GPNMB modulates neutrophil extracellular trap formation: therapeutic implications for ischemic stroke

Microglia are key immune-competent cells responding immediately to manipulate post-stroke neuroinflammation to shape the prognosis of stroke. GPNMB was reported to be upregulated after ischemic stroke and might influence the outcome. However, its detailed biological function and mechanism remain elusive. Here, we found that GPNMB was remarkably elevated in the ischemic brain and mainly distributed in microglia. Combining GPNMB knockout mice and recombinant GPNMB protein, we found that GPNMB could alleviate ischemic brain injury. Recombinant GPNMB (rGPNMB) administration could reduce neutrophil extracellular traps (NETs) formation, while knockout of GPNMB promoted NET formation in ischemic stroke. In addition, we found that CD44 functioned importantly in mediating the role of GPNMB inhibiting NET formation and alleviating ischemic brain injury. Depletion of neutrophils or inhibition of NET formation with DNase I could reduce the neuroprotective impact of GPNMB. Mechanistically, GPNMB might inhibit NET formation partly via modulating the Rac-ROS pathway after binding to the CD44 receptor. Finally, our data indicated that delayed rGPNMB administration retained neuroprotective impact in ischemic stroke. Our study revealed the importance of GPNMB in modulating NET formation and suggested a potential target for manipulating post-stroke neutrophil-associated neuroinflammation.