Tumor necrosis factor reduces lifespan of human endothelial cells in vitro

Featured Article: Deterioration of visual function mediated by senescence-associated endoplasmic reticulum stress in inflammatory tie2-TNF mice

Stress-associated premature senescence plays a major role in retinal diseases. In this study, we investigated the relationship between endothelial dysfunction, endoplasmic reticulum (ER) stress, and cellular senescence in the development of retinal dysfunction. We tested the hypothesis that constant endothelial activation by transmembrane tumor necrosis factor-α (tmTNF-α) exacerbates age-induced visual deficits via senescence-mediated ER stress in this model. To address this, we employed a mouse model of chronic vascular activation using endothelial-specific TNF-α-expressing (tie2-TNF) mice at 5 and 10 months of age. Visual deficits were exhibited by tie2-TNF mice at both 5 months and 10 months of age, with the older mice showing statistically significant loss of visual acuity compared with tie2-TNF mice at age 5 months. The neural defects, as measured by electroretinogram (ERG), also followed a similar trend in an age-dependent fashion, with 10-month-old tie2-TNF mice showing the greatest decrease in "b" wave amplitude at 25 cd.s.m² compared with age-matched wildtype (WT) mice and five-month-old tie2-TNF mice. While gene and protein expression from the whole retinal extracts demonstrated increased inflammatory (Icam1, Ccl2), stress-associated premature senescence (p16, p21, p53), and ER stress (Grp78, p-Ire1α, Chop) markers in five-month-old tie2-TNF mice compared with five-month-old WT mice, a further increase was seen in 10-month-old tie2-TNF mice. Our data demonstrate that tie2-TNF mice exhibit age-associated increases in visual deficits, and these data suggest that inflammatory endothelial activation is at least partly at play. Given the correlation of increased premature senescence and ER stress in an age-dependent fashion, with the loss of visual functions and increased endothelial activation, our data suggest a possible self-enhanced loop of unfolded protein response pathways and senescence in propagating neurovascular defects in this model. Impact statement Vision loss in most retinal diseases affects the quality of life of working age adults. Using a novel animal model that displays constant endothelial activation by tmTNF-α, our results demonstrate exacerbated age-induced visual deficits via premature senescence-mediated ER stress. We have compared mice of 5 and 10 months of age, with highly relevant human equivalencies of approximately 35- and 50-year-old patients, representing mature adult and middle-aged subjects, respectively. Our studies suggest a possible role for a self-enhanced loop of ER stress pathways and senescence in the propagation of retinal neurovascular defects, under conditions of constant endothelial activation induced by tmTNF-α signaling.

Premature senescence of endothelial cells upon chronic exposure to TNFα can be prevented by N-acetyl cysteine and plumericin

Cellular senescence is characterized by a permanent cell-cycle arrest and a pro-inflammatory secretory phenotype, and can be induced by a variety of stimuli, including ionizing radiation, oxidative stress, and inflammation. In endothelial cells, this phenomenon might contribute to vascular disease. Plasma levels of the inflammatory cytokine tumor necrosis factor alpha (TNFα) are increased in age-related and chronic conditions such as atherosclerosis, rheumatoid arthritis, psoriasis, and Crohn's disease. Although TNFα is a known activator of the central inflammatory mediator NF-κB, and can induce the intracellular generation of reactive oxygen species (ROS), the question whether TNFα can induce senescence has not been answered conclusively. Here, we investigated the effect of prolonged TNFα exposure on the fate of endothelial cells and found that such treatment induced premature senescence. Induction of endothelial senescence was prevented by the anti-oxidant N-acetyl cysteine, as well as by plumericin and PHA-408, inhibitors of the NF-κB pathway. Our results indicated that prolonged TNFα exposure could have detrimental consequences to endothelial cells by causing senescence and, therefore, chronically increased TNFα levels might possibly contribute to the pathology of chronic inflammatory diseases by driving premature endothelial senescence.

Docosahexaenoic acid prevented tumor necrosis factor alpha-induced endothelial dysfunction and senescence

We investigated how docosahexaenoic acid (DHA) regulated tumor necrosis factor-alpha (TNF-α)-induced senescence and dysfunction in endothelial cells (EC). We used RT-PCR to examine the expression of several genes related to senescence and dysfunction in EC. TNF-α-induced p21 protein levels were investigated by Western blot (WB) and fluorescence antibody techniques. TNF-α induced the senescence marker β-galactosidase and the expression of several senescence and endothelial dysfunction-related genes, e.g., CDKN1A, SHC1 and GLB1. DHA attenuated TNF-α-induced senescence-related gene expression and p21 protein expression. DHA attenuated TNF-α-induced gene expression related to dysfunction of EC, such as plasminogen activator inhibitor 1 (SERPINE1), lectin-like oxidized low-density lipoprotein receptor-1 (OLR1), thromboxane A2 receptor (TXA2R) and p38 MAPK (MAPK14). DHA reversed the TNF-α-mediated reduction of endothelial nitric oxide synthase (NOS3) gene expression. TNF-α-mediated upregulation of these genes was inhibited by allopurinol and apocynin. These results indicated that DHA regulated the expression of several genes that are associated with senescence and dysfunction of EC.

Chronic Gamma-Irradiation Induces a Dose-Rate-Dependent Pro-inflammatory Response and Associated Loss of Function in Human Umbilical Vein Endothelial Cells

A central question in radiation protection research is dose and dose-rate relationship for radiation-induced cardiovascular diseases. The response of endothelial cells to different low dose rates may contribute to help estimate risks for cardiovascular diseases by providing mechanistic understanding. In this study we investigated whether chronic low-dose-rate radiation exposure had an effect on the inflammatory response of endothelial cells and their function. Human umbilical vein endothelial cells (HUVECs) were chronically exposed to radiation at a dose of 1.4 mGy/h or 4.1 mGy/h for 1, 3, 6 or 10 weeks. We determined the pro-inflammatory profile of HUVECs before and during radiation exposure, and investigated the functional consequences of this radiation exposure by measuring their capacity to form vascular networks in matrigel. Expression levels of adhesion molecules such as E-selectin, ICAM-1 and VCAM-1, and the release of pro-inflammatory cytokines such as MCP-1, IL-6 and TNF-α were analyzed. When a total dose of 2 Gy was given at a rate of 4.1 mGy/h, we observed an increase in IL-6 and MCP-1 release into the cell culture media, but this was not observed at 1.4 mGy/h. The increase in the inflammatory profile induced at the dose rate of 4.1 mGy/h was also correlated with a decrease in the capacity of the HUVECs to form a vascular network in matrigel. Our results suggest that dose rate is an important parameter in the alteration of HUVEC inflammatory profile and function.

Reverse causal reasoning: applying qualitative causal knowledge to the interpretation of high-throughput data

Background

Gene expression profiling and other genome-scale measurement technologies provide comprehensive information about molecular changes resulting from a chemical or genetic perturbation, or disease state. A critical challenge is the development of methods to interpret these large-scale data sets to identify specific biological mechanisms that can provide experimentally verifiable hypotheses and lead to the understanding of disease and drug action.

Results

We present a detailed description of Reverse Causal Reasoning (RCR), a reverse engineering methodology to infer mechanistic hypotheses from molecular profiling data. This methodology requires prior knowledge in the form of small networks that causally link a key upstream controller node representing a biological mechanism to downstream measurable quantities. These small directed networks are generated from a knowledge base of literature-curated qualitative biological cause-and-effect relationships expressed as a network. The small mechanism networks are evaluated as hypotheses to explain observed differential measurements. We provide a simple implementation of this methodology, Whistle, specifically geared towards the analysis of gene expression data and using prior knowledge expressed in Biological Expression Language (BEL). We present the Whistle analyses for three transcriptomic data sets using a publically available knowledge base. The mechanisms inferred by Whistle are consistent with the expected biology for each data set.

Conclusions

Reverse Causal Reasoning yields mechanistic insights to the interpretation of gene expression profiling data that are distinct from and complementary to the results of analyses using ontology or pathway gene sets. This reverse engineering algorithm provides an evidence-driven approach to the development of models of disease, drug action, and drug toxicity.

Endothelial dysfunction and aging: an update

Aging is an important risk factor for the development of many cardiovascular diseases as atherosclerosis and hypertension with a common underlying circumstance: the progressive decline of endothelial function. Vascular endothelial dysfunction occurs during the human aging process and is accompanied by deterioration in the balance between vasodilator and vasoconstriction substances produced by the endothelium. This imbalance is mainly characterized by a progressive reduction of the bioavailability of nitric oxide (NO) and an increase in the production of cyclooxygenase (COX)-derived vasoconstrictor factors. Both circumstances are in turn related to an increased production of reactive oxygen and nitrogen species. The aim of this review is to describe the pathophysiological mechanisms involved in the endothelial function declination that accompanies the multifactorial aging process, including alterations related to oxidative stress and pro-inflammatory cytokines, senescence of endothelial cells and genetic factors.

Role of TNF-alpha in vascular dysfunction

Healthy vascular function is primarily regulated by several factors including EDRF (endothelium-dependent relaxing factor), EDCF (endothelium-dependent contracting factor) and EDHF (endothelium-dependent hyperpolarizing factor). Vascular dysfunction or injury induced by aging, smoking, inflammation, trauma, hyperlipidaemia and hyperglycaemia are among a myriad of risk factors that may contribute to the pathogenesis of many cardiovascular diseases, such as hypertension, diabetes and atherosclerosis. However, the exact mechanisms underlying the impaired vascular activity remain unresolved and there is no current scientific consensus. Accumulating evidence suggests that the inflammatory cytokine TNF (tumour necrosis factor)-α plays a pivotal role in the disruption of macrovascular and microvascular circulation both in vivo and in vitro. AGEs (advanced glycation end-products)/RAGE (receptor for AGEs), LOX-1 [lectin-like oxidized low-density lipoprotein receptor-1) and NF-κB (nuclear factor κB) signalling play key roles in TNF-α expression through an increase in circulating and/or local vascular TNF-α production. The increase in TNF-α expression induces the production of ROS (reactive oxygen species), resulting in endothelial dysfunction in many pathophysiological conditions. Lipid metabolism, dietary supplements and physical activity affect TNF-α expression. The interaction between TNF-α and stem cells is also important in terms of vascular repair or regeneration. Careful scrutiny of these factors may help elucidate the mechanisms that induce vascular dysfunction. The focus of the present review is to summarize recent evidence showing the role of TNF-α in vascular dysfunction in cardiovascular disease. We believe these findings may prompt new directions for targeting inflammation in future therapies.

Aging-induced proinflammatory shift in cytokine expression profile in coronary arteries

The phenotypic and functional changes of coronary arteries with aging promote ischemic heart disease. We hypothesized that these alterations reflect an aging-induced proinflammatory shift in vascular regulatory mechanisms. Thus, in isolated coronary arteries of young (3-month-old) and aged (25-month-old) male Fischer 344 rats the expression of 96 cytokines, chemokines, and their receptors were screened by a cDNA-based microarray technique. In aged vessels expressions of tumor necrosis factor (TNF)-alpha (3.3x), interleukin (IL)-1beta (3.0x), IL-6 (2.9x), IL-6Ralpha (2.8x) and IL-17 (6.1x) genes were significantly increased over young vessels. Quantitative reverse transcriptase-polymerase chain reaction confirmed these results. Western blotting demonstrated that protein expressions of TNF-alpha, IL-1beta, IL-6, and IL-17 were also significantly increased in vessels of aged rats compared with those of young rats. Immunofluorescent double labeling showed that in aged vessels IL-1beta and IL-6 are predominantly localized in the endothelium, whereas TNF-alpha and IL-17 are localized in smooth muscle. Thus, a proinflammatory shift in the profile of vascular cytokine expression may contribute to the aging-induced phenotypic changes in coronary arteries, promoting the development of ischemic heart disease in the elderly.

Exposure of tumor necrosis factor-alpha to luminal membrane of bovine brain capillary endothelial cells cocultured with astrocytes induces a delayed increase of permeability and cytoplasmic stress fiber formation of actin

Tumor necrosis factor-alpha (TNF-alpha), a proinflammatory cytokine, has long been known to be involved in the pathogenesis of central nervous system infections and of certain neurodegenerative diseases. However, the possible role of the blood-brain barrier (BBB), the active interface between the blood circulation and brain tissue, remained unknown during these pathological conditions. In our in vitro reconstructed BBB model, 1-hr exposure of recombinant human TNF-alpha (in concentrations of 50, 250, and 500 U/ml, respectively) to the luminal membrane of bovine brain capillary endothelial cells (BBCEC) did not change significantly the transendothelial flux of either sucrose (m.w. 342 Da), or inulin (m.w. 5 kDa) up to 4 hr (early phase), except for a slight decrease (P < 0.05) in sucrose permeation at 2-4 hr with the highest dose of TNF-alpha. On the other hand, at 16 hr after the 1-hr challenge with TNF-alpha (delayed phase) at all 3 concentrations, significant increase was induced in the permeability of BBCEC monolayers for both markers. These changes of permeability were accompanied by a selective reorganization of F-actin filaments into stress fibers, while the intracellular distribution of vimentin remained similar to the control. These results suggest that BBCEC can respond directly to TNF-alpha by a delayed increase of permeability and reorganization of actin filaments.

Bovine microvascular endothelial cells of separate morphology differ in growth and response to the action of interferon-gamma

Five cell types recently isolated from the bovine corpus luteum differed in their epithelioid morphology and their cytoskeleton, but shared common criteria of microvascular endothelial cells. To give strong evidence for the separate entity, the growth rate of the 5 phenotypically different cells was studied. They were seeded at low density on day 0. Most of these cells were treated with 200 to 1000 U recombinant bovine interferon-gamma (IFN-gamma) for 3 days. The untreated remainder served as controls. Cell counts were made for all cultures on days 4, 7, 10 and 13. Morphology: 13 d after treatment with IFN-gamma senescent cells as well as intact cells occurred in cultures of cell types 1 to 4. Cultures of cell type 5 were apparently unchanged and resembled their untreated counterparts. Desmin-positive cells in cultures of cell type 2 developed cell processes. Growth rate: In the absence of IFN-gamma, the growth rate was high for cell types 3 and 4, moderate for cell type 1, and low for cell types 2 and 5. The presence of IFN-gamma caused anti-proliferative effects. These were higher for cell types 3 and 4 than for cell types 1 and 2. IFN-gamma could be cytotoxic on cell type 3. In contrast, the cytokine tended to support the cell growth of cell type 5. These findings substantiate the postulate that endothelial cells exhibiting separate morphology in culture also function differently.

Murine tumor necrosis factor alpha is transported from blood to brain in the mouse

The cytokines are important components of the brain-immune axis. Recent work has shown that [125I]IL-1 alpha and [125I]IL-1 beta are transported from the blood into the brain by a saturable system. Here we show that murine tumor necrosis factor alpha (mTNF alpha) labeled with 125I (I-mTNF alpha) crosses the blood-brain barrier (BBB) after i.v. injection by a transport system different from that for the interleukins. Self inhibition with mTNF alpha showed that this transport system was saturable, and lack of inhibition by IL-1 alpha, IL-1 beta, IL-6, or MIP-1 alpha showed selectivity of the system. High performance liquid chromatography (HPLC) of the radioactivity recovered from brain and from cerebrospinal fluid after the i.v. injection of I-mTNF alpha showed that the cytokine crossed the BBB largely in intact form. Capillary depletion showed that the accumulation of I-mTNF alpha in the cerebral cortex was due to passage across the BBB rather than to sequestration by capillaries. Transport rate was not changed by acute treatment with the neurotoxin aluminium or by acute and chronic treatment with the cationic chelator deferoxamine, but it was more than three times faster in neonatal rats. Efflux of I-mTNF alpha from the brain was slower than would have been predicted based on reabsorption of cerebrospinal fluid, suggesting that TNF alpha is sequestered by the brain. The BBB was not disrupted by up to 50 micrograms kg-1 of mTNF alpha i.v. in either adult mice or neonatal rats as assessed by the BBB's impermeability to radioactively labeled albumin.(ABSTRACT TRUNCATED AT 250 WORDS)