Background: Utilizing Î²-amyloid precursor protein (Î²APP) as a substrate, Î±-, Î²-, and Î³-secretases are responsible for sequential cleavage events leading to the formation of Î²-amyloid, the classic pathologic hallmark of Alzheimer's Disease. Members of this class of proteases also catalyze the activation of numerous other membrane- localized proteins implicated in cell growth and neuroinflammation such as NOTCH and the Interleukin/TNF-receptor family, respectively. This investigation addresses if an in vitro Chlamydia pneumoniae infection of human astrocytes affects the processing of Î²APP through modifying the protein expression of the following Î²APP processing proteases: A Disintegrin and Metalloproteinase- 10 (ADAM10), Î²APP cleaving enzyme-1 (BACE1), and presenilin- 1 (PSEN1). Methods: Human astrocytoma cells (CCF-STTG1) were infected in vitro with Chlamydia pneumoniae strain AR39 (MOI=1). At 6-72 hours post infection, protein level of Î²-amyloid, ADAM10, BACE1, and presenilin-1 N-terminal fragment (NTF) relative to uninfected controls were detected by immunofluorescence and quantified by western blot analysis. Results: Cytoplasmic labeling of AÎ²1-42 was increased in infected cells relative to that of uninfected cells. Membrane-localized labeling of BACE1 and cytoplasmic labeling of PSEN1 NTF was also enhanced at earlier (6 hrs.) and later (48/72 hrs.) time points post infection relative to that of uninfected astrocytes. Increases in quantified BACE1 and PSEN1, but not ADAM10, followed a similar temporal increase most notable at 48 hrs. post infection. Conclusions: These data indicate that infection of human astrocytes with Chlamydia pneumoniae strain AR39 promotes the processing of Î²APP characteristic of Alzheimer's Disease through enhancing BACE1 and PSEN1, but not ADAM10, protein levels. Increases in active secretase protein may coincide with the 24-48 hr. lifecycle of Chlamydial intracellular growth and replication and the consequent astrocytic inflammatory response.
Available at: http://works.bepress.com/denah_appelt/44/