Activation of Lung p53 by Nutlin-3a Prevents and Reverses Experimental Pulmonary Hypertension

Abstract

Background— Induction of cellular senescence through activation of the p53 tumor suppressor protein is a new option for treating proliferative disorders. Nutlins prevent the ubiquitin ligase MDM2 (murine double minute 2), a negative p53 regulator, from interacting with p53. We hypothesized that cell senescence induced by Nutlin-3a exerted therapeutic effects in pulmonary hypertension (PH) by limiting the proliferation of pulmonary artery smooth muscle cells (PA-SMCs). Methods and Results— Nutlin-3a treatment of cultured human PA-SMCs resulted in cell growth arrest with the induction of senescence but not apoptosis; increased phosphorylated p53 protein levels; and expression of p53 target genes including p21, Bax, BTG2, and MDM2. Daily intraperitoneal Nutlin-3a treatment for 3 weeks dose-dependently reduced PH, right ventricular hypertrophy, and distal pulmonary artery muscularization in mice exposed to chronic hypoxia or SU5416/hypoxia. Nutlin-3a treatment also partially reversed PH in chronically hypoxic or transgenic mice overexpressing the serotonin-transporter in SMCs (SM22-5HTT+ mice). In these mouse models of PH, Nutlin-3a markedly increased senescent p21-stained PA-SMCs; lung p53, p21, and MDM2 protein levels; and p21, Bax, PUMA, BTG2, and MDM2 mRNA levels; but induced only minor changes in control mice without PH. Marked MDM2 immunostaining was seen in both mouse and human remodeled pulmonary vessels, supporting the use of Nutlins as a PH-targeted therapy. PH prevention or reversal by Nutlin-3a required lung p53 stabilization and increased p21 expression, as indicated by the absence of Nutlin-3a effects in hypoxia-exposed p53 −/− and p21 −/− mice. Conclusions— Nutlin-3a may hold promise as a prosenescence treatment targeting PA-SMCs in PH.

Reoxygenation Reverses Hypoxic Pulmonary Arterial Remodeling by Inducing Smooth Muscle Cell Apoptosis via Reactive Oxygen Species–Mediated Mitochondrial Dysfunction

“…More importantly, considerable evidence indicated that the thickened medial layer of HPH regressed most obviously during reoxygenation 41. The present study showed that the reversal of thickened medial layer played a crucial role in the reversal of hypoxic pulmonary arterial remodeling.…”

Proteomic Analysis Implicates Translationally Controlled Tumor Protein as a Novel Mediator of Occlusive Vascular Remodeling in Pulmonary Arterial Hypertension

“…46 Thus, TCTP is a promising candidate factor in the "pseudomalignant" changes in vascular cell phenotype that have recently been described in PAH. TCTP (histamine-releasing factor) 29 is also a potent mediator of chronic inflammation and has been implicated in the lack of resolution of airway inflammation in asthma.…”

The hypoxia-induced microRNA-130a controls pulmonary smooth muscle cell proliferation by directly targeting CDKN1A

“…Hypoxia induces proliferation of vascular smooth muscle cells, probably mediated by downregulation of CDKN1A 23 . In another study, this pro-proliferative and anti-senescent effect was enhanced in animals lacking CDKN1A 4 . Since miRNAs are an emerging group of factors that regulate gene expression, we performed an in silico approach to identify miRNAs that potentially target CDKN1A.…”

“…The contradictory results in our and previous studies are not fully explained at this moment, but might, similar to the paradoxical vasoconstriction induced by hypoxia, represent a unique feature of pulmonary vessels. Since the p53 activator Nutlin-3a required the presence of CDKN1A to improve hemodynamics and prevention of remodeling in hypoxia-induced PH 4 , we suggest that CDKN1A, rather than p53, is the critical factor that regulates proliferation of vascular smooth muscle cells in the development of pulmonary vascular remodeling.…”

“…Recently, activation of the tumor suppressor p53 in lungs by Nutlin-3a has been shown to prevent and reverse pulmonary arterial remodeling in experimental models for PH 4 . The pro-senescent and anti-proliferative effects of Nutlin-3a were abolished in p21-deficient animals, in which the gene for the cell cycle dependent kinase inhibitor (CDKN)1A (alias p21) was abolished.…”