Murine Mesenchymal Stem Cell Commitment to Differentiation Is Regulated by Mitochondrial Dynamics

Abstract

Mouse skin mesenchymal stem cells (msMSCs) are dermis CD105(+) CD90(+) CD73(+) CD29(+) CD34(-) mesodermal precursors which, after in vitro induction, undergo chondro, adipo, and osteogenesis. Extensive metabolic reconfiguration has been found to occur during differentiation, and the bioenergetic status of a cell is known to be dependent on the quality and abundance of the mitochondrial population, which may be regulated by fusion and fission. However, little is known regarding the impact of mitochondrial dynamics on the differentiation process. We addressed this knowledge gap by isolating MSCs from Swiss female mice, inducing these cells to differentiate into osteo, chondro, and adipocytes and measuring changes in mass, morphology, dynamics, and bioenergetics. Mitochondrial biogenesis was increased in adipogenesis, as evaluated through confocal microscopy, citrate synthase activity, and mtDNA content. The early steps of adipo and osteogenesis involved mitochondrial elongation, as well as increased expression of mitochondrial fusion proteins Mfn1 and 2. Chondrogenesis involved a fragmented mitochondrial phenotype, increased expression of fission proteins Drp1, Fis1, and 2, and enhanced mitophagy. These events were accompanied by profound bioenergetic alterations during the commitment period. Moreover, knockdown of Mfn2 in adipo and osteogenesis and the overexpression of a dominant negative form of Drp1 during chondrogenesis resulted in a loss of differentiation ability. Overall, we find that mitochondrial morphology and its regulating processes of fission/fusion are modulated early on during commitment, leading to alterations in the bioenergetic profile that are important for differentiation. We thus propose a central role for mitochondrial dynamics in the maintenance/commitment of mesenchymal stem cells.