Preclinical Alterations in the Serum of COL(IV)A3–/– Mice as Early Biomarkers of Alport Syndrome

Urinary Protein-Biomarkers Reliably Indicate Very Early Kidney Damage in Children With Alport Syndrome Independently of Albuminuria and Inflammation

Introduction

Alport syndrome (AS) is a hereditary type IV collagen disease. It starts shortly after birth, without clinical symptoms, and progresses to end-stage kidney disease early in life. The earlier therapy starts, the more effectively end-stage kidney disease can be delayed. Clearly then, to ensure preemptive therapy, early diagnosis is an essential prerequisite.

Methods

To provide early diagnosis, we searched for protein biomarkers (BMs) by mass spectrometry in dogs with AS stage 0. At this very early stage, we identified 74 candidate BMs. Of these, using commercial enzyme-linked immunosorbent assays (ELISAs), we evaluated 27 in dogs and 28 in children, 50 with AS and 104 healthy controls.

Results

Most BMs from blood appeared as fractions of multiple variants of the same protein, as shown by their chromatographic distribution before mass spectrometry. Blood samples showed only minor differences because ELISAs rarely detect disease-specific variants. However, in urine , several proteins, individually or in combination, were promising indicators of very early and preclinical kidney injury. The BMs with the highest sensitivity and specificity were collagen type XIII, hyaluronan binding protein 2 (HABP2), and complement C4 binding protein (C4BP).

Conclusion

We generated very strong candidate BMs by our approach of first examining preclinical AS in dogs and then validating these BMs in children at early stages of disease. These BMs might serve for screening purposes for AS before the onset of kidney damage and therefore allow preemptive therapy.

Radiation nephropathy: Mechanisms of injury and recovery in a murine model

BACKGROUND

Radiation nephropathy (RN) can be a severe late complication for patients treated with radiotherapy (RT) targeting abdominal and paraspinal tumors. Recent studies investigating the mechanisms of RT-mediated injury in the kidney have demonstrated that RT disrupts the cellular integrity of renal podocytes leading to cell death and loss of renal function.

AIM

To determine if RT-induced renal dysfunction is associated with alterations in podocyte and glomerular function, and whether RT-induced podocyte alterations were associated with changes in the glomerular basement membrane (GBM).

METHODS

C57BL/6 mice were treated with focal bilateral X-irradiation using a single dose (SD) of 4 Gy, 10 Gy, or 14 Gy or fractionated dosing (FD) of 5x6Gy or 24x2Gy. Then, 10-40 weeks after RT parameters of renal function were measured, along with glomerular filtration rate (GFR) and glomerular histology, as well as ultrastructural changes in GBM by transmission electron microscopy.

RESULTS

RT treatment resulted in persistent changes in renal function beginning at 10 weeks with little recovery up to 40 weeks post RT. Dose dependent changes were seen with increasing SD but no functional sparing was evident after FD. RT-induced loss of renal function was associated with expansion of the GBM and significant increases in foot process width, and associated with significant reduction in GFR, podocyte loss, and renal fibrosis.

CONCLUSION

For the first time, these data show that expansion of the GBM is one consequence of radiation injury, and disarrangement of the GBM might be associated with the death of podocytes. These data shed new light on the role podocyte injury and GBM in RT-induced renal dysfunction.

Potential Renal Damage Biomarkers in Alport Syndrome—A Review of the Literature

Alport syndrome (AS) is the second most common cause of inherited chronic kidney disease. This disorder is caused by genetic variants on COL4A3, COL4A4 and COL4A5 genes. These genes encode the proteins that constitute collagen type IV of the glomerular basement membrane (GBM). The heterodimer COL4A3A4A5 constitutes the majority of the GBM, and it is essential for the normal function of the glomerular filtration barrier (GFB). Alterations in any of collagen type IV constituents cause disruption of the GMB structure, allowing leakage of red blood cells and albumin into the urine, and compromise the architecture of the GFB, inducing inflammation and fibrosis, thus resulting in kidney damage and loss of renal function. The advances in DNA sequencing technologies, such as next-generation sequencing, allow an accurate diagnose of AS. Due to the important risk of the development of progressive kidney disease in AS patients, which can be delayed or possibly prevented by timely initiation of therapy, an early diagnosis of this condition is mandatory. Conventional biomarkers such as albuminuria and serum creatinine increase relatively late in AS. A panel of biomarkers that might detect early renal damage, monitor therapy, and reflect the prognosis would have special interest in clinical practice. The aim of this systematic review is to summarize the biomarkers of renal damage in AS as described in the literature. We found that urinary Podocin and Vascular Endothelial Growth Factor A are important markers of podocyte injury. Urinary Epidermal Growth Factor has been related to tubular damage, interstitial fibrosis and rapid progression of the disease. Inflammatory markers such as Transforming Growth Factor Beta 1, High Motility Group Box 1 and Urinary Monocyte Chemoattractant Protein- 1 are also increased in AS and indicate a higher risk of kidney disease progression. Studies suggest that miRNA-21 is elevated when renal damage occurs. Novel techniques, such as proteomics and microRNAs, are promising.

Discoidin domain receptor 1 activation links extracellular matrix to podocyte lipotoxicity in Alport syndrome

Background

Discoidin domain receptor 1 (DDR1) is a receptor tyrosine kinase that is activated by collagens that is involved in the pathogenesis of fibrotic disorders. Interestingly, de novo production of the collagen type I (Col I) has been observed in Col4a3 knockout mice, a mouse model of Alport Syndrome (AS mice). Deletion of the DDR1 in AS mice was shown to improve survival and renal function. However, the mechanisms driving DDR1-dependent fibrosis remain largely unknown.

Methods

Podocyte pDDR1 levels, Collagen and cluster of differentiation 36 (CD36) expression was analyzed by Real-time PCR and Western blot. Lipid droplet accumulation and content was determined using Bodipy staining and enzymatic analysis. CD36 and DDR1 interaction was determined by co-immunoprecipitation. Creatinine, BUN, albuminuria, lipid content, and histological and morphological assessment of kidneys harvested from AS mice treated with Ezetimibe and/or Ramipril or vehicle was performed.

Findings

We demonstrate that Col I-mediated DDR1 activation induces CD36-mediated podocyte lipotoxic injury. We show that Ezetimibe interferes with the CD36/DDR1 interaction in vitro and prevents lipotoxicity in AS mice thus preserving renal function similarly to ramipril.

Interpretation

Our study suggests that Col I/DDR1-mediated lipotoxicity contributes to renal failure in AS and that targeting this pathway may represent a new therapeutic strategy for patients with AS and with chronic kidney diseases (CKD) associated with Col4 mutations.

Funding

This study is supported by the NIH grants R01DK117599, R01DK104753, R01CA227493, U54DK083912, UM1DK100846, U01DK116101, UL1TR000460 (Miami Clinical Translational Science Institute, National Center for Advancing Translational Sciences and the National Institute on Minority Health and Health Disparities), F32DK115109, Hoffmann-La Roche and Alport Syndrome Foundation.

A novel frameshift mutation of COL4A5 in a Chinese family with presumed IgA nephropathy and chronic glomerulonephritis

BACKGROUND

Alport syndrome (ATS) is a hereditary nephritis with hereditary and clinical heterogeneity; the early clinical symptoms are atypical, which can easily lead to misdiagnosis. The proband, a 6-year-old girl, was found to have microscopic hematuria, proteinuria, and visual impairment at about 5 years old; the results of renal pathological examination revealed mesangial hyperplasia and IgA deposition. The proband's father exhibited gross hematuria, eye swelling, and bilateral hearing loss after the age of 5, renal function progressively decreased, and he underwent right renal allograft at the age of 23 due to renal failure. The proband and her father were clinically diagnosed as IgA nephropathy and chronic glomerulonephritis, respectively.

METHODS

For proband, targeted exome capture sequencing was performed using the Targeted Exome Capture Kit; this kit targets 162 genes known to cause renal diseases. The identified mutation was confirmed and analyzed for cosegregation by Sanger sequencing in other family members whose gDNA was available.

RESULTS

Targeted exome capture sequencing revealed a novel heterozygous variant (NM_000495, c.697delG, p.G233fs) in the COL4A5 gene of the proband; the variant was inherited from her father. The variant was likely pathogenic according to the criteria of the American College of Medical Genetics and Genomics.

CONCLUSION

In this study, we first report a c.697delG mutation of COL4A5 in two patients presumed IgA nephropathy and chronic glomerulonephritis. This study emphasizes on the diagnostic value of next-generation sequencing for hereditary kidney diseases to help in their timely and cost-effective diagnosis, determine appropriate treatments, and promote genetic counseling.

A next generation setup for pre-fractionation of non-denatured proteins reveals diverse albumin proteoforms each carrying several post-translational modifications

Proteomic biomarker search requires the greatest analytical reproducibility and detailed information on altered proteoforms. Our protein pre-fractionation applies orthogonal native chromatography and conserves important features of protein variants such as native molecular weight, charge and major glycans. Moreover, we maximized reproducibility of sample pre-fractionation and preparation before mass spectrometry by parallelization and automation. In blood plasma and cerebrospinal fluid (CSF), most proteins, including candidate biomarkers, distribute into a multitude of chromatographic clusters. Plasma albumin, for example, divides into 15-17 clusters. As an example of our technique, we analyzed these albumin clusters from healthy volunteers and from dogs and identified cluster-typical modification patterns. Renal disease further modifies these patterns. In human CSF, we found only a subset of proteoforms with fewer modifications than in plasma. We infer from this example that our method can be used to identify and characterize distinct proteoforms and, optionally, enrich them, thereby yielding the characteristics of proteoform-selective biomarkers.

Traditional Renal Biomarkers and New Approaches to Diagnostics

Traditional biomarkers of renal disease have a number of limitations, whether evaluating veterinary patients or performing preclinical toxicity studies. Serum creatinine and urea nitrogen are affected by nonrenal influences that limit their usefulness for detecting small but significant decreases in glomerular filtration rate (GFR) in veterinary patients. These nonrenal influences can be more controlled in preclinical studies than in clinical patients; however, because of its high functional reserve, these estimates of GFR are insensitive for detecting kidney injury prior to loss of a substantial proportion of functioning nephrons. Urine biomarkers can be highly sensitive for tubular or glomerular injury that might lead to irreversible damage to the nephron. Several proteins are qualified by the Food and Drug Administration for nonclinical application as urinary biomarkers of drug-induced nephrotoxicity, and many of these also have preliminary data supporting their usefulness for kidney injury in dogs and cats. In addition to these relatively recently identified biomarkers, efforts are underway to discover new renal biomarkers using a variety of techniques including liquid chromatography-mass spectrometry and small RNA sequencing. Ultimately, the interplay between preclinical studies and clinical patients in discovery and validation of renal biomarkers is critical to their successful implementation.

Alport syndrome: facts and opinions

In this commentary, I review recent advances in Alport syndrome genetics, diagnostics, and therapeutics. I also offer some opinions regarding strategies to optimize the early identification of affected individuals to promote early therapeutic intervention.

The intricacy of biomarker complexity-the identification of a genuine proteomic biomarker is more complicated than believed

Several reasons have been put forward to explain the irreproducibility of proteomic biomarker search. However, these reasons pertain to almost every part of biomarker search across the entire analytical workflow but are entirely experimental or methodological. However, in this article we point out that there is a further cause of such irreproducibility. This is not an additional methodological or experimental cause but arises directly from the biology of protein expression. It arises from the fact that disease changes the diversity within protein families. This cause of irreproducibility has been very little studied in relation to proteomic biomarker search. Gene expression is highly variable even in healthy people. Therefore, multiple proteoforms are also to be expected when gene expression is disrupted by disease, proteoforms that may be differently altered by pathology. In consequence, it is illogical to expect that the whole protein family produces a reliably usable biomarker. It is more reasonable to expect that a specific proteoform fulfills this role. Appropriate sample pre-fractionation methods and data analyses could help to identify this version, carrying the modification or the epitope required.

Acute phase proteins as promising biomarkers: Perspectives and limitations for human and veterinary medicine

Acute phase proteins (APPs) are highly conserved plasma proteins that are increasingly secreted by the liver in response to a variety of injuries, independently of their location and cause. APPs favor the systemic regulation of defense, coagulation, proteolysis, and tissue repair. Various APPs have been applied as general diagnostic parameters for a long time. Through proteomic techniques, more and more APPs have been discovered to be differentially altered. Since they are not consistently explainable by a stereotypic hepatic expression of sets of APPs, most of these results have unfortunately been neglected or attributed to the nonspecificity of the acute phase reaction. Moreover, it appears that various extrahepatic tissues are also able to express APPs. These extrahepatic APPs show focally specific roles in tissue homeostasis and repair and are released primarily into interstitial and distal fluids. Since these focal proteins might leak into the circulatory system, mixtures of hepatic and extrahepatic APP species can be expected in blood. Hence, a selective alteration of parts of APPs might be expected. There are several hints on multiple molecular forms and fragments of tissue-derived APPs. These differences offer the chance for multiple selective determinations. Thus, specific proteoforms might indeed serve as tissue-specific disease indicators.