Anexelekto (AXL) no more: microRNA-155 (miR-155) controls the "Uncontrolled" in SARS-CoV-2.

AXL is the gene that encodes the Anexelekto (AXL) receptor tyrosine kinase that demonstrates significant roles in various cellular processes, including cell growth, survival, and migration. Anexelekto is a Greek word meaning excessive and uncontrolled, semantically implying the crucial involvement of AXL in cancer and immune biology, and in promoting cancer metastasis. AXL overexpression appears to drive epithelial to mesenchymal transition, tumor angiogenesis, decreased antitumor immune response, and resistance to therapeutic agents. Recently, AXL has been reported to play important roles in several viral infections, including SARS-CoV-2. We have previously outlined the importance of microRNAs (miRNAs, miRs) and especially miR-155 in SARS-CoV-2 pathophysiology through regulation of the Renin-Angiotensin Aldosterone System (RAAS) and influence on several aspects of host innate immunity. MiRNAs are negative regulators of gene expression, decreasing the stability of target RNAs or limiting their translation and, enthrallingly, miR-155 is also involved in AXL homeostasis-both endogenously and pharmaceutically using repurposed drugs (e.g., metformin)-highlighting thrifty evolutionary host innate immunity mechanisms that successfully can thwart viral entry and replication. Cancer, infections, and immune system disturbances will increasingly involve miRNA diagnostics and therapeutics in the future.

Ginsenoside Rb1 attenuates age-associated vascular impairment by modulating the Gas6 pathway.

CONTEXT: Ginsenoside Rb1 (Rb1) exerts many beneficial effects and protects against cardiovascular disease. OBJECTIVE: To investigate whether Rb1 could attenuate age-related vascular impairment and identify the mechanism. MATERIALS AND METHODS: Female C57BL/6J mice aged 2 and 18 months, randomly assigned to Young, Young + 20 mg/kg Rb1, Old + vehicle, Old + 10 mg/kg Rb1 and Old + 20 mg/kg Rb1 groups, were daily intraperitoneal injected with vehicle or Rb1 for 3 months. The thoracic aorta segments were used to inspect the endothelium-dependent vasorelaxation. Left thoracic aorta tissues were collected for histological or molecular expression analyses, including ageing-related proteins, markers relevant to calcification and fibrosis, and expression of Gas6/Axl. RESULTS: We found that in Old + vehicle group, the expression of senescence proteins and cellular adhesion molecules were significantly increased, with worse endothelium-dependent thoracic aorta relaxation (58.35% ± 2.50%) than in Young group (88.84% ± 1.20%). However, Rb1 treatment significantly decreased the expression levels of these proteins and preserved endothelium-dependent relaxation in aged mice. Moreover, Rb1 treatment also reduced calcium deposition, collagen deposition, and the protein expression levels of collagen I and collagen III in aged mice. Furthermore, we found that the downregulation of Gas6 protein expression by 41.72% and mRNA expression by 52.73% in aged mice compared with young mice was abrogated by Rb1 treatment. But there was no significant difference on Axl expression among the groups. CONCLUSIONS: Our study confirms that Rb1 could ameliorate vascular injury, suggesting that Rb1 might be a potential anti-ageing related vascular impairment agent.

Screening of Differential Genes for Endometriosis and Expression Validation of the Potential Target GAS6 / 中国生物化学与分子生物学报

Growth arrest specific protein 6 (GAS6) plays an important role in the occurrence and development of tumors, and its signal transduction is involved in cell proliferation, adhesion and migration, but its related functions and molecular mechanisms in endometriosis (EMs) are still unclear. In this study, we searched and downloaded the transcriptome datasets of EMs from GEO database and performed GEO online analysis, and then screened out the differentially expressed genes and performed cluster analysis based on GO and KEGG pathway. The mRNA levels of the differentially expressed genes shared by more than three datasets were verified by qRT-PCR in the endometrium of ten women with no endometriosis and no clear disease and the ectopic endometrium of 11 patients with ovarian chocolate cysts. Immunohistochemistry and qRT-PCR were used to verify the expression of GAS6 and epithelial mesenchymal transition (EMT) marker genes, and immunofluorescence was used to co-label GAS6 and E-cadherin in endometriosis clinical samples. In this study, a total of 47 differentially expressed genes were screened out of the four transcriptome datasets, which were mainly enriched in processes such as cell migration and related signal pathways such as MAPK, PI3K-AKT, and tight junction. The mRNA levels of the nine differentially expressed genes shared by more than three datasets in endometriosis patients were consistent with the results of bioinformatics analysis. GAS6 expression levels in ectopic endometrium of EMs patients are higher than the control group (P < 0. 05), and EMs patients have the characteristics of EMT in the ectopic endometrial tissue, that is, the expression of E-cadherin is down-regulated (P < 0. 05) and the expression of vimentin is up-regulated (P < 0. 01). The expression of E-cadherin in the ectopic endometrial glandular epithelial cells of EMs patients is low while the expression of GAS6 is up-regulated, suggesting that GAS6 may mediate the EMT process in endometriosis. In conclusion, this study reveals that GAS6 is highly expressed in endometriosis patients and may mediate the EMT process to participate in the occurrence and development of endometriosis, providing a potential target for clinical treatment of endometriosis.

TAM receptors: A phosphatidylserine receptor family and its implications in viral infections.

Phosphatidylserine (PS) is an anionic phospholipid that is usually localized in the inner leaflets of the plasma membrane. However, the enzyme scramblase catalyzes the externalization of PS on the outer leaflet of the plasma membrane during apoptosis or cellular stress. This event prompts the recognition of PS displaying cells by phagocytes leading to "apoptotic clearance." Multiple PS receptors (PSRs) mediate this process including members from the TAM (Tyro3, Axl, Mertk) receptor Tyrosine kinases (RTKs) by interacting with PS via bridging proteins like Gas6 and ProS1. Ironically, this network (PS/TAM) that evolved for boosting cellular health through clearance of apoptotic and necrotic cells, has been manoeuvred by pathogens and tumor cells using "apoptotic mimicry." Enveloped viruses, responsible for most of the lethal epidemics and pandemics including the current SARS-CoV2 outbreak, have employed apoptotic mimicry to their advantage. In the current chapter, we summarize the existing knowledge regarding the involvement of PS/Gas6, ProS1/TAM in facilitating infectivity in a diverse set of cell lines, animals as well as organoids. This network executes a largely proviral role in facilitating infection as seen with Zika, Ebola, Influenza and Dengue viruses. However, this response varies with strains and the cells infected, and in some cases, this same signaling displays an antiviral function. We also report multiple studies that have used neutralizing antibodies and small molecule inhibitors in successfully reducing viral replication and ameliorating pathogenicity. Knowledge about this unique signaling pathway and measures that can be taken to inhibit it is most valuable now given how enveloped viruses lead to plagues on the entire globe.

Gamma-glutamyl carboxylated Gas6 mediates the beneficial effect of vitamin K on lowering hyperlipidemia via regulating the AMPK/SREBP1/PPARα signaling cascade of lipid metabolism.

The present study for the first time aims to examine the hypothesis that circulating gamma-glutamyl carboxylated growth arrest specific protein 6 (Gla-Gas6) deficiency may be associated with hyperlipidemia and vitamin K (VK) supplementation may ameliorate the impaired lipid homeostasis via activating Gas6 protein. Subjects with hyperlipidemia (n=22) and age-matched healthy controls (n=19) were included in this study. Results showed that plasma levels of Gla-Gas6 protein and VK were significantly lower in hyperlipidemic subjects compared to control. Moreover, Gla-Gas6 levels were significantly and positively correlated with VK (P=.034, r=0.452) and negatively with triglyceride (P=.022, r=-0.485) and total cholesterol (P=.043, r=-0.435) in hyperlipidemic subjects, which suggest that VK supplementation may have a positive effect in activating Gas6 protein and thereby reducing the aberrant plasma lipid levels. Further studies with high-fat diet (HFD)-fed animal model of hyperlipidemia demonstrated that VK supplementation (5 µg/kg body weight, 8 weeks) reduced the plasma lipid levels, stimulated both the plasma levels and the hepatic protein expression of Gla-Gas6 protein, and regulated the AMPK/SREBP1/PPARα signaling pathways of hepatic lipid metabolism in HFD-fed mice. Moreover, by using palmitic acid (PA, 0.75 mM)-treated both control and GGCX knockdown hepatocytes, this study dissected the direct role of Gla-Gas6 in mediating the positive effect of VK on preventing the PA-induced impaired hepatic lipid metabolism via regulating AMPK/SREBP1/PPARα pathways. Combining all, the present study demonstrated the beneficial effect of VK supplementation in preventing the impaired lipid homeostasis via activating VK-dependent Gas6 protein.

Testosterone delays vascular smooth muscle cell senescence and inhibits collagen synthesis via the Gas6/Axl signaling pathway.

Testosterone deficiency is associated with a higher incidence of cardiovascular diseases in men. However, its effect on cell senescence, which plays a causal role in vascular aging, remains unclear. Here, we tested the hypothesis that testosterone alleviated vascular smooth muscle cell (VSMC) senescence and collagen synthesis via growth arrest-specific protein 6 (Gas6)/Axl- and Akt/FoxO1a-dependent pathways. Testosterone significantly ameliorated angiotensin II-induced VSMC senescence and collagen overexpression. In addition, testosterone inhibited angiotensin II-induced matrix metalloproteinase-2 (MMP-2) activity, which played a pivotal role in facilitating age-related collagen deposition. Testosterone increased the expression of tissue inhibitor of metalloproteinase-2 but decreased the expression of MMP-2 and membrane type-1 metalloproteinase which contributed to increase MMP-2 activity. The effects on VSMCs senescence and collagen synthesis were mediated by restoration of angiotensin II-induced downregulation of Gas6 and Axl expression and a subsequent reduction of Akt and FoxO1a phosphorylation. The effects of testosterone were reversed by a Gas6 blocker, Axl-Fc, and a specific inhibitor of Axl, R428. Treatment of VSMCs with PI3K inhibitor LY294002 abrogated the downregulating effect of testosterone on MMP-2 activity. Furthermore, when FoxO1a expression was silenced by using a specific siRNA, the inhibitory effect of testosterone on MMP-2 activity was revered as well, that indicated this process was Akt/FoxO1a dependence. Taken together, Gas6/Axl and Akt/FoxO1a were involved in protective effects of testosterone on VSMCs senescence and collagen synthesis. Our results provide a novel mechanism underlying the protective effect of testosterone on vascular aging and may serve as a theoretical basis for testosterone replacement therapy.