Although experimental crescentic glomerulonephritis starts with an endocapillary inflammation, the crescents themselves seem to originate from the proliferation of parietal epithelial cells (PEC). In ...this study, an attempt was made to disclose a link between the two processes by a morphologic analysis of early stages of the disease. Mice were immunized with rabbit IgG in complete Freund's adjuvant on day -6. At day 0, they received an intravenous injection of a rabbit antiglomerular basement membrane serum. On days 3, 6, and 10, the kidneys were fixed by vascular perfusion for examination by light and electron microscopy. On day 3, morphologic alterations affected mainly the endocapillary compartment; most podocytes appeared to be intact. On day 6, alterations of podocytes were widespread, including foot process effacement and prominent microvillous transformation, and some crescents were found. On day 10, crescents were found in 40% of glomeruli. The most surprising finding was podocytes that adhered to both the glomerular basement membrane and the parietal basement membrane, thus forming bridges between the tuft and Bowman's capsule. Those podocyte bridges were sparse on day 3 but were regularly encountered on days 6 and 10 in glomeruli without crescents and also as a component of crescents. They were interposed between PEC and later between the cells of a crescent without formation of junctional connection with these cells. It is proposed that the spreading of podocytes on the parietal basement membrane represents a lesion of the parietal epithelium and that this process initiates the proliferation of PEC to form a crescent.
Ecological shifts from diatoms to other phytoplankton species have been related to decreasing Si:N and Si:P nutrient ratios. The Bay of Brest is such a perturbated ecosystem where Si has become ...limiting but where diatoms continue to dominate the phytoplankton throughout the productive period. Several hypothesis have been invoked to account for this dilemma. The most recent combines suspension feeder activity and Si recycling. Suspension feeder activity, stimulated by the proliferation of the invasive species Crepidula fornicata, would be the driving force of a biologically active silicate pump which would (1) retain Si within the Bay during spring and (2) provide the Si necessary for diatoms during summer. During the year 2000, this hypothesis was successfully tested. Direct evidence of silicic acid limitation has been provided, and during summer, benthic fluxes measured at a site with a high density of C. fornicata are one order of magnitude higher than those measured at the site with no C. fornicata. Seasonal budgets of Si inputs and diatom demand demonstrated that diatom production during summer depends strongly on Si recycling at the sediment-water interface. Thus, if C. fornicata decreases benthic biodiversity and perturbates the development of the native Great Scallop (Pecten maximus), it also helps the Bay cope with elevated N inputs. The proposed removal of C. fornicata might be economically desirable from a fisheries economic viewpoint, but it clearly would be associated, in the present context of excessive N inputs, to a potential risk of harmful algal blooms during summer.
Background. From a diagnostic point of view it would be important to learn more about the relationship between the immune responses underlying glomerulonephritis and the patterns of glomerular ...lesions. A murine model of anti-GBM glomerulonephritis in which inflammation is driven by delayed-type hypersensitivity (DTH) has been studied extensively. The aim of this study was to uncover histological features that might be specific for anti-GBM glomerulonephritis driven by a humoral immune response. Methods. BALB/c mice were immunized with rabbit IgG in incomplete Freund's adjuvant. Six days later, on day 0, they received rabbit anti-GBM serum intravenously. Proteinuria was assessed with dipsticks. Mice were killed on days 4, 8 or 14. Kidneys from days 4 and 8 were processed for immunofluorescence and histology. On day 14 mice were perfusion-fixed for electron microscopy. Results. Proteinuria started on day 3. Autologous IgG and of C3 were found along the GBM. There was only slight infiltration with macrophages and no measurable infiltration by CD4 T cells, indicating the virtual absence of DTH. Besides infiltration with neutrophils there were little histological alterations on day 4. On day 8 many loops were hyalinized. On day 14, cellular crescents were found in 23% of glomeruli. Subendothelial spaces contained hyaline material, cells and fibrin. Podocytes displayed effacement of foot processes and apical microprotrusions. Podocyte bridges were common. These alterations were identical to those reported in the standard model that produces a DTH-like inflammation. Conclusion. The qualitative pattern of histological damage in a murine model of anti-GBM glomerulonephritis does not depend on the underlying immunological process.
Background. Autosomal dominant polycystic kidney disease (ADPKD) is characterized by dysregulated tubular epithelial cell growth, resulting in the formation of multiple renal cysts and progressive ...renal failure. To date, there is no effective treatment for ADPKD. The mammalian target of rapamycin (mTOR) is an atypical protein kinase and a central controller of cell growth and proliferation. We examined the effect of the mTOR inhibitor sirolimus (rapamycin) on renal functional loss and cyst progression in the Han:SPRD rat model of ADPKD. Methods. Five-week-old male heterozygous cystic (Cy/+) and wild-type normal (+/+) rats were administered sirolimus (2 mg/kg/day) orally through the drinking water for 3 months. The renal function was monitored throughout the treatment phase, and rats were sacrificed thereafter. Kidneys were analysed histomorphometrically, and for the expression and phosphorylation of S6K, a well-characterized target of mTOR in the regulation of cell growth. Results. The steady increase in BUN and creatinine in Cy/+ rats was reduced by 39 and 34%, respectively with sirolimus after 3 months treatment. Kidney weight and 2-kidney/total body weight (2K/TBW) ratios were reduced by 34 and 26% in sirolimus-treated Cy/+ rats. Cyst volume density was also reduced by 18%. Of importance, Cy/+ rats displayed enhanced levels of total and phosphorylated S6K. Sirolimus effectively reduced total and phosphorylated levels of S6K. Conclusion. We conclude that oral sirolimus markedly delays the loss of renal function and retards cyst development in Han:SPRD rats with ADPKD. Our data also suggest that activation of the S6K signalling pathway plays an important role in the pathogenesis of PKD. Sirolimus could be a useful drug to retard progressive renal failure in patients with ADPKD.
The original asphalt binder Superpave specification criteria for fatigue, G super(*)sin delta , has received considerable criticism as a specification requirement. A time sweep using the dynamic ...shear rheometer (DSR) has been proposed as an alternative test method for the Superpave specification. The "modulus versus number of cycles" relationships generated in the time sweep test have the appearance of typical fatigue curves. In this paper, the data was examined with respect to its validity as measure of fatigue. Special attention was given to parameters that affect or could be confounded with "true" fatigue response: apparent fatigue can generate phenomena susceptible to interfere with the fatigue behavior:- Initial value of the complex modulus of the material. Behaviour in repeated shear depends markedly on the initial stiffness of the binder. If the initial stiffness is low, damage can occur as a result of plastic flow at the outer edge of the asphalt binder.- The influence of the rest periods at different time of the test.- The drop of the modulus at the beginning of the curves.- Steric hardening occurring with time, apparently even during loading, may have some effect on fatigue like when the time sweep is applied over an extended period of time. Binder type: this procedure showed significant differences in the behavior of various modified binders.Original Abstract: Le critere original G super(*)sin delta , sur la fatigue des liants dans les specifications Superpave est aujourd'hui tres fortement remis en question. Un essai rheologique de balayage dans le temps employant le rheometre a cisaillement dynamique (DSR) a ete propose comme methode d'essai alternative. L'evolution du module de rigidite ainsi obtenue en fonction du nombre de cycles a l'apparence d'une courbe de fatigue classique. Dans cet article, les donnees ont ete etudiees au regard de leur validite pour mesurer la fatigue. Une attention particuliere a ete donnee aux parametres qui affectent ou pourraient etre confondus avec une reponse en fatigue vraie. Une fatigue apparente peut en effet generer des phenomenes susceptibles d'interferer avec le comportement en fatigue:- La valuer initiale du module complexe du materiau. Le comportement sous cisaillement repete en depend beaucoup. Si cette rigidite est trop faible, un endommagement peut se produire par suite d'un ecoulement plastique du liant a la circonference de l'echantillon.- L'influence de periodes de repos a differents moments de l'essai.- La chute du module au debut des courbes.- Le durcissement sterique qui se produit en fonction du temps, meme sous chargement, peut avoir des effets sur la fatigue lorsque le balayage est applique pendant des temps extremement longs.- La nature du liant: cette procedure a montre des comportements significativement differents pour des bitumes modifies varies.
In adults, the kidneys are the major site of production of the glycoprotein hormone erythropoietin (EPO), but the type of renal cell producing EPO has not yet been identified. In the present study we ...used non-radioactive in situ hybridization with a digoxigenin-labeled cRNA probe to localize cells that produce erythropoietin (EPO) in kidneys of anemic rats. Cryostat sections from both native and perfusion-fixed tissue were used. Cells containing EPO mRNA were found exclusively in the peritubular space of the renal cortex. Using high-resolution interference contrast optics, we found that cells expressing EPO mRNA were not associated with the lumina of peritubular capillaries but rather were located in the angles between adjacent tubules or between tubules and vessels. These spaces are predominantly occupied by resident interstitial fibroblasts and by their cytoplasmic processes. To further identify the type of cell containing EPO mRNA, a double-labeling protocol was established that permitted on the same tissue section both in situ hybridization for EPO mRNA and parallel immunolabeling of ecto-5'-nucleotidase (5'-Nu), a surface marker of peritubular interstitial fibroblasts. The combined labeling technique revealed that a clear majority of cells expressing EPO mRNA also displayed staining for anti-5'-Nu. Staining for EPO mRNA was localized in central perinuclear parts of the interstitial cells, whereas 5'-Nu label was present on the cell surface, including the cytoplasmic processes. These data indicate that peritubular fibroblasts are cellular sites for production of erythropoietin.
Using mice double deficient for tumor necrosis factor (TNF) and lymphotoxin alpha (LT alpha), we demonstrated that TNF and/or LT alpha are necessary for development of a normal splenic ...microarchitecture and for isotype switch after immunization with sheep red blood cells (SRBC). In the present study, we extended these observations by determining which TNF receptor (TNFR) is involved in morphological and functional differentiation of the spleen. Spleen morphology and antibody response were investigated in wild-type, TNFR1-/-, TNFR2-/- and TNF/LT alpha-/- mice immunized with SRBC. TNF/LT alpha-/- mice, which have a complete disruption of the TNF/LT alpha signaling system including the LT beta-receptor pathway, displayed an abnormal microarchitecture, and isotype switch did not take place. TNFR1-/- and TNFR2-/- mice displayed a normal spleen microarchitecture and mounted an IgM and IgG antibody response to SRBC. However, the IgG production in TNFR1-/- mice was minimal, with citers leveling off 6 d after immunization. In this strain, immunofluorescence revealed a lack of follicular dendritic cells (FDC) network, detected with FDC-M1 as well as anti-CR1, and a lack of germinal centers, detected with peanut agglutinin. In conclusion, whereas normal splenic microarchitecture and isotype switch might require the LT beta receptor, differentiation of FDC network, development of germinal centers, and full IgG response depend on signaling via TNFR1.
Adenosine exerts various effects via membrane receptors in the kidney. It reduces the glomerular filtration rate by altering the resistance of the glomerular arterioles, and it inhibits the release ...of renin as well as neurotransmission. Adenosine receptors have been further found at different levels of the nephron as well as in glomerular cells. Little is known concerning the mechanisms that regulate the extracellular concentration of adenosine, namely, its production, transport, and catabolism. In the present review we first summarize the pathways of adenosine formation. Then we focus on the ecto-5'-nucleotidase, which seems to represent the major source of extracellular adenosine in the kidney; that enzyme is present in tubular luminal membranes, in fibroblasts, and in mesangial cells. In tubules the enzyme probably plays a role in the salvage of nucleotides present in the primary urine. The activity in fibroblasts is strategically located to convert any AMP released by tubules into adenosine in the close vicinity of glomerular arterioles, and it probably plays a predominant role in most of the regulatory mechanisms involving adenosine. Ecto-5'-nucleotidase activity in fibroblasts increases in anemia, maybe as a response to local hypoxia.
We searched for morphological evidence to support the hypothesis that stem cells are responsible for renal tubular cell proliferation. The rationale of the study was that if proliferation relies on ...progenitors, mitotically active cells should be less differentiated than their neighbors. As the retention of the thymidine analog BrdU has been the only approach employed to identify stem cells in the kidney up to now we additionally characterized BrdU-retaining cells. Rat kidneys were fixed by perfusion. Cycling cells identified by mitotic figures or the expression of the proliferating cell nuclear antigen (PCNA) were examined by light microscopy and electron microscopy as well as immunofluorescence for four differentiation markers. Newborn rats were injected with BrdU in order to detect label-retaining cells. After a period of 8, 14 and 35 weeks the kidneys were examined for BrdU by immunofluorescence and the four differentiation markers mentioned above. All cycling cells showed the same degree of differentiation compared to non-cycling cells. Most of the detected label-retaining cells were differentiated. We conclude that cycling cells in tubules of the healthy kidney are differentiated and that the retention of label is not a criterion to identify stem cells in renal tubules.
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