Abstract
Background: Calcium oxalate monohydrate (COM) is an aetiologic factor for urolithiasis. However, how Human Kidney-2 (HK-2) cells respond to a high COM has not yet been completely elucidated.Materials and methods: A gel-based proteomics approach was applied to investigate COM-induced cellular proteomic changes. The COM-induced upregulation of calcium-sensing receptor (CaSR) in HK-2 cells was studied. Surface phospholipids (PS), which play a role in urolithiasis formation by mediating adhesion of HK-2 cells, were labelled in the inner or outer leaflet of the plasma membrane of HK-2 cells with fluorescent nitrobenzoxadiazole (NBD) to form NBD-PS to detect transmembrane movements of PS. After labelling, HK-2 cells were exposed to COM in the presence of the CaSR-specific agonist gadolinium chloride (GdCl3) or the CaSR-specific antagonist NPS2390. Inward and outward transmembrane movements of PS were tracked with a fluorescence quenching assay. Surface-expressed PS was detected by an annexin V binding assay. Changes in aminophospholipid translocase (APLT), oxidative stress (OS), levels of apoptosis-related proteins in HK-2 cells and crystal adhesion were also assessed.Results: COM increased CaSR and surface-expressed PS levels, decreased APLT activity, impaired inward transport of PS, and enhanced outward transport of PS. However, pretreatment with GdCl3 further effectively inhibited the inward movement of PS and APLT activity and increased surface-expressed PS levels compared with COM treatment alone. In contrast, NPS2390 promoted the inward movement of PS and APLT activity and decreased surface-expressed PS levels compared with COM treatment alone. COM increased OS, apoptosis of HK-2 cells and crystal adhesion onto cells, and this increase was further enhanced by GdCl3 pretreatment but attenuated by NPS2390 treatment.Conclusions: These results strongly suggest that COM-induced CaSR generation may affect crystal adhesion by regulating PS externalization, apoptosis and OS in HK-2 cells.