Plaque vicinity as a hotspot of microglial turnover in a mouse model of Alzheimer's disease

Abstract

Microglia, the major immune cells of the brain, are functionally heterogeneous but in vivo functional properties of these cells are rarely studied at single‐cell resolution. By using microRNA‐9 regulated viral vectors for multicolor labeling and longitudinal in vivo monitoring of individual microglia, we followed their fate in the cortex of healthy adult mice and at the onset of amyloidosis in a mouse model of Alzheimer's disease. In wild‐type mice, microglia were rather mobile (16% of the cells migrated at least once in 10–20 days) but had a low turnover as documented by low division and death rates. Half of the migratory events were tightly associated with blood vessels. Surprisingly, basic migration properties of microglia (i.e., fraction of migrating cells, saltatory migration pattern, speed of migration, translocation distance, and strong association with blood vessels) were preserved in amyloid‐depositing brains, despite amyloid plaques becoming the major destination of migration. Besides, amyloid deposition significantly increased microglial division and death rates. Moreover, the plaque vicinity became a hotspot of microglial turnover, harboring 33% of all migration, 70% of death and 54% of division events.

Microglia contact cerebral vasculature through gaps between astrocyte endfeet

“…31, 32 Microglia soma can also shift over the course of several hours or weeks, 32–34 with many of these movements associated with blood vessels. 34 To illustrate that microglia-vascular contacts may be transient, we used in vivo two-photon microscopy to image microglia soma and processes spatially associated with pericytes on blood vessels at the arteriole and venule ends of the vascular tree, and within the capillary bed, through cranial windows implanted in NG2DsRed×CX3CR1 +/GFP mice. Microglia (CX3CR1 +/GFP ) and pericytes (NG2DsRed) were repetitively imaged over 7-minute periods.…”

“…32 Other studies suggest ∼14-16% of microglia soma shift >5 μm over the course of days to several weeks. 33, 34 Interestingly, as many as half of these migratory movements may be associated with blood vessels. 34 Determining migration in static EM images is clearly challenging, however evidence suggests the nuclear-centrosome (NC) axis may provide a surrogate of cell migration in many cells, including microglia.…”

“…33, 34 Interestingly, as many as half of these migratory movements may be associated with blood vessels. 34 Determining migration in static EM images is clearly challenging, however evidence suggests the nuclear-centrosome (NC) axis may provide a surrogate of cell migration in many cells, including microglia. 35, 38, 39 Although a role for the centrosome in microglia migration has not been definitively established, there is one report that microglia centrosomes can move up to 2 µm/min toward apoptotic neurons in the zebrafish optic tectum 3 days post-fertilisation in vivo .…”

Morphotype-specific calcium signaling in human microglia

“…MicroRNA-9 (miR-9) is a microRNA that promotes the degradation of mRNA with a specific complementary sequence. Because in mice miR-9 is expressed in virtually all CNS cells except microglia, it can be used for cell type-specific labeling of microglia [ 10 , 33 , 34 ]. This cell type specificity, however, relies on the interaction between the endogenous miR-9 and the exogenous substrate and thus can be overridden, if the concentration of exogenous mRNA is high or the concentration of endogenous miR-9 is low.…”

“…Production of miR9-regulated lentiviral vectors was described previously [ 34 , 35 ]. In brief, cell-free supernatants containing viral particles were produced by transient transfection of HEK293T packaging cells with the respective lentiviral construct along with the packing plasmids psPAX2 and pMD2G, following standard procedures.…”