Abstract
Background: Drugs that safely promote weight loss are required to treat the obesity crisis. The gut hormone peptide YY 3-36 (PYY(3-36)) is secreted post-prandially to suppress appetite via the Y2 receptor (Y2R). However, it is unclear whether PYY(3-36) acts directly on the Y2R in the hypothalamic arcuate nucleus (ARC) or the afferent vagus nerve to inhibit food intake. Understanding the pathways by which PYY(3-36) mediates its anorectic effects may facilitate the therapeutic targeting of this system. Methods: Y2R knockdown in the ARC (ARC-Y2R-KD) was achieved by stereotactic injection of Cre-expressing adeno-associated virus (AAV-Cre) in Y2R-flox C57Bl/6 mice. Y2R KD in the vagus was achieved by bilateral microinjection of AAV-Cre into the nodose ganglia (NG), where the cell bodies of vagal afferents reside. An alternative germline model of sensory nerve Y2R knockdown was generated using Nav1.8-Cre mice crossed with the Y2R-flox strain (Nav1.8-Y2R-KD). Feeding behaviour over 10 days in metabolic cages and the effects of endogenously released (after oral gavage of a nutrient bolus) or exogenously-administered PYY(3-36) were investigated. Results: NG-Y2R-KD animals had 60% reduction in NG Y2R mRNA but remained responsive to cholecystokinin, a positive control of vagal functionality. This is the first example of receptor specific adult vagal deafferentation in mice. The Nav1.8-Y2R-KD model achieved 30% receptor KD. Feeding patterns in the ARC-Y2R-KD and NG-Y2R-KD groups were highly different from their controls, with smaller, faster meals in the KD groups. The anorectic effects (at the next meal) of endogenous PYY(3-36) were attenuated in NG-Y2R-KD. Low dose exogenous PYY(3-36) at 5 µg/kg significantly reduced 2h post injection food intake (FI) in the control groups (n=8; P=0.045) but this was abrogated in the NG-Y2R-KD group. This pattern was mirrored in the Nav1.8-Y2R-KD model: low dose PYY(3-36) significantly reduced FI 1h post-IP compared to vehicle in controls (-0.19±0.05 g; P =0.036; n=8) but not in the Nav1.8-Y2R-KD (-0.004±0.111 g; n=3). Peripherally-administered PYY(3-36) at a high dose (30 µg/kg) decreased FI in all groups, including ARC-Y2R-KD. Summary: These results suggest that endogenous PYY(3-36) modulates meal patterning. The vagus nerve mediates physiological PYY(3-36) signalling but alternative pathways, not exclusively via the ARC, may be more important in mediating its pharmacological effects. This is relevant for the design of more effective weight loss agents.