Introduction: Osteogenic and adipogenic differentiation from common mesenchymal progenitor cells are inverse processes and often regulated reciprocally. Increased adipogenic differentiation with concurrent decreased osteogenic differentiation of bone marrow cells are closely correlated with age-related bone diseases such as osteoporosis. The objective of this study is to describe that low molecular weight silk peptides from acid digested silk fibroin can alter adipogenic and osteogenic potentials in pluripotent cells.

Methods: For adipocyte differentiation, C3H10T1/2 and 3T3-L1 cells were cultured and standard adipogenic hormonal stimuli and treated with control or silk peptides for 2 days after confluence. The cultures were fed every 2 days and incubated in 5% CO2 incubators. For osteoblast differentiation, C3H10T1/2 cells were differentiated and treated with control or silk peptides at confluence. Cells differentiated for 10 days were washed and equilibrated. For Von Kossa staining, the cells were then fixed with 4% paraformaldehyde and stained with 5% silver nitrate. The total RNAs were extracted using TRIzol reagent (Invitrogen) and real time PCR was performed.

Results: Silk peptides stimulated alkaline phosphatase (ALP) activities, osteoblast differentiation, and induced the expression of osteoblast markers in murine multipoint cells. In contrast, silk peptides inhibited adipogenic differentiation and the expression of adipogenic markers. Molecular studies show that silk peptides determine adipocyte and osteoblast differentiation of mesenchymal stem cells through the inhibition of Notch signaling. Furthermore, notch singling inhibitors enhance osteoblast differentiation while blocking adipocyte differentiation similar to the effects of silk peptides.

Conclusions: We show that hydrolyzed silk pepetides can block adipogenesis while promoting osteogenesis in mesenchymal stem cells. Our results also demonstrate that silk peptides modulate the fates of mesenchymal stem cells via inhibition of the Notch pathway. Given the mechanisms of action and cell biological responses, silk peptides may represent a new approach for the treatment of age-related osteoporosis and other bone diseases.

Patient Care: It will be helpful to improve the osteogenesis for the spine patients

Learning Objectives: To know the osteogenic effect of silk fibroin.

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