Chromatin as a target antigen in human and murine lupus nephritis

The present review focuses on pathogenic molecular and transcriptional events in patients with lupus nephritis. These factors are renal DNaseI, exposed chromatin fragments and the corresponding chromatin-reactive autoantibodies. Lupus nephritis is the most serious complication in human systemic lupus erythematosus, and is characterised by deposition of chromatin fragment-IgG complexes in the mesangial matrix and glomerular basement membranes. The latter deposition defines end-stage disease. This event is stringently linked to a renal-restricted shutdown of expression of the DNaseI gene, as determined by loss of DNaseI mRNA level and DNaseI enzyme activity. The major aim of the present review is to generate new therapeutic strategies based on new insight into the disease pathogenesis

B Cell Tolerance to Deiminated Histones in BALB/c, C57BL/6, and Autoimmune-Prone Mouse Strains

https://doi.org/10.3389/fimmu.2017.00362 Deimination, a posttranslational modification of arginine to citrulline carried out by peptidylarginine deiminases, may compromise tolerance of self-antigens. Patients with connective tissue autoimmunity, particularly rheumatoid arthritis (RA), systemic lupus erythematosus (SLE), or Felty’s syndrome, present with autoantibodies to deiminated histones (dH), which thus form a category of antibodies to citrullinated protein antigens (ACPA). In general, ACPA are a sensitive diagnostic for RA and may form in response to the release of nuclear chromatin (DNA plus dH) from granulocytes, usually referred to as neutrophil extracellular traps. The aim of this study was to examine spontaneously autoimmune mice for autoantibodies and T cell responses to dH. We compared IgG binding to deiminated and non-deiminated histones (nH) by ELISA and Western blotting in spontaneously autoimmune strains of (NZB × NZW) F1 and NZM2410 together with their derivative congenic strains, C57BL/6.Sle1 and C57BL/6.Sle1.Sle3, which display profound autoreactivity against nuclear self-antigens. The splenocyte proliferation against the two antigens was determined in the spontaneously autoimmune (NZB × NZW) F1 strain from which other autoimmune strains used in the study were derived. Immunizations with dH and nH were attempted in BALB/c mice to assess their splenocyte response. Splenocytes from BALB/c mice and from autoimmune mice at the time of conversion to autoimmunity proliferated strongly in response to dH, yet serum IgG from autoimmune (NZB × NZW) F1, NZM2410, and C57BL/6.Sle1.Sle3 mice displayed a remarkable bias against binding to dH. At the time of seroconversion, the antibodies already exhibited preference for nH, and only nH were recovered from circulating immune complexes. Analysis of histone deimination showed constitutive deimination in thymic extracts from C57BL/6 and C57BL/6.Sle1.Sle2.Sle3 triply congenic mice and in spleens of autoimmune triply congenic mice. Our study demonstrates that tolerance mechanisms against dH are intact in BALB/c and C57BL/6 mice and continue to be effective in mice with overt autoimmunity to nH. We conclude that, in contrast to human RA and SLE patients, where we frequently observe autoantibodies against dH, autoimmune mice maintain strong tolerance mechanisms to prevent the development of autoantibodies to dH

Anti-dsDNA Antibodies Promote Initiation, and Acquired Loss of Renal Dnase1 Promotes Progression of Lupus Nephritis in Autoimmune (NZBxNZW)F1 Mice

BACKGROUND:Lupus nephritis is characterized by deposition of chromatin fragment-IgG complexes in the mesangial matrix and glomerular basement membranes (GBM). The latter defines end-stage disease. METHODOLOGY/PRINCIPALS: In the present study we determined the impact of antibodies to dsDNA, renal Dnase1 and matrix metalloprotease (MMP) mRNA levels and enzyme activities on early and late events in murine lupus nephritis. The major focus was to analyse if these factors were interrelated, and if changes in their expression explain basic processes accounting for lupus nephritis. FINDINGS:Early phases of nephritis were associated with chromatin-IgG complex deposition in the mesangial matrix. A striking observation was that this event correlated with appearance of anti-dsDNA antibodies and mild or clinically silent nephritis. These events preceded down-regulation of renal Dnase1. Later, renal Dnase1 mRNA level and enzyme activity were reduced, while MMP2 mRNA level and enzyme activity increased. Reduced levels of renal Dnase1 were associated in time with deficient fragmentation of chromatin from dead cells. Large fragments were retained and accumulated in GBM. Also, since chromatin fragments are prone to stimulate Toll-like receptors in e.g. dendritic cells, this may in fact explain increased expression of MMPs. SIGNIFICANCE:These scenarios may explain the basis for deposition of chromatin-IgG complexes in glomeruli in early and late stages of nephritis, loss of glomerular integrity and finally renal failure

Nuclear group I introns in self-splicing and beyond

Group I introns are a distinct class of RNA self-splicing introns with an ancient origin. All known group I introns present in eukaryote nuclei interrupt functional ribosomal RNA genes located in ribosomal DNA loci. The discovery of the Tetrahymena intron more than 30 years ago has been essential to our understanding of group I intron catalysis, higher-order RNA structure, and RNA folding, but other intron models have provided information about the biological role. Nuclear group I introns appear widespread among eukaryotic microorganisms, and the plasmodial slime molds (myxomycetes) contain an abundance of self-splicing introns. Here, we summarize the main conclusions from previous work on the Tetrahymena intron on RNA self-splicing catalysis as well as more recent work on myxomycete intron biology. Group I introns in myxomycetes that represent different evolutionary stages, biological roles, and functional settings are discussed

LMW Heparin Prevents Increased Kidney Expression of Proinflammatory Mediators in (NZBxNZW)F1 Mice

We have previously demonstrated that continuous infusion of low molecular weight (LMW) heparin delays autoantibody production and development of lupus nephritis in (NZBxNZW)F1 (B/W) mice. In this study we investigated the effect of LMW heparin on renal cytokine and chemokine expression and on nucleosome-mediated activation of nucleosome-specific splenocytes. Total mRNA extracted from kidneys of heparin-treated or -untreated B/W mice was analysed by qPCR for the expression of several cytokines, chemokines, and Toll-like receptors. Splenocytes taken from B/W mice were stimulated with nucleosomes with or without the presence of heparin. Splenocyte cell proliferation as thymidine incorporation and the expression of costimulatory molecules and cell activation markers were measured. Heparin treatment of B/W mice reduced the in vivo expression of CCR2, IL1�, and TLR7 compared to untreated B/W mice. Nucleosome-induced cell proliferation of splenocytes was not influenced by heparin. The expression of CD80, CD86, CD69, CD25, CTLA-4, and TLR 2, 7, 8, and 9 was upregulated upon stimulation by nucleosomes, irrespective of whether heparin was added to the cell culture or not. In conclusion, treatment with heparin lowers the kidney expression of proinflammatory mediators in B/W mice but does not affect nucleosomal activation of splenocytes

The long noncoding RNA NEAT1 and nuclear paraspeckles are up-regulated by the transcription factor HSF1 in the heat shock response

The long noncoding RNA (lncRNA) NEAT1 (nuclear enriched abundant transcript 1) is the architectural component of nuclear paraspeckles, and it has recently gained considerable attention as it is abnormally expressed in pathological conditions such as cancer and neurodegenerative diseases. NEAT1 and paraspeckle formation are increased in cells upon exposure to a variety of environmental stressors and believed to play an important role in cell survival. The present study was undertaken to further investigate the role of NEAT1 in cellular stress response pathways. We show that NEAT1 is a novel target gene of heat shock transcription factor 1 (HSF1) and is up-regulated when the heat shock response pathway is activated by sulforaphane (SFN) or elevated temperature. HSF1 binds specifically to a newly identified conserved heat shock element in the NEAT1 promoter. In line with this, SFN induced the formation of NEAT1-containing paraspeckles via an HSF1-dependent mechanism. HSF1 plays a key role in the cellular response to proteotoxic stress by promoting the expression of a series of genes, including those encoding molecular chaperones. We have found that the expression of HSP70, HSP90, and HSP27 is amplified and sustained during heat shock in NEAT1-depleted cells compared with control cells, indicating that NEAT1 feeds back via an unknown mechanism to regulate HSF1 activity. This interrelationship is potentially significant in human diseases such as cancer and neurodegenerative disorders

The expression of the long NEAT1_2 isoform is associated with human epidermal growth factor receptor 2-positive breast cancers

The long non-coding RNA NEAT1 locus is transcribed into two overlapping isoforms, NEAT1_1 and NEAT1_2, of which the latter is essential for the assembly of nuclear paraspeckles. NEAT1 is abnormally expressed in a wide variety of human cancers. Emerging evidence suggests that the two isoforms have distinct functions in gene expression regulation, and recently it was shown that NEAT1_2, but not NEAT1_1, expression predicts poor clinical outcome in cancer. Here, we report that NEAT1_2 expression correlates with HER2-positive breast cancers and high-grade disease. We provide evidence that NEAT1_1 and NEAT1_2 have distinct expression pattern among different intrinsic breast cancer subtypes. Finally, we show that NEAT1_2 expression and paraspeckle formation increase upon lactation in humans, confirming what has previously been demonstrated in mice