Intraperitoneal protein injection in the axolotl: the amphibian kidney as a novel model to study tubulointerstitial activation

BACKGROUND: A substantial body of experimental evidence suggests that protein loading causes activation of proximal tubular epithelial cells with consecutive interstitial fibrosis. These studies have mostly been performed using mammalian in vivo models of glomerular damage or tissue cultures of mammalian tubulointerstitial cells. The kidney of the axolotl contains not only closed nephrons, but also nephrons with ciliated peritoneal funnels called nephrostomes that have access to the peritoneal fluid. Injection of protein into the peritoneal cavity fails to expose closed nephrons to a protein load, but causes selective uptake and transient storage of proteins in tubular epithelial cells of nephrons with nephrostomes. The purpose of the present study was to determine whether (a) the axolotl kidney can be used as a model to assess protein uptake by tubular cells in vivo in the absence of glomerular damage, and (b) this is accompanied by any evidence of tubular epithelial cell activation and interstitial fibrosis. METHODS: Male and female axolotl (80 to 120 g of weight) were given a daily intraperitoneal injection of 1.5 mL endotoxin-free calf serum or saline as control. Kidneys were harvested after 4 or 10 days using perfusion fixation for light microscopy (fibrous tissue stain) and saline perfusion for immunohistochemistry (fibronectin, TGF-beta and collagen I). RESULTS: The findings document selective storage of protein and lipids, progressive with time, in proximal tubular epithelial cells of nephrons draining the coelomic cavity. In addition, progressive focal accumulation of fibrous tissue was noted around protein-storing tubules. Immunohistochemical staining demonstrated the presence of fibronectin and TGF-beta in the tubular epithelial cells and interstitial cells. CONCLUSION: The axolotl kidney provides a novel in vivo model to study tubulointerstitial activation and induction of interstitial fibrosis by protein loading. The findings are independent of alterations of glomerular function that may have potential confounding effects on peritubular hemodynamics, pO2, cell traffic, etc.     

Cortical and papillary absorptive defects in gentamicin nephrotoxicity

Renal function was examined in rats given daily injections of gentamicin (100 to 150 mg/kg) for 10 to 14 days. Whole kidney inulin clearance fell and urine volume increased. Single nephron GFR of surface nephrons varied. Some nephrons had no filtration, some had low rates, and some had high rates. Abnormal renal tubular epithelial inulin permeability was demonstrated by microinjection. Micropuncture of individual nephrons early and later in their course demonstrated reduced fluid reabsorption along the proximal convoluted tubule of superficial nephrons. Rates of fluid delivery to the late proximal and distal tubule were elevated. The rate of fluid reabsorption in the superficial loop of Henle was increased. Maximal urine osmolality and papillary tissue content of urea was reduced. The polyuria, therefore, results from decreased fluid reabsorption by proximal tubules and, probably, by papillary collecting ducts. The decrease in proximal fluid reabsorption is probably secondary to impaired solute reabsorption. A decrease in collecting duct fluid absorption can be attributed to the observed decrease in papillary solute concentration.     

Creation of a functioning chimeric mammalian kidney

The possibility of adding new nephrons to the mammalian kidney was studied. Embryonic metanephric tissue was implanted into the renal cortex of neonatal mice less than 24 hours old, and the development of the chimeric kidney was followed over the following two to four weeks. Donor tissue was obtained from the homozygous beige mouse and a mouse line transgenic for the beta-globin gene, which provided distinct cellular and nuclear markers which were used to distinguish donor from recipient nephrons. Differentiation and growth of donor nephrons occurred in the host kidney and included vascularized glomeruli, mature proximal tubules, and tubular extensions into the renal medulla. Glomerular filtration was demonstrable in donor nephrons using FITC-dextran as a marker of filtration into the proximal tubules. Transplantation of metanephric tissue into adult mouse kidneys did not lead to glomerular or tubular differentiation. This study demonstrates the feasibility of adding functioning nephrons to mammalian kidneys in species in which there is ongoing nephrogenesis post-natally.     

Long-term effects of 24-hr unilateral ureteral obstruction on renal function in the rat

To characterize the pattern of recovery following release of unilateral ureteral obstruction of 24-hr duration, rats were studied with whole kidney clearance techniques, 3 hrs, 8, 14, and 60 days after release. The single nephron glomerular filtration rate (SNGFR) of superficial and juxtamedullary nephrons was estimated with a modification of Hanssen's technique in rats studied 8 and 60 days after ureteral release. The whole kidney glomerular filtration rates (GFR) were decreased markedly 3 hrs after relief of obstruction, but gradually increased and by 14 days, the GFR of the postobstructed kidney (POK) and the contralateral kidney (CK) were comparable. This recovery of GFR was not a consequence of a homogeneous improvement in SNGFR. At 8 days, more than 15% of superficial and juxtamedullary nephrons were not filtering in the POK. This decrease in the percent of filtering nephrons persisted to 60 days post release, indicating a permanent loss of nephron units. The SNGFR of the residual nephrons of the POK was significantly greater than that of the CK at 8 and 60 days following ureteral release. Thus, acute unilateral ureteral obstruction results in a permanent loss of filtering nephrons, which is offset by hyperfiltration of those remaining. Abnormalities in renal tubule function persisted beyond the time (14 days) when whole kidney GFR had returned to normal. These abnormalities were in distal tubule function. Urine osmolality was consistently lower at all time intervals post release, as was net acid excretion. The results of the present study suggest that these abnormalities are a consequence of the reduction in the number of filtering juxtamedullary nephrons and/or to abnormalities in collecting duct function.     

Renal microradiography of experimental ureteral obstruction in the rabbit

Microradiography of nephrons in kidneys perfusion-fixed with glutaraldehyde permits examination of large numbers of nephrons. This technique was applied to rabbits between one and 14 days following unilateral ureteral ligation. Kidneys without ureteral occlusion served as controls. By two days after ureteral obstruction there was dilatation of the ducts of Bellini and papillary collecting ducts. At three to four days there was splaying and tortuosity of the loops of Henle. By eight to 10 days the proximal straight tubules were noted to be dilated and helically twisted. After two weeks of ureteral obstruction there was dilatation of Bowman's space with encroachment on the glomerular capillary tuft. At this time many proximal convoluted tubules began to show atrophic changes. These morphologic alterations may due in part to back pressure on the nephrons, with retrograde progression as the duration of urinary tract obstruction is increased. The distal convoluted tubule and the descending limb of the loop of Henle were not noted to be abnormal during the study.     

Ontogenesis of angiotensin-I converting enzyme in human kidney

The kidney distribution of angiotensin-I converting enzyme (ACE) was studied in 14 fetuses (11 to 30 weeks old) and 7 children (2 days to 13 years old) by immunohistochemistry using specific antibodies to human kidney ACE. Immunohistochemical techniques included indirect immunofluorescence on cryostat sections of frozen tissue, immunoperoxidase and immunofluorescence of fixed tissue embedded in Paraplast, and immunoelectron microscopy. The ACE distribution in the fetal kidneys was independent of the age of the fetus. ACE was detected in two locations: 1) on the basolateral membranes and primary apical microvilli of epithelial cells from early differentiating proximal tubules; the labeling was intense in brush borders of fully developed proximal tubules; and 2) on glomerular endothelial cells; cells were lined by reaction product as soon as capillaries invaded the inferior cleft of the S-shaped body. Tubular ACE distribution was identical in the postnatal kidneys. The staining of the glomerular endothelium was extremely inconstant. The presence of ACE in proximal tubular cells and glomerular endothelial cells at the beginning of nephron differentiation may indicate that it is involved in the development of nephron function and renal hemodynamic.     

Renal structural and functional changes after unilateral ureteral obstruction in rabbits

Renal structural and functional changes following unilateral ureteral ligation for periods of 3 days to 6 weeks were studied in rabbits. The renal pelvic pressure increased to 20 cm H2O within 3 days of obstruction and in contrast to some previous investigations it was still raised after 6 weeks. Interstitial oedema, collapse of proximal tubules and dilatation of distal tubules were the earliest observed histological changes. Later findings were interstitial fibrosis, widespread atrophy of proximal tubules and, in the latest stages, dilatation of the collecting duct system. Thus, the distal tubules appeared considerably less resistant than the collecting ducts, to the increased pressure. Renal functional changes were studied one hour after release of obstruction of 3 days, 1-2-4 or 6 weeks' duration. In comparison to the contralateral kidney a rapid decrease of blood flow and glomerular filtration occurred in spite of a normal glomerular structure and collapsed proximal tubules and were probably related to haemodynamic disturbances such as arteriolar constriction. Although absolute electrolyte excretion was much reduced, the fractional excretion of several electrolytes, especially magnesium was increased already after 3 days of obstruction. These findings can presumably be correlated to the dilatation and early epithelial alterations in the distal tubules in which magnesium is predominantly reabsorbed.     

Podocyte-derived BMP7 is critical for nephron development

Individuals with congenital renal hypoplasia display a defect in the growth of nephrons during development. Many genes that affect the initial induction of nephrons have been identified, but little is known about the regulation of postinductive stages of kidney development. In the absence of the growth factor bone morphogenic protein 7 (BMP7), kidney development arrests after induction of a small number of nephrons. The role of BMP7 after induction, however, has not been fully investigated. Here, we generated a podocyte-specific conditional knockout of BMP7 (Bmp7(flox/flox);Nphs2-Cre(+) [BMP7 CKO]) to study the role of podocyte-derived BMP7 in nephron maturation. By postnatal day 4, 65% of BMP7 CKO mice had hypoplastic kidneys, but glomeruli demonstrated normal patterns of laminin and collagen IV subunit expression. Developing proximal tubules, however, were reduced in number and demonstrated impaired cellular proliferation. We examined signaling pathways downstream of BMP7; the level of cortical phosphorylated Smad1, 5, and 8 was unchanged in BMP CKO kidneys, but phosphorylated p38 mitogen-activated protein kinase was significantly decreased. In addition, beta-catenin was reduced in BMP7 CKO kidneys, and its localization to intracellular vesicles suggested that it had been targeted for degradation. In summary, these results define a BMP7-mediated regulatory axis between glomeruli and proximal tubules during kidney development.     

Acquired cystic disease of the kidney analyzed by microdissection

Four cases of acquired cystic disease of the kidney (ACDK) were studied by the microdissection technique (MD) of Darmady and Baert to analyze the cystic transformation. No patient had a history or clinical evidence of the adult polycystic disease of the kidney (APDK). Hypothetical models related the pathogenesis of cystic transformation to either obstructive or degenerative factors. Microdissection was performed in four nephrectomy specimens of hemodialyzed patients and a total of 155 nephrons were isolated. The atrophy of the glomeruli has already been described histopathologically but MD demonstrated the existence of nephrons consisting of sclerotic glomeruli and enlarged segments between the atrophic convoluted proximal and distal tubules. Diverticula and cysts were located, above all along the proximal (mainly dilated) convoluted tubules: they were always in continuity with the tubules. Phase contrast microscopy showed a patent lumen in 80% of the proximal and distal convoluted tubules, and a regular lining of the cysts. These data support the hypothesis that ACDK is the result of hyperplasia and dilation of remaining nephrons, rather than a result of obstruction and/or fibrosis.     

Acute and chronic changes in renal function following unilateral nephrectomy

Free-flow micropuncture was used to assess proximal and distal tubular function in rats immediately (2 to 5 hours), five days and 30 days after uninephrectomy (UN); results were compared with those in sham-operated littermates. Excretion rates of water, sodium and potassium were approximately doubled in the remaining kidney of UN rats. Two to five hours after UN there were small increases in glomerular filtration rate (GFR) and single nephron GFR which at this stage were not accompanied by an increase in absolute proximal reabsorption; that is, fractional proximal reabsorption fell. After five days, GFR and single nephron GFR had increased further; at this stage absolute proximal reabsorption was also significantly elevated. After 30 days, kidney weight, GFR, single nephron GFR and absolute proximal reabsorption had all increased by approximately 40%, and glomerulotubular balance in the proximal tubule had been fully restored. Data derived from distal tubular collections indicated that at every stage after UN: (a) fluid delivery to both early and late distal puncture sites was increased; (b) in contrast, there was no increase in sodium delivery to the late distal tubule, suggesting that the natriuresis resulted from reduced sodium reabsorption beyond the distal tubule and/or increased delivery of sodium from deep nephrons; and (c) there was a marked increase in potassium secretion into the accessible portion of the distal tubule which was more than adequate to explain the observed kaliuresis.     

Increased expression of ornithine decarboxylase in distal tubules of early diabetic rat kidneys: are polyamines paracrine hypertrophic factors?

Polyamines are small biogenic molecules that are essential for cell cycle entry and progression and proliferation. They can also contribute to hypertrophy. The activity of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine biosynthesis, increases in the early diabetic kidney to enable renal hypertrophy. Inhibition of ODC in early diabetes attenuates diabetic renal hypertrophy and glomerular hyperfiltration. The current studies examine the temporal profile of renal ODC protein expression and localization, intrarenal polyamine levels, and sites of proliferation in kidneys of rats during the first 7 days of streptozotocin diabetes. ODC mRNA and protein content were increased in diabetic kidneys. High-performance liquid chromatography analysis showed increased intrarenal polyamine concentrations peaking after 24 h of diabetes. A subsequent increase in the number of proliferating proximal tubular cells was detected by in vivo 5-bromodeoxyuridine (BrdU) incorporation on day 3. Surprisingly, immunohistochemical studies revealed that increased ODC protein was apparent only in distal nephrons, whereas the main site of diabetic kidney hypertrophy is the proximal tubule. These findings raise the possibility that polyamines produced in the distal nephron may mediate the early diabetic kidney growth of the proximal tubules via a paracrine mechanism.     

肾盂内高压灌流对肾单位结构影响的实验研究

目的建立肾盂内高压灌流的动物模型，观察肾盂内高压灌流对肾单位结构的影响，探讨经皮肾镜时肾盂内灌流的安全压力。方法建立活体猪的肾盂内高压灌流动物模型（n=10），在无加压灌流至40．00kPa（1kPa=7．5mmHg）高压灌流间，每6．67kPa作为一个压力级别灌流10min，穿刺获取肾实质组织，分别在光镜（HE染色、六胺银染色）及透射电镜下观察各级压力梯度下肾小球、肾小囊及近曲肾小管的形态变化。结果肾盂内灌流压在6．67—20．00kPa时，肾单位各结构保持完整；当肾盂内灌流压达到26．66kPa，透射电镜下可见肾近曲小管上皮细胞细胞器扩张，胞质内空泡形成，微绒毛紊乱、脱落等细胞受损表现；当肾盂内灌流压达33．33～40．00kPa，可观察到肾小囊基底膜断裂、肾小囊壁破裂，红细胞及蛋白质漏入肾小囊，近曲小管上皮细胞微绒毛脱落、胞质内大量空泡形成，细胞膜及细胞器膜破裂等结构损伤表现。结论肾盂内灌流压力超过26．66kPa可对肾单位造成结构破坏，进行经皮。肾镜手术过程中，应注意保持肾盂内压不超过26．66kPa，避免对肾单位造成结构破坏。     

Three-dimensional reconstruction of the mouse nephron

Renal function is crucially dependent on renal microstructure which provides the basis for the regulatory mechanisms that control the transport of water and solutes between filtrate and plasma and the urinary concentration. This study provides new, detailed information on mouse renal architecture, including the spatial course of the tubules, lengths of different segments of nephrons, histotopography of tubules and vascular bundles, and epithelial ultrastructure at well-defined positions along Henle's loop and the distal convolution of nephrons. Three-dimensional reconstruction of 200 nephrons and collecting ducts was performed on aligned digital images, obtained from 2.5-mum-thick serial sections of mouse kidneys. Important new findings were highlighted: (1) A tortuous course of the descending thin limbs of long-looped nephrons and a winding course of the thick ascending limbs of short-looped nephrons contributed to a 27% average increase in the lengths of the corresponding segments, (2) the thick-walled tubules incorporated in the central part of the vascular bundles in the inner stripe of the outer medulla were identified as thick ascending limbs of long-looped nephrons, and (3) three types of short-looped nephron bends were identified to relate to the length and the position of the nephron and its corresponding glomerulus. The ultrastructure of the tubule segments was identified and suggests important implications for renal transport mechanisms that should be considered when evaluating the segmental distribution of water and solute transporters within the normal and diseased kidney.     

Reduced number of glomeruli in kidneys with neonatally induced partial ureteropelvic obstruction in pigs

PURPOSE: We quantify the structural components of the nephron in adult pig kidneys with neonatally induced unilateral hydronephrosis in comparison with nonobstructed kidneys. MATERIALS AND METHODS: The study included 11 pigs with unilateral partial ureteropelvic obstruction induced 2 days after birth and 8 sham operated control pigs. Obstructed kidney glomerular filtration rate was significantly reduced at age 4 weeks but did not differ from control kidneys after 24 weeks. At age 24 weeks the kidneys were perfusion fixed, and the number and volume of glomeruli and tubular lengths were measured using stereological methods. RESULTS: Mean obstructed kidney volume did not differ from that of control kidneys. Mean number plus or minus standard deviation of glomeruli in the obstructed kidneys was reduced by 28% compared to that of control kidneys (502 +/- 163 x 103 versus 697 +/- 161 x 103, p = 0.02), whereas no difference in mean glomerular volume was observed. Mean length of the proximal or distal tubules did not differ between obstructed and control kidneys. Mean number or volume of glomeruli in nonobstructed kidneys contralateral to obstructed kidneys did not differ from that of control kidneys. The individual number of glomeruli in the obstructed kidneys was not associated with function of these kidneys. CONCLUSIONS: Neonatally induced unilateral partial ureteropelvic obstruction causes impaired nephrogenesis with a significant reduction in the number of nephrons, which is not reflected in measurements of kidney function in this model. The reduction in the number of glomeruli suggests that congenital unilateral obstruction impairs nephrogenesis.     

Recovery following relief of unilateral ureteral obstruction in the neonatal rat

BACKGROUND: Obstructive nephropathy is a primary cause of renal insufficiency in infants and children. This study was designed to distinguish the reversible and irreversible cellular consequences of temporary unilateral ureteral obstruction (UUO) on the developing kidney. METHODS: Rats were subjected to UUO or sham operation in the first 48 hours of life, and the obstruction was removed five days later (or was left in place). Kidneys were removed for study 14 or 28 days later. In additional groups, kidneys were removed at the end of five days of obstruction. Immunoreactive distribution of renin was determined in arterioles, and the distribution of epidermal growth factor, transforming growth factor-beta1, clusterin, vimentin, and alpha-smooth muscle actin was determined in tubules and/or interstitium. The number of glomeruli, glomerular maturation, tubular atrophy, and interstitial collagen deposition was determined by morphometry. Renal cellular proliferation and apoptosis were measured by proliferating cell nuclear antigen and the TdT uridine-nick-end-label technique, respectively. The glomerular filtration rate was measured by inulin clearance. RESULTS: Renal microvascular renin maintained a fetal distribution with persistent UUO; this was partially reversed by the relief of obstruction. Although glomerular maturation was also delayed and glomerular volume was reduced by UUO, the relief of obstruction prevented the reduction in glomerular volume. Although relief of obstruction did not reverse a 40% reduction in the number of nephrons, the glomerular filtration rate of the postobstructed kidney was normal. The relief of obstruction did not improve tubular cell proliferation and only partially reduced apoptosis induced by UUO. This was associated with a persistent reduction in the tubular epidermal growth factor. In addition, the relief of obstruction reduced but did not normalize tubular expression of transforming growth factor-beta1, clusterin, and vimentin, all of which are evidence of persistent tubular injury. The relief of obstruction significantly reduced interstitial fibrosis and expression of alpha-smooth muscle actin by interstitial fibroblasts, but not to normal levels. CONCLUSIONS: The relief of obstruction in the neonatal rat attenuates, but does not reverse, renal vascular, glomerular, tubular, and interstitial injury resulting from five days of UUO. Hyperfiltration by remaining nephrons and residual tubulointerstitial injury in the postobstructed kidney are likely to lead to deterioration of renal function later in life.     

Congenital murine polycystic kidney disease

In the current study, the ontogeny of tubular cyst formation was studied in the CPK mouse, a murine strain with autosomal recessive polycystic kidney disease. Utilizing the technique of intact nephron microdissection in addition to standard light and transmission electron microscopy, the earliest morphologic alterations in CPK kidneys were localized in fetal tissue at 17 days of gestation to the distal portion of developing proximal tubules. During disease progression, from birth to 21 days of postnatal age, there was a shift in the site of cystic nephron involvement from proximal tubule to collecting tubules without involvement of other nephron segments. Cysts were enlarged tubular segments which remained in continuity with other portions of the nephron and were not associated with abnormalities in the overall pattern of nephron growth or differentiation. Analysis suggested that alterations in transtubular transport in abnormally shortened proximal tubular segments of juxtamedullary nephrons may have pathogenic importance in the early stages of cyst formation, and that epithelial hyperplasia and cytoskeletal alterations may have a role in progressive proximal tubular cystic enlargement. Cellular hyperplasia of epithelial walls of normally formed tubules was a prominent feature of cyst formation and progressive enlargement in collecting tubules. Such data form the basis for future studies into specific pathophysiological processes which may be operative in specific nephron segments during different stages of cyst formation in the CPK mouse.A preliminary report of this work was presented at the Annual Meeting of the Society for Pediatric Research, Washington DC, USA, May 1986, and has appeared in abstract form (Pediatr Res 20: 446A, 1986)     

Pathophysiology of the kidney in rats with Heymann nephritis

Alterations in kidney function were assessed early in the course of Heymann nephritis that was induced in rats by immunization with Fx1A, an extract prepared from rat kidney cortex. Whole kidney and single nephron function were evaluated by clearance and micropuncture techniques. Kidney function was studied in stage 1 of Heymann nephritis, before the onset of proteinuria, and in stage 2, when antibodies are deposited along the brush border of proximal tubules. Although overall kidney function was similar in rats in stage 1 and normal controls, glucose reabsorption was somewhat depressed in the first part of the proximal convoluted tubule in stage 1. Both whole kidney and single nephron glomerular filtration rates were depressed in stage 2. Proteinuria in stage 2 was characterized by an increased albumin sieving coefficient, which resulted in an elevated excretion of albumin. Furthermore, several proximal tubule functions (glucose and fluid reabsorption and PAH extraction) were substantially depressed in stage 2. These findings demonstrate that immunological injury to the proximal tubules in stage 2 of Heymann nephritis produces a significant impairment of proximal function.     

Electron microscopic study of renal failure in a case of polycystic kidney disease

The glomeruli and cortical tubules from an azotemic boy with polycystic kidney disease were examined by electron microscopy. Most prominent changes were found in the convoluted part of proximal tubules, which were undergoing severe focal cytoplasmic degradation. The straight portions showed similar but less pronounced changes. The distal and the collecting tubules were unaffected except for slight epithelial flattening. The glomerular visceral and parietal epithelial cells showed marked pynocytotic activity related to the proteinaceous fluid that filled and cystically dilated the Bowman capsular spaces. These findings indicate that the destruction of the renal parenchyma inbetween the cysts ensues to urine flow obstruction. There is no explanation yet why the proximal tubules are most severely affected.     

Tubules are the major site of M-CSF production in experimental kidney disease: correlation with local macrophage proliferation

BACKGROUND: Local proliferation of macrophages occurs within both the glomerulus and the interstitium in severe forms of human and experimental glomerulonephritis and plays an important role in amplifying renal injury. Macrophage colony-stimulating factor (M-CSF) is thought to be the growth factor driving this local macrophage proliferation. Previous studies have found that glomeruli are the predominant source of M-CSF production. However, this is difficult to reconcile with the prominent macrophage accumulation and proliferation seen in the interstitial compartment in glomerulonephritis. To address this issue, we localized M-CSF expression in rat models of glomerular versus tubulointerstitial injury and examined its relationship to local macrophage proliferation. METHODS: M-CSF expression (Northern blotting, in situ hybridization, immunostaining, Western blotting) and local macrophage proliferation (double immunostaining) was examined in normal rat kidney on days 1 and 14 of rat anti-glomerular basement membrane (anti-GBM) glomerulonephritis and on day 5 following unilateral ureteric obstruction. RESULTS: M-CSF mRNA and protein expression were identified in small numbers of glomerular podocytes, approximately 25% of cortical tubules, and most medullary tubules in normal rat kidney. Northern blotting showed a significant increase in whole kidney M-CSF mRNA in rat anti-GBM glomerulonephritis. Up-regulation of glomerular and, most prominently, tubular M-CSF production was confirmed by three independent methods: in situ hybridization, immunostaining, and Western blotting. The increase in M-CSF expression colocalized with local macrophage proliferation (ED1+PCNA+ cells) in both the glomerulus and tubulointerstitium. On day 5 after ureter ligation, there was a significant increase in tubular M-CSF mRNA and protein expression in the obstructed kidney, with no change in glomerular M-CSF. In parallel with M-CSF expression, macrophage accumulation and proliferation was prominent in the interstitium, but was absent from glomeruli. CONCLUSIONS: The tubular epithelial cell is the major site of M-CSF production within the injured kidney. Indeed, substantial macrophage accumulation and local proliferation can occur in the tubulointerstitium in the absence of glomerular inflammation. These results suggest that M-CSF production within the kidney, particularly by tubular epithelial cells, plays an important role in regulating local macrophage proliferation in experimental kidney disease.     

Integration of new embryonic nephrons into the kidney

The current report summarizes our experiments exploring the feasibility of creating a chimeric kidney, that is, an organ constituted by cells derived from more than one fertilized ovum. The overall strategy has been to obtain donor renal tissue from avian and murine embryos and to implant this into the host avian mesonephric mesoderm or into the cortex of murine neonatal kidney. In both models, donor cells were distinguished from the host by the presence of characteristic nuclear or cytoplasmic markers. Examination of quail to chick transplants showed the tandem development of mesonephric tissue in the form of bilobed organ. In the mouse chimeric kidney, examined 2 to 4 weeks postnatally, transplanted metanephric tissue grew and developed glomeruli, proximal tubules, and cords of cells, which extended into the medulla of the host kidney. Before death, intravenous FITC-dextran was administered to the host mouse. Some transplanted tubules were connected to filtering glomeruli, as judged by the presence of fluorescein within their lumens. These experimental models provide novel means with which to study nephrogenesis in vivo. Finally, if the embryonic donor tissue could be genetically engineered before implantation, the prospect of "nephron therapy" arises, in which altered implanted nephrons could deliver therapeutically useful molecules into the urine or kidney interstitium.