Brain methylome remodeling selectively regulates neuronal activity genes linking to emotional behaviors in mice exposed to maternal immune activation

How early life experience is translated into storable epigenetic information leading to behavioral changes remains poorly understood. Here we found that Zika virus (ZIKV) induced-maternal immune activation (MIA) imparts offspring with anxiety- and depression-like behavior. By integrating bulk and single-nucleus RNA sequencing (snRNA-seq) with genome-wide 5hmC (5-hydroxymethylcytosine) profiling and 5mC (5-methylcytosine) profiling in prefrontal cortex (PFC) of ZIKV-affected male offspring mice, we revealed an overall loss of 5hmC and an increase of 5mC levels in intragenic regions, associated with transcriptional changes in neuropsychiatric disorder-related genes. In contrast to their rapid initiation and inactivation in normal conditions, immediate-early genes (IEGs) remain a sustained upregulation with enriched expression in excitatory neurons, which is coupled with increased 5hmC and decreased 5mC levels of IEGs in ZIKV-affected male offspring. Thus, MIA induces maladaptive methylome remodeling in brain and selectively regulates neuronal activity gene methylation linking to emotional behavioral abnormalities in offspring.

Reversing lysosome-ribosome circuit dysregulation mitigates C9FTD/ALS neurodegeneration and behaviors

G4C2 repeat expansion in C9orf72 causes the most common familial frontotemporal dementia and amyotrophic lateral sclerosis (C9FTD/ALS). The pathogenesis includes haploinsufficiency of C9orf72, which forms a protein complex with Smcr8, as well as G4C2 repeat-induced gain of function including toxic dipeptide repeats (DPRs). The key in vivo disease-driving mechanisms and how loss- and gain-of-function interplay remain poorly understood. Here, we identified dysregulation of a lysosome-ribosome biogenesis circuit as an early and key disease mechanism using a physiologically relevant mouse model with combined loss- and gain-of-function across the aging process. C9orf72 deficiency exacerbates FTD/ALS-like pathologies and behaviors in C9ORF72 bacterial artificial chromosome (C9-BAC) mice with G4C2 repeats under endogenous regulatory elements from patients. Single nucleus RNA sequencing (snRNA-seq) and bulk RNA-seq revealed that C9orf72 depletion disrupts lysosomes in neurons and leads to transcriptional dysregulation of ribosomal protein genes, which are likely due to the proteotoxic stress response and resemble ribosomopathy defects. Importantly, ectopic expression of C9orf72 or its partner Smcr8 in C9FTD/ALS mutant mice promotes lysosomal functions and restores ribosome biogenesis gene transcription, resulting in the mitigation of DPR accumulation, neurodegeneration as well as FTD/ALS-like motor and cognitive behaviors. Therefore, we conclude that loss- and gain-of-function crosstalk in C9FTD/ALS converges on neuronal dysregulation of a lysosome-ribosome biogenesis circuit leading to proteotoxicity, neurodegeneration and behavioral defects.