The expression and role of ADAMTS9 during differentiation of human embryonic stem cells

Abstract

A Disintegrin-like And Metalloproteinase with Thrombospondin (TSP)-Type I sequence motifs 9 (ADAMTS9) is widely expressed in mouse and human fetal tissues. ADAMTS9 null mice cannot survive beyond E7.5 and its haploinsufficiency is associated with cardiac and aortic anomalies. This project hypothesized that ADAMTS-9 plays an important role during early embryogenesis. By using human embryonic stem cells (hESCs) as a model, the objectives of this study were to study the expression of ADAMTS9 and to determine the effects of ADAMTS9 perturbation on hESC differentiations.

The expression of ADAMTS9 was compared between undifferentiated and differentiated hESCs. Its mRNA was maintained at similar levels in different passages of normal hESC lines. Interestingly, significantly lower expression was detected in karyotypically abnormal VAL4A when compared to the normal cells (H9 and VAL3). ADAMTS9 immunoreactivity was detected in cells located at the boundary of hESC colonies. The expression of ADAMTS9 was then studied during differentiation of hESC. ADAMTS9 mRNA and protein expression increased time-dependently during the first 24 days? of embryoid body (EB) formation. The expression pattern was similar to that of mesoderm and endoderm markers. Upon more specific lineage differentiation induced by retinoic acid and bone morphogenesis protein 4, ADAMTS9 mRNA expression was significantly increased. The positive correlation of ADAMTS9 with ESC differentiation was also found in mouse system, in which ADAMTS9 was increased time-dependently during mouse EB formation and down-regulated during reprogramming from somatic cells into induced pluripotent cells.

Previous studies have shown that down-regulation of ADAMTS9 in several tumor tissues was attributed to ADAMTS9 hypomethylation. However, the present study demonstrated that the expression of ADAMTS9 was reduced in hESC after treatments with inhibitors of DNA methylation (5-aza-2?deoxycytidine) and histone deacetylase (VPA).

The cellular localization of ADAMTS9 during hESC differentiation was further studied by co-localization of ADAMTS9 with several lineage specific markers. It was found that ADAMTS9 co-localized with mesoderm and endoderm markers. The functional role of ADAMTS9 in hESCs was then studied by transient ADAMTS9 knockdown. ADAMTS9 siRNA significantly decreased the expression level of mesoderm marker, REN. Thus, the role of ADAMTS9 during mesoderm differentiation was followed.

ADAMTS9 was found to be dramatically increased after mesoderm differentiation of hESCs. In mesodermal cells, ADAMTS9 was co-expressed with vascular endothelial markers, VEGF and CD31, but not with pericyte markers, alpha muscle actin. Lentiviral vector encoding ADMATS9 shRNA was used for long term knockdown of ADAMTS9. ADAMTS9 down-regulation had no effect on the proliferation of hESCs. In agreement with the siRNA study, ADAMTS9 shRNA also significantly reduced the expression of REN. Upon mesoderm differentiation, ADAMTS9 knockdown resulted in a decreasing trend of mesoderm marker, CD34.

In conclusion, the present study demonstrated a positive association of ADAMTS9 expression with hESC differentiation. ADAMTS9 was dramatically induced during mesoderm differentiation and its knockdown led to down-regulation of mesoderm markers. Together with the fact that ADAMTS9 expression was associated with endothelial cell markers suggested its possible role during endothelial cells formation. The roles of ADAMTS9 during hESC differentiation and early embryo development warrant further investigation.