Gas6 Attenuates Sepsis-Induced Tight Junction Injury and Vascular Endothelial Hyperpermeability via the Axl/NF-κB Signaling Pathway

C1632 protects against LPS-induced acute lung injury by regulating AXL-mediated MAPK/NF-κB signaling pathway

Acute lung injury (ALI), a leading pulmonary inflammatory disorder, is associated with high morbidity and mortality rates. AXL, a member of the TAM family, plays a significant role in the innate immune and inflammatory responses. This study aimed to evaluate the therapeutic potential of C1632 and its mechanisms in the treatment of LPS-induced ALI/ARDS. The results demonstrated that C1632 pretreatment inhibited the transcription, expression, and secretion of LPS-induced inflammatory factors (IL-6, TNF-α) and vascular adhesion molecules (VCAM-1, ICAM-1). Furthermore, it reduced inflammatory cell infiltration in the lungs, thereby alleviating LPS-induced histopathological changes and lung injury in mice. Mechanistically, C1632 suppressed AXL transcription and expression, which inhibited the activation of the MAPK/NF-κB signaling pathway triggered by LPS stimulation. Both in vitro and in vivo studies confirmed that C1632 administration did not exhibit significant cytotoxicity. Additionally, it did not cause functional or structural damage to the liver and kidneys in mice, nor did it induce other acute toxic effects. In summary, these findings suggest that AXL is a novel target for MAPK/NF-κB signaling pathway mediated anti-inflammatory treatment and C1632 is a promising therapeutic agent for ALI/ARDS treatment.

AXL/GAS6 signaling governs differentiation of tumor-associated macrophages in breast cancer

Most epithelial cancers are infiltrated by prognostically relevant myelomonocytic cells. Immunosuppressive tumor associated macrophages (TAMs) and their precursor monocytic myeloid-derived suppressor cells (MDSCs) have previously been associated with worse outcomes in human breast cancer (BCa), yet the mechanism of immunosuppressive TAMs-polarization from myelomonocytic precursors is not completely understood. In this study, we show that persuaded AXL/GAS6 pathway alters macrophage phenotype from HLA-DRhighCD206lowCD163low classical phagocytic into HLA-DRlowCD206highCD163high immunosuppressive ones with accelerated BCa progression, and increased angiogenesis signature and invasion ability of cancer cells at tumor beds. Notably, both AXL and GAS6 expressions are upregulated in human invasive breast carcinoma, with maximum expression in triple negative histology type. Mechanistically, we demonstrate that AXL/GAS6 signaling drives immunosuppression by governing increased immunosuppressive IL10 production while dampening IL-1β expression within the tumor microenvironment (TME) of BCa. Further, AXL/GAS6 signaling promotes angiogenesis through the activation of PI3K/AKT and NF-κB signaling pathways. Our results unveil role of AXL/GAS6 axis in the differentiation of TAMs, which governs malignant growth, and suggest that therapies that uncouple AXL/GAS6 axis may exhibit therapeutic opportunity for otherwise undruggable Triple Negative Breast Cancer (TNBC) patients.

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.

GAS6 as a potential target to alleviate neuroinflammation during Japanese encephalitis in mouse models

Viral encephalitis is characterized by inflammation of the brain parenchyma caused by a variety of viruses, among which the Japanese encephalitis (JE) virus (JEV) is a typical representative arbovirus. Neuronal death, neuroinflammation, and breakdown of the blood brain barrier (BBB) constitute vicious circles of JE progression. Currently, there is no effective therapy to prevent this damage. Growth arrest specific gene 6 (GAS6) is a secreted growth factor that binds to the TYRO3, AXL, and MERTK (TAM) family of receptor tyrosine kinases and has been demonstrated to participate in neuroprotection and suppression of inflammation in many central nervous system (CNS) diseases which has great potential for JE intervention. In this study, we found that GAS6 expression in the brain was decreased and was reversely correlated with viral load and neuronal loss. Mice with GAS6/TAM signalling deficiency showed higher mortality and accelerated neuroinflammation during peripheral JEV infection, accompanied by BBB breakdown. GAS6 directly promoted the expression of tight junction proteins in bEnd.3 cells and strengthened BBB integrity, partly via AXL. Mice administered GAS6 were more resistant to JEV infection due to increased BBB integrity, as well as decreased viral load and neuroinflammation. Thus, targeted GAS6 delivery may represent a strategy for the prevention and treatment of JE especially in patients with impaired BBB.

Immunological role of Gas6/TAM signaling in hemostasis and thrombosis

The immune system is an emerging regulator of hemostasis and thrombosis. The concept of immunothrombosis redefines the relationship between coagulation and immunomodulation, and the Gas6/Tyro3-Axl-MerTK (TAM) signaling pathway builds the bridge across them. During coagulation, Gas6/TAM signaling pathway not only activates platelets, but also promotes thrombosis through endothelial cells and vascular smooth muscle cells involved in inflammatory responses. Thrombosis appears to be a common result of a Gas6/TAM signaling pathway-mediated immune dysregulation. TAM TK and its ligands have been found to be involved in coagulation through the PI3K/AKT or JAK/STAT pathway in various systemic diseases, providing new perspectives in the understanding of immunothrombosis. Gas6/TAM signaling pathway serves as a breakthrough target for novel therapeutic strategies to improve disease management. Many preclinical and clinical studies of TAM receptor inhibitors are in process, confirming the pivotal role of Gas6/TAM signaling pathway in immunothrombosis. Therapeutics targeting the TAM receptor show potential both in anticoagulation management and immunotherapy. Here, we review the immunological functions of the Gas6/TAM signaling pathway in coagulation and its multiple mechanisms in diseases identified to date, and discuss the new clinical strategies that may generated by these roles.

IDN5706 Inhibits Synovial Inflammation via Inducing M2 Polarization of Synovial Macrophages in Osteoarthritis Rats

INTRODUCTION

IDN5706 is a tetrahydro derivative of hyperforin. In this study, we aimed to explore the effect of IDN5706 on synovial macrophages in osteoarthritis (OA) rats and the underlying mechanisms.

METHODS

OA rats were employed for the in vivo experiments, and RAW264.7 cells were employed for the in vitro experiments. Histopathological changes in synovium were examined using hematoxylin-eosin staining. Cell apoptosis in synovium was assessed by TUNEL staining. Macrophage polarization was determined by immunohistochemical analysis and flow cytometry. The mRNA expression and protein level of genes were detected by qRT-PCR and Western blot. The efferocytosis of macrophages was assessed by flow cytometry.

RESULTS

IDN5706 reversed the increased CD86-positive cells (M1 macrophages) and decreased CD206-positive cells (M2 macrophages), both in synovium and synovial fluid of OA rats. The in vitro experiments further confirmed the promotion effect of IDN5706 on M2 macrophages, accompanied by the elevated Arg-1 and reduced iNOS. Also, the upregulated p-mTOR in synovium and synovial fluid of OA rats were reversed by IDN5706, and the decreased M1 macrophages and increased M2 macrophages induced by IDN5706 were reversed by the mTOR activator. IDN5706 enhanced the efferocytosis of IL-4-treated RAW264.7 cells, and the animal experiments further revealed the involvement of efferocytosis in the improvement of OA by IDN5706.

CONCLUSIONS

IDN5706 enhanced the efferocytosis of synovial macrophages by inducing M2 polarization via inhibiting p-mTOR, thus suppressing synovial inflammation and OA development, providing a theoretical basis for IDN5706 as a clinical drug for inflammatory diseases.

Research progress on microcirculatory disorders in septic shock: A narrative review

Hemodynamic coherence plays a critical role in the outcomes of septic shock. Due to the potential negative consequences of microcirculatory disorders on organ failure and clinical outcomes, the maintenance of a balance between the macrocirculation and microcirculation is a topic of significant research focus. Although physical methods and specialized imaging techniques are used in clinical practice to assess microcirculation, the use of monitoring devices is not widespread. The integration of microcirculation research tools into clinical practice poses a significant challenge for the future. Consequently, this review aims to evaluate the impact of septic shock on the microcirculation, the methods used to monitor the microcirculation and highlight the importance of microcirculation in the treatment of critically ill patients. In addition, it proposes an evaluation framework that integrates microcirculation monitoring with macrocirculatory parameters. The optimal approach should encompass dynamic, multiparametric, individualized, and continuous monitoring of both the macrocirculation and microcirculation, particularly in cases of hemodynamic separation.

Adjunctive sepsis therapy with aminophylline (STAP): a randomized controlled trial

BACKGROUND

Sepsis is a serious disease caused by infection. Aminophylline has anti-asthma and anti-inflammatory effects. We aimed to explore the safety and effect of aminophylline in sepsis.

METHODS

We conducted a clinical randomized controlled trial involving 100 patients diagnosed with sepsis within 48 h after intensive care unit (ICU) admission in two sites. All patients were randomized in a 1:1 ratio to receive standard therapy with or without aminophylline. The primary clinical outcome was all-cause mortality at 28 days.

RESULTS

From September 27, 2018 to February 12, 2020, we screened 277 septic patients and eventually enrolled 100 patients, with 50 assigned to the aminophylline group and 50 to the usual-care group. At 28 days, 7 of 50 patients (14.0%) in the aminophylline group had died, compared with 16 of 50 (32.0%) in the usual-care group ( P  = 0.032). Cox regression showed that the aminophylline group had a lower hazard of death (hazard ratio = 0.312, 95% confidence interval: 0.129-0.753). Compared with the usual-care group, patients in the aminophylline group had a longer survival time ( P  = 0.039 by the log-rank test). The effects of aminophylline on vasopressor dose, oxygenation index, and sequential organ failure assessment score were time-dependent with treatment. There were no significant differences in total hospitalization days, ICU hospitalization days, and rates of serious adverse events (all P > 0.05). No adverse events were observed in the trial.

CONCLUSIONS

Aminophylline as an adjunct therapy could significantly reduce the risk of death and prolong the survival time of patients with sepsis.

TRIAL REGISTRATION

ChiCTR.org.cn, ChiCTR1800019173.

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.

WNK1 collaborates with TGF-β in endothelial cell junction turnover and angiogenesis

Angiogenesis is essential for growth of new blood vessels, remodeling existing vessels, and repair of damaged vessels, and these require reorganization of endothelial cell-cell junctions through a partial endothelial-mesenchymal transition. Homozygous disruption of the gene encoding the protein kinase WNK1 results in lethality in mice near embryonic day (E) 12 due to impaired angiogenesis. This angiogenesis defect can be rescued by endothelial-specific expression of an activated form of the WNK1 substrate kinase OSR1. We show that inhibition of WNK1 kinase activity not only prevents sprouting of endothelial cells from aortic slices but also vessel extension in inhibitor-treated embryos ex vivo. Mutations affecting TGF-β signaling also result in abnormal vascular development beginning by E10 and, ultimately, embryonic lethality. Previously, we demonstrated cross-talk of WNK1 with TGF-β-regulated SMAD signaling, and OSR1 was identified as a component of the TGF-β interactome. However, molecular events jointly regulated by TGF-β and WNK1/OSR1 have not been delineated. Here, we show that inhibition of WNK1 promotes TGF-β-dependent degradation of the tyrosine kinase receptor AXL, which is involved in TGF-β-mediated cell migration and angiogenesis. We also show that interaction between OSR1 and occludin, a protein associated with endothelial tight junctions, is an essential step to enable tight junction turnover. Furthermore, we show that these phenomena are WNK1 dependent, and sensitive to TGF-β. These findings demonstrate intimate connections between WNK1/OSR1 and multiple TGF-β-sensitive molecules controlling angiogenesis and suggest that WNK1 may modulate many TGF-β-regulated functions.

Vitamin K Effects on Gas6 and Soluble Axl Receptors in Intensive Care Patients: An Observational Screening Study

Growth arrest-specific gene 6 protein (Gas6) is avitamin K-dependent tissue bound protein. Gas6 has been shown to promote growth and therapy resistance among different types of cancer as well as thromboembolism. The aim of this prospective screening study: ClinicalTrials.gov; Identifier: NTC3782025, was to evaluate the effects of intravenously administered vitamin K1 on Gas6 and its soluble (s)Axl receptor plasma levels in intensive care patients. Vitamin K1 was intravenously injected in non-warfarin treated patients with prolonged Owren prothrombin time international normalized ratio (PT-INR) > 1.2 and blood samples were retrieved before and 20-28 h after injection. Citrate plasma samples from 52 intensive care patients were analysed for different vitamin K dependent proteins. There was a significant, but small increase in median Gas6. Only one patient had a large increase in sAxl, but overall, no significant changes in sAxl Gas6 did not correlate to PT-INR, thrombin generation assay, coagulation factors II, VII, IX and X, but to protein S and decarboxylated matrix Gla protein (dp-ucMGP). In conclusion, there was a small increase in Gas6 over 20-28 h. The pathophysiology and clinical importance of this remains to be investigated. To verify a true vitamin K effect, improvement of Gas6 carboxylation defects needs to be studied.

Gas6 Ameliorates Inflammatory Response and Apoptosis in Bleomycin-Induced Acute Lung Injury

Acute lung injury (ALI) is characterized by alveolar damage, lung edema, and exacerbated inflammatory response. Growth arrest-specific protein 6 (Gas6) mediates many different functions, including cell survival, proliferation, inflammatory signaling, and apoptotic cell clearance (efferocytosis). The role of Gas6 in bleomycin (BLM)-induced ALI is unknown. We investigated whether exogenous administration of mouse recombinant Gas6 (rGas6) has anti-inflammatory and anti-apoptotic effects on BLM-induced ALI. Compared to mice treated with only BLM, the administration of rGas6 reduced the secretion of proinflammatory cytokines, including tumor necrosis factor-α, interleukin-1β, and macrophage inflammatory protein-2, and increased the secretion of hepatocyte growth factor in bronchoalveolar lavage (BAL) fluid. rGas6 administration also reduced BLM-induced inflammation and apoptosis as evidenced by reduced neutrophil recruitment into the lungs, total protein levels in BAL fluid, caspase-3 activity, and TUNEL-positive lung cells in lung tissue. Apoptotic cell clearance by alveolar macrophages was also enhanced in mice treated with both BLM and rGas6 compared with mice treated with only BLM. rGas6 also had pro-resolving and anti-apoptotic effects in mouse bone marrow-derived macrophages and alveolar epithelial cell lines stimulated with BLM in vitro. These findings indicate that rGas6 may play a protective role in BLM-induced ALI.

Transcriptomic Analysis Reveals Differential Expression of Genes between Lung Capillary and Post Capillary Venules in Abdominal Sepsis

Lung endothelial cell dysfunction plays a central role in septic-induced lung injury. We hypothesized that endothelial cell subsets, capillary endothelial cells (capEC) and post capillary venules (PCV), might play different roles in regulating important pathophysiology in sepsis. In order to reveal global transcriptomic changes in endothelial cell subsets during sepsis, we induced sepsis in C57BL/6 mice by cecal ligation and puncture (CLP). We confirmed that CLP induced systemic and lung inflammation in our model. Endothelial cells (ECs) from lung capillary and PCV were isolated by cell sorting and transcriptomic changes were analyzed by bioinformatic tools. Our analysis revealed that lung capEC are transcriptionally different than PCV. Comparison of top differentially expressed genes (DEGs) of capEC and PCV revealed that capEC responses are different than PCV during sepsis. It was found that capEC are more enriched with genes related to regulation of coagulation, vascular permeability, wound healing and lipid metabolic processes after sepsis. In contrast, PCV are more enriched with genes related to chemotaxis, cell–cell adhesion by integrins, chemokine biosynthesis, regulation of actin filament process and neutrophil homeostasis after sepsis. In addition, we predicted some transcription factor targets that regulate a significant number of DEGs in sepsis. We proposed that targeting certain DEGs or transcriptional factors would be useful in protecting against sepsis-induced lung damage.

Evolution of NETosis markers and DAMPs have prognostic value in critically ill COVID-19 patients

Coronavirus disease 19 (COVID-19) presents with disease severities of varying degree. In its most severe form, infection may lead to respiratory failure and multi-organ dysfunction. Here we study the levels and evolution of the damage associated molecular patterns (DAMPS) cell free DNA (cfDNA), extracellular histone H3 (H3) and neutrophil elastase (NE), and the immune modulators GAS6 and AXL in relation to clinical parameters, ICU scoring systems and mortality in patients (n = 100) with severe COVID-19. cfDNA, H3, NE, GAS6 and AXL were increased in COVID-19 patients compared to controls. These measures associated with occurrence of clinical events and intensive care unit acquired weakness (ICUAW). cfDNA and GAS6 decreased in time in patients surviving to 30 days post ICU admission. A decrease of 27.2 ng/mL cfDNA during ICU stay associated with patient survival, whereas levels of GAS6 decreasing more than 4.0 ng/mL associated with survival. The presence of H3 in plasma was a common feature of COVID-19 patients, detected in 38% of the patients at ICU admission. NETosis markers cfDNA, H3 and NE correlated well with parameters of tissue damage and neutrophil counts. Furthermore, cfDNA correlated with lowest p/f ratio and a lowering in cfDNA was observed in patients with ventilator-free days.

Role of tight junction-associated MARVEL protein marvelD3 in migration and epithelial-mesenchymal transition of hepatocellular carcinoma

MarvelD3, a recently identified tight junction membrane protein, could be associated with hepatocellular carcinoma (HCC). We aimed to investigate the role of marvelD3 in Epithelial-Mesenchymal Transition (EMT) and migration of HCC and explore the underlying molecular mechanisms. First, we assessed marvlD3 expression in HCC and normal liver tissues and found loss of marvelD3 expression was significantly correlated with the occurrence and TNM stage of HCC. Second, we detected that marvelD3 was downregulated in HCC cells with transforming growth factor β1 and snail/slug-induced EMT. Finally, we analyzed expression of marvelD3 protein was significantly associated with EMT and the NF-κB signaling pathway. Our study demonstrated that MarvelD3 inhibited EMT and migration of HCC cells along with inhibiting NF-κB signaling pathway.Abbreviations: HCC, Hepatocellular carcinoma; TJ, Tight junction; MARVEL, MAL and related proteins for vesicle trafficking and membrane link; EMT, Epithelial-mesenchymal transition; NF-κB, Nuclear factor kappa B; TAMPs, Tight junction-associated marvel proteins; TGF-β1, Transforming growth factor-β1; MMP9, matrix metallopeptidase 9; RT-PCR, Real-time PCR; IHC, Immunohistochemistry; IF, Immunofluorescence.

Aminophylline modulates the permeability of endothelial cells via the Slit2-Robo4 pathway in lipopolysaccharide-induced inflammation

Sepsis and septic shock are the main cause of mortality in intensive care units. The prevention and treatment of sepsis remains a significant challenge worldwide. The endothelial cell barrier plays a critical role in the development of sepsis. Aminophylline, a non-selective phosphodiesterase inhibitor, has been demonstrated to reduce endothelial cell permeability. However, little is known regarding the role of aminophylline in regulating vascular permeability during sepsis, as well as the potential underlying mechanisms. In the present study, the Slit2/Robo4 signaling pathway, the downstream protein, vascular endothelial (VE)-cadherin and endothelial cell permeability were investigated in a lipopolysaccharide (LPS)-induced inflammation model. It was indicated that, in human umbilical vein endothelial cells (HUVECs), LPS downregulated Slit2, Robo4 and VE-cadherin protein expression levels and, as expected, increased endothelial cell permeability in vitro during inflammation. After administration of aminophylline, the protein expression levels of Slit2, Robo4 and VE-cadherin were upregulated and endothelial cell permeability was significantly improved. These results suggested that the permeability of endothelial cells could be mediated by VE-cadherin via the Slit2/Robo4 signaling pathway. Aminophylline reduced endothelial permeability in a LPS-induced inflammation model. Therefore, aminophylline may represent a promising candidate for modulating vascular permeability induced by inflammation or sepsis.

Resolving inflammation by TAM receptor activation

The control of inflammation is strictly regulated to ensure the adequate intensity and duration of an inflammatory response, enabling the removal of the trigger factors and the restoration of the integrity of the tissues and their functions. This process is coordinated by anti-inflammatory and pro-resolving mediators that regulate the cellular and molecular events necessary to restore homeostasis, and defects in this control are associated with the development of chronic and autoimmune diseases. The TAM family of receptor tyrosine kinases-Tyro3, Axl, and MerTK-plays an essential role in efferocytosis, a key process for the resolution of inflammation. However, new studies have demonstrated that TAM receptor activation not only reduces the synthesis of pro-inflammatory mediators by different cell types in response to some stimuli but also stimulates the production of anti-inflammatory and pro-resolving molecules that control the inflammation. This review provides a comprehensive view of TAM receptor family members as important players in controlling inflammatory responses through anti-inflammatory and pro-resolving actions.

Growth Arrest-Specific Factor 6 (GAS6) Is Increased in COVID-19 Patients and Predicts Clinical Outcome

Background: Growth arrest-specific factor 6 (GAS6) and the Tyro3, AXL, and MERTK (TAM) receptors counterbalance pro-inflammatory responses. AXL is a candidate receptor for SARS-CoV-2, particularly in the respiratory system, and the GAS6/AXL axis is targeted in current clinical trials against COVID-19. However, GAS6 and TAMs have not been evaluated in COVID-19 patients at emergency admission. Methods: Plasma GAS6, AXL, and MERTK were analyzed in 132 patients consecutively admitted to the emergency ward during the first peak of COVID-19. Results: GAS6 levels were higher in the SARS-CoV-2-positive patients, increasing progressively with the severity of the disease. Patients with initial GAS6 at the highest quartile had the worst outcome, with a 3-month survival of 65%, compared to a 90% survival for the rest. Soluble AXL exhibited higher plasma concentration in deceased patients, without significant differences in MERTK among SARS-CoV-2-positive groups. GAS6 mRNA was mainly expressed in alveolar cells and AXL in airway macrophages. Remarkably, THP-1 human macrophage differentiation neatly induces AXL, and its inhibition (bemcentinib) reduced cytokine production in human macrophages after LPS challenge. Conclusions: Plasma GAS6 and AXL levels reflect COVID-19 severity and could be early markers of disease prognosis, supporting a relevant role of the GAS6/AXL system in the immune response in COVID-19.

Growth Arrest-Specific Gene 6 Administration Ameliorates Sepsis-Induced Organ Damage in Mice and Reduces ROS Formation In Vitro

Sepsis is a widespread life-threatening disease, with a high mortality rate due to inflammation-induced multiorgan failure (MOF). Thus, new effective modulators of the immune response are urgently needed to ameliorate the outcome of septic patients. As growth arrest-specific gene 6 (Gas6)/Tyro3, Axl, MerTK (TAM) receptors signaling has shown immunomodulatory activity in sepsis, here we sought to determine whether Gas6 protein injection could mitigate MOF in a cecal slurry mouse model of sepsis. Mice, divided into different groups according to treatment-i.e., placebo (B), ampicillin (BA), Gas6 alone (BG), and ampicillin plus Gas6 (BAG)-were assessed for vitality, histopathology and cytokine expression profile as well as inducible nitric oxide synthase (iNOS), ALT and LDH levels. BAG-treated mice displayed milder kidney and lung damage and reduced levels of cytokine expression and iNOS in the lungs compared to BA-treated mice. Notably, BAG-treated mice showed lower LDH levels compared to controls. Lastly, BAG-treated cells of dendritic, endothelial or monocytic origin displayed reduced ROS formation and increased cell viability, with a marked upregulation of mitochondrial activity. Altogether, our findings indicate that combined treatment with Gas6 and antibiotics ameliorates sepsis-induced organ damage and reduces systemic LDH levels in mice, suggesting that Gas6 intravenous injection may be a viable therapeutic option in sepsis.

Treatment with Atorvastatin During Vascular Remodeling Promotes Pericyte-Mediated Blood-Brain Barrier Maturation Following Ischemic Stroke

We previously showed that newly formed vessels in ischemic rat brain have high blood-brain barrier (BBB) permeability at 3 weeks after stroke due to a lack of major endothelial tight junction proteins (TJPs), which may exacerbate edema in stroke patients. Atorvastatin was suggested a dose-dependent pro-angiogenic effect and ameliorating BBB permeability beyond its cholesterol-lowering effects. This study examined our hypothesis that, during vascular remodeling after stroke, treatment with atorvastatin could facilitate BBB maturation in remodeling vasculature in ischemic brain. Adult spontaneously hypertensive rats underwent middle cerebral artery occlusion with reperfusion (MCAO/RP). Atorvastatin, at dose of 3 mg/kg, was delivered daily starting at 14 days after MCAO/RP onset for 7 days. The rats were studied at multiple time points up to 8 weeks with multimodal-MRI, behavior tests, immunohistochemistry, and biochemistry. The delayed treatment of atorvastatin significantly reduced infarct size and BBB permeability, restored cerebral blood flow, and improved the neurological outcome at 8 weeks after MCAO/RP. Postmortem studies showed that atorvastatin promoted angiogenesis and stabilized the newly formed vessels in peri-infarct areas. Importantly, atorvastatin facilitated maturation of BBB properties in the new vessels by promoting endothelial tight junction (TJ) formation. Further in vivo and in vitro studies demonstrated that proliferating peri-vascular pericytes expressing neural-glial antigen 2 (NG2) mediated the role of atorvastatin on BBB maturation through regulating endothelial TJ strand formations. Our results suggested a therapeutic potential of atorvastatin in facilitating a full BBB integrity and functional stroke recovery, and an essential role for pericyte-mediated endothelial TJ formation in remodeling vasculature.

The effects of sepsis on endothelium and clinical implications

ABSTRACT

Sepsis accounts for nearly 700 000 deaths in Europe annually and is caused by an overwhelming host response to infection resulting in organ failure. The endothelium is an active contributor to sepsis and as such represents a major target for therapy. During sepsis, endothelial cells amplify the immune response and activate the coagulation system. They are both a target and source of inflammation and serve as a link between local and systemic immune responses. In response to cytokines produced by immune cells, the endothelium expresses adhesion molecules and produces vasoactive compounds, inflammatory cytokines, and chemoattractants, thus switching from an anticoagulant to procoagulant state. These responses contribute to local control of infection, but systemic activation can lead to microvascular thrombosis, capillary permeability, hypotension, tissue hypoxia, and ultimately tissue damage. This review focuses on the role of the endothelium in leucocyte adhesion and transmigration as well as production of reactive oxygen and nitrogen species, microRNAs and cytokines, formation of signalling microparticles, and disseminated intravascular coagulation. We also discuss alterations in endothelial permeability and apoptosis. Finally, we review the diagnostic potential of endothelial markers and endothelial pathways as therapeutic targets for this devastating disease.

Therapeutic aspects of the Axl/Gas6 molecular system

Axl receptor tyrosine kinase (RTK) and its ligand, growth arrest-specific protein 6 (Gas6), are involved in several biological functions and participate in the development and progression of a range of malignancies and autoimmune disorders. In this review, we present this molecular system from a drug discovery perspective, highlighting its therapeutic implications and challenges that need to be addressed. We provide an update on Axl/Gas6 axis biology, exploring its role in fields ranging from angiogenesis, cancer development and metastasis, immune response and inflammation to viral infection. Finally, we summarize the molecules that have been developed to date to target the Axl/Gas6 molecular system for therapeutic and diagnostic applications.

Role of Vitamin K-Dependent Factors Protein S and GAS6 and TAM Receptors in SARS-CoV-2 Infection and COVID-19-Associated Immunothrombosis

The vitamin K-dependent factors protein S (PROS1) and growth-arrest-specific gene 6 (GAS6) and their tyrosine kinase receptors TYRO3, AXL, and MERTK, the TAM subfamily of receptor tyrosine kinases (RTK), are key regulators of inflammation and vascular response to damage. TAM signaling, which has largely studied in the immune system and in cancer, has been involved in coagulation-related pathologies. Because of these established biological functions, the GAS6-PROS1/TAM system is postulated to play an important role in SARS-CoV-2 infection and progression complications. The participation of the TAM system in vascular function and pathology has been previously reported. However, in the context of COVID-19, the role of TAMs could provide new clues in virus-host interplay with important consequences in the way that we understand this pathology. From the viral mimicry used by SARS-CoV-2 to infect cells, to the immunothrombosis that is associated with respiratory failure in COVID-19 patients, TAM signaling seems to be involved at different stages of the disease. TAM targeting is becoming an interesting biomedical strategy, which is useful for COVID-19 treatment now, but also for other viral and inflammatory diseases in the future.

Crosstalk between Akt and NF-κB pathway mediates inhibitory effect of gas6 on monocytes-endothelial cells interactions stimulated by P. gingivalis-LPS

Correlation between periodontitis and atherosclerosis is well established, and the inherent mechanisms responsible for this relationship remain unclear. The biological function of growth arrest‐specific 6 (gas6) has been discovered in both atherosclerosis and inflammation. Inhibitory effects of gas6 on the expression of inflammatory factors in human umbilical vein endothelial cells (HUVECs) stimulated by Porphyromonas gingivalis lipopolysaccharide (P. gingivalis‐LPS) were reported in our previous research. Herein, the effects of gas6 on monocytes‐endothelial cells interactions in vitro and their probable mechanisms were further investigated. Gas6 protein in HUVECs was knocked down with siRNA or overexpressed with plasmids. Transwell inserts and co‐culturing system were introduced to observe chemotaxis and adhering affinity between monocytes and endothelial cells in vitro. Expression of gas6 was decreased in inflammatory periodontal tissues and HUVECs challenged with P. gingivalis‐LPS. The inhibitory effect of gas6 on chemotaxis and adhesion affinity between monocytes and endothelial cells was observed, and gas6 promoted Akt phosphorylation and inhibited NF‐κB phosphorylation. To our best knowledge, we are first to report that gas6 inhibit monocytes‐endothelial cells interactions in vitro induced by P. gingivalis‐LPS via Akt/NF‐κB pathway. Additionally, inflammation‐mediated inhibition of gas6 expression is through LncRNA GAS6‐AS2, rather than GAS6‐AS1, which is also newly reported.

Gas6/TAM Axis in Sepsis: Time to Consider Its Potential Role as a Therapeutic Target

Tyrosine kinase receptors are transmembrane proteins involved in cell signaling and interaction. Among them, the TAM family (composed by Tyro 3, Axl, and Mer) represents a peculiar subgroup with an important role in many physiological and pathological conditions. Despite different mechanisms of activation (e.g., protein S and Galactin-3), TAM action is tightly related to their common ligand, a protein named growth arrest-specific 6 (Gas6). Since the expression of both TAM and Gas6 is widely distributed among tissues, any alteration of one of these components can lead to different pathological conditions. Moreover, as they are indispensable for homeostasis maintenance, in recent years a growing interest has emerged regarding their role in the regulation of the inflammatory process. Due to this involvement, many authors have demonstrated the pivotal role of the Gas6/TAM axis in both sepsis and the sepsis-related inflammatory responses. In this narrative review, we highlight the current knowledge as well as the last discoveries on TAM and Gas6 implication in different clinical conditions, notably in sepsis and septic shock. Lastly, we underline not only the feasible use of Gas6 as a diagnostic and prognostic biomarker in certain systemic acute conditions but also its potential therapeutic role in these life-threatening diseases.