Lack of CUL4B in Adipocytes Promotes PPARγ-Mediated Adipose Tissue Expansion and Insulin Sensitivity

Area of Science:

• Biochemistry
• Molecular Biology
• Metabolic Research

Background:

• Obesity and associated diseases involve dysregulated peroxisome proliferator-activated receptor γ (PPARγ) signaling.
• Understanding PPARγ regulators is key to combating obesity.
• Ubiquitin E3 ligases targeting PPARγ and their in vivo functions remain largely uncharacterized.

Purpose of the Study:

• To identify ubiquitin E3 ligases that regulate PPARγ stability and function.
• To investigate the role of CUL4B-RING E3 ligase (CRL4B) in PPARγ degradation.
• To determine the in vivo effects of CRL4B on adipogenesis and metabolic phenotypes.

Main Methods:

• Investigated CRL4B's interaction with PPARγ.
• Assessed PPARγ polyubiquitination and proteasomal degradation upon CUL4B manipulation.
• Generated adipocyte-specific Cul4b knockout (AKO) mice.
• Analyzed metabolic phenotypes, including body fat, insulin sensitivity, and glucose tolerance in AKO mice on a high-fat diet.

Main Results:

• CRL4B promotes PPARγ polyubiquitination and proteasomal degradation, negatively regulating PPARγ.
• Depletion of CUL4B upregulates PPARγ-regulated genes and enhances adipogenesis.
• Adipocyte-specific Cul4b knockout mice on a high-fat diet show increased adipogenesis and body fat accumulation.
• AKO mice exhibit improved insulin sensitivity, glucose tolerance, and reduced adipose tissue inflammation.

Conclusions:

• CRL4B plays a critical role in regulating PPARγ stability and adipogenesis.
• Inhibition of CRL4B mimics the beneficial metabolic effects of PPARγ agonists.
• CRL4B represents a potential therapeutic target for obesity and related metabolic syndromes.