Soluble amyloid precursor protein alpha (sAPPα) can recover matrix-metalloproteinase inhibitor-induced deficits in mesenchymal stem cell (MSC) proliferation. (a) Western blot analysis shows that levels of secreted sAPP are dramatically reduced in MSCs after treatment with matrix-metalloproteinase inhibitor GM6001 (GM) when compared with MSCs treated with an inactive inhibitor (NC). Actin from cell lysates was used as a protein-loading control. (b) Optical density of expression intensity of sAPP (a) normalized to actin. (c) MSC proliferation as assayed by total cell number after 3 days in culture is significantly reduced by GM6001 in a dose-dependent manner. Red diamond indicates 1 μM NC, blue diamonds indicate GM6001, green diamond indicates 1 μM GM6001 + 10 nM sAPPα, and dotted line indicates the number of cells originally plated. (d) The number of MSCs counted after 3 days of 1 μM NC, 1 μM GM6001, or 1 μM GM6001 + 10 nM sAPPα treatment after original plating of 1,000 cells per well. (e) Dose response of sAPPα effect on proliferation of MSCs after 1 μM GM6001 addition. Red diamond indicates 1 μM NC, blue diamond indicates 1 μM GM6001, and green diamonds indicate recombinant sAPPα. Error bars represent standard error of the mean. *P < 0.01, analysis of variance with post hoc analysis. A.U., arbitrary units.