Symposium 1
Authors: MOHAN Chandra 
Published: November 2023

Proteomics has been a very informative tool in uncovering several biomarkers that may have clinical utility in managing patients with lupus nephritis (LN). Both non-targeted (mass spectrometry-based) and targeted (ligand-based) proteomics point to promising biomarkers in the urine of LN patients.

Aptamer-based interrogation of 1129 proteins using the Somascan platform, followed by ELISA-validation in two independent cohorts has indicated that the urine proteins that best distinguish active LN from controls were ALCAM, PF-4, properdin, and VCAM-1 among African Americans, E-selectin, VCAM-1, BFL-1 and Hemopexin among Caucasians, and ALCAM, VCAM-1, TFPI and PF-4 among Asians (PMID: 32366845). Most of these urine proteins correlate significantly with disease activity indices and surpass conventional metrics in identifying active LN. Several elevated urinary molecules are also expressed within LN kidneys, based on single-cell RNA-seq analysis. Of these, ALCAM has been validated in a large multi-ethnic, multi-national cohort of LN subjects, and has also been shown to be a pathogenic driver and therapeutic target in LN (PMID: 34981775).

Antibody array based screening of 1000 proteins using the Raybiotech Kiloplex platform has identified urine L-selectin, Angptl4, TGF[Formula: see text] 1, TPP1, TSP-1, FOLR2, PDGFR[Formula: see text], and PRX2, as markers of active renal lupus, outperforming conventional metrics, with L-selectin, Angptl4 and TGF[Formula: see text] 1 tracking well with concurrent or pending disease flares in LN (PMID: 32651195). Of these, urine L-selectin has been validated in large multi-ethnic/national cohorts of LN subjects (under review).

Proteomic screens of LN urine using an electrochemiluminescence platform (Mesoscale/MSD) has identified IL-7, IL-12p40, IL-15, IP-10, and TARC as markers of active renal lupus that correlated significantly with disease activity (PMID: 30618193). Very recent global proteomic screens of LN urine using a proximity ligation assay platform from Olink has added several additional biomarker candidates that have been successfully ELISA-validated (under review).

Given the plethora of urine biomarkers that have been identified using proteomics, it now becomes important to validate the clinical utility of these urine proteins, using multiple well-annotated patient cohorts, across ethnicities. Among the completed studies, we now know that some urine proteins are diagnostic of concurrent renal pathology LN Class or Activity Index or Chronicity index (e.g. CD163: PMID: 32351512; VCAM-1: PMID: 29076253; Angiostatin: PMID: 29076253; Hemopexin, Kim-1 and Lipoxcalin-2/NGAL; Renin and SAP; PMID: 20065116), while others exhibit prognostic value (e.g., ALCAM and VCAM-1; PMID: 31722419). Ongoing studies also show that most of the urine proteins interrogated in LN are not elevated in circulation (PMID: 36091001), but are expressed within LN kidneys, as ascertained by immunohistochemistry (Clinical Immunology, 2022) and Imaging Mass Cytometry (Tissue CyTOF).

To facilitate monitoring of urinary biomarkers in outpatient clinics or to enable self-monitoring of disease status by the patient from the comfort of one’s home, we have recently engineered a smartphone-readable nanophosphor-based lateral flow assay for point of care monitoring of urine ALCAM (Frontiers in Immunology, 2022). The long-term goal is to decipher the clinical utility of different urine biomarkers in managing lupus and LN in the clinics, to empower LN patients with easy-to-use tools to monitor their own disease status, and to understand the mechanistic significance of the uncovered molecules in renal disease pathogenesis. Ongoing research on this front is summarized at: https://mohanlab.bme.uh.edu/ .