CD47 Gene
Overview
CD47, also known as Cluster of Differentiation 47 or integrin-associated protein (IAP), is a transmembrane glycoprotein encoded by the CD47 gene located on chromosome 3q13.1 in humans. CD47 functions as a critical "don't eat me" signal that protects cells from phagocytic clearance by macrophages and other immune cells. The protein consists of an extracellular immunoglobulin (Ig) domain and a transmembrane domain with a short cytoplasmic tail. CD47 is widely expressed across cell types, including neurons, glial cells, and immune cells, making it a ubiquitous regulator of innate immunity. Its role extends beyond simple immune evasion to include cell adhesion, apoptotic cell recognition, and thrombospondin binding, establishing CD47 as a multifunctional molecule with significant implications for both health and disease states.
Function and Biology
CD47 primarily exerts its biological effects through interaction with signal regulatory protein alpha (SIRPα), a transmembrane receptor expressed on myeloid cells including macrophages, dendritic cells, and microglia. When CD47 engages SIRPα, it initiates an inhibitory signaling cascade that suppresses phagocytosis, allowing cells displaying CD47 to evade immune clearance. This "don't eat me" signal operates through SIRPα's immunoreceptor tyrosine-based inhibitory motifs (ITIMs), which recruit SHP-1 and SHP-2 phosphatases that dampen activation signals in phagocytes.
...CD47 Gene
Overview
CD47, also known as Cluster of Differentiation 47 or integrin-associated protein (IAP), is a transmembrane glycoprotein encoded by the CD47 gene located on chromosome 3q13.1 in humans. CD47 functions as a critical "don't eat me" signal that protects cells from phagocytic clearance by macrophages and other immune cells. The protein consists of an extracellular immunoglobulin (Ig) domain and a transmembrane domain with a short cytoplasmic tail. CD47 is widely expressed across cell types, including neurons, glial cells, and immune cells, making it a ubiquitous regulator of innate immunity. Its role extends beyond simple immune evasion to include cell adhesion, apoptotic cell recognition, and thrombospondin binding, establishing CD47 as a multifunctional molecule with significant implications for both health and disease states.
Function and Biology
CD47 primarily exerts its biological effects through interaction with signal regulatory protein alpha (SIRPα), a transmembrane receptor expressed on myeloid cells including macrophages, dendritic cells, and microglia. When CD47 engages SIRPα, it initiates an inhibitory signaling cascade that suppresses phagocytosis, allowing cells displaying CD47 to evade immune clearance. This "don't eat me" signal operates through SIRPα's immunoreceptor tyrosine-based inhibitory motifs (ITIMs), which recruit SHP-1 and SHP-2 phosphatases that dampen activation signals in phagocytes.
Beyond SIRPα interaction, CD47 serves as a ligand for thrombospondin-1 (TSP-1), a matricellular protein involved in cell adhesion, migration, and angiogenesis. CD47 also interacts with integrins, particularly αvβ3 and αvβ5, influencing cell survival and migration pathways. Additionally, CD47 participates in the recognition and clearance of apoptotic cells, with alterations in CD47 expression affecting the efficiency of dead cell removal by professional phagocytes.
Role in Neurodegeneration
CD47 dysregulation emerges as a significant factor in multiple neurodegenerative conditions. In Alzheimer's disease, reduced CD47 expression on neurons and altered expression on amyloid-beta-containing cells may enhance their susceptibility to microglial phagocytosis. Conversely, aberrant CD47 upregulation on damaged neurons could impair their clearance, promoting neuroinflammation and disease progression. In Parkinson's disease, CD47 modulation affects the fate of dopaminergic neurons, with dysregulated CD47 signaling potentially compromising the balance between neuronal protection and clearance of pathological protein aggregates.
In amyotrophic lateral sclerosis (ALS), motor neurons show altered CD47 expression patterns that may affect their survival in the context of neuroinflammatory environments. The CD47-SIRPα axis regulates microglial activation states, with dysregulation potentially shifting microglia toward pro-inflammatory phenotypes that exacerbate neuronal death. In multiple sclerosis, CD47 expression on oligodendrocytes and myelin-associated cells influences their recognition and elimination by activated immune cells, contributing to demyelination.
Molecular Mechanisms
CD47-mediated neuroprotection involves several interconnected pathways. Engagement of CD47 by SIRPα recruits protein tyrosine phosphatase SHP-1, which dephosphorylates and inactivates Src family kinases necessary for phagocytic cup formation and engulfment. This creates a dominant inhibitory signal that overrides the stimulatory signals from pattern recognition receptors and complement receptors on macrophages and microglia.
In the context of neurodegeneration, CD47 expression levels directly influence microglial activation and neuroinflammatory responses. Downregulation of CD47 on stressed or dying neurons enhances their phagocytosis by microglia, while excessive CD47 expression may prevent clearance of pathological protein aggregates. CD47 also modulates the interaction between neurons and astrocytes through integrin signaling, affecting the neuroinflammatory microenvironment.
Clinical and Research Significance
CD47 represents a promising therapeutic target for neurodegenerative diseases. SIRPα-Fc fusion proteins and anti-CD47 blocking antibodies are under investigation for enhancing clearance of pathological cells in Alzheimer's disease. Conversely, CD47-enhancing strategies or SIRPα antagonists may protect vulnerable neurons from premature phagocytic removal in conditions like ALS. Understanding CD47 biology in neuroinflammation could enable immune-modulating therapies that tip the balance toward neuroprotection while maintaining beneficial immune surveillance.
- Signal Regulatory Protein Alpha (SIRPα)
- Thrombospondin-1 (TSP-1)
- Integrin signaling
- Microglial activation
- Phagocytosis and complement system
- Neuroinflammation
Pathway Diagram
The following diagram shows the key molecular relationships involving CD47 Gene discovered through SciDEX knowledge graph analysis:
Mermaid diagram (expand to render)
Disease Associations
Top DisGeNET gene-disease associations for this gene are listed below. Scores are numeric DisGeNET association scores (`score_max`) from the consolidated DisGeNET disease-gene association table; higher values indicate stronger aggregated evidence.
| Disease | DisGeNET score | Evidence sources | Supporting PMID count |
|---|---:|---|---:|
| hematologic cancer | 0.003 | BeFree/LHGDN | 3 |
| anemia | 0.003 | BeFree/LHGDN | 2 |
| multiple sclerosis | 0.001 | BeFree | 5 |
| melanoma | 0.001 | BeFree | 4 |
| prostate cancer | 0.001 | BeFree | 2 |
Source: DisGeNET-derived consolidated disease-gene associations (`dhimmel/disgenet`, gene symbol `CD47`).