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Am J Physiol Endocrinol Metab 294: E928-E938, 2008. First published February 12, 2008; doi:10.1152/ajpendo.00606.2007
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A general and islet cell-enriched overexpression of IGF-I results in normal islet cell growth, hypoglycemia, and significant resistance to experimental diabetes

Katie Robertson,1 Yarong Lu,1 Kristine De Jesus,1 Bing Li,1 Qing Su,1 P. Kay Lund,2 and Jun-Li Liu1,3

1Fraser Laboratories for Diabetes Research, Department of Medicine, McGill University Health Centre, Montreal, Quebec, Canada; 2Department of Cell and Molecular Physiology, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina; and 3Montreal Diabetes Research Centre, Montreal, Quebec, Canada

Submitted 18 September 2007 ; accepted in final form 5 February 2008

Insulin-like growth factor I (IGF-I) is normally produced from hepatocytes and various other cells and tissues, including the pancreas, and is known to stimulate islet cell replication in vitro, prevent Fas-mediated β-cell destruction and delay the onset of diabetes in nonobese diabetic mice. Recently, however, the notion that IGF-I stimulates islet cell growth has been challenged by the results of IGF-I and receptor gene targeting. To test the effects of a general, more profound increase in circulating IGF-I on islet cell growth and glucose homeostasis, we have characterized MT-IGF mice, which overexpress the IGF-I gene under the metallothionein I promoter. In early reports, a 1.5-fold-elevated serum IGF-I level caused accelerated somatic growth and pancreatic enlargement. We demonstrated that the transgene expression, although widespread, was highly concentrated in the β-cells of the pancreatic islets. Yet, islet cell percent and pancreatic morphology were unaffected. IGF-I overexpression resulted in significant hypoglycemia, hypoinsulinemia, and improved glucose tolerance but normal insulin secretion and sensitivity. Pyruvate tolerance test indicated significantly suppressed hepatic gluconeogenesis, which might explain the severe hypoglycemia after fasting. Finally, due to a partial prevention of β-cell death against onset of diabetes and/or the insulin-like effects of IGF-I overexpression, MT-IGF mice (which overexpress the IGF-I gene under the metallothionein I promoter) were significantly resistant to streptozotocin-induced diabetes, with diminished hyperglycemia and prevention of weight loss and death. Although IGF-I might not promote islet cell growth, its overexpression is clearly antidiabetic by improving islet cell survival and/or providing insulin-like effects.

pancreatic islets; streptozotocin; metallothionein promoter; gluconeogenesis; insulin-like growth factor I


Address for reprint requests and other correspondence: J.-L. Liu, Fraser Laboratories, Rm. M3-15, Royal Victoria Hospital, 687 Pine Ave. West, Montreal, QC, Canada H3A 1A1 (e-mail: jun-li.liu{at}mcgill.ca)






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