Regulation of IGFBP-2 expression during fasting

Area of Science:

• Metabolic regulation
• Molecular endocrinology
• Gene transcription

Background:

• Insulin-like growth factor (IGF)-binding protein-2 (IGFBP-2) attenuates IGF-1 action and is implicated in metabolic disorder prevention.
• The precise regulatory mechanisms governing IGFBP-2 expression, particularly during metabolic stress like fasting, are not fully understood.
• Understanding IGFBP-2 regulation is crucial for deciphering its role in metabolic homeostasis.

Purpose of the Study:

• To elucidate the transcriptional regulation of the Igfbp-2 gene by peroxisome-proliferator-activated receptor (PPAR) α in the liver.
• To investigate the role of PPARα in modulating Insulin-like growth factor 1 (IGF-1) signaling.
• To determine the direct interaction between PPARα and the Igfbp-2 gene promoter.

Main Methods:

• Analysis of Igfbp-2 and PPARα expression levels in liver during fasting.
• Treatment of primary cultured hepatocytes with Wy14643 (a selective PPARα agonist) and assessment of Igfbp-2 gene expression.
• Gene expression analysis in Pparα null mice under fasting conditions and Wy14643 treatment.
• Transient transfection and chromatin immunoprecipitation assays to confirm PPARα binding to the Igfbp-2 promoter.
• Assessment of IGF-1 receptor (IGF-1R) levels and Akt phosphorylation in response to Wy14643 treatment.

Main Results:

• Fasting increased both Igfbp-2 and PPARα expression in the liver.
• Wy14643 significantly induced Igfbp-2 gene expression in primary hepatocytes, an effect absent in Pparα null mice.
• PPARα directly bound to a specific region on the Igfbp-2 promoter, confirming transcriptional activation.
• Wy14643 treatment decreased IGF-1R levels and Akt phosphorylation in hepatocytes, but not in those from Pparα null mice.

Conclusions:

• PPARα directly activates hepatic Igfbp-2 gene transcription, particularly during fasting.
• PPARα controls IGF-1 signaling by up-regulating hepatic IGFBP-2.
• This mechanism highlights a novel pathway linking PPARα activation to metabolic regulation via IGF-1 signaling modulation.