Protein metabolism during nutrient deprivation and refeeding of neonatal heart cells

Immunohistochemical Distribution of Basement Membrane Type IV Collagen and Laminin in Synovial Sarcoma

Aims

To investigate the distribution of basement membrane components type IV collagen and laminin in synovial sarcomas.

Methods

Paraffin sections from four synovial sarcomas were studied by the peroxidase-antiperoxldase procedure using specific antibodies to type IV collagen and laminin.

Results

Type IV collagen and laminin immunoreactivity was confined around epithelial areas in biphasic tumors. Several interruptions and discontinuities of the linear basement membrane profile were seen in sites of transition between mesenchymal and epithelial tissue. Moreover, a spot-like immunoreactivity was often observed in the spindle cell component of biphasic tumors. Monophasic tumors were either negative or showed a pericellular staining for both type IV collagen and laminin.

Conclusions

The distribution of basement membrane components is clearly related to the formation of epithelial elements in biphasic synovial sarcoma. The spot-like immunoreactivity of the spindle cell component, and the basement membrane interruptions at the boundary between mesenchymal and epithelial tissue, are both consistent with early basement membrane formation by developing epithelium. These findings support the concept that synovial sarcomas are basically soft tissue carcinosarcomas and that the epithelial component of the tumors develops by conversion of mesenchyme to epithelium.

Epithelial cells in culture: injured or differentiated cells?

Isolation of epithelial cells for cell culture is based on destruction of epithelial integrity. The consequences are manifold: cell polarity and specific cell functions are lost; cells acquire non-epithelial characteristics and start to proliferate. This situation may also occur in situ when parts of the epithelium are lost, either by apoptosis or necrosis by organ or tissue injury. During recovery from this injury, surviving epithelial cells proliferate and may restore epithelial integrity and finally re-differentiate into functional epithelial cells. In vitro, this re-differentiation is mostly not complete due to sub-optimal culture conditions. Therefore cultured epithelial cells resemble wounded or injured epithelia rather than healthy and well differentiated epithelia. The value of an in vitro cell model is the extent to which it helps to understand the function of the cells in situ. A variety of parameters influence the state of differentiation of cultured cells in vitro. Although each of these parameters had been studied, the picture how they co-ordinately influence the state of differentiation of epithelial cells in vitro is incomplete. Therefore we discuss the influence of the isolation method and cell culture on epithelial cells, and outline strategies to achieve highly differentiated epithelial cells for the use as an in vitro model.

A novel model of surgical injury in adult rat kidney: a "pouch model"

Regenerative mechanisms after surgical injury have been studied in many organs but not in the kidney. Studying surgical injury may provide new insights into mechanisms of kidney regeneration. In rodent models, extrarenal tissues adhere to surgical kidney wound and interfere with healing. We hypothesized that this can be prevented by wrapping injured kidney in a plastic pouch. Adult rats tolerated 5/6 nephrectomy with pouch application well. Histological analysis demonstrates that application of the pouch effectively prevented formation of adhesions and induced characteristic wound healing manifested by formation of granulation tissue. Additionally, selected tubules of the wounded kidney extended into the granulation tissue forming branching tubular epithelial outgrowths (TEOs) without terminal differentiation. Tubular regeneration outside of renal parenchyma was not previously observed, and suggests previously unrecognized capacity for regeneration. Our model provides a novel approach to study kidney wound healing.

Application of regenerative medicine for kidney diseases

Following recent advancements of stem cell research, the potential for organ regeneration using somatic stem cells as an ultimate therapy for organ failure has increased. However, anatomically complicated organs such as the kidney and liver have proven more refractory to stem cell-based regenerative techniques. At present, kidney regeneration is considered to require one of two approaches depending on the type of renal failure, namely acute renal failure (ARF) and chronic renal failure (CRF).The kidney has the potential to regenerate itself provided that the damage is not too severe and the kidney's structure remains intact. Regenerative medicine for ARF should therefore aim to activate or support this potent. In cases of the irreversible damage to the kidney, which is most likely in patients with CRF undergoing long-term dialysis, self-renewal is totally lost. Thus, regenerative medicine for CRF will likely involve the establishment of a functional whole kidney de novo. This article reviews the challenges and recent advances in both approaches and discusses the potential approach of these novel strategies for clinical application.

Three-dimensional culture alters primary cardiac cell phenotype

The directed formation of complex three-dimensional (3D) tissue architecture is a fundamental goal in tissue engineering and regenerative medicine. The growth of cells in 3D structures is expected to influence cellular phenotype and function, especially relative cell distribution, expression profiles, and responsiveness to exogenous signals; however, relatively few studies have been carried out to examine the effects of 3D reaggregation on cells from critical target organs, like the heart. Accordingly, we cultured primary cardiac ventricular cells in a 3D model system using a serum-free medium to test the hypothesis that expression profiles, multicellular organizational pathways, tissue maturation markers, and responsiveness to hormone stimulation were significantly altered in stable cell populations grown in 3D versus 2D culture. We found that distinct multi-cellular structures formed in 3D in conjunction with changes in mRNA expression profile, up-regulation of endothelial cell migratory pathways, decreases in the expression of fetal genes (Nppa and Ankrd1), and increased sensitivity to tri-iodothyronine stimulation when compared to parallel 2D cultures comprising the same cell populations. These results indicate that the culture of primary cardiac cells in 3D aggregates leads to physiologically relevant alterations in component cell phenotype consistent with cardiac ventricular tissue formation and maturation.

Do stem cells exist in the adult kidney?

Adult stem cells exist in many organs and play a critical role in normal cell turnover and the response to injury. The existence of adult stem cells in the mammalian kidney remains controversial. Kidney stem cells have been isolated and characterized by many groups, often with discrepant results. This article will review the current state of knowledge regarding adult kidney stem cells and discuss future directions for kidney stem cell research.

Isolation and characterization of kidney-derived stem cells

Acute kidney injury is followed by regeneration of damaged renal tubular epithelial cells. The purpose of this study was to test the hypothesis that renal stem cells exist in the adult kidney and participate in the repair process. A unique population of cells that behave in a manner that is consistent with a renal stem cell were isolated from rat kidneys and were termed multipotent renal progenitor cells (MRPC). Features of these cells include spindle-shaped morphology; self-renewal for >200 population doublings without evidence for senescence; normal karyotype and DNA analysis; and expression of vimentin, CD90 (thy1.1), Pax-2, and Oct4 but not cytokeratin, MHC class I or II, or other markers of more differentiated cells. MRPC exhibit plasticity that is demonstrated by the ability of the cells to be induced to express endothelial, hepatocyte, and neural markers by reverse transcriptase-PCR and immunohistochemistry. The cells can differentiate into renal tubules when injected under the capsule of an uninjured kidney or intra-arterially after renal ischemia-reperfusion injury. Oct4 expression was seen in some tubular cells in the adult kidney, suggesting these cells may be candidate renal stem cells. It is proposed that MRPC participate in the regenerative response of the kidney to acute injury.

Prednisolone suppresses cyclosporin A-induced apoptosis but not cell cycle arrest in MDCK cells

Cyclosporin A (CsA) is a potent immunosuppressive agent, and can cause severe adverse effects including nephrotoxicity partly due to generation of reactive oxygen species (ROS). Glucocorticoids, which are widely used in combination with CsA, have been shown to reduce oxidative injuries in various cells, but its mechanism is not understood well. To investigate the effects of prednisolone (Pd) on CsA-induced cellular damage and ROS generation in Madin-Darby canine kidney (MDCK) tubular epithelial cells, cells were treated with CsA, CsA plus Pd, or CsA plus vitamin E. Pretreatment with Pd protected cells from CsA-induced apoptosis but not from G(0)/G(1) cell cycle arrest even at its maximal protective concentration (30 microM), whereas vitamin E almost completely inhibited both CsA-induced apoptosis and cell cycle arrest at 1 microM concentration. In addition, Pd reduced the amount of CsA-induced ROS and showed partly restored catalase which was down-regulated by 10 microM CsA at both the mRNA and protein levels. Vitamin E completely abolished CsA-induced ROS generation and catalase attenuation at 10 microM concentration. Finally, the effects of 1 microM vitamin E on CsA-induced ROS and apoptosis as well as cell cycle arrest were similar to those of 30 microM Pd. We conclude that, in MDCK cells, Pd protects against CsA-induced cytotoxicity by suppressing ROS generation, although its protective effect is weaker than that of vitamin E.

Leukemia inhibitory factor is involved in tubular regeneration after experimental acute renal failure

Leukemia inhibitory factor (LIF) is known to play a crucial role in the conversion of mesenchyme into epithelium during nephrogenesis. This study was carried out to test the hypothesis that LIF and LIF receptor (LIFR) are involved in the renal epithelial regeneration after acute renal failure. First, the authors investigated the spatiotemporal expression of LIF and LIFR in fetal and adult rat kidney. In developing kidney, LIF was expressed in the ureteric buds and LIFR was located in nephrogenic mesenchyme and the ureteric buds; in adult kidney, LIF and LIFR expression was confined to the collecting ducts. Next, the authors examined the expression of LIF and LIFR during the recovery phase after ischemia-reperfusion injury. Real-time PCR analysis revealed that LIF mRNA expression was significantly increased from day 1 to day 7 after reperfusion and that LIFR mRNA was upregulated from day 4 to day 14. Histologic analysis demonstrated that the increased expression of LIF mRNA and protein was most marked in the outer medulla, especially in the S3 segment of the proximal tubules. To elucidate the mitogenic role of LIF in the regeneration process, cultured rat renal epithelial (NRK 52E) cells were subjected to ATP depletion (an in vitro model of acute renal failure), and LIF expression was found to be enhanced during recovery after ATP depletion. Blockade of endogenous LIF with a neutralizing antibody significantly reduced the cell number and DNA synthesis during the recovery period. These results suggest that LIF participates in the regeneration process after tubular injury.

Expression and function of the developmental gene Wnt-4 during experimental acute renal failure in rats

The Wnt-beta-catenin pathway plays key roles in embryogenesis. Wnt-4 is known to be expressed in the mesonephric duct in embryonic development. It is tempting to speculate that the Wnt-4-beta-catenin pathway contributes to the recovery from acute renal failure (ARF). This study used an in vivo model of ARF rats to clarify the significance of the Wnt-4-beta-catenin pathway in ARF. ARF was induced by clamping the rat left renal artery for 1 h. At 3, 6, 12, 24, 48, and 72 h after reperfusion, whole kidney homogenate and total RNA were extracted for examination by Western blot analysis and real-time RT-PCR. Wnt-4 mRNA and protein expression were strongly increased at 3 to 12 h and 6 to 24 h after ischemia, respectively. In immunohistologic examination, Wnt-4 was expressed in the proximal tubules and co-expressed with aquaporin-1, GM130, and PCNA. Cyclin D1 and cyclin A were expressed at 24 to 48 h after reperfusion. In addition, the overexpression of Wnt-4 and beta-catenin promoted the cell cycle and increased the promoter activity and protein expression of cyclin D1 in LLC-PK1 cells. Taken together, these data suggest that the Wnt-4-beta-catenin pathway plays a key role in the cell cycle progression of renal tubules in ARF. The Wnt-4-beta-catenin pathway may regulate the transcription of cyclin D1 and control the regeneration of renal tubules in ARF.

Upregulation of ciliary neurotrophic factor (CNTF) and CNTF receptor alpha in rat kidney with ischemia-reperfusion injury

Ciliary neurotrophic factor (CNTF) is presumed to play a role as a survival factor in neuronal cells, but little is known about its role in the kidney. To investigate this, the expression of CNTF and CNTF receptor alpha (CNTFR alpha) was analyzed in the ischemic rat kidney. An ischemia/reperfusion (I/R) injury was induced by clamping both renal arteries for 45 min. Animals were killed at 1, 2, 3, 5, 7, 14, and 28 d after ischemia. The expression of CNTF and CNTFR alpha was monitored by reverse transcription-PCR, in situ hybridization, immunoblotting, immunohistochemistry, and electron microscopy. In sham-operated rat kidneys, CNTF expression was weak and limited to the descending thin limb of the loop of Henle. With I/R injury, CNTF mRNA and protein expressions were strikingly increased as compared with the sham-operated rat kidney, and the immunoreactivity of CNTF was mainly observed in the regenerating proximal tubules. The expression of CNTFR alpha mRNA was also increased after I/R injury, and its location and expression patterns were similar to the expression of CNTF. These findings suggest a possible role of CNTF as a growth factor during renal tubular repair processes after I/R injury and an autocrine or paracrine function of CNTF acting against CNTFR alpha.

HCaRG, a novel calcium-regulated gene coding for a nuclear protein, is potentially involved in the regulation of cell proliferation

Since a negative calcium balance is present in spontaneously hypertensive rats, we searched for the gene(s) involved in this dysregulation. A cDNA library was constructed from the spontaneously hypertensive rat parathyroid gland, which is a key regulator of serum-ionized calcium. From seven overlapping DNA fragments, a 1100-base pair novel cDNA containing an open reading frame of 224 codons was reconstituted. This novel gene, named HCaRG (hypertension-related, calcium-regulated gene), was negatively regulated by extracellular calcium concentration, and its basal mRNA levels were higher in hypertensive animals. The deduced protein showed no transmembrane domain, 67% alpha-helix content, a mutated calcium-binding site (EF-hand motif), four putative "leucine zipper" motifs, and a nuclear receptor-binding domain. At the subcellular level, HCaRG had a nuclear localization. We cloned the human homolog of this gene. Sequence comparison revealed 80% homology between rats and humans at the nucleotide and amino acid sequences. Tissue distribution showed a preponderance in the heart, stomach, jejunum, kidney (tubular fraction), liver, and adrenal gland (mainly in the medulla). HCaRG mRNA was significantly more expressed in adult than in fetal organs, and its levels were decreased in tumors and cancerous cell lines. We observed that after 60-min ischemia followed by reperfusion, HCaRG mRNA declined rapidly in contrast with an increase in c-myc mRNA. Its levels then rose steadily to exceed base line at 48 h of reperfusion. HEK293 cells stably transfected with HCaRG exhibited much lower proliferation, as shown by cell count and [(3)H]thymidine incorporation. Taken together, our results suggest that HCaRG is a nuclear protein potentially involved in the control of cell proliferation.

Cell biology and molecular mechanisms of injury in ischemic acute renal failure

The pathogenesis of acute renal failure has been attributed to persistent vasoconstriction and leukocyte-endothelial interactions, resulting in inflammation and compromise of local blood flow to the outer medulla, the loss of tubular epithelial cell polarity with multiple functional sequelae, necrosis or apoptosis of epithelial cells, and the de-differentiation, migration and proliferation of surviving cells. In this paper, the authors present their views of pathophysiology of ischemic acute renal failure.

Cardiac organogenesis in vitro: reestablishment of three-dimensional tissue architecture by dissociated neonatal rat ventricular cells

The mammalian heart does not regenerate in vivo. The heart is, therefore, an excellent candidate for tissue engineering approaches and for the use of biosynthetic devices in the replacement or augmentation of defective tissue. Unfortunately, little is known about the capacity of isolated heart cells to re-establish tissue architectures in vitro. In this study, we examined the possibility that cardiac cells possess a latent organizational potential that is unrealized within the mechanically active tissue but that can be accessed in quiescent environments in culture. In the series of experiments presented here, total cell populations were isolated from neonatal rat ventricles and recombined in rotating bioreactors containing a serum-free medium and surfaces for cell attachment. The extent to which tissue-like structure and contractile function were established was assessed using a combination of morphological, physiological, and biochemical techniques. We found that mixed populations of ventricular cells formed extensive three-dimensional aggregates that were spontaneously and rhythmically contractile and that large aggregates of structurally-organized cells contracted in unison. The cells were differentially distributed in these aggregates and formed architectures that were indistinguishable from those of intact tissue. These architectures arose in the absence of three-dimensional cues from the matrix, and the formation of organotypic structures was apparently driven by the cells themselves. Our observations suggest that cardiac cells possess an innate capacity to re-establish complex, three-dimensional, cardiac organization in vitro. Understanding the basis of this capacity, and harnessing the organizational potential of heart cells, will be critical in the development of tissue homologues for use in basic research and in the engineering of biosynthetic implants for the treatment of cardiac disease.

The repetitive activation of extracellular signal-regulated kinase is required for renal regeneration in rat

In this study, we investigated the activation of p42 extracellular signal-regulated kinase (ERK2) during renal regeneration after HgCl2-induced acute renal failure (ARF) in rat. ERK2 activation was observed at 5 and 29 hr after HgCl2 injection, respectively. The tyrosine phosphorylation of hepatocyte growth factor receptor (c-MET) occurred between 2.5 and 5 hr after the treatment. On the other hand, the phosphorylation of epidermal growth factor receptor (EGFR) was transiently observed at 29 hr after the injection. The peak of ornithine decarboxylase activity as a marker of G1 phase was at 10 hr, and subsequently the labeling index of proliferating cell nuclear antigen as a marker of S phase increased at 53 hr. These results indicate that the repetitive activation of ERK2 related to the phosphorylation of c-MET and EGFR is required for the renal regeneration in HgCl2-induced ARF of rat.

Properties of a polarized primary culture from rat renal inner medullary collecting duct (IMCD) cells

A primary culture from rat renal IMCD cells was established to investigate the permeability characteristics of the luminal and contraluminal plasma membranes of the papillary collecting duct in vitro. Freshly isolated IMCD cells were grown on filters in a special "epithelial cell" medium. Confluency was proved with an epithelial volt/ohm meter. After 7 d of culture the transepithelial resistance reached more than 1000 omega x cm2. A polarization of the cells with regard to a basolateral localization of a lactate efflux system, and an L-alanine transport system was achieved. The hypotonicity-activated release systems for the organic osmolytes sorbitol and betaine were also located basolaterally, whereas taurine, glycerophosphorylcholine, and myo-inositol left the cells at both cell poles but with different capacity. Morphological observations revealed also that the monolayer was well differentiated. Thus, a model of a renal collecting duct epithelium was established which can be used to analyze polarized and differentiated transport processes across the epithelial cells and their plasma membranes.

Immunolocalization of acidic fibroblast growth factor and receptors in the tubulointerstitial compartment of chronically rejected human renal allografts

Tubular damage and loss associated with interstitial inflammation and fibrosis may be the most important determinants in chronic renal allograft rejection. To elucidate potential pathophysiologic mechanisms associated with tubulointerstitial lesions, we examined the expression of a fibrogenic cytokine, acidic fibroblast growth factor (FGF-1) and its high-affinity receptors, in both relevant renal transplant controls (n=5) and tissue from patients (n=19) who underwent nephrectomy after graft loss, secondary to chronic rejection. In situ hybridization and immunohistochemical analyses demonstrated minimal expression of FGF-1 mRNA and protein in the tubulointerstitial compartment of the normal human kidney. In contrast, tubulointerstitial lesions in kidney allografts experiencing chronic rejection demonstrated the exaggerated appearance of both FGF-1 protein and mRNA in resident inflammatory and tubular epithelial cells. Patterns of staining were consistent throughout tubular compartments and did not appear to be localized to any particular region. The tubulointerstitium in kidneys with findings of chronic rejection also exhibited increased immunodetection of proliferating cell nuclear antigen in the tubular epithelium, inflammatory cell infiltrate, and neovascular structures. The enhanced appearance of FGF-1 and readily detectable fibroblast growth factor receptors suggests that this polypeptide mitogen may serve as an important mediator of growth and repair responses, associated with development of angiogenesis and tubulointerstitial lesions during chronic rejection of human renal allografts.

Transforming growth factor alpha and epidermal growth factor expression in experimental murine polycystic kidney disease

Cystic change in polycystic kidney disease (PKD) is associated with epithelial hyperplasia, altered fluid and electrolyte transport, and de-differentiation of renal tubular epithelium. The role of polypeptide growth factors as potential modulators of cystic change remains an area of controversy. In this study, the expression of epidermal growth factor (EGF) and transforming growth factor-alpha (TGF alpha) were assessed by immunohistochemistry and image analysis in glucocorticoid-induced PKD in the newborn mouse. Newborn C3H mice received either 200 mg/kg methylprednisolone acetate (MPA) or 0.9% saline as a control. EGF expression was not detected in significant quantities in either MPA-treated or control animals. TGF alpha, however, was expressed in immature control kidney in a largely basolateral distribution. Expression increased significantly in association with cystic change in MPA-treated animals and was localized to the apical cell surface, implying altered polarity of secretion. There is no evidence that EGF is a mitogen in this early developmental model of PKD. TGF alpha, however, may be an important mediator of cystic change in immature or de-differentiated renal tubular epithelium.

Arrested development of the neonatal kidney following chronic ureteral obstruction

PURPOSE

The purpose of this study was to investigate the role of growth-related peptides in the impairment of renal growth and development resulting from unilateral ureteral obstruction (UUO) in the neonatal rats.

MATERIALS AND METHODS

Sprague-Dawley rats underwent UUO or sham-operation in the first 48-hours of life, and kidneys were harvested 1 to 28 days later. Renal messenger RNA (mRNA) was quantitated for renin, transforming growth factor-beta 1 (TGF-beta 1) and epidermal growth factor (EGF). Renal interstitial volume was measured in Masson-trichrome-stained sections, and renin and alpha-smooth muscle actin (alpha-SM actin) distribution were determined by immunocytochemistry.

RESULTS

The normal developmental increase in renal mass and DNA content were suppressed in ipsilateral UUO and increased in the intact opposite kidney. Renal interstitial volume was increased more than 10-fold by ipsilateral UUO. Unilateral ureteral obstruction resulted in a sustained increased in ipsilateral renal renin mRNA and persistence of fetal renin distribution. Renin in the contralateral kidney was suppressed. Transforming growth factor-beta 1 expression increased progressively in the obstructed kidney, but decreased after 7 days in sham-operated kidneys. While renal EGF expression was undetectable in the normal sham kidney during the first 3 days of life, it increased steadily with maturation. However, EGF expression remained suppressed in the obstructed kidney. Whereas alpha-SM actin disappeared from the interstitium of normal rat kidneys by 15 days of age, it persisted in the obstructed neonatal kidney.

CONCLUSIONS

As revealed by changes in expression of growth-related peptides, neonatal UUO delays ipsilateral renal development, which may contribute to impaired renal growth.

Disease processes in epithelia: the role of the actin cytoskeleton and altered surface membrane polarity

The establishment and maintenance of cell polarity is essential for normal epithelial function. Disruption of the underlying processes, either as a primary inborn defect or as a secondary result of other pathologic processes, can lead to loss of epithelial polarity and further cellular and organ-level dysfunction. Continued elucidation of the processes involved may prove fruitful both in the understanding of basic cell biology and in the understanding and treatment of a variety of disease states.

C-fos expression is hypersensitive to serum-stimulation in cultured cystic kidney cells from the C57BL/6J-cpk mouse

Cystic kidneys of the C57BL/6J-cpk murine model of polycystic kidney disease show a marked overexpression of the proto-oncogenes c-fos, c-myc, and c-Ki-ras, consistent with an increased rate of cell proliferation and an altered state of differentiation. To determine if cystic cells have increased responsiveness to stimulation with mitogenic agents, quiescent primary cultures from normal and cystic cpk kidneys were treated with fetal bovine serum (FBS), 8-bromo-cAMP (cAMP), or epidermal growth factor (EGF). The level of c-fos induction following stimulation by FBS was found to be dramatically higher in cystic cells than in normal cells; whereas induction by cAMP or EGF was essentially the same in both cell types and much less than that seen in FBS-stimulated cells. To determine if this serum hypersensitivity reflects an increased proliferative state in vivo, c-fos induction was examined in cultures derived from normal kidneys stimulated to regenerate by folic acid-induced acute renal injury. As with cystic kidneys, the folic acid-injured kidneys showed increased c-fos responsiveness to FBS in cell culture. These experiments suggest that cystic and regenerating kidneys have an altered phenotypic state in vivo that is manifested in cell culture by serum hypersensitivity. However, whereas the folic acid-injured kidneys ultimately reestablish normal kidney function, cystic kidneys further progress to renal failure, suggesting that cystic epithelial cells are locked in this altered state of differentiation.

Characterization and developmental expression of Xenopus C/EBP gene

The Xenopus homolog of the transcription factor C/EBP (CCAAT/enhancer core binding protein), cloned from an adult Xenopus liver cDNA library, encodes a protein whose sequence is 67% homologous to that of rat C/EBP at the amino acid level, with virtually identical sequence of the basic-zipper region at the carboxyl terminus. As determined by gel electrophoretic mobility shift assays, the protein synthesized from xC/EBP cDNA bound specifically to the consensus binding site for C/EBP-like proteins. Northern blotting and RNase protection revealed a single species of xC/EBP mRNA of 2.7 kb which was most abundant in adult Xenopus liver, with smaller amounts in spleen, kidney, oviduct and brain and undetectable in heart and skeletal muscle. Although a small amount of this transcript could be detected in unfertilized eggs and early embryos, its accumulation rose sharply at the onset of metamorphosis (stage 55/56), and continued to increase through metamorphic climax to reach its highest level in stage 66 froglet liver, but thereafter declining in adult liver. In situ hybridization revealed a uniform pattern of distribution of xC/EBP mRNA in the liver and fat body throughout metamorphosis. Towards the end of metamorphosis, high levels of xC/EBP mRNA were detected in epithelial cells of the digestive tract. However, the spatial pattern of cells expressing the transcript changed markedly in the developing kidney. Our results suggest that xC/EBP may be involved as a transcription factor in the establishment of the adult phenotype during post-embryonic development of Xenopus.

The distal nephron is preferentially infiltrated by inflammatory cells in acute interstitial nephritis

In acute interstitial nephritis (AIN), mononuclear cells invade the tubules (tubulitis). The segmental localization of tubulitis is not precisely known. To clarify this question, formalin-fixed kidney biopsy specimens from 13 patients with AIN were studied stereologically by identifying cortical tubules with segment-specific markers. The periodic acid-Schiff reaction, peanut lectin, and antibodies against Tamm-Horsfall protein and epidermal cytokeratins all applied to the same section were used to identify the proximal tubules (PTs), distal convoluted tubules, distal straight tubules, and the cortical collecting system (connecting tubules and cortical collecting ducts), respectively. Morphometrically, an estimate of the relative volume of the inflammatory cell infiltrates within each category of tubular segments was obtained. Inflammatory cells were infrequently found in PTs (1.2%) but were frequently localized in distal tubules and the cortical collecting system (7.6%). There was no difference in the amount of the inflammatory cell infiltrate within these segments. Re-examination of an electron microscopic study of AIN carried out in this laboratory revealed that mononuclear cells were rarely seen in convoluted PTs but were frequently observed in straight PTs and all segments distal to them. The observations indicate that it is the distal nephron which is primarily affected by inflammatory cell infiltration in AIN.

Regulation of rat proximal tubule epithelial cell growth by fibroblast growth factors, insulin-like growth factor-1 and transforming growth factor-beta, and analysis of fibroblast growth factors in rat kidney

Growth factors may play an important role in regulating the growth of the proximal tubule epithelium. To determine which growth factors could be involved, we have investigated the mitogenicity of various purified factors in rat kidney proximal tubule epithelial (RPTE) cells cultured in defined medium. Fibroblast growth factors, aFGF (acidic FGF) and bFGF (basic FGF), stimulate DNA synthesis in a dose-dependent manner, with ED50 values of 4.5 and 3.2 ng/ml, respectively; their effects are not additive. With cholera toxin in the medium, both aFGF and bFGF can replace insulin or epidermal growth factor (EGF) to attain the maximum level of cell growth, but they cannot replace cholera toxin. Cholera toxin specifically potentiates the effects of FGFs on DNA synthesis. At high cell density, both insulin and insulin-like growth factor 1 (IGF-1) induce DNA synthesis more effectively than EGF, FGFs and cholera toxin. The high concentration (0.2-1.0 microgram/ml) of insulin required for cell growth can be replaced by a low concentration of IGF-1 (10-20 ng/ml), indicating that insulin probably acts through a low affinity interaction with the IGF-1 receptor. Transforming growth factor-beta 1 (TGF-beta 1) inhibits DNA synthesis induced by individual factors and combinations of factors in a concentration-dependent manner. Northern blot analysis shows that mRNA for TGF-beta 1, IGF-1, and aFGF, but not bFGF are present in rat kidney. Western blot analysis and bioassay data confirmed that the majority of FGF-like protein in rat kidney is aFGF. The data suggest that in addition to EGF, IGFs, and TGF-beta, FGFs may also be important kidney-derived regulators of proximal tubule epithelial cell growth in vivo and in vitro.

Expression of transforming growth factor-alpha and epidermal growth factor receptor in human fetal kidneys

Beginning at the fifth week of fetal life, successive generations of individual nephrons are induced by contact between metanephric mesenchyme and ureteric bud. Following phenotypic transformation, cells of each primitive renal vesicle undergo a phase of rapid cell division. In order to identify genes which might regulate nephron development in man, we screened adult and fetal kidney RNA for expression of a panel of growth-related genes. Among the genes which were expressed at higher levels in fetal kidney was the epidermal growth factor (EGF) receptor. There is controversy as to the most likely physiologic EGF receptor ligand in fetal kidney; we were able to identify a transcript for transforming growth factor-alpha (TGF-alpha) but not EGF on Northern blots of fetal kidney RNA. Since the abundance of TGF-alpha mRNA is low, we confirmed its presence by polymerase chain reaction amplification. Using specific radioimmunoassays, we also provide direct evidence for TGF-alpha but not EGF peptide in extracts of fetal kidney and mid-gestational amniotic fluid. We suggest that TGF-alpha/EGF receptor interactions may serve an important function in development of human fetal kidney.

Developing nephrons in adolescent dogfish, Scyliorhinus caniculus (L.), with reference to ultrastructure of early stages, histogenesis of the renal countercurrent system, and nephron segmentation in marine elasmobranchs

Light and electron microscopy of the excretory kidney of adolescent dogfish, Scyliorhinus caniculus (L.), revealed immature and mature nephrons as well as four developmental stages of nephrons. At stage I the nephron was characterized by a condensed mass of mesenchymal cells in the center of several concentric layers of connective tissue. At stage II of the nephron, the S-shaped body was an elongate cyst with a high prismatic epithelium that was connected by a developing collecting tubule with the collecting duct system. At stage III, the developing nephrons already possess the essential features of the mature nephron but lack complete differentiation. Developing renal corpuscles had one afferent arteriole and two efferent vessels. Developing tubules ran four times between the lateral bundle zone and the mesial tissue zone before they joined the collecting duct system. A continuous sheath of flat cells, encompassing the collecting duct system, extended around the developing lateral bundle. A rudimentary central vessel ran from the developing lateral bundle to the venous sinusoid capillaries between the mesial convolutions. Developmental stage IV was similar to the mature nephron, however, renal corpuscles and tubular segments were smaller than those of mature nephrons. Conclusive evidence for morphological homology of elasmobranch nephron segments and collecting tubule-collecting duct system with those of other vertebrates is provided. The origin and nature of the central vessel and the bundle sheath is clarified. These specific structures of marine elasmobranch kidney supposedly are of great functional relevance for the renal countercurrent system that in turn is essential for ion- and osmo-regulation.

Fetal mouse kidney maturation in vitro: coordinated influences of epidermal growth factor, transferrin and hydrocortisone

We have investigated the individual and combined actions of epidermal growth factor (EGF), transferrin and hydrocortisone on the maturation of whole fetal mouse metanephroi maintained in serum-free conditions for up to 5 days. The presence of EGF (100 ng/ml) resulted in elevated levels of [3H]-thymidine incorporation when compared to controls; autoradiograms showed that the proliferation of mesenchymal cells in the nephrogenic zone is particularly enhanced as verified by cell counting. Brush border hydrolase activities (alkaline phosphatase and gamma-glutamyltransferase), on the other hand, were significantly diminished. Transferrin (5 micrograms/ml) slightly stimulated DNA synthesis and potentiated EGF mitogenic action. The activation of DNA replication by the growth factor seems to be mediated through the protein kinase C pathway. When added alone, hydrocortisone (10(-6) M) strongly inhibited DNA synthesis, stimulated hydrolase activities and exerted a positive effect on brush border differentiation. When combined with EGF or to EGF + transferrin, hydrocortisone counteracted the effects of these latter peptides on DNA synthesis and enzyme activities. Considering the earlier observation of a reciprocal relation between proliferation and differentiation during the neotubulogenic phase of kidney development, the results described in the current study suggest that synergistic and synarchic actions of these heterologous factors are involved in the regulation of tubulogenesis.

Altered growth regulation of rat kidney proximal tubule epithelial cells transformed in vitro by SV40 viral DNA: fibroblast growth factors (heparin-binding growth factors) are potent inducers of anchorage-independent growth

The majority of renal cancers are thought to arise from the proximal tubule epithelium, but little is known about their etiology. In this investigation, we have established an in vitro model to study the transformation of these target cells using rat kidney proximal tubule epithelial cells (RPTE) transformed in defined medium with SV40-viral DNA. Selection by passaging cells onto plastic surfaces yielded a population of cells (SV-RPTE) that expressed keratin and vimentin along with SV40 large-T antigen. The cells were morphologically transformed and lost their differentiated character as determined by several RPTE markers. SV-RPTE cells grew in soft agar in serum-supplemented medium containing insulin, epidermal growth factor, and cholera toxin, but were unable to grow when serum and growth factors were not combined. Acidic and basic fibroblast growth factors (aFGF and bFGF) were unique since they were the only single factor that induced anchorage-independent growth in the presence of serum alone. Transforming growth factor-beta 1 (TGF-beta 1) was a potent inhibitor of anchorage-independent growth, but the inhibition was partially overcome by a combination of growth factors. The growth factor responses of SV-RPTE in monolayer cultures differed from those in soft agar; the cells were more sensitive to growth stimulation by insulin and insulin-like growth factor, neither of which stimulated anchorage-independent growth. SV-RPTE cells in monolayer cultures had also lost the sensitivity to growth inhibition by TGF-beta 1 characteristic of normal RPTE. The RPTE transformation model described here will be very useful for investigating the molecular basis and etiology of renal cancers. Furthermore, the data suggest that maintenance of the transformed phenotype by aFGF and bFGF and loss of negative growth regulation by TGF-beta 1 could play a role in renal carcinogenesis.

Polypeptide growth factors and the kidney: a developmental perspective

A variety of polypeptides with stimulatory or inhibitory effects on cell proliferation have been identified. In addition to stimulating or inhibiting the proliferation of cells and maintaining their viability, polypeptide growth factors play significant roles in embryogenesis and differentiation. The current review focuses on five specific polypeptide growth factor families (epidermal growth factor, insulin-like growth factors, transforming growth factors, platelet-derived growth factor, and fibroblast growth factors) and discusses their possible relationship to normal renal physiology, abnormal renal pathophysiology, and renal organogenesis. On the basis of current data, it is clear that polypeptide growth factors are multifunctional agents with important effects on renal function and renal organogenesis.