The Cell Junction Protein Afadin Negatively Regulates Insulin Action and Modulates Adipose Tissue Function

Abstract

Adipose tissue dysfunction is one of the main culprits triggering metabolic imbalance associated with obesity. We identified the cell junction protein Afadin as one of the most highly phosphorylated proteins in response to insulin/IGF-1 stimulation using quantitative phospho-proteomic analysis in pre-adipocytes, and investigated the role of Afadin in mediating insulin action and in adipocyte biology. We found that phosphorylation of Afadin occurred in response to insulin in both pre- and mature adipocytes obtained from mice and human subjects. In addition, Afadin phosphorylation was observed in mouse adipose tissues following insulin injection, and after re-feeding, indicating physiological relevance. In obese mice, however, brown fat insulin-induced phosphorylation of Afadin was abolished. Surprisingly, glucose and insulin tolerance were improved in Fat-specific Afadin knock-out (KO) mice on a high fat diet, despite similar body weight gain and adipose mass as wild type controls. Furthermore, ablation of Afadin in vitro did not affect adipogenesis. Yet, prolonged insulin-induced phosphorylation of Akt was observed in KO adipocytes, and was associated with increased insulin-mediated fatty-acid uptake. Finally, phosphorylation of Afadin regulates the docking of several proteins, which may be involved in the regulation of insulin action and adipocyte metabolism. Thus, Afadin is a novel bona fide substrate of the insulin signaling pathway, and is involved in the regulation of insulin action and metabolism. Disclosure M. Lundh: None. M.S. Isidor: None. K. Plucinska: None. F. Shamsi: None. P. Petersen: None. Y. Tseng: Other Relationship; Self; Chugai Pharmaceutical Co., Ltd.. Research Support; Self; MedImmune. B. Emanuelli: None.