Mechanistic Insights of Chemicals and Drugs as Risk Factors for Systemic Lupus Erythematosus

Screening of SLE-susceptible SNPs in One Chinese Family with Systemic Lupus Erythematosus

Background:

Systemic lupus erythematosus (SLE) is a complex autoimmune disease, which mainly affects childbearing-aged women. Although its pathogenesis is not fully clear yet, studies have shown that genetic factors are vital in exploring SLE pathogenic mechanisms.

Objective:

The purpose of this study is to predict and screen potential pathogenic single nucleotide polymorphisms (SNPs). By comparing the genomes of members of a family with SLE and performing functional analysis on mutation loci, possible pathogenic polymorphisms are screened. These analyses lay the foundation for further research mechanisms.

Method:

Genomic alignment, variant calling and functional annotation were performed and then ~92,778 original SNPs were obtained for each specimen. We found that the patient/healthyspecific SNPs show different conservative score distribution. Many patient-specific SNPs were detected in SLE-related pathways. We therefore investigated the patient-specific SNPs from four diverse perspectives, including nonsynonymous variations in exon regions, expression quantitative trait loci (eQTLs), RNA binding sites and RNA-binding protein (RBP) binding sites.

Results:

18 potential pathogenic SNPs were identified in SLE risk genes, which were associated with functional loci. Systematic literature study was then performed to verify these potential pathogenic SNPs.

Conclusion:

This study could help to better explain possible genetic mechanisms of SLE from the perspective of variation. It could provide effective strategy for the accurate diagnosis and personalized treatment of SLE patients.

Oxidative DNA Damage Accelerates Skin Inflammation in Pristane-Induced Lupus Model

Systemic Lupus Erythematosus (SLE) is a chronic inflammatory autoimmune disease in which type I interferons (IFN) play a key role. The IFN response can be triggered when oxidized DNA engages the cytosolic DNA sensing platform cGAS-STING, but the repair mechanisms that modulate this process and govern disease progression are unclear. To gain insight into this biology, we interrogated the role of oxyguanine glycosylase 1 (OGG1), which repairs oxidized guanine 8-Oxo-2'-deoxyguanosine (8-OH-dG), in the pristane-induced mouse model of SLE. Ogg1 ^-/- mice showed increased influx of Ly6C^hi monocytes into the peritoneal cavity and enhanced IFN-driven gene expression in response to short-term exposure to pristane. Loss of Ogg1 was associated with increased auto-antibodies (anti-dsDNA and anti-RNP), higher total IgG, and expression of interferon stimulated genes (ISG) to longer exposure to pristane, accompanied by aggravated skin pathology such as hair loss, thicker epidermis, and increased deposition of IgG in skin lesions. Supporting a role for type I IFNs in this model, skin lesions of Ogg1 ^-/- mice had significantly higher expression of type I IFN genes (Isg15, Irf9, and Ifnb). In keeping with loss of Ogg1 resulting in dysregulated IFN responses, enhanced basal and cGAMP-dependent Ifnb expression was observed in BMDMs from Ogg1 ^-/- mice. Use of the STING inhibitor, H151, reduced both basal and cGAMP-driven increases, indicating that OGG1 regulates Ifnb expression through the cGAS-STING pathway. Finally, in support for a role for OGG1 in the pathology of cutaneous disease, reduced OGG1 expression in monocytes associated with skin involvement in SLE patients and the expression of OGG1 was significantly lower in lesional skin compared with non-lesional skin in patients with Discoid Lupus. Taken together, these data support an important role for OGG1 in protecting against IFN production and SLE skin disease.

Isoniazid-induced Lupus: When the Cure Can Be Lethal

A 50-year-old female with a past medical history of bone tuberculosis diagnosed nine months ago was admitted in our infirmary for persistent fever with no evident cause. The patient was treated with isoniazid, rifampicin, pyrazinamide, and ethambutol for seven months and for the past two months, she was taking isoniazid and rifampicin. She went to our emergency room (ER) for back pain and fever that she had been experiencing for the last month. She was admitted with suspicion of disseminated tuberculosis that was never confirmed. Physical examination was unremarkable. Blood tests showed an elevation of inflammation parameters. A computed tomography (CT) scan of the chest showed a mild pleural effusion. She remained with fever during the three weeks in the infirmary while undergoing many other studies that were all negative. The back pain would change sides, and three consecutive thoracic radiographies showed a small-sized pleural effusion that was either predominantly right-sided or left-sided. Several differential diagnoses were considered in the process, namely an active infection, neoplasia, or autoimmune disease. The search for circulating lupus anticoagulant was positive. Antinuclear antibodies (ANA) were positive and the anti-histone antibody was strongly positive. At this point, we suspected a drug-induced lupus diagnosis, and isoniazid was discontinued. Following discontinuation of isoniazid, back pain and fever subsided and patient was discharged after one week. This case is a diagnostic challenge because of the rarity and symptom severity of isoniazid-induced lupus. Isoniazid rarely induced this lupus-like syndrome, with an incidence of considerably less than 1%.