Impaired dynamic X-chromosome inactivation maintenance in T cells is a feature of spontaneous murine SLE that is exacerbated in female-biased models

OBJECTIVE

Systemic lupus erythematosus (SLE) is a highly female-biased systemic autoimmune disease, but the molecular basis for this female bias remains incompletely elucidated. B and T lymphocytes from patients with SLE and female-biased mouse models of SLE exhibit features of epigenetic dysregulation on the X chromosome which may contribute to this strong female bias. We therefore examined the fidelity of dynamic X-chromosome inactivation maintenance (dXCIm) in the pathogenesis of two murine models of spontaneous lupus-NZM2328 and MRL/lpr-with disparate levels of female-bias to determine whether impaired dXCIm contributes to the female bias of disease.

METHODS

CD23+ B cells and CD3+ T cells were purified from age-matched C57BL/6 (B6), MRL/lpr, and NZM2328 male and female mice, activated in vitro, and processed for Xist RNA fluorescence in situ hybridization, H3K27me3 immunofluorescence imaging, qPCR, and RNA sequencing analyses.

RESULTS

The dynamic relocalization of Xist RNA and the canonical heterochromatin mark, H3K27me3, to the inactive X chromosome was preserved in CD23+ B cells, but impaired in activated CD3+ T cells from the MRL/lpr model (p < 0.01 vs. B6), and even more impaired in the heavily female-biased NZM2328 model (p < 0.001 vs. B6; p < 0.05 vs. MRL/lpr). RNAseq of activated T cells from NZM2328 mice revealed the female-biased upregulation of 32 X-linked genes distributed broadly across the X chromosome, many of which have roles in immune function. Many genes encoding Xist RNA-interacting proteins were also differentially expressed and predominantly downregulated, which may account for the observed mislocalization of Xist RNA to the inactive X chromosome.

CONCLUSIONS

Although evident in T cells from both the MRL/lpr and NZM2328 models of spontaneous SLE, impaired dXCIm is more severe in the heavily female-biased NZM2328 model. The aberrant X-linked gene dosage in female NZM2328 mice may contribute towards the development of female-biased immune responses in SLE-prone hosts. These findings provide important insights into the epigenetic mechanisms contributing to female-biased autoimmunity.

Anti-CD40L Accelerates Renal Disease and Adenopathy in MRL-lpr Mice in Parallel with Decreased Thymocyte Apoptosis

The CD40/CD40L (CD40 ligand) axis regulates several interactions between T cells and B cells. Blocking of CD40 engagement by CD40L inhibits Ig class switch by B cells as well as diminishes T cell response to an immunizing Ag. For these reasons, disruption of CD40/CD40L interactions by anti-CD40L administration or by genetic disruption of CD40L has ameliorated a variety of autoimmune conditions. More recent findings suggest that a direct signal can be transmitted to T cells via their expressed CD40L, which can costimulate proliferation with CD3 or promote germinal center formation. It is therefore possible that treatment with anti-CD40L Ab might produce a different outcome than observed in genetically CD40L-deficient mice. In this regard, we observe that in contrast to the genetic deletion of CD40L in MRL-lpr mice, which diminishes autoimmune disease but has little effect on adenopathy, administration of anti-CD40L to MRL-lpr mice accelerates both of these parameters. This difference appears to result from anti-CD40L actively delivering a signal that inhibits T cell apoptosis in lpr mice. This was confirmed by in vitro studies demonstrating that CD40L cross-linking on lpr thymocytes inhibited apoptosis and surface TCR down-modulation induced by CD3 ligation.

Anti-CD40 Ligand Antibody Treatment of SNF1 Mice with Established Nephritis: Preservation of Kidney Function

Prior studies have demonstrated that treatment of young, prenephritic lupus-prone mice with Ab directed against CD40 ligand (CD40L) prolongs survival and decreases the incidence of severe nephritis. In this report, we show that for (SWR × NZB)F1 (SNF1) animals with established lupus nephritis, long-term treatment with anti-CD40L beginning at either 5.5 or 7 mo of age prolonged survival and decreased the incidence of severe nephritis. “Older” mice were chosen for these studies to more closely resemble the clinical presentation of patients with established renal disease. We show that age at the start of treatment, which typically correlates with severity of disease, is an important factor when determining an efficacious therapeutic protocol since animals that began treatment at 7 mo of age required a more aggressive treatment protocol than animals at 5.5 mo of age. Remarkably, several anti-CD40L-treated animals beginning treatment at age 5.5 mo demonstrated a decline in proteinuria, as opposed to increasing proteinuria levels seen in hamster IgG (HIg)-treated controls, and histologic examination of kidneys from anti-CD40L-treated mice revealed dramatically diminished inflammation, sclerosis/fibrosis, and vasculitis, in marked contrast to the massive inflammation and kidney destruction observed in control animals that received hamster IgG. Spleens from anti-CD40L-treated mice also exhibited markedly reduced inflammation and fibrosis compared with controls. Together, these results show that treatment of older, nephritic SNF1 animals with long-term anti-CD40L immunotherapy significantly prolongs survival, reduces the severity of nephritis, and diminishes associated inflammation, vasculitis, and fibrosis.