Hepatic FoxO1 ablation exacerbates lipid abnormalities during hyperglycemia

Area of Science:

• Metabolic disease
• Molecular biology
• Endocrinology

Background:

• Diabetes mellitus is associated with impaired lipid metabolism and cardiovascular disease.
• Insulin resistance and hyperglycemia are key features of diabetes with unclear roles in lipid dysregulation.
• Transcription factor Forkhead box protein 1 (FoxO1) is regulated by insulin and nutrients and plays a role in hepatic glucose production.

Purpose of the Study:

• To investigate the role of FoxO1 in regulating lipid metabolism in the diabetic liver.
• To test the hypothesis that FoxO1 controls hepatic lipid metabolism beyond its known role in glucose production.

Main Methods:

• Created mice with liver-specific deletion of FoxO1 (L-FoxO1).
• Induced hyperglycemia in L-FoxO1 mice and littermate controls using streptozotocin.
• Monitored serum lipids, very-low-density lipoprotein (VLDL) secretion, and hepatic gene expression related to lipid metabolism.

Main Results:

• Liver-specific FoxO1 ablation in hyperglycemic mice led to increased VLDL secretion, elevated cholesterol, and higher plasma free fatty acids.
• L-FoxO1 mice showed increased levels of sterol regulatory element-binding protein 2 (SREBP-2) and fibroblast growth factor 21 (FGF21) without changes in lipogenic genes.
• FoxO1 appears to fine-tune lipolysis via FGF21, and its absence increases substrates for hepatic lipid synthesis and VLDL secretion.

Conclusions:

• FoxO1 plays a protective role against excessive hepatic lipid production during hyperglycemia.
• Inhibition of FoxO1, potentially through intensive insulin treatment, may paradoxically worsen lipid abnormalities in diabetes.
• Findings suggest FoxO1 is a potential therapeutic target for managing dyslipidemia in diabetic patients.