A Glycovariant of Human CD44 is Characteristically Expressed on Human Mesenchymal Stem Cells

The clinical effectiveness of systemically-administered human mesenchymal stem cells (hMSCs) depends on their capacity to engage vascular endothelium. hMSCs derived from bone marrow (BM-hMSCs) natively lack endothelial binding capacity but express a CD44 glycovariant containing N-linked sialyllactosamines that can be α(1,3)-fucosylated using fucosyltransferase- VI (FTVI) to enforce sLeX decorations, thereby creating hematopoietic cell E-/L-selectin ligand (HCELL). HCELL expression programs potent shear-resistant adhesion of circulating cells to endothelial beds expressing E-selectin. An alternative source of hMSCs is adipose tissue (A-hMSCs), and we assessed whether A-hMSCs bind E-selectin and/or possess sialyllactosamine-decorated CD44 accessible to α(1,3)-fucosylation. Similar to BM-hMSCs, we found that A-hMSCs natively lack E-selectin ligands, but FTVI-mediated cell surface α(1,3)-fucosylation induces sLeX expression and robust E-selectin binding secondary to conversion of CD44 into HCELL. Moreover, treatment with the α(1,3)-fucosyltransferase FTVII also generated expression of HCELL on both BM-hMSCs and A-hMSCs, with sLeX decorations created on N-linked glycans of the “standard” CD44 (CD44s) isoform. The finding that hMSCs from both source tissues each lack native E-selectin ligand expression prompted examination of the expression of glycosyltransferases that direct lactosaminyl glycan synthesis. These studies reveal that both types of hMSCs conspicuously lack transcripts encoding α(1,3)-fucosyltransferases but equally express glycosyltransferases critical to creation of sialyllactosamines. Collectively, these data indicate that assembly of a sialyllactosaminyl-decorated CD44s glycovariant is a conserved feature of hMSCs derived from adipose tissue and marrow, thus identifying a CD44 glycosignature of these cells and supporting the applicability of cell surface α(1,3)-fucosylation in programming migration of systemically-administered A-hMSCs to sites of tissue injury/inflammation. Application of Glycosyltransferase-Programmed Stereosubstitution (GPS) to enforce HCELL expression. Cell surface CD44 can be converted to the HCELL glycoform by glycan engineering via GPS. Note glycan structures (including sLeX) and component steps in the strategy to create HCELL by α(1,3)-fucosylation of “acceptor” sialylated CD44 on the hMSC membrane. The “β1-4” linkage as shown between Gal and GlcNAc defines a “Type 2” lactosamine unit. When this structure contains a fucose substitution in a 1,3-linkage to N-acetylglucosamine it is known as ‘sialylated Lewis x' (sLeX): Treatment of hMSCs with either fucosyltransferase VI (FTVI) or fucosyltransferase VII (FTVII) drives α(1,3)-fucosylation of CD44 glycans, thereby generating sLeX and, accordingly, engendering HCELL. Data indicate that assembly of a sialyllactosaminyl-decorated CD44s glycovariant is a conserved feature of hMSCs derived from adipose tissue and marrow, thus identifying a CD44 glycosignature of these cells and supporting the applicability of cell surface α(1,3)-fucosylation in programming migration of systemically-administered A-hMSCs to sites of tissue injury/inflammation. Color key figures correspond to respective monosaccharides. This article is protected by copyright. All rights reserved.