Does IGF-I stimulate pancreatic islet cell growth?

Area of Science:

• Endocrinology
• Metabolism
• Molecular Biology

Background:

• Insulin-like growth factor I (IGF-I) and its receptor (IGF-IR) are present in pancreatic islet cells.
• IGF-I was traditionally viewed as a growth factor for islet cells, promoting DNA synthesis and preventing beta-cell destruction.

Purpose of the Study:

• To re-evaluate the role of IGF-I in islet cell development and function.
• To investigate the complex regulatory mechanisms of IGF-I in the endocrine pancreas.

Main Methods:

• Analysis of gene-targeted mouse models with specific gene knockouts (e.g., insulin receptor, IGF-IR, IGF-I).
• Evaluation of liver- and pancreatic-specific IGF-I deficiency (LID and PID mice).
• Consideration of gene redundancy, indirect effects, and ligand-receptor cross-activations within the insulin/IGF family.

Main Results:

• Early embryonic inactivation of insulin receptor and IGF-IR, or IGF-I and IGF-II, showed no impact on islet cell development.
• Specific inactivation of IGF-IR in beta cells did not alter beta-cell mass.
• Liver- and pancreatic-specific IGF-I deficiency suggested an inhibitory role for IGF-I on islet cell growth, potentially via growth hormone or Reg gene regulation.

Conclusions:

• Locally produced and systemic IGF-I may not positively regulate islet cell growth.
• IGF-I might act as a negative regulator of islet cells through various pathways including growth hormone and insulin release, hyperglycemia, and Reg gene expression.
• These findings challenge the established view and complicate the therapeutic use of IGF-I for beta-cell loss.