FoxO transcription factors regulate urea cycle through Ass1

Area of Science:

• Biochemistry
• Molecular Biology
• Metabolic Regulation

Background:

• High-protein diets increase amino acid degradation and nitrogen excretion via urea cycle enzymes in the liver.
• Krüppel-like factor 15 (KLF15) is a known regulator of amino acid catabolism and ureagenesis.
• FoxO transcription factors are identified as upstream regulators of KLF15 in hepatic amino acid metabolism.

Purpose of the Study:

• To investigate the role of FoxO transcription factors in hepatic amino acid metabolism, particularly ureagenesis, under high-protein diet conditions.
• To elucidate the relationship between FoxOs, KLF15, and the regulation of urea cycle enzymes in response to dietary protein intake.

Main Methods:

• Knockdown of FoxOs in mice to assess effects on urea cycle-related amino acids (arginine, ornithine).
• Utilized KLF15 knockout mice and an in vivo Ad-luc reporter system to examine FoxO regulation of hepatic Ass1 expression.
• Chromatin immunoprecipitation (ChIP) analysis to evaluate FoxOs DNA binding and nuclear protein levels under high-protein diet.

Main Results:

• FoxOs knockdown significantly altered arginine and ornithine concentrations, key urea cycle amino acids.
• FoxOs were confirmed to directly regulate hepatic Ass1 expression independently of KLF15 under high-protein intake.
• High-protein diet enhanced FoxOs DNA binding activity without changing their nuclear protein levels.

Conclusions:

• FoxO transcription factors play a direct role in regulating ureagenesis through a KLF15-independent pathway in response to high-protein diets.
• This study identifies a novel mechanism by which FoxOs control nitrogen excretion, contributing to the understanding of metabolic adaptation to dietary protein.