Biology subjects

Bonnycastle, K.

Publications and source records attributed to Bonnycastle, K..

3 recordsLinked to original sources

bioRxiv2024

Convergent depression of activity-dependent bulk endocytosis in rodent models of autism spectrum disorders.

The key pathological mechanisms underlying autism spectrum disorders (ASDs) remain relatively undetermined, potentially due to the heterogenous nature of the condition. Targeted studies of a series of monogenic ASDs have revealed postsynaptic dysfunction as a central conserved mechanism. Presynaptic dysfunction is emerging as an additional disease locus in neurodevelopmental disorders, however it is unclear whether this dysfunction drives ASDs or is an adaptation to the altered brain microenvironment. To determine this, we performed a high content analysis of key stages of the synaptic vesicle lifecycle in a series of preclinical models of monogenic ASDs. These models were specifically selected to have perturbations in a diverse palette of genes that were expressed either at the pre- or post-synapse. However, all models displayed a common trait of hyperexcitability. We determined that SV fusion events and SV cargo trafficking were unaffected in all models investigated. However, a key convergent phenotype was revealed, a depression in activity-dependent bulk endocytosis (ADBE). This suggests that the depression in ADBE is a homeostatic mechanism to correct hyperexcitability in the ASD brain.

neuroscience↗

bioRxiv2023

Reversal of cell, circuit and seizure phenotypes in a mouse model of DNM1 epileptic encephalopathy

Pathogenic heterozygous missense mutations in the DNM1 gene result in a novel form of epileptic encephalopathy. DNM1 encodes for the large GTPase dynamin-1, an enzyme with an obligatory role in the endocytosis of synaptic vesicles (SVs) at mammalian nerve terminals. Pathogenic DNM1 mutations cluster within regions required for its essential GTPase activity, implicating disruption of this enzyme activity as being central to epileptic encephalopathy. We reveal that the most prevalent pathogenic mutation of DNM1, R237W, disrupts dynamin-1 enzyme activity and SV endocytosis when overexpressed in central neurons. To determine how this dominant-negative heterozygous mutant impacted cell, circuit and behaviour when expressed from its endogenous locus, we generated a mouse carrying the R237W mutation. Neurons isolated from heterozygous mice displayed dysfunctional SV endocytosis, which translated into altered excitatory neurotransmission and seizure-like phenotypes. Importantly, these phenotypes were corrected at the cell, circuit and in vivo level by the drug, BMS-204352, which accelerates SV endocytosis. This study therefore provides the first direct link between dysfunctional SV endocytosis and epilepsy, and importantly reveals that SV endocytosis is a viable therapeutic route for monogenic intractable epilepsies.

neuroscience↗

bioRxiv2020

FMRP sustains presynaptic function via control of activity-dependent bulk endocytosis

Synaptic vesicle (SV) recycling defects are linked to neurodevelopmental disorders, including fragile X syndrome (FXS), which results from loss of fragile X mental retardation protein (FMRP) encoded by the FMR1 gene. Hyperexcitability of neuronal circuits is a key feature of FXS, therefore we investigated whether SV recycling was affected by the absence of FMRP during increased neuronal activity. We revealed that primary neuronal cultures from a Fmr1 knockout rat model display a specific defect in activity-dependent bulk endocytosis (ADBE). This defect resulted in an inability of Fmr1 knockout neurons to sustain SV recycling during high frequency stimulation. Using a molecular replacement strategy, we also revealed that a human FMRP mutant that cannot bind BK channels failed to correct ADBE dysfunction in knockout neurons, however this dysfunction was corrected by BK channel agonists. Therefore, FMRP performs a key role in sustaining neurotransmitter release via selective control of ADBE, suggesting intervention via this endocytosis mode may correct hyperexcitabiltiy observed in FXS. SUMMARYFragile X syndrome (FXS) is caused by loss of fragile X mental retardation protein (FMRP). Bonnycastle et al show that FMRP is specifically required for activity-dependent bulk endocytosis (ADBE), revealing 1) FMRP sustains neurotransmitter release and 2) intervention via ADBE may correct circuit hyperexcitabilty in FXS.

neuroscience↗