Vitexin attenuates autoimmune hepatitis in mouse induced by syngeneic liver cytosolic proteins via activation of AMPK/AKT/GSK-3ß/Nrf2 pathway.

Autoimmune hepatitis (AIH) is a chronic progressive liver disease that currently does not have a successful therapeutic option. Vitexin, a bioflavonoid isolated from various medicinal plants, possesses a variety of activities; however, whether vitexin protects against AIH remains unclear. Therefore, the current study aims to investigate the hepatoprotective effects and mechanism of action of vitexin in both an experimental autoimmune hepatitis (EAH) mouse model and in D-galactosamine/lipopolysaccharide (D-GalN/LPS)-induced hepatocyte injury. Syngeneic liver antigen S100 was used to establish EAH. Vitexin treatment significantly decreased the infiltration of inflammatory and CD4+ T cells in the liver, reduced ALT and AST levels in the serum and attenuated hepatic injury due to oxidative stress. Moreover, vitexin mitigated the upregulation of Bax and cleaved caspase-3 and the downregulation of Bcl-2 in the livers of AIH mice. These regulations were accompanied by not only increased phosphorylation of AMPK, AKT and GSK-3ß but also activation of Nrf2. Furthermore, vitexin inhibited apoptosis and the overexpression of inflammatory cytokines in D-GalN/LPS-treated AML12 cells. In addition, vitexin enhanced the phosphorylation of AMPK, AKT and GSK-3ß. When AML12 cells were treated with an inhibitor of AMPK/AKT or specific siRNA targeting Nrf2, vitexin did not further induce the activation of Nrf2/HO-1. A molecular docking study confirmed that vitexin could interact with AMPK through hydrogen bonding interactions. In conclusion, vitexin ameliorated hepatic injury in EAH mice through activation of the AMPK/AKT/GSK-3ß pathway and upregulation of the Nrf2 gene.

Acidic Fibroblast Growth Factor Promotes Endothelial Progenitor Cells Function via Akt/FOXO3a Pathway.

Acidic fibroblast growth factor (FGF1) has been suggested to enhance the functional activities of endothelial progenitor cells (EPCs). The Forkhead homeobox type O transcription factors (FOXOs), a key substrate of the survival kinase Akt, play important roles in regulation of various cellular processes. We previously have shown that FOXO3a is the main subtype of FOXOs expressed in EPCs. Here, we aim to determine whether FGF1 promotes EPC function through Akt/FOXO3a pathway. Human peripheral blood derived EPCs were transduced with adenoviral vectors either expressing a non-phosphorylable, constitutively active triple mutant of FOXO3a (Ad-TM-FOXO3a) or a GFP control (Ad-GFP). FGF1 treatment improved functional activities of Ad-GFP transduced EPCs, including cell viability, proliferation, antiapoptosis, migration and tube formation, whereas these beneficial effects disappeared by Akt inhibitor pretreatment. Moreover, EPC function was declined by Ad-TM-FOXO3a transduction and failed to be attenuated even with FGF1 treatment. FGF1 upregulated phosphorylation levels of Akt and FOXO3a in Ad-GFP transduced EPCs, which were repressed by Akt inhibitor pretreatment. However, FGF1 failed to recover Ad-TM-FOXO3a transduced EPCs from dysfunction. These data indicate that FGF1 promoting EPC function is at least in part mediated through Akt/FOXO3a pathway. Our study may provide novel ideas for enhancing EPC angiogenic ability and optimizing EPC transplantation therapy in the future.

SIRT1 Protects Against Oxidative Stress-Induced Endothelial Progenitor Cells Apoptosis by Inhibiting FOXO3a via FOXO3a Ubiquitination and Degradation.

Cell loss due to apoptosis induced by oxidative stress is a major hurdle for endothelial progenitor cells (EPCs)-based therapy. Sirtuin 1 (SIRT1) plays important roles in many pathophysiological processes by deacetylating various substrates, including forkhead transcription factor (FOXO). However, after deacetylation, the fate of FOXO protein remains to be explored. In the present study, we investigated whether SIRT1 exerted a protective effect on hydrogen peroxide (H(2)O(2))-induced EPCs apoptosis and, if so, what the underlying mechanism might be. EPCs were isolated and obtained from human umbilical cord blood by density gradient centrifugation and identified by morphology, tube formation ability, cell surface markers, and the ability to take up acetylated low-density lipoprotein (Dil-Ac-LDL) and bind ulex europaeus agglutinin 1 (FITC-UEA-1). Immunofluorescence showed that SIRT1 is localized in the nucleus of EPCs in the presence or absence of H(2)O(2). SIRT1 protein level in EPCs was increased by the treatment with H(2)O(2) for 24 h. Incubation of EPCs with H(2)O(2) dose dependently induced EPCs apoptosis. SIRT1 overexpression reduced the rate of EPCs apoptosis induced by H(2)O(2), whereas SIRT1 downregulation and EX527, a specific SIRT1 inhibitor, exerted the opposite effect. SIRT1 overexpression decreased the total FOXO3a protein expression, whereas SIRT1 downregulation and EX527 increased the amount of FOXO3a protein. SIRT1 reduced FOXO3a transcriptional activity according to Bim expression. Co-immunoprecipitation assay showed that SIRT1 could bind to FOXO3a, reduce its acetylation level and increase its ubiquitination level. To sum up, our work demonstrated that SIRT1 had a pivotally protective role in the regulation of EPCs apoptosis induced by H(2)O(2) and that SIRT1 protected against apoptosis by inhibiting FOXO3a via FOXO3a ubiquitination and subsequent degradation.

Overexpression or silencing of FOXO3a affects proliferation of endothelial progenitor cells and expression of cell cycle regulatory proteins.

Endothelial dysfunction is involved in the pathogenesis of many cardiovascular diseases such as atherosclerosis. Endothelial progenitor cells (EPCs) have been considered to be of great significance in therapeutic angiogenesis. Furthermore, the Forkhead box O (FOXO) transcription factors are known to be important regulators of cell cycle. Therefore, we investigated the effects of changes in FOXO3a activity on cell proliferation and cell cycle regulatory proteins in EPCs. The constructed recombinant adenovirus vectors Ad-TM (triple mutant)-FOXO3a, Ad-shRNA-FOXO3a and the control Ad-GFP were transfected into EPCs derived from human umbilical cord blood. Assessment of transfection efficiency using an inverted fluorescence microscope and flow cytometry indicated a successful transfection. Additionally, the expression of FOXO3a was markedly increased in the Ad-TM-FOXO3a group but was inhibited in the Ad-shRNA-FOXO3a group as seen by western blotting. Overexpression of FOXO3a suppressed EPC proliferation and modulated expression of the cell cycle regulatory proteins including upregulation of the cell cycle inhibitor p27(kip1) and downregulation of cyclin-dependent kinase 2 (CDK2), cyclin D1 and proliferating cell nuclear antigen (PCNA). In the Ad-shRNA-FOXO3a group, the results were counter-productive. Furthermore, flow cytometry for cell cycle analysis suggested that the active mutant of FOXO3a caused a noticeable increase in G1- and S-phase frequencies, while a decrease was observed after FOXO3a silencing. In conclusion, these data demonstrated that FOXO3a could possibly inhibit EPC proliferation via cell cycle arrest involving upregulation of p27(kip1) and downregulation of CDK2, cyclin D1 and PCNA.

Hydrogen peroxide induced impairment of endothelial progenitor cell viability is mediated through a FoxO3a dependant mechanism.

OBJECTIVES: Increased oxidative stress has been suggested to contribute to the functional impairment of endothelial progenitor cells (EPCs). The Forkhead box O transcription factors (FoxOs) are critical regulators involved in various cellular processes including cell apoptosis. Here, we investigated whether FoxOs are required in oxidative stress induced EPC apoptosis. METHODS AND RESULTS: EPCs were cultured from cord blood derived mononuclear cells and treated with hydrogen peroxide (H2O2) for induction of oxidative stress. Incubation with H2O2 dose dependently reduced viability and increased apoptosis in EPCs. Western blotting showed that EPCs predominantly expressed FoxO3a and the expression was markedly increased upon H2O2 treatment. Transduction with adenoviral vectors expressing either a wide-type or a non-phosphorylatable, constitutively active mutant of FoxO3a led to further increased apoptosis of EPCs after H2O2 treatment. Conversely, FoxO3a silencing rescued EPCs from these H2O2 induced deleterious effects. Overexpression of FoxO3a also increased the level of the pro-apoptotic protein Bim, whereas FoxO3a silencing downregulated H2O2 induced Bim expression. Furthermore, Matrigel assay demonstrated that FoxO3a overexpression significantly impaired the tube forming ability of EPCs, whereas its silencing completely protected EPCs from H2O2 induced decrease of capillary formation. CONCLUSIONS: These data suggest that oxidative stress induced impairment of EPC survival is mediated through a FoxO3a dependant mechanism, possibly by transcriptional regulation of Bim. Our data indicate FoxO3a as a potential therapeutic target for improvement of EPC number and function in patients with ischemic heart disease.