The Reversal Effect And Mechanism Of IGF-1 On Dexamethasone-Inhibited Osteogenic Differentiation In Mesenchymal Stem Cells

Glucocorticoid-induced osteoporosis is a common clinical disease caused by high dose administration of glucocorticoids,such as Dexamethasone and Prednisone.There is no efficacious prevention and treatment in current clinical practice,and some severe cases may lead to Osteonecrosis of the Femoral Head.It has been reported that glucocorticoids can inhibit bone formation by supression of osteogenic differentiation in Mesenchymal Stem Cells(MSCs).In our study,we recruited Bone Morphogenetic Protein-9(BMP9)induced MSCs as an osteogenic differentiation model.With RT-PCR,Western blot,Alkaline Phosphatase(ALP)staining,Alizarin Red S staining and Immunofluorescence staining,we were determined to further validate the inhibitory effect of Dexamethasone on osteogenic differentiation and then analyze the effect and mechanism of insulin-like growth factor 1(IGF-1)on osteogenic differentiation inhibited by Dexamethasone.The results showed that high concentration of Dexamethasone can significantly inhibit the expression of osteogenic markers,such as Runx2 and OPN in Mouse Embryonic Eibroblasts(MEFs).Based on this,overexpression of IGF-1 can promote the expression of the above osteogenic markers,suggesting that IGF-1 can reverse the inhibitory effect of Dexamethasone on osteogenic differentiation to some extent.With further investigation,we found that Dexamethasone can inhibit Akt phosphorylation,and Ly294002,an inhibitor of PI3 K,can block the reversal effect of IGF-1 on Dexamethasone-inhibited osteogenic differentiation,indicating that IGF-1 may exert its reversal effect via the PI3K/Akt signaling pathway.Finally,we found that IGF-1 can enhance the expression of cyclooxygenase 2(COX-2),while silencing COX-2 or using its inhibitor NS398 can block the reversal effect of IGF-1 on Dexamethasone-inhibited osteogenic differentiation,suggesting that COX-2 is also involved in the reversal process of IGF-1/PI3K/Akt.These results revealed that IGF-1 may reverse the inhibitory osteogenic effect of Dexamethasone in MSCs via PI3K/Akt signaling pathway,which may be associated with the up-regulation of COX-2.