The proteomic profile of Von Economo neurons supports their selective vulnerability in bvFTD

Abstract

AbstractBackgroundVon Economo neurons (VENs) are long‐range projection neurons embedded in Layer 5 of the anterior cingulate gyrus (ACC) and frontoinsular cortex. VENs are selectively vulnerable in a number of diseases, most notably in those associated with behavioural, social, and cognitive changes, including the behavioural variant frontotemporal dementia (bvFTD). In particular, VENs of bvFTD donors with TDP43 or FUS pathology appear to be more vulnerable compared to donors with tau pathology. Unravelling the characteristics of VENs and the cause of their vulnerability in specific subtypes of FTD, will provide invaluable insight into disease mechanisms and potential avenues for drug therapeutics.MethodSingle‐cell laser capture microdissection (LCM) in combination with proteomics was used to analyse the proteome of VENs compared to neighbouring Layer 5 pyramidal neurons of the ACC (ACC‐PYR) and the superior frontal gyrus (SFG‐PYR), a region adjacent to the ACC. Immunohistochemistry (IHC) was performed on 10µm thick fresh frozen sections of the ACC and SFG from four neurologically healthy control donors with the neurofilament marker, SMI32. 1000 VENs and three times 1000 ACC‐PYR, and SFG‐PYR were then delineated and captured using LCM. After protein separation, all samples were analysed by label‐free mass spectrometry (LC‐MS/MS) in a data independent manner.ResultAn average 2660 proteins were detected per sample, which accumulated in a total detection of 4718 different proteins over all samples. 69 proteins had a significant change in abundance between VENs and SFG‐PYR, and 36 proteins when VENs were paired against ACC‐PYR. A number of proteins were validated with IHC. GO‐pathway analysis revealed RNA processing and splicing, neurofilament bundle assembly and cytoskeleton organization to be among top deregulated pathways, with many proteins localised to the ribonucleoprotein complex.ConclusionWe show a number proteins involved in RNA processing to be differentially expressed in VENs compared to neighbouring pyramidal neurons. Since TDP43 and FUS proteins are also involved in RNA processing we hypothesise that the selective vulnerability of VENs in specific FTD subtypes is through altered RNA metabolism.