Angiotensin II induces secretion of plasminogen activator inhibitor 1 and a tissue metalloprotease inhibitor-related protein from rat brain astrocytes

Collagen receptor- and metalloproteinase-dependent hypertensive stress response in mesangial and glomerular endothelial cells

Progressive alteration of the extracellular matrix (ECM) is the characteristic of hypertensive nephropathy (HN). Both mesangial and endothelial cells have the ability to synthesize and degrade ECM components, including collagens through the activation of matrix metalloproteinases (MMPs) in stress conditions, such as in hypertension. On the other hand, hydrogen sulfide (H2S) has been shown to mitigate hypertensive renal matrix remodeling. Surprisingly, whether H2S ameliorates receptor-mediated (urokinase plasminogen activator receptor-associated protein, uPARAP/Endo180) collagen dysregulation in Ang-II hypertension is not clear. The purpose of this study was to determine whether Ang-II alters the expression of Endo180, tissue plasminogen activator (tPA), MMPs, and their tissue inhibitors (TIMPs) leading to the dysregulation of cellular collagen homeostasis and whether H2S mitigates the collagen turnover. Mouse mesangial cells (MCs) and glomerular endothelial cells (MGECs) were treated without or with Ang-II and H2S donor GYY (GYY4137) for 48 h. Cell lysates were analyzed by Western blot and RT-PCR, and cells were analyzed by immunocytochemistry. The results indicated that, while Ang-II differentially expressed MMP-13 and TIMP-1 in MCs and in MGECs, it predominantly decreased tPA, Endo 180, and increased plasminogen activator inhibitor-1 (PAI-1), MMP-14, and collagen IIIA and IV in both the cell types. Interestingly, H2S donor GYY treatment normalized the above changes in both the cell types. We conclude that Ang-II treatment causes ECM remodeling in MCs and MGECs through PAI-1/tPA/Endo180 and MMP/TIMP-dependent collagen remodeling, and H2S treatment mitigates remodeling, in part, by modulating these pathways.

Close association of p38 and JNK with plasminogen-dependent upregulation of PAI-1 in rat astrocytes in vitro

As reported previously, stimulation of astrocytes with plasminogen (PLGn) remarkably enhances their production/release of plasminogen activator inhibitor-1 (PAI-1). In addition, both p38 mitogen-activated protein kinase (p38MAPK) and c-Jun N-terminal kinase (JNK) are activated in these astrocytes. However, it remains to be determined whether the MAPK activation is associated with the PAI-1 induction in PLGn-stimulated astrocytes. In the present study, we investigated the relationship between MAPK activity and PAI-1 induction in PLGn-stimulated astrocytes. PLGn stimulation led to definitive phosphorylation of three MAPKs: external signal regulated kinase (ERK), JNK and p38. These results suggest that all of these MAPKs, either alone or in combination, are involved in PAI-1 induction. To verify this association, an inhibition experiment was carried out by using inhibitors specific for each MAPK. The results of the immunoblotting analysis indicated that 20 microM SB203580 (the p38 inhibitor) or SP600125 (the JNK inhibitor) suppressed approximately 85% or 40% of PLGn-inducible PAI-1, respectively. Only 20% inhibition was achieved by pretreatment of astrocytes with 20 microM PD98059 (the inhibitor of MEK1/2, an upstream kinase of ERK). In conclusion, p38 and JNK were shown to be the major MAPKs involved in the signaling cascade leading to PAI-1 induction in astrocytes stimulated with PLGn.

Short-term effects of angiotensin receptor blockers on blood pressure control, and plasma inflammatory and fibrinolytic parameters in patients taking angiotensin-converting enzyme inhibitors

INTRODUCTION

Angiotensin-converting enzyme (ACE) inhibitors reduce cardiovascular events in patients with established vascular disease and heart failure (HF). ACE-inhibitors have important effects on fibrinolytic balance, which may be the underlying mechanism for a reduction in cardiovascular events. Although angiotensin-receptor blockers (ARBs) offer greater tolerability than ACE-inhibitors, the major ARB trials have demonstrated a lack of reduction in myocardial infarction (MI) occurrence and mortality in contrast to ACE-inhibitors. In this study, we investigated the combined effects of ARBs and ACE-inhibitors on fibrinolytic and inflammatory parameters in patients with uncontrolled hypertension.

METHODS

Twenty-four patients with uncontrolled hypertension despite taking adequate doses of ACE-inhibitor therapy were selected. Patients were started on Candesartan 16 mg once a day. Plasma plasminogen activator inhibitor (PAI-1) antigen (Ag), tissue plasminogen activator (t-PA) Ag, thrombin-activatable fibrinolysis inhibitor (TAFI) % activity and high sensitivity C-reactive protein (hsCRP) levels, were measured during low salt intake at baseline and two weeks after therapy with an ARB.

RESULTS

Addition of ARB to the regimen reduced systolic (155+/-17 vs. 139+/-13, p<0.001), and diastolic (91+/-9 vs. 81+/-8, p<0.001) blood pressures (BP). No significant changes were observed in PAI-1 Ag (66+/-51 vs. 68+/-52, p=0.9), t-PA Ag (12.6+/-5.3 vs. 13.3+/-4.7, p=0.3), TAFI % activity (119+/-30 vs. 118+/-32, p=0.9) and hsCRP (3.9+/-3.4 vs. 3.6+/-3.6, p=0.7) levels after adding an ARB.

CONCLUSIONS

Combined ARB and ACE-inhibitor use provide better BP control without any detrimental effect in plasma inflammatory and fibrinolytic parameters.

Impact of cilazapril on fibrinolytic system in hypertensive patients

Impaired fibrinolysis is associated with thromboembolic complications in hypertensive patients. Cardiovascular morbidity/mortality rates have been reported high even after lowering the elevated blood pressure with antihypertensive drugs. We investigated the effects of clinically used dosages of cilazapril on the fibrinolytic system in hypertensive patients. The present study was performed among 30 hypertensive patients (22 women, eight men), who received 2.5-5.0 mg cilazapril daily for 1 month. Before and after the cilazapril treatment, patients' venous blood was drawn for fibrinolytic tests. The fibrinolytic activity was examined utilizing the euglobulin clot lysis time and fibrin plate methods. Using the fibrin plate method, as compared with the pretreatment group, we observed a 57% increased activity in the hypertensive patients receiving cilazapril (P < 0.001). When assessed by the euglobulin clot lysis time method, the activity due to cilazapril treatment was found to be relatively low, although highly significant (approximately 20%, P < 0.001). Changes in fibrinolytic activity were observed in 23 (77%) hypertensive patients after cilazapril treatment; however, their blood pressure remained normal. The remaining seven patients' (23%) blood pressures and fibrinolytic activity did not change significantly after cilazapril treatment. In conclusion, we suggest that the observed differential fibrinolytic activity between the pre and post cilazapril treatment values is due to the plasminogen activators released from the vascular endothelium, which may have been stimulated by cilazapril. It appears that cilazapril is not only an angiotensin-converting enzyme inhibitor but also a stimulator for fibrinolytic activity, which may be an added component in reducing thromboembolic complications in hypertensive patients.

Bradykinin B2 receptor knockout mice are protected from thrombosis by increased nitric oxide and prostacyclin

Bradykinin (BK) liberates nitric oxide, prostacyclin, and tissue plasminogen activator from endothelial cells. We hypothesized that BK B2 receptor knockout (KO) mice (BKB2R(-/-)) have increased thrombosis risk. Paradoxically, the BKB2R(-/-) mice have long bleeding times and delayed carotid artery thrombosis, 78 +/- 6.7 minutes, versus 31 +/- 2.7 minutes in controls. The mechanism(s) for thrombosis protection was sought. In BKB2R(-/-) plasma coagulation, fibrinolysis and anticoagulant proteins are normal except for an increased prekallikrein and decreased factor XI. BKB2R(-/-) mice have elevated BK 1-5 (160 +/- 75 fmol/mL, vs 44 +/- 29 fmol/mL in controls) and angiotensin II (182 +/- 41 pg/mL, vs 49 +/- 7 pg/mL in controls). Ramipril treatment shortens vessel occlusion time. BKB2R(-/-) mice have elevated plasma 6-keto-PGF1alpha (666 +/- 232 ng/mL, vs 23 +/- 5.3 ng/mL in controls) and serum nitrate (61 +/- 5.3 microM, vs 24 +/- 1.8 microM in controls). Treatment with L-NAME (NG-mono-methyl-L-arginine ester) or nimesulide shortens the thrombosis time. BKB2R(-/-) mice have increased angiotensin receptor 2 (AT2R) mRNA and protein expression. Treatment with an AT2R antagonist, PD123 319, normalizes the thrombosis time and nitrate and 6-keto-PGF1alpha. The long bleeding times in BKB2R(-/-) mice also correct with L-NAME and nimesulide therapy. In BKB2R(-/-) mice, angiotensin II binding to an overexpressed AT2R promotes thromboprotection by elevating nitric oxide and prostacyclin. These investigations indicate a pathway for thrombosis risk reduction via the plasma kallikrein/kinin and renin angiotensin systems.

Interleukin-1β enhances the angiotensin-induced expression of plasminogen activator inhibitor-1 through angiotensin receptor upregulation in human astrocytes

Plasminogen activator inhibitor-1 (PAI-1) regulates not only fibrinolysis but extracellular matrix remodeling, and angiotensin II is known to play an important role in controlling the expression of PAI-1 in astrocytes. We have studied the effect of interleukin-1beta (IL-1beta), one of major cytokines also active in the nervous system, on the angiotensin II-induced expression of PAI-1 in human astrocytes. Cultures of normal human astrocytes were stimulated with IL-1beta and angiotensin II, and the expression of mRNAs for angiotensin II type 1 receptor (AT1) and PAI-1 was analyzed by reverse transcription-polymerase chain reaction (RT-PCR) or real-time quantitative PCR. PAI-1 protein in astrocyte-conditioned medium was measured by enzyme-linked immunosorbent assay (ELISA). IL-1beta enhanced the expression of AT1 in astrocytes in time- and concentration-dependent manners. After 24-h stimulation, 10 ng/ml IL-1beta and 10 nM angiotensin II increased the levels of PAI-1 protein in astrocyte-conditioned medium by 1.9-fold and 1.8-fold of the basal value, respectively. There was no synergistic effect when the cells were stimulated simultaneously with IL-1beta and angiotensin II. When the cells were stimulated, with angiotensin II, 16 h after the stimulation with IL-1beta, the production of PAI-1 was enhanced by 1.4-fold as compared to the cells stimulated only with IL-1beta. CV-11794, an AT1 antagonist, inhibited the enhanced PAI-1 production in response to angiotensin II. We conclude that IL-1beta increases angiotensin II-induced PAI-1 secretion by astrocytes through the induction of AT1, and the enhanced secretion of PAI-1 may modulate functions of plasminogen activators in the nervous system.

Short-term effects of exogenous angiotensin II on plasma fibrinolytic balance in normal subjects

OBJECTIVE

Numerous studies have provided evidence for a direct functional link between the renin-angiotensin-aldosterone system and the fibrinolytic system. Angiotensin II has been suggested to mediate this interrelationship because this peptide was shown to stimulate plasminogen activator inhibitor-1 (PAI-1) in experimental settings. However, evidence from studies in man regarding effects of Angiotensin II on fibrinolytic function remains controversial.

METHODS

In the present study, we have therefore infused Angiotensin II at doses of 1, 3 and 10 ng kg(-1) min(-1), each over 45 min, in 9 healthy volunteer subjects without and with pretreatment with a single dose of the Angiotensin II (type 1) (AT1)-receptor antagonist valsartan (160 mg).

RESULTS

Angiotensin II infusion dose-dependently increased plasma Angiotensin II concentrations and systolic/diastolic arterial blood pressure from 121 +/- 2/70 +/- 2 mmHg to 146 +/- 2/97 +/- 1 mmHg (p < 0.001). The maximum increase in blood pressure was completely abolished (118 +/- 3/72 +/- 1 mmHg) when Angiotensin II was infused in volunteers pretreated with valsartan. In spite of the marked hemodynamic changes seen with the Angiotensin II infusion, no effect could be demonstrated on the activity and antigen concentration of PAI-1. Furthermore, pretreatment of the volunteers with valsartan markedly blunted the increase in arterial blood pressure but was not associated with changes in PAI-1.

CONCLUSION

In conclusion, in healthy volunteer subjects, short-term infusion of Angiotensin II without and with concomitant administration of an AT1-receptor antagonist has no effect on PAI-1 activities and plasma concentrations.

A mutant, noninhibitory plasminogen activator inhibitor type 1 decreases matrix accumulation in experimental glomerulonephritis

In fibrotic renal disease, elevated TGF-beta and angiotensin II lead to increased plasminogen activator inhibitor type 1 (PAI-1). PAI-1 appears to reduce glomerular mesangial matrix turnover by inhibiting plasminogen activators, thereby decreasing plasmin generation and plasmin-mediated matrix degradation. We hypothesized that therapy with a mutant human PAI-1 (PAI-1R) that binds to matrix vitronectin but does not inhibit plasminogen activators, would enhance plasmin generation, increase matrix turnover, and decrease matrix accumulation in experimental glomerulonephritis. Three experimental groups included normal, untreated disease control, and PAI-1R-treated nephritic rats. Plasmin generation by isolated day 3 glomeruli was dramatically decreased by 69%, a decrease that was reversed 43% (P < 0.02) by in vivo PAI-1R treatment. At day 6, animals treated with PAI-1R showed significant reductions in proteinuria (48%, P < 0.02), glomerular staining for periodic acid-Schiff positive material (33%, P < 0.02), collagen I (28%, P < 0.01), collagen III (34%, P < 0.01), fibronectin (48%, P < 0.01), and laminin (41%, P < 0.01), and in collagen I (P < 0.01) and fibronectin mRNA levels (P < 0.02). Treatment did not alter overexpression of TGF-beta1 and PAI-1 mRNAs, although TGF-beta1 protein was significantly reduced. These observations strongly support our hypothesis that PAI-1R reduces glomerulosclerosis by competing with endogenous PAI-1, restoring plasmin generation, inhibiting inflammatory cell infiltration, decreasing local TGF-beta1 concentration, and reducing matrix accumulation.

The kallikrein-kinin and the renin-angiotensin systems have a multilayered interaction

Understanding the physiological role of the plasma kallikrein-kinin system (KKS) has been hampered by not knowing how the proteins of this proteolytic system, when assembled in the intravascular compartment, become activated under physiological conditions. Recent studies indicate that the enzyme prolylcarboxypeptidase, an ANG II inactivating enzyme, is a prekallikrein activator. The ability of prolylcarboxypeptidase to act in the KKS and the renin-angiotensin system (RAS) indicates a novel interaction between these two systems. This interaction, along with the roles of angiotensin converting enzyme, cross talk between bradykinin and angiotensin-(1-7) action, and the opposite effects of activation of the ANG II receptors 1 and 2 support a hypothesis that the plasma KKS counterbalances the RAS. This review examines the interaction and cross talk between these two protein systems. This analysis suggests that there is a multilayered interaction between these two systems that are important for a wide array of physiological functions.

Chronic thrombotic microangiopathy associated with antineoplastic therapy with minimal hematologic effects

OBJECTIVE

To describe 6 patients who developed progressive renal failure and renal thrombotic microangiopathy (TM) not accompanied by the characteristic hematologic disturbances of TM syndromes.

PATIENTS AND METHODS

Portions of renal biopsy specimens from each patient were examined by light and electron microscopy for histopathologic evidence of TM. Antecedent clinical events, laboratory evidence of hemolysis and thrombocytopenia, and clinical outcome were documented. Medical records were reviewed and clinical data, including laboratory values, treatment, and outcome, were recorded.

RESULTS

In each case, a slowly progressive uremia evolved after radiation and/or chemotherapy without laboratory evidence of acute hemolysis or thrombocytopenia. Renal biopsy specimens in all cases showed TM and tubulointerstitial scarring, suggesting both acute and chronic renal injury. Two of the 6 patients underwent plasma exchange therapy without improvement of renal function. Three patients treated with angiotensin-converting enzyme inhibitors for coexisting systemic hypertension remained stable or had mild improvement in renal function.

CONCLUSIONS

A small subset of patients treated for malignancy developed slowly evolving uremia associated with renal TM without marked hematologic abnormalities. In the absence of thrombocytopenia and other typical laboratory findings, the diagnosis of renal TM may be overlooked.

L-158,809 and (D-Ala(7))-angiotensin I/II (1-7) decrease PAI-1 release from human umbilical vein endothelial cells

The endothelium is a major source of plasminogen activator inhibitor-1 (PAI-1), which plays a critical role in the regulation of fibrinolysis. There are many reports on the increase in the expression of PAI-1 by angiotensin II (Ang II). In the present study, we investigated the effects of angiotensin-related substances on the release of PAI-1 from human umbilical vein endothelial cells (HUVECs). Ang II increased PAI-1 and tissue plasminogen activator (t-PA) release, while its metabolite angiotensin-(1-7) (Ang-(1-7)) amino acid fragment decreased them. Angiotensin Type 1 (AT1) receptor antagonist, L-158,809 (L-1), and Ang-(1-7) receptor antagonist, (D-Ala(7))-angiotensin I/II (1-7) (D-Ala), decreased PAI-1 and t-PA release; angiotensin Type 2 (AT2) antagonist, PD123,319 (PD), however, did not have any effects on the release of PAI-1 and t-PA. The addition of the equal concentration or 10-times-higher concentration of L-1 to Ang II did not change PAI-1 release compared to that by Ang II. Although Ang-(1-7) and L-1 decreased PAI-1 release, there were no additional effects on the decrease of the amounts of PAI-1 by the mixture of Ang-(1-7) and the equal concentration or 10-times-higher concentration of L-1 compared to those by Ang-(1-7). The equal concentration of D-Ala to Ang II did not change the amounts of PAI-1, but the addition of the 10-times-higher concentration of D-Ala to Ang II resulted in significant decrease of the amounts of PAI-1 compared to those by Ang II. The addition of equal concentration or 10-times-higher concentration of D-Ala to Ang-(1-7) showed the significant decrease of the amounts of PAI-1 compared to those by Ang-(1-7). In conclusion, L-158,809 and (D-Ala(7))-angiotensin I/III (1-7) may be used as profibrinolytic drugs.

Plasminogen activator inhibitor-1 and haemostasis in obesity

The connection between obesity and disordered haemostasis is well established, but incompletely understood. There is a strong link between inhibition of fibrinolysis and obesity, and elevation of the plasma inhibitor, plasminogen activator inhibitor-1 (PAI-1), is regarded as a central factor. Here we explore the increased risk of atherothrombotic disorders in obese subjects, and the evidence for metabolic and genetic causes. There is a clear relationship between plasma PAI-1 and obesity, and adipose tissue synthesises PAI-1, as has been shown in mouse and rat models, and more recently in human material. This tissue also produces several effector molecules that can up regulate PAI-1. These molecules include transforming growth factor beta, tumour necrosis factor alpha, angiotensin II and interleukin 6, all of which up regulate PAI-1 in various cell types. The issue of whether adipose tissue directly contributes to plasma PAI-1, or whether it primarily contributes indirectly, its products stimulating other cells to produce PAI-1 that feeds into the plasma pool, is not yet resolved. Finally, we briefly examine other proteins of haemostasis that are products of adipose tissue. Further studies are needed to define the regulation of these proteins, in adipose tissue itself and in other cells influenced by its products, in order to extend recent insights into the links between obesity and haemostasis.

Suppression of experimental abdominal aortic aneurysms in the rat by treatment with angiotensin-converting enzyme inhibitors

PURPOSE

Pathologic remodeling of the extracellular matrix is a critical mechanism in the development and progression of abdominal aortic aneurysms (AAAs). Although angiotensin-converting enzyme (ACE) inhibitors are known to alter vascular wall remodeling in other conditions, their effects on AAAs are unknown. In this study we assessed the effect of ACE inhibitors in a rodent model of aneurysm development.

METHODS

Male Wistar rats underwent transient aortic perfusion with porcine pancreatic elastase, followed by treatment with one of three ACE inhibitors (captopril [CP], lisinopril [LP], or enalapril [EP]), an angiotensin (AT)1 receptor antagonist (losartan [LOS]), or water alone (9 rats in each group). Blood pressure and aortic diameter (AD) were measured before elastase perfusion and on day 14, with an AAA defined as an increase in AD (DeltaAD) of more than 100%. The structural features of the aortic wall were examined by means of light microscopy.

RESULTS

Aneurysmal dilatation consistently developed within 14 days of elastase perfusion in untreated rats, coinciding with the development of a transmural inflammatory response and destruction of the elastic media (mean DeltaAD, 223% +/- 28%). All three ACE inhibitors prevented AAA development (mean DeltaAD: CP, 67% +/- 4%; LP, 18% +/- 12%; and EP, 14% +/- 3%; each P <.05 vs controls). ACE inhibitors also attenuated the degradation of medial elastin without diminishing the inflammatory response. Surprisingly, the aneurysm-suppressing effects of ACE inhibitors were dissociated from their effects on systemic hemodynamics, and LOS had no significant effect on aneurysm development compared with untreated controls (mean DeltaAD, 186% +/- 19%).

CONCLUSION

Treatment with ACE inhibitors suppresses the development of elastase-induced AAAs in the rat. Although this is associated with the preservation of medial elastin, the mechanisms underlying these effects appear to be distinct from hemodynamic alterations alone or events mediated solely by AT1 receptors. Further studies are needed to elucidate how ACE inhibitors influence aortic wall matrix remodeling during aneurysmal degeneration.

Angiotensin II-induced calcium signalling in neurons and astrocytes of rat circumventricular organs

The subfornical organ and organum vasculosum laminae terminalis represent neuroglial circumventricular organ structures bordering the anterior third cerebral ventricle. Owing to the absence of the blood-brain barrier, the cellular elements of the subfornical organ and the organum vasculosum laminae terminalis can be reached by circulating messenger molecules transferring afferent information. As demonstrated for the control of extracellular fluid composition, the circulating hormone angiotensin II acts on these sensory circumventricular organs to induce drinking, elevated peripheral resistance and neurohypophyseal hormone release via interaction with membrane-spanning receptor proteins. To characterize the cell-specific distribution of angiotensin II receptors within the circumventricular organs, primary cell cultures derived from the subfornical organ or organum vasculosum laminae terminalis of five- to six-day-old rat pups were used to measure alterations in intracellular calcium at the single cell level. Neurons and astrocytes were identified by immunocytochemical staining for specific marker proteins. Bath application of angiotensin II (10(-10)-10(-6) M) dose-dependently induced calcium transients in neurons (19.6%) and astrocytes (15.7%), and angiotensin II threshold concentrations to elicit intracellular calcium signalling proved to be one order of magnitude higher in astrocytes as compared to neurons (10(-9) M). At angiotensin II concentrations higher than 10(-7) M, pronounced desensitization of the angiotensin II receptor occurred. Employing the angiotensin II receptor antagonists losartan (DUP-753; AT1-receptor) and PD-123319 (AT2-receptor), exclusive expression of the AT1 receptor subtype coupled to intracellular calcium concentration signalling could be demonstrated for neurons and astrocytes. In all cells examined, the angiotensin II-evoked increase in intracellular calcium concentrations could be fully suppressed in the absence of extracellular calcium. Co-activation by angiotensin II and other agents (vasopressin, its fragment 8-arginine-vasopressin(4-9), oxytocin, endothelin) was indicated for subfornical organ neurons and organum vasculosum laminae terminalis astrocytes.

Saralasin-induced inhibition of ovulation in the in vitro perfused rat ovary is not replicated by the angiotensin II type-2 receptor antagonist PD123319

OBJECTIVE

Our aim was to explain the effect of the nonspecific angiotensin II antagonist saralasin and the specific angiotensin II type-2 receptor antagonist PD123319 on ovulation.

STUDY DESIGN

Saralasin, 1 micromol/L (n = 5), and PD123319 10 micromol/L (n = 6), were administered to in vitro perfused rat ovary. Prostaglandin (prostaglandin E2, prostaglandin F2alpha, 6-keto-prostaglandin F1alpha), hydroxy-eicosatetraenoic acid (12-hydroxy-eicosatetraenoic acid, 15-hydroxy-eicosatetraenoic acid), estradiol, and progesterone levels in the perfusate and the ovulation rate were compared (Mann-Whitney U test) with controls.

RESULTS

Saralasin significantly (P < .01) inhibited the ovulation rate (3.0 +/- 1.4) versus control (13.1 +/- 1.0) and reduced prostaglandin E2 (at 3 hours P < .01 and 20 hours P < .05) and 6-keto-prostaglandin F1alpha (at 20 hours P < .05) levels. Saralasin did not alter prostaglandin F2alpha, hydroxy-eicosatetraenoic acids, or steroid levels. PD123319 decreased 15-hydroxy-eicosatetraenoic acid levels at 3 hours (P < .05) but had no effects on other eicosanoids, steroid levels, or the ovulation rate.

CONCLUSION

Angiotensin II plays an important role in ovulation in the rat and is associated with ovarian prostaglandin synthesis. This effect is not selectively regulated via the angiotensin II type-2 receptor.

Molecular cloning of the cDNA coding sequence of IL-2 receptor-gamma (gammac) from human and murine forebrain: expression in the hippocampus in situ and by brain cells in vitro

IL-2 has been implicated in various neurobiological processes of the mammalian CNS. To understand how IL-2 acts in the brain, our lab has sought to determine the molecular pharmacological characteristics of brain IL-2 receptors (IL-2R). The lymphocyte IL-2Rgamma, an essential subunit for IL-2 signaling, is also a common subunit (gammac) for multiple immune cytokine receptors (e.g., IL-4R, IL-7R, IL-9R, IL-15R). Having previously cloned the alpha and beta subunits of the IL-2R heterotrimer complex from normal murine forebrain, we examined the hypothesis that the brain IL-2Rgamma is derived from the same or a closely related gene coding sequence as that expressed by lymphocytes. In this study, we cloned and sequenced the full-length IL-2Rgamma coding region from saline-perfused mouse forebrain and from a human hippocampal library. The cDNA sequences of IL-2Rgamma from human and murine brain were 100% homologous to their lymphocyte sequences. Northern blot analysis showed that the mRNA transcripts in murine brain were the expected size, but the predominant transcript expressed in the brain was different than in the spleen. Compared to the spleen, very low levels of IL-2Rgamma were expressed in the forebrain. In the murine hippocampus, a region where a number of neurobiological actions of IL-2 have been reported, IL-2Rgamma mRNA was detected over the dentate gyrus and CA1-CA4 by in situ hybridization histochemistry. IL-2Rgamma was found to be constitutively expressed by murine HN33.dw hippocampal neuronal cells, murine NB41A3 neuroblastoma cells, astrocyte-enriched mixed glial cell cultures, and in SCID mouse forebrain. The human cortical neuronal cell lines, HCN-1A and HCN-2, did not express the IL-2Rgamma gene. These data suggest the possibility that, in addition to being essential in IL-2 signaling in brain, IL-2Rgamma could be a common subunit (gammac) for multiple cytokine receptors which may be operative in the mammalian CNS.

Interactions of transforming growth factor-beta and angiotensin II in renal fibrosis

Overproduction of transforming growth factor-beta clearly underlies tissue fibrosis in numerous experimental and human diseases. Transforming growth factor-beta's powerful fibrogenic action results from simultaneous stimulation of matrix protein synthesis, inhibition of matrix degradation, and enhanced integrin expression that facilitates matrix assembly. In animals, overexpression of transforming growth factor-beta by intravenous injection, transient gene transfer, or transgene insertion has shown that the kidney is highly susceptible to rapid fibrosis. The same seems true in human disease, where excessive transforming growth factor-beta has been demonstrated in glomerulonephritis, diabetic nephropathy, and hypertensive glomerular injury. A possible explanation for the kidney's particular susceptibility to fibrosis may be the recent discovery of biologically complex interactions between the renin-angiotensin system and transforming growth factor-beta. Alterations in glomerular hemodynamics can activate both the renin-angiotensin system and transforming growth factor-beta. Components of the renin-angiotensin system act to further stimulate production of transforming growth factor-beta and plasminogen activator inhibitor leading to rapid matrix accumulation. In volume depletion, transforming growth factor-beta is released from juxtaglomerular cells and may act synergistically with angiotensin II to accentuate vasoconstriction and acute renal failure. Interaction of the renin-angiotensin system and transforming growth factor-beta has important clinical implications. The protective effect of inhibition of the renin-angiotensin system in experimental and human kidney diseases correlates closely with the suppression of transforming growth factor-beta production. This suggests that transforming growth factor-beta, in addition to blood pressure, should be a therapeutic target. Higher doses or different combinations of drugs that block the renin-angiotensin system or entirely new drug strategies may be needed to achieve a greater antifibrotic effect.

Mechanism of fibrosis in experimental tacrolimus nephrotoxicity

The clinical use of tacrolimus (FK506) is limited by nephrotoxicity. The pathogenesis of fibrosis in chronic FK506 nephrotoxicity remains unknown. Because transforming growth factor (TGF)-beta plays a key role in the fibrogenesis of many diseases, including cyclosporine nephrotoxicity, we studied a salt-depleted rat model of chronic FK506 nephropathy in which clinically relevant FK506 blood levels are obtained and which shows similarities to the lesions described in patients receiving FK506. Pair-fed rats were treated with either FK506 (1 mg/kg/day s.c.) or an equivalent dose of vehicle and were killed at 7 or 28 days. Characteristic histologic changes of tubular injury, interstitial fibrosis, and arteriolopathy developed in FK506-treated rats at 28 days and were accompanied by worsening kidney function, decreased concentrating ability, and enzymuria. FK506-treated kidneys had a progressive increase in the expression of TGF-beta1 and matrix proteins (biglycan, tenascin, fibronectin, and type I collagen). This effect seems to be specific because the expression of type IV collagen, a basement membrane collagen, was not affected. Matrix deposition was present mostly in the tubulointerstitium and vessels in accordance with the FK506 chronic lesion. The expression of plasminogen activator inhibitor-1, a protease inhibitor influenced by TGF-beta, followed TGF-beta1 and matrix proteins, suggesting that the fibrosis of chronic FK506 nephropathy likely involves the dual action of TGF-beta1 on matrix deposition and degradation. Since both peripheral and tissue renin expression were elevated with FK506, the renin-angiotensin system may play a role in the pathogenesis of this condition.

Angiotensin II blockade decreases TGF-beta1 and matrix proteins in cyclosporine nephropathy

Angiotensin II (Ang II) is implicated in fibrosis but the precise mechanism of this effect remains unclear. In a model of chronic cyclosporine (CsA) nephropathy, we previously showed that TGF-beta1 plays a role in CsA-induced tubulointerstitial fibrosis and arteriolopathy by stimulating extracellular matrix (ECM) protein synthesis and inhibiting ECM degradation through increasing the synthesis of plasminogen activator inhibitor (PAI)-1. We hypothesized that Ang II contributes to fibrosis by inducing TGF-beta1. Salt-depleted rats were given placebo, CsA alone, CsA + nilvadipine, CsA + hydralazine/hydrochlorthiazide, CsA + losartan (AT1 receptor antagonist) or CsA + enalapril (Ang converting enzyme inhibitor) and were sacrificed at 7 and 28 days. All treated groups achieved similar blood pressures and glomerular filtration rates. The lesion of chronic CsA nephropathy was ameliorated by concomitant therapy with losartan or enalapril at 28 days, a phenomenon not observed in the other treatment groups. Similarly, Ang II blockade resulted in decreased expression of TGF-beta1 and PAI-1 by Northern and ELISA. Similarly, the expression of ECM proteins directly influenced by TGF-beta decreased with Ang II blockade. These results suggest that CsA-induced fibrosis in this model is independent of renal hemodynamics and is mediated, at least partly, through Ang II induction of TGF-beta1 expression.

Angiotensin II and L-arginine in tissue fibrosis: more than blood pressure

Angiotensin II (Ang II) blockade and restriction of dietary protein are thought to retard progression of renal disease primarily by reducing glomerular capillary pressure and thereby reducing injury to renal tissues. Relatively recent data suggest that both of these therapies may also act through pressure-independent mechanisms to reduce repair processes that follow tissue injury and which, if not self-limited, can continue to cause tissue fibrosis and organ failure. We review recent data suggesting that Ang II is a profibrotic molecule independent of blood pressure. Therapeutic actions of dietary restriction of total protein and restriction of the amino acid L-arginine that appear independent of pressure are also discussed. These effects are separated into those that reduce injury and those that reduce tissue repair. Finally, we ask whether the Ang II blockade or restriction of dietary protein could be more effective if they were aimed not only at limiting injury, but also at halting excessive repair.

The renin-angiotensin system and fibrinolysis

In addition to causing vasoconstriction and the retention of salt and water, angiotensin inhibits fibrinolysis, thereby promoting clot formation and protecting against hemorrhage. Activation of the renin-angiotensin system (RAS) can disturb the balance of the fibrinolytic system by stimulating excess production of plasminogen activator inhibitor type 1 (PAI-1) and increasing the risk of thrombotic events. This risk is exacerbated by angiotensin-converting enzyme (ACE)-induced degradation of bradykinin, which normally stimulates production of tissue-type plasminogen activator (t-PA). Modification of the RAS via ACE inhibition may protect against thrombosis by limiting vascular expression of PAI-1 and augmenting bradykinin-induced production of t-PA. Survivors of myocardial infarction treated with an ACE inhibitor have demonstrated a reduction in PAI-1 activity and preservation of the normal ratio of PAI-1 to t-PA. This effect on the fibrinolytic system may contribute to the favorable impact ACE inhibition has been demonstrated to have on the incidence of recurrent myocardial infarction.

Dual effects of angiotensin II on the plasminogen/plasmin system in rat mesangial cells

Previous studies indicate that angiotensin II (Ang II) stimulates extracellular matrix synthesis through induction of transforming growth factor-beta (TGF-beta) expression. Here we investigate Ang II effects on the plasmin protease system. Plasmin both degrades extracellular matrix itself and activates metalloproteinases which then degrade collagens. Plasmin production is determined by the balance between plasminogen activators (PA) and their inhibitors (PAI-1,2). The data presented here indicate that Ang II treatment of mesangial cells in culture markedly increases PAI-1 gene transcription and PAI-1 mRNA levels but does not change the half life of PAI-1 mRNA. Increased PAI-1 protein was detected 24 hours after Ang II stimulation with a concomitant decrease of PA activity. To determine whether these effects were mediated by TGF-beta, cells were coincubated with Ang II and neutralizing antibody to TGF-beta. Induction of PAI-1 at four hours was not altered but the prolonged effect of Ang II on PAI-1 protein synthesis was markedly diminished. Thus, Ang II acts both through rapid, direct transcriptional up-regulation of the PAI-1 gene and through induction of TGF-beta, providing sustained changes in the PAI-1/PA system, which would favor extracellular matrix accumulation by inhibiting turnover. These data provide further evidence that Ang II can act as a potent fibrogenic molecule independent of its effects on blood pressure.

Angiotensin induction of PAI-1 expression in endothelial cells is mediated by the hexapeptide angiotensin IV

Recent studies from this laboratory have demonstrated that angiotensin II (Ang II) stimulates the expression of plasminogen activator inhibitor 1 (PAI-1) in cultured endothelial cells. This response does not appear to be mediated via an interaction with either the AT1 or the AT2 receptor subtype. Since a novel angiotensin receptor has been identified in a variety of tissues that specifically binds the hexapeptide Ang IV (Ang II, [3-8]), we therefore examined the effects of Ang IV on the expression of PAI-1 mRNA in bovine aortic endothelial cells. Ang IV stimulated dose- and time-dependent increases in the expression of PAI-1 mRNA. The effect of Ang IV (10 nM) was not inhibited by Dup 753 (1.0 microM), a highly specific antagonist of the AT1 receptor, or by PD123177 (1.0 microM), a highly specific antagonist of the AT2 receptor. In contrast, the AT4 receptor antagonist, WSU1291 (1.0 microM), effectively prevented PAI-1 expression. Although larger forms of angiotensin (i.e., Ang I, Ang II, and Ang III) are capable of inducing PAI-1 expression, this property is lost in the presence of converting enzyme or aminopeptidase inhibitors. These results indicate that the hexapeptide Ang IV is the form of angiotensin that stimulates endothelial expression of PAI-1. This effect appears to be mediated via the stimulation of an endothelial receptor that is specific for Ang IV.

Angiotensin II regulates the expression of plasminogen activator inhibitor-1 in cultured endothelial cells. A potential link between the renin-angiotensin system and thrombosis

Plasminogen activator-inhibitor C-1 (PAI-1) plays a critical role in the regulation of fibrinolysis, serving as the primary inhibitor of tissue-type plasminogen activator. Elevated levels of PAI-1 are a risk factor for recurrent myocardial infarction, and locally increased PAI-1 expression has been described in atherosclerotic human arteries. Recent studies have shown that the administration of angiotensin converting enzyme inhibitors reduces the risk of recurrent myocardial infarction in selected patients. Since angiotensin II (Ang II) has been reported to induce PAI-1 production in cultured astrocytes, we have hypothesized that one mechanism that may contribute to the beneficial effect of angiotensin converting enzyme inhibitors is an effect on fibrinolytic balance. In the present study, we examined the interaction of Ang II with cultured bovine aortic endothelial cells (BAECs) and the effects of this peptide on the production of PAI-1. 125I-Ang II was found to bind to BAECs in a saturable and specific manner, with an apparent Kd of 1.4 nM and Bmax of 74 fmol per mg of protein. Exposure of BAECs to Ang II induced dose-dependent increases in PAI-1 antigen in the media and in PAI-1 mRNA levels. Induction of PAI-1 mRNA expression by Ang II was not inhibited by pretreating BAECs with either Dup 753 or [Sar1, Ile8]-Ang II, agents that are known to compete effectively for binding to the two major angiotensin receptor subtypes. These data indicate that Ang II regulates the expression of PAI-1 in cultured endothelial cells and that this response is mediated via a pharmacologically distinct form of the angiotensin receptor.

Retrovirus-mediated transfer of an angiotensin type I receptor (AT1-R) antisense sequence decreases AT1-Rs and angiotensin II action in astroglial and neuronal cells in primary cultures from the brain

The AT1-R has been implicated in many cellular and physiological actions of angiotensin II (AII) in the brain. A retrovirus vector (LNSV) containing an AT1B-R antisense sequence (AT1B-AS) (termed LNSV-AT1B-AS) was constructed and used to determine the feasibility of using viral-mediated gene transfer to control AT1-Rs and AII actions in astroglial and neuronal cells in primary cultures from rat brain. Briefly, a 1.26-kb antisense sequence corresponding to nt -132 to +1128 of AT1-R cDNA was cloned into the LNSV vector, the vector was transfected into PA317 cells, and transfected cells were selected in G418. Incubation of brain cells with culture medium containing LNSV-AT1B-AS viral particles showed that AT1B-AS was integrated into the genome and transcribed in brain cells. This was associated with a significant decrease in AT1-Rs and in the AII-stimulated increase of c-fos mRNA, a measure of AT1-R function. These observations show that the AT1B-AS gene can be transferred into astroglial cells in culture by LNSV and that such a transfer inhibits AT1-Rs and the AII stimulation of cellular activities. In addition, the usefulness of this approach to study AII-dependent pathophysiology in primary neuronal cultures from brain, in particular, is established.

Angiotensin II increases plasminogen activator inhibitor type 1 and tissue-type plasminogen activator messenger RNA in cultured rat aortic smooth muscle cells

BACKGROUND

The role of angiotensin as a vasoconstrictor is well established. Lately, several other actions of this hormone on vascular smooth muscle (VSM) cells have been recognized including the induction of hypertrophy and/or DNA synthesis. Platelet-derived growth factor (PDGF), a mitogen recently shown to increase plasminogen activator inhibitor type 1 (PAI-1) synthesis in VSM cells, shares with angiotensin II (Ang II) several steps of its intracellular signaling pathway.

METHODS AND RESULTS

The expression of PAI-1 and tissue-type plasminogen activator (TPA) mRNA in cultured rat VSM cells was studied. Northern blot analysis demonstrated a severalfold increase in the PAI-1 mRNA 3 to 8 hours after stimulation with 300 nmol/L Ang II. A similar response for TPA mRNA was observed. This induction did not require the synthesis of an intermediate protein or peptide because it was not affected by cycloheximide. In the cell-conditioned supernatant, the net result was an increase in PAI-1 activity from 4.18 +/- 1.8 to 13.2 +/- 6.8 IU/mL 6 hours after the addition of 300 nmol/L Ang II (mean +/- SD, P < or = .008, n = 6). The Ang II-induced increase in PAI activity was dose related, with a maximal effect at a concentration of 23 nmol/L (n = 3) and an ED50 of 3.3 +/- 1.5 nmol/L (n = 3). [Sar1-Ile8]angiotensin II, a specific competitive antagonist of Ang II, blocked 90 +/- 9% (n = 3) of the PAI activity induced by 10 nmol/L Ang II. In basal conditions, fibrin overlay zymography demonstrated the presence of free TPA. After stimulation with Ang II, lysis caused by the in situ dissociation of TPA was also present in the region of the TPA/PAI-1 complex. Angiotensin I (Ang I) elicited an increase in PAI activity similar to that obtained with equivalent doses of Ang II. Captopril (5 micrograms/mL), an inhibitor of the angiotensin-converting enzyme (ACE), completely prevented the Ang I effect, demonstrating that VSM cells display an ACE-like activity.

CONCLUSIONS

Recent research has demonstrated the existence of a localized vascular renin-angiotensin system. The finding that Ang II can potentially modulate the plasminogen activation in the arterial wall has important biological and therapeutical implications for the evolution of arterial wall thrombi and the migration of cells through the vessel wall in the genesis of atherosclerotic lesions. We speculate that the reduction in thrombotic events observed in patients with a previous myocardial infarction and in high-renin, hypertensive patients treated with ACE inhibitors could be due at least in part to the decreased production of PAI-1 by VSM cells caused by these agents.

Peptide receptors in astroglia: focus on angiotensin II and atrial natriuretic peptide

Astroglial cells derived from the mammalian central nervous system contain a wide variety of peptide receptors, including specific sites for angiotensin II (AII) and atrial natriuretic peptide (ANP). The AII receptors present in these cells are primarily of the AT1 subtype. The ANP receptors present in these cells consist of a mix of ANP-A and ANP-B sites ("biological receptors") and also ANP-C sites ("clearance receptors"). Available evidence indicates that activation of AII receptors results in a stimulation of astroglial proliferation, whereas ANP has an antiproliferative effect in these cells. Intracellular pathways which may mediate these effects of AII and ANP on cell proliferation are discussed, including the presentation of novel data on the activation of protein kinase C and of glucose uptake by AII. We also consider the possibility that the opposing actions of AII and ANP on astroglial proliferation may represent another facet of the mutual antagonism between these two peptides, which has been observed throughout mammalian systems.

Properties of angiotensin II receptors in glial cells from the adult corpus callosum

The existence and the properties of angiotensin II receptors in the adult bovine and human corpus callosum (CC) were investigated by using Xenopus oocytes and primary glial cell cultures. In oocytes injected with CC mRNA, angiotensin II elicited oscillatory Cl- currents due to activation of the inositol phosphate/Ca(2+)-receptor-channel coupling system. The receptors expressed in oocytes and in CC cultures were pharmacologically similar to the AT1 receptor type as assayed by binding. Northern blot analysis and in situ hybridization studies in sections from CC and in glial cultures revealed that the receptors were molecularly related to the AT1 receptor and that they were present in astrocytes. In these cells, activation of the receptors with angiotensin II increased de novo DNA synthesis, promoted the release of aldosterone, and induced c-Fos expression. These findings indicate that CC astrocytes possess functional AT1 receptors that participate in various physiological processes.

Endopeptidases 24.16 and 24.15 are responsible for the degradation of somatostatin, neurotensin, and other neuropeptides by cultivated rat cortical astrocytes

Several neuropeptides, including neurotensin, somatostatin, bradykinin, angiotensin II, substance P, and luteinizing hormone-releasing hormone but not vasopressin and oxytocin, were actively metabolized through proteolytic degradation by cultivated astrocytes obtained from rat cerebral cortex. Because phenanthroline was an effective degradation inhibitor, metalloproteases were responsible for neuropeptide fragmentation. Neurotensin was cleaved by astrocytes at the Pro10-Tyr11 and Arg8-Arg9 bonds, whereas somatostatin was cleaved at the Phe6-Phe7 and Thr10-Phe11 bonds. These cleavage sites have been found previously with endopeptidases 24.16 and 24.15 purified from rat brain. Addition of specific inhibitors of these proteases, the dipeptide Pro-Ile and N-[1-(RS)-carboxy-3-phenylpropyl]-Ala-Ala-Phe-4-aminobenzoate, significantly reduced the generation of the above neuropeptide fragments by astrocytes. The presence of endopeptidases 24.16 and 24.15 in homogenates of astrocytes could also be demonstrated by chromatographic separations of supernatant solubilized cell preparations. Proteolytic activity for neurotensin eluted after both gel and hydroxyapatite chromatography at the same positions as found for purified endopeptidase 24.16 or 24.15. In incubation experiments or in chromatographic separations no phosphoramidon-sensitive endopeptidase 24.11 (enkephalinase) or captopril-sensitive peptidyl dipeptidase A (angiotensin-converting enzyme) could be detected in cultivated astrocytes. Because astrocytes embrace the neuronal synapses where neuropeptides are released, we presume that the endopeptidases 24.16 and 24.15 on astrocytes are strategically located to contribute significantly to the inactivation of neurotensin, somatostatin, and other neuropeptides in the brain.

Angiotensin II type 1 receptor-mediated stimulation of c-fos gene expression in astroglial cultures

Angiotensin II (ANG II) stimulates plasminogen activator inhibitor 1 (PAI-1) gene expression in astroglial cells prepared from rat brains. In this study, we investigated whether c-fos gene expression may be involved in this cellular action of ANG II. Incubation of astroglial cultures with ANG II caused a time- and dose-dependent transient stimulation of the steady-state levels of c-fos mRNA, with a maximal stimulation of 50-fold observed with 100 nM ANG II within 30-45 min. This stimulation was completely abolished by the presence of the type 1 ANG II (AT1) receptor antagonist losartan but not by the type 2 ANG II receptor blocker PD-123177. Depolarization of brain cell cultures with 50 mM K+ also caused a 100-fold increase in c-fos mRNA levels, an effect partially blocked by losartan. These observations show that AT1 receptor activation stimulates expression of the c-fos gene, which may act as a third messenger in the regulation of cellular actions of ANG II, including PAI-1 gene expression in astroglial cells.

Insulin-like growth factor I receptors and IGF-I actions in neuronal cultures from the brain

Neurons in primary culture have been used to study IGF-I receptors and IGF-I-induced cellular actions in the brain. Intact neurons in culture specifically bind [125I]IGF with high affinity. The potency for the competition of [125I]IGF-I binding was IGF-I > IGF-II > insulin. A curvilinear Scatchard plot represented high-affinity (0.15 nM) and low-affinity (3 nM) binding sites with a Bmax of 142 fmol and 618 fmol/mg protein, respectively. These binding sites are predominantly localized on neurites with relatively few sites on the cell soma. IGF-I induced synthesis of protein(s) in the M(r) range of 48,000-50,000 with pI values of 6.1-6.4. These observations show that IGF-I receptor mediates induction of specific proteins and suggest that these proteins may be involved in the neurotrophic activity of IGF-I in the brain.

Molecular profile of reactive astrocytes--implications for their role in neurologic disease

The central nervous system responds to diverse neurologic injuries with a vigorous activation of astrocytes. While this phenomenon is found in many different species, its function is obscure. Understanding the molecular profile characteristic of reactive astrocytes should help define their function. The purpose of this review is to provide a summary of molecules whose levels of expression differentiate activated from resting astrocytes and to use the molecular profile of reactive astrocytes as the basis for speculations on the functions of these cells. At present, reactive astrocytosis is defined primarily as an increase in the number and size of cells expressing glial fibrillary acidic protein. In vivo, this increase in glial fibrillary acidic protein-positive cells reflects predominantly phenotypic changes of resident astroglia rather than migration or proliferation of such cells. Upon activation, astrocytes upmodulate the expression of a large number of molecules. From this molecular profile it becomes apparent that reactive astrocytes may benefit the injured nervous system by participating in diverse biological processes. For example, upregulation of proteases and protease inhibitors could help remodel the extracellular matrix, regulate the concentration of different proteins in the neuropil and clear up debris from degenerating cells. Cytokines are key mediators of immunity and inflammation and could play a critical role in the regulation of the blood-central nervous system interface. Neurotrophic factors, transporter molecules and enzymes involved in the metabolism of excitotoxic amino acids or in the antioxidant pathway may help protect neurons and other brain cells by controlling neurotoxin levels and contributing to homeostasis within the central nervous system. Therefore, an impairment of astroglial performance has the potential to exacerbate neuronal dysfunction. Based on the synopsis of studies presented, a number of issues become apparent that deserve a more extensive analysis. Among them are the relative contribution of microglia and astrocytes to early wound repair, the characterization of astroglial subpopulations, the specificity of the astroglial response in different diseases as well as the analysis of reactive astrocytes with techniques that can resolve fast physiologic processes. Differences between reactive astrocytes in vivo and primary astrocytes in culture are discussed and underline the need for the development and exploitation of models that will allow the analysis of reactive astrocytes in the intact organism.

Characterization of "plasma proteins" secreted by cultured rat macroglial cells

The brain is isolated behind a blood-tissue barrier that restricts the access of circulating proteins to neural cells. There is evidence that some of these proteins are synthesized within the central nervous system. The present study examines the synthesis and secretion of such proteins by cultured macroglial cells. Primary glial cultures were derived from cortical and subcortical regions of neonatal rat brains, and subsequent secondary cultures were enriched in type-1 astrocytes, type-2 astrocytes, or oligodendrocytes. Newly synthesized proteins were immunoprecipitated from the culture media using antisera directed against whole rat serum. All three types of glial cells secreted a range of plasma proteins. In general, type-1 astrocytes secreted more of these proteins than did type-2 astrocytes or oligodendrocytes, although the one-dimensional polyacrylamide gel electrophoresis (PAGE) profiles were specific for each cell type. Anti-sera directed against specific plasma proteins identified three of the most abundant proteins secreted by type-1 astrocytes as transferrin, alpha-2-macroglobulin, and ceruloplasmin. Northern blot analysis of cellular RNA confirmed that type-1 astrocytes contained transferrin mRNA, and that it was more abundant in cultures derived from subcortical regions than from cortical regions. In situ hybridization studies revealed that virtually all type-1 and type-2 astrocytes contained transferrin mRNA. Since the proteins identified in this study have been proposed to have a variety of neurotrophic roles in the central nervous system, these data further extend the range of possible functions that glial cells may serve in the CNS.

Angiotensin II receptor subtypes are coupled with distinct signal-transduction mechanisms in neurons and astrocytes from rat brain

Both neurons and astrocytes contain specific receptors for angiotensin II (AII). We used selective ligands for the AT1 and AT2 types of AII receptors to investigate the expression of functional receptor subtypes in astrocyte cultures and neuron cultures from 1-day-old (neonatal) rat brain. In astrocyte cultures, competition of 125I-labeled AII (125I-AII) specific binding with AT1 (DuP753) or AT2 (PD123177, CGP42112A, [Phe(p-NH2)6]AII) selective receptor ligands revealed a potency series of AII greater than DuP753 much greater than CGP42112A greater than [Phe(p-NH2)6]AII greater than PD123177. These results suggest a predominance of the AT1 receptor subtype in neonatal astrocytes. Also, in astrocyte cultures, AII stimulated increases in inositolphospholipid hydrolysis that were significantly reduced by the AT1 receptor antagonist DuP753 but not altered by the AT2 receptor antagonist PD123177. In neonatal neuron cultures, competition of 125I-AII specific binding with the above ligands revealed a potency series of CGP42112A = AII greater than [Phe(p- NH2)6]AII greater than PD123177 much greater than DuP753. 125I-AII specific binding to neonate neuronal cultures was reduced 73-84% by 1 microM PD123177, and the residual 125I-AII specific binding was eliminated by DuP753. Also, in neuron cultures, AII induced decreases in basal cGMP that were completely blocked by PD123177 or CGP42112A but not by DuP753. Our results suggest that astrocyte cultures from neonatal rat brains contain predominantly AT1 receptors that are coupled to a stimulation of inositophospholipid hydrolysis. In contrast, neuron cultures from neonatal rat brain contain mostly AT2 receptors that are coupled to a reduction in basal cGMP levels, but a smaller population of AT1 receptors is also present in these neurons.