ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Granulation tissue formation is an example of new tissue development in an adult. Its rich vascular network has been thought to derive via angiogenic sprouting and extension of preexisting vessels from the surrounding tissue. The possibility that circulating cells of hematopoietic origin can differentiate into vascular endothelial cells (ECs) in areas of vascular remodeling has recently gained credibility. However, no quantitative data have placed the magnitude of this contribution into a physiological perspective. We have used hematopoietic chimeras to determine that 0.2% to 1.4% of ECs in vessels in control tissues derived from hematopoietic progenitors during the 4 months after irradiation and hematopoietic recovery. By contrast, 8.3% to 11.2% of ECs in vessels that developed in sponge-induced granulation tissue during 1 month derived from circulating hematopoietic progenitors. This recruitment of circulating progenitors to newly forming vessels would be difficult to observe in standard histological studies, but it is large enough to be encouraging for attempts to manipulate this contribution for therapeutic gain.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Abstract—In response to increased ventricular wall tension or neurohumoral stimuli, the myocardium undergoes an adaptive hypertrophy response that temporarily augments pump function. Although initially beneficial, sustained cardiac hypertrophy can lead to decompensation and cardiomyopathy. Recent studies have focused on characterizing the molecular mechanisms that underlie cardiac hypertrophy. An increasing number of signal transduction pathways have been identified as important regulators of the hypertrophic response, including the low–molecular weight GTPases (Ras, RhoA, and Rac), mitogen-activated protein kinases, protein kinase C, and calcineurin. This review will discuss an emerging body of evidence that implicates the calcium-calmodulin–activated protein phosphatase calcineurin as a physiological regulator of the cardiac hypertrophic response. Although the sufficiency of calcineurin to promote cardiomyocyte hypertrophy in vivo and in vitro is established, its overall necessity as a hypertrophic mediator is currently an area of ongoing debate. The use of the calcineurin-inhibitory agents cyclosporine A and FK506 have suggested a necessary role for calcineurin in many, but not all, animal models of hypertrophy or cardiomyopathy. The evidence implicating a role for calcineurin signaling in the heart will be weighed against a growing body of literature suggesting necessary roles for a diverse array of intracellular signaling pathways, highlighting the multifactorial nature of the hypertrophic program.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Abstract—Thromboxane A2(TxA2) causes platelet aggregation, vasoconstriction, and inhibition of endothelial cell (EC) migration and prevents vascular tube formation via its specific receptors (TP), of which there are two isoforms (TP&agr; and TP&bgr;), both expressed in human ECs. In this study, we demonstrate that the TxA2mimetic IBOP increases apoptosis of human ECs and inhibits the phosphorylation of Akt kinase, an intracellular mediator required for cell survival. Treatment with IBOP destroyed EC networks formed on a basement membrane matrix in vitro. To distinguish the role of the TP isoforms, each isoform was expressed in TP-null ECs to create TP&agr; and TP&bgr; ECs. IBOP induced apoptosis and inhibited phosphorylation of Akt kinase in both TP&agr; and TP&bgr;. IBOP increased cAMP levels in TP&agr; but not in TP&bgr;. Apoptosis induced by IBOP in TP&agr; was not affected by either the adenylyl cyclase activator forskolin or the protein kinase A inhibitor 14-22 amide or H-89, whereas that in TP&bgr; was suppressed by forskolin and enhanced by the protein kinase A inhibitor 14-22 amide or H-89, suggesting that the TP isoforms differ in their signal pathways in mediating apoptosis. In conclusion, apoptosis may be the mechanism by which TxA2-mediated destruction of vascular structures in ECs occurs; although both TP isoforms induce apoptosis, possibly via inhibiting Akt phosphorylation, the signaling differs in each isoform, in that activation of the adenylyl cyclase pathway prevents apoptosis caused by TP&bgr;, but not by TP&agr;, stimulation.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Abstract—Pathogenesis of macrovascular complications of diabetes may involve an activation of the transcription factor nuclear factor-&kgr;B (NF-&kgr;B) by hyperglycemia and advanced glycosylation end products (AGEs). Activation of NF-&kgr;B is believed to be dependent on activation of the Rho family of GTPases. Although the precise mechanism of the Rho-mediated action is not completely understood, posttranslational modification of the Rho proteins by geranylgeranylation is required for their subsequent activation. We observed that in cultured vascular smooth muscle cells (VSMCs), insulin stimulated the activity of geranylgeranyltransferase (GGTase) I and increased the amounts of geranylgeranylated Rho-A from 47% to 60% (P<0.05). GGTI-286, an inhibitor of GGTase I, blocked both effects of insulin. Increased availability of prenylated Rho-A significantly augmented the abilities of angiotensin II (Ang II), hyperglycemia, and AGEs to activate NF-&kgr;B, as measured by NF-&kgr;B response-element luciferase reporter activity. Preincubations of VSMCs with insulin for 24 hours doubled NF-&kgr;B transactivation by Ang II, hyperglycemia, and AGEs. This priming effect of insulin was completely inhibited by GGTI-286. We demonstrate for the first time, to our knowledge, that insulin potentiates NF-&kgr;B–dependent transcriptional activity induced by hyperglycemia, AGEs, and Ang II in VSMCs by increasing the activity of GGTase I and the availability of geranylgeranylated Rho-A.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Abstract—On the basis of the patterns of conserved amino acid sequence, the angiotensin II type 2 (AT2) receptor belongs to the family of serpentine receptors, which relay signals from extracellular stimuli to heterotrimeric G proteins. However, the AT2receptor signal transduction mechanisms are poorly understood. We have measured AT2-triggered activation of purified heterotrimeric proteins in urea-extracted membranes from cultured COS-7 cells expressing the recombinant receptor. This procedure removes contaminating GTP-binding proteins without inactivating the serpentine receptor. Binding studies using [125I] angiotensin (Ang) II revealed a single binding site with aKd=0.45 and a capacity of 627 fmol/mg protein in the extracted membranes. The AT2receptor caused a rapid activation of &agr;iand &agr;obut not of &agr;qand &agr;s, as measured by radioactive guanosine 5′-3-O-(thio)triphosphate (GTP&ggr;S) binding. Activation required the presence of activated receptors, &bgr;&ggr;, and &agr; subunits. As a first step aimed at developing an in vitro assay to examine AT2receptor pharmacology, we tested a battery of Ang II–related ligands for their ability to promote AT1or AT2receptor–catalyzed Giactivation. Two proteolytic fragments of Ang II, Ang III and Ang1–7, also promoted activation of &agr;ithrough the AT2receptor. Furthermore, we found that [Sar1,Ala8]Ang II is an antagonist for both AT1and AT2receptors and that CPG42112 behaves as a partial agonist for the AT2receptor. In combination with previous observations, these results show that the AT2receptor is fully capable of activating Giand provides a new tool for exploring AT2receptor pharmacology and interactions with G-protein trimers.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Abstract—Cardiac beating arises from the spontaneous rhythmic excitation of sinoatrial (SA) node cells. Here we report that SA node pacemaker activity is critically dependent on Ca2+/calmodulin-dependent protein kinase II (CaMKII). In freshly dissociated rabbit single SA node cells, inhibition of CaMKII by a specific peptide inhibitor, autocamtide-2 inhibitory peptide (AIP, 10 &mgr;mol/L), or by KN-93 (0.1 to 3.0 &mgr;mol/L), but not its inactive analog, KN-92, depressed the rate and amplitude of spontaneous action potentials (APs) in a dose-dependent manner. Strikingly, 10 &mgr;mol/L AIP and 3 &mgr;mol/L KN-93 completely arrested SA node cells, which indicates that basal CaMKII activation is obligatory to the genesis of pacemaker AP. To understand the ionic mechanisms of the CaMKII effects, we measured L-type Ca2+current (ICa, L), which contributes both to AP upstroke and to pacemaker depolarization. KN-93 (1 &mgr;mol/L), but not its inactive analog, KN-92, decreasedICa, Lamplitude from 12±2 to 6±1 pA/pF without altering the shape of the current-voltage relationship. Both AIP and KN-93 shifted the midpoint of the steady-state inactivation curve leftward and markedly slowed the recovery ofICa, Lfrom inactivation. Similar results were observed using the fast Ca2+chelator BAPTA, whereas the slow Ca2+chelator EGTA had no significant effect, which suggests that CaMKII activity is preferentially regulated by local Ca2+transients. Indeed, confocal immunocytochemical imaging showed that active CaMKII is highly localized beneath the surface membrane in the vicinity of L-type channels and that AIP and KN-93 significantly reduced CaMKII activity. Thus, we conclude that CaMKII plays a vital role in regulating cardiac pacemaker activity mainly via modulatingICa, Linactivation and reactivation, and local Ca2+is critically involved in these processes.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID

摘要:

Abstract—This study investigated the possible roles of strongly binding myosin crossbridges in determining loaded shortening and power output in cardiac myocytes. Single skinned cardiac myocytes were attached between a force transducer and position motor, and shortening velocities were measured over a range of loads during varying levels of Ca2+activation. Lowering the [Ca2+] slowed shortening velocities, decreased relative power output, and increased the curvature of length traces. We tested the hypothesis that Ca2+activation dependence of loaded shortening is determined primarily by strongly binding crossbridges or by [Ca2+] per se, which was done by measuring loaded shortening before and after addition ofN-ethylmaleimide–conjugated myosin subfragment-1 (NEM-S1), a strongly binding myosin analogue that cooperatively enhances thin filament activation. At fixed [Ca2+], NEM-S1 reduced the curvature of length traces and sped loaded shortening velocities. Even when [Ca2+] was adjusted so that force was equal with and without NEM-S1, myocyte shortening was faster and exhibited less curvature with NEM-S1. In the presence of NEM-S1, peak relative power output was also significantly greater during activations either at the same [Ca2+] or when [Ca2+] was adjusted to achieve the same force. Consequently, NEM-S1 eliminated any Ca2+dependence of relative power output that is normally observed in cardiac myocytes. These results indicate that strongly binding crossbridges play a significant role in determining loaded shortening and power output and suggest that previously observed Ca2+dependence of power output is mediated by alterations in numbers of crossbridges bound to the thin filament.

ISSN:0009-7330    

出版商:OVID    

年代:2000

数据来源: OVID