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

Does serum Gas6 level change in active uveitis?

Purpose

The aim of this study was to investigate serum Growth Arrest-Specific Protein 6 (Gas6) levels in the active and inactive periods of uveitis.

Material and methods

In this study, serum Gas6 levels were evaluated in 21 patients during active and inactive periods. After measuring serum Gas6 levels in the active phase, the serum Gas6 test was repeated in the inactive period. Commercial Enzyme-Linked Immunosorbent Assay (ELISA) kits (Gas6, WKEA Med Supplies Corporation, NY, USA) were used to measure Gas6 levels. Plasma concentrations were analyzed with an ELISA reader at 450 nm following the manufacturer's instructions.

Results

In the study, the mean age of 21 patients was 33 (7-62) years. The mean follow-up period was 30.05 ± 18.76 months. While the average Gas6 value measured during active uveitis attacks was 1.02 ± 0.39 ng/mL (range: 0.54-2.12), the Gas6 value during the passive period was 0.71 ± 0.23 ng/mL (range: 0.39-1.17). The Gas6 level during active uveitis attacks was significantly higher than during the passive period (p = 0.04).

Conclusion

The findings of this study suggest a notable elevation in serum Gas6 levels across all cases of active uveitis, irrespective of the underlying etiology, whether infectious or noninfectious. To successfully integrate serum Gas6 levels into the diagnostic and follow-up protocols for active uveitis, additional comprehensive investigations are imperative.

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 and AXL Promote Insulin Resistance by Rewiring Insulin Signaling and Increasing Insulin Receptor Trafficking to Endosomes

Growth arrest-specific 6 (GAS6) is a secreted protein that acts as a ligand for TAM receptors (TYRO3, AXL, and MERTK). In humans, GAS6 circulating levels and genetic variations in GAS6 are associated with hyperglycemia and increased risk of type 2 diabetes. However, the mechanisms by which GAS6 influences glucose metabolism are not understood. Here, we show that Gas6 deficiency in mice increases insulin sensitivity and protects from diet-induced insulin resistance. Conversely, increasing GAS6 circulating levels is sufficient to reduce insulin sensitivity in vivo. GAS6 inhibits the activation of the insulin receptor (IR) and reduces insulin response in muscle cells in vitro and in vivo. Mechanistically, AXL and IR form a complex, while GAS6 reprograms signaling pathways downstream of IR. This results in increased IR endocytosis following insulin treatment. This study contributes to a better understanding of the cellular and molecular mechanisms by which GAS6 and AXL influence insulin sensitivity.

ARTICLE HIGHLIGHTS

Association between plasma growth arrest-specific protein 6 and carotid atherosclerosis in type 2 diabetes mellitus

BACKGROUND AND AIMS

Growth arrest-specific 6 protein (Gas6) has been established to play important roles in various biological processes, but little is currently known on the role of Gas6 signaling in humans. This research explored the association between Gas6 expression and carotid atherosclerosis (AS) in type 2 diabetes mellitus (T2DM).

METHODS AND RESULTS

As many as 126 T2DM patients were recruited in this study and classified into two groups based on their carotid intima-media thickness (CIMT). Meanwhile, 50 healthy individuals were recruited for the normal control group (NC). The subgroups were compared in terms of clinical data and Gas6 expression levels. Gas6 levels were decreased in T2DM patients with or without AS compared to NC subjects (9.64 ± 1.41 ng/ml, 11.38 ± 2.08 ng/ml, and 13.64 ± 2.61 ng/ml, respectively) (p < 0.001). The interaction between Gas6 and AS in T2DM was analyzed by logistic regression model and receiver operating characteristic (ROC) curve analysis. Decreased Gas6 expression was an independent risk factor relevant to AS in T2DM (p = 0.027). The area under the ROC curve to estimate the diagnostic value of low Gas6 expression for AS in T2DM was 0.750. The correlation between Gas6 and other parameters was evaluated by Pearson correlation analysis and linear regression model. Body mass index (BMI), hemoglobin A1c (HbA1c) and tumor necrosis factor-α(TNF-α) were independently correlated with Gas6.

CONCLUSION

Low Gas6 expression is an independent risk factor for AS in T2DM. Gas6 expression is affected by BMI, HbA1c and TNF-α levels.

Growth arrest-specific 6 modulates adiponectin expression and insulin resistance in adipose tissue

AIMS/INTRODUCTION

Obesity is characterized by disturbed adipocytokine expression and insulin resistance in adipocytes. Growth arrest-specific 6 (GAS6) is a gene encoding the Gas6 protein, which is expressed in fibroblasts, and its related signaling might be associated with adipose tissue inflammation, glucose intolerance and insulin resistance. The aim of this study was to investigate the associations among Gas6, adipocytokines and insulin resistance in adipocytes.

MATERIALS AND METHODS

Mature Simpson Golabi Behmel Syndrome adipocytes were treated with high levels of insulin to mimic insulin resistance, and were examined for the expressions of Gas6, cytokines and adipocytokines from preadipocytes in differentiation. In an animal study, high-fat diet-induced obese mice were used to verify the Gas6 expression in vitro.

RESULTS

During the differentiation of adipocytes, the expression of Gas6 gradually decreased, and was obviously downregulated with adipocyte inflammation and insulin resistance. Gas6 levels were found to be in proportion to the expression of adiponectin, which has been regarded as closely relevant to improved insulin sensitivity after metformin treatment. Similar results were also confirmed in the animal study.

CONCLUSIONS

Our results suggest that Gas6 might modulate the expression of adiponectin, and might therefore be associated with insulin resistance in adipose tissues.

Possible Association of Elevated Plasma Levels of Growth Arrest-Specific Protein 6 and the Soluble Form of Tyrosine Kinase Receptor Axl with Low Hepatitis C Viral Load in Patients with Type 2 Diabetes Mellitus

This study aimed to investigate the plasma levels of Gas6 and soluble Axl (sAxl) in patients with chronic hepatitis C virus (HCV) infection with and without type 2 diabetes mellitus (T2DM). The study involved four groups; 50 patients with chronic HCV, 50 patients with T2DM, 50 patients with chronic HCV and T2DM, and 31 age- and sex-matched healthy controls. T2DM was diagnosed according to American Diabetes Association criteria, HCV antibodies were detected by enzyme-linked immunosorbent assays (ELISA) and confirmed by real-time-polymerase chain reaction. Plasma Gas6 and sAxl levels were assayed in all groups by ELISA. Significant low levels of GAS 6 in HCV/T2DM group versus HCV group were detected (7.92 ± 5.18 vs. 16.09 ± 7.36, respectively, p = 0.000), but higher than T2DM and control groups (p ≥ 0.05), although nonsignificant. HCV load was higher in the HCV group than the HCV/T2DM group (1,888,300 ± 5,595,070 vs. 1,417,900 ± 4,066,460 copies/mL, respectively, p = 0.632). Among HCV group, significant positive correlations were detected between Gas6 and sAxl levels with HCV viral load (r = 0.48, p = 0.000 and r = 0.43, p = 0.002, respectively), while among HCV/T2DM group, significant negative correlations were detected (r = -0.29, p = 0.04 and r = -0.34, p = 0.014, respectively). Significant negative correlations were detected between Gas6/sAxl levels and glycated hemoglobin (r = -0.36, p = 0.01 and r = -0.4, p = 0.003, respectively) in T2DM despite the positive correlations detected in HCV/T2DM (r = 0.27, p = 0.053 and r = 0.55, p = 0.000, respectively). In conclusion, Gas6/Axl system in combined HCV/T2DM diseases may affect the pathogenesis and can alter the biomarkers and complications of both diseases in a manner that differs from a solitary disease.

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.

Vitamin K: a nutrient which plays a little-known role in glucose metabolism

PURPOSE OF REVIEW

Type 2 diabetes is one of the most important public health diseases. Type 2 diabetes pathophysiology involves multiple pathways, in which micronutrients could play a role. Among them, interest has grown concerning vitamin K. The purpose of this review is to expose the latest studies on the role of vitamin K in glucose metabolism, a poorly known function of this vitamin.

RECENT FINDINGS

Animal experimentations and human observational and interventional studies were analyzed to evaluate the role of this vitamin in glucose metabolism. Daily intake of vitamin K seems to improve glucose metabolism and low intakes could be involved in type 2 diabetes pathophysiology. Recent data show that vitamin K could act on glucose metabolism via downstream targets such as osteocalcin, growth arrest-specific 6 protein, and matrix Gla protein.

SUMMARY

This review depicts new insights into the role of vitamin K in glucose metabolism regulation and depicts also the probable mechanisms underlying this association. Further studies will be needed to determine the dose and the duration of vitamin K treatment to achieve the strongest metabolic effect. Maybe the best strategy to improve glucose metabolism would be 'cocktails' of micronutrients associating vitamin K.

Circulating Gas6 is associated with reduced human carotid atherosclerotic plaque burden in high risk cardiac patients

OBJECTIVE

Pre-clinical studies suggest that growth arrest-specific protein 6 (Gas6), a member of the vitamin K dependent family of proteins, is implicated in atherosclerosis. A role for Gas6 in stabilizing atherosclerotic plaque has been suggested. Our aim was to determine the association between Gas6 and measures of carotid artery atherosclerosis in humans undergoing elective coronary angiography. Secondary aims were to determine the association between Gas6 and sex, diabetes, and obesity.

METHODS

In 204 outpatients referred for coronary angiography, EDTA plasma was collected and a focused carotid ultrasound performed. Degree of angiographic coronary artery disease was scored. Carotid intima media thickness as well as maximum plaque height, plaque area, and grayscale median were measured by vascular sonography. Gas6 was assessed by enzyme-linked immunosorbent assay.

RESULTS

We found that Gas6 concentrations were lower in males and were associated with diabetes, obesity, and lower kidney function. After adjustment for age, sex, kidney function, BMI and traditional cardiac risk factors; diabetes was associated with higher levels of Gas6, whilst there was a significant inverse relationship between Gas6 and total plaque area. Gas6 was inversely associated with maximum plaque height and total plaque area in adjusted multi-variable models.

CONCLUSIONS

We observed higher levels of Gas6 in participantswith adverse cardiovascular risk profiles (e.g. diabetes, obesity) yet Gas6 was independently associated with reduced plaque height and total plaque area. These findings suggest that Gas6 may play a role in human atherosclerotic plaque remodeling.

Plasma Growth Arrest-Specific 6 Protein and Genetic Variations in the GAS6 Gene in Patients with Metabolic Syndrome

BACKGROUND

Growth arrest-specific 6 (Gas6) is a vitamin K-dependent protein secreted by immune cells, endothelial cells, vascular smooth muscle cells, and adipocytes. Recent studies indicate that Gas6 and receptors of the TAM (Tyro3, Axl, and Mer) family may be involved in the pathogenesis of obesity, systemic inflammation, and insulin resistance. The aim of this study was to investigate the association between plasma Gas6 protein and the c.843 + 7G>A Gas6 polymorphism in metabolic syndrome (MetS).

METHODS

Two hundred five adults (88 men and 117 women) were recruited in this study. Plasma Gas6 concentration, general, and biochemical data were measured. All subjects were genotyped for the c.843 + 7G>A Gas6 polymorphism.

RESULTS

Plasma Gas6 concentrations decreased in parallel with various MetS components in all groups (P = 0.017 for trend). Patients in the second and third tertiles of Gas6 level had higher high-density lipoprotein cholesterol (HDL-C) levels than those in the first tertile overall and in the female group. Plasma Gas6 levels were significantly positively correlated with HDL-C level and negatively with fasting glucose level in the female patients. The A allele and genotype AA in single nucleotide polymorphism c.843 + 7G>A were less frequent in the subjects with MetS compared to those without MetS.

CONCLUSIONS

Our results demonstrated a positive correlation between Gas6 protein values and HDL-C and reinforce the association with fasting glucose. In addition, the presence of c.843 + 7G>A Gas6 polymorphisms, especially the AA genotype, had an association with MetS. The potential role of the Gas6/TAM system in MetS deserves further investigation.

Implication of a novel Gla-containing protein, Gas6 in the pathogenesis of insulin resistance, impaired glucose homeostasis, and inflammation: A review

Growth arrest specific 6 (Gas6), a vitamin K-dependent protein plays a significant role in the regulation of cellular homeostasis via binding with TAM-receptor tyrosine kinases. Several studies reported the role of Gas6 in cancer, glomerular injury, obesity, and inflammation, however, very little is known about its role in insulin resistance (IR) and impaired glucose metabolism. Majority of the studies reported an inverse correlation of Gas6 protein levels or gene polymorphism with plasma glucose, HbA1c, IR, and inflammatory cytokines among type 2 diabetes (T2D) and obese subjects. However, few studies reported a positive correlation of Gas6 protein levels or gene polymorphism with IR and inflammation among obese subjects. This review for the first time provides an overview of the association of Gas6 protein levels or gene polymorphism with IR, glucose intolerance, and inflammation among T2D and obese subjects. This review also depicts the probable mechanism underlying the association of Gas6 with glucose intolerance and inflammation. The outcome of this review will increase the understanding about the role of Gas6 in the pathogenesis of IR, glucose intolerance and inflammation and that should in turn lead to the design of clinical interventions to improve glucose metabolism and the lives of the T2D patients.

Circulating Des-gamma-carboxy prothrombin is not associated with cardiovascular calcification or stiffness: The Multi-Ethnic Study of Atherosclerosis (MESA)

BACKGROUND AND AIMS

Vitamin K-dependent protein (VKDP) activity may have a role in preventing cardiovascular calcification, but has not previously been studied in large, generally healthy populations.

METHODS

Using an elevated ankle-brachial index (ABI) as a measure of medial vascular calcification, we performed a case-cohort analysis within the Multi-Ethnic Study of Atherosclerosis, measuring Des-gamma-carboxy prothrombin (DCP) to estimate VKDP activity. In secondary analyses of the weighted subcohort, we examined the cross-sectional associations between DCP and prevalent vascular calcification of the coronary vessels, aortic and mitral valves, and aortic wall, and with vascular stiffness.

RESULTS

In adjusted analysis, cases (n = 104) had 0.21 ng/ml (-0.94-0.52) lower DCP concentrations than the subcohort (n = 613). Furthermore, amongst the 717 participants in the weighted cohort, VKDP activity was not associated with coronary artery, mitral valve, aortic valve or aortic wall calcification, nor was it associated with vascular stiffness.

CONCLUSIONS

Our negative results do not support a role of circulating VKDP activity in cardiovascular calcification in community-dwelling adults.

Association between the growth arrest-specific 6 (Gas6) gene polymorphism c.834 + 7G>A and preeclampsia

OBJECTIVE

Preeclampsia (PE) is a hypertensive disease of pregnancy complicating 2-8% of all pregnancies. The exact pathophysiology still remains unknown. Growth arrest-specific 6 (Gas6) is a member of the vitamin K-dependent protein family and it has been suggested as a novel atherothrombotic risk factor with anti-angiogenic and pro-atherogenic properties. The goal of the our study was to investigate the relationships between the c.834 + 7G > A polymorphism of GAS6, plasma Gas6 levels and PE.

METHODS

A total of 150 women, including 82 preeclamptic pregnant women and 68 normotensive pregnant (NP) women, were recruited in the current study. Blood samples were taken from all participants. Plasma Gas6 levels measured by an enzyme-linked immunosorbent assay. GAS6 polymorphism was determined using a PCR-RFLP method.

RESULTS

The plasma Gas6 levels of preeclamptic patients were significantly lower than those of NP women (8.65 ± 3.70 ng/ml and 10.89 ± 4.23 ng/ml respectively, p < 0.001). The GG genotype was the most prevalent, and the risk of PE was 3.5-fold higher in pregnant women with GG genotype compared to woman with AA genotype (p < 0.01). The A allele was less frequent in preeclamptic patients than in control subjects (OR = 2.118, 95% CI = 1.330-3.371, p < 0.001).

CONCLUSIONS

Our results suggest that GAS6 c.834 + 7G > A polymorphism may have a pivotal role in the pathogenesis of PE suggesting that the A allele has a protective role for PE.

The Involvement of GAS6 Signaling in the Development of Obesity and Associated Inflammation

Growth arrest-specific 6 (GAS6), a vitamin K-dependent protein, plays a role in the survival, proliferation, migration, differentiation, adhesion, and apoptosis of cells. GAS6 is highly expressed during growth arrest, followed by a sharp decrease during differentiation in adipocytes. The functions of GAS6 signaling are limited to TAM (Tyro3, Axl, and Mer) receptors and are dependent on the cell type. While many studies have focused on the role of GAS6 in inflammation and cancer, only few studies focused on its roles of GAS6 in obesity. Accordingly, the participation of GAS6 in the progression of obesity remains controversial. In this review, we summarize the results of current studies from clinical and basic research to elucidate the possible role of GAS6 signaling in obesity and associated disorders. In addition, this summary may offer a direction to develop clinical therapeutic strategies for the prevention and treatment of obesity and related complications.