The pathologic paradigm for renal progression is advancing tubulointerstitial fibrosis. Whereas mechanisms underlying fibrogenesis have grown in scope and understanding in recent decades, effective human treatment to directly halt or even reverse fibrosis remains elusive. Here, we examine key features mediating the molecular and cellular basis of tubulointerstitial fibrosis and highlight new insights that may lead to novel therapies. How to prevent chronic kidney disease from progressing to renal failure awaits even deeper biochemical understanding.

Mechanisms of Tubulointerstitial Fibrosis

Purpose of review Tubulointerstitial fibrosis is the final common pathway to end-stage renal disease. Understanding the mechanisms of tubulointerstitial fibrosis is essential in establishing novel therapeutic strategies for the prevention or arrest of progressive kidney diseases. The present review focuses on a newly proposed mechanism of tubulointerstitial fibrosis, one that emphasizes the roles of epithelial-mesenchymal transition and cellular activation. Recent findings Among the cells that accumulate in the renal interstitium, fibroblasts are the principal effectors mediating tubulointerstitial fibrosis. By contrast, the phagocytosis of extracellular matrix and apoptotic cells by macrophages may actually exert a beneficial effect. Interstitial fibroblasts are more heterogeneous than expected, and during renal fibrosis new fibroblasts are derived mainly through epithelial-mesenchymal transition. The intracellular signaling pathways leading to initiation of epithelial-mesenchymal transition remain largely unknown, though recent studies have identified beta-catenin and Smad3 activation of lymphoid enhancer factor, integrin-linked kinase, and small GTPases and mitogen-activated protein kinases as key components. Transforming growth factor-beta is believed to be a critical fibrogenic factor, but recent studies have also focused on transforming growth factor-beta independent pathways as mechanisms of tubulointerstitial fibrosis. As the mechanisms underlying tubulointerstitial fibrosis leading to epithelial-mesenchymal transition have been identified, so have cytokines that efficiently antagonize renal fibrosis, particularly bone morphogenic protein-7 and hepatocyte growth factor. Summary In combination with traditional angiotensin converting enzyme inhibitors, newly identified cytokines may eventually form the basis for new therapeutic strategies aimed at inhibiting the progression of renal disease.

Mechanisms of tubulointerstitial fibrosis.

New developments in the genetics, pathogenesis, and therapy of IgA nephropathy.

This European Community Biomedicine and Health Research-supported, multicenter, randomized, placebo-controlled, double-blind trial investigated the effect of an angiotensin-converting enzyme inhibitor (ACE-I) in children and young people with IgA nephropathy (IgAN), moderate proteinuria (>1 and 50 ml/min per 1.73 m(2). Sixty-six patients who were 20.5 yr of age (range 9 to 35 yr), were randomly assigned to Benazepril 0.2 mg/kg per d (ACE-I) or placebo and were followed for a median of 38 mo. The primary outcome was the progression of kidney disease, defined as >30% decrease of CrCl; secondary outcomes were (1) a composite end point of >30% decrease of CrCl or worsening of proteinuria until > or =3.5 g/d per 1.73 m(2) and (2) proteinuria partial remission ( 6 mo. Analysis was by intention to treat. A single patient (3.1%) in the ACE-I group and five (14.7%) in the placebo group showed a worsening of CrCl >30%. The composite end point of >30% decrease of CrCl or worsening of proteinuria until nephrotic range was reached by one (3.1%) of 32 patients in the ACE-I group, and nine (26.5%) of 34 in the placebo group; the difference was significant (log-rank P = 0.035). A stable, partial remission of proteinuria was observed in 13 (40.6%) of 32 patients in the ACE-I group versus three (8.8%) of 34 in the placebo group (log-rank P = 0.033), with total remission in 12.5% of ACE-I-treated patients and in none in the placebo group (log-rank P = 0.029). The multivariate Cox analysis showed that treatment with ACE-I was the independent predictor of prognosis; no influence on the composite end point was found for gender, age, baseline CrCl, systolic or diastolic BP, mean arterial pressure, or proteinuria.

IgACE: A Placebo-Controlled, Randomized Trial of Angiotensin-Converting Enzyme Inhibitors in Children and Young People with IgA Nephropathy and Moderate Proteinuria

It is unclear whether peritoneal dialysis (PD) compared with hemodialysis (HD) confers a survival advantage in end-stage renal disease (ESRD) patients with coronary artery disease (CAD). This hypothesis was tested in a national cohort of 107,922 patients starting dialysis therapy between May 1, 1995, and July 31, 1997. Data on patient characteristics were obtained from the Center for Medicare and Medicaid Services Medical Evidence Form (CMS) and linked to mortality data from the United States Renal Data System (USRDS). Patients were classified on the basis of CAD presence and followed until death or the end of 2 yr. Nonproportional Cox regression models estimated the relative risk (RR) of death for patients with and without CAD by dialysis modality using primarily the intent-to-treat but also the as-treated approach. Diabetic patients (DM) and nondiabetic patients (non-DM) were analyzed separately. Among DM, patients with CAD treated with PD had a 23% higher RR (95% CI, 1.12 to 1.34) compared with similar HD patients, whereas patients without CAD receiving PD had a 17% higher RR (CI, 1.08 to 1.26) compared with HD. Among non-DM, patients with CAD treated with PD had a 20% higher RR (CI. 1.10 to 1.32) compared with HD patients, whereas patients without CAD had similar survival on PD or HD (RR = 0.99; CI, 0.93 to 1.05). The mortality risk for new ESRD patients with CAD differed by treatment modality. In both DM and non-DM, patients with CAD treated with PD had significantly poorer survival compared with HD. Whether differences in solute clearance and/or cardiac risk profiles between PD and HD may explain these findings deserves further investigation.

Mortality Differences by Dialysis Modality among Incident ESRD Patients with and without Coronary Artery Disease

Background IgA nephropathy (IgAN) is the most common primary glomerulonephritis worldwide and is characterized by extremely variable clinical and morphological features and outcome. TGF-beta1 has a key role in fibrogenesis and the progression of renal damage. Its production is under genetic control. Methods We recruited 105 Italian biopsy-proven IgAN patients for genotyping for the TGF-beta1 C-509T, T869C (COD 10) and G915C (COD 25) polymorphisms; 200 healthy blood donors were used as normal controls. Glomerular and interstitial mRNA levels of TGF-beta1 were assessed by real-time PCR in 34 patients to seek relationships with clinical, renal histopathological features and outcome. Results The genotype distributions in the IgAN population were not statistically different from the controls. The COD 10 TT genotype was associated with more severe histological damage as assessed by Lee's classification (CC 50%, CT 39.6% and TT 17.2% were graded as mild; CC 35.7%, CT 43.7% and TT 44.8% as moderate, and CC 14.3%, CT 16.7% and TT 37.9% as severe [p=0.0049]) and with severe interstitial infiltrates (CC 10.4%, CT 35.2% and TT 54.2% [p=0.03]). A higher interstitial immunodeposition was observed for TGF-beta1, collagen IV and alpha-SMA in patients with the COD 10 T allele (p=0.045, p=0.049, p=0.032, respectively). The T allele was associated with significantly higher TGF-beta1 mRNA levels in the interstitium (TT+CT vs. CC: 0.52 +/- 0.16 vs. 0.18 +/- 0.10 copies/mL, respectively; p=0.000). The T allele was also associated with higher mRNA levels in glomeruli, though the difference was not statistically significant. Finally, the T allele was significantly associated with a worse prognosis, the end points being reached by 40% of TT+CT and 32% of CC patients (p=0.009). Conclusions In primary IgA nephropathy, the T allele of the TGF-beta1 COD 10 C/T polymorphism seems to be associated with more severe histological lesions, higher renal TGF-beta1 mRNA levels and a worse prognosis. This polymorphism seems to be functionally relevant and to have a prognostic impact.

Primary IgA nephropathy is more severe in TGF-beta1 high secretor patients.

Background IgA nephropathy (IgAN) is the most common primary glomerulonephritis in the general population. There is accumulating evidence that immunosuppressive treatment is efficacious in IgAN. However, it is critical to define appropriate indicators for this therapy especially in the wake of potentially deleterious side effects to immunosuppressives. Methods This study retrospectively reviewed IgAN cases collected since 1981 to identify clinical and/or histological parameters for disease progression; 310 patients with biopsy proven IgAN, diagnosed from January 1981 to March 2004, were included. Results We defined a clinical prognostic index (CPI) using multivariate analysis, which incorporated these clinical/ histological parameters. Semiquantitative scores were assigned as follows: 2 points if creatinine (Cr) was >1.4 mg/dL, 1 point if proteinuria was >1 g/24 hr, 1 point if a patient was affected by hypertension, and 1 point if a patient was older than 30 yrs. Dividing our population into two groups (scores 0-2 = low CPI group; scores 3-5 = high CPI group), we demonstrated a significantly different 10-yr renal survival rate; in the low CPI group, renal survival since time of biopsy at 10 yrs was 91.7%; in the high CPI group the renal survival at 10 yrs was 35%. We validated the CPI in an independent sample from Verona (validation group) and demonstrated similar results for the CPI. Conclusions The CPI is convenient to use for defining the risk of disease progression.

A validated model of disease progression in IgA nephropathy.

The dialytic failure of the peritoneal membrane.

https://www.kidney-international.org/article/S0085-2538(15)49302-0/pdf

Precocious activation of genes of the renin-angiotensin system and the fibrogenic cascade in IgA glomerulonephritis

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Primary IgA nephropathy is more severe in TGF-beta1 high secretor patients.

A validated model of disease progression in IgA nephropathy.

The dialytic failure of the peritoneal membrane.

Precocious activation of genes of the renin-angiotensin system and the fibrogenic cascade in IgA glomerulonephritis