Physiological Condition Dependent Changes in Ciliary GPCR Localization in the Brain

Abstract

Primary cilia are small immotile cellular appendages which mediate diverse types of singling and are found on most mammalian cell types including throughout the central nervous system. Cilia are known to 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. Heterologous cell line and model systems like C. elegans and Chlamydomonas have implicated both dynamic GPCR cilia localization and cilia length and shape changes as key for signaling. However, it is unclear if mammalian ciliary GPCRs utilize similar mechanisms in vivo and under what physiological conditions these processes may occur. Here, we use the ciliary GPCRs, melanin concentrating hormone receptor 1 (MCHR1) and neuropeptide-Y receptor 2 (NPY2R) as model ciliary receptors to determine if dynamic localization to cilia occurs. We tested physiological conditions in which these GPCRs have been implicated such as feeding behavior, obesity, and circadian rhythm. Cilia were imaged using confocal microscopy and analyzed with a computer assisted approach allowing for unbiased and high throughput analysis of cilia. We analyzed GPCR positive cilia, cilia frequency as well as cilia length and receptor occupancy. Interestingly we observed changes in ciliary length, receptor occupancy, and cilia frequency under different conditions, but no consistent theme across GPCRs or brain nuclei was observed. A better understanding of the subcellular localization dynamics of ciliary GPCRs could reveal unrecognized molecular mechanisms regulating behaviors like feeding.

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).…”

Neuronal cilia in energy homeostasis

“…For instance, the MCH/MCHR1 signaling pathway has a well-defined role in energy homeostasis [for a review see ( Al-Massadi et al, 2021 )]. MCHR1 localizes to cilia in many areas of the mouse and rat brain, including the olfactory bulb, hippocampus, amygdala, hypothalamus, and spinal cord ( Niño-Rivero et al, 2019 ; Diniz et al, 2020 ; Brewer et al, 2022 ). Using optogenetics, and chemogenetics, activation and inhibition of the MCH pathway causes cilia shortening and lengthening, respectively, in the brain as measured with ADCY3s staining ( Alhassen et al, 2022 ).…”