Marrow adipocytes inhibit the differentiation of mesenchymal stem cells into osteoblasts via suppressing BMP-signaling.
BACKGROUND
Reduced bone formation is associated with increased bone marrow fat in many bone-loss related diseases including aging, post-menopause, and anorexia nervosa. Several lines of evidence suggested the regulation of osteogenesis and adipogenesis of the bone marrow-derived mesenchymal (skeletal) stem cells (BMSCs) by paracrine mediators. This study aimed to investigate the impact of adipocytes-secreted factors on the cell proliferation and osteoblast differentiation of BMSCs.


METHODS
Serum free conditioned medium (CM-Adipo) was collected from stromal ST2 cells-derived adipocytes. Cell viability, quantitative alkaline phosphatase (ALP) activity assay, Alizarin red staining for matrix mineralization and osteogenic gene array expression were performed to determine the effect of CM-Adipo on cell proliferation and osteoblast differentiation of primary murine BMSCs (mBMSCs). Regulation of BMPs and NF-κB signaling pathways by CM-Adipo were detected by Western blot analysis and gene reporter assay.


RESULTS
CM-Adipo showed no effect on cell viability/proliferation of primary mBMSCs as compared to CM-control. On the other hand, CM-Adipo significantly inhibited the commitment of mBMSCs into osteoblastic cell lineage in dose-dependent manner. CM-Adipo was found to dramatically inhibit the BMP2-induced osteoblast differentiation and to activate the inflammatory NF-κB signaling in mBMSCs. Interestingly, treatment of mBMSCs with the selective inhibitor of NF-κB pathway, BAY11-770682, showed to retrieve the inhibitory effect of CM-Adipo on BMP2-induced osteoblast differentiation in mBMSCs.


CONCLUSIONS
Our data demonstrated that the marrow adipocytes exert paracrine inhibitory effect on the osteoblast differentiation of mBMSCs by blocking BMPs signaling in a mechanism mediated by adipokines-induced NF-κB pathway activation.
Molecular Endocrinology Laboratory (KMEB), Department of Endocrinology, Odense University Hospital and University of Southern Denmark, Odense, Denmark. babdallah@health.sdu.dk.|Department of Biological Sciences, College of Science, King Faisal University, Hofuf, Saudi Arabia. babdallah@health.sdu.dk.|Faculty of Science, Helwan University, Cairo, Egypt. babdallah@health.sdu.dk.
Basem M
BM
Abdallah
D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D001854:Bone Marrow Cells / Q000166:cytology / Q000378:metabolism*; D055396:Bone Morphogenetic Protein 2 / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D018920:Coculture Techniques; D008297:Male; D059630:Mesenchymal Stem Cells / Q000166:cytology / Q000378:metabolism*; D051379:Mice; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism*; D015398:Signal Transduction
C525719:Bmp2 protein, mouse; D055396:Bone Morphogenetic Protein 2
Adipocyte; BMSCs; Mesenchymal stem cells; Osteoblast; Paracrine factors; osteoblast differentiation