Involvement of THBS1 in the impaired angiogenic function of LBW-ECFCs. LBW-ECFCs (< 1500 g) were transiently transfected with scrambled siRNA or siRNA specific for THBS1, and cells were recovered 48 hours later for function testing. Representative experiments: (A) Capillary tube formation (original magnification 4×/0.13). Scale bars represent 200 μm. (C) Sprout formation from 3D spheroids (original magnification ×20). Scale bars represent 50 μm by LBW-ECFCs transfected with scrambled siRNA (scr), siRNA THBS1, or from wt-CT-ECFCs. (B) Quantification of tube length and branches by silenced ECFCs. (D) Total number of sprouts by spheroids (left panel) and total length of sprouts (right panel). (E) Proliferation of THBS1-silenced ECFCs: 48 hours after transfection, 10 000 LBW-ECFCs/well were plated, and BrdU incorporation was assayed. Data are mean ± SEM of 3 independent experiments performed in triplicate. *P < .05. **P < .01. ***P < .001.