Fetal IGF-1 Overexposure Causes Intrinsic Pancreatic Insulin Secretion Defects

Insulin-like Growth Factor 1 (IGF-1) is crucial for fetal growth and development, but its dysregulation can impact long-term metabolic health. High IGF-1 levels in utero are sometimes associated with increased risk of insulin resistance and type 2 diabetes later in life. However, the precise mechanisms by which fetal IGF-1 overexposure directly affects the developing pancreas and its ability to secrete insulin have been unclear, especially whether the defect is intrinsic to the islet or secondary to peripheral changes. This study addresses how a sustained increase in fetal IGF-1 directly impairs pancreatic beta-cell function and glucose-stimulated insulin secretion (GSIS).

The study revealed a significant impairment in glucose-stimulated insulin secretion in IGF-1-infused fetal sheep. Specifically, GSIS was reduced by 43% compared to control animals (p<0.01), indicating a substantial functional deficit. Pancreatic islets isolated from IGF-1-treated fetuses showed an intrinsic defect, with insulin content decreased by 28% (p<0.05) and a 2.1-fold reduction in insulin gene expression. The most critical finding was that this reduction in glucose-stimulated insulin secretion was due to an intrinsic defect within the pancreatic islets themselves, rather than solely peripheral insulin resistance. Furthermore, key genes involved in beta-cell development and function, such as PDX1, were downregulated by 35% (p<0.01) in the IGF-1-exposed islets, suggesting altered transcriptional programming.