GO:1990963 establishment of blood-retinal barrier: Barrier Assembly, Genes, Functions and Research Methods
Research-grade guide for scientists and biopharma professionals
Key Takeaways
• GO:1990963 describes the biological process that establishes the blood-retinal barrier (BRB), a dual-level structure formed by retinal pigment epithelium (outer BRB) and retinal vascular endothelium (inner BRB).
• The BRB is essential for retinal homeostasis, and its disruption is a hallmark of diabetic retinopathy, age-related macular degeneration, and other retinal neurodegenerative diseases.
• Key molecular players include tight junction proteins (e.g., claudins, occludin, ZO-1), transporters, and signaling pathways such as Tie2/Akt/mTOR and Src/Akt/cofilin.
• Experimental models range from 2D cell cultures and 3D microphysiological systems to animal models of diabetes and HIV-1 infection.
• CRISPR-based approaches enable precise knockout, point mutation, knock-in, and overexpression of genes involved in BRB establishment, accelerating target discovery.
• Understanding BRB establishment informs therapeutic strategies for retinal diseases, including anti-VEGF therapies and cell-based models for drug screening.
Description
The blood-retinal barrier (BRB) is a specialized structure that separates the retina from the systemic circulation, maintaining the delicate microenvironment required for visual function. The establishment of the BRB (GO:1990963) is a dynamic developmental and homeostatic process that involves the formation of tight junctions in two distinct cellular layers: the retinal pigment epithelium (RPE) and the retinal vascular endothelium. This process is critical for preventing the leakage of blood-borne molecules and cells into the retina, and its failure is associated with a spectrum of retinal pathologies. Researchers studying retinal development, disease mechanisms, and therapeutic interventions require a deep understanding of the molecular and cellular events that establish and maintain the BRB. This article synthesizes current knowledge on the establishment of the BRB, highlighting key genes, regulatory pathways, and experimental models, with a focus on how CRISPR-based tools can be applied to dissect this process.
establishment of blood-retinal barrier At A Glance
| GO ID | GO:1990963 |
|---|---|
| GO term | establishment of blood-retinal barrier |
| Ontology | biological_process |
| Synonym | establishment of blood-retina barrier, establishment of BRB |
| Major function | Formation of a selective barrier between blood and retina via tight junctions in RPE and retinal endothelial cells |
| Cellular location | Outer BRB: retinal pigment epithelium; Inner BRB: retinal vascular endothelium |
| Key structural components | Tight junction proteins (claudins, occludin, ZO-1), adherens junction proteins, transporters |
| Related processes | Angiogenesis, epithelial polarization, tight junction assembly, vascular maturation |
What Is GO:1990963?
According to the Gene Ontology, GO:1990963 (establishment of blood-retinal barrier) is defined as the establishment of the barrier between the blood and the retina. The blood-retinal barrier is located at two levels, forming an outer barrier in the retinal pigment epithelium and an inner barrier in the endothelial membrane of the retinal vessels. Both these membranes have tight junctions of the 'nonleaky' type.
Why Is establishment of blood-retinal barrier Important in Cell Biology?
The establishment of the blood-retinal barrier is fundamental for retinal health, as it controls the exchange of nutrients, ions, and waste products while protecting the retina from potentially harmful blood-borne factors. Disruption of this barrier is a common feature of major retinal diseases, including diabetic retinopathy, age-related macular degeneration, and retinal neurodegenerative disorders. Understanding how the BRB is established can reveal therapeutic targets to prevent or reverse barrier breakdown, and it is essential for developing accurate in vitro models for drug testing and disease modeling.
• Maintains retinal homeostasis by regulating the passage of molecules and cells.
• Protects retinal neurons from blood-derived toxins and immune cells.
• Its breakdown is a key event in diabetic retinopathy and macular edema.
• Implicated in retinal neurodegenerative diseases such as glaucoma and retinitis pigmentosa.
• Essential for the development of cell-based therapies and retinal organoids.
• Serves as a target for anti-angiogenic and anti-permeability therapies.
• Provides a model for studying tight junction biology and epithelial/endothelial polarity.
• Enables drug screening platforms that mimic the human BRB.
• Influenced by systemic factors such as inflammation, hyperglycemia, and HIV infection.
• Critical for the success of retinal gene therapy and drug delivery.
What Happens During establishment of blood-retinal barrier?
Specification and differentiation of RPE and retinal endothelial cells
In simple terms: The cells that will form the barrier first need to become the right type.
The establishment of the BRB begins with the specification of retinal pigment epithelial (RPE) cells from the optic vesicle and the differentiation of retinal vascular endothelial cells. These processes are driven by transcription factors such as MITF and OTX2 for RPE, and by VEGF and Notch signaling for endothelial cells. Proper differentiation is a prerequisite for the subsequent formation of tight junctions and barrier function.
Formation of tight junctions in the outer BRB (RPE)
In simple terms: The RPE cells seal themselves together to create a leak-proof layer.
In the outer BRB, RPE cells form tight junctions that are characterized by the presence of claudins (e.g., claudin-19), occludin, and zonula occludens-1 (ZO-1). These junctions restrict paracellular diffusion and are essential for the barrier function. The assembly of these junctions is regulated by interactions with the underlying Bruch's membrane and the choroid.
Formation of tight junctions in the inner BRB (retinal endothelium)
In simple terms: The blood vessels in the retina also seal themselves to prevent leakage.
The inner BRB is formed by tight junctions between retinal endothelial cells, which are supported by pericytes and Müller glia. Key tight junction proteins include claudin-5, occludin, and ZO-1. Signaling through Tie2/Akt/mTOR and Src/Akt/cofilin pathways modulates the integrity of these junctions.
Maturation and maintenance of the barrier
In simple terms: Once formed, the barrier must be kept strong and functional.
After initial formation, the BRB undergoes maturation, which involves the recruitment of pericytes and the establishment of a proper basement membrane. Maintenance requires continuous signaling, including the Tie2/Akt/mTOR pathway, which promotes endothelial survival and barrier stability. Disruption of these signals leads to barrier breakdown, as seen in diabetic retinopathy.
Integration with retinal function
In simple terms: The barrier works together with retinal cells to support vision.
The established BRB interacts with retinal neurons and glia to maintain the optimal environment for phototransduction. For example, Müller glia contribute to the induction of tight junctions in endothelial cells. This integration ensures that the retina receives nutrients while being protected from harmful blood components.
Key Genes Involved in GO:1990963 establishment of blood-retinal barrier
The following genes and proteins are critically involved in the establishment and maintenance of the blood-retinal barrier, based on published literature.
| Gene | Major Role | Research Relevance |
|---|---|---|
| CLDN5 | Tight junction protein in inner BRB | Knockout leads to barrier leakage; target for diabetic retinopathy |
| CLDN19 | Tight junction protein in outer BRB | Mutations cause retinal degeneration; model for RPE barrier |
| OCLN | Tight junction protein in both BRB layers | Regulates paracellular permeability; studied in inflammation |
| TJP1 (ZO-1) | Scaffolding protein linking tight junctions to cytoskeleton | Essential for junction assembly; knockout is embryonic lethal |
| TIE2 (TEK) | Receptor tyrosine kinase mediating angiopoietin signaling | Activation by LECT2 ameliorates BRB impairment |
| AKT1 | Serine/threonine kinase in survival signaling | Mediates Tie2-induced barrier protection |
| MTOR | Kinase regulating cell growth and survival | Involved in Tie2/Akt/mTOR pathway for BRB maintenance |
| SRC | Non-receptor tyrosine kinase | Inhibits microglial phagocytosis to protect inner BRB |
| CFL1 (cofilin) | Actin depolymerizing factor | Regulated by Src/Akt signaling in BRB protection |
| EPO | Erythropoietin | Protects inner BRB by inhibiting microglia phagocytosis |
| LECT2 | Leukocyte cell-derived chemotaxin 2 | Ameliorates BRB impairment via Tie2/Akt/mTOR |
| VEGFA | Vascular endothelial growth factor | Induces permeability; target of anti-VEGF therapies |
| RPE65 | Retinal pigment epithelium-specific protein | Marker of RPE differentiation; mutations cause blindness |
| MITF | Transcription factor for RPE development | Regulates RPE specification and barrier formation |
| OTX2 | Transcription factor for RPE and retinal development | Essential for RPE differentiation |
| CDH5 (VE-cadherin) | Adherens junction protein in endothelium | Required for endothelial barrier integrity |
| PECAM1 (CD31) | Endothelial cell adhesion molecule | Marker of retinal endothelial cells; involved in leukocyte migration |
| AQP4 | Water channel in Müller glia | Regulates retinal water homeostasis and BRB function |
How Is establishment of blood-retinal barrier Regulated?
The establishment and maintenance of the blood-retinal barrier are regulated by multiple signaling pathways. The Tie2/Akt/mTOR pathway promotes endothelial survival and tight junction integrity; activation of Tie2 by LECT2 ameliorates BRB impairment in diabetes. The Src/Akt/cofilin pathway mediates erythropoietin-induced protection of the inner BRB by inhibiting microglial phagocytosis. Additionally, VEGF signaling increases vascular permeability and is a key target in diseases with BRB breakdown. Inflammatory cytokines and oxidative stress can disrupt tight junctions, while factors such as PM2.5 exposure have been shown to damage the outer BRB.
establishment of blood-retinal barrier and Human Disease
| Gene | Disease / Biology | Potential Experimental Model |
|---|---|---|
| LECT2 | Diabetic retinopathy; BRB impairment | Knockout mouse; overexpression in endothelial cells |
| EPO | Diabetic retinopathy; inner BRB protection | Conditional knockout; recombinant EPO treatment |
| CLDN5 | Barrier leakage; diabetic macular edema | Endothelial-specific knockout; point mutation |
| VEGFA | Macular edema; neovascular AMD | Overexpression; anti-VEGF treatment models |
| TIE2 | Vascular stability; BRB maintenance | Knock-in of activating mutations; knockout |
Diabetic retinopathy and macular edema
Diabetic retinopathy is a leading cause of blindness, characterized by BRB breakdown and macular edema. Hyperglycemia-induced activation of VEGF and inflammatory pathways leads to tight junction disruption and endothelial cell death. LECT2 has been shown to ameliorate BRB impairment secondary to diabetes via Tie2/Akt/mTOR signaling, and erythropoietin protects the inner BRB by inhibiting microglia phagocytosis through Src/Akt/cofilin signaling. These findings highlight potential therapeutic targets for diabetic retinopathy.
Retinal neurodegenerative diseases
The BRB plays a critical role in retinal neurodegenerative diseases such as glaucoma, age-related macular degeneration, and retinitis pigmentosa. Barrier dysfunction allows the infiltration of immune cells and blood-derived factors, exacerbating neuronal damage. Understanding the establishment of the BRB may lead to strategies that preserve barrier integrity and slow neurodegeneration.
HIV-1-associated retinal complications
HIV-1 infection can disrupt the blood-retinal barrier, leading to retinal complications. Mechanisms include viral protein-induced oxidative stress and inflammatory signaling that compromise tight junctions. Studying BRB establishment in the context of HIV-1 may inform therapies to prevent retinal damage in infected individuals.
Environmental exposure and outer BRB damage
Exposure to airborne fine particulate matter (PM2.5) has been shown to cause diverse outer BRB damages and increase disease susceptibility. This highlights the role of environmental factors in BRB integrity and the need for models that mimic real-world exposures.
From establishment of blood-retinal barrier-Related Genes to Experimental Models
| Research Question | Suitable Model |
|---|---|
| Does gene X regulate tight junction assembly in RPE? | RPE-specific knockout (e.g., CRISPR-Cas9) |
| Does a point mutation in CLDN5 affect barrier function? | Knock-in of patient-derived mutation in iPSC-derived endothelial cells |
| Can overexpression of LECT2 protect against BRB breakdown? | Lentiviral overexpression in diabetic mouse retina |
| What is the role of EPO in microglial phagocytosis? | Conditional knockout of EPO receptor in microglia |
| How does PM2.5 exposure affect outer BRB? | 3D outer BRB model with PM2.5 exposure |
| Can a 3D microphysiological system mimic diabetic retinopathy? | 3D outer BRB with choriocapillaris in a microfluidic device |
How to Study the establishment of blood-retinal barrier Process
| Method | What It Measures | Typical Application |
|---|---|---|
| TEER | Transepithelial electrical resistance | Quantify barrier tightness in RPE and endothelial monolayers |
| Permeability assay | Flux of tracers (e.g., FITC-dextran) | Assess paracellular leakage |
| Immunofluorescence | Localization of tight junction proteins | Visualize claudin-5, ZO-1 in BRB models |
| RNA-seq | Global gene expression | Identify regulators of BRB establishment |
| Proteomics | Protein abundance and modifications | Discover novel barrier components |
| CRISPR screen | Gene essentiality for barrier function | Identify targets that protect or disrupt BRB |
| Microphysiological system | Organ-level barrier function | Model diabetic retinopathy and drug testing |
| Animal models | In vivo barrier integrity | Study disease mechanisms and therapies |
Transcriptomic and proteomic profiling
RNA-seq and proteomics can identify genes and proteins differentially expressed during BRB establishment. For example, comparing RPE and endothelial cells before and after tight junction formation reveals key regulators. These approaches can be combined with CRISPR screens to pinpoint essential genes.
Imaging of barrier integrity
Confocal microscopy and electron microscopy visualize tight junction ultrastructure and localization of proteins such as claudin-5 and ZO-1. Functional assays like transepithelial electrical resistance (TEER) and permeability tests using tracers quantify barrier integrity in vitro.
3D cell culture models
Multilayered 3D cellular models of the retinal-blood barrier have been established to study barrier formation and drug permeability. Advanced microphysiological systems incorporating choriocapillaris enable more physiologically relevant studies of diabetic retinopathy.
Animal models
Rodent models of diabetes (e.g., streptozotocin-induced) and HIV-1 infection are used to study BRB disruption in vivo. These models allow assessment of therapeutic interventions and genetic manipulations.
How CRISPR Can Be Used to Study GO:1990963 establishment of blood-retinal barrier
Knockout
CRISPR-Cas9 knockout of genes such as CLDN5 or TJP1 in retinal endothelial or RPE cells can reveal their essential roles in BRB establishment. For example, knockout of CLDN5 leads to barrier leakage, mimicking diabetic macular edema. Knockout models are valuable for target validation and understanding gene function.
Point Mutation
Introducing patient-derived point mutations (e.g., in CLDN19) using CRISPR base editing or homology-directed repair allows study of specific variants in BRB dysfunction. Such models can elucidate how single amino acid changes affect tight junction assembly and barrier properties.
Knock-in
Knock-in of reporter genes (e.g., fluorescent tags on ZO-1) enables live imaging of tight junction dynamics during BRB establishment. Knock-in of disease-associated mutations (e.g., in TIE2) can model vascular anomalies and test targeted therapies.
Overexpression
CRISPR activation (CRISPRa) or lentiviral overexpression of protective genes such as LECT2 or EPO can enhance BRB integrity in disease models. Overexpression studies help identify therapeutic candidates that strengthen the barrier.
How EDITGENE Supports establishment of blood-retinal barrier Research
Researchers studying establishment of blood-retinal barrier-related genes often need to determine whether a candidate gene is causally involved in barrier formation or maintenance. This requires precise genetic manipulation, which can be achieved through CRISPR-based knockout, point mutation, knock-in, or overexpression models. EDITGENE provides comprehensive services to support such studies, from cell line generation to library screening and bioinformatics analysis.
Contact EDITGENE today to design your custom CRISPR model for establishment of blood-retinal barrier research.
Frequently Asked Questions About establishment of blood-retinal barrier
What is the blood-retinal barrier?
The blood-retinal barrier is a specialized structure that separates the retina from the blood, composed of the retinal pigment epithelium (outer barrier) and retinal vascular endothelium (inner barrier), both with tight junctions.
What is GO:1990963?
GO:1990963 is the Gene Ontology term for the biological process of establishing the blood-retinal barrier, including the formation of tight junctions in RPE and retinal endothelial cells.
What genes are involved in the establishment of the blood-retinal barrier?
Key genes include CLDN5, CLDN19, OCLN, TJP1, TIE2, AKT1, MTOR, SRC, CFL1, EPO, LECT2, and VEGFA, among others.
How is the blood-retinal barrier disrupted in diabetic retinopathy?
Hyperglycemia and inflammation lead to activation of VEGF and other pathways, causing tight junction disruption and endothelial cell death, resulting in barrier leakage.
What models are used to study the blood-retinal barrier?
Models include 2D cell cultures, 3D microphysiological systems, and animal models such as diabetic rodents and HIV-1-infected models.
What is the role of LECT2 in the blood-retinal barrier?
LECT2 ameliorates blood-retinal barrier impairment secondary to diabetes via activation of the Tie2/Akt/mTOR signaling pathway.
How does erythropoietin protect the blood-retinal barrier?
Erythropoietin protects the inner blood-retinal barrier by inhibiting microglia phagocytosis via Src/Akt/cofilin signaling in experimental diabetic retinopathy.
Can CRISPR be used to study blood-retinal barrier genes?
Yes, CRISPR knockout, point mutation, knock-in, and overexpression models enable precise manipulation of BRB-related genes to study their functions.
What diseases are associated with blood-retinal barrier breakdown?
Diseases include diabetic retinopathy, age-related macular degeneration, retinal neurodegenerative diseases, and HIV-1-associated retinal complications.
How can I model the blood-retinal barrier in vitro?
You can use multilayered 3D cellular models or microphysiological systems that incorporate RPE and endothelial cells to mimic the outer and inner barriers.
Conclusion
The establishment of the blood-retinal barrier (GO:1990963) is a complex biological process essential for retinal health, involving the coordinated formation of tight junctions in the RPE and retinal endothelium. Dysregulation of this process contributes to major retinal diseases, making it a critical area of research. Advances in CRISPR-based gene editing and 3D culture models are accelerating the discovery of molecular players and therapeutic targets. EDITGENE offers a suite of services to support these studies, from custom cell models to high-throughput screening, empowering researchers to unravel the mechanisms of BRB establishment and dysfunction.
References
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- 3. Qin YJ et al.. 2022. LECT2 Ameliorates Blood-Retinal Barrier Impairment Secondary to Diabetes Via Activation of the Tie2/Akt/mTOR Signaling Pathway.. Invest Ophthalmol Vis Sci 63(3):7 PMID: 35262733
- 4. Gu Y et al.. 2023. Acute and continuous exposure of airborne fine particulate matter (PM(2.5)): diverse outer blood-retinal barrier damages and disease susceptibilities.. Part Fibre Toxicol 20(1):50 PMID: 38110941
- 5. Nam U et al.. 2023. Generation of a 3D Outer Blood-Retinal Barrier with Advanced Choriocapillaris and Its Application in Diabetic Retinopathy in a Microphysiological System.. ACS Biomater Sci Eng 9(8):4929-4939 PMID: 37494673
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- 8. Xie H et al.. 2021. Erythropoietin protects the inner blood-retinal barrier by inhibiting microglia phagocytosis via Src/Akt/cofilin signalling in experimental diabetic retinopathy.. Diabetologia 64(1):211-225 PMID: 33104828
