Abstract

Glucose homeostasis in the brain is crucial for maintaining cellular function and energy balance, a process primarily governed by the hypothalamus. Tanycytes, specialized glial cells lining the walls of the third ventricle, play a pivotal role in glucose sensing. These cells integrate metabolic and nutrient signals, regulating energy balance through mechanisms involving glucose transporters (GLUTs), glucokinase, and sweet taste receptors (STRs). STRs are composed of T1R2 and T1R3 subunits and function as G-protein-coupled receptors (GPCRs) primarily associated with detecting sweet compounds. Recent evidence indicates that STRs are expressed in tanycytes, where they play a role in glucose sensing by regulating intracellular calcium and cAMP levels and promoting ATP release. The primary cilium, a microtubule-based organelle, is a specialized structure found in various cell types, including tanycytes. Functioning as an "antenna," it facilitates signal transduction by integrating extracellular signals. This organelle is enriched with GPCRs, which are essential for its signaling functions. However, no evidence has been reported regarding the expression or signaling of STRs in the primary cilia of tanycytes. To test this, we employed fluorescence imaging to investigate STR localization by detecting T1R2, a subunit of STRs, and assessing its co-localization with the ciliary marker IFT88 in in vitro models. Using genetically encoded sensors and confocal microscopy, we tracked calcium and cAMP dynamics in both in vitro models and ex vivo hypothalamic brain slices. Exposure to sweet agonists revealed a distinctive decrease in cAMP levels within the primary cilium, particularly in response to glucose. Interestingly, treatment with Pertussis Toxin (PTX), a specific Gαi/o inhibitor, did not alter cytoplasmic calcium or cAMP responses but induced an increase in cAMP levels within the primary cilium in response to glucose. This finding underscores the role of the Gαi/o subunit in modulating cAMP signaling. Let me know if you'd like further refinements This study demonstrates that STRs are localized in primary cilia, where their activation uniquely reduces cAMP levels via the Gαi/o subunit, distinct from cytoplasmic responses. These findings suggest a specific adenylate cyclase inhibitory mechan