Endothelial endoplasmic reticulum and nitrative stress in endothelial dysfunction in the atherogenic rabbit model

DNMT3B activates FGFR3-mediated endoplasmic reticulum stress by regulating PTPN2 promoter methylation to promote the development of atherosclerosis

Endoplasmic reticulum (ER) stress is closely associated with atherosclerosis (AS). Nevertheless, the regulatory mechanism of ER stress in endothelial cells during AS progression is unclear. Here, the role and regulatory mechanism of DNA (cytosine-5-)- methyltransferase 3 beta (DNMT3B) in ER stress during AS progression were investigated. ApoE^-/- mice were fed with high fat diet to construct AS model in vivo. HE and Masson staining were performed to analyze histopathological changes and collagen deposition. HUVECs stimulated by ox-LDL were used as AS cellular model. Cell apoptosis was examined using flow cytometry. DCFH-DA staining was performed to examine ROS level. The levels of pro-inflammatory cytokines were assessed using ELISA. In addition, MSP was employed to detect PTPN2 promoter methylation level. Our results revealed that DNMT3B and FGFR3 were significantly upregulated in AS patient tissues, whereas PTPN2 was downregulated. PTPN2 overexpression attenuate ox-LDL-induced ER stress, inflammation and apoptosis in HUVECs and ameliorated AS symptoms in vivo. PTPN2 could suppress FGFR3 expression in ox-LDL-treated HUVECs, and FGFR3 knockdown inhibited ER stress to attenuate ox-LDL-induced endothelial cell apoptosis. DNMT3B could negatively regulate PTPN2 expression and positively FGFR2 expression in ox-LDL-treated HUVECs; DNMT3B activated FGFR2 expression by increasing PTPN2 promoter methylation level. DNMT3B downregulation repressed ox-LDL-induced ER stress, inflammation and cell apoptosis in endothelial cells, which was reversed by PTPN2 silencing. DNMT3B activated FGFR3-mediated ER stress by increasing PTPN2 promoter methylation level and suppressed its expression, thereby boosting ER stress to facilitate AS progression.

Protein tyrosine nitration in atherosclerotic endothelial dysfunction

Accumulation of reactive oxygen species (ROS) can induce both protein tyrosine nitration and endothelial dysfunction in atherosclerosis. Endothelial dysfunction refers to impaired endothelium-dependent vasorelaxation that can be triggered by an imbalance in nitric oxide (NO) production and consumption. ROS reacts with NO to generate peroxynitrite, decreasing NO bioavailability. Peroxynitrite also promotes protein tyrosine nitration in vivo that can affect protein structure and function and further damage endothelial function. In this review, we discuss the process of protein tyrosine nitration, increased expression of nitrated proteins in cardiovascular disease and their association with endothelial dysfunction, and the interference of tyrosine nitration with antioxidants and the protective role in endothelial dysfunction. These may lead us to the conception that protein tyrosine nitration may be one of the causes of endothelial dysfunction, and help us gain information about the mechanism of endothelial dysfunction underlying atherosclerosis.

Is Mental Stress the Primary Cause of Glaucoma?

The prognosis of going blind is very stressful for patients diagnosed with "glaucoma". Worries and fear of losing independence is a constant mental burden, with secondary risks of depression and social isolation. But stress is not only a result of glaucoma but also a possible cause (risk factor). This should not be surprising, given that chronic stress can trigger "psychosomatic" organ dysfunctions anywhere in the body. Why should the organ "eye" be an exception? Indeed, glaucoma patients often suspect that severe emotional stress caused their visual field loss or "foggy vision". The hypothesis that stress is a possible cause of glaucoma is supported by different observations: (i) acute and chronic stress increases intraocular pressure and (ii) long-term stress can lead to vascular dysregulation of the microcirculation in the eye and brain ("Flammer's syndrome"), leading to partial hypoxia and hypoglycaemia (hypo-metabolism). Even if nerve cells do not die, they may then become inactive ("silent" neurons). (iii) Degenerative changes have been reported in the brain of glaucoma patients, affecting not only anterograde or transsynaptic areas of the central visual pathway, but degeneration is also found (iv) in brain areas involved in emotional appraisal and the physiological regulation of stress hormones. There are also psychological hints indicating that stress is a cause of glaucoma: (v) Glaucoma patients with Flammer's syndrome show typical personality traits that are associated with low stress resilience: they often have cold hands or feet, are ambitious (professionally successful), perfectionistic, obsessive, brooding and worrying a lot. (vi) If stress hormone levels and inflammation parameters are reduced in glaucoma patients by relaxation with meditation, this correlates with normalisation of intraocular pressure, and yet another clue is that (vii) visual field improvements after non-invasive current stimulation therapy, that are known to improve circulation and neuronal synchronisation, are much most effective in patients with stress resilient personalities. An appreciation of stress as a "cause" of glaucoma suggests that in addition to standard therapy (i) stress reduction through relaxation techniques should be recommended (e.g. meditation), and (ii) self-medication compliance should not be induced by kindling anxiety and worries with negative communication ("You will go blind!"), but communication should be positive ("The prognosis is optimistic").

Role of Endoplasmic Reticulum Stress in Atherosclerosis and Its Potential as a Therapeutic Target

Endoplasmic reticulum (ER) stress is closely associated with atherosclerosis and related cardiovascular diseases (CVDs). It occurs due to various pathological factors that interfere with ER homeostasis, resulting in the accumulation of unfolded or misfolded proteins in the ER lumen, thereby causing ER dysfunction. Here, we discuss the role of ER stress in different types of cells in atherosclerotic lesions. This discussion includes the activation of apoptotic and inflammatory pathways induced by prolonged ER stress, especially in advanced lesional macrophages and endothelial cells (ECs), as well as common atherosclerosis-related ER stressors in different lesional cells, which all contribute to the clinical progression of atherosclerosis. In view of the important role of ER stress and the unfolded protein response (UPR) signaling pathways in atherosclerosis and CVDs, targeting these processes to reduce ER stress may be a novel therapeutic strategy.

Rosuvastatin protects against endothelial cell apoptosis in vitro and alleviates atherosclerosis in ApoE-/- mice by suppressing endoplasmic reticulum stress

The development of abnormal lipid-induced atherosclerosis is initiated with endothelial cell apoptosis. Vascular endothelial cells possess highly developed endoplasmic reticulum (ER), which is involved in lipid metabolism, indicating that ER stress may contribute chiefly to the induction of endothelial cell apoptosis. Based on its ability to reduce cholesterol levels, rosuvastatin may play an endothelial and vascular protective role by regulating ER stress. In the present study, the involvement of the inhibition of the ER stress-induced endothelial injury was investigated in combination with the lipid lowering effects of rosuvastatin. This compound can be used to inhibit cholesterol synthesis in atherosclerosis. Rosuvastatin decreased the apoptotic rates of human umbilical vascular endothelial cells (HUVECs) that had been stimulated with ox-low density lipoprotein (LDL) in vitro and repressed the mRNA levels of CHOP, sXBP1 and caspase-12, and decreased caspase-12 activity, as well as the content of glucose-regulated protein 78 (GRP78), phosphorylated (p)-protein kinase RNA-like ER kinase (PERK), p-inositol-requiring protein 1α (IRE1α) and p-eIF2α proteins. In addition, ApoE^-/- mice were fed with atherogenic chow for 8 weeks for atherosclerosis induction and rosuvastatin was provided by intragastric administration for an additional 4 weeks. Subsequently, the atherosclerotic plaque formation in the aorta was evaluated by Oil Red O and hematoxylin and eosin staining, and the serum LDL, high-density lipoprotein, total cholesterol (TC) and triacylglycerol (TG) levels were measured. In addition, the induction of apoptosis of endothelial cells and the expression levels of GRP78, p-PERK, p-IRE1α and p-eIF2α were assessed in the aorta. Rosuvastatin repressed atherosclerotic plaque formation and endothelial apoptosis in the aorta and decreased LDL and TG levels in the serum, as determined by in vivo results. Furthermore, it downregulated the expression levels of protein chaperone GRP78, p-PERK, p-IRE1α and p-eIF2α in the aortic intima. The data indicated that rosuvastatin could protect HUVECs from ER stress-induced apoptosis triggered by oxidized LDL. It could also inhibit atherosclerosis formation in ApoE^-/- mice aorta by regulating the PERK/eIF2α/C/EBPα-homologous protein and IRE1α/sXBP1 signaling pathways. Taken collectively, the present study demonstrated the preventive and therapeutic effects of rosuvastatin in protecting from the development of endothelial cell dysfunction diseases.

Mental stress as consequence and cause of vision loss: the dawn of psychosomatic ophthalmology for preventive and personalized medicine

The loss of vision after damage to the retina, optic nerve, or brain has often grave consequences in everyday life such as problems with recognizing faces, reading, or mobility. Because vision loss is considered to be irreversible and often progressive, patients experience continuous mental stress due to worries, anxiety, or fear with secondary consequences such as depression and social isolation. While prolonged mental stress is clearly a consequence of vision loss, it may also aggravate the situation. In fact, continuous stress and elevated cortisol levels negatively impact the eye and brain due to autonomous nervous system (sympathetic) imbalance and vascular dysregulation; hence stress may also be one of the major causes of visual system diseases such as glaucoma and optic neuropathy. Although stress is a known risk factor, its causal role in the development or progression of certain visual system disorders is not widely appreciated. This review of the literature discusses the relationship of stress and ophthalmological diseases. We conclude that stress is both consequence and cause of vision loss. This creates a vicious cycle of a downward spiral, in which initial vision loss creates stress which further accelerates vision loss, creating even more stress and so forth. This new psychosomatic perspective has several implications for clinical practice. Firstly, stress reduction and relaxation techniques (e.g., meditation, autogenic training, stress management training, and psychotherapy to learn to cope) should be recommended not only as complementary to traditional treatments of vision loss but possibly as preventive means to reduce progression of vision loss. Secondly, doctors should try their best to inculcate positivity and optimism in their patients while giving them the information the patients are entitled to, especially regarding the important value of stress reduction. In this way, the vicious cycle could be interrupted. More clinical studies are now needed to confirm the causal role of stress in different low vision diseases to evaluate the efficacy of different anti-stress therapies for preventing progression and improving vision recovery and restoration in randomized trials as a foundation of psychosomatic ophthalmology.

GPR55 agonist lysophosphatidylinositol and lysophosphatidylcholine inhibit endothelial cell hyperpolarization via GPR-independent suppression of Na+-Ca2+ exchanger and endoplasmic reticulum Ca2+ refilling

Lysophosphatidylinositol (LPI) and lysophosphatidylcholine (LPC) are lipid signaling molecules that induce endothelium-dependent vasodilation. In addition, LPC suppresses acetylcholine (Ach)-induced responses. We aimed to determine the influence of LPC and LPI on hyperpolarizing responses in vitro and in situ endothelial cells (EC) and identify the underlying mechanisms. Using patch-clamp method, we show that LPI and LPC inhibit EC hyperpolarization to histamine and suppress Na⁺/Ca²⁺ exchanged (NCX) currents in a concentration-dependent manner. The inhibition is non-mode-specific and unaffected by intracellular GDPβS infusion and tempol, a superoxide dismutase mimetic. In excised mouse aorta, LPI strongly inhibits the sustained and the peak endothelial hyperpolarization induced by Ach, but not by SKA-31, an opener of Ca²⁺-dependent K⁺ channels of intermediate and small conductance. The hyperpolarizing responses to consecutive histamine applications are strongly reduced by NCX inhibition. In a Ca²⁺-re-addition protocol, bepridil, a NCX inhibitor, and KB-R7943, a blocker of reversed NCX, inhibit the hyperpolarizing responses to Ca²⁺-re-addition following Ca²⁺ stores depletion. These finding indicate that LPC and LPI inhibit endothelial hyperpolarization to Ach and histamine independently of G-protein coupled receptors and superoxide anions. Reversed NCX is critical for ER Ca²⁺ refilling in EC. The inhibition of NCX by LPI and LPC underlies diminished endothelium-dependent responses and endothelial dysfunction accompanied by increased levels of these lipids in the blood.

Plasma and Aorta Biochemistry and MMPs Activities in Female Rabbit Fed Methionine Enriched Diet and Their Offspring

This study investigated whether a high Met diet influences biochemical parameters, MMPs activities in plasma, and biochemical and histological remodeling in aorta, in both pregnant female rabbits and their offspring. Four female rabbit groups are constituted (each n = 8), nonpregnant control (NPC), pregnant control (PC) that received normal commercial chow, nonpregnant Met (NPMet), and pregnant Met (PMet) that received the same diet supplemented with 0,35% L-methionine (w/w) for 3 months (500 mg/d). All pregnant females realize 3 successive pregnancies. Plasma results showed that Met excess increased Hcy, raised CRP in NPMet and decreased it in PMet, enhanced significantly proMMP-2 and proMMP-9 activities in NPMet, and reduced them in PMet. Aorta showed a rise in collagen level, essentially in PMet, a reduction of elastin content in both PMet and NPMet, and a significant decrease in lipid content in PMet, with histological changes that are more pronounced in NPMet than PMet. Met excess enhanced proMMP-9 activities in NPMet while it decreased them in PMet. PMet newborn presented increase in uremia and CRP and significant rise of active MMP-2 and MMP-9 forms. In aorta, media and adventitia thickness increased, total lipids content decreased, proMMP-9 activity decreased, and proMMP-2 activity increased.

Insulin Is a Key Modulator of Fetoplacental Endothelium Metabolic Disturbances in Gestational Diabetes Mellitus

Gestational diabetes mellitus (GDM) is a disease of the mother that associates with altered fetoplacental vascular function. GDM-associated maternal hyperglycaemia result in fetal hyperglycaemia, a condition that leads to fetal hyperinsulinemia and altered L-arginine transport and synthesis of nitric oxide, i.e., endothelial dysfunction. These alterations in the fetoplacental endothelial function are present in women with GDM that were under diet or insulin therapy. Since these women and their newborn show normal glycaemia at term, other factors or conditions could be altered and/or not resolved by restoring normal level of circulating D-glucose. GDM associates with metabolic disturbances, such as abnormal handling of the locally released vasodilator adenosine, and biosynthesis and metabolism of cholesterol lipoproteins, or metabolic diseases resulting in endoplasmic reticulum stress and altered angiogenesis. Insulin acts as a potent modulator of all these phenomena under normal conditions as reported in primary cultures of cells obtained from the human placenta; however, GDM and the role of insulin regarding these alterations in this disease are poorly understood. This review focuses on the potential link between insulin and endoplasmic reticulum stress, hypercholesterolemia, and angiogenesis in GDM in the human fetoplacental vasculature. Based in reports in primary culture placental endothelium we propose that insulin is a factor restoring endothelial function in GDM by reversing ERS, hypercholesterolaemia and angiogenesis to a physiological state involving insulin activation of insulin receptor isoforms and adenosine receptors and metabolism in the human placenta from GDM pregnancies.