Hypoxia induces a specific set of stress proteins in cultured endothelial cells

Alpha-enolase staining patterns in the renal tissues of cats with and without chronic kidney disease

Renal α-enolase has variable expression in inflammatory and neoplastic diseases. Therefore, in order to define the distribution of α-enolase in renal tissues of cats, an immunohistochemistry assay was validated and described here. Tissues from 29 cats with IRIS Stage 2-4 CKD, 8 control cats < 2 years of age, and 4 control cats> 10 years of age were assessed. Interstitial nephritis was the predominant histopathological finding in the CKD group. The control cats < 2 years of age had moderate α-enolase immunoreactivity in tubular epithelium but staining was absent to mild in glomeruli. In contrast, α-enolase was moderate to high in tubular epithelium and glomeruli in control cats > 10 years of age. In cats with CKD, α-enolase was decreased in tubules that were degenerative or atrophic, similar to normal tubules in control groups, and moderate to high in glomeruli. When compared between the study groups, the results suggest that alpha-enolase decreases in damaged tubules and increases in the glomeruli of older cats prior to the development of detectable CKD. Further studies will be required to determine whether these findings relate to the pathogenesis or could be used in the diagnosis of feline CKD.

The Effect of Hypoxia on Cardiovascular Disease: Friend or Foe?

Savla, Jainy J., Benjamin D. Levine, and Hesham A. Sadek. The effect of hypoxia on cardiovascular disease: Friend or foe? High Alt Med Biol. 19:124-130, 2018.-Over 140 million people reside at altitudes exceeding 2500 m across the world, resulting in exposure to atmospheric (hypobaric) hypoxia. Whether this chronic exposure is beneficial or detrimental to the cardiovascular system, however, is uncertain. On one hand, multiple studies have suggested a protective effect of living at moderate and high altitudes for cardiovascular risk factors and cardiovascular disease (CVD) events. Conversely, residence at high altitude comes at the tradeoff of developing diseases such as chronic mountain sickness and high-altitude pulmonary hypertension and worsens outcomes for diseases such as chronic obstructive pulmonary disease. Interestingly, recently published data show a potential role for severe hypoxia as a unique and unexpected therapy after myocardial infarction. In this review, we will discuss the current literature evaluating the effects of altitude exposure and the accompanying hypoxia on health and the potential therapeutic applications of hypoxia on CVD.

Hypoxia alters the recruitment of tropomyosins into the actin stress fibres of neuroblastoma cells

Background

Neuroblastoma is the most common extracranial solid tumor of childhood. The heterogeneous microenvironment of solid tumors contains hypoxic regions associated with poor prognosis and chemoresistance. Hypoxia implicates the actin cytoskeleton through its essential roles in motility, invasion and proliferation. However, hypoxia-induced changes in the actin cytoskeleton have only recently been observed in human cells. Tropomyosins are key regulators of the actin cytoskeleton and we hypothesized that tropomyosins may mediate hypoxic phenotypes.

Methods

Neuroblastoma (SH-EP) cells were incubated ± hypoxia (1 % O₂, 5 % CO₂) for up to 144 h, before examining the cytoskeleton by confocal microscopy and Western blotting.

Results

Hypoxic cells were characterized by a more organized actin cytoskeleton and a reduced ability to degrade gelatin substrates. Hypoxia significantly increased mean actin filament bundle width (72 h) and actin filament length (72–96 h). This correlated with increased hypoxic expression and filamentous organization of stabilizing tropomyosins Tm1 and Tm2. However, isoform specific changes in tropomyosin expression were more evident at 96 h.

Conclusions

This study demonstrates hypoxia-induced changes in the recruitment of high molecular weight tropomyosins into the actin stress fibres of a human cancer. While hypoxia induced clear changes in actin organization compared with parallel normoxic cultures of neuroblastoma, the precise role of tropomyosins in this hypoxic actin reorganization remains to be determined.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1741-8) contains supplementary material, which is available to authorized users.

Cloning and expression analysis of a HSP70 gene from Korean rockfish (Sebastes schlegeli)

The gene encoding HSP70 was isolated from Korean rockfish Sebastes schlegeli by homologous cloning and rapid amplification of cDNA ends (RACE). The full-length of HSP70 cDNA was composed of 2259 bp and encoded a polypeptide of 639 amino acids. BLAST analysis showed that HSP70 of S. schlegeli shared high identities with those of the Lates calcarifer, Oreochromis niloticus, Seriola quinqueradiata HSP70s (88-89%). Our current study also revealed that HSP70 of Korean rockfish was expressed in many tissues by RT-PCR under unstressed condition. Quantitative real-time PCR showed that the expression patterns of Korean rockfish HSP70 were developmental stage-dependency. The expression of HSP70 was measured by quantitative real-time PCR after different oxygen treatments. The results showed that expression of HSP70 increased significantly after exposure to hypoxia for 30 min in gill and ovary, and then decreased for 60 min, and the level in spleen and liver gradually increased and reached the highest at 60 min. In addition, in gill, spleen and liver, the HSP70 mRNA level reached the maximum in hypoxia group after one hour different oxygen concentration stress. Increased amounts of serum thyroxine (T4), and triiodothyronine (T3) were also found during 30 min hypoxia treatment and 60 min normoxia group in our study. All of the results provide information to further study the mechanism of physiology and immune function under stress conditions of ovoviviparous teleosts.

Endothelial cell preservation at hypothermic to normothermic conditions using clinical and experimental organ preservation solutions

INTRODUCTION

Endothelial barrier function is pivotal for the outcome of organ transplantation. Since hypothermic preservation (gold standard) is associated with cold-induced endothelial damage, endothelial barrier function may benefit from organ preservation at warmer temperatures. We therefore assessed endothelial barrier integrity and viability as function of preservation temperature and perfusion solution, and hypothesized that endothelial cell preservation at subnormothermic conditions using metabolism-supporting solutions constitute optimal preservation conditions.

METHODS

Human umbilical vein endothelial cells (HUVEC) were preserved at 4-37°C for up to 20 h using Ringer's lactate, histidine-tryptophan-ketoglutarate solution, University of Wisconsin (UW) solution, Polysol, or endothelial cell growth medium (ECGM). Following preservation, the monolayer integrity, metabolic capacity, and ATP content were determined as positive parameters of endothelial cell viability. As negative parameters, apoptosis, necrosis, and cell activation were assayed. A viability index was devised on the basis of these parameters.

RESULTS

HUVEC viability and barrier integrity was compromised at 4°C regardless of the preservation solution. At temperatures above 20°C, the cells' metabolic demands outweighed the preservation solutions' supporting capacity. Only UW maintained HUVEC viability up to 20°C. Despite high intracellular ATP content, none of the solutions were capable of sufficiently preserving HUVEC above 20°C except for ECGM.

CONCLUSION

Optimal HUVEC preservation is achieved with UW up to 20°C. Only ECGM maintains HUVEC viability at temperatures above 20°C.

The effect of hypoxia on in vitro prevascularization of a thick soft tissue

Prevascularizing an implantable tissue is one strategy to improve oxygen (O(2)) transport throughout larger tissues upon implantation. This study examined the role of hypoxia both during (i.e., as a stimulus) and after (i.e., mimicking implant conditions) vascularization of an implantable tissue. Tissues consisted of microcarrier beads coated with human umbilical vein endothelial cells embedded in fibrin. The fibrin was covered with a monolayer of normal human lung fibroblasts (NHLFs), or exposed to conditioned media from NHLFs. Capillary networks developed at 20% or 1% O(2) tension for 8 days. In some experiments, tissues were supplemented with vascular endothelial growth factor (VEGF) and basic fibroblast growth factor, whereas in others the tissues prevascularized at 20% O(2) were transferred to 1% O(2) for 8 additional days. Maximal capillary formation occurred in media conditioned by NHLFs at 20% O(2), supplemented with VEGF (concentration >10 pM). Hypoxia (1% O(2)) did not stimulate basic fibroblast growth factor production and decreased in vitro angiogenesis, despite an increase in endogenous VEGF production. Hypoxia also degraded a preformed capillary network within 4 days. Hence, strategies to prevascularize implantable tissues may not require the physical presence of stromal cells, but will likely require fibroblast-derived growth factors in addition to VEGF to maintain capillary growth.

Acute stress-induced colonic tissue HSP70 expression requires commensal bacterial components and intrinsic glucocorticoid

Induction of heat shock protein (HSPs) has a protective effect in cells under stress. Physical stressors, such as restraint, induce HSPs in colonic tissue in vivo, but the mechanism of HSP induction is not yet clear. Because commensal bacteria support basal expression of colon epithelial HSP70, we postulated that stress responses may enhance the interaction of commensal bacteria and the colonic tissue. Restraining C57BL/6 mice for 2h effectively induced HSP70 in colonic epithelia. Both blockade of stress-induced glucocorticoid by RU486 or elimination of commensal bacteria by antibiotics independently abrogated restraint-induced HSP70 augmentation. Oral administration of LPS to commensal-depleted mice restored restraint-induced HSP70 augmentation. Because TLR4 expression was absent from the epithelial surface, and was limited to lamina propria and muscularis externa, we examined how LPS reaches the lamina propria. Alexa-LPS administered in the colonic lumen was only detected in the lamina propria of the restrained mice. Expression of the tight junction component ZO-1 in the epithelia, which regulates the passage of luminal substances through the epithelia, was reduced after restraint, but reversed by RU486. In conclusion, HSP70 induction in colonic epithelial cells under restraint requires both stress-induced glucocorticoid and luminal commensal bacteria, and LPS plays a significant role. Glucocorticoid-dependent attenuation of epithelial tight junction integrity may facilitate the access of LPS into the lamina propria, where TLR4, known to be required for HSP70 induction, is abundantly expressed. Sophisticated regulation of colonic protection against stressors involving the general stress response and the luminal environment has been demonstrated.

Sustained endothelial progenitor cell dysfunction after chronic hypoxia-induced pulmonary hypertension

Circulating endothelial progenitor cells (EPCs) contribute to neovascularization of ischemic tissues and repair of injured endothelium. The role of bone marrow-derived progenitor cells in hypoxia-induced pulmonary vascular remodeling and their tissue-engineering potential in pulmonary hypertension (PH) remain largely unknown. We studied endogenous mobilization and homing of EPCs in green fluorescent protein bone marrow chimeric mice exposed to chronic hypoxia, a common hallmark of PH. Despite increased peripheral mobilization, as shown by flow cytometry and EPC culture, bone marrow-derived endothelial cell recruitment in remodeling lung vessels was limited. Moreover, transfer of vascular endothelial growth factor receptor-2+/Sca-1+/CXCR-4+-cultured early-outgrowth EPCs failed to reverse PH, suggesting hypoxia-induced functional impairment of transferred EPCs. Chronic hypoxia decreased migration to stromal cell-derived factor-1alpha, adhesion to fibronectin, incorporation into a vascular network, and nitric oxide production (-41%, -29%, -30%, and -32%, respectively, vs. normoxic EPCs; p < .05 for all). The dysfunctional phenotype of hypoxic EPCs significantly impaired their neovascularization capacity in chronic hind limb ischemia, contrary to normoxic EPCs cultured in identical conditions. Mechanisms contributing to EPC dysfunction include reduced integrin alphav and beta1 expression, decreased mitochondrial membrane potential, and enhanced senescence. Novel insights from chronic hypoxia-induced EPC dysfunction may provide important cues for improved future cell repair strategies.

An update on Behçet's disease

Behçet's disease (Adamantiades-Behçet's disease, ABD) is a multisystemic inflammatory disease, the pathogenesis of which is still a mystery. Many questions are still to be answered and the available diverse data need to be brought together to be compared and analysed. There is at least consensus on the effect of possible, but currently unknown, environmental triggering factor(s) against a background of genetic susceptibility. The possible aetiological factors form a broad spectrum, with infectious agents being the most probable ones. Whatever the stimulus is, the target tissue seems to be the small blood vessels, with various consequences of either vasculitis and/or thrombosis in many organ systems. The endothelium seems to be the primary target in this disease; however, it may just be the subject of the bizarre behaviour of the immune system. The diverse existing data could be interpreted in favour of either explanation. A similar confusion exists about the thrombotic tendency in Adamantiades-Behçet's disease, in terms of whether a primary hypercoagulability is present or whether it is secondary to inflammation. Recent interesting immunological data promise a way out of the existing dilemma. These findings will be outlined within the context of possible hypotheses and attention will be paid to further investigations that are needed.

Hypoxia suppresses elastin repair by rat lung fibroblasts

Macrophage and neutrophil proteinases damage lung elastin, disrupting alveolar epithelium and filling alveoli with inflammatory exudate. Alveolar collapse and regional hypoxia occur. Whether low oxygen tension alters fibroblast-mediated lung repair is unknown. To determine the effect of chronic hypoxia on repair of enzyme-induced elastin disruption, primary rat lung fibroblasts produced elastin matrix for 5 wk before treatment with porcine pancreatic elastase (PPE). After exposure to PPE or saline, cultures recovered for 2 wk in normoxia (21% O2) or hypoxia (3% O2). Hypoxia suppressed regeneration of hot alkali-resistant elastin, achieving only 49% of the repair achieved in normoxic cultures. Vascular smooth muscle cells and lung fibroblasts repair elastin by two pathways: de novo synthesis and salvage repair. Although both pathways were affected, hypoxia predominantly inhibited de novo synthesis, decreasing formation of new elastin matrix by 63% while inhibiting salvage repair by only 36%. Prolonged hypoxia alone downregulated steady-state levels of elastin mRNA by 45%, whereas PPE had no significant effect on elastin gene expression. Electron microscopy documented preservation of intracellular organelles and intact nuclei. Together, these data suggest that regional hypoxia limits lung elastin repair following protease injury at least in part by inhibiting elastin gene expression.

Analysis of expression and posttranslational modification of proteins during hypoxia

The cellular responses to hypoxia are complex and characterized by alterations in the expression of a number of genes, including stress-related genes and corresponding proteins that are necessary to maintain homeostasis. The purpose of this article is to review previous and recent studies that have examined the changes in the expression and posttranslational modification of proteins in response to chronic sustained and intermittent forms of hypoxia. A large number of studies focused on the analysis of either the single protein or a subset of related proteins using one-dimensional gel electrophoresis to separate a complex set of proteins from solubilized tissues or cell extracts, followed by immunostaining of proteins using antibodies that are specific to either native or posttranslationally modified forms. On the other hand, only a limited number of studies have examined the global perturbations on protein expression by hypoxia using proteomics approach involving two-dimensional electrophoresis coupled with mass spectrometry. Results derived from specific protein analysis of a variety of tissues and cells showed that hypoxia, depending on the duration and severity of the stimulus, affects the level and the state of posttranslational modification of a subset of proteins that are associated with energy metabolism, stress response, cell injury, development, and apoptosis. Some of these earlier findings are further corroborated by recent studies that utilize a global proteomics approach, and, more importantly, results from these proteomics investigations on the effects of hypoxia provide new protein targets for further functional analysis. The anticipated new information stems from the analysis of expression, and posttranslational modification of these novel protein targets, along with gene expression profiles, offers exciting new opportunities to further define the mechanisms of cellular responses to hypoxia and to control more effectively the clinical consequences of prolonged or periodic lack of oxygen.

Hypoxic up-regulation of triosephosphate isomerase expression in mouse brain capillary endothelial cells

A protein with a molecular mass of 27kDa was induced by hypoxia in a mouse brain capillary endothelial cell line and identified as triosephosphate isomerase (TPI) by amino-terminal sequencing. Hypoxia caused an elevation of the TPI protein level, concomitant with an increase of the TPI mRNA level. However, hypoxia resulted in an insufficient elevation of TPI activity level, compared to an increase of TPI protein level. When cells expressing the recombinant TPI protein with histidine tag were exposed to hypoxia and the TPI protein was affinity-purified, the catalytic activity (specific activity) of the TPI protein purified from hypoxic cells was substantially lower than that obtained from normoxic cells. In addition, three TPI isoforms with an electrophoretic multiplicity were found; two of the three isoforms were substantially increased in response to the hypoxia, but the level of the most acidic isoform was barely changed. The induction of TPI gene expression by hypoxia was suppressed by (1) a chelator of intracellular Ca(2+), (2) a blocker of non-selective cation channels, (3) a blocker of Na(+)/Ca(2+) exchangers, (4) an inhibitor of Ca(2+)/calmodulin-dependent protein kinases, and (5) an inhibitor of c-jun/AP-1 activation.

Hypoxia up-regulates glyceraldehyde-3-phosphate dehydrogenase in mouse brain capillary endothelial cells: involvement of Na+/Ca2+ exchanger

The molecular regulatory mechanisms and the characterization of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in hypoxia were studied in a mouse brain capillary endothelial cell line, MBEC4. Activation of GAPDH gene expression by hypoxia was suppressed by an intracellular Ca(2+) chelator and inhibited by a non-selective cation channel blocker or a Na(+)/Ca(2+) exchanger (NCX) blocker. Sequencing of reverse transcription-PCR products demonstrated that MBEC4 expressed an mRNA encoding NCX3, which functions even under cellular ATP-depleted conditions, in addition to mRNAs encoding NCX1 and NCX2. The inhibition of Ca(2+)/calmodulin-dependent protein kinases or c-Jun/AP-1 activation caused a significant decrease in the activation of GAPDH mRNA by hypoxia. These results suggest that hypoxia stimulates Ca(2+) influx through non-selective cation channels and causes the reverse operation of the three NCX isoforms, and consequently, increased intracellular Ca(2+) up-regulates GAPDH gene expression through an AP-1-dependent pathway. Furthermore, subcellular fractionation experiments showed that hypoxia increased GAPDH proteins not only in the cytosolic fraction, but also in the nuclear and particulate fractions, in which GAPDH should play no roles in glycolysis. However, the GAPDH activity did not rise in proportion to the increase of GAPDH protein by hypoxia even in the cytosolic fraction. These results suggest that not all hypoxia-induced GAPDH molecules contribute to glycolysis.

Heme oxygenase/carbon monoxide signaling pathways: regulation and functional significance

Carbon monoxide (CO), a gaseous second messenger, arises in biological systems during the oxidative catabolism of heme by the heme oxygenase (HO) enzymes. HO exists as constitutive (HO-2, HO-3) and inducible isoforms (HO-1), the latter which responds to regulation by multiple stress-stimuli. HO-1 confers protection in vitro and in vivo against oxidative cellular stress. Although the redox active compounds that are generated from HO activity (i.e. iron, biliverdin-IXα, and bilirubin-IXα) potentially modulate oxidative stress resistance, increasing evidence points to cytoprotective roles for CO. Though not reactive, CO regulates vascular processes such as vessel tone, smooth muscle proliferation, and platelet aggregation, and possibly functions as a neurotransmitter. The latter effects of CO depend on the activation of guanylate cyclase activity by direct binding to the heme moiety of the enzyme, stimulating the production of cyclic 3′:5′-guanosine monophosphate. CO potentially interacts with other intracellular hemoprotein targets, though little is known about the functional significance of such interactions. Recent progress indicates that CO exerts novel anti-inflammatory and anti-apoptotic effects dependent on the modulation of the p38 mitogen activated protein kinase (MAPK)-signaling pathway. By virtue of these effects, CO confers protection in oxidative lung injury models, and likely plays a role in HO-1 mediated tissue protection.

Heme oxygenase-1: molecular mechanisms of gene expression in oxygen-related stress

Disturbances of intracellular redox equilibrium may alter eukaryotic gene expression patterns in the manifestation of an adaptive stress response. The inducible heme oxygenase-1 gene, ho-1, responds dramatically to changes in cellular redox potential provoked by multiple agents (oxidants, xenobiotics, reactive oxygen species, nitric oxide, and ultraviolet-A radiation) as well as deviations in oxygen tension in excess or deficit of normal physiological levels. This dual response to hyperoxic and hypoxic states renders ho-1 an intriguing model system for studying oxygen-regulated gene expression. The complexation or depletion of reduced glutathione apparently represents an underlying mechanism by which oxidants trigger the response. Chelatable iron levels also influence the induction of ho-1 as evidenced by the inhibitory effects of iron-chelating compounds. Redox-sensitive protein kinase cascades (e.g., mitogen-activated protein kinases) participate in ho-1 regulation. Recent progress in understanding ho-1 transcription has identified two distal enhancer regions (E1, E2) in the mouse ho-1 gene that mediate the response to many inducing conditions. This review will examine the potential roles of iron, glutathione, and reactive oxygen species in the upstream events leading to ho-1 activation following oxygen related stress.

Identification of protein disulfide isomerase as an endothelial hypoxic stress protein

Endothelial cells (EC) exposed to hypoxia upregulate a unique set of five stress proteins. These proteins are upregulated in human and bovine aortic and pulmonary artery EC and are distinct from heat shock or glucose-regulated proteins. We previously identified two of these proteins as the glycolytic enzymes glyceraldehyde-3-phosphate dehydrogenase and enolase and postulated that the remaining proteins were also glycolytic enzymes. Using SDS-PAGE, tryptic digestion, and NH(2)-terminal amino acid sequencing, we report here the identification of the 56-kDa protein as protein disulfide isomerase (PDI). PDI is upregulated by hypoxia at the mRNA level and follows a time course similar to that of the protein, with maximal upregulation detected after exposure to 18 h of 0% O(2). Neither smooth muscle cells nor fibroblasts upregulate PDI to the same extent as EC, which correlates with their decreased hypoxia tolerance. Upregulation of PDI specifically in EC may contribute to their ability to tolerate hypoxia and may occur through PDI's functions as a prolyl hydroxylase subunit, protein folding catalyst, or molecular chaperone.

Low oxygen tension stimulates collagen synthesis and COL1A1 transcription through the action of TGF-beta1

Recent findings point to low oxygen tension (hypoxia) as an important mechanism for the expression of several eukaryotic genes. We have previously shown that hypoxia (2% O2), when compared to standard oxygen tension (20% O2), upregulates the mRNA levels of the human alpha1(I) (COL1A1) procollagen gene and transforming growth factor-beta1 (TGF-beta1) in human dermal fibroblasts. In this report, we determined the effect of hypoxia on collagen synthesis and transcription. Exposure of human dermal fibroblasts to hypoxia for 24-72 h led to a threefold, dose-dependent increase in collagenous protein (P < 0.0001; r = 0.9794) and to enhanced type I procollagen deposition, as shown by direct immunofluorescence. Transient transfections with a series of luciferase- and CAT-promoter constructs of the human COL1A1 gene (spanning from -2.5 kb to +113 bp) showed that hypoxia increases the transcriptional activity of constructs having 5' endpoints between -804 bp and -107 bp, with loss of stimulation at -84 bp. Maximal increase in promoter activity in hypoxia was observed between -190 and -174 bp of the proximal promoter, once a cKrox repressor site (-199 to -224 bp) was deleted. Upregulation of COL1A1 mRNA levels in hypoxia was blocked by a TGF-beta1 anti-sense oligonucleotide, and failed to occur in fibroblasts from TGF-beta1 knock-out mice. Co-transfection and overexpression with a Smad7 construct abrogated the increase in COL1A1 promoter activity observed in hypoxia. Upregulated transcriptional activity of the TGF-beta1 promoter in hypoxia was found to be maximal between -453 and -175 bp from the transcriptional start site. Since hypoxia is a critical feature of the early phases of wound repair, we conclude that it may act as a potent physiologic stimulus for collagen synthesis. TGF-beta1 appears to be a critical component of this response.

Heme oxygenase/carbon monoxide signaling pathways: regulation and functional significance

Carbon monoxide (CO), a gaseous second messenger, arises in biological systems during the oxidative catabolism of heme by the heme oxygenase (HO) enzymes. HO exists as constitutive (HO-2, HO-3) and inducible isoforms (HO-1), the latter which responds to regulation by multiple stress-stimuli. HO-1 confers protection in vitro and in vivo against oxidative cellular stress. Although the redox active compounds that are generated from HO activity (i.e. iron, biliverdin-IXalpha, and bilirubin-IXa) potentially modulate oxidative stress resistance, increasing evidence points to cytoprotective roles for CO. Though not reactive, CO regulates vascular processes such as vessel tone, smooth muscle proliferation, and platelet aggregation, and possibly functions as a neurotransmitter. The latter effects of CO depend on the activation of guanylate cyclase activity by direct binding to the heme moiety of the enzyme, stimulating the production of cyclic 3':5'-guanosine monophosphate. CO potentially interacts with other intracellular hemoprotein targets, though little is known about the functional significance of such interactions. Recent progress indicates that CO exerts novel anti-inflammatory and anti-apoptotic effects dependent on the modulation of the p38 mitogen activated protein kinase (MAPK)-signaling pathway. By virtue of these effects, CO confers protection in oxidative lung injury models, and likely plays a role in HO-1 mediated tissue protection.

Induction of endothelial cell cytoplasmic lipid bodies during hypoxia

Lipid bodies (LBs), lipid-rich cytoplasmic inclusions found in many cell types, seem to act as nonmembrane sites of eicosanoid formation. Because alterations in eicosanoid products have been demonstrated in endothelial cells (ECs) during hypoxia, we investigated induction of LBs in systemic and pulmonary ECs exposed to acute and/or chronic hypoxia. LBs in ECs were O(2)-concentration dependent, increasing approximately fivefold during acute exposure to 0% O(2) in both cell types. During chronic exposure to 3% O(2), LBs were induced only in systemic ECs. LBs were not induced by other cellular stresses (heat shock or glucose deprivation). Subsequent studies suggested that protein kinase C-dependent and tyrosine kinase-dependent pathways are important in LB induction during hypoxia. PGH synthase was demonstrated in LBs in every case in which they were induced. These are the initial studies to demonstrate induction of LBs in ECs and to demonstrate LB induction during exposure to hypoxia in any cell type. These results imply that in ECs, LBs are structurally distinct inducible sites for synthesis of eicosanoid mediators.

Regulation of endothelial heme oxygenase activity during hypoxia is dependent on chelatable iron

The regulation of heme oxygenase (HO) activity and its dependence on iron was studied in bovine aortic endothelial cells (BAEC) subjected to hypoxia-reoxygenation (H/R). HO activity was induced by hypoxia (10 h) and continued to increase during the reoxygenation phase. HO-1 protein levels were strongly induced by hypoxia from undetectable levels and remained elevated at least 8 h postreoxygenation. Addition of the Fe(3+) chelator desferrioxamine mesylate (DFO) or the Fe(2+) chelator o-phenanthroline during hypoxia alone or during the entire H/R period inhibited the induction of HO activity and HO-1 protein levels. However, DFO had no effect and o-phenanthroline had a partial inhibitory effect on HO activity and protein levels when added only during reoxygenation. Loading of BAEC with Fe(3+) enhanced the activation of the HO-1 gene by H/R, whereas loading with L-aminolevulinic acid, which stimulates heme synthesis, had little effect. These results suggest that chelatable iron participates in regulating HO expression during hypoxia.

Efficient translation of mouse hypoxia-inducible factor-1alpha under normoxic and hypoxic conditions

The heterodimeric hypoxia-inducible factor-1 (HIF-1), consisting of the subunits HIF-1alpha and HIF-1beta/ARNT, is a master transcriptional regulator of oxygen homeostasis. Under hypoxic conditions, HIF-1alpha levels very rapidly increase, mostly due to protein stabilization. However, translational regulation of HIF-1alpha has not been directly analyzed so far. Mouse HIF-1alpha exists as two mRNA isoforms (termed mHIF-1alphaI.1 and mHIF-1alphaI. 2) containing structurally different 5'-termini which might modulate translation initiation. Whereas the in vitro translation efficiency of these two mRNA isoforms was about equal, the mHIF-1alphaI.2 5'-untranslated region (5'-UTR) conferred significantly higher in vivo luciferase reporter gene activity than the mHIF-1alphaI.1 5'-UTR. Similar corresponding luciferase mRNA levels indicate translational rather than transcriptional alterations. Reporter gene expression was not affected upon exposure of transiently transfected cells to hypoxia (1% oxygen). Direct assessment of translational regulation by polysomal profile analysis of HeLaS3 cells showed that HIF-1alpha (and to a lower extent ARNT) mRNA was found mainly in the translationally active polyribosomal fractions under both normoxic and hypoxic conditions. In contrast, the association of mRNAs for beta-actin and ribosomal protein L28 with the polyribosomal fractions was substantially reduced under hypoxic conditions, suggesting decreased overall protein synthesis. Thus, efficient translation of mouse HIF-1alpha in a situation where the general translation efficiency is reduced represents a prerequisite for the very rapid accumulation of HIF-1alpha protein upon exposure to hypoxia.

Role of calpain in hypoxic inhibition of nitric oxide synthase activity in pulmonary endothelial cells

Pulmonary artery endothelial cells (PAEC) were exposed to normoxia or hypoxia (0% O(2)-95% N(2)-5% CO(2)) in the presence and absence of calpain inhibitor I or calpeptin, after which endothelial nitric oxide synthase (eNOS) activity and protein content were assayed. Exposure to hypoxia decreased eNOS activity but not eNOS protein content. Both calpain inhibitor I and calpeptin prevented the hypoxic decrease of eNOS activity. Incubation of calpain with total membrane preparations of PAEC caused dose-dependent decreases in eNOS activity independent of changes in eNOS protein content. Exposure of PAEC to hypoxia also caused time-dependent decreases of heat shock protein 90 (HSP90) that were prevented by calpain inhibitor I and calpeptin. Moreover, the HSP90 content in anti-eNOS antibody-induced immunoprecipitates from hypoxic PAEC lysates was reduced, and repletion of HSP90 reversed the decrease of eNOS activity in these immunoprecipitates. Incubation of PAEC with a specific inhibitor of HSP90 (geldanamycin) mimicked the hypoxic decrease of eNOS activity. These results indicate that the hypoxia-induced reduction in eNOS activity in PAEC is due to a decrease in HSP90 caused by calpain activation.

Hypoxic signal transduction in critical illness

Derangements in tissue perfusion occur during critical illness, and the resulting deficit in oxygen delivery may play an important role in the pathogenesis of hemorrhagic and septic shock. Cells and organisms have developed a variety of adaptive strategies to maintain adequate energy production to maintain normal cellular function under hypoxic conditions. Recent studies from our laboratory suggest that certain proinflammatory cytokines, which are likely to be elaborated during or after shock, can interfere with the ability of cells to adapt to hypoxia, and thereby contribute to the development of organ system dysfunction.

Hypoxia increases glyceraldehyde-3-phosphate dehydrogenase transcription in rat alveolar epithelial cells

Alveolar epithelial type II (ATII) cells are particularly hypoxia-tolerant in vitro. As one of the mechanisms of hypoxia tolerance is the induction of certain proteins, one of which is glyceraldehyde-3-phosphate dehydrogenase (GAPDH), we investigated whether hypoxia modified GAPDH expression in ATII cells. Hypoxia induced a time- and O(2) concentration-dependent accumulation of GAPDH mRNA in cultured rat ATII cells (2- to 3-fold the normoxic value after 18 h in 0% O(2)), an effect completely reversed by reoxygenation. GAPDH mRNA induction was accounted for by an increase in GAPDH gene transcription during hypoxia with no change in mRNA stability. GAPDH protein synthesis increased 3- to 4-fold after 18 h of 0% O(2), while the GAPDH protein steady-state level rose by 75%. GAPDH enzymatic activity in hypoxic cell homogenates increased by 45%. These results indicate that hypoxia induces GAPDH expression in ATII cells through an increase in transcription.

Perinatal hypoxia-ischemia decreased neuronal but increased cerebral vascular endothelial IGFBP3 expression

In adults, insulin-like growth factor binding protein 3 (IGFBP3) is the main carrier protein for circulating insulin-like growth factors (IGFs) (IGF-I and -II). While most IGFBP3 is synthesized in the liver, it is also expressed locally by many cell types including vascular endothelial cells. The regulation of this endothelial IGFBP3 expression, especially in response to hypoxic-ischemic injury, has not been investigated in vivo. Using in situ hybridization histochemistry, we studied the cellular distribution of IGFBP3 mRNA in rat brains following hypoxic-ischemic injury at 1, 5, 24, and 72 h of recovery. In normal P7 rat brain, IGFBP3 mRNA was found in neurons within the thalamus, hippocampus, and amygdaloid. Low levels of IGFBP3 mRNA were also detected in cerebral vascular endothelial cells. After the hypoxic-ischemic injury, the levels of neuronal IGFBP3 mRNA substantially decreased within 24 h in areas that were normally supplied by the middle cerebral artery. In the meantime, there was an immediate increase in IGFBP3 expression in vascular endothelial cells throughout the affected hemisphere. This vascular IGFBP3 expression was further enhanced with the highest level at 24 h of recovery whereas neuronal IGFBP3 expression was further decreased. By 72 h of recovery, IGFBP3 was no longer expressed in vascular endothelial cells. Taken together, the activation of IGFBP3 is a likely mechanism by which vascular endothelial cells respond to hypoxic-ischemic insult. In addition, increased endothelial IGFBP3 may modulate the interaction of IGFs with IGF-I receptors at the site of injury and/or act independently on endothelial cell growth.

Expression of stress proteins, adhesion molecules, and interleukin-8 in endothelial cells after preservation and reoxygenation

Endothelial activation is a central feature of preservation-induced allograft injury. The present study aims at a quantitative assessment of stress proteins, adhesion molecules, and interleukin-8 in a cell culture-based model of organ preservation. Human umbilical vein endothelial cells were exposed to cold, hypoxic storage in University of Wisconsin (UW), histidine-tryptophane-ketoglutarate (HTK), and EuroCollins solutions for 8 h with subsequent rewarming/reoxygenation (rew/reox) for 1 and 4 h. A cell-based ELISA was designed for detection of heat shock proteins (HSP) 60 and 70, intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), and endothelial leukocyte adhesion molecule-1 (ELAM-1). Immunohistochemical staining was performed for comparison. Interleukin-8 was quantified by ELISA. HSP 70 was expressed after cold storage in HTK and EuroCollins solution and after rew/reox in all groups. A constitutive expression of HSP 60 was observed with further upregulation after rew/reox following cold storage in all experimental groups. ICAM-1 was clearly upregulated, but VCAM-1 showed only weak expression after cold storage and rew/reox. ELAM-1 was detectable in minimal amounts after cold storage but was considerably upregulated after 4 h of rew/reox. A significant increase of interleukin-8 release could be found after 4 h of rew/reox following storage in EuroCollins solution. Expression of stress proteins can be considered as a new parameter of preservation-associated endothelial activation. Apart from possible protective effects, allograft vasculopathy could be in part a consequence of the antigeneic potential of heat shock proteins connected with effects caused by adhesion molecules and inflammatory cytokines.

Endothelial cell hypoxic stress proteins

The vascular endothelium is an important mediator of vascular tone, inflammatory-immune reactions, vascular permeability, angiogenesis, and hemostasis. Endothelial functions may be altered by changes in the local cellular environment, particularly changes in oxygen tension. The mechanisms by which endothelial cells (ECs) respond and adapt to hypoxia are unknown; however, the EC is one of the more hypoxia-tolerant mammalian cell types. Cultured ECs exposed to hypoxia up-regulate a set of stress proteins, termed hypoxia-associated proteins (HAPs), that are distinct from the classically described stress proteins induced by heat shock (heat-shock proteins, HSPs) or glucose deprivation (glucose-regulated proteins, GRPs). Two of these proteins have been identified as the glycolytic enzymes glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and non-neuronal enolase (NNE). GAPDH expression during hypoxia is regulated primarily at the level of transcription, while the mechanism of NNE mRNA accumulation remains unclear. GAPDH, NNE, and the other HAPs are up-regulated by transitional metals and deferoxamine; however, unlike the situation with other hypoxia-regulated proteins such as erythropoietin, the up-regulation of GAPDH, NNE, and the other HAPs by hypoxia is not inhibited by carbon monoxide. Subcellular fractionation of hypoxic EC has shown that GAPDH and NNE are up-regulated in the cytoplasmic fraction as would be expected for a glycolytic enzyme; however, a protein corresponding to GAPDH is also up-regulated in the nuclear fraction. This suggests that GAPDH and perhaps NNE have functions aside from their catalytic function in glycolysis. It is unknown whether the up-regulation of GAPDH, NNE, and the other HAPs in ECs is related to the relative ability of ECs to adapt to hypoxia; however, other more-hypoxia-sensitive cells do not up-regulate HAPs.

Direct physical factors and PGI2 and TXA2 secretions by a human endothelial cell line: in vitro investigation of pressure and shear stress applied independently or in synergy

The direct effect of two types of mechanical stress was measured through the prostacyclin (PGI2) and thromboxane A2 (TXA2) secretions by a confluent monolayer of cells from the EA.hy926 line. Eight values of constant pressure were applied in the gas phase above the culture medium, around atmospheric pressure taken as a control (0 mm Hg), from -500 to +760 mm Hg. Three amplitudes of sinewave modulated pressure (+/- 40; +/- 80; +/- 160 mm Hg) were explored at a frequency of 1 Hz. Modulated pressure (+/- 40 mm Hg) was also applied synergetically to a shear stress generated under steady state conditions by a rectilinear laminar motion of the medium. The cells remained adherent and exhibited unchanged morphology and viability. Constant pressure or depressure increased both PGI2 and TXA2 release but to an extent depending on the pressure value. Under pressure, the PGI2/TXA2 ratio was unchanged, but was higher under depressure, compared to the control. Pressure modulation strongly stimulated the secretion of PGI2 but had no effect on TXA2. Modulation strongly increased the PGI2/TXA2 ratio to a similar extent for the three amplitudes. Pressure-shear synergy enhanced secretion of PGI2 markedly more than shear stress alone, but the level reached was similar to the one induced by pressure modulation. No cumulative effect on the secretion of PGI2 was observed, whereas TXA2 synthesis undergoes a more than cumulative effect. The PGI2/TXA2 ratio remained unchanged under shear alone or under combined shear-pressure modulation but was higher with the modulated pressure alone. These results demonstrate that pressure has an outstanding effect on secretion that may be origin to local disturbances of the vascular system, thus inducing pathologies such as thrombosis or atherosclerosis.

Hypoxic regulation of endothelial glyceraldehyde-3-phosphate dehydrogenase

The glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is induced by hypoxia in endothelial cells (EC). To define the mechanisms by which GAPDH is regulated by hypoxia, EC were exposed to cobalt, other transition metals, carbon monoxide (CO), deferoxamine, or cycloheximide in the presence or absence of hypoxia for 24 h, and GAPDH protein and mRNA levels were measured. GAPDH was induced in cells by the transition metals cobalt, nickel, and manganese and by deferoxamine, and GAPDH mRNA induction by hypoxia was blocked by cycloheximide. GAPDH induction by hypoxia, unlike that of other hypoxia-regulated genes, was not inhibited by CO or by 4,6-dioxoheptanoic acid, an inhibitor of heme synthesis. GAPDH induction was not altered by mediators of protein phosphorylation, a calcium channel blocker, a calcium ionophore, or alterations in redox state. GAPDH induction by hypoxia or transitional metals was partially blocked by sodium nitroprusside but was not altered by the inhibitor of nitric oxide synthase N omega-nitro-L-arginine. These findings suggest that GAPDH induction by hypoxia in EC occurs via mechanisms other than those involved in other hypoxia-responsive systems.

Receptor-stimulated phospholipase C activity in human umbilical artery cultured endothelial cells grown in a low oxygen environment

Endothelial cells of the human umbilical blood vessels are widely cultured in an oxygen tension (21%) far above that in which they exist in vivo (3%). This study investigates the effect of the long term culture (ca. 1 month) of human umbilical artery endothelial cells in a reduced oxygen environment (3%: HUAEC3) in comparison to cells grown in a 'normoxic' environment (21%: HUAEC21). Despite reports of altered metabolic pathways and reduced membrane integrity in other cell types, the characteristics of HUAEC3 were found to be similar to those of HUAEC21 with respect to morphology, immunocytochemical profile and in vitro growth rates. Cellular glutathione was maintained in these cells although ATP levels in HUAEC3 were found to be significantly lower than those observed in HUAEC21. The phosphoinositide responses of the HUAEC3 to a variety of agonists were also found to be of similar magnitude to those observed in HUAEC21. In addition, the pharmacological characteristics of the phospholipase C-linked histamine H1 and P2y2 (P2U) receptors were not changed by culture of cells in a low oxygen environment.

Effect of hypercarbia on surface proteins of cultured bovine endothelial cells

Hypercarbia is a common complication of respiratory failure, and the technique of "permissive hypercapnia" is used to ventilate individuals with increased peak airway pressures on mechanical ventilators, resulting in elevated arterial PCO2. We studied the effects of hypercarbia on cultured bovine aortic and main pulmonary artery endothelial cell surface proteins, assessing cell surface iodination using lactoperoxidase bound to latex microspheres. We found that 4 h of exposure to 10% CO2 increased the display of substances of apparent molecular masses of 27, 47, and 52 kDa. This effect was not mimicked by acidotic media. Western blots of detergent extracts of main pulmonary artery endothelial cell monolayers did not show increased expression of carbonic anhydrase IV (molecular mass = 52 kDa) after incubation under hypercarbic conditions. Hypercarbia did not change the pattern of [35S]methionine incorporation into endothelial cell proteins. We conclude that hypercarbia of 4-h duration changes iodinated endothelial cell surface proteins. We speculate that this effect may be related to changes in secretion or display of apical cell membrane-associated proteins.

Caerulein pancreatitis increases mRNA but reduces protein levels of rat pancreatic heat shock proteins

We have recently reported that preconditioning through hyperthermia induces expression of pancreatic heat shock proteins (HSPs) and protects against caerulein pancreatitis. Here, we investigate caerulein-mediated effects on pancreatic HSPs without prior hyperthermia. Caerulein time and dose dependently increased pancreatic mRNA levels of the constitutive isoform of HSP70 (HSC70). However, pancreatic HSC70 protein levels were decreased, as were HSP60 protein levels. Also, in contrast to hyperthermia preconditioning, caerulein did not induce measurable levels of mRNA or protein of the inducible isoform of HSP70. Thus the pancreas reacts to different kinds of stress (hyperthermia vs. hyperstimulation) with differential induction of HSP mRNAs. Clearly, hyperthermia leads to induction of HSP protein expression, whereas caerulein treatment does not. Therefore, our current study further supports the idea that hyperthermia-induced protection against caerulein pancreatitis may be mediated through increased protein levels of pancreatic HSPs. It is further tempting to hypothesize that failure to appropriately increase HSP protein levels in response to high doses of caerulein might be a factor in the development of pancreatitis.

Induction of cystine transport and other stress proteins by disulfiram: effects on glutathione levels in cultured cells

Disulfiram (Antabuse) (DSF) has been reported to protect rats and other animals from the effects of hyperbaric hyperoxia at 4 to 6 ATA (atmospheres). In contrast, DSF and diethyldithiocarbamate (DDC), its metabolite, accelerate the toxic effects in rats of 100% oxygen at 1 to 2 ATA. We have examined the effects of DSF and DDC on glutathione (GSH) levels in bovine pulmonary artery endothelial cells and Chinese hamster ovary cells. Increases in intracellular GSH occurred 8 to 24 h after addition of DSF to the culture media. These increases in intracellular GSH were associated with increases in the rate of uptake of cystine into the cells. DDC was a less effective inducer of cystine uptake and increased intracellular GSH levels than was DSF. At the concentrations used, neither DDC nor DSF caused significant decreases in intracellular superoxide dismutase levels. Exogenous sulfhydryl compounds including GSH and cysteine partially blocked the induction of cystine transport by DSF or DDC, suggesting that the induction might be mediated through a sulfhydryl reaction between DSF and some cellular components. The increases in GSH in the cultured cells were not significant by 4 h of exposure. In contrast, other stress proteins including heme oxygenase are induced by 2 to 4 h after DSF addition. In previously reported in vivo studies, DSF treatment protected against hyperbaric oxygen damage after as little as 1 to 4 h pre-exposure. This suggests that effects of DSF exposure other than GSH augmentation may be responsible for the protective effects seen in vivo.

Hypoxia-ischemia, but not hypoxia alone, induces the expression of heme oxygenase-1 (HSP32) in newborn rat brain

Heme oxygenase (HO) is the rate-limiting enzyme in the degradation of heme to produce bile pigments and carbon monoxide. The HO-1 isozyme is induced by a variety of agents such as heat, heme, and hydrogen peroxide. Evidence suggests that the bile pigments serve as antioxidants in cells with compromised defense mechanisms. Because hypoxia-ischemia (HI) increases the level of oxygen free radicals, the induction of HO-1 expression in the brain during ischemia could modulate the response to oxidative stress. To study the possible involvement of HO-1 in neonatal hypoxia-induced ischemic tolerance, we examined the brains of newborn rat pups exposed to 8% O2 (for 2.5 to 3 hours), and the brain of chronically hypoxic rat pups with congenital cardiac defects (Wistar Kyoto; WKY/ NCr). Heme oxygenase-1 immunostaining did not change after either acute or chronic hypoxia, suggesting that HO-1 is not a good candidate for explaining hypoxia preconditioning in newborn rat brain. To study the role of HO-1 in neonatal HI, 1-week-old rats were subjected to right carotid coagulation and exposure to 8% O2/92% N2 for 2.5 hours. Whereas HO enzymatic activity was unchanged in ipsilateral cortex and subcortical regions compared with the contralateral hemisphere or control brains, immunocytochemistry and Western blot analysis showed increased HO-1 staining in ipsilateral cortex, hippocampus, and striatum at 12 to 24 hours up to 7 days after HI. Double fluorescence immunostaining showed that HO-1 was expressed mostly in ED-1 positive macrophages. Because activated brain macrophages have been associated with the release of several cytotoxic molecules, the presence of HO-1 positive brain macrophages may determine the tissue vulnerability after HI injury.

Vascular endothelial growth factor mediates reactive angiogenesis in the postnatal developing brain

Although chronic sublethal hypoxia has been shown to promote angiogenesis in the developing brain, the pathogenesis of this response is unknown. We hypothesized that this response may be mediated in part by vascular endothelial growth factor (VEGF). We reared newborn rats (P3) in a chamber with FIO2 of 9.5 +/- 1% (exposed, E). At P33, the animals were removed from the chamber and the brains prepared for immunohistochemistry, mRNA extraction, or horseradish peroxidase (HRP) permeability studies. We also isolated beagle brain germinal matrix endothelial cells from PND 1 beagle pups and placed them in three-dimensional (3-D) coculture with PND 1 rat forebrain astrocytes. Cultures were grown for 6 days in 11% O2 and compared to control 3-D cocultures. When compared to age-matched controls, the experimental rats had significantly increased cortical vascular density (vessels/mm2: 518 +/- 18 vs. 400 +/- 15, P = 0.025). HRP studies demonstrated significantly increased permeability in all cortical vessels examined in experimental rats compared to controls. Compared to controls, VEGF mRNA from hypoxic pups was increased 2.4 times, and immunohistochemical studies of VEGF protein confirmed this finding. Similarly, when compared to controls, hypoxic cocultures of brain microvascular endothelial cells and astrocytes demonstrated significant increase in tubelike structures representing in vitro angiogenesis. Additionally, astrocyte VEGF protein levels increased 4.4-fold in hypoxic compared to control astrocyte cultures and VEGF protein levels increased 1.7-fold in hypoxic compared to control cocultures. Finally, addition of VEGF (10 ng/ml culture medium) to BBMEC alone in 3-D culture elicited not only significant proliferation (P = 0.001) but also increased tube formation. These data demonstrate that the developing brain responds to chronic sublethal hypoxia with increases in permeability and angiogenesis and suggest that VEGF mediates this response.

Distinct effect of hypoxia on endothelial cell proliferation and cycling

Endothelial cells (EC) occupy a strategic location in the vasculature as a barrier between the intravascular compartment and underlying tissues; as such, they are often exposed to stresses, such as decreases in ambient oxygen, diminished metabolic substrate, or changes in temperature, that could affect their ability to divide and proliferate. The present study characterizes cell counts, cell cycle distribution, and bromodeoxyuridine incorporation in pulmonary artery and aortic EC exposed to acute and/or chronic hypoxia and other cellular stresses. During hypoxia, EC division slows but does not arrest; progression through the G1-to-S transition point and/or progression from S to G2/M is altered with an increased percent of EC in S phase. These changes in EC cell cycle distribution with hypoxia are dependent on the origin of the EC as well as the ambient oxygen concentration; moreover, they are distinct from changes observed with elevated temperature or glucose deprivation. and differ from the quiescent pattern induced by serum deprivation or high-density confluence. These findings demonstrate that hypoxia exerts a distinct effect on the cell cycle distribution and proliferation of EC.

[Roles of vasoactive factors synthetized by endothelium in pulmonary arterial hypertension]

Pulmonary vascular endothelium synthesizes and releases two groups of vasoactive substances, namely the endothelium-derived relaxing and contracting factors. Among the former, the effects of nitric oxide (NO), formerly known as endothelium-derived relaxing factor (EDRF), and those of the so-called endothelium-derived hyperpolarizing factor (EDHF) have been extensively investigated. Among the latter, endothelin is probably one of the most potent endogenous vasoconstrictors. NO is a free radical which can be readly inactivated by hemoglobin. NO has all the characteristics of a gas, whereas its pharmacological properties are consistent with those of an endogenous nitrovasodilator. Therefore, inhalation of the gas NO is now considered as one of the most promising means to treat persistent pulmonary hypertension of the newborn. EDHF relaxes vascular smooth muscle through activation of ATP-dependent potassium channels. Both the chemical nature and the physiological role of EDHF are still unclear. The pharmacological properties of endothelin are far from being unequivocal. It is a potent vasoconstrictor, when it directly acts on vascular smooth muscle. However, it can also induce the release of NO and EDHF, hence causing vasorelaxation. These effects of endothelin are mediated by various transduction pathways. Activations of ET-B receptors located on endothelium on the one hand, and ET-A receptors located on smooth muscle on the other hand, are responsible for relaxation and constriction of vascular smooth muscle, respectively. Such highly complex cellular mechanisms highlight the need for further insight into the physiology of the cell related to the pulmonary circulation. This, in turn, will help to better define the target upon which one can try to correct the abnormal function of the cell underlying the pathophysiological processes.

Ischemic tissue oxygen capacitance after hyperbaric oxygen therapy: a new physiologic concept

In an effort to better understand the effects of hyperbaric oxygen therapy on ischemic tissue, we monitored the real-time changes in subcutaneous tissue oxygen tension before, during, and after exposure to hyperbaric oxygen treatments. We identified an elevation of the tissue oxygen partial pressure to over 300 mmHg during the treatment period (up from a baseline mean of 24 mmHg) in a sustained ischemia rabbit ear model (n = 22 rabbits). There was no sustained change in tissue oxygen tension beyond the period of treatment. This manner of response is consistent with several current theories used to explain the mechanism of action of hyperbaric oxygen therapy. It is also consonant with our opinion that molecular oxygen, when delivered at high pressure, can function both as a respiratory metabolite and as a signal transducer. We also studied the impact of nontherapeutic 100% oxygen at 1 atm on tissue. The sustained peak tissue oxygen tension during such challenges increased in direct proportion to the number of hyperbaric oxygen treatments given. The clinical relevance and extension of these findings are discussed.

Stress proteins and atherosclerosis

Several cytotoxic stimuli of a different nature are involved in the complex etiology of atherosclerosis. Cells of the vasculature may potentially cope with the presence of these stressors through the increased synthesis of stress proteins (or heat shock proteins, hsps), an ubiquitous and conserved defense response. Evidence exists that the expression of two stress proteins of intermediate molecular weight, hsp60 and hsp70, is higher at sites of atherosclerotic lesions than it is in normal tissue. The role of hsps in atherosclerosis is controversial. While hsp70 is likely to be involved in cytoprotection, hsp60 is probably acting as an autoantigen, and may trigger both cell-mediated and antibody-mediated immune responses.

The role of the microcirculation in multiple organ dysfunction syndrome (MODS): a review and perspective

Major advances in intensive care medicine during the past two decades have altered the spectrum of disease encountered by intensive care physicians, anaesthesiologists, traumatologists and pathologists. One of the most important manifestations of severe trauma or infections is the multiple organ dysfunction syndrome (MODS), a life-threatening condition that often ends in multiple organ failure (MOF) and death. Evidence gathered from clinical and morphological observations in humans, taken together with experimental animal studies and a vast accumulation of in vitro data, clearly indicate that the microcirculation lies at the centre of this complex process, which results in peripheral vascular insufficiency, inadequate oxygen delivery to vital organs, and hence, severe organ dysfunction. The multifunctional nature of the endothelium makes it a prime candidate for study of the pathomechanisms of MODS. This paper reviews the evidence for the hypothesis that the microcirculation, and in particular its endothelial component, has a central role in the pathogenesis of MODS. The evidence is reviewed principally from the standpoints of classical morbid anatomy and cell pathobiology.

Non-neuronal enolase is an endothelial hypoxic stress protein

The hypoxia-associated proteins (HAPs) are five cell-associated stress proteins (M(r) 34, 36, 39, 47, and 57) up-regulated in cultured vascular endothelial cells (EC) exposed to hypoxia. While hypoxic exposure of other cell types induces heat shock and glucose-regulated proteins, EC preferentially up-regulate HAPs. In order to identify the 47-kDa HAP, protein from hypoxic bovine EC lysates was isolated, digested with trypsin, and sequenced. Significant identity was found with enolase, a glycolytic enzyme. Western analyses confirmed that non-neuronal enolase (NNE) is up-regulated in hypoxic EC. Western analysis of subcellular fractions localized NNE primarily to the cytoplasm and confirmed that it was up-regulated 2.3-fold by hypoxia. Interestingly, NNE also appeared in the nuclear fraction of EC but was unchanged by hypoxia. Northern analyses revealed that NNE mRNA hypoxic up-regulation began at 1-2 h, peaked at 18 h, persisted for 48 h, and returned to base line after return to 21% O2 for 24 h. Hypoxia maximally up-regulated NNE mRNA levels 3.4-fold. While hypoxic up-regulation of NNE may have a protective effect by augmenting anaerobic metabolism, we speculate that enolase may contribute to EC hypoxia tolerance through one or more of its nonglycolytic functions.

Protection of hypoxia-induced ATP decrease in endothelial cells by ginkgo biloba extract and bilobalide

Due to their localization at the interface between blood and tissue, endothelial cells are the first target of any change occurring within the blood, and alterations of their functions can seriously impair organs. During hypoxia, which mimics in vivo ischemia, a cascade of events occurs in the endothelial cells, starting with a decrease in ATP content and leading to their activation and release of inflammatory mediators. EGb 761 and one of its constituents, bilobalide, were shown to inhibit the hypoxia-induced decrease in ATP content in endothelial cells in vitro. Under these conditions, glycolysis was activated, as evidenced by increased glucose transport, as well as increased lactate production. Bilobalide was found to increase glucose transport under normoxic but not hypoxic conditions. In addition, EGb and bilobalide prevented the increase in total lactate production observed after 60 min of hypoxia. However, after 120 min of hypoxia, the total lactate production was similar under normoxic and hypoxic conditions, and both compounds increased this production. These results indicate that glycolysis slowed down between the 60th and 120th minute of hypoxia, while EGb and bilobalide delayed the onset of glycolysis activation. In another experimental model, both compounds were shown to increase the respiratory control ratio of mitochondria isolated from liver of rats treated orally. Since ischemia is known to uncouple mitochondria, the protection of ATP content and the delay in glycolysis activation observed during hypoxia in the presence of EGb 761 or bilobalide is best explained by a protection of mitochondrial respiratory activity, at least during the first 60 min of hypoxia incubation. Both products retain the ability to form ATP, thereby reducing the cell's need to induce glycolysis, probably by preserving ATP regeneration by mitochondria as long as oxygen is available.

Changes associated with tyrosine phosphorylation during short-term hypoxia in retinal microvascular endothelial cells in vitro

The occlusion of capillary vessels results in low oxygen tension in adjacent tissues which triggers a signaling cascade that culminates in neovascularization. Using bovine retinal capillary endothelial cells (BRCEC), we investigated the effects of short-term hypoxia on DNA synthesis, phosphotyrosine induction, changes in the expression of basic fibroblast growth factor receptor (bFGFR), protein kinase C (PKC alpha), heat shock protein 70 (HSP70), and SH2-containing protein (SHC). The effect of protein tyrosine kinase (PTK) and phosphatase inhibitors on hypoxia-induced phosphotyrosine was also studied. Capillary endothelial cells cultured in standard normoxic (pO2 = 20%) conditions were quiesced in low serum containing medium and then exposed to low oxygen tension or hypoxia (pO2 = 3%) in humidified, 5% CO2, 37 degrees C, tissue culture chambers, on a time-course of up to 24 h. DNA synthesis was potentiated by hypoxia in a time-dependent manner. This response positively correlated with the cumulative induction of phosphotyrosine and the downregulation of bFGFR (M(r) approximately 85 kDa). Protein tyrosine kinase inhibitors, herbimycin-A, and methyl 2,5-dihydroxycinnamate, unlike genistein, markedly blocked hypoxia-induced phosphotyrosine. Prolonged exposure of cells to phosphatase inhibitor, sodium orthovanadate, also blocked hypoxia-induced phosphotyrosine. The expression of HSP70, PKC alpha, and SHC were not markedly altered by hypoxia. Taken together, these data suggest that short-term hypoxia activates endothelial cell proliferation in part via tyrosine phosphorylation of cellular proteins and changes in the expression of the FGF receptor. Thus, endothelial cell mitogenesis and neovascularization associated with low oxygen tension may be controlled by abrogating signaling pathways mediated by protein tyrosine kinase and phosphatases.

Induction of heat-shock proteins does not prevent renal tubular injury following ischemia

The possible protective effect of heat-shock proteins (HSPs) on ischemic injury to renal cells was assessed in two different experimental models: ischemia-reflow in intact rats and medullary hypoxic injury as seen in the isolated perfused rat kidney. Heat shock was induced by raising the core temperature of rats to 42 degrees C for 15 minutes. Following this, Northern blots showed enhanced gene expression of HSP70, HSP60 and ubiquitin at one hour and reaching a maximum by six hours after heat shock in all regions of the kidney, but most prominently in medulla and papilla. The HSP70 protein in the kidney, estimated by immunohistochemical means, was detectable 24 hours following heat shock and further increased at 48 hours following heat shock. In the first set of experiments, the animals underwent uninephrectomy followed by cross clamping of the remaining renal artery for 40 minutes prior to reflow. Serum creatinine and urea nitrogen rose to 3.15 +/- 0.98 and 126.4 +/- 62.5 mg/dl at 24 hours. No significant differences were observed at 24, 48 and 72 hours after reflow between these values in control rats and rats pretreated with heat shock 48 hours earlier. Severe morphological damage to proximal tubules of the renal cortex was observed to the same extent in both groups. In a second set of experiments, the right kidney was removed either 24 or 48 hours after heat shock and perfused in isolation for 90 minutes. Functional and morphological parameters were compared with those of isolated perfused kidneys obtained from animals that had not been subjected to heat shock.(ABSTRACT TRUNCATED AT 250 WORDS)