摘要:

The antiphospholipid (aPL) syndrome is an acquired autoimmune disorder of unknown etiology in which patients present with thrombosis together with laboratory evidence for antibodies in blood that recognize anionic phospholipid-protein complexes. The main antigenic target for the aPL antibodies has been identified to be &bgr;2glycoprotein I (&bgr;2GPI), a phospholipid-binding protein. The high affinity of aPL antibody-&bgr;2GPI complex for phospholipid membranes seems to be a critical step in the mechanism of this disease. This review focuses on some of the major mechanisms that have been proposed to explain this disorder.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Type IIA secretory phospholipase A2(sPLA2) is an acute-phase reactant that plays a role in atherogenesis and is expressed in atherosclerotic arterial walls displaying inflammatory features. This generates a relevant question addressing the biological effects of this enzyme on monocytic cells, in view of the role of these cells in the inflammatory process associated with atherosclerosis. sPLA2produced a mild activation of the p42 mitogen-activated protein module of the mitogen-activated protein kinase (MAPK) cascade and a prominent activation of c-Jun N-terminal kinase in THP-1 monocytes. This activation showed both an early and a late peak, different from that elicited by tumor necrosis factor-&agr; (TNF-&agr;), which only showed the first peak. This was accompanied by activation of arachidonate metabolism, as judged from both the activation of the cytosolic phospholipase A2(cPLA2) and the induction of cyclooxygenase-2 (COX-2) expression. sPLA2also elicited the production of monocyte chemoattractant protein-1 (MCP-1) and showed a synergistic effect with TNF-&agr; on both COX-2 induction and MCP-1 production. sPLA2upregulated the expression of Fas ligand at the cell surface, but it did not influence Fas expression nor cell survival of monocytes. In summary, these data indicate that some of the atherogenic effects of sPLA2can be exerted by engagement of an sPLA2-binding structure on monocytic cells, most probably the M-type receptor for sPLA2, which produces the activation of the MAPK cascade, induces a proinflammatory phenotype, and upregulates the cell surface expression of Fas ligand.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Hepatocyte growth factor (scatter factor) is an angiogenic growth factor that binds to its cellular transmembrane receptor, c-met. Both HGF and c-met are expressed by vascular smooth muscle and endothelial cells, where HGF may exert autocrine and paracrine effects. We have found that human aortic smooth muscle cells (HASMCs) and human umbilical vein endothelial cells (HUVECs) release a soluble, truncated form of c-met. Receptor shedding was induced by treatment of the cells with phorbol 12-myristate 13-acetate (PMA) and by the ligand, HGF. Shedding was inhibited by cycloheximide, a metalloproteinase inhibitor, and protein kinase C inhibitors. The soluble form of c-met was able to bind HGF, although with reduced affinity (Kd≈10 nmol/L) compared with the membrane bound receptor. Conditioned medium containing soluble c-met inhibited the induction of Akt phosphorylation by HGF in HUVECs. The soluble truncated form of c-met was detectable in the plasma of 5 healthy volunteers. The shedding of c-met may represent a novel mechanism for regulating the mitogenic, motogenic, and morphogenic effects of hepatocyte growth factor.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

AT1receptor activation leads to vasoconstriction, blood pressure increase, free radical release, and cell growth. AT1receptor regulation contributes to the adaptation of the renin-angiotensin system to long-term stimulation and serves as explanation for the involvement of the AT1receptor in the pathogenesis of cardiovascular disease. The molecular mechanisms involved in AT1receptor regulation are poorly understood. Here, we report that angiotensin II accelerates AT1receptor mRNA decay in vascular smooth muscle cells. A cognate mRNA region within the 3′ untranslated region at bases 2175 to 2195 governs the inducible decay of the AT1receptor mRNA. Sequential protein purifications led to the discovery of a novel mRNA binding protein, calreticulin, which mediates destabilization of the AT1receptor mRNA. Angiotensin II–caused phosphorylation of calreticulin enables binding of calreticulin to the AT1receptor mRNA at bases 2175 to 2195 and propagates calreticulin-induced acceleration of AT1receptor mRNA decay. Thus, a novel mRNA binding protein, calreticulin, is discovered, which causes AT1receptor mRNA degradation via binding to a distinct mRNA region in the 3′ untranslated region. These findings display a novel mechanism of posttranscriptional mRNA processing.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

The increase in myofilament Ca2+responsiveness on an increase in sarcomere length (SL) is, in part, the cellular basis for Frank-Starling’s law of the heart. It has been suggested that a decrease in myofilament lattice spacing (LS) in response to an increase in SL underlies this phenomenon. This hypothesis is supported by previous studies in which reduced muscle width induced by osmotic compression was associated with an increase in Ca2+sensitivity, mimicking those changes observed with an increase in SL. To evaluate this hypothesis, we directly measured LS by synchrotron x-ray diffraction as function of SL in skinned rat cardiac trabeculae bathed in 0% to 6% dextran solutions (MW 413 000). We found that EC50, [Ca2+] at which force is half-maximal, at SL between 1.95 and 2.25 &mgr;m did not vary in proportion to LS when 3% or 6% dextran solutions were applied. We also found that moderate compression (1% dextran) of skinned trabeculae at SL=2.02 &mgr;m reduced LS (LS=42.29±0.14 nm) to match that of uncompressed fibers at a long SL (SL=2.19 &mgr;m; LS=42.28±0.15 nm). Whereas increasing SL from 2.02 to 2.19 &mgr;m significantly increased Ca2+sensitivity as indexed by the EC50parameter (2.87±0.11 &mgr;mol/L to 2.52±0.12 &mgr;mol/L), similar reduction in myofilament lattice spacing achieved by compression with 1% dextran did not alter Ca2+sensitivity (2.87±0.10 &mgr;mol/L) at the short SL. We conclude that alterations in myofilament lattice spacing may not be the mechanism that underlies the sarcomere length–induced alteration of calcium sensitivity in skinned myocardium.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Mitral regurgitation (MR) causes ventricular dilation, a blunted myocardial force-frequency relation, and increased crossbridge force-time integral (FTI). The mechanism of FTI increase was investigated using sinusoidal length perturbation analysis to compare crossbridge function in skinned left ventricular (LV) epicardial muscle strips from 5 MR and 5 nonfailing (NF) control hearts. Myocardial dynamic stiffness was modeled as 3 parallel viscoelastic processes. Two processes characterize intermediate crossbridge cycle transitions,B(work producing) andC(work absorbing) with Q10s of 4 to 5. No significant differences in moduli or kinetic constants of these processes were observed between MR and NF. The third process,A, characterizes a nonenzymatic (Q10=0.9) work-absorbing viscoelasticity, whose modulus increases sigmoidally with [Ca2+]. Effects of temperature, crossbridge inhibition, or variation in [MgATP] support associating the calcium-dependent portion ofAwith the structural “backbone” of the myosin crossbridge. Extension of the conventional sinusoidal length perturbation analysis allowed using the A modulus to index the lifetime of the prerigor, AMADP crossbridge. This index was 75% greater in MR than in NF (P=0.02), suggesting a mechanism for the previously observed increase in crossbridge FTI. Notably, theA-process modulus was inversely correlated (r2=0.84,P=0.03) with in vivo LV ejection fraction in MR patients. The longer prerigor dwell time in MR may be clinically relevant not only for its potential role as a compensatory mechanism (increased economy of tension maintenance and increased resistance to ventricular dilation) but also for a potentially deleterious effect (reduced elastance and ejection fraction).

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

It has long been recognized that activation of sympathetic &bgr;-adrenoceptors (&bgr;-ARs) increases the spontaneous beating rate of sinoatrial nodal cells (SANCs); however, the specific links between stimulation of &bgr;-ARs and the resultant increase in firing rate remain an enigma. In the present study, we show that the positive chronotropic effect of &bgr;-AR stimulation is critically dependent on localized subsarcolemmal ryanodine receptor (RyR) Ca2+releases during diastolic depolarization (CRDD). Specifically, isoproterenol (ISO; 0.1 &mgr;mol/L) induces a 3-fold increase in the number of CRDDs per cycle; a shift to higher CRDD amplitudes (from 2.00±0.04 to 2.17±0.03 F/F0;P<0.05 [F and F0refer to peak and minimal fluorescence]); and an increase in spatial width (from 3.80±0.44 to 5.45±0.47 &mgr;m;P<0.05). The net effect results in an augmentation of the amplitude of the local preaction potential subsarcolemmal Ca2+transient that, in turn, accelerates the diastolic depolarization rate, leading to an increase in SANC firing rate. When RyRs are disabled by ryanodine, &bgr;-AR stimulation fails to amplify subsarcolemmal Ca2+releases, fails to augment the diastolic depolarization rate, and fails to increase the SANC firing rate, despite preserved &bgr;-AR stimulation-induced augmentation of L-type Ca2+current amplitude. Thus, the RyR Ca2+release acts as a switchboard to link &bgr;-AR stimulation to an increase in SANC firing rate: recruitment of additional localized CRDDs and partial synchronization of their occurrence by &bgr;-AR stimulation lead to an increase in the heart rate.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

We previously reported the generation of 2 novel transgenic mouse models containing the human renin (hREN) gene encoded on P1 artificial chromosomes (PAC) containing large amounts of 5′-flanking DNA. These mice exhibit a very narrow tissue-specific expression profile and exhibit tightly regulated expression in kidney in response to physiological cues. In brain, transcription of hREN occurs from an alternative upstream promoter, causing translation to initiate within exon-II and potentially generating an intracellular form of active renin. Double transgenic mice containing a PAC transgene and the human angiotensinogen (hAGT) gene (P+/A+) are moderately hypertensive. We tested whether increased RAS activity in the brain contributes to the mechanism of hypertension in P+/A+ double transgenic mice. Expression of hREN mRNA in brain was confirmed in 4 independent PAC transgenic lines and utilization of the alternative transcription start site in brain was confirmed in each line. Human REN immunostaining was observed in the dorsal cochlear nucleus, hypothalamus, and cortex. P+/A+ mice exhibited a greater fall in mean arterial pressure after intracerebroventricular injection of losartan than controls. P+/A+ mice exhibited a greater drop in arterial pressure after intravenous injection of a vasopressin V1receptor antagonist, and an equivalent drop in arterial pressure after intravenous injection of a ganglion blocker compared with controls. These results support the hypothesis that renin is endogenously expressed in the brain and suggest that increased brain RAS activity may contribute to the maintenance of moderate hypertension in P+/A+ transgenic mice at least in part by a vasopressin-dependent mechanism.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

To test the hypothesis that local vascular production of angiotensin II is necessary for the normal regulation of blood pressure, we engineered a new line of genetically altered mice that lack endothelial angiotensin-converting enzyme (ACE). This was accomplished using a novel strategy of targeted homologous recombination to separate the transcriptional control of somatic ACE from its endogenous promoter and to substitute control to the albumin promoter. These new mice, termed ACE.3, do not produce ACE within the lung, the aorta, or any vascular structure. ACE activity within the kidney is only about 14% that of wild-type mice and is limited to tubular epithelium. In contrast, hepatic ACE expression in ACE.3 mice is about 87-fold that of wild-type. The blood pressure, plasma angiotensin II levels, response to ACE inhibitors, and renal function of ACE.3−/−mice are indistinguishable from littermate wild-type mice. These data show that, under basal conditions, the normal regulation of blood pressure and renal function is possible in a mouse devoid of endothelial ACE.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID

摘要:

Nitric oxide (NO), a potent regulator of myocardial contractility, has been implicated in the development of heart failure; however, no study exists describing the relation between expression of inducible nitric oxide synthase (iNOS), formation of NO in vivo, and cardiac contractility. We have therefore generated transgenic (TG) mice overexpressing iNOS under the cardiospecific &agr;-myosin heavy chain (&agr;-MHC) promoter. In vitro, iNOS activity in hearts of two transgenic lines was 260- to 400-fold above controls (wild type [WT]), but TG mice were viable and appeared normal. Ventricular mass/body weight ratio did not differ; heart rate and cardiac output as well as mean arterial blood pressure were decreased by 10%. NOxlevels of hearts and blood of TG mice were 2.5- and 2-fold above WT controls, respectively. In the isolated heart, release of the NO oxidation products nitrate and nitrite, an index of in vivo NOS activity, was 40-fold over WT. However, cardiac hemodynamics and levels of ATP and phosphocreatine were unaltered. The high iNOS activity was associated with reduced cardiac l-arginine in TG hearts to only 15% of the WT, indicating limited substrate availability, whereas l-citrulline was 20-fold elevated. Our findings demonstrate that the heart can tolerate high levels of iNOS activity without detrimental functional consequences. The concept that iNOS-derived NO is the triggering factor in the pathomechanism leading to heart failure therefore needs to be reevaluated.

ISSN:0009-7330    

出版商:OVID    

年代:2002

数据来源: OVID