Reduced fragmentation of apoptotic chromatin is associated with nephritis in lupus‐prone (NZB × NZW)F₁ mice

Abstract

Objective. Antinucleosome autoantibodies are pathogenic factors in lupus nephritis. Defects in apoptotic pathways may result in increased levels of apoptotic nucleosomes. The objectives of this study were 1) to determine whether low molecular weight oligonucleosomes are present in the kidneys of autoimmune (NZB ؋ NZW)F 1 mice, 2) to analyze whether the presence of glomerular membrane-associated TUNELpositive electron-dense structures reflect the existence of low molecular weight oligonucleosomes, and 3) to determine an eventual temporal relationship between glomerular electron-dense structures, oligonucleosomes, and proteinuria in these mice.Methods. DNA was isolated from mouse 111s34 hybridoma cells and from the kidneys of normal BALB/c mice in which apoptosis was induced by camptothecin and from the kidneys of (NZB ؋ NZW)F 1 mice at ages 4 weeks, 8 weeks, 20 weeks, and >26 weeks (nephritic mice). The DNA fragmentation pattern was determined with an Agilent bioanalyzer. An electron microscopybased TUNEL assay was performed to detect apoptotic chromatin in glomerular membranes, and immunoelectron microscopy was used to determine antibody binding. Transcription levels for nucleases associated with apoptosis and necrosis were determined by real-time polymerase chain reaction.Results. DNA from camptothecin-treated cell lines and BALB/c mouse kidneys, but not that from untreated (NZB ؋ NZW)F 1 mouse kidneys, demonstrated DNA cleavage consistent with apoptotic fragmentation. DNA from (NZB ؋ NZW)F 1 mice was devoid of apoptotic fragmentation, irrespective of the age of the mice, whereas TUNEL-positive chromatin particles were detected in glomerular membranes in nephritic mice. Renal DNase I transcription was reduced in nephritic mice. Nucleosomal DNA fragmentation in response to camptothecin exposure was highly reduced in (NZB ؋ NZW)F 1 mouse kidneys compared with that in their normal counterparts.Conclusion. The results of this study demonstrate that TUNEL-positive chromatin particles are deposited in the glomeruli of nephritic (NZB ؋ NZW)F 1 mice, due to reduced fragmentation and clearance of chromatin.

Mouse dendritic cells matured by ingestion of apoptotic blebs induce T cells to produce interleukin‐17

“…Indeed, experimental interference with apoptosis or with the clearance of apoptotic material can lead to the development of antinuclear autoantibodies and lupus disease manifestations like glomerulonephritis in mice (6). Accordingly, the clearance of apoptotic material by phagocytes appears to be impaired both in lupus mice and in SLE patients (7,8).…”

Identification of New Pathogenic Players in Lupus: Autoantibody-Secreting Cells Are Present in Nephritic Kidneys of (NZBxNZW)F1 Mice

“…These Ags could be nucleosomal structures bound via histone positively charged N termini to intrinsic glomerular components [e.g., heparan sulfate, laminin, or collagen IV (7)(8)(9)(10)]. Recent studies suggest that autoantibodies rather react with apoptotic chromatin fragments deposited in the glomeruli of nephritic NZB/W mice and lupus patients, this apoptotic material resulting from a reduced fragmentation and clearance of chromatin (11)(12)(13). Another possible pathway involves cross-reactions of lupus anti-DNA/nucleosome autoantibodies with glomerular constituents, such as a-actinin, laminin, mesangial cells, or mesangial matrix structures (14)(15)(16).…”

BAFF Expression is Increased in Patients with Lupus Nephritis and Associated with Antinucleosome Antibodies, C1 Inhibitor, Α-1-Acid-Glycoprotein and Endothelial Activation Markers

“…This correlation has not yet been described in the literature, but would suggest a role for BAFF in anti-nucleosome production in LN. Immune deposits which consist of oligo-nucleosomes, are located in the basement membrane in the renal glomeruli [27] in LN and are considered the result of ineffective clearance of apoptotic material [28,29]; this may then trigger antigen presenting cells to produce BAFF, that subsequently is involved in the production of anti-nucleosome Ab.…”