FIG. 1.

The influence of oxygen tensions on the formation of prevascular structures in MSC/ECFC co-cultures. CD31 immunostaining of pellets at 12 days (A, B) and 22 days (C, D) consisting of MSC and ECFCs. The pellets were cultured at either normoxia (N in A, C) or hypoxia (H in B, D). Only pellets containing ECFCs and cultured under normoxia demonstrate formation of tubular structures. Sections were counterstained with hematoxylin. Control pellets containing MSCs only were negative (inset in D). The total length (K) and total number of junctions (L) of the CD31-positive structures normalized to total section area were significantly increased for the normoxic co-cultures (*p<0.05). Localization of α-smooth muscle actin (E) around CD31-positive structures (F), with an overlay in (H) and (I) and nuclear counterstain in (G). (J) Elongated nuclei (arrowheads) typical for smooth muscle cell differentiation were observed in the α-smooth muscle actin (red) cells. Scale bar in (A) denotes scale for A–D, whereas bar in (E) represents the scale for E–J. ECFC, endothelial colony forming cell; MSC, multipotent stromal cell. Color images available online at www.liebertonline.com/tea