Counteracting epigenetic mechanisms regulate the structural development of neuronal circuitry in human neurons

Abstract

Autism spectrum disorders (ASD) are associated with defects in neuronal connectivity and are highly heritable. Genetic findings suggest that there is an overrepresentation of chromatin regulatory genes among the genes associated with ASD. ASH1 like histone lysine methyltransferase (ASH1L) was identified as a major risk factor for ASD. ASH1L methylates Histone H3 on Lysine 36, which is proposed to result primarily in transcriptional activation. However, how mutations in ASH1L lead to deficits in neuronal connectivity associated with ASD pathogenesis is not known. We report that ASH1L regulates neuronal morphogenesis by counteracting the catalytic activity of Polycomb Repressive complex 2 group (PRC2) in stem cell-derived human neurons. Depletion of ASH1L decreases neurite outgrowth and decreases expression of the gene encoding the neurotrophin receptor TrkB whose signaling pathway is linked to neuronal morphogenesis. The neuronal morphogenesis defect is overcome by inhibition of PRC2 activity, indicating that a balance between the Trithorax group protein ASH1L and PRC2 activity determines neuronal morphology. Thus, our work suggests that ASH1L may epigenetically regulate neuronal morphogenesis by modulating pathways like the BDNF-TrkB signaling pathway. Defects in neuronal morphogenesis could potentially impair the establishment of neuronal connections which could contribute to the neurodevelopmental pathogenesis associated with ASD in patients with ASH1L mutations.

Dysregulation of The Chromatin Environment Leads to Differential Alternative Splicing as A Mechanism Of Disease In a Human Model of Autism Spectrum Disorders

“…We used a control iPSC line I-93-7 obtained from a healthy neurotypical male individual that was previously characterized 35 . Human iPSCs were cultured as previously described 35,36 . Briefly, cells were cultured using a feeder-free system and mTeSR media (STEMCELL technologies catalog # 85850).…”

“…Differential gene expression for a subset of genes was validated using qPCR as previously described 36 . Primers were purchased in IDT (Supplementary Table S3).…”

“…We used a control iPSC line I-93-7 obtained from a healthy neurotypical male individual that was previously characterized 35 . Human iPSCs were cultured as previously described 35,36 .…”

The role of histone methyltransferases in neurocognitive disorders associated with brain size abnormalities

“…However, additional evidence suggests that ASH1L functions in a cell-type dependent manner affecting additional processes important for neuronal morphogenesis and synaptic function. For example, knockdown of ASH1L in human ESC-derived neurons led to severe reduction in neurite outgrowth (Lalli et al, 2020;Cheon et al, 2022). In vivo, knockout of Ash1l in mice lead to an overall growth retardation at later postnatal stages and revealed cortical malformations (Gao et al, 2021b).…”

“…Recently, mice with loss of Ash1l revealed growth delays and ASD/ID-like social behaviors (Gao et al, 2021b). Knockdown of ASH1L in human ESC-derived cortical neurons lead to decreased neurite length and arbor complexity (Cheon et al, 2022). Similarly, depletion of ASH1L in human iPSC-derived NPCs resulted in delayed neural differentiation and maturation (Lalli et al, 2020).…”