Adaptor protein APPL1 coordinates HDAC3 to modulate brown adipose tissue thermogenesis in mice

The activation of brown adipose tissue (BAT) is considered as a promising therapeutic target for obesity. APPL1 (Adaptor protein containing the Pleckstrin homology domain, Phosphotyrosine binding domain and Leucine zipper motif) is an intracellular adaptor protein and its genetic variation is correlated with BMI and body fat distribution in diabetic patients. However, little is known about the roles of APPL1 in BAT thermogenesis.

In this study, adipose tissue specific knockout (ASKO) mice were generated to evaluate APPL1's role in BAT thermogenesis in vivo, and possible signaling pathways were further explored in cultured brown adipocytes.

After high fat diet challenge, APPL1 ASKO mice developed more severe obesity, glucose intolerance and insulin resistance compared with control mice. Metabolic cage study showed that APPL1 deficiency impaired energy expenditure and adaptive thermogenesis in ASKO mice. PET-CT analysis showed decreased standardized uptake value (SUV) in the inter-scapular region which indicated impaired BAT activity in ASKO mice. Further study showed deletion of APPL1 attenuated brown fat specific gene expression, such as UCP1 and PGC1α in both BAT and brown adipocytes. In cultured brown adipocytes, upon cAMP stimulation, APPL1 shuttled from cytosol to nuclei. Co-IP and ChIP study showed that APPL1 could directly interact with histone deacetylase 3 (HDAC3) to mediate chromatin remodeling and UCP1 gene expression.

Our data demonstrated the essential role of APPL1 in regulating brown adipocytes thermogenesis via interaction with HDAC3, which may have potential therapeutic implications for treatment of obesity.