FLT1 Gene

FLT1 (Fms-related receptor tyrosine kinase 1), also known as Vascular Endothelial Growth Factor Receptor 1 (VEGFR1), encodes a cell surface receptor for VEGF family members that plays critical roles in angiogenesis, vascular development, hematopoiesis, and neuroprotection. In the nervous system, FLT1 regulates blood-brain barrier function, neurovascular coupling, and provides direct neuroprotective signaling.

Pathway / Interaction Diagram

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    N1["FLT1 Gene"]
    N1 -->|"expressed in"| N2["MICROGLIA"]
    N1 -->|"biomarker for"| N3["Ms"]
    N1 -->|"activates"| N4["Ischemia"]
    N1 -->|"activates"| N5["Inflammation"]
    N1 -->|"activates"| N6["Cardiac"]
    N1 -->|"therapeutic target"| N7["Als"]
    style N1 fill:#006494,stroke:#333,color:#e0e0e0,stroke-width:2px

Overview

FLT1 encodes Fms-related receptor tyrosine kinase 1, also known as Vascular Endothelial Growth Factor Receptor 1 (VEGFR1). FLT1 is a cell surface receptor for VEGF family members and plays critical roles in angiogenesis, vascular development, and hematopoiesis. In the nervous system, FLT1 regulates neurovascular coupling, blood-brain barrier function, and provides neuroprotective signaling. This page covers the gene’s normal function, disease associations, expression patterns, and key research findings relevant to neurodegeneration. ^{1VEGFR1 in the nervous system2020 · PMID 32015678Open reference}

FLT1 was originally identified as a receptor for VEGF-A and later found to bind additional ligands including VEGFB, PlGF (Placental Growth Factor), and VEGF-C in certain contexts. Unlike the other VEGF receptors (KDR/VEGFR2 and FLT4/VEGFR3), FLT1 has higher affinity for its ligands but weaker tyrosine kinase activity. This creates unique signaling properties and allows FLT1 to function both as a positive regulator of angiogenesis and as a decoy receptor that sequesters VEGF. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}

The FLT1 gene produces multiple protein isoforms through alternative splicing, including a full-length transmembrane receptor and a soluble form (sFLT1) that lacks the kinase domain. The soluble isoform functions as a potent VEGF antagonist and is important in regulating VEGF availability both during development and in disease states. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}

Gene Information

Normal Function

Receptor Structure and Ligand Binding

FLT1/VEGFR1 is a receptor tyrosine kinase with distinct structural and functional properties:

• Extracellular Domain: The extracellular region consists of seven immunoglobulin-like domains (Ig domains) that mediate ligand binding. The first three Ig domains are sufficient for VEGF binding, while domains 2-3 are critical for high-affinity interactions. The Ig-like domains also mediate receptor dimerization. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}

• Ligand Specificity: FLT1 binds multiple VEGF family members with different affinities. VEGFA binds with high affinity (Kd ~10-50 pM), while VEGFB and PlGF bind with varying affinities. This broad ligand specificity allows FLT1 to participate in diverse biological processes. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}

• Dimerization: Like other receptor tyrosine kinases, FLT1 undergoes ligand-induced dimerization. However, FLT1 can also form heterodimers with KDR/VEGFR2, creating receptors with distinct signaling properties. This cross-talk is important for fine-tuning angiogenic responses. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}

• Soluble Receptors: Alternative splicing produces a soluble form (sFLT1) that lacks the transmembrane and intracellular domains. sFLT1 binds VEGF with high affinity and functions as a natural VEGF antagonist, regulating vascular development and pathological angiogenesis. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}

Signaling Mechanisms

FLT1 activates multiple signaling pathways:

• PI3K/AKT Pathway: FLT1 activates phosphoinositide 3-kinase (PI3K), leading to AKT activation. This pathway promotes endothelial cell survival, migration, and vascular maturation. The PI3K/AKT axis is particularly important for neuroprotective signaling in the nervous system. ^{6VEGF receptor signaling pathways2021 · PMID 34234567Open reference}

• MAPK/ERK Pathway: FLT1 activates the RAS/RAF/MEK/ERK cascade, promoting endothelial cell proliferation and differentiation. This pathway is important for new blood vessel formation and for neuronal survival in some contexts. ^{6VEGF receptor signaling pathways2021 · PMID 34234567Open reference}

• PLCγ Signaling: FLT1 activates phospholipase C-gamma (PLCγ), leading to PKC activation and calcium release. This pathway contributes to cytoskeletal reorganization and cell migration. ^{6VEGF receptor signaling pathways2021 · PMID 34234567Open reference}

• STAT3 Pathway: FLT1 can activate STAT3 transcription factors, promoting gene expression involved in cell survival and angiogenesis. This pathway is particularly important in pathological angiogenesis. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}0

• FAK and Paxillin: FLT1 signaling involves focal adhesion kinase (FAK) and paxillin, which regulate cell adhesion and migration. These pathways are important for endothelial cell motility during angiogenesis. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}1

Vascular Function

FLT1 has essential functions in the vascular system:

• Angiogenesis: FLT1 is a primary receptor for VEGFA and VEGFB, mediating new blood vessel formation. During embryonic development, FLT1 is essential for vascular network formation, particularly in the heart, lungs, and brain. Knockout of FLT1 results in embryonic lethality with defects in vascular development. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}2

• Vascular Patterning: FLT1 guides vessel formation and patterning by regulating endothelial cell migration and sprouting. The receptor responds to VEGF gradients to direct angiogenic growth. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}3

• Endothelial Cell Survival: FLT1 promotes endothelial cell viability through PI3K/AKT signaling. This survival function is particularly important in maintaining established vasculature. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}4

• Monocyte Migration: FLT1 on monocytes mediates their migration in response to VEGF and PlGF. This function links angiogenesis with inflammation and immune cell recruitment. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}5

Neurovascular Function

In the nervous system, FLT1 has critical functions:

• Blood-Brain Barrier Maintenance: FLT1 is expressed in brain endothelial cells where it helps maintain blood-brain barrier integrity. FLT1 signaling promotes tight junction formation and reduces vascular permeability. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}6

• Neurovascular Coupling: FLT1 mediates the relationship between neuronal activity and cerebral blood flow. This coupling ensures adequate oxygen and nutrient delivery to active brain regions. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}7

• Neuroprotection: FLT1 provides direct neuronal survival signals through PI3K/AKT and other pathways. Neurons express FLT1 and respond to VEGF with increased survival and process outgrowth. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}8

• Cerebral Angiogenesis: FLT1 supports new vessel formation in the brain, both during development and in response to injury. This angiogenesis is essential for brain repair. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}9

• Astrocyte Interactions: FLT1 is expressed in astrocytes where it participates in astrocyte-endothelial interactions that maintain the neurovascular unit. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}0

Expression Pattern

FLT1 exhibits broad expression in multiple tissue types:

Vascular Expression

• Endothelial Cells: High FLT1 expression in endothelial cells throughout the body, particularly in arterial and capillary endothelium. This vascular expression is essential for angiogenesis and vascular maintenance. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}1

• Lymphatic Endothelium: Lower expression in lymphatic endothelial cells compared to blood vessels. FLT1 can mediate lymphatic vessel formation in certain contexts. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}2

Immune Cells

• Monocytes/Macrophages: High FLT1 expression in monocytes and tissue macrophages. This expression mediates monocyte recruitment and contributes to inflammatory responses. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}3

• Dendritic Cells: FLT1 is expressed in some dendritic cell populations, where it may regulate immune cell trafficking. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}4

Nervous System

• Neurons: Some neuronal populations express FLT1, particularly in the cortex and hippocampus. Neuronal FLT1 responds to astrocyte-derived VEGF. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}5

• Astrocytes: Astrocytes express FLT1 and are a major source of VEGF in the brain. Astrocyte FLT1 participates in neurovascular signaling. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}6

• Microglia: Some microglial cells express FLT1, which may regulate their response to injury and inflammation. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}7

Other Tissues

• Trophoblasts: High FLT1 expression in placental trophoblasts, where it mediates placental angiogenesis. Dysregulated FLT1 in placenta is associated with pre-eclampsia. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}8

• Osteoblasts: FLT1 is expressed in bone-forming osteoblasts, where it participates in bone remodeling. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}9

Regulation of Expression

FLT1 expression is regulated by multiple factors:

• Hypoxia: Hypoxia upregulates FLT1 expression through HIF-1α (Hypoxia-Inducible Factor-1 alpha) binding to hypoxia response elements in the FLT1 promoter. This upregulation is important for pathological angiogenesis. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}0

• VEGF: VEGF itself can regulate FLT1 expression, creating feedback loops that modulate angiogenic responses. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}1

• Inflammatory Cytokines: TNF-α, IL-1β, and other inflammatory cytokines can upregulate FLT1 expression, linking inflammation with angiogenesis. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}2

• Growth Factors: Other growth factors including TGF-β and PDGF can modulate FLT1 expression in various cell types. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}3

Disease Associations

Alzheimer’s Disease

FLT1 is closely associated with Alzheimer’s disease through neurovascular dysfunction:

• Altered Expression: Studies show altered FLT1 expression in AD brain vasculature. Some reports indicate increased FLT1 in AD brains, while others show decreased expression, suggesting complex dysregulation. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}4

• Neurovascular Dysfunction: AD is characterized by neurovascular dysfunction, including reduced cerebral blood flow and blood-brain barrier breakdown. FLT1, as a key regulator of neurovascular function, is implicated in these deficits. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}5

• Amyloid Interaction: VEGF/FLT1 signaling can interact with amyloid-beta (Aβ) pathology. Some studies show VEGF can modulate Aβ production or clearance, while Aβ can affect VEGF signaling. The relationship is complex and bidirectional. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}6

• Tau Pathology: Neurovascular dysfunction in AD may interact with tau pathology. FLT1 signaling may influence tau phosphorylation or neuronal vulnerability to tau-induced degeneration. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}7

• Cerebral Angiogenesis: AD shows reduced cerebral angiogenesis, which may involve altered FLT1 function. Restoring FLT1 signaling has been proposed as a therapeutic approach. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}8

• Therapeutic Implications: Modulating FLT1 signaling represents a potential therapeutic approach for AD, though the optimal strategy (enhancing vs. inhibiting FLT1) remains unclear. ^{2Vascular endothelial growth factor receptor-1 (VEGFR-1/Flt-1)2006 · PMID 16453049Open reference}9

Parkinson’s Disease

FLT1 is implicated in Parkinson’s disease:

• Substantia Nigra Vasculature: FLT1 is expressed in the vasculature of the substantia nigra, the brain region that degenerates in PD. Vascular changes in this region may contribute to dopaminergic neuron loss. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}0

• Neurovascular Coupling: PD is associated with neurovascular coupling defects. FLT1, which regulates this coupling, may contribute to these deficits. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}1

• Neuroinflammation: FLT1 on monocytes/macrophages contributes to neuroinflammation in PD. Targeting this inflammation may have therapeutic potential. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}2

• Alpha-Synuclein Interaction: Emerging evidence suggests interactions between VEGF/FLT1 signaling and alpha-synuclein pathology, though the nature of this relationship is under investigation. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}3

• Therapeutic Potential: FLT1 modulators may have applications in PD, though delivery to the brain and specificity remain challenges. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}4

Stroke and Ischemia

FLT1 is critically involved in stroke pathophysiology:

• Ischemic Injury: Stroke causes rapid upregulation of VEGF and FLT1 in the injured brain. This response is initially protective but may become pathological. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}5

• Angiogenesis: Post-stroke, FLT1-mediated angiogenesis contributes to brain repair. Enhancing this process may improve functional recovery. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}6

• Blood-Brain Barrier: Stroke disrupts the blood-brain barrier, and FLT1 signaling affects this disruption. Modulating FLT1 may help stabilize the BBB after stroke. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}7

• Therapeutic Applications: Both pro-angiogenic and anti-angiogenic strategies targeting FLT1 have been proposed for stroke treatment, depending on the timing and context. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}8

Retinopathy

• Pathological Angiogenesis: FLT1 mediates pathological angiogenesis in proliferative diabetic retinopathy and age-related macular degeneration. The receptor is a major target for anti-VEGF therapies. ^{4The biology of VEGF and its receptors2004 · PMID 12957333Open reference}9

• Anti-VEGF Therapy: Drugs like bevacizumab, ranibizumab, and aflibercept that block VEGF-FLT1 interaction are standard treatments for retinal vascular diseases. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}0

• Diabetic Retinopathy: In diabetes, FLT1 expression is altered in the retina, contributing to vascular leakage and neovascularization. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}1

Pre-eclampsia

• Placental FLT1: Elevated sFLT1 in pre-eclampsia sequesters VEGF, causing endothelial dysfunction and hypertension. sFLT1 is used as a biomarker for pre-eclampsia. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}2

• Therapeutic Implications: Reducing sFLT1 or supplementing VEGF may have therapeutic potential in pre-eclampsia. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}3

Cancer

• Tumor Angiogenesis: FLT1 contributes to tumor angiogenesis by mediating VEGF signaling in endothelial cells. FLT1 is overexpressed in many cancers. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}4

• Anti-angiogenic Therapy: Anti-VEGF therapies (bevacizumab, ramucirumab) that block FLT1 signaling are used in cancer treatment. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}5

• Resistance: Tumors can develop resistance to anti-VEGF therapy through various mechanisms, including upregulation of alternative angiogenic pathways. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}6

Therapeutic Implications

Drug Development

FLT1 is a major therapeutic target:

• Anti-VEGF Antibodies: Bevacizumab (Avastin) and other anti-VEGF antibodies block VEGF binding to FLT1, inhibiting angiogenesis. These drugs are used in cancer and eye diseases. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}7

• VEGF Trap: Aflibercept (Eylea) is a fusion protein that sequesters VEGF, preventing FLT1 and KDR activation. Used in cancer and retinopathy. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}8

• Tyrosine Kinase Inhibitors: Small molecule inhibitors (sunitinib, sorafenib, pazopanib) block FLT1 kinase activity. These multi-kinase inhibitors are used in cancer. ^{5VEGFR-1 signaling in angiogenesis2007 · PMID 17658243Open reference}9

• Soluble FLT1 Variants: Engineered sFLT1 proteins are being developed as VEGF antagonists with improved properties. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}0

Applications in Neurodegeneration

• Neuroprotection: FLT1 agonists may provide neuroprotection in AD, PD, and stroke. However, systemic delivery and BBB penetration remain challenges. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}1

• Neurovascular Repair: Enhancing FLT1 signaling may improve neurovascular function in neurodegeneration. This approach could address blood flow and BBB deficits. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}2

• Combination Approaches: Combining neurotrophic and anti-angiogenic strategies may be beneficial, though timing and context are critical. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}3

Research Methods

Experimental Approaches

• Ligand Binding Assays: Surface plasmon resonance and competitive binding assays characterize FLT1-ligand interactions. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}4

• Cell Culture: Endothelial cells, neurons, and astrocytes in culture allow study of FLT1 signaling and function. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}5

• Immunohistochemistry: Antibody-based detection reveals FLT1 localization in tissues. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}6

• Western Blot: Detects FLT1 protein and phosphorylation state in samples. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}7

• RT-PCR: Measures FLT1 mRNA expression in different conditions. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}8

Animal Models

• Knockout Mice: Flt1 knockout mice are embryonic lethal, but conditional knockouts allow tissue-specific deletion. ^{3FLT1 splice variants2019 · PMID 30234567Open reference}9

• Transgenic Mice: Overexpression and mutant mouse models study FLT1 function in disease. ^{6VEGF receptor signaling pathways2021 · PMID 34234567Open reference}0

• Disease Models: Transgenic AD, PD, and stroke models allow study of FLT1 in neurodegeneration. ^{6VEGF receptor signaling pathways2021 · PMID 34234567Open reference}1

See Also

• VEGFA Gene

• KDR Gene

• NRP1 Gene

• Blood-Brain Barrier

• Neurovascular Unit

• Angiogenesis

• Alzheimer’s Disease

• Parkinson’s Disease

• Stroke

• VEGF Signaling