Scripties UMCG - Rijksuniversiteit Groningen
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KIM-1 mediates the uptake of exosomes and transfer of MHC II

(2016) Kramers, B.J.

Urinary exosomes (EXO) are lipid membrane bound structures that mediate intercellular signaling through the transfer of proteins, miRNA and other factors. Kidney injury molecule 1 (KIM-1) acts as a phosphatidylserine (PS) receptor, inducing the uptake of apoptotic cells and necrotic debris. We hypothesize that KIM-1 acts as an endocytosis receptor, taking up EXO containing PS and mediating the intercellular exchange of signaling molecules, such as MHC II. LLC-PK1 cells expressing KIM-1 (PK1-KIM1) and cells expressing empty vector (PK1-pcDNA) were incubated with liposomes composed of PS and fluorescently labeled phosphatidylcholine (PC) or EXO isolated from LLC-PK1 cells, mouse dendritic cells (DC) or human urine by ultracentrifugation. EXO were fluorescently labeled with CytoTracker dye or MHC II-GFP. Uptake was quantified by measuring fluorescence intensity and flow cytometry. EXO were characterized by western blot and electron microscopy. MHC-II levels in urinary EXO from healthy subjects and CKD patients were determined by western blot. PK1-KIM-1 took up significantly more liposomes than PK1-pcDNA. EXO derived from LLC-PK1 cells, DCs and urine were positive for EXO markers HSP70, Flot-1 and TSG101. The diameter of EXO were between 30-150 nm. KIM-1 expressing cells took up significantly more EXO than empty vector expressing cells independent of the source of EXO. Urinary EXO from CKD patients were found to carry MHC II while EXO from healthy subjects were MHC II negative. We found the transfer of MHC II to primary PTCs to be greater in cells expressing KIM-1 after incubation with DC-derived EXO. We conclude that KIM-1 is a PTC receptor for EXO. MHC-II on EXO can be transferred to and presented by KIM-1 positive cells, suggesting EXO may serve to link dendritic cell activation to PTC MHC II expression and antigen presentation cells in inflammatory settings.

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