Oxygen-mediated regulation of skeletal muscle satellite cell proliferation and adipogenesis in culture

Major problems in stem cell biology revolve around defining the developmental potential of cell populations and understanding how their potential is maintained or progressively restricted. Oxygen (O(2)) is an obvious environmental factor which has received little attention in culturing skeletal muscle progenitor cells. In this work, we examine the effects of O(2) levels on the developmental potential, proliferative capacity, and phenotype of the adult skeletal muscle fiber progenitor population (satellite cells), and cell lines that model multipotential embryonic paraxial mesoderm from which skeletal muscle develops. Both satellite cell proliferation and survival of mature fibers increased in physiologic (6%) O(2) vs. non-physiologic 20% O(2) used in virtually all traditional cell culture. Six percent O(2) conditions also accelerated the up-regulation of multiple MyoD family myogenic regulatory factors (MRFs). An unexpected finding was that fiber-adherent satellite cells could assume a non-myogenic phenotype. By the criteria of molecular markers and gross lipid accumulation, satellite cells were found to assume an adipocyte phenotype, and did so more prominently in 20% O(2) than in physiologic O(2). Selection of the adipogenic fate and execution of adipogenesis by multipotential mesenchymal cell lines was also dramatically higher in traditional 20 vs. 6% O(2), and decreased adipogenesis in physiologic O(2) was associated with significantly less expression of the adipogenic regulator, PPAR gamma. These results suggest that regulatory pathways affected by O(2) are important for satellite cell proliferation, execution of cell fate, and parent muscle survival in culture, and so may play a role in vivo under normal or pathologic conditions.