The Formation of Extracellular Matrix During Chondrogenic Differentiation of Mesenchymal Stem Cells Correlates with Increased Levels of Xylosyltransferase I

Abstract

In vitro differentiation of mesenchymal stem cells (MSCs) into chondrogenic cells and their transplantation is promising as 1,4-N-acetylgalactosaminyltransferase), and GlcAC5E (glucuronyl C5 epimerase). All key enzymes showed a similar regulation with temporarily downregulated mRNA levels (up to ؊87-fold) after chondrogenic induction. In accordance to previous studies, we observed a similar increase in the expression of PG core proteins. In conclusion, we could show that key enzymes for CS, DS, and HS synthesis, especially XT-I, are useful markers for the developmental stages of chondrogenic differentiation.

EXTL2, a Member of the EXT Family of Tumor Suppressors, Controls Glycosaminoglycan Biosynthesis in a Xylose Kinase-dependent Manner

“…FAM20B is reportedly a Xyl kinase that regulates GAG biosynthesis (5) and controls the timing of endochondral ossification by inhibiting chondrocyte maturation (32). In addition, the expression level of EXTL2 reportedly increases during chondrogenesis (34). Based on these findings, we propose that EXTL2 plays an important role in the regulation of GAG synthesis in concert with FAM20B and that an imbalance between EXTL2 and FAM20B functions may lead to abnormal endochondral ossification.…”

Comparative Analysis of Mesenchymal Stem Cells from Bone Marrow, Cartilage, and Adipose Tissue

“…Fourteen days after induction, the cell pellets were xed with 4% paraformaldehyde, embedded in paraf n and cut into 5 μm sections [15]. Sections were stained with 1% toluidine blue (Sigma, USA) at pH 2.5 for 30 min and rinsed with tap water.…”

Human xylosyltransferases in health and disease

“…The promoters of the xylosyltransferase genes have not yet been characterized, and therefore cell-typespecific transcriptional response elements are not yet identified. However, it has been shown that both xylosyltransferase genes are differentially regulated during transforming growth factor (TGF) b 3 -induced chondrogenic differentiation of mesenchymal stem cells [59]. XT-I is the predominant xylosyltransferase in the early phase of chondrogenic stem cell differentiation and XT-II is upregulated 7 days after induction.…”

“…Until now, the amino acids in the xylosyltransferase stem regions where the proteolytic cleavage occurs have not been identified. Xylosyltransferase secretion seems to be independent of cell type and organ system, as xylosyltransferase activity has been identified in culture supernatants of all cell lines investigated [42,59,87] and in many human body fluids, including blood, synovial fluid, semen, follicular fluid and liquor cerebrospinalis [28, 42, 87, 96 -99]. Until now, no UDP-xylose has been found in the extracellular space, indicating that no xylosyltransferasemediated xylose transfer to protein substrates occurs due to the lack of donor substrates.…”

“…This increased proteoglycan biosynthesis during skeletal growth and bone formation also results in increased xylosyltransferase activity, which was shown to correlate with the growth rate of the vertebral column in sheep [149] and with bone formation markers in humans [C. Gçtting, unpublished data]. Furthermore, the osteogenic differentiation of mesenchymal stem cells also leads to a stagedependent increase in xylosyltransferase expression [B. Müller and C. Gçtting, manuscript submitted], which is also observed during chondrogenic differentiation of stem cells [59]. On the other hand, reduced xylosyltransferase levels are found during cartilage aging [150].…”