Estrogen receptor alpha modulates mesangial cell responses to toll-like receptor ligands.

The female predominance in lupus is incompletely understood. The mechanisms for this difference are multifactorial involving the sex chromosomes, the hormones, and their receptors. We, and others, demonstrated that estrogen receptor alpha (ERα)-deficient female mice developed significantly less lupus-like renal disease. This protective effect of ERα deficiency occurred despite no impact on glomerular immune complex deposition. We hypothesized that decreased renal disease in ERα-deficient mice was due to a dampened renal response to inflammatory stimuli. Given the role of Toll-like receptors (TLRs) in lupus, we assessed whether there was an interaction between TLR responses and ERα. Herein, we show that TLR3, 4, and 7 ligands all enhanced mesangial cell (MC) ERα expression, whereas neither estrogen, nor ERα, impacted TLR3, 4, or 7 expression in MCs. The lack of ERα markedly decreased MC production of interleukin 6 and monocyte chemoattractant protein 1 (MCP-1) following addition of TLR3, 4, and 7 ligands. In MCs, TLR ligands induced ERα phosphorylation and nuclear localization. TLR3-induced nuclear factor κB nuclear translocation in MCs was not significantly affected by estrogen or ERα. Finally, we demonstrate that female MCs express more TLR3 and respond to TLR ligands with a significantly increased production of interleukin-6 compared with male MCs. These results identify a significant impact/interaction of ERα in TLR-mediated inflammatory responses in MCs.

A GA microsatellite in the Fli1 promoter modulates gene expression and is associated with systemic lupus erythematosus patients without nephritis.

INTRODUCTION: The transcription factor Fli1 is implicated in the pathogenesis of systemic lupus erythematosus (SLE). Recently, a GA(n) polymorphic microsatellite was characterized in the mouse Fli1 promoter that modulates promoter activity and is truncated in two lupus mouse models compared to non-autoimmune prone mice. In this work, we characterize a homologous GA(n) microsatellite in the human Fli1 promoter. The purpose of this study is to determine the effect of the microsatellite length on Fli1 promoter activity in vitro and to determine if the length of the GA(n) microsatellite is associated with SLE and/or specific disease characteristics. METHODS: Constructs with variable lengths of the GA(n) microsatellite in the Fli1 promoter were generated and analyzed in promoter/reporter (P/R) assays in a human T cell line. Using three SLE patient cohorts and matched controls, microsatellite length was measured and association with the presence of disease and the occurrence of specific disease manifestations was assessed. RESULTS: P/R assays demonstrated that the presence of a shorter microsatellite resulted in higher Fli1 promoter activity. A significant association was observed in the lupus cohort SLE in Gullah Health (SLEIGH) between the GA(26) base pair allele and absence of nephritis. CONCLUSIONS: This study demonstrates that a GA(n) microsatellite in the human Fli1 promoter is highly polymorphic. The length of the microsatellite is inversely correlated to Fli1 promoter activity in a human T cell line. Although no association between microsatellite length and lupus was observed, an association between a specific microsatellite length and patients without nephritis in the SLEIGH cohort was observed.

Impact of estrogen receptor deficiency on disease expression in the NZM2410 lupus prone mouse.

Systemic lupus erythematosus (SLE) occurs nine times more often in females than males. The purpose of this study was to determine the impact of estrogen receptor (ER) null genotypes on disease in lupus prone NZM2410 (NZM) and MRL/lpr mice, as a method to define the role of estrogen receptor signaling in lupus. ER alpha deficient NZM females, but not males, had significantly prolonged survival, reduced proteinuria, renal pathology scores and serum urea nitrogen levels compared to wildtype mice, despite higher serum anti-dsDNA levels. ER alpha deficient MRL/lpr female, but not male, mice also had significantly less proteinuria and renal pathology scores with no effect on autoantibody levels. Deficiency of ER beta had no effect on disease in either strain or sex. Taken together, these data demonstrate a key role for ER alpha, but not ER beta, in the development of lupus like disease, but not autoimmunity, in female NZM and MRL/lpr mice.

Inflammatory modulation of PPAR gamma expression and activity.

Nitric oxide (NO) production increases with age in the lupus-prone MRL/lpr mouse, paralleling disease activity. One mechanism for excess NO production in MRL/lpr mice may be a defect in down-regulatory mechanisms of the iNOS pathway. A potential modulator of NO is the nuclear hormone receptor peroxisome proliferation activated receptor gamma (PPARgamma). We demonstrate that renal PPARgamma protein expression was altered as disease progressed in MRL/lpr mice, which paralleled increased iNOS protein expression. Additionally, MRL/lpr-derived primary mesangial cells expressed less PPARgamma than BALB/c mesangial cells and produced more NO in response to LPS and IFNgamma. Furthermore, PPARgamma activity was reduced in mesangial cells following exposure to inflammatory mediators. This activity was restored with the addition of a NOS enzyme inhibitor. These results indicate that the activation of inflammatory pathways may lead to reduced activity and expression of PPARgamma, further exacerbating the disease state.

A novel PPAR response element in the murine iNOS promoter.

The nuclear hormone receptor peroxisome proliferation activated receptor gamma (PPARgamma) is a modulator of inflammation including down-regulation of inducible nitric oxide synthase (iNOS) and nitric oxide (NO) production. PPARgamma agonists reduce iNOS expression and NO production in a dose-dependent manner in macrophages, mesangial cells and other inflammatory cells. However, the mechanisms involved in the inhibition of iNOS expression by PPARgamma and its agonists are not fully understood. Here we show that the PPARgamma agonist ciglitazone dose-dependently inhibited a murine iNOS-luciferase reporter construct by up to 50% in transfected mesangial cells. Blocking de novo protein synthesis in mesangial cells had no effect on PPARgamma agonist activity, indicating that ciglitazone acts directly to inhibit iNOS transcription. We identified a novel PPAR response element (PPRE) in the murine iNOS promoter that is homologous to the PPRE consensus sequence. In binding assays PPARgamma directly binds to this response element in vitro and can function as a positive element in response to PPARgamma agonists when placed in front of a reporter gene. Site-directed mutagenesis of this PPRE in a murine iNOS promoter/reporter construct did not block the inhibitory activity of a synthetic PPARgamma agonist on the iNOS promoter/reporter construct in transfected mesangial cells. However, the mutated construct exhibited lower basal expression, and higher expression in response to inflammatory stimuli compared to the intact construct. These data suggest that the iNOS PPRE contributes to positive basal expression and negative expression of iNOS in response to inflammatory stimuli. The PPRE is not necessary, however, for synthetic PPARgamma agonists to inhibit iNOS expression.

Peroxisome proliferation-activated receptor (PPAR)gamma is not necessary for synthetic PPARgamma agonist inhibition of inducible nitric-oxide synthase and nitric oxide.

Peroxisome proliferation-activated receptor (PPAR)gamma agonists inhibit inducible nitric-oxide synthase (iNOS), tumor necrosis factor-alpha, and interleukin-6. Because of these effects, synthetic PPARgamma agonists, including thiazolidinediones, are being studied for their impact on inflammatory disease. The anti-inflammatory concentrations of synthetic PPARgamma agonists range from 10 to 50 microM, whereas their binding affinity for PPARgamma is in the nanomolar range. The specificity of synthetic PPARgamma agonists for PPARgamma at the concentrations necessary for anti-inflammatory effects is thus in question. We report that PPARgamma is not necessary for the inhibition of iNOS by synthetic PPARgamma agonists. RAW 264.7 macrophages possess little PPARgamma, yet lipopolysaccharide (LPS)/interferon (IFN)gamma-induced iNOS was inhibited by synthetic PPARgamma agonists at 20 microM. Endogenous PPARgamma was inhibited by the transfection of a dominant-negative PPARgamma construct into murine mesangial cells. In the transfected cells, synthetic PPARgamma agonists inhibited iNOS production at 10 microM, similar to nontransfected cells. Using cells from PPARgamma Cre/lox conditional knockout mice, baseline and LPS/IFNgamma-induced nitric oxide levels were higher in macrophages lacking PPARgamma versus controls. However, synthetic PPARgamma agonists inhibited iNOS at 10 microM in the PPARgamma-deficient cells, similar to macrophages from wild-type mice. These results indicate that PPARgamma is not necessary for inhibition of iNOS expression by synthetic PPARgamma agonists at concentrations over 10 microM. Intrinsic PPARgamma function, in the absence of synthetic agonists, however, may play a role in inflammatory modulation.

A novel diagnostic screen for defects in the Fanconi anemia pathway.

Fanconi anemia (FA) is an autosomal recessive chromosomal instability syndrome characterized by congenital abnormalities, progressive bone marrow failure, and cancer predisposition. Although patients with FA are candidates for bone marrow transplantation or gene therapy, their phenotypic heterogeneity can delay or obscure diagnosis. The current diagnostic test for FA consists of cytogenetic quantitation of chromosomal breakage in response to diepoxybutane (DEB) or mitomycin C (MMC). Recent studies have elucidated a biochemical pathway for Fanconi anemia that culminates in the monoubiquitination of the FANCD2 protein. In the current study, we develop a new rapid diagnostic and subtyping FA assay amenable for screening broad populations at risk of FA. Primary lymphocytes were assayed for FANCD2 monoubiquitination by immunoblot. The absence of the monoubiquitinated FANCD2 isoform correlated with the diagnosis of FA by DEB testing in 11 known patients with FA, 37 patients referred for possible FA, and 29 healthy control subjects. Monoubiquitination of FANCD2 was normal in other bone marrow failure syndromes and chromosomal breakage syndromes. A combination of retroviral gene transfer and FANCD2 immunoblotting provides a rapid subtyping assay for patients newly diagnosed with FA. These new FA screening assays would allow efficient testing of broad populations at risk.