Urinary Biomarkers Associated With Pathogenic Pathways Reflecting Histologic Findings in Lupus Nephritis

Objective: There is a pressing need to understand the pathogenesis of histologic findings and identify the biomarkers for predicting the histologic severity in lupus nephritis (LN). This study aimed to identify the pathogenic signal pathway and elucidate urinary biomarkers for predicting the presence or severity of histologic findings in LN. Methods: Urine samples from patients with biopsy-proven active LN were screened for 1,305 proteins using an aptamer-based proteomic assay. The diversity and expansion of individual renal histologic features in LN were quantified to identify the urinary proteins associated with the histologic findings found in each score. Candidate urinary proteins were validated in a validation cohort. Immunohistochemical staining of the renal tissues was performed to clarify the localization of the candidate proteins. Results: Cluster analysis extracted five histologic subgroups according to their correlations with each histologic finding in LN. Protein groups that correlated with each histologic subgroup revealed a distinct pathogenesis in LN using pathway analyses. Enzyme-linked immunosorbent assay validation revealed that urinary calgranulin B (S100A9), monocyte chemotactic protein 1 (MCP-1), and insulin-like growth factor binding protein 5 (IGFBP-5) levels could specifically predict the presence and severity of active glomerular lesions, interstitial inflammation, and interstitial fibrosis, respectively. Immunohistochemical staining revealed the localization of these proteins in each lesion. Conclusion: Renal histologic findings may reflect the different pathogeneses involved in each lesion, and estimating the urinary calgranulin B, MCP-1, and IGFBP-5 levels may be useful in predicting the presence and severity of histologic findings in LN.