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

Abstract

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.

Annexin A1 protects against cerebral ischemia–reperfusion injury by modulating microglia/macrophage polarization via FPR2/ALX-dependent AMPK-mTOR pathway

“…While it is not known if the low ANXA1 persists before stroke and can be linked to underlying conditions for stroke such as atherosclerosis, this finding suggest that plasma ANXA1 may predict clinical outcomes of AIS and the effectiveness of EVT therapies. In addition, the cause of reduced plasma ANXA1 is not known; it can be consumptive because ANXA1 is a member of annexins that share the ability to bind the anionic phospholipid phosphatidylserine, which is expressed on the surface of injured and apoptotic cells that increase significantly during AIS [ 34 ]. Alternatively, the synthesis and release of ANXA1 may be inhibited during AIS.…”

Classification of Cell-in-Cell Structures: Different Phenomena with Similar Appearance

“…This can result in the reorganization of neuronal architecture and synapses [64]. As mentioned before, molecules such as LPS, LTA, and β-amyloid can induce PS exposure on viable cells such as neurons [49]. PS exposure can also be induced by hypoxia associated with transient ischemia [65].…”

“…Some extracellular molecules, including dimeric galectin 1, lipopolysaccharide (LPS), lipoteichoic acid (LTA), and β-amyloid or S-nitrosylated cellular proteins can induce PS exposure without inducing apoptosis [44][45][46][47][48]. Moreover, the process has been reported to be reversible [45,46,49,50].…”

The semantics of microglia activation: neuroinflammation, homeostasis, and stress

“…This secondary tissue damage may also contribute to the infiltration of peripheral monocytes in the brain parenchyma, where they proliferate and gradually take over as the predominant phagocytes at the site of injury [53]. Both microglia and peripheral monocytes are involved with clearing debris after stroke, which attenuates inflammation; however they may also phagocytose injured yet viable neurons, leading to greater tissue damage [54][55][56]. While these findings indicate that microglia drive pathology in stroke, there is evidence to suggest microglia also play a neuroprotective role.…”