Breaking BIN1 : investigating mechanisms of synaptic dysfunction in Alzheimer’s disease
Year: 2025
Type: dissertation
Abstract: Amyloid-β (Aβ) production is one of the earliest pathological alterations in the Alzheimer’s disease (AD) patients’ brain and has been the primary focus of therapeutic research. Yet, synapse loss best correlates with cognitive decline in AD; therefore, identifying the mechanisms driving synapse dysfunction should become a major therapeutic target. BIN1, an endocytic regulator and a significant risk gene for in late-onset AD (LOAD), has an unclear synaptic role. Our previous studies linked Bin1 to the endocytic recycling of BACE1, thereby leading to BACE1 accumulation and increased Aβ42 production. We have shown that mutations in Bin1 associated with LOAD, rs754834233 (PL) and rs138047593 (KR), lead to Bin1 loss of function in amyloidogenesis. However, Bin1’s synaptic function is ill-defined, with evidence suggesting roles at both presynaptic and postsynaptic sites that could affect synaptic transmission. Indeed, two previous studies suggest that Bin1 regulates the synaptic vesicle (SV) cycle, especially during SV release. After SV release, SV endocytic recycling involves compensatory endocytosis and SV reformation from an intermediate endosomal compartment, which requires scission and may depend on Bin1 activity. Moreover, we hypothesized that this function might be disrupted by the LOAD mutations, leading to synapse dysfunction. In this study, we assessed Bin1 function in inhibitory and excitatory synapses in primary mouse cortical neuron cultures. We found that Bin1 localizes presynaptically and has a crucial role in inhibitory synapses by regulating the SV exocytosis and endocytosis. Bin1 knockdown reduced synaptic endosome size in inhibitory neurons, likely by increasing SV exocytosis and endocytosis. In contrast, Bin1 knockdown only reduced exocytosis in excitatory neurons. Interestingly, inhibitory synapse loss was not rescued by the LOAD-associated Bin1 mutants or Aβ inhibition. Our results support that Bin1 loss of function may disrupt synapses prior to Aβ-dependent synapse dysfunction. Using immunoprecipitation coupled with mass spectrometry-based proteomic analysis, we found that the LOAD mutations disrupted Bin1 interactions, particularly with partners related to the SV cycle, actin dynamics, and intracellular trafficking. Using coimmunoprecipitation and proximity ligation assay, we confirmed that Bin1 mutants exhibited reduced interaction with regulators of SV cycle, VAMP2, SV2, dynamin, clathrin, and synaptojanin-1. Notably, clathrin overexpression restored GABAergic synapse density in Bin1 knockdown neurons, underscoring Bin1’s crucial role in the clathrin-mediated SV cycle. Bin1 knockdown increased neuronal hyperexcitability, likely due to the loss of inhibitory synapse function. This effect was mitigated by the antiepileptic levetiracetam, suggesting that Bin1 risk variants may lower the threshold for the development of seizures and contribute to AD development. Collectively, these findings suggest that the Bin1 mutation’s main impact is on the regulation of inhibitory synapse function, possibly contributing to the synaptic defects observed in Alzheimer’s disease.
Author: Barata, Mariana Afonso
Language: English
Subfield: Cellular and Molecular Neuroscience
Field: Neuroscience
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7064487744