The present study utilized a novel transgenic mouse model that expresses an inducible dominant negative mutation of the transforming growth factor (TGF)-beta type II receptor (DnTGFbetaRII mouse) to test the hypothesis that TGF-beta signaling plays an important role in the pathogenesis of chronic hypoxia-induced increases in pulmonary arterial pressure and vascular and alveolar remodeling. Nine- to 10-wk-old male DnTGFbetaRII and control nontransgenic (NTG) mice were exposed to normobaric hypoxia (10% O2) or air for 6 wk. Expression of DnTGFbetaRII was induced by drinking 25 mM ZnSO4 water beginning 1 wk before hypoxic exposure. Hypoxia-induced increases in right ventricular pressure, right ventricular mass, pulmonary arterial remodeling, and muscularization were greatly attenuated in DnTGFbetaRII mice compared with NTG controls. Furthermore, the stimulatory effects of hypoxic exposure on pulmonary arterial and alveolar collagen content, appearance of alpha-smooth muscle actin-positive cells in alveolar parenchyma, and expression of extracellular matrix molecule (including collagen I and III, periostin, and osteopontin) mRNA in whole lung were abrogated in DnTGFbetaRII mice compared with NTG controls. Hypoxic exposure had no effect on systemic arterial pressure or heart rate in either strain. These data support the hypothesis that endogenous TGF-beta plays an important role in pulmonary vascular adaptation to chronic hypoxia and that disruption of TGF-beta signaling attenuates hypoxia-induced pulmonary hypertension, right ventricular hypertrophy, pulmonary arterial hypertrophy and muscularization, alveolar remodeling, and expression of extracellular matrix mRNA in whole lung.
"These discrepancies may be ascribable to differences in measurement techniques: the previous studies relied on mRNA analysis  or TGF-β protein measurement in pulmonary arteries , , whereas we measured both lung and serum TGF-β protein contents. Upregulation of TGF-β has also been reported in several animal models of PAH , , and decreased TGF-β signaling related to dominant negative TGF-β type II receptor (TGF-βRII) overexpression ,  or anti-TGF-β antibody  protects against PAH. Over the last 10 years, the importance of ALK1 and ENG in the pathogenesis of PAH has been established, notably by the identification of gene mutations , . "
[Show abstract][Hide abstract] ABSTRACT: Mutations affecting transforming growth factor-beta (TGF-β) superfamily receptors, activin receptor-like kinase (ALK)-1, and endoglin (ENG) occur in patients with pulmonary arterial hypertension (PAH). To determine whether the TGF-β/ALK1/ENG pathway was involved in PAH, we investigated pulmonary TGF-β, ALK1, ALK5, and ENG expressions in human lung tissue and cultured pulmonary-artery smooth-muscle-cells (PA-SMCs) and pulmonary endothelial cells (PECs) from 14 patients with idiopathic PAH (iPAH) and 15 controls. Seeing that ENG was highly expressed in PEC, we assessed the effects of TGF-β on Smad1/5/8 and Smad2/3 activation and on growth factor production by the cells. Finally, we studied the consequence of ENG deficiency on the chronic hypoxic-PH development by measuring right ventricular (RV) systolic pressure (RVSP), RV hypertrophy, and pulmonary arteriolar remodeling in ENG-deficient (Eng+/-) and wild-type (Eng+/+) mice. We also evaluated the pulmonary blood vessel density, macrophage infiltration, and cytokine expression in the lungs of the animals. Compared to controls, iPAH patients had higher serum and pulmonary TGF-β levels and increased ALK1 and ENG expressions in lung tissue, predominantly in PECs. Incubation of the cells with TGF-β led to Smad1/5/8 phosphorylation and to a production of FGF2, PDGFb and endothelin-inducing PA-SMC growth. Endoglin deficiency protected mice from hypoxic PH. As compared to wild-type, Eng+/- mice had a lower pulmonary vessel density, and no change in macrophage infiltration after exposure to chronic hypoxia despite the higher pulmonary expressions of interleukin-6 and monocyte chemoattractant protein-1. The TGF-β/ALK1/ENG signaling pathway plays a key role in iPAH and experimental hypoxic PH via a direct effect on PECs leading to production of growth factors and inflammatory cytokines involved in the pathogenesis of PAH.
PLoS ONE 06/2014; 9(6):e100310. DOI:10.1371/journal.pone.0100310 · 3.23 Impact Factor
"For example, Nox4 is abundantly expressed in pulmonary vascular wall cells, and its expression is selectively upregulated in the lungs of hypoxia-exposed mice, as well as in the vascular media of patients with idiopathic pulmonary arterial hypertension (IPAH). Emerging evidence demonstrates that hypoxic increases in Nox4 expression are mediated in part by increased transforming growth factor β (TGF-β)-1, a multifunctional matrix protein that contributes to the pathogenesis of many vascular diseases, pulmonary vascular remodeling, and PH. Recently, NF-kB, and hypoxia-inducible factor-1α (HIF1-α) were shown to modulate the transcriptional expression of Nox4 by binding to its promoter. "
[Show abstract][Hide abstract] ABSTRACT: Transforming growth factor-β1 (TGF- β1) and thrombospondin-1 (TSP-1) are hypoxia-responsive mitogens that promote vascular smooth muscle cell (SMC) proliferation, a critical event in the pathogenesis of pulmonary hypertension (PH). We previously demonstrated that hypoxia-induced human pulmonary artery smooth muscle (HPASMC) cell proliferation and expression of the NADPH oxidase subunit, Nox4, were attenuated by the peroxisome proliferator-activated receptor γ (PPARγ) agonist, rosiglitazone. The current study examines the hypothesis that rosiglitazone regulates Nox4 expression and HPASMC proliferation by attenuating TSP-1 signaling. Selected HPASMC were exposed to normoxic or hypoxic (1% O(2)) environments or TSP-1 (0-1 μg/ ml) for 72 hours ± administration of rosiglitazone (10 μM). Cellular proliferation, Nox4, TSP-1, and TGF-β1 expression and reactive oxygen species generation were measured. Mice exposed to hypoxia (10% O(2)) for three weeks were treated with rosiglitazone (10 mg/kg/day) for the final 10 days, and lung TSP-1 expression was examined. Hypoxia increased TSP-1 and TGF-β1 expression and HPASMC proliferation, and neutralizing antibodies to TSP-1 or TGF-β1 attenuated proliferation. Rosiglitazone attenuated hypoxia-induced HPASMC proliferation and increases in mouse lung and HPASMC TSP-1 expression, but failed to reduce increases in TGF-β1 expression or Nox4 expression and activity caused by direct TSP-1 stimulation. Transfecting HPASMC with siRNA to Nox4 attenuated hypoxia- or TSP-1-stimulated HPASMC proliferation. These findings provide novel evidence that TSP-1-mediated Nox4 expression plays a critical role in hypoxia-induced HPASMC proliferation. PPARγ activation with exogenous ligands attenuates TSP-1 expression to reduce Nox4 expression. These results clarify mechanisms of hypoxia-induced SMC proliferation and suggest additional pathways by which PPARγ agonists may regulate critical steps in the pathobiology of PH.
"Collagen fibrils from periostin (Postn)-null mice are reduced in size, somewhat disorganized, and less efficiently cross-linked, indicating that periostin facilitates proper organization of the ECM [23, 131, 132]. In addition, periostin is induced via TGF-β signaling and may then enable collagen realignment in response to TGF-β [130, 133, 134]. Postn-deficient hearts subjected to pressure overload or ischemic insult exhibited less fibrosis but more frequent rupture of the ventricular wall [132, 135]. "
[Show abstract][Hide abstract] ABSTRACT: Cardiac hypertrophy entails complex structural remodeling involving rearrangement of muscle fibers, interstitial fibrosis, accumulation of extracellular matrix, and angiogenesis. Many of the processes underlying cardiac remodeling have features in common with chronic inflammatory processes. During these processes, nonmyocytes, such as endothelial cells, fibroblasts, and immune cells, residing in or infiltrating into the myocardial interstitium play active roles. This paper mainly addresses the functional roles of nonmyocytes during cardiac remodeling. In particular, we focus on the communication between cardiomyocytes and nonmyocytes through direct cell-cell interactions and autocrine/paracrine-mediated pathways.
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