Neutrophil Secretory Proteins Inhibit Calcium Oxalate Crystallisation and Crystal Growth, but Promote Crystal Aggregation

Abstract

Neutrophil secretory proteins are frequently found in calcium oxalate (CaOx) kidney stone matrix, suggesting their involvement in stone pathogenesis, but with unclear mechanisms. We therefore investigated the effects of secretome (a set of secretory proteins) from CaOx monohydrate (COM)-exposed versus control dHL-60 (neutrophil-like) cells on crystal nucleation (crystallisation), growth, aggregation and invasion. Quantitative proteomics was also performed to identify significantly altered secretory proteins, followed by analyses of their physicochemical properties and biological relevance. The data demonstrated that both COM-treated and control secretomes inhibited crystallisation and crystal growth, but the inhibitory effects from the COM-treated secretome were slightly weaker. By contrast, both of them promoted crystal aggregation, with the more potent effect from the COM-treated secretome. However, neither of them had a modulatory effect on crystal invasion. Quantitative proteomics revealed 20 decreased and 9 increased proteins in the COM-treated secretome compared with the control. Analyses of physicochemical properties showed that the increased secretory proteins tended to have a lower instability index and a smaller number of oxalate-binding motifs/protein. Main molecular functions of the increased group were catalytic, hydrolase and transporter activities, whereas those of the decreased group included RNA binding, molecular adaptor activity and catalytic activity. These data indicate that the neutrophil secretome inhibits crystallisation and crystal growth but promotes crystal aggregation. The COM-treated secretome exerts weaker inhibitory effects on crystallisation and growth but has a stronger promoting effect on crystal aggregation. These findings enhance our understanding of the roles of neutrophils in kidney stone pathogenesis.