The Interplay of Lipoproteins and Innate Immune Responses in Systemic Lupus Erythematosus and its Role in Premature Cardiovascular Disease.

Systemic lupus erythematosus (SLE) is an autoimmune syndrome that primarily affects women and leads to significant internal organ damage. Patients with SLE exhibit a high risk for premature atherosclerotic cardiovascular disease (CVD) not associated with traditional risk factors. It is therefore necessary to establish specific biomarkers for CVD risk in SLE patients and to further elucidate the interplay between the aberrant innate immune system and lipoprotein biology present in SLE atherosclerosis. Recent evidence links oxidized high-density lipoprotein (oxHDL) with accelerated “typical” CVD. It remains to be determined whether these modifications also occur in SLE, which mechanisms lead to this modification, and what impact oxHDL has on SLE CVD innate immune responses. We hypothesized that the chronic oxidative environment in SLE promotes pro-atherogenic alterations to HDL. We further posited that neutrophil extracellular trap (NET) formation, which is enhanced in SLE, significantly contributes to HDL oxidation. Finally, we predicted that SLE HDL skews macrophages toward pro-inflammatory and pro-atherosclerotic pathways. We demonstrated that lupus patients had high levels of oxHDL and impaired HDL-associated vasoprotective activity. We found that the oxidative machinery externalized in NETs induces HDL oxidation. Indeed, when we suppressed NETosis in lupus-prone mice in vivo, levels of oxHDL significantly decreased. When healthy macrophages were exposed to this SLE HDL, they displayed high levels of inflammation. While healthy HDL blocked toll-like receptor (TLR)-induced inflammatory cytokine production, SLE HDL failed to abrogate this inflammation. This was linked to an impaired ability of SLE HDL to promote the transcriptional repressor activating transcription factor 3 (ATF3). These SLE HDL-induced effects were largely dependent on its binding the lectin-like oxidized low-density lipoprotein receptor (LOX1R). Finally, administration of an HDL mimetic to lupus-prone mice, in vivo, decreased their inflammatory cytokine profile and enhanced ATF3 mRNA levels. These studies identify a specific oxidation pattern that could be used as a SLE CVD biomarker, as well as the potential therapeutic benefits of altering NET and lipoprotein activity in lupus. Additionally, we showed two innate immune response pathways that may contribute to SLE CVD. NET-derived oxidative species induce HDL oxidation. This oxHDL, in turn, stimulates pro-inflammatory, pro-atherogenic responses in macrophages.PHDImmunologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/116769/1/cksm_1.pd

Type I interferons modulate vascular function, repair, thrombosis, and plaque progression in murine models of lupus and atherosclerosis

Objective Patients with systemic lupus erythematosus (SLE) have a notable increase in atherothrombotic cardiovascular disease (CVD) which is not explained by the Framingham risk equation. In vitro studies indicate that type I interferons (IFNs) may play prominent roles in increased CV risk in SLE. However, the in vivo relevance of these findings, with regard to the development of CVD, has not been characterized. This study was undertaken to examine the role of type I IFNs in endothelial dysfunction, aberrant vascular repair, and atherothrombosis in murine models of lupus and atherosclerosis. Methods Lupus‐prone New Zealand mixed 2328 (NZM) mice and atherosclerosis‐prone apolipoprotein E– knockout (apoE −/− ) mice were compared to mice lacking type I IFN receptor (INZM and apoE −/− IFNAR −/− mice, respectively) with regard to endothelial vasodilatory function, endothelial progenitor cell (EPC) function, in vivo neoangiogenesis, plaque development, and occlusive thrombosis. Similar experiments were performed using NZM and apoE −/− mice exposed to an IFNα‐containing or empty adenovirus. Results Loss of type I IFN receptor signaling improved endothelium‐dependent vasorelaxation, lipoprotein parameters, EPC numbers and function, and neoangiogenesis in lupus‐prone mice, independent of disease activity or sex. Further, acute exposure to IFNα impaired endothelial vasorelaxation and EPC function in lupus‐prone and non–lupus‐prone mice. Decreased atherosclerosis severity and arterial inflammatory infiltrates and increased neoangiogenesis were observed in apoE −/− IFNAR −/− mice, compared to apoE −/− mice, while NZM and apoE −/− mice exposed to IFNα developed accelerated thrombosis and platelet activation. Conclusion These results support the hypothesis that type I IFNs play key roles in the development of premature CVD in SLE and, potentially, in the general population, through pleiotropic deleterious effects on the vasculature.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/93543/1/34504_ftp.pd

Neutrophil Extracellular Trap–Derived Enzymes Oxidize High‐Density Lipoprotein: An Additional Proatherogenic Mechanism in Systemic Lupus Erythematosus

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/108351/1/art38703.pd

Brief Report:vitamin D deficiency is associated with endothelial dysfunction and increases type I interferon gene expression in a Murine model of systemic lupus erythematosus

Objective: Patients with systemic lupus erythematosus (SLE) have an increased risk of cardiovascular disease (CVD) and impaired endothelial repair. Although vitamin D deficiency is associated with increased CVD risk in the general population, a causal relationship has not been demonstrated. We aimed to determine whether vitamin D deficiency directly modulates endothelial dysfunction and immune responses in a murine model of SLE. Methods: Vitamin D deficiency was induced in lupus-prone MRL/lpr mice by dietary restriction for 6 weeks. Endothelium-dependent vasorelaxation was quantified using aortic ring myography, and endothelial repair mechanisms were assessed by evaluating the phenotype and function of bone marrow endothelial progenitor cells (EPCs) and with the use of an in vivo Matrigel plug model. Lupus disease activity was determined by evaluating expression of interferon-stimulated genes (ISGs) in splenic tissue, positivity for serum autoantibodies, and renal histology. To validate the findings, expression of ISGs was also measured in whole blood from vitamin D–deficient and vitamin D–sufficient patients with SLE. Results: Vitamin D deficiency resulted in impaired endothelium-dependent vasorelaxation and decreases in neoangiogenesis without a change in the total number of EPCs. There were no differences in anti–double-stranded DNA titers, proteinuria, or glomerulonephritis (activity or chronicity) between vitamin D–deficient or sufficient mice. Vitamin D deficiency was associated with a trend toward increased ISG expression both in mice and in patients with SLE. Conclusion: These findings indicate that vitamin D deficiency is associated with hampered vascular repair and reduced endothelial function, and may modulate type I interferon responses.</p

Brief Report: Deficiency of Complement 1r Subcomponent in Early-Onset Systemic Lupus Erythematosus: The Role of Disease-Modifying Alleles in a Monogenic Disease

Objective: To identify a genetic cause of early-onset systemic lupus erythematosus (SLE) in a large consanguineous family from Turkey and to study the mechanisms of the disease. Methods: We performed whole-exome sequencing and single-nucleotide polymorphism array genotyping in family members with and without SLE. Protein and gene expression, cytokine profile, neutrophil extracellular trap (NET) formation, and presence of low-density granulocytes were evaluated in patient primary cells and serum samples. Results: We identified a novel, homozygous, loss-of-function mutation (p.Pro445Leufs*11) in the C1R gene. Using the Sanger method of DNA sequencing in 14 family members, we confirmed the presence of the mutation in 4 patients with SLE and in an asymptomatic 9-year-old girl. Complement levels were low in sera from patients with truncated C1r protein. Two siblings with SLE who were available for detailed evaluation exhibited strong type I interferon (IFN) inflammatory signatures despite their disease being clinically inactive at the time of sampling. The type I IFN transcriptional signature in the patients’ blood correlated with disease expressivity, whereas the neutrophil signature in peripheral blood mononuclear cells was likely associated with disease severity. The female patient with SLE with the most severe phenotype presented with a stronger neutrophil signature, defined by enhanced NET formation and the presence of low-density granulocytes. Analysis of exome data for modifying alleles suggested enrichment of common SLE-associated variants in the more severely affected patients. Lupus-associated HLA alleles or HLA haplotypes were not shared among the 4 affected subjects. Conclusion: Our findings revealed a novel high-penetrance mutation in C1R as the cause of monogenic SLE. Disease expressivity in this family appears to be influenced by additional common and rare genetic variants

Peptidylarginine deiminase inhibition disrupts NET formation and protects against kidney, skin and vascular disease in lupus-prone MRL/lpr mice.

OBJECTIVES: An imbalance between neutrophil extracellular trap (NET) formation and degradation has been described in systemic lupus erythematosus (SLE), potentially contributing to autoantigen externalisation, type I interferon synthesis and endothelial damage. We have demonstrated that peptidylarginine deiminase (PAD) inhibition reduces NET formation and protects against lupus-related vascular damage in the New Zealand Mixed model of lupus. However, another strategy for inhibiting NETs-knockout of NOX2-accelerates lupus in a different murine model, MRL/lpr. Here, we test the effects of PAD inhibition on MRL/lpr mice in order to clarify whether some NET inhibitory pathways may be consistently therapeutic across models of SLE. METHODS: NET formation and autoantibodies to NETs were characterised in lupus-prone MRL/lpr mice. MRL/lpr mice were also treated with two different PAD inhibitors, Cl-amidine and the newly described BB-Cl-amidine. NET formation, endothelial function, interferon signature, nephritis and skin disease were examined in treated mice. RESULTS: Neutrophils from MRL/lpr mice demonstrate accelerated NET formation compared with controls. MRL/lpr mice also form autoantibodies to NETs and have evidence of endothelial dysfunction. PAD inhibition markedly improves endothelial function, while downregulating the expression of type I interferon-regulated genes. PAD inhibition also reduces proteinuria and immune complex deposition in the kidneys, while protecting against skin disease. CONCLUSIONS: PAD inhibition reduces NET formation, while protecting against lupus-related damage to the vasculature, kidneys and skin in various lupus models. The strategy by which NETs are inhibited will have to be carefully considered if human studies are to be undertaken