Circular RNAs: Potential Star Molecules Involved in Diabetic Retinopathy

The hsa_circ_0004805/hsa_miR-149-5p/TGFB2 axis plays critical roles in the pathophysiology of diabetic retinopathy in vitro and in vivo

The aim of this study was to investigate the mechanism underlying the role of a recently identified hsa_circ_0004805/hsa_miR-149-5p/transforming growth factor beta 2 (TGFB2) axis in the progression of diabetic retinopathy (DR). Quantitative reverse transcription-polymerase chain reaction (qRT-PCR) analysis suggested that hsa_circ_0004805 was highly expressed in aqueous humor samples of patients with DR, whereas hsa_miR-149-5p showed the opposite trend. Meanwhile, the results of a dual-luciferase reporter assay indicated that hsa_miR-149-5p directly interacted with both hsa_circ_0004805 and TGFB2. Using a variety of assays (Cell Counting Kit-8, EdU-labeling, Transwell, flow cytometric, wound healing, tube formation assays), we found that the overexpression of hsa_circ_0004805 significantly downregulated the level of hsa_miR-149-5p and promoted DNA synthesis, proliferation, migration, and tube formation in human retinal microvascular epithelial cells (hRECs) cultivated in a high-glucose environment. In contrast, hsa_miR-149-5p mimics inhibited DNA synthesis, proliferation, migration, and tube formation in hRECs by reducing the expression of its downstream target TGFB2 as well as the levels of phosphorylated SMAD2; however, these effects were reversed by the overexpression of hsa_circ_0004805. In a streptozotocin-induced Sprague-Dawley rat model of DR, retinal vascular leakage, capillary decellularization, loss of pericytes, fibrosis, and gliosis were evident, which could be reversed by vitreous microinjection of rat miR-149-5p mimics (rno-miR-149-5p agomir). Combined, our findings indicated that, under hyperglycemia, the hsa_circ_0004805/hsa_miR-149-5p/TGFB2 axis plays a critical role in the retinal pathophysiology associated with the development of DR, and has potential as a therapeutic target in the treatment of this condition.

Extracellular vesicles as a new horizon in the diagnosis and treatment of inflammatory eye diseases: A narrative review of the literature

Extracellular vesicles include exosomes, microvesicles, and apoptotic bodies. Their cargos contain a diverse variety of lipids, proteins, and nucleic acids that are involved in both normal physiology and pathology of the ocular system. Thus, studying extracellular vesicles may lead to a more comprehensive understanding of the pathogenesis, diagnosis, and even potential treatments for various diseases. The roles of extracellular vesicles in inflammatory eye disorders have been widely investigated in recent years. The term “inflammatory eye diseases” refers to a variety of eye conditions such as inflammation-related diseases, degenerative conditions with remarkable inflammatory components, neuropathy, and tumors. This study presents an overview of extracellular vesicles’ and exosomes’ pathogenic, diagnostic, and therapeutic values in inflammatory eye diseases, as well as existing and potential challenges.

Circ_0006667 contributes to high glucose-induced retinal pigment epithelial cell dysfunction by mediating miR-7-5p/TGFA axis in diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a common complication of diabetes mellitus and it can lead to visual impairment and blindness. The loss of retinal pigment epithelial (RPE) cells is associated with the etiology of DR. Moreover, dysregulated circular RNAs (circRNAs) are implicated in DR progression. Therefore, this project aims to explore the role and potential mechanism of circ_0006667 in DR.

METHODS

RPE cells (ARPE-19) were stimulated with high glucose (33 mM; HG group) for 24 h to establish the DR cell model. Circ_0006667, microRNA-7-5p (miR-7-5p), and transforming growth factor alpha (TGFA) expression was determined by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Cell viability, proliferation, and apoptosis were analyzed by 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), 5-ethynyl-2'-deoxyuridine (EdU), and flow cytometry. CyclinD1, Cleaved-caspase-3, and TGFA protein levels were detected using western blot. Using Circinteractome and starBase analysis, the binding miR-7-5p and circ_0006667 or TGFA was predicted, and then validated using dual-luciferase reporter and RNA Immunoprecipitation (RIP).

RESULTS

Circ_0006667 expression was up-regulated in DR patients and HG-induced ARPE-19 cells. HG stimulation suppressed ARPE-19 cell proliferation and promoted cell apoptosis and inflammation, which were alleviated via circ_0006667 silence. Circ_0006667 acted as a molecular sponge for miR-7-5p, and circ_0006667 absence-mediated protective effects in HG-induced ARPE-19 cells were largely overturned by the interference of miR-7-5p. miR-7-5p directly targeted TGFA, and miR-7-5p overexpression protected ARPE-19 cells from HG-induced dysfunction largely by down-regulating TGFA. Circ_0006667 can up-regulate the expression of TGFA by sponging miR-7-5p in ARPE-19 cells.

CONCLUSION

Circ_0006667 silencing protected ARPE-19 cells from HG-induced dysfunction by mediating miR-7-5p/TGFA axis.

Emerging roles of circular RNAs in retinal diseases

Retinal disorders are a group of ocular diseases whose onset is associated with a number of aberrant molecular and cellular processes or physical damages that affect retinal structure and function resulting in neural and vascular degeneration in the retina. Current research has primarily focused on delaying retinal disease with minimal success in preventing or reversing neuronal degeneration. In this review, we explore a relatively new field of research involving circular RNAs, whose potential roles as biomarkers and mediators of retinal disease pathogenesis have only just emerged. While knowledge of circular RNAs function is limited given its novelty, current evidence has highlighted their roles as modulators of microRNAs, regulators of gene transcription, and biomarkers of disease development and progression. Here, we summarize how circular RNAs may be implicated in the pathogenesis of common retinal diseases including diabetic retinopathy, glaucoma, proliferative vitreoretinopathy, and age-related macular degeneration. Further, we explore the potential of circular RNAs as novel biomarkers and therapeutic targets for the diagnosis and treatment of retinal diseases.

CircFAT1 regulates retinal pigment epithelial cell pyroptosis and autophagy via mediating m6A reader protein YTHDF2 expression in diabetic retinopathy

Diabetic retinopathy (DR) is a serious blinding complication of diabetes. At present, the therapeutic intervention effect is limited. We aimed to investigate the circRNA expression profiles in retinal proliferative fibrovascular membranes of patients with DR and explore the effect of circFAT1 on pyroptosis and autophagy of high glucose (HG)-induced retinal pigment epithelial (RPE) cells and its molecualr mechanism. In this study, circRNA sequencing was performed to determine the expression profiles of circRNAs in DR patients. The expression of circFAT1 was measured by qRT-PCR. Cell counting kit-8, transmission electron microscope, western blot, immunofluorescence and enzyme-linked immunosorbent assay were conducted to explore the roles of HG and circFAT1 in RPE cell pyroptosis and autophagy. RNA pull down was used to determine the binding protein of circFAT1. Our data showed that HG significantly reduced the viability of RPE cells, inhibited cell autophagy and contributed to cell pyroptosis. In addition, a total of 189 differentially expressed circRNAs (DEcircRNAs) were identified between DR patients and non-DR patients, including 93 upregulated and 96 downregulated DEcircRNAs in the retinal proliferative fibrovascular membranes of DR patients. Pathway analysis showed that DEcircRNAs were mainly involved in MAPK signaling pathway, TGF-beta signaling pathway and adherens junction. Moreover, circFAT1 was significantly downregulated in retinal proliferative fibrovascular membranes of DR patients and HG-induced RPE cells. CircFAT1 overexpression remarkably enhanced the expression of LC3B, while reduced the expression of GSDMD in HG-induced RPE cells. RNA pull down combined with western blot analysis indicated that circFAT1 bound to m6A reader YTHDF2. YTHDF2 overexpression significantly increased the protein expression of LC3B in HG-induced RPE cells. In summary, circFAT1 promoted autophagy and inhibited pyroptosis of RPE cells induced by HG, and could combine with YTHDF2. This study provides new ideas for DR prevention and treatment.

CircSLC16A12 absence inhibits high glucose-induced dysfunction in retinal microvascular endothelial cells through mediating miR-140-3p/FGF2 axis in diabetic retinopathy

BACKGROUND

Diabetic retinopathy (DR) is a common microvascular complication of diabetes mellitus which can cause irreversible visual impairment and blindness. We intended to investigate the function of circular RNA (circRNA) solute carrier family 16 member 12 (SLC16A12) in DR progression.

METHODS

Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blot assay were applied to measure RNA and protein expression. Cell apoptosis was analyzed by flow cytometry (FCM) analysis. The angiogenesis ability was assessed by tube formation assay. Enzyme-linked immunosorbent assay (ELISA) was performed to analyze the release of inflammatory cytokines. Cell oxidative stress status was evaluated using commercial kits. Dual-luciferase reporter assay, RNA immunoprecipitation (RIP) assay, and RNA-pull down assay were conducted to confirm the intermolecular interactions.

RESULTS

CircSLC16A12 level was enhanced in the serum samples of DR patients and high glucose (HG)-treated HRECs. CircSLC16A12 absence protected HRECs from HG-induced apoptosis, blood-retinal barrier (BRB) injury, tube formation, inflammatory response, and oxidative stress. CircSLC16A12 acted as a sponge for microRNA-140-3p (miR-140-3p), and circSLC16A12 knockdown-mediated effects were largely reversed by the absence of miR-140-3p in HRECs under HG condition. miR-140-3p interacted with the 3' untranslated region (3'UTR) of fibroblast growth factor 2 (FGF2), and the overexpression of FGF2 largely overturned miR-140-3p overexpression-mediated effects in HRECs. CircSLC16A12 interference reduced the expression of FGF2 by up-regulating miR-140-3p in HRECs.

CONCLUSION

CircSLC16A12 silencing suppressed HG-induced dysfunction in HRECs partly by targeting miR-140-3p/FGF2 axis.

Circular RNA circZNF532 facilitates angiogenesis and inflammation in diabetic retinopathy via regulating miR-1243/CARM1 axis

BACKGROUND

Diabetic retinopathy (DR) is a serious complication of diabetes. Numerous reports have validated that circular RNAs (circRNAs) participate in DR progression. This study aimed to elucidate the role and potential mechanism of circRNA zinc finger protein 532 (circZNF532) in DR.

METHODS

The levels of circZNF532, miR-1243, and coactivator associated arginine methyltransferase 1 (CARM1) in DR patients and human retinal microvascular endothelial cells (hRMECs) were determined by quantitative real-time PCR and western blot. Colony formation assay, transwell assay, tube formation assay and enzyme-linked immunosorbent assay were used to assess the biological function of hRMECs. The binding relationship between miR-1243 and circZNF532/CARM1 was verified by dual-luciferase reporter and RNA immunoprecipitation assays.

RESULTS

circZNF532 and CARM1 levels were increased, while miR-1243 level was reduced in DR patients and high glucose (HG)-stimulated hRMECs. In terms of mechanism, miR-1243 competitively bound to circZNF532 and CARM1. Down-regulation of circZNF532 restrained HG-induced hRMECs proliferation, migration, invasion, angiogenesis and inflammation via regulating miR-1243. In addition, miR-1243 inhibited HG-triggered hRMECs progression via targeting CARM1.

CONCLUSION

circZNF532 facilitated HG-induced angiogenesis and inflammation in hRMECs via modulating the miR-1243/CARM1 pathway, suggesting that circZNF532 might be a potential biomarker for DR treatment.

Circ-ADAM9 Promotes High Glucose-Induced Retinal Pigment Epithelial Cell Injury in DR via Regulating miR-338-3p/CARM1 Axis

Background. Circular RNAs (circRNAs) have been reported to be involved in the regulation of retinal pigment epithelial (RPE) cell injury and are closely related to the development of diabetic retinopathy (DR). More research is needed to confirm the role and mechanism of circ-ADAM9 in DR progression. Methods. High glucose (HG)-induced RPE cells (ARPE-19) were used to mimic the hyperglycemia condition. The expression of circ-ADAM9, microRNA (miR)-338-3p, and coactivator-associated arginine methyltransferase 1 (CARM1) was measured using quantitative real-time PCR. Cell proliferation and apoptosis were determined using MTT assay, EdU assay, and flow cytometry. The protein expression of apoptosis markers and CARM1 was examined by the western blot analysis. Also, MDA level and SOD activity were determined to assess cell oxidative stress. In addition, the interaction between miR-338-3p and circ-ADAM9 or CARM1 was confirmed by dual-luciferase reporter assay and RIP assay. Results. The expression of circ-ADAM9 was upregulated in DR patients and HG-induced ARPE-19 cells. Silenced circ-ADAM9 could promote proliferation and inhibit inflammation, apoptosis, and oxidative stress in HG-induced ARPE9 cells. In terms of mechanism, circ-ADAM9 could sponge miR-338-3p to upregulate CARM1. The inhibitory effect of circ-ADAM9 knockdown on HG-induced ARPE9 cell injury could be reversed by an miR-338-3p inhibitor. As a target of miR-338-3p, CARM1 knockdown could alleviate HG-induced ARPE9 cells’ injury, and its overexpression also could reverse the negatively regulation of miR-338-3p on HG-induced ARPE9 cell injury. Conclusion. Circ-ADAM9 contributed to HG-induced ARPE9 cell injury by regulating miR-338-3p/CARM1 axis, which provided effective targets for DR treatment.

Hyperglycemia-induced increasing of RELB/circ_0008590 in NF-κB pathway is repressed by miR-1243 in human retinal microvascular endothelial cells

Background

To investigate the abnormal expression of circ_0008590 and its parent gene, reticuloendotheliosis viral oncogene related B (RELB) in human retinal microvascular endothelial cells (hRECs) in hyperglycemia and the potential mechanism.

Methods

The levels of RELB, circ_0008590, and miR-1243 in hRECs or clinical samples were detected by quantitative reverse transcription-polymerase chain reaction (qRT-PCR). Dual-luciferase reporter assay was used to test the interaction between RELB/circ_0008590 and miR-1243. Cell Counting Kit-8 (CCK-8), Transwell, flow cytometry (FCM), wound healing, and tube formation assays were used for the physiological investigation. The interaction between human RELB and circ_0008590 was studied in streptozotocin (STZ) induced diabetic retinopathy (DR) C57BL/6 mice.

Results

The levels of circ_0008590 and RELB were increased in hRECs in hyperglycemia; during the progression of DR, the levels of circ_0008590 and RELB messenger RNA (mRNA) in aqueous humor were first decreased and then increased, whereas miR-1243 showed an opposite trend. Both RELB 3'-untranslated region (UTR) and circ_0008590 shared a similar binding site for miR-1243. Further, miR-1243 mimic suppressed the proliferation and migration of hRECs, promoting the apoptosis ratio, which could be rescued by the overexpression of circ_0008590. In STZ-induced DR mice, miR-1243 agomir rescued the effects of the overexpression of human RELB.

Conclusions

In hyperglycemia, high expression of RELB/circ_0008590 could be suppressed by miR-1243, and the nuclear factor-κB (NF-κB) pathway is subsequently affected.

Circular RNAs: Novel target of diabetic retinopathy

In diabetic patients, diabetic retinopathy (DR) is the leading cause of blindness and seriously affects the quality of life. However, current treatment methods of DR are not satisfactory. Advances have been made in understanding abnormal protein interactions and signaling pathways in DR pathology, but little is known about epigenetic regulation. Non-coding RNAs, such as circular RNAs (circRNAs), have been shown to be associated with DR. In this review, we summarized the function of circRNAs and indicated their roles in the pathogenesis of DR, which may provide new therapeutic targets for clinical treatment.