Kichul Ko

The Emerging Role of the Inflammasome in Kidney Diseases

Purpose of review To focus on the latest data that elucidate the role of the NLRP3 inflammasome in kidney diseases. Recent findings The NLRP3 inflammasome is not limited by the traditional microbial stimuli of innate immunity and its connection with autophagy, apoptosis, fibrosis, and pro-inflammatory cytokines has broader implications for a variety of kidney diseases. In a wide spectrum of glomerular and tubulointerstitial diseases, the NLRP3 inflammasome is upregulated in both classical immune cells such as infiltrating macrophages and resident dendritic cells as well as in renal tubular epithelial cells, and even podocytes. Inhibition of the NLRP3 inflammasome ameliorates renal injury in a variety of animal models. Interestingly, this extends to models of proteinuria, which suggests that the deleterious effect of albuminuria on the proximal tubular epithelium and podocytes is, in part, mediated by inflammasome activation. Summary Recent studies in animal models, and limited studies in humans, suggest a broad role for inflammasome activation in renal disease. Surprisingly, individual components of the inflammasome, independent of inflammasome activation, may also contribute to progressive renal injury. Additional, studies are needed to define the relative importance of the inflammasome in specific diseases and the therapeutic opportunities afforded by targeting the inflammasome.

Interferon Regulatory Factor 5 in the Pathogenesis of Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is an autoimmune disease characterized by multiple genetic risk factors, high levels of interferon alpha (IFN-α), and the production of autoantibodies against components of the cell nucleus. Interferon regulatory factor 5 (IRF5) is a transcription factor which induces the transcription of IFN-α and other cytokines, and genetic variants of IRF5 have been strongly linked to SLE pathogenesis. IRF5 functions downstream of Toll-like receptors and other microbial pattern-recognition receptors, and immune complexes made up of SLE-associated autoantibodies seem to function as a chronic endogenous stimulus to this pathway. In this paper, we discuss the physiologic role of IRF5 in immune defense and the ways in which IRF5 variants may contribute to the pathogenesis of human SLE. Recent data regarding the role of IRF5 in both serologic autoimmunity and the overproduction of IFN-α in human SLE are summarized. These data support a model in which SLE-risk variants of IRF5 participate in a “feed-forward” mechanism, predisposing to SLE-associated autoantibody formation, and subsequently facilitating IFN-α production downstream of Toll-like receptors stimulated by immune complexes composed of these autoantibodies.

Activation of the Interferon Pathway is Dependent Upon Autoantibodies in African-American SLE Patients, but Not in European-American SLE Patients

Background: In systemic lupus erythematosus (SLE), antibodies directed at RNA-binding proteins (anti-RBP) are associated with high serum type I interferon (IFN), which plays an important role in SLE pathogenesis. African-Americans (AA) are more likely to develop SLE, and SLE is also more severe in this population. We hypothesized that peripheral blood gene expression patterns would differ between AA and European-American (EA) SLE patients, and between those with anti-RBP antibodies and those who lack these antibodies. Methods: Whole blood RNA from 33 female SLE patients and 16 matched female controls from AA and EA ancestral backgrounds was analyzed on Affymetrix Gene 1.0 ST gene expression arrays. Ingenuity Pathway Analysis was used to compare the top differentially expressed canonical pathways amongst the sample groups. An independent cohort of 116 SLE patients was used to replicate findings using quantitative real-time PCR (qPCR). Results: Both AA and EA patients with positive anti-RBP antibodies showed over-expression of similar IFN-related canonical pathways, such as IFN Signaling (P = 1.3 × 10−7 and 6.3 × 10−11 in AA vs. EA respectively), Antigen Presenting Pathway (P = 1.8 × 10−5 and 2.5 × 10−6), and a number of pattern recognition receptor pathways. In anti-RBP negative (RBP−) patients, EA subjects demonstrated similar IFN-related pathway activation, whereas no IFN-related pathways were detected in RBP−AA patients. qPCR validation confirmed similar results. Conclusion: Our data show that IFN-induced gene expression is completely dependent on the presence of autoantibodies in AA SLE patients but not in EA patients. This molecular heterogeneity suggests differences in IFN-pathway activation between ancestral backgrounds in SLE. This heterogeneity may be clinically important, as therapeutics targeting this pathway are being developed.

Genetic ancestry, serum interferon-α activity, and autoantibodies in systemic lupus erythematosus.

Objective. To investigate and refine the relationships among systemic lupus erythematosus (SLE) and related autoantibodies, interferon-α (IFN-α), and various ancestral backgrounds. Methods. We investigated quantitatively defined genetic ancestry through principal component analysis in place of self-reported ancestry. Results. African ancestry was found to be associated with presence of anti-RNP antibody (p = 0.0026), and anti-RNP was correlated with high levels of IFN-α (p = 2.8 × 10−5). Conclusion. Our data support a model in which African ancestry increases the likelihood of SLE-associated autoantibody formation, which subsequently results in higher levels of serum IFN-α.

Widely divergent transcriptional patterns between SLE patients of different ancestral backgrounds in sorted immune cell populations.

Systemic lupus erythematosus (SLE) is a complex autoimmune disease of uncertain etiology. Patients from different ancestral backgrounds demonstrate differences in clinical manifestations and autoantibody profiles. We examined genome-wide transcriptional patterns in major immune cell subsets across different ancestral backgrounds. Peripheral blood was collected from African-American (AA) and European-American (EA) SLE patients and controls. CD4 T-cells, CD8 T-cells, monocytes, and B cells were purified by flow sorting, and each cell subset from each subject was run on a genome-wide expression array. Cases were compared to controls of the same ancestral background. The overlap in differentially expressed gene (DEG) lists between different cell types from the same ancestral background was modest (<10%), and only 5-8% overlap in DEG lists was observed when comparing the same cell type between different ancestral backgrounds. IFN-stimulated gene (ISG) expression was not up-regulated synchronously in all cell types from a given patient, for example a given subject could have high ISG expression in T and B cells, but not in monocytes. AA subjects demonstrated more concordance in ISG expression between cell types from the same individual, and AA patients demonstrated significant down-regulation of metabolic gene expression which was not observed in EA patients. ISG expression was significantly decreased in B cells in patients taking immunosuppressants, while ISGs in other cell types did not differ with medication use. In conclusion, gene expression was strikingly different between immune cell subsets and between ancestral backgrounds in SLE patients. These findings emphasize the critical importance of studying multiple ancestral backgrounds and multiple cell types in gene expression studies. Ancestral backgrounds which are not studied will not benefit from personalized medicine strategies in SLE.

Gene-expression-guided selection of candidate loci and molecular phenotype analyses enhance genetic discovery in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a highly heterogeneous autoimmune disorder characterized by differences in autoantibody profiles, serum cytokines, and clinical manifestations. We have previously conducted a case-case genome-wide association study (GWAS) of SLE patients to detect associations with autoantibody profile and serum interferon alpha (IFN-α). In this study, we used public gene expression data sets to rationally select additional single nucleotide polymorphisms (SNPs) for validation. The top 200 GWAS SNPs were searched in a database which compares genome-wide expression data to genome-wide SNP genotype data in HapMap cell lines. SNPs were chosen for validation if they were associated with differential expression of 15 or more genes at a significance of P < 9 × 10−5. This resulted in 11 SNPs which were genotyped in 453 SLE patients and 418 matched controls. Three SNPs were associated with SLE-associated autoantibodies, and one of these SNPs was also associated with serum IFN-α (P < 4.5 × 10−3 for all). One additional SNP was associated exclusively with serum IFN-α. Case-control analysis was insensitive to these molecular subphenotype associations. This study illustrates the use of gene expression data to rationally select candidate loci in autoimmune disease, and the utility of stratification by molecular phenotypes in the discovery of additional genetic associations in SLE.

Bcl-2 as a Therapeutic Target in Human Tubulointerstitial Inflammation.

In lupus nephritis, tubulointerstitial inflammation (TII) is associated with in situ adaptive immune cell networks that amplify local tissue damage. Since conventional therapy appears ineffective for severe TII, and these patients often progress to renal failure, understanding in situ mechanisms might reveal new therapeutic targets. This study was undertaken to assess whether dysregulated apoptotic regulators maintain local adaptive immunity and drive inflammation in TII.

THU0491 Genome-Wide Transcriptional Profiling of Isolated Immune Cell Populations from SLE Patients with Different Ancestral Backgrounds

Background Systemic lupus erythematosus (SLE) is a complex multi-system autoimmune disease of uncertain etiology. Patients from different ancestral backgrounds demonstrate differences in clinical manifestations and autoantibody profiles. Objectives In this study we examined genome-wide transcriptional patterns in major immune cell subsets across different ancestral backgrounds. Methods Peripheral blood was collected and run on 208 Illumina HumanHT-12 V4 expression BeadChip arrays. Subjects included 21 African-American (AA) and 21 European-American (EA) SLE patients, 5 AA and 5 EA controls. CD4+ T-cells, CD8+ T-cells, monocytes and B cells were purified by flow sorting. Each cell subset from each subject was run on a separate array. Differentially expressed genes (DEGs) were determined by comparing cases and controls of the same ancestral background. Results The overlap in DEG lists between different cell types from the same ancestral background was very modest (<1%). Typically between 5-10% of DEGs were shared when comparing the same cell type between different ancestral backgrounds. Global IFN-stimulated gene (ISG) expression revealed that AA subjects demonstrated more concordance across all studied cell types. Two subgroups of patients were identified based on the ISG expression profiles. One subgroup showed higher ISGs expression in all cell types, and the other subgroup had higher ISG expression only in T and B lymphocytes but not in monocytes. Conclusions We find striking differences in gene expression between different immune cell subsets and between ancestral backgrounds in SLE patients. The IFN signature is diverse, with different transcripts represented in different cell populations, and signature-positive cell subsets differed in EA vs. AA patients. Disclosure of Interest : None declared DOI 10.1136/annrheumdis-2014-eular.5291

FRI0263 Activation of the interferon pathway is dependent upon autoantibodies in african american sle patients, but not in european-american sle patients

Background Lupus is a heterogeneous autoimmune disease characterized by anti-RNA-binding protein autoantibodies and high circulating levels of interferon. The disease is more prevalent and more severe in African-Americans as compared to European-Americans. Objectives We aimed to explore how IFN-related gene expression pathways differ in patients according to their ancestry and anti-RBP profile. Methods Whole blood from 33 female SLE patients and 16 matched controls from EA and AA ancestral backgrounds was analyzed through Affymetrix gene expression arrays, and the data were further studied through Ingenuity Pathways Analysis for canonical pathway comparison. An independent replication cohort of more than 100 SLE patient samples and 30 controls was used to test the hypotheses generated by the microarray data, using qPCR to quantify gene expression. Results Both EA and AA patients with positive anti-RBP (RBP+) showed involvement of IFN-related canonical pathways including IFN Signaling (P = 5.8 x 10-11 and 1.3 x 10-7 respectively), and a number of pattern recognition receptor pathways. All of these pathways were also involved in EA patients with negative anti-RBP (RBP-) but they were completely absent in AA patients with RBP-. The microarray results were confirmed by a replication study through qPCR on 3 IFN-inducible genes, IFIT1, MX1 and PKR. Conclusions Our data show that IFN-induced gene expression is completely dependent on the presence of autoantibodies in AA SLE patients but not in EA patients. Disclosure of Interest: None Declared