Development Of Focal Segmental Glomerulosclerosis Research Articles

Up-Regulation of Connexin43 in Glomerular Podocytes in Response to Injury

Podocyte injury or podocyte loss in the renal glomerulus has been proposed as the crucial mechanism in the development of focal segmental glomerulosclerosis. However, it is poorly understood how podocytes respond to injury. In this study, glomerular expression of connexin43 (Cx43) gap junction protein was examined at both protein and transcript levels in an experimental model of podocyte injury, puromycin aminonucleoside (PAN) nephrosis. A striking increase in the number of immunoreactive dots with anti-Cx43 antibody was demonstrated along the glomerular capillary wall in the early to nephrotic stage of PAN nephrosis. The conspicuous change was not detected in the other areas including the mesangium and Bowman's capsule. Immunoelectron microscopy showed that the immunogold particles for Cx43 along the capillary wall were localized predominantly at the cell-cell contact sites of podocytes. Consistently, Western blotting and ribonuclease protection assay revealed a distinct increase of Cx43 protein, phosphorylation, and transcript in glomeruli during PAN nephrosis. The changes were detected by 6 hours after PAN injection. These findings indicate that the increase of Cx43 expression is one of the earliest responses that have ever been reported in podocyte injury. To show the presence of functional gap junctional intercellular communication (GJIC) in podocytes, GJIC was assessed in podocytes in the primary culture by transfer of fluorescent dye, Lucifer yellow, after a single-cell microinjection. Diffusion of the dye into adjacent cells was observed frequently in the cultured podocytes, but scarcely in cultured parietal epithelial cells of Bowman's capsule, which was compatible with their Cx43 staining. Thus, it is concluded that Cx43-mediated GJIC is present between podocytes, suggesting that podocytes may respond to injury as an integrated epithelium on a glomerulus rather than individually as a separate cell.

Familial focal segmental glomerulosclerosis.

There is increasing recognition of the importance of genetic factors in the development of focal segmental glomerulosclerosis and related proteinuric disorders. Recently, four genes have been identified which, when defective, cause focal segmental glomerulosclerosis or nephrosis. All of these genes appear to be important in the maintenance of glomerular podocyte function. However, not all cases of familial nephrosis or proteinuria are explained by defects in these genes.

Tracer studies in the rat demonstrate misdirected filtration and peritubular filtrate spreading in nephrons with segmental glomerulosclerosis.

In two genetic models of "classic" focal segmental glomerulosclerosis (FSGS), the Milan normotensive and the Fawn-hooded hypertensive rats, tracer studies were performed to test the hypothesis that misdirected glomerular filtration and peritubular filtrate spreading are relevant mechanisms that contribute to nephron degeneration in this disease. Two exogenous tracers, lissamine green and horse spleen ferritin, were administered by intravenous injection and subsequently traced histologically in serial kidney sections. In contrast to control rats, both tracers in kidneys of Milan normotensive and Fawn-hooded hypertensive rats with established FSGS were found to accumulate extracellularly at the following sites: (1) within tuft adhesions to Bowman's capsule and associated paraglomerular spaces, (2) at the glomerulotubular junction contained within extensions of the paraglomerular spaces onto the tubule, and (3) within subepithelial peritubular spaces eventually encircling the entire proximal convolution of an affected nephron. This distribution strongly suggests the existence of misdirected filtration into tuft adhesions to Bowman's capsule and subsequent spreading of the filtrate around the entire circumference of a glomerulus and, alongside the glomerulotubular junction, onto the outer aspect of the corresponding tubule. This leads to an interstitial response that consists of the formation of a barrier of sheet-like fibroblast processes around the affected nephron, which confines the filtrate spreading and, subsequently, the destructive process to the affected nephron. No evidence was found that either misdirected filtration and peritubular filtrate spreading themselves or the associated tubulo-interstitial process led to the transfer of the injury from an affected nephron to an unaffected nephron. It is concluded that in the context of FSGS development, misdirected filtration and peritubular filtrate spreading are important damaging mechanisms that underlie the extension of glomerular injury to the corresponding tubulointerstitium, thus leading finally to degeneration of both the glomerulus and the tubule of a severely injured nephron.

Significance of ACE Genotypes and Medical Treatments in Childhood Focal Glomerulosclerosis

Backtround: There is little information on the significance of angiotensin-converting enzyme (ACE) genotypes and medical treatments in children with primary focal segmental glomerulosclerosis (FSGS). Methods: A multicenter retrospective study was performed on the role of ACE genotypes and medical treatments in 43 Japanese children with FSGS (20 males and 23 females), including 17 children who progressed to end-stage renal failure during the mean observation period of 6.9 ± (SD) 5.0 years. Results: The incidence of the D allele of the ACE gene was higher in the whole group of 43 children with FSGS and in a subgroup of 28 steroid-resistant FSGS children (p < 0.05) than in the 130 children of the healthy control group (0.48, 0.48, and 0.33, respectively). ACE genotypes did not affect renal survival in the whole FSGS group nor in the steroid-resistant subgroup. Among the 28 steroid-resistant children, treatment with ciclosporin was effective in delaying the development of end-stage renal failure (p = 0.044), independently of other treatment regimens. Conclusion: The present study of Japanese children with FSGS showed that the D allele of the ACE gene is associated with the development of FSGS, but not associated with the progression of FSGS which was greatly ameliorated with ciclosporin, irrespective of ACE genotypes.

Phenotypic Characteristics and Cyclin-Dependent Kinase Inhibitors Repression in Hyperplastic Epithelial Pathology in Idiopathic Focal Segmental Glomerulosclerosis

Hyperplastic glomerular epithelial lesion is an important determinant of the progression of idiopathic focal segmental glomerulosclerosis (FGS). The proliferation and differentiation of glomerular epithelial cells and parietal epithelial cells (PECs) are regulated differently by cyclin and cyclin-dependent kinase inhibitors (CKIs) during nephrogenesis. To access the cellular mechanism underlying epithelial hyperplasia in the development of FGS, the present study applied immunohistochemistry to 21 cases of FGS to demonstrate expression of cell-cycle molecules and phenotypic characterization in proliferative epithelial lesions in FGS. The materials included segmental sclerosis (18.1%), which was divided into monolayer epithelial lesions (64.6%) and cellular lesions (35.4%). All of the cellular lesions expressed cytokeratin, frequently with Ki-67 (82.4%) and less frequently with cyclin A (17.7%), but were invariably negative for podocyte markers (PHM-5 and synaptopodin) and CKIs (p27kip1 and p57kip2). Podocytes in nonsclerotic tuft in the same glomeruli with cellular lesions strongly expressed CKIs and podocyte markers. Moreover, electron microscopy showed that some large proliferating cells with prominent nucleoli have a broad cell base attached to Bowman's capsule. These cells have cilia and a junctional complex with neighboring hyperplastic cells, some of which directly cover the glomerular basement membrane. This suggests that cellular lesions are of PEC origin. Monolayer epithelial lesions also exclusively exhibited a PEC phenotype with reciprocal expression of podocyte markers and cytokeratin. In addition, CKIs are weakly expressed in monolayer epithelial lesions, suggesting a re-entry of cell-cycle quiescent. In conclusion, proliferation of PEC, sustained by repression of CKIs in nature and simultaneous activation of cyclin A, is the actual molecular background to the cellular lesions in FGS. Cellular lesions may result in monolayer epithelial lesions that retain the PEC phenotype and enter a common pathway to glomerulosclerosis.

Oxidized LDL, glomerular mesangial cells and collagen

Lipid deposits, foam cell collection and accumulation of mesangial matrix components are recognized as early events in the development of focal segmental glomerulosclerosis (FSGS). Studies have suggested that oxidative stress is increased in uremic patients. Oxidized low-density lipoprotein (Ox-LDL) has been identified in the lesions of FSGS. Dietary antioxidants reduced not only the staining intensity of Ox-LDL but also the severity of renal injury in rats with experimental FSGS possibly by making lipoproteins resistant to oxidation. In vitro studies showed that LDL during its incubation with human mesangial cells (HMC) was peroxidatively modified and stimulated α1(I), α1(III), and α1(IV) collagen mRNA expression. Vitamin E, an antioxidant, and antibody against Ox-LDL caused a marked reduction in collagen mRNA stimulated by LDL. These findings suggest that LDL deposited and oxidized in the glomeruli may be implicated in the development of glomerulosclerosis by facilitating excessive mesangial matrix generation.

Expression of the cyclin kinase inhibitor, p27kip1, in developing and mature human kidney

Expression of the cyclin kinase inhibitor, p27kip1, in developing and mature human kidney

Podocytes undergo phenotypic changes and express macrophagic-associated markers in idiopathic collapsing glomerulopathy

Podocytes undergo phenotypic changes and express macrophagic-associated markers in idiopathic collapsing glomerulopathy

Different effect of estrogen administration from castration on glomerular injury in unilaterally nephrectomized male Sprague-Dawley rats.

We have already reported an equally attenuating effect of castration or estrogen administration on the development of focal segmental glomerulosclerosis (FSGS) in the animal models of a short-term experimental period ended at 24 weeks. In the present study, to clarify the importance of the experimental period in studying the pathogenesis of the development of FSGS, we investigated a long-term effect of castration or estrogen administration on FSGS using an experimental model of uninephrectomized Sprague-Dawley (SD) rats ended at 54 weeks. Thirty male SD rats received unilaterally right nephrectomy at 6 weeks of age. They were divided into three groups: group 1 was control; group 2 was castrated at 6 weeks, and group 3 was administered 0.2 mg estrogen subcutaneously once a month from 6 weeks of age. Body weight, urinary protein, serum albumin and other serum constituents were investigated every 12 weeks from 18 to 54 weeks of age. Each group was studied morphologically at the end of the experiment. Castration attenuated glomerular injury to the same extent as seen in the study of a short-term experimental period, while estrogen administration failed to attenuate glomerular injury, although each treatment equally suppressed an urinary excretion of a sex-related low-molecular-weight (LMW) protein. Castration reduced significantly kidney weight (KW), glomerular volume (GV) and serum growth hormone (GH) levels, but estrogen treatment failed to reduce KW and GV, and conversely elevated GH levels. These results suggest that a sex-related LMW protein influenced by castration or estrogen treatment may not play an important role in the development of FSGS and that an increase in plasma GH levels may contribute to the failure of an attenuating effect of estrogen on glomerular injury.

Focal glomerulosclerosis and maximal glomerular hypertrophy in human nephronopenia.

This study examines the relationship of the degree of glomerular hypertrophy in nephronopenia to the development of focal segmental glomerulosclerosis (FGS) in humans. To this end, group mean glomerular diameters in a variety of acquired and congenital nephronopenic states in native kidneys and long-surviving renal allografts with and without FGS were analyzed and compared. The results indicate that all groups of native nephronopenic kidneys without FGS develop significant and equivalent glomerular hypertrophy. By contrast, long-surviving renal allografts without FGS do not undergo glomerular hypertrophy. For groups with FGS, long-surviving renal homografts had a significantly smaller mean glomerular diameter when compared with any other group of native nephronopenic kidneys. There was no significant difference among group mean glomerular diameters of native nephronopenic kidneys with FGS. Pairwise comparisons in each category of nephronopenia indicated that, except in the groups with uninephrectomy, the mean glomerular diameters were significantly larger in those with FGS than without. These observations are interpreted to indicate that nephronopenic individuals with native kidneys, by undergoing glomerular hypertrophy, consume much or all their capacity for glomerular enlargement. This brings them closer to their maximal diameters at which FGS develops. Finally, long-surviving renal allografts without nephronopenic FGS do not undergo glomerular hypertrophy. However, when FGS develops in long-surviving allografts, it does so at glomerular diameters significantly smaller than in native nephronopenic kidneys, reflecting their decreased capacity to undergo glomerular hypertrophy, acquiring maximal diameters at a smaller dimension than native nephronopenic kidneys.

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.

Attenuating effect of castration or oestrogen administration on glomerular injury in adriamycin‐induced nephropathy of rats

Summary: To clarify the role of sex‐related factors in the development of focal segmental glomerulosclerosis (FSGS) we investigated the effect of castration or oestrogen administration in adriamycin (ADR)‐induced nephropathy of Sprague‐Dawley rats. At 6 weeks of age, group 1 (control group) and group 3 were shamoperated and group 2 was castrated. Adriamycin 2 mg/kg was administered intravenously to all rats at 8 weeks of age twice at a 20‐day interval. Group 3 was administered 0.2 mg oestrogen subcutaneously once a month. Bodyweight (BW) and urinary protein were measured every 4 weeks (mm 15 to 23 weeks of age. Blood pressure and serum constituents were measured at 15 and 23 weeks of age. Each group was studied morphologically at 23 weeks of age. Adriamycin induced massive proteinuria in group 1, whereas castration or oestrogen significantly attenuated proteinuria, accompanied by a significant reduction of urinary sex‐related low molecular weight (LMW) protein. the glomerulosclerosis index was significantly higher in the control group than in the castrated group or oestrogen‐treated group. Attenuation in glomerular injury was more associated with reduction of urinary sex‐related LMW protein than the reduction of serum testosterone. These observations suggest that sex‐related factors, such as a sex‐related LMW protein, influenced by castration or oestrogen administration may play a contributory role in the development of glomerulosclerosis in ADR‐induced nephropathy.

Escherichia coli-macrophage interactions modulate mesangial cell proliferation and matrix synthesis.

Patients with chronic renal interstitital diseases often develop glomerular lesions (focal segmental glomerular sclerosis). Because mesangial expansion (enhanced mesangial cell (MC) growth and matrix accumulation) has been demonstrated to precede the development of focal segmental glomerulosclerosis, we studied the effect of the interaction between bacteria such as Escherichia coli and macrophages on MC proliferation and matrix synthesis. We determined the effect of control media (CM), E. coli supernatant (ESP), serum-free macrophage supernatant (MSP), and E. coli-treated macrophage supernatants (HB101-MSP, H10-MSP) on the proliferation of MCs and synthesis of laminin (a component of mesangial matrix). ESP did not alter MC growth, whereas E. coli MSP increased the mean MC number by 5- to 6-fold when compared to cells treated with CM. Both HB101-MSP and H10-MSP stimulated greater (p < 0.05) incorporation of [3H]thymidine when compared with MSP (HB101-MSP 3.1 +/- 0.4, H10-MSP 2.7 +/- 0.3 vs. MSP 1.6 +/- 0.2 x 10(6) cpm/micrograms protein). When MC proliferation was judged by incorporation of bromodeoxyuridine, both HB101-MSP- and H10-MSP-treated cells showed a greater (p < 0.01) number of proliferating cells compared with cells treated with either MSP or CM. MC treated with H10-MSP grew in a specific pattern and showed a tendency to form hillocks (foci of cell proliferation and matrix aggregation). Both HB101-MSP and H10-MSP enhanced (p < 0.01) synthesis of laminin compared with CM. HB101-MSP-induced enhanced laminin synthesis was attenuated when MCs were treated with anti-transforming growth factor (TGF)-beta antibodies. HB101-MSP also increased mRNA expression of TGF-beta by MCs. These results indicate that E. coli-macrophage interaction has the potential to cause mesangial expansion.

Preliminary description of focal segmental glomerulosclerosis in patients with renovascular disease

Summary Background Primary and secondary forms of focal segmental glomerulosclerosis (FSGS) are common causes of glomerular proteinuria. Secondary forms of FSGS seem to be the result of adaptive changes that follow a reduction in renal mass. We saw an elderly patient with severe bilateral renal vascular disease (RVD) who had FSGS on percutaneous biopsy. To find out whether elderly patients with atherosclerotic RVD are predisposed to the development of FSGS, we reviewed all cases of FSGS at our institution between 1990 and 1995. Methods We identified 59 cases of biopsy-proven FSGS and examined clinical, histological, and radiographic records. Findings Of the 59 patients, 24 were older than 50 years; eight of these had RVD. No patient under the age of 50 had RVD. Seven of the eight patients with RVD and FSGS had substantial proteinuria at presentation. All had typical glomerular lesions with focal segmental tuft collapse and synechiae; other glomeruli were hypertrophic. All patients showed further decline in renal function on follow-up. Interpretation The association of FSGS and RVD may represent an under-recognised aetiology of significant proteinuria in elderly patients.

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.

Experimental focal segmental glomerulosclerosis: correlation with protein excretion, glomerular filtration rate, and renal plasma flow.

A rat model of focal segmental glomerulosclerosis (FSGS) produced by repeated injections of aminonucleoside (AMN) of puromycin was used to evaluate the relative roles of hemodynamic alterations and AMN-induced glomerular visceral epithelial cell injury in the development of FSGS. Twenty rats received three intraperitoneal injections of AMN on days 1, 21, and 28 and developed significant proteinuria. On day 50, 14 rats (group 1) underwent selective left renal perfusion with AMN and six rats (group 2) received left renal perfusion with saline. At sacrifice on day 70 or 110, group 2 rats had similar values in left and right kidneys for glomerular filtration rate (GFR), effective renal plasma flow (ERPF), and the amount of FSGS (13.1 +/- 5.6% in left and 12.9 +/- 7.8% in right). In contrast, group 1 rats manifested a significantly higher amount of FSGS in right kidneys as compared to left kidneys (3.1 +/- 1.3% in left and 6.3 +/- 2.0% in right, as well as significantly diminished GFR and ERPF in left as compared to right kidneys. A higher degree of FSGS was seen in kidneys with a higher GFR and ERPF. A positive correlation was observed between the mean 24-h protein excretion of the rats and the percentage of FSGS in left and right kidneys (r = 0.66, p less than 0.01).