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Hypothalamic tanycytes as mediators of maternally programmed seasonal plasticity

ABSTRACT: Environments with seasonal fluctuations requires inhabitants to anticipate their metabolic demands to survive. Drastic changes in food availability and temperature impose pressing challenges, especially during the first weeks of life. Offspring born early and late in the breeding season require different metabolic strategies. The mother’s melatonin levels ensures this in utero, acting as an internal mirror of day length. The melatonin levels programs the offspring to either grow fast and reproduce quickly (early born), or grow slow and delay maturation until next spring (late born). Thyroid hormone availability is altered by the melatonin signal and drives these differing metabolic strategies. Tanycytes located in the ependymal zone of the 3rd ventricle of the hypothalamus are at the crux of this change in thyroid hormone availability. Current literature provide ample evidence that these cells serve as a gatekeeper of metabolic feedback circuits, and photoperiodic history cues. Despite recent advances, our mechanistic understanding of how tanycytes regulate metabolic trajectories remains elusive. Here we used a well-established maternal photoperiodic programming paradigm to decipher the mechanism tanycytes utilise to dictate the offspring metabolic trajectory. The paradigm only rely on variable gestational light exposure to alter metabolic phenotype. Laser capture microdissection of ependymal zone enabled us to perform RNAseq on tanycyte enriched samples.

ORGANISM(S): Phodopus sungorus

PROVIDER: GSE204883 | GEO | 2023/11/02

REPOSITORIES: GEO

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Project description: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.

Project description:Background: Neuronal and glial differentiation in the murine hypothalamus is not complete at birth, but continues over the first two weeks postnatally. Nutritional status and Leptin deficiency can influence the maturation of neuronal projections and glial patterns, and hypothalamic gliosis occurs in mouse models of obesity. Gnasxl constitutes an alternative transcript of the genomically imprinted Gnas locus and encodes a variant of the signalling protein GÎ±s, termed XLÎ±s, which is expressed in defined areas of the hypothalamus. Gnasxl-deficient mice show postnatal growth retardation and undernutrition, while surviving adults remain lean and hypermetabolic with increased sympathetic nervous system (SNS) activity. Effects of this knock-out on the hypothalamic neural network have not yet been investigated. Results: RNAseq analysis for gene expression changes in hypothalami of Gnasxl-deficient mice indicated Glial fibrillary acid protein (Gfap) expression to be significantly down-regulated in adult samples. Histological analysis confirmed a reduction in Gfap-positive glial cell numbers specifically in the hypothalamus. This reduction was observed in adult tissue samples, whereas no difference was found in hypothalami of postnatal stages, indicating an adaptation in adult Gnasxl-deficient mice to their earlier growth phenotype and hypermetabolism. Especially noticeable was a loss of many Gfap-positive Î±-tanycytes and their processes, which form part of the ependymal layer that lines the medial and dorsal regions of the 3rd ventricle, while Î²-tanycytes along the median eminence (ME) and infundibular recesses appeared unaffected. This was accompanied by local reductions in Vimentin and Nestin expression. Hypothalamic RNA levels of glial solute transporters were, unchanged, indicating a potential compensatory up-regulation in the remaining astrocytes and tanycytes. Conclusion: Gnasxl deficiency does not directly affect glial development in the hypothalamus, since it is expressed in neurons, and Gfap-positive astrocytes and tanycytes appear normal during early postnatal stages. The loss of Gfap-expressing cells in adult hypothalami appears to be a consequence of the postnatal undernutrition, hypoglycaemia and continued hypermetabolism and leanness of Gnasxl-deficient mice, which contrasts with gliosis observed in obese mouse models. Since Î±-tanycytes also function as adult neural progenitor cells, these findings might indicate further developmental abnormalities in hypothalamic formations of Gnasxl-deficient mice, potentially including neuronal composition and projections. 6 wildtype and 6 Gnasxlm+/p- RNA isolates were used, which were pooled in pairs in equal concentrations prior to rRNA removal using the RiboMinus kit (Life Technologies)

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Hypothalamic tanycytes as mediators of maternally programmed seasonal plasticity

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