P080 NEUTROPHIL EXTRACELLULAR TRAPS DEFICIENCY AGGRAVATES CHRONIC COLITIS

Neutrophils can release their DNA as neutrophil extracellular traps (NETs) via a programmed cell death known as NETosis; this process is dependent on peptidyl arginine deiminase-4 (PAD4, aka Padi4) activity to facilitate the rapid de-condensation of chromatin into NETs. We envision that the formation of NETs would be an appropriate immune response in the gut, which is continuously exposed to trillions of bacteria. To test this hypothesis, we employed the NETs-deficient Pad4KO mice and their WT littermates in two well-established models of murine colitis, i.e., loss of IL-10 signaling (immune hyperactivation) and chemical-induced injury (DSS). Upon treatment with αIL-10R mAb, Pad4KO mice developed robust chronic colitis, as exemplified by splenomegaly, colomegaly, increased levels of serum and fecal lipocalin 2 (Lcn2). Histological analysis revealed colonic crypt elongation, heightened immune cell infiltrates, and loss of goblet cells in the colitic Pad4KO mice. In comparison, αIL-10R-treated WT littermates exhibited modest colitis. We theorized that NETs may function as a ‘safety net’ which confine the pro-inflammatory neutrophil granule proteins (NGP) and prevent them to cause further damage. Indeed, the concentration and activity of NGP [i.e., Lcn2, myeloperoxidase (MPO) and neutrophil elastase (NE)], in serum and in colons, were strikingly elevated in colitic Pad4KO mice, when compared to WT mice. Intriguingly, the level of colonic secretory leukocyte protease inhibitor (SLPI) was reduced in the colitic Pad4KO mice. Such impaired SLPI response coupled with the ‘spillover’ of neutrophil granule proteins may, in part, explain the aggravated colitogenesis in mice lacking NETs. Similarly, upon DSS treatment the Pad4KO mice developed more severe chronic colitis than WT mice. Taken together, our findings advance the notion that gastrointestinal NETs are beneficial and caution that the use of PAD4 or NETs inhibitors may not be favorable for intestinal diseases.