Different subtypes of wasteosomes in the human hippocampus

Abstract

Wasteosomes (also known as corpora amylacea) are polyglucosan bodies that amass waste substances. They are generated in the central nervous system during normal aging and neurodegenerative processes, then extruded into the cerebrospinal fluid and finally phagocytised by macrophages in the cervical lymph nodes. In this work we study the possible existence of different wasteosomes depending on their location in the human hippocampus. We performed staining techniques combined with digestion with γ-amylase. These techniques were Lugol’s iodine, periodic acid-Schiff and concanavalin A staining, and a double indirect immunofluorescence to detect the neo-epitopes and the protein p62. Results showed there are two subtypes of wasteosomes with respect to their behaviour towards γ-amylase and their content in neo-epitopes and protein p62. Wasteosomes in the inner areas of the hippocampus contained more protein p62, less neo-epitopes, and had a less resistant polymerised structure towards γ-amylase. Conversely, wasteosomes in the peripheral areas of the hippocampus contained less protein p62, more neo-epitopes, and had a more resistant polymerised structure towards γ-amylase. The differences observed could be related to different maturation stages. Wasteosomes in the inner areas could have a less phosphorylated and a more branched amylopectin-like polymer structure, whereas wasteosomes in the peripheral areas could have a mainly phosphorylated and a less branched amylose-like polymer structure. These findings reinforce that wasteosomes are involved in the elimination of brain waste substances, for which reason they undergo a maturation process during which composition and structural changes may occur. Key words: corpora amylacea, wasteosomes, γ-amylase, human hippocampus.