The late‐onset Alzheimer's disease genetic risk factor CD2AP impacts synapses via actin dynamics

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AbstractBackgroundIn late‐onset Alzheimer’s disease (LOAD) the causal mechanisms of synaptic dysfunction that underlie the memory deficits that lead to dementia are not established. The search for genetic risk factors in LOAD led to the identification of more than 20 genes and three main mechanisms: endocytic trafficking, lipid metabolism and immune response. Here we aim to establish causality between a mutation in CD2AP, one of the endocytic trafficking risk factors, and synaptic dysfunction. Since CD2AP is a regulator of the actin cytoskeleton dynamics which is essential for spine morphology, we hypothesize that a LOAD mutation CD2AP may impact spines by deregulating actin.MethodWe have analyzed synapses and spines density as well as spinal actin in cortical mouse primary neurons either transiently overexpressing wild‐type and mutant CD2AP‐GFP as well as GFP as control or infected with lentivirus expressing GFP and shCD2AP or non‐targeting shRNA as control. Moreover, we investigated CD2AP synaptic localization by immunofluorescence microscopy. We used quantitative single‐cell analysis using ICY and Imaris software.ResultWe discovered that a pool of CD2AP is present in spines; and that both CD2AP wild‐type and mutant are significantly enriched in spines. Spines length decreased with larger spine heads, by CD2AP wild‐type and more pronouncedly by mutant CD2AP overexpression. Indicating that CD2AP might function at synapses, by regulating spine morphology. Indeed, synapses density was reduced by CD2AP knockdown. Mechanistically, we found that spinal F‐actin increased by CD2AP wild‐type and more pronouncedly by mutant CD2AP overexpression compared to control neurons. We are currently investigating whether spinal F‐actin is altered by CD2AP knockdown.ConclusionThese results indicate that CD2AP regulates spine morphology and thus synapses. A LOAD mutant CD2AP may interfere with its function by dysregulating actin dynamics at spines. Overall CD2AP variants may contribute to LOAD development by directly interfering with synapses.