Phosphoproteomics identifies microglial Siglec-F inflammatory response during neurodegeneration

Alzheimers disease (AD) is characterized by the appearance of amyloid-{beta} 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 (IFN{gamma}) 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. HighlightsO_LIPhosphoproteomics analysis of CK-p25, 5XFAD, and Tau P301S mouse models finds dysregulated signaling networks associated with Alzheimers disease pathologies. C_LIO_LIA phosphorylation site on Siglec-F is found to be upregulated across all three models of disease. C_LIO_LIExpression of Siglec-F and its human paralog Siglec-8 is increased in reactive microglia. C_LIO_LIOverexpression of Siglec-F and Siglec-8 in vitro drives an endocytic and pyroptotic inflammatory response. C_LI In BriefPhosphoproteome signaling changes associated with Alzheimers 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.