A novel role for SHARPIN in amyloid-beta phagocytosis and inflammation by peripheral blood-derived macrophages in Alzheimers disease

INTRODUCTION: Defective immune cell-mediated clearance of amyloid-beta (Aβ) and Aβ-associated inflammatory activation of immune cells are key contributors of Aβ accumulation and neurodegeneration in Alzheimers disease (AD), however, the underlying mechanisms remain elusive. METHODS: Differentiated THP-1 cells treated with Aβ and AD patient-derived macrophages were used as in-vitro model. The role of SHARPIN was analysed in differentiated THP-1 cells using siRNA-mediated knockdown followed by immunoblotting, ELISA, real-time PCR, immunoprecipitation and flow cytometry. Differentiated SHSY5Y cells were used to study inflammation-mediated apoptosis. RESULTS: SHARPIN was found to regulate Aβ- phagocytosis and NLRP3 expression in THP-1 derived macrophages. Further, it was found to promote macrophage polarization to an M1 (pro-inflammatory) phenotype resulting in enhanced inflammation and associated neuronal death, demonstrated using in-vitro culture systems. SHARPIN expression by blood-derived macrophages was further found to be higher in the early stages of AD, which correlates with Aβ40/42 concentration in the plasma and age of the study subjects. DISCUSSION: The novel protein, SHARPIN has been shown to play critical roles in regulation of Aβ-phagocytosis and inflammation in AD and the mechanism by which SHARPIN is activated by Aβ in macrophages has been elucidated.