Complement C3 deficiency attenuates chronic hypoxia-induced pulmonary hypertension in mice

Phosphoproteomics analysis of serum from dogs affected with pulmonary hypertension secondary to degenerative mitral valve disease

Pulmonary hypertension (PH), a common complication in dogs affected by degenerative mitral valve disease (DMVD), is a progressive disorder characterized by increased pulmonary arterial pressure (PAP) and pulmonary vascular remodeling. Phosphorylation of proteins, impacting vascular function and cell proliferation, might play a role in the development and progression of PH. Unlike gene or protein studies, phosphoproteomic focuses on active proteins that function as end-target proteins within signaling cascades. Studying phosphorylated proteins can reveal active contributors to PH development. Early diagnosis of PH is crucial for effective management and improved clinical outcomes. This study aimed to identify potential serum biomarkers for diagnosing PH in dogs affected with DMVD using a phosphoproteomic approach. Serum samples were collected from healthy control dogs (n = 28), dogs with DMVD (n = 24), and dogs with DMVD and PH (n = 29). Phosphoproteins were enriched from the serum samples and analyzed using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Data analysis was performed to identify uniquely expressed phosphoproteins in each group and differentially expressed phosphoproteins among groups. Phosphoproteomic analysis revealed nine uniquely expressed phosphoproteins in the serum of dogs in the DMVD+PH group and 15 differentially upregulated phosphoproteins in the DMVD+PH group compared to the DMVD group. The phosphoproteins previously implicated in PH and associated with pulmonary arterial remodeling, including small nuclear ribonucleoprotein G (SNRPG), alpha-2-macroglobulin (A2M), zinc finger and BTB domain containing 42 (ZBTB42), hemopexin (HPX), serotransferrin (TRF) and complement C3 (C3), were focused on. Their unique expression and differential upregulation in the serum of DMVD dogs with PH suggest their potential as biomarkers for PH diagnosis. In conclusion, this phosphoproteomic study identified uniquely expressed and differentially upregulated phosphoproteins in the serum of DMVD dogs with PH. Further studies are warranted to validate the diagnostic utility of these phosphoproteins.

A novel complement C3 inhibitor CP40-KK protects against experimental pulmonary arterial hypertension via an inflammasome NLRP3 associated pathway

BACKGROUND

Pulmonary arterial hypertension (PAH) is a severe cardiopulmonary disease characterized by complement dependent and proinflammatory activation of macrophages. However, effective treatment for complement activation in PAH is lacking. We aimed to explore the effect and mechanism of CP40-KK (a newly identified analog of selective complement C3 inhibitor CP40) in the PAH model.

METHODS

We used western blotting, immunohistochemistry, and immunofluorescence staining of lung tissues from the monocrotaline (MCT)-induced rat PAH model to study macrophage infiltration, NLPR3 inflammasome activation, and proinflammatory cytokines (IL-1β and IL-18) release. Surface plasmon resonance (SPR), ELISA, and CH50 assays were used to test the affinity between CP40-KK and rat/human complement C3. CP40-KK group rats only received CP40-KK (2 mg/kg) by subcutaneous injection at day 15 to day 28 continuously.

RESULTS

C3a was significantly upregulated in the plasma of MCT-treated rats. SPR, ELISA, and CH50 assays revealed that CP40-KK displayed similar affinity binding to human and rat complement C3. Pharmacological inhibition of complement C3 cleavage (CP40-KK) could ameliorate MCT-induced NLRP3 inflammasome activity, pulmonary vascular remodeling, and right ventricular hypertrophy. Mechanistically, increased proliferation of pulmonary arterial smooth muscle cells is closely associated with macrophage infiltration, NLPR3 inflammasome activation, and proinflammatory cytokines (IL-1β and IL-18) release. Besides, C3a enhanced IL-1β activity in macrophages and promoted pulmonary arterial smooth muscle cell proliferation in vitro.

CONCLUSION

Our findings suggest that CP40-KK treatment was protective in the MCT-induced rat PAH model, which might serve as a therapeutic option for PAH.

Activation of the alternative complement pathway modulates inflammation in thoracic aortic aneurysm/dissection

Thoracic aortic aneurysm/dissection (TAAD) is a lethal vascular disease, and several pathological factors participate in aortic medial degeneration. We previously discovered that the complement C3a-C3aR axis in smooth muscle cells promotes the development of thoracic aortic dissection (TAD) through regulation of matrix metalloproteinase 2. However, discerning the specific complement pathway that is activated and elucidating how inflammation of the aortic wall is initiated remain unknown. We ascertained that the plasma levels of C3a and C5a were significantly elevated in patients with TAD and that the levels of C3a, C4a, and C5a were higher in acute TAD than in chronic TAD. We also confirmed the activation of the complement in a TAD mouse model. Subsequently, knocking out Cfb (Cfb) or C4 in mice with TAD revealed that the alternative pathway and Cfb played a significant role in the TAD process. Activation of the alternative pathway led to generation of the anaphylatoxins C3a and C5a, and knocking out their receptors reduced the recruitment of inflammatory cells to the aortic wall. Moreover, we used serum from wild-type mice or recombinant mice Cfb as an exogenous source of Cfb to treat Cfb KO mice and observed that it exacerbated the onset and rupture of TAD. Finally, we knocked out Cfb in the FBN1C1041G/+ Marfan-syndrome mice and showed that the occurrence of TAA was reduced. In summary, the alternative complement pathway promoted the development of TAAD by recruiting infiltrating inflammatory cells. Targeting the alternative pathway may thus constitute a strategy for preventing the development of TAAD.NEW & NOTEWORTHY The alternative complement pathway promoted the development of TAAD by recruiting infiltrating inflammatory cells. Targeting the alternative pathway may thus constitute a strategy for preventing the development of TAAD.

Chronic hypoxia disrupts T regulatory cell phenotype contributing to the emergence of exTreg-TH17 cells

The imbalance between pro-inflammatory T helper 17 (TH17) cells and anti-inflammatory regulatory T cells (Tregs) has been implicated in multiple inflammatory and autoimmune conditions, but the effects of chronic hypoxia (CH) on this balance have yet to be explored. CH-exposed mice have an increased prevalence of TH17 cells in the lungs with no change in Tregs. This imbalance is significant because it precedes the development of pulmonary hypertension (PH), and TH17 cells are a major contributor to CH-induced PH. While Tregs have been shown to attenuate or prevent the development of certain types of PH through activation and adoptive transfer experiments, why Tregs remain unable to prevent disease progression naturally, specifically in CH-induced PH, remains unclear. Our study aimed to test the hypothesis that increased TH17 cells observed following CH are caused by decreased circulating levels of Tregs and switching of Tregs to exTreg-TH17 cells, following CH. We compared gene expression profiles of Tregs from normoxia or 5-day CH splenocytes harvested from Foxp3tm9(EGFP/cre/ERT2)Ayr/J x Ai14-tdTomato mice, which allowed for Treg lineage tracing through the presence or absence of EGFP and/or tdTomato expression. We found Tregs in CH exposed mice contained gene profiles consistent with decreased suppressive ability. We determined cell prevalence and expression of CD25 and OX40, proteins critical for Treg function, in splenocytes from Foxp3tm9(EGFP/cre/ERT2)Ayr/J x Ai14-tdTomato mice under the same conditions. We found TH17 cells to be increased and Tregs to be decreased, following CH, with protein expression of CD25 and OX40 in Tregs matching the gene expression data. Finally, using the lineage tracing ability of this mouse model, we were able to demonstrate the emergence of exTreg-TH17 cells, following CH. These findings suggest that CH causes a decrease in Treg suppressive capacity, and exTregs respond to CH by transitioning to TH17 cells, both of which tilt the Treg-TH17 cell balance toward TH17 cells, creating a pro-inflammatory environment.

Beneficial effects of Panax notoginseng (Burkill) F. H. Chen flower saponins in rats with metabolic hypertension by inhibiting the activation of the renin-angiotensin-aldosterone system through complement 3

BACKGROUND

Metabolic hypertension (MH) has become the most common type of hypertension in recent years due to unhealthy eating habits and lifestyles of people, such as over-eating alcohol, high fat, and sugar diets (ACHFSDs). Therefore, effective means to combat MH are needed. Previous studies have shown that Panax notoginseng (Burkill) F. H. Chen flower saponins (PNFS) can lower blood pressure in spontaneously hypertensive rats (SHR). However, whether it acts on MH and its mechanism of action remain unclear.  METHODS: The pharmacodynamic effects of PNFS were evaluated in rats with ACHFSDs-induced MH. The blood pressure, blood biochemical, grip strength, face temperature, vertigo time, and liver index were estimated. The histological changes in the liver and aorta were observed using hematoxylin and eosin staining. The levels of ET-1, TXB₂, NO, PGI₂, Renin, ACE, Ang II, and ALD in plasma were detected using ELISA. The levels of C3, KLF5, LXRα, and Renin in kidney tissues were measured using qRT-PCR.The expression levels of C3, KLF5, LXRα, and Renin in kidney tissues were examined using Western blotting.

RESULTS

In the present study, PNFS was found to reduce blood pressure, face temperature, and vertigo time, increase grip strength and improve dyslipidemia in rats with MH. In addition, PNFS decreased the plasma levels of ET-1 and TXB₂, elevated the levels of NO and PGI₂, and improved pathological aortic injury. Meanwhile, PNFS decreased the plasma levels of Renin, ACE, Ang II, and ALD. QRT-PCR and Western bolt showed that PNFS downregulated C3, KLF5, LXRα, and Renin protein and mRNA expression in the kidneys of rats with MH.

CONCLUSION

The finding of the present study suggested that PNFS could downregulate C3 and KLF-5 expression in rats with MH, thereby inhibiting the overactivation of the renin-angiotensin-aldosterone system, while improving vascular endothelial function and ultimately reducing blood pressure in rats with MH.

C3-dependent effector functions of complement

C3 is the central effector molecule of the complement system, mediating its multiple functions through different binding sites and their corresponding receptors. We will introduce the C3 forms (native C3, C3 [H₂ O], and intracellular C3), the C3 fragments C3a, C3b, iC3b, and C3dg/C3d, and the C3 expression sites. To highlight the important role that C3 plays in human biological processes, we will give an overview of the diseases linked to C3 deficiency and to uncontrolled C3 activation. Next, we will present a structural description of C3 activation and of the C3 fragments generated by complement regulation. We will proceed by describing the C3a interaction with the anaphylatoxin receptor, followed by the interactions of opsonins (C3b, iC3b, and C3dg/C3d) with complement receptors, divided into two groups: receptors bearing complement regulatory functions and the effector receptors without complement regulatory activity. We outline the molecular architecture of the receptors, their binding sites on the C3 activation fragments, the cells expressing them, the diversity of their functions, and recent advances. With this review, we aim to give an up-to-date analysis of the processes triggered by C3 activation fragments on different cell types in health and disease contexts.

Association of long-term air pollution exposure with the risk of prediabetes and diabetes: Systematic perspective from inflammatory mechanisms, glucose homeostasis pathway to preventive strategies

BACKGROUND

Limited evidence suggests the association of air pollutants with a series of diabetic cascades including inflammatory pathways, glucose homeostasis disorder, and prediabetes and diabetes. Subclinical strategies for preventing such pollutants-induced effects remain unknown.

METHODS

We conducted a cross-sectional study in two typically air-polluted Chinese cities in 2018-2020. One-year average PM₁, PM_2.5, PM₁₀, SO₂, NO₂, and O₃ were calculated according to participants' residence. GAM multinomial logistic regression was performed to investigate the association of air pollutants with diabetes status. GAM and quantile g-computation were respectively performed to investigate individual and joint effects of air pollutants on glucose homeostasis markers (glucose, insulin, HbA1c, HOMA-IR, HOMA-B and HOMA-S). Complement C3 and hsCRP were analyzed as potential mediators. The ABCS criteria and hemoglobin glycation index (HGI) were examined for their potential in preventive strategy.

RESULTS

Long-term air pollutants exposure was associated with the risk of prediabetes [Prevalence ratio for O₃ (PR_O₃) = 1.96 (95% CI: 1.24, 3.03)] and diabetes [PR_PM₁ = 1.18 (95% CI: 1.05, 1.32); PR_PM_2.5 = 1.08 (95% CI: 1.00, 1.16); PR_O₃ = 1.35 (95% CI: 1.03, 1.74)]. PM₁, PM₁₀, SO₂ or O₃ exposure was associated with glucose-homeostasis disorder. For example, O₃ exposure was associated with increased levels of glucose [7.67% (95% CI: 1.75, 13.92)], insulin [19.98% (95% CI: 4.53, 37.72)], HOMA-IR [34.88% (95% CI: 13.81, 59.84)], and decreased levels of HOMA-S [-25.88% (95% CI: -37.46, -12.16)]. Complement C3 and hsCRP played mediating roles in these relationships with proportion mediated ranging from 6.95% to 60.64%. Participants with HGI ≤ -0.53 were protected from the adverse effects of air pollutants.

CONCLUSION

Our study provides comprehensive insights into air pollutant-associated diabetic cascade and suggests subclinical preventive strategies.

Hemodynamically Unloading the Distal Pulmonary Circulation in Pulmonary Hypertension: A Modeling Study

Pulmonary hypertension (PH) is a progressive disease that is characterized by a gradual increase in both resistive and reactive pulmonary arterial (PA) impedance. Previous studies in a rodent model of PH have shown that reducing the hemodynamic load in the left lung (by banding the left PA) reverses this remodeling phenomenon. However, banding a single side of the pulmonary circulation is not a viable clinical option, so-using in silico modeling-we evaluated if the banding effect can be recreated by replacing the proximal vasculature with a compliant synthetic PA. We developed a computational model of the pulmonary circulation by combining a one-dimensional model of the proximal vasculature with a zero-dimensional line transmission model to the 12th generation. Using this model, we performed four simulations: (1) Control; (2) PH; (3) PH with a stenosis in the left PA; and (4) PH with proximal vessel compliance returned to Control levels. Simulations revealed that vascular changes associated with PH result in an increase in pulse pressure (PP), maximum pressure (Pmax), maximum wall shear stress (WSS), and maximum circumferential stress (σθθ) relative to controls, in the distal circulation. Banding the left PA reduced these measurements of hemodynamic stress in the left lung, but increases them in the right lung. Furthermore, left PA banding increased reactive PA impedance. However, returning the proximal PA compliance to Control levels simultaneously decreased all measures of hemodynamic stress in both lungs, and returned reactive PA impedance to normal levels. In conclusion, if future in vivo studies support the idea of hemodynamic unloading as an effective therapy for PH, this can be surgically achieved by replacing the proximal PA with a compliant prosthesis, and it will have the added benefit of reducing reactive right ventricular afterload.

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.

Rivaroxaban Attenuates Right Ventricular Remodeling in Rats with Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) is a progressive condition that frequently results in right ventricular (RV) remodeling. The objectives of this study are to investigate effects of rivaroxaban on RV remodeling in a rat model of PAH, created with Sugen5416 and chronic hypoxia, and the in vitro effects of rivaroxaban on human cardiac microvascular endothelial cells (HCMECs). To create the PAH model, male Sprague-Dawley rats were subcutaneously injected with Sugen5416 (20 mg/kg) and exposed to 2 weeks of hypoxia (10% O2), followed by 2 weeks of exposure to normoxia. The animals were then divided into 2 groups with or without administration of rivaroxaban (12 mg/kg/d) for a further 4 weeks. HCMECs were cultured under hypoxic conditions (37 °C, 1% O2, 5% CO2) with Sugen5416 and with or without rivaroxaban. In the model rats, RV systolic pressure and Fulton index increased by hypoxia with Sugen5416 were significantly decreased when treated with rivaroxaban. In HCMECs, hypoxia with Sugen5416 increased the expression of protease-activated receptor-2 (PAR-2) and the phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and nuclear factor-kappa B (NF-κB), while treatment with rivaroxaban significantly suppressed the expression of these proteins. Rivaroxaban attenuated RV remodeling in a rat model of PAH by reducing ERK, JNK and NF-κB activation. Rivaroxaban has the possibility of providing additive effects on RV remodeling in patients with PAH.

A proteome signature of umbilical cord serum associated with congenital diaphragmatic hernia

Congenital diaphragmatic hernia (CDH) is a congenital anomaly characterized by a defect in the diaphragm. Despite the recent improvements in its treatment, CDH is associated with a high rate of neonatal mortality, which is often related to pulmonary hypoplasia (PH) as well as pulmonary hypertension. A better understanding of the underlying pathological mechanisms of PH in CDH could help establish a new treatment to improve its prognosis. In this study, we investigated serum biological profiles in neonates with CDH. For comprehensive investigation, umbilical cord serum samples were collected from isolated CDH cases (n = 4) and matched healthy controls (n = 4). Samples were analyzed using liquid chromatography–tandem mass spectrometry. A total of 697 proteins were detected; of them, 98 were identified as differentially expressed proteins. Among these differentially expressed proteins, complement C1q subcomponent showed the largest fold change, followed by complement C5. In the pathway enrichment analysis, the complement and coagulation cascades expressed the most significant enrichment (p = 2.4 × 10⁻²⁶). Thus, the complement pathway might play some role in the pathophysiology of CDH.

Fli1 deficiency induces endothelial adipsin expression, contributing to the onset of pulmonary arterial hypertension in systemic sclerosis

OBJECTIVES

Adipsin, or complement factor D, is a serine proteinase catalysing complement factor C3 breakdown, leading to the production of opsonin (C3b), membrane attack complex (C5b-C9) and anaphylatoxins (C3a and C5a). Since adipsin is potentially associated with pulmonary arterial hypertension in SSc, we investigated adipsin expression in dermal small vessels of SSc-involved skin, the mechanism regulating adipsin expression in endothelial cells, and the correlation of serum adipsin levels with SSc clinical symptoms.

METHODS

Adipsin expression was assessed by immunohistochemistry with skin sections of SSc and healthy subjects. mRNA levels of target genes and transcription factor binding to the ADIPSIN promoter were evaluated by quantitative reverse transcription PCR and chromatin immunoprecipitation, respectively. Serum adipsin levels were determined by enzyme-linked immunosorbent assay.

RESULTS

Adipsin expression was remarkably increased in dermal small vessels of SSc-involved skin as compared with those of healthy control skin. Consistent with the notion that Fli1 deficiency induces SSc-like phenotypes in various types of cells, FLI1 siRNA enhanced adipsin expression at protein and mRNA levels and Fli1 bound to the ADIPSIN promoter in human dermal microvascular endothelial cells. Serum adipsin levels were significantly lower in diffuse cutaneous SSc patients than in limited cutaneous SSc patients and healthy controls, and were associated positively with elevated right ventricular systolic pressure and inversely with interstitial lung disease by multivariate regression analysis.

CONCLUSION

Adipsin is up-regulated at least partially by Fli1 deficiency in endothelial cells, potentially contributing to the development of pulmonary vascular involvement in SSc.

Plasma proteoglycan prolargin in diagnosis and differentiation of pulmonary arterial hypertension

Aims

Right ventricular dysfunction may arise because of pulmonary arterial hypertension (PAH). Development of new diagnostic methods able to identify PAH and allow for earlier treatment initiation, before the development of vascular remodelling and manifest right heart failure (HF), could potentially improve prognosis. Proteoglycans and inflammatory proteins are involved in vascular remodelling. We aimed to investigate their potential as biomarkers to differentiate PAH in a dyspnoeic population.

Methods and results

Plasma from 152 patients with PAH (n = 48), chronic thrombo‐embolic pulmonary hypertension (n = 20), pulmonary hypertension due to HF with reduced (n = 36) or preserved (n = 33) ejection fraction, and HF without pulmonary hypertension (n = 15) and 20 healthy controls were analysed with proximity extension assays. Haemodynamics were assessed in the patients with right heart catheterization. Plasma prolargin levels in PAH were lower compared with all the other studied disease groups (P < 0.001) but higher than the controls' levels (P = 0.003). Receiver operating characteristic curve of prolargin as a PAH‐differentiating marker in a pooled population, encompassing all the other studied disease groups, had a sensitivity of 74% and a specificity of 83.3% (area under the curve = 0.84, P < 0.001). Prolargin correlated with the mean right atrial pressure (r_s = 0.65, P < 0.001), N‐terminal pro‐brain natriuretic peptide (r_s = 0.64, P < 0.001), cardiac index (r_s = −0.31, P = 0.029), stroke volume index (r_s = −0.41, P = 0.004), right ventricular stroke work index (r_s = −0.31, P = 0.032), six‐minute walking distance (r_s = −0.41, P = 0.005), and mixed venous blood oxygen saturation (r_s = −0.42, P = 0.003).

Conclusions

Plasma prolargin levels differentiate PAH patients from controls and the other investigated dyspnoea groups including HF. Its potential in PAH differentiation may be enhanced by inclusion in a multi‐marker panel. Larger studies are needed to evaluate its discriminative ability of PAH in relation to other dyspnoea aetiologies and its potential role in PAH risk stratification and pathobiology.

Effect of EZH2 on pulmonary artery smooth muscle cell migration in pulmonary hypertension

Pulmonary hypertension (PH) is a life‑threatening disease that often involves vascular remodeling. Although pulmonary arterial smooth muscle cells (PASMCs) are the primary participants in vascular remodeling, their biological role is not entirely clear. The present study analyzed the role of enhancer of zeste homolog 2 (EZH2) in vascular remodeling of PH by investigating the behavior of PASMCs. The expression levels of EZH2 in PASMCs in chronic thromboembolic pulmonary hypertension (CTEPH), a type of PH, were detected. The role of EZH2 in PASMC migration was investigated by wound‑healing assay following overexpression and knockdown. Functional enrichment analysis of the whole‑genome expression profiles of PASMCs with EZH2 overexpression was performed using an mRNA Human Gene Expression Microarray. Quantitative (q)PCR was performed to confirm the results of the microarray. EZH2 expression levels increased in CTEPH cell models. The overexpression of EZH2 enhanced PASMC migration compared with control conditions. Functional enrichment analysis of the differentially expressed genes following EZH2 overexpression indicated a strong link between EZH2 and the immune inflammatory response and oxidoreductase activity in PASMCs. mRNA expression levels of superoxide dismutase 3 were verified by qPCR. The results suggested that EZH2 was involved in the migration of PASMCs in PH, and may serve as a potential target for the treatment of PH.

Platelet activation contributes to hypoxia-induced inflammation

Inflammation is central to the pathogenesis of pulmonary vascular remodeling and pulmonary hypertension (PH). Inflammation precedes remodeling in preclinical models, thus supporting the concept that changes in immunity drive remodeling in PH. Platelets are recognized as mediators of inflammation, but whether platelets contribute to hypoxia-driven inflammation has not been studied. We utilized a murine hypoxia model to test the hypothesis that platelets drive hypoxia-induced inflammation. We evaluated male and female 9-wk-old normoxic and hypoxic mice and in selected experiments included hypoxic thrombocytopenic mice. Thrombocytopenic mice were generated with an anti-GP1bα rat IgG antibody. We also performed immunostaining of lung sections from failed donor controls and patients with idiopathic pulmonary arterial hypertension. We found that platelets are increased in the lungs of hypoxic mice and hypoxia induces platelet activation. Platelet depletion prevents hypoxia-driven increases in the proinflammatory chemokines CXCL4 and CCL5 and attenuates hypoxia-induced increase in plasma CSF-2. Pulmonary interstitial macrophages are increased in the lungs of hypoxic mice; this increase is prevented in thrombocytopenic mice. To determine the potential relevance to human disease, lung sections from donors and patients with advanced idiopathic pulmonary arterial hypertension (iPAH) were immunostained for the platelet-specific protein CD41. We observed iPAH lungs had a two-fold increase in CD41, compared with controls. Our data provide evidence that the platelet count is increased in the lungs and activated in mice with hypoxia-induced inflammation and provides rationale for the further study of the potential contribution of platelets to inflammatory mediated vascular remodeling and PH.

Perivascular Inflammation in Pulmonary Arterial Hypertension

Perivascular inflammation is a prominent pathologic feature in most animal models of pulmonary hypertension (PH) as well as in pulmonary arterial hypertension (PAH) patients. Accumulating evidence suggests a functional role of perivascular inflammation in the initiation and/or progression of PAH and pulmonary vascular remodeling. High levels of cytokines, chemokines, and inflammatory mediators can be detected in PAH patients and correlate with clinical outcome. Similarly, multiple immune cells, including neutrophils, macrophages, dendritic cells, mast cells, T lymphocytes, and B lymphocytes characteristically accumulate around pulmonary vessels in PAH. Concomitantly, vascular and parenchymal cells including endothelial cells, smooth muscle cells, and fibroblasts change their phenotype, resulting in altered sensitivity to inflammatory triggers and their enhanced capacity to stage inflammatory responses themselves, as well as the active secretion of cytokines and chemokines. The growing recognition of the interaction between inflammatory cells, vascular cells, and inflammatory mediators may provide important clues for the development of novel, safe, and effective immunotargeted therapies in PAH.

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

Pulmonary (arterial) hypertension (PH/PAH) is a life-threatening cardiopulmonary disorder. Experimental evidence suggests involvement of inflammatory and autoimmune processes in pathogenesis of PH/PAH, however the triggering and disease-promoting mechanisms remain unknown. The complement system is a key arm of innate immunity implicated in various pro-inflammatory and autoimmune diseases, yet, surprisingly little is known about the role of complement in PH/PAH pathogenesis. The preponderance of the existing data associates complement with PH/PAH via analysis of plasma and does not study the lung directly. Therefore, we aimed to resolve this by analyzing both the mechanisms of local lung-specific complement activation and the correlation of dysregulated plasma complement to clinical outcome in PAH patients. In our recent studies, reviewed herein, we show, for the first time, that  immunoglobulin-driven activation of the complement cascade, specifically its alternative pathway, in the pulmonary perivascular areas, is a key mechanism initiating pro-inflammatory processes in the early stage of experimental hypoxic PH (a form of "sterile inflammation"). In human patients with end-stage PAH, we have demonstrated that perivascular deposition of immunoglobulin G (IgG) and activation of the complement cascade are "longitudinally" persistent in the disease. We also showed, using unbiased network analysis, that plasma complement signaling, including again the Alternative pathway, is a prognostic factor of survival in patients with idiopathic PAH (IPAH). Based on these initial findings, we suggest that vascular-specific, immunoglobulin-driven dysregulated complement signaling triggers and maintains pulmonary vascular remodeling and PH. Future experiments in this area would facilitate discoveries on whether complement signaling can serve both as a biomarker and therapeutic target in PH/PAH.

Assessment of lung glucose uptake in patients with systemic lupus erythematosus pulmonary arterial hypertension: a quantitative FDG-PET imaging study

PURPOSE

Pulmonary arterial hypertension (PAH) is a recognized complication of systemic lupus erythematosus (SLE-PAH) patients and its lung pathology shares similarity to idiopathic PAH (IPAH) with distinctive inflammatory feature. FDG-PET reports glucose metabolism from both hyperproliferative and inflammatory cellular elements of vascular pathology in PAH. We explored the application of FDG-PET in reporting SLE-PAH pulmonary vascular pathology.

METHODS

Sixty-minute dynamic FDG-PET imaging was applied in 14 SLE-PAH patients, 20 IPAH patients and 10 healthy volunteers. Patlak analysis was used to quantify lung FDG uptake (influx rate Ki).

RESULTS

Mean lung FDG uptake in SLE-PAH (Ki 0.00714 ± 0.000602 mL/g/min) was significantly higher than that of the healthy volunteers (Ki 0.000262 ± 0.000168 mL/g/min) (p < 0.05). SLE-PAH patients with SLE disease activity score SLEDAI ≥ 5 demonstrated significantly increased lung FDG uptake (Ki 0.001075 ± 0.00055 mL/g/min) than those with SLEDAI < 5 (Ki 0.000233 ± 0.00017 mL/g/min) (p = 0.0038) and IPAH (Ki 0.000524 ± 0.000314 mL/g/min) (p = 0.0025). Lung FDG uptake in SLE-PAH correlated with SLEDAI score and plasma complement C3 and C4 levels (Ki vs SLEDAI, r = 0.607, p = 0.021; Ki vs C3, r = - 0.568, p = 0.034; Ki vs C4, r = - 0.661, p = 0.010). There were no significantly correlations between lung FDG uptake and pulmonary vascular haemodynamics and 6 min walking distance in both IPAH and SLE-PAH patients.

CONCLUSIONS

Our data indicated that increased lung FDG uptake in SLE-PAH patients correlates with SLE disease activity (SLEDAI) and immune/inflammatory status (C3 and C4). FDG-PET imaging may be developed as a potential intrapulmonary disease activity marker in SLE-PAH patients.

Cellular inflammation in pulmonary hypertension: Detailed analysis of lung and right ventricular tissue, circulating immune cells and effects of a dual endothelin receptor antagonist

Growing evidence suggests that inflammation is crucially involved in the pathogenesis of pulmonary hypertension (PH) and consecutive right heart failure. The present study analyzed the inflammatory response in lung and right ventricle in a rat model of PH and evaluated the effects of the dual endothelin receptor antagonist (ERA) Macitentan. PH was induced by monocrotalin (60 mg/kg body weight s.c.) in Sprague-Dawley rats (PH, n = 10) and compared to healthy controls (CON, n = 10) as well as monocrotalin-induced, macitentan-treated rats (THER, n = 10). Detection of Dendritic cells (DCs), regulatory T cells (Tregs) and others as well as RT-PCR based inflammatory gene expression analysis were performed. Circulating DCs and Tregs were quantified by flow cytometry in the rat model and in PH patients (n = 70) compared to controls (n = 52). Inflammatory cells were increased in lung and right ventricular tissue, whereas DCs and Tregs were decreased in blood. Expression of 17 genes in the lung and 20 genes in the right ventricle were relevantly (>2.0 fold) regulated in the PH group. These effects were, at least in part, attenuated in response to Macitentan treatment. In humans as well as rats, immune cells showed significant correlations to clinical, echocardiographic, and haemodynamic parameters. PH is accompanied by a distinct inflammatory response in lung and right but not left ventricular tissue attenuated by Macitentan. Correlations of circulating DCs as well as tissue resident immune cells with parameters reflecting right ventricular function raise the idea of both, promising biomarkers and novel treatment strategies.

Immunoglobulin-driven Complement Activation Regulates Proinflammatory Remodeling in Pulmonary Hypertension

Rationale: Pulmonary hypertension (PH) is a life-threatening cardiopulmonary disorder in which inflammation and immunity have emerged as critical early pathogenic elements. Although proinflammatory processes in PH and pulmonary arterial hypertension (PAH) are the focus of extensive investigation, the initiating mechanisms remain elusive.Objectives: We tested whether activation of the complement cascade is critical in regulating proinflammatory and pro-proliferative processes in the initiation of experimental hypoxic PH and can serve as a prognostic biomarker of outcome in human PAH.Methods: We used immunostaining of lung tissues from experimental PH models and patients with PAH, analyses of genetic murine models lacking specific complement components or circulating immunoglobulins, cultured human pulmonary adventitial fibroblasts, and network medicine analysis of a biomarker risk panel from plasma of patients with PAH.Measurements and Main Results: Pulmonary perivascular-specific activation of the complement cascade was identified as a consistent critical determinant of PH and PAH in experimental animal models and humans. In experimental hypoxic PH, proinflammatory and pro-proliferative responses were dependent on complement (alternative pathway and component 5), and immunoglobulins, particularly IgG, were critical for activation of the complement cascade. We identified Csf2/GM-CSF as a primary complement-dependent inflammatory mediator. Furthermore, using network medicine analysis of a biomarker risk panel from plasma of patients with PAH, we demonstrated that complement signaling can serve as a prognostic factor for clinical outcome in PAH.Conclusions: This study establishes immunoglobulin-driven dysregulated complement activation as a critical pathobiological mechanism regulating proinflammatory and pro-proliferative processes in the initiation of experimental hypoxic PH and demonstrates complement signaling as a critical determinant of clinical outcome in PAH.

The FGL2 prothrombinase contributes to the pathological process of experimental pulmonary hypertension

In situ thrombus formation is one of the major pathological features of pulmonary hypertension (PH). The mechanism of in situ thrombosis has not been clearly identified. Fibrinogen-like protein 2 (FGL2) prothrombinase is an immune coagulant that can cleave prothrombin to thrombin, which then converts fibrinogen into fibrin. This mechanism triggers in situ thrombus formation directly, bypassing both the intrinsic and extrinsic coagulation pathways. FGL2 prothrombinase is mainly expressed in endothelial cells and mediates multiple pathological processes. This implies that it may also play a role in PH. In this study, we examined the expression of FGL2 in idiopathic pulmonary arterial hypertension (IPAH) patients, and in monocrotaline-induced rat and hypoxia-induced mouse PH models. Fgl2−/− mice were used to evaluate the development of PH and explore associated pathological changes. These included in situ thrombosis, vascular remodeling, and endothelial apoptosis. Following these analyses, we examined possible signaling pathways downstream of FGL2 in PH. We show FGL2 is upregulated in pulmonary vascular endothelium in human IPAH and in two animal PH models. Genetic knockout of Fgl2 limited the development of PH, indicated by decreased in situ thrombus formation, less vascular remodeling, and reduced endothelial dysfunction. In addition, loss of FGL2 downregulated PAR1 (proteinase-activated receptor 1) expression and decreased the overactivation and consumption of platelets in hypoxia-induced PH. These results indicate FGL2 participate in the development of PH and loss of FGL2 could attenuate PH by reducing in situ thrombosis and suppressing PAR1 signaling. Thus we provide evidence that suggests FGL2 prothrombinase presents a potential therapeutic target for clinical treatment of PH.

NEW & NOTEWORTHY This is the first study to demonstrate that fibrinogen-like protein 2 (FGL2) participates in the pathological progression of pulmonary hypertension (PH) in human idiopathic pulmonary arterial hypertension, a monocrotaline rat PH model, and a hypoxia mouse PH model. Genetic knockout of Fgl2 significantly limited the development of PH indicated by reduced in situ thrombosis, vascular remodeling, and endothelial dysfunction, and suppressed PAR1 (proteinase-activated receptor 1) signaling and overactivation of platelets on PH. These results suggest FGL2 presents a potential therapeutic target for clinical treatment of PH.

Hypoxia-induced Pulmonary Hypertension in Different Mouse Strains: Relation to Transcriptome

Patients with pulmonary arterial hypertension (PAH) can harbor mutations in several genes, most commonly in BMPR2. However, disease penetrance in patients with BMPR2 mutations is low. In addition, most patients do not carry known PAH gene mutations, suggesting that other factors determine susceptibility to PAH. To begin to identify additional genomic factors contributing to PAH pathogenesis, we exposed 32 mouse strains to chronic hypoxia. We found that the PL/J strain has extremely high right ventricular systolic pressure (RVSP; 86.58 mm Hg) but minimal lung remodeling. To identify potential genomic factors contributing to the high RVSP, RNAseq analysis of PL/J lung mRNAs and microRNAs (miRNAs) after hypoxia was performed, and it demonstrated that 4 of 43 upregulated miRNAs in the Dlk1-Dio3 imprinting region are predicted to target T cell marker mRNAs. These target mRNAs, as well as the numbers of T cells were downregulated. In addition, C5a and its receptor, C5AR1, were increased. Analysis of Rho-associated protein kinase (Rock) 2 mRNA expression, in the RhoA/Rock pathway, demonstrated a significant increase in PL/J. Inhibition of Rock2 ameliorated a portion of the elevated RVSP. In addition, we identified miR-150-5p as a potential regulator of Rock2 expression. In conclusion, we identified two possible pathways contributing to the hypoxia pulmonary hypertension phenotype of extreme RVSP elevation: aberrant T cell expression driven by hypoxia-induced miRNAs and increased expression of C5a and C5AR1. We suggest that the PL/J mouse will be a good model for seeking mechanism(s) of RVSP elevation in hypoxia-induced PAH.

Complement C3 participates in the function and mechanism of traumatic brain injury at simulated high altitude

BACKGROUND

Traumatic brain injury (TBI) leads to severe mortality and disability, in which secondary injury induced by complement activation plays an important role. TBI tends to be associated with more severe cerebral edema and worse neurological functional recovery if it occurs in high-altitude areas than in low-altitude areas. However, the underlying mechanism of this difference is unknown. Thus, we used cobra venom factor (CVF) to deplete complement C3 in simulated high-altitude areas to explore whether the differences in outcome at different altitudes are related to secondary injury caused by complement C3.

METHODS

The weight-drop model was adopted to induce TBI in rats. Rats were randomly divided into the following groups: sham + saline (sham), high altitude + TBI + saline (HAT), high altitude + TBI + CVF (H-CVF), low altitude + TBI + saline (LAT), and low altitude + TBI + CVF (L-CVF). Brain contusion and edema volumes, brain water content, myelin basic protein (MBP) expression, tumor necrosis factor alpha (TNF-a) expression, interleukin 1 beta (IL1B) expression, mortality rate, neurological function, and complement component 3 (C3) mRNA expression were measured by techniques such as Evans blue fluorescence, Perls staining, TUNEL staining, ELISA, immunohistochemistry and Western blotting to evaluate correlations between complement activation and secondary injury.

RESULTS

The activation of complement after TBI was significantly higher at high altitude than at low altitude. High-altitude TBI resulted in a leakier blood-brain barrier, more severe cerebral edema and higher mortality than low-altitude TBI did. In addition, high-altitude TBI tended to be associated with more MBP degradation, ferric iron deposition, neuronal apoptosis, and inflammatory factor deposition than low-altitude TBI. All of these effects of TBI were partially reversed by inhibiting complement activation using CVF.

CONCLUSION

Our study provided evidence that TBI at high altitude leads to severe edema and high mortality and disability rates. Complement C3 activation is one of the important factors contributing to secondary brain injury.

Evidence for the Fucoidan/P-Selectin Axis as a Therapeutic Target in Hypoxia-induced Pulmonary Hypertension

Rationale: Pulmonary arterial hypertension (PAH) is characterized by vascular remodeling and excessive proliferation of pulmonary artery smooth muscle cells (PASMCs). Fucoidan, a polysaccharidic ligand of the adhesion molecule P-selectin, exhibits antiproliferative properties. The effects of the fucoidan/P-selectin axis on vascular remodeling and pulmonary hypertension (PH) after hypoxia remain unexplored. Objectives: We aimed to evaluate the therapeutic potential of targeting the fucoidan/P-selectin axis in PH. Methods: Mice with PH induced by chronic hypoxia (35 d) were given either fucoidan (from Fucus vesiculosus) or anti-P-selectin antibody (Rb40.34) during Days 21-35. Right ventricular (RV) function was determined by echocardiography. Vascular morphometry was assessed by immunohistochemistry. Human and experimental PH lungs and PASMCs were used for assessment of P-selectin expression and function. Measurements and Main Results: Fucoidan attenuated chronic hypoxia-induced PH in mice, reducing pulmonary vascular remodeling and restoring RV function. In vitro, fucoidan inhibited hypoxia and growth factor-stimulated PASMC proliferation and migration. Chronic hypoxia caused an upregulation of P-selectin in the medial layer of the small pulmonary arteries. P-selectin was persistently upregulated in PASMCs of human and hypoxia-induced experimental PH. HIF-1α (hypoxia-inducible factor 1α) directly bound to the P-selectin promoter and transcriptionally activated P-selectin in hypoxia. P-selectin blockage resulted in a marked reduction of PASMC proliferation in vitro. Blockage of P-selectin by administration of anti-P-selectin Rb40.34 antibody and P-selectin-deficient mice improved vascular remodeling and restored RV function. Conclusions: Fucoidan is a potent natural adjuvant that represents a promising therapeutic approach for PH. Our data indicate a previously unrecognized role of P-selectin in the proliferative response of PASMCs associated with PH.

Adverse effects of BMPR2 suppression in macrophages in animal models of pulmonary hypertension

Inflammatory cells contribute to irreversible damage in pulmonary arterial hypertension (PAH). We hypothesized that in PAH, dysfunctional BMPR2 signaling in macrophages contributes to pulmonary vascular injury and phenotypic changes via proinflammatory cytokine production. Studies were conducted in: (1) Rosa26-rtTA2 3 X TetO7-Bmpr2delx4 FVB/N mice (mutant Bmpr2 is universally expressed, BMPR2delx4 mice) given a weekly intra-tracheal liposomal clodronate injections for four weeks; and (2) LysM-Cre X floxed BMPR2 X floxed eGFP monocyte lineage-specific BMPR2 knockout (KO) mouse model (Bmpr2 gene expression knockdown in monocytic lineage cells) (BMPR2KO) following three weeks of sugen/hypoxia treatment. In the BMPR2delx4 mice, increased right ventricular systolic pressure (RVSP; P  < 0.05) was normalized by clodronate, and in monocyte lineage-specific BMPR2KO mice sugen hypoxia treatment increased (P  < 0.05) RVSP compared to control littermates, suggesting that suppressed BMPR2 in macrophages modulate RVSP in animal models of PH. In addition, in these mouse models, muscularized pulmonary vessels were increased (P  < 0.05) and surrounded by an increased number of macrophages. Elimination of macrophages in BMPR2delx4 mice reduced the number of muscularized pulmonary vessels and macrophages surrounding these vessels. Further, in monocyte lineage-specific BMPR2KO mice, there was significant increase in proinflammatory cytokines, including C-X-C Motif Chemokine Ligand 12 (CXCL12), complement component 5 a (C5a), Interleukin-16 (IL-16), and secretory ICAM. C5a positive inflammatory cells present in and around the pulmonary vessels in the PAH lung could potentially be involved in pulmonary vessel remodeling. In summary, our data indicate that, in BMPR2-related PAH, macrophages with dysfunctional BMPR2 influence pulmonary vascular remodeling and phenotypic outcomes via proinflammatory cytokine production.

Exploration of Acute Phase Proteins and Inflammatory Cytokines in Early Stage Diagnosis of Acute Mountain Sickness

Wang, Chi, Hui Jiang, Jinyan Duan, Jingwen Chen, Qi Wang, Xiaoting Liu, and Chengbin Wang. Exploration of acute phase proteins and inflammatory cytokines in early stage diagnosis of acute mountain sickness. High Alt Med Biol. 19:170-177, 2018.

BACKGROUND

Early diagnosis of acute mountain sickness (AMS) is currently based on personal appreciation of the severity of symptoms. A more objective method to diagnose AMS is required. Inflammatory cytokines and acute phase proteins have been reported to be different at high altitude.

METHODS

A total of 104 male soldiers rapidly ascending from Beijing (20-60 m) to Germu, Qinghai (3200 m), were divided into AMS group and non-AMS group according to the Lake Louis Score system. Blood pressure, pulse rate, and oxygen saturation were measured. Forty-nine blood samples were collected before and on the 3rd day after ascending to the high altitude. Serum haptoglobin (Hp), transferrin (Tf), and complement C3 were detected by immune scattered nephelometry, whereas serum interleukin-1beta (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α) were detected by chemical luminescence immunity analyzer. The sensitivity, specificity, and receiver operating characteristic curve were evaluated. Youden index with the maximum value was used to determine cutoff values of each parameter. Logistic regression was performed to determine the diagnostic efficiency of combination of three cytokines.

RESULTS

Differences of physical indexes between AMS group and non-AMS group were of no statistical significance. In AMS group, serum Tf significantly increased while Hp decreased when compared with non-AMS group. Serum IL-1β, IL-6, and TNF-α were higher in the AMS group than in the non-AMS group. The cutoff values for Tf, Hp, IL-1β, IL-6, and TNF-α were 263.5 mg/dL, 119.35 mg/dL, 6.2 pg/mL, 15.05 pg/mL, and 18.35 pg/mL, respectively. Area under the curve (AUC) of combining three cytokines together was higher than AUC of each cytokine separately.

CONCLUSIONS

Acute phase proteins and inflammatory cytokines (IL-1β, IL-6, and TNF-α) show significant changes between the AMS group and the non-AMS group. Combination of inflammatory cytokines or acute phase proteins improves the specificity for diagnosis of AMS. This might provide objective indexes for scanning and screening individuals susceptible to AMS in the early stage of rapid ascending.

Inflammation and autoimmunity in pulmonary hypertension: is there a role for endothelial adhesion molecules? (2017 Grover Conference Series)

While pulmonary hypertension (PH) has traditionally not been considered as a disease that is directly linked to or, potentially, even caused by inflammation, a rapidly growing body of evidence has demonstrated the accumulation of a variety of inflammatory and immune cells in PH lungs, in and around the wall of remodeled pulmonary resistance vessels and in the vicinity of plexiform lesions, respectively. Concomitantly, abundant production and release of various inflammatory mediators has been documented in both PH patients and experimental models of PH. While these findings unequivocally demonstrate an inflammatory component in PH, they have fueled an intense and presently ongoing debate as to the nature of this inflammatory aspect: is it a mere bystander of or response to the actual disease process, or is it a pathomechanistic contributor or potentially even a trigger of endothelial injury, smooth muscle hypertrophy and hyperplasia, and the resulting lung vascular remodeling? In this review, we will discuss the present evidence for an inflammatory component in PH disease with a specific focus on the potential role of the endothelium in this scenario and highlight future avenues of experimental investigation which may lead to novel therapeutic interventions.

Upregulation of Human Endogenous Retrovirus-K Is Linked to Immunity and Inflammation in Pulmonary Arterial Hypertension

BACKGROUND

Immune dysregulation has been linked to occlusive vascular remodeling in pulmonary arterial hypertension (PAH) that is hereditary, idiopathic, or associated with other conditions. Circulating autoantibodies, lung perivascular lymphoid tissue, and elevated cytokines have been related to PAH pathogenesis but without a clear understanding of how these abnormalities are initiated, perpetuated, and connected in the progression of disease. We therefore set out to identify specific target antigens in PAH lung immune complexes as a starting point toward resolving these issues to better inform future application of immunomodulatory therapies.

METHODS

Lung immune complexes were isolated and PAH target antigens were identified by liquid chromatography tandem mass spectrometry, confirmed by enzyme-linked immunosorbent assay, and localized by confocal microscopy. One PAH antigen linked to immunity and inflammation was pursued and a link to PAH pathophysiology was investigated by next-generation sequencing, functional studies in cultured monocytes and endothelial cells, and hemodynamic and lung studies in a rat.

RESULTS

SAM domain and HD domain-containing protein 1 (SAMHD1), an innate immune factor that suppresses HIV replication, was identified and confirmed as highly expressed in immune complexes from 16 hereditary and idiopathic PAH versus 12 control lungs. Elevated SAMHD1 was localized to endothelial cells, perivascular dendritic cells, and macrophages, and SAMHD1 antibodies were prevalent in tertiary lymphoid tissue. An unbiased screen using metagenomic sequencing related SAMHD1 to increased expression of human endogenous retrovirus K (HERV-K) in PAH versus control lungs (n=4). HERV-K envelope and deoxyuridine triphosphate nucleotidohydrolase mRNAs were elevated in PAH versus control lungs (n=10), and proteins were localized to macrophages. HERV-K deoxyuridine triphosphate nucleotidohydrolase induced SAMHD1 and proinflammatory cytokines (eg, interleukin 6, interleukin 1β, and tumor necrosis factor α) in circulating monocytes, pulmonary arterial endothelial cells, and also activated B cells. Vulnerability of pulmonary arterial endothelial cells (PAEC) to apoptosis was increased by HERV-K deoxyuridine triphosphate nucleotidohydrolase in an interleukin 6-independent manner. Furthermore, 3 weekly injections of HERV-K deoxyuridine triphosphate nucleotidohydrolase induced hemodynamic and vascular changes of pulmonary hypertension in rats (n=8) and elevated interleukin 6.

CONCLUSIONS

Our study reveals that upregulation of the endogenous retrovirus HERV-K could both initiate and sustain activation of the immune system and cause vascular changes associated with PAH.

Dangerous liaisons: complement, coagulation, and kallikrein/kinin cross-talk act as a linchpin in the events leading to thromboinflammation

Innate immunity is fundamental to our defense against microorganisms. Physiologically, the intravascular innate immune system acts as a purging system that identifies and removes foreign substances leading to thromboinflammatory responses, tissue remodeling, and repair. It is also a key contributor to the adverse effects observed in many diseases and therapies involving biomaterials and therapeutic cells/organs. The intravascular innate immune system consists of the cascade systems of the blood (the complement, contact, coagulation, and fibrinolytic systems), the blood cells (polymorphonuclear cells, monocytes, platelets), and the endothelial cell lining of the vessels. Activation of the intravascular innate immune system in vivo leads to thromboinflammation that can be activated by several of the system's pathways and that initiates repair after tissue damage and leads to adverse reactions in several disorders and treatment modalities. In this review, we summarize the current knowledge in the field and discuss the obstacles that exist in order to study the cross-talk between the components of the intravascular innate immune system. These include the use of purified in vitro systems, animal models and various types of anticoagulants. In order to avoid some of these obstacles we have developed specialized human whole blood models that allow investigation of the cross-talk between the various cascade systems and the blood cells. We in particular stress that platelets are involved in these interactions and that the lectin pathway of the complement system is an emerging part of innate immunity that interacts with the contact/coagulation system. Understanding the resulting thromboinflammation will allow development of new therapeutic modalities.

Three-dimensional micro computed tomography analysis of the lung vasculature and differential adipose proteomics in the Sugen/hypoxia rat model of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a rare disease characterized by significant vascular remodeling. The obesity epidemic has produced great interest in the relationship between small visceral adipose tissue depots producing localized inflammatory conditions, which may link metabolism, innate immunity, and vascular remodeling. This study used novel micro computed tomography (microCT) three-dimensional modeling to investigate the degree of remodeling of the lung vasculature and differential proteomics to determine small visceral adipose dysfunction in rats with severe PAH. Sprague-Dawley rats were subjected to a subcutaneous injection of vascular endothelial growth factor receptor blocker (Sugen 5416) with subsequent hypoxia exposure for 3 weeks (SU/hyp). At 12 weeks after hypoxia, microCT analysis showed a decrease in the ratio of vascular to total tissue volume within the SU/hyp group (mean ± standard deviation: 0.27 ± 0.066; P = 0.02) with increased vascular separation (0.37 ± 0.062 mm; P = 0.02) when compared with the control (0.34 ± 0.084 and 0.30 ± 0.072 mm). Differential proteomics detected an up-regulation of complement protein 3 (C3; SU/hyp∶control ratio = 2.86) and the adipose tissue-specific fatty acid binding protein-4 (FABP4, 2.66) in the heart adipose of the SU/hyp. Significant remodeling of the lung vasculature validates the efficacy of the SU/hyp rat for modeling human PAH. The upregulation of C3 and FABP4 within the heart adipose implicates small visceral adipose dysfunction. C3 has been associated with vascular stiffness, and FABP4 suppresses peroxisome proliferator-activated receptor, which is a major regulator of adipose function and known to be downregulated in PAH. These findings reveal that small visceral adipose tissue within the SU/hyp model provides mechanistic links for vascular remodeling and adipose dysfunction in the pathophysiology of PAH.

Hypoxic stress -responsive genes in air breathing catfish, Clarias magur (Hamilton 1822) and their possible physiological adaptive function

The Indian catfish, Clarias magur (previous name C. batrachus) is an air breathing fish, inhabitant of aquatic bodies characterized by low dissolved oxygen levels. It is exposed to hypoxic conditions in its natural habitat. Thus, it can be useful model to study the mechanism of hypoxia stress tolerance. In C. magur, molecular processes facilitating its adaptation to hypoxia stress remain largely unexplored, in part due to unavailability of genomic resources. The suppression subtractive hybridization technique (SSH) was employed to compare the differential expression of transcripts under experimental hypoxic conditions, to that of normoxic conditions. Twelve subtracted cDNA libraries (six each forward and reverse) were constructed from brain, heart, liver, muscle, spleen and head kidney tissues. A total of 2020 clones were screened and sequenced, resulting into 1805 high quality expressed sequence tags (ESTs). Annotation of these differentially expressed ESTs resulted into the identification of genes involved in vast majority of pathways/processes affecting metabolism, cellular processes, signal transduction and/or immune functions. Additionally, 18 potential novel genes expressed in hypoxia stress exposed fish were also identified. The study had catalogued the differentially expressed genes from hypoxia stress induced C. magur, where most of them are reported for the first time in a hypoxia-tolerant fish species. The results not only provided insights for the hypoxia stress altered cellular functions in C. magur, but also generated a valuable functional genomics resource to assist targeted studies on functional genomics and future genome projects.

Plasma Proteomic Study in Pulmonary Arterial Hypertension Associated with Congenital Heart Diseases

Pulmonary arterial hypertension associated with congenital heart disease (CHD-PAH) has serious consequence and plasma protein profiles in CHD-PAH are unknown. We aimed to reveal the differential plasma proteins in 272 CHD patients with or without PAH. Various types of CHD-PAH were studied. Differential plasma proteins were first detected by iTRAQ proteomic technology and those with significant clinical relevance were selected for further ELISA validation in new cohort of patients. Among the 190 differential plasma proteins detected by iTRAQ, carbamoyl-phosphate synthetase I (CPSI, related to urea cycle and endogenous nitric oxide production) and complement factor H-related protein 2 (CFHR2, related to complement system and coagulant mechanism) were selected for further ELISA validation in new cohort of 152 patients. Both CPSI and CFHR2 were down-regulated with decreased plasma levels (p < 0.01). Thus, we for the first time in CHD-PAH patients identified a large number of differential plasma proteins. The decreased CPSI expression in CHD-PAH patients may reveal a mechanism related to endogenous nitric oxide and the decrease of CFHR2 protein may demonstrate the deficiency of the immune system and coagulation mechanism. The findings may open a new direction for translational medicine in CHD-PAH with regard to the diagnosis and progress of the disease.

Contact activation of C3 enables tethering between activated platelets and polymorphonuclear leukocytes via CD11b/CD18

Complement component C3 has a potential role in thrombotic pathologies. It is transformed, without proteolytic cleavage, into C3(H2O) upon binding to the surface of activated platelets. We hypothesise that C3(H2O) bound to activated platelets and to platelet-derived microparticles (PMPs) contributes to platelet-PMN complex (PPC) formation and to the binding of PMPs to PMNs. PAR-1 activation of platelets in human whole blood from normal individuals induced the formation of CD16+/CD42a+ PPC. The complement inhibitor compstatin and a C5a receptor antagonist inhibited PPC formation by 50 %, while monoclonal antibodies to C3(H2O) or anti-CD11b inhibited PPC formation by 75-100 %. Using plasma protein-depleted blood and blood from a C3-deficient patient, we corroborated the dependence on C3, obtaining similar results after reconstitution with purified C3. By analogy with platelets, PMPs isolated from human serum were found to expose C3(H2O) and bind to PMNs. This interaction was also blocked by the anti-C3(H2O) and anti-CD11b monoclonal antibodies, indicating that C3(H2O) and CD11b are involved in tethering PMPs to PMNs. We confirmed the direct interaction between C3(H2O) and CD11b by quartz crystal microbalance analysis using purified native C3 and recombinant CD11b/CD18 and by flow cytometry using PMP and recombinant CD11b. Transfectants expressing CD11b/CD18 were also shown to specifically adhere to surface-bound C3(H2O). We have identified contact-activated C3(H2O) as a novel ligand for CD11b/CD18 that mediates PPC formation and the binding of PMPs to PMNs. Given the various roles of C3 in thrombotic reactions, this finding is likely to have important pathophysiological implications.

Combined genetic effects of EGLN1 and VWF modulate thrombotic outcome in hypoxia revealed by Ayurgenomics approach

BACKGROUND

Extreme constitution "Prakriti" types of Ayurveda exhibit systemic physiological attributes. Our earlier genetic study has revealed differences in EGLN1, key modulator of hypoxia axis between Prakriti types. This was associated with differences in high altitude adaptation and susceptibility to high altitude pulmonary edema (HAPE). In this study we investigate other molecular differences that contribute to systemic attributes of Prakriti that would be relevant in predictive marker discovery.

METHODS

Genotyping of 96 individuals of the earlier cohort was carried out in a panel of 2,800 common genic SNPs represented in Indian Genomic Variation Consortium (IGVC) panel from 24 diverse populations. Frequency distribution patterns of Prakriti differentiating variations (FDR correction P < 0.05) was studied in IGVC and 55 global populations (HGDP-CEPH) panels. Genotypic interactions between VWF, identified from the present analysis, and EGLN1 was analyzed using multinomial logistic regression in Prakriti and Indian populations from contrasting altitudes. Spearman's Rank correlation was used to study this genotypic interaction with respect to altitude in HGDP-CEPH panel. Validation of functional link between EGLN1 and VWF was carried out in a mouse model using chemical inhibition and siRNA studies.

RESULT

Significant differences in allele frequencies were observed in seven genes (SPTA1, VWF, OLR1, UCP2, OR6K3, LEPR, and OR10Z1) after FDR correction (P < 0.05). A non synonymous variation (C/T, rs1063856) associated with thrombosis/bleeding susceptibility respectively, differed significantly between Kapha (C-allele) and Pitta (T-allele) constitution types. A combination of derived EGLN1 allele (HAPE associated) and ancestral VWF allele (thrombosis associated) was significantly high in Kapha group compared to Pitta (p < 10(-5)). The combination of risk-associated Kapha alleles was nearly absent in natives of high altitude. Inhibition of EGLN1 using (DHB) and an EGLN1 specific siRNA in a mouse model lead to a marked increase in vWF levels as well as pro-thrombotic phenotype viz. reduced bleeding time and enhanced platelet count and activation.

CONCLUSION

We demonstrate for the first time a genetic link between EGLN1 and VWF in a constitution specific manner which could modulate thrombosis/bleeding susceptibility and outcomes of hypoxia. Integration of Prakriti in population stratification may help assemble common variations in key physiological axes that confers differences in disease occurrence and patho-phenotypic outcomes.

Complement system in lung disease

In addition to its established contribution to innate immunity, recent studies have suggested novel roles for the complement system in the development of various lung diseases. Several studies have demonstrated that complement may serve as a key link between innate and adaptive immunity in a variety of pulmonary conditions. However, the specific contributions of complement to lung diseases based on innate and adaptive immunity are just beginning to emerge. Elucidating the role of complement-mediated immune regulation in these diseases will help to identify new targets for therapeutic interventions.

Inflammation and immunity in the pathogenesis of pulmonary arterial hypertension

This review summarizes an expanding body of knowledge indicating that failure to resolve inflammation and altered immune processes underlie the development of pulmonary arterial hypertension. The chemokines and cytokines implicated in pulmonary arterial hypertension that could form a biomarker platform are discussed. Pre-clinical studies that provide the basis for dysregulated immunity in animal models of the disease are reviewed. In addition, we present therapies that target inflammatory/immune mechanisms that are currently enrolling patients, and discuss others in development. We show how genetic and metabolic abnormalities are inextricably linked to dysregulated immunity and adverse remodeling in the pulmonary arteries.

Tissue factor, protease activated receptors and pathologic heart remodelling

Tissue factor is the primary initiator of coagulation cascade and plays an essential role in haemostasis and thrombosis. In addition, tissue factor and coagulation proteases contribute to many cellular responses via activation of protease activated receptors. The heart is an organ with high levels of constitutive tissue factor expression. This review focuses on the role of tissue factor, coagulation proteases and protease activated receptors in heart haemostasis and the pathological heart remodelling associated with myocardial infarction, viral myocarditis and hypertension.

Combination of erythropoietin and sildenafil can effectively attenuate hypoxia-induced pulmonary hypertension in mice

Pulmonary hypertension (PH) is an incurable disease that often leads to right ventricular hypertrophy and right heart failure. This study investigated single versus combined therapy with sildenafil and erythropoietin on hypoxia-induced pulmonary hypertension in mice. Mice were randomized into 5 groups and exposed to either hypoxia (10% oxygen) or normoxia for a total of 5 weeks. Hypoxic mice were treated with saline solution, erythropoietin (500 IU/kg 3 times weekly), sildenafil (10 mg/kg daily), or a combination of the two drugs for the last 2 weeks of hypoxic exposure. We measured right ventricular pressures using right heart catheterization, and the ventilatory response to hypoxia was recorded via whole-body plethysmography. Histological analyses were performed to elucidate changes in pulmonary morphology and appearance of right heart hypertrophy. Plasma levels of cardiotrophin-1 and atrial natriuretic peptide were quantified. Treatment with either erythropoietin or sildenafil alone lowered the hypoxia-induced increase of pulmonary pressure and reduced pulmonary edema formation, pulmonary vascular remodeling, and right ventricular hypertrophy. Notably, the combination of the two drugs had the most prominent effect. Changes in cardiotrophin-1 and atrial natriuretic protein levels confirmed these observations. The combination treatment with erythropoietin and sildenafil demonstrated an attenuation of the development of hypoxia-induced PH in mice that was superior to that observed for either drug when given alone.

Recombinant human interferon alpha 2b prevents and reverses experimental pulmonary hypertension

Pulmonary hypertension (PH) is a progressive and fatal disease with no cure. Vascular remodeling in PH involves intraluminal growth of endothelial and smooth muscle cells, leading to obliterative vascular lesions. Cell growth in these lesions is quasi-neoplastic, with evidence of monoclonality, apoptosis resistance and cancer-like metabolic derangements. Herein we tested the effect of human interferon alpha 2b (IFNα), a pleiotropic cytokine and anti-cancer therapeutic, on the development and progression of PH in the rat SU5416/hypoxia (SUH) model and mouse hypoxia model of the disease. In both models IFNα attenuated the development of PH and reversed established PH as assessed by measuring right ventricular systolic pressure and right ventricular hypertrophy. The effect of IFNα was dependent on the type I interferon receptor (IFNAR) since mice lacking a subunit of the IFNAR were not protected by IFNα. Morphometric analysis of pulmonary aterioles from hypoxic mice or SUH rats showed that IFNα inhibited pulmonary vascular remodeling in both models and that IFNα reversed remodeling in SUH rats with established disease. Immunohistochemical staining revealed that IFNα decreased the number of PCNA and Tunel positive cells in the wall of pulmonary arterioles. In vitro, IFNα inhibited proliferation of human pulmonary artery smooth muscle cells and as well as human pulmonary artery endothelial cell proliferation and apoptosis. Together these findings demonstrate that IFNα reverses established experimental PH and provide a rationale for further exploration of the use of IFNα and other immunotherpies in PH.

Supplementing exposure to hypoxia with a copper depleted diet does not exacerbate right ventricular remodeling in mice

Background

Pulmonary hypertension and subsequent right ventricular (RV) failure are associated with high morbidity and mortality. Prognosis is determined by occurrence of RV failure. Currently, adequate treatment for RV failure is lacking. Further research into the molecular basis for the development of RV failure as well as the development of better murine models of RV failure are therefore imperative. We hypothesize that adding a low-copper diet to chronic hypoxia in mice reinforces their individual effect and that the combination of mild pulmonary vascular remodeling and capillary rarefaction, induces RV failure.

Methods

Six week old mice were subjected to normoxia (N; 21% O₂) or hypoxia (H; 10% O₂) during a period of 8 weeks and received either a normal diet (Cu+) or a copper depleted diet (Cu-). Cardiac function was assessed by echocardiography and MRI analysis.

Results and Conclusion

Here, we characterized a mouse model of chronic hypoxia combined with a copper depleted diet and demonstrate that eight weeks of chronic hypoxia (10%) is sufficient to induce RV hypertrophy and subsequent RV failure. Addition of a low copper diet to hypoxia did not have any further deleterious effects on right ventricular remodeling.

Genetic deletion of toll-like receptor 4 on platelets attenuates experimental pulmonary hypertension

RATIONALE

Recent studies demonstrate a role for toll-like receptor 4 (TLR4) in the pathogenesis of pulmonary hypertension (PH); however, the cell types involved in mediating the effects of TLR4 remain unknown.

OBJECTIVES

The objective of this study was to determine the contribution of TLR4 expressed on nonparenchymal cells to the pathogenesis of PH.

METHODS AND RESULTS

TLR4 bone marrow chimeric mice revealed an equal contribution of TLR4 on nonparenchymal and parenchymal cells in the pathogenesis of PH as determined by measuring right ventricular (RV) systolic pressure and RV hypertrophy. However, the deletion of TLR4 from myeloid lineage cells had no effect on the development of PH because we found no difference in RV systolic pressure or RV hypertrophy in wild-type versus LysM-TLR4(-/-) mice. To explore the potential role of platelet TLR4 in the pathogenesis of PH, platelet-specific TLR4(-/-) mice were generated (PF4-TLR4(-/-) mice). TLR4(-/-) platelets from either global TLR4(-/-) or PF4-TLR4(-/-) mice were functional but failed to respond to lipopolysaccharide, demonstrating a lack of TLR4. PF4-TLR4(-/-) mice demonstrated significant protection from hypoxia-induced PH, including attenuated increases in RV systolic pressure and RV hypertrophy, decreased platelet activation, and less pulmonary vascular remodeling. The deletion of TLR4 from platelets attenuated serotonin release after chronic hypoxia, and lipopolysaccharide-stimulated platelets released serotonin and promoted pulmonary artery smooth muscle cell proliferation in a serotonin-dependent manner.

CONCLUSIONS

Our data demonstrate that TLR4 on platelets contributes to the pathogenesis of PH and further highlights the role of platelets in PH.

Relevant issues in the pathology and pathobiology of pulmonary hypertension

Knowledge of the pathobiology of pulmonary hypertension (PH) continues to accelerate. However, fundamental gaps remain in our understanding of the underlying pathological changes in pulmonary arteries and veins in the different forms of this syndrome. Although PH primarily affects the arteries, venous disease is increasingly recognized as an important entity. Moreover, prognosis in PH is determined largely by the status of the right ventricle, rather than the levels of pulmonary artery pressures. It is increasingly clear that although vasospasm plays a role, PH is an obstructive lung panvasculopathy. Disordered metabolism and mitochondrial structure, inflammation, and dysregulation of growth factors lead to a proliferative, apoptosis-resistant state. These abnormalities may be acquired, genetically mediated as a result of mutations in bone morphogenetic protein receptor-2 or activin-like kinase-1, or epigenetically inherited (as a result of epigenetic silencing of genes such as superoxide dismutase-2). There is a pressing need to better understand how the pathobiology leads to severe disease in some patients versus mild PH in others. Recent recognition of a potential role of acquired abnormalities of mitochondrial metabolism in the right ventricular myocytes and pulmonary vascular cells suggests new therapeutic approaches, diagnostic modalities, and biomarkers. Finally, dissection of the role of pulmonary inflammation in the initiation and promotion of PH has revealed a complex yet fascinating interplay with pulmonary vascular remodeling, promising to lead to novel therapeutics and diagnostics. Emerging concepts are also relevant to the pathobiology of PH, including a role for bone marrow and circulating progenitor cells and microribonucleic acids. Continued interest in the interface of the genetic basis of PH and cellular and molecular pathogenetic links should further expand our understanding of the disease.

A comprehensive review: the evolution of animal models in pulmonary hypertension research; are we there yet?

Pulmonary hypertension (PH) is a disorder that develops as a result of remodeling of the pulmonary vasculature and is characterized by narrowing/obliteration of small pulmonary arteries, leading to increased mean pulmonary artery pressure and pulmonary vascular resistance. Subsequently, PH increases the right ventricular afterload, which leads to right ventricular hypertrophy and eventually right ventricular failure. The pathophysiology of PH is not fully elucidated, and current treatments have only a modest impact on patient survival and quality of life. Thus, there is an urgent need for improved treatments or a cure. The use of animal models has contributed extensively to the current understanding of PH pathophysiology and the investigation of experimental treatments. However, PH in current animal models may not fully represent current clinical observations. For example, PH in animal models appears to be curable with many therapeutic interventions, and the severity of PH in animal models is also believed to correlate poorly with that observed in humans. In this review, we discuss a variety of animal models in PH research, some of their contributions to the field, their shortcomings, and how these have been addressed. We highlight the fact that the constant development and evolution of animal models will help us to more closely model the severity and heterogeneity of PH observed in humans.

An insight into the changes in human plasma proteome on adaptation to hypobaric hypoxia

Adaptation to hypobaric hypoxia is required by animals and human in several physiological and pathological situations. Hypobaric hypoxia is a pathophysiological condition triggering redox status disturbances of cell organization leading, via oxidative stress, to proteins, lipids, and DNA damage. Identifying the molecular variables playing key roles in this process would be of paramount importance to shed light on the mechanisms known to counteract the negative effects of oxygen lack. To obtain a molecular signature, changes in the plasma proteome were studied by using proteomic approach. To enrich the low-abundance proteins in human plasma, two highly abundant proteins, albumin and IgG, were first removed. By comparing the plasma proteins of high altitude natives with those of a normal control group, several proteins with a significant alteration were found. The up-regulated proteins were identified as vitamin D-binding protein, hemopexin, alpha-1-antitrypsin, haptoglobin β-chain, apolipoprotein A1, transthyretin and hemoglobin beta chain. The down-regulated proteins were transferrin, complement C3, serum amyloid, complement component 4A and plasma retinol binding protein. Among these proteins, the alterations of transthyretin and transferrin were further confirmed by ELISA and Western blotting analysis. Since all the up- and down- regulated proteins identified above are well-known inflammation inhibitors and play a positive anti-inflammatory role, these results show that there is some adaptive mechanism that sustains the inflammation balance in high altitude natives exposed to hypobaric hypoxia.

High mobility group box 1 contributes to the pathogenesis of experimental pulmonary hypertension via activation of Toll-like receptor 4

Survival rates for patients with pulmonary hypertension (PH) remain low, and our understanding of the mechanisms involved are incomplete. Here we show in a mouse model of chronic hypoxia (CH)-induced PH that the nuclear protein and damage-associate molecular pattern molecule (DAMP) high mobility group box 1 (HMGB1) contributes to PH via a Toll-like receptor 4 (TLR4)-dependent mechanism. We demonstrate extranuclear HMGB1 in pulmonary vascular lesions and increased serum HMGB1 in patients with idiopathic pulmonary arterial hypertension. The increase in circulating HMGB1 correlated with mean pulmonary artery pressure. In mice, we similarly detected the translocation and release of HMGB1 after exposure to CH. HMGB1-neutralizing antibody attenuated the development of CH-induced PH, as assessed by measurement of right ventricular systolic pressure, right ventricular hypertrophy, pulmonary vascular remodeling and endothelial activation and inflammation. Genetic deletion of the pattern recognition receptor TLR4, but not the receptor for advanced glycation end products, likewise attenuated CH-induced PH. Finally, daily treatment of mice with recombinant human HMGB1 exacerbated CH-induced PH in wild-type (WT) but not Tlr4(-/-) mice. These data demonstrate that HMGB1-mediated activation of TLR4 promotes experimental PH and identify HMGB1 and/or TLR4 as potential therapeutic targets for the treatment of PH.

Molecular pathogenesis of pulmonary arterial hypertension

Recent clinical and experimental studies are redefining the cellular and molecular bases of pulmonary arterial hypertension (PAH). The genetic abnormalities first identified in association with the idiopathic form of PAH--together with a vast increase in our understanding of cell signaling, cell transformation, and cell-cell interactions; gene expression; microRNA processing; and mitochondrial and ion channel function--have helped explain the abnormal response of vascular cells to injury. Experimental and clinical studies now converge on the intersection and interactions between a genetic predisposition involving the BMPR2 signaling pathway and an impaired metabolic and chronic inflammatory state in the vessel wall. These deranged processes culminate in an exuberant proliferative response that occludes the pulmonary arterial (PA) lumen and obliterates the most distal intraacinar vessels. Here, we describe emerging therapies based on preclinical studies that address these converging pathways.