Figure 4. Evidence supporting breast MSC endothelial differentiation. (A) bMSCs form extensive vascular-like structures 4 d after culturing within Matrigel^® (20x light and fluorescent images). DAPI (lower panel) allowed the visualization of nuclei. (B) bMSCs also form vessel-like structures when subcutaneously injected within Matrigel^® into athymic nude mice. Masson Trichrome and H&E histochemical staining permits the identification of numerous small vessel-like structures with red blood cells within lumens (upper panels), suggesting a connection to the host’s vascular system. Shown are specimens obtained 2 weeks after subcutaneous inoculation, however vascular networks were observed as early as 4 d (data not shown). No evidence of vascular-like structures in xenografts following the subcutaneous injection of BJ fibroblasts within Matrigel^®. Shown is a 6-d xenograft, however, similar negative findings were observed at days 2, 4, 9 and 14 post-injection. (C) qRT-PCR data comparing eNOS expression levels in subcutaneous xenografts 6 d after inoculation with BJ fibroblasts, bMSCs or HUVECs all within Matrigel^®.