Inhibition of metastasis-associated gene 1 expression affects proliferation and osteogenic differentiation of immortalized human mesenchymal stem cells

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MTA1 is known to be responsible for independent nucleosome remodelling and deacetylase complexes with ability to regulate divergent cellular pathways. However, additional biological functions have, up to now, remained largely unexplored. The present study was initiated to investigate involvement of MTA1 in osteogenic differentiation of immortalized human mesenchymal stem cells (MSCs). MSCs were examined for expression of MTA1 and stably transfected clones expressing shRNA to MTA1 were generated. Cells were grown under osteogenic and non-osteogenic conditions. Effects of silencing on cell proliferation, calcium deposition and alkaline phosphatase (ALP) activity were studied. mRNA expression of bone sialoprotein (BSP), osteopontin (OSP), runt-related transcription factor 2 (Runx2), osteocalcin (OC), collagen type I (Col1A) and ALP were analysed. Transfected cells showed reduction in proliferation and significant increase in calcium deposition and expression of osteogenic marker genes, BSP, OSP, Runx2, OC and Col1A, when they were grown under osteogenic conditions. Under non-osteogenic conditions, expression of BSP and OSP were also markedly upregulated, whereas expression of osteogenic marker genes, Runx2, OC and Col1A, was almost unaffected. Expression of ALP was slightly suppressed under non-osteogenic conditions but significantly increased under osteogenic differentiation conditions, as assessed by enzyme activity and mRNA expression assays. Our data collectively suggest that endogenously produced MTA1 constrains osteogenic differentiation of MSCs and that targeting of this molecule may provide a novel strategy for enhancing bone regeneration.