Leveraging Enhancer RNA to decode AKT-ChREBP Regulatory Axis for Brown Fat Formation and Function
Principle Investigator: Hee Woong Lim, PhD, Division of Biomedical Informatics
The brown adipose tissue (BAT) in humans is associated with the improvement or prevention of the primary and secondary effects of overweight and obesity. However, extensive retrospective analyses have shown that only a minuscule portion of adults sustain significant BAT amounts. In fact, BAT presence declines with age after infancy, as the incidence of metabolic and cardiovascular diseases increases. Thus, understanding the mechanism of BAT formation is of high significance to support BAT-mediated therapeutics. However, the signaling pathways and transcriptional networks essential for BAT formation and maintenance remain under-defined. In our preliminary study, the deletion of the kinases AKT1 and AKT2 surprisingly block brown adipocyte progenitor differentiation in vivo. Provocatively, the critical importance of AKT signaling for both differentiation and maintenance of BAT in vivo does not subscribe to current pre-established dogmas. These striking observations strongly indicate a novel AKT mediated mechanism essential in vivo for brown adipogenesis and survival. Our mechanistic data suggest that this is controlled by a new effector of AKT, the transcription factor ChREBPb.
We are testing our central hypothesis that the PI3K/mTOR signaling pathway control brown fat precursor through the AKT-ChREBPb axis. To this end, we are leveraging enhancer RNA (eRNA) as a tool to capture and monitor the activity of transcriptional regulatory elements along the brown adipogenesis. eRNAs are small non-coding RNAs transcribed from enhancer regions. Although their molecular functions are still elusive, they are spatially and temporally sensitive markers for enhancers. Importantly, eRNA's presence more accurately marks enhancer activity and often displays dynamic changes at enhancers, even with subtle differences in histone modification, suggesting specificity and sensitivity of eRNA actions. Despite its great potential, eRNA has been an unexplored area of regulatory genomics at Cincinnati Children’s.
We are leveraging our established csRNA-seq platform to investigate the function of the AKT-ChREBPb regulatory axis for BAT formation and function in mice by analyzing the genome-wide eRNA profile and by doing a comparative analysis on in vivo and in vitro models in combination with CUT&RUN for ChREBP binding sites mapping. Together, this study will reveal distinct regulatory modules that govern brown adipogenesis and functions and the key transcription factors (TFs) and yield testable hypotheses to develop this application further for future R21/R01 applications.