| UniProt ID | [P31431](https://www.uniprot.org/uniprotkb/P31431) |
| Gene | [SDC4](/genes/sdc4) |
| MW | ~22 kDa (core) |
| Location | Ubiquitous, focal adhesions |
| PDB | [1EJP](https://www.rcsb.org/structure/1EJP) |
Syndecan-4 Protein is a protein that ### Cell Adhesion and Migration. This page describes its structure, normal nervous system function, role in neurodegenerative disease, and potential as a therapeutic target.
Syndecan-4 (SDC4, also known as ryudocan or amphiglycan) is a ubiquitously expressed heparan sulfate proteoglycan (HSPG) that serves as a key cell adhesion molecule, signaling scaffold, and mediator of pathological protein interactions. While less brain-specific than Syndecan-3, Syndecan-4 plays important roles in neuroinflammation, blood-brain barrier function, and neurodegenerative disease pathology.[1]
Syndecan-4 is the most widely expressed syndecan family member with a compact structure:[2]
The cytoplasmic domain contains a central serine residue (Ser179) whose phosphorylation regulates PKCα binding and downstream signaling.
Syndecan-4 is essential for cell-matrix adhesion:[3]
In the nervous system:[4]
Syndecan-4 contributes to neuroinflammatory processes:[5]
The heparan sulfate chains on Syndecan-4 bind neurodegenerative proteins:[6]
| Protein | Binding | Functional Consequence |
|---|---|---|
| Amyloid-β | High | Aggregation, clearance |
| Tau | Moderate | Cellular uptake |
| Alpha-synuclein | Moderate | Fibril binding |
| Prion protein | High | PrP^Sc binding, internalization |
In neurodegeneration, Syndecan-4 shedding from endothelial cells:[7]
Targeting Syndecan-4 has therapeutic potential:
| Approach | Application | Status |
|---|---|---|
| Soluble SDC4 ectodomain | Aβ clearance | Preclinical |
| Anti-SDC4 antibodies | Reduce inflammation | Research |
| HS mimetics | Block protein binding | Preclinical |
| Shedding inhibitors | Preserve BBB | Conceptual |
| Interacting Partner | Type | Function |
|---|---|---|
| Fibronectin | Physiological | Cell adhesion |
| Integrins (α5β1) | Physiological | Focal adhesion |
| PKCα | Physiological | Signaling |
| FGF2 | Physiological | Growth factor presentation |
| Amyloid-β | Pathological | Aggregation, clearance |
| Tau fibrils | Pathological | Cellular uptake |
Syndecan-4 undergoes regulated intramembrane proteolysis:[8]
Couchman JR, et al. Syndecan-4 and focal adhesion function. Curr Opin Cell Biol. 1999;11(5):616-623. doi:. [10.1016/S0955-0674(99)00018-8](https://doi.org/10.1016/S0955-0674(99). 1999. ↩︎
Choi Y, et al. The basic sequence in the cytoplasmic domain of syndecan-4 regulates the phosphorylation of Ser179 and its association with PKCα. J Biol Chem. 2017;292(34):14268-14278. doi:. 10.1074/jbc.M117.794589. 2017. ↩︎
Bass MD, et al. Syndecan-4-dependent signaling regulates focal adhesion dynamics. J Biol Chem. 2007;282(42):30703-30713. doi:. 10.1074/jbc.M703489200. 2007. ↩︎
Nakanishi K, et al. Syndecan-4 in the central nervous system. J Histochem Cytochem. 2010;58(7):597-607. doi:. 10.1369/jhc.2010.956110. 2010. ↩︎
Siebert JR, et al. Synergistic effects of microglia-derived cytokines on astrocyte proliferation. J Neuroimmunol. 2014;269(1-2):33-39. doi:. 10.1016/j.jneuroim.2014.02.008. 2014. ↩︎
Holmes BB, et al. Heparan sulfate proteoglycans mediate internalization and propagation of specific proteopathic seeds. Proc Natl Acad Sci USA. 2013;110(33):E3138-3147. doi:. 10.1073/pnas.1301440110. 2013. ↩︎
Arai C, et al. Identification of soluble syndecan-4 as a biomarker of blood-brain barrier dysfunction. Fluids Barriers CNS. 2022;19(1):68. doi:. 10.1186/s12987-022-00368-2. 2022. ↩︎
Fitzgerald ML, et al. Shedding of syndecan-1 and -4 ectodomains is regulated by multiple signaling pathways and mediated by a TIMP-3 metalloproteinase inhibitor-sensitive protease. J Biol Chem. 2000;275(1):467-475. doi:. 10.1074/jbc.275.1.467. 2000. ↩︎