Abstract

The primary cilium, a microtubule-based organelle that extends into the extracellular space, plays a crucial role in signal transduction and is present in various cell types. It acts as an 'antenna' for signal conversion through different pathways, containing various types of proteins, such as G-protein-coupled receptors (GPCRs). Notably, it is involved in the regulation of glucose homeostasis, a vital process for cellular function and energy balance, which includes glucose detection associated with both metabolic (GLUTs and glucokinase) and independent mechanisms. Sweet taste receptors (STR), which are GPCRs composed of subunits T1R2/R3, are activated by sweet compounds. Activation of STR results in elevated cytoplasmic calcium and cAMP levels, accompanied by ATP release into the extracellular space. We propose that STR is present in the primary cilium and modulates cAMP levels. To confirm this hypothesis, we employed a fluorescent approach to visualize primary cilium formation and detect STR using the T1R2 subunit. We assessed co-localization between T1R2 and IFT88, a primary cilium marker. Furthermore, to monitor calcium and cAMP fluctuations in both the cytoplasm and primary cilium, we conducted experiments using genetically modified sensors and probes in confocal microscopy. Upon exposure to various sweet agonists, a distinctive decrease in cAMP levels was observed within the primary cilium, particularly in response to glucose treatment. This study demonstrates that STRs are present in primary cilia, where their activation leads to a unique decrease in cAMP levels, distinct from cytoplasmic responses. These findings suggest the existence of a distinct adenylate cyclase inhibitory mechanism for STRs within the primary cilium.