| First Author | Gonzalez-Gil A | Year | 2022 |
| Journal | J Biol Chem | Volume | 298 |
| Issue | 6 | Pages | 101960 |
| PubMed ID | 35452678 | Mgi Jnum | J:334166 |
| Mgi Id | MGI:7283278 | Doi | 10.1016/j.jbc.2022.101960 |
| Citation | Gonzalez-Gil A, et al. (2022) Human brain sialoglycan ligand for CD33, a microglial inhibitory Siglec implicated in Alzheimer's disease. J Biol Chem 298(6):101960 |
| abstractText | Alzheimer's disease (AD) is characterized by accumulation of misfolded proteins. Genetic studies implicate microglia, brain-resident phagocytic immune cells, in AD pathogenesis. As positive effectors, microglia clear toxic proteins, whereas as negative effectors, they release proinflammatory mediators. An imbalance of these functions contributes to AD progression. Polymorphisms of human CD33, an inhibitory microglial receptor, are linked to AD susceptibility; higher CD33 expression correlates with increased AD risk. CD33, also called Siglec-3, is a member of the sialic acid-binding immunoglobulin-type lectin (Siglec) family of immune regulatory receptors. Siglec-mediated inhibition is initiated by binding to complementary sialoglycan ligands in the tissue environment. Here, we identify a single sialoglycoprotein in human cerebral cortex that binds CD33 as well as Siglec-8, the most abundant Siglec on human microglia. The ligand, which we term receptor protein tyrosine phosphatase zeta (RPTPzeta)(S3L), is composed of sialylated keratan sulfate chains carried on a minor isoform/glycoform of RPTPzeta (phosphacan) and is found in the extracellular milieu of the human brain parenchyma. Brains from human AD donors had twofold higher levels of RPTPzeta(S3L) than age-matched control donors, raising the possibility that RPTPzeta(S3L) overexpression limits misfolded protein clearance contributing to AD pathology. Mice express the same structure, a sialylated keratan sulfate RPTPzeta isoform, that binds mouse Siglec-F and crossreacts with human CD33 and Siglec-8. Brains from mice engineered to lack RPTPzeta, the sialyltransferase St3gal4, or the keratan sulfate sulfotransferase Chst1 lacked Siglec binding, establishing the ligand structure. The unique CD33 and Siglec-8 ligand, RPTPzeta(S3L), may contribute to AD progression. |
