Different types of segmental sclerosing glomerular lesions in six experimental models of proteinuria

In Vivo assessment of hypertensive nephrosclerosis using ultrasound localization microscopy

PURPOSE

As a typical chronic kidney disease (CKD), hypertensive nephrosclerosis (HN) is a common syndrome of hypertension, characterized by chronic kidney microvascular damage. Early diagnosis of microvascular damage using conventional ultrasound imaging encounters challenges in sensitivity and specificity owing to the inherent diffraction limit. Ultrasound localization microscopy (ULM) has been developed to obtain microvasculature and microvascular hemodynamics within the kidney, and would be a promising tool for early diagnosis of CKD.

METHODS

In this study, the advantage of quantitative indexes obtained by using ULM (mean arterial blood flow speeds of different segments of interlobular arteries) over indexes obtained using conventional clinical serum (β2-microglobulin, serum urea nitrogen and creatinine) and urine (24-hour urine volume and urine protein) tests and ultrasound Doppler imaging [peak systolic velocity (PSV), end-diastolic velocity (EDV) and resistance index (RI)] and contrast-enhanced ultrasound imaging [CEUS; rise time (RT), peak intensity (IMAX), mean transit time (mTT) and area under the time-intensity curve (AUC)] for early diagnosis of HN was investigated. Examinations were carried out on 6 spontaneously hypertensive rats (SHR) and 5 normal Wistar-Kyoto (WKY) rats at the age of 10 weeks.

RESULTS

The experimental results showed that the indicators derived from conventional clinical inspections (serum and urine tests) and ultrasound imaging (PSV, EDV, RI, RT, IMAX, mTT and AUC) did not show significant difference between hypertensive and healthy rats (p > 0.05), while the TTP of the SHR group (28.52 ± 5.52 s) derived from CEUS is significantly higher than that of the WKY group (18.68 ± 7.32 s; p < 0.05). The mean blood flow speed in interlobular artery of SHR (12.47 ± 1.06 mm/s) derived from ULM is significantly higher than that of WKY rats (10.13 ± 1.17 mm/s; p < 0.01).

CONCLUSION

The advantages of ULM over conventional clinical inspections and ultrasound imaging methods for early diagnosis of HN were validated. The quantitative results showed that ULM can effectively diagnose HN at the early stage by detecting the blood flow speed changes of interlobular arteries. ULM may promise a reliable technique for early diagnosis of HN in the future. This article is protected by copyright. All rights reserved.

Genomic Research in Rat Models of Kidney Disease

Current understanding of the mechanisms underlying renal disease in humans is incomplete. Consequently, our ability to prevent the occurrence of renal disease or treat established kidney disease is limited. Investigating kidney disease directly in humans poses objective difficulties, which has led investigators to seek experimental animal models that simulate renal disease in humans. Animal models have thus become a tool of major importance in the study of renal physiology and have been crucial in shedding light on the complex mechanisms involved in kidney function and in our current understanding of the pathophysiology of renal disease. Among animal models, the rat has been the preferred and most commonly used species for the investigation of renal disease. This chapter reviews what has been achieved over the years, using the rat as a tool for the investigation of renal disease in humans, focusing on the contribution of rat genetics and genomics to the elucidation of the mechanisms underlying the pathophysiology of the major types of renal disease, including primary and secondary renal diseases.

Problems with 'focal segmental glomerulosclerosis'

The term 'focal segmental glomerulosclerosis (FSGS)' has been applied to many different conditions. All classifications of 'FSGS', including those describing 'variants', perpetuate the misconceptions that the entities included have something in common and that the term 'FSGS' has some value. With a rigorous approach to renal biopsies showing segmental lesions, especially with knowledge of clinical circumstances and with detailed analysis of features such as the appearance of lesions and their position within glomeruli, a pathologist can provide information that is clinically more useful than merely the bald diagnosis 'FSGS'. More precise terms should be used. 'Overload changes' can be used to describe the changes seen in reduced renal mass. 'Tip changes' can be seen in many conditions and are not a disease in themselves. 'The glomerular tip lesion as originally defined' means the occurrence of tip changes in otherwise normal glomeruli, in the nephrotic syndrome. 'Early classical segmental sclerosing glomerulopathy' is the combination of tip changes and otherwise abnormal glomeruli, in the nephrotic syndrome. 'Late classical segmental sclerosing glomerulopathy' means segmental lesions at various sites within glomeruli, in the nephrotic syndrome. 'Collapsing glomerulopathy' is distinctive, and its inclusion in classifications emphasises the lack of specificity of 'FSGS'.

Phosphate overload induces podocyte injury via type III Na-dependent phosphate transporter

Uptake of P(i) at the cellular membrane is essential for the maintenance of cell viability. However, phosphate overload is also stressful for cells and can result in cellular damage. In the present study, we investigated the effects of the transgenic overexpression of type III P(i) transporter Pit-1 to explore the role of extracellular P(i) in glomerular sclerosis during chronic renal disease. Pit-1 transgenic (TG) rats showed progressive proteinuria associated with hypoalbuminemia and dyslipidemia. Ultrastructural analysis of TG rat kidney by transmission electron microscopy showed a diffuse effacement of the foot processes of podocytes and a thickening of the glomerular basement membrane, which were progressively exhibited since 8 wk after birth. TG rats died at 32 wk of age due to cachexia. At this time, more thickening of the glomerular basement membrane and segmental sclerosis were observed in glomeruli of the TG rats. Immunohistochemical examination using anti-connexin 43 and anti-desmin antibodies suggested the progressive injury of podocytes in TG rats. TG rats showed higher P(i) uptake in podocytes than wild-type rats, especially under low P(i) concentration. When 8-wk-old wild-type and TG rats were fed a 0.6% normal phosphate (NP) or 1.2% phosphate (HP) diet for 12 wk, HP diet-treated TG rats showed more progressive proteinuria and higher serum creatinine levels than NP diet-treated TG rats. In conclusion, our findings suggest that overexpression of Pit-1 in rats induces phosphate-dependent podocyte injury and damage to the glomerular barrier, which result in the progression of glomerular sclerosis in the kidney.

Omega-3 and renal function in older adults

Chronic kidney disease (CKD) is a major public health problem and can result in end-stage renal disease with need for dialysis or transplantation. In Europe up to 12% of the adult population had some renal impairment, while in the United States the end stage of CKD has increased dramatically from 209.000 in 1991 to 472.000 in 2004. Diabetes and hypertension are major causes of kidney pathology. Infection, particularly ascending infection, is more common with increasing age, as both immune function declines and associated pathology predisposing to infection, such as obstructive uropathy, becomes more common. Most pathological changes in the kidney appear to be initiated by oxidative stress, followed by an inflammatory reaction. Oxidative stress results from an imbalance between free radicals and their detoxification by endogenous and exogenous scavengers, including polyunsaturated fatty acids (PUFA). Recent studies showed that PUFA supplementation slowed the rate of loss of renal function in patients with IgA nephropathy. Then, studies of omega-3 supplementation in dialysis patients describe salutary effects on triglyceride levels and dialysis access patency. We examined the relationship between total plasma PUFA levels and change in creatinine clearance over a three-year follow-up in the older persons enrolled in the InCHIANTI study, a population-based epidemiology study conducted in Tuscany, Italy. This study showed that older adults with low total plasma PUFA levels have a greater decline in creatinine clearance over three years of follow-up. These findings suggest that a higher dietary intake of PUFA may be protective against progression to chronic kidney disease.

Genomic research in rat models of kidney disease

Current understanding of the mechanisms underlying renal disease in humans is incomplete. Consequently, our ability to prevent the occurrence of renal disease or treat kidney disease once it develops is limited. There are objective difficulties in investigating kidney disease directly in humans, leading investigators to resort to experimental animal models that simulate renal disease in humans. Animal models have thus been a tool of major importance in the study of normal renal physiology and have been crucial in shedding light on the complex mechanisms involved in normal kidney function and in our current understanding of and ability to treat renal disease. Among the animal models, rat has been the preferred and most commonly used species for the investigation of renal disease. This chapter reviews what has been achieved over the years, using rat as a tool for the investigation of renal disease in humans, focusing on the contribution of rat genetics and genomics to the elucidation of the mechanisms underlying the pathophysiology of the major types of renal disease, including primary and secondary renal diseases.

Actin -related protein 3 (Arp3) is mutated in proteinuric BUF/Mna rats

The BUF/Mna strain of rat is a model of focal and segmental glomerulosclerosis (FSGS) in which a quantitative trait locus (QTL) for proteinuria, Pur1, has been identified. The aim of the present study was to identify candidates for the Pur1 gene. To narrow the Pur1 QTL, we performed fine QTL mapping and single nucleotide polymorphism (SNP) genotyping. To identify candidate genes, sequencing and gene-expression analyses of all genes contained in the narrowed locus were conducted. The narrowed Pur1 region contained 25 genes. Among these genes, only the Arp3 gene was mutated in the BUF/Mna strain; it contained a missense mutation that caused an (L)111(F) substitution. This leucine is conserved across species. Gene-expression analysis failed to identify any other candidate genes for Pur1. Arp3-mediated actin assembly abnormalities were visible in immunohistochemical and electron microscopic examinations of podocytes in old BUF/Mna rats. Taken together, these data suggest that Arp3 is a candidate for the Pur1 gene. This observation is consistent with our growing recognition that abnormal signaling-induced assembly of actin in podocytes leads to the development of FSGS.

Renal ageing

The function of the kidney, as well as its morphology, changes markedly with age. The glomerular filtration rate falls progressively, independent of overt pathology. Glomerular, vascular and accompanying parenchymal changes occur and other disorders associated with ageing, such as diabetes and hypertension, have a stochastic deleterious effect on both form and function. Declining renal function with age has important implications, not only for individual homeostasis but also for the use of drug therapy and for the receipt and donation of organs for transplantation. Molecular mechanisms and cellular changes underlying some of the functional and structural changes associated with ageing are becoming clearer, as are some of the ways in which genetic background, age and disease can combine to produce functional damage.

Involvement of Transglutaminase-2 in Pathological Changes in Renal Disease

BACKGROUND

Transglutaminase (Tg)-2 is shown to be related to renal fibrosis. However, its roles in human kidney disease have not been fully studied.

METHODS

Using immunohistochemistry, we examined Tg-2 expression in renal biopsy specimens from 22 patients with IgA nephropathy (IgAN) and correlated the intensity of Tg-2 staining with clinical and histopathological parameters. We compared the distribution and intensity of Tg-2 staining with those of transforming growth factor (TGF)-beta staining.

RESULTS

In normal human kidneys, Tg-2 staining was not significant. In IgAN kidneys, glomerular Tg-2 staining correlated with serum creatinine (S-Cr), creatinine clearance (Ccr), urinary protein excretion, glomerular sclerosis, and mesangial cell proliferation. Tubulointerstitial Tg-2 correlated with S-Cr, Ccr, N-acetyl-beta-glucosaminidase, urinary beta(2)-microglobulin, and tubulointerstitial injuries. Tg-2 staining in the vicinity of vascular poles of glomeruli preceded the development of mesangial lesions, and was more remarkable in cases with renal impairment. The distribution and intensity of Tg-2 staining were not consistent with those of TGF-beta staining. In glomerular crescents, Tg-2 staining was remarkable.

CONCLUSION

The present study showed a correlation between Tg-2 expression and renal function and pathological changes. Tg-2 expression in the vicinity of vascular poles was notable because that may be an initial marker of glomerular injury.

Cellular focal segmental glomerulosclerosis: Clinical and pathologic features

Five pathologic variants of idiopathic focal segmental glomerulosclerosis (FSGS) are recognized: collapsing (COLL), cellular (CELL), glomerular tip lesion (GTL), perihilar, and not otherwise specified (NOS). The prognostic significance of CELL FSGS has not been determined. We compared the presenting clinical and pathologic characteristics in 225 patients with CELL (N=22), COLL (N=56), GTL (N=60), and NOS (N=87) variants of idiopathic FSGS. CELL, COLL, and tip lesion all showed greater frequency and severity of nephrotic syndrome, and shorter time to biopsy compared to NOS. Predictors of end-stage renal disease (ESRD) for all FSGS patients included initial serum creatinine, % global sclerosis, % COLL lesions, chronic tubulo-interstitial injury score, and lack of remission response. COLL FSGS had the highest rate of renal insufficiency at presentation, most extensive glomerular involvement and chronic tubulo-interstitial disease, fewest remissions (13.2%), and highest rate of ESRD (65.3%). GTL patients were older and showed the highest remission rate (75.8%) and lowest rate of ESRD (5.7%). CELL variant showed intermediate rates of remission (44.5%) and ESRD (27.8%) compared to COLL and tip lesion. CELL variant may include cases of unsampled tip or COLL lesion, underscoring the importance of adequate sampling. Our data support the view that CELL and COLL FSGS are not equivalent and validates an approach to pathologic classification that distinguishes between COLL, CELL, and tip lesion variants of FSGS.

Pathways to nephron loss starting from glomerular diseases-insights from animal models

Studies of glomerular diseases in animal models show that progression toward nephron loss starts with extracapillary lesions, whereby podocytes play the central role. If injuries remain bound within the endocapillary compartment, they will undergo recovery or be repaired by scaring. Degenerative, inflammatory and dysregulative mechanisms leading to nephron loss are distinguished. In addition to several other unique features, the dysregulative mechanisms leading to collapsing glomerulopathy are particular in that glomeruli and tubules are affected in parallel. In contrast, in degenerative and inflammatory diseases, tubular injury is secondary to glomerular lesions. In both of the latter groups of diseases, the progression starts in the glomerulus with the loss of the separation between the tuft and Bowman's capsule by forming cell bridges (parietal cells and/or podocytes) between the glomerular and the parietal basement membranes. Cell bridges develop into tuft adhesions to Bowman's capsule, which initiate the formation of crescents, either by misdirected filtration (proteinaceous crescents) or by epithelial cell proliferation (cellular crescents). Crescents may spread over the entire circumference of the glomerulus and, via the glomerulotubular junction, may extend onto the tubule. Two mechanisms concerning the transfer of a glomerular injury onto the tubulointerstitium are discussed: (1) direct encroachment of extracapillary lesions and (2) protein leakage into tubular urine, resulting in injury to the tubule and the interstitium. There is evidence that direct encroachment is the crucial mechanism. Progression of chronic renal disease is underlain by a vicious cycle which passes on the damage from lost and/or damaged nephrons to so far healthy nephrons. Presently, two mechanisms are discussed: (1) the loss of nephrons leads to compensatory mechanisms in the remaining nephrons (glomerular hypertension, hyperfiltration, hypertrophy) which increase their vulnerability to any further challenge (overload hypothesis); and (2) a proteinuric glomerular disease leads, by some way or another, to tubulointerstitial inflammation and fibrosis, accounting for the further deterioration of renal function (fibrosis hypothesis). So far, no convincing evidence has been published that in primary glomerular diseases fibrosis is harmful to healthy nephrons. The potential of glomerular injuries to regenerate or to be repaired by scaring is limited. The only option for extracapillary injuries with tuft adhesion is repair by formation of a segmental adherent scar (i.e., segmental glomerulosclerosis).

Evolution of nephrotic-associated focal segmental glomerulosclerosis and relation to the glomerular tip lesio11See Editorial by Haas,P. 1188

BACKGROUND

Several entities or variants within focal segmental glomerulosclerosis (FSGS) have been described, but their changes with time and interrelationships are undetermined.

METHODS

Changes with time were studied in two series of segmental sclerosing lesions in the nephrotic syndrome, one of 22 specimens from ten patients in a trial, the other of 176 specimens from 121 consecutive patients.

RESULTS

The earliest lesions were probably all at the tubular origin, equivalent to the tip variant of FSGS. In some patients, lesions remained at this site, but progression to renal failure was accompanied by morphologic progression, with development of lesions at various sites, equivalent to FSGS, not otherwise specified (NOS). Progression was more likely if there were large lesions, abnormal mesangium, and extensive acute tubular damage. Patients with lesions at the tubular origin at presentation had a shorter duration of symptoms and less chronic renal damage than those with multiple lesions, were more likely to have a complete response of the nephrotic syndrome, and were less likely to progress to renal failure. Recurrent nephrotic syndrome occurred in 12 of 14 allografts at risk, and was usually accompanied by lesions at the tubular origin, then multiple lesions.

CONCLUSION

At least some patients with FSGS (NOS) have evolved from the tip variant. The tip variant has been considered a distinct entity. Another interpretation is that it includes two conditions, one an early form of classic FSGS, and the other closely related to minimal change nephropathy (MCN), equivalent to the glomerular tip lesion as originally defined.

Glomerular tip lesion: a distinct entity within the minimal change disease/focal segmental glomerulosclerosis spectrum

BACKGROUND

The glomerular tip lesion (GTL) is a distinctive but controversial histopathologic lesion occurring in patients with idiopathic nephrotic syndrome. The relationship of GTL to minimal change disease (MCD) and idiopathic focal segmental glomerulosclerosis (FSGS) has been disputed.

METHODS

In order to define the clinical features and natural history of GTL, we retrospectively reviewed the presenting clinical features, biopsy findings and outcome of 47 cases. Presenting clinical features of GTL were compared to those of controls with MCD (N= 61) or idiopathic FSGS (N= 50).

RESULTS

The cohort of GTL consisted of 45 adults and two children (mean age 47.5 years; range 12 to 79 years), including 76.6% Caucasians and 53% males. At presentation, 93.6% of patients had edema, 89.1% had nephrotic syndrome (mean urine protein 8.31 g, mean serum albumin 2.27 g/dL, and mean cholesterol 340.6 mg/dL), and 34.8% had renal insufficiency. Mean time from onset of renal disease to biopsy was 2.4 months. At biopsy, glomerular segmental lesions included GTL alone in 26%, GTL and peripheral lesions in 6%, GTL and indeterminate lesions in 36%, and GTL with peripheral and indeterminate lesions in 32%. No initial biopsy contained perihilar sclerosis and most (81%) segmental lesions were cellular. Follow-up data were available in 29 patients, of whom 21 received steroids alone and eight received sequential therapy with steroids and a cytotoxic agent. At a mean follow-up of 21.5 months, 58.6% of patients achieved complete remission of nephrotic syndrome, 13.8% had partial remission, and 27.6% had persistent nephrotic proteinuria. Only one patient progressed to end-stage renal disease (ESRD). Predictors of nonremission included severity of proteinuria at presentation and % peripheral lesions. When compared to controls with MCD and idiopathic FSGS, GTL more closely resembled MCD with respect to high incidence of nephrotic syndrome (P < 0.001), severity of proteinuria (P < 0.05), short duration from onset to biopsy (P < 0.001), and absence of chronic tubulointerstitial disease (P < 0.0054).

CONCLUSION

Within the MCD/FSGS spectrum, GTL is a distinctive and prognostically favorable clinical-pathologic entity whose presenting features and outcome more closely approximate those of MCD.

Evidence that soyasaponin Bb retards disease progression in a murine model of polycystic kidney disease

BACKGROUND

We reported a lessened cyst growth in the pcy mouse model of polycystic kidney disease (PKD) when mice were fed a soy protein isolate (SPI)-based diet and hypothesized that the soyasaponins may be associated with this therapeutic effect. The effects of feeding a saponin-enriched alcohol extract (SEAE) from SPI, an isoflavone- and saponin-enriched soy supplement (Novasoy 400), or a 99.5% pure soyasaponin Bb powder on cyst growth are reported here.

METHODS

The therapeutic effects of the soyasaponins were studied in 60-day-old male pcy mice in two separate, 90-day feeding trials. In the first study, mice were fed either a casein-based (control) diet, a diet in which SPI replaced the casein or the control diet supplemented with SEAE. In the second study, mice were fed the control diet unsupplemented or supplemented with either a soyasaponin- and isoflavone-enriched soy product (Novasoy 400) or a 99.5% pure soyasaponin Bb powder.

RESULTS

In study 1, kidney weight, water content, and plasma creatinine and urea levels were markedly reduced in the SEAE-fed animals compared to tissues from the control group; likewise, mice fed the SPI-based diet showed a decreased plasma creatinine, but only a slightly reduced plasma urea. In study 2, kidney weight, water content, plasma creatinine and urea levels were significantly reduced in mice fed the soyasaponin Bb powder and the Novasoy-400 supplement, compared to controls.

CONCLUSION

Soyasaponin Bb can impede kidney enlargement and cyst growth in the pcy mouse model of PKD. Further studies are needed to determine its most effective dose and mechanism of action.

Animal models of FSGS: lessons for pathogenesis and treatment

Glomerulosclerosis in a heterogeneous pattern, ie, focal and segmental glomerulosclerosis (FSGS), is a common endpoint in a variety of settings, including idiopathic FSGS, and scarring secondary to other renal or systemic diseases. These different causes contribute to the diverse clinical outcomes of histological focal sclerosis, and the varying histologic manifestations of sclerosis. Numerous models have been established in the rat that aim to mirror the various elements of human glomerulosclerosis. With the availability of knockout gene technology, many, but not all of these models have been translated to mouse species. This review will focus on the remnant kidney model, the podocyte injury models of puromycin aminonucleoside or adriamycin injection, and examples of newly developed genetic models, such as knockout of CD2 associated protein (CD2AP).

The glomerulo-tubular junction: a target in renal diseases

Both global and segmental glomerulopathies may damage specific areas of the renal glomerulus. Diseases associated with glomerular hyperperfusion cause lesions at the vascular pole, while diseases associated with proteinuria often damage the tubular pole. Atubular glomeruli are now known to be plentiful in a variety of common renal diseases. These glomeruli are disconnected from their tubule at the tubular pole and therefore cannot participate in the production of urine. It is widely believed that the disconnection is a result of external compression by periglomerular fibrosis. However, the variable anatomy and cell populations within both the glomerulus and the beginning of the proximal tubule at the glomerulo-tubular junction may also have important roles to play in the response to damage at this sensitive site of the nephron.

Glomerular prolapse as precursor of one type of segmental sclerosing lesions

A distinctive segmental glomerular abnormality is confined to the region of the tubular opening. The hypothesis was that this followed prolapse of the tuft into the tubule. Analysis was made of 39 renal biopsy specimens with acute postinfective glomerulonephritis, later material from ten cases, four specimens from three women with pre-eclampsia, and 21 control specimens, with morphometry of glomeruli and immunohistological examination for immunoproteins and monocytes/macrophages. Prolapse was found in 14 specimens with acute postinfective glomerulonephritis, associated in eight with adhesion to Bowman's capsule and local alterations in the tuft, which together constitute early tip changes. Another three had early tip changes only and eight others had thin adhesions between the tuft and capsule next to the tubular opening. Later material confirmed this order of development and showed another late change, with sclerosed and hyaline material in the tuft and adhesion at the tubular origin. Findings in pre-eclampsia were comparable. Glomeruli were significantly larger in acute postinfective glomerulonephritis than in controls and were shown by others to be larger in pre-eclampsia than in normal pregnancy. Immunohistology showed IgM and a few foamy monocytes/macrophages in early tip changes but not in prolapsed loops. Glomerular prolapse appears to be a temporary consequence of acute enlargement of the tuft, probably causes mechanical damage to epithelial cells, and is a precursor of permanent structural changes near the tubular origin. This gives a unifying hypothesis to explain how these changes can be seen in acute postinfective glomerulonephritis, pre-eclampsia, and many other human and experimental renal disorders.

Progression of glomerular diseases: is the podocyte the culprit?

The stereotyped development of the glomerular lesions in many animal models and human forms of progressive renal disease suggests that there are common mechanisms of disease progression. We propose the outline of such a mechanism based on following aspects: (1) The glomerulus is a complex structure, the stability of which depends on the cooperative function of the basement membrane, mesangial cells and podocytes, counteracting the distending forces originating from the high glomerular hydrostatic pressures. Failure of this system leads to quite uniform architectural lesions. (2) There is strong evidence that the podocyte is incapable of regenerative replication post-natally; when podocytes are lost for any reason they cannot be replaced by new cells. Loss of podocytes may therefore lead to areas of "bare" GBM. which represent potential starting points for irreversible glomerular injury. (3) Attachment of parietal epithelial cells to bare GBM invariably occurs when bare GBM coexists with architectural lesions, leading to the formation of a tuft adhesion to Bowman's capsule, the first "committed" lesion progressing to segmental sclerosis. (4) Within an adhesion the tuft merges with the interstitium, allowing filtration from perfused capillaries inside the adhesion towards the interstitium. The relevance of such filtration is as yet unclear but may play a considerable role in progression to global sclerosis and interstitial fibrosis.

Tuft-to-capsule adhesions and their precursors: differences between the vascular and tubular poles of the human glomerulus

Human glomerular capillary tufts were removed by microdissection and scanning electron microscopy was used to examine the surface of the capillary tuft and the interior of its Bowman's capsule in order to identify connections between the tuft and capsule. Glomeruli were examined in histologically normal renal cortex from 12 kidneys removed for tumour and 12 renal allografts removed for end-stage rejection. In normal kidney, the glomerular tuft was connected to Bowman's capsule by single podocytes and their processes. At the vascular pole, these were predominantly associated with parietal podocytes which lined Bowman's capsule. At the tubular pole, occasional podocytic processes derived from the capillary tuft bridged Bowman's space and connected to Bowman's capsule where there were no parietal podocytes. These podocytic connections were also found in all rejected transplants, but in addition adhesions were identified which consisted of thicker connections between the tuft and capsule. At the vascular pole, tuft-to-capsule adhesions were found in all 12 kidneys; these were always associated with parietal podocytes. Tubular pole adhesions were identified in ten of the 12 transplants. They were associated with abnormal squamous cells, but not with parietal podocytes. When the capillary tuft herniated into the proximal tubule, the tuft sometimes formed an adhesion with the origin of the proximal tubule. These observations suggest that podocyte connections between the glomerular tuft and Bowman's capsule may be precursors of glomerular adhesions at the vascular pole. Since tuft-to-capsule adhesions at the vascular pole differ morphologically from those at the tubular pole, this may reflect different pathogenetic mechanisms at the opposite poles of the glomerulus.

The development of focal segmental glomerulosclerosis in masugi nephritis is based on progressive podocyte damage

We analysed the sequence of structural changes leading to focal segmental glomerulosclerosis (FSGS) in chronic Masugi nephritis. The protocol resulted in an immediate onset of the disease and the development of segmental sclerosis in a considerable proportion of glomeruli within 28 days of serum injection. Throughout the study, the degree of structural damage was significantly correlated with protein excretion. Even 1 day after injection of the serum, the whole spectrum of early lesions was encountered involving all three cell types. Endothelial detachments, mesangiolysis and podocyte foot process effacement were most prominent. There was focal persistence of capillary microthrombosis but, generally, mesangial and endothelial injuries recovered. The development of podocyte lesions was different: on one hand recovery was seen leading to the re-establishment of an interdigitating foot process pattern, and on the other persistent podocyte detachments from peripheral capillaries allowed the attachment of parietal epithelial cells to "naked" portions of the glomerular basement membrane (GBM), and thus to the formation of a tuft adhesion to Bowman's capsule. Progressive podocyte degeneration at the flanks of an adhesion permitted expansion of the adhesion by encroachment of parietal cells onto the tuft along the denuded GBM. Inside an adhesion, capillaries and mesangial areas either collapse or become obstructed by hyalinosis or thrombosis. Resident cells disappear progressively from inside an adhesion; macrophages may invade. Segmental sclerosis in this model consists of collapsed tuft structures adhering broadly to the cortical interstitium. Proliferation of mesangial cells did not contribute to this development. Recovery of endothelial and mesangial lesions was associated with cell proliferation in early stages of the disease; podocyte proliferation was not encountered at any stage. We conclude that the inability to replace an outmatched podocyte crucially underlies the development of sclerosis. Severe podocyte damage cannot be repaired but leads to tuft adhesions to Bowman's capsule followed by progressive collapse of tuft structures inside an adhesion, resulting in segmental glomerulosclerosis.

Wild-type p53 transgenic mice exhibit altered differentiation of the ureteric bud and possess small kidneys

Transgenic mice expressing wild-type murine p53 under the control of the mouse mammary tumor virus long terminal repeat (MMTV LTR) undergo progressive renal failure due to abnormal kidney development. Similar phenotypes are observed in two transgenic lines that express wild-type p53 within the ureteric bud but not in transgenic animals expressing a dominant-negative p53 mutant allele. Defective differentiation of the ureteric bud, as evidenced by altered marker expression during development, accompanies expression of the p53 transgene. At E17.5-18.5, metanephric mesenchymal cells undergo high rates of apoptosis, and fewer cells than normal are converted to tubular epithelium. As a result, p53 transgenic kidneys grow to only half of their expected size and contain about half of the normal number of nephrons, with compensatory hypertrophy of the glomeruli. In this setting, rather than arrest the cell cycle or induce apoptosis directly, abnormally high levels of wild-type p53 appear to alter cellular differentiation in embryonic ureteric buds and cause secondary effects (apoptosis and inefficient conversion to epithelium) in the adjacent undifferentiated mesenchyme.

Long-term treatment of rats with FGF-2 results in focal segmental glomerulosclerosis

Long-term treatment (8 and 13 weeks) of rats with FGF-2 led to albuminuria and to increase in serum creatinine indicating the development of chronic renal failure. Histologically, the classic picture of focal segmental glomerulosclerosis (FSGS) was found; males were more severely affected than females. Among the early changes podocyte lesions were most prominent. Surprisingly, mitotic figures in podocytes and a considerable fraction of bi(multi)nucleated podocyte profiles were found in treated animals (roughly 16% in males, 8% in females). Since an increase of cell number of podocytes was not evident, we conclude that FGF-2 stimulates podocytes to re-enter the cell cycle and to undergo mitosis (nuclear division). However, podocytes-probably due to their highly differentiated cell shape in the adult-are unable to complete cell division (cytokinesis) resulting in bi- or multinucleated cells; in others cell division may fail totally leading to podocyte degeneration. Most podocytes in FGF-2-treated rats exhibited degenerative changes including cell body attenuation, extensive pseudocyst formation, widespread foot process effacement, as well as detachments from the glomerular basement membrane (GBM). The development of FSGS in this model is very uniform. In the case of podocyte detachments from peripheral capillaries, parietal cells become attached to naked GBM-areas, establishing the nidus for development of a tuft adhesion to Bowman's capsule. Tuft adhesions grow by encroaching of parietal cells onto adjacent capillary loops, resulting eventually in a solid synechia with collapsed capillaries, that is, what represents segmental sclerosis. The distribution of adhesions on the inner surface of Bowman's capsule appeared to be random, including all locations between the vascular and urinary pole. The two main aspects of this study (inability of podocytes to replicate and development of FSGS based on progressing podocyte degeneration) may be part of a vicious cycle. FGF-2 stimulates podocytes to enter cell division thereby conveying them into a hazardous situation. If a podocyte fails and degenerates it cannot be replaced, aggravating the situation for the remaining cells and possibly increasing their predisposition to respond to mitogenic stimuli. Similar mechanisms may constitute the development of FSGS in other experimental as well as human glomerulopathies.

Pathogenesis of segmental glomerular changes at the tubular origin, as in the glomerular tip lesion

Segmental abnormalities at the glomerulo-tubular junction, or tip changes, are a common and early feature in several experimental and human renal disorders. Scanning and transmission electron microscopic study of an experimental model, Lewis rats given anti-glomerular basement membrane antibodies, showed that at 5 days there were monocytes/macrophages in glomerular capillary loops next to the tubular origin, with abnormalities of visceral epithelium, including prolapse of groups of these cells into the tubular origin. At 12 days, there was contact and adhesion between glomerular capillary loops and Bowman's capsule. Transmission electron microscopic study of human renal biopsies showed that the human tip changes resembled the later lesions seen in rats, with intracapillary foam cells confirmed by immunohistological study to be monocytes/macrophages. These findings show that abnormalities of the glomerular tuft precede adhesion to Bowman's capsule and that the earliest changes recognized by light microscopy in human renal biopsies are relatively late in their natural history, meaning at least several days old. Prolapse of visceral epithelial cells into the tubular origin may explain the characteristic site of tip changes.

Glomerular morphometry in childhood reflux nephropathy, emphasizing the capillary changes

As a consequence of nephron loss, reflux nephropathy (RN) causes considerable glomerular hypertrophy. To examine the relative contributions of capillary dilatation and growth in producing hypertrophy, glomeruli contained in unscarred areas of renal biopsies from 19 children with RN were compared with those in 16 children with minimal change nephrotic syndrome and 16 with recurrent hematuria, who were used as controls representing normal childhood growth. Using computerized digitometry we measured the mean glomerular tuft area (GTA) in all complete, undistorted, nonsclerotic glomeruli in periodic acid-Schiff (PAS) stains. Measurements were repeated in four glomeruli of uniform size in periodic acid-silver methenamine stains, the results (GTA4) correlating significantly with GTA. In the same four glomeruli we measured the mean individual capillary luminal area (CLA) and counted the mean number of lumens per glomerulus (N). Mean mesangial area (MA) was calculated as GTA4 - (CLA x N). Cells per distal mesangial region were counted in PAS stains. GTA, GTA4, N, MA and mesangial cell counts were significantly greater in RN than controls, but CLA and fractional MA (MA/GTA%) did not differ. N correlated highly significantly with GTA4 in both RN and controls, but CLA did not do so. These findings are consistent with capillary growth by subdivision being the main mechanism of glomerular hypertrophy when nephron loss occurs during childhood, and the identity of the regressions of N versus GTA4 in RN and controls suggests that compensatory hypertrophy resembles the normal glomerular growth pattern in this age group.

Focal segmental glomerular sclerosis, a type of intractable chronic glomerulonephritis, is a stem cell disorder

The etiopathogenesis of focal and segmental glomerular sclerosis (FGS) remains unknown. Using a new animal model for FGS (FGS mouse), we demonstrate here that bone marrow transplantation from normal mice to FGS mice with a high grade of proteinuria (+ + +) ameliorates FGS, and that the transplantation of bone marrow cells or purified hemopoietic stem cells (HSCs) from FGS mice induces FGS in normal mice. These findings strongly suggest that FGS is a stem cell disorder; the abnormalities may be genetically programmed at the level of HSCs.

Segmental sclerosing glomerular lesions

Segmental sclerosing glomerular lesions are usually all grouped together and called focal segmental glomerulosclerosis. This has meant that the term that was originally used for a defined clinical entity is now applied to a variety of conditions in man and experimental animals, with the assumption that the morphological changes are the same in all conditions. Studies of the position of segmental lesions within glomeruli, the size of glomeruli and the proportion of glomeruli affected have shown that this assumption is wrong. Such studies have identified a disease that corresponds to the original clinical concept of focal segmental glomerulosclerosis. This begins with the nephrotic syndrome in patients whose renal biopsies show large glomeruli with mesangial hypercellularity and segmental lesions at every tubular origin. Later the biopsies have segmental lesions throughout the glomerular tuft. This disease differs clinically and pathologically from other conditions that have segmental sclerosing lesions, such as in patients with reduced renal mass or patients with hypertension and proteinuria. The term focal segmental glomerulosclerosis is now too ambiguous and unsatisfactory to be used without qualification.

Glomerular morphometry in reflux nephropathy: functional and radiological correlations

Using computerized digitometry, we investigated the relationships between renal size, glomerular filtration rate (GFR), proteinuria, incidence of segmental and global glomerulosclerosis, glomerular size, hilar arteriolar wall thickness and hyaline deposition in renal biopsies obtained from 24 children and adolescents with reflux nephropathy, of whom only 4 were hypertensive. Age-matched controls comprised minimal-change nephrotic syndrome (6) and recurrent haematuria with normal biopsy (13). The mean sectional area of patients' glomeruli was double that of controls. Glomerular size correlated with the amount of proteinuria (measured as protein/creatinine ratios in early morning urine) and inversely with renal size and GFR. Segmental sclerosis, invariably of hilar origin, was observed in 8 patients and the percentage of glomeruli affected correlated strongly with glomerular size and proteinuria. Global sclerosis was found equally in patients and controls, and showed no similar correlations. Compared with controls, patients' hilar arterioles showed increased wall thickness, more intramural hyaline deposits and decreased luminal diameter when related to glomerular size. The proteinuria and glomerular changes are consistent with hyperfiltration, while the previously undescribed hilar vascular changes, which both precede and accompany sclerosis, resemble abnormalities reported experimentally following renal ablation.

Effect of cholesterol on the position of segmental lesions in unilaterally nephrectomized rats

Different positions of segmental lesions within glomeruli may correspond to different pathogenetic mechanisms. The effect of a high cholesterol diet on the position of lesions had not previously been investigated. This was studied in rats following unilateral nephrectomy, as a change in position would suggest a different mechanism of damage. Thirty-two female WAG/ola rats had unilateral nephrectomy. Half the rats were given a diet supplemented with 4 per cent cholesterol and 1 per cent cholic acid. At death, six at 10 weeks after nephrectomy and the rest at 24 weeks, kidney sections were examined microscopically. There were significantly more segmental lesions in the cholesterol-fed rats than in the controls, and these lesions were almost entirely at the glomerular hilum in both groups. Significantly more glomeruli contained foamy cells in the cholesterol-fed group, both within lesions and away from them. These findings confirmed that in reduced renal mass, segmental lesions are mainly hilar. The diet increases the number of glomeruli affected by lesions, but these are still mainly hilar. Therefore one possibility is that hypercholesterolaemia worsens the hyperfiltration effect on glomeruli. The diet also produces foamy cells scattered throughout the glomeruli but these do not appear to develop into segmental lesions.

Glomerular capsular herniation in focal glomerular sclerosis

Renal biopsy from a patient with focal segmental sclerosing glomerulopathy (FSSG) and nephrotic syndrome showed localized rupture of Bowman's capsule with herniation of a glomerular loop into the adjacent periglomerular connective tissue. Another glomerulus contained similar changes. Glomerular capsular herniation may be frequent, but unrecognized, in FSSG and would explain many of the morphological features seen in both primary and secondary forms.

Protein-loading test, urinary albumin excretion and renal morphology in diagnosis of subclinical diabetic nephropathy

The acute effects of protein loading (1.5 g kg-1) on glomerular filtration rate (GFR) and urinary albumin excretion (UAE) were investigated in 23 type-I diabetic patients with no clinical nephropathy, and in 7 healthy subjects (controls). The results were compared with renal morphology data. In controls and in 14 diabetic patients (group 1) GFR increased by 27 and 37%, respectively, corresponding to normal renal reserve, but in 9 patients (group 2) GFR decreased by 20%, indicating the absence of a renal reserve. Microalbuminuria was found in none of the patients in group 1 and in 50% of patients in group 2. Two hours after the load UAE increased in all groups, but the increase was most marked in group 2, despite the fall in GFR. The two groups of patients did not differ with regard to the duration and control of diabetes, but differed markedly in terms of baseline GFR (131 vs. 195 ml min-1, P less than 0.01, in groups 1 and 2, respectively). Renal morphology showed minimal non-specific glomerular injury in group 1, and signs of glomerulosclerosis in group 2. We conclude that the impaired renal response to protein load precedes other subclinical manifestations of diabetic renal injury, and may be useful in the diagnosis of latent diabetic nephropathy.

Prognostic significance of proteinuria one year after onset of diarrhea-associated hemolytic-uremic syndrome

We examined the prognostic value of changes in the amount of proteinuria, measured as protein/creatinine ratios in early-morning urine samples, in 40 children who had had diarrhea-associated hemolytic-uremic syndrome. One year after diagnosis, 87% of those who seemed to have fully recovered had normal urinary protein/creatinine ratios, compared with none of those with poor outcomes (p less than 0.001). None of those with poor outcomes achieved normal protein/creatinine ratios during follow-up to a maximum of 5 1/2 years, but 93% of those who made a full clinical recovery no longer had proteinuria. Measurement of the protein/creatinine ratio in an early-morning sample of urine is a simple, cost-effective, and noninvasive means of monitoring the progress of patients with diarrhea-associated hemolytic-uremic syndrome, provided that a technique sensitive at low protein concentrations is employed.

Renal functional reserve in diabetic patients without clinical nephropathy: comparisons with renal morphology

The acute effect of a protein loading test (1.5 g kg-1) on glomerular filtration rate (GFR) was examined in 10 Type 1 diabetic patients without clinical nephropathy to evaluate the renal functional reserve. GFR was measured before (baseline) and after (test) ingestion of the protein load. Two groups of diabetic patients were distinguished: those who exhibited normal renal reserve equal to that in healthy individuals (change in GFR 35 +/- 17 (+/- SD)%) and those who had no renal reserve (change in GFR -20 +/- 20%). These groups did not differ in the duration and control of diabetes nor in the level of urinary albumin excretion. However baseline GFR was 120 +/- 34 and 209 +/- 46 ml min-1 in diabetic patients with and without renal reserve, respectively. Renal morphology revealed hilar glomerular lesions composed of severely expanded mesangium only in diabetic patients without renal reserve. Minimal structural nephropathy was observed in those who exhibited normal renal reserve. We suggest that the impaired response of GFR to protein loading precedes other subclinical manifestations of renal lesions in diabetic patients.

Determinants of glomerular cross-sectional area

A method of measurement of glomerular cross-sectional area was applied to 267 renal biopsies from 19 groups of patients with well-defined pathological and clinical conditions. There was a correlation between the mean glomerular area for each group and the percentage of global sclerosis in each group. A few groups had glomeruli that were larger than would be expected from their percentage of global sclerosis, probably due to cellular proliferation and/or infiltration. A few groups had glomeruli that were smaller than would be expected from their percentage of global sclerosis, probably due to ischaemic shrinkage. These observations indicate that as well as the known influence of body size on the glomerular area, the number of functioning glomeruli in the body has an important effect on the glomerular area.

The glomerular changes in children with reflux nephropathy

While heavy proteinuria and focal segmental glomerulosclerosis (FSGS) are well-recognized features of progressive reflux nephropathy in adults, little is known of their early evolution. We have studied the glomerular changes in renal biopsy specimens obtained from 24 patients aged 5.2-18.8 years, in whom urinary protein excretion was measured as early morning urine protein creatinine ratios, using the Coomassie blue dye-binding method. Segmental sclerotic lesions were found in eight biopsies and traced through serial sections to a hilar origin in every instance. There was a strong positive correlation between the extent of glomerular involvement and the amount of proteinuria (P less than 0.0001). Parahilar hyaline deposits were observed in 16 biopsies, including five of the eight showing FSGS. All unsclerosed glomeruli were enlarged, and the hilar arterioles showed both enlargement and thickening, their walls frequently containing subendothelial hyaline deposits. Since in most patients renal function was comparatively well preserved, despite extensive loss of renal substances, we believe that these glomerular and vascular changes represent the stages in the evolution of hyperfiltration. Microproteinuria is the earliest clinical manifestation of FSGS, and should be sought routinely in all patients with reflux nephropathy.

Analysis of the position of segmental lesions in glomeruli in vasculitic-type glomerulonephritis and other disorders

A method was developed of plotting the position of segmental lesions in glomeruli on histological sections of kidney. Using a Leitz Imagan semi-automatic image analyser, the outline of lesions was traced, as was the outline of Bowman's capsule. The centre of gravity of a lesion, computed by the image analyser, was plotted with reference to the line through the hilum and the centre of gravity of the glomerulus, by taking its angle to that line and its proportional distance between that line and Bowman's capsule. Points representing all lesions were transferred onto a circle graphically representing a glomerulus. Lesions in 11 renal biopsies with the glomerular tip lesion were clustered at the tubular origin. Lesions in four necropsy kidneys from patients with one kidney were clustered at both the vascular pole and the tubular origin. Lesions in 13 renal biopsies with acute vasculitic-type glomerulonephritis were shown to be randomly scattered by nearest-neighbour analysis, after allowance had been made for an edge effect due to the method of plotting lesions and for an area where the arterioles passed through Bowman's capsule. Scientific analysis of the position of segmental lesions is possible and has confirmed previous suggestions that there are at least three general sites in which these lesions can be distributed in glomeruli: at the tip, at the vascular pole, and randomly.

Determination of urinary glutathione S-transferase and lactate dehydrogenase for differentiation between proximal and distal nephron damage

Cytosolic glutathione S-transferase (GST) activity is confined to the proximal convoluted and straight tubules. Damage to these parts of the nephron should result in leakage of GST into the urinary space. Lactate dehydrogenase (LDH), in contrast, is more generally distributed along the nephron. Measurement of both enzyme activities could therefore be expected to discriminate between different localizations of nephrotoxicity. To test this hypothesis, we determined both enzyme activities in 24 h urine samples from 10-12 female Sprague-Dawley rats, each treated with single i.p. injections of puromycin aminonucleoside (PAN, 130 mg/kg), Na2 CrO4 10, 20, 30 mg/kg), mercuric chloride (HgCl2, 0.5, 0.75, 1.0 mg/kg), folic acid (125, 350, 375 mg/kg), ethyleneimine (0.5, 2.0, 5.0 microliters/kg). Bovine serum albumin (BSA) was injected by the same method, twice daily on 3 consecutive days (2.5, 7.14 g/kg). The results obtained indicate a characteristic dose- and time-dependent pattern of excreted enzyme activities for each of the tested compounds. In both models with primarily glomerular damage, proximal tubular parts were also affected, as could be demonstrated by increased urinary GST and histopathological changes. Damage, mainly to the S1/S2 segment by 20 or 30 mg Na2 CrO4/kg, resulted in moderate to marked increases in LDH excretion, while GST was only moderately elevated at 30 mg/kg. Extreme increases in GST and LDH output were measured after predominant S3 segment damage after 0.75 and 1.0 mg HgCl2/kg. The distally active compounds, folic acid and ethyleneimine, did not increase GST excretion at lower doses. At the high doses, a small rise in GST excretion indicated some, probably secondary, proximal tubular involvement, which correlated with the histopathological findings in these groups.

A simple method for assessment of glomerular size and its use in the study of kidneys in acromegaly and compensatory renal enlargement

As measurement of absolute glomerular size is difficult we developed a method of assessing glomerular size that was simple and practical and could be used to compare the kidneys in different groups of patients. Using a semi-automatic image analyser, the cross-sectional area of 100 randomly-selected glomeruli, outlined by Bowman's capsule, was measured on sections of kidneys taken at necropsy. The mean of the logarithms of the largest 25 areas was calculated. The method was applied to compare control kidneys (53) with the kidneys in acromegalics (20), in patients with one kidney (10) and in patients with asymmetrical kidneys (12). Kidneys were heavier in the three test groups than in controls. Glomerular sizes were similar in controls and in acromegalics but were larger in single and disparate kidneys. There was a relationship between glomerular size and kidney weight within the control group and across the four groups taken together. This only partly accounted for the observed differences in glomerular size between the groups. Histological comparison of the acromegalic and single kidneys showed more global glomerulosclerosis in single kidneys and also segmental lesions, mainly at the glomerular hilum, only in the single kidneys. These findings show that renal enlargement occurs in acromegaly and in single and disparate kidneys but is accompanied by markedly different glomerular features. This implies different mechanisms for the renal enlargement. The method of assessing glomerular size is useful in the study of these and other conditions affecting the kidney.