KIM-1–mediated phagocytosis reduces acute injury to the kidney
Li Yang, Craig R. Brooks, Sheng Xiao, Venkata Sabbisetti, Melissa Y. Yeung, Li-Li Hsiao, Takaharu Ichimura, Vijay Kuchroo, Joseph V. Bonventre
Li Yang, Craig R. Brooks, Sheng Xiao, Venkata Sabbisetti, Melissa Y. Yeung, Li-Li Hsiao, Takaharu Ichimura, Vijay Kuchroo, Joseph V. Bonventre
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Research Article Nephrology

KIM-1–mediated phagocytosis reduces acute injury to the kidney

Abstract

Kidney injury molecule 1 (KIM-1, also known as TIM-1) is markedly upregulated in the proximal tubule after injury and is maladaptive when chronically expressed. Here, we determined that early in the injury process, however, KIM-1 expression is antiinflammatory due to its mediation of phagocytic processes in tubule cells. Using various models of acute kidney injury (AKI) and mice expressing mutant forms of KIM-1, we demonstrated a mucin domain–dependent protective effect of epithelial KIM-1 expression that involves downregulation of innate immunity. Deletion of the mucin domain markedly impaired KIM-1–mediated phagocytic function, resulting in increased proinflammatory cytokine production, decreased antiinflammatory growth factor secretion by proximal epithelial cells, and a subsequent increase in tissue macrophages. Mice expressing KIM-1Δmucin had greater functional impairment, inflammatory responses, and mortality in response to ischemia- and cisplatin-induced AKI. Compared with primary renal proximal tubule cells isolated from KIM-1Δmucin mice, those from WT mice had reduced proinflammatory cytokine secretion and impaired macrophage activation. The antiinflammatory effect of KIM-1 expression was due to the interaction of KIM-1 with p85 and subsequent PI3K-dependent downmodulation of NF-κB. Hence, KIM-1–mediated epithelial cell phagocytosis of apoptotic cells protects the kidney after acute injury by downregulating innate immunity and inflammation.

Authors

Li Yang, Craig R. Brooks, Sheng Xiao, Venkata Sabbisetti, Melissa Y. Yeung, Li-Li Hsiao, Takaharu Ichimura, Vijay Kuchroo, Joseph V. Bonventre

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Figure 9

Expression of WT KIM-1, but not KIM-1Δmucin, in PTCs downregulates NF-κB activity in a PI3K-dependent manner.

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Expression of WT KIM-1, but not KIM-1Δmucin, in PTCs downregulates NF-κB...
(A) Immunoblot analysis of p–NF-κB in I/R kidneys from WT KIM-1 or KIM-1Δmucin mice (n = 4 animals). (B) p–NF-κB expression in WT KIM-1 or KIM-1Δmucin primary PTCs (representative of 4 experiments). (C) NF-κB activity in LLC-PK1 cells expressing WT KIM-1 or KIM-1Δmucin plus NF-κB–responsive promotor driving luciferase (normalized to Renilla luciferase driven by a constitutive promotor) (n = 4). **P < 0.0001; *P < 0.01. (D and E) Representative immunoprecipitation analysis of KIM-1 phosphorylation and interaction with p85 from 4 experiments. (D) LLC-PK1 cell lysates from WT and KIM-1Δmucin–expressing cells were immunoprecipitated with an Ab against phosphorylated tyrosine residues and probed for KIM-1 by immunoblotting. (E) FLAG-tagged KIM-1 or KIM-1Δmucin was immunoprecipitated from lysates with anti-FLAG Abs and probed for p85 or KIM-1 by immunoblotting. (F) Representative images of LLC-PK1 cells expressing WT or KIM-1Δmucin incubated with apoptotic cells. Cells were stained for KIM-1 (green), p85 (red), and apoptotic cell proteins (blue). Scale bar: 10 μm. (G) Confocal z plane of WT KIM-1 cells stained as in E and imaged in a z series. N, LLC-PK1 cell nucleus. (H) 3D reconstruction of z series from G of KIM-1/p85 colocalization at a phagocytic event (upper right and individual channels in lower panels). Images in G and H are representative of 3 experiments. Scale bar: 5 μm (G and H). (I) Immunoblot analysis of p–NF-κB in KIM-1 or KIM-1Δmucin primary PTCs treated with vehicle or the PI3K inhibitors wortmannin or LY294002 (immunoblots are representative of 3 experiments). Groups were compared by ANOVA followed by Bonferroni’s post-hoc analysis.