Growth Arrest Specific-6 and Axl Coordinate Inflammation and Hypertension

Functions of TAM Receptors and Ligands Protein S and Gas6 in Atherosclerosis and Cardiovascular Disease

Atherosclerosis and cardiovascular disease are associated with high morbidity and mortality in industrialized nations. The Tyro3, Axl, and Mer (TAM) family of receptor tyrosine kinases is involved in the amplification or resolution of atherosclerosis pathology and other cardiovascular pathology. The ligands of these receptors, Protein S (PS) and growth arrest specific protein 6 (Gas6), are essential for TAM receptor functions in the amplification and resolution of atherosclerosis. The Axl-Gas6 interaction has various effects on cardiovascular disease. Mer and PS dampen inflammation, thereby protecting against atherosclerosis progression. Tyro3, the least studied TAM receptor in cardiovascular disease, appears to protect against fibrosis in post-myocardial infarction injury. Ultimately, PS, Gas6, and TAM receptors present an exciting avenue of potential therapeutic targets against inflammation associated with atherosclerosis and cardiovascular disease.

Screening and identification of key biomarkers associated with endometriosis using bioinformatics and next-generation sequencing data analysis

Background

Endometriosis is a common cause of endometrial-type mucosa outside the uterine cavity with symptoms such as painful periods, chronic pelvic pain, pain with intercourse and infertility. However, the early diagnosis of endometriosis is still restricted. The purpose of this investigation is to identify and validate the key biomarkers of endometriosis.

Methods

Next-generation sequencing dataset GSE243039 was obtained from the Gene Expression Omnibus database, and differentially expressed genes (DEGs) between endometriosis and normal control samples were identified. After screening of DEGs, gene ontology (GO) and REACTOME pathway enrichment analyses were performed. Furthermore, a protein–protein interaction (PPI) network was constructed and modules were analyzed using the Human Integrated Protein–Protein Interaction rEference database and Cytoscape software, and hub genes were identified. Subsequently, a network between miRNAs and hub genes, and network between TFs and hub genes were constructed using the miRNet and NetworkAnalyst tool, and possible key miRNAs and TFs were predicted. Finally, receiver operating characteristic curve analysis was used to validate the hub genes.

Results

A total of 958 DEGs, including 479 upregulated genes and 479 downregulated genes, were screened between endometriosis and normal control samples. GO and REACTOME pathway enrichment analyses of the 958 DEGs showed that they were mainly involved in multicellular organismal process, developmental process, signaling by GPCR and muscle contraction. Further analysis of the PPI network and modules identified 10 hub genes, including vcam1, snca, prkcb, adrb2, foxq1, mdfi, actbl2, prkd1, dapk1 and actc1. Possible target miRNAs, including hsa-mir-3143 and hsa-mir-2110, and target TFs, including tcf3 (transcription factor 3) and clock (clock circadian regulator), were predicted by constructing a miRNA-hub gene regulatory network and TF-hub gene regulatory network.

Conclusions

This investigation used bioinformatics techniques to explore the potential and novel biomarkers. These biomarkers might provide new ideas and methods for the early diagnosis, treatment and monitoring of endometriosis.

Posttranslationally modified self-peptides promote hypertension in mouse models

Posttranslational modifications can enhance immunogenicity of self-proteins. In several conditions, including hypertension, systemic lupus erythematosus, and heart failure, isolevuglandins (IsoLGs) are formed by lipid peroxidation and covalently bond with protein lysine residues. Here, we show that the murine class I major histocompatibility complex (MHC-I) variant H-2Db uniquely presents isoLG-modified peptides and developed a computational pipeline that identifies structural features for MHC-I accommodation of such peptides. We identified isoLG-adducted peptides from renal proteins, including sodium glucose transporter 2, cadherin 16, Kelch domain-containing protein 7A, and solute carrier family 23, that are recognized by CD8+ T cells in tissues of hypertensive mice, induce T cell proliferation in vitro, and prime hypertension after adoptive transfer. Finally, we find patterns of isoLG-adducted antigen restriction in class I human leukocyte antigens that are similar to those in murine analogs. Thus, we have used a combined computational and experimental approach to define likely antigenic peptides in hypertension.

Immunological insights into hypertension: unraveling triggers and potential therapeutic avenues

Hypertension remains the leading cause of morbidity and mortality worldwide. Despite its prevalence, the development of novel antihypertensive therapies has only recently accelerated, with novel agents not yet commercialized, leaving a substantial proportion of individuals resistant to existing treatments. The intricate pathophysiology of hypertension is now understood to involve chronic low-grade inflammation, which places the immune system in the spotlight as a potential target for new therapeutics. This review explores the factors that initiate and sustain an immune response in hypertension, offering insights into potential targets for new treatments. Several factors contribute to immune activation in hypertension, including diet and damage-associated molecular pattern (DAMP) generation. Diets rich in fat or sodium can promote inflammation by inducing intestinal barrier dysfunction and triggering salt-sensitive receptors in T cells and dendritic cells. DAMPs, such as extracellular adenosine triphosphate and heat-shock protein 70, are released during episodes of increased blood pressure, contributing to immune cell activation and inflammation. Unconventional innate-like γδ T cells contribute to initiating and maintaining an immune response through their potential involvement in antigen presentation and regulating cytokine-mediated responses. Immunologic memory, sustained through the formation of effector memory T cells after exposure to hypertensive insults, likely contributes to maintaining an immune response in hypertension. When exposed to hypertensive insults, these memory cells are rapidly activated and contribute to elevated blood pressure and end-organ damage. Evidence from human hypertension, although limited, supports the relevance of distinct immune pathways in hypertension, and highlights the potential of targeted immune interventions in human hypertension. Diet and acute bouts of high blood pressure result in the release of dietary triggers, neoantigens, and damage-associated molecular patterns (DAMPs), which promote immune system activation. Elements such as lipopolysaccharides (LPS), sodium, heat-shock protein (HSP)70, extracellular adenosine triphosphate (eATP), and growth arrest-specific 6 (GAS6) promote activation of innate immune cells such as dendritic cells (DCs) and monocytes (Mo) through their respective receptors (toll-like receptor [TLR]4, amiloride-sensitive epithelial sodium channel [ENaC], TLR2/4, P2X7 receptor [P2RX7], and Axl) leading to costimulatory molecule expression and interleukin (IL)-1β and IL-23 production. The neoantigens HSP70 and isolevuglandins (IsoLGs) are presented to T cells by DCs and possibly γδ T cells, triggering T cell activation, IL-17 and interferon (IFN)-γ production, and the formation of T effector memory (TEM) cells in the kidney, perivascular adipose tissue, bone marrow, and spleen. Exposure of TEM cells to their cognate antigen or previous activating stimuli causes these cells rapid expansion and activation. Cumulatively, this inflammatory state contributes to hypertension and end-organ damage. The figure was created using images from smart.servier.com and is licensed under a Creative Commons Attribution 4.0 license (CC BY 4.0).

Immune mechanisms in the pathophysiology of hypertension

Hypertension is a leading risk factor for morbidity and mortality worldwide. Despite current anti-hypertensive therapies, most individuals with hypertension fail to achieve adequate blood pressure control. Moreover, even with adequate control, a residual risk of cardiovascular events and associated organ damage remains. These findings suggest that current treatment modalities are not addressing a key element of the underlying pathology. Emerging evidence implicates immune cells as key mediators in the development and progression of hypertension. In this Review, we discuss our current understanding of the diverse roles of innate and adaptive immune cells in hypertension, highlighting key findings from human and rodent studies. We explore mechanisms by which these immune cells promote hypertensive pathophysiology, shedding light on their multifaceted involvement. In addition, we highlight advances in our understanding of autoimmunity, HIV and immune checkpoints that provide valuable insight into mechanisms of chronic and dysregulated inflammation in hypertension.

Immune Mechanisms in Hypertension

It is now apparent that immune mediators including complement, cytokines, and cells of the innate and adaptive immune system contribute not only to blood pressure elevation but also to the target organ damage that occurs in response to stimuli like high salt, aldosterone, angiotensin II, and sympathetic outflow. Alterations of vascular hemodynamic factors, including microvascular pulsatility and shear forces, lead to vascular release of mediators that affect myeloid cells to become potent antigen-presenting cells and promote T-cell activation. Research in the past 2 decades has defined specific biochemical and molecular pathways that are engaged by these stimuli and an emerging paradigm is these not only lead to immune activation, but that products of immune cells, including cytokines, reactive oxygen species, and metalloproteinases act on target cells to further raise blood pressure in a feed-forward fashion. In this review, we will discuss these molecular and pathophysiological events and discuss clinical interventions that might prove effective in quelling this inflammatory process in hypertension and related cardiovascular diseases.

Innovative assessment of lipid-induced oxidative stress and inflammation in harvested human endothelial cells

Studying acute changes in vascular endothelial cells in humans is challenging. We studied ten African American women and used the J-wire technique to isolate vein endothelial cells before and after a four-hour lipid and heparin infusion. Dynamic changes in lipid-induced oxidative stress and inflammatory markers were measured with fluorescence-activated cell sorting. We used the surface markers CD31 and CD144 to identify human endothelial cells. Peripheral blood mononuclear cells isolated from blood were used as a negative control. The participants received galantamine (16 mg/day) for 3 months. We previously demonstrated that galantamine treatment effectively suppresses lipid-induced oxidative stress and inflammation. In this study, we infused lipids to evaluate its potential to increase the activation of endothelial cells, as assessed by the levels of CD54+ endothelial cells and expression of Growth arrest-specific 6 compared to the baseline sample. Further, we aimed to investigate whether lipid infusion led to increased expression of the oxidative stress markers IsoLGs and nitrotyrosine in endothelial cells. This approach will expedite the in vivo identification of novel pathways linked with endothelial cell dysfunction induced by oxidative stress and inflammatory cytokines. This study describes an innovative method to harvest and study human endothelial cells and demonstrates the dynamic changes in oxidative stress and inflammatory markers release induced by lipid infusion.

NETosis Drives Blood Pressure Elevation and Vascular Dysfunction in Hypertension

BACKGROUND

Neutrophil extracellular traps (NETs) are composed of DNA, enzymes, and citrullinated histones that are expelled by neutrophils in the process of NETosis. NETs accumulate in the aorta and kidneys in hypertension. PAD4 (protein-arginine deiminase-4) is a calcium-dependent enzyme that is essential for NETosis. TRPV4 (transient receptor potential cation channel subfamily V member 4) is a mechanosensitive calcium channel expressed in neutrophils. Thus, we hypothesize that NETosis contributes to hypertension via NET-mediated endothelial cell (EC) dysfunction.

METHODS

NETosis-deficient Padi4-/- mice were treated with Ang II (angiotensin II). Blood pressure was measured by radiotelemetry, and vascular reactivity was measured with wire myography. Neutrophils were cultured with or without ECs and exposed to normotensive or hypertensive uniaxial stretch. NETosis was measured by flow cytometry. ECs were treated with citrullinated histone H3, and gene expression was measured by quantitative reverse transcription PCR. Aortic rings were incubated with citrullinated histone H3, and wire myography was performed to evaluate EC function. Neutrophils were treated with the TRPV4 agonist GSK1016790A. Calcium influx was measured using Fluo-4 dye, and NETosis was measured by immunofluorescence.

RESULTS

Padi4-/- mice exhibited attenuated hypertension, reduced aortic inflammation, and improved EC-dependent vascular relaxation in response to Ang II. Coculture of neutrophils with ECs and exposure to hypertensive uniaxial stretch increased NETosis and accumulation of neutrophil citrullinated histone H3. Histone H3 and citrullinated histone H3 exposure attenuates EC-dependent vascular relaxation. Treatment of neutrophils with the TRPV4 agonist GSK1016790A increases intracellular calcium and NETosis.

CONCLUSIONS

These observations identify a role of NETosis in the pathogenesis of hypertension. Moreover, they define an important role of EC stretch and TRPV4 as initiators of NETosis. Finally, they define a role of citrullinated histones as drivers of EC dysfunction in hypertension.

Immunoproteasomal Processing of IsoLG-Adducted Proteins Is Essential for Hypertension

BACKGROUND

Hypertension is characterized by CD8+ (cluster differentiation 8) T cell activation and infiltration into peripheral tissues. CD8+ T cell activation requires proteasomal processing of antigenic proteins. It has become clear that isoLG (isolevuglandin)-adduced peptides are antigenic in hypertension; however, IsoLGs inhibit the constitutive proteasome. We hypothesized that immunoproteasomal processing of isoLG-adducts is essential for CD8+ T cell activation and inflammation in hypertension.

METHODS

IsoLG adduct processing was studied in murine dendritic cells (DCs), endothelial cells (ECs), and B8 fibroblasts. The role of the proteasome and the immunoproteasome in Ang II (angiotensin II)-induced hypertension was studied in C57BL/6 mice treated with bortezomib or the immunoproteasome inhibitor PR-957 and by studying mice lacking 3 critical immunoproteasome subunits (triple knockout mouse). We also examined hypertension in mice lacking the critical immunoproteasome subunit LMP7 (large multifunctional peptidase 7) specifically in either DCs or ECs.

RESULTS

We found that oxidant stress increases the presence of isoLG adducts within MHC-I (class I major histocompatibility complex), and immunoproteasome overexpression augments this. Pharmacological or genetic inhibition of the immunoproteasome attenuated hypertension and tissue inflammation. Conditional deletion of LMP7 in either DCs or ECs attenuated hypertension and vascular inflammation. Finally, we defined the role of the innate immune receptors STING (stimulator of interferon genes) and TLR7/8 (toll-like receptor 7/8) as drivers of LMP7 expression in ECs.

CONCLUSIONS

These studies define a previously unknown role of the immunoproteasome in DCs and ECs in CD8+ T cell activation. The immunoproteasome in DCs and ECs is critical for isoLG-adduct presentation to CD8+ T cells, and in the endothelium, this guides homing and infiltration of T cells to specific tissues.

GAS6 attenuates sepsis-induced cardiac dysfunction through NLRP3 inflammasome-dependent mechanism

Sepsis is a major health threat and often results in heart failure. Growth arrest-specific gene 6 (GAS6), a 75-kDa vitamin K-dependent protein, participates in immune regulation and inflammation through binding to AXL (the TAM receptor family). This study was designed to examine the myocardial regulatory role of GAS6 in sepsis. Serum GAS6 levels were increased in septic patients and mice while myocardial GAS6 levels were decreased in septic mice. Single-cell RNA sequencing further revealed a decline in GAS6 levels of nearly all cell clusters including cardiomyocytes. GAS6 overexpression via adeno-associated virus 9 (AAV9) overtly improved cardiac dysfunction in cecum ligation and puncture (CLP)-challenged mice, along with alleviated mitochondrial injury, endoplasmic reticulum stress, oxidative stress, and apoptosis. However, GAS6-elicited beneficial effects were removed by GAS6 knockout. The in vitro study was similar to these findings. Our data also noted a downstream effector role for NLRP3 in GAS6-initiated myocardial response. GAS6 knockout led to elevated levels of NLRP3, the effect of which was reconciled by GAS6 overexpression. Taken together, these results revealed the therapeutical potential of targeting GAS6/AXL-NLRP3 signaling in the management of heart anomalies in sepsis.

Endothelial mechanical stretch regulates the immunological synapse interface of renal endothelial cells in a sex-dependent manner

Increased mechanical endothelial cell stretch contributes to the development of numerous cardiovascular and renal pathologies. Recent studies have shone a light on the importance of sex-dependent inflammation in the pathogenesis of renal disease states. The endothelium plays an intimate and critical role in the orchestration of immune cell activation through upregulation of adhesion molecules and secretion of cytokines and chemokines. While endothelial cells are not recognized as professional antigen-presenting cells, in response to cytokine stimulation, endothelial cells can express both major histocompatibility complex (MHC) I and MHC II. MHCs are essential to forming a part of the immunological synapse interface during antigen presentation to adaptive immune cells. Whether MHC I and II are increased under increased mechanical stretch is unknown. Due to hypertension being multifactorial, we hypothesized that increased mechanical endothelial stretch promotes the regulation of MHCs and key costimulatory proteins on mouse renal endothelial cells (MRECs) in a stretch-dependent manner. MRECs derived from both sexes underwent 5%, 10%, or 15% uniaxial cyclical stretch, and immunological synapse interface proteins were determined by immunofluorescence microscopy, immunoblot analysis, and RNA sequencing. We found that increased endothelial mechanical stretch conditions promoted downregulation of MHC I in male MRECs but upregulation in female MRECs. Moreover, MHC II was upregulated by mechanical stretch in both male and female MRECs, whereas CD86 and CD70 were regulated in a sex-dependent manner. By bulk RNA sequencing, we found that increased mechanical endothelial cell stretch promoted differential gene expression of key antigen processing and presentation genes in female MRECs, demonstrating that females have upregulation of key antigen presentation pathways. Taken together, our data demonstrate that mechanical endothelial stretch regulates endothelial activation and immunological synapse interface formation in renal endothelial cells in a sex-dependent manner.NEW & NOTEWORTHY Endothelial cells contribute to the development of renal inflammation and have the unique ability to express antigen presentation proteins. Whether increased endothelial mechanical stretch regulates immunological synapse interface proteins remains unknown. We found that antigen presentation proteins and costimulatory proteins on renal endothelial cells are modulated by mechanical stretch in a sex-dependent manner. Our data provide novel insights into the sex-dependent ability of renal endothelial cells to present antigens in response to endothelial mechanical stimuli.

Axl promotes intracranial aneurysm rupture by regulating macrophage polarization toward M1 via STAT1/HIF-1α

Background

Macrophage infiltration and polarization are crucial for the pathogenesis of intracranial aneurysm (IA) rupture. Axl, a receptor tyrosine kinase, is involved in inflammation and efferocytosis in multiple organs. Upregulated soluble Axl in cerebrospinal fluid (CSF) and plasma is correlated with intracranial aneurysm rupture. This study aimed to investigate the role of Axl in IA rupture and macrophage polarization.

Methods

Male C57BL/6J mice were used to induce IA. The level of Axl from control vessels and unruptured and ruptured IA samples was detected. In addition, the relationship between Axl and macrophages was confirmed. The pathway of Axl-mediated macrophage polarization was explored after IA induction in vivo and in bone marrow-derived macrophages (BMDMs) stimulated by LPS/IFN-γ in vitro. The animals were randomized into three groups and treated intraperitoneally with the vehicle, selective AXL antagonist R428, and recombinant mouse growth arrest-specific 6 (rmGas6) for 21 consecutive days. Then, we evaluated the influence of Axl on IA rupture by administrating R428 to inhibit or rmGas6 to activate the Axl receptor in vivo.

Results

Compared with that in normal vessels, Axl expression was significantly upregulated in unruptured IA samples. The ruptured IA tissue exhibited significantly higher expression of Axl than the unruptured IA tissue. Axl and F4/80 were coexpressed in IA tissue and LPS/IFN-γ-stimulated BMDMs. R428 treatment significantly reduced the rate of M1-like macrophage infiltration and IA rupture. In contrast, rmGas6 treatment promoted M1 macrophage infiltration and IA rupture. Mechanistically, R428 inhibited the phosphorylation of Axl and STAT1 and the expression of hypoxia-inducible factor-1α (HIF-1α) and decreased the levels of IL-1β, NOS2, and MMP9 in LPS/IFN-γ-stimulated BMDMs. rmGas6 promoted the phosphorylation of Axl and STAT1 and the expression of HIF-1α. In addition, STAT1 knockdown abolished Axl-mediated M1 macrophage polarization.

Conclusion

The inhibition of Axl reduced macrophage polarization toward the M1 phenotype via the STAT1/HIF-1α signaling pathway and prevented IA rupture in mice. This finding suggests that pharmacological inhibition of Axl might be used to prevent the progression and rupture of IA.

Endothelial Cell Dysfunction and Increased Cardiovascular Risk in Patients With Chronic Kidney Disease

The endothelium is considered to be the gatekeeper of the vessel wall, maintaining and regulating vascular integrity. In patients with chronic kidney disease, protective endothelial cell functions are impaired due to the proinflammatory, prothrombotic and uremic environment caused by the decline in kidney function, adding to the increase in cardiovascular complications in this vulnerable patient population. In this review, we discuss endothelial cell functioning in healthy conditions and the contribution of endothelial cell dysfunction to cardiovascular disease. Further, we summarize the phenotypic changes of the endothelium in chronic kidney disease patients and the relation of endothelial cell dysfunction to cardiovascular risk in chronic kidney disease. We also review the mechanisms that underlie endothelial changes in chronic kidney disease and consider potential pharmacological interventions that can ameliorate endothelial health.

Immunoproteasomal Processing of Isolevuglandin Adducts in Hypertension

Isolevuglandins (isoLGs) are lipid aldehydes that form in the presence of reactive oxygen species (ROS) and drive immune activation. We found that isoLG-adducts are presented within the context of major histocompatibility complexes (MHC-I) by an immunoproteasome dependent mechanism. Pharmacologic inhibition of LMP7, the chymotrypsin subunit of the immunoproteasome, attenuates hypertension and tissue inflammation in the angiotensin II (Ang II) model of hypertension. Genetic loss of function of all immunoproteasome subunits or conditional deletion of LMP7 in dendritic cell (DCs) or endothelial cells (ECs) attenuated hypertension, reduced aortic T cell infiltration, and reduced isoLG-adduct MHC-I interaction. Furthermore, isoLG adducts structurally resemble double-stranded DNA and contribute to the activation of STING in ECs. These studies define a critical role of the immunoproteasome in the processing and presentation of isoLG-adducts. Moreover they define a role of LMP7 as a regulator of T cell activation and tissue infiltration in hypertension.

Network medicine: an approach to complex kidney disease phenotypes

Scientific reductionism has been the basis of disease classification and understanding for more than a century. However, the reductionist approach of characterizing diseases from a limited set of clinical observations and laboratory evaluations has proven insufficient in the face of an exponential growth in data generated from transcriptomics, proteomics, metabolomics and deep phenotyping. A new systematic method is necessary to organize these datasets and build new definitions of what constitutes a disease that incorporates both biological and environmental factors to more precisely describe the ever-growing complexity of phenotypes and their underlying molecular determinants. Network medicine provides such a conceptual framework to bridge these vast quantities of data while providing an individualized understanding of disease. The modern application of network medicine principles is yielding new insights into the pathobiology of chronic kidney diseases and renovascular disorders by expanding the understanding of pathogenic mediators, novel biomarkers and new options for renal therapeutics. These efforts affirm network medicine as a robust paradigm for elucidating new advances in the diagnosis and treatment of kidney disorders.

Plasma GAS6 predicts mortality risk in acute heart failure patients: insights from the DRAGON-HF trial

BACKGROUND

Growth arrest-specific 6 (GAS6) is a vitamin K-dependent protein related to inflammation, fibrosis, as well as platelet function. Genetic ablation of GAS6 in mice protects against cardiac hypertrophy and dysfunction. Nonetheless, the association between plasma GAS6 levels and acute heart failure (AHF) patients is still unknown.

METHODS

We measured plasma GAS6 concentrations in 1039 patients with AHF who were enrolled in the DRAGON-HF trial (NCT03727828). Mean follow-up of the study was 889 days. The primary endpoint is all-cause death.

RESULTS

In total, there were 195 primary endpoints of all-cause death and 135 secondary endpoints of cardiovascular death during the mean follow-up duration of 889 days. The higher levels of GAS6 were associated with higher rates of all-cause and cardiovascular death (P < 0.05). Baseline plasma GAS6 levels were still strongly correlated with clinical outcomes in different models after adjustment for clinical factors and N-terminal pro-brain natriuretic peptide (NT-proBNP, P < 0.05). GAS6 could further distinguish the risks of clinical outcomes based on NT-proBNP measurement.

CONCLUSION

Elevated plasma GAS6 levels were associated with an increased risk of all-cause and cardiovascular death in patients with AHF. Trial registration NCT03727828 (DRAGON-HF trial) clinicaltrials.gov.

Pharmacological inhibition of protein tyrosine kinases axl and fyn reduces TNF-α-induced endothelial inflammatory activation in vitro

Major surgery induces systemic inflammation leading to pro-inflammatory activation of endothelial cells. Endothelial inflammation is one of the drivers of postoperative organ damage, including acute kidney injury Tumour Necrosis Factor alpha (TNF-α) is an important component of surgery-induced pro-inflammatory activation of endothelial cells. Kinases, the backbone of signalling cascades, can be targeted by pharmacological inhibition. This is a promising treatment option to interfere with excessive endothelial inflammation. In this study, we identified activated kinases as potential therapeutic targets. These targets were pharmacologically inhibited to reduce TNF-α-induced pro-inflammatory signalling in endothelial cells. Kinome profiling using PamChip arrays identified 64 protein tyrosine kinases and 88 serine-threonine kinases, the activity of which was determined at various timepoints (5-240 min) following stimulation with 10 ng/ml TNF-α in Human umbilical vein endothelial cells in vitro. The PTKs Axl and Fyn were selected based on high kinase activity profiles. Co-localisation experiments with the endothelial-specific protein CD31 showed Axl expression in endothelial cells of glomeruli and Fyn in arterioles and glomeruli of both control and TNF-α-exposed mice. Pharmacological inhibition with Axl inhibitor BMS-777607 and Fyn inhibitor PP2 significantly reduced TNF-α-induced pro-inflammatory activation of E-selectin, VCAM-1, ICAM-1, IL-6 and IL-8 at mRNA and VCAM-1, ICAM-1, and IL-6 at protein level in HUVEC in vitro. Upon pharmacological inhibition with each inhibitor, leukocyte adhesion to HUVEC was also significantly reduced, however to a minor extent. In conclusion, pre-treatment of endothelial cells with kinase inhibitors BMS-777607 and PP2 reduces TNF-α-induced endothelial inflammation in vitro.

Prognostic value of plasma sAXL in patients with heart failure: insights from the DRAGON-HF trial

BACKGROUND

Little is known about the predictive value of soluble AXL (sAXL) in heart failure (HF). This study aimed to describe the prognostic value of plasma sAXL in patients with symptomatic HF.

METHODS

This is a multicentre observational prospective cohort study (Registration No. NCT03727828). Plasma sAXL were measured on admission. The primary endpoint is a composite of cardiovascular mortality and HF rehospitalization. Associations between plasma sAXL levels and clinical endpoints are described using Cox regression models and Kaplan-Meier methods.

RESULTS

A total of 1030 symptomatic HF patients were enrolled in the study; the mean age (65% men) was 71 ± 12 years, with a median follow-up of 32 months (IQR: 26-41 months). The mean baseline sAXL levels were 20.03 ± 6.74 ng/mL. Plasma sAXL positively associated with NYHA classification and negatively associated with left ventricular ejection fraction (both P < 0.001). Cox regression showed that 1-SD increment of sAXL was associated with primary endpoint [HR (CI): 1.128 (1.024-1.242)], cardiovascular mortality [1.112 (1.032-1.198)], all-cause mortality [1.142 (1.057-1.234)], and HF rehospitalization [1.122 (1.030-1.224)] after adjustment for potential confounders including NT-proBNP. Kaplan-Meier curves revealed that patients with the highest sAXL levels were at the highest risk of primary endpoint events, cardiovascular mortality, and all-cause mortality (all P values < 0.001). Furthermore, both Kaplan-Meier method and Categorical analysis demonstrated that the combined use of sAXL and NT-proBNP were more likely to predict all-cause or cardiovascular mortality (both P < 0.001). Similar results were observed when separating patients with respect to left ventricular ejection fraction, namely, in HFrEF, HFmrEF, and HFpEF groups.

CONCLUSIONS

Plasma sAXL concentrations are of great importance in predicting clinical outcomes in HF patients, independent of NT-proBNP, suggesting that sAXL is a promising prognostic marker for further study.

Role of Axl in target organ inflammation and damage due to hypertensive aortic remodeling

We have shown that excessive endothelial cell stretch causes release of growth arrest-specific 6 (GAS6), which activates the tyrosine kinase receptor Axl on monocytes and promotes immune activation and inflammation. We hypothesized that GAS6/Axl blockade would reduce renal and vascular inflammation and lessen renal dysfunction in the setting of chronic aortic remodeling. We characterized a model of aortic remodeling in mice following a 2-wk infusion of angiotensin II (ANG II). These mice had chronically increased pulse wave velocity, and their aortas demonstrated increased mural collagen. Mechanical testing revealed a marked loss of Windkessel function that persisted for 6 mo following ANG II infusion. Renal function studies showed a reduced ability to excrete a volume load, a progressive increase in albuminuria, and tubular damage as estimated by periodic acid Schiff staining. Treatment with the Axl inhibitor R428 beginning 2 mo after ANG II infusion had a minimal effect on aortic remodeling 2 mo later but reduced the infiltration of T cells, γ/δ T cells, and macrophages into the aorta and kidney and improved renal excretory capacity, reduced albuminuria, and reduced evidence of renal tubular damage. In humans, circulating Axl+/Siglec6+ dendritic cells and phospho-Axl+ cells correlated with pulse wave velocity and aortic compliance measured by transesophageal echo, confirming chronic activation of the GAS6/Axl pathway. We conclude that brief episodes of hypertension induce chronic aortic remodeling, which is associated with persistent low-grade inflammation of the aorta and kidneys and evidence of renal dysfunction. These events are mediated at least in part by GAS6/Axl signaling and are improved with Axl blockade.NEW & NOTEWORTHY In this study, a brief, 2-wk period of hypertension in mice led to progressive aortic remodeling, an increase in pulse wave velocity, and evidence of renal injury, dysfunction, and albuminuria. This end-organ damage was associated with persistent renal and aortic infiltration of CD8+ and γ/δ T cells. We show that this inflammatory response is likely due to GAS6/Axl signaling and can be ameliorated by blocking this pathway. We propose that the altered microvascular mechanical forces caused by increased pulse wave velocity enhance GAS6 release from the endothelium, which in turn activates Axl on myeloid cells, promoting the end-organ damage associated with aortic stiffening.

Update on Immune Mechanisms in Hypertension

The contribution of immune cells in the initiation and maintenance of hypertension is undeniable. Several studies have established the association between hypertension, inflammation, and immune cells from the innate and adaptive immune systems. Here, we provide an update to our 2017 American Journal of Hypertension review on the overview of the cellular immune responses involved in hypertension. Further, we discuss the activation of immune cells and their contribution to the pathogenesis of hypertension in different in vivo models. We also highlight existing gaps in the field of hypertension that need attention. The main goal of this review is to provide a knowledge base for translational research to develop therapeutic strategies that can improve cardiovascular health in humans.

Inhibition of Gas6 promotes crystalline silica-induced inflammatory response of macrophages via blocking autophagy flux

Inhalation of crystalline silica (CS) can cause silicosis, which is one of the most serious interstitial lung diseases worldwide. Autophagy dysfunction is an essential step in silicosis progression. In this study, we aim to identify the effect of growth arrest-specific protein 6 (Gas6) during autophagy induction and macrophage inflammatory response caused by CS. After RAW 264.7 macrophages exposed to CS, the levels of Gas6 and autophagy markers (p62, Beclin1, and LC3-II/LC3-I) were increased, accompanied with enhanced inflammatory cytokines secretion. Using autophagy activator (rapamycin) repressed, whereas autophagy inhibitor (3-methyladenine) promoted inflammatory cytokines release. Besides, inhibition of Gas6 aggravated CS-induced inflammatory response, and autophagy inhibition facilitated the promoted effect of Gas6 silencing, resulting in elevated expression of inflammatory cytokines. These findings reveal the protective effects of Gas6 and autophagy in macrophages in response to CS exposure, and highlight the autophagy regulated by Gas6 may be a potential prevention target for CS-induced lung inflammatory response.

AXL and MERTK receptor tyrosine kinases inhibition protects against pancreatic necrosis via selectively limiting CXCL2-related neutrophil infiltration

BACKGROUND

Acute pancreatitis (AP) was initiated within pancreatic parenchymal cells and sustained by uncontrolled inflammatory responses. AXL and MERTK receptor tyrosine kinases play a crucial role in negatively regulating the innate immunity. Therefore, this study aimed to investigate the role and underlying mechanism of AXL and MERTK in AP.

METHODS

Experimental AP was induced by ten hourly intraperitoneal administration of caerulein in global, hematopoietic- and pancreas-specific Axl and Mertk deficient mice. Pancreatitis severity was assessed biochemically and histologically. Pancreatic transcriptomics and pancreatic infiltrating immune cells were profiled. Some mice were given R428, an antagonist of AXL and MERTK. AXL and MERTK in peripheral leukocytes were measured by flow cytometry.

FINDINGS

The levels of AXL and MERTK in pancreatic tissue and pancreatic CD45⁺ cells were dynamically altered at 6 h and 12 h after the 1st injection of caerulein. Global and hematopoietic-specific, but not pancreas-specific deletion of Axl and Mertk protected against pancreatic necrosis and trypsinogen activation. Pancreatic transcriptomic analysis revealed that differentially expressed gene signatures were mainly related to metabolic and inflammatory pathways. Furthermore, deletion or inhibition of Axl and Mertk selectively inhibited pancreatic neutrophil infiltration, which was primarily related to CXCL2 secreted by pro-inflammatory macrophages. Increased levels of MERTK in peripheral leukocytes were correlated with more severe form of AP.

INTERPRETATION

Our findings reveal that specific AXL/MERTK antagonist may be a novel and potential early treatment for AP and the levels of MERTK in peripheral leukocytes may be a promising biomarker for predicting pancreatic severity in patients with AP.

FUNDING

National Natural Science Foundation of China, Shanghai Natural Science Foundation, a Shanghai Young Talent Award and a Shanghai Young Orient Scholar Award.

RESEARCH IN CONTEXT

Evidence before this study Acute pancreatitis (AP) is a common inflammatory disorder of the exocrine pancreas, the severity of which was determined by the extent of pancreatic necrosis, with no targeted therapy. AP was initiated by signals within pancreatic parenchymal cells and sustained by uncontrolled innate immune responses. One of the three crucial regulatory roles for AXL and MERTK is to negatively regulate innate immune responses. Added value of this study Global and hematopoietic-, but not pancreas-specific Axl and Mertk deficiency protected against pancreatitis, primarily pancreatic necrosis. Deletion of Axl and Mertk selectively inhibited pancreatic neutrophil infiltration that was related to CXCL2 secreted by pro-inflammatory macrophages. AXL and MERTK antagonist similarly reduced pancreatitis severity via limiting CXCL2-mediated pancreatic neutrophil infiltration. Higher levels of MERTK, but not AXL in peripheral leukocytes were correlated with more severe form of acute pancreatitis. Implications of all the available evidence A specific AXL/MERTK antagonist may be a novel and potential early treatment for AP. The level of MERTK on peripheral leukocytes may be a promising biomarker for predicting disease severity in patients with AP.

Endothelial cells: potential novel regulators of renal inflammation

Substantial evidence has supported the role of endothelial cell (EC) activation and dysfunction in the development of hypertension, chronic kidney disease (CKD), and lupus nephritis (LN). In both humans and experimental models of hypertension, CKD, and LN, ECs become activated and release potent mediators of inflammation including cytokines, chemokines, and reactive oxygen species that cause EC dysfunction, tissue damage, and fibrosis. Factors that activate the endothelium include inflammatory cytokines, mechanical stretch, and pathological shear stress. These signals can activate the endothelium to promote upregulation of adhesion molecules, such as intercellular adhesion molecule-1 and vascular cell adhesion molecule-1, which promote leukocyte adhesion and migration to the activated endothelium. More importantly, it is now recognized that some of these signals may in turn promote endothelial antigen presentation through major histocompatibility complex II. In this review, we will consider in-depth mechanisms of endothelial activation and the novel mechanism of endothelial antigen presentation. Moreover, we will discuss these proinflammatory events in renal pathologies and consider possible new therapeutic approaches to limit the untoward effects of endothelial inflammation in hypertension, CKD, and LN.

A 3-Mbp fragment on rat chromosome 1 affects susceptibility both to stroke and kidney injury under salt loading in the stroke-prone spontaneously hypertensive rat: a genetic approach using multiple congenic strains

We have previously reported that a major quantitative trait locus (QTL) responsible for susceptibility to salt-induced stroke in the stroke-prone spontaneously hypertensive rat (SHRSP) is located in a 3-Mbp region on chromosome 1 covered by SHRSP.SHR-(D1Rat23-D1Rat213)/Izm (termed Pr1.31), a congenic strain with segments from SHRSP/Izm introduced into the stroke-resistant SHR/Izm. Here, we attempted to narrow down the candidate region on chromosome 1 further through analyses of subcongenic strains constructed for the target region. Simultaneously, salt-induced kidney injury was evaluated through the measurement of urinary albumin and the gene expression of renal tubular injury markers (Kim-1 and Clu) to explore a possible mechanism leading to the onset of stroke. All subcongenic strains examined in this study showed lower susceptibility to salt-induced stroke than SHRSP. Interestingly, Pr1.31 had the lowest stroke susceptibility when compared with newly constructed subcongenic strains harboring fragments of the congenic sequence in Pr1.31. Although Kim-1 and Clu expression after 1 week of salt loading in Pr1.31 did not differ significantly from those in SHRSP, the urinary albumin level of Pr1.31 was significantly lower than those of the other subcongenic strains and that of SHRSP. The present results indicated that, although the congenic fragment in Pr1.31 harbored the gene(s) related to salt-induced organ damages, further genetic dissection of the candidate region was difficult due to multiple QTLs suggested in this region. Further analysis using Pr1.31 will unveil genetic and pathophysiological mechanisms underlying salt-induced end organ damages in SHRSP.