<b>Lysyl oxidase promotes actin-dependent neutrophil activation and cytotoxicity towards retinal endothelial cells in diabetes</b>

<p dir="ltr">Activated neutrophils contribute to retinal endothelial cell (EC) death and capillary degeneration associated with early diabetic retinopathy (DR), a major vision-threatening complication of diabetes. However, the factors and mechanisms driving neutrophil activation and cytotoxicity in diabetes remain insufficiently understood. Here we show that lysyl oxidase (LOX), a matrix crosslinking and stiffening enzyme that increases retinal EC susceptibility to activated neutrophils, simultaneously activates neutrophils in its soluble form. Specifically, treatment of diabetic mice with LOX inhibitor β-aminopropionitrile (BAPN) prevented the diabetes-induced increase in neutrophil activation (extracellular release of neutrophil elastase and superoxide) and cytotoxicity towards co-cultured mouse retinal ECs. Mouse neutrophils and differentiated (neutrophil-like) human HL-60 cells treated with recombinant LOX alone exhibited significant activation and cytotoxicity. Mechanistically, this LOX-induced neutrophil activation was associated with biphasic F-actin remodeling, with the initial and rapid (~10 min) F-actin depolymerization followed by a significant increase in F-actin polymerization and polarization. Preventing the initial F-actin depolymerization blocked LOX-induced neutrophil activation and cytotoxicity towards co-cultured retinal ECs. Finally, we show that this biphasic F-actin remodeling is essential for LOX-induced membrane aggregation of azurophilic granule marker CD63 and NADPH organizer p47^phox that are associated with extracellular release of neutrophil elastase and superoxide, respectively. By revealing a previously unrecognized causal link between LOX and actin-dependent neutrophil activation in diabetes, these findings provide fresh mechanistic insights into the proinflammatory role of LOX in early DR that goes beyond its canonical matrix-stiffening effects.</p>