Kidney injury molecule–1 is a phosphatidylserine receptor that confers a phagocytic phenotype on epithelial cells
Takaharu Ichimura, … , Jeremy S. Duffield, Joseph V. Bonventre
Takaharu Ichimura, … , Jeremy S. Duffield, Joseph V. Bonventre
Published April 15, 2008
Citation Information: J Clin Invest. 2008;118(5):1657-1668. https://doi.org/10.1172/JCI34487.
View: Text | PDF
Research Article Nephrology

Kidney injury molecule–1 is a phosphatidylserine receptor that confers a phagocytic phenotype on epithelial cells

Abstract

Following injury, the clearance of apoptotic and necrotic cells is necessary for mitigation and resolution of inflammation and tissue repair. In addition to macrophages, which are traditionally assigned to this task, neighboring epithelial cells in the affected tissue are postulated to contribute to this process. Kidney injury molecule–1 (KIM-1 or TIM-1) is an immunoglobulin superfamily cell-surface protein not expressed by cells of the myeloid lineage but highly upregulated on the surface of injured kidney epithelial cells. Here we demonstrate that injured kidney epithelial cells assumed attributes of endogenous phagocytes. Confocal images confirm internalization of apoptotic bodies within KIM-1–expressing epithelial cells after injury in rat kidney tubules in vivo. KIM-1 was directly responsible for phagocytosis in cultured primary rat tubule epithelial cells and also porcine and canine epithelial cell lines. KIM-1 was able to specifically recognize apoptotic cell surface-specific epitopes phosphatidylserine, and oxidized lipoproteins, expressed by apoptotic tubular epithelial cells. Thus, KIM-1 is the first nonmyeloid phosphatidylserine receptor identified to our knowledge that transforms epithelial cells into semiprofessional phagocytes.

Authors

Takaharu Ichimura, Edwin J.P.v. Asseldonk, Benjamin D. Humphreys, Lakshman Gunaratnam, Jeremy S. Duffield, Joseph V. Bonventre

×

Figure 6

The KIM-1 ectodomain binds specifically to the surface of apoptotic epithelial cells and binds specifically to PS and PE.

Options: View larger image (or click on image) Download as PowerPoint
The KIM-1 ectodomain binds specifically to the surface of apoptotic epit...
(A) Flow cytometric histogram plots of fluorescence of normal live LLC-PK1 epithelial cells (left panel) or apoptotic LLC-PK1 epithelial cells (right panel), labeled with KIM1-Fc followed by anti–hIgG-FITC (green), anti–hIgG-FITC alone (red), or no reagents (blue). Note an approximately 50-fold increase in binding of KIM1-Fc to apoptotic cells. (B) Representative photomicrographs of an apoptotic LLC-PK1 cell labeled with KIM1-Fc (green, right panel) and a normal, live LLC-PK1 cell labeled identically (left panel). Nuclei were faintly stained with DAPI (blue) in both cells. Original magnification, ×60. (C) Graph of mean peak fluorescence for binding of KIM1-Fc to apoptotic cells in the absence or presence of the calcium chelators EDTA/EGTA, assessed by flow cytometry. KIM1-Fc binding was abolished by calcium chelators, and binding was restored by the addition of an excess of calcium to the chelators (*P = 0.006). (D) Graph of phagocytosis inhibition by PS liposomes. Pretreatment of KIM-1–expressing cells with PS liposomes almost completely abolished KIM-1–mediated phagocytosis of apoptotic cells (A.C.) (**P = 0.007), while equimolar PC liposomes had no effect. Error bars indicate SD. (E) In vitro binding curves for purified KIM1-Fc binding to equimolar phospholipid coated ELISA plates. KIM1-Fc binding was detected by anti-human IgG — HRP conjugated antibody followed by a colorimetric assay. Note KIM1-Fc binds to aminophospholipids PS and PE but not PC or anionic phosphatidic acid (PA), whereas control Fc proteins, human IgG and c-Ret–Fc do not bind.