Fluoride ion toxicity in rabbit kidney thick ascending limb cells.

BACKGROUND AND OBJECTIVE: Some halogenated agents, especially methoxyflurane, because of a higher level of fluoride production, induce a renal concentrating defect that could be related to an ascending limb impairment. We investigated the mechanisms of fluoride toxicity on an immortalized cell line. METHODS: Cells were cultured for 2, 6 or 24 h in the presence of fluoride. Toxicity evaluation was based on: cell numbers, protein content, leucine-incorporation, lactate dehydrogenase (LDH) and N-acetyl-beta-glucosaminidase (NAG) releases, Na-K-ATPase and Na-K-2Cl activities, electron microscope studies. Infrared analysis and fluoride microdetermination allowed crystal components. RESULTS: At 5 mmol after 24 h, fluoride decreased cell numbers (-14%, *P < 0.05), protein content (-16%*), leucine incorporation (-54%*), Na-K-2Cl activity (-84%*), increased LDH (+145%*) and NAG release (+190%*). Na-K-ATPase was more sensitive and impaired from 1 mmol for 24h and after 2 h at 5 mmol. Crystal formation in mitochondria occurred after 6 h at 5 mmol. Infra-red analysis and fluoride microdetermination established that crystals contained sodium, phosphate and fluoride. CONCLUSIONS: The results suggest that the Na-K-ATPase pump is a major target for fluoride toxicity in Henle's loop.

Regulation of vitamin D-1alpha-hydroxylase in a human cortical collecting duct cell line.

BACKGROUND: Recent studies have shown that renal expression of 25-hydroxyvitamin D3-1alpha-hydroxylase (1alpha-OHase) is not restricted to proximal tubules. To investigate the significance of this expression, we characterized the regulation of 1alpha-OHase expression and activity in a human cortical collecting duct cell line (HCD). METHODS: Expression of 1alpha-OHase mRNA and protein was assessed by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot analyses. Enzyme activity was quantified using 25-hydroxyvitamin D3 as the substrate; conversion to 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] and 24,25-dihydroxyvitamin D3 was then determined by thin-layer chromatography. RESULTS: HCD cells expressed mRNA and protein for 1alpha-OHase. However, basal 1,25(OH)2D3 production was lower than that observed in proximal tubule HKC-8 cells. In both cell lines, synthesis of 1,25(OH)2D3 was increased by forskolin, parathyroid hormone, and low calcium medium. Conversely, treatment with 1,25(OH)2D3 itself decreased 1alpha-OHase activity. This effect was more pronounced in HCD cells, which also demonstrated significantly higher levels of 24-hydroxylase activity. The most striking induction of 1alpha-OHase activity was observed in the HCD cells following incubation with lipopolysaccharide, which was coincident with the expression of mRNA for both CD14 and Toll-like receptor 4. CONCLUSIONS: These results highlight the capacity for synthesis of 1,25(OH)2D3 in cells from more distal areas of the nephron. However, more sensitive feedback regulation and immune induction of 1alpha-OHase in the HCD cells suggest a more localized role for 1,25(OH)2D3 production in the distal nephron.

Matrix metalloproteinase 9 protects mice from anti-glomerular basement membrane nephritis through its fibrinolytic activity.

Matrix metalloproteinase (MMP)9/gelatinase B is increased in various nephropathies. To investigate its role, we used a genetic approach. Adult MMP9-deficient (MMP9(-/)-) mice showed normal renal histology and function at 3 mo. We investigated the susceptibility of 3-mo-old mice to the accelerated model of anti-glomerular basement membrane nephritis, in which fibrin is an important mediator of glomerular injury and renal impairment. Unexpectedly, nephritis was more severe in MMP9(-/)- than in control mice, as attested by levels of serum creatinine and albuminuria, and the extent of crescents and fibrin deposits. Circulating or deposited immunoglobulin G, interleukin (IL)-1beta, or IL-10 were the same in MMP9(-/-) and MMP9(+/+) mice. However, we found that fibrin is a critical substrate for MMP9, and in its absence fibrin accumulated in the glomeruli. These data indicate that MMP9 is required for a novel protective effect on the development of fibrin-induced glomerular lesions.

Do matrix metalloproteinases MMP-2 and MMP-9 (gelatinases) play a role in renal development, physiology and glomerular diseases?

Metalloproteinases MMP-2 and MMP-9 (also called gelatinases) are involved in cell invasion and in embryonic development and organogenesis. A growing number of reports suggest that MMP-2 and MMP-9 play some role in renal development, renal tubule physiology and glomerular pathophysiology. This editorial will focus on recent controversial data, especially those obtained from studies on MMP-9-deficient mice, which shed new light on the functions of gelatinases in normal and diseased kidneys.

Adult Fanconi syndrome secondary to light chain gammopathy. Clinicopathologic heterogeneity and unusual features in 11 patients.

Fifty-seven cases of Ig light chain-associated Fanconi syndrome (FS) have been reported so far, mostly as isolated reports. The pioneering work by Maldonado and associates (35), who reviewed the first 17 cases in 1975, led to the unifying concept that patients with FS and Bence Jones proteinuria have a special form of plasma cell dyscrasia characterized by slow progression of the tumor and by prominent crystal formation in proximal tubule cells, in the absence of myeloma casts in the distal tubule. We carefully reappraised these characteristics in a series of 11 patients. Ten renal biopsy specimens were available for electron microscopy, adding to the 15 previously reported cases with ultrastructural studies. Moreover, 10 of the kappa light chains could be entirely or partially sequenced and tested for their resistance to cathepsin B, a lysosomal protease present in proximal tubule cells. Our series showed an unexpected clinicopathologic heterogeneity. Seven patients presented with the typical clinical and pathologic features of FS and low-mass myeloma or monoclonal gammopathy of undetermined significance (MGUS), in keeping with Maldonado et al's description. Crystals in bone marrow cells were detected in patients of this group, only. Three patients who presented with full-blown FS exhibited, however, the characteristic features of myeloma cast nephropathy in the setting of high-mass myeloma. One patient of this group also had numerous crystals in proximal tubule cells. The eleventh patient had complete FS with MGUS, but no crystals in proximal tubule cells even after electron microscopy. Contrasting with the clinicopathologic heterogeneity, genetic and biochemical analyses of the light chains showed a striking homogeneity. First, they all were of the kappa type. Second, 8 of 9 belonged to the V kappa I variability subgroup, which indicates that FS light chains are related by the sequence of their variable regions. Third, the 8 V kappa I light chain sequences most likely originated from only 2 germline genes, LCO2/012 and LCO8/018. Fourth, all 5 LCO2/012-derived sequences presented an unusual hydrophobic or nonpolar residue at position 30. These sequence peculiarities may account for unusual physicochemical properties of the light chains including the resistance of their variable domain V kappa to proteolysis by cathepsin B, observed in 7 of 9 patients in our series, while light chains isolated from patients with myeloma cast nephropathy are completely digested. Resistance of V kappa to proteolysis in FS patients can explain the accumulation of the light chain in the endocytotic compartment of the proximal tubule cells, leading to impairment of proximal tubule functions.

Mother-to-child transmitted WT1 splice-site mutation is responsible for distinct glomerular diseases.

Mutations in the Wilms' tumor suppressor gene (WT1) are linked with Denys-Drash syndrome (DDS), a rare childhood disease characterized by diffuse mesangial sclerosis and renal failure of early onset, XY pseudohermaphroditism, and high risk of Wilms' tumor. KTS (lysine-threonine-serine) splice site mutations in WT1 intron 9 have been described in patients with Frasier syndrome, another rare syndrome defined by focal and segmental glomerulosclerosis (FSGS), XY pseudohermaphroditism, and frequent occurrence of gonadoblastoma. Cases of Frasier syndrome raise the question whether splice site mutations may also be found in XX females with isolated FSGS. A girl (index case) presented with the nephrotic syndrome at 9 mo of age. The diagnosis of DDS was based on the finding of diffuse mesangial sclerosis in the kidney biopsy and of a XY karyotype. The index case's mother had had proteinuria since she was 6 years of age. A renal biopsy was performed when she was 28 and disclosed FSGS. The same splice site mutation in intron 9 (WT1 1228+5 G-->A) involving one allele was found in the child and in her mother, but not in other members of the kindred (including the parents, the two brothers, and the two sisters of the index case's mother) who were free of renal symptoms. Quantification of WT1 +KTS/-KTS isoforms in the index case's father and one index case's maternal uncle showed a normal +KTS/-KTS ratio of 1.50. In contrast, the index case and her mother had a low ratio (0.40 and 0.34, respectively), within the range reported in Frasier syndrome. In conclusion, this study shows that the KTS splice site mutation is not specific for Frasier syndrome, but that it can also be found in DDS and in a normal female (XX) with FSGS, a woman who achieved normal pregnancy. It is suggested that WT1 splice site mutations should be sought in phenotypically normal females who present with FSGS or with related glomerulopathies of early onset.

Kappa light chain-associated Fanconi's syndrome: molecular analysis of monoclonal immunoglobulin light chains from patients with and without intracellular crystals.

Plasma cell dyscrasias may be responsible for Fanconi's syndrome, due to the toxicity of a free monoclonal kappa light chain toward kidney proximal tubules. Eight cases of Fanconi's syndrome were analyzed. We compared the structures of VkappaI variability subgroup V domains from five cases of Fanconi's syndrome and one myeloma without renal involvement. Among Fanconi cases, four putative structures were obtained after molecular modeling by homology, and the other had previously been refined by X-ray crystallography. The complete sequences of one VkappaI, one VkappaIII and N-terminal sequences of two VkappaI light chains, from patients with different forms of Fanconi's syndrome, were compared with four previously studied sequences. All three kappa chains responsible for a 'classical' form with intralysosomal crystals and a low mass myeloma, were encoded by the LCO2/O12 germline gene and had an unusual non-polar residue exposed to the solvent in the CDR-L1 loop. Of both VkappaI light chains from patients with Fanconi's syndrome without intracellular crystals, one derived from LCO2/O12 and the other from LCO8/O18 gene. Another feature that could be related to non-crystallization was the absence of accessible side chains in the CDR-L3 loop which is known to be implicated in dimer formation.

Nodular glomerulosclerosis with deposition of monoclonal immunoglobulin heavy chains lacking C(H)1.

The objective of this study was to further characterize the clinical and immunopathologic features of heavy chain deposition disease (HCDD), a recently described entity. Four patients were diagnosed as having HCDD on a kidney biopsy. All presented with nodular glomerulosclerosis with deposition of gamma1 heavy chains lacking CH1 epitopes, but without light chains. Two different patterns were observed in the serum. First, patients 1 and 2 had a circulating monoclonal IgGlambda containing a short gamma1 heavy chain lacking CH1 epitopes, with an apparent molecular weight of 40 kD consistent with a complete CH1 deletion. Biosynthetic experiments also showed that the deleted heavy chain was produced in excess compared with light chains, and was secreted in vitro together with half Ig molecules, although these abnormal components were not detected by Western blot analysis of whole serum. Second, patients 3 and 4 had a circulating monoclonal IgG1lambda with an apparently normal, nondeleted heavy chain subunit, but serum fractionation followed by immunoblotting revealed an isolated monoclonal gamma1 chain lacking CH1 epitopes. These data strongly suggest that renal deposition of a CH1-deleted heavy chain circulating in low amounts in the serum as a free unassembled subunit is a major feature of HCDD. The CH1 deletion is most likely responsible for the premature secretion in blood of the heavy chain by a clone of plasma cells.

Matrix metalloproteinase 2 (MMP2) and MMP9 are produced by kidney collecting duct principal cells but are differentially regulated by SV40 large-T, arginine vasopressin, and epidermal growth factor.

We analyzed the expression and regulation of matrix metalloproteinase 2 (MMP2) and MMP9 gelatinases in a rabbit kidney collecting duct principal cell line (RC.SVtsA58) (Prié, D., Ronco, P. M., Baudouin, B., Géniteau-Legendre, M., Antoine, M., Piedagnel, R., Estrade, S., Lelongt, B., Verroust, P. J., Cassingéna, R., and Vandewalle, A. (1991) J. Cell Biol. 113, 951-962) infected with the temperature-sensitive (ts) SV40 strain tsA58. At the permissive temperature (33 degreesC), cells produced only MMP2. Shifting cells to a nonpermissive temperature (39.5 degreesC) induced a marked increase in total gelatinolytic activity due to an increase of MMP2 and an induction of MMP9 synthesis. This effect was attributed to large-T inactivation at 39.5 degreesC because it was abolished by re-infecting the cells with wild-type SV40 strain LP. Run-on experiments showed that negative regulation of MMP2 and MMP9 by large-T was transcriptional and posttranscriptional, respectively. MMP2 and MMP9 were also produced by primary cultures of collecting duct cells. In rabbit kidney, both MMP2 and MMP9 were almost exclusively expressed in collecting duct cells, where an unexpected apical localization was observed. Arginine vasopressin and epidermal growth factor, which exert opposite hydroosmotic effects in the collecting duct, also exhibited contrasted effects on MMP9 synthesis. Epidermal growth factor increased but arginine vasopressin suppressed MMP9 at a posttranscriptional level, whereas MMP2 was not affected. These results suggest a specific physiological role of MMP2 and MMP9 in principal cells of renal collecting duct.

The cell adhesion molecule L1 is developmentally regulated in the renal epithelium and is involved in kidney branching morphogenesis.

We immunopurified a surface antigen specific for the collecting duct (CD) epithelium. Microsequencing of three polypeptides identified the antigen as the neuronal cell adhesion molecule L1, a member of the immunoglobulin superfamily. The kidney isoform showed a deletion of exon 3. L1 was expressed in the mesonephric duct and the metanephros throughout CD development. In the adult CD examined by electron microscopy, L1 was not expressed on intercalated cells but was restricted to CD principal cells and to the papilla tall cells. By contrast, L1 appeared late in the distal portion of the elongating nephron in the mesenchymally derived epithelium and decreased during postnatal development. Immunoblot analysis showed that expression, proteolytic cleavage, and the glycosylation pattern of L1 protein were regulated during renal development. L1 was not detected in epithelia of other organs developing by branching morphogenesis. Addition of anti-L1 antibody to kidney or lung organotypic cultures induced dysmorphogenesis of the ureteric bud epithelium but not of the lung. These results suggest a functional role for L1 in CD development in vitro. We further postulate that L1 may be involved in the guidance of developing distal tubule and in generation and maintenance of specialized cell phenotypes in CD.

PAI-1 secretion and matrix deposition in human peritoneal mesothelial cell cultures: transcriptional regulation by TGF-beta 1.

BACKGROUND: Plasminogen activator inhibitor-1 (PAI-1), the main inhibitor of plasminogen activators in plasma and in peritoneum, impairs plasmin formation that is essential for the repair processes of the mesothelium damaged by peritoneal dialysis fluids and peritonitis. The fibrogenetic cytokine transforming growth factor-beta (TGF-beta) displays variable effects on extracellular matrix remodeling enzymes and their inhibitors depending on tissues and cell lines. We previously found an unexpected stimulating effect of TGF-beta 1 on matrix metalloproteinase-9 in peritoneal mesothelial cells. In this study, we analyzed the effects of TGF-beta 1 on PAI-1 production and deposition in extracellular matrix. METHODS: We used primary cultured mesothelial cells and a recently established human peritoneal mesothelial cell line (HMrSV5). Cell-associated and secreted plasminogen activators and their inhibitors were detected and characterized by substrate gel zymography. PAI-1 was identified by reverse zymography and by Western blotting, and total PAI-1 was measured by ELISA. Secreted and cell-associated PA activity was measured by its ability to activate plasminogen into plasmin, that is, by the release of paranitroaniline from the plasmin synthetic substrate S-2251. PAI-1 mRNA accumulation was assessed by Northern blot. In vitro nuclear run-on assays were carried out to determine whether TGF-beta 1 had transcriptional effects on PAI-1 expression. Finally, the subcellular distribution of PAI-1 was analyzed by immunofluorescence and by immunogold silver staining. RESULTS: TGF-beta 1 increased PAI-1 antigen in the conditioned media of HMrSV5 cells, in a time- and concentration-dependent manner. This induced a dramatic decrease of free tPA in the cell medium and of membrane-bound uPA, and a parallel increase of high molecular weight PA-PAI complexes. Consequently, secreted and cell-associated plasminogen activator activities were considerably reduced. In primary cultured peritoneal mesothelial cells, TGF-beta 1 also induced PAI-1 secretion and the shift of tPA toward high molecular weight complexes. TGF-beta 1 increased PAI-1 mRNA in a time- and concentration-dependent manner. This effect was at least in part transcriptional since an approximately threefold increase in the rate of PAI-1 gene transcription was observed in nuclei sampled after a four-hour cell exposure to 5 ng/ml TGF-beta 1. Finally, TGF-beta 1 substantially increased the amount of intracellular and matrix-associated PAI-1. CONCLUSIONS: These results suggest that excessive TGF-beta 1 stimulated PAI-1 could prevent appropriate peritoneal healing by impairing the degradation of fibrin and of unorganized matrix components, and by interfering with cell migration.

Polarized distribution of Na+/H+ exchanger isoforms in rabbit collecting duct cells.

The present study describes two Na+/H+ exchanger (NHE) isoforms in an immortalized rabbit renal cortical collecting tubule cell line (RC.SV3). Na+/H+ exchange activity was assayed using fluorescence measurements of intracellular pH (pHi) in monolayers mounted in a cuvette containing two fluid compartments, making it possible to independently measure Na+/H+ exchange activity on either the apical or basolateral surface. RC.SV3 monolayers express Na+/H+ exchange activities in both the apical and basolateral membrane domains. The two exchangers have half-saturation constants (Km) for external sodium and sensitivities to dimethylamiloride, to HOE-694 and to cimetidine and clonidine consistant with the NHE-1 isoform on the basolateral cell surface and the NHE-2 isoform on the apical surface. Protein kinase A inhibition of basolateral exchanger activity was significantly higher than that of the apical exchanger. Protein kinase C significantly stimulated both exchangers equally. RT-PCR analysis found RNA for only NHE-1 and NHE-2, and immunofluorescence with an antibody against NHE-1 demonstrated a basolateral location for this isoform. The results suggest that RC.SV3 cells have two Na+/H+ exchange activities separated spatially to the two cellular membranes, with the NHE-1 and the NHE-2 isoforms located on the basolateral and the apical membranes, respectively.

Matrix metalloproteinases MMP2 and MMP9 are produced in early stages of kidney morphogenesis but only MMP9 is required for renal organogenesis in vitro.

We analyzed matrix metalloproteinase (MMP) production by 11-d embryonic mouse kidneys and the effects of these enzymes on subsequent renal organogenesis. In vivo, immunolocalization of metalloproteinases by laser scanning confocal microscopy and zymograms of kidney lysates showed that the mesenchyme of embryonic kidneys synthesized both MMP9 and MMP2 enzymes. In vitro, embryonic kidneys also secreted both enzymes when cultured in a medium devoid of hormone, growth factor, and serum for 24 h during which T-shaped branching of the ureter bud appeared. We then evaluated the role of MMP2 and MMP9 in kidney morphogenesis by adding anti-MMP2 or anti-MMP9 IgGs to the culture medium of 11-d kidneys for 24 or 72 h. Although it inhibited activity of the mouse enzyme, anti-MMP2 IgGs had no effect on kidney morphogenesis. In contrast, anti-MMP9 IgGs with enzyme-blocking activity impaired renal morphogenesis, in a concentration-dependent manner, by inhibiting T-shaped branching and further divisions of the ureter bud. This effect was irreversible, still observed after inductive events and reproduced by exogenous tissue inhibitor of metalloproteinase 1 (TIMP1), the natural inhibitor of MMP9. These data provide the first demonstration of MMP9 and MMP2 production in vivo by 11-d embryonic kidneys and further show that MMP9 is required in vitro for branching morphogenesis of the ureter bud.

Receptors for natriuretic peptides in a human cortical collecting duct cell line.

The aim of the present study was to analyze the expression of natriuretic peptide receptors in human collecting duct, by using a newly established SV40 cell line (HCD). ANP and C-type natriuretic peptide (CNP) induced a concentration-dependent increase in cGMP suggesting the presence of type-A (NPR-A) and type-B (NPR-B) receptors, respectively. Threshold concentrations were 1 pM and 1 nM, respectively, and stimulated over basal cGMP ratios were 500 and 160 at 0.1 microM ANP and CNP. The urodilatin concentration-response curve was similar to that of ANP. [125I]-ANP bound specifically to HCD cells in a time-dependent fashion, reaching a plateau-phase between one and two hours at 4 degrees C. Equilibrium saturation binding curves suggested a single group of receptor sites (Kd = 421 +/- 55 pM, Bmax = 49.2 +/- 8.8 fmol/mg protein, Hill coefficient = 1.44 +/- 0.1, N = 6). Binding of [125I]-ANP was not displaced by CNP or by C-ANP (4-23), a specific ligand of clearance receptors (NPR-C), and thus occurred mainly via NPR-A. Neither Northern blot analysis nor RT-PCR could detect NPR-C mRNA, although the latter was clearly identified in control human glomerular visceral epithelial cells. In contrast, PCR products with the expected lengths were obtained for NPR-A and NPR-B. In conclusion, HCD cells express both NPR-A and NPR-B, as demonstrated by mRNA and cGMP production studies, but fail to produce NPR-C. This suggests that the human cortical collecting duct is a target for ANP, CNP and urodilatin.

Hyperosmolality suppresses but TGF beta 1 increases MMP9 in human peritoneal mesothelial cells.

Peritoneal mesothelial cells are directly exposed to hyperosmolar dialysates which may enhance extracellular matrix accumulation and hence compromise ultrafiltration. Because these cells are laid on a type IV collagen containing basement membrane, we examined the pattern of type IV collagenases produced by cultured human mesothelial cells and their regulation by hyperosmolality and TGF beta 1. A cell line (HMrSV5) exhibiting major features of normal peritoneal mesothelial cells was derived from a primary culture retrovirally transduced with SV40 large-T antigen. Zymography and Western blot analysis showed that: (i) human peritoneal mesothelial cells produced and excreted MMP2 and MMP9 and their inhibitors TIMP1 and TIMP2; (ii) hyperosmolality drastically reduced the expression of MMP9 irrespective of the osmolyte used in a time- and concentration-dependent manner; (iii) TGF beta 1 unexpectedly increased MMP9 activity and protein in exponentially growing cells and could restore MMP9 activity suppressed by hyperosmolality in confluent cultures. To exclude a specific effect of SV40 large-T antigen on matrix metalloproteinases production and regulation, these results were confirmed in primary cultures derived from visceral peritoneal samples from different donors. Therefore, the hyperosmolality of dialysates may favor an accumulation of type IV collagen and thickening of peritoneal basement membrane, while TGF beta 1 released during infections may induce the degradation of type IV collagen and its replacement by interstitial collagens.

Gene transfer into the kidney: current status and limitations.

Gene therapy is obviously a controversial issue and a wave of suspicion has dampened the initial enthusiasm raised by this new therapeutic approach. It has now become fashionable to downplay the potential for gene therapy in most fields including kidney-related diseases. In our opinion, this is an unfair and unrealistic view of the future. In fact, gene therapy of well-selected kidney diseases will certainly become feasible, but a large data base on vectors and transfer methods both in the normal kidney and in disease models has first to be collected. Any significant progress in the biology of the vectors, in the cellular interactions of the newly introduced DNA, and in the regulation and persistency of the transgene should be rapidly translated to the kidney in relevant experimental models. Herein, we present the use and current limitations of gene transfer to the kidney and the potential therapeutic perspectives.