KitL restores impaired tPA-mediated PαS-MSC expansion in Plg^−/− and MMP-9^−/− mice. (A) Original gel and (B) densitometric quantification of MMP-2 and MMP-9 after gelatin zymography from supernatants derived from PαS-MSCs stimulated with/without tPA at indicated time points (n = 3/group). (C) Representative western blot of soluble KitL released in supernatant of cultured PαS-MSCs treated with vehicle or tPA with or without the MMP inhibitor MMI 270 (n = 3/group). (D) Immunohistologic staining (left) and FACS plot (right) for c-Kit expression in ex vivo cultured PαS-MSCs. T17B was used as a positive control. Nuclei were counterstained using DAPI (n = 3/group). Scale bars, 50 µm. (E) Absolute numbers of cultured PαS-MSCs per well after addition of rec. KitL or vehicle for 4 days as determined by hemocytometer counting (n = 3/group). (F) Representative FACS blots and (G) the absolute numbers of PαS-MSCs per femur from WT B6, Plg^−/−, and MMP-9^−/− mice after 2 days of injection of rec. KitL or vehicle as determined by FACS analysis (n = 3/group). (H) Absolute numbers of PαS-MSCs per femur from WT B6 mice treated for 2 days with rec. tPA in the absence and presence of neutralizing c-Kit antibody. For comparison, WT B6 data of Figure 2B are used for reference (n = 4/group). Mean ± SEM. *P < .05; **P < .01; ***P < .001 by Student t test. Data are representative of 2 independent experiments.