ＡＴＲ－Ｘ症候群

ATR-X syndrome, caused by mutations in the ATRX gene, leads to intellectual disability and neurodevelopmental deficits, with previous mouse models implicating forebrain ATRX loss in cognitive impairment. However, the region-specific requirements of neuronal ATRX for cognitive function remain unclear. Here, we generated conditional knockout mice with predominant deletion of ATRX in hippocampal CA1 pyramidal neurons in both pure C57Bl/6J and hybrid C57Bl/6J + 129S2/Sv genetic backgrounds. Immunofluorescence confirmed efficient ATRX loss in CA1 neurons, with mosaic expression throughout other forebrain structures. Behavioral analyses revealed that T29-1 CaMKIIα-Cre ATRX knockout mice exhibited significant hypoactivity and increased anxiety traits, particularly in the open field, but retained normal hippocampal-dependent contextual fear memory and spatial learning and memory. In contrast, we confirmed that mice with robust forebrain-wide ATRX ablation in excitatory neurons (R1ag#5 CaMKIIα-Cre-mediated) displayed deficits in these cognitive domains. Our findings demonstrate that ATRX-related intellectual disability requires disruption of broader hippocampal or forebrain circuits to elicit cognitive impairments in learning and memory.

Mutations in the ATRX gene are a primary cause of alpha-thalassemia intellectual disability X-linked (ATRX) syndrome, which is characterized by intellectual disability, autism, and a range of brain structural abnormalities, including microcephaly. We previously showed that mice with conditional ATRX ablation in forebrain excitatory neurons display deficits in fear memory and autism-related behaviors, with some effects exhibiting sexual dimorphism. In this study, we used high-resolution magnetic resonance imaging (MRI) to systematically characterize brain structural changes associated with these behavioral abnormalities. Whole-brain analysis revealed male-specific microcephaly, while subregional analysis identified significant reductions in hippocampal structures and increased volume of the caudal cortex in mutant animals of both sexes. We also identified structural alterations in regions retaining ATRX expression, such as the thalamus, midbrain, cerebellum, and several fiber tracts. These findings suggest that ATRX loss disrupts the coordinated development of interconnected brain regions. Overall, our results implicate impaired cortico-thalamic-cerebellar connectivity as a potential neural substrate underlying the autistic-like behaviors observed in this mouse model, providing new insights into the neurobiological basis of ATR-X syndrome.

Astrocytes are increasingly recognized as active regulators of synaptic transmission and memory, yet the epigenetic mechanisms underlying their contribution to cognitive processes remain poorly defined. Here, we investigated the role of the chromatin remodeler ATRX in astrocytes by generating mice with inducible, astrocyte-specific Atrx deletion (aiKO) using tamoxifen administration at postnatal days 10-12, resulting in ATRX loss in approximately half of hippocampal and cortical astrocytes. Transcriptomic profiling of hippocampal tissue at 1 and 3 months revealed differentially expressed genes, with early enrichment for cytoskeletal and immune pathways and later dysregulation of energy metabolism, ion transport, and synaptic gene sets. Electrophysiological recordings from CA1 pyramidal neurons in aiKO slices demonstrated increased neuronal excitability and decreased frequency of spontaneous excitatory postsynaptic currents, indicating non-cell-autonomous neuronal dysfunction. Morphological analysis identified a transient reduction in dendritic branching at 1 month and a selective loss of thin dendritic spines by 3 months, without changes in total dendrite length or overall spine density. Behaviorally, aiKO mice displayed normal locomotion, anxiety, and short-term memory, but exhibited deficits in 24-h novel object recognition and long-term spatial memory in the Morris water maze. These findings demonstrate that ATRX-mediated chromatin remodeling in astrocytes is essential for maintaining hippocampal transcriptional homeostasis, neuronal function, and long-term memory. Our results highlight a critical role for astrocytic epigenetic regulation in cognitive processes and suggest that astrocyte dysfunction may contribute to the pathogenesis of ATR-X syndrome and related intellectual disability disorders, underscoring the importance of targeting multiple cell types for therapeutic intervention.

Chromatin remodeling proteins are evolutionarily conserved factors involved in a wide range of biological processes. In this review, we describe ATRX, a chromatin remodeling protein belonging to the SWI/SNF2 family. Its association with different protein complexes, and its roles in embryonic development, sexual differentiation, as well as retinal and brain function. We further discuss and integrate current findings on pathologies associated with ATRX dysfunction such as ATR-X syndrome, focusing on its etiology, clinical features, and potential diagnostic tools. Finally, we propose that ATRX may contribute to the progression of certain neurodegenerative diseases and review recent literature supporting this hypothesis.