Mapping and functional characterization of proteolytic cleavage of murine kidney injury molecule-1
Abstract
Kidney injury molecule-1 (KIM-1) is a transmembrane glycoprotein expressed apically on proximal tubule epithelia during acute kidney injury (AKI). KIM-1, as a phagocytic receptor, facilitates clearance of apoptotic cells (efferocytosis) from tubular lumen, thereby reducing inflammation and promoting repair. Human KIM-1 undergoes spontaneous and accelerated ectodomain shedding into urine and blood via metalloproteases; tumour necrosis factor-a converting enzyme (TACE/ADAM17) and a disintegrin and metalloprotease 10 (ADAM10). Blood and urine KIM-1 are clinical AKI biomarkers, however, biological significance of KIM-1 shedding is unknown. To study this in vivo in mice, I first aimed to identify murine KIM-1 cleavage site and study its functional relevance in vitro.
I202 was mapped out as the potential cleavage site and mutated to Q or A. Mutants showed significantly reduced ability to accelerate KIM-1 shedding and efferocytosis. ADAM10 mediated both baseline and accelerated shedding of murine KIM-1. Surprisingly, ADAM10-mediated KIM-1 shedding was required for efficient efferocytosis.