Expression and Localization of the Bromodomain PHD Finger Transcription Factor (BPTF) in Primary Murine Cells, Cell Lines, and Tissues from N471D Washc5 Knock-In Mice

Abstract

Spastic paraplegia 8 (SPG8) is characterized as a pure form of autosomal dominant hereditary spastic paraplegia (HSP), a heterogeneous group of clinically and genetically neurodegenerative disorders impairing the central-motor-system. Caused by mutations in strumpellin (UniProt ID: Q8C2E7), a core member of the Wiskott-Aldrich syndrome protein and SCAR homolog (WASH) complex, families linked to SPG8 are considered to have one of the more aggressive subtypes of HSP. One of these identified mutations is N471D, a point mutation located in the highly conserved third spectrin-like repeat of strumpellin. Recent proteomic studies reported an upregulation of Bromodomain PHD finger ranscription factor (BPTF) in the brain tissue of both, homo- and heterozygous N471D Washc5 knock-in mice (Clemen et al., 2021). Although the protein has been described in the context of different neurodegenerative disorders, its roles and functions remain elusive and need to be investigated. The aim of this study was to investigate the localization and expression pattern of BPTF across several cell lines and tissue types. Immunocytochemistry analysis revealed, that the protein of interest was found to be primarily expressed in the nucleus. Throughout all investigated cell types, BPTF was mainly co-localized with euchromatin, clustering adjacent to heterochromatin. Further biochemical analyses revealed that BPTF was expressed in all cell and tissue types; with the only exception being the heart. Supporting the observed nuclear localization of BPTF obtained during immunofluorescence imaging, BPTF was exclusively expressed in the nuclear extraction fraction of both, cells and tissue. Notably, immunoblot analysis of BPTF levels in tissues derived from homo- and heterozygous N471D Washc5 knock-in mice revealed that BPTF was significantly decreased in the brain tissue of both, homo- and heterozygous N471D Washc5 knock-in mice compared to their wildtype siblings.