Docosahexaenoic Acid Enhances Dexamethasone-Mediated Suppression of Interferon-Regulated Genes in NZBWF1 Macrophages: Implications for Steroid-Sparing Lupus Treatment

Introduction: Glucocorticoids (GC) are one of the most common anti-inflammatory treatments for autoimmune diseases such as systemic lupus erythematosus (lupus). Chronic use of GCs leads to several deleterious side-effects and diminished quality of life, inciting a need for steroid-sparing therapeutics. Polyunsaturated fatty acids (PUFA), such as docosahexaenoic acid (DHA), have been shown to inhibit proinflammatory and Type I Interferon (IFN) gene signatures in macrophages, which are central to initiation of autoimmunity triggered by inhaled environmental toxicants such as bacterial lipopolysaccharide (LPS). The goal of the present study was to determine whether combination treatment with suboptimal concentrations of DHA and GC in LPS-primed alveolar-like macrophages could potentiate the anti-inflammatory effects of DHA and GC individual treatment. Methods: RNAseq was used to evaluate whether DHA could potentiate the anti-inflammatory effects of the GC dexamethasone (DEX) in LPS-stimulated fetal liver-derived alveolar-like macrophages (FLAMs) isolated from NZBWF1 lupus-prone mice. FLAMs were treated were treated with suboptimal concentrations of either DHA alone, DEX alone, or DHA+DEX in combination prior to LPS stimulation (20 ng/mL) for 4 or 8 hr. Results: LPS stimulation resulted in significant enrichment of innate immunity and Type I/II IFN pathways with corresponding upregulation of gene sets falling under these pathways at both timepoints. LPS-primed FLAMs treated in combination with suboptimal concentrations of DHA and DEX exhibited combinatorial affects greater than DHA and DEX treatment alone. DHA+DEX co-treatment resulted in downregulation of innate immunity and Type I/II IFN pathways initially altered by LPS treatment. Lastly, DHA+DEX co-treatment exhibited superior downregulation of individual Type I/II IFN genes compared to DHA and DEX treatment alone. Discussion: Our findings demonstrate that while DHA and DEX can significantly alter LPS-stimulated gene expression in alveolar-like macrophages when used in high enough concentrations alone, DHA can be used to potentiate the anti-inflammatory effects of DEX when both are used at lower concentrations. This study provides promising evidence that DHA can potentially be used to lower requisite amounts GCs required to reduce inflammation.