Heat Shock Protein Inducer Suppresses Osteogenic Differentiation of Human Mesenchymal Stem Cells

The key processes determining cell differentiation are the synthesis of new proteins and restructuring of the extracellular matrix. The production of matrix and cytosolic proteins, in turn, requires the constant involvement of the heat shock protein system — chaperones that ensure the proper folding of newly synthesized protein molecules and maintain their functional state. The aim of this study was to evaluate the effect of the heat shock protein inducer geranylgeranylacetone (GGA) on the differentiation of human mesenchymal stem cells. The study found that pretreating cells with GGA for 24 hours altered the pattern of calcium responses to the pro- osteogenic stimulus, parathyroid hormone. There was an increase in the number of cells responding to anti- osteogenic calcium oscillations associated with a decrease in the osteogenic potential of MSCs. Induction of osteogenic differentiation demonstrated a decrease in calcium deposition and and gene expression. However, the addition of GGA had no significant effect on adipogenic differentiation. In search of a possible anti- osteogenic mechanism for the action of GGA, we analyzed the MSC proteomes treated with GGA or DMSO as controls. We found that incubation with GGA resulted in the absence of several proteins. Among these, calmodulin proteins (CALM1, CALM2, and CALM3), coactivators of adenylate cyclases, and proteins that regulate the actin cytoskeleton play a key role in osteogenesis. Thus, we demonstrated that the effect of GGA leads to a significant reduction in the capacity of MSCs for osteogenic, but not adipogenic, differentiation. A more detailed study of the mechanism of GGA action on embryonic and postnatal stem cells will further elucidate key features of the formation of new osteoblasts during embryogenesis and postnatal tissue renewal.