Molecular Basis of Nitrative Stress in the Pathogenesis of Pulmonary Hypertension

RNA m6A methylation and regulatory proteins in pulmonary arterial hypertension

m6A (N6‑methyladenosine) is the most common and abundant apparent modification in mRNA of eukaryotes. The modification of m6A is regulated dynamically and reversibly by methyltransferase (writer), demethylase (eraser), and binding protein (reader). It plays a significant role in various processes of mRNA metabolism, including regulation of transcription, maturation, translation, degradation, and stability. Pulmonary arterial hypertension (PAH) is a malignant cardiopulmonary vascular disease characterized by abnormal proliferation of pulmonary artery smooth muscle cells. Despite the existence of several effective and targeted therapies, there is currently no cure for PAH and the prognosis remains poor. Recent studies have highlighted the crucial role of m6A modification in cardiovascular diseases. Investigating the role of RNA m6A methylation in PAH could provide valuable insights for drug development. This review aims to explore the mechanism and function of m6A in the pathogenesis of PAH and discuss the potential targeting of RNA m6A methylation modification as a treatment for PAH.

Endothelial PHD2 deficiency induces nitrative stress via suppression of caveolin-1 in pulmonary hypertension

BACKGROUND

Nitrative stress is a characteristic feature of the pathology of human pulmonary arterial hypertension. However, the role of nitrative stress in the pathogenesis of obliterative vascular remodelling and severe pulmonary arterial hypertension remains largely unclear.

METHOD

Our recently identified novel mouse model (Egln1Tie2Cre, Egln1 encoding prolyl hydroxylase 2 (PHD2)) has obliterative vascular remodelling and right heart failure, making it an excellent model to use in this study to examine the role of nitrative stress in obliterative vascular remodelling.

RESULTS

Nitrative stress was markedly elevated whereas endothelial caveolin-1 (Cav1) expression was suppressed in the lungs of Egln1Tie2Cre mice. Treatment with a superoxide dismutase mimetic, manganese (III) tetrakis (1-methyl-4-pyridyl) porphyrin pentachloride or endothelial Nos3 knockdown using endothelial cell-targeted nanoparticle delivery of CRISPR-Cas9/guide RNA plasmid DNA inhibited obliterative pulmonary vascular remodelling and attenuated severe pulmonary hypertension in Egln1Tie2Cre mice. Genetic restoration of Cav1 expression in Egln1Tie2Cre mice normalised nitrative stress, reduced pulmonary hypertension and improved right heart function.

CONCLUSION

These data suggest that suppression of Cav1 expression secondary to PHD2 deficiency augments nitrative stress through endothelial nitric oxide synthase activation, which contributes to obliterative vascular remodelling and severe pulmonary hypertension. Thus, a reactive oxygen/nitrogen species scavenger might have therapeutic potential for the inhibition of obliterative vascular remodelling and severe pulmonary arterial hypertension.

Luteolin ameliorates hypoxia-induced pulmonary hypertension via regulating HIF-2α-Arg-NO axis and PI3K-AKT-eNOS-NO signaling pathway

BACKGROUND

Pulmonary hypertension (PH) is a devastating disease with poor prognosis and high mortality. Hypoxia induced pulmonary hypertension (HPH) is a persistent threat to human health, especially to people who live on high altitude plateau. Pulmonary vascular endothelial cell is involved in numerous pathophysiological processes, including in vasoconstriction, oxidative stress, cell growth and differentiation. Endothelial cells (ECs) are the first layer to be exposed to changed oxygen levels and hypoxia could lead to ECs dysfunction. Endothelial-derived nitric oxide (NO) is the most important bioactive molecule, which could regulate endothelial homeostasis. PH pathophysiology has been linked to the disruption of NO pathways.

PURPOSE

Luteolin is a kind of plant active ingredient with multiple pharmacological activities. The purpose of this study is to detect the effect of luteolin on HPH with in vivo, ex vivo and in vitro analyses and to further elucidate luteolin's pharmaceutical mechanism with NO related signaling pathway regulation.

METHODS

Hypobaric chamber was used to establish HPH animal model. Rats were intragastrically administrated luteolin for 28 days. Then hemodynamic indexes, histopathological changes, pulmonary artery endothelial function, NO content and arginase activity in lung tissue, NO related pathway proteins expression were measured to evaluate the effect of luteolin on HPH. PAECs were treated with 1% O₂ and incubated with or without luteolin. PAECs vitality, NO content in cells supernatant, and NO related pathway proteins expression were tested to reveal the protective mechanism of luteolin.

RESULTS

Luteolin decreased mean pulmonary hypertension of HPH rats, alleviated right ventricular and pulmonary vascular remodeling. Immunofluorescence staining (vWF), isolated perfused/ventilated rat lung experiment indicated that luteolin protected pulmonary vascular endothelial function of HPH rats. Luteolin increased NO content in PAECs supernatant while decreased NO level in lung tissues of HPH rats. Further, it was demonstrated that luteolin inhibited HIF-2α-Arg axis in PAECs and HPH rats. PI3K-AKT-eNOS signaling pathway was upregulated in PAECs, but which was downregulated in lung tissues of HPH rats. Pharmacological effect of luteolin was equivalent or better than sildenafil.

CONCLUSION

Luteolin ameliorated HPH in rats by protecting pulmonary vascular endothelial function via regulating HIF-2α-Arg-NO axis and PI3K-AKT-eNOS-NO signaling pathway. This study may provide a novel perspective and approach to alleviate the devastating disease of HPH.

Antiproliferation- and Apoptosis-Inducible Effects of a Novel Nitrated [6,6,6]Tricycle Derivative (SK2) on Oral Cancer Cells

The benzo-fused dioxabicyclo[3.3.1]nonane core is the central framework in several natural products. Using this core, we had developed a novel nitrated [6,6,6]tricycle-derived compound containing an n-butyloxy group, namely, SK2. The anticancer potential of SK2 was not assessed. This study aimed to determine the antiproliferative function and investigated possible mechanisms of SK2 acting on oral cancer cells. SK2 preferentially killed oral cancer cells but caused no harmful effect on non-malignant oral cells. After the SK2 exposure of oral cancer cells, cells in the sub-G1 phase accumulated. This apoptosis-like outcome of SK2 treatment was validated to be apoptosis via observing an increasing annexin V population. Mechanistically, apoptosis signalers such as pancaspase, caspases 8, caspase 9, and caspase 3 were activated by SK2 in oral cancer cells. SK2 induced oxidative-stress-associated changes. Furthermore, SK2 caused DNA damage (γH2AX and 8-hydroxy-2'-deoxyguanosine). In conclusion, a novel nitrated [6,6,6]tricycle-derived compound, SK2, exhibits a preferential antiproliferative effect on oral cancer cells, accompanied by apoptosis, oxidative stress, and DNA damage.

Endothelial cells in the pathogenesis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease that involves pulmonary vasoconstriction, small vessel obliteration, large vessel thickening and obstruction, and development of plexiform lesions. PAH vasculopathy leads to progressive increases in pulmonary vascular resistance, right heart failure and, ultimately, premature death. Besides other cell types that are known to be involved in PAH pathogenesis (e.g. smooth muscle cells, fibroblasts and leukocytes), recent studies have demonstrated that endothelial cells (ECs) have a crucial role in the initiation and progression of PAH. The EC-specific role in PAH is multi-faceted and affects numerous pathophysiological processes, including vasoconstriction, inflammation, coagulation, metabolism and oxidative/nitrative stress, as well as cell viability, growth and differentiation. In this review, we describe how EC dysfunction and cell signalling regulate the pathogenesis of PAH. We also highlight areas of research that warrant attention in future studies, and discuss potential molecular signalling pathways in ECs that could be targeted therapeutically in the prevention and treatment of PAH.