Glomerular localization of circulating single-stranded DNA in mice. Dependence on the molecular weight of DNA

EBV load is associated with cfDNA fragmentation and renal damage in SLE patients

BACKGROUND

For long Epstein-Barr virus (EBV) has been suspected to be involved in the pathogenesis of systemic lupus erythematosus (SLE). The aim of this study was to verify the association between EBV, cell-free DNA (cfDNA) and kidney disease in SLE.

METHODS

Blood samples were obtained from 43 SLE patients and 50 healthy individuals. EBV load was measured via real-time PCR assay. Sizing and quantification of plasma cfDNA was performed on Bioanalyzer. We proposed that the uniformity of cfDNA fragmentation can be described using cfDNA fragmentation index.

RESULTS

SLE patients with chronic kidney disease (CKD +) had higher EBV load compared to CKD(-) patients (P = 0.042). Patients with high cfDNA level had higher EBV load (P = 0.041) and higher cfDNA fragmentation index (P < 0.001) compared to patients with low cfDNA level. Among patients with high cfDNA level, EBV load was higher in CKD(+) group compared to CKD(-) group (P = 0.035). EBV load was positively correlated with the fragmentation index in all SLE patients (P = 0.028, R² = 0.13), and the correlation was even more pronounced in CKD (+) patients (P < 0.001, R² = 0.20).

CONCLUSIONS

We showed that EBV load was associated with non-uniform cfDNA fragmentation, higher cfDNA levels, and kidney disease in SLE patients. Although the causality of this relationship could not be determined with the current study, it brings rationale for further investigations on the role of EBV and cfDNA interplay in SLE pathogenesis.

Self-assembled VEGF-R2 targeting DNA aptamer-collagen fibers stimulate an angiogenic-like endothelial cell phenotype

Vascularization of engineered tissue is one of the hallmark challenges of tissue engineering. Leveraging self-assembled nucleic acid-collagen complexes (NACCs), we mixed a VEGF-R2 targeting aptamer or its receptor agonist divalent assembly with type I collagen to assemble NACC microfibers. Human umbilical vein endothelial cells (HUVECs) quickly remodeled these fibers into tubulogenic-like structures over 48 h. Moreover, NACCs made with the receptor agonist divalent aptamer assembly promoted enhanced expression of von Willebrand factor (vWF), angiopoietin-2 (ANGPT-2), and matrix metalloproteinase-2 (MMP-2) by HUVECs as measured by either immunocytochemistry or ELISA. The findings suggest, endothelial cell phenotype was directed by both biochemical cues afforded by the agonist behavior of the divalent aptamer assembly as well as by the biophysical cues afforded by the fibrous topography. Collectively, these results support the development of an angiogenic endothelial cell phenotype stimulated by the VEGF-R2 agonist NACC fibers. Thus, the combination of engineered DNA aptamer nanotechnology and DNA-collagen complexation phenomena is a promising biofunctional natural scaffold material system for tissue engineering and regenerative medicine applications.

Mineralized DNA-collagen complex-based biomaterials for bone tissue engineering

DNA is a highly polyanionic biomolecule that complexes with both collagen and hydroxyapatite. By combining these complexes, we synthesized nucleic-acid collagen complexes (NACC) mineralized with hydroxyapatite. The composite complexes were made using a short, monodisperse single-stranded DNA, type I collagen, and mineralizing medium. They rapidly self-assembled into both mineralized NACC microfibers and 3D NACC gels. At the nanoscale, these complexes are hierarchical, interwoven, curly nanofibrils resembling native extracellular matrix, which mineralized an interpenetrating nanocrystalline hydroxyapatite phase. Mineralization was able to be done either before or after NACC formation enabling temporal control of the process. In response to the NACC material, primary human osteoblasts took on an osteocyte-like morphology. Moreover, the cells agglomerated and remodeled the NACC gels into densified, tissue-like structures within 3 days. NACC fibers and gels have promise not only as osteoconductive coatings and scaffolds, but as coatings and scaffolds for any tissue using this new form of naturally-derived biomaterials.

Oligomer Length Defines the Self-Assembly of Single-Stranded DNA-Collagen Complex Fibers

Collagen and single-stranded DNA (ssDNA) complex to self-assemble into fibers depending on the length of the ssDNA and the relative amounts of collagen and ssDNA in solution. We report for the first time that when monodisperse, random sequences of ssDNA in the range of 15-90 nucleotides and type I collagen were mixed together at room temperature, fibers several tens of micrometers in length and as large as 10 μm in diameter were formed. Fiber formation was rapid and spontaneous, requiring no further treatment after mixing. Most notably, more ssDNA oligomers were incorporated into the fibers formed using shorter ssDNA oligomers. Endothelial cells formed angiogenic-like structures using the fibers with elevated expression of von Willebrand factor for cells in direct contact with the fibers. These fibers open the door to future applications in the administration and functionality of ssDNA and collagen.

Cell-free DNA: the role in pathophysiology and as a biomarker in kidney diseases

Cell-free DNA (cfDNA) is present in various body fluids and originates mostly from blood cells. In specific conditions, circulating cfDNA might be derived from tumours, donor organs after transplantation or from the foetus during pregnancy. The analysis of cfDNA is mainly used for genetic analyses of the source tissue -tumour, foetus or for the early detection of graft rejection. It might serve also as a nonspecific biomarker of tissue damage in critical care medicine. In kidney diseases, cfDNA increases during haemodialysis and indicates cell damage. In patients with renal cell carcinoma, cfDNA in plasma and its integrity is studied for monitoring of tumour growth, the effects of chemotherapy and for prognosis. Urinary cfDNA is highly fragmented, but the technical hurdles can now be overcome and urinary cfDNA is being evaluated as a potential biomarker of renal injury and urinary tract tumours. Beyond its diagnostic application, cfDNA might also be involved in the pathogenesis of diseases affecting the kidneys as shown for systemic lupus, sepsis and some pregnancy-related pathologies. Recent data suggest that increased cfDNA is associated with acute kidney injury. In this review, we discuss the biological characteristics, sources of cfDNA, its potential use as a biomarker as well as its role in the pathogenesis of renal and urinary diseases.

Pathogenic autoantibodies in lupus nephritis

Lupus nephritis is a major complication of systemic lupus erythematosus (SLE) and is associated with a high rate of morbidity and mortality. While many different immunologic and nonimmunologic factors contribute to disease expression in lupus nephritis, a large body of evidence suggests that the production of anti-DNA antibodies and the formation of glomerular immune deposits are important initial events in the pathogenesis of the disease. This review will summarize our current understanding of the differences between pathogenic and nonpathogenic autoantibodies, the mechanisms by which these autoantibodies induce renal injury and the effector mechanisms which are subsequently activated by the deposited autoantibodies that ultimately lead to the expression of the different lupus lesions.

Anti-DNA antibodies can bind to the glomerulus via two distinct mechanisms

It is generally assumed that antibodies to double stranded DNA (anti-DNA) play a pivotal role in the pathogenesis of SLE nephritis. Recently, we reported that anti-DNA antibodies can bind to heparan sulphate proteoglycan (HSPG), a constituent of the glomerular basement membrane (GBM), via histones and DNA. We postulated that these histone/DNA/anti-DNA complexes can bind via their histone part to the glomerulus in vivo. To test this hypothesis we performed in vitro binding studies with isolated GBM loops and renal perfusion studies in the rat using histones, DNA and an anti-DNA monoclonal antibody (mAb) with high avidity for dsDNA. A strong granular binding of anti-DNA mAb to isolated GBM loops occurred via histones and DNA and a moderate granular binding was found via DNA alone. Anti-DNA mAb alone did not bind to the GBM loops. After perfusion of histones, DNA and immediately thereafter anti-DNA, we found with immunoelectron microscopy (IEM) a strong binding to endothelial cells in the glomerulus and to a lesser extent in the GBM. When the anti-DNA mAb was injected i.v. one hour after perfusion of histones and DNA, we observed a strong fine granular binding to the capillary wall by immunofluorescence (IF) in a membranous pattern along with some minor mesangial deposits. After perfusion of DNA alone followed by anti-DNA mAb, binding in the glomerulus was less than with histones and DNA, and was more restricted to the mesangium. No direct binding to the glomerulus was observed after perfusion with anti-DNA mAb alone, histones and anti-DNA mAb, or histones, DNA and a control mAb.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-DNA antibodies form immune deposits at distinct glomerular and vascular sites

To investigate the capacity of lupus autoAb to produce glomerular immune deposits (ID) and nephritis, 24 murine monoclonal (m) anti-DNA antibodies (Ab), derived from either MRL-lpr/lpr, SNF1 or NZB lupus-prone mice and selected based on properties shared with nephritogenic Ig, were administered i.p. (as hybridomas) and i.v. (as purified Ig) to normal mice; at least four mice/mAb were evaluated. Three general patterns of immune deposit formation (IDF) were observed: extracellular ID within glomeruli (+/- blood vessels, N = 8); intranuclear ID (N = 5); or minimal or no ID (N = 11). The four MRL m anti-DNA Ab that produced significant extracellular ID demonstrated different disease profiles including: (a) mesangial and subendothelial ID with anti-basement membrane staining, associated with proliferative glomerulonephritis, PMN infiltration, and proteinuria; (b) diffuse fine granular mesangial and extraglomerular vascular ID, associated with proliferative glomerulonephritis and proteinuria; (c) dense intramembranous ID and intraluminal ID, associated with capillary wall thickening, mesangial interposition and expansion, aneurysmal dilatation and intraluminal occlusion of glomerular capillary loops, and heavy proteinuria; and (d) mesangial and extraglomerular vascular ID, associated with mild segmental mesangial expansion, without proteinuria. These MRL mAb were derived from four different mice, and they had variable pIs and isotypes. They all cross reacted with multiple autoantigens (autoAg), however, their autoAg binding profiles were distinguishable. Among the SNF1 derived mAb, four produced histologically and clinically indistinguishable disease characterized by diffuse mesangial and capillary wall ID, associated with cellular proliferation/infiltration and proteinuria. Three of the four mAb were derived from the same mouse and were clonally related; they were: IgG2b with SWR allotype, relatively cationic, highly cross reactive with similar Ag binding patterns, idiotypically related and encoded by identical VH and nearly identical VL sequences. We conclude that both the capacity of lupus autoAb to form ID and the location of IDF are dependent on properties unique to individual Ig. The results also indicate that the Ag binding region of the autoAb is influential in this process, and they suggest that multiple Ab-Ag interactions contribute to IDF in individuals with lupus nephritis. Furthermore, these observations raise the possibility that the pathologic and clinical abnormalities resulting from these interactions are influenced by the location of IDF, and that the dominant interaction, in a given individual, may be highly influential in the phenotypic expression of nephritis.