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pSIVA: Apoptosis DetectionKit in Live Cells

Reference 1.

Microglia use TAM receptors to detect and engulf amyloid beta plaques

Nat Immunol. 2021 May ; 22(5): 586–594. https://www.nature.com/articles/s41590-021-00913-5

Two microglial TAM receptor tyrosine kinases - Axl and Mer - have been linked to Alzheimer’s disease, but their roles in disease have not been tested experimentally. We find that in Alzheimer’s disease and its mouse models, induced expression of Axl and Mer in amyloid plaque-associated microglia was coupled to induced plaque decoration by the TAM ligand Gas6 and its co-ligand phosphatidylserine. In the APP/PS1 mouse model of Alzheimer’s disease, genetic ablation of Axl and Mer resulted in microglia that were unable to normally detect, respond to, organize, or phagocytose amyloid beta plaques. These major deficits notwithstanding, TAM-deficient APP/PS1 mice developed fewer dense-core plaques than APP/PS1 mice with normal microglia. Our findings reveal that the TAM system is an essential mediator of microglial recognition and engulfment of amyloid plaques, and that TAM-driven microglial phagocytosis does not inhibit, but rather promotes, dense-core plaque development.

Reference 2.

TMEM16F Aggravates Neuronal Loss by Mediating Microglial Phagocytosis of Neurons in a Rat Experimental Cerebral Ischemia and Reperfusion Model

Front. Immunol., 07 July 2020 | https://doi.org/10.3389/fimmu.2020.01144

Cerebral ischemia is a severe, acute condition, normally caused by cerebrovascular disease, and results in high rates of disability, and death. Phagoptosis is a newly recognized form of cell death caused by phagocytosis of viable cells, and has been reported to contribute to neuronal loss in brain tissue after ischemic stroke. Previous data indicated that exposure of phosphatidylserine to viable neurons could induce microglial phagocytosis of such neurons. Phosphatidylserine can be reversibly exposed to viable cells as a result of a calcium-activated phospholipid scramblase named TMEM16F. TMEM16F-mediated phospholipid scrambling on platelet membranes is critical for hemostasis and thrombosis, which plays an important role in Scott syndrome and has been confirmed by much research. However, few studies have investigated the association between TMEM16F and phagocytosis in ischemic stroke. In this study, a middle-cerebral-artery occlusion/reperfusion (MCAO/R) model was used in adult male Sprague-Dawley rats in vivo, and cultured neurons were exposed to oxygen-glucose deprivation/reoxygenation (OGD/R) to simulate cerebral ischemia-reperfusion (I/R) injury in vitro. We found that the protein level of TMEM16F was significantly increased at 12 h after I-R injury both in vivo and in vitro, and reversible phosphatidylserine exposure was confirmed in neurons undergoing I/R injury in vitro. Additionally, we constructed a LV-TMEM16F-RNAi transfection system to suppress the expression of TMEM16F during and after cerebral ischemia. As a result, TMEM16F knockdown alleviated motor function injury and decreased the microglial phagocytosis of viable neurons in the penumbra through inhibiting the “eat-me” signal phosphatidylserine. Our data indicate that reducing neuronal phosphatidylserine-exposure via deficiency of TMEM16F blocks phagocytosis of neurons and rescues stressed-but-still-viable neurons in the penumbra, which may contribute to reducing infarct volume and improving functional recovering.