Chronic Hypoxia-induced Pulmonary Vascular Remodeling Research Articles

Hypoxia-induced autophagy activation through NF-κB pathway regulates cell proliferation and migration to induce pulmonary vascular remodeling

ObjectivesThis study aimed to investigate whether autophagy mediated cell proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs) under hypoxia and to validate the underlying mechanism. MethodsThe rat model of chronic hypoxia-induced pulmonary vascular remodeling was established. Rat primary PASMCs were isolated and cultured in vitro in hypoxia or normoxia to explore the underlying mechanism. ResultsHypoxia exposure for 21 days induced pulmonary vascular remodeling in rats, accompanied by enhanced proliferation and decreased apoptosis, as well as induced expression of autophagic marker LC3II in their lungs. Furthermore, in vitro assays revealed that hypoxia exposure significantly promoted cell proliferation and migration, but inhibited apoptosis of PASMCs compared with normoxia treatment. Besides, hypoxia exposure led to an increase of cell fractions in S phase and a decrease in G0/G1 of PASMCs, whereas had no significant effect on cell population in G2/M phase. Moreover, the autophagy inhibitor 3-MA significantly decreased the hypoxia-induced upregulated expression of LC3II in PASMCs and abrogated the effect of hypoxia on cell proliferation, cell apoptosis, cell cycle, and cell migration of PASMCs. Additionally, inhibition of NF-κB pathway by PDTC suppressed the hypoxia-induced upregulation of NF-κB activity, LC3II, and cell cycle regulators (cyclin D1, CDK4, and CDK6) in PASMCs, and abolished the hypoxia-mediated regulation of cell proliferation, apoptosis, cycle, and migration of PASMCs. ConclusionIn summary, hypoxia could induce autophagy activation through NF-κB pathway, and thereby regulate cell proliferation and migration to induce pulmonary vascular remodeling.

Mitochondrial transplantation attenuates hypoxic pulmonary hypertension.

Mitochondria are essential for the onset of hypoxia-induced pulmonary vasoconstriction and pulmonary vascular-remodeling, two major aspects underlying the development of pulmonary hypertension, an incurable disease. However, hypoxia induces relaxation of systemic arteries such as femoral arteries and mitochondrial heterogeneity controls the distinct responses of pulmonary versus femoral artery smooth muscle cells to hypoxia in vitro. The aim of this study was to determine whether mitochondrial heterogeneity can be experimentally exploited in vivo for a potential treatment against pulmonary hypertension. The intact mitochondria were transplanted into Sprague-Dawley rat pulmonary artery smooth muscle cells in vivo via intravenous administration. The immune-florescent staining and ultrastructural examinations on pulmonary arteries confirmed the intracellular distribution of exogenous mitochondria and revealed the possible mitochondrial transfer from pulmonary artery endothelial cells into smooth muscle cells in part through their intercellular space and intercellular junctions. The transplantation of mitochondria derived from femoral artery smooth muscle cells inhibited acute hypoxia-triggered pulmonary vasoconstriction, attenuated chronic hypoxia-induced pulmonary vascular remodeling, and thus prevented the development of pulmonary hypertension or cured the established pulmonary hypertension in rats exposed to chronic hypoxia. Our findings suggest that mitochondrial transplantation possesses potential implications for exploring a novel therapeutic and preventive strategy against pulmonary hypertension.

Antagonism of stem cell factor/c-kit signaling attenuates neonatal chronic hypoxia-induced pulmonary vascular remodeling.

BackgroundAccumulating evidence suggests that c-kit positive cells are present in the remodeled pulmonary vasculature bed of patients with pulmonary hypertension (PH). Whether stem cell factor (SCF)/ c-kit regulated pathways potentiate pulmonary vascular remodeling is unknown. Here, we tested the hypothesis that attenuated c-kit signaling would decrease chronic hypoxia-induced pulmonary vascular remodeling by decreasing pulmonary vascular cell mitogenesis.MethodsNeonatal FVB/NJ mice treated with non-immune IgG (PL), or c-kit neutralizing antibody (ACK2) as well as c-kit mutant mice (WBB6F1- Kit W− v/ +) and their congenic controls, were exposed to normoxia (FiO2=0.21) or hypoxia (FiO2=0.12) for two weeks. Following this exposure, right ventricular systolic pressure (RVSP), right ventricular hypertrophy (RVH), pulmonary vascular cell proliferation and remodeling were evaluated.ResultsAs compared to chronically hypoxic controls, c-kit mutant mice had decreased RVSP, RVH, pulmonary vascular remodeling and proliferation. Consistent with these findings, administration of ACK2 to neonatal mice with chronic hypoxia-induced PH decreased RVSP, RVH, pulmonary vascular cell proliferation and remodeling. This attenuation in PH was accompanied by decreased extracellular signal-regulated protein kinase (ERK) 1/2 activation.ConclusionSCF/c-kit signaling may potentiate chronic hypoxia-induced vascular remodeling by modulating ERK activation. Inhibition of c-kit activity may be a potential strategy to alleviate PH.

Transferrin Receptor 1 in Chronic Hypoxia-Induced Pulmonary Vascular Remodeling.

Iron is associated with the pathophysiology of several cardiovascular diseases, including pulmonary hypertension (PH). In addition, disrupted pulmonary iron homeostasis has been reported in several chronic lung diseases. Transferrin receptor 1 (TfR1) plays a key role in cellular iron transport. However, the role of TfR1 in the pathophysiology of PH has not been well characterized. In this study, we investigate the role of TfR1 in the development of hypoxia-induced pulmonary vascular remodeling. PH was induced by exposing wild-type (WT) mice and TfR1 hetero knockout mice to hypoxia for 4 weeks and evaluated via assessment of pulmonary vascular remodeling, right ventricular (RV) systolic pressure, and RV hypertrophy. In addition, we assessed the functional role of TfR1 in pulmonary artery smooth muscle cells in vitro. The morphology of pulmonary arteries did not differ between WT mice and TfR1 hetero knockout mice under normoxic conditions. In contrast, TfR1 hetero knockout mice exposed to 4 weeks hypoxia showed attenuated pulmonary vascular remodeling, RV systolic pressure, and RV hypertrophy compared with WT mice. In addition, the depletion of TfR1 by RNA interference attenuated human pulmonary artery smooth muscle cells proliferation induced by platelet-derived growth factor-BB (PDGF-BB) in vitro. These results suggest that TfR1 plays an important role in the development of hypoxia-induced pulmonary vascular remodeling.

The role of inflammation in hypoxic pulmonary hypertension: from cellular mechanisms to clinical phenotypes.

Hypoxic pulmonary hypertension (PH) comprises a heterogeneous group of diseases sharing the common feature of chronic hypoxia-induced pulmonary vascular remodeling. The disease is usually characterized by mild to moderate pulmonary vascular remodeling that is largely thought to be reversible compared with the progressive irreversible disease seen in World Health Organization (WHO) group I disease. However, in these patients, the presence of PH significantly worsens morbidity and mortality. In addition, a small subset of patients with hypoxic PH develop "out-of-proportion" severe pulmonary hypertension characterized by pulmonary vascular remodeling that is irreversible and similar to that in WHO group I disease. In all cases of hypoxia-related vascular remodeling and PH, inflammation, particularly persistent inflammation, is thought to play a role. This review focuses on the effects of hypoxia on pulmonary vascular cells and the signaling pathways involved in the initiation and perpetuation of vascular inflammation, especially as they relate to vascular remodeling and transition to chronic irreversible PH. We hypothesize that the combination of hypoxia and local tissue factors/cytokines ("second hit") antagonizes tissue homeostatic cellular interactions between mesenchymal cells (fibroblasts and/or smooth muscle cells) and macrophages and arrests these cells in an epigenetically locked and permanently activated proremodeling and proinflammatory phenotype. This aberrant cellular cross-talk between mesenchymal cells and macrophages promotes transition to chronic nonresolving inflammation and vascular remodeling, perpetuating PH. A better understanding of these signaling pathways may lead to the development of specific therapeutic targets, as none are currently available for WHO group III disease.

MiR-21 regulates chronic hypoxia-induced pulmonary vascular remodeling

Chronic hypoxia causes pulmonary vascular remodeling leading to pulmonary hypertension (PH) and right ventricle (RV) hypertrophy. Aberrant expression of microRNA (miRNA) is closely associated with a number of pathophysiologic processes. However, the role of miRNAs in chronic hypoxia-induced pulmonary vascular remodeling and PH has not been well characterized. In this study, we found increased expression of miR-21 in distal small arteries in the lungs of hypoxia-exposed mice. Putative miR-21 targets, including bone morphogenetic protein receptor (BMPR2), WWP1, SATB1, and YOD1, were downregulated in the lungs of hypoxia-exposed mice and in human pulmonary artery smooth muscle cells (PASMCs) overexpressing miR-21. We found that sequestration of miR-21, either before or after hypoxia exposure, diminished chronic hypoxia-induced PH and attenuated hypoxia-induced pulmonary vascular remodeling, likely through relieving the suppressed expression of miR-21 targets in the lungs of hypoxia-exposed mice. Overexpression of miR-21 enhanced, whereas downregulation of miR-21 diminished, the proliferation of human PASMCs in vitro and the expression of cell proliferation associated proteins, such as proliferating cell nuclear antigen, cyclin D1, and Bcl-xL. Our data suggest that miR-21 plays an important role in the pathogenesis of chronic hypoxia-induced pulmonary vascular remodeling and also suggest that miR-21 is a potential target for novel therapeutics to treat chronic hypoxia associated pulmonary diseases.

Toll-like receptor 4–deficient mice are resistant to chronic hypoxia-induced pulmonary hypertension

ABSTRACTCurrent data suggest that Toll-like receptor 4 (TLR4), a key molecule in the innate immune response, may also be activated following tissue injury. Activation of this receptor is known to induce the production of several proinflammatory cytokines. Given that pulmonary inflammation has been shown to be a key contributor to chronic hypoxia-induced pulmonary vascular remodeling, the authors hypothesized that TLR4-deficient mice would be less susceptible to pulmonary hypertension (PH) as compared to mice with intact TLR4. TLR4-deficient and TLR4-intact strains of inbred mice were exposed to 4, 8, and 16 weeks of hypoxia (0.10 FiO2) or normoxia (0.21 FiO2) in a normobaric chamber. After chronic hypoxic exposure, TLR4-intact mice developed significant PH evidenced by increased right ventricular systolic pressure, right ventricular hypertrophy, and pulmonary artery medial thickening. In contrast, TLR4-deficient mice had no significant change in any of these parameters and this was associated with decreased pulmonary vascular inflammatory response as compared to the TLR4-intact mice. These results suggest that TLR4 deficiency may decrease the susceptibility to developing PH by attenuating the pulmonary vascular inflammatory response to chronic hypoxia.

Soluble Guanylate Cyclase-α1 Deficiency Selectively Inhibits the Pulmonary Vasodilator Response to Nitric Oxide and Increases the Pulmonary Vascular Remodeling Response to Chronic Hypoxia

Nitric oxide (NO) activates soluble guanylate cyclase (sGC), a heterodimer composed of alpha- and beta-subunits, to produce cGMP. NO reduces pulmonary vascular remodeling, but the role of sGC in vascular responses to acute and chronic hypoxia remains incompletely elucidated. We therefore studied pulmonary vascular responses to acute and chronic hypoxia in wild-type (WT) mice and mice with a nonfunctional alpha1-subunit (sGCalpha1-/-). sGCalpha1-/- mice had significantly reduced lung sGC activity and vasodilator-stimulated phosphoprotein phosphorylation. Right ventricular systolic pressure did not differ between genotypes at baseline and increased similarly in WT (22+/-2 to 34+/-2 mm Hg) and sGCalpha1-/- (23+/-2 to 34+/-1 mm Hg) mice in response to acute hypoxia. Inhaled NO (40 ppm) blunted the increase in right ventricular systolic pressure in WT mice (22+/-2 to 24+/-2 mm Hg, P<0.01 versus hypoxia without NO) but not in sGCalpha1-/- mice (22+/-1 to 33+/-1 mm Hg) and was accompanied by a significant rise in lung cGMP content only in WT mice. In contrast, the NO-donor sodium nitroprusside (1.5 mg/kg) decreased systemic blood pressure similarly in awake WT and sGCalpha1-/- mice as measured by telemetry (-37+/-2 versus -42+/-4 mm Hg). After 3 weeks of hypoxia, the increases in right ventricular systolic pressure, right ventricular hypertrophy, and muscularization of intra-acinar pulmonary vessels were 43%, 135%, and 46% greater, respectively, in sGCalpha1-/- than in WT mice (P<0.01). Increased remodeling in sGCalpha1-/- mice was associated with an increased frequency of 5'-bromo-deoxyuridine-positive vessels after 1 and 3 weeks (P<0.01 versus WT). Deficiency of sGCalpha1 does not alter hypoxic pulmonary vasoconstriction. sGCalpha1 is essential for NO-mediated pulmonary vasodilation and limits chronic hypoxia-induced pulmonary vascular remodeling.

NFATc3 Mediates Chronic Hypoxia-induced Pulmonary Arterial Remodeling with α-Actin Up-regulation

Physiological responses to chronic hypoxia include polycythemia, pulmonary arterial remodeling, and vasoconstriction. Chronic hypoxia causes pulmonary arterial hypertension leading to right ventricular hypertrophy and heart failure. During pulmonary hypertension, pulmonary arteries exhibit increased expression of smooth muscle-alpha-actin and -myosin heavy chain. NFATc3 (nuclear factor of activated T cells isoform c3), which is aCa(2+)-dependent transcription factor, has been recently linked to smooth muscle phenotypic maintenance through the regulation of the expression of alpha-actin. The aim of this study was to determine if: (a) NFATc3 is expressed in murine pulmonary arteries, (b) hypoxia induces NFAT activation, (c) NFATc3 mediates the up-regulation of alpha-actin during chronic hypoxia, and (d) NFATc3 is involved in chronic hypoxia-induced pulmonary vascular remodeling. NFATc3 transcript and protein were found in pulmonary arteries. NFAT-luciferase reporter mice were exposed to normoxia (630 torr) or hypoxia (380 torr) for 2, 7, or 21 days. Exposure to hypoxia elicited a significant increase in luciferase activity and pulmonary arterial smooth muscle nuclear NFATc3 localization, demonstrating NFAT activation. Hypoxia induced up-regulation of alpha-actin and was prevented by the calcineurin/NFAT inhibitor, cyclosporin A (25 mg/kg/day s.c.). In addition, NFATc3 knock-out mice did not showed increased alpha-actin levels and arterial wall thickness after hypoxia. These results strongly suggest that NFATc3 plays a role in the chronic hypoxia-induced vascular changes that underlie pulmonary hypertension.

Cytochrome P450 Epoxygenase Gene Function in Hypoxic Pulmonary Vasoconstriction and Pulmonary Vascular Remodeling

We assessed pulmonary cytochrome P450 (CYP) epoxygenase expression and activity during hypoxia and explored the effects of modulating epoxygenase activity on pulmonary hypertension. The acute hypoxic vasoconstrictor response was studied in Swiss Webster mice, who express CYP2C29 in their lungs. Animals were pretreated with vehicle, the epoxygenase inhibitor (N-methylsulfonyl-6-[2-propargyloxyphenyl] hexanamide) or an inhibitor of the soluble epoxide hydrolase. Whereas the epoxygenase inhibitor attenuated hypoxic pulmonary constriction (by 52%), the soluble epoxide hydrolase inhibitor enhanced the response (by 39%), indicating that CYP epoxygenase-derived epoxyeicosatrienoic acids elicit pulmonary vasoconstriction. Aerosol gene transfer of recombinant adenovirus containing the human CYP2C9 significantly elevated mean pulmonary artery pressure and total pulmonary resistance indices, both of which were sensitive to the inhibitor sulfaphenazole. The prolonged exposure of mice to hypoxia increased CYP2C29 expression, and transcript levels increased 5-fold after exposure to normobaric hypoxia (FIO2 0.07) for 2 hours. This was followed by a 2-fold increase in protein expression and by a significant increase in epoxyeicosatrienoic acid production after 24 hours. Chronic hypoxia (7 days) elicited pulmonary hypertension and pulmonary vascular remodeling, effects that were significantly attenuated in animals continually treated with N-methylsulfonyl-6-[2-propargyloxyphenyl] hexanamide (-46% and -55%, respectively). Our results indicate that endogenously generated epoxygenase products are associated with hypoxic pulmonary hypertension in mice and that selective epoxygenase inhibition significantly reduces acute hypoxic pulmonary vasoconstriction and chronic hypoxia-induced pulmonary vascular remodeling. These observations indicate potential novel targets for the treatment of pulmonary hypertension and highlight a pivotal role for CYP epoxygenases in pulmonary responses to hypoxia.

HIGHLIGHTED TOPIC: Pulmonary Circulation and Hypoxia

In 1946, Ulf von Euler and Goran Liljestrand published revolutionary findings on the impact of hypoxia as a stimulant for vasoconstriction in the pulmonary circulation. More than 50 years later, exploring the mechanistic basis for this relationship is still a vital area of research. Among the many

Evidence that hypoxic pulmonary vascular remodeling in rats is polyamine dependent.

This study tested the hypothesis that the polyamines, a family of low-molecular-weight organic cations with documented regulatory roles in cell growth and differentiation, are mediators of chronic hypoxia-induced pulmonary vascular remodeling. Relative to room air controls, chronically hypoxic animals (inspired O2 fraction = 0.1; 21 days) exhibited higher pulmonary arterial pressures (measured in room air), thicker medial layers in pulmonary arteries of 50-100 microns diam, increased hematocrits, and right ventricular hypertrophy. In addition, lung contents of the polyamines, putrescine, spermidine, and spermine were greater in hypoxic animals than in controls. alpha-Difluoromethylornithine (DFMO), an inhibitor of polyamine synthesis, attenuated the hypoxia-induced elevations in lung putrescine and spermidine content and blunted the increases in pulmonary arterial pressure and medial thickness. Neither the increased hematocrit nor right ventricular hypertrophy associated with chronic hypoxia were abrogated by DFMO. In addition, DFMO failed to influence vasoconstrictor responses provoked by acute hypoxic ventilation in isolated, buffer-perfused rat lungs. These observations suggest that depression of polyamine biosynthesis with DFMO blunts the sustained increase in pulmonary arterial pressure by attenuating hypoxia-induced medial thickening.