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Decreasing the expression of PICALM reduces endocytosis and the activity of β-secretase: Implications for Alzheimer's disease

Thomas, Rhian S.; Henson, Alex; Gerrish, Amy; Jones, Lesley; Williams, Julie; Kidd, Emma J.

Decreasing the expression of PICALM reduces endocytosis and the activity of β-secretase: Implications for Alzheimer's disease Thumbnail


Authors

Alex Henson

Amy Gerrish

Lesley Jones

Julie Williams

Emma J. Kidd



Abstract

© 2016 The Author(s). Background: Polymorphisms in the gene for phosphatidylinositol binding clathrin assembly protein (PICALM), an endocytic-related protein, are associated with a small, increased risk of developing Alzheimer's disease (AD), strongly suggesting that changes in endocytosis are involved in the aetiology of the disease. We have investigated the involvement of PICALM in the processing of amyloid precursor protein (APP) to understand how PICALM could be linked to the development of AD. We used siRNA to deplete levels of PICALM, its isoforms and clathrin heavy chain in the human brain-derived H4 neuroglioma cell line that expresses endogenous levels of APP. We then used Western blotting, ELISA and immunohistochemistry to detect intra- and extracellular protein levels of endocytic-related proteins, APP and APP metabolites including β-amyloid (Aβ). Levels of functional endocytosis were quantified using ALEXA 488-conjugated transferrin and flow cytometry as a marker of clathrin-mediated endocytosis (CME). Results: Following depletion of all the isoforms of PICALM by siRNA in H4 cells, levels of intracellular APP, intracellular β-C-terminal fragment (β-CTF) and secreted sAPPβ (APP fragments produced by β-secretase cleavage) were significantly reduced but Aβ40 was not affected. Functional endocytosis was significantly reduced after both PICALM and clathrin depletion, highlighting the importance of PICALM in this process. However, depletion of clathrin did not affect APP but did reduce β-CTF levels. PICALM depletion altered the intracellular distribution of clathrin while clathrin reduction affected the subcellular pattern of PICALM labelling. Both PICALM and clathrin depletion reduced the expression of BACE1 mRNA and PICALM siRNA reduced protein levels. Individual depletion of PICALM isoforms 1 and 2 did not affect APP levels while clathrin depletion had a differential effect on the isoforms, increasing isoform 1 while decreasing isoform 2 expression. Conclusions: The depletion of PICALM in brain-derived cells has significant effects on the processing of APP, probably by reducing CME. In particular, it affects the production of β-CTF which is increasingly considered to be an important mediator in AD independent of Aβ. Thus a decrease in PICALM expression in the brain could be beneficial to slow or prevent the development of AD.

Citation

Thomas, R. S., Henson, A., Gerrish, A., Jones, L., Williams, J., & Kidd, E. J. (2016). Decreasing the expression of PICALM reduces endocytosis and the activity of β-secretase: Implications for Alzheimer's disease. BMC Neuroscience, 17(1), https://doi.org/10.1186/s12868-016-0288-1

Journal Article Type Article
Acceptance Date Jul 11, 2016
Publication Date Jul 18, 2016
Deposit Date Jan 20, 2017
Publicly Available Date Mar 29, 2024
Journal BMC Neuroscience
Electronic ISSN 1471-2202
Publisher BioMed Central
Peer Reviewed Peer Reviewed
Volume 17
Issue 1
DOI https://doi.org/10.1186/s12868-016-0288-1
Keywords Alzheimer’s disease, amyloid precursor protein, β-C-terminal fragment, β-Secretase, clathrin-mediated, endocytosis, PICALM
Public URL https://uwe-repository.worktribe.com/output/909618
Publisher URL http://dx.doi.org/10.1186/s12868-016-0288-1