Immunohistochemical distribution of type VI collagen in developing human kidney

The coordinated activities of collagen VI and XII in maintenance of tissue structure, function and repair: evidence for a physical interaction

Collagen VI and collagen XII are structurally complex collagens of the extracellular matrix (ECM). Like all collagens, type VI and XII both possess triple-helical components that facilitate participation in the ECM network, but collagen VI and XII are distinct from the more abundant fibrillar collagens in that they also possess arrays of structurally globular modules with the capacity to propagate signaling to attached cells. Cell attachment to collagen VI and XII is known to regulate protective, proliferative or developmental processes through a variety of mechanisms, but a growing body of genetic and biochemical evidence suggests that at least some of these phenomena may be potentiated through mechanisms that require coordinated interaction between the two collagens. For example, genetic studies in humans have identified forms of myopathic Ehlers-Danlos syndrome with overlapping phenotypes that result from mutations in either collagen VI or XII, and biochemical and cell-based studies have identified accessory molecules that could form bridging interactions between the two collagens. However, the demonstration of a direct or ternary structural interaction between collagen VI or XII has not yet been reported. This Hypothesis and Theory review article examines the evidence that supports the existence of a functional complex between type VI and XII collagen in the ECM and discusses potential biological implications.

COL28 promotes proliferation, migration, and EMT of renal tubular epithelial cells

Type XXVIII collagen (COL28) is involved in cancer and lung fibrosis. COL28 polymorphisms and mutations might be involved in kidney fibrosis, but the exact role of COL28 in renal fibrosis is unknown. This study explored the function of COL28 in renal tubular cells by examining the expression of COL28 mRNA and the effects of COL28 overexpression in human tubular cells. COL28 mRNA expression and localization were observed in normal and fibrotic kidney tissues from humans and mice using real-time PCR, western blot, immunofluorescence, and immunohistochemistry. The consequences of COL28 overexpression on cell proliferation, migration, cell polarity, and epithelial-to-mesenchymal transition (EMT) induced by TGF-β1 were examined in human tubular HK-2 cells. COL28 expression was low in human normal renal tissues, mainly observed in the renal tubular epithelial cells and especially in proximal renal tubules. COL28 protein expression in human and mouse obstructive kidney disease was higher than in normal tissues (p < 0.05) and more significant in the UUO2-Week than the UUO1-Week group. The overexpression of COL28 promoted HK-2 cell proliferation and enhanced their migration ability (all p < 0.05). TGF-β1 (10 ng/ml) induced COL28 mRNA expression in HK-2 cells, decreased E-cadherin and increased α-SMA in the COL28-overexpression group compared with controls (p < 0.05). ZO-1 expression decreased while COL6 increased in the COL28-overexpression group compared with controls (p < 0.05). In conclusion, COL28 overexpression promotes the migration and proliferation of renal tubular epithelial cells. The EMT could also be involved. COL28 could be a therapeutic target against renal- fibrotic diseases.

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.

Collagen VI as a driver and disease biomarker in human fibrosis

Fibrosis of visceral organs such as the lungs, heart, kidneys and liver remains a major cause of morbidity and mortality and is also associated with many other disorders, including cancer and metabolic disease. In this review, we focus upon the microfibrillar collagen VI, which is present in the extracellular matrix (ECM) of most tissues. However, expression is elevated in numerous fibrotic conditions, such as idiopathic pulmonary disease (IPF), and chronic liver and kidney diseases. Collagen VI is composed of three subunits α1, α2 and α3, which can be replaced with alternate chains of α4, α5 or α6. The C-terminal globular domain (C5) of collagen VI α3 can be proteolytically cleaved to form a biologically active fragment termed endotrophin, which has been shown to actively drive fibrosis, inflammation and insulin resistance. Tissue biopsies have long been considered the gold standard for diagnosis and monitoring of progression of fibrotic disease. The identification of neoantigens from enzymatically processed collagen chains have revolutionised the biomarker field, allowing rapid diagnosis and evaluation of prognosis of numerous fibrotic conditions, as well as providing valuable clinical trial endpoint determinants. Collagen VI chain fragments such as endotrophin (PRO-C6), C6M and C6Mα3 are emerging as important biomarkers for fibrotic conditions.

Molecular characterization of the human kidney interstitium in health and disease

The gene expression signature of the human kidney interstitium is incompletely understood. The cortical interstitium (excluding tubules, glomeruli, and vessels) in reference nephrectomies (N = 9) and diabetic kidney biopsy specimens (N = 6) was laser microdissected (LMD) and sequenced. Samples underwent RNA sequencing. Gene signatures were deconvolved using single nuclear RNA sequencing (snRNAseq) data derived from overlapping specimens. Interstitial LMD transcriptomics uncovered previously unidentified markers including KISS1, validated with in situ hybridization. LMD transcriptomics and snRNAseq revealed strong correlation of gene expression within corresponding kidney regions. Relevant enriched interstitial pathways included G-protein coupled receptor. binding and collagen biosynthesis. The diabetic interstitium was enriched for extracellular matrix organization and small-molecule catabolism. Cell type markers with unchanged expression (NOTCH3, EGFR, and HEG1) and those down-regulated in diabetic nephropathy (MYH11, LUM, and CCDC3) were identified. LMD transcriptomics complements snRNAseq; together, they facilitate mapping of interstitial marker genes to aid interpretation of pathophysiology in precision medicine studies.

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.

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.

Markers of Collagen Formation and Degradation Reflect Renal Function and Predict Adverse Outcomes in Patients With Type 1 Diabetes

OBJECTIVE

Patients with type 1 diabetes (T1D) have a higher risk of developing chronic kidney disease, cardiovascular events (CVEs), and mortality than the general population. We hypothesized that two previously published biomarkers, namely PRO-C6, a biomarker of collagen type VI formation, and C3M, a biomarker of collagen type III degradation, may be associated with impaired renal function and have prognostic value for adverse renal, CVE, and mortality in patients with T1D.

RESEARCH DESIGN AND METHODS

PRO-C6 and C3M in serum (sPRO-C6, sC3M) and urine (uPRO-C6, uC3M) were measured by ELISA in 663 patients with T1D ranging from normoalbuminuric to macroalbuminuric. Association of the biomarkers with mortality, CVEs, heart failure, decline in estimated glomerular filtration rate (eGFR) ≥30%, and end-stage renal disease (ESRD) were tested in Cox proportional hazards models after log₂ transformation and adjusted for relevant clinical characteristics. Hazard ratios (HRs) were reported per doubling of biomarker levels.

RESULTS

High levels of sPRO-C6 were independently associated with a higher risk of all-cause mortality (HR 2.26 [95% CI 1.31-3.87], P < 0.0031). There was an association with higher risk of CVEs (n = 94) and heart failure (n = 28) but not after adjustment (P ≥ 0.58). In relation to renal outcomes, adjusted sPRO-C6 was associated with a higher risk of eGFR decline ≥30% in T1D, with eGFR >45 and >30 mL/min/1.73 m², and with a higher risk of ESRD (all P ≤ 0.03). Higher uPRO-C6 was associated with a lower risk of decline in eGFR.

CONCLUSIONS

In patients with T1D, higher sPRO-C6 was an independent predictor of both decline in eGFR and development of ESRD and of all-cause mortality. Higher uPRO-C6 was also associated with a lower risk of decline in eGFR.

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.

Renal Graft Fibrosis and Inflammation Quantification by an Automated Fourier-Transform Infrared Imaging Technique

Renal interstitial fibrosis and interstitial active inflammation are the main histologic features of renal allograft biopsy specimens. Fibrosis is currently assessed by semiquantitative subjective analysis, and color image analysis has been developed to improve the reliability and repeatability of this evaluation. However, these techniques fail to distinguish fibrosis from constitutive collagen or active inflammation. We developed an automatic, reproducible Fourier-transform infrared (FTIR) imaging-based technique for simultaneous quantification of fibrosis and inflammation in renal allograft biopsy specimens. We generated and validated a classification model using 49 renal biopsy specimens and subsequently tested the robustness of this classification algorithm on 166 renal grafts. Finally, we explored the clinical relevance of fibrosis quantification using FTIR imaging by comparing results with renal function at 3 months after transplantation (M3) and the variation of renal function between M3 and M12. We showed excellent robustness for fibrosis and inflammation classification, with >90% of renal biopsy specimens adequately classified by FTIR imaging. Finally, fibrosis quantification by FTIR imaging correlated with renal function at M3, and the variation in fibrosis between M3 and M12 correlated well with the variation in renal function over the same period. This study shows that FTIR-based analysis of renal graft biopsy specimens is a reproducible and reliable label-free technique for quantifying fibrosis and active inflammation. This technique seems to be more relevant than digital image analysis and promising for both research studies and routine clinical practice.

Cyclin D1 in human neuroblastic tumors recapitulates its developmental expression: An immunohistochemical study

The protein cyclin D1 (CD1), which belongs to a family of proteins functioning as regulators of CDKs (cyclin-dependent kinases) throughout the cell cycle, has been immunohistochemically detected in a wide variety of human malignant tumors. The aim of the present study was to investigate immunohistochemically the expression and distribution of CD1 in the developing human peripheral sympathetic nervous system (PSNS) and in childhood peripheral neuroblastic tumors (neuroblastomas, ganglioneuroblastomas, and ganglioneuromas). The above mentioned fetal and neoplastic tissues represent an in vivo model in which undifferentiated neuroblastic cells undergo ganglion cell differentiation. During development, a strong nuclear expression of CD1 was restricted to neuroblasts, disappearing progressively from the maturing ganglion cells with increasing gestational age. In neoplastic tissues, CD1 immunoreactivity was restricted to neuroblastic cell component of all neuroblastomas and ganglioneuroblastomas, whereas it was absent or only focally detectable in maturing/mature ganglion cell component of differentiating neuroblastomas, ganglioneuroblastomas, and ganglioneuromas. We conclude that CD1 is a reliable marker, which can be used routinely to stain neuroblastic cells in both developing and neoplastic tissues. Furthermore, our results indicate that CD1 expression in childhood peripheral neuroblastic tumors recapitulates the changes during normal development of PSNS, as previously reported for Bcl-2 oncoprotein, c-ErbB2, insulin-like growth factor 2, β-2-microglobulin, and cathepsin D. This is consistent with the current view that childhood peripheral neuroblastic tumors exhibit gene expression profiles mirroring those occurring during PSNS development.

Collagen VI is a basement membrane component that regulates epithelial cell-fibronectin interactions

Collagen VI is a heterotrimer composed of three α chains (α1, α2, α3) widely expressed throughout various interstitial matrices. Collagen VI is also found near the basement membranes of many tissues where it serves as an anchoring meshwork. The aim of this study was to investigate the distribution and role of collagen VI at the epithelial-stromal interface in the intestine. Results showed that collagen VI is a bona fide epithelial basal lamina component and constitutes the major collagen type of epithelial origin in this organ. In vitro, collagen VI co-distributes with fibronectin. Targeted knockdown of collagen VI expression in intestinal epithelial cells was used to investigate its function. Depletion of collagen VI from the matrix led to a significant increase in cell spreading and fibrillar adhesion formation coinciding with an upregulation of fibronectin expression, deposition and organization as well as activation of myosin light chain phosphorylation by the myosin light chain kinase and Rho kinase dependent mechanisms. Plating cells deficient for collagen VI on collagen VI rescued the phenotype. Taken together, these data demonstrate that collagen VI is an important basal lamina component involved in the regulation of epithelial cell behavior most notably as a regulator of epithelial cell-fibronectin interactions.

Organ-specific collagen expression: implications for renal disease

Chronic kidney disease is characterized by progressive accumulation of extracellular matrix and scarring, leading to the loss of kidney function. Excess deposition of the collagen family of proteins is the hallmark of kidney fibrosis. In this review, we survey the collagens that are associated with renal disease and we highlight the use of a transgenic approach to identify cis-acting sequences in the collagen type I promoter which are capable of directing collagen type I expression specifically in the kidney. Ultimately it may be possible to use this approach to halt the accumulation of collagen selectively in this organ.

[Nephrogenic adenoma of the bladder: metaplasia or embryologic alteration?]

OBJECTIVES

To present a new case of nephrogenic adenoma of the bladder and to review the current concepts on the etiopathogenesis of this lesion.

CLINICAL CASE

Seventy years old female with repetitive haematuria who was diagnosed as having a nephrogenic adenoma of the bladder which was extirpated by cold biopsy forceps. No tumoral relapse was detected after 16 months of follow up.

DISCUSSION

In the light of the present knowledges, the origin of nephrogenic adenoma is a phenomenon of urothelial metaplasia due to a chronic irritative stimulus wich would lead a cellular proliferation with potentialities to originate mesonephric tissues and which starting point could be on not completely involutioned mesonephric cellular rests and/or on de-differentiated mature urothelial cells.

Comparative immunohistochemical analysis of the expression of cytokeratins, vimentin and alpha-smooth muscle actin in human foetal mesonephros and metanephros

The human mesonephros is currently regarded as a simplified version of the foetal metanephros, primarily due to the close morphological resemblance between these two structures. The aim of the present study was to define whether human mesonephric and foetal metanephric nephrons share immunophenotypical traits in their corresponding structures (glomeruli, proximal and distal tubules). For this purpose we first investigated immunohistochemically the overall expression and topographical distribution of cytokeratins 7, 8, 18, 19, and 20, vimentin and alpha-smooth muscle actin in mature mesonephric nephrons and compared the results with those obtained in maturing-stage foetal metanephric nephrons. No expression of cytokeratins 7 and 20 was found. Cytokeratins 8, 18, and 19 and vimentin showed a restricted and basically coincident expression along the different components of both mesonephric and metanephric nephrons. These findings indicate that the intermediate filament protein profile of human mature mesonephric nephrons closely recapitulates that observed in developing metanephros and thereby strengthens the concept that human mesonephros, a transient ontogenic structure, is largely similar to the foetal metanephros. The sole difference between human mesonephros and foetal metanephros was the divergent expression of alpha-smooth muscle actin. This protein exhibited an increasingly accentuated mesangial expression paralleling the morphological maturation of metanephric glomerulus, whereas it was absent from the mesonephric one. This would suggest that the mesangial cells in these two renal structures have a different function during the foetal life.

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.