Targeted expression of human growth hormone gene to the fat or to the cartilage in spontaneous dwarf rats.

2005 Fiscal Year Final Research Report Summary

• Project/Area Number: 15590982
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Single-year Grants
• Section: 一般
• Research Field: Endocrinology
• Research Institution: University of Miyazaki (2004-2005); 宮崎医科大学 (2003)
• Principal Investigator: KATAKAMI Hideki The University of Miyazaki, Graduate School, Department of Medicine, Lecturer (50204417)
• Project Period (FY): 2003 – 2005
• Keywords: fat cell-specific hGH expression / chondrocyte-specific hGH expression GH of fat cells / development and differentiation by / hGH-transgenic rats / leptin gene / alphal-collagene gene / IGF-1-independent GH action

Research Abstract

A strain of spontaneous dwarf rats (SDR, dr) is discovered and fully characterized in Japan. They are small and short caused by a point mutation at the splice junction between the third intron and the forth exon of the rat GH gene, which was identified by us and others. They provide us an opportunity to study the IGF-1-independent GH actions to various tissues, such as fat and cartilage. In order to elucidate the IGF-1-independent direct actions of growth hormone to the fat tissue or cartilage, we first generated kimeric genes of the human GH gene (2.1kbp) coupled with leptin gene promoter (-3.5kbp, Lep-hGH : 5.7kbp) or human alpha 1-collagne gene promoter (-5.2kbp, α 1C-hGH : 7.3kbp). By injecting the Lep-hGH gene and frozen sperm into oocytes of dr, we successfully generated a line of human GH-transgenic dr with targeted expression to the fat tissue (Lep-hGH-dr). Lep-hGH-dr expressed hGH not only in fat tissues, but also in testes or ovaries. Small amounts of the hGH gene expressed in the stomach, adrenal and kidney. Lep-hGH-dr showed increased both in weight (1.3-1.5 times, vs. control dr) and body fat (140-150%, vs. control dr). Serum hGH levels in Lep-hGH-dr were detectable by an ultrasensitive EIA, 8.1-949.1pg/ml.
Routine bacteriological examination detected contamination with M. pulmonis in the transgenic rat colony. All of the transgenic rats, including Lep-hGH-dr, were sacrificed. Subsequent physiological and histological analyses of Lep-hGH-dr, and generation of α 1C-hGH-dr were both terminated.
Based on these results, we conclude that the segment of -2.4kbp upstream promoter of human leptin gene is sufficient to target the hGH gene expression to the fat tissue. The questions have remained unsolved, i.e., whether insufficient amount of expressed hGH gene in the fat or low levels of circulating hGH resulted in unexpected obesity and modest acceleration of growth in Lep-hGH-dr.