Impact of putative cilia targeting sequences on APP trafficking

• Published in: Alzheimer's & dementia Vol. 16
• Main Author: Swaminathan, Swathi
• Format: Journal Article
• Language: English
• Published: 01.12.2020
• ISSN: 1552-5260; 1552-5279
• DOI: 10.1002/alz.044841

Background Primary cilia are non‐motile, sensory antennae protruding from most eukaryotic cells. These cilia are enveloped in plasma membrane that is adorned with an array of receptor proteins and are essential in regulating fundamental neurophysiological activities, including neurogenesis and memory encoding. In the mature brain, both neurons and astrocytes exhibit a single primary cilium. Defects in the primary cilia lead to a myriad of diseases, one such being impaired neuronal development and cognitive domains, also compromised in Alzheimer’s disease (AD). AD is primarily characterized by the accumulation of amyloid β plaques (Aβ) on the brain. Aβ plaques result from the proteolytic cleavage of the Aβ peptide, a product of the amyloid precursor protein (APP). In our lab, we have previously shown that increased Aβ disrupts primary cilia structure and APP co‐localization at the primary cilium, indicating a possible functional role of APP in AD pathogenesis. At the base of all primary cilia is a protein complex responsible for maintaining a distinct protein and lipid profile from the cytoplasm. Therefore, only those proteins intended for the primary cilia are trafficked from the Golgi to the base of the primary cilia, which is believed to be mediated by specific cilia targeting sequences.Examples of cilia targeting sequences include VxPx, RVxP, AxxxQ amino acid sequences. Method In order to characterize these putative cilia targeting sequences, we utilized site directed mutagenesis to create and compare mutants of all the putative sequences and confocal microscopy in multiple cell lines like MDCKs, astrocytes and neurons. These experiments were conducted to investigate the consequences of disrupting the cilia targeting sequences in APP 695. Result We have identified a total of 7 putative cilia targeting sequences in the human APP 695 isoform and also found that only one of the seven targeting sequences is located in the C‐terminal ectodomain of the isoform. Conclusion Since most motor proteins identified at the cytoplasmic C‐terminus are responsible for trafficking APP to its destination, we believe that this cilium targeting sequence may be responsible for APP localization at the primary cilia,thereby rendering them as a potential therapeutic target for AD.