Immunohistochemical localization of collagen VI in diabetic glomeruli

Therapeutic Targets for Diabetic Kidney Disease: Proteome-Wide Mendelian Randomization and Colocalization Analyses

At present, safe and effective treatment drugs are urgently needed for diabetic kidney disease (DKD). Circulating protein biomarkers with causal genetic evidence represent promising drug targets, which provides an opportunity to identify new therapeutic targets. Summary data from two protein quantitative trait loci studies are presented, one involving 4,907 plasma proteins data from 35,559 individuals and the other encompassing 4,657 plasma proteins among 7,213 European Americans. Summary statistics for DKD were obtained from a large genome-wide association study (3,345 cases and 2,372 controls) and the FinnGen study (3,676 cases and 283,456 controls). Mendelian randomization (MR) analysis was conducted to examine the potential targets for DKD. The colocalization analysis was used to detect whether the potential proteins exist in the shared causal variants. To enhance the credibility of the results, external validation was conducted. Additionally, enrichment analysis, assessment of protein druggability, and the protein-protein interaction networks were used to further enrich the research findings. The proteome-wide MR analyses identified 21 blood proteins that may causally be associated with DKD. Colocalization analysis further supported a causal relationship between 12 proteins and DKD, with external validation confirming 4 of these proteins, and TGFBI was affirmed through two separate group data sets. These results indicate that targeting these four proteins could be a promising approach for treating DKD, and warrant further clinical investigations.

ARTICLE HIGHLIGHTS

Combination Therapy of RAS Inhibition and SGLT2 Inhibitors Decreases Levels of Endotrophin in Persons with Type 2 Diabetes

We investigated for the first time the effect of combination therapy of renin-angiotensin system inhibition (RASi) and sodium-glucose co-transporter-2 inhibitors (SGLT2is) on endotrophin (ETP), a pro-fibrotic signaling molecule reflecting collagen type VI formation, measured in the plasma of persons with type 2 diabetes (T2D). ETP was measured using the PRO-C6 ELISA in 294 individuals from the "Drug combinations for rewriting trajectories of renal pathologies in type 2 diabetes" (DC-ren) project. In the DC-ren study, kidney disease progression was defined as a >10% decline in the estimated glomerular filtration rate (eGFR) to an eGFR < 60 mL/min/1.73 m2. Among the investigated circulating markers, ETP was the most significant predictor of future eGFR. Combination therapy of RASi and SGLT2is led to a significant reduction in ETP levels compared to RASi monotherapy (p for slope difference = 0.002). Higher levels of baseline plasma ETP were associated with a significantly increased risk of kidney disease progression (p = 0.007). In conclusion, plasma ETP identified individuals at higher risk of kidney disease progression. The observed decreased levels of plasma ETP with combination therapy of RASi and SGLT2is in persons with T2D may reflect a reduced risk of kidney disease progression following treatment with SGLT2is.

Dual amylin and calcitonin receptor agonist treatment reduces biomarkers associated with kidney fibrosis in diabetic rats

Dual amylin and calcitonin receptor agonists (DACRAs) are effective treatments for obesity and type 2 diabetes (T2D). They provide beneficial effects on body weight, glucose control, and insulin action. However, whether DACRAs protect against diabetes-related kidney damage remains unknown. We characterize the potential of long-acting DACRAs (KBP-A, Key Bioscience Peptide-A) as a treatment for T2D-related pathological alterations of the kidney extracellular matrix (ECM) in Zucker diabetic fatty rats (ZDF). We examined levels of endotrophin (profibrotic signaling molecule reflecting collagen type VI formation) and tumstatin (matrikine derived from collagen type IVα3) in serum and evaluated kidney morphology and collagen deposition in the kidneys. We included a study in obese Sprague-Dawley rats to further investigate the impact of KBP-A on ECM biomarkers. In ZDF vehicles, levels of endotrophin and tumstatin increased, suggesting disease progression along with an increase in blood glucose levels. These rats also displayed damage to their kidneys, which was evident from the presence of collagen formation in the medullary region of the kidney. Interestingly, KBP-A treatment attenuated these increases, resulting in significantly lower levels of endotrophin and tumstatin than the vehicle. Levels of endotrophin and tumstatin were unchanged in obese Sprague-Dawley rats, supporting the relation to diabetes-related kidney complications. Furthermore, KBP-A treatment normalized collagen deposition in the kidney while improving glucose control. These studies confirm the beneficial effects of DACRAs on biomarkers associated with kidney fibrosis. Moreover, these antifibrotic effects are likely associated with improved glucose control, highlighting KBP-A as a promising treatment of T2D and its related late complications.NEW & NOTEWORTHY These studies describe the beneficial effects of using a dual amylin and calcitonin receptor agonist (DACRA) for diabetes-related kidney complications. DACRA treatment reduced levels of serological biomarkers associated with kidney fibrosis. These reductions were further reflected by reduced collagen expression in diabetic kidneys. In general, these results validate the use of serological biomarkers while demonstrating the potential effect of DACRAs in treating diabetes-related long-term complications.

Limited Hyperoxia-Induced Proliferative Retinopathy (LHIPR) as a Model of Retinal Fibrosis, Angiogenesis, and Inflammation

The progression to fibrosis and traction in retinopathy of prematurity (ROP) and other ischemic retinopathies remains an important clinical and surgical challenge, necessitating a comprehensive understanding of its pathogenesis. Fibrosis is an unbalanced deposition of extracellular matrix components responsible for scar tissue formation with consequent tissue and organ impairment. Together with retinal traction, it is among the main causes of retinal detachment and vision loss. We capitalize on the Limited Hyperoxia Induced Retinopathy (LHIPR) model, as it reflects the more advanced pathological phenotypes seen in ROP and other ischemic retinopathies. To model LHIPR, we exposed wild-type C57Bl/6J mouse pups to 65% oxygen from P0 to P7. Then, the pups were returned to room air to recover until later endpoints. We performed histological and molecular analysis to evaluate fibrosis progression, angiogenesis, and inflammation at several time points, from 1.5 months to 9 months. In addition, we performed in vivo retinal imaging by optical coherence tomography (OCT) or OCT Angiography (OCTA) to follow the fibrovascular progression in vivo. Although the retinal morphology was relatively preserved, we found a progressive increase in preretinal fibrogenesis over time, up to 9 months of age. We also detected blood vessels in the preretinal space as well as an active inflammatory process, altogether mimicking advanced preretinal fibrovascular disease in humans.

Endotrophin as a risk marker of mortality and kidney complications in a type 1 diabetes cohort

Hyperglycemia triggers pathological pathways leading to fibrosis, where extracellular matrix (ECM) components are accumulated. We investigated the potential of endotrophin, a pro-fibrotic molecule generated during collagen type VI formation, as a risk marker for complications to type 1 diabetes. Endotrophin was measured in serum and urine from 1,468 persons with type 1 diabetes. Outcomes included a composite kidney endpoint, first major adverse cardiovascular event (MACE), all-cause mortality, progression of albuminuria, incident heart failure, and sight-threatening diabetic eye disease. Cox proportional hazards models adjusted for conventional risk factors were applied. A doubling of serum endotrophin was independently associated with the kidney endpoint (n = 30/1,462; hazard ratio 3.39 [95% CI: 1.98-5.82]), all-cause mortality (n = 93/1,468; 1.44 [1.03-2.0]), and progression of albuminuria (n = 80/1,359; 1.82 [1.32-2.52]), but not with first MACE, heart failure, or sight-threatening diabetic eye disease after adjustment. Urinary endotrophin was not associated with any outcome after adjustment. Serum endotrophin was a risk marker for mortality and kidney complications in type 1 diabetes. Biomarkers of ECM remodeling, such as serum endotrophin, may identify persons with active pro-fibrotic processes at risk for complications in diabetes and where antifibrotic agents may reduce this risk.

Endotrophin is a risk marker of complications in CANagliflozin cardioVascular Assessment Study (CANVAS): a randomized controlled trial

BACKGROUND

Enhanced de-novo collagen type VI (COL VI) formation has been associated with kidney and cardiovascular fibrosis. We hypothesized that endotrophin (ETP), a product specifically generated during collagen type VI formation, may be prognostic for heart failure (HF), cardiovascular death (CVD), kidney endpoints, and all-cause mortality in patients with type 2 diabetes.

METHODS

We measured ETP in plasma (P-ETP) and urine (U-ETP) samples collected at baseline and follow-up (year 3) from the randomized controlled trial, CANagliflozin cardioVascular Assessment Study (CANVAS), by use of the PRO-C6 ELISA measuring COL VI formation and ETP. At baseline, plasma and urine samples were available for 3531 and 3423 patients, respectively. At year 3, plasma and urine samples were available for 2178 (61.7%) and 2070 (60.5%) patients, respectively Patients were followed for a median of 6.1 years, and endpoints included: incident HF, CVD, three kidney composite endpoints, and all-cause mortality. Backward selection was used to identify variables to be included in the analyses. Robustness of the association with outcome was assessed by bootstrap analyses.

RESULTS

In univariable analysis, P-ETP predicted all investigated outcomes (all p < 0.0001), remained independently associated with all outcomes after adjustment for conventional risk factors (all p < 0.004), and increased C-statistics of the models for the outcomes HF, CVD, HFCVD, all-cause mortality, and kidney composite 2 (ΔC ≥ 0.002). In bootstrap analysis, P-ETP was retained with a frequency ranging from 41.0 to 98.4% for all outcomes. Levels of U-ETP were associated with outcomes in univariable analysis, but associations with most outcomes were lost after adjustment for conventional risk factors. The increase in P-ETP over time was greater with increasing albuminuria stage (p < 0.0001) and was independently associated with the kidney endpoints (p < 0.03). In the placebo arm, the increase in P-ETP was prognostic for all-cause mortality (HR [95% CI]; 1.14 [1.05-1.23], p = 0.003). Whereas levels of P-ETP were not impacted by treatment, levels of U-ETP significantly increased with canagliflozin treatment.

CONCLUSIONS

P-ETP generated during COL VI formation predicts cardiovascular, kidney and mortality outcomes in patients with type 2 diabetes. As ETP identifies patients at increased risk of experiencing relevant outcomes, it may be used for patient enrichment in future clinical trials. Trial Registry Number (ClinicalTrials.gov Identifier): NCT01032629.

Biochemical composition of the glomerular extracellular matrix in patients with diabetic kidney disease

In the glomeruli, mesangial cells produce mesangial matrix while podocytes wrap glomerular capillaries with cellular extensions named foot processes and tether the glomerular basement membrane (GBM). The turnover of the mature GBM and the ability of adult podocytes to repair injured GBM are unclear. The actin cytoskeleton is a major cytoplasmic component of podocyte foot processes and links the cell to the GBM. Predominant components of the normal glomerular extracellular matrix (ECM) include glycosaminoglycans, proteoglycans, laminins, fibronectin-1, and several types of collagen. In patients with diabetes, multiorgan composition of extracellular tissues is anomalous, including the kidney, so that the constitution and arrangement of glomerular ECM is profoundly altered. In patients with diabetic kidney disease (DKD), the global quantity of glomerular ECM is increased. The level of sulfated proteoglycans is reduced while hyaluronic acid is augmented, compared to control subjects. The concentration of mesangial fibronectin-1 varies depending on the stage of DKD. Mesangial type III collagen is abundant in patients with DKD, unlike normal kidneys. The amount of type V and type VI collagens is higher in DKD and increases with the progression of the disease. The GBM contains lower amount of type IV collagen in DKD compared to normal tissue. Further, genetic variants in the α3 chain of type IV collagen may modulate susceptibility to DKD and end-stage kidney disease. Human cellular models of glomerular cells, analyses of human glomerular proteome, and improved microscopy procedures have been developed to investigate the molecular composition and organization of the human glomerular ECM.

Endotrophin, a collagen type VI-derived matrikine, reflects the degree of renal fibrosis in patients with IgA nephropathy and in patients with ANCA-associated vasculitis

BACKGROUND

Renal fibrosis is the hallmark of chronic kidney disease (CKD) and is characterized by an imbalanced extracellular matrix remodelling. Endotrophin (ETP) is a signalling molecule released from collagen type VI (COL VI). ETP can be measured by the PRO-C6 assay, which quantifies the levels of COL VI formation. ETP levels were previously associated with mortality and disease progression in patients with CKD. We hypothesized that serum and urinary ETP levels correlate with the degree of interstitial fibrosis in kidney biopsies from patients with immunoglobulin A nephropathy (IgAN) and patients with anti-neutrophil cytoplasmic antibody-associated vasculitis (AAV).

METHODS

We examined a cohort of 49 IgAN and 47 AAV patients. A validation cohort of 85 IgAN patients was included. ETP was measured in serum (S-ETP) and urine (U-ETP/Cr) samples, taken on the same day before renal biopsy was performed, using the enzyme-linked immunosorbent assay PRO-C6. The biopsies were evaluated for interstitial fibrosis and tubular atrophy according to the Banff and MEST-C scores.

RESULTS

S-ETP and U-ETP/Cr levels correlated with kidney function, increased CKD severity, correlated with the extent of interstitial fibrosis and gradually increased with increasing degree of interstitial fibrosis and tubular atrophy. ETP outperformed the known fibrosis biomarker Dickkopf-3 for discrimination of patients with high fibrotic burden. The association of S-ETP and U-ETP/Cr with the level of kidney fibrosis was confirmed in the validation cohort.

CONCLUSIONS

We demonstrated that high levels of circulating and excreted ETP are not only indicative of lower kidney function, but also reflect the burden of fibrosis in the kidneys.

Elevated glucose alters global gene expression and tenascin-C alternative splicing in mesangial cells

Mesangial cells are the major extracellular matrix (ECM)-producing cells in the kidney glomerulus and, when exposed to elevated glucose levels, they up-regulate assembly of fibronectin (FN) and other ECM proteins. Increases in glucose concentration are known to alter gene expression; here we investigated the connection between increased ECM production and changes in gene expression in mesangial cells. Comparison of mesangial cells grown in normal or high glucose conditions by RNA-sequencing showed significant expression changes in over 6000 genes and, when grouped by KEGG pathway analysis, identified the ECM-receptor interaction and focal adhesion pathways among the top 5 upregulated pathways. Of note was the significant increase in expression of tenascin-C (TN-C), a known regulator of FN matrix assembly. Mouse TN-C has multiple isoforms due to alternative splicing of 6 FNIII repeat exons. In addition to the transcriptional increase with high glucose, exon inclusion via alternative splicing was also changed resulting in production of higher molecular weight isoforms of TN-C. Mesangial cells grown in normal glucose secreted small isoforms with 1–2 variable repeats included whereas in high glucose large isoforms estimated to include 5 repeats were secreted. Unlike the smaller isoforms, the larger TN-C was not detected in the FN matrix. This change in TN-C isoforms may affect the regulation of FN matrix assembly and in this way may contribute to increased ECM accumulation under high glucose conditions.

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Elevated glucose alters gene expression in cultured mesangial cells.

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RNA-sequencing identifies increased expression of ECM proteins and receptors.

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High glucose changes tenascin-C isoform expression by alternative splicing.

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Differential ECM localization is detected for large vs small tenascin-C isoforms.

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Switch in tenascin-C may contribute to ECM accumulation in the diabetic glomerulus.

DNA damage in human glomerular endothelial cells induces nodular glomerulosclerosis via an ATR and ANXA2 pathway

Collagen type VI (COL6) deposition occurs in various glomerular diseases, causing serious pathological damage like nodular lesions. However, the mechanisms underlying the deposition of COL6 remain unclear. In renal biopsy samples, immunohistochemical analyses revealed that COL6 and phosphorylated histone H2AX (γ-H2AX), a DNA damage marker, were detected mainly in diabetic nodular glomerulosclerosis, in which the γ-H2AX-positive area was identified as the independent factor significantly associated with the COL6-positive area (β: 0.539, t = 2.668). In in vitro studies, COL6 secretion from human renal glomerular endothelial cells (HRGECs) was assessed by measuring the decrease in the cytoplasmic COL6-positive cells and an increase in the amount of COL6 in the culture medium. Mitomycin C (MMc) treatment of HRGECs increased the number of γ-H2AX-positive cells and COL6 secretion, which were suppressed by a specific inhibitor of ataxia telangiectasia and Rad3-related (ATR). MMc-induced COL6 secretion was also suppressed by Annexin A2 (ANXA2) siRNA transfection. Moreover, the inhibition of ATR activity did not induce any extra suppression in the MMc-induced COL6 secretion by ANXA2 siRNA transfected cells. These results confirm that nodular glomerulosclerosis partially results from DNA damage in the glomerulus and that DNA damage-induced COL6 secretion from HRGECs occurs through an ATR and ANXA2-mediated pathway.

Biopsy-Controlled Non-Invasive Quantification of Collagen Type VI in Kidney Transplant Recipients: A Post-Hoc Analysis of the MECANO Trial

The PRO-C6 assay, a reflection of collagen type VI synthesis, has been proposed as a non-invasive early biomarker of kidney fibrosis. We aimed to investigate cross-sectional and longitudinal associations between plasma and urine PRO-C6 and proven histological changes after kidney transplantation. The current study is a post-hoc analysis of 94 participants of the MECANO trial, a 24-month prospective, multicenter, open-label, randomized, controlled trial aimed at comparing everolimus-based vs. cyclosporine-based immunosuppression. PRO-C6 was measured in plasma and urine samples collected 6 and 24 months post-transplantation. Fibrosis was evaluated in biopsies collected at the same time points by Banff interstitial fibrosis/tubular atrophy (IF/TA) scoring and collagen staining (Picro Sirius Red; PSR); inflammation was evaluated by the tubulo-interstitial inflammation score (ti-score). Linear regression analyses were performed. Six-month plasma PRO-C6 was cross-sectionally associated with IF/TA score (Std. β = 0.34), and prospectively with 24-month IF/TA score and ti-score (Std. β = 0.24 and 0.23, respectively) (p < 0.05 for all). No significant associations were found between urine PRO-C6 and any of the biopsy findings. Fibrotic changes and urine PRO-C6 behaved differentially over time according to immunosuppressive therapy. These results are a first step towards non-invasive fibrosis detection after kidney transplantation by means of collagen VI synthesis measurement, and further research is required.

Identifying collagen VI as a target of fibrotic diseases regulated by CREBBP/EP300

Fibrotic diseases remain a major cause of morbidity and mortality, yet there are few effective therapies. The underlying pathology of all fibrotic conditions is the activity of myofibroblasts. Using cells from freshly excised disease tissue from patients with Dupuytren's disease (DD), a localized fibrotic disorder of the palm, we sought to identify new therapeutic targets for fibrotic disease. We hypothesized that the persistent activity of myofibroblasts in fibrotic diseases might involve epigenetic modifications. Using a validated genetics-led target prioritization algorithm (Pi) of genome wide association studies (GWAS) data and a broad screen of epigenetic inhibitors, we found that the acetyltransferase CREBBP/EP300 is a major regulator of contractility and extracellular matrix production via control of H3K27 acetylation at the profibrotic genes, ACTA2 and COL1A1 Genomic analysis revealed that EP300 is highly enriched at enhancers associated with genes involved in multiple profibrotic pathways, and broad transcriptomic and proteomic profiling of CREBBP/EP300 inhibition by the chemical probe SGC-CBP30 identified collagen VI (Col VI) as a prominent downstream regulator of myofibroblast activity. Targeted Col VI knockdown results in significant decrease in profibrotic functions, including myofibroblast contractile force, extracellular matrix (ECM) production, chemotaxis, and wound healing. Further evidence for Col VI as a major determinant of fibrosis is its abundant expression within Dupuytren's nodules and also in the fibrotic foci of idiopathic pulmonary fibrosis (IPF). Thus, Col VI may represent a tractable therapeutic target across a range of fibrotic disorders.

Targeting Collagen Type III in Proteinuric Kidney Disease: Informing Drug Potential Using the Jaccard–Tanimoto Index

Collagenofibrotic glomerulopathy, a collagen type III kidney disease, is associated with proteinuria and accumulation ofcollagen type III in the glomerulus specifically the mesangium and/or capillary walls. The puromcyin aminonucleoside (PAN) nephropathy model was evaluated to examine the relation between COL3A1 mRNA and proteinuria. In Wistar rats administered PAN, a robust increase in proteinuria was accompanied by glomerular hypertrophy and expansion of both the Bowman’s capsule and Bowman’s space. An ~4-fold increase in renal COL3A1 mRNA was observed in the PAN cohort with urine protein exhibiting a direct (r = 0.8) and significant correlation with kidney COL3A1 mRNA level. Both Picrosirius red polarized microscopy and immunohistochemical analysis showed localization of collagen type III to the glomerular mesangium. Gene ontology-driven transcriptomic analysis reveals a robust COL3A1 network in the glomerular compartment.

Collagen turnover profiles in chronic kidney disease

Renal fibrosis is a hallmark of chronic kidney disease (CKD) caused by an imbalance between formation and degradation of extracellular matrix proteins. We investigated the collagen turnover profile of 81 non-dialysis CKD stage 2-5 patients by measuring peptides reflecting formation and degradation of collagen type (COL) I, III, IV, and VI. Based on the collagen turnover profile, we identified four clusters of patients. Cluster 1 contained one patient with prostate cancer, who had a distinct collagen turnover. The other clusters generally had severe (Cluster 2), moderate (Cluster 4), or mild CKD (Cluster 3). Cluster 4 patients were characterized by higher levels of COL III, COL IV, and COL VI (all p < 0.001) degradation fragments in plasma, while patients in Clusters 2 and 4 had higher levels of COL VI formation (p < 0.05). COL IV fragments in plasma were lower in Cluster 2 (p < 0.01). Urinary COL III fragments decreased from Cluster 3 to 4, and from Cluster 4 to 2 (both p < 0.001). We show that patients with similar kidney function have a different collagen remodeling profile, suggesting that different phenotypes exist with different disease activity and potentially disease progression. Biomarkers of collagen remodeling could provide additional information to traditional markers of renal function.

Glucose fluctuation increased mesangial cell apoptosis related to AKT signal pathway

INTRODUCTION

Blood glucose fluctuation is an important factor for the development of diabetic complications. Glucose fluctuation aggravated the renal injury in diabetic nephropathy. In the present study, our aim was to investigate the effects of blood glucose fluctuation on the glomerular mesangal cells and its related mechanism.

MATERIAL AND METHODS

Mesangial cells were divided into four groups: the normal glucose group (NG) cells were incubated in normal glucose conditions (5.6 mmol/l); the high glucose group (HG) cells were treated with 25 mmol/l; the glucose fluctuation (FG) group received 5.6 mmol/l and 25 mmol/l glucose repeated 3 times; the mannitol group (MG) received 5.6 mmol/l glucose plus 24.4 mmol/l mannitol as a control. Cell viability and apoptosis were detected, reactive oxygen species (ROS) level, superoxide dismutase (SOD) activity and malonaldehyde (MDA) levels were measured. Phosphorylated ser/thr protein kinase (P-AKT, phosphor-Ser473), phosphorylated glycogen synthase kinase-3β (P-GSK-3β, phosphor-Ser9) and cleaved cysteinyl aspartate-specific proteinase-3 (cleaved caspase-3) levels were assessed using western blot.

RESULTS

Data suggested that mesangial cells in the FG group show higher cell viability in 12 h, and lower cell viability from 48 h. The FG group showed cell apoptosis accompanied by a significant MDA level increase and SOD activity decrease in 48 h. More importantly, glucose fluctuation could aggravate oxidative stress in glomerular mesangial cells. Furthermore, the P-AKT level was lower, and increased P-GSK-3β and cleaved caspase-3 levels were higher in the FG group than in the HG group.

CONCLUSIONS

Glucose fluctuation aggravates mesangial cell apoptosis, which may be partly induced by activating oxidative stress and inhibiting the AKT signaling pathway.

Higher Collagen VI Formation Is Associated With All-Cause Mortality in Patients With Type 2 Diabetes and Microalbuminuria

OBJECTIVE

Type 2 diabetes is a common risk factor for the development of chronic kidney disease (CKD). Enhanced de novo collagen type VI (COL VI) formation has been associated with renal fibrosis and CKD. We investigated the hypothesis that PRO-C6, a product specifically generated during COL VI formation, is prognostic for adverse outcomes in patients with type 2 diabetes and microalbuminuria.

RESEARCH DESIGN AND METHODS

In a prospective, observational study, we measured PRO-C6 in the serum (S-PRO-C6) and urine (U-PRO-C6) of 198 patients with type 2 diabetes and microalbuminuria without symptoms of coronary artery disease. Patients were followed for a median of 6.5 years, and end points were a composite of cardiovascular events (n = 38), all-cause mortality (n = 26), and reduction of estimated glomerular filtration rate (eGFR) of >30% (disease progression [n = 42]). Cox models were unadjusted and adjusted for the conventional risk factors of sex, age, BMI, systolic blood pressure, LDL cholesterol, smoking, HbA_1c, plasma creatinine, and urinary albumin excretion rate.

RESULTS

Doubling of S-PRO-C6 increased hazards for cardiovascular events (hazard ratio 3.06 [95% CI 1.31-7.14]), all-cause mortality (6.91 [2.96-16.11]), and disease progression (4.81 [1.92-12.01]). Addition of S-PRO-C6 to a model containing conventional risk factors improved relative integrated discrimination by 22.5% for cardiovascular events (P = 0.02), 76.8% for all-cause mortality (P = 0.002), and 53.3% for disease progression (P = 0.004). U-PRO-C6 was not significantly associated with any of the outcomes.

CONCLUSIONS

S-PRO-C6 generated during COL VI formation predicts cardiovascular events, all-cause mortality, and disease progression in patients with type 2 diabetes and microalbuminuria.

Urinary endotrophin predicts disease progression in patients with chronic kidney disease

Renal fibrosis is the central pathogenic process in progression of chronic kidney disease (CKD). Collagen type VI (COL VI) is upregulated in renal fibrosis. Endotrophin is released from COL VI and promotes pleiotropic pro-fibrotic effects. Kidney disease severity varies considerably and accurate information regarding CKD progression may improve clinical decisions. We tested the hypothesis that urinary endotrophin derived during COL VI deposition in fibrotic human kidneys is a marker for progression of CKD in the Renal Impairment in Secondary Care (RIISC) cohort, a prospective observational study of 499 CKD patients. Endotrophin localised to areas of increased COL VI deposition in fibrotic kidneys but was not present in histologically normal kidneys. The third and fourth quartiles of urinary endotrophin:creatinine ratio (ECR) were independently associated with one-year disease progression after adjustment for traditional risk factors (OR (95%CI) 3.68 (1.06–12.83) and 8.65 (2.46–30.49), respectively). Addition of ECR quartiles to the model for disease progression increased prediction as seen by an increase in category-free net reclassification improvement (0.45, 95% CI 0.16–0.74, p = 0.002) and integrated discrimination improvement (0.04, 95% CI 0.02–0.06, p < 0.001). ECR was associated with development of end-stage renal disease (ESRD). It is concluded that ECR predicts disease progression of CKD patients.

Novel differences in renal gene expression in a diet-induced obesity model

Obesity is a significant risk factor for both chronic kidney disease and end-stage renal disease. To better understand disease development, we sought to identify novel genes differentially expressed early in disease progression. We first confirmed that mice fed a high-fat (HF) diet exhibit early signs of renal injury including hyperfiltration. We then performed RNA-Seq using renal cortex RNA from C57BL6/J male mice fed either HF or control (Ctrl) diet. We identified 1,134 genes differentially expressed in the cortex on HF vs. Ctrl, of which 31 genes were selected for follow-up analysis. This included the 9 most upregulated, the 11 most downregulated, and 11 genes of interest (primarily sensory receptors and G proteins). Quantitative (q)RT-PCR for these 31 genes was performed on additional male renal cortex and medulla samples, and 11 genes (including all 9 upregulated genes) were selected for further study based on qRT-PCR. We then examined expression of these 11 genes in Ctrl and HF male heart and liver samples, which demonstrated that these changes are relatively specific to the renal cortex. These 11 genes were also examined in female renal cortex, where we found that the expression changes seen in males on a HF diet are not replicated in females, even when the females are started on the diet sooner to match weight gain of the males. In sum, these data demonstrate that in a HF-diet model of early disease, novel transcriptional changes occur that are both sex specific and specific to the renal cortex.

Nodular lesions in diabetic nephropathy: Collagen staining and renal prognosis

AIMS

Nodular lesions are one of the most characteristic pathological changes of advanced diabetic nephropathy (DN). Previous studies have demonstrated that the pattern of both routine and collagen staining of nodular lesions changes during their development. However, the association between such changes of staining and the renal prognosis remains unclear.

METHODS

Among 252 patients with biopsy-proven DN, 67 met the selection criteria and were enrolled to investigate this relationship. In all patients, nodular lesions were stained with periodic acid Schiff, periodic acid methenamine silver, and Masson trichrome stains, and immunostaining was done for type I, III, IV, V, and VI collagen. The endpoint was commencement of dialysis due to end-stage renal disease.

RESULTS

At least one mesangiolytic nodular lesion (MNL) that showed faint staining for PAS and PAM was found in 61% of the patients. MNLs were negative for type IV collagen staining, unlike the strong positivity of non-MNLs, while type V and VI collagen staining were strongly positive in all nodular lesions. Cox proportional hazards regression analysis revealed that the hazard ratio (HR) for the endpoint was significantly higher in patients with at least one MNL than in patients with no MNLs after adjustment for known promoters of renal progression (HR: 2.94; 95% confidence interval: 1.24-7.07).

CONCLUSIONS

MNLs may reflect characteristic differences of collagen production and could be a useful prognostic indicator in patients with nodular lesions. Further investigation of the mechanism underlying these differences of collagen production could contribute to finding new therapeutic targets for DN.

Serum endotrophin, a type VI collagen cleavage product, is associated with increased mortality in chronic kidney disease

Background

Patients with chronic kidney disease (CKD) are at increased risk of end-stage renal disease (ESRD) and early mortality. The underlying pathophysiological processes are not entirely understood but may include dysregulation of extracellular matrix formation with accelerated systemic and renal fibrosis. We assessed the relationship between endotrophin (ETP), a marker of collagen type VI formation, and adverse outcomes in a cohort of patients with CKD.

Methods

We measured serum ETP levels in 500 patients from the Renal Impairment in Secondary Care (RIISC) study, a prospective observational study of patients with high-risk CKD. Patients were followed up until death or progression to ESRD. Cox regression analysis was used to assess the relationship between ETP and risk of adverse outcomes.

Results

During a median follow-up time of 37 months, 104 participants progressed to ESRD and 66 died. ETP level was significantly associated with progression to ESRD (HR 1.79 [95% CI 1.59–2.02] per 10 ng/mL increase; HR 11.05 [4.98–24.52] for highest vs lowest quartile; both P<0.0001). ETP level was also significantly associated with mortality (HR 1.60 [1.35–1.89] per 10 ng/mL increase; HR 12.14 [4.26–34.54] for highest vs lowest quartile; both P<0.0001). After adjustment for confounding variables, ETP was no longer significantly associated with progression to ESRD but remained independently associated with mortality (HR 1.51 [1.07–2.12] per 10 ng/mL increase, P = 0.019).

Conclusions

Serum ETP level is independently associated with mortality in CKD. This study provides the basis for further exploratory work to establish whether collagen type VI formation is mechanistically involved in the increased mortality risk associated with CKD.

The impact of insulin resistance on the kidney and vasculature

Insulin resistance is a systemic disorder that affects many organs and insulin-regulated pathways. The disorder is characterized by a reduced action of insulin despite increased insulin concentrations (hyperinsulinaemia). The effects of insulin on the kidney and vasculature differ in part from the effects on classical insulin target organs. Insulin causes vasodilation by enhancing endothelial nitric oxide production through activation of the phosphatidylinositol 3-kinase pathway. In insulin-resistant states, this pathway is impaired and the mitogen-activated protein kinase pathway stimulates vasoconstriction. The action of insulin on perivascular fat tissue and the subsequent effects on the vascular wall are not fully understood, but the hepatokine fetuin-A, which is released by fatty liver, might promote the proinflammatory effects of perivascular fat. The strong association of salt-sensitive arterial hypertension with insulin resistance indicates an involvement of the kidney in the insulin resistance syndrome. The insulin receptor is expressed on renal tubular cells and podocytes and insulin signalling has important roles in podocyte viability and tubular function. Renal sodium transport is preserved in insulin resistance and contributes to the salt-sensitivity of blood pressure in hyperinsulinaemia. Therapeutically, renal and vascular insulin resistance can be improved by an integrated holistic approach aimed at restoring overall insulin sensitivity and improving insulin signalling.

Drug-induced nephrotoxicity and its biomarkers

Nephrotoxicity occurs when kidney-specific detoxification and excretion do not work properly due to the damage or destruction of kidney function by exogenous or endogenous toxicants. Exposure to drugs often results in toxicity in kidney which represents the major control system maintaining homeostasis of body and thus is especially susceptible to xenobiotics. Understanding the toxic mechanisms for nephrotoxicity provides useful information on the development of drugs with therapeutic benefi ts with reduced side effects. Mechanisms for drug-induced nephrotoxicity include changes in glomerular hemodynamics, tubular cell toxicity, inflammation, crystal nephropathy, rhabdomyolysis, and thrombotic microangiopathy. Biomarkers have been identifi ed for the assessment of nephrotoxicity. The discovery and development of novel biomarkers that can diagnose kidney damage earlier and more accurately are needed for effective prevention of drug-induced nephrotoxicity. Although some of them fail to confer specificity and sensitivity, several promising candidates of biomarkers were recently proved for assessment of nephrotoxicity. In this review, we summarize mechanisms of drug-induced nephrotoxicity and present the list of drugs that cause nephrotoxicity and biomarkers that can be used for early assessment of nephrotoxicity.

Quantitative proteomic profiling identifies new renal targets of copper(II)-selective chelation in the reversal of diabetic nephropathy in rats

This study aimed to identify new diabetic nephropathy (DN)-related proteins and renal targets of the copper(II)-selective chelator, triethylenetetramine (TETA) in streptozotocin-diabetic rats. We used the recently developed iTRAQ technology to compare renal protein profiles among non-diabetic, diabetic, and TETA-treated diabetic rats. In diabetic kidneys, tubulointerstitial nephritis antigen (TINag), voltage-dependent anion-selective channel (VDAC) 1, and VDAC2 were up-regulated in parallel with alterations in expression of proteins with functions in oxidative stress and oxidative phosphorylation (OxPhos) pathways. By contrast, mitochondrial HSP 60, Cu/Zn-superoxide dismutase, glutathione S-transferase alpha3 and aquaporin-1 were down-regulated in diabetic kidneys. Following TETA treatment, levels of D-amino acid oxidase-1, epoxide hydrolase-1, aquaporin-1, and a number of mitochondrial proteins were normalized, with concomitant amelioration of albuminuria. Changes in levels of TINag, collagen VIalpha1, actinin 4alpha, apoptosis-inducing factor 1, cytochrome C, histone H3, VDAC1, and aquaporin-1 were confirmed by Western blotting or immunohistochemistry. Changes in expression of proteins related to tubulointerstitial function, podocyte structure, and mitochondrial apoptosis are implicated in the mechanism of DN and their reversal by TETA. These findings are consistent with the hypothesis that this new experimental therapy may be useful for treatment of DN.

Insulin increases gelatinase activity in rat glomerular mesangial cells via ERK- and PI-3 kinase-dependent signalling

Diabetic nephropathy is associated with increased accumulation of the extracellular matrix (ECM) in the kidney, which ultimately leads to kidney failure. This may occur due to excessive synthesis of ECM components or reduced degradation, a process primarily mediated by matrix metalloproteinases (MMPs). The direct effect of insulin on ECM synthesis and degradation in glomerular mesangial cells (GMCs) is unclear. Here, we show an increased gelatinase activity in conditioned media from insulin-treated rat GMCs, determined by gelatin zymography. Furthermore, we show using the specific inhibitors LY294002 and PD98059 that insulin induced increased gelatinase activity via an intracellular signalling mechanism involving phosphatidylinositol-3 kinase (PI-3K) and the extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinases (MAPKs) respectively. In addition, we demonstrate that PI-3 kinase and ERK1/2 MAPK are activated by insulin in GMCs. The appearance of protease activity at approximately 72 kDa suggested that MMP-2 activity may be induced by insulin, however, we did not detect an increase in MMP-2 expression by Western blotting. In summary, our results suggest that insulin can induce gelatinase activity in GMCs, and it is possible that loss of this input in insulin-resistant type 2 diabetic individuals may contribute to ECM accumulation and the development of nephropathy.

Carnosine as a protective factor in diabetic nephropathy: association with a leucine repeat of the carnosinase gene CNDP1

The risk of diabetic nephropathy is partially genetically determined. Diabetic nephropathy is linked to a gene locus on chromosome 18q22.3-q23. We aimed to identify the causative gene on chromosome 18 and to study the mechanism by which the product of this gene could be involved in the development of diabetic nephropathy. DNA polymorphisms were determined in 135 case (diabetic nephropathy) and 107 control (diabetes without nephropathy) subjects. The effect of carnosine on the production of extracellular matrix components and transforming growth factor-beta (TGF-beta) after exposure to 5 and 25 mmol/l d-glucose was studied in cultured human podocytes and mesangial cells, respectively. A trinucleotide repeat in exon 2 of the CNDP1 gene, coding for a leucine repeat in the leader peptide of the carnosinase-1 precursor, was associated with nephropathy. The shortest allelic form (CNDP1 Mannheim) was more common in the absence of nephropathy (P = 0.0028, odds ratio 2.56 [95% CI 1.36-4.84]) and was associated with lower serum carnosinase levels. Carnosine inhibited the increased production of fibronectin and collagen type VI in podocytes and the increased production of TGF-beta in mesangial cells induced by 25 mmol/l glucose. Diabetic patients with the CNDP1 Mannheim variant are less susceptible for nephropathy. Carnosine protects against the adverse effects of high glucose levels on renal cells.

Clinicopathologic characteristics of nodular glomerulosclerosis in Chinese patients with type 2 diabetes

BACKGROUND

Nodular glomerulosclerosis is a distinct entity that is highly specific for diabetic glomerulopathy. However, clinicopathologic characteristics of this nodular lesion are largely undefined in patients with type 2 diabetes.

METHODS

An autopsy study was conducted to investigate the clinical, histopathologic, and histochemical characteristics of 351 consecutive cases with type 2 diabetes. In addition, immunohistochemical staining was performed in a representative subset of 50 cases.

RESULTS

Nodular glomerulosclerosis was found in 37.6%. Hypertension, elevated serum creatinine and urea levels, renal failure, myocardial infarction, low body mass index, and large glomerular matrix area were the significant risk factors for nodular glomerulosclerosis. Proteinuria (protein > 0.5 g/24 h), renal insufficiency (serum creatinine > or = 2.0 mg/dL [> or =178 micromol/L]), and renal failure were found in 28.1%, 33.6%, and 7.6% of patients with type 2 diabetes with nodular glomerulosclerosis, respectively. Glomerular matrix fractions were 42.1% +/- 13.3%, 32.3% +/- 15.3%, and 22.7% +/- 8.0% in patients with nodular glomerulosclerosis, non-nodular glomerulopathy (glomerulopathy in the absence of Kimmelstiel-Wilson nodule), and near-normal glomeruli with age-related minimal changes, respectively (analysis of variance, P < 0.001). Immunoreactivity for collagen type IV, fibronectin, and laminin was localized at the periphery of mesangial nodules. Mesangial cells at the periphery of mesangial nodules showed increased staining intensity for alpha-smooth muscle actin (alpha-SMA) and transforming growth factor-beta1 (TGF-beta1). Nodular lesions also showed a marked increase in number of glomerular CD68-positive macrophages.

CONCLUSION

In patients with type 2 diabetes, nodular glomerulosclerosis is related to hypertension, advanced renal disease, and prevalent myocardial infarction. Glomerular macrophage infiltration, expression of alpha-SMA by mesangial cells, and overexpression of TGF-beta1 are the cellular changes associated with abnormal extracellular matrix deposition in nodular glomerulosclerosis.

Association of glomerulopathy with the 5'-end polymorphism of the aldose reductase gene and renal insufficiency in type 2 diabetic patients

The expression of nephropathy in type 2 diabetes has several levels of abnormalities. To define the primary abnormalities of diabetic nephropathy, we conducted an autopsy study of 186 consecutive patients with type 2 diabetes to determine correlations among the aldose reductase gene, renal histopathologies, extracellular matrix, glomerular function, and clinical characteristics. Compared with cases of near-normal renal structure (n = 51) and atypical diabetic glomerulopathy (n = 75), patients with classic diabetic glomerulopathy (n = 60) had advanced glomerular disease, as reflected by elevated plasma creatinine levels (133.2 +/- 59.8 vs. 166.0 +/- 65.7 vs. 243.8 +/- 82.6 micromol/l; P < 0.001), glomerular matrix fractions (20.8 +/- 6.7 vs. 33.5 +/- 16.8 vs. 39.2 +/- 14.3%; P < 0.001), and risk of renal failure (odds ratio [OR] 1 vs. 3.5 vs. 21.4; P < 0.001). Compared with noncarriers of the aldose reductase z-2 allele (n = 92) and z-2 heterozygotes (n = 77), z-2 homozygotes (n = 17) had elevated plasma creatinine (164.1 +/- 73.7 vs. 190.6 +/- 60.9 vs. 241.1 +/- 86.2 micromol/l; P < 0.001) and an increased risk of classic diabetic glomerulopathy (OR 1 vs. 0.9 vs. 3.3; P = 0.026). Overexpression of transforming growth factor-beta1, mesangial cell transdifferentiation by expression of alpha-smooth muscle actin, and aberrant deposition of collagen type IV, fibronectin, and laminin were found in classic diabetic glomerulopathy. These data suggest genetic, biochemical, pathophysiological, and clinical correlations among the aldose reductase gene, extracellular matrix, classic diabetic glomerulopathy, and renal insufficiency. Gene mutation, cellular transdifferentiation, growth factor upregulation, extracellular matrix expansion, and glomerular filtration impairment are the primary abnormalities in type 2 diabetic patients with nephropathy.

Antibody response against perlecan and collagen types IV and VI in chronic renal allograft rejection in the rat

Chronic rejection is the leading cause of late renal transplant failure. Various structural lesions are observed in grafts undergoing chronic rejection including glomerular basement membrane (GBM) duplications. The well-established Fisher (F344) to Lewis (LEW) rat renal transplant model for chronic rejection was used to assess the presence and role of the humoral immune response against graft antigens during chronic rejection. LEW recipients of F344 allografts develop transplant glomerulopathy and produce IgG1 antibodies directed against F344 GBM preparations that are detectable 3 weeks after transplantation. Glomerular IgG1 deposition was observed that in vitro co-localized with a rabbit anti-rat GBM antiserum in rejecting F344 grafts; elution experiments of isolated glomeruli yielded IgG1 antibodies reactive in vitro with F344 GBM, but not LEW GBM. Prevention of acute rejection by transient treatment of the recipients with cyclosporin A completely abrogated the production of anti-GBM antibodies. Using proteomic techniques we identified the antigens recognized by the LEW posttransplant sera as being the heparan sulfate proteoglycan perlecan and the alpha1 chain of collagen type VI in association with the alpha5 chain of collagen type IV. In conclusion, LEW recipients of F344 kidney grafts produce IgG1 antibodies against donor type perlecan and alpha1(VI)/alpha5(IV) collagen and develop transplant glomerulopathy. These data implicate an important role for the humoral immune response in the development of glomerulopathy during chronic rejection.

Collagen VII expression in glomerular sclerosis

Glomerular sclerosis is the final stage of a variety of kidney diseases and matrix molecules not normally expressed in the extracellular matrix are synthesized and accumulate during the sclerotic process. Collagen type VII is the major component of the anchoring fibrils at the dermal-epidermal junction, but it is usually not present in normal glomeruli. The aim of this study was to investigate whether this type of fibrillary collagen, different from types I and III, is expressed in chronically diseased glomerular extracellular matrix. The presence and distribution of collagen VII have been examined in 50 renal biopsies by indirect immunofluorescence staining, standard electron microscopy, and immuno-electron microscopy. In selected cases, collagen VII mRNA expression was also measured by RT-PCR on isolated glomeruli. Cases included focal segmental glomerulosclerosis, minimal change disease, membranous glomerulonephritis, IgA nephropathy, SLE nephritis, diabetic glomerulosclerosis, ischaemic renal disease, extracapillary glomerulonephritis, and end-stage renal disease. Collagen VII protein and mRNA expression was absent or present in trace amounts in normal kidneys or in disorders with only a mild increase of mesangial matrix, without scarring of the tuft. Maximal expression was evident in the presence of adhesions between the glomerular tuft and Bowman's capsule or fibrous crescents. The results showed that collagen VII is actively synthesized and laid down in areas of glomerular and/or tubular scarring, irrespective of the underlying disease, confirming the de novo expression of fibrillary collagens in diseased renal extracellular matrix. The appearance of an anchoring collagen may be a response to support mechanical stress and it takes part in the process of cell proliferation and tissue repair.

Quantitative immunoelectron microscopy of type VI collagen in glomeruli in type I diabetic patients

BACKGROUND

The nature of the extracellular matrix (ECM) accumulating in the glomerular basement membrane (GBM) and mesangium (Mes) in diabetes is unknown. Type IV collagen (Col IV) as estimated by quantitative immunoelectron microscopy was reduced in type I diabetic patients (D) with rapid ("fast-track") compared with slow ("slow-track") development of diabetic nephropathy (DN) lesions and controls (C). Col VI is another ECM component suggested to account for Mes matrix (MM) expansion in DN.

METHODS

Col VI ECM density was evaluated in eight "slow-track" {Mes fractional volume [Vv(Mes/glom)] <0.32, duration> 20 years} and seven "fast-track" patients [Vv(Mes/glom)> 0.37, duration <20 years diabetes] and in eight C. Quantitative immunoelectron microscopy was performed using polyclonal antibodies to Col VI. Gold particle density (PDG) in MM and the inner layer (IL) of the GBM was measured using stereologic methods.

RESULTS

GBM IL PDG was decreased in both fast-track (1.7 +/- 1.6/microm2, mean +/- SD, P < 0.002) and slow-track (3.9 +/- 2.4, P < 0.02) D versus C (10.8 +/- 7.9). GBM IL PDG was also lower in the fast-track versus slow-track D (P < 0.04). Mes matrix PDG/microm2 was decreased in fast-track D (3.2 +/- 3.6) versus C (14.1 +/- 14.6, P < 0.02); a similar trend was seen in slow-track D (5.7 +/- 5.6, P < 0.1). There was no significant difference in MM PDG between the slow-track and fast-track D.

CONCLUSION

Col VI density in MM and GBM is decreased in diabetic patients with slowly and rapidly developing renal lesions. This leaves the nature of ECM accumulation in DN unexplained. At least in part, glomerular ECM compositional change is related to diabetes per se and may be independent of the severity of lesions.

Troglitazone halts diabetic glomerulosclerosis by blockade of mesangial expansion

BACKGROUND

Renal complications of long-term, poorly controlled type 2 diabetes mellitus include glomerulosclerosis and interstitial fibrosis. The onset and progression of these complications are influenced by underlying pathophysiologies such as hyperglycemia, hypertriglyceridemia, and hypercholesterolemia. Troglitazone, a thiazolidinedione, has been shown to ameliorate these metabolic defects. However, it was not known whether therapeutic intervention with troglitazone would prevent the onset and progression of glomerulosclerosis.

METHODS

Sixty male ZDF/Gmitrade mark rats and 30 age-matched Zucker lean rats were in the study. The ZDF/Gmitrade mark rats were divided into two groups, one in which blood glucose levels were uncontrolled (30 animals) and another (30) in which blood glucose was controlled via dietary administration of troglitazone. Ten animals from each group were sacrificed at one, three, and six months into the study. The kidneys were harvested and processed for immunostaining with BM-CSPG, a marker for mesangial matrix. Images of 200 glomeruli per animal were captured using digital imaging microscopy, and the index of mesangial expansion (total area mesangium/total area of tuft) per glomerular section was measured.

RESULTS

The administration of troglitazone ameliorated the metabolic defects associated with type 2 diabetes mellitus. Moreover, the glomeruli from tissue sections of animals given troglitazone showed no mesangial expansion when compared with normoglycemic control animals, whereas the uncontrolled diabetic animals showed significant mesangial expansion at all time intervals.

CONCLUSIONS

Therapeutic intervention with the thiazolidinedione troglitazone halts the early onset and progression of mesangial expansion in the ZDF/Gmitrade mark rat, preventing the development of glomerulosclerosis in this animal model of type 2 diabetes mellitus.

Molecular mechanism of diabetic nephropathy

Diabetic nephropathy is one of the main causes of renal end-stage disease. Morphologically, the development of diabetic nephropathy is characterized by progressive thickening of the glomerular basement membrane and by expansion of the mesangial matrix which correlates to glomerular filtration function. In vitro studies with cultured mesangial cells revealed that elevated glucose concentrations increase collagen synthesis similar to the in vivo situation. These studies showed that hyperglycemia may be toxic either by non-enzymatic reaction of glucose with proteins and subsequent formation of advanced glucosylation end products or by increased metabolism leading to increased oxidative stress and activation of protein kinase C resulting in increased production of cytokines. Particularly, de novo synthesis of transforming growth factor beta1 (TGF-beta1) is induced and TGF-beta1 appears also involved since blockage of this prosclerotic factor inhibits high glucose-induced collagen synthesis. Interestingly, it could be demonstrated that angiotensin II also stimulates TGF-beta1 production possibly via the same signal transduction pathway. Besides the classical clinical chemical parameters for evaluation of renal function, the measurement of urinary albumin excretion is now widely used for detection of developing diabetic nephropathy. Since diabetes causes glomerular and tubular changes, tubular marker proteins may be used to detect early renal damage. An increased urinary excretion of matrix proteins (e.g. collagen) and cytokines (e.g. TGF-beta1) was found in early diabetic nephropathy. However, the diagnostic value of these new parameters remains to be established.

Effects of epidermal growth factor on collagen expression by rat kidney mesangial cells in culture

Increased collagen production by mesangial cells plays a key role in the development and progression of glomerular sclerosis. These changes reflect in part the impact of growth factors on mesangial cells. Since mesangial cells possess receptors for epidermal growth factor (EGF) and since previous studies have documented that EGF affects collagen synthesis in other cell types, we have examined the effects of EGF on collagen biosynthesis by rat kidney mesangial (RKM) cells in culture. Exposure for 24 h to EGF did not substantially affect the growth rate of RKM cells. While the types of collagen produced by RKM cells (types I, III, IV and V) were unaltered by exposure to EGF, total collagen production was reduced ( approximately 50%). This decrease in collagen expression was not uniform for each collagen type. Type I collagen production was inhibited by approximately 50%, both type III and type IV expression were each reduced by approximately 30%, but type V collagen production was suppressed by only approximately 15%. The reduction in type I collagen synthesis was accounted for mainly by a decrease in type I homotrimer production. Since type I molecules represent approximately 95% of the total collagen produced, the decrease in overall collagen expression reflects a specific suppression by EGF on type I homotrimer production in mesangial cells. As EGF exposure resulted in a decrease in collagen production, these results suggest that the increases in synthesis and deposition of collagen observed in several glomerular diseases likely do not reflect the short-term effects of EGF on mesangial cells. Rather, these findings suggest the possibility that EGF or EGF-like growth factors may ameliorate the effects of other soluble factors that cause enhanced matrix production and deposition in renal diseases.

Soluble collagen VI drives serum-starved fibroblasts through S phase and prevents apoptosis via down-regulation of Bax

We previously showed that soluble, pepsin-solubilized collagen VI increases de novo DNA synthesis in serum-starved HT1080 and 3T3 fibroblasts up to 100-fold compared with soluble collagen I, reaching 80% of the stimulation caused by 10% fetal calf serum. Here we show that collagen VI also inhibits apoptotic cell death in serum-starved cells as evidenced by morphological criteria, DNA laddering, complementary apoptosis assays (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling, enzyme-linked immunosorbent assay, and fluorescence-activated cell sorting), and quantification of apoptosis-regulating proteins. In the presence of starving medium alone or collagen I, the proapoptotic Bax was up-regulated 2-2.5-fold, compared with soluble collagen VI and fetal calf serum, whereas levels of the antiapoptotic Bcl-2 protein remained unaffected. In accordance with its potent stimulation of DNA synthesis, soluble collagen VI carries serum-starved HT1080 and Balb 3T3 fibroblasts through G(2) as shown by fluorescence-activated cell sorting analysis, whereas cells exposed to medium and collagen I where arrested at G(1)-S. This was accompanied by a 2-3-fold increase in cyclin A, B, and D1 protein expression. Collagen VI-induced inhibition of apoptotic cell death may be operative during embryogenesis, wound healing, and fibrosis when elevated tissue and blood levels of collagen VI are observed, thus initiating a feedback loop of mesenchymal cell activation and proliferation.

Expansion of cortical interstitium is limited by converting enzyme inhibition in type 2 diabetic patients with glomerulosclerosis. The Diabiopsies Group

Renal interstitial expansion is now considered a useful marker of progression of several nephropathies. This study describes a multicenter, prospective, double-blind, placebo-controlled, randomized trial of the effects of Perindopril (4 mg/d) on kidney structure and function over 2 yr in 26 type 2 diabetic patients with proteinuria ranging from 70 to 4210 mg/d and relatively preserved GFR (creatinine clearance >60 ml/min). All patients underwent baseline renal biopsy, but four (15%) were not randomized because of the presence of nondiabetic nephropathy. The remaining 22 were randomized ( 11 to Perindopril [PE], 11 to placebo [PO]), and 19 (9 PE, 10 PO) underwent follow-up biopsy at 2 yr. BP was controlled equally in both groups throughout. Proteinuria increased in PO patients (+1562 mg/d) but declined in PE patients (-156 mg/d) (P < 0.05). Morphometric analysis was performed by light microscopy using a Biocom computer. Over the 2 yr, mean cortical interstitial fractional volume identical at baseline increased significantly in PO patients (31.7 +/- 5.3 versus 40.2 +/- 11.1%; P = 0.001) but was unchanged in PE patients (33.8 +/- 4.9 versus 34.7 +/- 6.6%; P = 0.50). It is concluded that: (1) nondiabetic nephropathy is present in approximately 15% of albuminuric type 2 diabetic patients; and (2) Perindopril prevents interstitial expansion in hypertensive patients with biopsy-proven diabetic glomerulopathy. These results support a role of angiotensin II in the progression of interstitial changes in type 2 diabetic patients with nephropathy.

An ultrastructural study of the colocalization of biglycan and decorin with AA amyloid fibrils in human renal glomeruli

An investigation was undertaken on paraformaldehyde-fixed, Lowicryl resin-embedded renal biopsies from patients with AA amyloidosis to study the association of two small chondroitin sulphate/dermatan sulphate proteoglycans, decorin and biglycan, with amyloid fibrils using an ultrastructural immunogold technique. Biglycan was present in glomerular endothelial cells in both normal kidney and in amyloidosis, but little biglycan or decorin was present in the normal mesangial matrix. By contrast, conspicuous amounts of both biglycan and decorin were seen to be associated with amyloid fibrils in the glomerular matrix in cases of renal AA amyloidosis. The results further emphasise the close association between amyloid and extracellular matrix components which are now considered to be an integral part of the amyloid fibrils.

High glucose-induced transforming growth factor beta1 production is mediated by the hexosamine pathway in porcine glomerular mesangial cells

Previous studies revealed that exposure of mesangial cells to high glucose concentration induces the production of matrix proteins mediated by TGF-beta1. We tested if structural analogues of D-glucose may mimic the high glucose effect and found that D-glucosamine was strikingly more potent than D-glucose itself in enhancing the production of TGF-beta protein and subsequent production of the matrix components heparan sulfate proteoglycan and fibronectin in a time- and dose-dependent manner. D-Glucosamine also promoted conversion of latent TGF-beta to the active form. Therefore, we suggested that the hexosamine biosynthetic pathway (the key enzyme of which is glutamine:fructose-6-phosphate amidotransferase [GFAT]) contributes to the high glucose-induced TGF-beta1 production. Inhibition of GFAT by the substrate analogue azaserine or by inhibition of GFAT protein synthesis with antisense oligonucleotide prevented the high glucose-induced increase in cellular glucosamine metabolites and TGF-beta1 expression and bioactivity and subsequent effects on mesangial cell proliferation and matrix production. Overall, our study indicates that the flux of glucose metabolism through the GFAT catalyzed hexosamine biosynthetic pathway is involved in the glucose-induced mesangial production of TGF-beta leading to increased matrix production.

Type VI collagen in glomeruli of short- and long-term experimental diabetic rats

Type VI collagen was revealed by high-resolution immunocytochemistry in renal glomeruli from short- and long-term streptozotocin-injected hyperglycaemic rats and from their age-matched normoglycaemic controls. The labellings obtained over the glomerular basement membrane and the mesangial matrix were assessed by quantitative evaluations. The labellings over the glomerular basement membrane were low and sparse in the young normoglycaemic animals but became consistent and increased in intensity with age and in both the short- and long-term diabetic animals. For the mesangial matrix, this was labelled more systematically, and its intensity increased with age and in the short-term hyperglycaemic animals. For the long-term hyperglycaemic animals, the intensities of labelling resembled those of their age-matched controls. These results indicate that type VI collagen appears to be a minor constituent of the extracellular matrix of the rat glomeruli, rather concentrated in the mesangial area in the young control animal. Concomitant with the general modifications of the extracellular matrix occurring with age and diabetes, this component increases, but apparently not with the length of the hyperglycaemic state.

Morphogenesis of the glomerular filter: the synchronous assembly and maturation of two distinct extracellular matrices

The morphogenesis of the glomerular filtration apparatus during pre- and postnatal development in the rodent involves the coordinated assembly of two closely apposed but morphologically different extracellular matrices, the glomerular capillary basement membrane and the mesangial matrix. The cellular origin of these matrices is known to be distinct and complex; however, the mechanisms by which these matrices are assembled during morphogenesis are not entirely understood. It has been shown that in the earliest stages of glomerular morphogenesis the nascent glomerular basement membrane exists as a four-layered structure, the product of both the visceral epithelium and capillary endothelium. During the latter stages of glomerular development, the quadrilaminar structure becomes a trilaminar basement membrane, the event thought to occur by fusion of closely apposed basement membrane layers. In subsequent stages of maturation and throughout the life of the animal, the visceral epithelial cells, which line the periphery of the glomerular capillary, are the primary source of newly synthesized basement membrane material. The mesangial matrix, which lacks the specific organization of a basement membrane, first occurs in the developing glomerulus as a diffuse matrix central to the developing glomerular capillaries. During glomerular maturation the mesangial matrix undergoes a compaction/arborization coincident with the ramification of the vascular histoarchitecture of the glomerular tuft. Recent advances in the cell biology of basement membrane now demonstrate that there is a divergence in isoforms of the molecules that comprise the glomerular capillary basement membrane and mesangial matrices during development, possibly coincidental with functional specialization during the process of glomerular maturation.

Mast cells and type VIII collagen in human diabetic nephropathy

Renal injury in diabetes mellitus is associated with progressive interstitial fibrosis and extracellular matrix accumulation. However, the phenotypes of cells forming the interstitial infiltrate in diabetic nephropathy have not been precisely defined. There is increasing evidence for the association of mast cells with angiogenesis, chronic inflammatory conditions and fibrosis. We have recently shown that human mast cells can produce the non-fibrillar short chain type VIII collagen in vivo. Using immunohistochemistry, in situ hybridisation and reverse transcriptase-polymerase chain reaction, we examined the contribution of mast cells and type VIII collagen to the fibrotic changes occurring in biopsy-proven diabetic nephropathy. We observed that the number of interstitial mast cells was significantly increased in diabetic nephropathy compared with normal kidney tissue. In specimens from diabetic subjects, intense immunohistochemical staining for type VIII collagen was detected in mast cells, on periglomerular fibres and in perivascular and interstitial sites. The expression of type VIII collagen in periglomerular and interstitial sites coincided with that of alpha smooth muscle actin, a marker for myofibroblastic differentiation mRNA for type VIII collagen was detected by reverse transcriptase-polymerase chain reaction in diabetic nephropathy and in a human mast cell line. By in situ hybridisation the transcripts for type VIII collagen were localised to renal mast cells. The increased number of mast cells and the elevated type VIII collagen deposition in human diabetic nephropathy provides a potential link between the extracellular matrix accumulation and the fibrosis observed in this condition.

Immunohistochemical distribution of type VI collagen in developing human kidney

The distribution of type VI collagen was investigated immunohistochemically in the developing human kidney from 15 to 32 weeks gestational age and it was compared with that observed in the normal infantile and adult human kidney. In fetal kidney, type VI collagen was widely distributed as a fibrillar network in the subcapsularly undifferentiated mesenchyme and intertubular interstitium, and as a basement membrane-like structure around the ureteral bud branches, tubules, and collecting ducts. During nephrogenesis, type VI collagen disappeared from the induced mesenchyme close to the tips of ureteral branches, while it formed a distinct basement membrane-like structure around the early stages of nephron differentiation (comma-shaped and S-shaped bodies) and later along Bowman's capsule of capillary loop and maturing glomeruli A strong immureactivity for type VI collagen was also found in the glomerular basement membrane and mesangial areas of capillary loop and maturing glomeruli. In infantile kidney, type VI collagen showed a distribution pattern similar to that observed during the fetal period. In adult human kidney, glomerular basement membrane showed a weak positivity for type VI collagen and the basement membrane-like staining around Bowman's capsule, tubules, and collecting ducts was less evident than in fetal and infantile kidney. Our immunohistochemical findings suggest that type VI collagen is a normal component of the glomerular and extraglomerular extracellular matrix of developing human kidney and that it undergoes changes in the expression during maturation.

Significance of increased accumulation of type VI collagen and transforming growth factor beta 1 in tubulointerstitial damage in hypertensive nephrosclerosis: an immunohistochemical study

The distribution of type VI collagen and transforming growth factor beta 1 (TGF beta 1) was studied by immunohistochemistry in 12 renal biopsy specimens of hypertensive nephrosclerosis and five control cases. In control kidneys, the immunostaining of type VI collagen was found in the mesangium, glomerular basement membrane and tubular basement membrane. For TGF beta 1, mesangium, glomerular basement membrane, tubular basement membrane and tubular epithelial cells stained positively in the control kidneys. In contrast to the control cases, markedly increased immunostaining for both type VI collagen and TGF beta 1 was consistently observed in tubulointerstitial damage in hypertensive nephrosclerosis. These immunohistochemical findings provide the evidence for a parallel increase of both type VI collagen and TGF beta 1 during the process of tubulointerstitial injury in hypertensive nephrosclerosis. From the results of the present study, it is speculated that TGF beta 1 may contribute to the tubulointerstitial injury by stimulating increased synthesis of various extracellular matrix including type VI collagen.

Distribution of extracellular matrix glycoproteins in the human mesonephros

We analyzed the expression and distribution of collagen types IV and VI, laminin and fibronectin during the development and regression of the mesonephros in human embryos and fetuses ranging from 6 to 12 weeks of gestation by indirect immunoperoxidase methods. Type IV collagen, laminin and fibronectin were detected along the glomerular, tubular and capsular basement membranes of developing and mature nephrons. Only type IV collagen and fibronectin were found in the mesangium. Type VI collagen formed a delicate interstitial fibrillar network and a continuous basement membrane-like structure along the mesonephric nephrons. Basement membranes (GBM) of developing and mature glomeruli showed a distinct continuous staining for this collagen. The mesangial matrix was rich in type VI collagen. Mesonephric involution started during the 8th week of gestation and coincided with a moderate expansion of mesangial matrix and progressive collapse of the capillary walls, while the tubules became thinner and shorter. Staining for all extracellular matrix glycoproteins studied showed GBM wrinkling, gradual disintegration of some capillary loops and glomerulosclerosis. The sclerotic glomeruli were strongly positive for type IV collagen and less positive for type VI collagen and fibronectin. Laminin was absent. Our results indicate that collagen types IV, VI, laminin and fibronectin may be involved in the development and regression of the human mesonephros.