Growth arrest-specific protein 6 plasma concentrations during septic shock

Isopropyl 3-(3,4-dihydroxyphenyl) 2-hydroxypropanoate protects septic myocardial injury via regulating GAS6/Axl-AMPK signaling pathway

In a previous study, we used metabolomic techniques to identify a new metabolite of Danshen Dripping Pills called isopropyl 3-(3,4-dihydroxyphenyl)-2-hydroxypropanoate (IDHP), which has potential as a drug candidate for cardiovascular diseases. This study aimed to explore the protective effects of IDHP against septic myocardial injury, as well as its molecular mechanism. Wild type or GAS6 knockout mice injured by cecal ligation and puncture (CLP) were used to observe the effect of IDHP. Here, we found that a specific concentration of IDHP (60 mg/kg) significantly increased the survival rate of septic mice to about 75 % at 72 h post CLP, and showed improvements in sepsis score, blood biochemistry parameters, cardiac function, and myocardial tissue damage. Furthermore, IDHP inhibited myocardial oxidative stress, inflammatory response, apoptosis, and mitochondrial dysfunction. Molecularly, we discovered that IDHP treatment reversed the CLP-induced downregulation of GAS6, Axl, and p-AMPK/AMPK expression. In addition, GAS6 knockout reversed the positive effect of IDHP in septic mice, indicated by more severe myocardial tissue damage, oxidative stress, inflammatory response, and mitochondrial dysfunction. GAS6 knockout also resulted in decreased levels of GAS6, Axl, and p-AMPK/AMPK. Taken together, our study provides evidence that IDHP has significant cardioprotective effects against sepsis by regulating the GAS6/Axl-AMPK signaling pathway. This finding has important therapeutic potential for treating sepsis.

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.

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.

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.

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.

Gas6/Axl signaling attenuates alveolar inflammation in ischemia-reperfusion-induced acute lung injury by up-regulating SOCS3-mediated pathway

Background

Axl is a cell surface receptor tyrosine kinase, and activation of the Axl attenuates inflammation induced by various stimuli. Growth arrest-specific 6 (Gas6) has high affinity for Axl receptor. The role of Gas6/Axl signaling in ischemia-reperfusion-induced acute lung injury (IR-ALI) has not been explored previously. We hypothesized that Gas6/Axl signaling regulates IR-induced alveolar inflammation via a pathway mediated by suppressor of cytokine signaling 3 (SOCS3).

Methods

IR-ALI was induced by producing 30 min of ischemia followed by 90 min of reperfusion in situ in an isolated and perfused rat lung model. The rats were randomly allotted to a control group and IR groups, which were treated with three different doses of Gas6. Mouse alveolar epithelium MLE-12 cells were cultured in control and hypoxia-reoxygenation (HR) conditions with or without Gas6 and Axl inhibitor R428 pretreatment.

Results

We found that Gas6 attenuated IR-induced lung edema, the production of proinflammatory cytokines in perfusates, and the severity of ALI ex vivo. IR down-regulated SOCS3 expression and up-regulated NF-κB, and Gas6 restored this process. In the model of MLE-12 cells with HR, Gas6 suppressed the activation of TRAF6 and NF-κB by up-regulating SOCS3. Axl expression of alveolar epithelium was suppressed in IR-ALI but Gas6 restored phosphorylation of Axl. The anti-inflammatory effect of Gas6 was antagonized by R428, which highlighted that phosphorylation of Axl mediated the protective role of Gas6 in IR-ALI.

Conclusions

Gas6 up-regulates phosphorylation of Axl on alveolar epithelium in IR-ALI. The Gas6/Axl signaling activates the SOCS3-mediated pathway and attenuates IR-related inflammation and injury.

Gas6 attenuates lipopolysaccharide‑induced TNF‑α expression and apoptosis in H9C2 cells through NF‑κB and MAPK inhibition via the Axl/PI3K/Akt pathway

Therapeutic agents used to treat sepsis‑induced cardiac dysfunction are designed to suppress tumor necrosis factor (TNF)‑α release and inhibit cell apoptosis. Exogenous administration of growth arrest‑specific 6 (Gas6) exerts several biological and pharmacological effects; however, the role of Gas6 in sepsis‑induced myocardial dysfunction remains unclear. In this study, H9C2 cardiomyocytes were stimulated with LPS (10 µg/ml) to mimic septic cardiac dysfunction and Gas6 (100 ng/ml) was applied exogenously. Subsequently, mitogen‑activated protein kinase (MAPK) and nuclear factor (NF)‑κB activation, TNF‑α expression, and apoptosis in the presence or absence of TP‑0903 (15 nM) and Wortmannin (3 nM) were evaluated. The morphological alterations of H9C2 cells were visualized by phase‑contrast microscopy. Cell viability was determined using the Cell Counting kit 8 assay and lactate dehydrogenase release, and TNF‑α release was analyzed by ELISA analysis. Cell apoptosis was analyzed by flow cytometry and TUNEL assay. Nuclear morphological alterations were detected by Hoechst staining and caspase‑3 activity was measured using biochemical methods. The expression levels of Bax and Bcl‑2, and the phosphorylation and expression levels of Axl, Akt, IκB‑α, p65, c‑Jun N‑terminal protein kinase (JNK), extracellular signal‑regulated kinase (ERK) and p38 were determined by western blotting. Furthermore, immunofluorescence analysis was performed to visualize translocation of NF‑κB p65. The results demonstrated that Gas6 suppressed TNF‑α release and inhibited cell apoptosis, and attenuated nuclear factor (NF)‑κB and mitogen‑activated protein kinase (MAPK) activation via the Axl/PI3K/Akt pathway. Furthermore, the cardioprotective properties of Gas6 on the suppression of LPS‑induced TNF‑α release and apoptosis were abolished by treatment with TP‑0903 (an Axl inhibitor) and Wortmannin (a PI3K inhibitor). Pretreatment with TP‑0903 and Wortmannin abrogated the effects of Gas6 on phosphorylated‑IκB‑α, IκB‑α, NF‑κB, ERK1/2, JNK and p38 MAPK. These findings suggested that activation of Axl/PI3K/Akt signaling by Gas6 may inhibit LPS‑induced TNF‑α expression and apoptosis, as well as MAPK and NF‑κB activation.

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

Vascular endothelial functional dysregulation and barrier disruption are involved the initiation and development of sepsis. Growth arrest-specific protein 6 (Gas6), one of the endogenous ligands of TAM receptors (Tyro3, Axl, and Mertk), is confirmed to have beneficial functions in hemostasis, inflammation, and cancer growth. Here, we demonstrated the protective effects of Gas6 on multi-organ dysfunction syndrome (MODS) in sepsis and the underlying mechanisms. We investigated Gas6-ameliorated MODS by inhibiting vascular endothelial hyperpermeability in a mouse model of sepsis. Additionally, in vitro, under lipopolysaccharide (LPS) stimulation in vascular endothelial cells, Gas6 attenuated vascular endothelial hyperpermeability by reinforcing the tight junction proteins occludin, zonula occludens-1 (ZO-1), and claudin5. Furthermore, Gas6 substantially suppressed NF-κB p65 activation. In addition, blocking the Gas6 receptor, Axl, partially reduced the protective effect of Gas6 on the vascular endothelial barrier and diminished the inhibitive effect of Gas6 on NF-κB p65 activation. Taken together, this study suggests that Gas6 has a protective effect on MODS in sepsis by inhibiting the vascular endothelial hyperpermeability and alteration of tight junction and that the Axl/NF-κB signaling pathway underlies these effects.

Association of circulating growth differentiation factor-15, Krüppel-like factor 4 and growth arrest-specific 6 with coronary artery disease

BACKGROUND

Current assessment tools for patients with acute chest pain are either traumatic (coronary angiography) or unreliable (measurement of cardiac troponin concentrations). We investigated whether the novel cardiovascular stress markers, serum growth differentiation factor-15 (GDF-15), Krüppel-like factor 4 (KLF4) and growth arrest-specific 6 (gas6) may be useful biomarkers of coronary artery disease (CAD).

METHODS

A total of 350 male patients were enrolled, 198 with CAD and 152 controls, based on coronary angiography. GDF-15, KLF4 and gas6 concentrations were measured using commercial enzyme-linked immunosorbent assay kits. Multivariate logistic regression and multivariate linear regression were performed to evaluate potential associations of GDF-15, KLF4 and gas6 with risk of CAD or CAD severity.

RESULTS

Serum GDF-15, KLF4 and gas6 concentrations were significantly higher in male patients with CAD than in control subjects (P < .05), and they correlated significantly with involvement of coronary vessels (P < .05). After adjusting for confounding factors, we found that circulating GDF-15 concentrations remained positively associated with the presence of CAD (odds ratio [OR] per 1-standard deviation [SD] increase, 3.182; 95% confidence interval [CI] 1.586 to 6.382; P = .001), as did KLF4 concentrations (OR per 1-SD increase, 13.05; 95% CI 2.940 to 57.921, P = .001). Moreover, circulating GDF-15 concentrations were positively associated with the Gensini score (estimated SD change per 1-SD increase, 22.091; 95% CI 9.147 to 35.035, P = .001), as were KLF4 concentrations (estimated SD change per 1-SD increase, 27.996; 95% CI 10.082 to 45.910, P = .002). Gas6, in contrast, showed no relationship to presence of CAD or Gensini score.

, CONCLUSIONS

In this case-control study, increased concentrations of circulating GDF-15 and KLF4 were significantly associated with the presence and severity of CAD.

A high Gas6 level in plasma predicts venous thromboembolism recurrence, major bleeding and mortality in the elderly: a prospective multicenter cohort study

Essentials Predictive ability of pro-hemostatic Gas6 for recurrent venous thromboembolism (VTE) is unknown. We measured Gas6 levels in 864 patients with VTE over 3 years. High Gas6 (> 157%) at diagnosis is associated with VTE recurrence, major bleeding and mortality. Gas6 plasma levels measured 12 months after the index VTE are discriminatory for VTE recurrence. SUMMARY: Background Growth arrest-specific gene 6 (Gas6) is a prohemostatic protein with an unknown predictive ability for recurrent venous thromboembolism (VTE). In the elderly, VTE results in higher mortality but does not have a higher rate of recurrence than in younger patients. Consequently, anticoagulation management in the elderly is challenging. Objective To prospectively investigate the performance of Gas6 in predicting VTE recurrence, major bleeding and mortality in the elderly. Methods Consecutive patients aged ≥ 65 years with acute VTE were followed for a period of 3 years. Primary outcomes were symptomatic VTE recurrence, major bleeding, and mortality. Plasma Gas6 was measured with ELISA. Results Gas6 levels were measured in 864 patients at the time of the index VTE (T1) and, in 70% of them, also 12 months later (T2). The Gas6 level at T1 was discriminatory for VTE recurrence (C-statistic, 0.56; 95% confidence interval [CI] 0.51-0.62), major bleeding (0.60, 95% CI 0.55-0.65) and mortality (0.69, 95% CI 0.65-0.73) up to 36 months. VTE recurrence up to 24 months after T2 was discriminated by the Gas6 level at T2 (0.62, 95% CI 0.54-0.71). High Gas6 levels (> 157%) and continuous Gas6 levels at T1 were associated with VTE recurrence up to 6 months and 12 months, respectively. Conclusions In elderly patients, a high Gas6 level is associated with higher risks of VTE recurrence, major bleeding, and death. These findings support further studies to assess the performance of Gas6 in adjusting the length of anticoagulation.

Protective Effects of Growth Arrest-Specific Protein 6 (Gas6) on Sepsis-Induced Acute Kidney Injury

Acute kidney injury (AKI) is a serious complication of sepsis, which has a high mortality rate. Growth arrest-specific protein 6 (Gas6), the protein product of the growth arrest specific gene 6, has been shown to have an anti-apoptotic effect as well as pro-survival capability. Here, we investigated the effects of Gas6 on sepsis-associated AKI in mice subjected to cecal ligation and puncture (CLP). We found that the administration of rmGas6 significantly reduced serum urea nitrogen and creatinine and improved the survival of septic mice. Furthermore, the renal pathological damage induced by CLP was attenuated by rmGas6 treatment. Finally, rmGas6 reduced the renal tissue apoptotic index and the expression of Bax, while it upregulated the expression of Bcl-2. The data suggest that rmGas6 might be used as a potential therapeutic agent for sepsis-induced AKI.

Ligand Activation of TAM Family Receptors-Implications for Tumor Biology and Therapeutic Response

The TAM family of receptors (i.e., Tyro3, Axl, and Mertk), and their ligands Growth arrest specific factor 6 (Gas6) and Protein S (Pros1) contribute to several oncogenic processes, such as cell survival, invasion, migration, chemo-resistance, and metastasis, whereby expression often correlates with poor clinical outcomes. In recent years, there has been great interest in the study of TAM receptors in cancer, stemming both from their roles as oncogenic signaling receptors, as well as their roles in tumor immunology. As a result, several classes of TAM inhibitors that include small molecule tyrosine kinase inhibitors, monoclonal antibodies, decoy receptors, as well as novel strategies to target TAM ligands are being developed. This paper will review the biology of TAM receptors and their ligands with a focus on cancer, as well as evidence-based data for the continued pursuit of TAM/Gas6 inhibitors in clinical practice.

Study of Early Elevated Gas6 Plasma Level as a Predictor of Mortality in a Prospective Cohort of Patients with Sepsis

BACKGROUND

Growth arrest-specific gene 6 (Gas6), a vitamin K-dependent protein interacting with anionic phospholipids and TAM tyrosine kinase receptors, is elevated in plasma of septic patients. Previous studies did not find different levels between survivors and non-survivors at admission because either they included a low number of patients (<50) or a low number of non-survivors (5%).

OBJECTIVES

To determine, in a larger cohort of septic patients comprising an expected number of non-survivors, the performance of the plasma level of Gas6 and its soluble receptor Axl (sAxl) within 24 hours of admission to predict in-ICU mortality.

PATIENTS

Septic adults with or without shock.

METHODS

Gas6 and sAxl were prospectively measured by ELISA at day 0, 3, 7, and then weekly until discharge or death.

RESULTS

We evaluated 129 septic patients, including 82 with and 47 without shock, with in-ICU mortality rate of 19.4% and in-hospital mortality rate of 26%. Gas6 level was higher in non-survivors than in survivors (238 vs. 167%, P = 0.003); this difference remained constant during the ICU stay. The area under the ROC curve for Gas6 (0.695 [95% CI: 0.58-0.81]) was higher than for sAxl, procalcitonin, CRP, IL-1beta, IL-6 and-alpha, and slightly higher than for IL-8, IL-10, SOFA and APACHEII scores in predicting in-ICU mortality. Considering 249% as a cut-off value, Gas6 measurement had a negative predictive value for mortality of 87%.

CONCLUSION

It seems that Gas6 plasma level within 24 hours of ICU admission may predicts in-ICU mortality in patients with sepsis. If our result are confirmed in external validation, Gas6 plasma level measurement could contribute to the identification of patients who may benefit most from more aggressive management.

Circulating growth arrest-specific protein 6 levels are associated with erythropoietin resistance in hemodialysis patients

Growth arrest-specific protein 6 (Gas6) works synergistically with erythropoietin (EPO) to increase the proliferation and maturation of erythroblasts. However, the role of Gas 6 levels on EPO resistance in hemodialysis (HD) patients remains unclear. Therefore, the objective of this study was the first to examine the correlation between plasma Gas6 levels and EPO resistance in HD patients. We enrolled 134 HD patients and 85 healthy individuals. The HD patients were divided into 2 groups: 98 non-EPO-resistant patients and 36 EPO-resistant patients. Plasma levels of Gas6, interleukin 6 (IL-6), high-sensitivity C-reactive protein (hs-CRP), and albumin were quantified. Compared with non-EPO-resistant patients, EPO-resistant patients had elevated plasma concentrations of Gas6 (15.4 ± 3.3 vs. 13.7 ± 3.2 ng/mL, P = 0.006), IL-6 (3.1 ± 3.1 vs. 2.1 ± 1.5 pg/mL, P = 0.009), and hs-CRP (12.7 ± 25.2 vs. 4.5 ± 5.5 mg/L, P = 0.002). In EPO-resistant HD patients, plasma Gas6 levels were negatively correlated with albumin levels (r = −0.388, P < 0.021). Elevated Gas6 levels are associated with EPO resistance in HD patients. Also, EPO resistance is related to inflammation and malnutrition. Thus, circulating Gas6 levels could be used as the potential marker in HD patients with EPO resistance.

Growth arrest-specific 6 and cardiometabolic risk factors in patients with psoriasis

OBJECTIVES

An increased risk for cardiovascular disease with psoriasis has been reported. Growth Arrest-Specific 6 (GAS6) amplifies pro-inflammatory endothelial cell activation via TAM receptors. However, it also inhibits inflammation by multiple mechanisms including phagocytosis. The objective of this study was to investigate whether plasma GAS6 levels are associated with conventional cardiometabolic (CM) risk factors in patients with psoriasis.

METHODS

Forty patients diagnosed with psoriasis (22 male, mean age: 43.3 ± 13.8 years) and 40 age-/sex-matched healthy controls (22 male, mean age: 39.3 ± 8.9 years) were included in the study. CM risk factors (hypertension, hyperlipidemia, diabetes mellitus, and cigarette smoking) were identified. GAS6 levels were measured by ELISA.

RESULTS

There were no significant differences between the plasma GAS6 levels of patients with psoriasis compared to the control group (6.6 ± 2.0 ng/mL, 7.6 ± 2.8 ng/mL, respectively, P > 0.05). However, GAS6 levels of patients with psoriasis having a smoking history (n = 11) were significantly lower than both patients with psoriasis who had no smoking history (n = 29) and controls (5.5 ± 1.7 ng/mL, 6.9 ± 1.9 ng/mL, 7.6 ± 2.8 ng/mL, respectively, P < 0.05). Similarly, psoriasis patients with at least one CM risk factor showed lower GAS6 levels compared to subjects without any CM risk factor (5.7 ± 1.7 ng/mL, 7.3 ± 2.0 ng/mL, P < 0.01). There was no correlation between the GAS6 level, disease duration or PASI score (r = 0.150, -0.150, and P = 0.310, 0.398, respectively).

CONCLUSIONS

This pilot study provides the first evidence in humans for an association between low plasma GAS6 levels and conventional risk factors in psoriasis. Further large scale, prospective studies are needed to confirm these results.

Postmortem serum protein growth arrest-specific 6 levels in sepsis-related deaths

Growth arrest-specific 6 (Gas6) is widely expressed in leukocytes, platelets, endothelial cells, and monocytes. It regulates various processes including granulocyte adhesion to the endothelium, cell migration, thrombus stabilization, and cytokine release. In humans, increased plasma Gas6 levels have been described in patients with sepsis and septic shock. In this study, Gas6 concentrations were measured in postmortem serum from femoral blood in a series of sepsis-related fatalities and control cases. The aims were twofold: first, to determine whether Gas6 can be reliably determined in postmortem serum; and second, to assess its diagnostic potential in identifying sepsis-related deaths. Two study groups were prospectively formed, a sepsis-related fatalities group (24 cases) and a control group (24 cases) including cases of deep vein thrombosis and fatal pulmonary embolism, cases of systemic inflammatory response syndrome in severe trauma, cases of end-stage renal failure, and cases of hanging (non-septic, non-SIRS, non-end stage renal failure cases). The preliminary results of this study seem to indicate that Gas6 can be effectively measured in postmortem serum. However, Gas6 levels in sepsis-related fatalities do not appear to be clearly distinguishable from concentrations in pulmonary embolism, severe trauma, and end-stage renal failure cases. These findings tend to support previous reports that indicated that Gas6 behaves as an acute phase reactant and can be considered a general marker of inflammation rather than a specific biomarker of sepsis.

Growth arrest-specific protein 6 protects against renal ischemia-reperfusion injury

BACKGROUND

Renal injury caused by ischemia-reperfusion (I/R) often occurs after shock or transplantation. Growth arrest-specific protein 6 (Gas6) is a secreted protein that binds to the TAM-Tyro3, Axl, Mer-family tyrosine kinase receptors, which modulate the inflammatory response and activate cell survival pathways. We hypothesized that Gas6 could have a protective role in attenuating the severity of renal injury after I/R.

MATERIALS AND METHODS

Adult mice were subjected to 45 min of bilateral renal ischemia. Recombinant mouse Gas6 (rmGas6, 5 μg per mouse) or normal saline (vehicle) was administered intraperitoneally 1 h before ischemia and all subjects were sacrificed at 23 h after I/R for blood and tissue analysis. The expression of protein and messenger RNA (mRNA) was assessed by Western blotting and quantitative polymerase chain reaction, respectively.

RESULTS

Treatment with rmGas6 significantly decreased serum levels of creatinine and blood urea nitrogen by 29% and 27%, respectively, improved the renal histologic injury index, and reduced the apoptosis in the kidneys, compared with the vehicle. Renal mRNA levels of interleukin 1β, interleukin 6, tumor necrosis factor α, keratinocyte-derived chemokine and macrophage inflammatory protein 2 were decreased significantly by 99%, 60%, 53%, 58%, and 43%, with rmGas6 treatment, respectively. After I/R, renal I-kappa-B α levels were reduced by 40%, whereas they returned to sham levels with rmGas6 treatment. The mRNA levels of inducible nitric oxide synthase and cyclooxygenase 2 were reduced by 79% and 70%, respectively, whereas the expression of cyclin D1 was increased by 2.1-fold in the rmGas6-treated group, compared with the vehicle.

CONCLUSIONS

Gas6 suppresses the nuclear factor κB pathway and promotes cell proliferation, leading to the reduction of inflammation and protection of renal injury induced by I/R.

The association of Tyro3/Axl/Mer signaling with inflammatory response, disease activity in patients with primary Sjögren's syndrome

OBJECTIVES

Defects in Tyro3/Axl/Mer signaling may lead to impaired phagocytosis of apoptotic cells, eventually contributing to the development of autoimmune disease. The association of TAM signaling with several autoimmune disease has been investigated, but it remains unclear in primary Sjögren's syndrome. Therefore, the aim of this study was to evaluate the level of TAM signaling in primary Sjögren's syndrome with its clinical significance.

METHODS

Real-Time Polymerase Chain Reaction was used to determine the mRNA expression of Mer, Tyro-3, Axl, Gas6, and Protein S in Peripheral Blood Mononuclear Cell from 43 pSS and 46 control. The Enzyme-Linked Immunosorbent Assay method was used to test plasma levels of soluble TAM signaling from those individuals, and the relationship of their levels with clinical characteristic was evaluated.

RESULTS

The mRNA expression levels of Tyro-3, Axl were decreased in pSS patients. When considering the plasma level, increased levels of soluble Mer was observed with statistically significant difference. Soluble Mer levels were positively correlated with IgG levels (r=0.53, P<0.01), Erythrocyte Sedimentation Rate levels (r=0.44, P<0.01) and Sjögren's Syndrome Disease Activity Index (r=0.48, P<0.01). And the levels of soluble Mer in patients with the presence of SSA/SSB were higher than those without SSA/SSB.

CONCLUSIONS

The plasma levels of sMer were increased in pSS patients, which was associated with inflammatory response and disease activity.

Monocyte and plasma expression of TAM ligand and receptor in renal failure: Links to unregulated immunity and chronic inflammation

Chronic inflammation is increased in patients with chronic kidney disease (CKD) and contributes to cardiovascular morbidity and mortality. Specific immune mechanisms and pathways that drive and maintain chronic inflammation in CKD are not well described. The TAM ligands (Gas6 and protein S) and receptors (Axl and Mer) have been recently recognized as playing a prominent role in immune regulation. The receptors exist in both soluble and cell-bound forms; the soluble receptors (sAxl and sMer) are believed to compete with the bound receptors and thus inhibit their function. In this study, we determined the expression of cell-bound and soluble TAM proteins in patients with CKD. CKD patients had significantly lower expression of Mer in monocytes, yet increased expression of soluble TAM receptors sAxl and sMer in plasma compared to controls. The metalloproteinase ADAM 17, responsible for cleavage of Mer to its soluble form, was increased in patient monocytes. Elevated levels of soluble TAM receptors were more evident in patients with progressive renal failure. These observations suggest that functional deficiency of TAM receptor-mediated regulation of inflammation may contribute to chronic inflammation in patients with CKD.

Patients with acute-on-chronic liver failure have increased numbers of regulatory immune cells expressing the receptor tyrosine kinase MERTK

BACKGROUND & AIMS

Characteristics of decompensated cirrhosis and acute-on-chronic liver failure (ACLF) include susceptibility to infection, immuneparesis, and monocyte dysfunction. MER receptor tyrosine kinase (MERTK) is expressed by monocytes and macrophages and contributes to down-regulation of innate immune responses. We investigated whether MERTK expression is altered on monocytes from patients with liver failure.

METHODS

We analyzed blood and liver samples collected from patients admitted to the liver intensive therapy unit at King's College Hospital in London from December 2012 through July 2014. Patients had either ACLF (n = 41), acute decompensation of cirrhosis without ACLF (n = 9), cirrhosis without decompensation (n = 17), or acute liver failure (n = 23). We also analyzed samples from healthy individuals (controls, n = 29). We used flow cytometry to determine the level of innate immune function, and associated the findings with disease severity. We developed an assay to measure recruitment and migration of immune cells from the tissue parenchyma. Immunohistochemistry and confocal microscopy were used to determine levels of MERTK in bone marrow, liver, and lymph node tissues. We performed immunophenotype analyses and measured the production of tumor necrosis factor and interleukin 6 and intracellular killing of Escherichia coli by monocytes and peritoneal macrophages incubated with lipopolysaccharide, with or without an inhibitor of MERTK (UNC569).

RESULTS

The number of monocytes and macrophages that expressed MERTK was greatly increased in the circulation, livers, and lymph nodes of patients with ACLF, compared with patients with stable cirrhosis and controls. MERTK expression (mean fluorescence intensity) correlated with the severity of hepatic and extrahepatic disease and systemic inflammatory responses. Based on immunophenotype, migration, and functional analyses, MERTK-expressing monocytes migrate across the endothelia to localize into tissue sites and regional lymph nodes. Expression of MERTK reduced the response of cultured monocytes to lipopolysaccharide; the addition of UNC569 restored production of inflammatory cytokines in response to lipopolysaccharide.

CONCLUSIONS

Patients with ACLF have increased numbers of immunoregulatory monocytes and macrophages that express MERTK and suppress the innate immune response to microbes. The number of these cells correlates with disease severity and the inflammatory response. MERTK inhibitors restore production of inflammatory cytokines by immune cells from patients with ACLF, and might be developed to increase the innate immune response in these patients.

Mer signaling increases the abundance of the transcription factor LXR to promote the resolution of acute sterile inflammation

The receptor tyrosine kinase Mer plays a central role in inhibiting the inflammatory response of immune cells to pathogens. We aimed to understand the function of Mer signaling in the resolution of sterile inflammation in experiments with a Mer-neutralizing antibody or with Mer-deficient (Mer-/-) mice in a model of sterile, zymosan-induced acute inflammation. We found that inhibition or deficiency of Mer enhanced local and systemic inflammatory responses. The exacerbated inflammatory responses induced by the lack of Mer signaling were associated with reduced abundance of the transcription factors liver X receptor α (LXRα) and LXRβ and decreased expression of their target genes in peritoneal macrophages, spleens, and lungs. Similarly, treatment of mice with a Mer/Fc fusion protein, which prevents the Mer ligand Gas6 (growth arrest-specific protein 6) from binding to Mer, exacerbated the inflammatory response and decreased the abundance of LXR. Coadministration of the LXR agonist T0901317 with the Mer-neutralizing antibody inhibited the aggravating effects of the antibody on inflammation in mice. In vitro exposure of RAW264.7 cells or primary peritoneal macrophages to Gas6 increased LXR abundance in an Akt-dependent manner. Thus, we have elucidated a previously uncharacterized pathway involved in the resolution of acute sterile inflammation: Enhanced Mer signaling during the recovery phase increases the abundance and activity of LXR to inactivate the inflammatory response in macrophages.

Gene expression in obliterative bronchiolitis-like lesions in 2,3-pentanedione-exposed rats

Obliterative bronchiolitis (OB) is an irreversible lung disease characterized by progressive fibrosis in the small airways with eventual occlusion of the airway lumens. OB is most commonly associated with lung transplant rejection; however, OB has also been diagnosed in workers exposed to artificial butter flavoring (ABF) vapors. Research has been limited by the lack of an adequate animal model of OB, and as a result the mechanism(s) is unclear and there are no effective treatments for this condition. Exposure of rats to the ABF component, 2,3-pentanedione (PD) results in airway lesions that are histopathologically similar to those in human OB. We used this animal model to evaluate changes in gene expression in the distal bronchi of rats with PD-induced OB. Male Wistar Han rats were exposed to 200 ppm PD or air 6 h/d, 5 d/wk for 2-wks. Bronchial tissues were laser microdissected from serial sections of frozen lung. In exposed lungs, both fibrotic and non-fibrotic airways were collected. Following RNA extraction and microarray analysis, differential gene expression was evaluated. In non-fibrotic bronchi of exposed rats, 4683 genes were significantly altered relative to air-exposed controls with notable down-regulation of many inflammatory cytokines and chemokines. In contrast, in fibrotic bronchi, 3807 genes were significantly altered with a majority of genes being up-regulated in affected pathways. Tgf-β2 and downstream genes implicated in fibrosis were significantly up-regulated in fibrotic lesions. Genes for collagens and extracellular matrix proteins were highly up-regulated. In addition, expression of genes for peptidases and peptidase inhibitors were significantly altered, indicative of the tissue remodeling that occurs during airway fibrosis. Our data provide new insights into the molecular mechanisms of OB. This new information is of potential significance with regard to future therapeutic targets for treatment.

Plasma growth arrest-specific protein 6 levels in premenopausal and postmenopausal women: the role of endogenous estrogen

Growth arrest-specific 6 (Gas6) is a vitamin K-dependent protein that interacts with receptor tyrosine kinases of the Tyro-3, AXL, Mer (TAM) family. The Gas6/TAM system contributes to the regulation of cell survival and proliferation, cell adhesion and migration, and inflammatory cytokines release. Plasma Gas6 plays an important role in the inflammatory process, and is involved in diverse human diseases. Few studies have investigated gender-specific variations in plasma Gas6 concentration. Hence, the aim of this study was to determine whether plasma Gas6 levels are associated with sex hormones in premenopausal and postmenopausal women. A total of 103 premenopausal and 135 postmenopausal women were recruited. Plasma Gas6 concentration, estradiol (E2), and sex hormone-binding globulin were assayed. The free estrogen index (FEI) was calculated. The results showed significantly lower Gas6 levels in the postmenopausal compared to the premenopausal women (P < 0.005). Plasma Gas6 levels were positively correlated with E2 levels in the pre- and postmenopausal women (r = 0.359, P < 0.001 and r = 0.261, P = 0.002, respectively). Gas6 levels were also correlated with FEI in the pre- and postmenopausal women (r = 0.234, P = 0.017 and r = 0.188, P = 0.029, respectively). After adjusting for confounders, the correlations still remained significant. In multiple stepwise regression analysis, only E2 in premenopausal and both age and E2 in postmenopausal women were independently correlated with the plasma Gas6 levels (all P < 0.001). These results suggest that plasma Gas6 is associated with sex hormones in both pre- and postmenopausal women, indicating a potential role of sex hormones in the Gas6/TAM system.

Growth arrest-specific protein 6 attenuates neutrophil migration and acute lung injury in sepsis

Sepsis is an acute inflammatory condition that can result in multiple organ failure and acute lung injury. Growth arrest-specific protein 6 (Gas6) is a broad regulator of the innate immune response involved with the nuclear factor κB signaling pathway. We hypothesized that Gas6 could have a protective role in attenuating the severity of acute lung injury and sepsis. Male mice were subjected to sepsis by cecal ligation and puncture (CLP) after which recombinant murine Gas6 (rmGas6; 5 μg/mouse) or normal saline (vehicle) was administered intravenously. Blood and lung tissues were collected at 20 h after CLP for various measurements. Treatment with rmGas6 significantly reduced serum levels of the injury markers aspartate aminotransferase, alanine aminotransferase, and lactate dehydrogenase, as well as proinflammatory cytokines interleukin 6 (IL-6) and IL-17, compared with the vehicle group (P < 0.05). The parenchyma of the lungs damaged by CLP was attenuated by rmGas6 treatment. Lung mRNA levels of tumor necrosis factor α, IL-1β, IL-6, IL-17, and macrophage inflammatory protein 2 (MIP-2) were decreased by 60%, 86%, 82%, 93%, and 82%, respectively, with rmGas6 treatment as determined by real-time reverse transcriptase-polymerase chain reaction (P < 0.05). The degradation of IκB-α induced by CLP in the lungs was inhibited by rmGas6 treatment. The number of neutrophils and myeloperoxidase activity in the lungs were significantly reduced in the rmGas6 group. Moreover, rmGas6 reduced the in vitro migration of differentiated human promyelocytic HL60 cells by 64%. Finally, the 10-day survival rate of mice subjected to CLP was increased from 31% in the vehicle group to 67% in the rmGas6 group (P < 0.05). Thus, Gas6 has potential to be developed as a novel therapeutic agent to treat patients with sepsis and acute lung injury.

Expression of growth arrest-specific protein 6 and Axl molecules in the left internal mammary artery of patients undergoing coronary artery bypass grafting

AIMS

Studies have demonstrated that using a left internal mammary artery (LIMA) graft yields excellent long-term results in coronary artery bypass grafting (CABG). The growth arrest-specific 6 (Gas6) gene and its receptor, Axl, are crucial in vascular haemostasis and atherosclerosis. The objective of this study was to determine the expression of Gas6 and Axl molecules in the aorta and LIMA in patients undergoing CABG.

METHODS

Plasma and tissue specimens were collected from 19 patients undergoing elective CABG. The expression of the Gas6 and Axl in the injured aorta and LIMA was examined using reverse transcription PCR (RT-PCR), real-time RT-PCR, western blot and immunohistochemical staining.

RESULTS

In CABG patients, the mRNA, immunoreactivity and protein expressions of the Gas6 and Axl were considerably higher in the LIMA than those in the aorta. Further analysis revealed that the expression of the Gas6 positively correlated with that of Axl in the LIMA and aorta. The plasma Gas6 level was considerably and positively correlated with the expression of Gas6 protein in the LIMA and aorta.

CONCLUSIONS

The present study discovered that the higher expression of Gas6/Axl pathway components in the LIMA compared with that in the aorta may partly explain the less frequent atherosclerotic events involving the LIMA compared with other arteries. Moreover, Gas6 may play a critical and protective role in human vascular biology.

Serum growth arrest-specific protein 6 levels are elevated in adult-onset Still's disease

We investigated the growth arrest-specific protein 6 in adult-onset Still's disease. Serums were collected from 52 adult-onset Still's disease patients with follow-up samples of 21 patients. The growth arrest-specific protein 6 levels in adult-onset Still's disease were higher compared to those in the normal controls (25.37±7.71 vs. 19.86±5.01 ng/mL, p<0.001). However, growth arrest-specific protein 6 did not correlate with disease activity. Also, growth arrest-specific protein 6 was not decreased after activity was resolved in the follow-up. The growth arrest-specific protein 6 in adult-onset Still's disease patients were higher than the normal controls. However, growth arrest-specific protein 6 was not correlated with disease activity.

The levels of plasma growth arrest-specific protein 6 is associated with insulin sensitivity and inflammation in women

AIMS

Vitamin K-dependent growth arrest-specific protein 6 (Gas6) and its receptors of the TAM (TYRO-3/Axl/Mer) family are ubiquitously expressed in immune, cardiovascular, and reproductive systems. They play pivotal roles of regulating tissue homeostasis via anti-inflammatory effects. Recent studies show that the Gas6/TAM system is involved in glucose tolerance-related metabolic disorders. Our aim was to investigate the link between Gas6 protein, insulin sensitivity and inflammatory cytokines in men and women.

METHODS

A total of 278 adults (126 men and 152 women) were recruited in this study. Plasma Gas6 concentration and various biochemical, proinflammatory and endothelial markers were measured. Insulin sensitivity was estimated by homeostasis model assessment.

RESULTS

Waist, fasting and 2h post-load glucose, and glycated hemoglobin (HbA1C) were significantly lower in women than in men. Age, high-density lipoprotein cholesterol, and highly-sensitive C-reactive protein levels were significantly higher in women than in men. Plasma Gas6 levels were negatively correlated with waist (r = -0.187, P = 0.022), HOMA-IR (r = -0.171, P=0.035), interleukin 6 (r = -0.362, P < 0.001), and E-selectin (r = -0.216, P = 0.008), while they were positively correlated with insulin sensitivity (QUICKI) (r = 0.168, P = 0.039) in women, but not in men. Stepwise multiple regression analysis showed that TNF-α was independently correlated with plasma Gas6 levels in both the sexes (P < 0.001).

CONCLUSION

Plasma Gas6 is associated with obesity, insulin sensitivity, inflammation, and endothelial dysfunction in women and may be a general marker of inflammatory conditions in women.

Increased concentrations of plasma growth arrest-specific 6 and its soluble tyrosine kinase receptor sAxl in Taiwanese women with pelvic inflammatory disease

BACKGROUNDS

To investigate the concentrations of plasma growth arrest-specific protein 6 (Gas6) and its soluble tyrosine kinase receptor sAxl in women with pelvic inflammatory disease (PID) and their association with clinical outcomes of PID.

METHODS

Blood specimens were consecutively collected from the 64 patients with PID before and after treatment and 70 healthy women in university hospital. Concentrations of plasma Gas6 and sAxl were detected using enzyme-linked immunosorbent assay.

RESULTS

The concentration of plasma Gas6 and sAxl was significantly increased in the patients with PID compared to the healthy controls, and then reduced significantly after treatment. Gas6 was significantly correlated with sAxl. When we selected 7.5 and 15.2 ng/ml as the cutoff concentration of plasma Gas6 and sAxl to detect PID respectively, the sensitivities of Gas6 and sAxl were 76.6% and 75.0%. When Gas6 and sAxl were combined, the sensitivity rose to 92.2%. They were not related to the incidences of tuboovarian abscesses and surgery, which were, however, significantly associated with length of hospital stay.

CONCLUSIONS

Novel application of Gas6 or sAxl in combination had a high sensitivity to detect PID and is important in order to prevent severe sequelae.

Plasma concentrations predict aortic expression of growth-arrest-specific protein 6 in patients undergoing coronary artery bypass grafting

AIMS

The tyrosine kinase receptor Axl is expressed in the vasculature, and growth arrest-specific protein 6 (Gas6) is its ligand. Plasma Gas6 levels have been shown to be associated with endothelial dysfunction markers and cardiovascular events. We set out to determine the plasma Gas6 levels in patients undergoing coronary artery bypass grafting (CABG) and investigate the expression of Gas6 and Axl in the aorta.

METHODS AND RESULTS

Immunoassays were used to investigate plasma Gas6 levels in CABG patients (n = 19) and control subjects (n = 20). The expression of Gas6 and Axl in the injured aorta were examined by reverse transcription-polymerase chain reactions, real-time reverse transcription-polymerase chain reactions, western blotting, and immunohistochemical staining. Plasma Gas6 levels were significantly lower in CABG patients than in matched control subjects. In CABG patients, plasma Gas6 levels were negatively correlated with fasting glucose, E-selectin, and vascular cell adhesion molecule-1 levels. The levels predicted the operative mortality rate and were positively correlated with plasma soluble Axl (sAxl) levels and Gas6 expression in the aorta. Moreover, Gas6 expression was positively correlated with Axl expression in the aorta.

CONCLUSION

We concluded that plasma Gas6 is associated with fasting glucose, endothelial dysfunction markers, sAxl values, and vascular Gas6 expression in CABG patients, and it predicts the operative mortality of these patients. These findings suggest that the Gas6/Axl system is crucial in vascular biology.

Diagnostic and prognostic markers in sepsis

Sepsis is a common and serious complication in intensive care unit patients. An important factor in optimizing survival rates in septic patients is the ability to start treatment early in the course of disease; there is, therefore, a need for accurate diagnostic tests. In recent years, there has been a move away from the rather vague and nonspecific signs that were previously used to diagnose sepsis towards the possible adjunctive role of biomarkers. Many biomarkers have been proposed and assessed clinically, but none alone is specific enough to definitively determine diagnosis. The future direction of research is most likely a greater focus on the use of panels or combinations of markers with clinical signs. Some biomarkers may also be useful for prognosis and guiding therapy. Here, the authors will review our changing approaches to sepsis diagnosis and discuss some of the markers that seem most relevant at the present time.

Serum growth arrest-specific protein 6 levels are a reliable biomarker of disease activity in systemic lupus erythematosus

PURPOSE

Growth arrest-specific protein 6 (Gas6) has been suggested to be a biomarker of disease activity in patients with systemic lupus erthematosus (SLE). We investigated the clinical significance of this protein in Korean SLE.

METHODS

Blood samples were collected from 150 SLE patients and 50 normal controls (NC). In addition, follow-up samples were collected from 50 SLE patients.

RESULTS

Serum Gas6 levels of SLE patients (43.01 ± 28.02 ng/mL) were higher than those of NC (20.15 ± 9.23 ng/mL, p<0.001). When evaluated sensitivity and specificity of the Gas6 for diagnosing SLE using ROC curves, the sensitivity and specificity were 72.7 % and 84 % with a cut-off value of 25.3 ng/mL. In the ROC analysis of Gas6, anti-dsDNA antibody, ESR, complement 3 and complement 4 to identify patients with active lupus, area under the curve (AUC) of Gas6 was highest with 0.763. Serum Gas6 levels were significantly higher in the patients with serositis (70.04 ± 30.85 ng/mL) and renal disorder (65.66 ± 32.28 ng/mL) compared to those without (41.88 ± 27.44 ng/mL, p=0.033, 40.3 ± 26.33 ng/mL, p=0.001, respectively). Gas6 levels were correlated positively with anti-dsDNA antibody (r=0.199, p=0.015), ESR (r=0.204, p=0.013) and SLEDAI (r=0.512, p<0.001). In addition, serum Gas6 levels were correlated negatively with hemoglobin (r= -0.165, p=0.043), lymphocyte count (r= -0.165, p=0.043), complement 3 (r= -0.343, p<0.001) and complement 4 (r= -0.316, p<0.001). Furthermore, change in serum Gas6 levels was correlated with change in SLEDAI levels in the SLE patients that were followed up (r=0.524, p<0.001).

CONCLUSION

These results suggest that serum Gas6 can be a reliable clinical marker for monitoring disease activity and treatment response in SLE.

Growth arrest-specific gene 6 (Gas6) levels are elevated in patients with chronic renal failure

BACKGROUND

The TAM receptors (tyro3, axl and mer) and their ligands (vitamin K-dependent proteins-Gas6 and Protein S) are crucial modulators of inflammation, which may be relevant in chronic kidney disease (CKD). Gas6 and axl have multiple roles in mediating vascular atherosclerosis and injury, thrombosis and inflammation, yet nothing is known about the Gas6-axl pathway in humans with CKD. Given the prevalence of chronic inflammation and vascular disease in this population, we measured TAM ligands in patients with various levels of renal function.

METHODS

Gas6 and protein S were quantified in the plasma by ELISA in three patient groups: end-stage renal disease on chronic hemodialysis (HD), CKD and normal controls.

RESULTS

Significantly increased levels of Gas6 and protein S were found in CKD patients compared with normal controls (P < 0.01 and <0.001, respectively). In HD patients, Gas6 levels were elevated compared with controls (P < 0.001) and positively associated with low albumin (r = 0.33; P = 0.01), dialysis vintage (r = 0.36; P = 0.008) and IV iron administration (r = 0.33; P = 0.01). The levels of Gas6 rose with CKD stage and were inversely associated with estimated GFR (P < 0.0001).

CONCLUSIONS

Dysregulation of circulating Gas6 is associated with renal disease and inversely proportional to renal function. Low albumin and higher IV iron administration were associated with higher Gas6 levels, suggesting a possible connection between inflammation and oxidative stress mediated by iron. Protein S levels were also elevated in CKD patients, but the relevance of this finding needs to be further investigated.

Inhibiting Mer receptor tyrosine kinase suppresses STAT1, SOCS1/3, and NF-κB activation and enhances inflammatory responses in lipopolysaccharide-induced acute lung injury

Mer signaling participates in a novel inhibitory pathway in TLR activation. The purpose of the present study was to examine the role of Mer signaling in the down-regulation of TLR4 activation-driven immune responses in mice, i.t.-treated with LPS, using the specific Mer-blocking antibody. At 4 h and 24 h after LPS treatment, expression of Mer protein in alveolar macrophages and lung tissue decreased, sMer in BALF increased significantly, and Mer activation increased. Pretreatment with anti-Mer antibody did not influence the protein levels of Mer and sMer levels. Anti-Mer antibody significantly reduced LPS-induced Mer activation, phosphorylation of Akt and FAK, STAT1 activation, and expression of SOCS1 and -3. Anti-Mer antibody enhanced LPS-induced inflammatory responses, including activation of the NF-κB pathway; the production of TNF-α, IL-1β, and MIP-2 and MMP-9 activity; and accumulation of inflammatory cells and the total protein levels in BALF. These results indicate that Mer plays as an intrinsic feedback inhibitor of the TLR4- and inflammatory mediator-driven immune responses during acute lung injury.

The growth arrest-specific 6 (Gas6) gene polymorphism c.834+7G>A is associated with type 2 diabetes

AIMS

The plasma protein growth arrest-specific 6 (Gas6) is important to the inflammatory process and involved in the development of diabetic renal and vascular complications. Recently, Gas6 protein also represents a novel independent risk factor of type 2 diabetes. We further investigated the association of c.843+7G>A Gas6 polymorphism and type 2 diabetes.

METHODS

A total of 278 adults, including 96 with normal glucose tolerance (NGT), 82 with impaired glucose tolerance (IGT), and 100 with type 2 diabetes were recruited. All subjects were genotyped for c.843+7G>A Gas6 polymorphism.

RESULTS

Plasma Gas6 concentrations were significantly lower among patients with type 2 diabetes compared to subjects with IGT and NGT. Subjects with Gas6 c.843+7AA genotype had higher Gas6 levels and lower glucose values than GG genotype. The AA genotype and A allele were less frequent in patients with type 2 diabetes compared with NGT subjects. In univariate analysis, the AA genotype was found to be associated with a decreased risk for type 2 diabetes. Moreover, the association was even stronger after adjustment for established diabetes risk factors.

CONCLUSIONS

The Gas6 c.843+7AA genotype and A allele are less prevalent in type 2 diabetes, which may have a protective role for type 2 diabetes.

Plasma concentrations of Gas6 and sAxl correlate with disease activity in systemic lupus erythematosus

OBJECTIVES

SLE is a systemic autoimmune disease with an annual incidence of 3.8 per 100,000. Several pathogenic mechanisms are believed to be operating in SLE, including an impaired clearance of apoptotic cells, activation of the type I IFN pathway and generation of autoimmune leucocytes. Growth arrest-specific protein 6 (Gas6) and its receptor Axl are known to regulate inflammation and may be implicated in lupus pathogenesis. We have recently developed immunological methods to quantify the vitamin-K-dependent protein Gas6 and its soluble receptor sAxl in human plasma, which we have used to investigate the role of Gas6 and soluble Axl in SLE.

METHODS

We have investigated the relation between the plasma concentrations of Gas6 and sAxl and disease activity and specific symptoms in 96 SLE patients.

RESULTS

Gas6 and sAxl concentrations correlated with SLEDAI (r = 0.48, P < 0.001 and r = 0.39, P < 0.001, respectively). Furthermore, concentrations of Gas6 and sAxl correlated with ESR and CRP and inversely with haemoglobin levels. Gas6 and sAxl concentrations were significantly higher in patients with anti-DNA antibodies, leucopenia and GN.

CONCLUSION

The plasma concentrations of Gas6 and sAxl vary with disease activity in SLE, in particular GN, and may have a role in lupus pathogenesis. Furthermore, Gas6 and sAxl may be of use as biomarkers of disease activity.

GAS6 in systemic inflammatory diseases: with and without infection

Vitamin K-dependent proteins are not only essential regulators of blood coagulation. A recent paper in Critical Care describes the levels of the vitamin K-dependent GAS6 and the soluble form of its receptor Axl in plasma from patients with sepsis of systemic inflammation. The results confirm that GAS6 is elevated during septicemia, but the fact that inflammatory conditions without infection produce a similar effect suggests it is inflammation that induces the synthesis of GAS6, rather than the interactions with bacteria or other infectious agents. The soluble form of the GAS6 receptor Axl was induced less compared with the effect observed in GAS6. This is important as the two proteins form an inactive complex in plasma, suggesting that a functional GAS6 form could be synthesized under these conditions. GAS6 has been proposed as a broad regulator of the innate immune response. GAS6 synthesis is therefore likely to be a regulatory mechanism during systemic inflammation. Recent advances provide the necessary tools for further research, including genetic screenings of the components of this system.

Growth arrest-specific protein 6 is hepatoprotective against murine ischemia/reperfusion injury

Growth arrest-specific gene 6 (GAS6) promotes growth and cell survival during tissue repair and development in different organs, including the liver. However, the specific role of GAS6 in liver ischemia/reperfusion (I/R) injury has not been previously addressed. Here we report an early increase in serum GAS6 levels after I/R exposure. Moreover, unlike wild-type (WT) mice, Gas6(-/-) mice were highly sensitive to partial hepatic I/R, with 90% of the mice dying within 12 hours of reperfusion because of massive hepatocellular injury. I/R induced early hepatic protein kinase B (AKT) phosphorylation in WT mice but not in Gas6(-/-) mice without significant changes in c-Jun N-terminal kinase phosphorylation or nuclear factor kappa B translocation, whereas hepatic interleukin-1β (IL-1β) and tumor necrosis factor (TNF) messenger RNA levels were higher in Gas6(-/-) mice versus WT mice. In line with the in vivo data, in vitro studies indicated that GAS6 induced AKT phosphorylation in primary mouse hepatocytes and thus protected them from hypoxia-induced cell death, whereas GAS6 diminished lipopolysaccharide-induced cytokine expression (IL-1β and TNF) in murine macrophages. Finally, recombinant GAS6 treatment in vivo not only rescued GAS6 knockout mice from severe I/R-induced liver damage but also attenuated hepatic damage in WT mice after I/R.

CONCLUSION

Our data have revealed GAS6 to be a new player in liver I/R injury that is emerging as a potential therapeutic target for reducing postischemic hepatic damage.

Plasma protein growth arrest-specific 6 levels are associated with altered glucose tolerance, inflammation, and endothelial dysfunction

OBJECTIVE

Plasma protein growth arrest-specific 6 (Gas6) is important to the inflammatory process and is involved in the development of diabetic renal and vascular complications. We set out to determine whether plasma Gas6 levels are associated with altered glucose tolerance, insulin sensitivity, inflammation, and endothelial dysfunction.

RESEARCH DESIGN AND METHODS

A total of 278 adults, including 96 with normal glucose tolerance (NGT), 82 with impaired glucose tolerance (IGT), and 100 with type 2 diabetes were recruited. Plasma Gas6 concentration and biochemical, proinflammatory, and endothelial variables were determined. Insulin sensitivity was examined by homeostasis model assessment.

RESULTS

Plasma Gas6 concentration was significantly lower among patients with type 2 diabetes compared with subjects with NGT (P < 0.001). The plasma Gas6 value was inversely correlated with fasting glucose, tumor necrosis factor (TNF)-alpha, interleukin (IL)-6, and vascular cell adhesion molecule (VCAM)-1. In multivariate logistic regression analysis, after adjustment for established diabetes risk factors, higher plasma Gas6 concentrations were significantly associated with a decreased risk of type 2 diabetes. Moreover, the association became slightly stronger after further adjustment for TNF-alpha, IL-6, high-sensitive C-reactive protein, E-selectin, intercellular adhesion molecule-1, and VCAM-1.

CONCLUSIONS

Plasma Gas6 is associated with altered glucose tolerance, inflammation, and endothelial dysfunction. It also may represent a novel independent risk factor of type 2 diabetes and a potential surrogate marker of inflammation and endothelial dysfunction.

Plasma concentrations of Gas6 and soluble Axl correlate with disease and predict mortality in patients with critical limb ischemia

INTRODUCTION

Critical limb ischemia (CLI) is a severe peripheral arterial disease, characterized by rest pain, ulcers and gangrene in the legs. Gas6 is a vitamin K-dependent protein, which binds and activates the tyrosine kinase receptor Axl. Gas6-mediated Axl-signaling influences endothelial activation, neointima formation and immune regulation. Axl can be cleaved and soluble Axl (sAxl) is detectable in circulation.

DESIGN AND METHODS

We quantified plasma concentrations of Gas6 and sAxl in 189 CLI patients and 204 controls.

RESULTS

Gas6 and sAxl concentrations were increased in the CLI patients (p<0.0001) and correlated to C-reactive protein, interleukin-6, tumor necrosis factor alpha and neopterin. Patients who died within 3years of sampling (n=84) had increased concentrations of Gas6 and sAxl as compared to survivors (p=0.0009 and p=0.0011).

CONCLUSIONS

Plasma concentrations of Gas6 and sAxl correlate to inflammation and predict survival. This indicates that Gas6 and sAxl have a role in CLI, presumably connected to the inflammatory process.

Gas6 is complexed to the soluble tyrosine kinase receptor Axl in human blood

BACKGROUND

The vitamin K-dependent Gas6 protein (product of growth arrest specific gene 6) binds to, and activates the TAM receptor tyrosine kinases Tyro3, Axl and Mer. It has been suggested that Gas6 and the TAM receptors are important for primary platelet functions, but Gas6 cannot be found in human platelets. However, Gas6 is present in human plasma at a concentration of around 0.2 nM, which is a thousand-fold lower than that of the homologous protein S. The Axl and Mer receptors can be cleaved close to the cell membrane, yielding soluble molecules consisting of the extracellular parts of the receptors.

OBJECTIVE

To investigate if soluble Axl (sAxl) is present in human serum and plasma and if Gas6 circulates in complex with sAxl.

METHODS

We expressed recombinant sAxl, raised antibodies and developed and validated an ELISA for Axl. Serum and plasma were analyzed using ELISAs for Gas6, Axl and sAxl-Gas6 complexes. Serum was gel filtered and fractions analyzed by the different ELISAs to determine if Gas6 in serum is free or complexed. Immunoprecipitation was used to investigate binding between Gas6 and sAxl in serum.

RESULTS

sAxl is present in serum and plasma at around 0.6 nM and all Gas6 is bound to sAxl. No complexes between Gas6 and the soluble forms of Mer and Tyro3 could be detected, indicating that sAxl is the physiological binder of Gas6 in human serum.

CONCLUSIONS

Gas6 in circulation is bound to sAxl suggesting circulating Gas6 to be inhibited and incapable of stimulating the TAM receptors.

Plasma concentrations of Gas6 (growth arrest specific protein 6) and its soluble tyrosine kinase receptor sAxl in sepsis and systemic inflammatory response syndromes

INTRODUCTION

Gas6, the protein product of the growth arrest specific gene 6, is present in human circulation at subnanomolar concentrations. It is secreted by endothelial cells and is important for the activation of endothelium during inflammation. Axl, the tyrosine kinase receptor for Gas6, is also present in endothelium and can be cleaved and released into the circulation. The soluble of form Axl (sAxl), which is present in plasma, can bind Gas6 and inhibit Axl-mediated cell signalling.

METHODS

We have developed reproducible and accurate enzyme-linked immunosorbent assays for both Gas6 and sAxl and used them to investigate plasma samples from 70 patients with severe sepsis, 99 patients with sepsis, 42 patients with various infections causing fever but no systemic inflammatory response syndrome (SIRS), 20 patients with SIRS without verified infection, and 100 blood donors that served as controls. Correlations between Gas6 and sAxl concentrations and other commonly used analytes were investigated.

RESULTS

The patients with severe sepsis, sepsis, infection or SIRS had all increased concentrations of Gas6, approximately double compared to what was found in the controls. The concentrations of sAxl were also increased in the patient groups compared to the controls. Gas6 correlated with C-reactive protein, procalcitonin and interleukin 6, whereas sAxl correlated to bilirubin and procalcitonin.

CONCLUSIONS

We can confirm results of earlier studies showing that circulating Gas6 is increased in sepsis and related syndromes. sAxl is increased, but less pronounced than Gas6. The concentrations of Gas6 and sAxl correlate with a number of inflammatory markers, suggesting a role in systemic inflammation.

TAM receptor ligands in lupus: protein S but not Gas6 levels reflect disease activity in systemic lupus erythematosus

INTRODUCTION

The TAM (tyro 3, axl, mer) kinases are key regulators of innate immunity and are important in the phagocytosis of apoptotic cells. Gas6 and protein S are ligands for these TAM kinases and bind to phosphatidyl serine residues exposed during apoptosis. In animal models, absence of TAM kinases is associated with lupus-like disease. To test whether human systemic lupus erythematosus (SLE) patients might have deficient levels of TAM ligands, we measured Gas 6 and protein S levels in SLE.

METHODS

107 SLE patients were recruited. Of these, 45 SLE patients were matched age, gender and ethnicity with normal controls (NC). Gas6 and free protein S were measured with sandwich enzyme linked immunosorbent assays (ELISAs).

RESULTS

Overall, the plasma concentrations of Gas6 and free protein S were not different between 45 SLE patients and 45 NC. In SLE patients, the levels of free protein S were positively correlated with age (r = 0.2405, P = 0.0126), however those of Gas6 were not. There was no correlation between the concentrations of Gas6 and free protein S in individuals. Levels of free protein S were significantly lower in SLE patients with a history of serositis, neurologic disorder, hematologic disorder and immunologic disorder. Gas6 levels were elevated in patients with a history of neurologic disorder. The SLE patients with anti-Sm or anti-cardiolipin IgG showed lower free protein S levels. Circulating free protein S was positively correlated with complement component 3 (C3) (r = 0.3858, P < 0.0001) and complement component 4 (C4) (r = 0.4275, P < 0.0001). In the patients with active BILAG hematologic involvement, the levels of free protein S were lower and those of Gas6 were higher.

CONCLUSIONS

In SLE, free protein S was decreased in patients with certain types of clinical history and disease activity. Levels of free protein S were strongly correlated with C3 and C4 levels. Gas6 levels in SLE patients differed little from levels in NC, but they were elevated in the small numbers of patients with a history of neurological disease. The correlation of decreased protein S levels with lupus disease activity is consistent with a role for the TAM receptors in scavenging apoptotic cells and controlling inflammation. Protein S appears more important functionally in SLE patients than Gas6 in this regard.

Plasma concentrations of growth arrest-specific protein 6 and protein S in patients with acute pancreatitis

BACKGROUND

The aim of the present study was to clarify the changes in plasma concentrations of growth arrest-specific protein 6 (Gas6) and protein S (PS) in patients with mild or severe acute pancreatitis (AP).

METHODS

The study group comprised 29 consecutive patients with AP (24 males, five females; mean age, 54.8 +/- 15.0 years) and 20 healthy controls (10 males, 10 females; mean age, 53.0 +/- 15.3 years). Plasma concentrations of Gas6 and PS were measured by enzyme-linked immunosorbent assay.

RESULTS

The concentration of Gas6 was significantly higher in both severe and mild AP than in healthy controls, and was significantly correlated with two of the multiple organ failure assessment scores. Furthermore, when compared with survivors, the concentrations of Gas6 in non-survivors of severe AP were significantly increased. The concentrations of free PS and total PS were significantly decreased compared with normal controls, but there was no difference between cases and controls in the concentrations of C4 binding protein-PS.

CONCLUSION

Plasma concentrations of Gas6 and PS correlate with disease severity. High concentrations of Gas6 reflect microcirculatory abnormalities, and phagocytosis of dying cells in sepsis associated with severe AP.

Plasma concentrations of growth arrest specific protein 6 and the soluble form of its tyrosine kinase receptor Axl as markers of large abdominal aortic aneurysms

OBJECTIVE

The tyrosine kinase receptor Axl is expressed in the vasculature and Gas6 is the ligand. The extracellular part of Axl (sAxl) can be found in circulation. The aim of this study was to determine plasma concentrations of Gas6 and sAxl in patients with abdominal aortic aneurysms (AAA) and to evaluate if Gas6 and sAxl can be used as biomarkers.

DESIGN AND METHODS

Immunoassays for sAxl and Gas6 were used to investigate plasma from AAA patients. Patients with large (n=123) or small AAA (n=122) were compared with healthy controls (n=141).

RESULTS

Gas6 correlated positively and sAxl correlated negatively with AAA size. As a consequence, the calculated Gas6/sAxl ratios correlated even better to AAA size. Forty percent of all patients with a large AAA had higher Gas6/sAxl ratio than any in the control group.

DISCUSSION

The Gas6/Axl system might be involved in AAA pathogenesis, and the Gas6/sAxl ratio may be useful as a biomarker.

Growth arrest specific protein 6 participates in DOCA-induced target-organ damage

Growth arrest-specific protein 6 (Gas 6) is involved in inflammatory kidney diseases, vascular remodeling, cell adhesion, and thrombus formation. We explored a role for Gas 6 in aldosterone-induced target organ damage. We observed that Gas 6 was upregulated in rats with high aldosterone levels. Mineralocorticoid receptor blockade prevented target organ damage and decreased the elevated Gas 6 expression. Vascular smooth muscle cells given aldosterone increased their Gas 6 expression in vitro. To test the pathophysiological relevance, we investigated the effects of deoxycorticosterone acetate (DOCA) on Gas 6 gene-deleted ((-/-)) mice. After 6 weeks DOCA, Gas 6(-/-) mice developed similar telemetric blood pressure elevations compared to wild-type mice but were protected from cardiac hypertrophy. Cardiac expression of interleukin 6 and collagen IV was blunted in Gas 6(-/-) mice, indicating reduced inflammation and fibrosis. Gas 6(-/-) mice also had an improved renal function with reduced albuminuria, compared to wild-type mice. Renal fibrosis and fibronectin deposition in the kidney were also reduced. Gas 6 deficiency reduces the detrimental effects of aldosterone on cardiac and renal remodeling independent of blood pressure reduction. Gas 6 appears to play a role in mineralocorticoid receptor-mediated target organ damage. Furthermore, because warfarin interferes with Gas 6 protein expression, the findings could be of clinical relevance for anticoagulant choices.

Plasma level of growth arrest-specific 6 (GAS6) protein and genetic variations in the GAS6 gene in patients with acute coronary syndrome

Growth arrest-specific gene 6 (GAS6) encodes a vitamin K-dependent protein that regulates inflammation, angiogenesis, and atherosclerotic plaque formation. The level of GAS6 expression is associated with plaque stability and stroke. We explored the role of GAS6 in cardiovascular disease, particularly in acute coronary syndrome (ACS). We determined the plasma levels of GAS6 protein by using an enzyme-linked immunosorbent assay method and investigated the role of the single nucleotide polymorphism (c.834+7G>A) in ACS. The median (interquartile range) plasma GAS6 levels were 16.9 microg/L (13-28 microg/L) in healthy control subjects and 10.65 microg/L (5.7-27.5 microg/L) in patients with ACS. The genotype frequencies for GG, AG, and AA, respectively, in patients with ACS were 66% (37/56), 29% (16/56), and 5% (3/56) and were 35% (14/40), 45% (18/40), 20% (8/40) in the control group. The AA genotype and A allele were less frequent in patients with ACS than in control subjects (P < .001). Our study indicates that GAS6 plasma concentrations at admission reflect the presence of common cardiovascular risk factors and can predict cardiovascular events. In addition, the AA genotype and A allele of the GAS6 gene relate to ACS, which may have a protective role against ACS.