Modulation of IGF mRNA abundance during muscle denervation atrophy.
Changes in skeletal muscle activity cause dramatic alterations in muscle mass. Increased load on a muscle (synergistic overload) results in muscle hypertrophy. During hypertrophy, skeletal muscle concentrations of insulin-like growth factors (IGF-I and IGF-II) mRNAs increase. To clarify the role of IGFs in regulating muscle mass, this study examined whether IGF-I and -II mRNA levels were altered during decreased muscle activity (denervation). Gastrocnemius weights decreased 4.2%, 7.7%, 18.1%, 27.7%, 35.1%, 45.0%, and 60.3% at 2, 3, 5, 7, 10, 12, and 17 d following denervation, respectively. Muscle DNA content remained constant throughout the first 12 d after surgery, but increased above control levels at day 17. During the first week after surgery, gastrocnemius IGF-II mRNA remained constant. However, IGF-II mRNA abundance was 2.5-fold greater than controls by 10 d of denervation, 3-fold by 12 d, and 6.8-fold by 17 d. On the other hand, IGF-I mRNA levels were not affected by denervation. In conclusion, although increased muscle activity results in a change of IGF-I mRNA expression, decreased muscle activity has no effect on IGF-I mRNA expression. In contrast, IGF-II mRNA levels increase with long-term denervation as well as with increased muscle activity. This study suggests that muscle activity may not be the only factor affecting IGF-I and -II expression.
Czerwinski
S M
SM
Department of Animal Sciences, University of Illinois, Urbana 61801.
Novakofski
J
J
Bechtel
P J
PJ
D000818:Animals; D002455:Cell Division; D004247:DNA / Q000032:analysis / Q000096:biosynthesis; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000032:analysis / Q000235:genetics*; D007335:Insulin-Like Growth Factor II / Q000032:analysis / Q000235:genetics*; D009119:Muscle Contraction; D009121:Muscle Denervation; D009133:Muscular Atrophy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009929:Organ Size; D012333:RNA, Messenger / Q000032:analysis*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
D012333:RNA, Messenger; D007334:Insulin-Like Growth Factor I; D007335:Insulin-Like Growth Factor II; D004247:DNA