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Muscle mechano growth factor is preferentially induced by growth hormone in growth hormone‐deficient lit/lit mice
Author(s) -
Iida Keiji,
Itoh Emina,
Kim DongSun,
Del Rincon Juan P.,
Coschigano Karen T.,
Kopchick John J.,
Thorner Michael O.
Publication year - 2004
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2004.069500
Subject(s) - growth hormone receptor , medicine , endocrinology , skeletal muscle , growth factor , gene isoform , insulin like growth factor , biology , receptor , messenger rna , hormone , basal (medicine) , gene expression , chemistry , growth hormone , insulin , gene , biochemistry
Two muscle insulin‐like growth factor‐I (IGF‐I) mRNA splice variants (IGF‐IEa and IGF‐IEb) have been identified in rodents. IGF‐IEb, also called mechano growth factor (MGF) has been found to be upregulated by exercise or muscle damage. Growth hormone (GH) is the principal regulator of IGF‐I expression in several tissues including skeletal muscle. Therefore, we investigated the effect of chronic GH excess or disruption of GH receptor (GHR) signalling, and the acute effect of GH administration on expression of muscle IGF‐I isoforms using transgenic mice that express bovine GH (bGH), GHR gene‐disrupted (GHR–/–) mice and GH‐deficient lit/lit mice before and after exogenous GH administration. MGF mRNA in skeletal muscle was increased in bGH mice whereas it was decreased in GHR–/– mice compared with control animals. Exogenous GH administration to dwarf lit/lit mice significantly increased muscle MGF but not IGF‐IEa mRNA 4 h after treatment. Twelve hours after GH treatment, both MGF and IGF‐IEa mRNAs in muscle were increased compared with vehicle‐treated lit/lit mice. In contrast in GH‐sufficient lit/+ mice, both MGF and IGF‐IEa mRNAs were increased 4 h after and returned to the basal level 12 h after GH treatment. Hepatic IGF‐I isoforms were regulated in parallel by GH. Thus, our results demonstrated that: (1) MGF mRNA in skeletal muscle is expressed in parallel with GH action; (2) MGF mRNA in muscle is produced preferentially in the situation of GH deficiency in contrast to the pattern in the GH‐sufficient state; and (3) the induction of IGF‐I isoforms by GH is tissue‐specific.