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

Autophagy and diabetes

The current literature findings on autophagy’s beneficial and detrimental roles in diabetes mellitus (DM) and diabetes-related comorbidities were reviewed. The effects of oral hypoglycaemic medicines and autophagy in DM. Autophagy plays an important function in cellular homeostasis by promoting cell survival or initiating cell death in physiological settings was also assessed. Although autophagy protects insulin-target tissues, organelle failure caused by autophagy malfunction influences DM and other metabolic diseases. Endoplasmic reticulum and oxidative stress enhance autophagy levels, making it easier to regulate stress-induced intracellular changes. Evidence suggests that autophagy-caused cell death can occur when autophagy is overstimulated and constitutively activated, which might prevent or develop DM. Even though the precise role of autophagy in DM complications is uncertain, deregulation of the autophagic machinery is strongly linked to beta cell destruction and the aetiology of DM. Thus, improving autophagy dysfunction is a possible therapeutic objective in treating DM and other metabolic disorders.

Autophagy in peritoneal fibrosis

Peritoneal dialysis (PD) is a widely accepted renal replacement therapy for patients with end-stage renal disease (ESRD). Morphological and functional changes occur in the peritoneal membranes (PMs) of patients undergoing long-term PD. Peritoneal fibrosis (PF) is a common PD-related complication that ultimately leads to PM injury and peritoneal ultrafiltration failure. Autophagy is a cellular process of "self-eating" wherein damaged organelles, protein aggregates, and pathogenic microbes are degraded to maintain intracellular environment homeostasis and cell survival. Growing evidence shows that autophagy is involved in fibrosis progression, including renal fibrosis and hepatic fibrosis, in various organs. Multiple risk factors, including high-glucose peritoneal dialysis solution (HGPDS), stimulate the activation of autophagy, which participates in PF progression, in human peritoneal mesothelial cells (HPMCs). Nevertheless, the underlying roles and mechanisms of autophagy in PF progression remain unclear. In this review, we discuss the key roles and potential mechanisms of autophagy in PF to offer novel perspectives on future therapy strategies for PF and their limitations.

A novel sprayable thermosensitive hydrogel coupled with zinc modified metformin promotes the healing of skin wound

A novel sprayable adhesive is established (ZnMet-PF127) by the combination of a thermosensitive hydrogel (Pluronic F127, PF127) and a coordination complex of zinc and metformin (ZnMet). Here we demonstrate that ZnMet-PF127 potently promotes the healing of traumatic skin defect and burn skin injury by promoting cell proliferation, angiogenesis, collagen formation. Furthermore, we find that ZnMet could inhibit reactive oxygen species (ROS) production through activation of autophagy, thereby protecting cell from oxidative stress induced damage and promoting healing of skin wound. ZnMet complex exerts better effects on promoting skin wound healing than ZnCl₂ or metformin alone. ZnMet complex also displays excellent antibacterial activity against Staphylococcus aureus or Escherichia coli, which could reduce the incidence of skin wound infections. Collectively, we demonstrate that sprayable PF127 could be used as a new drug delivery system for treatment of skin injury. The advantages of this sprayable system are obvious: (1) It is convenient to use; (2) The hydrogel can cover irregular skin defect sites evenly in a liquid state. In combination with this system, we establish a novel sprayable adhesive (ZnMet-PF127) and demonstrate that it is a potential clinical treatment for traumatic skin defect and burn skin injury.

Chloroquine regulates the proliferation and apoptosis of palate development on mice embryo by activating P53 through blocking autophagy in vitro

Cleft lip and palate is one of the most frequent congenital developmental defects. Autophagy is a highly conserved process of cell self-degradation in eukaryotes, involving multiple biological processes in which chloroquine (CQ) is the most common inhibitor. However, whether CQ affects and how it affects palate development is unknown. Mouse embryonic palatal cells (MEPCs) were treated with CQ to observe cell viability, apoptosis, migration, osteogenic differentiation by cell proliferation assay, flow cytometric analysis, scratch assay, and alizarin red staining. PI staining was used to measure cell cycle distribution. Immunofluorescence (IF) assay and transmission electron microscopy were used to detect autophagosomes. The autophagy-related factors (LC3 and P62), apoptosis-related markers (P53, caspase-3 cleaved caspase-3, BAX, and BCL-2), and cell cycle-related proteins (P21, CDK2, CDK4, cyclin D1, and cyclin E) were all measured by western blot. CQ inhibited the proliferation of MEPCs by arresting the G0/G1 phase of the cell cycle in a concentration- and time-dependent manner with cell cycle-related proteins P21 upregulated and CDK2, CDK4, cyclin D1, and cyclin E downregulated. Then we detected CQ also induced cell apoptosis in a dose-dependent manner by decreasing the BCL-2/BAX ratio and increasing cleaved caspase-3. Next, it was investigated that migration and osteogenesis of MEPCs decreased with CQ treatment in a dose-dependent manner. Meanwhile, CQ blocked the autophagy pathway by upregulating LC3II and P62 expressions which activated the P53 pathway. CQ activates P53 which affects MEPC biological characteristics by changing the proliferation and apoptosis of MEPCs through inhibiting autophagy.

Inhibition of PI3K/AKT/mTOR Signalling Pathway Activates Autophagy and Suppresses Peritoneal Fibrosis in the Process of Peritoneal Dialysis

Peritoneal dialysis (PD) is an important part of replacement therapy for kidney failure. However, long-term PD treatment can cause peritoneal fibrosis. Autophagy may be involved in the pathological mechanism of peritoneal fibrosis (PF). Although autophagy is currently known to be involved in course of PF, its specific effects still lack in-depth research. In this experiment, a high-glucose (HG)-induced peritoneal fibrosis rat model was successfully established via intraperitoneal injection of HG peritoneal dialysate, and the phosphatidylinositol 3-kinase (PI3K) inhibitor LY294002 and the mechanistic target of rapamycin (mTOR) inhibitor rapamycin were used to treat peritoneal fibrosis rats. In addition, in vitro studies of high glucose-induced peritoneal fibrosis were performed using rat peritoneal mesothelial cells (PMCs). In vivo and in vitro experiments showed that LY294002 and rapamycin effectively inhibited the process of PF induced by high glucose. In addition, LY294002 and rapamycin were found to alleviate fibrosis by eliminating intracellular reactive oxygen species (ROS) levels, promoting the expression of the epithelial mesenchymal transdifferentiation proteins zonula occludens-1 (ZO-1) and E-cadherin, and inhibiting the expression of p-PI3K, PI3K, p-mTOR, mTOR, the fibroblast-specific proteins ferroptosis suppressor protein 1 (FSP1), and alpha-smooth muscle actin (α-SMA). Moreover, LY294002 and rapamycin promoted expression of autophagy-related proteins LC3-II/I, p62, and beclin-1. The current data indicated that inhibition of PI3K/AKT/mTOR signalling pathway activated autophagy and suppressed PF in the process of PD. Therefore, intervention in this signalling pathway may become a research goal for the prevention and treatment of PF, which has important clinical significance.

Changes in Plasma VEGF and PEDF Levels in Patients with Central Serous Chorioretinopathy

Background and Objectives: Retinal pigment epitheliopathy and hyperpermeability of choroidal vessels were postulated to be involved in the pathogenesis of central serous chorioretinopathy (CSC). Imbalanced levels of vascular endothelial growth factor (VEGF) and pigment-epithelium–derived factor (PEDF) were previously implicated in the development of chorioretinal diseases characterized by increased vascular permeability. We aimed to compare the plasma levels of proangiogenic VEGF and antiangiogenic PEDF for 26 patients with acute CSC, 26 patients with chronic CSC, and 19 controls. Materials and Methods: VEGF and PEDF levels were measured using a multiplex immunoassay or enzyme-linked immunosorbent assay. Correlations with disease duration were assessed. Results: VEGF levels differed between groups (p = 0.001). They were lower in patients with acute CSC (p = 0.042) and chronic CSC (p = 0.018) than in controls. PEDF levels were similar in all groups. The VEGF-to-PEDF ratio was lower in CSC patients than in controls (p = 0.04). A negative correlation with disease duration was noted only for PEDF levels in the group with chronic CSC (rho = −0.46, p = 0.017). Discussion: Our study confirmed that patients with CSC have imbalanced levels of VEGF and PEDF. This finding may have important implications for the pathogenesis of CSC. VEGF-independent arteriogenesis rather than angiogenesis may underlie vascular abnormalities in these patients.

Blockade of Autophagy Prevents the Development and Progression of Peritoneal Fibrosis

Peritoneal fibrosis (PF) is a major cause of ultrafiltration failure in long-term peritoneal dialysis (PD) patients. Nevertheless, limited measures have been shown to be effective for the prevention and treatment of PF. Some views reveal that activation of autophagy ameliorates PF but others demonstrate that autophagy promotes PF. It is obvious that the role of autophagy in PF is controversial and further studies are needed. Here, we investigated the role of autophagy in rat models of PF and damaged cultured human peritoneal mesothelial cells (HPMCs). Autophagy was highly activated in fibrotic peritoneum from two PF rat models induced by 4.25% peritoneal dialysate fluid (PDF) and 0.1% chlorhexidine gluconate (CG). Blockade of autophagy with 3-MA effectively prevented PF in both models and reversed epithelial to mesenchymal transition (EMT) by down-regulating TGF-β/Smad3 signaling pathway and downstream nuclear transcription factors Slug and Snail. Treatment with 3-MA also inhibited activation of EGFR/ERK1/2 signaling pathway during PF. Moreover, 3-MA prominently decreased STAT3/NF-κB-mediated inflammatory response and macrophage infiltration, and prevented peritoneal angiogenesis through downregulation of β-catenin signal. In addition, TGF-β1 stimulation up-regulated autophagic activity as evidenced by the increased autophagosome in vitro. Exposure of HPMCs to TGF-β1 resulted in the induction of EMT and activation of TGF-β/Smad3, EGFR/ERK1/2 signaling pathways. Treatment with 3-MA blocked all these responses. In addition, delayed administration of 3-MA was effective in reducing EMT induced by TGF-β1. Taken together, our study indicated that autophagy might promote PF and 3-MA had anti-fibrosis effect in vivo and in vitro. These results suggest that autophagy could be a potential target on PF therapy for clinical patients with long-term PD.

PEDF-Mediated Mitophagy Triggers the Visual Cycle by Enhancing Mitochondrial Functions in a H2O2-Injured Rat Model

Retinal degenerative diseases result from oxidative stress and mitochondrial dysfunction, leading to the loss of visual acuity. Damaged retinal pigment epithelial (RPE) and photoreceptor cells undergo mitophagy. Pigment epithelium-derived factor (PEDF) protects from oxidative stress in RPE and improves mitochondrial functions. Overexpression of PEDF in placenta-derived mesenchymal stem cells (PD-MSCs; PD-MSCs^PEDF) provides therapeutic effects in retinal degenerative diseases. Here, we investigated whether PD-MSCs^PEDF restored the visual cycle through a mitophagic mechanism in RPE cells in hydrogen peroxide (H₂O₂)-injured rat retinas. Compared with naïve PD-MSCs, PD-MSCs^PEDF augmented mitochondrial biogenesis and translation markers as well as mitochondrial respiratory states. In the H₂O₂-injured rat model, intravitreal administration of PD-MSCs^PEDF restored total retinal layer thickness compared to that of naïve PD-MSCs. In particular, PTEN-induced kinase 1 (PINK1), which is the major mitophagy marker, exhibited increased expression in retinal layers and RPE cells after PD-MSC^PEDF transplantation. Similarly, expression of the visual cycle enzyme retinol dehydrogenase 11 (RDH11) showed the same patterns as PINK1 levels, resulting in improved visual activity. Taken together, these findings suggest that PD-MSCs^PEDF facilitate mitophagy and restore the loss of visual cycles in H₂O₂-injured rat retinas and RPE cells. These data indicate a new strategy for next-generation MSC-based treatment of retinal degenerative diseases.

Effect of glycemic control and dyslipidemia on plasma vascular endothelial growth factor and pigment epithelium-derived factor in diabetic retinopathy patients in Northern Nigeria

OBJECTIVES

The disruption of the reciprocal regulation between vascular endothelial growth factor (VEGF) and pigment epithelium-derived factor (PEDF) has been associated with the pathogenesis of diabetic retinopathy (DR). This study assessed the levels of VEGF, PEDF, indices of glycemia, and lipid profile in diabetic patients with retinopathy.

METHODS

One hundred fifty participants comprised 50 type 2 diabetic patients with DR, 50 without DR and 50 non-diabetic normotensive controls, aged 30-80 years, were randomly recruited for this case-control study. The study was carried out from November 2017 to December 2018. VEGF, PEDF, glycated hemoglobin (HbA1c), fasting plasma glucose, and lipid profile were determined using standard methods. Blood pressures (BP) and anthropometric indices were measured. Chi-squared test of independence, analysis of variance, and Pearson's correlation were used to analyze data. Statistical significance was set at P < 0.05 and 95% confidence interval.

RESULTS

Both diabetic groups had significantly higher (P = 0.001) systolic and diastolic BP, VEGF, PEDF, HbA1c, fasting plasma glucose, triglycerides, total, high-density lipoprotein-cholesterol (HDL-C), and low-density lipoprotein-cholesterol (LDL-C) levels and significantly lower (P = 0.005) VEGF/PEDF than the controls. However, the diabetics with retinopathy had significantly higher (P = 0.001) HDL-C, LDL-C, VEGF, and PEDF levels compared to the diabetics without retinopathy. There were no significant differences (P > 0.05) in the levels of VEGF, PEDF, and VEGF/PEDF in both groups of diabetics that had good glycemic control and poor glycemic control. There was also no significant difference (P > 0.05) in the levels of VEGF and PEDF between the dyslipidemic and non-dyslipidemic subjects in both diabetic groups.

CONCLUSION

DR is associated with higher levels of VEGF and PEDF while good glycemic control and dyslipidemia seem not to have a profound effect on VEGF and PEDF levels in diabetics with or without DR. Higher PEDF levels are associated with higher atherogenic risk in the diabetics with retinopathy.

A Re-Appraisal of Pathogenic Mechanisms Bridging Wet and Dry Age-Related Macular Degeneration Leads to Reconsider a Role for Phytochemicals

Which pathogenic mechanisms underlie age-related macular degeneration (AMD)? Are they different for dry and wet variants, or do they stem from common metabolic alterations? Where shall we look for altered metabolism? Is it the inner choroid, or is it rather the choroid–retinal border? Again, since cell-clearing pathways are crucial to degrade altered proteins, which metabolic system is likely to be the most implicated, and in which cell type? Here we describe the unique clearing activity of the retinal pigment epithelium (RPE) and the relevant role of its autophagy machinery in removing altered debris, thus centering the RPE in the pathogenesis of AMD. The cell-clearing systems within the RPE may act as a kernel to regulate the redox homeostasis and the traffic of multiple proteins and organelles toward either the choroid border or the outer segments of photoreceptors. This is expected to cope with the polarity of various domains within RPE cells, with each one owning a specific metabolic activity. A defective clearance machinery may trigger unconventional solutions to avoid intracellular substrates’ accumulation through unconventional secretions. These components may be deposited between the RPE and Bruch’s membrane, thus generating the drusen, which remains the classic hallmark of AMD. These deposits may rather represent a witness of an abnormal RPE metabolism than a real pathogenic component. The empowerment of cell clearance, antioxidant, anti-inflammatory, and anti-angiogenic activity of the RPE by specific phytochemicals is here discussed.

Phosphorylation of STAT3 and ERBB2 mediates hypoxia‑induced VEGF release in ARPE‑19 cells

Neovascularization in the retina can cause loss of vision. Vascular endothelial growth factor (VEGF) serves an important role in the pathogenesis of retinal vascular diseases. Hypoxia is a notable cause of VEGF release and both STAT3 and ERBB2 are known to be associated with VEGF. In addition, STAT3 and ERBB2 interact with each other. In the present study, it was hypothesized that signal transducer and activator of transcription 3 (STAT3) and erbB-2 receptor tyrosine kinase 2 (ERBB2) may be involved in the regulation of hypoxia-induced VEGF in the retina. Cells of the retinal pigment epithelium (RPE) are an important source of VEGF. Therefore, the RPE-derived human cell line ARPE-19 was exposed to hypoxia. Hypoxia-induced phosphorylation of STAT3 and ERBB2 in ARPE-19 cells was decreased by AG490, an inhibitor of Janus kinase 2, as were hypoxia-induced VEGF release and tube formation in human umbilical vein endothelial cells. Thus, phosphorylation of ERBB2 and STAT3 regulates hypoxia-induced VEGF release in ARPE-19 cells. The results of the present study suggested that inhibition of ERBB2 and STAT3-mediated pathways under hypoxia may represent a new strategy for treating retinal vascular disease.

Effects of FTMT Expression by Retinal Pigment Epithelial Cells on Features of Angiogenesis

Aberrant angiogenesis is a pathological feature of a number of diseases and arises from the uncoordinated expression of angiogenic factors as response to different cellular stresses. Age-related macular degeneration (AMD), a leading cause of vision loss, can result from pathological angiogenesis. As a mutation in the mitochondrial ferritin (FTMT) gene has been associated with AMD, its possible role in modulating angiogenic factors and angiogenesis was investigated. FTMT is an iron-sequestering protein primarily expressed in metabolically active cells and tissues with high oxygen demand, including retina. In this study, we utilized the human retinal pigment epithelial cell line ARPE-19, both as undifferentiated and differentiated cells. The effects of proinflammatory cytokines, FTMT knockdown, and transient and stable overexpression of FTMT were investigated on expression of pro-angiogenic vascular endothelial growth factor (VEGF) and anti-angiogenic pigment epithelial-derived factor (PEDF). Proinflammatory cytokines induced FTMT and VEGF expression, while NF-κB inhibition significantly reduced FTMT expression. VEGF protein and mRNA expression were significantly increased in FTMT-silenced ARPE-19 cells. Using an in vitro angiogenesis assay with endothelial cells, we showed that conditioned media from FTMT-overexpressing cells had significant antiangiogenic effects. Collectively, our findings indicate that increased levels of FTMT inhibit angiogenesis, possibly by reducing levels of VEGF and increasing PEDF expression. The cellular models developed can be used to investigate if increased FTMT may be protective in angiogenic diseases, such as AMD.