Involvement of formyl-peptide-receptor-like-1 and phospholipase D in the internalization and signal transduction of amyloid beta 1-42 in glial cells

Recent studies suggest that the formyl-peptide-receptor-like-1 (FPRL1) plays an essential role in the inflammatory responses of host defense mechanisms and neurodegenerative disorders such as Alzheimer's disease (AD). We therefore analyzed whether amyloid β1-42 (Aβ1-42) increased the activity of phospholipase D (PLD) via FPRL1, which is an enzyme involved in the secretion, endocytosis and receptor signaling. PLD activity was determined using a transphosphatidylation assay. The internalization of Aβ1-42 via FPRL1 was visualized using fluorescence microscopy and quantified by ELISA (Enzyme Linked Immunosorbent Assay). Determining receptor activity by extracellular-signal regulated kinases 1/2 (ERK1/2) phosphorylation and cAMP level measurement verified the Aβ1-42-induced activation of FPRL1. We were able to show that Aβ1-42 is rapidly internalized via FPRL1 in astrocytes and microglia. PLD was additionally activated by Aβ1-42 and via FPRL1 in rat glial cells. Furthermore, the ERK1/2 phosphorylation by FPRL1 agonists was dependent on the PLD product phosphatidic acid (PA). Together, these data suggest that PLD plays an important role in the regulation of Aβ1-42-induced endocytosis and FPRL1 receptor signaling.