Omega-3 fatty acid intake suppresses induction of diverse autoantibody repertoire by crystalline silica in lupus-prone mice

Abstract

Inhalation of crystalline silica (cSiO 2) in the workplace is etiologically linked to lupus and other autoimmune diseases. Exposing lupus-prone NZBWF1 mice to respirable cSiO 2 unleashes a vicious cycle of inflammation and cell death in the lung that triggers interferon-regulated gene expression, ectopic lymphoid structure (ELS) development, elevation of local and systemic autoantibodies (AAbs), and glomerulonephritis. However, cSiO 2-induced inflammation and onset of autoimmunity can be prevented by inclusion of the x-3 polyunsaturated fatty acid docosahexaenoic acid (DHA) into the diet of these mice. Since cSiO 2 both causes cell death and interferes with efferocytosis, secondary necrosis of residual cell corpses might provide a rich and varied autoantigen (AAg) source in the lung. While it is known that the particle induces anti-nuclear and anti-dsDNA AAbs in NZBWF1 mice, the full extent of the cSiO 2-induced AAb response relative to specificity and isotype is not yet understood. The purpose of this study was to test the hypotheses that cSiO 2 exposure induces a wide spectrum of AAbs in the pulmonary and systemic compartments, and that dietary DHA intervention prevents these changes. Archived tissue fluid samples were obtained from a prior study in which NZBWF1 mice were fed purified isocaloric diets containing no DHA (control) or DHA corresponding calorically to human doses of 2 and 5 g/day. Mice were intranasally instilled with 1 mg cSiO 2 or saline vehicle weekly for 4 weeks, then groups euthanized 1, 5, 9, or 13 weeks post-instillation (PI) of the last cSiO 2 dose. Bronchoalveolar lavage fluid (BALF) and plasma from each time point were subjected to AAb profiling using a microarray containing 122 AAgs. cSiO 2 triggered robust IgG and IgM AAb responses against lupus-associated AAgs, including DNA, histones, ribonucleoprotein, Smith antigen, Ro/SSA, La/SSB, and complement as early as 1 week PI in BALF and 5 weeks PI in plasma, peaking at 9 and 13 weeks PI, respectively. Importantly, cSiO 2 also induced AAbs to AAgs associated with rheumatoid arthritis (collagen II, fibrinogen IV, fibrinogen S, fibronectin, and vimentin), Sj€ ogren's syndrome (a-fodrin), systemic sclerosis (topoisomerase I), vasculitis (MPO and PR3), myositis (Mi-2, TIF1-c, MDA5), autoimmune hepatitis (LC-1), and celiac disease (TTG). cSiO 2 elicited comparable but more modest IgA AAb responses in BALF and plasma. cSiO 2-induced AAb production was strongly associated with time dependent inflammatory/autoimmune gene expression, ELS development, and glomerulonephritis. AAb responses were dose-dependently suppressed by DHA supplementation and negatively correlated with the x-3 index, an erythrocyte biomarker of x-3 content in tissue phospholipids. Taken together, these findings suggest that cSiO 2 exposure elicits a diverse multi-isotype repertoire of AAbs, many of which have been reported in individuals with lupus and other autoimmune diseases. Furthermore, induction of this broad AAb spectrum could be impeded by increasing x-3 tissue content v...

Rapid Induction of Pulmonary Inflammation, Autoimmune Gene Expression, and Ectopic Lymphoid Neogenesis Following Acute Silica Exposure in Lupus-Prone Mice

“…These findings are consistent with our previous studies showing that repeated exposures to 1 mg cSiO 2 triggered inflammation, ELS formation, and AAb production in female NZBWF1 mice (19,20). Recently, our laboratory has applied high-throughput AAb microarray profiling of 122 autoantigens to ascertain in female NZBWF1 mice how 4 weekly 1 mg cSiO 2 instillations influence the BALF and plasma AAb repertoire relative to specificity at 1, 5, 9, or 13 week PI of the last dose (24). Marked IgG and IgM AAb responses against lupus-associated autoantigens including ribonucleoprotein, Smith antigen, DNA, histones, Ro/SSA, SSB, and complement by 1 week PI in BALF and 5 week PI in plasma, peaking at 9 and 13 weeks PI, respectively.…”

“…#100008) and housed 4 animals per cage. This mouse strain was chosen because it has been previously used to recapitulate robust autoimmune triggering by cSiO 2 that was not seen in normal C57BL/6 mice (19)(20)(21)(22)(23)(24). Mice were given free access to drinking water and fed American Institute of Nutrition (AIN)-93G diet (Dyets Inc., Bethlehem, PA) under controlled conditions (humidity: 40-55%; lighting: 12-h light/dark cycles; and temperature: 24 ± 2 • C) as described previously (19,20).…”

Requisite Omega-3 HUFA Biomarker Thresholds for Preventing Murine Lupus Flaring

“…Again, ω-3 HUFA scores over 40% were associated with reduced ELS development and anti-dsDNA production ( Figure 6 ). A further feature of Study 2 was the use of high throughput autoantigen microarray for in-depth analysis of autoantibodies relative to specificity and isotype ( 44 ). Robust negative correlations were found between ω-3 HUFA score and IgG and IgM autoantibodies in both BALF and plasma with specificity for a broad range of host antigens (most r s values between −0.4 and −0.6, significance indicated by asterisks) ( Figure 7 ).…”

Silica Induction of Diverse Inflammatory Proteome in Lungs of Lupus-Prone Mice Quelled by Dietary Docosahexaenoic Acid Supplementation

“…Cohorts (n=8/group) were terminated at 1, 5, 9, and 13 wk post-instillation (PI) of the final cSiO 2 dose and bronchoalveolar lavage fluid (BALF), blood, and organs were collected, processed, and stored at -80 0 C as described previously (16). These specified times correspond with cSiO 2 -induced histopathologic, transcriptomic, and autoimmune effects in NZBWF1 mice (16,35,36).…”

“…Spearman rank correlations were also used to relate protein expression Z-scores with histological endpoints that included CD45R + (B cells), CD3 + (T cells), CD21/35 + (follicular dendritic cells), and lymphoid aggregates, expressed as percent of lung area analyzed, which are collectively indicative of ectopic lymphoid neogenesis (16). For correlations to autoantibody production, signal intensities for individual autoantibodies (Ab-score) were used (36).…”