Pulmonary arterial hypertension (PAH) is a pulmonary vasculopathy that causes right ventricular dysfunction and exercise limitation and progresses to death. New findings from translational studies ...have suggested alternative pathways for treatment. These avenues include sex hormones, genetic abnormalities and DNA damage, elastase inhibition, metabolic dysfunction, cellular therapies, and anti-inflammatory approaches. Both novel and repurposed compounds with rationale from preclinical experimental models and human cells are now in clinical trials in patients with PAH. Findings from these studies will elucidate the pathobiology of PAH and may result in clinically important improvements in outcome.
Pulmonary arterial hypertension (PAH) is a disease characterized by progressive loss and remodeling of the pulmonary arteries, resulting in right heart failure and death. Until recently, PAH was seen ...as a disease restricted to the pulmonary circulation. However, there is growing evidence that patients with PAH also exhibit systemic vascular dysfunction, as evidenced by impaired brachial artery flow-mediated dilation, abnormal cerebral blood flow, skeletal myopathy, and intrinsic kidney disease. Although some of these anomalies are partially due to right ventricular insufficiency, recent data support a mechanistic link to the genetic and molecular events behind PAH pathogenesis. This review serves as an introduction to the major systemic findings in PAH and the evidence that supports a common mechanistic link with PAH pathophysiology. In addition, it discusses recent studies describing morphological changes in systemic vessels and the possible role of bronchopulmonary anastomoses in the development of plexogenic arteriopathy. On the basis of available evidence, we propose a paradigm in which metabolic abnormalities, genetic injury, and systemic vascular dysfunction contribute to systemic manifestations in PAH. This concept not only opens exciting research possibilities but also encourages clinicians to consider extrapulmonary manifestations in their management of patients with PAH.
Right ventricular (RV) function is the primary prognostic factor for both morbidity and mortality in pulmonary hypertension (PH). RV hypertrophy is initially an adaptive physiological response to ...increased overload; however, with persistent and/or progressive afterload increase, this response frequently transitions to more pathological maladaptive remodeling. The mechanisms and disease processes underlying this transition are mostly unknown. Angiogenesis has recently emerged as a major modifier of RV adaptation in the setting of pressure overload. A novel paradigm has emerged that suggests that angiogenesis and angiogenic signaling are required for RV adaptation to afterload increases and that impaired and/or insufficient angiogenesis is a major driver of RV decompensation. Here, we summarize our current understanding of the concepts of maladaptive and adaptive RV remodeling, discuss the current literature on angiogenesis in the adapted and failing RV, and identify potential therapeutic approaches targeting angiogenesis in RV failure.
ABSTRACT
The cytokine IL‐10 has potent antifibrotic effects in models of adult fibrosis, but the mechanisms of action are unclear. Here, we report a novel finding that IL‐10 triggers a signal ...transducer and activator of transcription 3(STAT3)–dependent signaling pathway that regulates hyaluronan (HA) metabolism and drives adult fibroblasts to synthesize an HA‐rich pericellular matrix, which mimics the fetal regenerative wound healing phenotype with reduced fibrosis. By using cre‐lox‐mediated novel, inducible, fibroblast‐, keratinocyte‐, and wound‐specific STAT3‐knockdown postnatal mice—plus syngeneic fibroblast cell‐transplant models—we demonstrate that the regenerative effects of IL‐10 in postnatal wounds are dependent on HA synthesis and fibroblast‐specific STAT3‐dependent signaling. The importance of IL‐10‐induced HA synthesis for regenerative wound healing is demonstrated by inhibition of HA synthesis in a murine wound model by administering 4‐methylumbelliferone. Although IL‐10 and STAT3 signaling were intact, the antifibrotic repair phenotype that is induced by IL‐10 overexpression was abrogated in this model. Our data show a novel role for IL‐10 beyond its accepted immune‐regulatory mechanism. The opportunity for IL‐10 to regulate a fibroblast‐specific formation of a regenerative, HA‐rich wound extracellular matrix may lead to the development of innovative therapies to attenuate postnatal fibrosis in organ systems or diseases in which dysregulated inflammation and HA intersect.—Balaji, S., Wang, X., King, A., Le, L. D., Bhattacharya, S. S., Moles, C. M., Butte, M. J., de Jesus Perez, V.A., Liechty, K. W., Wight, T. N., Crombleholme, T. M., Bollyky, P. L., Keswani, S. G. Interleukin‐10‐mediated regenerative postnatal tissue repair is dependent on regulation of hyaluronan metabolism via fibroblast‐specific STAT3 signaling. FASEB J. 31, 868–881 (2017). www.fasebj.org
Long noncoding RNAs (lncRNAs) are emerging as important regulators of diverse biological functions. Their role in pulmonary arterial hypertension (PAH) remains to be explored.
To elucidate the role ...of TYKRIL (tyrosine kinase receptor-inducing lncRNA) as a regulator of p53/ PDGFRβ (platelet-derived growth factor receptor β) signaling pathway and to investigate its role in PAH.
Pericytes and pulmonary arterial smooth muscle cells exposed to hypoxia and derived from patients with idiopathic PAH were analyzed with RNA sequencing. TYKRIL knockdown was performed in above-mentioned human primary cells and in precision-cut lung slices derived from patients with PAH.
Using RNA sequencing data, TYKRIL was identified to be consistently upregulated in pericytes and pulmonary arterial smooth muscles cells exposed to hypoxia and derived from patients with idiopathic PAH. TYKRIL knockdown reversed the proproliferative (
= 3) and antiapoptotic (
= 3) phenotype induced under hypoxic and idiopathic PAH conditions. Owing to the poor species conservation of TYKRIL,
studies were performed in precision-cut lung slices from patients with PAH. Knockdown of TYKRIL in precision-cut lung slices decreased the vascular remodeling (
= 5). The number of proliferating cell nuclear antigen-positive cells in the vessels was decreased and the number of terminal deoxynucleotide transferase-mediated dUTP nick end label-positive cells in the vessels was increased in the LNA (locked nucleic acid)-treated group compared with control. Expression of PDGFRβ, a key player in PAH, was found to strongly correlate with TYKRIL expression in the patient samples (
= 12), and TYKRIL knockdown decreased PDGFRβ expression (
= 3). From the transcription factor-screening array, it was observed that TYKRIL knockdown increased the p53 activity, a known repressor of PDGFRβ. RNA immunoprecipitation using various p53 mutants demonstrated that TYKRIL binds to the N-terminal of p53 (an important region for p300 interaction with p53). The proximity ligation assay revealed that TYKRIL interferes with the p53-p300 interaction (
= 3) and regulates p53 nuclear translocation.
TYKRIL plays an important role in PAH by regulating the p53/PDGFRβ axis.
Pulmonary arterial hypertension (PAH) is a life-threatening disorder of the pulmonary circulation associated with loss and impaired regeneration of microvessels. Reduced pericyte coverage of ...pulmonary microvessels is a pathological feature of PAH and is caused partly by the inability of pericytes to respond to signaling cues from neighboring pulmonary microvascular endothelial cells (PMVECs). We have shown that activation of the Wnt/planar cell polarity pathway is required for pericyte recruitment, but whether production and release of specific Wnt ligands by PMVECs are responsible for Wnt/planar cell polarity activation in pericytes is unknown.
Isolation of pericytes and PMVECs from healthy donor and PAH lungs was carried out with 3G5 or CD31 antibody-conjugated magnetic beads. Wnt expression profile of PMVECs was documented via quantitative polymerase chain reaction with a Wnt primer library. Exosome purification from PMVEC media was carried out with the ExoTIC device. Hemodynamic profile, right ventricular function, and pulmonary vascular morphometry were obtained in a conditional endothelium-specific Wnt5a knockout ( Wnt5a
) mouse model under normoxia, chronic hypoxia, and hypoxia recovery.
Quantification of Wnt ligand expression in healthy PMVECs cocultured with pericytes demonstrated a 35-fold increase in Wnt5a, a known Wnt/planar cell polarity ligand. This Wnt5a spike was not seen in PAH PMVECs, which correlated with an inability to recruit pericytes in Matrigel coculture assays. Exosomes purified from media demonstrated an increase in Wnt5a content when healthy PMVECs were cocultured with pericytes, a finding that was not observed in exosomes of PAH PMVECs. Furthermore, the addition of either recombinant Wnt5a or purified healthy PMVEC exosomes increased pericyte recruitment to PAH PMVECs in coculture studies. Although no differences were noted in normoxia and chronic hypoxia, Wnt5a
mice demonstrated persistent pulmonary hypertension and right ventricular failure 4 weeks after recovery from chronic hypoxia, which correlated with significant reduction, muscularization, and decreased pericyte coverage of microvessels.
We identify Wnt5a as a key mediator for the establishment of pulmonary endothelium-pericyte interactions, and its loss could contribute to PAH by reducing the viability of newly formed vessels. We speculate that therapies that mimic or restore Wnt5a production could help prevent loss of small vessels in PAH.
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