The L1 cell adhesion molecule is a potential biomarker of human distal nephron injury in acute tubular necrosis

Development of a Sensitive Diagnostic Assay for Parkinson Disease Quantifying α-Synuclein-Containing Extracellular Vesicles

OBJECTIVE

To develop a reliable and fast assay to quantify the α-synuclein (α-syn)-containing extracellular vesicles (EVs) in CSF and to assess their diagnostic potential for Parkinson disease (PD).

METHODS

A cross-sectional, multicenter study was designed, including 170 patients with PD and 131 healthy controls (HCs) with a similar distribution of age and sex recruited from existing center studies at the University of Washington and Oregon Health and Science University. CSF EVs carrying α-syn or aggregated α-syn were quantified using antibodies against total or aggregated α-syn, respectively, and highly specific, sensitive, and rapid assays based on the novel Apogee nanoscale flow cytometry technology.

RESULTS

No significant differences in the number and size distribution of total EVs between patients with PD and HCs in CSF were observed. When examining the total α-syn-positive and aggregated α-syn-positive EV subpopulations, the proportions of both among all detected CSF EVs were significantly lower in patients with PD compared to HCs (p < 0.0001). While each EV subpopulation showed better diagnostic sensitivity and specificity than total CSF α-syn measured directly with an immunoassay, a combination of the 2 EV subpopulations demonstrated a diagnostic accuracy that attained clinical relevance (area under curve 0.819, sensitivity 80%, specificity 71%).

CONCLUSION

Using newly established, sensitive nanoscale flow cytometry assays, we have demonstrated that total α-syn-positive and aggregated α-syn-positive EVs in CSF may serve as a helpful tool in PD diagnosis.

CLASSIFICATION OF EVIDENCE

This study provides Class III evidence that total and aggregated α-syn-positive EVs in CSF identify patients with PD.

The Potential of Liquid Biopsy of the Brain Using Blood Extracellular Vesicles: The First Step Toward Effective Neuroprotection Against Neurodegenerative Diseases

Early diagnosis and biomarker-based ante-mortem tests are essential in efforts against the development of neurodegenerative diseases and can be considered primary neuroprotective measures. Blood is the ideal biofluid for a routine ante-mortem screening test. However, biomarker discovery in the blood is particularly difficult because of interference from factors both intrinsic and extrinsic to blood with the detection of hallmark neurodegenerative biomarkers, such as the pathological prion protein, amyloid-β, and others. Blood extracellular vesicles (EVs), such as exosomes, are cell-derived vesicles released into the blood from all parts of the body (including the brain and spinal cord). They are an enriched source of neural-derived EVs containing neurodegenerative biomarkers that mirror (in the blood) the condition present in the brain. The feasibility of using, and the reliability of, neural-derived blood EVs (NDBEVs) as a method of diagnosing Alzheimer disease and other neurodegenerative diseases has been assessed in strong proof-of-concept studies. Results from these studies strongly suggest that NDBEVs might represent the right strategy for specific, reliable, and early diagnosis of neurodegenerative diseases. Based on these results, NDBEVs might enable the creation of an ante-mortem blood test (liquid biopsy of the brain) for neurodegenerative diseases. This would enormously accelerate the therapy of neurodegenerative diseases. This review highlights the powerful potential of liquid biopsy of the brain using NDBEVs for early diagnosis and treatment of neurodegenerative diseases, and the challenges and limitations related to the identification of clinically applicable EV (exosomal) biomarkers using blood are discussed.

Extracellular vesicle-associated proteins as potential biomarkers

Every cell in the body secretes extracellular vesicles (EVs) possibly as cellular signaling components and these cell-derivatives can be found in multiple numbers in biological fluids. EVs have in the scientific field received great attention in relation to pathophysiology and disease diagnostics. Altered protein expressions associated with circulating EVs in diseased individuals can serve as biomarkers for different disease states. This capacity paves the way for non-invasive screening tools and early diagnostic markers. However, no isolation method of EVs has been acknowledged as the "golden standard," thus reproducibility of the studies remains inadequate. Increasing interest in EV proteins as disease biomarkers could give rise to more scientific knowledge with diagnostic applicability. In this chapter, studies of proteins believed to be associated with EVs within cancer, autoimmunity, metabolic and neurodegenerative diseases have been outlined.

Endosomal dysfunction impacts extracellular vesicle release: Central role in Aβ pathology

Alzheimer's Disease (AD) is characterized by progressive loss of cognitive abilities; senile plaques represent the major histopathological findings. Amyloid precursor protein (APP) processing machinery, and its product amyloid-beta (Aβ) peptide, have been found in extracellular vesicles (EVs), specifically exosomes, which allows for Aβ peptide aggregation and subsequent senile plaques deposition. We review the APP processing imbalance in EVs, autophagic and endosomal pathways in AD. Increased intraluminal vesicle (ILV) production and exosome release appear to counteract the endosomal dysfunction of APP processing; however, this process results in elevated amyloidogenic processing of APP and augmented senile plaque deposition. Several players related to APP processing and dysfunctional endosomal-lysosomal-exosomal (and other EVs) pathway are described, and the interconnected systems are discussed. The components Arc, p75, Rab11 and retromer complex emerge as candidates for key convergent mechanisms that lead to increased EVs loaded with APP machinery and Aβ levels, in atrophy and damage of basal forebrain cholinergic neurons in AD.

Profile of pathogenic proteins in total circulating extracellular vesicles in mild cognitive impairment and during the progression of Alzheimer's disease

Accumulating evidence suggests that the propagation of hyperphosphorylation of tau protein and the amyloid-β peptide can be mediated by extracellular vesicles (EVs) and be associated with the onset and the progression of Alzheimer's disease (AD). As EVs may transfer between the brain and the blood, we have thus hypothesized that the total plasma EVs (pEVs) may contain potential markers to predict the mild cognitive impairment (MCI) and AD progression. We have thus quantified AD-related proteins in isolated pEVs from controls, MCI and AD subjects. In pEVs, we observed early changes of total tau (tTau), amyloid precursor protein levels, and phospho-tau (pTau)-T181/tTau ratio from MCI subjects and late increases of Aβ42 and pTau-T181 levels from patients with moderate AD. Interestingly, abnormal amyloid precursor protein levels and pTau-T181/tTau ratio in pEVs demonstrated a high accuracy to define MCI and AD staging. Although larger samples sizes will be needed to generate well-powered investigations, these preliminary results highlighted the potential of AD-related proteins enriched in pEVs as a sensitive tool for differentiating patients with MCI to patients with AD and monitoring AD progression.

Extracellular vesicles as an emerging tool for the early detection of Alzheimer's disease

Alzheimer's disease (AD) is characterized by a series of interacting pathophysiological cascades, including the aggregation of β-amyloid plaques and the formation of neurofibrillary tangles derived from hyperphosphorylated tau proteins. AD is the cause of approximately 70 % of dementia, an irreversible and untreatable syndrome at its late stage. Hence, more efforts should be devoted to identifying at-risk or preclinical AD populations for early intervention and the improved design of drug trials. The exosome, a nanoscale subtype of extracellular vesicle that serves as a cell-to-cell communication messenger, is an emerging liquid biopsy tool for various diseases including AD. Recently, it has been discovered that brain-derived exosomes can flow through the blood-brain barrier to the peripheral blood, containing important protein and nucleic acid biomarkers that are associated with the pathogenesis and progression of AD. Other reports showed a strong involvement of exosomes in synaptic function, insulin resistance, and neuroinflammation, among others. Here, we summarize those studies and assess the value of exosomes as an emerging tool for the early detection of AD in conjunction with the current clinical diagnosis paradigm.

Exosomes as possible spread factor and potential biomarkers in Alzheimer's disease: current concepts

Increasing evidence points that important factors during development/spread of Alzheimer's disease in brain tissue are small extracellular vesicles, called exosomes. Exosomes comprise disease-related biomolecules such as the amyloid protein precursor, β-amyloid peptide and tau protein. Exosomes are hypothesized to facilitate the spread of β-amyloid peptide and tau protein from their cells of origin (e.g., neurons) to the extracellular space and to recipient cells to alter their phenotype and function. The roles of exosomes carry a rich biomolecules cargo in physiology and pathology is poorly understood. In this review, we will consider new information about the role of exosomes in Alzheimer's disease spreading and progression and underline their possible usefulness as the future diagnostic antemortem biomarkers in this devastating disorder.

Exosomes, an Unmasked Culprit in Neurodegenerative Diseases

Exosomes are extracellular nanovesicles (30–100 nm) generated from endosomal membranes and known to be released by all cell lineages of the Central Nervous System (CNS). They constitute important vesicles for the secretion and transport of multilevel information, including signaling, toxic, and regulatory molecules. Initially thought to have a function merely in waste disposal, the involvement of exosomes in neuronal development, maintenance, and regeneration through its paracrine and endocrine signaling functions has drawn particular attention in recent years. These vesicles, being involved in the clearance and cell-to-cell spreading of toxic molecules, have been naturally implicated in aging, and in several neurodegenerative diseases associated with pathological conversion of proteins, as well as in the transport of other disease-associated molecules, such as nucleic acids or pro-inflammatory cytokines. Our understanding of such unique form of communication may provide not only answers about (patho)physiological processes in the brain, but can also offer means to exploit these vesicles as vehicles for the delivery of biologically relevant molecules or as tools to monitor brain diseases in a non-invasive way. A promising field in expansion, the study of exosomes and related extracellular vesicles has just commenced to unveil their potential as therapeutic tools for brain disorders as well as biomarkers of disease state.

Focus on Extracellular Vesicles: Exosomes and Their Role in Protein Trafficking and Biomarker Potential in Alzheimer's and Parkinson's Disease

Growing evidence indicates that small extracellular vesicles, called exosomes, are prominent mediators of neurodegenerative diseases such as prion, Alzheimer's and Parkinson's disease. Exosomes contain neurodegenerative disease associated proteins such as the prion protein, β-amyloid and α-synuclein. Only demonstrated so far in vivo with prion disease, exosomes are hypothesised to also facilitate the spread of β-amyloid and α-synuclein from their cells of origin to the extracellular environment. In the current review, we will discuss the role of exosomes in Alzheimer's and Parkinson's disease including their possible contribution to disease propagation and pathology and highlight their utility as a diagnostic in neurodegenerative disease.

Exosomal transfer from human renal proximal tubule cells to distal tubule and collecting duct cells

OBJECTIVES

Exosomes are 50-90nm extracellular membrane particles that may mediate trans-cellular communication between cells and tissues. We have reported that human urinary exosomes contain miRNA that are biomarkers for salt sensitivity and inverse salt sensitivity of blood pressure. This study examines exosomal transfer between cultured human renal proximal tubule cells (RPTCs) and from RPTCs to human distal tubule and collecting duct cells.

DESIGN AND METHODS

For RPTC-to-RPTC exosomal transfer, we utilized 5 RPTC lines producing exosomes that were fluorescently labeled with exosomal-specific markers CD63-EGFP or CD9-RFP. Transfer between RPTCs was demonstrated by co-culturing CD63-EGFP and CD9-RFP stable clones and performing live confocal microscopy. For RPTC-to-distal segment exosomal transfer, we utilized 5 distal tubule and 3 collecting duct immortalized cell lines.

RESULTS

Time-lapse videos revealed unique proximal tubule cellular uptake patterns for exosomes and eventual accumulation into the multivesicular body. Using culture supernatant containing exosomes from 3 CD9-RFP and 2 CD63-EGFP RPTC cell lines, all 5 distal tubule cell lines and all 3 collecting duct cell lines showed exosomal uptake as measured by microplate fluorometry. Furthermore, we found that RPTCs stimulated with fenoldopam (dopamine receptor agonist) had increased production of exosomes, which upon transfer to distal tubule and collecting duct cells, reduced the basal reactive oxygen species (ROS) production rates in those recipient cells.

CONCLUSION

Due to the complex diversity of exosomal contents, this proximal-to-distal vesicular inter-nephron transfer may represent a previously unrecognized trans-renal communication system.

Urinary biomarkers in obstructive nephropathy

BACKGROUND AND OBJECTIVES

Obstructive nephropathy is a leading cause of CKD in children. The assessment of severity of renal impairment and the prediction of which children will progress to renal failure are, however, challenging.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This case-control study measured the urinary excretion of candidate biomarkers in 27 prevalent case-patients with posterior urethral valves (PUVs) and 20 age-matched controls, correlated their urinary concentration with GFR, and analyzed receiver-operating characteristic (ROC) curve and regression analyses to assess their performance as tests for low GFR.

RESULTS

The median urinary protein-to-creatinine ratio was higher in children with PUV (45 g/mol; range, 5-361 g/mol) than in controls (7 g/mol; range, 3-43 g/mol) (P<0.01) and correlated inversely with renal function (r = -0.44; P<0.05). In whole urine, excretion of aquaporin-2 was significantly decreased, whereas that of TGFβ and L1 cell adhesion molecule (L1CAM) was significantly increased. Whole-urine TGFβ excretion correlated inversely with GFR (r = -0.53; P<0.05). As tests for low GFR, whole-urine TGFβ, L1CAM, and urinary protein-to-creatinine ratio performed best, with areas under the ROC curves of 0.788, 0.795, and 0.814, respectively. By linear regression analysis, whole-urine TGFβ, L1CAM, and urinary protein-to-creatinine ratio were associated with low GFR in the case-patients.

CONCLUSIONS

Candidate biomarkers of obstructive nephropathy can be readily measured in whole urine and in urine exosomes. In boys with PUV, these biomarkers correlate with GFR.

Characterization of Renal Papillary Antigen 1 (RPA-1), a Biomarker of Renal Papillary Necrosis

Renal papillary necrosis (RPN) is a relatively common toxicity observed in preclinical drug safety testing. It is also observed in a variety of human diseases. RPN is difficult to diagnose without expensive scanning methods or histopathology. A noninvasive biomarker that could be detected at early stages of kidney damage would be of great value both to preclinical drug safety testing and in the clinic. An antibody raised to an unknown epitope of an antigen in rat kidney papilla was found to be specific for collecting duct cells in the kidney; this was termed renal papillary antigen 1 (RPA-1). In this study, the authors show that RPA-1 is an early biomarker of RPN in two different rat models of toxicity: 2-bromoethanamine (BEA) and N-phenylanthranilic acid (NPAA). RPA-1 can be detected in urine at early stages of toxicity and correlates well with the histopathology observed. We also characterized the biochemical properties of RPA-1 and found that the antigen is a high molecular weight membrane bound glycoprotein, with the epitope likely to be carried on an N-linked carbohydrate structure. This study demonstrates that RPA-1 is an excellent marker of RPN that can be used to detect this toxicity in preclinical safety testing.

Secondary prevention of acute kidney injury

PURPOSE OF REVIEW

Secondary prevention follows identification of acute kidney injury (AKI), in which functional outcome is incomplete. Secondary prevention requires biomarkers for early diagnosis and response to appropriate treatment, on-going injury and repair, and meaningful metrics to monitor outcome. This review summarizes recent research in these areas.

RECENT FINDINGS

Proteomics and genetic studies have identified new risk factors and biomarkers of AKI. Biomarker performance studies reveal differences in prognostic performance according to population and AKI definition. The first early secondary prevention study utilizing a urinary biomarker of AKI as a triaging tool to randomize to treatment has been completed. Recent creatinine-kinetic modelling has highlighted issues with defining AKI which continue to make comparison of treatment outcomes difficult. Biomarkers to monitor repair are emerging.

SUMMARY

The prognostic performance of novel biomarkers of AKI in a range of clinical settings is encouraging and critical to effective secondary prevention. Identification of cause and time-course of specific biomarkers are required before biomarker panels for secondary prevention are developed. Agreed standards around reporting of biomarker studies would facilitate comparisons between studies. Phase-specific biomarkers are required to triage to phase-specific treatment.

ADAM10 is expressed in human podocytes and found in urinary vesicles of patients with glomerular kidney diseases

Background

The importance of the Notch signaling in the development of glomerular diseases has been recently described. Therefore we analyzed in podocytes the expression and activity of ADAM10, one important component of the Notch signaling complex.

Methods

By Western blot, immunofluorescence and immunohistochemistry analysis we characterized the expression of ADAM10 in human podocytes, human urine and human renal tissue.

Results

We present evidence, that differentiated human podocytes possessed increased amounts of mature ADAM10 and released elevated levels of L1 adhesion molecule, one well known substrate of ADAM10. By using specific siRNA and metalloproteinase inhibitors we demonstrate that ADAM10 is involved in the cleavage of L1 in human podocytes. Injury of podocytes enhanced the ADAM10 mediated cleavage of L1. In addition, we detected ADAM10 in urinary podocytes from patients with kidney diseases and in tissue sections of normal human kidney. Finally, we found elevated levels of ADAM10 in urinary vesicles of patients with glomerular kidney diseases.

Conclusions

The activity of ADAM10 in human podocytes may play an important role in the development of glomerular kidney diseases.