No effect of aging on skeletal muscle insulin-like growth factor mRNAs.
This study examined the hypothesis that during aging insulin-like growth factor (IGF) mRNAs are reduced in skeletal muscle. IGF-I, IGF-II, and IGF-binding protein-5 (IGFBP-5) mRNAs were measured with a ribonuclease protection assay in the gastrocnemius of specific pathogen-free Fischer-344 rats. We hypothesized that IGF-I, IGF-II, and IGFBP-5 mRNA concentration (normalized to 18S RNA) in the gastrocnemius muscle of growing animals (3 mo) would be downregulated in a coordinated manner with muscle size during aging-associated atrophy. As indicated by muscle wet weight and total protein content, the gastrocnemius muscle was growing in the 3-mo group (P < 0.01 smaller compared with 12 mo), fully developed at 12 mo, and was atrophied at 24 mo of age (P < 0.05 compared with 12 mo). IGF-I mRNA concentration in the gastrocnemius of 12- and 24-mo-old rats was 39-49% less than in 3-mo-old rats (P < 0.05). Contrary to our hypothesis, there was not a significant skeletal muscle IGF-I mRNA difference between middle age (12 mo) and senescence (24 mo). Thus IGF-I mRNA changed during maturation (3-12 mo) but not during aging (12-24 mo). Skeletal muscle IGF-II mRNA concentration was not different among 3-, 12-, and 24-mo-old animals. Furthermore, animal age did not have an effect on IGFBP-5 mRNA concentration. We conclude that the aging-associated atrophy of skeletal muscle is not caused by altered pretranslational regulation of IGF-I, IGF-II, or IGFBP-5 in skeletal muscle.
Hamilton
M T
MT
Department of Integrative Biology, University of Texas Medical School, Houston 77030, USA.
Marsh
D R
DR
Criswell
D S
DS
Lou
W
W
Booth
F W
FW
D000375:Aging / Q000378:metabolism*; D000818:Animals; D001483:Base Sequence; D001835:Body Weight; D008969:Molecular Sequence Data; D018482:Muscle, Skeletal / Q000033:anatomy & histology / Q000378:metabolism*; D015345:Oligonucleotide Probes / Q000235:genetics; D009929:Organ Size; D012333:RNA, Messenger / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D013002:Somatomedins / Q000235:genetics*
D015345:Oligonucleotide Probes; D012333:RNA, Messenger; D013002:Somatomedins