Association of Urinary Laminin G-Like 3 and Free K Light Chains with Disease Activity and Histological Injury in IgA Nephropathy

Abstract

Summary Background and objectives IgA nephropathy has variable clinical presentation and progression. Its definitive diagnosis and prognosis require renal biopsy. The identification of new biomarkers allowing noninvasive diagnosis and monitoring of disease activity would be advantageous. This study analyzed the urine proteome of IgA nephropathy patients at an early stage of disease. Design, setting, participants, & measurements Urine from 49 IgA nephropathy patients, 42 CKD patients, and 40 healthy individuals was analyzed by surface-enhanced laser desorption/ionization time of flight/mass spectrometry. Differentially excreted proteins were identified by matrix-enhanced laser desorption/ionization time of flight/mass spectrometry, confirmed by immunologic methods, and validated in an independent set of patients (14 IgA nephropathy and 24 CKD). All patients were recruited at the Division of Nephrology of the University of Foggia from January of 2005 to March of 2007. Results Two proteins, with 21,598 and 23,458 m/z, were significantly decreased in IgA nephropathy and identified as Perlecan laminin G-like 3 peptide and Ig κ light chains, respectively. Western blot analysis confirmed the lower urinary excretion of laminin G-like 3 in IgA nephropathy patients compared with CKD patients and healthy individuals. Immunonephelometry analysis confirmed the lower urinary excretion of free κ light chains in IgA nephropathy patients compared with CKD patients and healthy individuals. Immunohistochemistry analysis justified the urinary excretion profile of such proteins in IgA nephropathy. Finally, urinary free κ light chains and laminin G-like 3 concentration inversely correlated with severity of clinical and histologic features of our IgA nephropathy cohort. Conclusions Laminin G-like 3 and free κ light chains can contribute to the noninvasive assessment of IgA nephropathy disease activity.

Lysine 63 ubiquitination is involved in the progression of tubular damage in diabetic nephropathy

“…Coomassie‐stained gel and ubiquitin‐Lys63‐immunoblotted membranes were compared to select, among all the immu‐ noprecipitated proteins, the Lys63‐ubiquitinated ones. Bands of interest were excised and trypsin digested according to our optimized protocol (27). Eluted peptides were analyzed by matrix‐assisted laser desorption/ionization‐time of flight/ tandem mass spectrometry (MALDI‐TOF/MS‐MS).…”

“…A peptide mixture of the selected protein bands was separately loaded on a prespotted anchor chip (Bruker Daltonics, Bremen, Germany). MS and MS/MS analyses were performed on an Autoflex IIITOF/TOF200 instrument (Bruker Daltonics) (27). Protein identification was performed on NCBInr and Swissprot databases with the Mascot search algorithm (Matrix Science, Boston, MA, USA; http://www.matrixscience.com/), with the following parameters: Homo sapiens (taxonomic category), trypsin (enzyme), carbamidomethyl (fixed modification for cysteine residues), and oxidation of methionine (variable modification).…”

Markers for the progression of IgA nephropathy

“…Decreased urinary levels of laminin G-like 3 peptide (perlecan) and free κ light chains were observed in patients with IgAN, and the levels of both inversely correlated with severity of clinical and histological features of IgAN patients [56]. …”

Biomarkers in IgA nephropathy: relationship to pathogenetic hits

“…The IgA nephropathy patients had lower excretion of laminin G-like 3 and free κ light chains compared to patients with other chronic kidney diseases and healthy controls [89]. Urinary laminin G-like 3 and free κ light chain concentrations were inversely correlated with severity of clinical and histologic features [89]. …”