Gene regulation mechanisms involving the inactive X in B cells during lupus disease

University Of Pennsylvania, Philadelphia PA

Investigators

Linked publications & trials

Abstract

Females are predisposed for developing systemic lupus erythematosus (SLE), but the underlying mechanisms remain obscure. Chronic inflammation is also a feature of SLE, and the majority of SLE patients have elevated type I interferon (IFN) levels and increased expression of interferon signature genes. B cells from female SLE patients exhibit aberrant expression of X-linked immunity-related genes, including TLR7, TASL, IRAK1, TIMP1, and BTK, suggesting that dysregulation of X-linked gene expression may contribute to the female bias of this disease. While Type I IFN has pleiotropic effects on the immune system, it also upregulates TLR7 expression, raising the intriguing possibility that chronic inflammation from elevated type I IFN further exacerbates dysfunctional X-linked gene expression to promote disease in female SLE patients. Females have two X- chromosomes and equilibration of X-linked gene dosage to that of males (XY) occurs by X-Chromosome Inactivation (XCI), maintained by Xist RNA, heterochromatic modifications, and a compact 3D chromosome architecture. We have shown that activated B cells from SLE patients and a female-biased mouse model of lupus (NZB/W F1) have reduced accumulation of Xist RNA and heterochromatic marks on the Xi, and abnormal expression of some X-linked genes in naïve and activated B cells. Impairments with XCI maintenance, using a B cell specific Xist deletion (Xist cKO) mouse model, revealed that female Xist cKO mice injected with pristane have elevated autoantibody production and increased numbers of germinal center B cells (GCs) and age- associated B cells (ABCs). Notably, type I IFNs can trigger rapid rearrangement of 3D chromosome compartments that govern gene expression and prior studies revealed that CD4+ T cells from SLE patients have widespread 3D chromosome architecture changes that was associated with differential gene expression, including that of TLR7. Based on these data, our central hypothesis is that chronic inflammation that accompanies SLE alters the enrichment of heterochromatic histone marks and spatial organization of the Xi in B cells, resulting in abnormal X-linked gene expression of TLR7, TASL and other X-linked immunity genes. We will test our hypotheses with the following aims: (1) How does chronic inflammation from elevated Type I IFN impact Xi gene expression, heterochromatic epigenetic modifications across the Xi, and Xi spatial organization in mouse B cell subsets in a lupus-like disease model? (2) Is there aberrant biallelic transcription of X-linked genes, altered enrichment of active and silent epigenetic modifications, and disrupted 3D architecture of the X chromosome in circulating B cells from SLE patients with high vs low type I IFN levels? IMPACT: Our novel and innovative genetic and molecular approaches will yield unprecedented mechanistic insight on the influence of chronic inflammation on the epigenetic mechanisms of XCI maintenance, and will enable the identification of new molecular pathways and targets of female-biased autoimmune disease that could be amenable for therapeutic intervention.