Genetic increase in serum Insulin-like Growth Factor-I (IGF-I) in C3H/HeJ compared with C57BL/6J mice is associated with increased transcription from the IGF-I exon 2 promoter

Martin L. Adamo, Xiuye Ma, Cheryl L. Ackert-Bicknell, Leah Rae Donahue, Wesley G. Beamer, Clifford J. Rosen

Research output: Contribution to journalArticle

30 Scopus citations

Abstract

C3H/HeJ (C3H) mice exhibit 30-40% higher serum IGF-I than do C57BL/6J (B6) mice, in association with increased bone mineral density and strength. These differences are inherited and thus provide a model for determining molecular mechanisms for genetic variation of serum IGF-I and downstream actions. We now report that increased serum IGF-I in C3H mice is associated with increased transcription from the minor exon 2 promoter in liver from female and male mice. The increase in hepatic IGF-I gene expression caused by increased abundance of IGF-I mRNA transcribed from the exon 2 promoter can quantitatively account for the increased serum IGF-I in C3H mice. Also, levels of both Ea and Eb IGF-I mRNAs are increased in livers of male C3H mice. Fasting lowered serum IGF-I and liver IGF-I mRNA levels in female mice of both strains. However, serum IGF-I and liver IGF-I mRNA levels remained higher in fasted C3H mice compared with fasted B6 mice. Levels of IGF-I transcripts initiated from exon 2 are also significantly increased in skeletal muscle, fat, ovaries, and kidneys of C3H mice. IGF binding protein (IGFBP)-5 mRNA levels are significantly higher in muscle and fat of C3H mice than in B6 mice. Levels of exon 1-containing transcripts are increased in whole femurs of male and female C3H mice. We conclude that increased transcription of the IGF-I gene occurs in a promoter- and tissue-specific manner in C3H mice. The increased IGF binding protein-5 mRNA levels in fat and muscle suggest that IGF-I signaling is increased in these tissues in C3H mice.

Original languageEnglish (US)
Pages (from-to)2944-2955
Number of pages12
JournalEndocrinology
Volume147
Issue number6
DOIs
StatePublished - Jun 1 2006

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ASJC Scopus subject areas

  • Endocrinology

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