Experimental nephrology最新文献

A key process in overall P(i)-homeostasis is renal proximal tubular reabsorption of inorganic phosphate (P(i)), which involves secondary active sodium/phosphate (Na(+)/P(i)) cotransport reabsorption at the brush border membrane. Among the two different molecularly identified Na(+)/P(i) cotransporters, the type-IIa Na(+)/P(i) cotransporter (NaPi-IIa) accounts for up to 70% of brush border membrane transport. Regulation of renal P(i) reabsorption centers around brush border membrane insertion and retrieval of transporter protein under the influence of hormonal and nonhormonal factors. Immunohistochemical and fluorescence techniques have provided new insights into the tissue distribution and the regulation processes. The intrinsic electrogenicity of NaPi-IIa, has allowed detailed studies of the transport kinetics of NaPi-IIa and, combined with mutagenesis methods, structure-function information at the protein level is emerging.

Tubulo-interstitial inflammation in the kidney is characterized by the presence of activated T cells. Both by the local production of cytokines, as well as by direct cell-cell interactions, these activated T cells might affect the immune and inflammatory response. Recently it has been demonstrated that these kidney-infiltrating T cells express CD40 ligand and that tubular epithelial cells (TECs) express CD40. In the present review we will discuss the potential implications of CD40-CD40L interactions for the activation of TECs and its immunological function.

Background/aim: The localization of inositol trisphosphate (IP(3)) receptor isoforms, types 1-3, in the kidney and their role in the regulation of the intracellular calcium concentration - [Ca(2+)](i) - are discussed.

Methods: Immunohistological studies with isoform-specific antibodies were performed to reveal the localization of IP(3) receptor isoforms. To examine the role of IP(3) receptor type 1 in the glomeruli, the responses of [Ca(2+)](i) to hormonal stimuli were examined in IP(3) receptor type 1 knockout mice.

Results: In the immunohistological study, type 1 receptor was present in arteries, afferent arterioles, and mesangial cells. Double staining with antibodies against aquaporin 2 and IP(3) type 2 receptor revealed that type 2 receptor was localized mainly in the intercalated cells. The type 3 receptor showed characteristic intracellular localization in the collecting duct cells of the cortex to the outer medulla. Immunostaining of type 3 receptor was most intense in the cytoplasm on the basolateral membrane side and was not seen on the apical side. The responses of [Ca(2+)](i) to angiotensin II and endothelin in the glomeruli were markedly attenuated in IP(3) receptor type 1 knockout mice.

Conclusions: The three isoforms of the IP(3) receptor showed distinctive localization in the kidney, and the type 1 receptor plays a major role in the regulation of [Ca(2+)](i) in the glomeruli. The physiological significance of the cell-specific localization, however, remains to be determined.

Sublytic complement injury to glomerular mesangial cells, mediated by the terminal membrane attack complex of complement (C5b-9), is a potential initiating mechanism in IgA nephropathy. Sublytic complement injury has been reported to result in the production of a variety of pro-inflammatory molecules and growth factors, including many regulated by the transcription factor NF-kappa B. To determine the importance of complement injury in the pro-inflammatory signalling which occurs in IgA nephropathy, we investigated NF-kappa B activation following sublytic complement injury to cultured rat glomerular mesangial cells (RMCs). A sublytic dose of rabbit anti-Thy 1.1 (THY) serum and normal human serum was selected based upon flow cytometry, chromium-release assay, and induction of superoxide production. No significant C5b-9-induced NF-kappa B activation was detected by electrophoretic mobility shift assays, luciferase activity of RMCs transfected with a NF-kappa B-driven luciferase reporter construct, nor by Northern blots for the NF-kappa B-responsive mRNA species monocyte chemoattractant protein-1 or I kappa B alpha. Furthermore, measurements of (3)H incorporation following sublytic complement injury showed inhibition of mesangial cell mitogenesis in comparison to the heat-inactivated serum treatment and to THY alone. The results of this study suggest that sublytic complement injury to RMC does not directly activate NF-kappa B nor induce mesangial cell proliferation in mesangial cells. Other mechanisms such as IgA immune complex formation must be required to produce these events in IgA nephropathy.

PKD1, the major gene mutated in autosomal dominant polycystic kidney disease, was identified in 1994, and fully sequenced in 1995. The protein which it encodes, polycystin-1, is the first member of a new family of proteins, whose functions presently remain unclear. This review seeks to highlight the difficulties researchers studying polycystin-1 have faced and to summarize the current areas of consensus and controversy between different groups, particularly with regard to the expression pattern, subcellular location and biochemical characterization of polycystin-1. Where relevant, more recent data regarding polycystin-2, the protein encoded by PKD2, will also be discussed.

Background: The development of acute renal failure (ARF) significantly enhances the mortality of patients with Gram-negative septic shock. The role of specific bacterial virulence factors different from lipopolysaccharides (LPS) in the deterioration of renal function in septic shock remains to be determined.

Methods: An Escherichia coli wild-type strain (536/21 WT, O6:K15:H31) was isolated from a patient suffering from a urinary tract infection. The strain expresses various virulence factors (e.g. hemolysin, fimbriae) genetically encoded by pathogenicity islands. The spontaneous deletion mutant 536/21 Del lacks the expression of these virulence factors. Isolated rat kidneys were perfused with a suspension (5 x 10(4)/ml) of the respective strain or control perfusion medium and the renal functional parameters were analyzed. Intrarenal deposition of E. coli was detected by immunohistology and Gram staining.

Results: The perfusion of the isolated perfused rat kidney with a uropathogenic E. coli wild-type strain (536/21 WT) caused an acute deterioration of renal function which was not observed in kidneys exposed to a deletion mutant of E. coli 536/21 lacking the expression of virulence factors. The glomerular filtration rate and the urine flow rate significantly decreased only in kidneys perfused with the E. coli wild-type strain, while there was no change versus controls in kidneys perfused with the deletion mutant.

Conclusions: Distinctive bacterial virulence factors different from LPS such as hemolysin and the presence of different fimbriae may contribute to the development of ARF in sepsis induced by E. coli. Anti-LPS strategies may not be sufficient to reduce the risk of ARF in Gram-negative septic shock.

Background: There is a genetic predisposition to human systemic lupus erythematosus (SLE). The genes that contribute to susceptibility are, for the most part, unknown. The introduction of new gene mapping techniques has opened the way to explore lupus genetics on a genome-wide basis.

Methods: Microsatellites are simple sequence repeats widely distributed throughout eukaryotic genomes. They exhibit length variation. This polymorphism can be exploited to provide a panoply of genome-wide markers. Thereby, loci linked with lupus have been mapped in lupus-prone mouse strains and in recently published studies in multi-case human families.

Results: More than 20 non-MHC (major histocompatibility complex) loci have now been linked with murine lupus. Nine non-MHC loci have been corroborated in human SLE. Some of the mouse intervals are syntenic with human loci raising the tantalizing possibility of common susceptibility genes. Although we await the results of formal gene identification, functional studies in back-cross and congenic analyses indicate that, in the mouse at least, disease genes act at multiple levels in disease development.

Conclusions: A large number of genes are involved in the pathogenesis of SLE. The data also suggest that even the MHC contribution is multiple. Having mapped disease loci, geneticists now face the task of closing down on the actual aetiological alleles and demonstrating how they might operate. This undertaking will add significantly to our understanding of disease development.

Although it has long been appreciated that retinoids play an essential role in kidney organogenesis, it has only recently been recognized that even mild fetal vitamin A deficiency syndromes can result in a reduction in nephron number. Recent studies have also begun to define the cellular and molecular events associated with retinoid actions in the fetal kidney and have demonstrated the essential function of retinoids in branching growth of the ureteric bud. Importantly, characterization of the renal developmental effects of RAR alpha/beta 2 double homozygous mice combined with metanephric organ culture studies have together shown that one essential function of retinoid action in the developing kidney is the maintenance of c-ret expression in the tips of the ureteric bud. However, many other potential retinoid target genes including midkine, sonic hedgehog, Hox d-11, matrix metalloproteinases, and tissue inhibitors of metalloproteinases appear to play important roles in renal development and might be important downstream mediators of retinoid effects in the developing kidney. It can, therefore, be anticipated that important new insights into fetal kidney development will be forthcoming in the near future, as the essential target genes affected by retinoid signal transduction are progressively elucidated.

Numerous renal abnormalities accompany thyroid disease, most of which have been ascribed to the effects of thyroid hormone on renal metabolism. In the present report, we investigate the renal expression of the nominally thyroid-specific proteins, thyroid-stimulating hormone (TSH) receptor (TSHR) and thyroglobulin (Tg), as potential links between renal and thyroid function. The expression of TSHR has been identified in several extrathyroidal tissues, but its presence in the kidney remains controversial. We have used reverse-transcriptase polymerase chain reaction and DNA sequencing to demonstrate the presence of TSHR transcript in human and mouse kidney, in a primary culture of human kidney, and in a green monkey kidney epithelioid cell line. Furthermore, human kidney cells responded to TSH with a 2.5- fold increase in intracellular cyclic adenosine monophosphate, suggesting the presence of functional TSHR protein. Comparison of renal expression of TSHR in a bovine growth hormone transgenic mouse model of progressive glomerulosclerosis with control mice suggested increased TSHR transcript in the renal cortex of transgenic animals. TSHR transcript was also detected in mouse mesangial cells in vitro which responded to TSH with significant increases in the formation of three-dimensional hillhocks. Polymerase chain reaction also confirmed the presence of Tg transcript in human and mouse kidneys and in mouse mesangial cells, but no effect of either TSH or cyclic adenosine monophosphate on Tg transcript levels could be discerned. Immunofluorescent staining with a monoclonal anti-Tg antibody identified positive staining in the cytoplasm of mesangial cells. These data suggest that the kidney is capable of expressing the thyroid-specific genes, TSHR and Tg, which could conceivably mediate effects of thyroid disease in the kidney.

Autoimmunity is thought to cause most varieties of glomerulonephritis including membranous nephropathy, minimal-change nephropathy, Goodpasture's disease and possibly IgA nephropathy. Much effort has been and is directed at understanding the mechanisms of immune system driven inflammation and of the consequent renal injury and repair or scarring. The purpose of this article is to focus attention on the way the immune system recognizes kidney autoantigens, a process that must be a pivotal in the initiation of autoimmune kidney disease.