High-fat diet enhances food-seeking behavior via sensitizing hunger-sensing neurons in Drosophila I

The function of the central nervous system to regulate food intake can be disrupted by sustained metabolic challenges such as high-fat diet (HFD), which may contribute to the development of various metabolic disorders. In the present study, we found that HFD specifically enhanced food-seeking behavior in fruit flies without altering flies' baseline metabolism and food consumption. Mechanistically, HFD increased the excitability of a small group of octopaminergic (OA) neurons to a hunger hormone named adipokinetic hormone (AKH), via increasing the accumulation of AKH receptor (AKHR) in these neurons. Upon HFD, excess dietary lipids are transported by a lipoprotein LTP to enter these OA+AKHR+ neurons via the cognate receptor LpR1, which in turn activated AMPK-TOR signaling and suppressed autophagy-dependent degradation of AKHR. Taken together, we uncovered a mechanism that linked HFD, AMPK-TOR signaling, neuronal autophagy, and food-seeking behavior, providing insight in the reshaping of neural circuitry under metabolic challenges and the progression of metabolic diseases. Overall design: As described previously (Yu et al., 2016), individual AKHR+ cells (visualized by GFP experession) were harvested from dissected fly brain under a fluorescence microscope with a glass micropipette pulled from thick-walled borosilicate capillaries (BF120-69-10, Sutter Instruments). Individual cells were immediately transferred to lysate buffer and underwent reverse transcription and cDNA amplification (SMARTer Ultra Low RNA Kit for Sequencing, Clonetech). The amplified cDNA were sonicated to ~250 bp fragments by the Covaris S2 system and then subjected to end-repair, dA-tail, adaptor ligation, and 12 cycles of PCR amplification using the library preparation kit (NEBNext Ultra II DNA Library Prep Kit, NEB). The cDNA libraries were sequenced by Illumina Hiseq 2500 platform. The sequenced raw data were first pre-processed to remove low-quality reads, adaptor sequences and amplification primer. Reads were mapped to Drosophila genome and mapped reads were selected for further analysis. FPKM (Fragments Per Kilobase Of Exon Per Million Fragments Mapped) was used to quantify gene expression.