Pigment Epithelium-Derived Factor Enhances Differentiation and Mineral Deposition of Human Mesenchymal Stem Cells.

Pigment epithelium-derived factor (PEDF) is a potent antiangiogenic factor found in a wide variety of tissues. Recent findings indicated that lack of PEDF leads to osteogenesis imperfecta type VI whose hallmark is a defect in mineralization. We investigated the effects of PEDF on human mesenchymal stem cells (hMSCs) and signaling pathways through which PEDF displays its activities in hMSCs. hMSCs incubated in a medium supplemented with PEDF induced expression of osteoblastic-related genes. In addition, PEDF induced alkaline phosphatase (ALP) activity in MSCs at 14 days of incubation in maintenance medium; hMSCs incubated in osteogenic medium in presence of PEDF expressed 19% more ALP activity (35.655 +/- 1.827 U/mg protein, p=.041 than cells incubated in the same medium without PEDF supplementation (29.956 +/- 2.100 U/g protein). hMSCs incubated in osteogenic medium in presence of PEDF deposited 50% more mineral (2.108 +/- 0.306 OD/ml per well per 1 x 10(4) cells per square centimeter, p=.017) than MSCs incubated in absence of the protein (1.398 +/- 0.098 OD/ml per well per 1 x 10(4) cells per square centimeter) as determined by Alizarin Red quantitation. Reduction in PEDF expression in MSCs by siRNA led to decreased ALP activity (33.552 +/- 2.009 U/ng protein of knockdown group vs. 39.269 +/- 3.533 U/ng protein of scrambled siRNA group, p=.039) and significant reduction in mineral deposition (0.654 +/- 0.050 OD/ml per well per 1 x 10(4) cells per square centimeter of knockdown group vs. 1.152 +/- 0.132 OD/ml per well per 1 x 10(4) cells per square centimeter of wild-type group, p=.010). Decreased ALP activity and mineral deposition were restored by supplementation with exogenous PEDF protein. PEDF activated ERK and AKT signaling pathways in MSCs to induce expression of osteoblastic-related genes. These data suggest that PEDF is involved in MSCs osteoblastic differentiation.