Regulation of hyaluronan-stimulated VCAM-1 expression in murine renal tubular epithelial cells. (73/3275)

BACKGROUND: Cytokines stimulate the expression of the adhesion molecule VCAM-1 in renal tubular epithelial cells. We have recently shown that VCAM-1 can also be upregulated by low molecular weight breakdown products of the matrix constituent hyaluronan (HA) (J Immunol 1998; 161: 3431-3437). The mechanisms of VCAM-I expression in response to HA remain to be defined. METHODS: Using a defined mouse cortical tubular (MCT) cell line we investigated the effect of protein kinase C (PKC) and tyrosine kinase (TK) inhibition on the HA-stimulated VCAM-1 expression by cell ELISA and RT PCR or Northern blotting. Furthermore, we examined the effect of PKC and TK inhibition on NF-kappaB. RESULTS: We found that the PKC inhibitor GF109203X (acting on conventional, novel and atypical isoforms) inhibited the HA-stimulated VCAM-1 expression in MCT cells dose-dependently up to 90%, whereas chelerythrine (acting on conventional and novel isoforms) had no effect. Downregulation of PKC with PMA did not prevent the HA-stimulated VCAM-1 expression, suggesting that Ca2+- and diacylglycerol-independent (atypical) isoforms of PKC are involved. The TK inhibitor genistein also inhibited the HA-stimulated VCAM-1 expression at the mRNA and protein level up to 70%. Interestingly, the HA-stimulated nuclear translocation of NF-kappaB could not be prevented with GF109203X and genistein. CONCLUSION: These data demonstrate that the HA-stimulated VCAM-1 expression in MCT cells involves PKC and TK pathways. The absence of an effect of PKC and TK inhibitors on the nuclear translocation of NF-kappaB suggests that additional transcription factors are involved for VCAM-1 expression.  (+info)

Distribution of glycosaminoglycans in rat renal tubular epithelium. (74/3275)

Polyanionic constituents of the glomerular capillary wall have been previously shown to have a primary role in the control of glomerular filtration. In the study presented here, the distribution and biochemical nature of polyanionic constituents in proximal (PT) and distal (DT) tubules have been investigated as possible determinants of tubulointerstitial function. For histochemical localization of sialic acid, paraffin sections were treated with Arachis hypogaea lectin (PNA) before and after neuraminidase treatment. Electron microscopic characterization of glycosaminoglycans (GAG) was performed on thin LR-white sections, using cationic colloidal gold (CCG) as an histochemical probe, and GAG-degrading enzymes. Without neuraminidase, PNA binded to collecting ducts but not to PT or DT. Neuraminidase pretreatment resulted in intense PNA binding to the tubulointerstitial blood vessels but only in mild apical tubular binding, which implies a lack of sialoglycoconjugates in the tubular basolateral membranes. In contrast, all PT and DT showed intense CCG binding to basolateral, but not to apical, membranes. All basement membranes showed CCG labeling, with considerable variations in labeling densities between PT (124 +/- 8.8/micron 2) and DT (52 +/- 1.8/micron 2), as well as between tubules and Bowman's capsule (P < 0.0001). Heparinase III treatment induced an almost complete loss of CCG binding in all basement and basolateral membranes, whereas chondroitinase ABC treatment led to a lesser but significant loss (P < 0.0001). The results indicate that rat tubulointerstitium expresses polyanionic constituents, consisting mainly of heparan and chondroitin sulfate. The role of these anionic sites in tubular function has yet to be clarified.  (+info)

Retrospective evaluation of alpha 2u-globulin accumulation in male rat kidneys following high doses of diisononyl phthalate. (75/3275)

Diisononyl phthalate (DINP), a widely used plasticizer, has been evaluated in two chronic studies in rats and one in mice. In the early 1980s, Exxon found no carcinogenic potential at the estimated maximum tolerated dose (MTD) of 0.6% (307 mg/kg/ day for male rats) administered in the diet of rats for 2 years. A recent study conducted at dietary levels up to 1.2% DINP (733 mg/kg/d for male rats) reported kidney tumors in male rats at the high treatment level, but not in female rats nor mice of either sex. Because these tumors occurred only in male rats, and only at high doses, the male rat-specific alpha 2u-globulin (alpha2UG) mechanism of action was investigated. Technological advances in immunohistochemical staining and computerized image analysis techniques permitted measuring the accumulation of alpha2UG in archived kidneys from the earlier Exxon study. Using archived tissue obtained at the 12-month interim sacrifice, we identified a dose-dependent accumulation of alpha2UG in specific regions of male rat kidneys only. An increase in cell proliferation was confirmed by immunohistochemical detection of proliferating-cell nuclear antigen (PCNA) and was confined to the areas of alpha2UG accumulation. H and E-stained sections revealed tubular epithelial hypertrophy and regeneration, consistent with the immunohistopathology findings. These findings are consistent with the alpha2UG mechanism of tumorigenesis, which is not regarded as relevant for humans. Thus, exposure to DINP produced a dose-dependent alpha2UG accumulation in male rat kidneys, significant at a dietary level of 0.6% and a likely mechanism for the kidney tumors seen only in male rats administered higher dietary levels of DINP.  (+info)

Progressive impairment of kidneys and reproductive organs in mice lacking Rho GDIalpha. (76/3275)

The Rho small G protein family members regulate various actin cytoskeleton-dependent cell functions. The Rho GDI (GDP dissociation inhibitor) family, consisting of Rho GDIalpha, -beta, and -gamma, is a regulator that keeps the Rho family members in the cytosol as the GDP-bound inactive form and translocates the GDP-bound form from the membranes to the cytosol after the GTP-bound form accomplishes their functions. Rho GDIalpha is ubiquitously expressed in mouse tissues and shows GDI activity on all the Rho family members in vitro. We have generated mice lacking Rho GDIalpha by homologous recombination to clarify its in vivo function. Rho GDIalpha -/- mice showed several abnormal phenotypes. Firstly, Rho GDIalpha -/- mice were initially viable but developed massive proteinuria mimicking nephrotic syndrome, leading to death due to renal failure within a year. Histologically, degeneration of tubular epithelial cells and dilatation of distal and collecting tubules were readily detected in the kidneys. Secondly, Rho GDIalpha -/- male mice were infertile and showed impaired spermatogenesis with vacuolar degeneration of seminiferous tubules in their testes. Thirdly, Rho GDIalpha -/- embryos derived from Rho GDIalpha -/- female mice were defective in the postimplantation development. In addition, these morphological and functional abnormalities showed age-dependent progression. These results suggest that the signaling pathways of the Rho family members regulated by Rho GDIalpha play important roles in maintaining the structure and physiological function of at least kidneys and reproductive systems in adult mice.  (+info)

Tubulointerstitial nephritis antigen: an extracellular matrix protein that selectively regulates tubulogenesis vs. glomerulogenesis during mammalian renal development. (77/3275)

Tubulointerstitial nephritis antigen (TIN-ag) is an extracellular matrix protein and is expressed in the renal tubular basement membranes. Its role in metanephric development was investigated. TIN-ag cDNA, isolated from the newborn mouse library, had an ORF of 1,425 nucleotides, a putative signal sequence, and an ATP/GTP-binding site. The translated sequence had approximately 80% identity with rabbit TIN-ag. Among various tissues, TIN-ag mRNA was primarily expressed in the newborn kidney. In the embryonic metanephros, TIN-ag expression was confined to the distal convolution or pole of the S-shaped body, the segment of the nascent nephron that is the progenitor of renal tubules. Treatment with TIN-ag antisense oligodeoxynucleotide induced dysmorphogenesis of the embryonic metanephroi, malformation of the S-shaped body, and a decrease in the tubular population, whereas the glomeruli were unaffected. Treatment also led to a decrease of TIN-Ag mRNA, de novo synthesis of TIN-ag protein, and its antibody reactivity. The mRNA expression of glomerular epithelial protein 1 (a marker for renal podocytes), anti-heparan-sulfate-proteoglycan antibody reactivity, and wheat germ agglutinin lectin staining of the metanephros were unaffected. The anti-TIN-ag antibody treatment also caused deformation of the S-shaped body and a reduction in the tubular population, whereas the glomeruli were unchanged. The data suggest that the TIN-ag, unlike other basement membrane proteins, selectively regulates tubulogenesis, whereas glomerulogenesis is largely unaffected.  (+info)

Glomerular ultrafiltration and apical tubular action of IGF-I, TGF-beta, and HGF in nephrotic syndrome. (78/3275)

In nephrotic glomerulopathies, there is ultrafiltration of high molecular weight forms of insulin-like growth factor-I (IGF-I), hepatocyte growth factor (HGF), and transforming growth factor-beta (TGF-beta), which are bioactive in tubular fluid and act through apical tubular receptors. Experimental evidence indicates that ultrafiltered IGF-I, HGF, and TGF-beta may contribute to increased tubular phosphate and sodium absorption, synthesis of extracellular matrix proteins, and secretion of chemokines such as monocyte chemoattractant protein-1 (MCP-1). Through these mechanisms, glomerular proteinuria may contribute to tubulointerstitial pathobiology in nephrotic syndrome.  (+info)

Molecular mechanisms of renal hypertrophy: role of p27Kip1. (79/3275)

There are two fundamentally different growth responses for cells comprising the nephron: hyperplasia or hypertrophy. Cells that progress through the normal cell cycle double their DNA content and eventually divide during mitosis. Those cells that hypertrophy stop the growth process in the G1-phase of the cell cycle; while they increase in size, protein and RNA content, they cannot duplicate their set of chromosomes because they never pass through the S-phase of the cell cycle. Hypertrophy may be an early compensatory mechanism to initially replace the loss of functioning tissue, however, this maladaptive process eventually fosters progressive loss of renal function. Since progression of the cell through the G1 to S-phases is regulated by cyclins D, E and A, which in turn bind and activate cyclin dependent kinases (CDKs), evidence has been accumulating on a particular CDK-inhibitor protein, p27Kip1, which is speculated to be a key to the complex process of the G1/S cell cycle transition. This article examines the mechanisms of the proliferative growth response following acute tubular necrosis, and compensatory hypertrophy of glomerular and tubule cells, with a particular focus on the protein p27Kip1.  (+info)

Mechanisms of chronic hypoxia-induced renal cell growth. (80/3275)

Chronic local tissue hypoxia appears to play an important role in the initiation and progression of chronic renal disease. We examined the effect of local hypoxia on cultured renal tubular epithelial and mesangial cell proliferation, dedifferentiation, and extracellular matrix synthesis. The underlying signaling mechanisms whereby hypoxia induces renal cell growth were evaluated. The roles of protein kinase C, p38 mitogen-activated protein kinase, TGF-beta1, osteopontin, and nitric oxide were determined.  (+info)