Streptomyces antiinflammaticus from Rehmannia glutinosa Produces Dual Immunomodulatory Metabolites That Upregulate IL-10 and Inhibit GSK3β/NF-κB

Strain RerS4 was isolated from the rhizosphere of the medicinal plant Rehmannia glutinosa and comprehensively identified for its taxonomic status and anti-inflammatory secondary metabolites. Polyphasic taxonomy combined with genome-based analyses, including average nucleotide identity (82.87–85.87%) and digital DNA-DNA hybridization (26.7–31.9%), confirmed that RerS4 represents a novel Streptomyces species, designated Streptomyces antiinflammaticus. Eight fermentation media were screened using an IL-6/TNF-α inhibitory bioassay in A549 and THP-1 cells, and GYM I medium with optimal anti-inflammatory activity was adopted for large-scale fermentation. Five secondary metabolites were purified from the fermentation broth, including one undescribed amide (1), alongside four known compounds (2–5). Bioactivity assays indicated that compounds 1 and 5 inhibited pro-inflammatory cytokine production. Mechanistically, both compounds suppressed the phosphorylation of p65 (Ser536) and GSK3β (Tyr216) in A549 cells. In THP-1 macrophages, compound 1 selectively targeted p65, while compound 5 inhibited both proteins. qPCR results revealed that compound 1 downregulated pro-inflammatory cytokines (IL-1β, IL-6, TNF-α) and upregulated the anti-inflammatory cytokine IL-10, whereas compound 5 reduced IFN-γ mRNA expression in A549 cells. This study demonstrates that Streptomyces antiinflammaticus is a valuable resource for distinctive anti-inflammatory and immunomodulatory natural products.