Intrinsic properties of muscle satellite cells are changed in response to long-term selection of mice for different growth traits

Abstract.

Satellite cell cultures were derived from mice selected long-term over 70 generations for body weight (DU-6, growth), carcass protein amount (DU-6P, protein) and an index combining body weight and endurance treadmill performance (DU-6+LB, growth + fitness) at 42 days of age and from an unselected control line (DU-Ks). They were grown under identical environmental conditions to examine intrinsic cellular differences in proliferation, protein metabolism and responsiveness to growth factors. Growth kinetics (DNA and protein amounts) were determined over a 12-day period. During exponential growth, all growth-selected cultures grew faster than the control culture: (DU-6+LB=DU-6P)>DU-6>DU-Ks. The differences in DNA and protein levels were maintained until day 8. DU-Ks cultures reached similar levels as the growth (DU-6) and protein (DU-6P) cultures in terms of DNA at day 12 of cultivation. Thus, the cultures from the growth and protein lines, but not from the growth + fitness line, exhibited larger protein:DNA ratios (cell size) than the control cultures. Cell cultures from the selected lines were more responsive to serum and epidermal growth factor in terms of [³H] thymidine incorporation into DNA, whereas no stimulation by insulin or insulin-like growth factor-I was detectable in cultures from selected lines or controls. During differentiation, protein metabolism in cultures from selected lines was characterised by higher rates of protein synthesis (PS) and degradation (PD), as measured by [³H] phenylalanine incorporation or release, respectively, than in control cells. The ratios of the relative differences from the control in PS and PD were only >1.0 in the growth and protein lines. In conclusion, long-term selection for growth therefore modifies the intrinsic capability of satellite cells for proliferation and protein metabolism, with changes being dependent on the selection trait.