Endocrine Abstracts

The ubiquitin-proteasome cascade has been described as a critical factor in adipocyte biology, insulin signaling and obesity, but the function of Nedd8, the ubiquitin-like protein with the closest homology to ubiquitin, remains unknown. Using 3T3-L1 preadipocyte cells, we found that MLN-4924, a specific neddylation inhibitor, blocks adipocyte differentiation. Screening for signaling and transcriptional factors driving adipogenesis, we found that neddylation blockade inhibits the expression of the master genes of adipogenesis, C/EBPα and PPARγ on RNA and protein levels. In 3T3-L1 mature adipocytes, MLN-4924 treatment reduced lipid droplets content without affecting lipolysis but fatty acids uptake, a process maintained by enzymes transcriptionally controlled by PPARγ. In adipocytes, MLN-4924 also strongly reduced C/EBPα and PPARγ expression as well as the expression of multiple downstream targets of PPARγ. Importantly, the PPARγ ligand, rosiglitazone reverted MLN-4924 effects on triglycerides lost.

In addition, we performed a preliminary in vivo study in WT mice chronically treated with MLN-4924. Pharmacological blockade of neddylation in vivo prevented high fat diet (HFD)-induced body weight increase and reduced adipocytes hypertrophy. Furthermore, conditional adipocyte-specific neddylation-deficient (Nae1^{Adipo-Cre-ERT2} KO) mice showed a decrease in body weight in obese (HFD 4 months) mice accompanied by changes in glucose tolerance.

Altogether, these results suggest that the inactivation of Nedd8 in fat cell precursors or mature adipocytes severely impairs adipocyte maturation and fat storage respectively by reducing C/EBPα and PPARγ levels.

Moreover, these observations demonstrate that neddylation, a new post-translational modification in adipocytes, is physiologically active in the regulation of adipocyte development, biology and metabolism.