Key regulatory genes controlling cell fate decisions of Mesenchymal Stem Cells (MSCs)

Given their biological properties, Mesenchymal Stem Cells (MSCs) represent a potentially precious therapeutic tool for clinical application. However, their optimal use depends on our understanding of the molecular mechanisms governing their expansion and differentiation, still poorly understood. The kinase receptor Kit and the transcription factor Prep1 are pleiotropic regulators playing key roles in development and differentiation of multiple tissues, including hematopoiesis. The aim of my study is to investigate whether Kit and Prep1 contribute also to the control of MSCs, particularly in their commitment and differentiation towards the osteogenic and the adipogenic lineages, as MSCs and their progeny, in particular osteoblasts, are essential components of the hematopoietic stem cell niche. As a first step, the expression profiles at the transcriptional and protein level were analyzed in undifferentiated MSCs, and during in vitro osteogenic and adipogenic differentiation. Subsequently, to gain insights into Prep1 function in mesenchymal cells, the effects of its in vivo downregulation were investigated by using hypomorphic mice exhibiting low levels of Prep1 product. The expression studies have shown that Kit and Prep1 are both expressed in undifferentiated MSCs and that their activity is inversely correlated during the adipogenic process. Furthermore, analysis of MSCs derived from a Kit/GFP transgenic mouse line indicates that regulatory elements that drive correct kit expression in hematopoietic, germ and cardiac cells are not sufficient to control kit activity in MSCs. In addition, the functional studies demonstrate that down-regulation of Prep1, while favouring in vitro adipogenesis, strongly compromise the osteogenic process, leading cells to apoptosis after osteogenic induction. Taken together, results indicate that Kit and Prep1 are involved in the regulation of murine MSCs, and provide the first evidence pointing to Prep1 as a crucial player in mesenchymal cell fate decisions.