Plasma Small Extracellular Vesicles with Complement Alterations in GRN/C9orf72 and Sporadic Frontotemporal Lobar Degeneration.

Sonia Bellini,Giulia D’Arrigo,Antonio Longobardi,Claudia Saraceno,Roland Nicsanu,Roberta Ghidoni,Rosanna Squitti,Claudia Verderio,Laura Canafoglia,Luisa Benussi,Cinzia Coppola,Gianfranco Puoti,Marta Lombardi,Giacomina Rossi,Martina Ricci,Sara Cimini,Giuliano Binetti,Clarissa Ferrari

doi:10.3390/cells11030488

Abstract

Cutting-edge research suggests endosomal/immune dysregulation in GRN/C9orf72-associated frontotemporal lobar degeneration (FTLD). In this retrospective study, we investigated plasma small extracellular vesicles (sEVs) and complement proteins in 172 subjects (40 Sporadic FTLD, 40 Intermediate/Pathological C9orf72 expansion carriers, and 49 Heterozygous/Homozygous GRN mutation carriers, 43 controls). Plasma sEVs (concentration, size) were analyzed by nanoparticle tracking analysis; plasma and sEVs C1q, C4, C3 proteins were quantified by multiplex assay. We demonstrated that genetic/sporadic FTLD share lower sEV concentrations and higher sEV sizes. The diagnostic performance of the two most predictive variables (sEV concentration/size ratio) was high (AUC = 0.91, sensitivity 85.3%, specificity 81.4%). C1q, C4, and C3 cargo per sEV is increased in genetic and sporadic FTLD. C4 (cargo per sEV, total sEV concentration) is increased in Sporadic FTLD and reduced in GRN+ Homozygous, suggesting its specific unbalance compared with Heterozygous cases. C3 plasma level was increased in genetic vs. sporadic FTLD. Looking at complement protein compartmentalization, in control subjects, the C3 and C4 sEV concentrations were roughly half that in respect to those measured in plasma; interestingly, this compartmentalization was altered in different ways in patients. These results suggest sEVs and complement proteins as potential therapeutic targets to mitigate neurodegeneration in FTLD.

Highlights

Frontotemporal lobar degeneration (FTLD) is among the most common forms of presenile dementia, mainly affecting people younger than 65, and accounting for up to15% of all dementias [1,2]
From the cause of frontotemporal lobar degeneration (FTLD) onset—loss of progranulin, C9orf72 gene expansion or pathological processes underlying Sporadic FTLD—a dysregulation of small extracellular vesicles (sEVs) production seems to be a common mechanism underlying the disease process. This new concept is supported by our investigation encompassing the assessment of plasma sEV indices in a relatively large group of FTLD patients, including sporadic patients, genetic patients
C9orf72 expansion carriers, genes encoding for progranulin (GRN) heterozygous mutation carriers), and GRN homozygous mutation carriers affected by neuronal ceroid lipofuscinosis (NCL), a lysosomal storage disorder

Summary

Introduction

Frontotemporal lobar degeneration (FTLD) is among the most common forms of presenile dementia, mainly affecting people younger than 65, and accounting for up to. Breakthrough molecular studies have suggested lysosomal/endosomal dysfunction, neurotoxic microglia activation, and immune system dysregulation as pathological features in GRN/C9orf72-associated FTLD [23,24]: GRN-FTLD brains exhibited signs of lysosomal dysfunction such as elevated lipofuscin accumulation, impaired activity of lysosomal enzymes [25], and elevated levels of lysosomal proteins [26]. We sought to investigate small EV (sEV) production and complement dysregulation in patients affected by sporadic and genetic FTLD to challenge whether differential molecular pathways are associated with the progressive loss of progranulin or C9orf or whether common mechanisms of immunity/endo-lysosomal pathways can explain pathophysiological processes underlying clinical FTLD subtype overlaps

Subjects

Biochemical Analyses

Statistical Analysis

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Discussion