Genetic variants associated with autoimmunity drive NFκB signaling and responses to inflammatory stimuli

Abstract

The transcription factor NFκB is a central regulator of inflammation and genome-wide association studies in subjects with autoimmune disease have identified a number of variants within the NFκB signaling cascade. In addition, causal variant fine-mapping has demonstrated that autoimmune disease susceptibility variants for multiple sclerosis (MS) and ulcerative colitis are strongly enriched within binding sites for NFkB. Here, we report that MS-associated variants proximal to NFκB1 and in an intron of TNFRSF1A (TNFR1) are associated with increased NFκB signaling after TNFα stimulation. Both variants result in increased degradation of IκBα, a negative regulator of NFκB, and nuclear translocation of p65 NFκB. The variant proximal to NFκB1 controls signaling responses by altering expression of NFκB itself, with the GG risk genotype expressing 20-fold more p50 NFκB and diminished expression of the negative regulators of the NFκB pathway TNFAIP3, BCL3, and CIAP1. Finally naïve CD4 T cells from patients with MS express enhanced activation of p65 NFκB. These results demonstrate that genetic variants associated with risk of developing MS alter NFκB signaling pathways, resulting in enhanced NFκB activation and greater responsiveness to inflammatory stimuli. As such, this suggests that rapid genetic screening for variants associated with NFκB signaling may identify individuals amenable to NFκB or cytokine blockade.

Genetic basis of autoimmunity

“…We recently found that MS-associated variants proximal to NFKB1 (rs228614) and in TNFRSF1A (TNFR1, rs1800693) are associated with increased NF-κB signaling after TNF-α stimulation (70). Both variants result in increased degradation of IκBα, a negative regulator of NF-κB and nuclear translocation of p65 NF-κB.…”

Inflammation in the spotlight—clinical relevance of genetic variants affecting nuclear factor κB and tumor necrosis factor receptor 1

“…This transcriptional change results in an exaggerated cytokine production response from monocytes after stimulation with TNFα, and exacerbates inflammatory responses. As well as with the genetic variant affecting (or associated with) NF-κB, the study by Housley and coworkers demonstrates that the likely causal impact of rs1800693 variations in inflammation and response to TNFα involves increased activation of the NF-κB pathway (18). Current authors' findings suggest that altered TNFα induced NF-κB signaling was due to rs1800693 SNP exerting regulatory effects through changes in TNFR1.…”

“…Firstly, these authors validated that naïve CD4 T cells from patients with MS exhibit increased IκBα degradation and higher phospho-p65 and NF-κB activation than age-matched healthy controls, and that this increased activation is mitigated by treatments affecting NF-κB (18). Then, they investigated whether stimulated circulating immune cells from subjects with different genotypes at rs228614 (AG; average heterozygosis ± standard deviation =0.5±0.008) resulted in greater degradation of IκBα and phosphorylation of p65 NF-κB in naïve CD4 T cells with the risk genotype (GG).…”

“…The authors used healthy control subjects carrying the risk or the protective variants, and the concordant impact of the rs228614 risk variant was identified after signaling induction. In addition, subjects with the GG risk genotype expressed p50 NF-κB at 20-fold higher level than the AA genotype, together with a loss of negative regulation of this pathway (18). They concluded that naïve CD4 T cells from subjects carrying MS risk variants affecting NF-κB1 exhibit increased p65 activation consistent with changes in NF- Then, the inflammatory cascade is amplified by proinflammatory cytokines released by these cells, further increasing cell recruitment, promoting activation of resident microglial cells, and compromising blood brain barrier.…”

“…One of the strongest genome-wide association signals related to inflammation lies on chromosome 4, near the NF-κB gene (18), the span region that encodes both NF-κB and mannosidase beta. This region contains more than 90 genetic variants that are in linkage disequilibrium, making the identification of the likely causal variants challenging in the context of disease.…”