Targeting SHIP1 for therapeutic intervention in Alzheimer’s disease

Abstract

Recent genome wide association studies (GWAS) and systems biology approaches have identified several Alzheimer,s disease (AD) risk associated genes; with many expressed in microglia, regulating functions such as motility, proliferation, survival and phagocytosis. Activation of the TREM2 signalling cascade mediates a protective phenotype, and variants of signalling molecules in the cascade are known to confer AD risk or protection. SHIP1 is a regulator of TREM2 signalling, acting as an inhibitor of the cascade by opposing Syk and PI3K phosphorylation, to prevent over-stimulation of the pathway. A SHIP1 variant (rs39349669) has been identified that confers AD risk by increasing SHIP1 expression, thereby inhibiting the TREM2 signalling cascade and reducing phagocytic signalling. We therefore hypothesise that inhibition of SHIP1 could restore the protective signalling pathway associated with TREM2. Utilising human WT TREM2 and TREM2 KO iPSC macrophages, we are working towards understanding the role of SHIP1 in regulating TREM2 mediated signalling cascades. We are investigating the effects of a SHIP1 inhibitor (3AC) on pSyk, pAkt, Ca2+ flux and phagocytosis following TREM2 stimulation with an activating antibody. In parallel, we have initiated screening activities to identify SHIP1 inhibitors. We have obtained a crystal structure of the phosphatase and C2 domains of SHIP1, and there is an ongoing effort to crystallise the protein with known inhibitors. We also plan to utilise the structure to initiate a fragment screen. Furthermore, a cell-free screening assay (Malachite green) has been developed to detect levels of inorganic phosphates released after SHIP1 mediated dephosphorylation of PI(3,4,5)P3 to PI(3,4)P2. We aim to demonstrate that SHIP1 regulates TREM2 signalling; is a druggable target; and that screening assays can be developed to identify inhibitors that will increase TREM2-mediated protective signalling in microglia. Targeting SHIP1 could therefore represent a novel therapeutic strategy for the treatment of AD.