Soluble receptor for advanced glycation end products (sRAGE) attenuates haemodynamic changes to chronic hypoxia in the mouse

Soluble receptors for advanced glycation end-products prevent unilateral ureteral obstruction-induced renal fibrosis

Introduction: The receptor for advanced glycation end products (RAGE) and its ligands, such as high-mobility group protein box 1 (HMGB1), play an important role in the accumulation of extracellular matrix in chronic kidney diseases with tubulointerstitial fibrosis. Blocking RAGE signaling with soluble RAGE (sRAGE) is a therapeutic candidate for renal fibrosis. Methods: NRK-52E cells were stimulated with or without HMGB1 and incubated with sRAGE in vitro. Sprague-Dawley rats were intraperitoneally treated with sRAGE after unilateral ureteral obstruction (UUO) operation in vivo. Results: HMBG1-stimulated NRK-52E cells showed increased fibronectin expression, type I collagen, α-smooth muscle actin, and connective tissue growth factor, which were attenuated by sRAGE. The mitogen-activated protein kinase (MAPK) pathway and nuclear translocation of nuclear factor kappa B (NF-κB) were enhanced in NRK-52E cells exposed to HMBG1, and sRAGE treatment alleviated the activation of the MAPK and NF-κB pathways. In the UUO rat models, sRAGE significantly ameliorated the increased renal fibronectin, type I collagen, and α-smooth muscle actin expressions. Masson's trichrome staining confirmed the anti-fibrotic effect of sRAGE in the UUO rat model. RAGE also significantly attenuated the activation of the MAPK pathway and NF-κB, as well as the increased number of infiltrated macrophages within the tubulointerstitium in the kidney of the UUO rat models. Conclusion: These findings suggest that RAGE plays a pivotal role in the pathogenesis of renal fibrosis and that its inhibition by sRAGE may be a potential therapeutic approach for renal fibrosis.

D-ribose and pathogenesis of Alzheimer's disease

It is estimated that the global prevalence of dementia will rise as high as 24 million and predicted to be double in every 20 years which is attributed to the fact that the ageing population is increasing and so more individuals are at risk of developing neurodegenerative diseases like Alzheimer's. Many scientists favored glycation of proteins such as tau, amyloid beta (Aβ) etc. as one of the important risk factor in Alzheimer's disease (AD). Since, D-ribose shows highest glycation ability among other sugars hence, produces advanced glycation end products (AGEs) rapidly. However, there are several other mechanisms suggested by researchers through which D-ribose may cause cognitive impairments. There is a concern related to diabetic patients since they also suffer from D-ribose metabolism, may be more prone to AD risk. Thus, it is imperative that the pathogenesis and the pathways involved in AD progression are explored in the light of ribosylation and AGEs formation for identifying suitable diagnostics marker for early diagnosis or finding promising therapeutic outcomes.

Expression of soluble receptor for advanced glycation end products is associated with disease severity in congenital diaphragmatic hernia

Pulmonary hypertension (PH) and lung hypoplasia are major contributors to morbidity and mortality in newborns with congenital diaphragmatic hernia (CDH). The soluble receptor for advanced glycation end products (sRAGE) is a marker of endothelial function and might be associated with disease severity in CDH newborns. In a cohort of 30 CDH newborns and 20 healthy control newborns, sRAGE concentration was measured at birth and at 6 h, 12 h, 24 h, 48 h, and 7-10 days. In healthy newborns, sRAGE was significantly higher at birth and at 48 h compared with CDH newborns (both P < 0.001). Among CDH newborns, sRAGE was significantly lower at birth (P = 0.033) and at 7-10 days (P = 0.035) in patients receiving extracorporeal membrane oxygenation (ECMO) compared with patients not receiving ECMO. In contrast, CDH newborns receiving ECMO had significantly higher values at 6 h (P = 0.001), 12 h (P = 0.004), and 48 h (0.032). Additionally, sRAGE correlated significantly with PH severity, intensity and duration of mechanical ventilation, and prenatally assessed markers of CDH severity (lung size, liver herniation). The probability to receive ECMO therapy was five times higher in CDH newborns with sRAGE concentrations below the calculated cutoff of 650 pg/ml at birth (P = 0.002) and nine times higher in CDH newborns with sRAGE concentrations above the cutoff of 3,500 pg/ml at 6 h (P = 0.001). These findings suggest a potential involvement of sRAGE in the pathophysiology of CDH and may act as a therapeutic target in future treatment approaches.

The Effects of Acute Hypoxia on Tissue Oxygenation and Circulating Alarmins in Healthy Adults

The binding of high-mobility group box-1 (HMGB-1) to the membrane receptor for advanced glycation end-products (mRAGE) is a key early mediator of non-infectious inflammation and its triggers include ischaemia/hypoxia. The effects of acute hypoxia on soluble RAGE (sRAGE) are unknown. Fourteen healthy adults (50 % women; 26.6±3.8 years) were assessed at baseline normoxia (T0), followed by four time-points (T90, 95, 100 and 180 min) over three hours of continuous normobaric hypoxia (NH, 4,450 m equivalent) and again 60 min after return to normoxia (T240). A 5-min exercise step test was performed during NH at T90. Plasma concentrations of HMGB-1, sRAGE VCAM-1, ICAM-1, VEGF IL-8 and IL-13 were measured using venous blood. Arterial and tissue oxygen saturations were measured using pulse oximetry (SpO2) and near-infrared spectroscopy (StO2), respectively. NH led to a significant reduction in SpO2, StO2, sRAGE and VEGF, which was compounded by exercise, before increasing to baseline values with normoxic restoration (T240). NH-exercise led to a paired increase in HMGB-1. sRAGE inversely correlated with HMGB-1 (r=-0.32; p=0.006), heart rate (r=-0.43; p=0.004) but was not linked to SpO2 or StO2. In conclusion, short-term NH leads to a fall in sRAGE and VEGF concentrations with a transient rise post NH-exercise in HMGB-1.

RAGE-mediated extracellular matrix proteins accumulation exacerbates HySu-induced pulmonary hypertension

Aims

Extracellular matrix (ECM) proteins accumulation contributes to the progression of pulmonary arterial hypertension (PAH), a rare and fatal cardiovascular condition defined by high pulmonary arterial pressure, whether primary, idiopathic, or secondary to other causes. The receptor for advanced glycation end products (RAGE) is constitutively expressed in the lungs and plays an important role in ECM deposition. Nonetheless, the mechanisms by which RAGE mediates ECM deposition/formation in pulmonary arteries and its roles in PAH progression remain unclear.

Methods and results

Expression of RAGE and its activating ligands, S100/calgranulins and high mobility group box 1 (HMGB1), were increased in both human and mouse pulmonary arterial smooth muscle cells (PASMCs) under hypoxic conditions and were also strikingly upregulated in pulmonary arteries in hypoxia plus SU5416 (HySu)-induced PAH in mice. RAGE deletion alleviated pulmonary arterial pressure and restrained extracellular matrix accumulation in pulmonary arteries in HySu-induced PAH murine model. Moreover, blocking RAGE activity with a neutralizing antibody in human PASMCs, or RAGE deficiency in mouse PASMCs exposed to hypoxia, suppressed the expression of fibrotic proteins by reducing TGF-β1 expression. RAGE reconstitution in deficient mouse PASMCs restored hypoxia-stimulated TGF-β1 production via ERK1/2 and p38 MAPK pathway activation and subsequently increased ECM protein expression. Interestingly, HMGB1 acting on RAGE, not toll-like receptor 4 (TLR4), induced ECM deposition in PASMCs. Finally, in both idiopathic PAH patients and HySu-induced PAH mice, soluble RAGE (sRAGE) levels in serum were significantly elevated compared to those in controls.

Conclusions

Activation of RAGE facilitates the development of hypoxia-induced pulmonary hypertension by increase of ECM deposition in pulmonary arteries. Our results indicate that sRAGE may be a potential biomarker for PAH diagnosis and disease severity, and that RAGE may be a promising target for PAH treatment.

All the "RAGE" in lung disease: The receptor for advanced glycation endproducts (RAGE) is a major mediator of pulmonary inflammatory responses

The receptor for advanced glycation endproducts (RAGE) is a pro-inflammatory pattern recognition receptor (PRR) that has been implicated in the pathogenesis of numerous inflammatory diseases. It was discovered in 1992 on endothelial cells and was named for its ability to bind advanced glycation endproducts and promote vascular inflammation in the vessels of patients with diabetes. Further studies revealed that RAGE is most highly expressed in lung tissue and spurred numerous explorations into RAGE's role in the lung. These studies have found that RAGE is an important mediator in allergic airway inflammation (AAI) and asthma, pulmonary fibrosis, lung cancer, chronic obstructive pulmonary disease (COPD), acute lung injury, pneumonia, cystic fibrosis, and bronchopulmonary dysplasia. RAGE has not yet been targeted in the lungs of paediatric or adult clinical populations, but the development of new ways to inhibit RAGE is setting the stage for the emergence of novel therapeutic agents for patients suffering from these pulmonary conditions.

Soluble Receptor for Advanced Glycation End Product Ameliorates Chronic Intermittent Hypoxia Induced Renal Injury, Inflammation, and Apoptosis via P38/JNK Signaling Pathways

Obstructive sleep apnea (OSA) associated chronic kidney disease is mainly caused by chronic intermittent hypoxia (CIH) triggered tissue damage. Receptor for advanced glycation end product (RAGE) and its ligand high mobility group box 1 (HMGB1) are expressed on renal cells and mediate inflammatory responses in OSA-related diseases. To determine their roles in CIH-induced renal injury, soluble RAGE (sRAGE), the RAGE neutralizing antibody, was intravenously administered in a CIH model. We also evaluated the effect of sRAGE on inflammation and apoptosis. Rats were divided into four groups: (1) normal air (NA), (2) CIH, (3) CIH+sRAGE, and (4) NA+sRAGE. Our results showed that CIH accelerated renal histological injury and upregulated RAGE-HMGB1 levels involving inflammatory (NF-κB, TNF-α, and IL-6), apoptotic (Bcl-2/Bax), and mitogen-activated protein kinases (phosphorylation of P38, ERK, and JNK) signal transduction pathways, which were abolished by sRAGE but p-ERK. Furthermore, sRAGE ameliorated renal dysfunction by attenuating tubular endothelial apoptosis determined by immunofluorescence staining of CD31 and TUNEL. These findings suggested that RAGE-HMGB1 activated chronic inflammatory transduction cascades that contributed to the pathogenesis of the CIH-induced renal injury. Inhibition of RAGE ligand interaction by sRAGE provided a therapeutic potential for CIH-induced renal injury, inflammation, and apoptosis through P38 and JNK pathways.

Effect of the sphingosine kinase 1 selective inhibitor, PF-543 on arterial and cardiac remodelling in a hypoxic model of pulmonary arterial hypertension

Recent studies have demonstrated that the expression of sphingosine kinase 1, the enzyme that catalyses formation of the bioactive lipid, sphingosine 1-phosphate, is increased in lungs from patients with pulmonary arterial hypertension. In addition, Sk1^−/− mice are protected from hypoxic-induced pulmonary arterial hypertension. Therefore, we assessed the effect of the sphingosine kinase 1 selective inhibitor, PF-543 and a sphingosine kinase 1/ceramide synthase inhibitor, RB-005 on pulmonary and cardiac remodelling in a mouse hypoxic model of pulmonary arterial hypertension. Administration of the potent sphingosine kinase 1 inhibitor, PF-543 in a mouse hypoxic model of pulmonary hypertension had no effect on vascular remodelling but reduced right ventricular hypertrophy. The latter was associated with a significant reduction in cardiomyocyte death. The protection involves a reduction in the expression of p53 (that promotes cardiomyocyte death) and an increase in the expression of anti-oxidant nuclear factor (erythroid-derived 2)-like 2 (Nrf-2). In contrast, RB-005 lacked effects on right ventricular hypertrophy, suggesting that sphingosine kinase 1 inhibition might be nullified by concurrent inhibition of ceramide synthase. Therefore, our findings with PF-543 suggest an important role for sphingosine kinase 1 in the development of hypertrophy in pulmonary arterial hypertension.

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PF-543, a sphingosine kinase 1 inhibitor reduces cardiac hypertrophy in a mouse pulmonary arterial hypertension (PAH) model

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This results in reduced cardiomyocyte apoptosis

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PF-543 reduces PARP processing and p53 expression and increases Nrf-2 expression in the right ventricle of mice with PAH

Plasma Levels of Receptor for Advanced Glycation End-Products and High-Mobility Group Box 1 in Patients With Pulmonary Hypertension

An increase of pulmonary artery pressure in patients with pulmonary hypertension (PH) results in right ventricular failure and ultimately death. High-mobility group box 1 (HMGB1), a nuclear protein, acts as a pro-inflammatory cytokine by activating receptor for advanced glycation end-products (RAGE) in the extracellular environment. The purpose of this study was to examine the clinical significance of circulating levels of HMGB1 and RAGE in patients with PH. Plasma levels of HMGB1 and soluble RAGE were measured in 27 patients with PH (14 with pulmonary arterial hypertension [PAH], 13 with chronic thromboembolic pulmonary hypertension [CTEPH]) and 30 normal subjects as control. There was no difference in the plasma levels of HMGB1 between the PH patients and the control subjects. However, plasma levels of soluble RAGE were significantly higher in the patients with PH than in the controls (P < 0.001). Plasma soluble RAGE levels were higher in PAH (P < 0.001) and CTEPH (P < 0.0001) than in the controls. In addition, there was a statistically significant positive correlation between pulmonary artery pressure and plasma levels of soluble RAGE (r = 0.403, P < 0.0001). In the CTEPH patients, soluble RAGE levels were reduced after balloon pulmonary angioplasty (P < 0.001). Plasma levels of soluble RAGE, but not HMGB1, might be a novel marker that reflects the pathological condition in patients with PH.

The Succinate Receptor GPR91 Is Involved in Pressure Overload-Induced Ventricular Hypertrophy

Background

Pulmonary arterial hypertension is characterized by increased pressure overload that leads to right ventricular hypertrophy (RVH). GPR91 is a formerly orphan G-protein-coupled receptor (GPCR) that has been characterized as a receptor for succinate; however, its role in RVH remains unknown.

Methods and Results

We investigated the role of succinate-GPR91 signaling in a pulmonary arterial banding (PAB) model of RVH induced by pressure overload in SD rats. GPR91 was shown to be located in cardiomyocytes. In the sham and PAB rats, succinate treatment further aggravated RVH, up-regulated RVH-associated genes and increased p-Akt/t-Akt levels in vivo. In vitro, succinate treatment up-regulated the levels of the hypertrophic gene marker anp and p-Akt/t-Akt in cardiomyocytes. All these effects were inhibited by the PI3K antagonist wortmannin both in vivo and in vitro. Finally, we noted that the GPR91-PI3K/Akt axis was also up-regulated compared to that in human RVH.

Conclusions

Our findings indicate that succinate-GPR91 signaling may be involved in RVH via PI3K/Akt signaling in vivo and in vitro. Therefore, GPR91 may be a novel therapeutic target for treating pressure overload-induced RVH.

The Role of HMGB1 in Cardiovascular Biology: Danger Signals

SIGNIFICANCE

Cardiovascular disease (CVD) is the leading cause of mortality worldwide. Accumulating evidence shows that dysregulated immune response contributes to several types of CVDs such as atherosclerosis and pulmonary hypertension (PH). Vascular intimal impairment and low-density lipoprotein oxidation trigger a complex network of innate immune responses and sterile inflammation.

RECENT ADVANCES

High-mobility group box 1 (HMGB1), a nuclear DNA-binding protein, was recently discovered to function as a damage-associated molecular pattern molecule (DAMP) that initiates the innate immune responses. These findings lead to the understanding that HMGB1 plays a critical role in the inflammatory response in the pathogenesis of CVD.

CRITICAL ISSUES

In this review, we highlight the role of extracellular HMGB1 as a proinflammatory mediator as well as a DAMP in coronary artery disease, cerebral artery disease, peripheral artery disease, and PH.

FUTURE DIRECTIONS

A key focus for future researches on HMGB1 location, structure, modification, and signaling will reveal HMGB1's multiple functions and discover a targeted therapy that can eliminate HMGB1-mediated inflammation without interfering with adaptive immune responses.

Role of RAGE in Alzheimer's Disease

Receptor for advanced glycation end products (RAGE) is a receptor of the immunoglobulin super family that plays various important roles under physiological and pathological conditions. Compelling evidence suggests that RAGE acts as both an inflammatory intermediary and a critical inducer of oxidative stress, underlying RAGE-induced Alzheimer-like pathophysiological changes that drive the process of Alzheimer's disease (AD). A critical role of RAGE in AD includes beta-amyloid (Aβ) production and accumulation, the formation of neurofibrillary tangles, failure of synaptic transmission, and neuronal degeneration. The steady-state level of Aβ depends on the balance between production and clearance. RAGE plays an important role in the Aβ clearance. RAGE acts as an important transporter via regulating influx of circulating Aβ into brain, whereas the efflux of brain-derived Aβ into the circulation via BBB is implemented by LRP1. RAGE could be an important contributor to Aβ generation via enhancing the activity of β- and/or γ-secretases and activating inflammatory response and oxidative stress. However, sRAGE-Aβ interactions could inhibit Aβ neurotoxicity and promote Aβ clearance from brain. Meanwhile, RAGE could be a promoting factor for the synaptic dysfunction and neuronal circuit dysfunction which are both the material structure of cognition, and the physiological and pathological basis of cognition. In addition, RAGE could be a trigger for the pathogenesis of Aβ and tau hyper-phosphorylation which both participate in the process of cognitive impairment. Preclinical and clinical studies have supported that RAGE inhibitors could be useful in the treatment of AD. Thus, an effective measure to inhibit RAGE may be a novel drug target in AD.

Increased pulmonary vascular expression of receptor for advanced glycation end products (RAGE) in experimental congenital diaphragmatic hernia

AIM OF THE STUDY

Persistent pulmonary hypertension (PH) continues to be a major cause of high mortality in congenital diaphragmatic hernia (CDH). The receptor for advanced glycation end products (RAGE) is a member of the immunoglobulin protein family. Recently, RAGE has been implicated in mediating pulmonary arterial smooth muscle cell proliferation and vascular remodeling in experimental PH. RAGE has been reported to be highly upregulated in lung tissue of patients with severe PH. We designed this study to investigate the hypothesis that RAGE expression is increased in nitrofen-induced CDH.

METHODS

Pregnant rats were exposed to nitrofen or vehicle on D9. Fetuses were sacrificed on D21 and divided into nitrofen (n=16) and control group (n=16). Quantitative real-time polymerase chain reaction, Western blotting, and confocal immunofluorescence were performed.

MAIN RESULTS

Pulmonary RAGE gene expression levels were significantly increased in nitrofen-induced CDH compared to controls (p<0.003). Western blotting and confocal microscopy revealed increased pulmonary RAGE protein expression in CDH compared to controls.

CONCLUSION

This study provides striking evidence of increased gene and protein expression of RAGE in the pulmonary vasculature of nitrofen-induced CDH, suggesting that increased expression of RAGE may play a role in the pathogenesis of PH in nitrofen-induced CDH.

Absence of the calcium-binding protein, S100A1, confers pulmonary hypertension in mice associated with endothelial dysfunction and apoptosis

AIMS

S100A1, a 10-kDa, Ca(2+)-binding protein, is expressed in endothelial cells (ECs) and binds eNOS. Its absence is associated with impaired production of nitric oxide (NO) and mild systemic hypertension. As endothelial dysfunction contributes to clinical and experimental pulmonary hypertension (PH), we investigated the impact of deleting S100A1 in mice, on pulmonary haemodynamics, endothelial function, NO production, associated signalling pathways, and apoptosis.

METHODS AND RESULTS

Compared with wild-type (WT), S100A1-knock-out mice (KO) exhibited increased right ventricular (RV) weight/body weight ratio and elevated RV pressure in the absence of altered left ventricular filling pressures, accompanied by increase in wall thickness of muscularized pulmonary arteries and a reduction in microvascular perfusion. In isolated lung preparations, KO revealed reduced basal NO, blunted dose-responsiveness to acetylcholine, and augmented basal and angiotensin (AII)-induced pulmonary vascular resistance (R₀) compared with WT. Pre-treatment of KO lungs with S100A1 attenuated the AII-induced increase in pulmonary arterial pressure and R₀. S100A1-induced phosphorylation of eNOS, Akt, and ERK1/2 is attenuated in pulmonary EC of KO compared with WT. Basal and TNF-α-induced EC apoptosis is greater in KO vs. WT, and cell survival is enhanced by S100A1 treatment.

CONCLUSION

Our data demonstrate that the absence of S100A1 results in PH by disruption of its normal capacity to (i) enhance pulmonary EC function by induction of eNOS activity and NO levels via Akt/ERK1/2 pathways and (ii) promote EC survival. The ability of exogenously administered S100A1 to rescue this phenotype makes it an attractive therapeutic target in the treatment of PH.

Local and systemic RAGE axis changes in pulmonary hypertension: CTEPH and iPAH

OBJECTIVE

The molecular determinants of chronic thromboembolic pulmonary hypertension (CTEPH) and idiopathic pulmonary arterial hypertension (iPAH) remain poorly understood. The receptor for advanced glycation endproducts (RAGE) and its ligands: HMGB1 and S100A9 are involved in inflammatory disorders. We sought to investigate the role of the RAGE axis in patients with CTEPH undergoing pulmonary endarterectomy (PEA), iPAH undergoing lung transplantation (LuTX). The high pulmonary vascular resistance in CTEPH/iPAH results in pressure overload of the right ventricle. We compared sRAGE measurements to that of patients with aortic valve stenosis (AVS) - pressure overload of the left ventricle.

METHODS

We enrolled patients with CTEPH(26), iPAH(15), AVS(15) and volunteers(33). Immunohistochemistry with antibodies to RAGE and HMGB1 was performed on PEA specimens and lung tissues. We employed enzyme-linked immunosorbent assays to determine the concentrations of sRAGE, esRAGE, HMGB1 and S100A9 in serum of volunteers and patients with CTEPH, iPAH, AVS before and after PEA, LuTX and aortic valve replacement (AVR).

RESULTS

In endarterectomised tissues from patients with CTEPH RAGE and HMGB1 were identified in myofibroblasts (α-SMA+vimentin+CD34-), recanalizing vessel-like structures of distal myofibrotic tissues and endothelium of neointima. RAGE was differentially expressed in prototypical Heath Edwards lesions in iPAH. We found significantly increased serum concentrations of sRAGE, esRAGE and HMGB1 in CTEPH. In iPAH, sRAGE and esRAGE were significantly higher than in controls. Serum concentrations of sRAGE were significantly elevated in iPAH(p<0.001) and CTEPH(p = 0.001) compared to AVS. Serum sRAGE was significantly higher in iPAH compared to CTEPH(p = 0.042) and significantly reduced in AVS compared to controls(p = 0.001). There were no significant differences in sRAGE serum concentrations before and after surgical therapy for CTEPH, iPAH or AVS.

CONCLUSIONS

Our data suggest a role for the RAGE pathway in the pathophysiology of CTEPH and iPAH. PEA improves the local control of disease but may not influence the systemic inflammatory mechanisms in CTEPH patients through the RAGE pathway.

Elevation of soluble form of receptor for advanced glycation end products (sRAGE) in recurrent pregnancy losses (RPL): possible participation of RAGE in RPL

OBJECTIVE

To determine whether the soluble receptor for advanced glycation end products (sRAGE) and immune inflammatory markers are associated with recurrent pregnancy losses (RPL).

DESIGN

Prospective case-control study.

SETTING

University clinic.

PATIENT(S)

A total of 93 women (age 35.8±4.6 years) were enrolled including 63 women with three or more recurrent pregnancy losses (RPL), and age-matched fertile controls with a history of at least one live birth and no history of pregnancy losses (n=30).

INTERVENTION(S)

Peripheral blood collection.

MAIN OUTCOME MEASURE(S)

Assessment of anthropometric, metabolic, and inflammatory immune variables.

RESULT(S)

Levels of sRAGE were statistically significantly higher in RPL patients than in control patients (1,528.9±704.5 vs. 1,149.9±447.4 pg/mL). In the multivariate analysis, the levels of insulin, plasminogen activator inhibitor-1, the resistance index of the uterine radial artery, and the ratio of tumor necrosis factor-α/interleukin-10 producing T helper cells were statistically significantly associated with the serum sRAGE level.

CONCLUSION(S)

Elevated levels of serum sRAGE are associated with RPL. The soluble receptor for advanced glycation end products might contribute to RPL by reducing uterine blood flow and subsequently causing ischemia in the fetus via inflammatory and thrombotic reactions.