ABSTRACT
Monocrotaline (MCT)-induces progressive disruption of endothelial cell membrane and caveolin-1 leading to pulmonary arterial hypertension (PAH). Treatment instituted early rescues caveolin-1 ...and attenuates PAH. To test the hypothesis that the poor response to therapy in established PAH is due to progressive deregulation of multiple signaling pathways, the authors investigated time-dependent changes in the expression of caveolin-1, gp130, PY-STAT3, Bcl-xL, and the molecules involved in NO signaling pathway (endothelial nitric oxide synthase eNOS, heat sock protein 90 HSP90, Akt, soluble guanylate cyclase sGC α1 and β1 subunits). PAH and right ventricular hypertrophy (RVH) were observed at 2 and 3 weeks. Progressive loss of endothelial caveolin-1 and sGC (α1, β1), PY-STAT3 activation, and Bcl-xL expression were observed at 1 to 3 weeks post-MCT. The expression of gp130 increased at 48 hours and 1 week, with a subsequent loss at 2 and 3 weeks. The expression of eNOS increased at 48 hours and 1 week post-MCT, with a significant loss at 3 weeks. The expression of HSP90 and Akt decreased at 2 and 3 weeks post-MCT concomitant with PAH. Thus, MCT induces progressive loss of membrane and cytosolic proteins, resulting in the activation of proliferative and antiapoptotic factors, and deregulation of NO signaling leading to PAH. An attractive therapeutic approach to treat PAH may be an attempt to rescue endothelial cell membrane integrity.
Pulmonary artery hypertension (PAH) is a sequela of a number of disparate diseases, often with a fatal consequence. Endothelial dysfunction is considered to be an early event during the development ...of PAH. Impaired availability of bioactive nitric oxide (NO) is a key underlying feature in most forms of clinical and experimental PAH. NO, generated by catalytic activity of endothelial NO synthase (eNOS) on l-arginine, modulates vascular function and structure. For optimal activation, eNOS is targeted to caveolae, the flask-shaped invaginations found on the surface of plasmalemmal membrane of a variety of cells, including endothelial cells. Caveolin-1, the major coat protein of caveolae, regulates eNOS activity. Evidence is accumulating to suggest that caveolin-1 may play a significant role in the pathogenesis of PAH. This review is intended to summarize recent findings indicating a role for caveolin-1 and caveolin-1/eNOS interrelationship in PAH.
Cyclosporine A, used to prevent graft-versus-host-disease, is known to induce endothelial injury. Endothelial dysfunction is an important feature of pulmonary arterial hypertension (PAH). In this ...article, we describe 2 children who developed cyclosporine-induced acute respiratory distress syndrome. Lung biopsy showed patchy loss of endothelial caveolin-1 and von Willebrand factor to occur early. Significant loss of endothelial caveolin-1 was associated with robust expression of caveolin-1 in smooth muscle cells with subsequent neointima formation leading to fatal PAH. Thus, patients who develop acute respiratory distress syndrome after immunosuppressive therapy are at risk of developing PAH.
Abstract only
Pulmonary arterial hypertension (PAH) is a progressive disease associated with right heart failure and premature death. Diagnosis of PAH is often made late and available therapy fails ...to reverse the disease process. To test the hypothesis that the poor response to therapy in PAH is due to the involvement of multiple signaling pathways, we investigated time‐dependent changes in the expression of caveolin‐1, PY‐STAT3, Bcl‐xL, and the molecules involved in NO signaling pathway (eNOS, HSP90, Akt) in rats at 48 hr, 1, 2, and 3 wks post‐monocrotaline (MCT). Progressive PAH, right ventricular hypertrophy and pulmonary vascular remodeling were observed at 2 and 3 wks post‐MCT. Progressive loss of endothelial caveolin‐1 coupled with activation of PY‐STAT3 and upregulation of Bcl‐xL preceded the onset of PAH. There was an early and progressive loss of Tie2 which colocalizes with caveolin‐1 and has been implicated in PAH. Expression of eNOS increased at 48 hr and 1 wk post‐MCT with a significant loss at 3 wks post‐MCT. At 2 wks post‐MCT concomitant with PAH, the expression of eNOS activating molecules HSP90 and Akt was significantly reduced, which is consistent with impaired NO availability as observed previously. We conclude that there is progressive deregulation of multiple signaling pathways leading to cell proliferation, inhibition of apoptosis and NO impairment in PAH. This may in part, explain the difficulties encountered in the treatment of PAH.
The nitric oxide-cyclic guanosine monophosphate signal-transduction mechanism plays a key role in the regulation of vascular tone and structure. Monocrotaline-induced pulmonary hypertension is ...associated with low bioavailability of nitric oxide. To characterize the mechanism(s) involved in this dysfunction, rats received a single subcutaneous injection of monocrotaline, normal saline (control), or monocrotaline plus daily L-arginine, a precursor of nitric oxide, in drinking water. Pulmonary artery pressure and right ventricular hypertrophy were assessed 2 weeks later. In addition, the authors evaluated the expression of endothelial nitric oxide synthase messenger RNA, endothelial nitric oxide synthase protein, cyclic guanosine monophosphate, and sulfhydryl levels in the lungs. Sulfhydryls are needed for the dynamic modulation of soluble guanylate cyclase by nitric oxide, which results in cyclic guanosine monophosphate formation. L-arginine treatment did not attenuate monocrotaline-induced pulmonary hypertension or right ventricular hypertrophy. Monocrotaline did not alter the expression of endothelial nitric oxide synthase messenger RNA or endothelial nitric oxide synthase protein in the lungs. Protein-bound sulfhydryls (28 +/- 5 vs. 75 +/- 16 pmol/microg protein) and cyclic guanosine monophosphate (0.63 +/- 0.05 vs. 1.06 +/- 0.017 pmol/microg protein) levels in the monocrotaline group were significantly low compared with controls. The low sulfhydryl levels, an indicator of oxidant stress, may account for the impaired availability of bioactive nitric oxide and low cyclic guanosine monophosphate levels. These results suggest that oxidative stress may, in part, contribute to the pathogenesis of pulmonary hypertension in the monocrotaline model.
Monocrotaline (MCT)‐induced pulmonary hypertension (PH) is associated with a loss of caveolin‐1 (caveolar membrane protein) expression and reciprocal activation of STAT3 (PY‐STAT3), a ...proproliferative facotor. In several cell systems, loss of caveolin‐1 is associated with the activation of cell proliferative pathways, and reduction in the expression of p21waf1/cip1, a cyclin‐dependent kinase that blocks DNA replication. To assess the role of caveolin‐1 and PY‐STAT3 in PH, MCT‐injected rats were treated with molsidomine or pyrrolidine dithiocarbamate (PDTC). Two wks post‐MCT, rats exhibited significant PH and RVH. Pulmonary arteries in these rats revealed a significant reduction in the expression of cav‐1 and p21waf1/cip1, and activation of PY‐STAT3. Molsidomine and PDTC significantly attenuated MCT‐induced PH and RVH. This attenuation of PH was associated not only with the preservation of caveolin‐1 and p21waf1/cip1, but also inhibition of PY‐STAT3 activation. Furthermore, PECAM‐1 and Tie2 (caveolar membrane proteins) were also rescued indicating a generalized restoration of endothelial cell membrane integrity. We conclude that the restoration of caveolin‐1 led to inhibition of PY‐STAT3 activation and an increase in the expression of p21waf1/cip1, resulting in the inhibition of cell proliferation and attenuation of PH. Thus, caveolin‐1 and PY‐STAT3 play a pivotal role in pulmonary vascular health.
Monocrotaline (MCT)‐induced pulmonary hypertension (PH) is preceded by an inflammatory response. We have previously shown that MCT‐induced PH is associated with upregulation of IL‐6 mRNA, activation ...of PY‐STAT3 and disruption of endothelial cell membrane proteins such as caveolin‐1, PECAM and Tie2. NF‐κB regulates genes involved in inflammation and cell proliferation, and in some cell systems NF‐κB is activated by STAT3. To investigate the role of NF‐κB in PH, rats received a single subcutaneous injection of MCT and pyrrolidine dithiocarbamate (PDTC, 50, 100 and 200 mg/kg/day), an inhibitor of NF‐κB. At 2 wks post‐MCT rats showed significant PH (mmHg 34±1.4 vs 18±0.8) and RVH (RV/LV, 0.35±0.02 vs 0.23±0.005) compared with the controls. Western blot analysis and immunofluorescence showed significant reduction in the expression of I‐κBα(NF‐κB inhibitory protein, 78%), caveolin‐1 (65%) and Tie2 (85%). PDTC treatment not only prevented the degradation of I‐κBα, and attenuated MCT‐induced PH and RVH, but also preserved caveolin‐1 and Tie2 in a dose dependent manner. We conclude that MCT affects the endothelial cell membrane integrity and the activation of NF‐κB may be an important step in the pathogenesis of PH.
We have previously shown that monocrotaline (MCT)‐induced pulmonary hypertension (PH) is associated with a reduction in caveolin‐1 expression and reciprocal activation of STAT3 (PY‐STAT3), a ...proproliferative transcription factor. Caveolin‐1 negatively regulates cell proliferation and is an inhibitor of STAT3 activation. Since hypoxia leads to a tight caveolin‐1/eNOS complex formation, we hypothesized that this complex may modulate caveolin‐1‐related signaling molecule (PY‐STAT3) involved in cell proliferation. Rats were subjected to hypobaric hypoxia (50 Kp) and examined at 48h, 1 and 2 wks. In addition, bovine pulmonary artery endothelial cells (BPAEC) were subjected to hypoxia (5% O2) for 24 hrs. Progressive PH and RVH were observed in rats exposed to hypoxia. eNOS expression was increased in the hypoxia groups (1.6‐2 fold) compared with the controls. Progressive activation of PY‐STAT3 was observed in the hypoxia‐exposed rat lungs (1.4‐4 fold). Hypoxia‐exposed BPAEC revealed alterations in eNOS/caveolin‐1 interrelationship and activation of PY‐STAT3. The expression of caveolin‐1 was not significantly altered in in‐vivo or in‐vitro model. We conclude that the hypoxia‐induced alterations in eNOS/caveolin‐1 interrelationship may influence inhibitory effects of caveolin‐1 on cell proliferation and that the activation of PY‐STAT3 plays a pivotal role in the pathogenesis of PH.
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