Lung mast cells and hypoxic pulmonary hypertension

PDK1 upregulates PINK1-mediated pulmonary endothelial cell mitophagy during hypoxia-induced pulmonary vascular remodeling

BACKGROUND

Hypoxic pulmonary hypertension (HPH) is a complication of lung diseases with pulmonary vascular remodeling, although the underlying molecular mechanisms have not been fully elucidated. This study investigated the underlying molecular events by using a rat HPH model and primary pulmonary microvascular endothelial cells (PMVECs).

METHODS AND RESULTS

This study first established a rat HPH model and cultured PMVECs for transmission electron microscopic analysis and manipulation of 3-phosphoinositide-dependent protein kinase 1 (PDK1) or phosphatase and tensin homolog-induced kinase 1 (PINK1) expression in vitro. After that, the cell viability was assessed and the expression of different proteins was assayed using cell viability and western blot assays, respectively. Reactive oxygen species production, apoptosis, NLR family pyrin domain containing 3 (NLRP3) expression, and the levels of interleukin (IL)-1β, IL-6, and IL-8 were also assessed, while the interaction of PDK1 and PINK1 was determined using co-immunoprecipitation/western blot assays. Hypoxia induced mitophagy in the PMVECs and upregulated PINK1/Parkin expression, whereas knockdown of PINK1 expression under hypoxic conditions inhibited cell proliferation but induced endothelial cell apoptosis in vitro, decreased reactive oxygen species production and NLRP3 expression, and reduced the levels of inflammatory factors in PMVECs. However, hypoxia induced PDK1 expression, whereas knockdown of PDK1 downregulated PINK1 expression. Furthermore, treatment of the model rats with the PDK1 inhibitor dichloroacetate (DCA) was able to decrease PINK1 expression. In addition, the PDK1 and PINK1 proteins could interact with each other in the mitochondria of PMVECs to regulate the cell viability.

CONCLUSIONS

This study revealed that PDK1 induced PMVEC proliferation but inhibited their apoptosis to participate in pulmonary vascular remodeling, ultimately leading to HPH through regulation of PINK1-mediated mitophagy signaling. Therefore, PINK1 is a novel therapeutic target for the control of HPH.

Immune Cells in Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a complex and serious cardiopulmonary disease; it is characterised by increased pulmonary arterial pressure and pulmonary vascular remodelling accompanied by disordered endothelial and smooth muscle cell proliferation within pulmonary arterioles and arteries. Although recent reports have suggested that dysregulated immunity and inflammation are key players in PAH pathogenesis, their roles in PAH progression remain unclear. Intriguingly, altered host immune cell distribution, number, and polarisation within the lung arterial vasculature have been linked to disease development. This review mainly focusses on the roles of different immune cells in PAH and discusses the underlying mechanisms.

Cytokines, Chemokines, and Inflammation in Pulmonary Arterial Hypertension

According to the World Symposium Pulmonary Hypertension (WSPH) classification, pulmonary hypertension (PH) is classified into five categories based on etiology. Among them, Group 1 pulmonary arterial hypertension (PAH) disorders are rare but progressive and often, fatal despite multiple approved treatments. Elevated pulmonary arterial pressure in patients with WSPH Group 1 PAH is mainly caused by increased pulmonary vascular resistance (PVR), due primarily to sustained pulmonary vasoconstriction and excessive obliterative pulmonary vascular remodeling. Growing evidence indicates that inflammation plays a critical role in the development of pulmonary vascular remodeling associated with PAH. While the role of auto-immunity is unclear, infiltration of inflammatory cells in and around vascular lesions, including T- and B-cells, dendritic cells, macrophages, and mast cells have been observed in PAH patients. Serum and plasma levels of chemokines, cytokines, and autoantibodies are also increased in PAH patients; some of these circulating molecules are correlated with disease severity and survival. Preclinical experiments have reported a key role of the inflammation in PAH pathophysiology in vivo. Importantly, anti-inflammatory and immunosuppressive agents have further exhibited therapeutic effects. The present chapter reviews published experimental and clinical evidence highlighting the canonical role of inflammation in the pathogenesis of PAH and as a major target for the development of anti-inflammatory therapies in patients with PAH.

mmu_circ_0000790 Is Involved in Pulmonary Vascular Remodeling in Mice with HPH via MicroRNA-374c-Mediated FOXC1

Recently, the identification of several circular RNAs (circRNAs) as vital regulators of microRNAs (miRNAs) underlines the increasing complexity of non-coding RNA (ncRNA)-mediated regulatory networks. This study aimed to explore the effects of mmu_circ_0000790 on the biological behaviors of pulmonary artery smooth muscle cells (PASMCs) in hypoxic pulmonary hypertension (HPH). The HPH mouse model and hypoxia-induced PASMC model were initially established, and the expression of mmu_circ_0000790 in the pulmonary vascular tissues and hypoxic PASMCs was determined using quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). A series of in vitro experiments such as dual-luciferase, RNA pull-down, and RNA-binding protein immunoprecipitation (RIP) assays were conducted to evaluate the interactions among mmu_circ_0000790, microRNA-374c (miR-374c), and forkhead transcription factor 1 (FOXC1). The potential physiological functions of mmu_circ_0000790, miR-374c, and FOXC1 in hypoxic PASMCs were investigated through gain- and loss-of function approaches. Upregulated mmu_circ_0000790 was found in both the HPH-pulmonary vascular tissues and hypoxic PASMCs. Additionally, mmu_circ_0000790 could competitively bind to miR-374c and consequently upregulate the target gene of miR-374c, FOXC1. It was also observed that mmu_circ_0000790 induced proliferation and inhibited apoptosis of hypoxic PASMCs, which further promoted the pulmonary vascular remodeling in mice with HPH. Therefore, we speculate that mmu_circ_0000790 may serve as a prospective target for the treatment of patients with HPH.

Myeloid-Derived Suppressor Cells and Pulmonary Hypertension

Myeloid–derived suppressor cells (MDSCs) comprised a heterogeneous subset of bone marrow–derived myeloid cells, best studied in cancer research, that are increasingly implicated in the pathogenesis of pulmonary vascular remodeling and the development of pulmonary hypertension. Stem cell transplantation represents one extreme interventional strategy for ablating the myeloid compartment but poses a number of translational challenges. There remains an outstanding need for additional therapeutic targets to impact MDSC function, including the potential to alter interactions with innate and adaptive immune subsets, or alternatively, alter trafficking receptors, metabolic pathways, and transcription factor signaling with readily available and safe drugs. In this review, we summarize the current literature on the role of myeloid cells in the development of pulmonary hypertension, first in pulmonary circulation changes associated with myelodysplastic syndromes, and then by examining intrinsic myeloid cell changes that contribute to disease progression in pulmonary hypertension. We then outline several tractable targets and pathways relevant to pulmonary hypertension via MDSC regulation. Identifying these MDSC-regulated effectors is part of an ongoing effort to impact the field of pulmonary hypertension research through identification of myeloid compartment-specific therapeutic applications in the treatment of pulmonary vasculopathies.

Immune cells and autoantibodies in pulmonary arterial hypertension

Analyses of immunity in pulmonary arterial hypertension (PAH) support the notion that maladaptation of the immune response exists. Altered immunity is an increasingly recognized feature of PAH. Indeed, a delicate balance between immunity and tolerance exists and any disturbance may result in chronic inflammation or autoimmunity. This is suggested by infiltration of various immune cells (e.g. macrophages, T and B lymphocytes) in remodeled pulmonary vessels. In addition, several types of autoantibodies directed against antinuclear antigens, endothelial cells (ECs) and fibroblasts have been found in idiopathic and systemic sclerosis-associated PAH. These autoantibodies may play an important role in EC apoptosis and in the expression of cell adhesion molecules. This review article provides an overview of immunity pathways highlighting their potential roles in pulmonary vascular remodeling in PAH and the possibility of future targeted therapy.

Effects of a Moderately Lower Temperature on the Proliferation and Degranulation of Rat Mast Cells

Mast cells are traditionally considered as key effector cells in IgE-mediated allergic diseases. However, the roles of mast cells have also been implicated in diverse physiological and pathological processes. Mast cells are distributed in various organs and tissues of various species. Some of the organs and tissues, such as testis, skin, and the upper part of the respiratory tract, have a temperature that is lower than the body's core temperature. The purpose of the present study was to investigate the effects of a lower temperature on the proliferation and degranulation of rat mast cells. Here, we demonstrate that cell growth was retarded at 35°C compared to 37°C for both rat peritoneal mast cells (RPMC) and RBL-2H3, a rat mast cell line. Furthermore, RPMC became more susceptible to degranulation at 35°C compared to 37°C. In contrast, degranulation of RBL-2H3 was not as sensitive to temperature change as RPMC. The functionality of mast cells in unique organs with a lower temperature warrants further analysis.

Possible role of lysophosphatidic acid in rat model of hypoxic pulmonary vascular remodeling

Pulmonary hypertension is characterized by cellular and structural changes in the vascular wall of pulmonary arteries. We hypothesized that lysophosphatidic acid (LPA), a bioactive lipid, is implicated in this vascular remodeling in a rat model of hypoxic pulmonary hypertension. Exposure of Wistar rats to 10% O2 for 3 weeks induced an increase in the mean serum levels of LPA, to 40.9 (log-detransformed standard deviations: 23.4-71.7) μM versus 21.6 (11.0-42.3) μM in a matched control animal group (P = 0.037). We also observed perivascular LPA immunohistochemical staining in lungs of hypoxic rats colocalized with the secreted lysophospholipase D autotaxin (ATX). Moreover, ATX colocalized with mast cell tryptase, suggesting implication of these cells in perivascular LPA production. Hypoxic rat lungs expressed more ATX transcripts (2.4-fold) and more transcripts of proteins implicated in cell migration: β2 integrin (1.74-fold), intracellular adhesion molecule 1 (ICAM-1; 1.84-fold), and αM integrin (2.70-fold). Serum from the hypoxic group of animals had significantly higher chemoattractant properties toward rat primary lung fibroblasts, and this increase in cell migration could be prevented by the LPA receptor 1 and 3 antagonists. LPA also increased adhesive properties of human pulmonary artery endothelial cells as well as those of human peripheral blood mononuclear cells, via the activation of LPA receptor 1 or 3 followed by the stimulation of gene expression of ICAM-1, β-1, E-selectin, and vascular cell adhesion molecule integrins. In conclusion, chronic hypoxia increases circulating and tissue levels of LPA, which might induce fibroblast migration and recruitment of mononuclear cells in pulmonary vasculature, both of which contribute to pulmonary vascular remodeling.

Mast cells and histamine: do they influence placental vascular network and development in preeclampsia?

The physiological course of pregnancy is closely related to adequate development of the placenta. Shallow invasion of trophoblast as well as decreased development of the placental vascular network are both common features of preeclampsia. To better understand the proangiogenic features of mast cells, in this study we aim to identify the potential relationship between the distribution of mast cells within the placenta and vascular network development. Material and Methods. Placentas from preeclampsia-complicated pregnancies (n = 11) and from physiological pregnancies (n = 11) were acquired after cesarean section. The concentration of histamine was measured, and immunohistochemical staining for mast cell tryptase was performed. Morphometric analysis was then performed. Results. We noticed significant differences between the examined groups. Notably, in the preeclampsia group compared to the control group, we observed a higher mean histamine concentration, higher mast cell density (MCD), lower mean mast cell (MMCA) and lower vascular/extravascular (V/EVT) index. In physiological pregnancies, a positive correlation was observed between the histamine concentration and V/VEVT index as well as MCD and the V/VEVT index. In contrast, a negative correlation was observed between MMCA and the V/EVT index in physiological pregnancies. Conclusions. Based on the data from our study, we suggest that a differential distribution of mast cells and corresponding changes in the concentration of histamine are involved in the defective placental vascularization seen in preeclamptic placentas.