Analysis of Astroglial Secretomic Profile in the Mecp2-Deficient Male Mouse Model of Rett Syndrome

Abstract

Mutations in the X-linked MECP2 gene are responsible for Rett syndrome (RTT), a severe neurological disorder. MECP2 is a transcriptional modulator that finely regulates the expression of many genes, specifically in the central nervous system. Several studies have functionally linked the loss of MECP2 in astrocytes to the appearance and progression of the RTT phenotype in a non-cell autonomous manner and mechanisms are still unknown. Here, we used primary astroglial cells from Mecp2-deficient (KO) pups to identify deregulated secreted proteins. Using a differential quantitative proteomic analysis, twenty-nine proteins have been identified and four were confirmed by Western blotting with new samples as significantly deregulated. To further verify the functional relevance of these proteins in RTT, we tested their effects on the dendritic morphology of primary cortical neurons from Mecp2 KO mice that are known to display shorter dendritic processes. Using Sholl analysis, we found that incubation with Lcn2 or Lgals3 for 48 h was able to significantly increase the dendritic arborization of Mecp2 KO neurons. To our knowledge, this study, through secretomic analysis, is the first to identify astroglial secreted proteins involved in the neuronal RTT phenotype in vitro, which could open new therapeutic avenues for the treatment of Rett syndrome.

Human iPSC-Derived Glia as a Tool for Neuropsychiatric Research and Drug Development

“…Co-culture of neurons with conditioned media from RTT-astrocytes reproduced these findings, highlighting the glial contribution to RTT [ 139 ]. Another study showed an increase in astrocyte-specific differentiation in iPSC-derived RTT-neurospheres, replicating previous findings from mouse models [ 140 , 141 , 142 ].…”

Potential of Multiscale Astrocyte Imaging for Revealing Mechanisms Underlying Neurodevelopmental Disorders

“…MeCP2 is highly expressed in neurons and may be involved in the formation of synaptic contacts and activity-dependent neuronal gene expression [ 105 ]. Astrocytes also express MeCP2, and MeCP2 deficiency in astrocytes causes significant abnormalities in the regulation of brain derived neurotrophic factor (BDNF), a ubiquitous regulator of neuronal dendritic and synaptic plasticity, and of cytokine production, suggesting that this deficit may alter brain inflammatory function [ 8 , 9 , 10 , 11 ]. Thus, astrocytes may drive Rett syndrome pathology via inflammatory reactions and insufficient BDNF signaling.…”

“…Astrocytes have multiple biological functions, including organization of the blood–brain barrier [ 3 ], clearance of metabolites [ 4 ], modulation of synaptic function to control NMDAR-dependent plasticity [ 5 ], and perisynaptic glutamate and potassium clearance [ 6 ]. Astrocyte dysfunction is implicated in numerous neurodevelopmental, neurodegenerative, and neuropsychiatric disorders such as Alexander’s disease [ 7 ], Rett syndrome [ 8 , 9 , 10 , 11 ], fragile X syndrome [ 12 ], epilepsy [ 13 , 14 , 15 ], and Huntington’s disease (HD) [ 16 ]. To understand the causes of these congenital diseases and create effective treatments, it is essential to fully elucidate the mechanisms of astrocyte development and the consequences of these developmental processes on brain structure and function.…”

Identification of Region-Specific Cytoskeletal and Molecular Alterations in Astrocytes of Mecp2 Deficient Animals

“…Curiously, transcriptional studies from Yasui’s and Delépine’s laboratories displayed very limited overlap, probably due to the use of different mouse models, different number of astrocyte passages in vitro , and/or to the presence of fetal bovine serum (FBS) in astrocyte cultures, with inter-vendor and inter-batch inconsistencies contributing to the variability. Further, a very recent proteomic analysis on the secretome derived from Mecp2 knock-out (KO) cortical astrocytes revealed several deregulated proteins, suggesting the importance of non-cell autonomous mechanisms for neuronal maturation ( Ehinger et al, 2021 ). Comparing data from the above-mentioned -omic studies, lipocalin 2 emerged as an interesting candidate and its addition to Mecp2 null neurons rescued morphological defects ( Yasui et al, 2013 ; Delépine et al, 2015 ; Ehinger et al, 2021 ).…”

“…Further, a very recent proteomic analysis on the secretome derived from Mecp2 knock-out (KO) cortical astrocytes revealed several deregulated proteins, suggesting the importance of non-cell autonomous mechanisms for neuronal maturation ( Ehinger et al, 2021 ). Comparing data from the above-mentioned -omic studies, lipocalin 2 emerged as an interesting candidate and its addition to Mecp2 null neurons rescued morphological defects ( Yasui et al, 2013 ; Delépine et al, 2015 ; Ehinger et al, 2021 ). In vivo , a multi-omic study combining RNA sequencing and proteomic analyses of the adult Mecp2 null cortex (P60) reported the alteration of 46 astrocyte-specific genes associated with astrocyte maturation and morphology, together with decreased levels of astrocytic proteins involved in apoptosis ( Pacheco et al, 2017 ).…”