MicroRNAs (miRNAs) are a class of noncoding RNA acting at a post-transcriptional level to control the expression of large sets of target mRNAs. While there is evidence that miRNAs deregulation plays a causative role in various complex disorders, their role in fibrotic kidney diseases is largely unexplored. Here, we found a strong up-regulation of miR-21 in the kidneys of mice with unilateral ureteral obstruction and also in the kidneys of patients with severe kidney fibrosis. In addition, mouse primary fibroblasts derived from fibrotic kidneys exhibited higher miR-21 expression level compared to those derived from normal kidneys. Expression of miR-21 in normal primary kidney fibroblasts was induced upon TGFβ exposure, a key growth factor involved in fibrogenesis. Finally, ectopic expression of miR-21 in primary kidney fibroblasts was sufficient to promote myofibroblast differentiation. As circulating miRNAs have been suggested as promising non-invasive biomarkers, we further assess whether circulating miR-21 levels are associated with renal fibrosis using sera from 42 renal transplant recipients, categorized according to their renal fibrosis severity, evaluated on allograft biopsies (Interstitial Fibrosis/Tubular Atrophy (IF/TA). Circulating miR-21 levels are significantly increased in patients with severe IF/TA grade (IF/TA grade 3: 3.0±1.0 vs lower grade of fibrosis: 1.5±1.2; p = 0.001). By contrast, circulating miR-21 levels were not correlated with other renal histological lesions. In a multivariate linear regression model including IF/TA grade and estimated GFR, independent associations were found between circulating miR-21 levels and IF/TA score (ß = 0.307, p = 0.03), and between miR-21 levels and aMDRD (ß = −0.398, p = 0.006). Altogether, these data suggest miR-21 has a key pathogenic role in kidney fibrosis and may represent a novel, predictive and reliable blood marker of kidney fibrosis.

Monoclonal immunoglobulin deposition disease (MIDD) is a rare complication of B-cell clonal disorders, defined by Congo red negative–deposits of monoclonal light chain (LCDD), heavy chain (HCDD), or both (LHCDD). MIDD is a systemic disorder with prominent renal involvement, but little attention has been paid to the description of extrarenal manifestations. Moreover, mechanisms of pathogenic immunoglobulin deposition and factors associated with renal and patient survival are ill defined. We retrospectively studied a nationwide cohort of 255 patients, with biopsy-proven LCDD (n = 212) (including pure LCDD [n = 154], LCDD with cast nephropathy (CN) [n = 58]), HCDD (n = 23), or LHCDD (n = 20). Hematological diagnosis was monoclonal gammopathy of renal significance in 64% and symptomatic myeloma in 34%. Renal presentation was acute kidney injury in patients with LCCD and CN, and chronic glomerular disease in the other types, 35% of whom had symptomatic extrarenal (mostly hepatic and cardiac) involvement. Sequencing of 18 pathogenic LC showed high isoelectric point values of variable domain complementarity determining regions, possibly accounting for tissue deposition. Among 169 patients who received chemotherapy (bortezomib-based in 58%), 67% achieved serum free light chain (FLC) response, including very good partial response (VGPR) or above in 52%. Renal response occurred in 62 patients (36%), all of whom had achieved hematological response. FLC response ≥ VGPR and absence of severe interstitial fibrosis were independent predictors of renal response. This study highlights an unexpected frequency of extrarenal manifestations in MIDD. Rapid diagnosis and achievement of deep FLC response are key factors of prognosis.

BackgroundThe roles of asymptomatic hyperuricemia or uric acid (UA) crystals in CKD progression are unknown. Hypotheses to explain links between UA deposition and progression of CKD include that (1) asymptomatic hyperuricemia does not promote CKD progression unless UA crystallizes in the kidney; (2) UA crystal granulomas may form due to pre-existing CKD; and (3) proinflammatory granuloma-related M1-like macrophages may drive UA crystal-induced CKD progression.MethodsMALDI-FTICR mass spectrometry, immunohistochemistry, 3D confocal microscopy, and flow cytometry were used to characterize a novel mouse model of hyperuricemia and chronic UA crystal nephropathy with granulomatous nephritis. Interventional studies probed the role of crystal-induced inflammation and macrophages in the pathology of progressive CKD.ResultsAsymptomatic hyperuricemia alone did not cause CKD or drive the progression of aristolochic acid I-induced CKD. Only hyperuricemia with UA crystalluria due to urinary acidification caused tubular obstruction, inflammation, and interstitial fibrosis. UA crystal granulomas surrounded by proinflammatory M1-like macrophages developed late in this process of chronic UA crystal nephropathy and contributed to the progression of pre-existing CKD. Suppressing M1-like macrophages with adenosine attenuated granulomatous nephritis and the progressive decline in GFR. In contrast, inhibiting the JAK/STAT inflammatory pathway with tofacitinib was not renoprotective.ConclusionsAsymptomatic hyperuricemia does not affect CKD progression unless UA crystallizes in the kidney. UA crystal granulomas develop late in chronic UA crystal nephropathy and contribute to CKD progression because UA crystals trigger M1-like macrophage-related interstitial inflammation and fibrosis. Targeting proinflammatory macrophages, but not JAK/STAT signaling, can attenuate granulomatous interstitial nephritis.

Renal proximal tubular epithelial cells play a central role in renal physiology and are among the cell types most sensitive to ischemia and xenobiotic nephrotoxicity. In order to investigate the molecular and cellular mechanisms underlying the pathophysiology of kidney injuries, a stable and well-characterized primary culture model of proximal tubular cells is required. An existing model of proximal tubular cells is hampered by the cellular heterogeneity of kidney; a method based on cell sorting for specific markers must therefore be developed. In this study, we present a primary culture model based on the mechanical and enzymatic dissociation of healthy tissue obtained from nephrectomy specimens. Renal epithelial cells were sorted using co-labeling for CD10 and CD13, two renal proximal tubular epithelial markers, by flow cytometry. Their purity, phenotypic stability and functional properties were evaluated over several passages. Our results demonstrate that CD10/CD13 double-positive cells constitute a pure, functional and stable proximal tubular epithelial cell population that displays proximal tubule markers and epithelial characteristics over the long term, whereas cells positive for either CD10 or CD13 alone appear to be heterogeneous. In conclusion, this study describes a method for establishing a robust renal proximal tubular epithelial cell model suitable for further experimentation.