Manipulation of autophagy: a novelly potential therapeutic strategy for retinal neovascularization

Homocysteine Suppresses Autophagy via AMPK-mTOR-TFEB Signaling in Human THP-1 Macrophages

ABSTRACT

Hyperhomocysteinemia is an independent risk factor for atherosclerosis. It is known that macrophage autophagy plays a protective role in atherosclerosis, and that hyperhomocysteinemia is strongly linked to autophagy. Therefore, it is of great significance to study the molecular mechanisms underlying the effect of homocysteine (Hcy) on macrophage autophagy. This study aimed to investigate the effects of Hcy on autophagy in a human acute monocytic leukemia cell line (THP-1). The Hcy-treated THP-1 cells exhibited increased levels of the autophagy substrate SQSTM1(p62), and decreased levels of the autophagy markers LC3 II/I and Beclin-1, indicating a decrease in autophagy in vitro. Furthermore, western blotting showed that Hcy significantly increased the levels of p-mTOR and nuclear TFEB and decreased the levels of p-AMPK and cytoplasmic TFEB. These data suggest that Hcy inhibits autophagosome formation in human THP-1 macrophages through the AMPK-mTOR-TFEB signaling pathway. Our findings provide new insights into the mechanisms of atherosclerotic diseases caused by Hcy.

Autophagy is required for the promoting effect of angiogenic factor with G patch domain and forkhead-associated domain 1 (AGGF1) in retinal angiogenesis

OBJECTIVE

To investigate the effect of angiogenic factor with G patch domain and forkhead-associated domain 1 (AGGF1) on retinal angiogenesis in ischemic retinopathy and its association with autophagy.

METHODS

RF/6A cells were divided into the control group, hypoxia group and high-glucose group, and the expression of AGGF1 in cells was detected. C57BL/6 J mice were divided into the control group, oxygen-induced retinopathy (OIR) group and diabetic retinopathy (DR) group, and AGGF1 expression in the retina was observed. RF/6A cells were then divided into the control group and different AGGF1 concentration groups, and the expression of autophagy marker, LC3 was detected. Then, RF/6A cells were divided into the control group, AGGF1 group, 3-methyladenine (3-MA, an early autophagy inhibitor) + AGGF1 group and chloroquine (CQ, a late autophagy inhibitor) + AGGF1 group, and the expression of autophagy markers, LC3 and p62, autophagic flux, as well as was key signaling pathway proteins in autophagy, PI3K, AKT, and mTOR was detected. Finally, the cell proliferation, migration and tube formation were detected in the four groups.

RESULTS

AGGF1 expression in RF/6A cells and in the retinas of OIR and DR mouse model was found to be increased in the state of hypoxic and high glucose condition. AGGF1 treatment led to increased expressions of LC3 and decreased p62; therby induced autophagic flux, and the phosphorylation of PI3K, AKT and mTOR was down-regulated in RF/6A cells. When autophagy was inhibited by 3-MA or CQ, confirmed by corresponding changes of these indicators of autophagy, cellular proliferation, migration and tube formation of RF/6A cells were weakened by AGGF1 treatment when compared with that of AGGF1 treatment alone.

CONCLUSION

This study experimentally revealed that AGGF1 activates autophagy to promote angiogenesis for ischemic retinopathy and inhibition of PI3K/AKT/mTOR pathway may be involved in the activation of autophagy by AGGF1.

Retinal neovascularization induced by mutant Vldlr gene inhibited in an inherited retinitis pigmentosa mouse model: an in-vivo study

AIM

To explore whether the retinal neovascularization (NV) in a genetic mutant mice model could be ameliorated in an inherited retinitis pigmentosa (RP) mouse, which would help to elucidate the possible mechanism and prevention of retinal NV diseases in clinic.

METHODS

The Vldlr ^-/- mice, the genetic mutant mouse model of retinal NV caused by the homozygous mutation of Vldlr gene, with the rd1 mice, the inherited RP mouse caused by homozygous mutation of Pde6b gene were bred. Intercrossing of the above two mice led to the birth of the F1 hybrids, further inbreeding of which gave birth to the F2 offspring. The ocular genotypes and phenotypes of the mice from all generations were examined, with the F2 offspring grouped according to the genotypes.

RESULTS

The rd1 mice exhibited the RP phenotype of outer retinal degeneration and loss of retinal function. The Vldlr ^-/- mice exhibited the phenotype of retinal NV obviously shown by the fundus fluorescein angiography. The F1 hydrides, with the heterozygote genotype, exhibited no phenotypes of RP or retinal NV. The F2 offspring with homozygous genotypes were grouped into four subgroups. They were the F2-I mice with the wild-type Pde6b and Vldlr genes (Pde6b^+/+ -Vldlr^+/+ ), which had normal ocular phenotypes; the F2-II mice with homozygous mutant Vldlr gene (Pde6b^+/+ -Vldlr^-/- ), which exhibited the retinal NV phenotype; the F2-III mice with homozygous mutant Pde6b gene (Pde6b^-/- -Vldlr^+/+ ), which exhibited the RP phenotype. Specifically, the F2-IV mice with homozygous mutant Vldlr and Pde6b gene (Pde6b^-/- -Vldlr^-/- ) showed only the RP phenotype, without the signs of retinal NV.

CONCLUSION

The retinal NV can be inhibited by the RP phenotype, which implies the role of a hyperoxic state in treating retinal NV diseases.

Different effects of anti-VEGF drugs (Ranibizumab, Aflibercept, Conbercept) on autophagy and its effect on neovascularization in RF/6A cells

INTRODUCTION

Choroidal neovascularization (CNV) is the main pathological change of wet age-related macular degeneration. Anti-VEGF drugs are the most commonly used treatment for CNV. The biggest drawback of anti-VEGF drugs is the recurrence of CNV, which requires repeated therapy several times. Autophagy activation may be involved in reducing the therapeutic effect of anti-VEGF drugs. So, this study aims to elucidate the effect and mechanism of anti-VEGF drugs on endothelial autophagy and neovascularization in vitro.

METHODS

RF/6A cells were randomly divided into five groups: The control group, hypoxia group (1% O₂, 5% CO₂, 94% N₂), anti-VEGF group (group1: Ranibizumab 100 μg/ml; group2: Aflibercept, 400 μg/ml; group3: Conbercept, 100 μg/ml). Autophagy-related proteins were examined by Western blot. RFP-GFP-LC3 was used to detect autophagy and autophagic flow. Subsequently, we used autophagy inhibitors (3-MA or CQ) to inhibit Conbercept induced autophagy and to observe its effect on angiogenesis in vitro. Proliferation, migration, and tube formation of endothelial cells can be used to study neovascularization in vitro. In this research, the CCK-8 assay was used to detect cell proliferation. Cell migration and tube formation were assessed by wound assay and matrix method, respectively. Flow cytometry and Tunel were used to detect cell apoptosis. Finally, the mechanism of Conbercept activated autophagy was studied. Western blot was used to detect the expression of p53 and DRAM (damage-regulated autophagy modulator), upstream activators of autophagy.

RESULTS

The protein levels of Beclin-1 and LC3-2/1 in Ranibizumab and Conbercept groups were significantly higher than in the hypoxia group(P < 0.05). While the expression of P62 was decreased (P < 0.05). The autophagic flux was showed the same results. However, Aflibercept showed the opposite effect on autophagy. Compared with the Conbercept group, autophagy inhibitor 3-MA or CQ can further inhibit cell proliferation and promotes cell apoptosis (P < 0.05). Conbercept significantly inhibited cell migration compared with the hypoxia group (633.08 ± 72.52 vs. 546.33 ± 24.61), while the autophagy inhibitor group (3-MA or CQ) had a more obvious inhibition effect (309.75 ± 86.36 and 263.33 ± 68.67) (P < 0.05). For tube formation, the number of tube formation was decreased significantly in the Conbercept group (32.00 ± 2.00) compared to the hypoxia group (39.00 ± 1.53) and even further reduced in 3-MA or CQ group (24.00 ± 3.61, 20.00 ± 2.65). The length of master segments in the hypoxia group was 15,668.00 ± 894.11. It was decreased in Conbercept (13,885.34 ± 730.03). In 3-MA or CQ group, the length of master segments dropped further (11,997.00 ± 433.66, 10,617.67 ± 543.21). Compare with the hypoxia group, the expression P53 and DRAM were increased in the Conbercept group (P < 0.05). Autophagy-related proteins LC-3, Beclin-1, and DRAM were inhibited by P53 inhibitor Pifithrin-α (PFTα) (P < 0.05).

CONCLUSION

Ranibizumab and Conbercept can trigger the autophagy of vascular endothelial cells while Aflibercept can inhibit it. The combination of Conbercept and autophagy inhibitor can significantly inhibit the formation of angiogenesis in vitro. The mechanism of autophagy activation is related to the activation of the p53/DRAM pathway.

Autophagy protects against retinal cell death in mouse model of cytomegalovirus retinitis

BACKGROUND

Extensive death of uninfected bystander neuronal cells is an important component of the pathogenesis of cytomegalovirus retinitis (CMV). Our previous results have shown that there is a functional relationship between autophagy and apoptosis during MCMV infection of retinal pigment epithelium (RPE). The purpose of this study was to determine whether autophagy plays a significant role in the death of retinal cells during MCMV retinitis.

METHODS

The retinas of adult BALB/c mice were infected with MCMV via supraciliary injection. Rapamycin, a mTOR inhibitor, was injected to MCMV-infected BALB/c mice intraperitoneally. Immunohistochemistry and western blot were performed to observe the spread pattern of virus in retinas and the levels of targeted proteins. Plaque assay was performed to determine the virus titer in different groups. Since Atg5 is a key gene regulating autophagy, we bred Atg5^flox/flox; Nestin-Cre mice to deeply elucidate the role of autophagy during MCMV retinitis. Atg5^flox/flox; Nestin-Cre mice were genotyped and infected with MCMV. Immunohistochemistry was performed to observe the type of virus-infected cells and apoptosis in retinas during MCMV retinitis.

RESULTS

In MCMV mouse model, MCMV infection in outer nuclear layer (ONL) and inner nuclear layer (INL) in the retinas caused cleaved caspase 3 positive apoptosis, which is not co-localized with early antigen (EA) positive virus infected cells in rapamycin treated group. Rapamycin treatment increased the levels of LC3B-II by inhibiting mTOR and decreased the levels of cleaved caspase-3 during MCMV retinitis. However, virus propagation was not affected by rapamycin. In Atg5^flox/flox; Nestin-Cre mice, RPE and glial cells were the main targets of viral infection, and number of EA positive retinal cells and TUNEL positive retinal cells was significantly increased compared to Atg5^flox/+; Nestin-Cre mice though there was no difference of virus propagation between Atg5^flox/flox; Nestin-Cre mice and Atg5^flox/+; Nestin-Cre mice.

CONCLUSIONS

Autophagy protects retinal cells from MCMV infection induced apoptosis through mTOR-mediated signaling pathway.

Autophagy: a new mechanism for regulating VEGF and PEDF expression in retinal pigment epithelium cells

AIM

To investigate the regulation of vascular endothelial growth factors (VEGF) and pigment epithelium-derived factor (PEDF) expression by autophagy in retinal pigment epithelium (RPE) cells on exposure to hypoxia.

METHODS

ARPE-19, an RPE cell line, was treated as following: the control group was kept in a normoxic incubator; the hypoxia group was incubated in a hypoxic incubator with 1% O₂/5% CO₂/94% N₂ for 24h; the hypoxia + 3-methyladenine (3-MA) group was pretreated with 10 mmol/L 3-MA for 1h and then in the hypoxic incubator for 24h; and the hypoxia + chloroquine (CQ) group was pretreated with 50 µmol/L CQ for 1h and then in the hypoxic incubator for 24h. The morphology and ultrastructure of the cells was observed by an inverted microscope or a transmission electronic microscope (TEM). Western blot was performed to assay the expression of autophagy-associated markers, including microtubule associated protein 1 light chain 3 B (LC3B), Beclin-1, Atg5 and p62. The concentration of VEGF and PEDF in the culture supernatant was determined by ELISA, and the ratio of VEGF/PEDF was calculated.

RESULTS

There were no obvious differences in cell morphology among different groups and autolysosomes could be observed in the cytoplasm in all groups. Compared to the control cells, the LC3B-II/I ratio and levels of Beclin-1 and Atg5 were significantly increased and p62 level was significantly decreased in the hypoxia group. With the increase of VEGF and decrease of PEDF concentration, the VEGF/PEDF ratio was significantly increased in the hypoxia group compared to the control cells. The LC3B-II/I ratio was significantly reduced by 3-MA treatment and increased by CQ treatment. The expressions of Beclin-1 and Atg5 were significantly reduced by 3-MA or CQ treatment, while expression of p62 was increased in the 3-MA or CQ treated cells. The concentration of VEGF was significantly decreased and PEDF increased, thereby the VEGF/PEDF ratio was decreased in the hypoxia + 3-MA group and hypoxia + CQ group compared with that in the hypoxia group.

CONCLUSION

Hypoxia leads to elevated autophagy in RPE cells, and expression of VEGF and PEDF might be regulated by autophagy on exposure to hypoxia to further participate in regulating the formation of retinal neovascularization.