ABSTRACT: The ependyma lining the third ventricle (3V) in the mediobasal hypothalamus is recognized as a critical player in controlling energy balance and glucose homeostasis. Its molecularly distinct cell types, namely diverse tanycyte subpopulations and typical ependymal cells, confer a high functional heterogeneity and plasticity to this complex ependymal system, but the molecular mechanisms governing its features, especially in the context of metabolic regulation, are still not fully understood.Here, 5481 hypothalamic ependymocytes were cataloged using FACS-assisted single-cell RNA sequencing from fed, 12h-fasted, and 24h-fasted adult male mice. We first observed the limitations of using standard clustering analysis to characterize the different ependymal cell subpopulations lining the 3V. Indeed, while typical ependymal cells and β2-tanycytes are sharply defined at the molecular level using this approach, other subpopulations (i.e., β1- and α-tanycytes) display fuzzy boundaries and very few specific markers. Moreover, 12h- and 24h-fasting dynamically modulate gene expression, increasing tanycyte subgroup heterogeneity. To better analyze the dynamic changes in tanycytes’ gene expression profile, we implemented a pseudospatial analysis based on 3V neuroanatomical distribution, which we validated using in-situ hybridization, immunohistochemistry, and histologic staining. This approach improved the characterization of tanycyte markers, refining our knowledge of specific versus shared features and the segregation of subgroup-specific versus general tanycyte functions. Importantly, we showed that fasting dynamically shifts patterns in gene expression and transcription activity along the 3V, inducing metabolic and functional switches in tanycyte subpopulations, particularly regarding lipid metabolism. Additionally, numerous functions related to tanycyte-neuron and tanycyte-synapse interactions, notably through Nrxn1 expression, present a functional dorso→ventral shift towards the arcuate nucleus during fasting. Altogether, this data shows that changes in energy status lead to a spatial redistribution of distinct cell type-specific responses along the 3V and gives new insights into molecular and functional diversity and plasticity within the tanycyte population.
