title: Macropinocytosis is the major mechanism for endocytosis of calcium oxalate crystals into renal tubular cells.
abstract: During an initial phase of kidney stone formation, the internalization of calcium oxalate (CaOx) crystals by renal tubular cells has been thought to occur via endocytosis. However, the precise mechanism of CaOx crystal endocytosis remained unclear. In the present study, MDCK renal tubular cells were pretreated with inhibitors specific to individual endocytic pathways, including nystatin (lipid raft/caveolae-mediated), cytochalasin D (actin-dependent or macropinocytosis), and chlorpromazine (CPZ; clathrin-mediated) before exposure to plain (non-labeled), or fluorescence-labeled CaOx monohydrate (COM) crystals. Quantitative analysis by flow cytometry revealed that pretreatment with nystatin and CPZ slightly decreased the crystal internalization, whereas the cytochalasin D pretreatment caused a marked decrease in crystal uptake. Immunofluorescence study and laser-scanning confocal microscopic examination confirmed that the cytochalasin D-pretreated cells had dramatic decrease of the internalized crystals, whereas the total number of crystals interacted with the cells was unchanged (crystals could adhere but were not internalized). These data have demonstrated for the first time that renal tubular cells endocytose COM crystals mainly via macropinocytosis. These novel findings will be useful for further tracking the endocytosed crystals inside the cells during the course of kidney stone formation.
authors.affiliation: Medical Proteomics Unit, Office for Research and Development, Faculty of Medicine, Siriraj Hospital, and Center for Research in Complex Systems Science (CRCSS), Mahidol University, 6th Floor SiMR Building, 2 Prannok Road, Bangkoknoi, Bangkok, 10700, Thailand.
authors.forename: Rattiyaporn
authors.initials: R
authors.lastname: Kanlaya
authors.forename: Kitisak
authors.initials: K
authors.lastname: Sintiprungrat
authors.forename: Sakdithep
authors.initials: S
authors.lastname: Chaiyarit
authors.forename: Visith
authors.initials: V
authors.lastname: Thongboonkerd
mesh_terms: D000818:Animals; D002129:Calcium Oxalate / Q000737:chemistry / Q000378:metabolism*; D002746:Chlorpromazine / Q000494:pharmacology; D003460:Crystallization; D015638:Cytochalasin D / Q000494:pharmacology; D004285:Dogs; D004705:Endocytosis / Q000187:drug effects; D007684:Kidney Tubules / Q000166:cytology / Q000187:drug effects; D061985:Madin Darby Canine Kidney Cells; D018613:Microscopy, Confocal; D009761:Nystatin / Q000494:pharmacology
chemical_list: D009761:Nystatin; D015638:Cytochalasin D; D002129:Calcium Oxalate; D002746:Chlorpromazine