expression of PAR-4 and PHLDA1 is prognostic for overall and disease-free survival in oral squamous cell carcinomas

PAR-4 is a tumor suppressor protein with a pro-apoptotic function and down-regulation of PAR-4 is seen in a variety of tumors. PHLDA1 gene overexpression has been shown to reduce cell proliferation and induce cell death in a variety of cell types. In this study, 229 cases of oral squamous cell carcinoma (OSCC), arranged in a tissue microarray, were analyzed by immunohistochemistry. PAR-4 expression was predominantly moderate to strong and expression of PHLDA1 was predominantly negative or weak. Cytoplasmic expression of PAR-4 was associated with advanced clinical stage. Expression of PHLDA1 was associated with advanced clinical stage of the tumour. Five-year overall and disease-free survival rates differed significantly between cases that did and cases that did not express PHLDA1, and by multivariate analysis, expression of PHLDA1 and PAR-4 were independent prognostic factors in OSCC patients. Expression of PAR-4 and PHLDA1 is altered in OSCC and might be a valuable prognostic indicator for this disease.

Deficiency of TDAG51 protects against atherosclerosis by modulating apoptosis, cholesterol efflux, and peroxiredoxin-1 expression

BACKGROUND

Apoptosis caused by endoplasmic reticulum (ER) stress contributes to atherothrombosis, the underlying cause of cardiovascular disease (CVD). T-cell death-associated gene 51 (TDAG51), a member of the pleckstrin homology-like domain gene family, is induced by ER stress, causes apoptosis when overexpressed, and is present in lesion-resident macrophages and endothelial cells.

METHODS AND RESULTS

To study the role of TDAG51 in atherosclerosis, male mice deficient in TDAG51 and apolipoprotein E (TDAG51(-/-)/ApoE(-/-)) were generated and showed reduced atherosclerotic lesion growth (56 ± 5% reduction at 40 weeks, relative to ApoE(-/-) controls, P<0.005) and necrosis (41 ± 4% versus 63 ± 8% lesion area in TDAG51(-/-)/ApoE(-/-) and ApoE(-/-), respectively; P<0.05) without changes in plasma levels of lipids, glucose, and inflammatory cytokines. TDAG51 deficiency caused several phenotypic changes in macrophages and endothelial cells that increase cytoprotection against oxidative and ER stress, enhance PPARγ-dependent reverse cholesterol transport, and upregulate peroxiredoxin-1 (Prdx-1), an antioxidant enzyme with antiatherogenic properties (1.8 ± 0.1-fold increase in Prdx-1 protein expression, relative to control macrophages; P<0.005). Two independent case-control studies found that a genetic variant in the human TDAG51 gene region (rs2367446) is associated with CVD (OR, 1.15; 95% CI, 1.07 to 1.24; P=0.0003).

CONCLUSIONS

These findings provide evidence that TDAG51 affects specific cellular pathways known to reduce atherogenesis, suggesting that modulation of TDAG51 expression or its activity may have therapeutic benefit for the treatment of CVD.

The UPR in atherosclerosis

Multiple systemic factors and local stressors in the arterial wall can disturb the functions of endoplasmic reticulum (ER), causing ER stress in endothelial cells (ECs), smooth muscle cells (SMCs), and macrophages during the initiation and progression of atherosclerosis. As a protective response to restore ER homeostasis, the unfolded protein response (UPR) is initiated by three major ER sensors: protein kinase RNA-like ER kinase (PERK), inositol-requiring protein 1α (IRE1α), and activating transcription factor 6 (ATF6). The activation of the various UPR signaling pathways displays a temporal pattern of activation at different stages of the disease. The ATF6 and IRE1α pathways that promote the expression of protein chaperones in ER are activated in ECs in athero-susceptible regions of pre-lesional arteries and before the appearance of foam cells. The PERK pathway that reduces ER protein client load by blocking protein translation is activated in SMCs and macrophages in early lesions. The activation of these UPR signaling pathways aims to cope with the ER stress and plays a pro-survival role in the early stage of atherosclerosis. However, with the progression of atherosclerosis, the extended duration and increased intensity of ER stress in lesions lead to prolonged and enhanced UPR signaling. Under this circumstance, the PERK pathway induces expression of death effectors, and possibly IRE1α activates apoptosis signaling pathways, leading to apoptosis of macrophages and SMCs in advanced lesions. Importantly, UPR-mediated cell death is associated with plaque instability and the clinical progression of atherosclerosis. Moreover, UPR signaling is linked to inflammation and possibly to macrophage differentiation in lesions. Therapeutic approaches targeting the UPR may have promise in the prevention and/or regression of atherosclerosis. However, more progress is needed to fully understand all of the roles of the UPR in atherosclerosis and to harness this information for therapeutic advances.

Hyperhomocysteinemia promotes insulin resistance by inducing endoplasmic reticulum stress in adipose tissue

Type 2 diabetes is a chronic inflammatory metabolic disease, the key point being insulin resistance. Endoplasmic reticulum (ER) stress plays a critical role in the pathogenesis of type 2 diabetes. Previously, we found that hyperhomocysteinemia (HHcy) induced insulin resistance in adipose tissue. Here, we hypothesized that HHcy induces ER stress, which in turn promotes insulin resistance. In the present study, the direct effect of Hcy on adipose ER stress was investigated by the use of primary rat adipocytes in vitro and mice with HHcy in vivo. The mechanism and the effect of G protein-coupled receptor 120 (GPR120) were also investigated. We found that phosphorylation or expression of variant ER stress markers was elevated in adipose tissue of HHcy mice. HHcy activated c-Jun N-terminal kinase (JNK), the downstream signal of ER stress in adipose tissue, and activated JNK participated in insulin resistance by inhibiting Akt activation. Furthermore, JNK activated c-Jun and p65, which in turn triggered the transcription of proinflammatory cytokines. Both in vivo and in vitro assays revealed that Hcy-promoted macrophage infiltration aggravated ER stress in adipose tissue. Chemical chaperones PBA and TUDCA could reverse Hcy-induced inflammation and restore insulin-stimulated glucose uptake and Akt activation. Activation of GPR120 reversed Hcy-induced JNK activation and prevented inflammation but not ER stress. Therefore, HHcy inhibited insulin sensitivity in adipose tissue by inducing ER stress, activating JNK to promote proinflammatory cytokine production and facilitating macrophage infiltration. These findings reveal a new mechanism of HHcy in the pathogenesis of insulin resistance.

Loss of TDAG51 results in mature-onset obesity, hepatic steatosis, and insulin resistance by regulating lipogenesis

Regulation of energy metabolism is critical for the prevention of obesity, diabetes, and hepatic steatosis. Here, we report an important role for the pleckstrin homology-related domain family member, T-cell death-associated gene 51 (TDAG51), in the regulation of energy metabolism. TDAG51 expression was examined during adipocyte differentiation. Adipogenic potential of preadipocytes with knockdown or absence of TDAG51 was assessed. Weight gain, insulin sensitivity, metabolic rate, and liver lipid content were also compared between TDAG51-deficient (TDAG51(-/-)) and wild-type mice. In addition to its relatively high expression in liver, TDAG51 was also present in white adipose tissue (WAT). TDAG51 was downregulated during adipogenesis, and TDAG51(-/-) preadipocytes exhibited greater lipogenic potential. TDAG51(-/-) mice fed a chow diet exhibited greater body and WAT mass, had reduced energy expenditure, displayed mature-onset insulin resistance (IR), and were predisposed to hepatic steatosis. TDAG51(-/-) mice had increased hepatic triglycerides and SREBP-1 target gene expression. Furthermore, TDAG51 expression was inversely correlated with fatty liver in multiple mouse models of hepatic steatosis. Taken together, our findings suggest that TDAG51 is involved in energy homeostasis at least in part by regulating lipogenesis in liver and WAT, and hence, may constitute a novel therapeutic target for the treatment of obesity and IR.

Genistein attenuates vascular endothelial impairment in ovariectomized hyperhomocysteinemic rats

Hyperhomocysteinemia (HHcy) is a well-known independent risk factor for vascular diseases in the general population. This study was to explore the effect of genistein (GST), a natural bioactive compound derived from legumes, on HHcy-induced vascular endothelial impairment in ovariectomized rats in vivo. Thirty-two adult female Wistar rats were assigned randomly into four groups (n = 8): (a) Con: control; (b) Met: 2.5% methionine diet; (c) OVX + Met: ovariectomy + 2.5% methionine diet; (d) OVX + Met + GST: ovariectomy + 2.5% methionine diet + supplementation with genistein. After 12 wk of different treatment, the rats' blood, toracic aortas and liver samples were collected for analysis. Results showed that high-methionine diet induced both elevation of plasma Hcy and endothelial dysfunction, and ovariectomy deteriorated these injuries. Significant improvement of both functional and morphological changes of vascular endothelium was observed in OVX + Met + GST group; meanwhile the plasma Hcy levels decreased remarkably. There were significant elevations of plasma ET-1 and liver MDA levels in ovariectomized HHcy rats, and supplementation with genistein could attenuate these changes. These results implied that genistein could lower the elevated Hcy levels, and prevent the development of endothelial impairment in ovariectomized HHcy rats. This finding may shed a novel light on the anti-atherogenic activities of genistein in HHcy patients.

TDAG51 mediates epithelial-to-mesenchymal transition in human proximal tubular epithelium

Epithelial-to-mesenchymal transition (EMT) contributes to renal fibrosis in chronic kidney disease. Endoplasmic reticulum (ER) stress, a feature of many forms of kidney disease, results from the accumulation of misfolded proteins in the ER and leads to the unfolded protein response (UPR). We hypothesized that ER stress mediates EMT in human renal proximal tubules. ER stress is induced by a variety of stressors differing in their mechanism of action, including tunicamycin, thapsigargin, and the calcineurin inhibitor cyclosporine A. These ER stressors increased the UPR markers GRP78, GRP94, and phospho-eIF2α in human proximal tubular cells. Thapsigargin and cyclosporine A also increased cytosolic Ca2+ concentration and T cell death-associated gene 51 (TDAG51) expression, whereas tunicamycin did not. Thapsigargin was also shown to increase levels of active transforming growth factor (TGF)-β1 in the media of cultured human proximal tubular cells. Thapsigargin induced cytoskeletal rearrangement, β-catenin nuclear translocation, and α-smooth muscle actin and vinculin expression in proximal tubular cells, indicating an EMT response. Subconfluent primary human proximal tubular cells were induced to undergo EMT by TGF-β1 treatment. In contrast, tunicamycin treatment did not produce an EMT response. Plasmid-mediated overexpression of TDAG51 resulted in cell shape change and β-catenin nuclear translocation. These results allowed us to develop a two-hit model of ER stress-induced EMT, where Ca2+ dysregulation-mediated TDAG51 upregulation primes the cell for mesenchymal transformation via Wnt signaling and then TGF-β1 activation leads to a complete EMT response. Thus the release of Ca2+ from ER stores mediates EMT in human proximal tubular epithelium via the induction of TDAG51.

Small-molecule screen identifies modulators of EWS/FLI1 target gene expression and cell survival in Ewing's sarcoma

Ewing's sarcoma family of tumors (EFT) is characterized by the presence of chromosomal translocations leading to the expression of oncogenic transcription factors such as, in the majority of cases, EWS/FLI1. Because of its key role in Ewing's sarcoma development and maintenance, EWS/FLI1 represents an attractive therapeutic target. Here, we characterize PHLDA1 as a novel direct target gene whose expression is repressed by EWS/FLI1. Using this gene and additional specific well-characterized target genes such as NROB1, NKX2.2 and CAV1, all activated by EWS/FLI1, as a read-out system, we screened a small-molecule compound library enriched for FDA-approved drugs that modulated the expression of EWS/FLI1 target genes. Among a hit-list of nine well-known drugs such as camptothecin, fenretinide, etoposide and doxorubicin, we also identified the kinase inhibitor midostaurin (PKC412). Subsequent experiments demonstrated that midostaurin is able to induce apoptosis in a panel of six Ewing's sarcoma cell lines in vitro and can significantly suppress xenograft tumor growth in vivo. These results suggest that midostaurin might be a novel drug that is active against Ewing's cells, which might act by modulating the expression of EWS/FLI1 target genes.

The Myocardial Unfolded Protein Response during Ischemic Cardiovascular Disease

Heart failure is a progressive and disabling disease. The incidence of heart failure is also on the rise, particularly in the elderly of industrialized societies. This is in part due to an increased ageing population, whom initially benefits from improved, and life-extending cardiovascular therapy, yet ultimately succumb to myocardial failure. A major cause of heart failure is ischemia secondary to the sequence of events that is dyslipidemia, atherosclerosis, and myocardial infarction. In the case of heart failure postmyocardial infarction, ischemia can lead to myocardial cell death by both necrosis and apoptosis. The extent of myocyte death postinfarction is associated with adverse cardiac remodeling that can contribute to progressive heart chamber dilation, ventricular wall thinning, and the onset of loss of cardiac function. In cardiomyocytes, recent studies indicate that myocardial ischemic injury activates the unfolded protein stress response (UPR) and this is associated with increased apoptosis. This paper focuses on the intersection of ischemia, the UPR, and cell death in cardiomyocytes. Targeting of the myocardial UPR may prove to be a viable target for the prevention of myocyte cell loss and the progression of heart failure due to ischemic injury.

The role of glucosamine-induced ER stress in diabetic atherogenesis

Cardiovascular disease (CVD) is the major cause of mortality in individuals with diabetes mellitus. However the molecular and cellular mechanisms that predispose individuals with diabetes to the development and progression of atherosclerosis, the underlying cause of most CVD, are not understood. This paper summarizes the current state of our knowledge of pathways and mechanisms that may link diabetes and hyperglycemia to atherogenesis. We highlight recent work from our lab, and others', that supports a role for ER stress in these processes. The continued investigation of existing pathways, linking hyperglycemia and diabetes mellitus to atherosclerosis, and the identification of novel mechanisms and targets will be important to the development of new and effective antiatherosclerotic therapies tailored to individuals with diabetes.

Integrated stress response modulates cellular redox state via induction of cystathionine γ-lyase: cross-talk between integrated stress response and thiol metabolism

The integrated stress response mediated by eukaryotic translation initiation factor 2α (eIF2α) phosphorylation maintains cellular homeostasis under endoplasmic reticulum (ER) stress. eIF2α phosphorylation induces activating transcription factor 4 (ATF4), a basic leucine zipper transcription factor that regulates the expression of genes responsible for amino acid metabolism, cellular redox state, and anti-stress responses. Cystathionine γ-lyase (CSE) and cystathionine β-synthase are critical enzymes in the transsulfuration pathway, which also regulate cellular redox status by modulating glutathione (GSH) levels. To determine the link between the integrated stress response and the transsulfuration pathway, we used homocysteine (Hcy) as an inducer of eIF2α phosphorylation and ATF4 gene induction. Mouse embryonic fibroblasts (MEFs) lacking ATF4 (ATF4(-/-)) had reduced GSH levels and increased reactive oxygen species and were susceptible to apoptotic cell death under normal culture conditions. Further, ATF4(-/-) MEFs were more sensitive to Hcy-induced cytotoxicity and showed significantly reduced intracellular GSH levels associated with apoptosis. ATF4(-/-) MEFs could be rescued from l-Hcy-induced apoptosis by β-mercaptoethanol medium supplementation that increases cysteine levels and restores GSH synthesis. ATF4(-/-) MEFs showed little or no CSE protein but did express cystathionine β-synthase. Further, ER stress-inducing agents, including tunicamycin and thapsigargin, induced the expression of CSE in ATF4(+/+) MEFs. Consistent with ATF4(-/-) MEFs, CSE(-/-) MEFs showed significantly greater apoptosis when treated with tunicamycin, thapsigargin, and l-Hcy, compared with CSE(+/+) MEFs. Liver and kidney GSH levels were also reduced in CSE(-/-) mice, suggesting that CSE is a critical factor in GSH synthesis and may act to protect the liver and kidney from a variety of conditions that cause ER stress.

PHLDA1 is a crucial negative regulator and effector of Aurora A kinase in breast cancer

Aurora A kinase is overexpressed in the majority of breast carcinomas. A chemical genetic approach was used to identify the malignant targets of Aurora A, which revealed pleckstrin-homology-like domain protein PHLDA1 as an Aurora A substrate. PHLDA1 downregulation is a powerful prognostic predictor for breast carcinoma, which was confirmed in our study. We further show that downregulation of PHLDA1 is associated with estrogen receptor (ER) expression in breast carcinoma. Aurora A directly phosphorylates PHLDA1 leading to its degradation. PHLDA1 also negatively regulates Aurora A, thereby triggering a feedback loop. We demonstrate the underlying mechanisms by which PHLDA1 upregulation strongly antagonizes Aurora-A-mediated oncogenic pathways, thereby revealing PHLDA1 degradation as a key mechanism by which Aurora A promotes breast malignancy. Thus, not surprisingly, PHLDA1 upregulation acts synergistically with Aurora A inhibition in promoting cell death. PHLDA1 overexpression might therefore be an alternative method to modulate Aurora A deregulation in breast carcinoma. Finally, this study led to the discovery of a mutation in the Aurora A active site that renders it amenable to the chemical genetic approach. Similar mutations are required for Aurora B, suggesting that this modified approach can be extended to other kinases that have hitherto not been amenable to this methodology.

Myocardial transcriptome analysis of human arrhythmogenic right ventricular cardiomyopathy

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiomyopathy primarily of the right ventricle characterized through fibrofatty replacement of cardiomyocytes. The genetic etiology in ARVC patients is most commonly caused by dominant inheritance and high genetic heterogeneity. Though histological examinations of ARVC-affected human myocardium reveals fibrolipomatous replacement, the molecular mechanisms leading to loss of cardiomyocytes are largely unknown. We therefore analyzed the transcriptomes of six ARVC hearts and compared our findings to six nonfailing donor hearts (NF). To characterize the ARVC-specific transcriptome, we compared our findings to samples from seven patients with idiopathic dilated cardiomyopathy (DCM). The myocardial DCM and ARVC samples were prepared from hearts explanted during an orthotopic heart transplantation representing myocardium from end-stage heart failure patients (NYHA IV). From each heart, left (LV) and right ventricular (RV) myocardial samples were analyzed by Affymetrix HG-U133 Plus 2.0 arrays, adding up to six sample groups. Unsupervised cluster analyses of the groups revealed a clear separation of NF and cardiomyopathy samples. However, in contrast to the other samples, the analyses revealed no distinct expression pattern in LV and RV of myocardial ARVC samples. We further identified differentially expressed transcripts using t-tests and found transcripts separating diseased and NF ventricular myocardium. Of note, in failing myocardium only ~15-16% of the genes are commonly regulated compared with NF samples. In addition both cardiomyopathies are clearly distinct on the transcriptome level. Comparison of the expression patterns between the failing RV and LV using a paired t-test revealed a lack of major differences between LV and RV gene expression in ARVC hearts. Our study is the first analysis of specific ARVC-related RV and LV gene expression patterns in terminal failing human hearts.

The effects of homocysteine and folic acid on angiogenesis and VEGF expression during chicken vascular development

Homocysteine (Hcy) has been implicated in the development of cardiovascular developmental defects. Additionally, in experimental studies, vasculotoxic properties of Hcy have been described. Although Hcy has been identified as a vascular pathogen, little is known about the direct effects Hcy exerts during early embryonic vascular development. Angiogenesis is a critical process involved in embryo survival and development. There are limited studies on the effects of Hcy on early embryonic vasculogenesis and angiogenesis. Folic acid (FA) is a B vitamin essential in embryo development, and FA supplementation may lead to reduced Hcy levels. Therefore, the purpose of our study was to explore the effects of Hcy and FA on early embryonic vascular development. Embryonic day (E) 3.5 chicken embryos were treated with a sham, Hcy or FA solution. We developed a computational program for systematic analysis of microscopic images obtained from the extra embryonic vascular beds. These results were combined with real-time PCR data on the expression of VEGF-A and its receptor in these vascular beds. Our data show that Hcy exposure inhibits early vascular development, displayed by a significant reduction of vessel area and altered composition of the vascular beds. Vascular beds of Hcy embryos for the greater part consisted of vessels of the smallest diameters, compared to middle size vessels in control and FA embryos. Hcy also reduced expression of VEGF-A and VEGFR-2. No significant effects of FA were found. We conclude that Hcy exposure causes impaired early extra embryonic vascular development, shown by altered composition of the vascular beds as well as reduced expression of VEGF-A and VEGFR-2. These effects of Hcy, and the consecutive cascade of events, may be involved in the development of cardiovascular developmental defects.

TSSC3 overexpression associates with growth inhibition, apoptosis induction and enhances chemotherapeutic effects in human osteosarcoma

Loss of expression of TSSC3, an apoptosis-related imprinted gene, has been reported in several cases of malignant tumors. However, the roles and mechanisms of TSSC3 in human osteosarcoma remain to be defined. In this study, we found TSSC3 to be downregulated during osteosarcoma transformation and progression in osteosarcoma cell lines and tissues. The SaOS2 cell line was used to further evaluate the precise role of TSSC3 in osteosarcoma development. Overexpression of TSSC3 markedly reduced cell vitality and growth, colony formation, Ki67 expression as well as cell cycle arrest in the G(0)/G(1) phase. Consistently, TSSC3 overexpression was associated with increased apoptosis assayed by annexin V/propidium iodide and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling staining. Subcutaneous injection of TSSC3 overexpressing SaOS2 cells into athymic nude mice showed that TSSC3 also inhibited tumorigenesis through growth inhibition and apoptosis induction in vivo. Further mechanistic studies revealed that the mitochondrial apoptosis pathway was required for TSSC3-mediated cell apoptosis. These findings support a suppressor role for TSSC3 in osteosarcoma development by regulating apoptosis. In addition, constitutive TSSC3 expression greatly enhanced the sensitivity of human osteosarcoma cells to the chemotherapeutic drugs cisplatin and epirubicin. Conversely, TSSC3 knockdown increased SaOS2 cell growth and decreased apoptosis in vitro and in vivo and reduced sensitivity of the cells to chemotherapy. This is the first study to demonstrate that TSSC3 has a potent tumor suppressor role in osteosarcoma, probably by inhibition of growth and induction of apoptosis via the mitochondrial apoptosis pathway.

The role of paraoxonase 1 in the detoxification of homocysteine thiolactone

The thioester homocysteine (Hcy)-thiolactone, product of an error-editing reaction in protein biosynthesis, forms when Hcy is mistakenly selected by methionyl-tRNA synthetase. Accumulating evidence suggests that Hcy-thiolactone plays an important role in atherothrombosis. The thioester chemistry of Hcy-thiolactone underlies its ability to form isopeptide bonds with protein lysine residues, which impairs or alters protein function and has pathophysiological consequences including activation of an autoimmune response and enhanced thrombosis. Mammalian organisms, including human, have evolved the ability to eliminate Hcy-thiolactone. One such mechanism involves paraoxonase 1 (PON1), which has the ability to hydrolyze Hcy-thiolactone. This article outlines Hcy-thiolactone pathobiology and reviews evidence documenting the role of PON1 in minimizing Hcy-thiolactone and N-Hcy-protein accumulation.

A reporter for tracking the UPR in vivo reveals patterns of temporal and cellular stress during atherosclerotic progression

Progression of human arteriosclerosis is associated with and promoted by induction of the endoplasmic reticulum (ER) stress pathway known as the unfolded protein response (UPR). Most studies that assess UPR markers in atherosclerosis rely on methodologies that suffer from low signal sensitivity, nonspecific immunohistochemistry, or inability to resolve differences between cellular subsets. To accurately monitor the UPR independently of artifacts generated postmortem, we describe here the first in vivo reporter for ER stress during atherosclerosis. Mice transgenic for the fluorescent XBP-1 ER stress indicator Erai were bred onto the Ldlr(-/-) background and fed an atherogenic diet. Subsequently, ERAI fluorescence at aortic roots was quantified and colocalized with lesional cell type. We found that the ERAI fluorescent signal increased as a function of time on the atherogenic diet and, in advanced lesions, was found close to necrotic cores. The majority of ERAI fluorescence localized to macrophages, and to a lesser extent, to intimal smooth muscle cells and patches of endothelial cells. These mice provide a valuable tool to monitor activation of the UPR in atherosclerosis and will be useful for future studies investigating relationships between pharmacologic and genetic modulators of UPR and atherosclerosis.

Trypanosoma cruzi infection induces a global host cell response in cardiomyocytes

Chagas' disease, caused by the hemoflagellate protozoan Trypanosoma cruzi, affects millions of people in South and Central America. Chronic chagasic cardiomyopathy, the most devastating manifestation of this disease, occurs in approximately one-third of infected individuals. Events associated with the parasite's tropism for and invasion of cardiomyocytes have been the focus of intense investigation in recent years. In the present study, we use murine microarrays to investigate the cellular response caused by invasion of primary murine cardiomyocytes by T. cruzi trypomastigotes. These studies identified 353 murine genes that were differentially expressed during the early stages of invasion and infection of these cells. Genes associated with the immune response, inflammation, cytoskeleton organization, cell-cell and cell-matrix interactions, apoptosis, cell cycle, and oxidative stress are among those affected during the infection. Our data indicate that T. cruzi induces broad modulations of the host cell machinery in ways that provide insight into how the parasite survives, replicates, and persists in the infected host and ultimately defines the clinical outcome of the infection.

Endoplasmic reticulum stress and lipid dysregulation

Cellular cholesterol homeostasis is a fundamental and highly regulated process. Transcription factors known as sterol regulatory element binding proteins (SREBPs) coordinate the expression of many genes involved in the biosynthesis and uptake of cholesterol. Dysregulation of SREBP activation and cellular lipid accumulation has been associated with endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR). This review will provide an overview of ER stress and the UPR as well as cholesterol homeostasis and SREBP regulation, with an emphasis on their interaction and biological relevance.

Methods and models for monitoring UPR-associated macrophage death during advanced atherosclerosis

During advanced atherosclerosis, chronic activation of the endoplasmic reticulum (ER) stress pathway, otherwise known as the unfolded protein response (UPR), is strongly associated with atherosclerotic plaque destabilization, the precursor to acute myocardial infarction and sudden death. Destabilized or vulnerable plaques are characterized by features that include thinning of a protective collagenous cap at the interface between the plaque and the vascular lumen and expansion of the necrotic core, a lipid-rich graveyard of dead macrophages. The cell biology of advanced plaque progression is complex and includes multiple cellular stressors that combine to promote chronic inflammation and progressive plaque deterioration. Several of these stressors converge at the ER, leading to activation of the UPR in multiple cell types. In macrophages, prolonged UPR activation triggers apoptosis, which when coupled to defective phagocytic clearance of these dying cells, leads to secondary necrosis and expansion of the plaque necrotic core. Though much insight has been gained recently on the role of the UPR in atherosclerosis, future studies are warranted to determine the cell-type specific contributions of ER stress to athero-progression and the therapeutic potential of UPR modulation. For such objectives to be met, reliable and standardized methodology must be utilized and developed. This chapter summarizes our current understanding of ER stress-induced macrophage apoptosis in atheromata and outlines both in vitro and in vivo methodologies to quantify the UPR in the context of experimental murine-advanced atherosclerosis.