Studies of familial Alzheimer's disease (AD) have revealed three important AD genes, Amyloid Precursor Protein (APP), Presenilin 1 (PS1) and Presenilin 2 (PS2), in which mutations lead to autosomal dominant AD with nearly complete penetrance. Recent literature and our preliminary studies suggest that the presenilins and the ?-secretase complex play a role in critical cellular pathways including the response to inflammatory stimuli. Conditional PS1/2 repression in mice leads to upregulation of inflammatory genes in the cortex and increased numbers of microglia. PS2 deficient mice develop adult pulmonary fibrosis, a condition presumed to be a result of chronic inflammation in the human. Systems analysis of multiple genomic datasets reveals PS2 is overrepresented in immune pathways and is co-regulated with critical innate immunity signaling molecules. We have shown that PS2 protein is increased in microglia from human AD brain tissue and in cultured microglia activated by inflammatory stimuli. We show that inflammatory stimuli also decrease ?-secretase mediated APP cleavage while ?-secretase inhibitors augment release of inflammatory cytokines by microglia. Using microglia stably expressing short hairpin RNA (shRNA) targeted against PS2 we have found that microglia deficient in PS2 expression manifest an exaggerated inflammatory response. We propose to study the mechanism by which PS2 contributes to neurodegenerative disease by characterizing the phenotype of microglia deficient in PS2 or expressing Familial AD (FAD) PS2 mutations in vitro. We hypothesize that PS2 down regulates an uncontrolled inflammatory response, contributing to a neurotoxic environment. We will compare cytokine release, neurotoxicity, phagocytosis behavior and y-secretase activity of cultured primary microglia following introduction of PS2 FAD mutation gene constructs using lentiviral gene transfer. Microglia expressing PS2 FAD mutations will be evaluated in comparison to microglia expressing control lentiviral vectors or lentivirus expressing PS2 shRNA to induce PS2 deficiency with the goal of assessing loss or gain of function effects of PS2 FAD mutation in microglia.
In addressing our hypothesis, we hope to significantly contribute to the general understanding of AD biology with the goal of revealing specific targets in PS related pathways for therapeutic intervention and potentially important information regarding therapies currently being evaluated in clinical trials.
|Jayadev, Suman; Case, Amanda; Alajajian, Betty et al. (2013) Presenilin 2 influences miR146 level and activity in microglia. J Neurochem 127:592-9|