Peptidyl
arginine deiminase (PAD)4 is a nuclear
enzyme that catalyzes the posttranslational conversion of
arginine residues to
citrulline. Posttranslational
protein citrullination has been implicated in several inflammatory
autoimmune diseases, including
rheumatoid arthritis,
colitis, and
multiple sclerosis. Here, we tested the hypothesis that PAD4 contributes to ischemic
acute kidney injury (AKI) by exacerbating the inflammatory response after renal
ischemia-reperfusion (I/R). Renal I/R injury in mice increased PAD4 activity as well as PAD4 expression in the mouse kidney. After 30 min of renal I/R, vehicle-treated mice developed severe AKI with large increases in plasma
creatinine. In contrast, mice pretreated with PAD4 inhibitors (2-chloroamidine or
streptonigrin) had significantly reduced renal I/R injury. Further supporting a critical role for PAD4 in generating ischemic AKI, mice pretreated with recombinant human PAD4 (rPAD4)
protein and subjected to mild (20 min) renal I/R developed exacerbated ischemic AKI. Consistent with the hypothesis that PAD4 regulates renal tubular
inflammation after I/R, mice treated with a PAD4 inhibitor had significantly reduced renal neutrophil
chemotactic cytokine (
macrophage inflammatory protein-2 and keratinocyte-derived
cytokine) expression and had decreased neutrophil infiltration. Furthermore, mice treated with rPAD4 had significantly increased renal tubular macrophage inflammatory protein-2 and keratinocyte-derived
cytokine expression as well as increased neutrophil infiltration and
necrosis. Finally, cultured mouse kidney proximal tubules treated with rPAD4 had significantly increased proinflammatory
chemokine expression compared with vehicle-treated cells. Taken together, our results suggest that PAD4 plays a critical role in renal I/R injury by increasing renal tubular inflammatory responses and neutrophil infiltration after renal I/R.