MicroRNA signature and function in retinal neovascularization

Critical roles of miR-21 in promotions angiogenesis: friend or foe?

MiRNAs are small RNA strands that are managed following transcription and are of substantial importance in blood vessel formation. It is essential to oversee the growth, differentiation, death, movement and construction of tubes by angiogenesis-affiliated cells. If miRNAs are not correctly regulated in regard to angiogenesis, it can deteriorate the health and lead to various illnesses, which include cancer, cardiovascular disorder, critical limb ischemia, Crohn's disease, ocular diseases, diabetic microvascular complications, and more. Consequently, it is vital to understand the crucial part that miRNAs play in the development of blood vessels, so we can develop reliable treatment plans for vascular diseases. This write-up will assess the critical role of miR-21/exosomal miR-21 in managing angiogenesis associated with bone growth, wound recovery, and other pathological conditions like tumor growth, ocular illnesses, diabetes, and other diseases connected to formation of blood vessels. Previous investigations have demonstrated that miR-21 is present at higher amounts in certain cancerous cells, and it influences a multitude of genes that moderate the increased creation of blood vessels. Furthermore, studies demonstrated that exosomal miR-21 has the capacity to interact with endothelial cells to foster tumor angiogenesis. For that reason, this review explains the critical importance of miR-21/exosomal miR-21 in managing both healthy and diseased states of angiogenesis.

Current Insights into Targeting Strategies for the Effective Therapy of Diseases of the Posterior Eye Segment

The eye is one a unique sophisticated human sense organ with a complex anatomical structure. It is encased by variety of protective barriers as responsible for vision. There has been a paradigm shift in the prevalence of several major vision threatening ocular conditions with enhanced reliance on computer-based technologies in our workaday life and work-from-home modalities although aging, pollution, injury, harmful chemicals, lifestyle changes will always remain the root cause. Treating posterior eye diseases is a challenge faced by clinicians worldwide. The clinical use of conventional drug delivery systems for posterior eye targeting is restricted by the ocular barriers. Indeed, for overcoming various ocular barriers for efficient delivery of the therapeutic moiety and prolonged therapeutic effect requires prudent and target-specific approaches. Therefore, for efficient drug delivery to the posterior ocular segment, advancements in the development of sustained release and nanotechnology-based ocular drug delivery systems have gained immense importance. Therapeutic efficacy and patient compliance are of paramount importance in clinical translation of these investigative drug delivery systems. This review provides an insight into the various strategies employed for improving the treatment efficacies of the posterior eye diseases. Various drug delivery systems such as systemic and intraocular injections, implants have demonstrated promising outcomes, along with that they have also exhibited side-effects, limitations and strategies employed to overcome them are discussed in this review. The application of artificial intelligence-based technologies along with an appreciation of disease, delivery systems, and patient-specific outcomes will likely enable more effective therapy for targeting the posterior eye segment.

Novel Function of Nogo-A as Negative Regulator of Endothelial Progenitor Cell Angiogenic Activity: Impact in Oxygen-Induced Retinopathy

Endothelial Progenitor Cells (EPCs) can actively participate in revascularization in oxygen-induced retinopathy (OIR). Yet the mechanisms responsible for their dysfunction is unclear. Nogo-A, whose function is traditionally related to the inhibition of neurite function in the central nervous system, has recently been documented to display anti-angiogenic pro-repellent properties. Based on the significant impact of EPCs in retinal vascularization, we surmised that Nogo-A affects EPC function, and proceeded to investigate the role of Nogo-A on EPC function in OIR. The expression of Nogo-A and its specific receptor NgR1 was significantly increased in isolated EPCs exposed to hyperoxia, as well as in EPCs isolated from rats subjected to OIR compared with respective controls (EPCs exposed to normoxia). EPCs exposed to hyperoxia displayed reduced migratory and tubulogenic activity, associated with the suppressed expression of prominent EPC-recruitment factors SDF-1/CXCR4. The inhibition of Nogo-A (using a Nogo-66 neutralizing antagonist peptide) or siRNA-NGR1 in hyperoxia-exposed EPCs restored SDF-1/CXCR4 expression and, in turn, rescued the curtailed neovascular functions of EPCs in hyperoxia. The in vivo intraperitoneal injection of engineered EPCs (Nogo-A-inhibited or NgR1-suppressed) in OIR rats at P5 (prior to exposure to hyperoxia) prevented retinal and choroidal vaso-obliteration upon localization adjacent to vasculature; coherently, the inhibition of Nogo-A/NgR1 in EPCs enhanced the expression of key angiogenic factors VEGF, SDF-1, PDGF, and EPO in retina; CXCR4 knock-down abrogated suppressed NgR1 pro-angiogenic effects. The findings revealed that hyperoxia-induced EPC malfunction is mediated to a significant extent by Nogo-A/NgR1 signaling via CXCR4 suppression; the inhibition of Nogo-A in EPCs restores specific angiogenic growth factors in retina and the ensuing vascularization of the retina in an OIR model.

MicroRNA-150 (miR-150) and Diabetic Retinopathy: Is miR-150 Only a Biomarker or Does It Contribute to Disease Progression?

Diabetic retinopathy (DR) is a chronic disease associated with diabetes mellitus and is a leading cause of visual impairment among the working population in the US. Clinically, DR has been diagnosed and treated as a vascular complication, but it adversely impacts both neural retina and retinal vasculature. Degeneration of retinal neurons and microvasculature manifests in the diabetic retina and early stages of DR. Retinal photoreceptors undergo apoptosis shortly after the onset of diabetes, which contributes to the retinal dysfunction and microvascular complications leading to vision impairment. Chronic inflammation is a hallmark of diabetes and a contributor to cell apoptosis, and retinal photoreceptors are a major source of intraocular inflammation that contributes to vascular abnormalities in diabetes. As the levels of microRNAs (miRs) are changed in the plasma and vitreous of diabetic patients, miRs have been suggested as biomarkers to determine the progression of diabetic ocular diseases, including DR. However, few miRs have been thoroughly investigated as contributors to the pathogenesis of DR. Among these miRs, miR-150 is downregulated in diabetic patients and is an endogenous suppressor of inflammation, apoptosis, and pathological angiogenesis. In this review, how miR-150 and its downstream targets contribute to diabetes-associated retinal degeneration and pathological angiogenesis in DR are discussed. Currently, there is no effective treatment to stop or reverse diabetes-caused neural and vascular degeneration in the retina. Understanding the molecular mechanism of the pathogenesis of DR may shed light for the future development of more effective treatments for DR and other diabetes-associated ocular diseases.

microRNA-126 inhibits vascular cell adhesion molecule-1 and interleukin-1beta in human dental pulp cells

BACKGROUND

Vascular cell adhesion molecule (VCAM-1) mediates pulpitis via regulating interleukin (IL)-1β. microRNA (miR)-126 was reported to regulate the VCAM-1 under many different pathophysiological circumstances. We investigated variations of miR-126 and VCAM-1 in inflamed patient pulp tissues and determined potential roles of miR-126 in pulpitis using human dental pulp cells (hDPCs) in vitro.

METHODS

We quantitatively measured the transcripts of miR-126 and VCAM-1 in inflamed human pulp tissues using qRT-PCR and compared with those from healthy human pulp tissues. In addition, we transfected miR-126 in hDPCs using plasmid DNA (pDNA)-encoding miR-126 delivered by polyethylenimine (PEI) nanoparticles.

RESULTS

The irreversible pulpitis significantly reduced miR-126 and increased the transcript of VCAM-1 in pulp tissues (p < 0.05). pDNA-encoding miR-126 delivered PEI nanoparticles and effectively upregulated the expression of miR-126 in hDPCs (p < 0.05). The overexpression of miR-126 could effectively suppress the transcripts and protein levels of VCAM-1 and IL-1β induced by Pg-LPS at 100ng/mL in DPCs (p < 0.05).

CONCLUSIONS

miR-126 is involved in pulpitis and downregulated the VCAM-1 and IL-1β in DPCs. miR-126 may be a potential target to attenuate the inflammation of pulpitis.

Therapeutic effects of mesenchymal stem cells-derived extracellular vesicles' miRNAs on retinal regeneration: a review

Extracellular vesicles (EVs), which consist of microvesicles and exosomes, are secreted from all cells to transform vital information in the form of lipids, proteins, mRNAs and small RNAs such as microRNAs (miRNAs). Many studies demonstrated that EVs' miRNAs have effects on target cells. Numerous people suffer from the blindness caused by retinal degenerations. The death of retinal neurons is irreversible and creates permanent damage to the retina. In the absence of acceptable cures for retinal degenerative diseases, stem cells and their paracrine agents including EVs have become a promising therapeutic approach. Several studies showed that the therapeutic effects of stem cells are due to the miRNAs of their EVs. Considering the effects of microRNAs in retinal cells development and function and studies which provide the possible roles of mesenchymal stem cells-derived EVs miRNA content on retinal diseases, we focused on the similarities between these two groups of miRNAs that could be helpful for promoting new therapeutic techniques for retinal degenerative diseases.

Salidroside Prevents Hypoxia-Induced Human Retinal Microvascular Endothelial Cell Damage Via miR-138/ROBO4 Axis

Purpose

Retinopathies are associated with the injury of retinal microvascular endothelial cells. Salidroside (SAL) is a medicinal supplement that has antioxidative and cytoprotective properties. We hypothesized that SAL might have a protective function in retinopathies. This research aims to explore the function and mechanism of SAL in hypoxia-induced retinal microvascular endothelial cell injury.

Methods

Human retinal microvascular endothelial cells (HRMECs) injury was induced by culturing under hypoxic condition. The function of SAL on HRMECs injury was investigated using cell counting kit-8, 5-ethynyl-2′-deoxyuridine (EdU) staining, flow cytometry, Western blotting, and enzyme linked immunosorbent assay. MicroRNA (miR)-138, roundabout 4 (ROBO4), and proteins in the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathways were examined using quantitative reverse transcription polymerase chain reaction or Western blotting. The target correlation was determined by dual-luciferase reporter analysis and RNA immunoprecipitation.

Results

Hypoxia resulted in proliferation inhibition, cycle arrest, apoptosis, inflammatory reaction, and oxidative stress in HRMECs. SAL attenuated hypoxia-induced HRMECs injury via increasing cell proliferation, and mitigating cycle arrest, apoptosis, inflammatory reaction, and oxidative stress. MiR-138 expression was enhanced by hypoxia, and decreased via SAL stimulation. MiR-138 upregulation reversed the influence of SAL on hypoxia-induced HRMECs injury. ROBO4 was targeted via miR-138. ROBO4 overexpression weakened the role of miR-138 in HRMECs injury. The PI3K/AKT/mTOR pathway was inactivated under hypoxic condition, and SAL increased the activation of PI3K/AKT/mTOR pathways by decreasing miR-138.

Conclusions

SAL protected against hypoxia-induced HRMECs injury through regulating miR-138/ROBO4 axis, indicating the protective potential of SAL in retinopathies.

MicroRNA-126 inhibits pathological retinal neovascularization via suppressing vascular endothelial growth factor expression in a rat model of retinopathy of prematurity

Vascular endothelial growth factor (VEGF) is the principal growth factor responsible for the retinal neovascularization in the pathogenesis of retinopathy of prematurity (ROP). Current therapies for ROP include laser ablation and intravitreal anti-VEGF injection. However, these treatments either destroy the peripheral retina or associate with problems of persistent peripheral avascular retina or later recurrence of ROP. In the present study we investigated a new therapeutic approach by exploring the potential role of a specific microRNA, miR-126, in regulating VEGFA expression and retinal neovascularization in a rat oxygen-induced retinopathy (OIR) model. We demonstrated that miR-126 mimic and plasmid effectively suppresses VEGFA mRNA expression in both human and rat retinal pigment epithelium cell lines, quantified with qRT-PCR. Animal experiments on rat OIR model revealed that intravitreal injection of miR-126 plasmid efficiently downregulated VEGFA expression in the intraocular fluid and retinal tissues measured by ELISA, and significantly suppressed retinal neovascularization, which was confirmed by calculating sizes of neovascularization areas on fluorescence microscopic images of flat mounted retina stained with Alexa Fluor 594-conjugated isolectin B4 to visualize blood vessels. Together, these results showed that intravitreal injection of miR-126 plasmid could inhibit retinal neovascularization by down-regulating VEGFA expression, suggesting a potential therapeutic effect for ROP.

MicroRNAs as diagnostic and prognostic biomarkers of age-related macular degeneration: advances and limitations

A main cause of vision loss in the elderly is age-related macular degeneration (AMD). Among the cellular, biochemical, and molecular changes linked to this disease, inflammation and angiogenesis appear as being crucial in AMD pathogenesis and progression. There are two forms of the disease: dry AMD, accounting for 80-90% of cases, and wet AMD. The disease usually begins as dry AMD associated with retinal pigment epithelium and photoreceptor degeneration, whereas wet AMD is associated with choroidal neovascularization resulting in severe vision impairment. The new vessels are largely malformed, leading to blood and fluid leakage within the disrupted tissue, which provokes inflammation and scar formation and results in retinal damage and detachment. MicroRNAs are dysregulated in AMD and may facilitate the early detection of the disease and monitoring disease progression. Two recent reviews of microRNAs in AMD had indicated weaknesses or limitations in four earlier investigations. Studies in the last three years have shown considerable progress in overcoming some of these concerns and identifying specific microRNAs as biomarkers for AMD. Further large-scale studies are warranted using appropriate statistical methods to take into account gender and age disparity in the study populations and confounding factors such as smoking status.

Circulating miRNAs in diabetic retinopathy patients: Prognostic markers or pharmacological targets?

In this study we analyzed the expression of circulating miRNAs, in the serum of diabetic retinopathy (DR) patients. Five miRNAs (hsa-miR-195-5p, hsa-miR-20a-5p, hsa-miR-20b-5p, hsa-miR-27b-3p and hsa-miR-451a) were validated as biomarkers for stratification of DR stages, from the early non-proliferative (NPDR) to the late proliferative (PDR) phase. Furthermore, circulating levels of these miRNAs correlated with retinal hyper-reflective spots (HRS), assessed by optical coherence tomography (OCT). The number of HRS increased with worsening of DR stages. On the contrary, no significant vascular density differences between NPDR and PDR patients were detected by angio-OCT (OCTA). A post-hoc bioinformatics analysis associated these five miRNAs to target genes belonging to the "Tumor Necrosis Factor alfa signaling" pathway, and several molecules were predicted to modify miRNAs expression. In conclusion, correlation between specific circulating miRNAs and intraretinal hyper-reflective spots was demonstrated, confirming that these miRNAs were validated as prognostic biomarkers, and also as potential pharmacological targets, warranting further clinical evaluation to explore novel therapeutics for diabetic retinopathy.

MicroRNAs in laser-induced choroidal neovascularization in mice and rats: their expression and potential therapeutic targets

Choroidal neovascularization characterizes wet age-related macular degeneration. Choroidal neovascularization formation involves a primarily angiogenic process that is combined with both inflammation and proteolysis. A primary cause of choroidal neovascularization pathogenesis is alterations in pro- and anti-angiogenic factors derived from the retinal pigment epithelium, with vascular endothelium growth factor being mainly responsible for both clinical and experimental choroidal neovascularization. MicroRNAs (miRNAs) which are short, non-coding, endogenous RNA molecules have a major role in regulating various pathological processes, including inflammation and angiogenesis. A review of recent studies with the mouse laser-induced choroidal neovascularization model has shown alterations in miRNA expression in choroidal neovascularization tissues and could be potential therapeutic targets for wet age-related macular degeneration. Upregulation of miR-505 (days 1 and 3 post-laser), miR-155 (day 14) occurred in retina; miR-342-5p (days 3 and 7), miR-126-3p (day 14) in choroid; miR-23a, miR-24, miR-27a (day 7) in retina/choroid; miR-505 (days 1 and 3) in retinal pigment epithelium/choroid; downregulation of miR-155 (days 1 and 3), miR-29a, miR-29b, miR-29c (day 5), miR-93 (day 14), miR-126 (day 14) occurred in retinal pigment epithelium/choroid. Therapies using miRNA mimics or inhibitors were found to decrease choroidal neovascularization lesions. Choroidal neovascularization development was reduced by overexpression of miR-155, miR-188-5p, miR-(5,B,7), miR-126-3p, miR-342-5p, miR-93, miR-126, miR-195a-3p, miR-24, miR-21, miR-31, miR-150, and miR-184, or suppression of miR-505, miR-126-3p, miR-155, and miR-23/27. Further studies are warranted to determine miRNA expression in mouse laser-induced choroidal neovascularization models in order to validate and extend the reported findings. Important experimental variables need to be standardized; these include the strain and age of animals, gender, number and position of laser burns to the eye, laser parameters to induce choroidal neovascularization lesions including wavelength, power, spot size, and duration.

MicroRNA 21 Emerging Role in Diabetic Complications: A Critical Update

BACKGROUND

Diabetes Mellitus is a multifactorial disease encompassing various pathogenic pathways. To avoid morbidity and mortality related to diabetic complications, early detection of disease complications as well as targeted therapeutic strategies are essential.

INTRODUCTION

MicroRNAs (miRs) are short non-coding RNA molecules that regulate eukaryotic posttranscriptional gene expression. MicroRNA-21 has diverse gene regulatory functions and plays a significant role in various complications of Type 2 diabetes mellitus (T2DM).

METHODS

The study included electronic database searches on Pubmed, Embase, and Web of Science with the search items MicroRNA21 and each of the diabetic complications. The search was carried out up to November, 2019.

RESULTS

MicroRNA-21 modulates diabetic cardiomyopathy by affecting vascular smooth muscle cell proliferation and apoptosis, cardiac cell growth and death, and cardiac fibroblast functions. At the renal tubules, miR-21 can regulate the mesangial expansion, interstitial fibrosis, macrophage infiltration, podocyte loss, albuminuria and fibrotic and inflammatory gene expression related to diabetic nephropathy. Overexpression of miR-21 has been seen to play a pivotal role in the pathogenesis of diabetic retinopathy by contributing to diabetes-induced endothelial dysfunction as well as low-grade inflammation.

CONCLUSION

Considering the raised levels of miR-21 in various diabetic complications, it may prove to be a candidate biomarker for diabetic complications. Further, miR-21 antagonists have shown great potential in the treatment of diabetic cardiomyopathy, diabetic nephropathy, diabetic retinopathy, and diabetic neuropathy related complications in the future. The current review is the first of its kind encompassing the roles miR-21 plays in various diabetic complications, with a critical discussion of its future potential role as a biomarker and therapeutic target.

Decreased miR-150 in obesity-associated type 2 diabetic mice increases intraocular inflammation and exacerbates retinal dysfunction

INTRODUCTION

Diabetic retinopathy (DR) is the leading cause of blindness among the working population in the USA. Current therapies, including anti-vascular endothelial growth factor treatments, cannot completely reverse the visual defects induced by DR. MicroRNA-150 (miR-150) is a regulator that suppresses inflammation and pathological angiogenesis. In patients with diabetes, miR-150 is downregulated. As chronic inflammation is a major contributor to the pathogenesis of DR, whether diabetes-associated decrease of miR-150 is merely associated with the disease progression or decreased miR-150 causes retinal inflammation and pathological angiogenesis is still unknown.

RESEARCH DESIGN AND METHODS

We used high-fat diet (HFD)-induced type 2 diabetes (T2D) in wild type (WT) and miR-150 knockout (miR-150-/-) mice for this study and compared retinal function and microvasculature morphology.

RESULTS

We found that WT mice fed with an HFD for only 1 month had a significant decrease of miR-150 in the blood and retina, and retinal light sensitivity also decreased. The miR-150-/- mice on the HFD developed diabetes similar to that of the WT. At 7-8 months old, miR-150-/- mice under normal diet had increased degeneration of retinal capillaries compared with WT mice, indicating that miR-150 is important in maintaining the structural integrity of retinal microvasculature. Deletion of miR-150 worsened HFD-induced retinal dysfunction as early as 1 month after the diet regimen, and it exacerbated HFD-induced T2DR by further increasing retinal inflammation and microvascular degeneration.

CONCLUSION

These data suggest that decreased miR-150 caused by obesity or diabetic insults is not merely correlated to the disease progression, but it contributes to the retinal dysfunction and inflammation, as well as the development of DR.

Cho S, Britton W, S. Kern T, Antonetti DA, Hellström A, E.H. Smith L. Targeting Neurovascular Interaction in Retinal Disorders

The tightly structured neural retina has a unique vascular network comprised of three interconnected plexuses in the inner retina (and choroid for outer retina), which provide oxygen and nutrients to neurons to maintain normal function. Clinical and experimental evidence suggests that neuronal metabolic needs control both normal retinal vascular development and pathological aberrant vascular growth. Particularly, photoreceptors, with the highest density of mitochondria in the body, regulate retinal vascular development by modulating angiogenic and inflammatory factors. Photoreceptor metabolic dysfunction, oxidative stress, and inflammation may cause adaptive but ultimately pathological retinal vascular responses, leading to blindness. Here we focus on the factors involved in neurovascular interactions, which are potential therapeutic targets to decrease energy demand and/or to increase energy production for neovascular retinal disorders.

Inhibitory role of miR-203 in the angiogenesis of mice with pathological retinal neovascularization disease through downregulation of SNAI2

BACKGROUND

Pathological retinal neovascularization is a disease characterized by abnormal angiogenesis in retina that is a major cause of blindness in humans. Previous reports have highlighted the involvement of microRNAs (miRNAs) in retinal angiogenesis. Therefore, we aimed at exploring the mechanism underlying miR-203 regulating the progression of pathological retinal neovascularization.

METHODS

Initially, the mouse model of pathological retinal neovascularization disease was established and the hypoxia-induced human retinal microvascular endothelial cells (HRMECs) were generated. Then, miR-203 and SNAI2 expression in HRMECs and retinal tissues was examined. Subsequently, the effects of miR-203 and SNAI2 on viability, migration, apoptosis and angiogenesis of HRMECs were investigated, with the expression of Bax, Ki-67, MMP-2, MMP-9, VEGF and CD34 measured. Finally, the regulation of miR-203 or SNAI2 on GSK-3β/β-catenin pathway was determined through examining the levels of phosphorylated p-GSK-3β and β-catenin.

RESULTS

Poorly expressed miR-203 and highly expressed SNAI2 were found in HRMECs and retinal tissues of pathological retinal neovascularization. Importantly, overexpressed miR-203 or silencing SNAI2 inhibited viability, migration and angiogenesis but promoted apoptosis of HRMECs, evidenced by elevated Bax expression but reduced expression of Ki-67, MMP-2, MMP-9, VEGF and CD34. Moreover, overexpression of miR-203 was found to repress the GSK-3β/β-catenin pathway by downregulating SNAI2.

CONCLUSION

Collectively, this study demonstrated that overexpression of miR-203 suppressed the angiogenesis in mice with pathological retinal neovascularization disease via the inactivation of GSK-3β/β-catenin pathway by inhibiting SNAI2, which provided a novel therapeutic insight for pathological retinal neovascularization disease.

Circular RNA-ZNF609 regulates corneal neovascularization by acting as a sponge of miR-184

Corneal neovascularization can cause abnormal blood vessels to grow in the normally transparent and translucent cornea leading to various sight-threatening eye diseases. microRNAs and circular RNAs are known to play essential roles in the regulation of numerous biological functions. It is urgently needed to understand the molecular mechanism of miRNAs and circular RNAs in the corneal neovascularization. We aimed to elucidate the role of a specific a circular RNA, cZNF609, in the corneal neovascularization. cZNF609 and miR-184 levels were determined by RT-qPCR. Luciferase reporter assay and RNA immunoprecipitation assay were conducted to verify the target of cZNF609. The biological function of cZNF609 and miR-184 were assessed via cell proliferation, migration, and tube formation assays in vitro as well as the corneal suture model in vivo. The up-regulation of cZNF609 and down-regulation of miR-184 were observed during corneal neovascularization. cZNF609 acted as a miR-184 sponge to block miR-184 activity. Overexpression of miR-184 suppressed HCEKs cell proliferation, migration in vitro, and angiogenesis in vivo. The miR-184-mediated inhibition effect can be rescued through the re-introduction of cZNF609. Mechanically, cZNF609/miR-184 interaction regulated the downstream Akt and VEGF signaling pathway. Intervention of cZNF609 and miR-184 may serve as a potential strategy for pathological corneal neovascularization treatment.

Identification of Diagnostic and Prognostic microRNAs for Recurrent Vitreous Hemorrhage in Patients with Proliferative Diabetic Retinopathy

MicroRNAs (miRNAs) can provide insight into the pathophysiological states of ocular tissues such as proliferative diabetic retinopathy (PDR). In this study, differences in miRNA expression in vitreous from PDR patients with and without incidence of recurrent vitreous hemorrhage (RVH) after the initial pars-plana vitrectomy (PPV) were analyzed, with the aim of identifying biomarkers for RVH. Fifty-four consented vitreous samples were analyzed from patients undergoing PPV for PDR, of which eighteen samples underwent a second surgery due to RVH. Ten of the sixty-six expressed miRNAs (miRNAs-19a, -20a, -22, -27a, -29a, -93, -126, -128, -130a, and -150) displayed divergences between the PDR vitreous groups and to the control. A significant increase in the miRNA-19a and -27a expression was determined in PDR patients undergoing PPV as compared to the controls. miRNA-20a and -93 were significantly upregulated in primary PPV vitreous samples of patients afflicted with RVH. Moreover, this observed upregulation was not significant between the non-RVH and control group, thus emphasizing the association with RVH incidence. miRNA-19a and -27a were detected as putative vitreous biomarkers for PDR, and elevated levels of miRNA-20a and -93 in vitreous with RVH suggest their biomarker potential for major PDR complications such as recurrent hemorrhage incidence.

MicroRNA expression profile in retina and choroid in oxygen-induced retinopathy model

Background

Ischemic retinopathies (IRs) are leading causes of visual impairment. They are characterized by an initial phase of microvascular degeneration and a second phase of aberrant pre-retinal neovascularization (NV). microRNAs (miRNAs) regulate gene expression, and a number play a role in normal and pathological NV. But, post-transcriptional modulation of miRNAs in the eye during the development of IRs has not been systematically evaluated.

Aims & methods

Using Next Generation Sequencing (NGS) we profiled miRNA expression in the retina and choroid during vasodegenerative and NV phases of oxygen-induced retinopathy (OIR).

Results

Approximately 20% of total miRNAs exhibited altered expression (up- or down-regulation); 6% of miRNA were found highly expressed in retina and choroid of rats subjected to OIR. During OIR-induced vessel degeneration phase, miR-199a-3p, -199a-5p, -1b, -126a-3p displayed a robust decreased expression (> 85%) in the retina. While in the choroid, miR-152-3p, -142-3p, -148a-3p, -532-3p were upregulated (>200%) and miR-96-5p, -124-3p, -9a-3p, -190b-5p, -181a-1-3p, -9a-5p, -183-5p were downregulated (>70%) compared to controls. During peak pathological NV, miR-30a-5p, -30e-5p and 190b-5p were markedly reduced (>70%), and miR-30e-3p, miR-335, -30b-5p strongly augmented (by up to 300%) in the retina. Whereas in choroid, miR-let-7f-5p, miR-126a-5p and miR-101a-3p were downregulated by (>81%), and miR-125a-5p, let-7e-5p and let-7g-5p were upregulated by (>570%) during NV. Changes in miRNA observed using NGS were validated using qRT-PCR for the 24 most modulated miRNAs. In silico approach to predict miRNA target genes (using algorithms of miRSystem database) identified potential new target genes with pro-inflammatory, apoptotic and angiogenic properties.

Conclusion

The present study is the first comprehensive description of retinal/choroidal miRNAs profiling in OIR (using NGS technology). Our results provide a valuable framework for the characterization and possible therapeutic potential of specific miRNAs involved in ocular IR-triggered inflammation, angiogenesis and degeneration.

MicroRNA-145 Regulates Pathological Retinal Angiogenesis by Suppression of TMOD3

Pathological angiogenesis is a hallmark of various vascular diseases, including vascular eye disorders. Dysregulation of microRNAs (miRNAs), a group of small regulatory RNAs, has been implicated in the regulation of ocular neovascularization. This study investigated the specific role of microRNA-145 (miR-145) in regulating vascular endothelial cell (EC) function and pathological ocular angiogenesis in a mouse model of oxygen-induced retinopathy (OIR). Expression of miR-145 was significantly upregulated in OIR mouse retinas compared with room air controls. Treatment with synthetic miR-145 inhibitors drastically decreased levels of pathological neovascularization in OIR, without substantially affecting normal developmental angiogenesis. In cultured human retinal ECs, treatment with miR-145 mimics significantly increased the EC angiogenic function, including proliferation, migration, and tubular formation, whereas miR-145 inhibitors attenuated in vitro angiogenesis. Tropomodulin3 (TMOD3), an actin-capping protein, is a direct miR-145 target and is downregulated in OIR retinas. Treatment with miR-145 mimic led to TMOD3 inhibition, altered actin cytoskeletal architecture, and elongation of ECs. Moreover, inhibition of TMOD3 promoted EC angiogenic function and pathological neovascularization in OIR and abolished the vascular effects of miR-145 inhibitors in vitro and in vivo. Overall, our findings indicate that miR-145 is a novel regulator of TMOD3-dependent cytoskeletal architecture and pathological angiogenesis and a potential target for development of treatments for neovascular eye disorders.

Impact of angiogenic activation and inhibition on miRNA profiles of human retinal endothelial cells

BACKGROUND

Human retinal microvascular endothelial cells (HRMVECs) are involved in the pathogenesis of retinopathy of prematurity. In this study, the microRNA (miRNA) expression profiles of HRMVECs were investigated under resting conditions, angiogenic stimulation (VEGF treatment) and anti-VEGF treatment.

MATERIALS AND METHODS

The miRNA profiles of HRMVECs under resting and angiogenic conditions (VEGF treatment), as well as after addition of aflibercept, bevacizumab or ranibizumab were evaluated by analyzing the transcriptome of small non-coding RNAs. Differentially expressed miRNAs were validated using qPCR and classified using Gene Ontology enrichment analysis.

RESULTS

Ten miRNAs were found to be significantly changed more than 2-fold. Seven of these miRNAs were changed between resting conditions and angiogenic stimulation. Four of these miRNAs (miR-139-5p/-3p and miR-335-5p/-3p) were validated by qPCR in independent experiments and were found to be associated with angiogenesis and cell migration in Gene Ontology analysis. In addition, analysis of the most abundant miRNAs in the HRMVEC miRNome (representing at least 1% of the miRNome) was conducted and identified miR-21-5p, miR-29a-3p, miR-100-5p and miR-126-5p/-3p to be differently expressed by at least 15% between resting conditions and angiogenic conditions. These miRNAs were found to be associated with apoptotic signaling, regulation of kinase activity, intracellular signal transduction, cell surface receptor signaling and positive regulation of cell differentiation in Gene Ontology analysis. No differentially regulated miRNAs between angiogenic stimulation and angiogenic stimulation plus anti-VEGF treatment were identified.

CONCLUSION

In this study we characterized the miRNA profile of HRMVECs under resting, angiogenic and anti-angiogenic conditions and identified several miRNAs of potential pathophysiologic importance for angioproliferative retinal diseases. Our results have implications for possible miRNA-targeted angiomodulatory approaches in diseases like diabetic retinopathy or retinopathy of prematurity.

The effects of microRNAs in activating neovascularization pathways in diabetic retinopathy

Diabetic retinopathy (DR) is one of the major complications of diabetes mellitus that causes diabetic macular edema and visual loss. DR is categorized, based on the presence of vascular lesions and neovascularization, into non-proliferative and proliferative DR. Vascular changes in DR correlate with the cellular damage and pathological changes in the capillaries of blood-retinal barrier. Several cytokines have been involved in inducing neovascularization. These cytokines activate different signaling pathways which are mainly responsible for the complications of DR. Recently; microRNAs (miRNAs) have been introduced as the key factors in the regulation of the cytokine expression which plays a critical role in neovascularization of retinal cells. Some studies have demonstrated that changing levels of miRNAs have essential role in the pathophysiology of vascular changes in patients with DR. The aim of this study is to identify the effects of miRNAs in the pathogenesis of DR via activating neovascularization pathways.

Changes in microRNA-mRNA Signatures Agree with Morphological, Physiological, and Behavioral Changes in Larval Mahi-Mahi Treated with Deepwater Horizon Oil

In this study, we performed a systematic evaluation of global microRNA-mRNA interactions associated with the developmental toxicity of Deepwater Horizon oil using a combination of integrated mRNA and microRNA deep sequencing, expression profiling, gene ontology enrichment, and functional predictions by a series of advanced bioinformatic tools. After exposure to water accommodated fraction (WAF) of both weathered slick oil (0.5%, 1%, and 2%) and source oil (0.125%, 0.25%, and 0.5%) from the Deep Water Horizon oil spill, four dose-dependent miRNAs were identified, including three up-regulated (miR-23b, miR-34b, and miR-181b) and one down-regulated miRNAs (miR-203a) in mahi-mahi hatchings exposed from 6 h postfertilization (hpf) to 48 hpf. Consistent with morphological, physiological, and behavioral changes, the target genes of these miRNAs were largely involved in the development of the cardiovascular, visual, nervous system and associated toxicity pathways, suggesting that miRNAs play an essential role in regulating the responses to oil exposure. The results obtained from this study improve our understanding of the role of miRNAs and their target genes in relation to dose-dependent oil toxicity and provide the potential of using miRNAs as novel biomarkers in future oil studies.

RNA sequencing identified specific circulating miRNA biomarkers for early detection of diabetes retinopathy

Diabetic retinopathy (DR) is the leading cause of blindness in patients with diabetes. However, biomarkers for early detection of DR are still lacking. MicroRNAs (miRNAs) regulate multiple biological functions and are often deregulated in DR. We aimed to investigate whether circulating miRNAs can be used as biomarkers of early-stage DR. We used RNA-seq and qRT-PCR to identify differential serum miRNAs in patients with type 2 diabetes mellitus with DR (T2DM-DR), T2DM without DR (T2DM-no-DR), and healthy controls. We validated differential circulating miRNAs in two phases using qRT-PCR assays. RNA-seq analysis identified 7 differential circulating miRNAs between T2DM-DR and T2DM-no-DR and 47 differential miRNAs between T2DM-DR and healthy subjects. Two-stage analysis verified that a profile of five serum miRNAs (hsa-let-7a-5p, hsa-miR-novel-chr5_15976, hsa-miR-28-3p, has-miR-151a-5p, has-miR-148a-3p) was significantly associated with T2DM-DR. Receiver-operator-characteristic analyses showed that a panel of three miRNAs (hsa-let-7a-5p, hsa-miR-novel-chr5_15976, and hsa-miR-28-3p) presented 0.92 sensitivity and 0.94 specificity for distinguishing T2DM-DR from T2DM-no-DR, and 0.93 sensitivity and 0.86 specificity for differentiating early-stage T2DM-DR (NPDR) from late-stage DR (PDR). Lentivirus-mediated overexpression of hsa-let-7a-5p in human retinal microvascular endothelial cells (HRMECs) significantly promoted proliferation rates of HRMECs. In conclusion, the three-miRNA signature from serum may serve as a noninvasive diagnostic biomarker for DR. Furthermore, we showed that DR-associated miRNAs may be involved in the pathogenesis of DR, at least in part, through modifying proliferation of HRMECs.

microRNA-181a inhibits ocular neovascularization by interfering with vascular endothelial growth factor expression

AIM

Excess angiogenesis or neovascularization plays a key role in the pathophysiology of several ocular diseases such as retinopathy of prematurity, diabetic retinopathy, and exudative age-related macular degeneration. microRNA-181a (miR-181a) was found highly expressed in retina and choroidal tissues. This study intends to investigate the role of miR-181a in the regulation of ocular neovascularization in different pathophysiological conditions.

METHOD

We performed the RNA sequence to identify the microRNAs components of anti-angiogenic lymphocyte-derived microparticles (LMPs). The effect of miR-181a on human retinal endothelial cells proliferation was assessed in vitro. The impact of miR-181a on angiogenesis was confirmed using in vitro angiogenesis assay, ex vivo choroidal explant, and in vivo retinal neovascularization. The expression of major angiogenic factors was assessed by real-time qPCR.

RESULTS

RNA sequence revealed that miR-181a is selectively enriched in LMPs. Importantly, the inhibition of miR-181a significantly abrogated the effect of LMPs on endothelial viability, but overexpression of miR-181a reduced endothelial cell viability in a dose-dependent manner. miR-181a strongly inhibited in vitro angiogenesis and ex vivo choroidal neovascularization. The strong anti-angiogenic effect of miR-181a was also displayed on the retinal neovascularization of the in vivo mouse model of oxygen-induced retinopathy. In keeping with its effect, several angiogenesis-related genes were dysregulated in the miR-181a overexpressed endothelial cells.

CONCLUSION

These data may open unexpected avenues for the development of miR-181a as a novel therapeutic strategy that would be particularly useful and relevant for the treatment of neovascular diseases.

Epigenetic modifications in hyperhomocysteinemia: potential role in diabetic retinopathy and age-related macular degeneration

To study Hyperhomocysteinemia (HHcy)-induced epigenetic modifications as potential mechanisms of blood retinal barrier (BRB) dysfunction, retinas isolated from three- week-old mice with elevated level of Homocysteine (Hcy) due to lack of the enzyme cystathionine β-synthase (cbs^-/- , cbs^+/- and cbs^+/+ ), human retinal endothelial cells (HRECs), and human retinal pigmented epithelial cells (ARPE-19) treated with or without Hcy were evaluated for (1) histone deacetylases (HDAC), (2) DNA methylation (DNMT), and (3) miRNA analysis. Differentially expressed miRNAs in mice with HHcy were further compared with miRNA analysis of diabetic mice retinas (STZ) and miRNAs within the exosomes released from Hcy-treated RPEs. Differentially expressed miRNAs were further evaluated for predicted target genes and associated pathways using Ingenuity Pathway Analysis. HHcy significantly increased HDAC and DNMT activity in HRECs, ARPE-19, and cbs mice retinas, whereas inhibition of HDAC and DNMT decreased Hcy-induced BRB dysfunction. MiRNA profiling detected 127 miRNAs in cbs^+/- and 39 miRNAs in cbs^-/- mice retinas, which were significantly differentially expressed compared to cbs^+/+ . MiRNA pathway analysis showed their involvement in HDAC and DNMT activation, endoplasmic reticulum (ER), and oxidative stresses, inflammation, hypoxia, and angiogenesis pathways. Hcy-induced epigenetic modifications may be involved in retinopathies associated with HHcy, such as age-related macular degeneration and diabetic retinopathy.

STAT3-mediated activation of miR-21 is involved in down-regulation of TIMP3 and neovascularization in the ischemic retina

Retinal neovascularization (RNV) is a sight threatening complication of ischemic retinopathies with limited therapeutic options. The transcription factor signal transducer and activator of transcription 3 (STAT3) has been shown to play a crucial role in promoting RNV. However, manipulating of STAT3 activity can cause significant adverse side effects due to its neurotrophic properties. In this study, we identified microRNA-21 (miR-21) as a downstream effector of STAT3 activity in the ischemic retinas and determined its role in promoting RNV through inhibition of its molecular target, the tissue inhibitor of matrix metalloproteinases 3 (TIMP3). Using human retinal endothelial cells (HREC) exposed to hypoxia and a mouse model of oxygen-induced retinopathy (OIR), we found that TIMP3 expression was significantly decreased at both mRNA and protein levels and this paralleled the activation of STAT3 and up-regulation of miR-21. Moreover, TIMP3 expression was restored by knockdown of STAT3 or blocking of miR-21 in HREC, thus, confirming TIMP3 as a downstream target of STAT3/miR-21 pathway. Finally, in a mouse model of OIR, blockade of miR-21 by a specific antisense (a.miR-21), halted RNV and this effect was associated with rescuing of TIMP3 expression. Our data show that miR-21 mediates STAT3 pro-angiogenic effects in the ischemic retina, thus suggesting its blockade as a potential therapy to prevent/halt RNV.

Evaluation of the plasma microRNA levels in stage 3 premature retinopathy with plus disease: preliminary study

PurposeIn the present study, we aimed to investigate the changes in plasma microRNA (miRNA) levels in premature infants diagnosed with premature retinopathy (ROP).Patients and methodsIn order to investigate the relationship of miRNAs with ROP, 13 premature infants admitted to Mersin University, Medical School, Department of Ophthalmology and diagnosed with ROP stage 3 with plus disease between January 2014-January 2015 were included in the study. Control group consisted of 15 premature infants with no ROP. The plasma miRNA levels were evaluated using high-throughput quantitative real-time PCR.ResultsThe results of study demonstrated that the expression level of miR-23a and miR-200b-3p was significantly upregulated in patients with ROP when compared with the control group (P<0.05). The expression level of miR-27b-3p and miR-214-3p was significantly downregulated in patients (P<0.05). In addition, expression of 17 miRNA (miR-410-3p, miR-17-5p, miR-451a, miR-31-5p, miR-132-3p, miR-183-5p, miR-184, miR-222-3p, miR-296-5p, miR-200a-3p, miR-328-3p,miR-96-5p, miR-199a-5p, miR-99a-5p, miR-106a-5p, miR-125b-5p, miR-155-5p) had upregulated or downregulated, but not statistically significantly different when compared with the control group.ConclusionsOur results suggest that plasma miRNA levels may alter in ROP and, some miRNAs might have an effect in the physiopathology of this disease. These molecules may have an important therapeutic role in patients who are unresponsive to anti-vascular endothelial growth factor therapy. However, further studies must be conducted for possible effects of miRNAs in vascular disorders of eye such as ROP. Moreover to define the relationship of these molecules with the disease more clearly, a multicenter study including more patients is necessary.

Survival Improvement in Human Retinal Pigment Epithelial Cells via Fas Receptor Targeting by miR-374a

Oxidative conditions of the eye could contribute to retinal cells loss through activating the Fas-L/Fas pathway. This phenomenon is one of the leading causes of some ocular diseases like age-related macular degeneration (AMD). By targeting proteins at their mRNA level, microRNAs (miRNAs) can regulate gene expression and cell function. The aim of the present study is to investigate Fas targeting by miR-374a and find whether it can inhibit Fas-mediated apoptosis in primary human retinal pigment epithelial (RPE) cells under oxidative stress. So, the primary human RPE cells were transfected with pre-miR-374a pLEX construct using polymeric carrier and were exposed to H₂ O₂ (200 μM) as an oxidant agent for induction of Fas expression. Fas expression at mRNA and protein level was evaluated by quantitative real-time PCR and Western blot analysis, respectively. These results revealed that miR-374a could prevent Fas upregulation under oxidative conditions. Moreover, Luciferase activity assay confirmed that Fas could be a direct target of miR-374a. The cell viability studies demonstrated that caspase-3 activity was negligible in miR-374a treated cells compared to the controls. Our data suggest miR-374a is a negative regulator of Fas death receptor which is able to enhance the cell survival and protect RPE cells against oxidative conditions. J. Cell. Biochem. 118: 4854-4861, 2017. © 2017 Wiley Periodicals, Inc.

Identification of cold-responsive miRNAs in rats by deep sequencing

miRNA is an endogenously noncoding sRNA, which is involved in post-transcription gene expression regulation of growth, tumor development and stress survival. As a biological marker, miRNA has been used for the early diagnosis of diseases and the evaluation of some physiological state. We constructed two small RNA libraries with the serums of rats treated or not with cold conditions (4℃ for 12h) by deep sequencing, in order to understand the miRNAs' expressions of cold-exposed rats and find new cold-responsive biological markers. 485 conserved miRNAs and 287 novel miRNAs were identified in the two libraries by comparing to the known miRNAs of rat in miRBase 21.0 Differential expression analysis showed that 56 conserved miRNAs and 3 novel miRNAs were expressed differentially in low ambient temperature. The qRT-PCR results confirmed that rno-miR-151-3p, rno-miR-210-3p, rno-miR-425-5p, rno-miR-383-5p, rno-miR-92a-3p, rno-miR-98-5p and rno-miR-328a-3p decreased significantly in rats serums treated with cold exposure. The expressions of the 7 miRNAs changed significantly in cold-exposed rats' livers too. rno-miR-383-5p decreased significantly, but all the others increased significantly. Thus, the 7 miRNAs were considered as cold-responsive miRNAs of rat. 670 target genes of the 7 cold-responsive miRNAs were predicted. KEGG analysis showed that they were enriched in 28 pathways and most of them were enriched by metabolic pathway. Overall, the results of this study suggest an important role for selected miRNA's in the response to cold stress.

Gene therapy for diabetic retinopathy: Are we ready to make the leap from bench to bedside?

Diabetic retinopathy (DR), a chronic and progressive complication of diabetes mellitus, is a sight-threatening disease characterized in the early stages by neuronal and vascular dysfunction in the retina, and later by neovascularization that further damages vision. A major contributor to the pathology is excess production of vascular endothelial growth factor (VEGF), a growth factor that induces formation of new blood vessels and increases permeability of existing vessels. Despite the recent availability of effective treatments for the disease, including laser photocoagulation and therapeutic VEGF antibodies, DR remains a significant cause of vision loss worldwide. Existing anti-VEGF agents, though generally effective, are limited by their short therapeutic half-lives, necessitating frequent intravitreal injections and the risk of attendant adverse events. Management of DR with gene therapies has been proposed for several years, and pre-clinical studies have yielded enticing findings. Gene therapy holds several advantages over conventional treatments for DR, such as a longer duration of therapeutic effect, simpler administration, the ability to intervene at an earlier stage of the disease, and potentially fewer side-effects. In this review, we summarize the current understanding of the pathophysiology of DR and provide an overview of research into DR gene therapies. We also examine current barriers to the clinical application of gene therapy for DR and evaluate future prospects for this approach.

Retinal expression of small non-coding RNAs in a murine model of proliferative retinopathy

Ocular neovascularization is a leading cause of blindness in proliferative retinopathy. Small non-coding RNAs (sncRNAs) play critical roles in both vascular and neuronal development of the retina through post-transcriptional regulation of target gene expression. To identify the function and therapeutic potential of sncRNAs in retinopathy, we assessed the expression profile of retinal sncRNAs in a mouse model of oxygen-induced retinopathy (OIR) with pathologic proliferation of neovessels. Approximately 2% of all analyzed sncRNAs were significantly altered in OIR retinas compared with normoxic controls. Twenty three microRNAs with substantial up- or down-regulation were identified, including miR-351, -762, -210, 145, -155, -129-5p, -150, -203, and -375, which were further analyzed for their potential target genes in angiogenic, hypoxic, and immune response-related pathways. In addition, nineteen small nucleolar RNAs also revealed differential expression in OIR retinas compared with control retinas. A decrease of overall microRNA expression in OIR retinas was consistent with reduced microRNA processing enzyme Dicer, and increased expression of Alu element in OIR. Together, our findings elucidated a group of differentially expressed sncRNAs in a murine model of proliferative retinopathy. These sncRNAs may exert critical post-transcriptional regulatory roles in regulating pathological neovascularization in eye diseases.

Endothelial microRNA-150 is an intrinsic suppressor of pathologic ocular neovascularization

Pathologic ocular neovascularization commonly causes blindness. It is critical to identify the factors altered in pathologically proliferating versus normally quiescent vessels to develop effective targeted therapeutics. MicroRNAs regulate both physiological and pathological angiogenesis through modulating expression of gene targets at the posttranscriptional level. However, it is not completely understood if specific microRNAs are altered in pathologic ocular blood vessels, influencing vascular eye diseases. Here we investigated the potential role of a specific microRNA, miR-150, in regulating ocular neovascularization. We found that miR-150 was highly expressed in normal quiescent retinal blood vessels and significantly suppressed in pathologic neovessels in a mouse model of oxygen-induced proliferative retinopathy. MiR-150 substantially decreased endothelial cell function including cell proliferation, migration, and tubular formation and specifically suppressed the expression of multiple angiogenic regulators, CXCR4, DLL4, and FZD4, in endothelial cells. Intravitreal injection of miR-150 mimic significantly decreased pathologic retinal neovascularization in vivo in both wild-type and miR-150 knockout mice. Loss of miR-150 significantly promoted angiogenesis in aortic rings and choroidal explants ex vivo and laser-induced choroidal neovascularization in vivo. In conclusion, miR-150 is specifically enriched in quiescent normal vessels and functions as an endothelium-specific endogenous inhibitor of pathologic ocular neovascularization.

Single and Compound Knock-outs of MicroRNA (miRNA)-155 and Its Angiogenic Gene Target CCN1 in Mice Alter Vascular and Neovascular Growth in the Retina via Resident Microglia

The response of the retina to ischemic insult typically leads to aberrant retinal neovascularization, a major cause of blindness. The epigenetic regulation of angiogenic gene expression by miRNAs provides new prospects for their therapeutic utility in retinal neovascularization. Here, we focus on miR-155, a microRNA functionally important in inflammation, which is of paramount importance in the pathogenesis of retinal neovascularization. Whereas constitutive miR-155-deficiency in mice results in mild vascular defects, forced expression of miR-155 causes endothelial hyperplasia and increases microglia count and activation. The mouse model of oxygen-induced retinopathy, which recapitulates ischemia-induced aberrant neovessel growth, is characterized by increased expression of miR-155 and localized areas of microglia activation. Interestingly, miR-155 deficiency in mice reduces microglial activation, curtails abnormal vessel growth, and allows for rapid normalization of the retinal vasculature following ischemic insult. miR-155 binds to the 3'-UTR and represses the expression of the CCN1 gene, which encodes an extracellular matrix-associated integrin-binding protein that both promotes physiological angiogenesis and harnesses growth factor-induced abnormal angiogenic responses. Single CCN1 deficiency or double CCN1 and miR-155 knock-out in mice causes retinal vascular malformations typical of faulty maturation, mimicking the vascular alterations of miR-155 gain of function. During development, the miR-155/CCN1 regulatory axis balances the proangiogenic and proinflammatory activities of microglia to allow for their function as guideposts for sprout fusion and anastomosis. Under ischemic conditions, dysregulated miR-155 and CCN1 expression increases the inflammatory load and microglial activation, prompting aberrant angiogenic responses. Thus, miR-155 functions in tandem with CCN1 to modulate inflammation-induced vascular homeostasis and repair.