Inflammation, immunity, and vascular remodeling in pulmonary hypertension; Evidence for complement involvement?

A bovine model of hypoxia-induced pulmonary hypertension reveals a gradient of immune and matrisome response with a complement signature found in circulation

Pulmonary hypertension (PH) is a progressive vascular disease characterized by vascular remodeling, stiffening, and luminal obstruction, driven by dysregulated cell proliferation, inflammation, and extracellular matrix (ECM) alterations. Despite the recognized contribution of ECM dysregulation to PH pathogenesis, the precise molecular alterations in the matrisome remain poorly understood. In this study, we employed a matrisome-focused proteomics approach to map the protein composition in a young bovine calf model of acute hypoxia-induced PH. Our findings reveal distinct alterations in the matrisome along the pulmonary vascular axis, with the most prominent changes observed in the main pulmonary artery. Key alterations included a strong immune response and wound repair signature, characterized by increased levels of complement components, coagulation cascade proteins, and provisional matrix markers. In addition, we observed upregulation of ECM-modifying enzymes, growth factors, and core ECM proteins implicated in vascular stiffening, such as collagens, periostin, tenascin-C, and fibrin(ogen). Notably, these alterations correlated with increased mean pulmonary arterial pressure and vascular remodeling. In the plasma, we identified increased levels of complement components, indicating a systemic inflammatory response accompanying the vascular remodeling. Our findings shed light on the dynamic matrisome remodeling in early-stage PH, implicating a wound-healing trajectory with distinct patterns from the main pulmonary artery to the distal vasculature. This study provides novel insights into the immune cell infiltration and matrisome alterations associated with PH pathogenesis and highlights potential biomarkers and therapeutic targets within the matrisome landscape.NEW & NOTEWORTHY Extensive immune cell infiltration and matrisome alterations associated with hypoxia-induced pulmonary hypertension in a large mammal model. Matrisome components correlate with increased resistance to identify candidate alterations that drive biomechanical manifestations of the disease.

Complement Immune System in Pulmonary Hypertension-Cooperating Roles of Circadian Rhythmicity in Complement-Mediated Vascular Pathology

Originally discovered in the 1890s, the complement system has traditionally been viewed as a "compliment" to the body's innate and adaptive immune response. However, emerging data have shown that the complement system is a much more complex mechanism within the body involved in regulating inflammation, gene transcription, attraction of macrophages, and many more processes. Sustained complement activation contributes to autoimmunity and chronic inflammation. Pulmonary hypertension is a disease with a poor prognosis and an average life expectancy of 2-3 years that leads to vascular remodeling of the pulmonary arteries; the pulmonary arteries are essential to host homeostasis, as they divert deoxygenated blood from the right ventricle of the heart to the lungs for gas exchange. This review focuses on direct links between the complement system's involvement in pulmonary hypertension, along with autoimmune conditions, and the reliance on the complement system for vascular remodeling processes of the pulmonary artery. Furthermore, circadian rhythmicity is highlighted as the disrupted homeostatic mechanism in the inflammatory consequences in the vascular remodeling within the pulmonary arteries, which could potentially open new therapeutic cues. The current treatment options for pulmonary hypertension are discussed with clinical trials using complement inhibitors and potential therapeutic targets that impact immune cell functions and complement activation, which could alleviate symptoms and block the progression of the disease. Further research on complement's involvement in interstitial lung diseases and pulmonary hypertension could prove beneficial for our understanding of these various diseases and potential treatment options to prevent vascular remodeling of the pulmonary arteries.

Integrated bioinformatics analysis and experimental animal models identify a robust biomarker and its correlation with the immune microenvironment in pulmonary arterial hypertension

Background

Pulmonary arterial hypertension (PAH) represents a substantial global risk to human health. This study aims to identify diagnostic biomarkers for PAH and assess their association with the immune microenvironment through the utilization of sophisticated bioinformatics techniques.

Methods

Based on two microarray datasets, differentially expressed genes (DEGs) were detected, and hub genes underwent a sequence of machine learning analyses. After pathways associated with PAH were assessed by gene enrichment analysis, the identified genes were validated using external datasets and confirmed in a monocrotaline (MCT)-induced rat model. In addition, three algorithms were employed to estimate the proportions of various immune cell types, and the link between hub genes and immune cells was substantiated.

Results

Using SVM, LASSO, and WGCNA, we identified seven hub genes, including (BPIFA1, HBA2, HBB, LOC441081, PI15, S100A9, and WIF1), of which only BPIFA1 remained stable in the external datasets and was validated in an MCT-induced rat model. Furthermore, the results of the functional enrichment analysis established a link between PAH and both metabolism and the immune system. Correlation assessment showed that BPIFA1 expression in the MCP-counter algorithm was negatively associated with various immune cell types, positively correlated with macrophages in the ssGSEA algorithm, and correlated with M1 and M2 macrophages in the CIBERSORT algorithm.

Conclusion

BPIFA1 serves as a modulator of PAH, with the potential to impact the immune microenvironment and disease progression, possibly through its regulatory influence on both M1 and M2 macrophages.

Assessing Heterogeneity in the N-Telopeptides of Type I Collagen by Mass Spectrometry

Collagen cross-links created by the lysyl oxidase and lysyl hydroxylase families of enzymes are a significant contributing factor to the biomechanical strength and rigidity of tissues, which in turn influence cell signaling and ultimately cell phenotype. In the clinic, the proteolytically liberated N-terminal cross-linked peptide of collagen I (NTX) is used as a biomarker of bone and connective tissue turnover, which is altered in several disease processes. Despite the clinical utility of these collagen breakdown products, the majority of the cross-linked peptide species have not been identified in proteomic datasets. Here we evaluate several parameters for the preparation and identification of these peptides from the collagen I-rich Achilles tendon. Our refined approach involving chemical digestion for protein solubilization coupled with mass spectrometry allows for the identification of the NTX cross-links in a range of modification states. Based on the specificity of the enzymatic cross-linking reaction we utilized follow-up variable modification searches to facilitate identification with a wider range of analytical workflows. We then applied a spectral library approach to identify differences in collagen cross-links in bovine pulmonary hypertension. The presented method offers unique opportunities to understand extracellular matrix remodeling events in development, aging, wound healing, and fibrotic disease that modulate collagen architecture through lysyl-hydroxylase and lysyl-oxidase enzymes.

TNF-α and IL-8 levels are positively correlated with hypobaric hypoxic pulmonary hypertension and pulmonary vascular remodeling in rats

The expression status of proinflammatory cytokines in high-altitude pulmonary arterial hypertension (PAH) has been well studied. However, the changes in interleukin (IL)-8 and tumor necrosis factor α (TNF-α) during the reversible changes in pulmonary vascular remodeling (PVR) in PAH after detaching from a hypobaric hypoxic environment have not been elucidated. This investigation elucidated a high-altitude PAH rat model. Then, PAH rats in the high-altitude group were maintained in the high-altitude area, and rats in the low-altitude group returned to the low-altitude area. After 0, 10, 20, and 30 days of PAH modeling, right ventricular systolic pressure (RVSP) and the mean pulmonary arterial pressure (mPAP) were assessed. Right ventricular (RV) hypertrophy was reflected by the ratio of RV/[left ventricle + interventricular septum (S)]. Pathological changes in PVR were accessed by hematoxylin-eosin staining, and medial wall thickness (WT%) and medial wall area (WA%) were measured. TNF-α and IL-8 levels in pulmonary artery tissues and blood were measured with Western blot assay and enzyme-linked immunosorbent assay, respectively. Our results showed that PAH rats exhibited a substantial increase in RVSP and mPAP, RV hypertrophy, PVR, and enhanced generation of TNF-α and IL-8. Then, we found that these pathological changes were gradually aggravated and TNF-α and IL-8 levels were increased in rats in the high-altitude group after 10, 20, and 30 days of PAH modeling. In contrast, the mPAP was decreased and PVR was alleviated in rats in the low-altitude group, accompanying with reduced TNF-α and IL-8 production. In conclusion, our study demonstrated that the generation of TNF-α and IL-8 was also reversible during the reversible changes in PVR after detaching from a hypobaric hypoxic environment. Thus, proinflammatory cytokine TNF-α and IL-8 levels are positively correlated with PVR severity.

Gut microbiota crosstalk mechanisms are key in pulmonary hypertension: The involvement of melatonin is instrumental too

The microbiota refers to a plethora of microorganisms with a gene pool of approximately three million, which inhabits the human gastrointestinal tract or gut. The latter, not only promotes the transport of nutrients, ions, and fluids from the lumen to the internal environment but is linked with the development of diseases including coronary artery disease, heart failure, and lung diseases. The exact mechanism of how the microbiota achieves crosstalk between itself and distant organs/tissues is not clear, but factors released to other organs may play a role, like inflammatory and genetic factors, and now we highlight melatonin as a novel mediator of the gut-lung crosstalk. Melatonin is present in high concentrations in the gut and the lung and has recently been linked to the pathogenesis of pulmonary hypertension (PH). In this comprehensive review of the literature, we suggest that melatonin is an important link between the gut microbiota and the development of PH (where suppressed melatonin-crosstalk between the gut and lungs could promote the development of PH). More studies are needed to investigate the link between the gut microbiota, melatonin and PH. Studies could also investigate whether microbiota genes play a role in the epigenetic aspects of PH. This is relevant because, for example, dysbiosis (caused by epigenetic factors) could reduce melatonin signaling between the gut and lungs, reduce subcellular melatonin concentrations in the gut/lungs, or reduce melatonin serum levels secondary to epigenetic factors. This area of research is largely unexplored and further studies are warranted.

Pathophysiology and pathogenic mechanisms of pulmonary hypertension: role of membrane receptors, ion channels, and Ca2+ signaling

The pulmonary circulation is a low-resistance, low-pressure, and high-compliance system that allows the lungs to receive the entire cardiac output. Pulmonary arterial pressure is a function of cardiac output and pulmonary vascular resistance, and pulmonary vascular resistance is inversely proportional to the fourth power of the intraluminal radius of the pulmonary artery. Therefore, a very small decrease of the pulmonary vascular lumen diameter results in a significant increase in pulmonary vascular resistance and pulmonary arterial pressure. Pulmonary arterial hypertension is a fatal and progressive disease with poor prognosis. Regardless of the initial pathogenic triggers, sustained pulmonary vasoconstriction, concentric vascular remodeling, occlusive intimal lesions, in situ thrombosis, and vascular wall stiffening are the major and direct causes for elevated pulmonary vascular resistance in patients with pulmonary arterial hypertension and other forms of precapillary pulmonary hypertension. In this review, we aim to discuss the basic principles and physiological mechanisms involved in the regulation of lung vascular hemodynamics and pulmonary vascular function, the changes in the pulmonary vasculature that contribute to the increased vascular resistance and arterial pressure, and the pathogenic mechanisms involved in the development and progression of pulmonary hypertension. We focus on reviewing the pathogenic roles of membrane receptors, ion channels, and intracellular Ca2+ signaling in pulmonary vascular smooth muscle cells in the development and progression of pulmonary hypertension.

MiRNAs in Systemic Sclerosis Patients with Pulmonary Arterial Hypertension: Markers and Effectors

Background: Pulmonary arterial hypertension (PAH) is a major cause of death in systemic sclerosis (SSc). Early detection may improve patient outcomes. Methods: We searched for circulating miRNAs that would constitute biomarkers in SSc patients with PAH (SSc-PAH). We compared miRNA levels and laboratory parameters while evaluating miRNA levels in white blood cells (WBCs) and myofibroblasts. Results: Our study found: 1) miR-26 and miR-let-7d levels were significantly lower in SSc-PAH (n = 12) versus SSc without PAH (SSc-noPAH) patients (n = 25); 2) a positive correlation between miR-26 and miR-let-7d and complement-C3; 3) GO-annotations of genes that are miR-26/miR-let-7d targets and that are expressed in myofibroblast cells, suggesting that these miRNAs regulate the TGF-β-pathway; 4) reduced levels of both miRNAs accompanied fibroblast differentiation to myofibroblasts, while macitentan (endothelin receptor-antagonist) increased the levels. WBCs of SSc-noPAH and SSc-PAH patients contained equal amounts of miR-26/miR-let-7d. During the study, an echocardiograph that predicted PAH development, showed increased pulmonary artery pressure in three SSc-noPAH patients. At study initiation, those patients and an additional SSc-noPAH patient, who eventually developed PAH, had miR-let-7d/miR-26 levels similar to those of SSc-PAH patients. This implies that reduced miR-let-7d/miR-26 levels might be an early indication of PAH. Conclusions: miR-26 and miR-let-7d may be serological markers for SSc-PAH. The results of our study suggest their involvement in myofibroblast differentiation and complement pathway activation, both of which are active in PAH development.

Impact of pregnancy in patients with systemic lupus erythematosus-associated pulmonary arterial hypertension: case series and literature review

Objective

This study aimed to investigate the clinical characteristics and outcomes of pregnancy complicated by SLE-associated pulmonary arterial hypertension (SLE-PAH) in a case series and literature review.

Methods

This single-centre retrospective study included 10 consecutive pregnancies complicated by SLE-PAH confirmed by right heart catheterisation (RHC) at Peking Union Medical College Hospital between 2009 and 2020. A literature search was conducted and 14 pregnancy cases complicated by SLE-PAH were reviewed.

Results

At the time of 10 patients’ initial visits, the average age was 30.00±5.72 years and the median disease duration of SLE and PAH was 34.5 (range 1–164) months and 2 (1–51) months. Two patients carried planned pregnancy, seven patients developed PAH during pregnancy and one pregnancy was unplanned. Further, nine patients had low disease activity, with Systemic Lupus Erythematosus Disease Activity Index between 0 and 4, and 30%, 30% and 40% of patients were of WHO functional class II, III and IV, respectively. All patients were evaluated by RHC and echocardiography. N-terminal pro-brain natriuretic peptide (NT-proBNP) levels were elevated in 70% of patients, with a median level of 776 (56–18 023) pg/mL. The median time of completed pregnancies in all patients was 31 (15–38) weeks and six patients delivered live infants. SLE activity and PAH severity improved in 70% of patients within 6 months after delivery. One patient died on the 15th day after induction of labour. In the remaining patients, all achieved a lupus low disease activity state; according to the European Society of Cardiology/European Respiratory Society risk stratification, seven were categorised at a lower risk state compared with their risk stratification during pregnancy, and two remained at intermediate risk. Additionally, 80% of patients exhibited mild impairments with WHO functional class I or II. The median NT-proBNP level was 184 (32–4003) pg/mL within 6 months after delivery. In the reviewed literature, the average age of patients was 30.09±5.37 years. The median time of completed pregnancies was 36 (28–40) weeks. More cases were planned and successful, and the survival rates of mothers and neonates were 85.71% and 92.86%, respectively.

Conclusions

Successful pregnancy could be possible in women with SLE-PAH if SLE-PAH treatment goals are achieved under proper therapies, careful monitoring and thorough evaluations.

Treating Inflammation Associated with Pulmonary Hypertension: An Overview of the Literature

Pulmonary hypertension (PH) comprises five groups of serious clinical entities characterized by pulmonary artery vasoconstriction and vascular remodeling leading to right heart failure and death. In addition to vascular remodeling, recruitment and exaggerated accumulation of several perivascular inflammatory cells is also observed, including macrophages, monocytes, T and B-lymphocytes, dendritic cells and mast cells distributed in pulmonary perivascular spaces and around remodeling pulmonary vessels. Current pulmonary arterial hypertension (PAH)-targeted therapies aim to improve functional capacity, pulmonary hemodynamic conditions, and delay disease progression. Nevertheless, PAH remains incurable, with a poor prognosis and is often refractory to drug therapy, highlighting the need for further research. In the last three decades, the best pathophysiological understanding of PAH has allowed for progression from a disease of little-known pathogenesis, without specific and effective therapy to expanding the arsenal of drugs on a cellular, genetic and molecular basis. This article provides an overview on current knowledge and progress in recent advances in pharmacological therapy in PAH.

Autoimmunity in Pulmonary Arterial Hypertension: Evidence for Local Immunoglobulin Production

Pulmonary arterial hypertension (PAH) is a progressive life-threatening disease. The notion that autoimmunity is associated with PAH is widely recognized by the observations that patients with connective tissue diseases or virus infections are more susceptible to PAH. However, growing evidence supports that the patients with idiopathic PAH (IPAH) with no autoimmune diseases also have auto-antibodies. Anti-inflammatory therapy shows less help in decreasing auto-antibodies, therefore, elucidating the process of immunoglobulin production is in great need. Maladaptive immune response in lung tissues is considered implicating in the local auto-antibodies production in patients with IPAH. In this review, we will discuss the specific cell types involved in the lung in situ immune response, the potential auto-antigens, and the contribution of local immunoglobulin production in PAH development, providing a theoretical basis for drug development and precise treatment in patients with PAH.

Mechanisms of SARS-CoV-2-induced lung vascular disease: potential role of complement

The outbreak of COVID-19 disease, caused by SARS-CoV-2 beta-coronovirus, urges a focused search for the underlying mechanisms and treatment options. The lung is the major target organ of COVID-19, wherein the primary cause of mortality is hypoxic respiratory failure, resulting from acute respiratory distress syndrome, with severe hypoxemia, often requiring assisted ventilation. While similar in some ways to acute respiratory distress syndrome secondary to other causes, lungs of some patients dying with COVID-19 exhibit distinct features of vascular involvement, including severe endothelial injury and cell death via apoptosis and/or pyroptosis, widespread capillary inflammation, and thrombosis. Furthermore, the pulmonary pathology of COVID-19 is characterized by focal inflammatory cell infiltration, impeding alveolar gas exchange resulting in areas of local tissue hypoxia, consistent with potential amplification of COVID-19 pathogenicity by hypoxia. Vascular endothelial cells play essential roles in both innate and adaptive immune responses, and are considered to be "conditional innate immune cells" centrally participating in various inflammatory, immune pathologies. Activated endothelial cells produce cytokines/chemokines, dynamically recruit and activate inflammatory cells and platelets, and centrally participate in pro-thrombotic processes (thrombotic microangiopathies). Initial reports presented pathological findings of localized direct infection of vascular endothelial cells with SARS-CoV-2, yet emerging evidence does not support direct infection of endothelial or other vascular wall cell and thus widespread endothelial cell dysfunction and inflammation may be better explained as secondary responses to epithelial cell infection and inflammation. Endothelial cells are also actively engaged in a cross-talk with the complement system, the essential arm of innate immunity. Recent reports present evidence for complement deposition in SARS-CoV-2-damaged lung microcirculation, further strengthening the idea that, in severe cases of COVID-19, complement activation is an essential player, generating destructive hemorrhagic, capillaritis-like tissue damage, clotting, and hyperinflammation. Thus, complement-targeted therapies are actively in development. This review is intended to explore in detail these ideas.

Donepezil Ameliorates Pulmonary Arterial Hypertension by Inhibiting M2-Macrophage Activation

Background: The beneficial effects of parasympathetic stimulation in pulmonary arterial hypertension (PAH) have been reported. However, the specific mechanism has not been completely clarified. Donepezil, an oral cholinesterase inhibitor, enhances parasympathetic activity by inhibiting acetylcholinesterase, whose therapeutic effects in PAH and its mechanism deserve to be investigated. Methods: The PAH model was established by a single intraperitoneal injection of monocrotaline (MCT, 50 mg/kg) in adult male Sprague-Dawley rats. Donepezil was administered via intraperitoneal injection daily after 1 week of MCT administration. At the end of the study, PAH status was confirmed by echocardiography and hemodynamic measurement. Testing for acetylcholinesterase activity and cholinergic receptor expression was used to evaluate parasympathetic activity. Indicators of pulmonary arterial remodeling and right ventricular (RV) dysfunction were assayed. The proliferative and apoptotic ability of pulmonary arterial smooth muscle cells (PASMCs), inflammatory reaction, macrophage infiltration in the lung, and activation of bone marrow-derived macrophages (BMDMs) were also tested. PASMCs from the MCT-treated rats were co-cultured with the supernatant of BMDMs treated with donepezil, and then, the proliferation and apoptosis of PASMCs were evaluated. Results: Donepezil treatment effectively enhanced parasympathetic activity. Furthermore, it markedly reduced mean pulmonary arterial pressure and RV systolic pressure in the MCT-treated rats, as well as reversed pulmonary arterial remodeling and RV dysfunction. Donepezil also reduced the proliferation and promoted the apoptosis of PASMCs in the MCT-treated rats. In addition, it suppressed the inflammatory response and macrophage activation in both lung tissue and BMDMs in the model rats. More importantly, donepezil reduced the proliferation and promoted the apoptosis of PASMCs by suppressing M2-macrophage activation. Conclusion: Donepezil could prevent pulmonary vascular and RV remodeling, thereby reversing PAH progression. Moreover, enhancement of the parasympathetic activity could reduce the proliferation and promote the apoptosis of PASMCs in PAH by suppressing M2-macrophage activation.

The lamp of medicine of Ancient Egypt is still burning

[No abstract. Showing first paragraph of article]In the land of Ancient Egypt, where the Pharaonic civilization flourished, one can encounter sophisticated methods of treating human illnesses. The Ancient Egyptians considered a disease and its treatment as a part of the divine intervention . The Biblical text of the Passover story tells that the divine can send a series of ten plagues, most are diseases that affected various aged groups (Exodus 7:8-12:30; Psalm 77:42-51; 104:26-36). Not only were surgery and medicine practiced with care some 5000 years ago; the Pharaonic public health systems were innovative, providing water and removing waste in many places.