Limited proteolysis of neutrophil granule proteins by the bacterial protease RgpB depletes neutrophil antimicrobial capacity

Neutrophils are highly abundant in the gingival tissues where they play an essential role in immune homeostasis by preventing microbial invasion. Here, we show that the oral periodontal pathogen Porphyromonas gingivalis utilizes its cysteine proteases (gingipains) to disengage phagosomal antimicrobial capacity. Arginine gingipains are a sub-family of trypsin-like proteases produced by P. gingivalis that cleave several host proteins at arginine residues. We find that RgpB-mediated proteolysis of host proteins is not limited to the extracellular or plasma membrane-associated host proteins, but it can also degrade several intracellular proteins in neutrophils. Using 2D-DIGE coupled with mass spectrometry, we identified several cytoskeletal and cytoplasmic proteins, including metabolic enzymes and antimicrobial proteins such as neutrophil elastase, myeloperoxidase, and proteinase 3 within neutrophil granules that were cleaved by RgpB. Strikingly, despite the breakdown of multiple proteins, RgpB-treated neutrophils did not undergo apoptosis but instead increased integrin expression and underwent broad transcriptional changes consistent with proinflammatory programming. However, despite their primed status and augmented inflammatory capacity, RgpB-treated neutrophils were conducive to intracellular bacterial survival due to the reduced activity of granule proteins and oxidative burst. Thus, our data show a previously unknown role for P. gingivalis proteases in the attenuation of neutrophil microbicidal capacity via proteolysis of intracellular proteins.