Author:

Keywords:

Science & Technology, Life Sciences & Biomedicine, Cell Biology, Geriatrics & Gerontology, Late-onset Alzheimer's disease, Endolysosomal homeostasis, Microglia, Membrane transport, Phagocytosis, AMYLOID PRECURSOR PROTEIN, TOLL-LIKE RECEPTORS, A-BETA, HUMAN BRAIN, CATHEPSIN-B, ION-CHANNEL, MOUSE MODEL, DEGRADATION, CLEARANCE, PEPTIDE, Late-onset Alzheimer’s disease, Alzheimer Disease, Humans, Lysosomes, C14/21/095#56286976, G056017N#54022109, G078117N#54021292, G0C4220N#55522043, 12ZL321N#55739363, 1S35019N|1S35021N#54462868, KA/20/085#56130159, 0601 Biochemistry and Cell Biology, 1103 Clinical Sciences, 1109 Neurosciences, Gerontology, 3101 Biochemistry and cell biology, 3202 Clinical sciences, 3209 Neurosciences

Abstract:

Microglia, the brain-resident immune cells, play an essential role in the upkeep of brain homeostasis. They actively adapt into specific activation states based on cues from the microenvironment. One of these encompasses the activated response microglia (ARMs) phenotype. It arises along a healthy aging process and in a range of neurodegenerative diseases, including Alzheimer's disease (AD). As the phenotype is characterized by an increased lipid metabolism, phagocytosis rate, lysosomal protease content and secretion of neuroprotective agents, it leaves to reason that the phenotype is adapted in an attempt to restore homeostasis. This is important to the conundrum of inflammatory processes. Inflammation per se may not be deleterious; it is only when microglial reactions become chronic or the microglial subtype is made dysfunctional by (multiple) risk proteins with single-nucleotide polymorphisms that microglial involvement becomes deleterious instead of beneficial. Interestingly, the ARMs up- and downregulate many late-onset AD-associated risk factor genes, the products of which are particularly active in the endolysosomal system. Hence, in this review, we focus on how the endolysosomal system is placed at the crossroad of inflammation and microglial capacity to keep pace with degradation.