It is demonstrated that Egfr knockout during the critical period of neuronal maturation results in a transient absence of astrocytes, with recovery observed in adult mice, and developmental disruption of EGFR signaling leads to transient astrocyte loss and impaired astrocyte–neuron crosstalk.
Abstract
Neural functions and circuit formation rely on intricate crosstalk among various cell types during critical periods. Disruptions or delays in this crosstalk between neurons and astrocytes lead to abnormal neural functions and neurodevelopmental disorders. However, the lack of robust mouse models to study the crosstalk between astrocytes and neurons thus renders unclear the implications of impeding such interactions. In this study, we demonstrate that Egfr knockout during the critical period of neuronal maturation results in a transient absence of astrocytes, with recovery observed in adult mice. This model thus provides a unique opportunity to investigate the effects of impaired astrocyte-neuron communication during development. Mechanically, we show that loss of Egfr disrupts the Egfr-pERK-Epb41l2 signaling axis, which in turn prevents glial progenitor cells from migrating outward. More importantly, Egfr deficiency during the critical period compromises astrocyte-neuron communication via the Sema6a-Plxna2/4 ligand-receptor pair. This impaired intercellular crosstalk reduces neuronal dendritic complexity and excitability, ultimately culminating in depressive-like behaviors in adult mice. This study shows that developmental disruption of EGFR signaling leads to transient astrocyte loss and impaired astrocyte–neuron crosstalk. Altered EGFR–pERK–EPB41L2 signaling and Sema6a–Plxna2/4 communication, results in reduced dendritic complexity, neuronal excitability, and long-term depressive-like behaviours.
Rett syndrome (RTT) is a severe X-linked neurodevelopmental disorder caused by loss-of-function mutations in the MECP2 gene and characterized by profound impairments in neuronal maturation and synaptic connectivity. Increasing evidence indicates that astrocyte dysfunction contributes to RTT pathogenesis through non-cell-autonomous mechanisms, although the molecular pathways underlying defective astrocyte-neuron communication are only partially understood. Astrocytes are the primary source of cholesterol in the brain and support neuronal maturation and synaptic function by supplying cholesterol through ApoE-containing lipoproteins. Although alterations in brain cholesterol metabolism have been reported in RTT, the underlying cellular mechanisms and their functional consequences remain poorly investigated. Here, we studied cholesterol homeostasis in Mecp2 knock-out (KO) astrocytes and its impact on neuron-astrocyte communication. Mecp2 KO astrocytes exhibited reduced nuclear localization of the transcriptional regulator Srebp2, together with the downregulation of genes involved in cholesterol biosynthesis and transport. These molecular alterations were associated with intracellular cholesterol and desmosterol accumulation, reduced Abca1 expression and defective ApoE lipidation, despite preserved ApoE expression and cholesterol secretion. Importantly, similar alterations were detected in acutely isolated astrocytes and in the cerebral cortex of Mecp2 deficient mice, demonstrating that impaired cholesterol homeostasis extends beyond in vitro models. Functionally, cholesterol supplementation of astrocyte-conditioned medium rescued the synaptic defects induced in wild-type neurons by Mecp2 KO astrocytes. Moreover, cholesterol treatment restored pre- and post-synaptic density, as well as axon initial segment length in Mecp2 heterozygous (HET) neurons. Together, these findings identify defective astrocyte-to- neuron cholesterol trafficking as a key mechanism contributing to neuronal dysfunction in RTT and suggest that strategies aimed at restoring cholesterol functional availability might represent a promising therapeutic avenue for RTT.
Francesca M. Postogna, Noemi Giancroce, C. Cabasino et al.· bioRxiv· 0 citations
Data show that LRRK2-G2019S impairs astrocyte specification and predisposes to a senescent phenotype, which contributes to the acquisition of a senescent-like phenotype in Parkinson’s disease patients.
Lisa M. Smits, S. Magni, K. Grzyb et al.· npj Parkinson's Disease· 0 citations
It is shown that neurogenesis is disrupted at multiple stages of lineage progression in both rodent and human neural stem cell models of Huntington's disease, and a panel of clinically relevant epigenetic compounds hold promise for stage-spanning therapeutic strategies capable of modifying disease trajectory.
Jessica Rosati, A. Casamassa, G. Ruotolo et al.· Cell Death and Differentiati...· 0 citations
Astrocytes are essential glial cells that maintain brain homeostasis. Upon brain injury, they become reactive astrocytes with altered morphology, gene expression, and function, including dysregulated Ca2+ signaling implicated in disease development and progression. P2Y1 receptor (P2Y1R), one of Gq-GPCRs, is upregulated in reactive astrocytes across multiple brain disorders, including Alzheimer's disease, epilepsy, and stroke; however, how this upregulation contributes to pathology has remained unclear. To address this question, we generated astrocyte-specific P2Y1R-overexpressing transgenic mice. P2Y1R overexpression in astrocytes induced neuronal hyperexcitability, as evidenced by increased hippocampal neuronal firing, abnormal EEG spikes, and heightened susceptibility to pilocarpine-induced seizures. Dual-color Ca2+ imaging of neurons and astrocytes, electrophysiology, transcriptome analysis of astrocytes, immunohistochemistry, and CRISPR/Cas9-mediated astrocyte-specific knockdown revealed that P2Y1R overexpression amplified both neuron-to-neuron and neuron-to-astrocyte signaling, with astrocytes becoming hypersensitive to neuronal activity-derived ATP. Astrocyte-specific transcriptomic analysis identified insulin-like growth factor binding protein 2 (IGFBP2) as a key downstream effector. IGFBP2, a secreted protein selectively expressed in astrocytes, enhanced glutamatergic synaptic transmission. Furthermore, co-upregulation of P2Y1R and IGFBP2 was confirmed in reactive astrocytes in both kainate-induced epilepsy and middle cerebral artery occlusion stroke models. These findings identify the P2Y1R-IGFBP2 signaling axis as a common pathological feature of reactive astrocytes across brain diseases and establish IGFBP2 as a novel glial-derived factor that could promote neuronal hyperexcitability.
E. Shigetomi, Schuichi Koizumi· Nihon yakurigaku zasshi. Fol...· 0 citations
The extracellular milieu, including extracellular vesicles (EVs), plays a pivotal role in brain development. In this study, we sought to elucidate the pathogenesis of progressive myoclonus epilepsy type 1 (EPM1), a disease caused by mutations in the CSTB gene, using cerebral organoids (COs) derived from patient cells. The results demonstrate that EPM1 COs display increased electrophysiological activity and disrupted excitatory/inhibitory (E/I) balance. Single-cell RNA sequencing analysis of ventral EPM1-COs revealed an abnormal specification of progenitor fate, with a shift toward dorsal neuron identities. We demonstrated that this misspecification is driven by a functional alteration of the ventral signaling niche, resulting from impaired EV dynamics and altered protein cargo. Mechanistically, we identified Sonic Hedgehog (SHH) as a direct physical interactor of CSTB and demonstrated that CSTB deficiency leads to reduced SHH content and secretion. Our findings establish CSTB as a safeguard of ventral patterning and identify the CSTB-SHH-EV axis as a potential therapeutic target for mitigating the E/I imbalance associated with EPM1.
Andrea Forero, Veronica Pravata, Fabrizia Pipicelli et al.· Science Advances· 0 citations
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