Secreted Clusterin protein inhibits osteoblast differentiation of bone marrow mesenchymal stem cells by suppressing ERK1/2 signaling pathway

Bone. 2018 May;110:221-229. doi: 10.1016/j.bone.2018.02.018. Epub 2018 Feb 21.

Abstract

Secreted Clusterin (sCLU, also known as Apolipoprotein J) is an anti-apoptotic glycoprotein involved in the regulation of cell proliferation, lipid transport, extracellular tissue remodeling and apoptosis. sCLU is expressed and secreted by mouse bone marrow-derived skeletal (stromal or mesenchymal) stem cells (mBMSCs), but its functional role in MSC biology is not known. In this study, we demonstrated that Clusterin mRNA expression and protein secretion in conditioned medium increased during adipocyte differentiation and decreased during osteoblast differentiation of mBMSCs. Treatment of mBMSC cultures with recombinant sCLU protein increased cell proliferation and exerted an inhibitory effect on the osteoblast differentiation while stimulated adipocyte differentiation in a dose-dependent manner. siRNA-mediated silencing of Clu expression in mBMSCs reduced adipocyte differentiation and stimulated osteoblast differentiation of mBMSCs. Furthermore, the inhibitory effect of sCLU on the osteoblast differentiation of mBMSCs was mediated by the suppression of extracellular signal-regulated kinase (ERK1/2) phosphorylation. In conclusion, we identified sCLU as a regulator of mBMSCs lineage commitment to osteoblasts versus adipocytes through a mechanism mediated by ERK1/2 signaling. Inhibiting sCLU is a possible therapeutic approach for enhancing osteoblast differentiation and consequently bone formation.

Keywords: Adipocyte; BMSCs; Clusterin; Mesenchymal stem cells; Osteoblast; Osteoblast differentiation; sCLU.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adipocytes / cytology
  • Adipocytes / metabolism
  • Alkaline Phosphatase / genetics
  • Alkaline Phosphatase / metabolism
  • Animals
  • Blotting, Western
  • Cell Differentiation / physiology
  • Cells, Cultured
  • Clusterin / metabolism*
  • Enzyme-Linked Immunosorbent Assay
  • MAP Kinase Signaling System / physiology*
  • Male
  • Mesenchymal Stem Cells / cytology*
  • Mesenchymal Stem Cells / metabolism*
  • Mice
  • Mice, Inbred C57BL
  • Osteoblasts / cytology*
  • Osteoblasts / metabolism*
  • Signal Transduction / physiology

Substances

  • Clusterin
  • Alkaline Phosphatase