Adult mice (12 mo) were fed a normal diet (18% protein), as well as diets with low protein
(8%) supplemented with increasing concentrations (50, 100, and 200 uM) of kynurenine (Kyn) or
with tryptophan (Trp; 1.5 mM) for 8 weeks. Myoprogenitor cells were also treated with Trp and
Kyn in vitro to determine their effects on cell proliferation and expression of myogenic differentiation
markers.