Aslebagh, Roshanak

AbstractAlzheimer's disease (AD) is a pervasive neurodegeneration disease with high heritability. In this study, we employed CRISPR‐Cas9‐engineered technology to investigate the effects of a rare mutation (rs144662445) in the A kinase anchoring protein 9 (AKAP9) gene, which is associated with AD in African Americans (AA), on tau pathology and the tau interactome in SH‐SY5Y P301L neuron‐like cells. The mutation significantly increased the level of phosphorylated tau, specifically at the site Ser396/Ser404. Moreover, analyses of the tau interactome measured by affinity purification‐mass spectrometry revealed that differentially expressed tau‐interacting proteins in AKAP9 mutant cells were associated with RNA translation, RNA localization and oxidative activity, recapitulating the tau interactome signature previously reported with human AD brain samples. Importantly, these results were further validated by functional studies showing a significant reduction in protein synthesis activity and excessive oxidative stress in AKAP9 mutant compared with wild type cells in a tau‐dependent manner, which are mirrored with pathological phenotype frequently seen in AD. Our results demonstrated specific effects of rs14462445 on mis‐processing of tau and suggest a potential role of AKAP9 in AD pathogenesis.

Abstract In neurodegenerative diseases, extracellular vesicles (EVs) transfer pathogenic molecules and are consequently involved in disease progression. We have investigated the proteomic profiles of EVs that were isolated from four different human‐induced pluripotent stem cell‐derived neural cell types (excitatory neurons, astrocytes, microglia‐like cells, and oligodendrocyte‐like cells). Novel cell type‐specific EV protein markers were then identified for the excitatory neurons (ATP1A3, NCAM1), astrocytes (LRP1, ITGA6), microglia‐like cells (ITGAM, LCP1), and oligodendrocyte‐like cells (LAMP2, FTH1), as well as 16 pan‐EV marker candidates, including integrins and annexins. To further demonstrate how cell‐type‐specific EVs may be involved in Alzheimer's disease (AD), we performed protein co‐expression network analysis and conducted cell type assessments for the proteomes of brain‐derived EVs from the control, mild cognitive impairment, and AD cases. A protein module enriched in astrocyte‐specific EV markers was most significantly associated with the AD pathology and cognitive impairment, suggesting an important role in AD progression. The hub protein from this module, integrin‐β1 (ITGB1), was found to be significantly elevated in astrocyte‐specific EVs enriched from the total brain‐derived AD EVs and associated with the brain β‐amyloid and tau load in independent cohorts. Thus, our study provides a featured framework and rich resource for the future analyses of EV functions in neurodegenerative diseases in a cell type‐specific manner.

AbstractBackgroundAlzheimer’s disease (AD) is a pervasive neurodegeneration disease with high heritability. Whole exome sequencing study identified two rare African American (AA)‐specific variants in AKAP9, a kinase anchor protein 9, (rs144662445 and rs149979685), that increased the odds of AD more than 2.75‐fold. However, the functional impact of the AKAP9 rs144662445 (I2558M) mutation in the central nervous system and the underlying mechanism in AD remain unclear.MethodAKAP9 I2558M mutation was introduced by CRISPR‐mediated knock‐in and validated by Sanger sequence in SH‐SY5Y cells stably expressing P301L Tau (SH‐SY5Y P301L cells), which was further differentiated into neuronal cells. Tau phosphorylated level between AKAP9 WT and I2558M cells was evaluated by immunocytochemistry and ELISA assay. Moreover, we analyzed the tau interactome in AKAP9 I2558M cells by affinity purification‐mass spectrometry. In silico analysis was performed to compare the differences between AKAP9 WT and mutation in tau‐interacting proteins. The protein synthesis and oxidative activity in SH‐SY5Y P301L neurons with and without I2558M were measured by using the Click‐iT protein synthesis kit and CellRox dye, respectively.ResultNo difference in the neuronal cell morphology was observed between differentiated WT and mutant SH‐SY5Y P301L cells. The AD‐associated AKAP9 I2558M mutation resulted in a significant increase in phosphorylated tau protein at residues S396 and S404 site in a differentiated SH‐SY5Y P301L cell line. The presence of this mutation altered the composition of tau‐interacting proteins, by increasing interaction of proteins associated with translation, RNA localization and oxidative activity. Importantly, functional studies showed a significant reduction in protein synthesis activity and excessive oxidative stress in AKAP9 mutant compared to wild type cells.ConclusionOur results demonstrated specific effects of rs14462445 on mis‐processing of tau and suggest a potential role of AKAP9 in AD pathogenesis.