Preface.
Endocytosis(endocytosis), also known as cytokinesis and endocytosis, is the process of transporting extracellular substances into the cell through the deformation movement of the plasma membrane. According to the different sizes of the entry substances and the different mechanisms of entry, endocytosis can be divided into three types: phagocytosis, swallowing, and receptor-mediated endocytosis.
1. Phagocytosis refers to the process of ingesting particulate matter larger than 1 m in diameter. When particulate matter is ingested, the cells are partially deformed, causing the plasma membrane to become depressed or pseudopodia forming to envelop the particles around human cells. The protrusion of pseudopodia is involved in actin, and cytophagocytosis can be inhibited with drugs that inhibit actin polymerization such as cytorelaxin.
2. Pinocytosis is the process by which cells ingest solutes or liquids. When the cell swallows, the local plasma membrane sinks to form a dimple that surrounds the liquid material, and then the foskus leave the plasma membrane to form vesicles and enter the cell. Swallowing is divided into liquid phase endocytosis and adsorption endocytosis. In the former method, non-specific cells ingest extracellular fluid and its soluble substances into the cell. In the latter approach, extracellular macromolecules, or particulate matter, are somehow adsorbed to the cell surface and are subsequently ingested into the cell. For example, cationic ferritin is first adsorbed on the surface of negatively charged cells by electrostatic action before being taken up by cells. Adsorption endocytosis has some specificity.
3. Receptor mediated endocytosis is the process by which cells rely on receptors on the cell surface to specifically uptake extracellular proteins or other compounds. The receptor on the cell surface is highly specific and binds to the corresponding ligand (the molecule that is endocytosed) to form a complex, and then this part of the plasma membrane is depressed to form a tunicola, which detaches from the plasma membrane to form a tunicolae, which ingests extracellular material into the cell. After being entered into the cell by vesicles, it takes off its coat and combines with the small vesicles of the endosomes to form large endosomes, which are acidic in content, separating the receptor from the ligand. Part of the membrane structure with the receptor sprouts, falls off, and then fuses with the plasma membrane, and the receptor returns to the plasma membrane to complete the recirculation of the receptor.
Phagocytosis and neurodegenerative diseases.
Citation 1: LC3-associated endocytosis facilitates -amyloid clearance and mitigates neurodegeneration in murine alzheimer's disease
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The study not only discovered LC3-associated endocytosis (LANDO) of LC3 Gabarap family proteins bound to endosomal membranes. Loss of lando leads to decreased recycling of -amyloid receptors, thereby reducing the sequential uptake and degradation of -amyloid by microglia. At the same time, the loss of lando affects the secondary uptake of -amyloid, resulting in increased extracellular-amyloid deposition and promoting inflammatory signaling. Thus, LANDO (LC3-associated endocytosis) in microglia promotes not only immune clearance, but also anti-inflammatory immune responses.
Citation 2: Trem2 drives microglia response to amyloid- via syk-dependent and-independent pathways
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Scientists have found that microglia respond to -amyloid by activating a signaling mechanism mediated by TREM2 involving SYK and DAP10. In mice expressing the human trem2r47h allele associated with Alzheimer's disease, antibody-mediated SYK activation rescues microglial activation.
Phagocytic activity is one of the most commonly used assays to assess microglial activity, and this process is closely related to glycolytic oxphos homeostasis.
Examples of microglial phagocytosis.
acidsensorThe labeled substances are absorbed by the cells, and when they reach acidic organelles such as lysosomes, the fluorescence is enhanced. Taking advantage of this property, we used acidsensor-labeled apoptotic cells with apoptotic cellscalceinCo-culture labeled THP-1 macrophages to assess phagocytic activity of apoptotic cells. As a result, corderyanin (green) and AcidSensor (dark red) double-positive cells were observed by flow cytometry, indicating that THP-1 macrophages engulfed apoptotic cells (Figure 1A). In addition, the proportion of double-positive cells decreased when cytochalasin D inhibited phagocytosis of THP-1 macrophages (Figures 1b and 1c), confirming that the detection system accurately assesses phagocytosis.
A recent report showed that inhibition of mitochondrial function induces cultured microglia (resident macrophages in the central nervous system) to switch to glycolysis and reduce phagocytosis*. To replicate this result, we performed a phagocytosis assay using mitochondria-inhibited THP-1 macrophages. The results showed that SCCPs were potent uncoupling agents for oxidative phosphorylation of mitochondria, which reduced the rate of THP-1 macrophagesMitochondrial membrane potential (MT-1, red).(Figure 2) and reduce phagocytosis (Figure 3).
Product Used: AcidSensor Labeling Kit Endocytic Internalization Assay [Catalog No.: A558].
Cellstain- Calcein-Am [Cat. No.: C542].
MT-1 MITOMP Detection Kit [Catalog No.: MT13].
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