Evaluation of long-term cultured endothelial cells as a model system for studying vascular ageing

Age-related morphology and function of human arterial endothelial cells

Endothelialization of cardiovascular implants is regarded as a promising strategy for long-term compatibility. While umbilical vein endothelial cells are typically applied in research, human arterial endothelial cells (HAEC) from elderly donors would be the obvious source for autologous cellularization strategies.In our approach, HAEC from 16 donors of varying age (16-63 years) were divided into two groups (<30 years and >30 years) and analyzed regarding morphology, viability, proliferation, function and senescence status.No age-related differences were found regarding morphology, viability, density, prostacyclin and nitrite secretion or collagen and laminin production. However, the metabolic activity was slightly decreased (p = 0.0374) and the membrane integrity marginally impaired (p = 0.0404) in cells from older donors. Two out of three senescence assays detected more senescence markers in cells from older donors.According to the assays applied here, HAEC from young and elderly donors up to the age of 63 years could be judged equally suitable for autologous cellularization strategies. However, this finding should be regarded with caution due to the extremely large variability between individual donors. Further studies comprising a larger sample size are necessary to investigate this issue more thoroughly.

A relationship exists between replicative senescence and cardiovascular health

A growing body of evidence demonstrates that the accumulation of senescent cells is a plausible ageing mechanism. It has been proposed that the senescence of vascular cells plays a causal role in the development of cardiovascular pathologies. A key prediction arising from this hypothesis is that cultures of cells derived from donors with cardiovascular disease will show reduced in vitro replicative capacities compared to those derived from disease-free controls. Accordingly, we carried out a formal review of the relationship among donor age, cardiovascular health status and maximum population doubling level attained in vitro by cultures of vascular smooth muscle and endothelial cells. Data were available to us on a total of 202 independent cell cultures. An inverse relationship was found to exist between replicative capacity and donor age in both endothelial and vascular smooth muscle cells. Cultures derived from donors with cardiovascular disease showed a lower overall replicative potential than age-matched healthy controls. In general the replicative potential at the start of the lifespan was found to be higher in those individuals without disease than those with disease and the difference in average cumulative population doublings (CPDs) in age-matched individuals in the two groups remained roughly constant throughout the lifetime. These results are consistent with the model in which the inherited replicative capacity of vascular cells is a stronger determinant of the onset of cardiovascular disease later in life, than wear-and-tear throughout the life course.

A new, rapid and reproducible method to obtain high quality endothelium in vitro

Human umbilical vein endothelial cells (HUVECs) cultured in vitro are a commonly used experimental system. When properly differentiated they acquire the so-called cobblestone phenotype; thereby mimicking an endothelium in vivo that can be used to shed light on multiple endothelial-related processes. In the present paper we report a simple, flexible, fast and reproducible method for an efficient isolation of viable HUVECs. The isolation is performed by sequential short trypsinization steps at room temperature. As umbilical cords are often damaged during labor, it is noteworthy that this new method can be applied even to short pieces of cord with success. In addition, we describe how to culture HUVECs as valid cobblestone cells in vitro on different types of extracellular matrix (basement membrane matrix, fibronectin and gelatin). We also show how to recognize mature cobblestone HUVECs by ordinary phase contrast microscopy. Our HUVEC model is validated as a system that retains important features inherent to the human umbilical vein endothelium in vivo. Phase contrast microscopy, immuno-fluorescence and electron microscopy reveal a tight cobblestone monolayer. Therein cells show Weibel-Palade bodies, caveolae and junctional complexes (comparable to the in vivo situation, as also shown in this study) and can internalize human low density lipoprotein. Isolation and culture of HUVECs as reported in this paper will result in an endothelium-mimicking experimental model convenient for multiple research goals.

Senescence-enhanced oxidative stress is associated with deficiency of mitochondrial cytochrome c oxidase in vascular endothelial cells

Cellular senescence-elevated oxidative stress plays a critical role in age-associated vascular endothelial dysfunction. We investigated whether deficiency of mitochondrial cytochrome c oxidase (complex IV) is causally linked to increased oxidant generation during cellular aging using senescent (passage 45) and young (passage 3) pulmonary artery endothelial cells (PAEC). In senescent PAEC, levels of O2- and H2O2 were elevated onefold, respectively, compared to those in young cells. Lipid peroxidation and protein carbonyl contents in aged cells were increased more than twofold compared to young cells. To determine whether lack of complex IV in senescent cells contributed to the increased oxidant generation, complex IV activity in young cells was specifically inhibited using antisense oligonucleotides directed against the mRNA of complex IV subunits. Levels of O2- and H2O2 in PAEC treated with antisense oligonucleotides were elevated onefold, respectively, which correlated with a similar increase in lipid (110%) and protein (20%) oxidation, compared to control oligonucleotides-transfected cells. Moreover, levels of nitrosylated proteins in antisense-transfected cells were increased 30%, compared to controls. These data demonstrate that deficiency of complex IV in senescent cells enhances oxidative and nitrosative stress, which may be responsible for senescence-induced endothelial cell loss and dysfunction.

Down-regulation of mitochondrial cytochrome c oxidase in senescent porcine pulmonary artery endothelial cells

Cellular aging is associated with dysfunction of the mitochondrial respiration chain. Deficiency of mitochondrial cytochrome c oxidase (complex IV) plays a critical role in aging-induced mitochondrial dysfunction. We investigated whether in vitro cellular aging causes the downregulation of complex IV activity and gene expression using senescent (passage 45) and young (passage 3) pulmonary artery endothelial cells (PAEC). In senescent PAEC, the catalytic activity of complex IV decreased 84%, compared to that in young cells. Relative protein levels of complex IV subunits I and IV (complex IV S1 and S4) in senescent cells decreased 91%, compared to those in young cells. This suggests that lack of complex IV S1 and S4 in senescent cells may contribute to the deficiency of complex IV. Total steady state levels of mRNA for complex IV S1 and S4 in senescent cells were decreased to 20% and 18% of those in young cells. The relative rates of mRNA synthesis of complex IV S1 and S4 were decreased 46% and 37% in senescent cells, respectively, compared to young cells. The degradation of complex IV S1 and S4 was increased 76% and 64% in senescent cells, compared to young cells. These data indicate that mitochondrial DNA-encoded subunit I and nuclear DNA-encoded subunit IV of complex IV are downregulated through reduced synthesis and enhanced degradation of their mRNA, which may be responsible for the deficiency of complex IV in replicative senescent PAEC.

Enhanced apoptosis in prolonged cultures of senescent porcine pulmonary artery endothelial cells

Senescent or aged endothelial cells in culture remain metabolically active after cessation of division, and are generally believed to eventually die. However, mechanisms underlying the terminal aging of cultured cells, i.e. from senescence to death, are poorly understood. Here, we report that culturing of replicative senescent endothelial cells for a prolonged period of time without passaging leads to enhanced programmed cell death or apoptosis. Senescent (passage 45) and young (passage 3) porcine pulmonary artery endothelial cells (PAEC) were cultured for 0-42 days post confluence. The cells attached to culture dishes and floating in medium were collected at 0, 7, 14, 21, 28, 35 and 42 days post confluence and were assessed for markers of apoptosis. Morphology studies showed that ratios between senescent and young cells attached to dishes declined to 45% after 42 days postconfluence. Apoptotic cells in prolonged cultures of senescent PAEC increased from 5 to 35% as determined by protein mass, DNA breakage, and caspase-3 activation. Steady state levels of Bcl-2, an anti-apoptotic protein, in senescent prolonged cultures decreased to less than 20% for all time points compared with young cells. Relative levels of Bad, a pro-apoptotic protein, in senescent cells were elevated from 60 to 130% during prolonged culturing. These results indicate that terminal cellular aging enhances apoptosis and the levels of Bcl-2/Bad may be associated with the apoptotic process in porcine lung endothelial cells.

Age dependency of neointima formation on vascular prostheses in dogs

Neointima formed quickly on vascular prostheses implanted in young dogs but not in aged dogs. Previously, we found that impeding neointima formation on vascular prostheses occurred more frequently in aged animals. From these observations, we hypothesized that neointima formation was age-dependent in dogs. To test the hypothesis, 26 fabric Dacron vascular prostheses were analyzed. Half of them were retrieved from aged dogs (more than 13 years old) while the other half were from young ones (less than 1 year old). The grafts were harvested at 8 weeks and 3 months after implantation. The graft surfaces were photographed and analyzed by computer for the ratio of the areas with and without thrombus. Light and scanning electron microscopic observation revealed that most of the thrombus-free areas were lined with endothelial cells. Then the endothelialized areas were calculated. Using data obtained from macroscopic, light microscopic, and scanning electron microscopic observations, the arithmetic means were calculated as the degree of neointima formation. In young animals, the degrees at 8 weeks and at 3 months were 89.1 +/- 8.5% (mean +/- SD) and 95.7 +/- 3.3%, respectively. In old animals, they were 27.9 +/- 5.9% and 31.5 +/- 6. 8%, respectively. From these results, we concluded that neointima formation was age-dependent in dogs.

Decline of shear stress-induced activation of extracellular signal-regulated kinases, but not stress-activated protein kinases, in in vitro propagated endothelial cells

We investigated the involvement of mitogen-activated protein kinase (MAPK) signal transduction pathways in human endothelial cells in response to shear stress and alterations of these kinases in in vitro-propagated endothelial cells (ECs). Potent activation (10-fold) of extracellular signal-regulated kinase (ERK2), a member of the MAPK family, occurred within 10 min of shear stress (5 dynes/cm2), whereupon rapid inactivation ensued. Shear stress also induced activation of stress-activated protein kinase (SAPK) or c-Jun NH2-terminal protein kinase (JNK) in ECs. Suramin pretreatment completely inhibited shear stress stimulation of ERK2, but not SAPK/JNK, highlighting a role for growth factor receptors in ERK activation. Translocation of ERK2 from the cytoplasm to the nucleus was observed in shear-stressed endothelial cells. In addition, we compared activities of MAPKs in shear-stressed cells derived from passages 4 and 10 (older). The magnitude of ERK2 activation was significantly lower in aged ECs compared to those of passage 4, while SAPK/JNK was not altered in the in vitro aged ECs. A similar level of ERK2 activation was found in both young and older cells stimulated with phorbol-12-myristate-13-acetate (PMA), indicating an age-related alteration of the plasma membrane. Taken together, these findings suggest that MAP kinase activation may be crucial for the expression of many genes in ECs stimulated by shear stress, and that an alteration in MAPK activities could contribute to the age-related decline in proliferative capacity.

Succinylated collagen crosslinked by thermal treatment for coating vascular prostheses

Vascular prostheses coated with collagen carefully prepared to avoid contamination were tested to see if it could induce endothelial cell lining throughout the graft surface in a natural way. The collagen fibers were succinylated. Hydrogel produced with the succinylated collagen was used for the sealant to reduce the amount of solid substance. To avoid contamination and the side effects of chemical reagents, the collagen thermally crosslinked under sterile conditions. A suspension of the collagen fibers was enmeshed in the interstices of Dacron fibers of fabric prostheses, which were then thermally crosslinked at 130 degrees C for 20 h. The prostheses were porous when the collagen fiber network was dry. Under wet conditions, however, the water permeability of the grafts was reduced to 0.1 ml/min from the 1,250 ml/min of the original prostheses. Three weeks after implantation in the abdominal aortas of dogs, 81.2 +/- 11% of the luminal surface was macroscopically thrombus free, and 56 +/- 14% was endothelialized. More than 95% of the coated collagen had been absorbed. Numerous fibroblasts had migrated into the graft walls, and capillary blood vessels had infiltrated the inside of the graft walls without foreign body reaction. In the controls, thrombus free areas averaged 9.0 +/- 5%, and endothelialized areas averaged 5.2 +/- 4%. Many giant cells, plasma cells, and lymphocytes had migrated into the graft walls, but no fibroblasts. These results suggest that rapid endothelialization is possible when clean collagen is used.

Modulation of angiotensin-converting enzyme in cultured human vascular endothelial cells

Previous work has suggested that not all immunoreactive angiotensin-converting enzyme (ACE) in tissues or cells is in a biologically active state. We have explored this possibility in cultured human umbilical vein endothelial cells (HUVEC), one of the most widely studied in vitro endothelial cell systems. Our approach included characterization of the effect of increasing passage number on ACE activity and expression of immunoreactive ACE at the single cell level, the subcellular compartmentalization of active ACE, and the effect of phorbol ester (PMA) treatment. We found that both ACE activity and expression of ACE antigen were downregulated by cultivation (30% of ACE-positive cells at seventh passage vs. 90% in primary culture). ACE downregulation is specific (number of CD31-positive cells did not change with cultivation) and correlated with downregulation of factor VIII-antigen. The percentage of ACE-positive cells in permeabilized HUVEC at third passage was almost twice that in nonpermeabilized HUVEC (90% vs. 50%), indicating that HUVEC contain intracellular immunoreactive ACE. ACE activity, however, was similar when measured in intact cells and in cell lysates. Moreover, diazonium salt of sulfanilic acid (DASA), a membrane-impermeable ACE inhibitor, inhibited ACE activity in intact cells and in cell lysates at the same extent, thus implying that intracellular ACE is inactive. PMA (100 nM) treatment increased the percentage of ACE-positive cells at third passage from 57 to 96%. ACE activity was increased 3-fold in cell and 1.5-fold in the culture medium of PMA-treated cells. Analysis of ACE activity in intact monolayers and cell lysates of control and PMA-treated cells revealed that all enzymatically active ACE in PMA-treated cells is localized on the plasma membrane and acts as an ectoenzyme. We conclude that expression of ACE by HUVEC is downregulated by repeated passage in culture but can be restored by PMA treatment. In addition, ACE expression is heterogeneous between neighboring cells, and total immunoreactive ACE protein associated with HUVEC includes an inactive pool of the enzyme.

Choice, isolation, and preparation of cells for bioartificial vascular grafts

Preparation of cells and tissues for bioartificial vascular grafts is discussed from the viewpoint of tissue engineering. In general, a neointima is not formed on vascular prostheses except at the anastomotic sites. Graft surfaces do not heal and are covered with fresh thrombi for a long period of time after implantation. The delayed healing is, so to speak, an intractable ulcer of the vascular wall. To overcome this problem, we have developed a tissue fragment transplantation method. We consider that neointima formation of vascular prostheses after implantation is a product of tissue engineering in vivo. Therefore, 3 essential elements for tissue engineering, i.e., cells, extracellular matrices, and cytokines, are required for neointima formation. Synthetic vascular prostheses lack one or more of these elements. In this study we demonstrated a standard healing process of fabric vascular prostheses and an antithrombogenic polymer graft using animal models. Then we showed the tissue fragment transplantation method using venous tissues, adipose tissues, and bone marrow. This method provided the 3 essential elements to the prostheses. To allow these elements to be actively engaged in neointima formation, we treated cells and tissues as clumps without enzymatic digestion. We also took advantage of the in vivo environment. With the results we demonstrate our way of thinking in relation to bioartificial vascular grafts.

Aging decreases the production of PGI2 in rat aortic endothelial cells

It has been suggested that progressive pathophysiologic modifications of endothelium are associated with aging. Aging has been shown to influence some specific functions at the cellular level. In the present study, the effects of aging on levels of prostacyclin (PGI2) production were examined in cultured rat aortic endothelial cells from young (six-week-old) and old (100-week-old) Wistar rats. The level of PGI2 production from rat aortic endothelial cells decreased significantly with increasing age, suggesting decreased function of the endothelial cells. The production of PGI2 stimulated by thrombin was decreased in old rat aortic endothelial cells compared to young rat aortic endothelial cells, whereas there was no difference in the rate of intracellular calcium mobilization caused by thrombin. These data indicate that aging nonuniformly affects both basal and agonist-induced levels of PGI2 production in rat aortic endothelial cells, and that this diminution in PGI2 production may be related to the age-related potentiation of various thrombotic events.

Human lymphocytes incubated in vitro share multiple characteristics with geriatric-derived lymphocytes: a potential in vitro model for aging?

Aging involves a complicated set of parallel reactions that result in multiple cellular and organismic changes and may eventuate in chronic illness. In the immune system, several alterations that correlate with age have been established. In the present study, we report the results of incubating lymphocytes in vitro in whole blood and, employing measures known to be age-dependent, compare these cells 'aged' in vitro with cells from geriatric patients aged in vivo. Cells from blood aged in vivo and incubated in vitro share a number of common characteristics that include decreased growth capacity, shifted growth patterns, increased suppression by adherent cells, decrease in CD5 surface antigen, similar responses to addition of exogenous IL-1, IL-2, PGE2, or indomethacin, and similar production of PGE2. Differences found between in vivo aging and in vitro incubation are IL-2 plasma levels and IL-2 production by activated cells monitored in conditioned minimal medium. Based on these observations, this in vitro system provides a simple method to generate cells that exhibit a very significant subset, but not all, of the characteristics associated with in vivo aging in lymphocytes.

Elevated promotion of prostacyclin production by synthetic lipid A analogs in aged human endothelial cells in culture

We examined the effects of E. coli lipopolysaccharide (LPS) and synthetic analogs of lipid A, a bioactive moiety of LPS, on the prostacyclin (PGI2) production by young and old human endothelial cells in vitro. PGI2 production by endothelial cells has been shown to decrease during in vitro cellular senescence as well as in vivo. LPS and all the analogs tested in this study did not stimulate PGI2 production by young endothelial cells more than twofold. However, LPS and the majority of the lipid A analogs examined stimulated the PGI2 production by old cells more than twofold (approximately two- to sixfold). These results indicate that the responses to certain stimuli sometimes differ markedly between young and old cells, and this should be carefully considered when evaluating the biological effects of various compounds. Furthermore, these results suggest that certain synthetic lipid A analogs can be used as drugs to prevent some age-related vascular diseases.

The vicious cycle of nonhealing neointima in fabric vascular prostheses

Delayed neointimal healing of a fabric vascular prosthesis was investigated in an animal study focusing on the relationship between red thrombus, fibrinolysis, and endothelialization on the luminal surface. Fabric vascular prostheses were implanted into the descending aortas of 72 dogs. Fifty-nine grafts were explanted from 1 h to 1,705 days after implantation. One hour after implantation, the graft wall was red in color due to fresh thrombus; however, at 1 day the luminal surface became white. Red thrombus reappeared at 1 week and remained present in the long-term. Microscopically the initial red thrombus contained numerous erythrocytes. The white thrombus at 1 day was composed of a dense fibrin network without erythrocytes. At 2 days numerous lacunae appeared in the fibrin layer, and at 3-5 days cavernae and low density fibrin areas were present secondary to fibrinolysis. These areas allowed the blood components to infiltrate into the fibrin layer, and as a result red thrombus reformed within it. The thrombi on the luminal surface in the long-term was always red in color and composed of complicated, multiple stages of thrombus formation, i.e., fresh thrombus with erythrocytes, dense fibrin without erythrocytes, low fibrin density areas, lacunae and cavernae in the fibrin layer, and blood component infiltration into these spaces. Thrombus was always newly formed and present, and involuted in parallel due to fibrinolysis, suggesting that these phenomena perpetuated in a vicious cycle. However, at the anastomoses fibrinolysis was present, but blood component infiltration was prevented by the endothelial cell lining. These results suggest that endothelialization may arrest the vicious cycle of nonhealing neointima in fabric vascular prostheses.

Endothelial cell senescence inhibits unidirectional endothelialization in vitro

We investigated the effects of cellular senescence on unidirectional endothelialization in vitro, simulating the anastomotic endothelialization of vascular prosthesis. The experiments were carried out with three different cumulative population-doubling levels (CPDLs) of bovine aortic endothelial cells (ECs), which have finite life span. Young ECs with 22 CPDL, middle aged with 46, and senescent with 70 at the time of inoculation were used. The effect of aging on unidirectional endothelialization, as well as cellular morphology and proliferative and migratory potentials of isolated cells, were qualitatively and quantitatively analyzed. The unidirectional endothelialization rate was determined by our newly designed method to prepare the square monolayer sheet with linear margins between cell-adhesion and noncell-adhesion regions. The results showed that endothelial cell senescence retarded not only proliferation and migration but also unidirectional endothelialization. Time-lapsed videomicroscopic study of unidirectional endothelialization process revealed that ECs at several rows back from the leading edge represented much slower rate of migration than did the ECs at the leading edge. These findings suggest that high cellular mobility observed for the ECs at the leading edge may result in localized excessive cell replication. Thus, atherosclerotic vessels containing senescent or injured ECs may have limited capability of anastomotic endothelialization.

Post-transcriptional regulation of interleukin 1 alpha in various strains of young and senescent human umbilical vein endothelial cells

Human umbilical vein endothelial cell (HUVEC) senescence in vitro is characterized by the loss of proliferative potential and an increase in cell size. Because HUVEC senescence in one strain (H101) has been characterized by the increase in the steady-state mRNA level for the signal-peptideless cytokine, interleukin (IL) 1 alpha, we have examined young and senescent populations of five additional HUVEC strains (H3605, H103, H928, H929, and H930) to determine whether the elevated levels of IL-1 alpha mRNA could be observed in all HUVEC strains. Consistent with the data from strain H101, strains H3605 and H930 also exhibited a low steady-state level of the IL-1 alpha mRNA in young populations compared to elevated levels of IL-1 alpha mRNA in the senescent populations. However, three strains (H103, H928, and H929) did not exhibit reduced levels of IL-1 alpha mRNA in the young populations, and interestingly, strain H928, at times, expressed relatively high IL-1 alpha mRNA levels in the young populations. In addition, expression of the steady-state level of plasminogen activator inhibitor 1 and cyclooxygenase 2 was elevated in senescent populations of all HUVEC strains examined, whereas young populations exhibited a low level of expression for these genes regardless of the IL-1 alpha mRNA level. Further, the level of the IL-1 alpha polypeptide was elevated in senescent HUVEC populations relative to young populations that expressed either a high or low level of the IL-1 alpha mRNA. We have also demonstrated that the elevated level of IL-1 alpha mRNA in the senescent population of strain H3605 may be regulated by mRNA stability; however, this mechanism does not apply to all the HUVEC strains examined in this study. Thus, we suggest that while mRNA levels of the IL-1-response genes for plasminogen activator inhibitor 1 and cyclooxygenase 2 are appropriate markers for HUVEC senescence, HUVEC strain-specific post-transcriptional mechanisms may exist to regulate the function of IL-1 alpha as a modifier of HUVEC senescence in vitro.

Senescence of aortic endothelial cells in culture: effects of basic fibroblast growth factor expression on cell phenotype, migration, and proliferation

Bovine aortic endothelial cells (BAEC) can be isolated in large numbers without major contamination by other cells and maintained in culture with a limited life span for about 100 population doublings. In order to study phenotypic changes of BAEC during long-term culture, stocks of different passages of BAEC were established and their morphological, migratory, and proliferative properties analyzed. Early-passage BAEC (passages 5-15) rapidly produce dense, cobblestone-like monolayers. Their growth beyond the monolayer configuration is characterized by the formation of an irregular network of spindle-shaped, crisscrossing BAEC growing either on top or beneath the monolayer, and by the assembly of elongated BAEC into well-differentiated capillary-like tubes. In contrast, senescent BAEC (passages 35-45) form perfect cobblestone monolayers that contain several, often multinucleated giant cells and a few capillary-like tubes but not the crisscrossing networks of their early-passage counterparts. The rates of BAEC migration and proliferation gradually decline during in vitro senescence. This decline is neutralized by exogenous basic fibroblast growth factor (bFGF) which elevates the migratory and proliferative capacities of early-passage and senescent BAEC to uniformly high levels. Northern blot analysis shows a gradual decline in bFGF message and an increase in laminin message during in vitro BAEC senescence. The present study supports the concept of autocrine growth regulation of BAEC and associates a decreased bFGF message with decreased rates of migration and proliferation as well as loss of the crisscrossing BAEC morphotype in senescent cultures.

Augmentation of endothelin-1, prostacyclin and thromboxane A2 secretion associated with in vitro ageing in cultured human umbilical vein endothelial cells

Differences in the secretion of the vascular regulators endothelin-1 (ET-1, prostacyclin (PGI2) and thromboxane A2 (TXA2) associated with ageing were investigated in cultured endothelial cells isolated from normal human umbilical veins (HUVECS). HUVECS at different population doubling levels (PDLs) were cultured in medium MCDB-104 supplemented with FBS and ECGF. Cell saturation density was determined by a Coulter counter, and concentrations of ET-1, PGI2 and TXA2 in the media were determined by radioimmunoassay. The cellular and nuclear size of HUVECS increased with advancing age, and the dividing ability decreased. Cell saturation density of HUVECS decreased 5-fold between PDLs 7 and 67 (P < 0.01). The secretion of ET-1 by HUVECS at a young stage of growth (PDL 7.6) increased linearly between 0 and 36 h of incubation (P < 0.01). ET-1 secretion increased approximately 3-fold between PDLs and 67 (P < 0.01). PGI2 secretion increased 6-fold between PDLs 7 and 67 (P < 0.01), and TXA2 secretion increased 18-fold between PDLs 7 and 67 (P < 0.01). The ratio of PGI2 to TXA2 secretion decreased 3-fold between PDLs 7 and 40 (P < 0.01), and remained at the lower ratio between PDLs 40 and 67. This data indicates that the anti-thrombotic or anti-vasoconstrictive role of endothelial cells may decrease during in vitro ageing.

A step in the process of prostacyclin production whose decline leads to the age-related decrease in production by human umbilical vein endothelial cells in culture

Human umbilical vein endothelial (HUVE) cells were examined at various culture ages for four steps of prostacyclin (PGI2) production ((1) incorporation of exogenous arachidonic acid into the cell membrane, (2) loss of arachidonic acid from the cell membrane to the cytoplasm, (3) conversion of arachidonic acid to PGI2 in the cytoplasm, (4) release of PGI2 to the outside of the cell) to determine the step whose decline leads to the age-related decrease in PGI2 production. Only conversion to PGI2 (step 3) showed the age-related decrease. Judging from these results, the authors conclude that the age-related decrease in PGI2 production is mainly due to the decrease in the ability of HUVE cells to convert arachidonic acid to PGI2 in the cytoplasm.

Age-related changes in the position of centrosomes in endothelial cells of the rabbit aorta

The position of centrosomes in endothelial cells (EC) lining the aorta was examined in rabbits at different ages, using en face preparations and immunofluorescent staining with a serum that specifically labels centrioles. The results obtained show that in young rabbits (4 h-6 weeks) the great majority of the EC (61%) had centrosomes on the heart side of the nucleus, whereas in older rabbits (6-156 weeks) only 41% of the EC had centrosomes oriented toward the heart. The results suggest that the orientation of structures normally associated with centrosomes such as the microtubule organizing centers and the Golgi apparatus also change with age. The change in the orientation of centrosomes and associated structures along the longitudinal axis of the cell with age could affect the function and behaviour of EC and their ability to respond to injury.

Organ-specific change in Dolichos biflorus lectin binding by myocardial endothelial cells during in vitro cultivation

Endothelial cells of the NMRI mouse strain express a cell surface glycoprotein recognized by the lectin Dolichos biflorus agglutinin (DBA). This study documents a marked organ-specific increase in DBA-specific lectin binding of myocardium-derived endothelial cells (MEC) of the NMRI/GSF mouse during in vitro cultivation. An up to 20-fold increase in DBA binding sites is observed in long-term culture, an increase not found in other NMRI-derived endothelial cell lines (e.g., brain, aorta). The increase appears restricted to DBA in that binding with other lectins (PNA, WGA) was unaltered. NMRI MEC cultures maintain typical endothelial cell attributes such as cobblestone morphology on confluence, expression of endothelial cell-specific surface markers, and production of angiotensin-converting enzyme. Cultures routinely become aneuploid within 4 passages, several passages before upregulation of the DBA binding site(s). Myocardial endothelial cells sorted to obtain DBAhi and DBAlo cell populations generally maintained their sorted phenotype for 3 to 4 passages. Limiting dilution cloning resulted in clones varying in DBA expression. Clones for DBAhi expression maintained their DBA affinity for at least 10 passages (> 30 doublings), whereas DBAlo clones gave rise to varying numbers of DBAhi cells within 2 to 4 passages. We hypothesize that the change in DBA affinity accompanies in vitro aging, that the change is independent of alterations in karyotype, and that the increase in DBA affinity may reflect a change in one or more other endothelial cell properties. Additional studies will be necessary to determine whether the in vitro changes are correlated with specific functional alterations and whether they accurately reflect progressive changes of MEC in vivo.

Epidermal growth factor suppresses in vitro senescence in the ability of human umbilical vein endothelial cells to proliferate, but not in the ability to produce prostacyclin

Addition of epidermal growth factor (EGF) to culture medium extended the replicative life span of human umbilical vein endothelial (HUVE) cells in culture. In brief, EGF suppresses the age-related decrease (in vitro senescence) in cell proliferative ability. However, the addition of EGF did not extend the culture period in which prostacyclin (PGI2) is actively produced by the cells. Therefore, EGF does not suppress the age-related decrease (in vitro senescence) in the ability of cultured HUVE cells to produce PGI2. These results suggest that the process of in vitro senescence in the cell proliferative ability is not necessarily correlated with that of in vitro senescence in the ability to produce PGI2.

Disassembly of F-actin filaments in human endothelial cells cultured on type V collagen

We examined the inhibitory activity of type V collagen on cell attachment and cell growth and the role of stress fibers and beta 1 integrin in cultured human endothelial cells. Human endothelial cells cultured on type V collagen attached temporarily to the substrate and formed stress fibers. However, the cells failed to proliferate and gradually detached from the substrate. After 24 h, the cells on type V collagen lacked discernible stress fibers (F-actin filaments) and exhibited dots in small aggregates of F-actin. In addition, the cells expressed little or no proteins as focal adhesions, including vinculin and beta 1 integrin. In contrast, the cells on fibronectin and type I collagen formed complete F-actin filaments, exhibited sufficient vinculin and beta 1 integrin, and grew logarithmically from 2 days. On the other hand, human smooth muscle cells formed complete F-actin filaments, revealed typical focal adhesions, and started to proliferate rapidly after 24 h on type V collagen as well as on fibronectin and type I collagen. Thus, the disassembly of F-actin filaments was observed as a specific phenomenon in human endothelial cells cultured on type V collagen. Moreover, the F-actin filaments disappeared from endothelial cells treated with cytochalasin D after 24 h and the cells detached from fibronectin and type I collagen with time, a result consistent with the observations on type V collagen. Accordingly, the disassembly of F-actin filaments in focal adhesions may result in the detachment of endothelial cells from type V collagen.

In vitro analysis of pulmonary inflammation using rat lung organ cultures

We have analyzed leukocyte to lung adhesive interactions and neutrophil-mediated lung injury using a rat lung organ culture system. Rat lung slices were maintained in tissue culture on gelatin sponges floating at the gas-liquid interface. Maintenance of three-dimensional alveolar structure, critical to the viability of lung tissue, was achieved by instilling 0.5% agarose (in 37 degrees C RPMI 1640) into the lungs during tissue explanation. Quantitative neutrophil to lung adhesive interactions were examined using an adaptation of the Woodruff-Stamper frozen section binding assay. Pretreatment of organ cultures with recombinant human tumor necrosis factor (rhTNF) resulted in a protein synthesis-dependent three- to fourfold increase in adhesiveness for neutrophils. Time course and mononuclear leukocyte binding experiments revealed that TNF-induced rat lung adhesiveness peaks at 4 h and is largely neutrophil-specific. Agonist-induced activation of neutrophils in the presence of [3H]leucine-labeled organ cultures resulted in lung injury as assessed by radioisotope release. These observations are consistent with endothelial cell culture data that indicate that TNF-induced endothelium exhibits a protein synthesis-dependent increase in adhesiveness for neutrophils. These data validate rat lung organ cultures as a model system that can be used to assess mechanisms of neutrophil adhesion and leukocyte-mediated tissue injury.

Cation transport in vascular endothelial cells and aging

To understand the generation and maintenance of Na and K gradients in cultured vascular endothelial cells, net Na and K movements were studied. Ouabain-sensitive (OS) net Na gain and K loss were estimated as the difference between the cation content in the presence of ouabain and that in the control. Ouabain- and furosemide-resistant (OFR) fluxes were determined in the presence of the two inhibitors. When the normal medium bicarbonate and phosphate buffers were replaced by N-2-hydroxyethylpiperazine-N'-2-ethane sulfonic acid both the OS and OFR fluxes decreased more than 50%. Ouabain-sensitive and ouabain- and furosemide-resistant fluxes decreased with increasing cellular age (passage number) an effect not observed when the cation movements were studied in the absence of bicarbonate and phosphate. These results suggest that cultured vascular endothelial cells possess bicarbonate- and phosphate-dependent Na and K pathways which account for a significant portion of their passive movements. Furthermore, the behavior of cation permeabilities with passage number suggests that these modulations may be related to the cellular aging process.

No relationship between the age-related decrease in prostacyclin production and the level of intracellular lipid peroxidation in human umbilical vein endothelial cells in culture

Some investigators have speculated that a decrease in prostacyclin production observed during ageing of endothelial cells is caused by an increase in intracellular lipid peroxide. We checked this speculation using an in vitro model to study the ageing of human vascular endothelial cells. For this purpose we determined the levels of intracellular lipid peroxide of endothelial cells at various culture ages, and found that the level of intracellular lipid peroxidation did not increase during in vitro ageing. Amounts of intracellular lipid peroxide also differed depending on the growth phase, the addition of heparin and the strain of endothelial cells, but the cells producing prostacyclin at a low level did not necessarily contain larger amounts of intracellular lipid peroxide. Therefore, we postulate that the age-related decrease in prostacyclin production is not due to an increase in the amount of intracellular lipid peroxide as a function of age.

Hyaluronic acid synthesis is absent in normal human endothelial cells irrespective of hyaluronic acid synthetase inhibitor activity, but is significantly high in transformed cells

The characteristics of glycosaminoglycan (GAG) synthesis in normal and transformed human endothelial cells were analyzed by the incorporation of [3H]glucosamine and by the activities of GAG synthetases. The GAG synthesized by normal endothelial cells consisted of mainly heparan sulfate (HS) and chondroitin sulfate/dermatan sulfate but little hyaluronic acid (HA) (less than 1%). The characteristics of GAG synthesis by normal cells reflected the synthetic enzyme activities for each individual GAG: the activity of HA synthetase was very low. In spite of this, the activity of HA synthetase inhibitor, induced in growth-retarded fibroblasts with low HA synthetase activity (Matuoka et al. (1987 J. Cell Biol., 104, 1105-1115), was very low in endothelial cells. In contrast to normal cells, transformed endothelial (ECV304) cells synthesized mainly HA (62% of total GAGs). These findings suggest that the regulatory system of GAG metabolism is cell type specific, and that transformation is accompanied by high levels of HA synthesis in endothelial cells.

Extension of the life-span of human endothelial cells by an interleukin-1 alpha antisense oligomer

The proliferative potential of human diploid endothelial cells is finite, and cellular senescence in vitro is accompanied by the failure of the endothelial cell to respond to exogenous growth factors. Senescent human endothelial cells were shown to contain high amounts of the transcript for the cytokine interleukin-1 alpha (IL-1 alpha), a potent inhibitor of endothelial cell proliferation in vitro. In contrast, transformed human endothelial cells did not contain detectable IL-1 alpha messenger RNA. Treatment of human endothelial cell populations with an antisense oligodeoxynucleotide to the human IL-1 alpha transcript prevented cell senescence and extended the proliferative life-span of the cells in vitro. Removal of the IL-1 alpha antisense oligomer resulted in the generation of the senescent phenotype and loss of proliferative potential. These data suggest that human endothelial cell senescence in vitro is a dynamic process regulated by the potential intracellular activity of IL-1 alpha.