Amyloid-ß deposits in human astrocytes contain truncated and highly resistant proteoforms.

Alzheimer's disease (AD) is a neurodegenerative disorder that develops over decades. Glial cells, including astrocytes are tightly connected to the AD pathogenesis, but their impact on disease progression is still unclear. Our previous data show that astrocytes take up large amounts of aggregated amyloid-beta (Aß) but are unable to successfully degrade the material, which is instead stored intracellularly. The aim of the present study was to analyze the astrocytic Aß deposits composition in detail in order to understand their role in AD propagation. For this purpose, human induced pluripotent cell (hiPSC)-derived astrocytes were exposed to sonicated Aß42 fibrils and magnetic beads. Live cell imaging and immunocytochemistry confirmed that the ingested Aß aggregates and beads were transported to the same lysosomal compartments in the perinuclear region, which allowed us to successfully isolate the Aß deposits from the astrocytes. Using a battery of experimental techniques, including mass spectrometry, western blot, ELISA and electron microscopy we demonstrate that human astrocytes truncate and pack the Aß aggregates in a way that makes them highly resistant. Moreover, the astrocytes release specifically truncated forms of Aß via different routes and thereby expose neighboring cells to pathogenic proteins. Taken together, our study establishes a role for astrocytes in mediating Aß pathology, which could be of relevance for identifying novel treatment targets for AD.

BDCA-2, a novel plasmacytoid dendritic cell-specific type II C-type lectin, mediates antigen capture and is a potent inhibitor of interferon alpha/beta induction.

Plasmacytoid dendritic cells are present in lymphoid and nonlymphoid tissue and contribute substantially to both innate and adaptive immunity. Recently, we have described several monoclonal antibodies that recognize a plasmacytoid dendritic cell-specific antigen, which we have termed BDCA-2. Molecular cloning of BDCA-2 revealed that BDCA-2 is a novel type II C-type lectin, which shows 50.7% sequence identity at the amino acid level to its putative murine ortholog, the murine dendritic cell-associated C-type lectin 2. Anti-BDCA-2 monoclonal antibodies are rapidly internalized and efficiently presented to T cells, indicating that BDCA-2 could play a role in ligand internalization and presentation. Furthermore, ligation of BDCA-2 potently suppresses induction of interferon alpha/beta production in plasmacytoid dendritic cells, presumably by a mechanism dependent on calcium mobilization and protein-tyrosine phosphorylation by src-family protein-tyrosine kinases. Inasmuch as production of interferon alpha/beta by plasmacytoid dendritic cells is considered to be a major pathophysiological factor in systemic lupus erythematosus, triggering of BDCA-2 should be evaluated as therapeutic strategy for blocking production of interferon alpha/beta in systemic lupus erythematosus patients.

BDCA-2, BDCA-3, and BDCA-4: three markers for distinct subsets of dendritic cells in human peripheral blood.

We have generated a panel of mAbs that identify three presumably novel human dendritic cell Ags: BDCA-2, BDCA-3, and BDCA-4. In blood, BDCA-2 and BDCA-4 are expressed on CD11c(-) CD123(bright) plasmacytoid dendritic cells, whereas BDCA-3 is expressed on small population of CD11c(+) CD123(-) dendritic cells. All three Ags are not detectable on a third blood dendritic cell population, which is CD1c(+) CD11c(bright) CD123(dim), or on any other cells in blood. BDCA-4 is also expressed on monocyte-derived and CD34(+) cell-derived dendritic cells. Expression of all three Ags dramatically changes once blood dendritic cells undergo in vitro maturation. BDCA-2 is completely down-regulated on plasmacytoid CD11c(-) CD123(bright) dendritic cells, expression of BDCA-3 is up-regulated on both plasmacytoid CD11c(-) CD123(bright) dendritic cells and CD1c(+) CD11c(bright) CD123(dim) dendritic cells, and expression of BDCA-4 is up-regulated on CD1c(+) CD11c(bright) CD123(dim) dendritic cells. BDCA-2 is rapidly internalized at 37 degrees C after mAb labeling. The three presumably novel Ags serve as specific markers for the respective subpopulations of blood dendritic cells in fresh blood and will be of great value for their further analysis and to evaluate their therapeutic potential.