The protective effect of A20 on atherosclerosis in apolipoprotein E-deficient mice is associated with reduced expression of NF-κB target genes

Abstract

Up-regulation of inflammatory responses is considered a driving force of atherosclerotic lesion development. One key regulator of inflammation is the A20 (also called TNF-␣-induced protein 3 or Tnfaip3) gene, which is responsible for NF-B termination and maps to an atherosclerosis susceptibility locus revealed by quantitative trait locus-mapping studies at mouse proximal chromosome 10. In the current study, we examined the role of A20 in atherosclerotic lesion development. At the aortic root lesion size was found to be increased in C57BL/6 (BG) apolipoprotein E-deficient (ApoE ؊/؊ ) mice haploinsufficient for A20, compared with B6 ApoE ؊/؊ controls that expressed A20 normally (60% in males and 23% in females; P < 0.001 and P < 0.05, respectively). In contrast, lesion size was found to be decreased in F 1 (B6؋FVB/N) mice overexpressing A20 by virtue of containing an A20 BAC transgene compared with nontransgenic controls (30% in males, P < 0.001, and 17% in females, P ‫؍‬ 0.02). The increase in lesions in the A20 haploinsufficient mice correlated with increased expression of proatherosclerotic NF-B target genes, such as vascular cell adhesion molecule 1, intercellular adhesion molecule 1, and macrophage-colony-stimulating factor, and elevated plasma levels of NF-B-driven cytokines. These findings suggest that A20 diminishes atherosclerosis by decreasing NF-B activity, thereby modulating the proinflammatory state associated with lesion development.A therosclerosis is a chronic inflammatory disease influenced by many genes, and mouse models are useful for identifying these genes and determining their mechanisms of action. We previously carried out an intercrosses between atherosclerosissensitive apolipoprotein E-deficient (ApoE Ϫ/Ϫ ) C57BL/6 (B6) and atherosclerosis-resistant ApoE Ϫ/Ϫ FVB mice, and by quantitative trait locus mapping identified an atherosclerosissusceptibility locus on proximal chromosome 10 (1, 2). A candidate gene in this region, A20, encodes a broadly expressed cytoplasmic protein that inhibits both TNF-␣-and IL-1␤/Tolllike receptor (TLR)-induced NF-B activation through mediating the destruction of receptor-interacting serine/threonine protein kinase 1 (RIP) and TNF receptor-associated factor 6 in their respective signaling complexes (3, 4). Up-regulation of NF-B activity leads to increased expression of many genes with established roles in atherosclerosis, including cytokines, chemokines, adhesion molecules, acute phase proteins, and regulators of apoptosis and cell proliferation. NF-B terminates its own activation by inducing the expression of I B␣ and A20. A20-deficient (A20 Ϫ/Ϫ ) mice die prematurely because of cachexia and spontaneous inflammation in several organs. This phenotype correlates with the failure to properly terminate TNF-induced NF-B activity in fibroblasts isolated from A20 Ϫ/Ϫ mice (5). We previously determined that A20 derived from B6 and FVB mice differs in a single amino acid residue (E627A; B6 vs. FVB). We showed this finding to be functionally significant by demonstrating...

A20: Central Gatekeeper in Inflammation and Immunity

“…Also, mutation of a single amino acid (E627A) has been shown to correlate with increased sensitivity to atherosclerosis in mice (62). Consistent with these data, overexpression of A20 is protective in a mouse model for atherosclerosis, whereas mice haploinsufficient for A20 show increased lesion size (63). Interestingly, different genome-wide association studies have shown that multiple polymorphisms in the A20 region are independently associated with several autoimmune diseases, including rheumatoid arthritis (64,65), systemic lupus erythomatosus (66,67), and Crohn disease (12).…”

“…A20 was subsequently shown to deubiquitinate Lys 48 or Lys 63 polyubiquitin chains in vitro (32). The real breakthrough came with the finding that A20 specifically removes Lys 63 polyubiquitin chains from RIP1 (23), an essential signaling protein that is recruited together with A20 to TNFR (33). Mutation of the active-site Cys 103 in the OTU domain abrogates the deubiquitinating and NF-B inhibitory activity of A20 (23,32).…”

“…Lys 63 -ubiquitinated signaling proteins are then recognized by specific ubiquitin-binding scaffolding proteins that assemble and activate downstream kinases (e.g. Lys 63 -ubiquitinated RIP1 (receptor-interacting protein 1) is recognized by the IKK␣/IKK␤ adaptor NEMO) (28).…”

Suppression of oxLDL‐Induced MMP‐9 and EMMPRIN Expression by Berberine via Inhibition of NF‐κB Activation in Human THP‐1 Macrophages

“…Therefore, the inhibition of NF-jB activation will impede the progress of atherosclerosis. In fact, the suppression of NF-jB activity by blocking IjB degradation results in significantly smaller atherosclerotic lesions as compared with those in control mice (Wolfrum et al, 2007). Several studies have also demonstrated the positive correlation between NF-jB activity and the incidence of myocardial infarction (Thiemermann, 2004;Majdalawieh and Ro, 2010).…”

G Protein-Coupled Receptor Dependent NF-κB Signaling in Atherogenesis

“…Intriguingly, A20 appears to have a protective effect against atherosclerosis in both mice and humans. In ApoE -/-mice, A20 haploinsufficiency results in a significant increase in atherosclerosis compared to normal A20 controls, whereas transgenic overexpression of A20 results in decreased atherosclerosis (Wolfrum et al, 2007). Moreover, in human diabetic patients, polymorphisms at the A20 locus leading to reduced levels of A20 expression are associated with increased coronary artery disease (Boonyasrisawat et al, 2007).…”