Microvascular endothelial cell culture

Isolation and culture of endothelial cells from embryonic rat yolk sac

Yolk sac blood islands are the first morphologic evidence of hematopoietic development during mammalian embryogenesis, and visseral yolk sac mesoderm gives rise to the first embryonic blood cells within a rich endothelial network. Present study reports the isolation and culture of endothelial cells from 11.5 days old embryonic rat yolk sac. The embryos were dissected from 11.5 days pregnant Wistar rat (Rattus norvegicus) and the external yolk sac membrane and embryos were removed under aseptic condition. After washing three times with Calcium-Magnesium free Hank’s balanced salt solution (CMF-HBSS), the tissue was minced, and fragments were incubated in CMF-HBSS containing 2mg/ml Trypsin, 100mg/ml collagenase I and 40mg/ml DNAse at 37°C until the tissue was completely dispersed. The digestion effect was then neutralized by fetal bovine serum at 1:3 (v/v). The cell suspension was centrifuged at 1000 rpm for 10 min., the supernatants were discarded and the cell pellets resuspended in Dulbecco modified Eagle medium containing 15% fetal bovine serum, 1.25mg/ml amphotericin B, 25mg/ml gentamycin sulphate and 100mg/ml endothelial cell growth supplement. The resuspended cells were plated in two diverse 25cm2 culture flasks for overnight differential adherence at 37°C. The non-adherent cells were removed by gentle aspiration and adherent cells refed with fresh medium. The cells were transferred using 1ml of 0.2% Trypsin when cultures reached near-confluence. The cultured yolk sac endothelial cells had characteristic cobblestone appearence and positive immunofluorescent staining for von Willebrand Factor (vWF). Weibel-Palade bodies, the major ultrastructural marker for endothelium, were also detected in cultured cells by electron microscopy.

Isolation of microvascular endothelial cells from cadaveric corneal limbus

Limbal microvascular endothelial cells (L-MVEC) contribute to formation of the corneal-limbal stem cell niche and to neovascularization of diseased and injuries corneas. Nevertheless, despite these important roles in corneal health and disease, few attempts have been made to isolate L-MVEC with the view to studying their biology in vitro. We therefore explored the feasibility of generating primary cultures of L-MVEC from cadaveric human tissue. We commenced our study by evaluating growth conditions (MesenCult-XF system) that have been previously found to be associated with expression of the endothelial cell surface marker thrombomodulin/CD141, in crude cultures established from collagenase-digests of limbal stroma. The potential presence of L-MVEC in these cultures was examined by flow cytometry using a more specific marker for vascular endothelial cells, CD31/PECAM-1. These studies demonstrated that the presence of CD141 in crude cultures established using the MesenCult-XF system is unrelated to L-MVEC. Thus we subsequently explored the use of magnetic assisted cell sorting (MACS) for CD31 as a tool for generating cultures of L-MVEC, in conjunction with more traditional endothelial cell growth conditions. These conditions consisted of gelatin-coated tissue culture plastic and MCDB-131 medium supplemented with foetal bovine serum (10% v/v), D-glucose (10 mg/mL), epidermal growth factor (10 ng/mL), heparin (50 μg/mL), hydrocortisone (1 μg/mL) and basic fibroblast growth factor (10 ng/mL). Our studies revealed that use of endothelial growth conditions are insufficient to generate significant numbers of L-MVEC in primary cultures established from cadaveric corneal stroma. Nevertheless, through use of positive-MACS selection for CD31 we were able to routinely observe L-MVEC in cultures derived from collagenase-digests of limbal stroma. The presence of L-MVEC in these cultures was confirmed by immunostaining for von Willebrand factor (vWF) and by ingestion of acetylated low-density lipoprotein. Moreover, the vWF(+) cells formed aligned cell-to-cell 'trains' when grown on Geltrex™. The purity of L-MVEC cultures was found to be unrelated to tissue donor age (32-80 years) or duration in eye bank corneal preservation medium prior to use (3-10 days in Optisol) (using multiple regression test). Optimal purity of L-MVEC cultures was achieved through use of two rounds of positive-MACS selection for CD31 (mean ± s.e.m, 65.0 ± 20.8%; p < 0.05). We propose that human L-MVEC cultures generated through these techniques, in conjunction with other cell types, will provide a useful tool for exploring the mechanisms of blood vessel cell growth in vitro.

Endothelial dysfunction in adipose triglyceride lipase deficiency

Systemic knockout of adipose triglyceride lipase (ATGL), the pivotal enzyme of triglyceride lipolysis, results in a murine phenotype that is characterized by progredient cardiac steatosis and severe heart failure. Since cardiac and vascular dysfunction have been closely related in numerous studies we investigated endothelium-dependent and -independent vessel function of ATGL knockout mice. Aortic relaxation studies and Langendorff perfusion experiments of isolated hearts showed that ATGL knockout mice suffer from pronounced micro- and macrovascular endothelial dysfunction. Experiments with agonists directly targeting vascular smooth muscle cells revealed the functional integrity of the smooth muscle cell layer. Loss of vascular reactivity was restored ~50% upon treatment of ATGL knockout mice with the PPARα agonist Wy14,643, indicating that this phenomenon is partly a consequence of impaired cardiac contractility. Biochemical analysis revealed that aortic endothelial NO synthase expression and activity were significantly reduced in ATGL deficiency. Enzyme activity was fully restored in ATGL mice treated with the PPARα agonist. Biochemical analysis of perivascular adipose tissue demonstrated that ATGL knockout mice suffer from perivascular inflammatory oxidative stress which occurs independent of cardiac dysfunction and might contribute to vascular defects. Our results reveal a hitherto unrecognized link between disturbed lipid metabolism, obesity and cardiovascular disease.

Urocortin induced expression of COX-2 and ICAM-1 via corticotrophin-releasing factor type 2 receptor in rat aortic endothelial cells

BACKGROUND AND PURPOSE

Our previous study showed that urocortin (Ucn1) exacerbates the hypercoagulable state and vasculitis in a rat model of sodium laurate-induced thromboangiitis obliterans. Furthermore, the inflammatory molecules COX-2 and ICAM-1 may participate in this effect. In the present study, the effects of Ucn1 on COX-2 and ICAM-1 expression in lipopolysaccharide (LPS)-induced rat aortic endothelial cells (RAECs) were investigated and the mechanisms involved explored.

EXPERIMENTAL APPROACH

RAECs were isolated from adult male Wistar rats, and identified at the first passage. Experiments were performed on cells, from primary culture, at passages 5-8. The expression of COX-2 and ICAM-1 at both mRNA and protein levels was determined by semi-quantitative RT-PCR and Western blot analysis. Levels of PGE(2) and soluble ICAM-1 (sICAM-1) in culture medium were measured by enzyme-linked immunosorbent assay. Furthermore, the phosphorylation status of p38MAPK, ERK1/2, JNK, Akt and NF-kappaB was analysed by Western blot; nuclear translocation of NF-kappaB was observed by immunofluorescence.

KEY RESULTS

Ucn1 augmented LPS-induced expression of COX-2 and ICAM-1 in RAECs in a time- and concentration-dependent manner. Ucn1 increased PGE(2) and sICAM-1 levels. These effects were abolished by the CRF(2) receptor antagonist, antisauvagine-30, but not by the CRF(1) receptor antagonist, NBI-27914. Moreover, Ucn2 activated p38MAPK and augmented NF-kappaB nuclear translocation and phosphorylation, whereas ERK1/2, JNK and Akt pathways were not involved in this process.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that Ucn1 exerts pro-inflammatory effects by augmenting LPS-induced expression of COX-2 and ICAM-1 in RAECs via CRF(2) receptors and the activation of p38MAPK and NF-kappaB.

A method of isolation and culture of microvascular endothelial cells from mouse skin

OBJECTIVES

The study of isolated microvascular endothelial cells from mice has long been impeded due to the many difficulties encountered in isolating and culturing these cells. We focused on developing a method to isolate microvascular endothelial cells from the skin fragments of newborn mice. We also aimed at establishing optimal culture conditions to sustain the growth of these cells.

METHODS AND RESULTS

Isolation of murine dermal microvascular endothelial cells (mDMEC) from P3 newborn mice was based first on enzymatic separation of the skin epidermal layer from the dermis using dispase and then on disaggregating dermal cellular elements using collagenase. The cells obtained from the dermis were subjected to a continuous density gradient centrifugation. Cells situated between densities 1.033 and 1.047 were then cultured on collagen IV-coated culture flasks using optimized growth culture conditions. Cells were characterized by endothelial appearance and by the presence and genetic expression of endothelial markers like CD31, NOS3, VEGFR-2 and Tie-2. Uptake of acetylated low-density lipoprotein (Ac-LDL) was used as a functional assay.

CONCLUSIONS

The methodology described herein for isolation and culture of murine microvascular endothelium offers a distinctive advantage for those using mouse models to study endothelial cell biology.

Outer Membrane Vesicles FromPorphyromonas gingivalisAffect the Growth and Function of Cultured Human Gingival Fibroblasts and Umbilical Vein Endothelial Cells

BACKGROUND

The purpose of this study was to examine the effects of outer membrane vesicles (OMV) obtained from Porphyromonas gingivalis (Pg) on the growth and function of human gingival fibroblasts (HGF) and human umbilical vein endothelial cells (HUVEC).

METHODS

OMV were obtained from a cell-free growth medium of Pg ATCC 33277 by 40% NH2SO4 precipitation and ultracentrifugation. Cell proliferation was measured by 3H-thymidine incorporation into growing HGF and HUVEC. Endothelial cell function was determined by their capacity to form a network of capillary tubes on an extracellular matrix (ECM).

RESULTS

Proliferating HGF and HUVEC demonstrated a significant dose-dependent inhibition of 3H-thymidine uptake when cultured with 0 to 40 microg/ml of OMV protein. HGF and HUVEC showed an IC50 of growth of about 9.0 microg/ml and 4.5 microg/ml of OMV protein, respectively. Capillary tube formation by HUVEC cultured on an ECM was suppressed by 70% to 80% with 5 microg/ml OMV protein after 18 hours of incubation. The presence of proteolytic enzymes in the OMV did not contribute to capillary tube disruption, since blocking enzyme activity with specific inhibitors did not reduce the suppression of capillary tube formation. After heating at 90 degrees C for 5 minutes, OMV significantly lost their capacity to suppress capillary tube formation.

CONCLUSIONS

OMV significantly inhibit the proliferation of cultured HGF and HUVEC in a dose-dependent manner. OMV suppressed the capillary tube formation by cultured HUVEC. The factor(s) appeared to be a protein and not endotoxin because its inhibitory activity was markedly reduced by heat inactivation. These studies suggest that OMV contribute to chronic periodontitis by suppressing cell proliferation and revascularization in periodontal tissues.

Inosculation of tissue-engineered capillaries with the host's vasculature in a reconstructed skin transplanted on mice

The major limitation for the application of an autologous in vitro tissue-engineered reconstructed skin (RS) for the treatment of burnt patients is the delayed vascularization of its relatively thick dermal avascular component, which may lead to graft necrosis. We have developed a human endothelialized reconstructed skin (ERS), combining keratinocytes, fibroblasts and endothelial cells (EC) in a collagen sponge. This skin substitute then spontaneously forms a network of capillary-like structures (CLS) in vitro. After transplantation to nude mice, we demonstrated that CLS containing mouse blood were observed underneath the epidermis in the ERS in less than 4 days, a delay comparable to our human skin control. In comparison, a 14-day period was necessary to achieve a similar result with the non-endothelialized RS. Furthermore, no mouse blood vessels were ever observed close to the epidermis before 14 days in the ERS and the RS. We thus concluded that the early vascularization observed in the ERS was most probably the result of inosculation of the CLS network with the host's capillaries, rather than neovascularization, which is a slower process. These results open exciting possibilities for the clinical application of many other tissue-engineered organs requiring a rapid vascularization.

Human dermal microvascular endothelial cells form vascular analogs in cultured skin substitutes after grafting to athymic mice

Cultured skin substitutes (CSS) consisting of autologous fibroblasts and keratinocytes combined with biopolymers are an adjunctive treatment for large excised burns. CSS containing two cell types are limited by anatomical deficiencies, including lack of a vascular plexus, leading to slower vascularization after grafting than split-thickness autograft. To address this limitation, CSS were prepared containing human keratinocytes, fibroblasts, and dermal microvascular endothelial cells (HDMEC) isolated from a single skin sample. After 16 days in culture, control CSS and CSS containing HDMEC (CSS+EC) were grafted to full-thickness wounds in athymic mice. In CSS+EC in vitro, HDMEC persisted in the dermal substitutes and formed multicellular aggregates. One wk after grafting, HDMEC in CSS+EC organized into multicellular structures, some containing lumens. By 4 wk after grafting, HDMEC were found in linear and circular organizations resembling vascular analogs associated with basement membrane deposition. In some cases, colocalization of HDMEC with mouse perivascular cells was observed. The results demonstrate HDMEC transplantation in a clinically relevant cultured skin model, persistence of HDMEC after grafting, and HDMEC organization into vascular analogs in vitro and in vivo. All cells were derived from the same donor tissue, indicating the feasibility of preparing CSS containing autologous HDMEC for grafting to patients.

Rho and rho kinase modulation of barrier properties: cultured endothelial cells and intact microvessels of rats and mice

Previous experiments using cultured endothelial monolayers indicate that Rho-family small GTPases are involved in modulation of endothelial monolayer permeability by regulating assembly of the cellular actin filament scaffold, activity of myosin-based contractility and junctional distribution of the Ca2+-dependent endothelial cell adhesion molecule, VE-cadherin. We investigated these mechanisms using both cultured endothelial cells (from porcine pulmonary artery and mouse heart) and vascular endothelium in situ (mouse aorta, and individually perfused venular microvessels of mouse and rat mesentery). Exposure to Clostridium difficile toxin B (100 ng x ml(-1)) inactivated 50-90% of all endothelial Rho proteins within 60-90 min. This was accompanied by considerable reduction of actin filament stress fibres and junctional F-actin in cultured endothelial monolayers and in mouse aortic endothelium in situ. Also, VE-cadherin became discontinuous along endothelial junctions. Inhibition of Rho kinase with Y-27632 (30 microM) for 90-120 min induced F-actin reduction both in vitro and in situ but did not cause redistribution or reduction of VE-cadherin staining. Perfusion of microvessels with toxin B increased basal hydraulic permeability (L(p)) but did not attenuate the transient increase in L(p) of microvessels exposed to bradykinin. Perfusion of microvessels with Y-27632 (30 microM) for up to 100 min reduced basal L(p) but did not attenuate the permeability increase induced by platelet activating factor (PAF) or bradykinin. These results show that toxin B-mediated reduction of endothelial barrier properties is due to inactivation of small GTPases other than RhoA. Rho proteins as well as RhoA-mediated contractile mechanisms are not involved in bradykinin- or PAF-induced hyperpermeability of intact microvessels.

Cyclic AMP and acidic fibroblast growth factor have opposing effects on tight and adherens junctions in microvascular endothelial cells in vitro

Endothelial adherens junctions (AJ) and tight junctions (TJ) are important determinants of vascular permeability and cell morphology. Here, we investigate their regulation, in primary human placental microvascular endothelial cell (HPMEC) cultures, by either aFGF plus heparin (ECGS) or elevated cAMP. The proliferation of HPMEC was weakly stimulated by ECGS, while cAMP was inhibitory. ECGS had little effect on transendothelial resistance (TER), but increased macromolecular permeability, whereas cAMP induced a twofold increase in TER and reduced macromolecular permeability. Ultrastructurally, ECGS-treated HPMEC exhibited an "activated" phenotype typified by proliferating cells, with poorly organized cell-cell junctions, whereas cAMP-treated cells appeared quiescent and markedly flattened with extended paracellular junctions, resembling endothelium in situ. The expression and localization of junctional molecules, F-actin, and junctional phosphotyrosine were examined by confocal microscopy and immunoblotting. Junctional molecules in ECGS-treated cells were less organized at lateral membranes than in control cells, whereas in cAMP-treated cells, they were highly localized at continuous contacts. These differences correlated with the intensity of junctional phosphotyrosine, being lowest with cAMP treatment. In the AJ of ECGS-treated and control cells, beta-catenin predominated but in cAMP-treated cells, gamma-catenin/plakoglobin was enriched. In addition, cAMP upregulated junctional expression of VE-cadherin and PECAM-1 and increased the levels of the TJ molecules occludin and ZO-1. The expression levels of junctional components, and their tyrosine phosphorylation, play an important role in dynamic regulation of endothelial cell-cell junctions.

Differential expression of nitric oxide by dermal microvascular endothelial cells from patients with scleroderma

Vascular abnormalities in scleroderma are fundamental to the pathogenesis of this disease. The objective of this study was to characterize dermal microvascular endothelial cells (DMEC) isolated from scleroderma patients with respect to growth and expression of the constitutive form of endothelial nitric oxide synthase (eNOS). DMEC from patients with both systemic sclerosis (SSc) and localized scleroderma (Loc Scl) contained small intact microvascular structures in contrast to single cell isolations obtained from control skin. Immunoaffinity selection on anti-PECAM-1 beads yielded pure populations of DMEC expressing normal markers. While the morphology and initial growth of SSc DMEC closely paralleled control cells, the growth of SSc DMEC decreased with time in culture (doubling time of 3 days vs. 5 days). Expression of ecNOS mRNA was reduced in both Loc Scl and SSc as shown by semi-quantitative RT-PCR (p < 0.001). Western blots showed variable but generally lower ecNOS protein levels and decreased levels of nitrogen oxides in media were found from both SSc and Loc Scl relative to control cells. The results indicate an intrinsic defect in the mechanism of nitric oxide production in DMEC isolated from scleroderma patients and suggest its possible involvement in the pathophysiology of scleroderma.

Human macrovascular endothelial cells: optimization of culture conditions

The purpose of this study is to identify optimal culture conditions to support the proliferation of human macrovascular endothelial cells. Two cell lines were employed: human saphenous vein endothelial cells (HSVEC) and human umbilical vein endothelial cells (HUVEC). The influence of basal nutrient media (14 types), fetal bovine serum (FBS), and mitogens (three types) were investigated in relation to cell proliferation. Additionally, a variety of extracellular matrix (ECM) substrate-coated culture dishes were also tested. The most effective nutrient medium in augmenting cell proliferation was MCDB 131. Compared to the more commonly used M199 medium, MCDB 131 resulted in a 2.3-fold increase in cell proliferation. Media containing 20% FBS increased cell proliferation 7.5-fold compared to serum-free media. Among the mitogens tested, heparin (50 microg/ml) and endothelial cell growth supplement (ECGS) (50 microg/ml) significantly improved cell proliferation. Epithelial growth factor (EGF) provided no improvement in cell proliferation. There were no statistical differences in cell proliferation or morphology when endothelial cells were grown on uncoated culture plates compared to plates coated with ECM proteins: fibronectin, laminin, gelatin, or collagen types I and IV. The culture environment yielding maximal HSVEC and HUVEC proliferation is MCDB 131 nutrient medium supplemented with 2 mM glutamine, 20% FBS, 50 microg/ml heparin, and 50 microg/ml ECGS. The ECM substrate-coated culture dishes offer no advantage.

Membrane-type matrix metalloproteinases in human dermal microvascular endothelial cells: expression and morphogenetic correlation

Membrane-type matrix metalloproteinases (MT-MMP) activate the zymogen form of MMP-2/Gelatinase A on cell surfaces and are expressed in invasive tumors. We sought to identify and characterize MT-MMP in a non-malignant cell type that undergoes a physiologic and reversible invasive phenotype during angiogenesis. Human dermal microvascular endothelial cells (HDMEC) were isolated from neonatal tissue and purified by anti-CD31 (PECAM) affinity beads. MT-MMP-1 and -3 transcripts were amplified by reverse transcriptase-polymerase chain reaction and northern blots showed a single 4.5 kB mRNA for MT-MMP-1 that was modulated by angiogenic factors and phorbol ester. Immunoblotting of reduced cellular extracts with different MT-MMP-1 antibodies showed the presence of the 63-65 kDa and 57-60 kDa forms, as well as additional forms at lower molecular weights. HDMEC membranes extracted with Triton X114 were incubated with gelatin-sepharose purified MMP-2 and MMP-9 to show activation of proenzymes. Pre-incubation of HDMEC with anti-MT-MMP-1 antibodies decreased proMMP-2 conversion activity only. The movement of HDMEC and the formation of tubule-like structures in three-dimensional collagen gels was markedly delayed by preincubation with the same anti-MT-MMP-1 antibodies. These results demonstrate the presence of MT-MMP in cutaneous microvascular cells in vitro. Modulation of these cell surface proteinases by angiogenic factors, demonstration of multiple processed forms, and specific attenuation of HDMEC morphogenetic patterns in three-dimensional collagen gels implicate their potential roles in the formation of new blood vessels in the skin.

Fluorescence activated cell sorting: a reliable method in tissue engineering of a bioprosthetic heart valve

BACKGROUND

Techniques of tissue engineering are used to seed human autologous cells in vitro on degradable mesh to create new functional tissue like a bioprosthetic heart valve. A precondition is subsequent seeding of native-valve-analogous pure endothelial and myofibroblast cell lines. The aim of this study is to find a safe method of isolating viable cell lines out of tissues from the operating room.

METHODS

Mixed cells from ascending aorta obtained from the operating room were incubated with an endothelial-specific fluorescent marker. The labeled cells were activated and sorted by flow cytometry. Isolated cell lines were cultured and thereafter square sheets of polymeric scaffold were seeded with myofibroblasts, followed by endothelial cells. The created tissue was stained with hematoxylin and eosin, van Gieson stain, and stains for factor VIII and CD34.

RESULTS

Control culture samples (n = 25) revealed vital uncontaminated endothelial and myofibroblast cell lines. Microscopy of the seeded meshes (n = 16) demonstrated a tissue-like structure. Van Gieson stain showed production of collagen. Endothelial cells formed a superficial monolayer, demonstrated by factor VIII and CD34; no invasive formation of capillaries was detectable.

CONCLUSIONS

These results demonstrate that fluorescence activated cell sorting is a reliable and safe method to gain pure vital autologous cell lines out of human mixed cells for subsequent seeding on degradable mesh and that those cells are active to form new tissue.

Granulocytes enhance adhesion of peripheral blood mononuclear cells to dermal endothelial cells

Interactions of all major peripheral blood leukocytes were studied during adhesion to human dermal microvascular endothelial cells (HDMEC). Simultaneous quantification of distinct leukocytic cell populations was carried in a recently established adhesion assay followed by FACS analysis. Adhesion of stimulated peripheral blood mononuclear cells (PBMC) was enhanced in the presence of granulocytes compared to adhesion of PBMC alone. This effect required direct cell-cell contact as granulocyte supernatant in the absence of granulocytes failed to yield the same extent of PBMC adhesion. Quantification of the common leukocyte beta2-integrin subunit (CD18) and the common leukocyte beta1-integrin subunit (CD29) as well as blocking with anti-CD18 antibodies revealed no differences between PBMC adhering alone or in company of granulocytes to HDMEC. Blocking E-selectin, however affected 'mixed' (i.e., PBMC in the presence of granulocytes) adhesion more profoundly than 'single' adhesion of PBMC. HDMEC subjected to 'mixed' leukocyte cell adhesion expressed E-selectin at 24 h after cytokine stimulation, while HDMEC without contact to leukocytes did no longer express E-selectin at this time. In conclusion, functionally diverse peripheral blood leukocytes can interact in order to enhance cell adhesion without up-regulation of leukocytic integrin expression via an E-selectin dependent mechanism.

A simple immunomagnetic protocol for the selective isolation and long-term culture of human dermal microvascular endothelial cells

Endothelial cells involved in tumor angiogenesis, wound healing, and inflammation are predominantly of microvascular origin and are functionally distinct from large vessel-derived endothelial cells which have been largely used for in vitro vascular research. To overcome the problems commonly involved in the culture of microvascular endothelial cells, including unreliable isolation techniques and low cell yields, we developed a simplified protocol for the selective cultivation of human dermal microvascular endothelial cells (HDMEC) obtained from neonatal foreskins, based on the transient, endothelial cell-specific induction of E-selection by tumor necrosis factor-alpha (TNF-alpha). Subconfluent primary cultures, consisting of a mixture of endothelial cells, fibroblasts, and keratinocytes, were treated with TNF-alpha for 6 h, and HDMEC were isolated by their selective binding to magnetic beads coupled with anti-E-selection monoclonal antibody. After two immunomagnetic purification steps, a homogenous population of HDMEC was obtained which showed typical cobblestone morphology, expressed CD31 and von Willebrand factor, proliferated in response to vascular endothelial growth factor, upregulated the expression of intercellular adhesion molecule-1 and vascular adhesion molecule-1 in response to TNF-alpha, and formed capillary-like tubes in a three-dimensional collagen type I matrix. This simple technique may facilitate a more widespread use of microvascular endothelial cell cultures obtained from different human or animal organs for functional in vitro studies.

Vascular activation of adhesion molecule mRNA and cell surface expression by ionizing radiation

During cutaneous inflammatory reactions the recruitment of circulating leukocytes into the tissue critically depends on the regulated expression of endothelial cell adhesion molecules (CAMs). Various proinflammatory stimuli upregulate endothelial CAMs, including cytokines and UV irradiation. We have investigated the effects of ionizing radiation (IR) on endothelial CAM expression. Organ cultures of normal human skin as well as cultured human dermal microvascular endothelial cells (HDMEC) were exposed to IR. Expression of three major endothelial CAMs was studied in skin organ cultures by immunohistochemistry and in cell culture by Northern blot analysis and flow cytometry. In skin organ cultures vascular immunoreactivity for ICAM-1, E-selectin, and VCAM-1 was strongly induced 24 h after exposure to 5 or 10 Gy of IR, while immunoreactivity for CD31/PECAM-1, a constitutively expressed endothelial cell adhesion molecule, remained unchanged. In cultured HDMEC IR upregulated ICAM-1, VCAM-1, and E-selectin mRNAs and cell surface expression in a time- and dose-dependent fashion. Cellular morphology and viability remained unaltered by IR up to 24 h postirradiation. This study characterizes microvascular activation of adhesion molecule expression in response to ionizing radiation in a clinically relevant IR dose range. The findings also underscore the ability of endothelial cells to integrate environmental electromagnetic stimuli.

Adhesion of leukocytes to dermal endothelial cells is induced after single-dose, but reduced after repeated doses of UVA

Approximately 20-50% of ultraviolet A (UVA) irradiation delivered to the skin surface may reach the human dermal microvascular endothelial cells (HDMEC) that play a pivotal role in cellular inflammatory tissue; however, the pathophysiologic role of HDMEC in UVA-induced skin changes is largely unknown. Based on previous in vivo and in vitro studies revealing UVA-induced expression of endothelial adhesion molecules, we studied isolated HDMEC under various conditions in order to further delineate the impact of UVA on these cells. The expression of cell adhesion molecules was determined by flow cytometry and the resulting changes of stable adhesion of leukocytes to endothelial cells were quantitated for granulocytes, lymphocytes, and monocytes using a newly developed multicellular adhesion assay. Additionally, antibody blocking experiments were performed to delineate the role of individual cell adhesion molecules in UVA-induced leukocyte adherence. High-dose polychromatic UVA (25 J per cm2, maximal emission at 375 nm) induced intercellular adhesion molecule-1 and E-selectin with different kinetics but correlating the adhesion of leukocyte subsets. This effect subsided, however, in the course of 3-6 daily applied UVA doses. Moreover, pro-inflammatory cytokine challenge by tumor necrosis factor-alpha and interleukin-1-alpha resulted in significantly weaker induction of intercellular adhesion molecule-1 and E-selectin in repeatedly UVA-exposed HDMEC. Differential quantitation of peripheral blood derived granulocytes, lymphocytes, and monocytes revealed reduced adhesion particularly of lymphocytes followed by monocytes and granulocytes compared with leukocyte adhesion to nonirradiated but cytokine-stimulated HDMEC. It is concluded that UVA substantially influences endothelial cell adhesion molecules expression and thus directly interferes with leukocyte adhesion to endothelial cells. Divergent UVA-induced effects in this respect can be attributed to the mode of UV exposure as well as to the condition of endothelial cells prior to UVA exposure.

Interleukin-10 induces E-selectin on small and large blood vessel endothelial cells

In vitro, expression of E-selectin is largely restricted to endothelial cells activated by inflammatory cytokines. Under activated conditions, cytokines such as interleukin (IL) 10, released by keratinocytes in large quantities, may also increase the expression of E-selectin on the dermal microvasculature. The aim of the present study was to investigate the expression of E-selectin on cultured human dermal microvascular endothelial cells (HDMEC) isolated from neonatal foreskins when exposed to IL-10. Expression of E-selectin was determined by immunofluorescence microscopy, FACS analysis, an HL-60 cell-binding assay, and quantitative polymerase chain reaction (PCR) analysis. For comparison with large blood vessel cells, the expression of E-selectin on human umbilical vein endothelial cells (HUVEC) was also determined in parallel by FACS and reverse transcriptase-PCR analysis under identical conditions. These studies demonstrate that IL-10 induces the expression of E-selectin on both HDMEC and HUVEC and that the level of expression of HDMEC is comparable with that induced by IL-1 beta and tumor necrosis factor-alpha. When HL-60 cells are incubated with HDMEC pretreated with IL-10, a consistent increase in adherence of HL-60 to endothelial cells is observed. This adherence was found to be mediated by L-selectin. PCR analysis and the quantification of E-selectin cDNA by a novel, highly sensitive and specific PCR-immunoassay demonstrate the induction of E-selectin mRNA at the transcriptional level. The induction of the expression of E-selectin by IL-10 on HDMEC may provide additional insights into the pathogenic mechanism of neutrophil accumulation at the site of inflammation in inflammatory skin diseases.

Differential activation of protein kinase C isozymes by phorbol ester and collagen in human skin microvascular endothelial cells

Human dermal microvascular endothelial cells participate in activities including inflammation, wound healing, and angiogenesis (neovascularization). Two stages of angiogenesis can be mimicked in vitro by two models of cultured foreskin human dermal microvascular endothelial cells: the differentiation of epithelioid endothelial cells to spindle-shaped mesenchymal-like cells induced by phorbol ester treatment; and the formation of vascular channels induced by exposing the luminal surface of endothelial cell monolayers to type I collagen gels. The mechanisms underlying these two processes, however, are largely unknown. Protein kinase C isozymes, which are activated by phorbol esters, are important mediators in the angiogenic process. In the current work, we identified the protein kinase C isozymes present in human dermal microvascular endothelial cells and determined which of the isozymes are activated in response to phorbol ester or to collagen treatments. Using western blot analysis, we found that microvascular endothelial cells contain at least six protein kinase C isozymes (alpha, beta, delta, epsilon, zeta, eta). Immunocytochemical studies demonstrated that the isozymes are located in distinct cellular compartments and that following treatment with phorbol 12-myristate 13-acetate or with a collagen gel overlay, most isozymes (protein kinase C alpha, beta1, betaII, delta, epsilon, eta) translocated to different parts of the cell. Moreover, for two of these isozymes (betaII and eta), the localization differs after phorbol 12-myristate 13-acetate treatment as compared with collagen treatment. These results demonstrate that agents that mimic two stages in the angiogenic process in vitro initiate diverse changes in the subcellular localization of specific protein kinase C isozymes and suggest a role for different isozymes in this process.

Novel fibroblast-specific monoclonal antibodies: properties and specificities

Specific detection of fibroblasts has been one of the unsolved problems in cell biology. Because monoclonal antibodies (MoAbs) might provide an easy and reproducible method of fibroblast detection, we have produced a panel of MoAbs raised against cell surface proteins of human dermal fibroblasts. Using flow cytometry and immunohistochemistry, we have shown that two of these MoAbs, FibAS01 and FibAS02, react exclusively with human fibroblasts. They do not react in vitro with human keratinocytes, endothelial cells, or blood cells. Immunohistologic experiments investigating the binding pattern of the MoAbs FibAS01 and FibAS02 in cryostat sections of different tissues confirmed the flow cytometric results. In human skin, the antibodies exclusively labeled fibroblasts. In other human tissues such as lymph nodes, placenta, kidney, muscle, thyroid gland, gall bladder, cartilage, and tendon, the specificity for fibroblasts was borne out. Neither antibody reacts with fibroblasts from mouse, rat, or pig. The isotype was defined as an IgG1 for both. By western blot analysis, both antibodies detected a molecule of 60-65 kDa under reducing and nonreducing conditions. By immunoelectron microscopy, we observed the antigens on the cell surface without any clustering at specific sites. These data demonstrate that the two MoAbs, FibAS01 and FibAS02, exclusively recognize human fibroblasts.

Transforming growth factor-beta controls cell-matrix interaction of microvascular dermal endothelial cells by downregulation of integrin expression

Transforming growth factor-beta (TGF-beta) is a pleiotropic regulatory factor of tissue remodeling. Angiogenesis, a prerequisite of tissue repair and tissue expansion, is induced by TGF-beta in vivo, while proliferation and migration of cultured endothelial cells are inhibited by TGF-beta. Indirect mechanisms stimulating angiogenesis and modification of TGF-beta effects by cell-matrix interaction have been postulated to account for this paradigm. Because cellular behavior in tissue remodeling is decisively determined by cell-matrix interactions, which in turn is mediated via integrins, we investigated the effect of TGF-beta on matrix-dependent endothelial cell functions. Integrin expression of human dermal microvascular endothelial cells (HDMEC) was measured by Northern blot and fluorescence-activated cell sorter analysis after TGF-beta treatment and correlated to cell-matrix interactions, which were studied in a colorimetric cell attachment assay as well as the Boyden chamber chemotaxis assay. We found a cell-specific downregulation of integrin expression in HDMEC on the level of mRNA as well as on the cell surface. This effect correlated well with the reduction of integrin-dependent cell adhesion to several matrix proteins, in particular to fibronectin. Moreover, TGF-beta decreased fibronectin-induced chemotaxis of HDMEC. Thus, TGF-beta controls cell-matrix interaction of HDMEC by down-regulation of integrin expression. This effect of TGF-beta reflects direct and cell-specific control mechanisms on microvascular cells that may be critical for the coordinated process of angiogenesis requiring a balance of stimulatory and inhibitory factors.

Isolation and characterization of brain microvascular endothelial cells from Saimiri monkeys. An in vitro model for sequestration of Plasmodium falciparum-infected erythrocytes

The adhesion of parasitized red blood cells (PRBC) to the endothelium (sequestration) may contribute to the pathogenic events in severe human malaria caused by P. falciparum. However, the factors involved in the pathophysiology, especially cerebral malaria are poorly understood. Previously, we have shown that the squirrel monkey Saimiri sciureus is a potential model for human cerebral malaria. In this paper we describe five stable clones of endothelial cell lines isolated immediately postmortem from different regions of the brain of Saimiri monkeys. The endothelial cell characteristics of these clones were confirmed by analyzing their ultrastructural aspects by transmission electron microscopy and by immunodetection of various endothelial cell markers. The Saimiri brain endothelial cell clones (SBEC) varied in their expression of different surface molecules. For example, various combinations of receptors involved in P. falciparum PRBC adherence such as CD36, ICAM-1 and E-selectin, were expressed at baseline values and could be up-regulated by human srTNF-alpha and human srIFN-gamma. One of the SBEC clones showed a strong cytoadherence for various laboratory strains of P. falciparum despite the absence of surface expression of any of the known endothelial receptors implicated in PRBC adherence. This finding suggests the existence of a new and uncharacterized PRBC binding receptor. The use of target organ specific endothelial cell lines expressing a number of different potential P. falciparum PRBC cytoadherence receptors, will be a useful in vitro system for the evaluation of strategies for the development of vaccine and antimalarial drugs to prevent human cerebral malaria.

A method for the isolation and serial propagation of keratinocytes, endothelial cells, and fibroblasts from a single punch biopsy of human skin

When multiple types of cells from normal and diseased human skin are required, techniques to isolate cells from small skin biopsies would facilitate experimental studies. The purpose of this investigation was to develop a method for the isolation and propagation of three major cell types (keratinocytes, microvascular endothelial cells, and fibroblasts) from a 4-mm punch biopsy of human skin. To isolate and propagate keratinocytes from a punch biopsy, the epidermis was separated from the dermis by treatment with dispase. Keratinocytes were dissociated from the epidermis by trypsin and plated on a collagen-coated tissue culture petri dish. A combination of two commercial media (Serum-Free Medium and Medium 154) provided optimal growth conditions. To isolate and propagate microvascular endothelial cells from the dermis, cells were released following dispase incubation and plated on a gelatin-coated tissue culture dish. Supplementation of a standard growth medium with a medium conditioned by mouse 3T3 cells was required for the establishment and growth of these cells. Epithelioid endothelial cells were separated from spindle-shaped endothelial cells and from dendritic cells by selective attachment to Ulex europeus agglutinin I-coated paramagnetic beads. To establish fibroblasts, dermal explants depleted of keratinocytes and endothelial cells were attached to plastic by centrifugation, and fibroblasts were obtained by explant culture and grown in Dulbecco's modified Eagle's medium (DMEM) containing fetal bovine serum (FBS). Using these isolation methods and growth conditions, two confluent T-75 flasks of keratinocytes, one confluent T-25 flask of purified endothelial cells, and one confluent T-25 flask of fibroblasts could be routinely obtained from a 4-mm punch biopsy of human skin.(ABSTRACT TRUNCATED AT 250 WORDS)

Ultraviolet-A radiation induces adhesion molecule expression on human dermal microvascular endothelial cells

Ultraviolet radiation is capable of inducing numerous skin reactions. Considerable amounts of UVA radiation penetrate the epidermis and reach the microvascular endothelium of the papillary dermis. In order to investigate putative direct effects of UV radiation on endothelial cells, we studied adhesion molecule expression by immunostaining procedures and FACS analysis, following irradiation of normal human skin and cultured human dermal endothelial cells. Enhanced immunostaining for ICAM-1 and E-selectin was detected in biopsies taken after in vivo UVA and UVB irradiation, compared with non-irradiated control skin. On cultured human dermal endothelial cells, however, ICAM-1 and E-selectin were inducible by UVA but not UVB. The induction was dose-dependent, peaking at 20 J/cm2 for both adhesion molecules, and time-dependent, peaking after 6 and 24 h for E-selectin and ICAM-1, respectively. Expression of VCAM-1 and PECAM/EndoCAM/CD31 was unaffected by any UV-radiation modality. The functional integrity of irradiated cells was monitored by an exclusion assay of the fluorescent dye 7-AAD, and by staining for the cytoskeletal proteins actin and vimentin. Our results demonstrate that dermal microvascular endothelial cells are a critical and direct target of UVA, and suggest they may play a pivotal role in UV-induced inflammatory skin conditions.

Histamine-modulated transdifferentiation of dermal microvascular endothelial cells

Homeostatic and inflammatory functions of skin microvessels are tightly regulated by vasoactive amines. Following stimulation with histamine, dermal microvascular endothelial cells (MEC) undergo a rapid change in phenotype (transdifferentiation) and subsequently exhibit an enhanced rate of growth. To elucidate mechanisms regulating MEC transdifferentiation, this study investigated the functional relationships among vimentin, Ca2+, and protein kinase C (PKC) in histamine-modulated dermal MEC in vitro. Distribution of vimentin and PKC in foreskin-derived MEC cultivated in a modified Iscove's medium was assessed with immunocytochemistry. Calcium ion kinetics in histamine-treated MEC were analyzed using the Ca2+ probe Fluo-3 in conjunction with interactive laser cytometry. Histamine, acting through H-1 receptors, produces a rapid (less than 100 ms) and differential elevation of free calcium in each of three cytological compartments defined by the vimentin cytoskeleton in epithelial MEC. A distinctive compartmentalized and nonuniform distribution of PKC precisely coincides with that observed for free-Ca2+ released in response to histamine. The studies reveal that histamine modulation of the MEC phenotype is associated with a rapid patterned reorganization of the vimentin skeleton. It is hypothesized that histamine induces vimentin post-translational modifications by activating a spatially localized interaction among cytoplasmic free Ca2+, PKC, and the vimentin matrix. The results further suggest that vimentin, in addition to its structural role, may participate in signal transduction and gene regulation processes in effecting MEC transdifferentiation.

Transforming growth factor-beta differentially regulates the adhesiveness of normal and psoriatic dermal microvascular endothelial cells for peripheral blood mononuclear cells

Lymphocytes adhere to dermal microvascular endothelial cells (DMEC) as the first step in their migration from the bloodstream into diseased skin. Psoriasis is characterized by an intense T-lymphocytic infiltrate in the dermis, which may be a consequence of the abnormal regulation of endothelial adhesiveness by cytokines released locally. In the present study, we investigated the effects of tumor necrosis factor-alpha (TNF), interleukin-1 (IL-1), IL-4, and transforming growth factor-beta 1 (TGF-beta) on the adhesiveness of DMEC isolated from psoriatic plaques or normal skin for human peripheral blood mononuclear cells (PBMC). The results showed that DMEC from both normal and psoriatic skin retain the capacity to adhere to 51Cr-labeled PBMC. Pretreatment of DMEC from normal skin with human recombinant IL-1 or TNF alone or in combination for 8 h significantly (p less than 0.01) enhanced their capacity to adhere to human PBMC. Similarly, treatment of normal DMEC with IL-4 also increased endothelial adhesiveness, although this cytokine required an incubation period of 24 h. In parallel studies, DMEC from psoriatic plaques were found to respond to the stimulatory effects of TNF, IL-1, and IL-4 in similar dose- and time-dependent manner. In contrast, although pretreatment of normal DMEC with TGF-beta (0.1 to 0.25 ng/ml) for 6 to 12 h significantly reduced (p less than 0.01) both the unstimulated and IL-1- and TNF-stimulated endothelial adhesiveness for normal PBMC, TGF-beta had no effect on the binding of unstimulated or cytokine-stimulated psoriatic DMEC to PBMC, even at concentrations as high as 2 ng/ml and incubation period of 36 h. These results suggest that cytokines stimulate the adhesiveness of DMEC through distinct pathways and provide evidence that TGF-beta may play an important regulatory role in the control of lymphocyte extravasation into normal skin. The altered responsiveness of psoriatic DMEC to TGF-beta may contribute to the intense dermal lymphocytic infiltrates in psoriasis.

Transforming growth factor-beta regulates the adhesive interactions between mononuclear cells and microvascular endothelium

Adhesion of leukocytes to the vascular endothelium is essential for the movements of cells from the bloodstream into inflammatory sites. In the present study, dermal microvascular endothelial cells (DMEC) isolated from normal porcine skin retained the capacity to adhere 51Cr-labeled porcine peripheral blood mononuclear cells (PBMC), nylon-wool-purified T cells, and isolated monocytes. Transforming growth factor-beta 1 (TGF-beta) decreased the capacities of DMEC to support the adhesion of these cells in a dose-dependent manner. Maximal inhibition was observed with a TGF-beta dose of 0.25 ng/ml and an incubation time of 6-12 h. TGF-beta did not affect the morphology of DMEC and had no adverse effect on the viability of the treated cells. The blocking effects of TGF-beta on PBMC adhesion to DMEC was neutralized by a polyclonal turkey anti-TGF-beta antiserum but not by control turkey serum. Although pretreatment of PBMC with TGF-beta decreased the capacity of these cells to adhere to normal DMEC monolayers, kinetic studies demonstrated that these effects required between 4 and 8 h incubation time. In addition, preincubation of DMEC with TGF-beta completely blocked their response to the stimulating effects of TNF-alpha, IL-1-beta, or both cytokines. Furthermore, TGF-beta also abrogated the enhanced adhesiveness of DMEC pretreated with TNF-alpha and IL-1-beta. These findings suggest that TGF-beta may play an important role in the down-regulation of inflammatory responses by decreasing vascular endothelial adhesiveness for mononuclear cells and monocytes.

Isolation and purification of microvascular endothelium from human decidual tissue in the late phase of pregnancy

Normal pregnancy demands significant structural and physiologic adaptations of the uterine microvasculature, to facilitate adequate placentation. In pregnancies complicated by pregnancy-associated hypertension (preeclampsia), this process is defective, resulting in a high incidence of intrauterine growth retardation. The microvascular endothelium, a focal point for both initiation and inhibition of coagulation and control of vascular tone, may well contribute to development and aggravation of these abnormalities. We describe a method for isolation, purification, and culture of human decidual endothelial cells from biopsies performed at the time of cesarean section. The separation procedure is technically simple, requires only a small piece of tissue, and takes approximately 2 hours to perform. Some of the unique features of these cells in culture are outlined. This technique will permit the close examination of various aspects of the function of these cells in normal pregnancy, and their comparison with cells from pregnancies complicated by hypertension.

Modulation of extracellular matrix proteins by endothelial cells undergoing angiogenesis in vitro

Angiogenesis results in part from the response of endothelial cells to the integrated action of morphogenic factors and extracellular matrix proteins. In this study we identified specific components of the extracellular matrix that were modulated in endothelial cells derived from bovine aorta and rat cerebral microvessels, both of which spontaneously form cords and tubes under standard culture conditions. SPARC (secreted protein, acidic and rich in cysteine) was upregulated 4.2-fold in aortic and 10-fold in microvascular cultures that had organized into cords and/or tubes. This Ca(2+)-binding glycoprotein was synthesized primarily by endothelial cells in the process of cord formation. Transcription of type I collagen was initiated in aortic endothelial cells undergoing angiogenesis in vitro and showed a 12-fold increase in similar cultures of microvascular cells. Type VIII collagen protein was upregulated to a lesser degree (4.3-fold in aortic and 1.8-fold in microvascular cells). Dense cytoplasmic staining for these two collagen types was seen in cells directly participating in the organization of cords. In contrast, the disparate levels of fibronectin observed in both types of endothelium indicated an indirect or secondary role for this glycoprotein in cord/tube formation in vitro. These results identify SPARC, type I collagen, and type VIII collagen as extracellular matrix components that are actively synthesized by endothelial cells undergoing angiogenesis in vitro. Moreover, expression of these proteins during the formation of tubes and cords appears to follow a biosynthetic program that is common to endothelial cells from both the macrovasculature and microvasculature.

Microvessel endothelial cell transdifferentiation: phenotypic characterization

Human dermal microvessel endothelial cells (MEC) have two basic functions: maintenance of tissue homeostasis and facilitation of inflammatory responses. The former requires that the endothelium expresses traits of an epithelium, while inflammatory reactions are associated with intimal disruption. Acute inflammation transiently alters endothelium, whereas chronic inflammation may result in vessel reorganization and MEC mesenchymalization. Foreskin MEC in vitro undergo a similar epithelial-mesenchymal modulation. In the presence of cAMP, cultivated dermal MEC exhibit the structural and functional characteristics of an epithelium. MEC grown in cAMP-deficient medium initially have a "transitional" configuration and are subsequently transformed into mesenchymal cells. If cAMP is replaced by histamine, MEC maintain a stable intermediate transitional configuration. Transitional MEC refed cAMP-supplemented medium revert to an epithelial phenotype, whereas parallel cultures fed cAMP-deficient medium are transformed into mesenchymal cells. Phenotypic modulation can be induced without cell division and thus provides a unique example of direct transdifferentiation. Our data furthermore suggest that this transdifferentiation results in the acquisition of properties usually attributed to cells of the reticuloendothelial system.