Effects of aging and calorie restriction on rat skeletal muscle glycogen synthase and glycogen phosphorylase.
Calorie restriction's (CR) effects on age-associated changes in glycogen-metabolizing enzymes were studied in rat soleus (SOL) and tibialis anterior (TA) muscles. Old (24 months) compared to young (6 months) rats maintained ad libitum on a standard diet had reduced glycogen synthase (GS) activity, lower muscle GS protein levels, increased phosphorylation of GS at site 3a with less activation in SOL. Age-associated impairments in GS protein and activation-phosphorylation were also shown in TA. There was an age-associated reduction in glycogen phosphorylase (GP) activity level in SOL, while brain/muscle isoforms (B/M) of GP protein levels were higher. GP activity and protein levels were preserved, but GP was inactivated in TA with age. Glycogen content was unchanged in both muscles. CR did not alter GS or GP activity/protein levels in young rats. CR hindered age-related decreases in GS activity/protein, unrelated to GS mRNA levels, and GS inactivation-phosphorylation; not on GP. In older rats, CR enhanced glycogen accumulation in SOL. Short-term fasting did not recapitulate CR effects in old rats. Thus, the predominant age-associated impairments on skeletal muscle GS and GP activities occur in the oxidative SOL muscle of rats, and CR can attenuate the loss of GS activity/activation and stimulate glycogen accumulation.
Montori-Grau
Marta
M
CIBER de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), Departament de Bioquímica i Biologia Molecular, IBUB, Facultat de Biologia, Universitat de Barcelona, Diagonal, 645, 08028 Barcelona, Spain.
Minor
Robin
R
Lerin
Carles
C
Allard
Joanne
J
Garcia-Martinez
Celia
C
de Cabo
Rafael
R
Gómez-Foix
Anna M
AM