Accelerated receptor shedding inhibits kidney injury molecule-1 (KIM-1)-mediated efferocytosis

Abstract

Efficient clearance of apoptotic cells (efferocytosis) prevents inflammation and permits repair following tissue injury. Kidney injury molecule-1 (KIM-1) is a receptor for phosphatidylserine, an “eat-me” signal exposed on the surface of apoptotic cells that marks them for phagocytic clearance. KIM-1 is upregulated on proximal tubule epithelial cells (PTECs) during ischemic acute kidney injury (AKI), enabling efferocytosis by surviving PTECs. KIM-1 is spontaneously cleaved at its ectodomain region to generate a soluble fragment that serves a sensitive and specific biomarker for AKI, but the biological relevance of KIM-1 shedding is unknown. Here, we sought to determine how KIM-1 shedding might regulate efferocytosis. Using cells that endogenously and exogenously express KIM-1, we found that hydrogen peroxide-mediated oxidative injury or PMA treatment accelerated KIM-1 shedding in a dose-dependent manner. KIM-1 shedding was also accelerated when apoptotic cells were added. Accelerated shedding or the presence of excess soluble KIM-1 in the extracellular milieu significantly inhibited efferocytosis. We also identified that TNF-α-converting enzyme (TACE or ADAM17) mediates both the spontaneous and PMA-accelerated shedding of KIM-1. While accelerated shedding inhibited efferocytosis, we found that spontaneous KIM-1 cleavage does not affect the phagocytic efficiency of PTECs. Our results suggest that KIM-1 shedding is accelerated by worsening cellular injury, and excess soluble KIM-1 competitively inhibits efferocytosis. These findings may be important in AKI when there is severe cellular injury.

Donor kidney injury molecule-1 promotes graft recovery by regulating systemic necroinflammation

“…An important, yet unanswered, question is whether endogenous clearance of apoptotic and necrotic cells, and reduction in the burden of secondary necrotic or necrotic cells, 28 To formally test if the inability of PTECs to clear dying cells would lead to increased passive release of HMGB1, we conducted an in vitro study where either healthy, apoptotic (UV light-induced) 31 or necrotic (heat-killed) 19 cells were fed to primary PTECs isolated from the kidneys of either KIM-1 −/− or KIM-1 +/+ mice, as shown previously, 20 and analyzed the conditioned media for HMGB1 after 24 hours ( Figure 4A). Virtually none to very little HMGB1 was detected by Western blot when healthy cells were fed to PTECs.…”

Extracellular Signal–Regulated Kinase 1/2 Regulates Mouse Kidney Injury Molecule-1 Expression Physiologically and Following Ischemic and Septic Renal Injury

“…The ectodomain, which contains an Ig-like domain and a glycosylated mucin domain, is cleaved by the metalloproteinase ADAM17 at the cellular membrane (Ichimura et al, 1998;Bailly et al, 2002;Gandhi et al, 2014). Membrane bound KIM-1 and cleaved KIM-1 increase with worsening renal injury (Zhang et al, 2007).…”

Evaluation of KIM-1 as an early biomarker of snakebite-induced AKI in mice

“…The associated loss of mitochondrial transmembrane potential (Fig. 2H) could indicate necrosis cell death pathway and could be associated to increase of ROS and Kim- 1 ectodomain externalization (Gandhi et al, 2014).…”