Protection against renal ischemia reperfusion injury by CD44 disruption.

Inflammation contributes to renal ischemia reperfusion (I/R) injury, potentially causing renal dysfunction. The inflammatory infiltrate mainly consists of neutrophils, which are deleterious for the renal tissue. Because CD44 is expressed by neutrophils and is rapidly upregulated by capillary endothelial cells after I/R injury, it was hypothesized that CD44 might play an important role in the development of I/R injury. This study showed that rapid CD44 upregulation on renal capillary endothelial cells mediates neutrophil recruitment to the postischemic tissue. Hence, CD44 deficiency led to decreased influx of neutrophils regardless of comparable levels in chemotactic factors expressed in the kidney. The reduced influx of neutrophils was associated with preserved renal function and morphology. Adoptive transfer experiments of labeled neutrophils revealed that endothelial CD44 rather than neutrophil CD44 mediates neutrophil migration. Activation of neutrophils increased cell-surface expression of hyaluronic acid (HA). Altogether, a novel mechanism in the recruitment of neutrophils that involves interaction of endothelial CD44 and neutrophil HA was found. Either blocking endothelial CD44 or removal of neutrophil HA decreased rolling and adhesion of neutrophils. Administration of anti-CD44 to mice reduced the influx of neutrophils into the postischemic tissue, associated with renal function preservation. Therefore, anti-CD44-based therapies may contribute to prevent or reduce renal I/R injury.