Phosphoproteomics identifies microglial Siglec-F inflammatory response during neurodegeneration

Abstract

SummaryAlzheimer’s disease (AD) is characterized by the appearance of amyloid-β plaques, neurofibrillary tangles, and inflammation in brain regions involved in memory. Using mass spectrometry, we have quantified the phosphoproteome of the CK-p25, 5XFAD, and Tau P301S mouse models of neurodegeneration. We identified a shared response involving Siglec-F which was upregulated on a subset of reactive microglia. The human paralog Siglec-8 was also upregulated on microglia in AD. Siglec-F and Siglec-8 were upregulated following microglial activation with interferon gamma (IFNγ) in BV-2 cell line and human stem-cell derived microglia models. Siglec-F overexpression activates an endocytic and pyroptotic inflammatory response in BV-2 cells, dependent on its sialic acid substrates and immunoreceptor tyrosine-based inhibition motif (ITIM) phosphorylation sites. Related human Siglecs induced a similar response in BV-2 cells. Collectively, our results point to an important role for mouse Siglec-F and human Siglec-8 in regulating microglial activation during neurodegeneration.HighlightsPhosphoproteomics analysis of CK-p25, 5XFAD, and Tau P301S mouse models finds dysregulated signaling networks associated with Alzheimer’s disease pathologies.A phosphorylation site on Siglec-F is found to be upregulated across all three models of disease.Expression of Siglec-F and its human paralog Siglec-8 is increased in reactive microglia.Overexpression of Siglec-F and Siglec-8in vitrodrives an endocytic and pyroptotic inflammatory response.In BriefPhosphoproteome signaling changes associated with Alzheimer’s disease (AD) are poorly characterized. Here, Morshed et al. apply phosphoproteomics to mouse models of AD to uncover a novel microglial receptor, Siglec-F, that is upregulated on a subset of inflammatory microglia across models of neurodegeneration. The human paralog, Siglec-8 is also found to be upregulated in late-onset AD microglia. Overexpression of Siglec-F and related human Siglecs activates pro-inflammatory signaling responses in BV-2 cells.