Elucidating a mechanism of tau hyperphosphorylation after DEK loss in vitro

Abstract

Our research group was the first to link DEK with Alzheimer's disease and age-related dementias (Ghisays et al., 2018). Since then, two independent labs have replicated and extended our findings by further connecting DEK with neurodegenerative diseases (Alzheimer's and Huntington's). DEK is a chromatin remodeling, nuclear protein that is associated with DNA replication and repair, cell proliferation, and apoptosis inhibition. Recently, we reported that DEK expression is necessary for proper neurite formation and that its deficiency leads to cell death and Tau overexpression and hyperphosphorylation (Greene et al., 2020). The purpose of the current study is to elucidate the mechanism by which DEK loss leads to Tau pathology in vitro, with the goal of illuminating novel pathways of Tauopathy in Alzheimer's disease. SH-SY5Y cells were differentiated into a neuronal-like phenotype. One week before the end of the differentiation, the cells were transferred to poly-lysine coated coverslips and were treated with kinase inhibitors of CamKII, Erk, PKC, PKA, DYRK, or GSK3β; these kinases are associated with Tau pathology in Alzheimer's disease. The media was changed every three days, containing the same dose of drug as the previous media change. At the end of differentiation, the relative expression levels of phosphorylated Tau were determined via immunofluorescence. Western blots were performed to corroborate our immunofluorescence findings. We found that the inhibitors of Erk and DYRK reduced phosphorylated Tau (Ser262) to control levels, while treatment with other kinase inhibitors did not rescue the Tau pathology phenotype in the DEK knockdown cells. Our results indicate that Erk and DYRK may phosphorylate Tau at Serine 262 after DEK loss in a neuronal cell model. Inhibition of these kinases rescues the Tau hyperphosphorylation phenotype in DEK-knockdown cells. These data may inform us of the molecular mechanism(s) by which DEK loss can lead to phenotypes of Alzheimer's disease and age-related dementias.