Endothelial dysfunction as a cellular mechanism for vascular failure

The regulation of vascular tone, vascular permeability, and thromboresistance is essential to maintain blood circulation and therefore tissue environments under physiological conditions. Atherogenic stimuli, including diabetes, dyslipidemia, and oxidative stress, induce vascular dysfunction, leading to atherosclerosis, which is a key pathological basis for cardiovascular diseases such as ischemic heart disease and stroke. We have proposed a novel concept termed "vascular failure" to comprehensively recognize the vascular dysfunction that contributes to the development of cardiovascular diseases. Vascular endothelial cells form the vascular endothelium as a monolayer that covers the vascular lumen and serves as an interface between circulating blood and immune cells. Endothelial cells regulate vascular function in collaboration with smooth muscle cells. Endothelial dysfunction under pathophysiological conditions contributes to the development of vascular dysfunction. Here, we address the barrier function and microtubule function of endothelial cells. Endothelial barrier function, mediated by cell-to-cell junctions between endothelial cells, is regulated by small GTPases and kinases. Microtubule function, regulated by the acetylation of tubulin, a component of the microtubules, is a target of atherogenic stimuli. The elucidation of the molecular mechanisms of endothelial dysfunction as a cellular mechanism for vascular failure could provide novel therapeutic targets of cardiovascular diseases.     

Pathological cardiac remodeling seen by the eyes of proteomics

Cardiac remodeling involves cellular and structural changes that occur as consequence of multifactorial events to maintain the homeostasis. The progression of pathological cardiac remodeling involves a transition from adaptive to maladaptive changes that eventually leads to impairment of ventricular function and heart failure. In this scenario, proteins are key elements that orchestrate molecular events as increased expression of fetal genes, neurohormonal and second messengers' activation, contractile dysfunction, rearrangement of the extracellular matrix and alterations in heart geometry. Mass spectrometry based-proteomics has emerged as a sound method to study protein dysregulation and identification of cardiac diseases biomarkers in plasma. In this review, we summarize the main findings related to large-scale proteome modulation of cardiac cells and extracellular matrix occurred during pathological cardiac remodeling. We describe the recent proteomic progresses in the selection of protein targets and introduce the renin-angiotensin system as an interesting target for the treatment of pathological cardiac remodeling.     

Cellular senescence in normal and adverse pregnancy

Cellular senescence (CS) is defined as a state of terminal proliferation arrest accompanied by morphological alterations, pro-inflammatory phenotype, and metabolic changes. In recent years, the implications of senescence in numerous physiological and pathological conditions such as development, tissue repair, aging, or cancer have been evident. Some inductors of senescence are tissue repair pathways, telomere shortening, DNA damage, degenerative disorders, and wound healing. Lately, it has been demonstrated that CS plays a decisive role in the development and progression of healthy pregnancy and labor. Premature maternal-fetal tissues senescence (placenta, choriamniotic membranes, and endothelium) is implicated in many adverse pregnancy outcomes, including fetal growth restriction, preeclampsia, preterm birth, and intrauterine fetal death. Here we discuss cellular senescence and its association with normal pregnancy development and adverse pregnancy outcomes. Current evidence allows us to establish the relevance of CS in processes associated with the appropriate development of placentation, the progression of pregnancy, and the onset of labor; likewise, it allows us to understand the undeniable participation of CS deregulation in pathological processes associated with pregnancy.     

Proteomic analysis and functional characterization of mouse brain mitochondria during aging reveal alterations in energy metabolism

Mitochondria are the main cellular source of reactive oxygen species and are recognized as key players in several age‐associated disorders and neurodegeneration. Their dysfunction has also been linked to cellular aging. Additionally, mechanisms leading to the preservation of mitochondrial function promote longevity. In this study we investigated the proteomic and functional alterations in brain mitochondria isolated from mature (5 months old), old (12 months old), and aged (24 months old) mice as determinants of normal “healthy” aging. Here the global changes concomitant with aging in the mitochondrial proteome of mouse brain analyzed by quantitative mass‐spectrometry based super‐SILAC identified differentially expressed proteins involved in several metabolic pathways including glycolysis, the tricarboxylic acid cycle, and oxidative phosphorylation. Despite these changes, the bioenergetic function of these mitochondria was preserved. Overall, this data indicates that proteomic changes during aging may compensate for functional defects aiding in preservation of mitochondrial function. The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium with the data set identifier PXD001370 ( http://proteomecentral.proteomexchange.org/dataset/PXD001370 ).     

Dual role of lipoproteins in endothelial cell dysfunction in atherosclerosis

The endothelium is a key constituent of the vascular wall, being actively involved in maintaining the structural integrity and proper functioning of blood vessels. Hyperlipidemia, diabetes, hypertension, smoking and aging are important risk factors for the dysfunction of endothelial cells (EC). Circulating lipoproteins (Lp) synthesized and secreted from the intestine or liver have an important role in supplying peripheral tissues with fatty acids from triglyceride rich lipoproteins (TGRLp) for energy production or storage, and cholesterol from low density lipoproteins (LDL) or high density lipoproteins (HDL) for the synthesis of cellular membranes and steroid hormones. Under pathological conditions, Lp may suffer alterations in concentration and composition and become aggressors for EC. Modified LDL, remnant Lp, TGRLp lipolysis products, dysfunctional HDL are involved in the changes induced in EC morphology (reduced glycocalyx, overdeveloped endoplasmic reticulum, Golgi apparatus and basement membrane), loose intercellular junctions, increased oxidative and inflammatory stress, nitric oxide/redox imbalance, excess Lp transport and storage, as well as loss of anti-thrombotic properties, all of these being characteristics of endothelial dysfunction. Normal HDL are able to counteract the harmful effects of atherogenic Lp in EC but under persistent pathological conditions they lose the protective properties and become pro-atherogenic. This review summarises recent advances in understanding the role of Lp in the induction of endothelial dysfunction and the initiation and progression of atherosclerotic lesions. Its main focus is the antagonistic role of atherogenic Lp (LDL, VLDL, dysfunctional HDL) versus anti-atherogenic Lp (HDL), also pointing out the potential targets for arresting or reversing this process.     

Reciprocal relationships between abnormal metabolic parameters and endothelial dysfunction

PURPOSE OF REVIEW: Endothelial dysfunction plays a crucial role in the pathogenesis of atherosclerosis and related cardiovascular diseases. Glucotoxicity, lipotoxicity, and inflammation all independently contribute to development of both endothelial dysfunction and insulin resistance. We review pathophysiological mechanisms underlying reciprocal relationships between endothelial dysfunction and insulin resistance and recent insights from therapeutic interventions to improve both metabolic and vascular function. RECENT FINDINGS: Shared causal factors such as glucotoxicity, lipotoxicity, and inflammation interact at multiple levels creating reciprocal relationships between insulin resistance and endothelial dysfunction that help to explain frequent clustering of metabolic and cardiovascular disorders. Metabolic abnormalities implicated in the development of insulin resistance, including hyperglycemia, elevated levels of free fatty acids, accumulation of advanced glycation end products, dyslipidemias, and decreased levels of adiponectin, also contribute importantly to endothelial dysfunction. Diet, exercise, cardiovascular drugs, and insulin sensitizers simultaneously improve endothelium-dependent vascular function, reduce inflammation, and improve insulin sensitivity by both distinct and interrelated mechanisms. SUMMARY: Pathophysiological mechanisms underlying reciprocal relationships between endothelial dysfunction and insulin resistance contribute to clustering of metabolic and cardiovascular diseases represented by the metabolic syndrome. Therapeutic interventions that target endothelial dysfunction or insulin resistance often simultaneously improve both metabolic and vascular function.     

Missing links in preeclampsia cell model systems of endothelial dysfunction

Preeclampsia, one of the main hypertensive disorders of pregnancy, is associated with circulating factors released by the ischemic placenta accompanied by systemic endothelial dysfunction. The etiology of preeclampsia remains poorly understood although it is associated with high maternal and fetal mortality and increased cardiovascular disease risk. Most cell model systems used for studying endothelial dysfunction have not taken into account hemodynamic physical factors such as shear-stress forces which may prevent extrapolation of cell data to in vivo settings. We overview the role of hemodynamic forces in modulating endothelial cell function and discuss strategies to reproduce this biological characteristic in vitro to improve our understanding of endothelial dysfunction associated with preeclampsia.     

Disease-modifying effects of metabolic perturbations in ALS/FTLD

Amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD) are two fatal neurodegenerative disorders with considerable clinical, pathological and genetic overlap. Both disorders are characterized by the accumulation of pathological protein aggregates that contain a number of proteins, most notably TAR DNA binding protein 43?kDa (TDP-43). Surprisingly, recent clinical studies suggest that dyslipidemia, high body mass index, and type 2 diabetes mellitus are associated with better clinical outcomes in ALS. Moreover, ALS and FTLD patients have a significantly lower incidence of cardiovascular disease, supporting the idea that an unfavorable metabolic profile may be beneficial in ALS and FTLD. The two most widely studied ALS/FTLD models, super-oxide dismutase 1 (SOD1) and TAR DNA binding protein of 43 kDA (TDP-43), reveal metabolic dysfunction and a positive effect of metabolic strategies on disease onset and/or progression. In addition, molecular studies reveal a role for ALS/FTLD-associated proteins in the regulation of cellular and whole-body metabolism. Here, we systematically evaluate these observations and discuss how changes in cellular glucose/lipid metabolism may result in abnormal protein aggregations in ALS and FTLD, which may have important implications for new treatment strategies for ALS/FTLD and possibly other neurodegenerative conditions.     

Development of a novel bioavailable inhibitor of the calmodulin-regulated protein kinase MLCK: a lead compound that attenuates vascular leak

Tissue barriers involving epithelial and endothelial cell layers are critical to homeostasis, regulating passage of water, macromolecules, cells and certain classes of small molecules via two distinct cellular mechanisms, transcellular or paracellular. Endothelial or epithelial barrier dysfunction is a key component of pathophysiology in diverse diseases and injuries that have a broad impact on survival and quality of life. However, effective and safe small molecule therapeutics for these disorders are lacking. Success in development would therefore fill a major unmet medical need across multiple disease areas. Myosin light chain kinase (MLCK), a highly specialized calcium/calmodulin (CaM) regulated protein kinase, modulates barrier function through its regulation of intracellular contractile processes. MLCK levels and activity are increased in various animal models of disease and in human clinical disease samples. Our prior work with a genetic knockout (KO) mouse strain for the long form of MLCK, MLCK210, has identified MLCK as a drug discovery target for endothelial and epithelial barrier dysfunction. We describe here the development of a selective, bioavailable, stable inhibitor of MLCK that attenuates barrier dysfunction in mice comparable to that seen with the MLCK KO mice. The inhibitor compound 6 is stable in human microsomal metabolic stability assays and can be synthesized in a high-yielding and facile synthetic process. These results provide a foundation for and demonstrate the feasibility of future medicinal chemistry refinement studies directed toward the development of novel therapies for disorders involving barrier dysfunction.     

Role of reactive oxygen and nitrogen species in the vascular responses to inflammation

Inflammation is a complex and potentially life-threatening condition that involves the participation of a variety of chemical mediators, signaling pathways, and cell types. The microcirculation, which is critical for the initiation and perpetuation of an inflammatory response, exhibits several characteristic functional and structural changes in response to inflammation. These include vasomotor dysfunction (impaired vessel dilation and constriction), the adhesion and transendothelial migration of leukocytes, endothelial barrier dysfunction (increased vascular permeability), blood vessel proliferation (angiogenesis), and enhanced thrombus formation. These diverse responses of the microvasculature largely reflect the endothelial cell dysfunction that accompanies inflammation and the central role of these cells in modulating processes as varied as blood flow regulation, angiogenesis, and thrombogenesis. The importance of endothelial cells in inflammation-induced vascular dysfunction is also predicated on the ability of these cells to produce and respond to reactive oxygen and nitrogen species. Inflammation seems to upset the balance between nitric oxide and superoxide within (and surrounding) endothelial cells, which is necessary for normal vessel function. This review is focused on defining the molecular targets in the vessel wall that interact with reactive oxygen species and nitric oxide to produce the characteristic functional and structural changes that occur in response to inflammation. This analysis of the literature is consistent with the view that reactive oxygen and nitrogen species contribute significantly to the diverse vascular responses in inflammation and supports efforts that are directed at targeting these highly reactive species to maintain normal vascular health in pathological conditions that are associated with acute or chronic inflammation.     

A potential strategy for treating atherosclerosis: improving endothelial function via AMP-activated protein kinase

Endothelial dysfunction is caused by many factors, such as dyslipidemia, endoplasmic reticulum(ER) stress, and inflammation.It has been demonstrated that endothelial dysfunction is the initial process of atherosclerosis. AMP-activated protein kinase(AMPK) is an important metabolic switch that plays a crucial role in lipid metabolism and inflammation. However, recent evidence indicates that AMPK could be a target for atherosclerosis by improving endothelial function. For instance, activation of AMPK inhibits the production of reactive oxygen species induced by mitochondrial dysfunction, ER stress, and NADPH oxidase. Moreover, activation of AMPK inhibits the production of pro-inflammatory factors induced by dyslipidemia and hyperglycemia and restrains production of perivascular adipose tissue-released adipokines. AMPK activation prevents endothelial dysfunction by increasing the bioavailability of nitric oxide. Therefore, we focused on the primary risk factors involved in endothelial dysfunction, and summarize the features of AMPK in the protection of endothelial function, by providing signaling pathways thought to be important in the pathological progress of risk factors.     

Relevance of disease- and organ-specific endothelial cells for in vitro research

The endothelium is a dynamic, heterogeneous, disseminated organ that possesses vital secretory, synthetic, metabolic and immunological functions. Endothelial dysfunction has been implicated as a key factor in the development of organ-specific vascular diseases. This minireview gives a brief overview on EC (endothelial cell) biomarkers in arterial and venous endothelium and critically discusses the different sources of ECs that are most frequently applied in in vitro assays and research. The relevance of organ- and disease-specific endothelial cell cultures for studying cellular responses as a basis for improving therapeutic interventions is highlighted with particular emphasis on endothelial dysfunction in transplant-associated coronary artery disease, in atherosclerotic lesions and in response to diabetes mellitus.     

Endothelial cell telomere dysfunction induces senescence and results in vascular and metabolic impairments

In advanced age, increases in oxidative stress and inflammation impair endothelial function, which contributes to the development of cardiovascular disease (CVD). One plausible source of this oxidative stress and inflammation is an increase in the abundance of senescent endothelial cells. Cellular senescence is a cell cycle arrest that occurs in response to various damaging stimuli. In the present study, we tested the hypothesis that advanced age results in endothelial cell telomere dysfunction that induces senescence. In both human and mouse endothelial cells, advanced age resulted in an increased abundance of dysfunctional telomeres, characterized by activation of DNA damage signaling at telomeric DNA. To test whether this results in senescence, we selectively reduced the telomere shelterin protein telomere repeat binding factor 2 (Trf2) from endothelial cells of young mice. Trf2 reduction increased endothelial cell telomere dysfunction and resulted in cellular senescence. Furthermore, induction of endothelial cell telomere dysfunction increased inflammatory signaling and oxidative stress, resulting in impairments in endothelial function. Finally, we demonstrate that endothelial cell telomere dysfunction-induced senescence impairs glucose tolerance. This likely occurs through increases in inflammatory signaling in the liver and adipose tissue, as well as reductions in microvascular density and vasodilation to metabolic stimuli. Cumulatively, the findings of the present study identify age-related telomere dysfunction as a mechanism that leads to endothelial cell senescence. Furthermore, these data provide compelling evidence that senescent endothelial cells contribute to age-related increases in oxidative stress and inflammation that impair arterial and metabolic function.     

Bioenergy sensing in the brain

Bioenergy homeostasis constitutes one of the most crucial foundations upon which other cellular and organismal processes may be executed. AMP-activated protein kinase (AMPK) has been shown to be the key player in the regulation of energy metabolism, and thus is becoming the focus of research on obesity, diabetes and other metabolic disorders. However, its role in the brain, the most energy-consuming organ in our body, has only recently been studied and appreciated. Widely expressed in the brain, AMPK activity is tightly coupled to the energy status at both neuronal and whole-body levels. Importantly, AMPK signaling is intimately implicated in multiple aspects of brain development and function including neuronal proliferation, migration, morphogenesis and synaptic communication, as well as in pathological conditions such as neuronal cell death, energy depletion and neurodegenerative disorders.     

Endothelial cell-specific reduction in mTOR ameliorates age-related arterial and metabolic dysfunction

Systemic inhibition of the mammalian target of rapamycin (mTOR) delays aging and many age-related conditions including arterial and metabolic dysfunction. However, the mechanisms and tissues involved in these beneficial effects remain largely unknown. Here, we demonstrate that activation of S6K, a downstream target of mTOR, is increased in arteries with advancing age, and that this occurs preferentially in the endothelium compared with the vascular smooth muscle. Induced endothelial cell-specific deletion of mTOR reduced protein expression by 60–70%. Although this did not significantly alter arterial and metabolic function in young mice, endothelial mTOR reduction reversed arterial stiffening and improved endothelium-dependent dilation (EDD) in old mice, indicating an improvement in age-related arterial dysfunction. Improvement in arterial function in old mice was concomitant with reductions in arterial cellular senescence, inflammation, and oxidative stress. The reduction in endothelial mTOR also improved glucose tolerance in old mice, and this was associated with attenuated hepatic gluconeogenesis and improved lipid tolerance, but was independent of alterations in peripheral insulin sensitivity, pancreatic beta cell function, or fasted plasma lipids in old mice. Lastly, we found that endothelial mTOR reduction suppressed gene expression of senescence and inflammatory markers in endothelial-rich (i.e., lung) and metabolically active organs (i.e., liver and adipose tissue), which may have contributed to the improvement in metabolic function in old mice. This is the first evidence demonstrating that reducing endothelial mTOR in old age improves arterial and metabolic function. These findings have implications for future drug development.     

The hypothalamus for whole-body physiology: from metabolism to aging

Obesity and aging are two important epidemic factors for metabolic syndrome and many other health issues, which contribute to devastating diseases such as cardiovascular diseases, stroke and cancers. The brain plays a central role in controlling metabolic physiology in that it integrates information from other metabolic organs, sends regulatory projections and orchestrates the whole-body function. Emerging studies suggest that brain dysfunction in sensing various internal cues or processing external cues may have profound effects on metabolic and other physiological functions. This review highlights brain dysfunction linked to genetic mutations, sex, brain inflammation, microbiota, stress as causes for whole-body pathophysiology, arguing brain dysfunction as a root cause for the epidemic of aging and obesity-related disorders. We also speculate key issues that need to be addressed on how to reveal relevant brain dysfunction that underlines the development of these disorders and diseases in order to develop new treatment strategies against these health problems.     

Brain Iron Toxicity: Differential Responses of Astrocytes,Neurons, and Endothelial Cells

Iron accumulation or iron overload in brain is commonly associated with neurodegenerative disorders such as Parkinson’s and Alzheimer’s diseases, and also plays a role in cellular damage following hemorrhagic stroke and traumatic brain injury. Despite the brain’s highly regulated system for iron utilization and metabolism, these disorders often present following disruptions within iron metabolic pathways. Such dysregulation allows saturation of proteins involved in iron transport and storage, and may cause an increase in free ferrous iron within brain leading to oxidative damage. Not only do astrocytes, neurons, and brain endothelial cells serve unique purposes within the brain, but their individual cell types are equipped with distinct protective mechanisms against iron-induced injury. This review evaluates iron metabolism within the brain under homeostatic and pathological conditions and focuses on the mechanism(s) of brain cellular iron toxicity and differential responses of astrocytes, neurons, and brain vascular endothelial cells to excessive free iron. Special issue dedicated to Dr. Moussa Youdim. An erratum to this article can be found at     

The molecular and physiological aspects of endothelial dysfunction. The role of endogenous chemical regulators

Monolayer of endothelial cells that cover the vascular channels are the major regulator of haemo-vascular homeostasis. Endothelium secretes the chemical factors that affect contraction of the muscular vascular cells, permeability of tissue, blood fluidity, intercellular interaction in vascular structure of the channel as a whole and of different regions. In its turn, the secretory function of endothelial cells is stimulated by mechanical or hormonal factors under a feedback system principle. Special features of morphology and biochemistry of vascular endothelium cells determine the micro-organs heterogeneity of the vascular channel depending on phenotine, gene expression, size and growth of endothelium cells. On this basis the processing biochemical disintegration develop either selectively or in a generalised form, and results in development of endothelial dysfunctions, as the original factor of many cardiovascular pathologies. Endothelial disfunction is a systemic pathology related to pathology of microstructure and hormonal function of endothelial cells representing a major tissue system of the vascular channel. Formation of hypertension states, ischemic cardiopathology, haemostasis changes, metabolic pathology (hypercholesterinemia and hyperglycemia) that lead to pathogenesis of arteriosclerosis, diabetes (etc.) as result of modified function of endothelium, and above all, pathology of production by dilator and constrictor substances, and the factors regulating interaction of endothelium with blood cells. The basic mechanism for development of the endothelial dysfunction is related to modification of synthesis and releasing of nitrogen oxide, a key regulator of the endothelial-vasal system. Physiologically active peptides (angiotensin II, endothelin-I, bradykinin, adrenomedullin and ANP) contribute to development of the processes related to the endothelium function and dysfunction. An important role is played, apparently, by growth peptide factors and specific proteins of cellular adhesion and membrane interaction--to integrins and selectins.