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

Major problems in stem cell biology revolve around defining the development al potential of cell populations and understanding how their potential is m aintained or progressively restricted. Oxygen (O-2) is an obvious environme ntal factor which has received little attention in culturing skeletal muscl e progenitor cells. In this work, we examine the effects of O-2 levels on t he developmental potential, proliferative capacity, and phenotype of the ad ult skeletal muscle fiber progenitor population (satellite cells), and cell lines that model multipotential embryonic paraxial mesoderm from which ske letal muscle develops. Both satellite cell proliferation and survival of ma ture fibers increased in physiologic (6%) O-2 vs non-physiologic 20% O-2 us ed in virtually all traditional cell culture. Six percent O-2 conditions al so accelerated the up-regulation of multiple MyoD family myogenic regulator y factors (MRFs). An unexpected finding was that fiber-adherent satellite c ells could assume a non-myogenic phenotype. By the criteria of molecular ma rkers and gross lipid accumulation, satellite cells were found to assume an adipocyte phenotype, and did so more prominently in 20% O-2 than in physio logic O-2. Selection of the adipogenic fate and execution of adipogenesis b y multipotential mesenchymal cell lines was also dramatically higher in tra ditional 20 vs. 6% O-2, and decreased adipogenesis in physiologic O-2 was a ssociated with significantly less expression of the adipogenic regulator, P PAR gamma. These results suggest that regulatory pathways affected by O-2 a re important for satellite cell proliferation, execution of cell fate, and parent muscle survival in culture, and so may play a role in vivo under nor mal or pathologic conditions. (C) 2001 Wiley-Liss, Inc.