Wasteosomes (corpora amylacea) of human brain can be phagocytosed and digested by macrophages

Abstract

Background Corpora amylacea of human brain, recently renamed as wasteosomes, are granular structures that appear during aging and also accumulate in specific areas of the brain in neurodegenerative conditions. Acting as waste containers, wasteosomes are formed by polyglucosan aggregates that entrap and isolate toxic and waste substances of different origins. They are expelled from the brain to the cerebrospinal fluid (CSF), and can be phagocytosed by macrophages. In the present study, we analyze the phagocytosis of wasteosomes and the mechanisms involved in this process. Accordingly, we purified wasteosomes from post-mortem extracted human CSF and incubated them with THP-1 macrophages. Immunofluorescence staining and time-lapse recording techniques were performed to evaluate the phagocytosis. We also immunostained human hippocampal sections to study possible interactions between wasteosomes and macrophages at central nervous system interfaces. Results We observed that the wasteosomes obtained from post-mortem extracted CSF are opsonized by MBL and the C3b complement protein. Moreover, we observed that CD206 and CD35 receptors may be involved in the phagocytosis of these wasteosomes by THP-1 macrophages. Once phagocytosed, wasteosomes become degraded and some of the resulting fractions can be exposed on the surface of macrophages and interchanged between different macrophages. However, brain tissue studies show that, in physiological conditions, CD206 but not CD35 receptors may be involved in the phagocytosis of wasteosomes. Conclusions The present study indicates that macrophages have the machinery required to process and degrade wasteosomes, and that macrophages can interact in different ways with wasteosomes. In physiological conditions, the main mechanism involve CD206 receptors and M2 macrophages, which trigger the phagocytosis of wasteosomes without inducing inflammatory responses, thus avoiding tissue damage. However, altered wasteosomes like those obtained from post-mortem extracted CSF, which may exhibit waste elements, become opsonized by MBL and C3b, and so CD35 receptors constitute another possible mechanism of phagocytosis, leading in this case to inflammatory responses.

Uncovering tau in wasteosomes (corpora amylacea) of Alzheimer’s disease patients

“…To detect wasteosomes, a mouse monoclonal IgG 2 a against p62 (1: 250; ab56416; Abcam, Cambridge, UK) was used. Although p62 is an autophagy selective adaptor that is found and can be identified in most cells, labeling of wasteosomes with an anti-p62 shows a large and distinctive accumulation of p62 on their surface with a highly intense labeling and a characteristic ring shape, which enables wasteosomes to be specifically and unmistakably distinguished from other autophagic structures stained with anti-p62 ( Augé et al, 2018a ; Riba et al, 2021b , 2022a ). The sections were then washed and incubated for 1 h at room temperature with the corresponding secondary antibodies: AF488 goat anti-mouse IgG 1 (1: 250; A-21121; Life Technologies, Eugene, OR, USA) and AF555 goat anti-mouse IgG 2 a (1: 250; A-21137; Life Technologies).…”

“…Natural IgMs can bind to certain neoepitopes, which are epitopes that are formed de novo in tissues or structures that have to be removed, and which can be present in wasteosomes ( Augé et al, 2019 ). These IgMs have been used to stain both wasteosomes and their equivalent structures in the mouse brain called periodic acid-Schiff (PAS) granules ( Manich et al, 2015 ; Augé et al, 2017 , 2018b , 2019 ; Riba et al, 2019 , 2021b , 2022a ; Wander et al, 2020 , 2022 ). Recent findings have pointed out the carbohydrate nature of the neoepitopes of wasteosomes, although their specific structure remains unknown ( Riba et al, 2021b ).…”

Endothelial cells and macrophages as allies in the healthy and diseased brain

“…One histological characteristic of old brains is the presence of corpora amylacea, which have recently been referred to as wasteosomes [ 100 ]. Corpora amylacea are mainly spherical bodies rich in polysaccharides and waste products, with a diameter ranging from < 2 µm to around 20 μm, found in the human brain, especially of the elderly.…”

Corpora amylacea negatively correlate with hippocampal tau pathology in Alzheimer’s disease

“…An alternative to the clearance of tau through the glymphatic system is corpora amylacea (CA)-mediated waste clearance, a mechanism present in the central nervous system and other tissues. CA, also known as wasteosomes ( Riba et al, 2022a , b , 2023 ), have recently been linked to the glymphatic system ( Riba et al, 2022b ). CA are granular bodies ranging from 10 to 50 μm that accumulate waste products throughout the brain ( Cavanagh, 1999 ; Navarro et al, 2018 ; Riba et al, 2019 ).…”