Changchun University of Chinese Medicine

The pathogenesis of autoimmune thyroiditis (AIT) is intricately linked to immune dysregulation, endocrine imbalance, and gut microbiota dysbiosis. The immune system drives autoimmune attacks against thyroid tissue through Th1/Th2 cell imbalance, Treg dysfunction, and excessive release of proinflammatory cytokines. Thyroid hormone regulation primarily occurs via the hypothalamic-pituitary-thyroid (HPT) axis. Elevated levels of TPOAb and TgAb in AIT patients can lead to hypothyroidism by affecting the HPT feedback loop. Thyroid hormone regulation of immune cell metabolism and differentiation, in turn, affects immune homeostasis, forming a bidirectional regulatory network. Recent studies further reveal that the gut microbiota influences systemic immune tolerance by regulating intestinal barrier integrity and metabolites (e.g. short-chain fatty acids and secondary bile acids). Abnormal abundance of specific genera (e.g. Bacteroides and Prevotella) can promote the production of thyroid autoantibodies (TPOAb/TgAb), and increased intestinal permeability caused by microbiota dysbiosis may facilitate cross-reactivity between microbial antigens and thyroid antigens. Furthermore, the gut microbiota indirectly regulates thyroid function through the HPT axis. This review aims to summarize the current knowledge regarding the specific molecular mechanisms of gut microbiota-immune-endocrine interactions in AIT, offer important references for researching the treatment directions of AIT.

Staphylococcus aureus pneumonia, particularly methicillin-resistant Staphylococcus aureus (MRSA), remains a major clinical challenge due to biofilm formation, complex regulatory programs, and rapid acquisition of antimicrobial resistance (AMR). The SaeRS two-component system is a central regulatory node controlling multiple infection-related pathways, making its response regulator SaeR an attractive therapeutic target. Targeting such upstream regulators provides an alternative strategy to conventional bactericidal approaches. Through a network pharmacology-guided screen, we identified saikosaponin D (SSD), an oleanane-type pentacyclic triterpenoid saponin from Bupleurum, as a candidate compound. Biophysical and biochemical assays, including cellular thermal shift assay (CETSA), surface plasmon resonance (SPR), and electrophoretic mobility shift assay (EMSA), demonstrated that SSD directly binds SaeR and impairs its DNA-binding capacity. This interference repressed SaeR-dependent transcription, resulting in reduced α-hemolysin and Panton-Valentine leucocidin (PVL) production, diminished hemolytic activity, decreased bacterial adhesion and invasion, and disruption of biofilm integrity through suppression of extracellular matrix components. In vivo, SSD conferred significant protection in both invertebrate and mammalian infection models. In Galleria mellonella, SSD improved survival, and in a murine model of MRSA pneumonia, SSD reduced pulmonary bacterial burden, alleviated inflammation and edema, and enhanced overall survival. Collectively, these findings establish SaeR as a druggable upstream regulator and highlight SSD as a natural product scaffold with translational potential for therapeutic development against MRSA infections.

Targeting bacterial virulence factors is considered a promising strategy because it poses a lower risk of promoting antibiotic resistance. This study investigated the therapeutic potential and underlying mechanism of prim-O-glucosylcimifugin (POG) against Staphylococcus aureus (S. aureus). In a diabetic mouse model, POG significantly reduced bacterial burden and accelerated wound healing, which was accompanied by enhanced tissue regeneration and collagen deposition, but no detectable toxicity. It also improved survival in a Galleria mellonella model infected with methicillin-resistant S. aureus. In vitro, POG did not inhibit bacterial growth, indicating an antivirulence rather than bactericidal mode of action. Transcriptomic analysis revealed that POG downregulated multiple virulence-associated genes, including α-hemolysin (hla), and disrupted quorum sensing, stress response, and metabolic pathways. Consistently, POG treatment suppressed hemolytic activity and the production of Hla. Molecular docking, molecular dynamics simulations, and cellular thermal shift assays confirmed the direct binding of POG to S. aureus caseinolytic protease P (SaClpP). Furthermore, fluorescence resonance energy transfer assays demonstrated that POG inhibited SaClpP activity in a dose-dependent manner, with an IC₅₀ of 14.27 μg/mL. In a clpP knockout strain, the suppressive effects of POG on Hla production and hemolytic activity were abolished, confirming SaClpP as the key target responsible for its antivirulence effects. Collectively, these results demonstrate that POG is a promising antivirulence agent that attenuates S. aureus pathogenicity by targeting SaClpP.