Background Notch signaling constitutes an evolutionarily conserved pathway that transduces signals between neighbouring cells and determines major decisions in cell proliferation, survival and differentiation. Notch signaling has been shown to play a pivotal role in T cell lineage specifications. T lymphocytes from patients with systemic lupus erythematosus (SLE) display a severely altered phenotype with several molecular and functional aberrations including defective capacities to up-regulate Notch-1 receptor expression upon T cell receptor activation (1-3).
Objectives The goal of the present study was to analyze basal Notch-1 expression levels and differential mechanisms of Notch-1 gene transcription in T cells from SLE patients and healthy controls.
Methods We analyzed basal Notch-1 mRNA expression using real-time quantitative PCR in total T cells from a cohort of 61 SLE patients (diagnosed according to ACR criteria) with 32 of them classified as active patients (SLEDAI ≥4) and 24 healthy control individuals. Subpopulations of these individuals were analyzed for Notch-1 protein expression in various T cell subsets by FACS surface staining (e.g. CD4+, CD8+, double negative T cells). Chromatin immunoprecipitation, CpG-DNA methyl-immunoprecipitation assays, transfection studies and reporter assays were performed to analyze mechanisms of Notch-1 regulation.
Results We demonstrate that also basal Notch-1 expression is decreased in T cells from active SLE patients at the messenger and protein level in various T cell subpopulations. Notch1 transcript numbers inversely correlate to disease activity in SLE patients. We provide evidence that both, enhanced histone H3 and CpG-DNA methylation of the human Notch1 promoter contribute to decreased Notch-1 expression in SLE T cells. Previous data from our group identified cAMP responsive element modulator (CREM)α, which is up-regulated in SLE T cells, as a key regulator of the epigenetic conformation and gene transcription, e.g. that of IL2 and IL17 genes. In this study, we observed increased CREMα binding to the Notch1 promoter which results in a significantly repressed Notch1 promoter activity and gene transcription.
Conclusions Our data suggest a critical role for Notch-1 in SLE immunopathogenesis and, for the first time, we present molecular mechanisms that mediate dysregulated Notch-1 expression in SLE T cells.
Amsen D et al. 2009. The different faces of Notch in T-helper-cell differentiation. Nat Rev Immunol 9:116-124.
Tsokos GC. 2011. Systemic lupus erythematosus. The New England Journal of Medicine 365:2110-2121.
Sodsai P et al. 2008. Defects in Notch1 upregulation upon activation of T Cells from patients with systemic lupus erythematosus are related to lupus disease activity. Lupus 17:645-653.
Disclosure of Interest None Declared