200-LB: Persistent cAMP Signaling Induces Adipocyte Browning through Biphasic Transcriptional and Epigenetic Remodeling

Beige adipocytes are inducible thermogenic cells formed in response to cold exposure and other environmental cues within white adipose tissue. Their capacity to produce heat would provide metabolic benefits against obesity and type 2 diabetes; however, the mechanisms underlying beige adipocyte recruitment, so-called adipocyte browning, induced by different stimuli remain unclear. Using our new adipocyte cell line with improved browning potentials, we compared adipocyte browning responses induced by cAMP (forskolin) versus PPARɣ activation (rosiglitazone) . Time-course RNA-seq revealed that chronic activation of cAMP but not PPARɣ resulted in a biphasic response. The cAMP signaling promoted tissue remodeling at the early phase and subsequently activated energy metabolism while inhibiting cell cycle, which resembles the kinetics of in vivo cold-induced browning. Those late-phase changes were highly correlated with those by PPARɣ activation. Consistently, the cAMP-driven effects were abolished by treatment with PPARɣ antagonists, suggesting PPARɣ as a converging point of its thermogenic actions. Assay for transposase-accessible chromatin sequencing (ATAC-seq) revealed unique dynamics of chromatin landscape distinct from transcriptional changes during cAMP-induced browning. Chromatin at early-induced genes opened acutely and stayed open until the late phase despite the rapid return of gene expression. The chromatin regions at late-induced genes also opened early, preceding transcriptional activation. Using a motif discovery method, we identified NFIL3 that was enriched in both early and late phases of cAMP-induced browning. Reduced thermogenic gene expression and mitochondrial respiration by NFIL3 knockdown suggest NFIL3 as a putative transcription factor mediating the biphasic response of adipocyte browning. These findings define new mechanisms that orchestrate transcriptional and epigenetic remodeling underlying beige adipocyte formation. Disclosure J. So: None. S. Taleb: None. J. Wann: None. O. Strobel: None. H. Roh: None. Funding American Diabetes Association (7-21-JDF-056) , National Institute of Health (DK129289)