PapRIV, a BV-2 microglial cell activating quorum sensing peptide

Background Quorum sensing peptides (QSPs) are bacterial peptides produced by Gram-positive bacteria to communicate with their peers in a cell-density dependent manner. These peptides do not only act as interbacterial communication signals, but can also have effects on the host. Compelling evidence demonstrates the presence of a gut-brain axis and more specifically, the role of the gut microbiota in microglial functioning. The aim of this study is to investigate microglial activating properties of a selected QSP (PapRIV) which is produced by Bacillus cereus species. Methods Gastro-intestinal transport of the peptide is investigated using the in vitro Caco-2 model while transport over the blood-brain barrier is investigated in mice using multiple time regression experiments. Microglial activation is assessed using ELISA, fluorometry, immunoblotting, qPCR and phase-contrast microscopy. In vivo plasma detection and ex vivo metabolization experiments are performed using UHPLC-MS/MS and UHPLC-UV/MS, respectively. Results PapRIV showed in vitro activating properties of BV-2 microglia cells and was able to cross the in vitro Caco-2 cell model and pass the blood-brain barrier in vivo. In vivo peptide presence was also demonstrated in mouse plasma. The peptide caused induction of IL-6, TNFα and ROS expression and increased the fraction of ameboid BV-2 microglia cells in an NF-κB dependent manner. Different metabolites were identified in serum, of which the main metabolite (DLPFEH) still remained active. Conclusions PapRIV is thus able to cross the gastro-intestinal tract and the blood-brain barrier and shows in vitro activating properties in BV-2 microglia cells, hereby indicating a potential role of this quorum sensing peptide in gut-brain interaction.