Chronic Tubulointerstitial Damage Research Articles

Proteinuria: detection and role in native renal disease progression

The presence of albuminuria or proteinuria constitutes a sign of kidney damage and, together with the estimation of glomerular filtration rate, is based on the evaluation of chronic kidney disease. Proteinuria is a strong marker for progression of chronic kidney disease, and it is also a marker of increased cardiovascular morbimortality. Filtration of albumin by the glomerulus is followed by tubular reabsorption, and thus, the resulting albuminuria reflects the combined contribution of these 2 processes. Dysfunction of both processes may result in increased excretion of albumin, and both glomerular injury and tubular impairment have been involved in the initial events leading to proteinuria. Independently of the underlying causes, chronic proteinuric glomerulopathies have in common the sustained or permanent loss of selectivity of the glomerular barrier to protein filtration. The integrity of the glomerular filtration barrier depends on its 3-layer structure (the endothelium, the glomerular basement membrane, and the podocytes). Increased intraglomerular hydraulic pressure or damage to glomerular filtration barrier may elicit glomerular or overload proteinuria. The mechanisms underlying glomerular disease are very variable and include infiltration of inflammatory cells, proliferation of glomerular cells, and malfunction of podocyte-associated molecules such as nephrin or podocin. Albumin is filtered by the glomeruli and reabsorbed by the proximal tubular cells by receptor-mediated endocytosis. Internalization by endocytosis is followed by transport into lysosomes for degradation. The multiligand receptors megalin and cubilin are responsible for the constitutive uptake in this mechanism. Albumin and its ligands induce expression of inflammatory and fibrogenic mediators resulting in inflammation and fibrosis resulting in the loss of renal function as a result of tubular proteinuria. TGF-β, which may be induced by albumin exposure, may also act in a feedback mechanism increasing albumin filtration and at the same time inhibiting megalin- and cubilin-mediated albumin endocytosis, leading to increased albuminuria. Urinary proteins themselves may elicit proinflammatory and profibrotic effects that directly contribute to chronic tubulointerstitial damage. Multiple pathways are involved, including induction of tubular chemokine expression, cytokines, monocyte chemotactic proteins, different growth factors, and complement activation, which lead to inflammatory cell infiltration in the interstitium and sustained fibrogenesis. This tubulointerstitial injury is one of the key factors that induce the renal damage progression. Therefore, high-grade proteinuria is an independent mediator of progressive kidney damage. Glomerular lesions and their effects on the renal tubules appear to provide a critical link between proteinuria and tubulointerstitial injury, although several other mechanisms have also been involved. Injury is transmitted to the interstitium favoring the self-destruction of nephrons and finally of the kidney structure.

Mean Glomerular Volume After Renal Transplantation in Patients Receiving Sirolimus and Cyclosporine A Compared With Elimination of Cyclosporine A at 3 Months

Glomerular enlargement after renal transplantation is associated with kidney allograft preservation. Increased glomerular size in donor biopsies is associated with donor age and with increased serum creatinine during follow-up, suggesting that older donors with larger glomeruli have exhausted their capacity for further glomerular adaptation (1). Allografts from younger donors with smaller glomeruli experience further increase of glomerular size after transplantation (2), which is associated with an improvement of renal function. The use of anticalcineurinic agents is associated with vasoconstriction and decreased glomerular filtration rate (GFR) (3). Sirolimus (SRL) has allowed withdrawing cyclosporine A (CsA) early after transplantation as it has been observed in the Rapamune Maintenance Regimen (RMR) study in which a steady improvement of GFR was observed in patients in the CsA withdrawal arm in comparison with the CsA maintenance group (4). We hypothesized that amelioration of GFR in patients after CsA withdrawal is related to glomerular size increase after transplantation. Sixty-four patients from a substudy (5) of the RMR trial conducted in Spain and Portugal with a donor and 1-year paired biopsies were reviewed. Details of the RMR study design and clinical results were published elsewhere (4–6). Of the 64 patients reviewed for this study, only 15 contained at least 10 glomerular sections in both biopsies (6 randomized to CsA elimination at 3 months and 9 maintained with CsA and SRL during the first year). Banff acute and chronic scores were blindly evaluated by a central pathologist. Vg was estimated according to the Weibel and Gomez formula using the mean glomerular area evaluated with an optical pen. Absolute differences between chronic Banff scores and mean glomerular volume (Vg) in both biopsies were calculated. Unpaired comparisons between means were done by Mann-Whitney U test and paired comparisons by Wilcoxon t test. The Vg in the donor and 1-year protocol biopsies in both groups is shown in Figure 1. In the CsA withdrawal group, a significant glomerular enlargement was observed (2.15±0.73× 106 μ3 in the donor and 2.66±0.78×106 μ3 in the 1-year biopsy, P=0.009) whereas in patients maintaining CsA, Vg decreased (2.87±0.81×106 μ3 in the donor and 2.27±0.70×106 μ3 in the 1-year biopsy, P=0.026). The Vg difference between the 1-year and the donor biopsy was significantly different between treatment arms (+0.51±0.31 vs. −0.60± 0.66×106 μ3, P=0.002).FIGURE 1.: Mean glomerular volume in donor and 1-year biopsies from patients randomized to cyclosporine A (CsA) maintenance or elimination at 3 months. Thin lines represent evolution of individual kidneys, and thick lines represent the mean for each group. SRL, sirolimus; P, prednisone.There was a positive correlation between Vg in the donor and 1-year biopsies (R=0.53; P=0.042), and this relationship was closer in patients eliminating CsA at 3 months (R=0.92, P=0.009) than in those maintaining CsA during the first year (R=0.65, P=0.059). The capsular tuft volume fraction was not different between both groups in the donor biopsy (0.58±0.13 vs. 0.61±0.07), whereas in the 1-year biopsy, it was lower in the CsA maintaining group (0.55±0.11 vs. 0.66± 0.34; P=0.045). Glomerular enlargement was associated with a lower progression of chronic lesions (Banff chronic score −0.7±1.0 vs. 2.5±1.7, P<0.01), whereas acute lesions at 1 year were not different between groups. Our data suggest that CsA prevents glomerular adaptation after transplantation and may contribute to explain why estimated GFR was superior in the CsA withdrawal group at 1 and 3 years of follow-up (4). In our study, it is important to remark that in patients receiving CsA and SRL during the first year, glomerular size significantly decreased, which may be the result of a synergistic effect of CsA and SRL impairing glomerular adaptation after renal transplantation by two different mechanisms: renal ischemia and inhibition of glomerular hypertrophy. This hypothesis is further sustained by the observation that 1-year capsule tuft volume fraction was lower in CsA- and SRL-treated patients. The higher degree of chronic tubulointerstitial damage observed in patients treated with CsA and SRL may constitute a third mechanism contributing to the impeded glomerular adaptation in patients receiving CsA and SRL. We have previously shown that interstitial inflammation and interstitial fibrosis are two major predictors of glomerular adaptation after transplantation (7). Thus, worse preservation of interstitial structure in CsA maintenance group may also account for the lack of glomerular adaptation because of peritubular capillary damage associated with interstitial fibrosis and inflammation. In summary, despite the number of cases included is low and consequently, these results should be interpreted with caution, we show that in stable grafts, the combination of CsA and SRL prevents glomerular enlargement after transplantation when compared with CsA withdrawal and SRL continuation. Joana Sellarés1 Francesc Moreso2 Juan Carlos Ruiz3 Daniel Seron2 1 Nephrology Department Hospital Universitari Bellvitge L'Hospitalet, Barcelona, Spain 2 Nephrology Department Hospital Vall d'Hebron Universitat Autonoma Barcelona Barcelona, Spain 3 Nephrology Department Hospital Universitario Marqués de Valdecilla Santander, Spain

Peroxisome Proliferator-Activated Receptor (PPAR)γ Can Inhibit Chronic Renal Allograft Damage

Chronic inflammation and fibrosis are the leading causes of chronic allograft failure. The nuclear receptor peroxisome proliferator-activated receptor (PPAR)gamma is a transcription factor known to have antidiabetogenic and immune effects, and PPARgamma forms obligate heterodimers with the retinoid X receptor (RXR). We have reported that a retinoic acid (RAR)/RXR-agonist can potently influence the course of renal chronic allograft dysfunction. In this study, in a Fischer to Lewis rat renal transplantation model, administration of the PPARgamma-agonist, rosiglitazone, independent of dose (3 or 30 mg/kgBW/day), lowered serum creatinine, albuminuria, and chronic allograft damage with a chronic vascular damage score as follows: 35.0 +/- 5.8 (controls) vs. 8.1 +/- 2.4 (low dose-Rosi; P < 0.05); chronic tubulointerstitial damage score: 13.6 +/- 1.8 (controls) vs. 2.6 +/- 0.4 (low dose-Rosi; P < 0.01). The deposition of extracellular matrix proteins (collagen, fibronectin, decorin) was strikingly lower. The expression of transforming growth factor-beta1 was inhibited, whereas that of bone morphogenic protein-7 (BMP-7) was increased. Intragraft mononuclear cells and activated fibroblast numbers were reduced by 50%. In addition, the migratory and proliferative activity of these cells was significantly inhibited in vitro. PPARgamma activation diminished the number of cells expressing the proinflammatory and fibrogenic proteoglycan biglycan. In macrophages its secretion was blocked by rosiglitazone in a predominantly PPARgamma-dependent manner. The combination of PPARgamma- and RAR/RXR-agonists resulted in additive effects in the inhibition of fibrosis. In summary, PPARgamma activation was potently immunosuppressive and antifibrotic in kidney allografts, and these effects were enhanced by a RAR/RXR-agonist.

Potassium channels: the 'master switch' of renal fibrosis?

Progressive renal fibrosis resulting from proliferation of interstitial fibroblasts is a hallmark of chronic kidney failure, whatever the origin. The intermediate/small-conductance Ca(2+)-activated K(+) channel (K(Ca)3.1) promotes mitogenesis in several cell types by altering the membrane potential, thus enabling extracellular Ca(2+) entry. Grgic et al. evaluated the role of K(Ca)3.1 in renal fibroblast proliferation, testing whether deficiency or pharmacological blockade of K(Ca)3.1 suppressed development of renal fibrosis. Mitogens stimulated K(Ca)3.1 in murine renal fibroblasts via a MEK-dependent mechanism, while selective blockade of K(Ca)3.1 inhibited fibroblast proliferation by promoting G0/G1 arrest. In a classical model of renal fibrosis, mouse unilateral ureteral obstruction (UUO), robust up-regulation of K(Ca)3.1 was detectable in affected kidneys. K(Ca)3.1 KO mice showed reduced expression of fibrotic marker expression, less chronic tubulointerstitial damage, collagen deposition and alpha-smooth muscle+ cells after UUO, with better preservation of functional renal parenchyma. The selective K(Ca)3.1 blocker TRAM-34 similarly attenuated progression of UUO-induced renal fibrosis in wild-type mice and rats. Thus, Grgic et al. believe that K(Ca)3.1 is involved in renal fibroblast proliferation and fibrogenesis, suggesting that K(Ca)3.1 may serve as a therapeutic target for the prevention of fibrotic kidney disease.

Donor age and renal P-glycoprotein expression associate with chronic histological damage in renal allografts.

The contributions of donor kidney quality (partially determined by donor age), allograft rejection, and calcineurin inhibitor nephrotoxicity on the progression of histologic damage of renal allografts are not completely defined. Moreover, the determinants of individual susceptibility to calcineurin inhibitor nephrotoxicity are not known but may include variability in drug transport and metabolism. In a prospective cohort of 252 adult renal allograft recipients treated with a combination of tacrolimus, mycophenolate mofetil, and corticosteroids, we studied 744 renal allograft biopsies obtained regularly from time of transplantation for 3 yr. We assessed determinants of histologic evolution, including tacrolimus exposure, renal P-glycoprotein (ABCB1) expression, and polymorphisms in the CYP3A4, CYP3A5, and ABCB1 genes. Within the first 3 yr after transplantation, we noted a progressive increase in interstitial fibrosis, tubular atrophy, glomerulosclerosis, and vascular intimal thickening. Older donor age, absence of P-glycoprotein expression at the apical membrane of tubular epithelial cells, and combined donor-recipient homozygosity for the C3435T variant in ABCB1 significantly associated with increased susceptibility to chronic allograft damage independent of graft quality at implantation. Changes in graft function over time reflected these associations with donor age and ABCB1 polymorphisms, but it was acute T cell-mediated and antibody-mediated rejection that determined early graft survival. In conclusion, the effects of older donor age reach beyond the quality of the allograft at implantation and continue to be important for histologic evolution in the posttransplantation period. In addition, ABCB1 genotype and expression of P-glycoprotein in renal tubular epithelial cells determine susceptibility to chronic tubulointerstitial damage of transplanted kidneys.

Renal fibrosis is attenuated by targeted disruption of K Ca 3.1 potassium channels

Proliferation of interstitial fibroblasts is a hallmark of progressive renal fibrosis commonly resulting in chronic kidney failure. The intermediate-conductance Ca(2+)-activated K(+) channel (K(Ca)3.1) has been proposed to promote mitogenesis in several cell types and contribute to disease states characterized by excessive proliferation. Here, we hypothesized that K(Ca)3.1 activity is pivotal for renal fibroblast proliferation and that deficiency or pharmacological blockade of K(Ca)3.1 suppresses development of renal fibrosis. We found that mitogenic stimulation up-regulated K(Ca)3.1 in murine renal fibroblasts via a MEK-dependent mechanism and that selective blockade of K(Ca)3.1 functions potently inhibited fibroblast proliferation by G(0)/G(1) arrest. Renal fibrosis induced by unilateral ureteral obstruction (UUO) in mice was paralleled by a robust up-regulation of K(Ca)3.1 in affected kidneys. Mice lacking K(Ca)3.1 (K(Ca)3.1(-/-)) showed a significant reduction in fibrotic marker expression, chronic tubulointerstitial damage, collagen deposition and alphaSMA(+) cells in kidneys after UUO, whereas functional renal parenchyma was better preserved. Pharmacological treatment with the selective K(Ca)3.1 blocker TRAM-34 similarly attenuated progression of UUO-induced renal fibrosis in wild-type mice and rats. In conclusion, our data demonstrate that K(Ca)3.1 is involved in renal fibroblast proliferation and fibrogenesis and suggest that K(Ca)3.1 may represent a therapeutic target for the treatment of fibrotic kidney disease.

A case of renal allograft loss associated with thrombotic microangiopathy during pregnancy

Abstract: A case with graft loss during pregnancy associated with thrombotic microangiopathy (TMA) is reported. The patient was a 27‐yr‐old female who had end‐stage renal disease because of immunoglobulin A (IgA) nephropathy at age 18. She received a kidney transplant at age 20 from her mother. Immunosuppressive therapy consisted of cyclosporine A (CyA), azathioprine (AZ), and prednisolone (PSL). The amount of serum creatinine (SCr) was 0.72 mg/dL at discharge one month after transplantation. Urinary occult blood and protein appeared five and 14 months after transplantation, respectively. SCr was gradually elevated. When she was 27‐yr old, she became pregnant. The amount of SCr was 1.74 mg/dL. The dose of CyA was 150 mg/d, AZ was 50 mg/d, and PSL was 5 mg/d. At 18 wk of gestation, severe hypertension and edema occurred and she was hospitalized. SCr was elevated to 3.26 mg/dL and severe hemolytic anemia with thrombocytopenia was recognized. On the third day after hospitalization, she underwent an abortion. Renal biopsy was performed on the seventh hospitalized day. Fibromyxomatous intimal thickening including foam cells, extensive hyaline changes, and fibrin thrombi were observed in the interlobular arteries or arterioles. Recurrent IgA nephropathy with extensive crescent formation was also diagnosed. Severe chronic tubulointerstitial damage was observed and tubulitis was mild. After the biopsy, she underwent plasma exchange and methyl‐prednisolone pulse therapy. Thrombocytopenia improved one month after the abortion. However, the graft function was lost and maintenance hemodialysis was started on the 46th day after termination of the pregnancy. In this case, it is suggested that pregnancy triggered TMA resulting in graft loss. Moreover, acute exacerbation of recurrent IgA nephropathy, pre‐existing CyA arteriopathy, and severe chronic tubulointerstitial damage also caused the deterioration of graft function as well as TMA.

Proximal tubular dysfunction associated with tenofovir in an HVC-HIV co-infected patient undergoing HVC therapy.

Sir, Tenofovir is an adenosine analogue, and exposure to ribavirin (RBV) could increase the intracellular phosphorylated metabolities of tenofovir. Nucleoside analogues essentially have mitochondrial toxicity. Nephrotoxicity of these nucleoside analogues in combination with HVC therapy is a rare complication [1]. We present the case of a 40-year-old white man, with HIV infection diagnosed in 2001 and VHC in 2006. The HIV infection was asymptomatic with a CD4+ lymphocyte count of 711 cells/μl and undetectable plasma HIV-RNA. The antiretroviral treatment was efavirenz (600 mg/day), emtricitabine (200 mg/day) and tenofovir disoproxil fumarate (300 mg/day). In November 2006, the patient initiated therapy for the VHC infection consisting of pegylated interferon and RBV therapy. The renal function was normal, with a serum creatinine of 86 μmol/l and a creatinine clearance of 100 ml/min/1.73 m2. Five months after initiation of treatment for the VHC infection, the patient showed general weakness and dyspnea. Blood and urine analyses on admission indicated the presence of anaemia (haemoglobin 6.4 g/dl and haematocrit 20.6%), renal failure (creatinine of 424 μmol/l, urea 10.7 mmol/l, MDRD 12.3 ml/min/1.73 m2 and proteinuria 1.13 g/24 h) and proximal tubular kidney dysfunction with hypophosphataemia, hypouricaemia, hyperchloraemic metabolic acidosis with normal anion gap and a low-molecular-weight proteinuria. A renal biopsy showed the presence of chronic tubulo-interstitial lesions and focal-segmental glomerulosclerosis (Figure ​(Figure11). Fig. 1 Optical microscopy. Hematoxilin-eosine. 100×: chronic tubulo-interstitial damage with some inflammation, and segmental sclerotic lesion in one glomerulus. The patient was diagnosed with HIV nephropathy and proximal tubular dysfunction secondary to tenofovir and RBV treatment. The administration of these drugs was stopped. Two months later the metabolic disorders completely regressed with partial recovery of renal function (creatinine of 186 μmol/l and MDRD of 37 ml/min/1.73 m2) and reduction of proteinuria (0.40 g/24 h). Some cases of acute tubular necrosis, isolated tubular defects such as Fanconi syndrome, distal tubular acidosis and nephrogenic diabetes insipidus, have been reported with reverse transcriptase inhibitors [2]. Tenofovir is eliminated by glomerular filtration and active tubular secretion. Hypothetically, this effect could enhance the risk of kidney tubular dysfunction in HVC-HIV co-infected patients undergoing HVC therapy, although tenofovir-related nephrotoxicity is apparently rare and mainly seen in patients with mild pre-existing renal impairment [3,4]. In the same manner as other reverse transcriptase inhibitors, RBV could compete with tenofovir for the human organic anion transporter-1 (hOAT1), on the basolateral membrane of the proximal tubules, resulting in an increased tenofovir concentration and tubular toxicity [1,5]. Conflict of interest statement. None declared.

End-stage renal disease secondary to IgA nephropathy in recessive dystrophic epidermolysis bullosa: a case report

Epidermolysis bullosa (EB) consists of a group of dominant or recessive autosomal diseases characterised by skin and mucosa fragility. The lesions leave erosions and scars that, in turn, can cause stenosis of tracheal, oesophageal, and genitourinary tract mucosae. The significantly increased survival of EB patients has determined the onset of complications never observed before, including genitourinary disorders such as hydroureteronephrosis, recurrent urinary tract infections, renal amyloidosis, IgA nephropathy and post-infectious glomerulonephritis. A 6-year-old boy diagnosed with recessive dystrophic EB Hallopeau-Siemens type (RDEB-HS) was referred to our clinic because of microhaematuria that evolved into intra-infectious macrohaematuria. Renal biopsy revealed an increase in both extracellular matrix and mesangial cells, with a focal segmental glomerulosclerosis with severe chronic tubulointerstitial damage. Immunofluorescence showed IgA mesangium deposits. Five years later, he was started on haemodialysis, because of worsening renal function. This is a rare case of a child with EB who was successfully treated with haemodialysis. The pertinent literature has been reviewed.

Immunephenotype of Glomerular and Interstitial Infiltrating Cells in Protocol Renal Allograft Biopsies and Histological Diagnosis

Patients with a protocol renal allograft biopsy simultaneously displaying interstitial fibrosis/tubular atrophy (IF/TA) and subclinical rejection (SCR) have a shortened graft survival than patients with a normal biopsy, or with a biopsy only displaying IF/TA or SCR. The poor outcome of these patients could be related with a more severe inflammation. We evaluate the immunophenotype of infiltrating cells in these diagnostic categories. Nonexhausted paraffin blocks from protocol biopsies done during the first year were stained with anti-CD45, CD3, CD20, CD68 and CD15 monoclonal antibodies. Glomerular and interstitial positive cells were counted. C4d deposition in peritubular capillaries was evaluated. Histological diagnoses were: normal (n = 80), SCR (n = 17), IF/TA (n = 42) and IF/TA + SCR (n = 17). Only interstitial CD20 positive cells were significantly increased in patients displaying IF/TA + SCR; normal (137 +/- 117), SCR (202 +/- 145), IF/TA (208 +/- 151) and IF/TA + SCR (307 +/- 180 cells/mm(2)), p < 0.01. The proportion of biopsies displaying C4d deposition was not different among groups. The upper tertile of CD20 positive interstitial cells was associated with a decreased death-censored graft survival (relative risk: 3.01, 95% confidence interval: 1.23-7.35; p = 0.015). These data suggest that B-cell interstitial infiltrates are associated with histological damage and outcome, but do not distinguish whether these infiltrates were the cause or the consequence of chronic tubulo-interstitial damage.

The Evolution of Nonimmune Histological Injury and Its Clinical Relevance in Adult-Sized Kidney Grafts in Pediatric Recipients

To describe the evolution, risk factors and impact of nonimmune histological injury after pediatric kidney transplantation, we analyzed 245 renal allograft protocol biopsies taken regularly from the time of transplantation to 2 years thereafter in 81 consecutive rejection-free pediatric recipients of an adult-sized kidney. Isometric tubular vacuolization was present early after transplantation was not progressive, and was associated with higher tacrolimus pre-dose trough levels. Chronic tubulo-interstitial damage and tubular microcalcifications were already noted at 3 months, were progressive and had a greater association with small recipient size, male donor gender, higher donor age and female recipient gender, but not with tacrolimus exposure. Renal function assessment showed that older recipients had a significant increase in absolute glomerular filtration rate with time after transplantation, which differed from small recipients who showed no increase. It is concluded that progressive, functionally relevant, nonimmune injury is detected early after adult-sized kidney transplantation in pediatric recipients. Renal graft ischemia associated with the donor-recipient size discrepancy appears to be a greater risk factor for this chronic histological injury, suggesting that the exploration of additional therapeutic approaches to increase allograft perfusion could further extend the graft survival benefit of adult-sized kidneys transplanted into small children.

Beyond Operational Tolerance: Effect of Ischemic Injury on Development of Chronic Damage in Renal Grafts

The induction of operational tolerance is the holy grail of clinical transplantation. However, in animal models with operational tolerance, long- term grafts still develop chronic damage. The elucidation of the impact of allogenic versus nonallogeneic factors in such a model is important. This study examined the effect of a clinically relevant combination of warm ischemia and cold preservation in the absence of allogeneic response (isografts) and in the context of operational tolerance. Dark Agouti (DA) rat kidneys were transplanted into DA recipients (isografts) or Albino Surgery recipients (allografts) tolerized by two transfusions of DA blood, under cover of cyclosporin A. Grafts were subjected to minimal cold preservation or to 30 mins warm ischemia followed by 24 hrs cold preservation. After an initial peak of renal dysfunction, serum creatinine concentration returned to normal in isografts and nonischemic allografts, but remained significantly elevated in ischemic allografts (P<0.0002) throughout 6 months follow-up. Both allograft groups developed proteinuria. At 6 months, ischemic isografts and nonischemic allografts demonstrated very mild tubular atrophy and interstitial fibrosis. Tubulointerstitial injury was significantly more severe in ischemic allografts (P<0.01 vs. nonischemic allografts) and was associated with increased infiltrating monocyte/macrophages and NK cells (P<0.05). Moderate glomerulosclerosis was a feature of both allograft groups (P<0.05). The modified allogeneic response in operationally tolerant recipients acts in synergy with ischemia/reperfusion injury in the development of chronic damage. Strategies to limit or modify the initial ischemia/reperfusion injury may ameliorate chronic tubulointerstitial damage. Progressive glomerular damage and proteinuria in allografts may require other pharmacological intervention.

13- cis Retinoic Acid Inhibits Development and Progression of Chronic Allograft Nephropathy

Chronic allograft nephropathy is characterized by chronic inflammation and fibrosis. Because retinoids exhibit anti-proliferative, anti-inflammatory, and anti-fibrotic functions, the effects of low and high doses of 13-cis-retinoic acid (13cRA) were studied in a chronic Fisher344-->Lewis transplantation model. In 13cRA animals, independent of dose (2 or 20 mg/kg body weight/day) and start (0 or 14 days after transplantation) of 13cRA administration, serum creatinine was significantly lower and chronic rejection damage was dramatically reduced, including subendothelial fibrosis of preglomerular vessels and chronic tubulointerstitial damage. The number of infiltrating mononuclear cells and their proliferative activity were significantly diminished. The mRNA expression of chemokines (MCP-1/CCL2, MIP-1alpha/CCL3, IP-10/CXCL10, RANTES/CCL5) and proteins associated with fibrosis (plasminogen activator inhibitor-1, transforming growth factor-beta1, and collagens I and III) were strikingly lower in treated allografts. In vitro, activated peritoneal macrophages of 13cRA-treated rats showed a pronounced decrease in protein secretion of inflammatory cytokines (eg, tumor necrosis factor-alpha, interleukin-6). The suppression of the proinflammatory chemokine RANTES/CCL5 x 13cRA in fibroblasts could be mapped to a promoter module comprising IRF-1 and nuclear factor-kappaB binding elements, but direct binding of retinoid receptors to promoter elements could be excluded. In summary, 13cRA acted as a potent immunosuppressive and anti-fibrotic agent able to prevent and inhibit progression of chronic allograft nephropathy.

Can renal fibrosis be reversed?

New therapeutic approaches are needed to address the current epidemic of chronic kidney disease. Beyond delaying the inevitable onset of end-stage kidney disease the ultimate dream of clinical therapy is disease regression. Degradation of the interstitial matrix proteins is potentially feasible, especially before the interstitial "scar" becomes highly organized. Currently the specific matrix-degrading proteases that perform this function in vivo have not been clearly identified although several candidates have been suggested. Reversing renal fibrosis will also mandate removal of interstitial myofibroblasts that are the major source of the fibrosis-associated interstitial matrix proteins. However, the greater therapeutic challenge pertains to the current inability to regenerate intact functional nephrons in a site where they have been destroyed. In chronic tubulointerstitial damage that typifies all progressive kidney diseases, it is not interstitial matrix accumulation per se that leads to renal functional decline but rather its destructive effects on neighboring cells. In particular, loss of peritubular capillaries and tubules are the morphological features that underlie declining renal function. Recent advances in several basic scientific fields of investigation such as matrix biology, developmental biology, angiogenesis, and stem cell biology have identified new candidate therapeutic targets. A powerful new molecular tool-box is at our disposal that can be used to begin to translate recent discoveries into the clinical research arena with the goal of reversing renal fibrosis in a functionally meaningful way.

C5b-9 does not mediate chronic tubulointerstitial disease in the absence of proteinuria

In nephrotic glomerular diseases, the intratubular assembly of the membrane attack complex (C5b-9) is one of the principal mediators of chronic tubulointerstitial damage. Here, we examined whether C5b-9 has a pathogenic role in tubulointerstitial disease in the absence of proteinuria. Three pathophysiologically distinct models of nonproteinuric chronic tubulointerstitial disease were induced in Piebald-Viral-Glaxo (PVG) rats, with or without C6 deficiency (C6+ and C6): (1) unilateral ureteric obstruction (UUO, days 1, 3, 6, 14, and 21; N= 5-6/group); (2) cyclosporine (CsA) nephropathy (15 mg/kg SC daily with 0.05% sodium diet; day 14, 35 N= 9/group); and (3) streptozotocin (STZ)-induced diabetes (day 90, N= 8/group). The peritubular deposition of C5b-9 increased in all three models. In UUO, the number of vimentin-positive tubules, interstitial volume expansion, and monocyte accumulation were similar in both the C6+ and C6- groups at all time points. There was a trend toward an earlier peak in myofibroblast accumulation in C6- rats with UUO (d3 vs. d6; P= 0.05), but this did not prevent fibrosis at later time points. In CsA nephropathy, cortical tubulointerstitial damage was also similar in both C6+ and C6- groups on day 14, despite equivalent CsA trough levels. Finally, in STZ-induced diabetes, rats did not develop proteinuria, and tubulointerstitial disease (distal tubule glycogen nephrosis, interstitial volume expansion, and tubular dilatation) was not altered by C6 deficiency. These data suggest that, in contrast to proteinuric states, C5b-9 does not have a significant impact on the progression of tubulointerstitial damage in nonproteinuric chronic renal disease.

Jun-N-terminal kinase regulates thrombin-induced PAI-1 gene expression in proximal tubular epithelial cells

Interstitial activation of the coagulation cascade is a common finding in acute and chronic tubulointerstitial damage. We previously demonstrated that thrombin may induce proximal tubular epithelial cells (PTEC) proliferation and regulate, through plasminogen activator inhibitor (PAI)-1 and urokinase-type plasminogen activator (u-PA), their profibrotic activity. The signaling pathways leading to these effects are still unknown. The PAI-1 promoter contains several activator protein-1 (AP-1) consensus sequences. AP-1 activation is induced by different agonists through jun-N-terminal kinase (JNK). Thus, we investigated the role of the JNK-AP-1 axis on thrombin-induced PAI-1 and u-PA expression in immortalized PTEC and its modulation by PKC and src, two key signaling enzymes. JNK and src activation was investigated by Western blotting, PAR-1 cellular surface expression by flow cytometry, PAI-1 and u-PA gene expression by Northern blotting, AP-1 activation by transient transfection, and DNA synthesis by (3)H-thymidine uptake. Thrombin and PMA induced a time-dependent increase of JNK phosphorylation in immortalized PTEC that was inhibited by PKC down-regulation. Both thrombin and PMA caused AP-1 activation, significantly reduced by src inhibition. Phorbol 12-myristate 13-acetate (PMA), indeed, induced an increase in src phosphorylation. Both PMA- and thrombin-stimulated PAI-1 gene expression was abolished by JNK, protein kinase C (PKC), and src inhibition, and this effect was regulated at the trascriptional level. PKC, but not src or JNK inhibition, abolished thrombin-elicited u-PA expression. Finally, JNK inhibition did not influence thrombin-induced proliferation. Our data suggest that thrombin activates the JNK-AP-1 axis in a PKC- and src-dependent manner in PTEC. This axis, necessary for thrombin-stimulated PAI-1 expression, but not for its fibrinolytic and regenerative effect, may represent a therapeutic target in acute and chronic tubulointerstitial damage.

Protocol biopsies as predictors of chronic allograft nephropathy

CHRONIC allograft nephropathy (CAN) is the most common cause of late graft loss. CAN is indicated by a sustained decline in renal function usually in conjunction with proteinuria and hypertension. Unfortunately, once the clinical diagnosis of CAN is histologically confirmed, the degree of renal scarring is usually too advanced to begin effective therapy. Histologically, CAN is recognized by the presence of chronic tubulointerstitial damage, its severity is graded as mild, moderate, or severe according to the extension of interstitial fibrosis and tubular atrophy. Two types of CAN are distinguished: CAN (a) defined as tubulointerstitial chronic damage in the absence of transplant vasculopathy and CAN (b) defined as tubulointerstitial chronic damage associated with transplant vasculopathy.

Tubulo-interstitial Disorders

<h2>Abstract</h2> Chronic renal failure (CRF) is accompanied by tubulo-interstitial atrophy and fibrosis, regardless of the cause. Disorders of the renal vasculature, the glomeruli or urinary drainage all culminate in chronic tubulo-interstitial damage, the severity of which is the histological feature that correlates best with progression to end-stage renal failure (ESRF). However, there are diverse conditions in which the tubulo-interstitium is the primary site of damage, and these may be considered together without inferring a common aetiology or pathogenesis. The diseases classified as tubulo-interstitial nephritis are considered below. Inherited disorders of tubular function are discussed in <i>MEDICINE</i> <b>31:5</b>, 32, acute tubular necrosis (ATN) in <i>MEDICINE</i> <b>31:6</b>, 43, and the renal manifestations of myeloma on page 99.

Expression of Nuclear Transcription Factor PAX2 in Renal Biopsies of Juvenile Nephronophthisis

PAX2, a homeotic gene of ‘paired box family’, is a nuclear transcription factor expressed in mesenchymal/epithelial conversion during the early stages of nephrogenesis; however, its repression is necessary for terminal differentiation of mature tubular cells. Transgenic overexpression in animal model causes epithelial hyperproliferation and microcyst formation. In humans, PAX2 expression has been observed in cystic and dysplasic tubular epithelia in kidney malformation and in kidney disease. We have investigated PAX2 expression and its colocalization with cytokeratin and/or vimentin in 17 biopsies of juvenile nephronophthisis (NPH), an autosomal-recessive renal disease characterized by diffuse renal fibrosis and occasional cysts. Fourteen cases were analyzed for deletion and mutation in the NPH1 gene locus and 33% resulted to be deleted or mutated; for the remaining cases the diagnosis was based on clinical and pathological criteria. The control group included 4 congenital dysplastic kidneys, and 10 biopsies of nephropathies with secondary chronic tubulointerstitial damage. In all cases of renal dysplasia a strong nuclear positivity was observed in immature tubules surrounded by αSMA-positive mesenchymal cells. In NI biopsies the tubular epithelia were almost PAX2 negative, although tubulointerstitial damage was severe. In 14/17 NPH1 moderate-to-strong nuclear PAX2 positivity of tubular cells was observed, particularly in cystic distal tubules located at the corticomedullary junction, but also in proximal tubular sections. The PAX2 signal co-localized more with cytokeratin staining than with vimentin. Our results confirm the observation of PAX2 expression in immature dysplastic tubules and its repression in mature renal tubular cells, also in the presence of severe secondary interstitial fibrosis. PAX2 seems to be overexpressed in NPH. The genetic defect of NPH, a disease probably due to a primary defect along the cascade of mesenchymal epithelial differentiation, could generate a functionally abnormal protein involved in focal adhesion signaling and cell/matrix interaction. The failure of PAX2 repression or its reactivation in NPH could be a marker of hyperproliferation and incomplete maturation of epithelial tubular cells, probably due to a defect cell/matrix cross-talk, and involved in interstitial fibrosis and cysts formation.

Medullary cystic disease and tubular basement membrane changes: clinicopathological characteristics of four patients

We describe herein the clinicopathological characteristics of four members of a family in which about half of the generation was affected by chronic renal failure after middle age. The inheritance was considered to be an autosomal dominant pattern. Clinically, neither sensorineural deafness nor ocular abnormalities were evident. In addition, there was neither hypokalemia nor hypercalcemia causing deterioration of renal function. Radiological examination revealed no cystic formation in the kidneys in any patients, although in two of them the examination was performed at the time of endstage renal disease. Histological examination showed chronic tubulo-interstitial damage with periglomerular fibrosis. On electron microscopy, characteristic but nonspecific thickening and lamination of tubular basement membrane were noted in all patients, while glomerular basement membrane was unremarkable in all patients. These findings suggest that our patients had medullary cystic disease. Demonstration of lamination and thickening of the tubular basement membrane by electron microscopy may be useful for the diagnosis of medullary cystic disease with undetectable cyst formation.