Heterogeneity of apical glycoconjugates in kidney collecting ducts: further studies using simultaneous detection of lectin binding sites and immunocytochemical detection of key transport enzymes

Harvest and primary culture of the murine aldosterone-sensitive distal nephron

The aldosterone-sensitive distal nephron (ASDN) exhibits axial heterogeneity in structure and function from the distal convoluted tubule to the medullary collecting duct. Ion and water transport is primarily divided between the cortex and medulla of the ASDN, respectively. Transcellular transport in this segment is highly regulated in health and disease and is integrated across different cell types. We currently lack an inexpensive, high-yield, and tractable technique to harvest and culture cells for the study of gene expression and physiological properties of mouse cortical ASDN. To address this need, we harvested tubules bound to Dolichos biflorus agglutinin lectin-coated magnetic beads from the kidney cortex and characterized these cell preparations. We determined that these cells are enriched for markers of distal convoluted tubule, connecting tubule, and cortical collecting duct, including principal and intercalated cells. In primary culture, these cells develop polarized monolayers with high resistance (1,000-1,500 Ω * cm(2)) and maintain expression and activity of key channels. These cells demonstrate an amiloride-sensitive short-circuit current that can be enhanced with aldosterone and maintain measurable potassium and anion secretion. Our method can be easily adopted to study the biology of the ASDN and to investigate phenotypic differences between wild-type and transgenic mouse models.

Heterogeneity of the MDCK cell line and its applicability for influenza virus research

Single-cell clones have been established from the MDCK cell line, characterized for their morphology and evaluated for their suitability for influenza virus research. Three discrete cell morphotypes were identified using light microscopy. Besides morphological features, the cell types can be distinguished by the level of expression of surface glycans recognized by peanut agglutinin (PNA). All clones were susceptible to infection by influenza viruses of different subtypes of influenza A virus (H1N1, H1N1pdm09, H3N2, H5N1) and influenza B virus, and all possessed on their surface terminally sialylated glycans with both types of glycosidic linkage (α2-3 and α2-6). The Type-1 cell lines were able to support a multicycle replication of influenza A and B viruses without help of an exogenous trypsin. In contrast, cell lines exhibiting Type-2 morphology were unable to support multicycle replication of influenza A viruses without trypsin supplementation. Western blot analysis of the hemagglutinin of H1N1 strains demonstrated that Type-2 cells were deficient in production of proteolytically activated hemagglutinin (no cleavage between HA1/HA2 was observed). HA1/HA2 cleavage of influenza B viruses in the Type-2 cells was also significantly impaired, but not completely abrogated, producing sufficient amount of activated HA to support efficient virus replication without trypsin. In contrast, all clones of Type-1 cells were able to produce proteolytically activated hemagglutinin of influenza A and B viruses. However, the growth kinetics and plaque size of influenza A viruses varied significantly in different clones. Influenza B virus also showed different plaque size, with the biggest plaque formation in the Type-2 cells, although the growth kinetics and peak infectivity titers were similar in all clones. Taken together, the study demonstrates that the population of original MDCK cells is represented by various types of cells that differ in their capacities to support replication of influenza A and B viruses.

The chick chorioallantoic membrane: a model of molecular, structural, and functional adaptation to transepithelial ion transport and barrier function during embryonic development

The chick chorioallantoic membrane is a very simple extraembryonic membrane which serves multiple functions during embryo development; it is the site of exchange of respiratory gases, calcium transport from the eggshell, acid-base homeostasis in the embryo, and ion and H(2)O reabsorption from the allantoic fluid. All these functions are accomplished by its epithelia, the chorionic and the allantoic epithelium, by differentiation of a wide range of structural and molecular peculiarities which make them highly specialized, ion transporting epithelia. Studying the different aspects of such a developmental strategy emphasizes the functional potential of the epithelium and offers an excellent model system to gain insights into questions partly still unresolved.

The lectin Dolichos biflorus agglutinin is a sensitive indicator of branching morphogenetic activity in the developing mouse metanephric collecting duct system

The urine collecting duct system of the metanephric kidney develops by growth and branching morphogenesis of an unbranched progenitor tubule, the ureteric bud. Bud branching is mainly dichotomous and new branches form from existing branch tips, which are also the main sites of cell proliferation in the system. This behaviour, and the fact that some genes (e.g. Wnt11, Sox9) are expressed only in tips, suggests that tip cells are in a specific state of differentiation. In this report, we show that the lectin Dolichos biflorus agglutinin (DBA), hitherto regarded and used as a general marker of developing renal collecting ducts, binds to most of the duct system but does not bind to the very tips of growing branches. The zone avoided by DBA corresponds to the zone that expresses Wnt11, and the zone that shows enhanced cell proliferation. If branching of the ureteric bud of cultured embryonic kidneys is inhibited in organ culture, by blocking the kidney's endogenous glial cell-derived neurothrophic factor (GDNF)-based branch-promoting signals, the DBA-binding zone extends to the very end of the tip but is lost from there when branching is re-activated. Similarly, if excess GDNF is provided to growing kidneys, the DBA-free zone expands. DBA-staining status therefore appears to be a sensitive indicator of the morphogenetic activity of the collecting duct system.

Regulation of cation transport in the distal nephron by mechanical forces

Thiazide and loop diuretics induce renal K(+) secretion, often leading to renal K(+) wasting and hypokalemia. This phenomenon has been proposed to reflect an increase in delivery to and reabsorption of Na(+) by the distal nephron, with a resultant increase in the driving force for passive K(+) efflux across the apical membrane. Recent studies suggest that cellular mechanisms that lead to enhanced rates of Na(+) reabsorption as well as K(+) secretion in response to increases tubular flow rates are more complex. Increases in tubular flow rates directly enhance the activity of apical membrane Na(+) channels and indirectly activate a class of K(+) channels, referred to as maxi-K, that are functionally inactive under low flow states. This review addresses the role of biomechanical forces, generated by variations in urinary flow rate and tubular fluid volume, in the regulation of transepithelial Na(+) and K(+) transport in the distal nephron. The question of why the distal nephron has evolved to include a component of flow-dependent K(+) secretion is also addressed.

Exploring the role of galectin 3 in kidney function: a genetic approach

Galectin 3 belongs to a family of glycoconjugate-binding proteins that participate in cellular homeostasis by modulating cell growth, adhesion, and signaling. We studied adult galectin 3 null mutant (Gal 3-/-) and wild-type (WT) mice to gain insights into the role of galectin 3 in the kidney. By immunofluorescence, galectin 3 was found in collecting duct (CD) principal and intercalated cells in some regions of the kidney, as well as in the thick ascending limbs at lower levels. Compared to WT mice, Gal 3-/- mice had approximately 11% fewer glomeruli (p < 0.04), associated with kidney hypertrophy (p < 0.006). In clearance experiments, urinary chloride excretion was found to be higher in Gal 3-/- than in WT mice (p < 0.04), but there was no difference in urinary bicarbonate excretion, in glomerular filtration, or urinary flow rates. Under chronic low sodium diet, Gal 3-/- mice had lower extracellular fluid (ECF) volume than WT mice (p < 0.05). Plasma aldosterone concentration was higher in Gal 3-/- than in WT mice (p < 0.04), which probably caused the observed increase in alpha-epithelial sodium channel (alpha-ENaC) protein abundance in the mutant mice (p < 0.001). Chronic high sodium diet resulted paradoxically in lower blood pressure (p < 0.01) in Gal 3-/- than in WT. We conclude that Gal 3-/- mice have mild renal chloride loss, which causes chronic ECF volume contraction and reduced blood pressure levels.

Mechanoregulation of intracellular Ca2+ concentration is attenuated in collecting duct of monocilium-impaired orpk mice

Autosomal recessive polycystic kidney disease (ARPKD) is characterized by the progressive dilatation of collecting ducts, the nephron segments responsible for the final renal regulation of sodium, potassium, acid-base, and water balance. Murine models of ARPKD possess mutations in genes encoding cilia-associated proteins, including Tg737 in orpk mice. New findings implicate defects in structure/function of primary cilia as central to the development of polycystic kidney disease. Our group (Liu W, Xu S, Woda C, Kim P, Weinbaum S, and Satlin LM, Am J Physiol Renal Physiol 285: F998-F1012, 2003) recently reported that increases in luminal flow rate in rabbit collecting ducts increase intracellular Ca(2+) concentration ([Ca(2+)](i)) in cells therein. We thus hypothesized that fluid shear acting on the apical membrane or hydrodynamic bending moments acting on the cilium increase renal epithelial [Ca(2+)](i). To further explore this, we tested whether flow-induced [Ca(2+)](i) transients in collecting ducts from mutant orpk mice, which possess structurally abnormal cilia, differ from those in controls. Isolated segments from 1- and 2-wk-old mice were microperfused in vitro and loaded with fura 2; [Ca(2+)](i) was measured by digital ratio fluorometry before and after the rate of luminal flow was increased. All collecting ducts responded to an increase in flow with an increase in [Ca(2+)](i), a response that appeared to be dependent on luminal Ca(2+) entry. However, the magnitude of the increase in [Ca(2+)](i) in 2- but not 1-wk-old mutant orpk animals was blunted. We speculate that this defect in mechano-induced Ca(2+) signaling in orpk mice leads to aberrant structure and function of the collecting duct in ARPKD.

The metanephros of the quail embryo. Developmental expression of carbonic anhydrase investigated by multiple approaches

The expression of carbonic anhydrase (CA) in the quail metanephros was investigated during embryonic development. The immunohistochemical localisation of the isoenzymes CAII and CAIII was compared with the distribution of enzyme activity visualised by a histochemical cobalt-precipitation procedure. The developmental profile of CA activity was also evaluated by means of a biochemical method. The occurrence of a moderate and diffuse CAII immunostaining from the first developmental appearance of the metanephros anlage testified to an early expression of carbonic anhydrase. This finding is discussed in relation to the involvement of the enzyme in the morphogenetic mechanisms leading to the establishment both of cell polarity and epithelial phenotype. CA expression in the renal sites that are positive in adults proved to be developmentally regulated. In the collecting duct system, enzyme activity could not be identified until the time of hatching. No CA was detected at any stage examined at the sites where, in adults, enzyme occurrence has previously been interpreted as a membrane-associated CA isoform. The differentiating renal tubules displayed no CAIII immunoreactivity. It can be argued that the bulk of the enzyme activity in the embryonic metanephros is due to the cytosolic isoenzyme CAII.

Lectin binding patterns in nonsensory regions of rat cochlea during postnatal development

The distribution of glycoconjugates was examined in the nonsensory regions of the rat cochlea during postnatal development using biotin-conjugated lectins. Temporal bones of rats at postnatal d 1 and at wk 2, 4 and 6 were fixed in 4% paraformaldehyde and 0.1% glutaraldehyde and processed for paraffin wax embedding. The dewaxed sections were incubated with 7 biotinylated lectins, followed by avidin-biotin-peroxidase complex. A different staining pattern was observed in the stria vascularis, spiral ligament and spiral limbus in the age groups examined. The staining intensity varied between lectins and the reaction product exhibited limited disparity. The staining intensity for WGA increased with age in all the 3 nonsensory regions. The staining patterns for the other lectins differed in the various nonsensory regions examined indicating tissue specificity. The limited variations in the lectin binding patterns after 2nd wk of postnatal life also indicate that the changes in the carbohydrate moieties are established during the fetal period of cochlear development and limited changes take place during postnatal maturation of the nonsensory regions.

Immunohistochemical localization of carbonic anhydrase isoenzymes II and III in quail kidney

The immunohistochemical localization of carbonic anhydrase isoenzymes has never been investigated in avian renal tissue previously. Enzyme activity has largely been documented by histochemical and physiological reports. In this investigation, specific antisera were used to study the distribution of the cytosolic carbonic anhydrase II and III isoenzymes in the quail kidney. Comparison between the present findings and the corresponding histochemical patterns, previously obtained in the same species by a cobalt phosphate precipitation method, resulted in the bulk of renal carbonic anhydrase activity being attributed to the carbonic anhydrase II isoenzyme. Conversely, moderate carbonic anhydrase III immunostaining appeared to be confined to the smooth muscle cells of ureteral and arteriolar walls. Indirect evidence of the occurrence, in the quail kidney, of a membrane-associated carbonic anhydrase form, antigenically distinct from the II and III isoforms, was inferred.

Lectin histochemistry of rainbow trout (Oncorhynchus mykiss) gill and skin

In order to characterize the glycoconjugate residues in skin and gills of the adult rainbow trout, the binding pattern of five biotinylated lectins with different carbohydrate specificities was examined. In the skin, mucous cells revealed binding sites for PNA and SBA; filament-containing cells were additionally labelled with Con A. However, the basal cell layer showed no reaction. In the gill, subpopulations of mucous cells reacted with Con A, PNA, SBA and UEA-I. This broader spectrum of glycoconjugates in gill mucous cells compared with the epidermal mucous cells could point to the additional function of gill mucus in ion and osmoregulation. Lectin binding sites were less common in the respiratory epithelial cells of the secondary lamellae than in those of the primary lamellae. Chloride cells revealed mannose, galactose and fucose residues. Immature chloride cells, as indicated by a comparison with Na+/K+ ATPase immunolabelling, reacted with Con A; subpopulations of them reacted with PNA, SBA and UEA-I. The results form the basis for further investigations in which these cell populations can be analysed under different environmental conditions.

Glycoconjugate expression in the chick embryonic chorioallantoic membrane: comparisons of the chorionic ectoderm and allantoic endoderm

BACKGROUND

The chorioallantoic membrane (CAM) of the chick embryo expands during embryogenesis to meet the increased oxygen demands during growth and differentiation. Temporal and spatial glycosylation patterns of CAM ectodermal and endodermal proteins likely contribute to differentiation of the functional attributes of the CAM.

METHODS

Using lectins for light and electron microscopic observations, we studied the patterns of glycoconjugate expression on the ectoderm and endoderm of the chorioallantoic membrane (CAM) of the chick at days 4.5, 5.0, 5.5, 6.0, and 10 of morphogenesis. For light microscopy, samples of unfixed CAM were incubated with the following FITC lectins: Con A, DBA, GSA-I, GSA-II, PNA, SBA, UEA-I, and WGA.

RESULTS

All lectins, except GSA-I and -II, gave positive results. The positive lectins, labeled with HRP, served to ultrastructurally localize PNA, SBA, and WGA, but not DBA binding to the luminal surface of the endoderm. UEA-I and Con A bound similarly except on day 10 when UEA-I no longer bound. On the ectodermal surface, only WGA bound at all times studied. PNA and SBA binding were present from days 5.0 to 6.0 but absent at days 4.5 and 10. DBA binding occurred through day 5.0 but was absent thereafter. UEA-I bound to the ectoderm at days 4.5, 5.0, and 10 but not days 5.5 and 6.0. Con A bound only on days 5.0 and 10.

CONCLUSION

That the ultrastructurally similar ectoderm and endoderm of the CAM display functional differences conforms to the hypothesis that differential expression of glycoconjugate microdomains likely contributes to such functional specialization.

Heterogenous distribution of glycoconjugates in the kidney of dogfish Scyliorhinus caniculus (L.) with reference to changes in the glycosylation pattern during ontogenetic development of the nephron

Eight fluorochrome-coupled lectins with different sugar specificities were applied to cryosections of dogfish kidney. Despite profound differences in renal architecture between elasmobranch fish and other vertebrates, the sequence of nephron segments as revealed by the lectin-binding pattern was rather similar to that of tetrapodes. Wheat germ agglutinin (WGA) bound to cell membranes of epithelial cells of glomeruli, proximal and distal tubules, their basement membranes, the collecting tubule, and epithelial cells. Among other broadly binding lectins were Ricinus communis agglutinin I (RCA-I), soybean agglutinin (SBA), peanut agglutinin (PNA), Lycopersicon esculentum agglutinin (LEA), and Jacalin, all of which marked proximal as well as distal portions of the renal tubule. Dolichos biflorus agglutinin (DBA) did not react with any renal structure. Ulex europaeus agglutinin I (UEA-I), which indicates the presence of alpha-L-fucose, very strongly and specifically marked single epithelial cells of the early distal nephron, all epithelial cells of the late distal tubule, the beginning of the collecting tubule in the mesial tissue zone, and single cells in the end portion of the collecting tubule in the lateral bundles. Binding of UEA-I to receptors of distal nephron cells could be useful for the identification of these cells in functional studies employing teased tubule and/or isolated cell preparations. Binding of UEA-I to dogfish kidney structures resembles staining with UEA-I conjugates of late distal tubules and collecting tubules in the kidneys of frog and other, higher vertebrates. Epithelial cells of early developmental stages showed, very rarely, binding sites for most lectin-fluorochrome conjugates. A large number of lectin binding sites was observed in the extracellular matrix of fibroblast layers surrounding the early anlage and the S-shaped body. Lectin binding sites of the nephron epithelia appeared in a sequential manner in the next stages of development of the nephron. Ontogenetic and phylogenetic aspects of the merging region between nephron proper (late distal tubule) and collecting system (collecting tubule) are discussed.

Sialylated glycoconjugates in chromophobe cell renal carcinoma compared with other renal cell tumors. Indication of its development from the collecting duct epithelium

The present study was designed to shed light on the extraordinary histochemical properties of the chromophobe cell renal carcinoma detected by Hale's colloidal iron reaction. Special emphasis was laid on the lectin histochemical analysis of cytoplasmic glycoconjugates. Binding of peanut agglutinin (PNA) and Erythrina cristagalli agglutinin (ECA) after enzymatic release of sialic acid and direct binding of Dolichos biflorus agglutinin (DBA) correlates well with the expression of binding sites for Sambucus nigra agglutinin (SNA) and Maackia amurensis agglutinin (MAA) revealing abundant sialylated carbohydrate moieties within the cytoplasm. This characteristic binding pattern differs considerably from the faint staining observed in the majority of other renal carcinomas, thus confirming that the chromophobe cell renal carcinoma is a distinct entity. However, the lectin binding pattern of renal oncocytoma obviously resembles that of chromophobe carcinoma indicating a close relationship between these renal tumors. Detailed analysis of adjacent renal parenchyma revealed a lectin binding pattern quite similar to that described in the chromophobe carcinomas exclusively in the intercalated cells lining the collecting duct. This finding suggests that the chromophobe cell renal carcinoma originates from the collecting duct epithelium. The detection of small complexes consisting of altered epithelia which display the morphological characteristics of chromophobe carcinoma and the histochemical properties of intercalated cells probably indicates the emergence of preneoplastic lesions preceding the development of chromophobe carcinoma. Even though further studies are clearly needed to elucidate the physiological role of the cellular glycoconjugates detected, the present results already provide valuable insight into the histogenesis and pathogenesis of the chromophobe cell renal carcinoma.

Renal carbonic anhydrase in the quail Coturnix coturnix japonica: I. Activity and distribution in male and female metanephros

Carbonic anhydrase activity was studied in the quail metanephros by means of histochemical, histophotometrical and biochemical methods. Male and female samples were examined separately in order to show sex-related differences in enzyme activity and localization. The staining patterns revealed differential distribution of reaction product in the different tubular segments. The initial portion of proximal tubules showed positivity on the brush border in female kidneys only. Extra situ investigations provided further evidence of sexual dimorphism resulting in higher values of enzyme activity for female than for male kidneys. In both sexes, marked staining was detected at the distal tubule level where histophotometric analysis confirmed the highest amount of reaction product. Moreover, the intracellular staining distribution at this site proved to be similar to that observed for mammalian proximal convoluted tubules. In the collecting ducts, a mosaic-like pattern was found with respect to both carbonic anhydrase staining and metachromatic properties. The functional significance of the presence of enzyme in the different renal tubules is discussed by comparison with the mammalian kidney. A model is proposed whereby the distal tubules represent the main sites of urinary acidification and bicarbonate reabsorption.