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The γ-secretase substrate proteome and its role in cell signaling regulation

ABSTRACT: γ-Secretase is involved in the regulated intramembrane proteolysis (RIP) of a variety of integral membrane proteins and generates the amyloid peptide (Aβ) in Alzheimer’s Disease (AD). Microglia are centrally involved in AD, but the substrates and function of γ-secretase in these cells remain largely unstudied. Using a novel γ-Secretase Substrate Identification (G-SECSI) method, we identified 85 substrates, of which 59 were previously unknown, in stem cell derived microglia-like cells. More than 60% of those are signalling receptors possibly involved in cell state regulation. Inhibition of γ-secretase using Semagacestat or selective genetic knockout alters the expression of homeostatic (HM) and disease-associated (DAM) genes, in particular when microglia are exposed to amyloid plaques in vivo. Thus, γ-secretase regulates tonic signaling via a spectrum of substrates in microglia in steady state, and its blockage results in the defective transition to the DAM response in AD.

INSTRUMENT(S): LTQ Orbitrap

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Embryonic Stem Cell

SUBMITTER: Andrew Howden

LAB HEAD: Bart De

PROVIDER: PXD039238 | Pride | 2023-11-14

REPOSITORIES: Pride

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Project description:GFAP and vimentin deficiency alters gene expression in astrocytes and microglia in wild-type mice and changes the transcriptional response of reactive glia in mouse model for Alzheimer's disease. Reactive astrocytes with an increased expression of intermediate filament (IF) proteins Glial Fibrillary Acidic Protein (GFAP) and Vimentin (VIM) surround amyloid plaques in Alzheimer's disease (AD). The functional consequences of this upregulation are unclear. To identify molecular pathways coupled to IF regulation in reactive astrocytes, and to study the interaction with microglia, we examined WT and APPswe/PS1dE9 (AD) mice lacking either GFAP, or both VIM and GFAP, and determined the transcriptome of cortical astrocytes and microglia from 15- to 18-month-old mice. Genes involved in lysosomal degradation (including several cathepsins) and in inflammatory response (including Cxcl5, Tlr6, Tnf, Il1b) exhibited a higher AD-induced increase when GFAP, or VIM and GFAP, were absent. The expression of Aqp4 and Gja1 displayed the same pattern. The downregulation of neuronal support genes in astrocytes from AD mice was absent in GFAP/VIM null mice. In contrast, the absence of IFs did not affect the transcriptional alterations induced by AD in microglia, nor was the cortical plaque load altered. Visualizing astrocyte morphology in GFAP-eGFP mice showed no clear structural differences in GFAP/VIM null mice, but did show diminished interaction of astrocyte processes with plaques. Microglial proliferation increased similarly in all AD groups. In conclusion, absence of GFAP, or both GFAP and VIM, alters AD-induced changes in gene expression profile of astrocytes, showing a compensation of the decrease of neuronal support genes and a trend for a slightly higher inflammatory expression profile. However, this has no consequences for the development of plaque load, microglial proliferation, or microglial activation. 2 cell types from 6 conditions: cortical microglia and cortical astrocytes from 15-18 month old APPswe/PS1dE9 mice compared to wildtype littermates. Biological replicates: microglia from APPswe/PS1dE9, N=7, microglia from WT, N=7, astrocytes from APPswe/PS1dE9, N=4, microglia from WT, N=4

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The γ-secretase substrate proteome and its role in cell signaling regulation

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