Identification of Stage‐Specific Genes Associated With Lupus Nephritis and Response to Remission Induction in (NZB × NZW)F1 and NZM2410 Mice

Abstract

Objective To elucidate the molecular mechanisms involved in renal inflammation during the progression, remission and relapse of nephritis in murine lupus models using transcriptome analysis. Methods Kidneys from NZB/W F1 and NZM2410 mice were harvested at intervals during their disease course or after remission induction. Genome wide expression profiles were obtained from microarray analysis of perfused kidneys. Real time PCR analysis for selected genes was used to validate the microarray data. Comparisons between groups using SAM, and unbiased analysis of the entire dataset using singular value decomposition and self-organizing map were performed. Results Few changes in the renal molecular profile were detected in pre-nephritic kidneys but a significant shift in gene expression, reflecting inflammatory cell infiltration and complement activation occurred at proteinuria onset. Subsequent changes in gene expression predominantly affected mitochondrial dysfunction and metabolic stress pathways. Endothelial cell activation, tissue remodeling and tubular damage were the major pathways associated with loss of renal function. Remission induction reversed most, but not all of the inflammatory changes and progression towards relapse was associated with recurrence of inflammation, mitochondrial dysfunction and metabolic stress signatures. Conclusion Immune cell infiltration and activation is associated with proteinuria onset and reverses with immunosuppressive therapy but disease progression is associated with renal hypoxia and metabolic stress. Optimal therapy of SLE nephritis may therefore need to target both immune and non-immune disease mechanisms. In addition, the overlap of a substantial subset of molecular markers with those expressed in human lupus kidneys suggests potential new biomarkers and therapeutic targets.

Molecular studies of lupus nephritis kidneys

“…Our studies show that remission induction with immunologic intervention reverses a large proportion of the abnormal renal gene expression profile of nephritis in both NZB/W and NZM2410 mice. Importantly, however, we showed in NZB/W mice that a mitochondrial and metabolic signature recurs during progression toward relapse before the reappearance of proteinuria, perhaps reflecting an increased propensity to hypoxia conferred by the initial tissue insult [35] (Fig. 3).…”

“…In the NZM2410 model, we found that infiltration with inflammatory cells was not sufficient to induce relapse of proteinuria. Rather, we identified podocyte loss, renal tubular dysfunction, endothelial cell activation and tissue remodeling as the functional features associated with clinical relapse and consequent renal failure in both models [35].…”

“…Of these, CXCL10 and VCAM-1 are soluble proteins that have already been identified as potential urinary biomarkers for human lupus nephritis [73,74]. Other genes in this group whose expression could be measured in the serum or urine include TIMP1 and EGF [35].…”

“…The second cluster of six modules contained genes that were downregulated during established proteinuria, reversed during remission and became downregulated again during impending relapse. These genes reflect the metabolic disturbances and mitochondrial dysfunction that are associated with tissue stress and hypoxia [35] (Fig. 3).…”

“…Our finding that the major changes in renal gene expression occur at the onset of clinical disease suggests that irreversible damage may progress rapidly, underscoring the need for early biomarkers of renal flare. We therefore used an unbiased approach to identify genes whose expression correlated most tightly with disease stage [35] and identified those genes that are also highly expressed in human SLE nephritis biopsies.…”