Physiological Condition-Dependent Changes in Ciliary GPCR Localization in the Brain

Abstract

Primary cilia are cellular appendages critical for diverse types of singling. They are found on most cell types, including cells throughout the central nervous system. Cilia preferentially localize certain G protein-coupled receptors (GPCRs) and are critical for mediating the signaling of these receptors. Several of these neuronal GPCRs have recognized roles in feeding behavior and energy homeostasis. Cell and model systems likeC. elegansandChlamydomonashave implicated both dynamic GPCR cilia localization and cilia length and shape changes as key for signaling. It is unclear if mammalian ciliary GPCRs utilize similar mechanismsin vivoand under what conditions these processes may occur. Here, we assess two neuronal cilia GPCRs, melanin-concentrating hormone receptor 1 (MCHR1) and neuropeptide-Y receptor 2 (NPY2R), as mammalian model ciliary receptors in the mouse brain. We test the hypothesis that dynamic localization to cilia occurs under physiological conditions associated with these GPCRs’ functions. Both receptors are involved in feeding behaviors, and MCHR1 is also associated with sleep and reward. Cilia were analyzed with a computer-assisted approach allowing for unbiased and high throughput analysis. We measured cilia frequency, length, and receptor occupancy. We observed changes in ciliary length, receptor occupancy, and cilia frequency under different conditions for one receptor but not another and in specific brain regions. These data suggest that dynamic cilia localization of GPCRs depends on properties of individual receptors and cells where they are expressed. A better understanding of subcellular localization dynamics of ciliary GPCRs could reveal unknown molecular mechanisms regulating behaviors like feeding.Significance StatementOften, primary cilia localize specific G protein-coupled receptors (GPCRs) for subcellular signaling. Cell lines and model systems indicate that cilia deploy dynamic GPCR localization and change their shape or length to modulate signaling. We used mice to assess neuronal cilia GPCRs under physiological conditions associated with the receptors’ known functions and ciliopathy clinical features like obesity. We show that particular cilia with specific GPCRs appear to dynamically alter their length while others appear relatively stable under these conditions. These results implicate multiple themes across cilia GPCR mediated signaling and indicate that not all cilia modulate GPCR signaling using the same mechanisms. These data will be important for potential pharmacological approaches to target cilia GPCR-mediated signaling.

Astrocyte-Specific Inhibition of the Primary Cilium Suppresses C3 Expression in Reactive Astrocyte

“…Primary cilium elongation could potentially alter the density of signalling molecules present in the primary cilium, thereby affecting downstream signalling (Macarelli et al 2023). Interestingly, it has been suggested that not only the regulation of primary cilium length but also the modulation of ciliated cell rate and receptor localization changes under different physiological conditions in the brain (Brewer et al 2023). Cilium length regulation may be involved in the control of C3-positive reactive astrocyte induction by modulating immune signalling pathways.…”

Astrocyte-specific inhibition of primary cilium functions improves cognitive impairment during neuroinflammation by suppressing A1 astrocyte differentiation

“…Primary cilium elongation could potentially alter the density of signalling molecules present in the primary cilium, thereby affecting downstream signalling (21). Interestingly, it has been suggested that not only the regulation of primary cilium formation but also the modulation of cilium length, formation rate, and receptor localization changes under different physiological conditions in the brain (39). Cilium length regulation may be involved in the control of A1 astrocyte differentiation by modulating immune signalling pathways.…”

Primary cilia control oligodendrocyte precursor cell proliferation in white matter injury via Hedgehog-independent CREB signaling

“… 65 With advancements in proximity-labeling technologies, it is now possible to consistently isolate and analyze proteins selectively localized to primary cilia. 26 , 66 Studies show that the composition of cilia can be dynamic 26 , 67 and clearly differs between cell types. For example, adenylate cyclase 3 is present in neuronal cilia but has been shown to fail to be detected in IMCD3 kidney cells.…”