N-CoR modulates osteogenic differentiation of rat mesenchymal stem cells through the PI3K/Akt-cell signaling pathway

Abstract

The nuclear receptor corepressor (N-CoR) is involved in the regulation of diverse transcription factors. We previously found that N-CoR could regulate adipogenic differentiation of rat mesenchymal stem cells (MSCs),but whether it modulated osteogenic differentiation of this type of cells was uncertain. Therefore, in the present study, we investigated the effect and mechanism of N-CoRon osteogenic differentiation of rat MSCs. The results showed that MSCs cultured in osteogenic medium successfully differentiated into osteogenic cells. Overexpression of N-CoR decreased cell proliferation, alkaline phosphatase (ALP)activity, calcium accumulation, mRNA expression of genes including bone sialoprotein (BSP), osteocalcin (OCN), osteopontin (OPN), Osterix and Runx2, and protein expression of phosphor-Akt(pAkt). Conversely, knocking down cellular N-CoR by small interfering RNA (siRNA) promoted pAkt activity and cell differentiation. Overexpression or knockdown of N-CoRhad no significant influences on the protein expression of pyruvate dehydrogenase kinase isozyme 1 (PDK1), phosphatidylinositol 3-kinase (PI3K) and total Akt, indicating that N-CoR regulated the changes in the PI3K/Akt signaling pathway by targeting pAkt. To further prove the function of the PI3K/Akt signaling in N-CoR-regulated osteogenic differentiation, we used the PI3K inhibitor (LY294002) to block the activation of the PI3K/Akt pathway and found that overexpression of N-CoR showed no effects on ALP activity, calcium level and mRNA expression of BSP, osteocalcin OCN, OPN, Osterix and Runx2 in rat MSCs following the inhibition of the PI3K/Akt pathway. These findings suggest that N-CoR regulates osteogenic differentiation of rat MSCs through suppression of the PI3K/Akt signaling pathway.