Background Nephritis is a major cause of morbidity and mortality in SLE. One of impediments to optimal management of this condition is a lack of biomarkers that forecast development of renal disease or that can be used to determine the response to therapy.
Objectives In this study we used gene expression microarrays to contrast the gene expression profile in active lupus patients with and without nephritis to identify potential biomarkers and immune mechanisms associated with nephritis.
Methods Affymetrix Human Gene 2.0ST arrays were used to assay gene expression in total RNA isolated from blood archived in PAXgene tubes for 38 active SLE patients with ≥4 ACR SLE classification criteria (25 biopsy proven nephritis, 13 active without nephritis) and 17 healthy controls. Data were analyzed with linear modeling, with corrections for multiple testing. Results were validated in a largely independent cohort of 22 healthy controls and 170 SLE patients (129 active (89 with and 40 without nephritis), 41 nephritis in remission), using Nanostring technology.
Results Comparison of gene expression between healthy controls and all SLE patients revealed 27 genes that were increased >1 log2 fold-change in SLE, the majority of which (25) were IFN-induced. When active SLE patients with and without nephritis were compared, there were 25 probes that demonstrated a >1 log2 fold-change with a false discovery rate of q <0.25 (chosen due to the small number of samples). Twenty-two of the probes were overexpressed in patients with nephritis, representing 19 independent genes, the majority of which (15) are preferentially expressed in neutrophils, particularly low density granulocytes (LDGs). There was no difference in the levels of IFN-induced gene expression between active SLE patients with and without nephritis. Examination of gene expression in the validation cohort confirmed these findings and showed that the levels of LDG gene expression in renal remissions were similar to active patients without nephritis. In secondary analyses, the levels of LDG genes correlated positively with the total SLEDAI (p<0.001) and the hematuria (p<0.01) and proteinuria (p<0.001) components of the SLEDAI. There was no association between any of the IFN or LDG genes and vasculitis, treatment, and for those patients with paired renal biopsies, biopsy class, activity or chronicity scores. There was also no correlation between the levels of LDG genes and the neutrophil count in any of the patient subsets. On examination of a subset of patients longitudinally, the LDG signature did not appear to respond rapidly to treatment, remaining relatively consistent in several patients despite marked changes in the SLEDAI, treatment, and neutrophil count.
Conclusions Patients with lupus nephritis have higher levels of LDG gene expression than those without nephritis. Given the high rate of spontaneous NETosis in this cell population, the findings are consistent with the concept that high levels of NETosing neutrophils promote renal disease in SLE.
Disclosure of Interest J. Wither Grant/research support from: CIHR and Eli Lilly and Company, S. Prokopec: None declared, B. Noamani: None declared, D. Bonilla: None declared, Z. Touma: None declared, H. Reich: None declared, J. Scholey: None declared, P. Fortin Grant/research support from: CIHR and Eli Lilly and Company, P. Boutros: None declared, C. Landolt-Marticorena: None declared
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