Adenosine induces endothelial apoptosis by activating protein tyrosine phosphatase: a possible role of p38alpha

Endothelial cell (EC) apoptosis is important in vascular injury, repair, and angiogenesis. Homocysteine and/or adenosine exposure of ECs causes apoptosis. Elevated homocysteine or adenosine occurs in disease states such as homocysteinuria and tissue necrosis, respectively. We examined the intracellular signaling mechanisms involved in this pathway of EC apoptosis. Inhibition of protein tyrosine phosphatase (PTPase) attenuated homocysteine- and/or adenosine-induced apoptosis and completely blocked apoptosis induced by the inhibition of S-adenosylhomocysteine hydrolase with MDL-28842. Consistent with this finding, the tyrosine kinase inhibitor genistein enhanced apoptosis in adenosine-treated ECs. Adenosine significantly elevated the PTPase activity in the ECs. Mitogen-activated protein kinase activities were examined to identify possible downstream targets for the upregulated PTPase(s). Extracellular signal-regulated kinase (ERK) 1 activity was slightly elevated in adenosine-treated ECs, whereas ERK2, c-Jun NH(2)-terminal kinase-1, or p38beta activities differed little. The mitogen-activated protein kinase-1 inhibitor PD-98059 enhanced DNA fragmentation, suggesting that increased ERK1 activity is a result but not a cause of apoptosis in adenosine-treated ECs. Adenosine-treated ECs had diminished p38alpha activity compared with control cells; this effect was blunted on PTPase inhibition. These results indicate that PTPase(s) plays an integral role in the induction of EC apoptosis upon exposure to homocysteine and/or adenosine, possibly by the attenuation of p38alpha activity.

Role of the Na/H antiport in pH-dependent cell death in pulmonary artery endothelial cells

We investigated the role of intracellular pH (pH(i)) and Na/H exchange in cell death in human pulmonary artery endothelial cells (HPAEC) following a metabolic insult (inhibition-oxidative phosphorylation, glycolysis). Metabolic inhibition in medium at pH 7. 4 decreased viability (0-15% live cells) over 6 h. Cell death was attenuated by maneuvers that decreased pH(i) and inhibited Na/H exchange (acidosis, Na/H antiport inhibitors). In contrast, cell death was potentiated by maneuvers that elevated pH(i) or increased Na/H exchange (monensin, phorbol ester treatment) before the insult. HPAEC demonstrated a biphasic pH(i) response following a metabolic insult. An initial decrease in pH(i) was followed by a return to baseline over 60 min. Maneuvers that protected HPAEC and inhibited Na/H exchange (acidosis, Na(+)-free medium, antiport inhibitors) altered this pattern. pH(i) decreased, but no recovery was observed, suggesting that the return of pH(i) to normal was mediated by antiport activation. Although Na/H antiport activity was reduced (55-60% of control) following a metabolic insult, the cells still demonstrated active Na/H exchange despite significant ATP depletion. Phorbol ester pretreatment, which potentiated cell death, increased Na/H antiport activity above the level observed in monolayers subjected to a metabolic insult alone. These results demonstrate that HPAEC undergo a pH-dependent loss of viability linked to active Na/H exchange following a metabolic insult. Potentiation of cell death with phorbol ester treatment suggests that this cell death pathway involves protein kinase C-mediated phosphorylation events.

Nucleotide-induced PMN adhesion to cultured epithelial cells: possible role of MUC1 mucin

Accumulation of intraluminal polymorphonuclear leukocytes (PMN) is a hallmark of inflammatory diseases of the airways. Extracellular nucleotides stimulate PMN adhesion to human main pulmonary artery endothelial cells (HPAEC) by a purinoceptor-mediated mechanism. We investigated the effects of nucleotides on adhesion of freshly isolated human PMN to cultured human tracheobronchial epithelial cells (HBEC). We found that extracellular ATP and UTP were much less effective in stimulating PMN adhesion to HBEC compared with HPAEC, whereas the bacterial chemotactic peptide N-formyl-Met-Leu-Phe stimulated PMN adhesion to both cell types to an equal degree. We investigated several mechanisms that might account for decreased nucleotide-induced PMN adhesion to HBEC. The ectonucleotidase-resistant ATP analog adenosine 5'-O-(3-thiotriphosphate) was also ineffective in stimulating PMN adhesion to HBEC, indicating that degradation of ATP by ectonucleotidase(s) was not responsible for altered PMN adhesion. HBEC responded to ATP and UTP with increased intracellular calcium, indicating that these cells are capable of purinoceptor-mediated responses. We found that ATP and UTP also did not stimulate PMN adhesion to Chinese hamster ovary (CHO) cells, which had been stably transfected with the gene for hamster Muc1, a cell-associated mucin. However, ATP and UTP did stimulate adhesion of PMN to nontransfected CHO cells. These results suggested that MUC1 mucin modulates PMN adhesion to epithelium. We found that cultured HBEC expressed more mRNA and protein for MUC1 mucin than did HPAEC. We conclude that extracellular nucleotides are less effective in stimulating PMN adhesion to epithelial cells than to endothelial cells and that overexpression of hamster Muc1 mucin inhibits nucleotide-induced PMN adhesion to CHO cells.

Effect of hypoxic exposure on Na+/H+ antiport activity, isoform expression, and localization in endothelial cells

Little is known about the effects of prolonged hypoxic exposure on membrane ion transport activity. The Na+/H+ antiport is an ion transport site that regulates intracellular pH in mammalian cells. We determined the effect of prolonged hypoxic exposure on human pulmonary arterial endothelial cell antiport activity, gene expression, and localization. Monolayers were incubated under hypoxic or normoxic conditions for 72 h. Antiport activity was determined as the rate of recovery from intracellular acidosis. Antiport isoform identification and gene expression were determined with RT-PCR and Northern and Western blots. Antiport localization and F-actin cytoskeleton organization were defined with immunofluorescent staining. Prolonged hypoxic exposure decreased antiport activity, with no change in cell viability compared with normoxic control cells. One antiport isoform [Na+/H+ exchanger isoform (NHE) 1] that was localized to the basolateral cell surface was present in human pulmonary arterial endothelial cells. Hypoxic exposure had no effect on NHE1 mRNA transcript expression, but NHE1 protein expression was upregulated. Immunofluorescent staining demonstrated a significant alteration of the F-actin cytoskeleton after hypoxic exposure but no change in NHE1 localization. These results demonstrate that the decrease in NHE1 activity after prolonged hypoxic exposure is not related to altered gene expression. The change in NHE1 activity may have important consequences for vascular function.

Mechanism of extracellular ATP- and adenosine-induced apoptosis of cultured pulmonary artery endothelial cells

Apoptosis may be important in the exacerbation of endothelial cell injury or limitation of endothelial cell proliferation. We have found that extracellular ATP (exATP) and adenosine cause endothelial apoptosis and that the development of apoptosis is linked to intracellular metabolism of adenosine [Dawicki, D. D., D. Chatterjee, J. Wyche, and S. Rounds. Am. J. Physiol. 273 (Lung Cell Mol. Physiol. 17): L485-L494, 1997]. In the present study, we investigated the mechanism of this effect. We found that exATP, adenosine, and the S-adenosyl-L-homocysteine (SAH) hydrolase inhibitor MDL-28842 caused apoptosis and decreased the ratio of S-adenosyl-L-methionine to SAH compared with untreated control cells. Using release of soluble [3H]thymidine as a measure of DNA fragmentation, we found that the effect of adenosine on soluble DNA release was potentiated by coincubation with homocysteine. These results suggest that the mechanism of exATP- and adenosine-induced endothelial cell apoptosis involves inhibition of SAH hydrolase. exATP-induced apoptosis was enhanced by an inhibitor of adenosine deaminase, whereas exogenous adenosine-induced apoptosis was partially inhibited by an adenosine deaminase inhibitor. These results suggest that adenosine deaminase may also be involved in the mechanism of adenosine-induced endothelial cell apoptosis. Adenosine and MDL-28842 caused intracellular acidosis as assessed with the fluorescent probe 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. The cell-permeant base chloroquine prevented adenosine-induced acidosis but not apoptosis. Thus, although intracellular acidosis is associated with adenosine-induced apoptosis, it is not necessary for this effect. We speculate that exATP- and adenosine-induced endothelial cell apoptosis may be due to an inhibition of methyltransferase(s) activity. Purine-induced endothelial cell apoptosis may be important in limiting endothelial cell proliferation after vascular injury.

Tibial insert undersurface as a contributing source of polyethylene wear debris

Sixty-seven ultrahigh molecular weight polyethylene tibial inserts from cementless total knee arthroplasties were retrieved at autopsy and revision surgery and analyzed for evidence of articular and nonarticular surface wear after a mean implantation time of 62.8 months (range, 4-131 months). Polyethylene cold flow and abrasive wear on the nonarticular insert surface (undersurface) were assigned a wear severity score (Grade 0-4). The severity of articular wear was assessed quantitatively and graded. Corresponding prerevision radiographs were evaluated for evidence of tibial metaphyseal osteolysis and osteolysis around tibial fixation screws. Exact nonparametric conditional inference methods were used to establish correlations between different variables and the occurrence of tibial metaphyseal osteolysis. Severe Grade 4 wear of the tibial insert undersurface was associated with tibial metaphyseal osteolysis or osteolysis around fixation screws. Time in situ statistically was related to Grade 4 undersurface wear and tibial metaphyseal osteolysis. The occurrence of tibial osteolysis was not related statistically to articular wear severity, insert thickness, or implant type. The main articulation between the femoral implant and ultrahigh molecular weight polyethylene insert has been assumed to be the primary source of polyethylene debris contributing to osteolysis and total knee arthroplasty implant failure. The undersurface of the insert is an additional source of polyethylene debris contributing to tibial metaphyseal osteolysis. To lessen polyethylene debris produced at this modular interface, the tibial implant locking mechanism should fix the insert firmly to the metal backing to decrease relative micromotion. Because motion between the insert and metal backing may be inevitable, the wear characteristics of the inner tray surface should be optimized to minimize wear debris production at this other articulation.

Differences in nucleotide effects on intracellular pH, Na+/H+ antiport activity, and ATP-binding proteins in endothelial cells

Bovine (BPAEC) and human (HPAEC) pulmonary artery endothelial cell monolayers were incubated with either ATP, ATP analogues, or UTP, followed by measurement of intracellular pH (pHi) and the rate of recovery from acidosis. ATP increased baseline pHi and the rate of acid recovery in BPAEC. This response was inhibited by the amiloride analogue, methyisobutylamiloride, demonstrating that activation of the Na+/H+ antiport was responsible for the increase in baseline pHi and the recovery from acidosis. This response had the features of both a P2Y and P2U purinergic receptor, based on the responses to a series of ATP analogues and UTP. In contrast, none of the nucleotides had any significant effect on pHi and Na+/H+ antiport activity in HPAEC. This difference in the response to extracellular nucleotides was not due to a difference in ATP metabolism between cell types, since the ectonucleotidase-resistant analogue. ATP gamma S, also had no effect on HPAEC. Analogues of cAMP had no effect on pHi or acid recovery in either cell type. Incubation of BPAEC and HPAEC with the photoaffinity ligand [32P] 8-AzATP indicated that both BPAEC and HPAEC possess an ATP-binding protein of 48 kDa. However, BPAEC exhibited an additional binding protein of 87 kDa. Thus, the contrasting response to extracellular ATP between bovine and human pulmonary artery endothelial cells may be related to differences in the signal transduction pathway leading to antiport activation, including different ATP-binding sites on the cell membrane.

Bilateral absence of the ovaries and distal fallopian tubes. A case report

BACKGROUND

Bilateral tuboovarian absence is extremely rare and is associated with infantile sexual development, primary amenorrhea and primary infertility.

CASE

A 23-year-old woman presented for evaluation of primary amenorrhea. Her examination revealed hypoplastic breasts, genitalia and uterus; ovaries could not be identified. Marked estrogen deficiency was confirmed by endocrinologic testing. The karyotype was normal female. The patient was started on combined hormone replacement therapy and subsequently developed normal menses; physical maturation progressed normally. At the age of 29 she underwent diagnostic laparoscopy for evaluation of her fertility potential, at which time the absence of both ovaries and distal fallopian tubes was confirmed.

CONCLUSION

Bilateral tuboovarian absence is an extremely rare cause of primary amenorrhea and is associated with infantile sexual development and primary infertility. Its etiology includes tuboovarian torsion and congenital malformation. In this case, congenital malformation appears to have been the more likely cause.

Effect of hyperoxia and exogenous oxidant stress on pulmonary artery endothelial cell Na+/H+ antiport activity

Little is known about the mechanisms of altered cell membrane function after hyperoxic exposure. We determined the effects of hyperoxic exposure and exogenous oxidant stress with xanthine/xanthine oxidase (X/XO) on Na+/H+ antiport activity. Pulmonary artery endothelial cell monolayers were incubated in 95% O2/5% CO2 (24 to 72 hours) simultaneously with controls placed in 21 % O2/5% CO2. Monolayers were then incubated for 2 hours in MEM with or without X/XO (100 micromol/L X; 0.01 U/ml XO). Antiport activity was determined as the rate of recovery from intracellular acidosis by measurement of intracellular pH (pH,) with 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein (BCECF). Hyperoxic exposure (72 hours) decreased Na+/H+ antiport activity as compared with that in control monolayers. Exogenous oxidant stress also decreased antiport activity in both control and hyperoxic cells, but this effect was more pronounced in hyperoxic cells at all time points. These changes occurred in the absence of overt cytotoxicity. Incubation with antioxidants (polyethylene glycol-superoxide dismutase (PEG-SOD), PEG-catalase, vitamin E), N-acetylcysteine, or phospholipase A2 (PLA2) inhibitors did not prevent the decrease in antiport activity after hyperoxic exposure. Conditioned medium experiments demonstrated that the diminished antiport activity was not related to release of a soluble mediator after hyperoxic exposure. These findings suggest that the diminished Na+/H+ antiport activity represents a sublethal form of membrane dysfunction that may be a component of the increased endothelial cell susceptibility to injury after hyperoxic exposure.

Effect of ATP-induced permeabilization on loading of the Na+ probe SBFI into endothelial cells

The fluoroprobe sodiumbinding benzofuran isophthalate (SBFI) is used to measure intracellular cytosolic sodium concentration ([Na]i). A problem with the use of this probe is the difficulty in loading it into cells. ATP reversibly increases membrane permeability of some cells via activation of receptors of the tetrabasic form of ATP (ATP4-). We investigated the effect of ATP-induced membrane permeabilization on loading of the acetoxymethyl ester (AM) form of SBFI (SBFI-AM) into bovine pulmonary arterial endothelial cells. Monolayers were incubated in a series of solutions that reversibly opened pores, loaded the fluoroprobe, and finally sealed the proes. ATP (1-5 mM) or 3'-O-(4-benzoyl)benzoyl-ATP (0.1-1 mM), an analogue 30-100x more specific for ATP4- receptors, was utilized to permeabilize the cell membrane. The signal-to-background ratio of the intracellular SBFI fluorescent signal was used as an indicator of the effectiveness of dye loading. ATP and 3'-O-(4-benzoyl)benzoyl-ATP significantly increased the signal-to-background ratio compared with the values obtained with the standard dye-loading procedure without ATP, indicating that permeabilization increased SBFI-AM entry into the cells. The permeabilization procedure produced a small decrease in cell viability, as determined with a fluorescent viability assay (ethidium dimer uptake), compared with the standard method of loading SBFI-AM. We used the procedure to measure baseline [Na]i and changes in [Na]i after the administration of ouabain (10(-4) M) and monensin (10(-5) M). Baseline [Na]i with this procedure (19.7 +/- 2.7 mM; n = 15 monolayers) was similar to measurements made in other cell types with the standard method of loading the probe. We conclude that 1) the ATP-induced permeabilization technique is an improved dye-loading method for SBFI-AM in endothelial cell monolayers that facilitates measurement of [Na]i and 2) these data suggest the presence of an ATP4 pore-forming mechanism in this cell type.

Oxidant stress decreases Na+/H+ antiport activity in bovine pulmonary artery endothelial cells

We determined the effects of oxidant stress by the use of tert-butyl hydroperoxide (t-BOOH) on Na+/H+ exchange in pulmonary artery endothelial cells. Monolayers were exposed to the hydroperoxide, followed by measurement of intracellular pH and the rate of recovery from acidosis by utilizing the pH-sensitive probe 2',7'-bis(carboxyethyl)-5(6)- carboxyfluorescein. t-BOOH (0.4 mM) decreased the rate of acid recovery after a 2-h exposure without evidence of overt cytotoxicity (51Cr-release assay). Glutathione repletion (N-acetyl-L-cysteine) abolished the effect of the hydroperoxide. Lowering intracellular glutathione with buthionine sulfoximine decreased the acid recovery rate at a dose of t-BOOH (0.04 mM) that was not normally associated with a change in this parameter. Preincubation with vitamin E had no protective effect. Dithiothreitol abolished the effect of the hydroperoxide, suggesting oxidation of protein sulfhydryl groups as a mechanism for the altered kinetics of acid recovery. There was no difference in cell buffering capacity between control and treated monolayers. The findings suggest that the decrease in Na+/H+ antiport activity in this model of oxidant stress represents an early perturbation of membrane function and illustrate the role of the glutathione redox system in maintaining the functional integrity of the Na+/H+ antiport in these cells.