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Nicola T, Ambalavanan N, Zhang W, James ML, Rehan V, Halloran B, Olave N, Bulger A, Oparil S, Chen YF. Hypoxia-induced inhibition of lung development is attenuated by the peroxisome proliferator-activated receptor-γ agonist rosiglitazone. Am J Physiol Lung Cell Mol Physiol 2011; 301:L125-34. [PMID: 21531777 DOI: 10.1152/ajplung.00074.2011] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Hypoxia enhances transforming growth factor-β (TGF-β) signaling, inhibiting alveolar development and causing abnormal pulmonary arterial remodeling in the newborn lung. We hypothesized that, during chronic hypoxia, reduced peroxisome proliferator-activated receptor-γ (PPAR-γ) signaling may contribute to, or be caused by, excessive TGF-β signaling. To determine whether PPAR-γ was reduced during hypoxia, C57BL/6 mice were exposed to hypoxia from birth to 2 wk and evaluated for PPAR-γ mRNA and protein. To determine whether rosiglitazone (RGZ, a PPAR-γ agonist) supplementation attenuated the effects of hypoxia, mice were exposed to air or hypoxia from birth to 2 wk in combination with either RGZ or vehicle, and measurements of lung histology, function, parameters related to TGF-β signaling, and collagen content were made. To determine whether excessive TGF-β signaling reduced PPAR-γ, mice were exposed to air or hypoxia from birth to 2 wk in combination with either TGF-β-neutralizing antibody or vehicle, and PPAR-γ signaling was evaluated. We observed that hypoxia reduced PPAR-γ mRNA and protein, in association with impaired alveolarization, increased TGF-β signaling, reduced lung compliance, and increased collagen. RGZ increased PPAR-γ signaling, with improved lung development and compliance in association with reduced collagen and TGF-β signaling. However, no reduction was noted in hypoxia-induced pulmonary vascular remodeling. Inhibition of hypoxia-enhanced TGF-β signaling increased PPAR-γ signaling. These results suggest that hypoxia-induced inhibition of lung development is associated with a mutually antagonistic relationship between reduced PPAR-γ and increased TGF-β signaling. PPAR-γ agonists may be of potential therapeutic significance in attenuating TGF-β signaling and improving alveolar development.
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Affiliation(s)
- Teodora Nicola
- Department of Pediatrics, University of Alabama at Birmingham, Birmingham, Alabama 35233, USA
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152
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Prostacyclins in pulmonary arterial hypertension: the need for earlier therapy. Adv Ther 2011; 28:251-69. [PMID: 21455725 DOI: 10.1007/s12325-011-0005-5] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2010] [Indexed: 10/18/2022]
Abstract
Pulmonary arterial hypertension (PAH) is a rare but serious condition, which if untreated, is associated with a 2-3-year median survival time. A number of treatment options are available for PAH, leading to improvements in exercise capacity, symptoms, and hemodynamics. However, the disease remains incurable and most patients will ultimately progress to right heart failure and death. Three classes of drugs are currently available to improve PAH outcomes, although this review will focus solely on a class of potent vasodilators known as prostacyclins. Currently, four prostacyclin analogs are licensed for the treatment of PAH: epoprostenol, treprostinil, and iloprost in the USA and some European countries, and beraprost in Japan and Korea. Prostacyclins have become the treatment of choice in patients with severe PAH, but there is also evidence to suggest that their earlier use may also benefit patients with mild-to-moderate disease. This review discusses the advantages of prostacyclins in terms of their usefulness in patients whose condition has deteriorated following monotherapy with other agents, and their integral role in combination therapy. The latter appears to offer the potential for pulmonary vasculature remodeling and could be regarded as an emerging paradigm to treat and prevent the progression of PAH.
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153
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Green DE, Sutliff RL, Hart CM. Is peroxisome proliferator-activated receptor gamma (PPARγ) a therapeutic target for the treatment of pulmonary hypertension? Pulm Circ 2011; 1:33-47. [PMID: 21547012 PMCID: PMC3085428 DOI: 10.4103/2045-8932.78101] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Pulmonary hypertension (PH), a progressive disorder associated with significant morbidity and mortality, is caused by complex pathways that culminate in structural and functional alterations of the pulmonary circulation and increases in pulmonary vascular resistance and pressure. Diverse genetic, pathological, or environmental triggers stimulate PH pathogenesis culminating in vasoconstriction, cell proliferation, vascular remodeling, and thrombosis. We conducted a thorough literature review by performing MEDLINE searches via PubMed to identify articles pertaining to PPARγ as a therapeutic target for the treatment of PH. This review examines basic and preclinical studies that explore PPARγ and its ability to regulate PH pathogenesis. Despite the current therapies that target specific pathways in PH pathogenesis, including prostacyclin derivatives, endothelin-receptor antagonists, and phosphodiesterase type 5 inhibitors, morbidity and mortality related to PH remain unacceptably high, indicating the need for novel therapeutic approaches. Consequently, therapeutic targets that simultaneously regulate multiple pathways involved in PH pathogenesis have gained attention. This review focuses on peroxisome proliferator-activated receptor gamma (PPARγ), a member of the nuclear hormone receptor superfamily of ligand-activated transcription factors. While the PPARγ receptor is best known as a master regulator of lipid and glucose metabolism, a growing body of literature demonstrates that activation of PPARγ exerts antiproliferative, antithrombotic, and vasodilatory effects on the vasculature, suggesting its potential efficacy as a PH therapeutic target.
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Affiliation(s)
- David E Green
- Department of Medicine, Emory University, Atlanta Veterans Affairs Medical Center, Decatur, Georgia, USA
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154
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Weng M, Raher MJ, Leyton P, Combs TP, Scherer PE, Bloch KD, Medoff BD. Adiponectin decreases pulmonary arterial remodeling in murine models of pulmonary hypertension. Am J Respir Cell Mol Biol 2010; 45:340-7. [PMID: 21075862 DOI: 10.1165/rcmb.2010-0316oc] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Remodeling of the pulmonary arteries is a common feature among the heterogeneous disorders that cause pulmonary hypertension. In these disorders, the remodeled pulmonary arteries often demonstrate inflammation and an accumulation of pulmonary artery smooth muscle cells (PASMCs) within the vessels. Adipose tissue secretes multiple bioactive mediators (adipokines) that can influence both inflammation and remodeling, suggesting that adipokines may contribute to the development of pulmonary hypertension. We recently reported on a model of pulmonary hypertension induced by vascular inflammation, in which a deficiency of the adipokine adiponectin (APN) was associated with the extensive proliferation of PASMCs and increased pulmonary artery pressures. Based on these data, we hypothesize that APN can suppress pulmonary hypertension by directly inhibiting the proliferation of PASMCs. Here, we tested the effects of APN overexpression on pulmonary arterial remodeling by using APN-overexpressing mice in a model of pulmonary hypertension induced by inflammation. Consistent with our hypothesis, mice that overexpressed APN manfiested reduced pulmonary hypertension and remodeling compared with wild-type mice, despite developing similar levels of pulmonary vascular inflammation in the model. The overexpression of APN was also protective in a hypoxic model of pulmonary hypertension. Furthermore, APN suppressed the proliferation of PASMCs, and reduced the activity of the serum response factor-serum response element pathway, which is a critical signaling pathway for smooth muscle cell proliferation. Overall, these data suggest that APN can regulate pulmonary hypertension and pulmonary arterial remodeling through its direct effects on PASMCs. Hence, the activation of APN-like activity in the pulmonary vasculature may be beneficial in pulmonary hypertension.
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Affiliation(s)
- Meiqian Weng
- Pulmonary and Critical Care Unit, Massachusetts General Hospital, Boston, MA 02114, USA
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155
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Sutliff RL, Kang BY, Hart CM. PPARgamma as a potential therapeutic target in pulmonary hypertension. Ther Adv Respir Dis 2010; 4:143-60. [PMID: 20530063 DOI: 10.1177/1753465809369619] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Pulmonary hypertension (PH) is a progressive disorder of the pulmonary circulation associated with significant morbidity and mortality. The pathobiology of PH involves a complex series of derangements causing endothelial dysfunction, vasoconstriction and abnormal proliferation of pulmonary vascular wall cells that lead to increases in pulmonary vascular resistance and pressure. Recent evidence indicates that the ligand-activated transcription factor, peroxisome proliferator-activated receptor gamma (PPARgamma) can have a favorable impact on a variety of pathways involved in the pathogenesis of PH. This review summarizes PPARgamma biology and the emerging evidence that therapies designed to activate this receptor may provide novel approaches to the treatment of PH. Mediators of PH that are regulated by PPARgamma are reviewed to provide insights into potential mechanisms underlying therapeutic effects of PPARgamma ligands in PH.
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Affiliation(s)
- Roy L Sutliff
- Division of Pulmonary, Allergy and Critical Care Medicine, Atlanta VA Medical Center, Decatur, GA 30033, USA.
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156
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Lu X, Murphy TC, Nanes MS, Hart CM. PPAR{gamma} regulates hypoxia-induced Nox4 expression in human pulmonary artery smooth muscle cells through NF-{kappa}B. Am J Physiol Lung Cell Mol Physiol 2010; 299:L559-66. [PMID: 20622120 DOI: 10.1152/ajplung.00090.2010] [Citation(s) in RCA: 117] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
NADPH oxidases are a major source of superoxide production in the vasculature. The constitutively active Nox4 subunit, which is selectively upregulated in the lungs of human subjects and experimental animals with pulmonary hypertension, is highly expressed in vascular wall cells. We demonstrated that rosiglitazone, a synthetic agonist of the peroxisome proliferator-activated receptor-γ (PPARγ), attenuated hypoxia-induced pulmonary hypertension, vascular remodeling, Nox4 induction, and reactive oxygen species generation in the mouse lung. The current study examined the molecular mechanisms involved in PPARγ-regulated, hypoxia-induced Nox4 expression in human pulmonary artery smooth muscle cells (HPASMC). Exposing HPASMC to 1% oxygen for 72 h increased Nox4 gene expression and H(2)O(2) production, both of which were reduced by treatment with rosiglitazone during the last 24 h of hypoxia exposure or by treatment with small interfering RNA (siRNA) to Nox4. Hypoxia also increased HPASMC proliferation as well as the activity of a Nox4 promoter luciferase reporter, and these increases were attenuated by rosiglitazone. Chromatin immunoprecipitation assays demonstrated that hypoxia increased binding of the NF-κB subunit, p65, to the Nox4 promoter and that binding was attenuated by rosiglitazone treatment. The role of NF-κB in Nox4 regulation was further supported by demonstrating that overexpression of p65 stimulated Nox4 promoter activity, whereas siRNA to p50 or p65 attenuated hypoxic stimulation of Nox4 promoter activity. These results provide novel evidence for NF-κB-mediated stimulation of Nox4 expression in HPASMC that can be negatively regulated by PPARγ. These data provide new insights into potential mechanisms by which PPARγ activation inhibits Nox4 upregulation and the proliferation of cells in the pulmonary vascular wall to ameliorate pulmonary hypertension and vascular remodeling in response to hypoxia.
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Affiliation(s)
- Xianghuai Lu
- Department of Medicine, Atlanta Veterans Affairs, Emory University Medical Centers, Georgia, USA
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157
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Blanquicett C, Kang BY, Ritzenthaler JD, Jones DP, Hart CM. Oxidative stress modulates PPAR gamma in vascular endothelial cells. Free Radic Biol Med 2010; 48:1618-25. [PMID: 20302927 PMCID: PMC2868091 DOI: 10.1016/j.freeradbiomed.2010.03.007] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/11/2009] [Revised: 03/05/2010] [Accepted: 03/09/2010] [Indexed: 12/27/2022]
Abstract
The peroxisome proliferator-activated receptor gamma (PPAR gamma) plays an important role in vascular regulation. However, the impact of oxidative stress on PPAR gamma expression and activity has not been clearly defined. Human umbilical vein endothelial cells (HUVECs) were exposed to graded concentrations of H(2)O(2) for 0.5-72h, or bovine aortic endothelial cells (BAECs) were exposed to alterations in extracellular thiol/disulfide redox potential (E(h)) of the cysteine/cystine couple. Within 2h, H(2)O(2) reduced HUVEC PPAR gamma mRNA and activity and reduced the expression of two PPAR gamma-regulated genes without altering PPAR gamma protein levels. After 4h H(2)O(2) exposure, mRNA levels remained reduced, whereas PPAR gamma activity returned to control levels. PPAR gamma mRNA levels remained depressed for up to 72 h after exposure to H(2)O(2), without any change in PPAR gamma activity. Catalase prevented H(2)O(2)-induced reductions in PPAR gamma mRNA and activity. H(2)O(2) (1) reduced luciferase expression in HUVECs transiently transfected with a human PPAR gamma promoter reporter, (2) failed to alter PPAR gamma mRNA half-life, and (3) transiently increased expression and activity of c-Fos and phospho-c-Jun. Treatment with the AP1 inhibitor curcumin prevented H(2)O(2)-mediated reductions in PPAR gamma expression. In addition, medium having an oxidized E(h) reduced BAEC PPAR gamma mRNA and activity. These findings demonstrate that oxidative stress, potentially through activation of inhibitory redox-regulated transcription factors, attenuates PPAR gamma expression and activity in vascular endothelial cells through suppression of PPAR gamma transcription.
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Affiliation(s)
| | | | | | | | - C. Michael Hart
- Address correspondence to: C. Michael Hart, M.D., Professor of Medicine, Division of Pulmonary and Critical Care Medicine, Atlanta VAMC (151-P), 1670 Clairmont Rd., Decatur, GA 30033, Phone: 404 – 321 – 6111 ext 7278, Fax: 404 – 728 – 7750,
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158
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Affiliation(s)
- Mark T Gladwin
- Pulmonary, Allergy and Critical Care Medicine, NW 628 Montefiore Hospital, 3459 Fifth Ave., Pittsburgh, PA 15213, USA.
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159
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Khoo NKH, Freeman BA. Electrophilic nitro-fatty acids: anti-inflammatory mediators in the vascular compartment. Curr Opin Pharmacol 2010; 10:179-84. [PMID: 20080062 DOI: 10.1016/j.coph.2009.11.003] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Revised: 11/02/2009] [Accepted: 11/14/2009] [Indexed: 11/30/2022]
Abstract
Vascular inflammatory disorders are often associated with both decreased NO bioavailability and a lack of responsiveness to NO, a consequence of impaired NO biosynthesis, dysregulated l-arginine metabolism, endothelial nitric oxide synthase (eNOS) uncoupling and NO consumption induced by redox reactions of NO. The latter is mediated via oxidative inflammatory conditions altering NO-dependent endothelial function, including vascular tone and cell proliferation. The redox reactions of NO and byproducts such as nitrite can react to yield electrophilic nitro-fatty acid derivatives (NO(2)-FAs) and exemplify a biochemical convergence of reactions participating in NO and lipid signaling. NO(2)-FAs represent a novel therapeutic strategy to treat vascular disorders by improving endothelial dysfunction through enhancing NO signaling and blocking vascular smooth muscle proliferation, inflammation, and maladaptive remodeling.
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Affiliation(s)
- Nicholas K H Khoo
- Department of Pharmacology and Chemical Biology, E1314 BST, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
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160
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Tian J, Smith A, Nechtman J, Podolsky R, Aggarwal S, Snead C, Kumar S, Elgaish M, Oishi P, Göerlach A, Fratz S, Hess J, Catravas JD, Verin AD, Fineman JR, She JX, Black SM. Effect of PPARgamma inhibition on pulmonary endothelial cell gene expression: gene profiling in pulmonary hypertension. Physiol Genomics 2009; 40:48-60. [PMID: 19825830 PMCID: PMC2807211 DOI: 10.1152/physiolgenomics.00094.2009] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Peroxisome proliferator-activated receptor type gamma (PPARgamma) is a subgroup of the PPAR transcription factor family. Recent studies indicate that loss of PPARgamma is associated with the development of pulmonary hypertension (PH). We hypothesized that the endothelial dysfunction associated with PPARgamma inhibition may play an important role in the disease process by altering cellular gene expression and signaling cascades. We utilized microarray analysis to determine if PPARgamma inhibition induced changes in gene expression in pulmonary arterial endothelial cells (PAEC). We identified 100 genes and expressed sequence tags (ESTs) that were upregulated by >1.5-fold and 21 genes and ESTs that were downregulated by >1.3-fold (P < 0.05) by PPARgamma inhibition. The upregulated genes can be broadly classified into four functional groups: cell cycle, angiogenesis, ubiquitin system, and zinc finger proteins. The genes with the highest fold change in expression: hyaluronan-mediated motility receptor (HMMR), VEGF receptor 2 (Flk-1), endothelial PAS domain protein 1 (EPAS1), basic fibroblast growth factor (FGF-2), and caveolin-1 in PAEC were validated by real time RT-PCR. We further validated the upregulation of HMMR, Flk-1, FGF2, and caveolin-1 by Western blot analysis. In keeping with the microarray results, PPARgamma inhibition led to re-entry of cell cycle at G(1)/S phase and cyclin C upregulation. PPARgamma inhibition also exacerbated VEGF-induced endothelial barrier disruption. Finally we confirmed the downregulation of PPARgamma and the upregulation of HMMR, Flk-1, FGF2, and Cav-1 proteins in the peripheral lung tissues of an ovine model of PH. In conclusion, we have identified an array of endothelial genes modulated by attenuated PPARgamma signaling that may play important roles in the development of PH.
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Affiliation(s)
- Jing Tian
- Pulmonary Vascular Disease Program, Vascular Biology Center, Medical College of Georgia, Augusta, Georgia 30912, USA
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161
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Tian J, Smith A, Nechtman J, Podolsky R, Aggarwal S, Snead C, Kumar S, Elgaish M, Oishi P, Göerlach A, Fratz S, Hess J, Catravas JD, Verin AD, Fineman JR, She JX, Black SM. Effect of PPARgamma inhibition on pulmonary endothelial cell gene expression: gene profiling in pulmonary hypertension. Physiol Genomics 2009. [PMID: 19825830 DOI: 10.1052/physiolgenomocs.00094.2009] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Peroxisome proliferator-activated receptor type gamma (PPARgamma) is a subgroup of the PPAR transcription factor family. Recent studies indicate that loss of PPARgamma is associated with the development of pulmonary hypertension (PH). We hypothesized that the endothelial dysfunction associated with PPARgamma inhibition may play an important role in the disease process by altering cellular gene expression and signaling cascades. We utilized microarray analysis to determine if PPARgamma inhibition induced changes in gene expression in pulmonary arterial endothelial cells (PAEC). We identified 100 genes and expressed sequence tags (ESTs) that were upregulated by >1.5-fold and 21 genes and ESTs that were downregulated by >1.3-fold (P < 0.05) by PPARgamma inhibition. The upregulated genes can be broadly classified into four functional groups: cell cycle, angiogenesis, ubiquitin system, and zinc finger proteins. The genes with the highest fold change in expression: hyaluronan-mediated motility receptor (HMMR), VEGF receptor 2 (Flk-1), endothelial PAS domain protein 1 (EPAS1), basic fibroblast growth factor (FGF-2), and caveolin-1 in PAEC were validated by real time RT-PCR. We further validated the upregulation of HMMR, Flk-1, FGF2, and caveolin-1 by Western blot analysis. In keeping with the microarray results, PPARgamma inhibition led to re-entry of cell cycle at G(1)/S phase and cyclin C upregulation. PPARgamma inhibition also exacerbated VEGF-induced endothelial barrier disruption. Finally we confirmed the downregulation of PPARgamma and the upregulation of HMMR, Flk-1, FGF2, and Cav-1 proteins in the peripheral lung tissues of an ovine model of PH. In conclusion, we have identified an array of endothelial genes modulated by attenuated PPARgamma signaling that may play important roles in the development of PH.
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Affiliation(s)
- Jing Tian
- Pulmonary Vascular Disease Program, Vascular Biology Center, Medical College of Georgia, Augusta, Georgia 30912, USA
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162
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Guignabert C, Alvira CM, Alastalo TP, Sawada H, Hansmann G, Zhao M, Wang L, El-Bizri N, Rabinovitch M. Tie2-mediated loss of peroxisome proliferator-activated receptor-gamma in mice causes PDGF receptor-beta-dependent pulmonary arterial muscularization. Am J Physiol Lung Cell Mol Physiol 2009; 297:L1082-90. [PMID: 19801450 DOI: 10.1152/ajplung.00199.2009] [Citation(s) in RCA: 116] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Peroxisome proliferator-activated receptor (PPAR)-gamma is reduced in pulmonary arteries (PAs) of patients with PA hypertension (PAH), and we reported that deletion of PPARgamma in smooth muscle cells (SMCs) of transgenic mice results in PAH. However, the sequelae of loss of PPARgamma in PA endothelial cells (ECs) are unknown. Therefore, we bred Tie2-Cre mice with PPARgamma(flox/flox) mice to induce EC loss of PPARgamma (Tie2 PPARgamma(-/-)), and we assessed PAH by right ventricular systolic pressure (RVSP), RV hypertrophy (RVH), and muscularized distal PAs in room air (RA), after chronic hypoxia (CH), and after 4 wk of recovery in RA (Rec-RA). The Tie2 PPARgamma(-/-) mice developed spontaneous PAH in RA with increased RVSP, RVH, and muscularized PAs vs. wild type (WT); both genotypes exhibited a similar degree of PAH following chronic hypoxia, but Tie2 PPARgamma(-/-) mice had more residual PAH compared with WT mice after Rec-RA. The Tie2 PPARgamma(-/-) vs. WT mice in RA had increased platelet-derived growth factor receptor-beta (PDGF-Rbeta) expression and signaling, despite an elevation in the PPARgamma target apolipoprotein E, an inhibitor of PDGF signaling. Inhibition of PDGF-Rbeta signaling with imatinib, however, was sufficient to reverse the PAH observed in the Tie2 PPARgamma(-/-) mice. Thus the disruption of PPARgamma signaling in EC is sufficient to cause mild PAH and to impair recovery from CH-induced PAH. Inhibition of heightened PDGF-Rbeta signaling is sufficient to reverse PAH in this genetic model.
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Affiliation(s)
- C Guignabert
- Vera Moulton Wall Center for Pulmonary Vascular Disease, Stanford Univ. School of Medicine, CA 94305-5162, USA
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