Exosomes derived from calcium oxalate-exposed macrophages enhance IL-8 production from renal cells, neutrophil migration and crystal invasion through extracellular matrix

Deposition of calcium oxalate (CaOx) crystals in renal interstitium is one of the key factors that cause progressive inflammation in kidney stone disease. Macrophages are responsible for elimination of these crystals but their roles to worsen inflammatory process remain under-investigated. This study thus aimed to define roles of exosomes released from macrophages exposed to CaOx crystals in mediating subsequent inflammatory cascades. Macrophages were incubated with or without CaOx monohydrate (COM) crystals for 16 h and their exosomes were isolated. Quantitative proteomics using nanoLC-ESI-Qq-TOF MS/MS revealed 26 proteins with significantly altered levels in exosomes derived from COM-treated macrophages (COM-treated exosomes) comparing to those derived from the controlled macrophages (controlled exosomes). Protein network analysis showed that these altered proteins were involved in cytoskeleton and actin binding, calcium binding, stress response, transcription regulation, immune response and extracellular matrix disassembly. Functional investigations revealed that COM-treated exosomes enhanced IL-8 production from renal tubular cells, activated neutrophil migration, had increased (exosomal) membrane fragility, had greater binding capacity to COM crystals, and subsequently enhanced crystal invasion through extracellular matrix migration chamber. These data indicate that macrophage exosomes play important roles in inflammatory response to COM crystals and may be involved in crystal invasion in the renal interstitium.