Homocysteine induces programmed cell death in human vascular endothelial cells through activation of the unfolded protein response

Increased Total Homocysteine Levels Predict the Risk of Incident Dementia Independent of Cerebral Small-Vessel Diseases and Vascular Risk Factors

BACKGROUND

Homocysteine has been identified as a potential risk factor for stroke, cerebral small-vessel diseases (SVD), and dementia.

OBJECTIVE

The present study aimed to investigate the predictive value of homocysteine levels on incident dementia while simultaneously controlling for MRI findings and vascular risk factors.

METHODS

Within a Japanese cohort of participants with vascular risk factors in an observational study, we evaluated the association between baseline total homocysteine (tHcy) levels (per 1 μmol/L and the tertile of tHcy), the prevalence of MRI-findings at baseline, and incident all-cause dementia. Baseline brain MRI was used to determine SVD (lacunas, white matter hyperintensities, and cerebral microbleeds [CMBs]) and atrophy (medial-temporal lobe atrophy and bicaudate ratio). Logistic regression analyses were used to estimate the cross-sectional association between tHcy and each of MRI findings. Cox proportional hazards analyses were performed to estimate the longitudinal association between tHcy and dementia.

RESULTS

In the 643 subjects (age: 67.2 ± 8.4 years, male: 59% ; education: 12.9 ± 2.6 years), multivariable analyses adjusted for several potential confounders, including estimated glomerular filtration rate (eGFR) and intima-media thickness, showed that highest tHcy tertile was associated with lacunas, CMBs, and strictly deep CMBs. During the mean 7.3-year follow-up (range: 2-13), 47 patients were diagnosed with dementia (Alzheimer's disease: 24; vascular dementia: 18; mixed-type: 3; other: 2). After adjusting for age, gender, APOE ɛ4, education, BMI, MMSE, hypertension, cerebrovascular events, eGFR, and MRI-findings, tHcy level (hazard ratios [HR]: 1.08, p = 0.043) and the highest tertile of tHcy (HR: 2.50, p = 0.047) for all-cause dementia remained significant.

CONCLUSIONS

Our results provide additional evidence of tHcy that contributes to increased susceptibility to dementia risk.

Upregulation of DAPK contributes to homocysteine-induced endothelial apoptosis via the modulation of Bcl2/Bax and activation of caspase 3

Hyperhomocysteinemia is characterized by an abnormally high level of homocysteine (Hcy) in the blood and is associated with cardiovascular diseases such as atherosclerosis. Endothelial dysfunction may lead to the pro-atherogenic effects associated with hyperhomocysteinemia. Endothelial dysfunction induced by Hcy has been previously investigated; however, the underlying molecular mechanism remains to be fully elucidated. The present study investigated whether death-associated protein kinase (DAPK) is involved in Hcy‑induced apoptosis in human umbilical vein endothelial cells (HUVECs). It was determined that Hcy treatment upregulated the mRNA and protein expression levels of DAPK in HUVECs. Additionally, it was identified that the knockdown of DAPK using small interfering RNA may attenuate the Hcy-induced apoptosis and dissipation of mitochondrial membrane potential. DAPK inhibition may also reverse the effect of Hcy by the upregulation of B cell leukemia/lymphoma 2 (Bcl2) and poly ADP‑ribose polymerase, and the downregulation of Bcl2‑associated X protein (Bax) and of caspase 3. In conclusion, the present study demonstrated that DAPK contributed to the Hcy‑induced endothelial apoptosis via modulation of Bcl2/Bax expression levels and activation of caspase 3.

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.

Homocysteine induces PUMA-mediated mitochondrial apoptosis in SH-SY5Y cells

Previous studies have reported that homocysteine induced endoplasmic reticulum (ER) stress in neuronal cells, proposing the underlying mechanism by which it could induce neurotoxicity. Induction of pro-apoptotic transcription factor C/EBP homologous protein (CHOP) and activation of caspase-4 by calpain have been suggested to be an important route in inducing apoptosis in response to ER stress. In this study, we investigated the molecular pathway of homocysteine-induced apoptosis in caspase-4 deficient SH-SY5Y human neuroblastoma cells. Homocysteine significantly increased mRNA levels of CHOP and p53, resulting in the upregulation of their downstream target gene, p53 up-regulated modulator of apoptosis (PUMA). In cells treated with homocysteine, Bcl-2-associated X protein (BAX) protein levels, cytochrome c release from the mitochondria, and caspase-9 activation were significantly increased. Consistently, a caspase-9 inhibitor significantly alleviated homocysteine-induced cytotoxicity. Significantly lower BAX mRNA levels and caspase-9 activation were observed in cells transfected with siRNA for PUMA. Taken together, our findings suggest that PUMA would be involved in the possible crosstalk between the ER and the mitochondria in the homocysteine-induced apoptosis of caspase-4 deficient SH-SY5Y cells.

Caspase-1 Inflammasome Activation Mediates Homocysteine-Induced Pyrop-Apoptosis in Endothelial Cells

RATIONALE

Endothelial injury is an initial mechanism mediating cardiovascular disease.

OBJECTIVE

Here, we investigated the effect of hyperhomocysteinemia on programed cell death in endothelial cells (EC).

METHODS AND RESULTS

We established a novel flow-cytometric gating method to define pyrotosis (Annexin V(-)/Propidium iodide(+)). In cultured human EC, we found that: (1) homocysteine and lipopolysaccharide individually and synergistically induced inflammatory pyroptotic and noninflammatory apoptotic cell death; (2) homocysteine/lipopolysaccharide induced caspase-1 activation before caspase-8, caspase-9, and caspase-3 activations; (3) caspase-1/caspase-3 inhibitors rescued homocysteine/lipopolysaccharide-induced pyroptosis/apoptosis, but caspase-8/caspase-9 inhibitors had differential rescue effect; (4) homocysteine/lipopolysaccharide-induced nucleotide-binding oligomerization domain, and leucine-rich repeat and pyrin domain containing protein 3 (NLRP3) protein caused NLRP3-containing inflammasome assembly, caspase-1 activation, and interleukin (IL)-1β cleavage/activation; (5) homocysteine/lipopolysaccharide elevated intracellular reactive oxygen species, (6) intracellular oxidative gradient determined cell death destiny as intermediate intracellular reactive oxygen species levels are associated with pyroptosis, whereas high reactive oxygen species corresponded to apoptosis; (7) homocysteine/lipopolysaccharide induced mitochondrial membrane potential collapse and cytochrome-c release, and increased B-cell lymphoma 2-associated X protein/B-cell lymphoma 2 ratio which were attenuated by antioxidants and caspase-1 inhibitor; and (8) antioxidants extracellular superoxide dismutase and catalase prevented homocysteine/lipopolysaccharide -induced caspase-1 activation, mitochondrial dysfunction, and pyroptosis/apoptosis. In cystathionine β-synthase-deficient (Cbs(-/-)) mice, severe hyperhomocysteinemia-induced caspase-1 activation in isolated lung EC and caspase-1 expression in aortic endothelium, and elevated aortic caspase-1, caspase-9 protein/activity and B-cell lymphoma 2-associated X protein/B-cell lymphoma 2 ratio in Cbs(-/-) aorta and human umbilical vein endothelial cells. Finally, homocysteine-induced DNA fragmentation was reversed in caspase-1(-/-) EC. Hyperhomocysteinemia-induced aortic endothelial dysfunction was rescued in caspase-1(-/-) and NLRP3(-/-) mice.

CONCLUSIONS

Hyperhomocysteinemia preferentially induces EC pyroptosis via caspase-1-dependent inflammasome activation leading to endothelial dysfunction. We termed caspase-1 responsive pyroptosis and apoptosis as pyrop-apoptosis.

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.

Potential role of folate in pre-eclampsia

Dietary deficiencies of folate and other B vitamin cofactors involved in one-carbon metabolism, together with genetic polymorphisms in key folate-methionine metabolic pathway enzymes, are associated with increases in circulating plasma homocysteine, reduction in DNA methylation patterns, and genome instability events. All of these biomarkers have also been associated with pre-eclampsia. The aim of this review was to explore the literature and identify potential knowledge gaps in relation to the role of folate at the genomic level in either the etiology or the prevention of pre-eclampsia. A systematic search strategy was designed to identify citations in electronic databases for the following terms: folic acid supplementation AND pre-eclampsia, folic acid supplementation AND genome stability, folate AND genome stability AND pre-eclampsia, folic acid supplementation AND DNA methylation, and folate AND DNA methylation AND pre-eclampsia. Forty-three articles were selected according to predefined selection criteria. The studies included in the present review were not homogeneous, which made pooled analysis of the data very difficult. The present review highlights associations between folate deficiency and certain biomarkers observed in various tissues of women at risk of pre-eclampsia. Further investigation is required to understand the role of folate in either the etiology or the prevention of pre-eclampsia.

The P5 disulfide switch: taming the aging unfolded protein response

Aging cells are characterized by a loss of proteostasis and a decreased ability to survive under environmental stress. Regulation of the UPR in aging cells has been under much scrutiny, and studies have shown that the UPR in these cells differs considerably from younger cells with regard to the induction of apoptosis and chaperone activity. The role of IRE-1 and PERK in UPR-associated apoptosis makes the regulation of these signaling cascades an important target of study. The seemingly contradictory findings regarding the role of P5 in activating and deactivating these responses warrant further investigation and may hold the key to unlocking the role of this protein in various pathological conditions. Another important target for study with regard to P5 is the effects of the localization of this protein in the mitochondria and the consequences, if any, of these effects on the activation of the UPR.

The potential physiological crosstalk and interrelationship between two sovereign endogenous amines, melatonin and homocysteine

The antioxidant melatonin and the non-proteinogenic excitotoxic amino acid homocysteine (Hcy) are very distinct but related reciprocally to each other in their mode of action. The elevated Hcy level has been implicated in several disease pathologies ranging from cardio- and cerebro-vascular diseases to neurodegeneration owing largely to its free radical generating potency. Interestingly, melatonin administration potentially normalizes the elevated Hcy level, thereby protecting the cells from the undesired Hcy-induced excitotoxicity and cell death. However, the exact mechanism and between them remain obscure. Through literature survey we have found an indistinct but a vital link between melatonin and Hcy i.e., the existence of reciprocal regulation between them, and this aspect has been thoroughly described herein. In this review, we focus on all the possibilities of co-regulation of melatonin and Hcy at the level of their production and metabolism both in basal and in pathological conditions, and appraised the potential of melatonin in ameliorating homocysteinemia-induced cellular stresses. Also, we have summarized the differential mode of action of melatonin and Hcy on health and disease states.

Folate Deficiency Could Restrain Decidual Angiogenesis in Pregnant Mice

The mechanism of birth defects induced by folate deficiency was focused on mainly in fetal development. Little is known about the effect of folate deficiency on the maternal uterus, especially on decidual angiogenesis after implantation which establishes vessel networks to support embryo development. The aim of this study was to investigate the effects of folate deficiency on decidual angiogenesis. Serum folate levels were measured by electrochemiluminescence. The status of decidual angiogenesis was examined by cluster designation 34 (CD34) immunohistochemistry and the expression of angiogenic factors, including vascular endothelial growth factor A (VEGFA), placental growth factor (PLGF), and VEGF receptor 2 (VEGFR2) were also tested. Serum levels of homocysteine (Hcy), follicle stimulating hormone (FSH), luteinizing hormone (LH), prolactin (PRL), progesterone (P4), and estradiol (E2) were detected by Enzyme-linked immunosorbent assay. The folate-deficient mice had a lower folate level and a higher Hcy level. Folate deficiency restrained decidual angiogenesis with significant abnormalities in vascular density and the enlargement and elongation of the vascular sinus. It also showed a reduction in the expressions of VEGFA, VEGFR2, and PLGF. In addition, the serum levels of P4, E2, LH, and PRL were reduced in folate-deficient mice, and the expression of progesterone receptor (PR) and estrogen receptor α (ERα) were abnormal. These results indicated that folate deficiency could impaire decidual angiogenesis and it may be related to the vasculotoxic properties of Hcy and the imbalance of the reproductive hormone.

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.

A direct regulatory interaction between chaperonin TRiC and stress-responsive transcription factor HSF1

Heat shock transcription factor 1 (HSF1) is an evolutionarily conserved transcription factor that protects cells from protein-misfolding-induced stress and apoptosis. The mechanisms by which cytosolic protein misfolding leads to HSF1 activation have not been elucidated. Here, we demonstrate that HSF1 is directly regulated by TRiC/CCT, a central ATP-dependent chaperonin complex that folds cytosolic proteins. A small-molecule activator of HSF1, HSF1A, protects cells from stress-induced apoptosis, binds TRiC subunits in vivo and in vitro, and inhibits TRiC activity without perturbation of ATP hydrolysis. Genetic inactivation or depletion of the TRiC complex results in human HSF1 activation, and HSF1A inhibits the direct interaction between purified TRiC and HSF1 in vitro. These results demonstrate a direct regulatory interaction between the cytosolic chaperone machine and a critical transcription factor that protects cells from proteotoxicity, providing a mechanistic basis for signaling perturbations in protein folding to a stress-protective transcription factor.

High homocysteine and blood pressure related to poor outcome of acute ischemia stroke in Chinese population

OBJECTIVES

To assess the association between plasma homocysteine (Hcy), blood pressure (BP) and poor outcome at hospital discharge among acute ischemic stroke patients, and if high Hcy increases the risk of poor outcome based on high BP status in a northern Chinese population.

METHODS

Between June 1, 2009 and May 31, 2013, a total of 3695 acute ischemic stroke patients were recruited from three hospitals in northern Chinese cities. Demographic characteristics, lifestyle risk factors, medical history, and other clinical characteristics were recorded for all subjects. Poor outcome was defined as a discharge modified Rankin Scale (mRS) score ≥3 or death. The association between homocysteine concentration, admission blood pressure, and risk of poor outcome following acute ischemic stroke was analyzed by using multivariate non-conditional logistic regression models.

RESULTS

Compared with those in the lowest quartile of Hcy concentration in a multivariate-adjusted model, those in the highest quartile of Hcy concentration had increased risk of poor outcome after acute ischemic stroke, (OR = 1.33, P<0.05). The dose-response relationship between Hcy concentration and risk of poor outcome was statistically significant (p-value for trend  = 0.027). High BP was significantly associated with poor outcome following acute ischemic stroke (adjusted OR = 1.44, 95%CI, 1.19-1.74). Compared with non-high BP with nhHcy, in a multivariate-adjusted model, the ORs (95% CI) of non-high BP with hHcy, high BP with nhHcy, and high BP with hHcy to poor outcome were 1.14 (0.85-1.53), 1.37 (1.03-1.84) and 1.70 (1.29-2.34), respectively.

CONCLUSION

The present study suggested that high plasma Hcy and blood pressure were independent risk factors for prognosis of acute ischemic stroke, and hHcy may further increase the risk of poor outcome among patients with high blood pressure. Additionally, the results indicate that high Hcy with high BP may cause increased susceptibility to poor outcome among acute ischemic stroke patients in a northern Chinese population.

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.

Functional analysis of single-nucleotide polymorphisms in the regulation of coactivator-associated arginine methyltransferase 1 expression and plasma homocysteine levels

BACKGROUND

Hyperhomocysteinemia is a risk factor for cardiovascular disease. Coactivator-associated arginine methyltransferase 1 (CARM1) participates in the synthesis of homocysteine, but whether the genetic variations regulate CARM1 expression and homocysteine levels remains unknown.

METHODS AND RESULTS

Functional analyses combined with an association study were conducted to identify the causal variant for CARM1 expression and homocysteine levels. Based on functional annotations obtained from Encyclopedia of DNA Elements, we selected 4 potentially functional single-nucleotide polymorphisms in the CARM1 gene and investigated their effect on CARM1 transcription levels in vivo. rs117569851, located in the promoter region of CARM1, as well as rs12460421 and rs4804544, was associated with CARM1 expression levels, and the last 2 single-nucleotide polymorphisms were discovered in high linkage disequilibrium with rs117569851 (r(2)=0.9 and 1.0) in our study sample. rs117569851 was further identified to be responsible for regulating CARM1 expression. The T allele disrupted the binding of early growth response-1, which led to the downregulation of transcriptional activity in vitro and CARM1 mRNA levels in vivo. In addition, rs117569851 was associated with plasma homocysteine levels in a Chinese population (n=406), with a 2.16 μmol/L decrease per copy of T allele.

CONCLUSIONS

The present study suggests that a noncoding variant in the CARM1-promoter functions as a regulator of gene transcription and homocysteine levels.

Homocysteine-induced apoptosis in endothelial cells coincides with nuclear NOX2 and peri-nuclear NOX4 activity

Apoptosis of endothelial cells related to homocysteine (Hcy) has been reported in several studies. In this study, we evaluated whether reactive oxygen species (ROS)-producing signaling pathways contribute to Hcy-induced apoptosis induction, with specific emphasis on NADPH oxidases. Human umbilical vein endothelial cells were incubated with 0.01–2.5 mM Hcy. We determined the effect of Hcy on caspase-3 activity, annexin V positivity, intracellular NOX1, NOX2, NOX4, and p47^phox expression and localization, nuclear nitrotyrosine accumulation, and mitochondrial membrane potential (ΔΨ_m). Hcy induced caspase-3 activity and apoptosis; this effect was concentration dependent and maximal after 6-h exposure to 2.5 mM Hcy. It was accompanied by a significant increase in ΔΨ_m. Cysteine was inactive on these parameters excluding a reactive thiol group effect. Hcy induced an increase in cellular NOX2, p47^phox, and NOX4, but not that of NOX1. 3D digital imaging microscopy followed by image deconvolution analysis showed nuclear accumulation of NOX2 and p47^phox in endothelial cells exposed to Hcy, but not in control cells, which coincided with accumulation of nuclear nitrotyrosine residues. Furthermore, Hcy enhanced peri-nuclear localization of NOX4 coinciding with accumulation of peri-nuclear nitrotyrosine residues, a reflection of local ROS production. p47^phox was also increased in the peri-nuclear region. The Hcy-induced increase in caspase-3 activity was prevented by DPI and apocynin, suggesting involvement of NOX activity. The data presented in this article reveal accumulation of nuclear NOX2 and peri-nuclear NOX4 accumulation as potential source of ROS production in Hcy-induced apoptosis in endothelial cells.

Hydrogen sulfide inhibits homocysteine-induced endoplasmic reticulum stress and neuronal apoptosis in rat hippocampus via upregulation of the BDNF-TrkB pathway

AIM

Homocysteine (Hcy) can elicit neuronal cell death, and hyperhomocysteinemia is a strong independent risk factor for Alzheimer's disease. The aim of this study was to examine the effects of hydrogen sulfide (H2S) on Hcy-induced endoplasmic reticulum (ER) stress and neuronal apoptosis in rat hippocampus.

METHODS

Adult male SD rats were intracerebroventricularly (icv) injected with Hcy (0.6 μmol/d) for 7 d. Before Hcy injection, the rats were treated with NaHS (30 or 100 μmol·kg(-1)·d(-1), ip) and/or k252a (1 μg/d, icv) for 2 d. The apoptotic neurons were detected in hippocampal coronal slices with TUNEL staining. The expression of glucose regulated protein 78 (GRP78), C/EBP homologous protein (CHOP), cleaved caspase-12, and BDNF in the hippocampus were examined using Western blotting assays. The generation of H2S in the hippocampus was measured with the NNDPD method.

RESULTS

Hcy markedly inhibited the production of endogenous H2S and increased apoptotic neurons in the hippocampus. Furthermore, Hcy induced ER stress responses in the hippocampus, as indicated by the upregulation of GRP78, CHOP, and cleaved caspase-12. Treatment with the H2S donor NaHS increased the endogenous H2S production and BDNF expression in a dose-dependent manner, and significantly reduced Hcy-induced neuronal apoptosis and ER stress responses in the hippocampus. Treatment with k252a, a specific inhibitor of TrkB (the receptor of BDNF), abolished the protective effects of NaHS against Hcy-induced ER stress in the hippocampus.

CONCLUSION

H2S attenuates ER stress and neuronal apoptosis in the hippocampus of Hcy-treated rats via upregulating the BDNF-TrkB pathway.

Hydrogen sulfide and the pathogenesis of atherosclerosis

SIGNIFICANCE

Stigmatized as a toxic environmental pollutant for centuries, hydrogen sulfide (H2S) has gained recognition over the last decade as an important gasotransmitter that functions in physiological and pathophysiological conditions, such as atherosclerosis.

RECENT ADVANCES

Atherosclerosis is a common disease that stems from the buildup of fatty/cholesterol plaques on the endothelial cells of arteries. The deposits mitigate thickening and stiffening of arterial tissue, which contributes to concomitant systemic or localized vascular disorders. Recently, it has been recognized that H2S plays an anti-atherosclerotic role, and its deficiency leads to early development and progression of atherosclerosis. This review article presents multiple lines of evidence for the protective effects of H2S against the development of atherosclerosis. Also highlighted are the characterization of altered metabolism of H2S in the development of atherosclerosis, underlying molecular and cellular mechanisms, and potential therapeutic intervention based on H2S supplementation for atherosclerosis management.

CRITICAL ISSUES

Although a protective role of H2S against atherosclerosis has emerged, controversy remains regarding the mechanisms underlying H2S-induced endothelial cell proliferation and angiogenesis as well as its anti-inflammatory properties. The therapeutic value of H2S to this pathophysiological condition has not been tested clinically but, nonetheless, it shows tremendous promise.

FUTURE DIRECTIONS

The efficiency and safety profile of H2S-based therapeutic approaches should be refined, and the mechanisms by which H2S exerts its beneficial effects should be elucidated to develop more specific and potent therapeutic strategies to treat atherosclerosis. Whether the therapeutic effects of H2S in animal studies are transferable to clinical studies merits future investigation.

Folate deficiency triggers an oxidative-nitrosative stress-mediated apoptotic cell death and impedes insulin biosynthesis in RINm5F pancreatic islet β-cells: relevant to the pathogenesis of diabetes

It has been postulated that folic acid (folate) deficiency (FD) may be a risk factor for the pathogenesis of a variety of oxidative stress-triggered chronic degenerative diseases including diabetes, however, the direct evidence to lend support to this hypothesis is scanty. For this reason, we set out to study if FD can trigger the apoptotic events in an insulin-producing pancreatic RINm5F islet β cells. When these cells were cultivated under FD condition, a time-dependent growth impediment was observed and the demise of these cells was demonstrated to be apoptotic in nature proceeding through a mitochondria-dependent pathway. In addition to evoke oxidative stress, FD condition could also trigger nitrosative stress through a NF-κB-dependent iNOS-mediated overproduction of nitric oxide (NO). The latter compound could then trigger depletion of endoplasmic reticulum (ER) calcium (Ca²⁺) store leading to cytosolic Ca²⁺ overload and caused ER stress as evidence by the activation of CHOP expression. Furthermore, FD-induced apoptosis of RINm5F cells was found to be correlated with a time-dependent depletion of intracellular gluthathione (GSH) and a severe down-regulation of Bcl-2 expression. Along the same vein, we also demonstrated that FD could severely impede RINm5F cells to synthesize insulin and their abilities to secret insulin in response to glucose stimulation were appreciably hampered. Even more importantly, we found that folate replenishment could not restore the ability of RINm5F cells to resynthesize insulin. Taken together, our data provide strong evidence to support the hypothesis that FD is a legitimate risk factor for the pathogenesis of diabetes.

Activation of the unfolded protein response in vascular endothelial cells of nondiabetic obese adults

CONTEXT

Activation of the unfolded protein response (UPR) is emerging as an important molecular signature of cardiometabolic diseases associated with obesity. However, despite the well-established role of the vascular endothelium in obesity-related cardiometabolic dysfunction, it is unclear whether the UPR is activated in endothelial cells of obese adults.

OBJECTIVE

The objective of the study was to determine whether markers of UPR activation are increased in endothelial cells (ECs) of nondiabetic obese adults with impaired endothelial function.

DESIGN, SETTING, AND PARTICIPANTS

Endothelial cells were obtained from antecubital veins of the nondiabetic obese adults [body mass index (BMI) ≥ 30 kg/m(2), n = 12] with impaired endothelial function and from their nonobese peers (BMI < 30 kg/m(2), n = 14).

MAIN OUTCOME VARIABLES

UPR activation via expression (quantitative immunofluorescence) of the proximal UPR sensors, inositol-requiring endoplasmic reticulum (ER)-to-nucleus signaling protein 1 (IRE1), RNA-dependent protein kinase-like ER eukaryotic initiation factor-2α kinase (PERK), and activating transcription factor 6 (ATF6), were the main outcome variables.

RESULTS

IRE1 expression was greater in obese vs nonobese individuals (0.84 ± 0.09 vs 0.47 ± 0.02 IRE1 intensity/human umbilical vein EC (HUVEC) intensity (n = 10/8, P < .01). Obese individuals also had greater EC activation of UPR stress sensors PERK and ATF6, indicated by increased expression of phosphorylated PERK [p-PERK; 0.49 ± 0.05 vs 0.36 ± 0.03, p-PERK (threonine 981) intensity/HUVEC intensity, n = 10 men, 13 women, P < .05] and nuclear localization of ATF6 (0.38 ± 0.05 vs 0.23 ± 0.02, nuclear ATF6 intensity/HUVEC intensity, n = 5 men, 9 women, P < .01), respectively. Stepwise linear regression analysis revealed that indices of body fat (BMI and waist circumference) were the strongest independent predictors of all 3 UPR mediators, explaining between 18% and 59% of the variance in endothelial cell expression of IRE1, p-PERK, and nuclear ATF6 localization.

CONCLUSION

These results provide novel evidence for UPR activation in the endothelial cells of nondiabetic obese adults with vascular endothelial dysfunction.

Notch activation promotes endothelial survival through a PI3K-Slug axis

RATIONALE

Loss of endothelial viability correlates with initiation and progress of vascular pathology. However, much remains to be learned about pathways required to maintain the balance between cell viability and apoptosis. Notch activation can enhance or inhibit apoptosis but its role in maintaining the endothelium needs further delineation.

OBJECTIVE

This study aims to identify the mechanisms by which Notch activation regulates endothelial viability.

METHODS AND RESULTS

Endothelial cells transduced with active Notch were treated with lipopolysaccharide (LPS) or homocysteine to induce endothelial apoptosis. Notch protected against LPS-induced cell death but exacerbated homocysteine-induced apoptosis. Inhibition of PI3K revealed that ligand-induced activation of endogenous Notch initiates parallel death and survival pathways and exhibits a differential effect on endothelial survival depending on the apoptotic stimulus. PI3K activity regulated the expression of Slug, which was required for survival in Notch-activated endothelial cells. Homocysteine, but not LPS, blocked both PI3K activity and Slug expression in Notch-activated cells, leading to increased endothelial apoptosis.

CONCLUSIONS

Notch signaling leads to activation of parallel survival and apoptotic pathways in endothelial cells. The interaction of Notch with other signaling pathways plays an important contextual role in regulating endothelial viability.

Apoptosis of bone marrow mesenchymal stem cells caused by homocysteine via activating JNK signal

Bone marrow mesenchymal stem cells (BMSCs) are capable of homing to and repair damaged myocardial tissues. Apoptosis of BMSCs in response to various pathological stimuli leads to the attenuation of healing ability of BMSCs. Plenty of evidence has shown that elevated homocysteine level is a novel independent risk factor of cardiovascular diseases. The present study was aimed to investigate whether homocysteine may induce apoptosis of BMSCs and its underlying mechanisms. Here we uncovered that homocysteine significantly inhibited the cellular viability of BMSCs. Furthermore, TUNEL, AO/EB, Hoechst 333342 and Live/Death staining demonstrated the apoptotic morphological appearance of BMSCs after homocysteine treatment. A distinct increase of ROS level was also observed in homocysteine-treated BMSCs. The blockage of ROS by DMTU and NAC prevented the apoptosis of BMSCs induced by homocysteine, indicating ROS was involved in the apoptosis of BMSCs. Moreover, homocysteine also caused the depolarization of mitochondrial membrane potential of BMSCs. Furthermore, apoptotic appearance and mitochondrial membrane potential depolarization in homocysteine-treated BMSCs was significantly reversed by JNK inhibitor but not p38 MAPK and ERK inhibitors. Western blot also confirmed that p-JNK was significantly activated after exposing BMSCs to homocysteine. Homocysteine treatment caused a significant reduction of BMSCs-secreted VEGF and IGF-1 in the culture medium. Collectively, elevated homocysteine induced the apoptosis of BMSCs via ROS-induced the activation of JNK signal, which provides more insight into the molecular mechanisms of hyperhomocysteinemia-related cardiovascular diseases.

Activation of AMP-activated protein kinase alleviates homocysteine-mediated neurotoxicity in SH-SY5Y cells

Mammalian AMP-activated protein kinase (AMPK) acts as a metabolite-sensing protein kinase in multiple tissues. Recent studies have shown that AMPK activation also regulates intracellular signaling pathways involved in cellular survival and apoptosis. Previously, we have reported that AMPK activation alleviates the endoplasmic reticulum (ER) stress-mediated neurotoxicity and tau hyperphosphorylation caused by palmitate. Therefore, we investigated whether AMPK activation alleviates ER stress-mediated neurotoxicity in SH-SY5Y human neuroblastoma cells incubated with homocysteine. Regulation of AMPK activity by isoflavone was also determined to investigate the underlying mechanism of its neuroprotective effect. Treatment of SH-SY5Y human neuroblastoma cells with N (1)-(β-D-ribofuranosyl)-5-aminoimidazole-4-carboxamide (AICAR), a pharmacological activator of AMPK, significantly protected cells against cytotoxicity imposed by tunicamycin and homocysteine. Homocysteine significantly suppressed AMPK activation, which was alleviated by AICAR. We observed a significant inhibition of the unfolded protein response by AICAR in cells incubated with homocysteine, suggesting a protective role of AMPK activation against ER stress-mediated neurotoxicity. AICAR also significantly reduced tau hyperphosphorylation by inactivating glycogen synthase kinase-3β and c-Jun N-terminal kinase in cells incubated with homocysteine. Furthermore, treatment of cells with soy isoflavone, genistein and daidzein significantly activated AMPK, which was repressed by tunicamycin and homocysteine. Therefore, our results suggest that AMPK activation by isoflavone as well as AICAR alleviates homocysteine-mediated neurotoxicity in SH-SY5Y cells.

Effect of L-homocysteine on endothelial cell-cell junctions following F-actin stabilization through tropomyosin-1 overexpression

Since the identification of actin in non‑muscle cells, it has been suggested that the regulation of the mechanical behaviors of the actin cytoskeleton regulates cellular shape changes and the generation of forces during cell migration and division. The maintenance of cell shape and polarity are important in the formation of cell-cell junctions. The aim of the present study was to determine the effect of L‑homocysteine thiolactone hydrochloride on EA.hy926 endothelial cells in the context of the maintenance cell-cell junctions through the stabilization of filamentous actin cytoskeleton (F‑actin). The actin filaments were stabilized by the overexpression of tropomyosin-1, which has the ability to stabilize actin filaments in muscle and non-muscle cells. The stabilization of F-actin induced a significant decrease in the percentage of late apoptotic and necrotic cells following treatment with L-homocysteine. Moreover, the migratory potential of the endothelial cells was greater in the cells overexpressing tropomyosin-1 treated with L-homocysteine. Additionally, our results indicated that the stabilization of F-actin in the EA.hy926 cells significantly increased the expression of junctional β‑catenin, as compared to the cells not overexpressing tropomyosin‑1. Similarly, the fluorescence intensity of junctional α-catenin was also increased in the cells with stabilized F‑actin cytoskeleton. However, this increase was only slightly higher than that observed in the EA.hy926 cells not overexpressing tropomyosin-1. Furthermore, the analysis of Zonula occludens (ZO)‑1 relative fluorescence demonstrated a statistically significant decrease in the cell-cell junction areas among the cells with stabilized F-actin cytoskeleton in comparison to the cells not overexpressing tropomyosin-1. Our results indicate that the stabilization of F-actin does not affect the migratory potential of cells, and consequently protects the EA.hy926 cells against the L-homocysteine-induced decrease in cell mobility. Moreover, it is suggested that α‑catenin may participate in the suppression of actin polymerization in the area of cell-cell junctions. It can be hypothesized that the stabilization of F-actin strengthens endothelial adherens and tight junctions by increasing the number of cell-cell junctions due to the amplification of β-catenin and the ZO‑1 fluorescence signal. However, ZO-1 stabilizes the endothelial barrier function through the stabilization of F-actin and F-actin itself stabilizes the localization of ZO-1.

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.

Homocysteine over-accumulation as the effect of potato leaves exposure to biotic stress

Homocysteine (Hcy) is a naturally occurring intermediate metabolite formed during methionine metabolism. It has been well documented that its excess can be extremely toxic to mammalian, yeast and bacterial cells. In spite of the metabolic value of Hcy known for decades, the role of this amino acid in the plant response to stress has not been recognized yet. In the presented study, using potato plant (Solanum tuberosum L.) and Phytophthora infestans as a model system, the presence and tissue localization of Hcy in leaves was examined by an immunohistochemical method. The over-production of Hcy was more evidenced in the susceptible than in the resistant genotype of potato starting from 48 hpi. Furthermore, the elevated level of Hcy was correlated in time with the up-regulation of genes engaged in its biosynthesis, e.g. cystathionine β-lyase and S-adenosyl-l-homocysteine hydrolase. The pharmacological approach with exogenous Hcy resulted in significant rise in lipid peroxidation and more potent late blight disease development in leaves of susceptible potato as well. Finally, it has been found that key defense enzymes, i.e. phenylalanine ammonia lyase and β-1,3-glucanase were up-regulated early in the resistant potato genotype, starting from 1st hpi. In turn, in the susceptible potato the time-lag in expression of these enzymes tuned with excess production of Hcy might facilitate leaf tissue colonization by pathogen. Based on obtained results it should be stated that Hcy over-accumulation is engaged in pathophysiological mechanism leading to the abolishment of the resistance and might be an informative disease hallmark both in plant and in animal system.

Homocysteine inhibits hepatocyte proliferation via endoplasmic reticulum stress

Homocysteine is an independent risk factor for coronary, cerebral, and peripheral vascular diseases. Recent studies have shown that levels of homocysteine are elevated in patients with impaired hepatic function, but the precise role of homocysteine in the development of hepatic dysfunction is unclear. In this study, we examined the effect of homocysteine on hepatocyte proliferation in vitro. Our results demonstrated that homocysteine inhibited hepatocyte proliferation by up-regulating protein levels of p53 as well as mRNA and protein levels of p21^Cip1 in primary cultured hepatocytes. Homocysteine induced cell growth arrest in p53-positive hepatocarcinoma cell line HepG2, but not in p53-null hepatocarcinoma cell line Hep3B. A p53 inhibitor pifithrin-α inhibited the expression of p21^Cip1 and attenuated homocysteine-induced cell growth arrest. Homocysteine induced TRB3 expression via endoplasmic reticulum stress pathway, resulting in Akt dephosphorylation. Knock-down of endogenous TRB3 significantly suppressed the inhibitory effect of homocysteine on cell proliferation and the phosphorylation of Akt. LiCl reversed homocysteine-mediated cell growth arrest by inhibiting TRB3-mediated Akt dephosphorylation. These results demonstrate that both TRB3 and p21^Cip1 are critical molecules in the homocysteine signaling cascade and provide a mechanistic explanation for impairment of liver regeneration in hyperhomocysteinemia.

Hyperhomocysteinemia and cardiovascular disease: new mechanisms beyond atherosclerosis

The association of hyperhomocysteinemia (Hhe) with cardiovascular disease (CVD) has been explored in detail over the last four decades since initial reports in the 1960s. Although several epidemiological studies have shown an association, convincing mechanistic studies are still lacking. However, recent prospective studies demonstrate a strong association of Hhe with coronary disease. Several pathogenic mechanisms have been studied in Hhe and indicate alterations in the various components of vascular disease, namely endothelial cells, vascular smooth muscle cells, platelets, and the coagulation/fibrinolytic systems. Increased oxidative stress, hypomethylation, and protein homocysteinylation have been proposed as potential molecular mechanisms in Hhe-induced CVD. In addition, recent studies indicate a novel link between Hhe and CVD, that is, direct effects on coronary arteriolar and myocardial remodeling resulting in cardiac dysfunction.

The impact of MRI white matter hyperintensities on dementia in Parkinson's disease in relation to the homocysteine level and other vascular risk factors

BACKGROUND

The role of white matter hyperintensities (WMH) and homocysteine (Hcy) and other vascular risk factors in the pathogenesis of Parkinson's disease (PD) dementia (PDD) remains unclear.

OBJECTIVE

The aim of the study was to assess the impact of WMH, Hcy and other biochemical and vascular risk factors on PDD.

METHODS

A total of 192 patients with PD and 184 age- and sex-matched healthy controls were included. A semistructured interview was used to assess demographic and clinical variables with respect to vascular risk factors (arterial hypertension, diabetes mellitus, atrial fibrillation, ischemic heart disease, obliterative atherosclerosis, hypercholesterolemia, smoking, alcohol intake). Unified Parkinson's Disease Rating Scale score, Hoehn-Yahr staging and the Schwab-England activities of daily living scale were used to assess motor abilities and activities of daily living. A complex neuropsychological examination with a battery of tests was used to classify patients into a group with dementia (PDD) and a group without dementia (PD). Neuroradiological examination of MRI scans included visual rating scales for WMH (according to the Wahlund and Erkinjunntti rating scales) and the Scheltens scale for hippocampal atrophy. Blood samples for Hcy, folate, vitamin B12, fibrinogen, lipids, glucose, creatinine, transaminases and thyroid stimulating hormone (TSH) were examined.

RESULTS

Among all patients, 57 (29.7%) fulfilled the diagnostic criteria for dementia. Significantly higher Hcy plasma levels were noted in PD and PDD groups compared to controls (p < 0.05) and in PDD when compared to PD (p < 0.05). According to multivariate regression analysis, WMH (Erkinjuntti scale), high Hcy, low vitamin B12 and folate plasma levels were independent risk factors for PDD. Vascular risk factors did not play any role in the pathogenesis of PDD and WMH.

CONCLUSIONS

WMH along with Hcy, folate and vitamin B12 may impact cognition in PD. Therapy with vitamin B12, folate and catechol-O-methyltransferase inhibitors may play a potential protective role against PDD.

Methyl donor deficiency affects small-intestinal differentiation and barrier function in rats

Dietary methyl donors and their genetic determinants are associated with Crohn's disease risk. We investigated whether a methyl-deficient diet (MDD) may affect development and functions of the small intestine in rat pups from dams subjected to the MDD during gestation and lactation. At 1 month before pregnancy, adult females were fed with either a standard food or a diet without vitamin B12, folate and choline. A global wall hypotrophy was observed in the distal small bowel (MDD animals 0·30 mm v. controls 0·58 mm; P< 0·001) with increased crypt apoptosis (3·37 v. 0·4 %; P< 0·001), loss of enterocyte differentiation in the villus and a reduction in intestinal alkaline phosphatase production. Cleaved caspase-3 immunostaining (MDD animals 3·37 % v. controls 0·4 %, P< 0·001) and the Apostain labelling index showed increased crypt apoptosis (3·5 v. 1·4 %; P= 0·018). Decreased proliferation was observed in crypts of the proximal small bowel with a reduced number of minichromosome maintenance 6 (MDD animals 52·83 % v. controls 83·17 %; P= 0·048) and proliferating cell nuclear antigen-positive cells (46·25 v. 59 %; P= 0·05). This lack of enterocyte differentiation in the distal small bowel was associated with an impaired expression of β-catenin and a decreased β-catenin–E-cadherin interaction. The MDD affected the intestinal barrier in the proximal small bowel by decreasing Paneth cell number after immunostaining for lysosyme (MDD animals 8·66 % v. controls 21·66 %) and by reducing goblet cell number and mucus production after immunostaining for mucin-2 (crypts 8·66 v. 15·33 %; villus 7 v. 17 %). The MDD has dual effects on the small intestine by producing dramatic effects on enterocyte differentiation and barrier function in rats.

The endoplasmic reticulum stress response in aging and age-related diseases

The endoplasmic reticulum(ER) is a multifunctional organelle within which protein folding, lipid biosynthesis, and calcium storage occurs. Perturbations such as energy or nutrient depletion, disturbances in calcium or redox status that disrupt ER homeostasis lead to the misfolding of proteins, ER stress and up-regulation of several signaling pathways coordinately called the unfolded protein response (UPR). The UPR is characterized by the induction of chaperones, degradation of misfolded proteins and attenuation of protein translation. The UPR plays a fundamental role in the maintenance of cellular homeostasis and thus is central to normal physiology. However, sustained unresolved ER stress leads to apoptosis. Aging linked declines in expression and activity of key ER molecular chaperones and folding enzymes compromise proper protein folding and the adaptive response of the UPR. One mechanism to explain age associated declines in cellular functions and age-related diseases is a progressive failure of chaperoning systems. In many of these diseases, proteins or fragments of proteins convert from their normally soluble forms to insoluble fibrils or plaques that accumulate in a variety of organs including the liver, brain or spleen. This group of diseases, which typically occur late in life includes Alzheimer's, Parkinson's, type II diabetes and a host of less well known but often equally serious conditions such as fatal familial insomnia. The UPR is implicated in many of these neurodegenerative and familial protein folding diseases as well as several cancers and a host of inflammatory diseases including diabetes, atherosclerosis, inflammatory bowel disease and arthritis. This review will discuss age-related changes in the ER stress response and the role of the UPR in age-related diseases.

Involvement of endoplasmic reticulum stress in homocysteine-induced apoptosis of osteoblastic cells

Hyperhomocysteinemia has been shown to increase the incidence of osteoporosis and osteoporotic fractures. Endoplasmic reticulum (ER) stress was recently shown to be associated with apoptosis in several types of cells. In this study, we determined the effect of homocysteine (Hcy) on the apoptosis of osteoblastic cells and investigated whether ER stress participates in Hcy-induced osteoblast apoptosis. Human osteoblastic cells were incubated with Hcy. Hcy dose-dependently decreased cell viability and increased apoptosis in osteoblastic cells. Osteoblastic cells are more susceptible to Hcy-mediated cell death than other cell types. Expression of cleaved caspase-3 was significantly increased by Hcy, and pretreatment with caspase-3 inhibitor rescued the cell viability by Hcy. Hcy treatment led to an increase in release of mitochondrial cytochrome c. It also triggered ER stress by increased expression of glucose-regulated protein 78, inositol-requiring transmembrane kinase and endonuclease 1α (IRE-1α), spliced X-box binding protein, activating transcription factor 4, and C/EBP homologous protein. Silencing IRE-1α expression by small interfering RNA effectively suppressed Hcy-induced apoptosis of osteoblastic cells. Our results suggest that hyperhomocysteinemia induces apoptotic cell death in osteoblasts via ER stress.

Permissive role of miR-663 in induction of VEGF and activation of the ATF4 branch of unfolded protein response in endothelial cells by oxidized phospholipids

OBJECTIVE

Atherosclerotic lesions contain high concentrations of oxidized phospholipids (OxPLs) known to induce VEGF via the ATF4 arm of unfolded protein response (UPR), and to promote angiogenic reactions thus potentially contributing to the progression and destabilization of atherosclerotic plaques. In order to get further insights into the mechanisms of cellular stress-induced angiogenesis we studied the role of a specific microRNA (miR-663) in the mechanisms of VEGF induction by OxPLs and inducers of UPR.

METHODS

miRNA and mRNA levels were determined using microarray profiling and qRT-PCR methods. Proteins were analyzed by Western blotting. miR-663 levels were changed by transfecting cells with synthetic oligonucleotides.

RESULTS

OxPAPC elevated miR-663 in two types of human endothelial cells (ECs). Knockdown of miR-663 inhibited upregulation of VEGF mRNA in ECs treated by OxPAPC, OxPAPS or OxPAPA. In addition, silencing of miR-663 suppressed upregulation by OxPAPC of ATF4 mRNA and protein, as well as a downstream gene TRIB. Similarly to the inhibition of OxPAPC effects, knockdown of miR-663 suppressed elevation of ATF4, VEGF and TRIB in response to another inducer of UPR, tunicamycin. Overexpression of miR-663 reversed the inhibition of VEGF induction by miR-663 inhibitor.

CONCLUSION

miR-663 is critically important for 2 key events induced in ECs by stress agents and oxidized lipids, namely induction of transcription factor ATF4 and its downstream gene VEGF. These findings allow hypothesizing that miR-663 plays a general role in control of the ATF4 branch of UPR induced by different agents.

Methyl deficient diet aggravates experimental colitis in rats

Inflammatory bowel diseases (IBD) result from complex interactions between environmental and genetic factors. Low blood levels of vitamin B12 and folate and genetic variants of related target enzymes are associated with IBD risk, in population studies. To investigate the underlying mechanisms, we evaluated the effects of a methyl-deficient diet (MDD, folate, vitamin B12 and choline) in an experimental model of colitis induced by dextran sodium sulphate (DSS), in rat pups from dams subjected to the MDD during gestation and lactation. Four groups were considered (n= 12–16 per group): C DSS⁻ (control/DSS⁻), D DSS⁻ (deficient/DSS⁻), C DSS⁺ (control/DSS⁺) and D DSS⁺ (deficient/DSS⁺). Changes in apoptosis, oxidant stress and pro-inflammatory pathways were studied within colonic mucosa. In rat pups, the MDD produced a decreased plasma concentration of vitamin B12 and folate and an increased homocysteine (7.8 ± 0.9 versus 22.6 ± 1.2 μmol/l, P < 0.001). The DSS-induced colitis was dramatically more severe in the D DSS⁺ group compared with each other group, with no change in superoxide dismutase and glutathione peroxidase activity, but decreased expression of caspase-3 and Bax, and increased Bcl-2 levels. The mRNA levels of tumour necrosis factor (TNF)-α and protein levels of p38, cytosolic phospolipase A2 and cyclooxygenase 2 were significantly increased in the D DSS⁺ pups and were accompanied by a decrease in the protein level of tissue inhibitor of metalloproteinases (TIMP)3, a negative regulator of TNF-α. MDD may cause an overexpression of pro-inflammatory pathways, indicating an aggravating effect of folate and/or vitamin B12 deficiency in experimental IBD. These findings suggest paying attention to vitamin B12 and folate deficits, frequently reported in IBD patients.

Curcumin has neuroprotection effect on homocysteine rat model of Parkinson

Parkinson's disease (PD) is a progressive neurological disorder which is emanated by dopaminergic death cell and depletion. Curcumin as a nontoxic matter has antioxidant, anti-inflammatory, and antiproliferative activities, and it involves antioxidant property same to vitamins C and E. In this study, we investigated the neuroprotective properties of the natural polyphenolic antioxidant compound, curcumin, against homocysteine (Hcy) neurotoxicity. Curcumin (50 mg/kg) was injected intraperitoneally (i.p.) once daily for a period of 10 days beginning 5 days prior to Hcy (2 μmol/μl) intracerebroventricular (i.c.v.) injection in rats. The studies included immunohistological and locomotor activity tests. These results suggest that homocysteine intracerebroventricular administration (2 μmol/μl i.c.v.) may induce changes in rat brain, and subsequently, polyphenol treatment curcumin 50 mg/kg (i.p.) was capable in improving locomotor function in insulted animal by protecting the nervous system against homocysteine toxicity.

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.

Mechanisms of ER stress-induced apoptosis in atherosclerosis

Endoplasmic reticulum (ER) stress is triggered by perturbations in ER function such as those caused by protein misfolding or by increases in protein secretion. Eukaryotic cells respond to ER stress by activating 3 ER-resident proteins, activating transcription factor-6, inositol requiring protein-1, and protein kinase RNA-like ER kinase (PERK). These proteins direct signaling pathways that relieve ER stress in a process known as the unfolded protein response (UPR). In pathological settings, however, prolonged UPR activation can promote cell death, and this process has recently emerged as an important concept in atherosclerosis. We review here the evidence for UPR activation and cell death in macrophages, smooth muscle cells, and endothelial cells in the context of advanced atherosclerosis as well as the existing literature regarding mechanisms of UPR-induced cell death. Knowledge in this area may suggest new therapeutic targets relevant to the formation of clinically dangerous atherosclerotic plaques.

TRB3 mediates homocysteine-induced inhibition of endothelial cell proliferation

Hyperhomocysteinemia (HHcy) has been shown to induce endothelial dysfunction, an early event in the progression of atherosclerosis. However, the underlying mechanism of endothelial cell injury in HHcy has not been clearly elucidated. In this study, we examined the effect of homocysteine on tribbles-related protein 3 (TRB3)-mediated cell-cycle arrest in human umbilical vein endothelial cells (HUVECs). Treatment of HUVECs with homocysteine (0-250 µmol/L) resulted in inhibition of cell proliferation assessed by [(3)H]-thymidine incorporation into DNA. Homocysteine induced cell-cycle arrest in the G1 phase by up-regulating the protein levels of p27(kip1). Under these conditions, homocysteine did not induce endoplasmic reticulum stress. However, homocysteine up-regulated the expression of TRB3, thus leading to the dephosphorylation of Akt (Thr308). Knock-down of endogenous TRB3 using siRNA significantly suppressed the inhibitory effect of homocysteine on the proliferation of HUVECs. Homocysteine-induced TRB3 expression was mediated by the cAMP/cAMP response element-binding protein (CREB) pathway. These results demonstrate that TRB3 is a critical molecule in the homocysteine-mediated cell-cycle arrest in endothelial cells.

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.

Vitamin B12 protects against superoxide-induced cell injury in human aortic endothelial cells

Superoxide (O(2)(•-)) is implicated in inflammatory states including arteriosclerosis and ischemia-reperfusion injury. Cobalamin (Cbl) supplementation is beneficial for treating many inflammatory diseases and also provides protection in oxidative-stress-associated pathologies. Reduced Cbl reacts with O(2)(•-) at rates approaching that of superoxide dismutase (SOD), suggesting a plausible mechanism for its anti-inflammatory properties. Elevated homocysteine (Hcy) is an independent risk factor for cardiovascular disease and endothelial dysfunction. Hcy increases O(2)(•-) levels in human aortic endothelial cells (HAEC). Here, we explore the protective effects of Cbl in HAEC exposed to various O(2)(•-) sources, including increased Hcy levels. Hcy increased O(2)(•-) levels (1.6-fold) in HAEC, concomitant with a 20% reduction in cell viability and a 1.5-fold increase in apoptotic death. Pretreatment of HAEC with physiologically relevant concentrations of cyanocobalamin (CNCbl) (10-50nM) prevented Hcy-induced increases in O(2)(•-) and cell death. CNCbl inhibited both Hcy and rotenone-induced mitochondrial O(2)(•-) production. Similarly, HAEC challenged with paraquat showed a 1.5-fold increase in O(2)(•-) levels and a 30% decrease in cell viability, both of which were prevented with CNCbl pretreatment. CNCbl also attenuated elevated O(2)(•-) levels after exposure of cells to a Cu/Zn-SOD inhibitor. Our data suggest that Cbl acts as an efficient intracellular O(2)(•-) scavenger.

Inhibition of hepatic glycogen synthesis by hyperhomocysteinemia mediated by TRB3

Recently, epidemiological and experimental studies have linked hyperhomocysteinemia (HHcy) to insulin resistance. However, whether HHcy impairs glucose homeostasis by affecting glycogenesis in the liver is not clear. In the present study, we investigated the effect of HHcy on hepatic glycogen synthesis. Hyperhomocysteinemia was induced in mice by drinking water containing two percent methionine. Mice with HHcy showed an increase in the phosphorylation of glycogen synthase and a significant decrease in hepatic glycogen content and the rate of glycogen synthesis. The expression of TRB3 (tribbles-related protein 3) was up-regulated in the liver of mice with HHcy, concomitantly with the dephosphorylation of glycogen synthase kinase-3β and Akt. The knockdown of TRB3 by short hairpin RNA suppressed the dephosphorylation of these two kinases. Homocysteine induced an increase in the levels of hepatic cAMP and cAMP response element-binding protein phosphorylation, which in turn up-regulated the expression of peroxisome proliferator-activated receptor (PPAR)-γ coactivator-1α and TRB3. The inhibition of PPAR-α by its inhibitor, MK886, or knockdown of PPAR-α by small interfering RNA significantly inhibited the expression of TRB3 induced by homocysteine. The current study demonstrates that HHcy impairs hepatic glycogen synthesis by inducing the expression of TRB3. These results provide a novel explanation for the development and progression of insulin resistance in HHcy.