Pierre Ronco

Proximal tubular cell synthesis and secretion of endothelin-1 on challenge with albumin and other proteins

Abnormal traffic of proteins through the glomerular capillary has an intrinsic renal toxicity possibly linked to the subsequent process of over-reabsorption by proximal tubular cells. We investigated in vitro the effect of different protein concentrations on proximal tubular cell endothelin-1 (ET-1) synthesis. Rabbit proximal tubular RC.SV1 cell line was grown to confluence in serum-free hormonally defined medium. Cells were incubated for 6 and 24 hours with serum-free medium containing bovine serum albumin (BSA, 0.1 to 10 mg/mL). ET-1, a locally released hormone that stimulates cell proliferation and promotes extracellular matrix protein synthesis, was measured in cell supernatant by radioimmunoassay. BSA induced a significant dose-dependent increase in proximal tubular cell ET-1 synthesis. BSA and fatty acid-free BSA stimulated tubular ET-1 synthesis and release to a comparable extent, indicating that the lipid component of the molecule is not involved in the observed phenomenon. Experiments in which tubular cells grown on filters in bicameral systems were incubated with BSA (10 mg/mL) showed that ET-1 release was predominantly basolateral. The stimulatory effect on tubular ET-1 synthesis and release was not specific to albumin but was shared by immunoglobulin (Ig) G and transferrin. Exposure of proximal tubular cells for 6 and 24 hours to both proteins (1 and 10 mg/mL) resulted in a dose-dependent increase in ET-1 synthesis. These data suggest that overexposure of proximal tubular cells to proteins, as it occurs in vivo in proteinuric renal diseases, may promote excessive tubular synthesis of ET-1, which is mostly secreted toward the interstitial compartment.(ABSTRACT TRUNCATED AT 250 WORDS)

Early-Childhood Membranous Nephropathy Due to Cationic Bovine Serum Albumin

BACKGROUND The M-type phospholipase A(2) receptor (PLA(2)R) was recently identified as a candidate antigen in 70% of cases of idiopathic membranous nephropathy, a common form of the nephrotic syndrome. The nature of antigens involved in other idiopathic and secondary membranous nephropathies remains unclear. METHODS We searched for antibodies against bovine serum albumin and circulating bovine serum albumin by means of enzyme-linked immunosorbent assay and Western blotting in serum specimens obtained from 50 patients with membranous nephropathy and 172 controls. The properties of immunopurified circulating bovine serum albumin obtained from serum specimens were analyzed with the use of two-dimensional sodium dodecyl sulfate-polyacrylamide-gel electrophoresis. We detected bovine serum albumin in glomerular deposits and analyzed the reactivity of eluted IgG. RESULTS Eleven patients, including four children, had high levels of circulating anti-bovine serum albumin antibodies, of both the IgG1 and IgG4 subclasses. These patients also had elevated levels of circulating bovine serum albumin, without an increase in circulating immune complex levels. Bovine serum albumin immunopurified from the serum specimens of these four children migrated in the basic range of pH, whereas the bovine serum albumin from adult patients migrated in neutral regions as native bovine serum albumin. Bovine serum albumin was detected in subepithelial immune deposits only in the children with both high levels of cationic circulating bovine serum albumin and bovine serum albumin-specific antibodies, and it colocalized with IgG in the absence of PLA(2)R. IgG eluted from such deposits was specific for bovine serum albumin. CONCLUSIONS Some patients with childhood membranous nephropathy have both circulating cationic bovine serum albumin and anti-bovine serum albumin antibodies. Bovine serum albumin is present in immune deposits, suggesting that cationic bovine serum albumin is pathogenic through binding to the anionic glomerular capillary wall and in situ formation of immune complexes, as shown in experimental models.

Expression and Functional Analysis of Water Channels in a Stably AQP2-transfected Human Collecting Duct Cell Line

In this study, we describe the establishment of a stably transfected epithelial cell line with the cDNA for the rat aquaporin 2 (AQP2). To this end, we used a human cell line (HCD) derived from the cortical collecting duct and having characteristics of principal cells (Prié, D., Friedlander, G., Coureau, C., Vandewalle, A., Cassigena, R., and Ronco, P. M. (1995) Kidney Int. 47, 1310-1318). The HCD cells were first screened for the constitutive expression of AQPs. By Western blot analysis, we found a low expression of immunoreactive AQP2 and AQP4 proteins. In contrast, transfected cells (clone CD8) probed with AQP2 antiserum expressed an intense 29-kDa protein on immunoblot in addition to a broad band between 35-45 kDa corresponding to the glycosylated form of the protein, indicating that full maturity of the protein is attained in transfected cells. Immunofluorescence demonstrated that AQP2 was located in intracellular vesicles. After vasopressin stimulation, the staining redistributed from an intracellular site to the apical pole of the cells, an effect similar to that described on collecting duct principal cells in vivo (Sabolic, I., Katsura, T., Verbavatz, J. M., and Brown, D. (1995) J. Membr. Biol. 143, 165-175) and in perfused tubules (Nielsen, S., Chou, C. L., Marples, D., Christensen, E. I., Kishore, B. K., and Knepper, M. A. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 1013-1017). The redistribution of AQP2 in CD8 cells was accompanied by an approximately 6-fold increase in osmotic water permeability coefficient (Pf), which was inhibited by 0.3 mM HgCl2. These data indicate that functional vasopressin-sensitive water channels are expressed in transfected cells. The stably transfected cells represent a suitable model to unravel by direct experimental approach the intracellular signals involved in the translocation of AQP2 to the apical plasma membrane in the presence of vasopressin.

Diagnosis, management, and prognosis of HNF1B nephropathy in adulthood

Mutations in HNF1B are responsible for a dominantly inherited disease with renal and nonrenal consequences, including maturity-onset diabetes of the young (MODY) type 5. While HNF1B nephropathy is typically responsible for bilateral renal cystic hypodysplasia in childhood, the adult phenotype is poorly described. To help define this we evaluated the clinical presentation, imaging findings, genetic changes, and disease progression in 27 adults from 20 families with HNF1B nephropathy. Whole-gene deletion was found in 11 families, point mutations in 9, and de novo mutations in half of the kindred tested. Renal involvement was extremely heterogeneous, with a tubulointerstitial profile at presentation and slowly progressive renal decline throughout adulthood as hallmarks of the disease. In 24 patients tested, there were cysts (≤5 per kidney) in 15, a solitary kidney in 5, hypokalemia in 11, and hypomagnesemia in 10 of 16 tested, all as characteristics pointing to HNF1B disease. Two patients presented with renal Fanconi syndrome and, overall, 4 progressed to end-stage renal failure. Extrarenal phenotypes consisted of diabetes mellitus in 13 of the 27 patients, including 11 with MODY, abnormal liver tests in 8 of 21, diverse genital tract abnormalities in 5 of 13 females, and infertility in 2 of 14 males. Thus, our findings provide data that are useful for recognition and diagnosis of HNF1B disease in adulthood and might help in renal management and genetic counseling.

Phospholipase A2 Receptor (PLA2R1) Sequence Variants in Idiopathic Membranous Nephropathy

The M-type receptor for phospholipase A2 (PLA2R1) is the major target antigen in idiopathic membranous nephropathy (iMN). Our recent genome-wide association study showed that genetic variants in an HLA-DQA1 and phospholipase A2 receptor (PLA2R1) allele associate most significantly with biopsy-proven iMN, suggesting that rare genetic variants within the coding region of the PLA2R1 gene may contribute to antibody formation. Here, we sequenced PLA2R1 in a cohort of 95 white patients with biopsy-proven iMN and assessed all 30 exons of PLA2R1, including canonical (GT-AG) splice sites, by Sanger sequencing. Sixty patients had anti-PLA2R1 in serum or detectable PLA2R1 antigen in kidney tissue. We identified 18 sequence variants, comprising 2 not previously described, 7 reported as rare variants (<1%) in the Single Nucleotide Polymorphism Database or the 1000 Genomes project, and 9 known to be common polymorphisms. Although we confirmed significant associations among 6 of the identified common variants and iMN, only 9 patients had the private or rare variants, and only 4 of these patients were among the 60 who were PLA2R positive. In conclusion, rare variants in the coding sequence of PLA2R1, including splice sites, are unlikely to explain the pathogenesis of iMN.

Nephropathy Associated with Infection by Human Immunodeficiency Virus: A Report on 11 Cases Including 6 Treated with Zidovudine

The human immunodeficiency virus (HIV) was recently suggested to be involved in generating kidney lesions in HIV-associated nephropathy (HIVN). The possibility that antiretroviral agents can slow down the usually explosive evolution of HIVN to end-stage renal failure (ESRF) has not been studied in many of the series of cases published. The present work is a retrospective analysis of 11 patients with histologically proven HIVN, 6 of whom were treated with zidovudine. Seven patients (group 1) either required dialysis at the outset, when HIVN was diagnosed, or progressed very fast to ESRF within 15-45 days. Two patients of this group were treated with zidovudine, but it had no effect on kidney function. In the remaining 4 patients (group 2), HIVN progressed more slowly than in group 1. All 4 patients were treated with zidovudine at an earlier stage of the disease than ESRF. Only 1 deteriorated to ESRF in 9 months. The 3 others, who did not have ESRF, were followed up for 13, 10 and 32 months, respectively. Although this is a preliminary study, its results do suggest that zidovudine can slow down the evolution of HIVN to ESRF. They highlight the need to screen HIV-positive patients regularly for proteinuria, in order to detect HIVN by renal biopsies at an early stage of renal lesion formation.

Characterization of monoclonal antibodies specific for rabbit renal brush-border hydrolases: application to immunohistological localization.

By use of immunodepletion studies, we characterized four monoclonal antibodies reactive with rabbit brush-border (BB) as specific for aminopeptidase N (AP), dipeptidylpeptidase IV (DPPIV), neutral endopeptidase (EP), and angiotensin-converting enzyme (ACE), and we used these antibodies for immunohistochemical detection of these four hydrolases. Expression within the kidney was studied by light and electron microscopy. All four hydrolases are expressed on the various segments of the proximal tubule. In addition, EP and DPPIV are detectable on visceral epithelial cells of the glomerulus and AP on the cells of Bowmans capsule. Outside the kidney, the four hydrolases are expressed within the digestive and genital tracts, where AP, EP, and DPPIV predominate on epithelial structures, whereas ACE is essentially located in vascular structures. The latter localization is also characteristic of ACE in the other organs studied, where clear-cut systematic distribution of the other hydrolases was often difficult to demonstrate. In addition, AP, DPPIV, and EP were detected on lymphoid cells. As compared to reports of data obtained essentially by enzymatic or immunoradiometric assays, these observations suggest considerable interspecies variations of extrarenal expression of the major BB hydrolases. This should be taken into account in attempting to define a general physiological role for a given enzyme.

Towards standard protocols and guidelines for urine proteomics: A report on the Human Kidney and Urine Proteome Project (HKUPP) symposium and workshop - 6 October 2007, Seoul, Korea and 1 November 2007, San Francisco, CA, USA

The Human Kidney and Urine Proteome Project (HKUPP) was initiated in 2005 to promote proteomics research in the nephrology field, to better understand kidney functions as well as pathogenic mechanisms of kidney diseases, and to define novel biomarkers and therapeutic targets. This project was first approved in 2005 by the Human Proteome Organisation (HUPO) as a Kidney Disease Initiative under an umbrella of the HUPO Disease Biomarker Initiative (DBI), and more recently was approved as the HKUPP Initiative in 2007. Several sub‐projects have been planned to achieve the ultimate goals. The most pressing is the establishment of “standard protocols and guidelines for urine proteome analysis”. This sub‐project had been extensively discussed during the first HKUPP symposium (during 6th HUPO Annual World Congress – October 2007, Seoul, Korea) and second workshop (during 40th American Society of Nephrology Renal Week – November 2007, San Francisco, CA, USA). Additional data and references have been collected after the symposium and workshop. An initial draft of standard protocols and guidelines for proteome analysis of non‐proteinuric urine (urine protein excretion ≤150 mg/day) will soon be released as the first HKUPP product.

HIV-associated kidney glomerular diseases: changes with time and HAART

BACKGROUND Treatment and co-morbidities of human immunodeficiency virus (HIV)-infected individuals have changed dramatically in the last 20 years with a potential impact on renal complications. Our objective was to assess the change in distribution of the glomerular diseases in HIV patients. METHODS We retrospectively analysed demographic, clinical, laboratory and renal histopathological data of 88 HIV-infected patients presenting with a biopsy-proven glomerular disease between 1995 and 2007. RESULTS In our study including 66% Black patients, HIV-associated nephropathy (HIVAN) was observed in 26 cases, classic focal segmental glomerulosclerosis (FSGS) in 23 cases, immune complex glomerulonephritis in 20 cases and other glomerulopathies in 19 patients. HIVAN decreased over time, while FSGS emerged as the most common cause of glomerular diseases (46.9%) in HIV-infected individuals undergoing kidney biopsy in the last 2004-07 period. Patients with HIVAN were usually Black (97%), with CD4 <200/mL (P = 0.01) and glomerular filtration rate <30 mL/min/1.73 m(2) (P < 0.01). Compared to HIVAN, patients with classic FSGS were less often Black (P < 0.01), have been infected for longer (P = 0.03), were more often co-infected with hepatitis C virus (P = 0.05), showed more often cardiovascular (CV) risk factors (P < 0.01), had less often CD4 <200/mL (P = 0.01), lower HIV viral load (P = 0.01) and tended to be older (P = 0.06). CONCLUSIONS Classic FSGS associated with metabolic and CV risk factors has overcome HIVAN in HIV-infected patients. Compared with other glomerulopathies, HIVAN remains strongly associated with severe renal failure, Black origin and CD4 lower than 200/mL at presentation.

Progression and regression in renal vascular and glomerular fibrosis

End‐stage renal disease (ESRD) is characterized by the development of fibrotic lesions in the glomerular, interstitial and vascular compartments. Renal fibrogenesis, a common complication of diabetes and hypertension, is a complex dynamic process involving several players such as inflammatory agents, cytokines, vasoactive agents and enzymes participating in extracellular matrix assembly, anchoring or degradation. The only available treatment today against chronic renal failure is dialysis or kidney transplantation, making thus ESRD one of the most expensive diseases to treat on a per‐patient basis. An emerging challenge for clinicians, maybe the nephrologists Holy Grail in the 21st century, is to stop definitively the decline of renal function and, if possible, to achieve regression of renal fibrosis and restoration of renal structure. Over the last 5 years, different approaches have been tested in experimental models of nephropathy with variable degree of success. In this review, we will focus on the mechanisms of the hypertension‐associated fibrosis and the few recent studies that gave promising results for a therapeutic intervention.