Rheumatoid arthritis (RA) is a chronic autoimmune disorder characterized by persistent synovitis, in which fibroblast-like synoviocytes (FLSs) serve as the primary effector cells that drive the destruction of joints. Baicalin has previously demonstrated efficacy in significantly ameliorating joint symptoms in rats with CIA. As such, this study aims to investigate its underlying molecular mechanisms and impact on the FLSs of rats with CIA through an integrated proteomics and transcriptomics analysis. A Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was conducted based on two datasets; it revealed that the retrograde endocannabinoid signaling pathway—associated with susceptibility to RA—is the only one involved in both the signaling and metabolic processes modulated by baicalin. Nineteen differentially expressed proteins (DEPs) downregulated by baicalin comprise seventeen subunits of NADH dehydrogenase and two receptors, glutamate receptor 2 (GRIA2) and γ-aminobutyric acid receptor subunit alpha-5 (GABRA5). Three differential metabolites (DMs) were also affected by baicalin: γ-aminobutyric acid (GABA) and phosphatidylcholine (PC) were upregulated and phosphatidylethanolamine (PE) was downregulated. Our findings suggest that the baicalin-mediated alleviation of joint synovitis is closely related to the upregulation of GABA and PC; downregulation of GRIA2, GABRA5, and PE; and preservation of mitochondrial homeostasis within the retrograde endocannabinoid signaling pathway in FLSs.

The respiratory mucosal system plays a critical role in the pathogenesis of allergic asthma (AA). Currently, therapeutic Fc fusion proteins are as a promising strategy for mucosal vaccine delivery systems. In this work, a plasmid encoding the Mycobacterium tuberculosis ESAT6-Fc fusion protein was successfully constructed, and high-purity ESAT6-Fc fusion protein was subsequently obtained. Administered via intranasal immunization in OVA-induced allergic asthma model mice, ESAT6-Fc fusion protein significantly alleviated airway inflammation and mucus production, and reduced the proportions of Th2 cells, Th17 cells, and eosinophils, while increasing the proportions of Th1 cells with no histopathological changes to major organs. To elucidate the underlying immune regulatory mechanisms of ESAT6, integrated transcriptomic and proteomic analyses were performed, revealing Th1/Th2 cell differentiation and Th17 cell differentiation as the two most significantly enriched pathways at both the gene and protein levels. CD3e (CD3E) and CD3g (CD3G), two essential subunits of the TCR–CD3 complex, were identified as core target factors. The validations from the ESAT6-Fc-treated AA lung tissues, as well as co-cultured TH0 cells from C57BL/6J mice and CD2.4 dendritic cells exposed to the ESAT6-Fc protein, were consistent with the aforementioned findings. ESAT6-Fc exhibits a safe profile with favorable efficacy against OVA-induced AA via intranasal immunization, and ESAT6 ameliorates AA by regulating the differentiation of Th0 cells into Th1 cells, which were closely associated with the down-regulation of CD3e and CD3g expression, presumably leading to the impairment of TCR–CD3 complex assembly. ESAT6-Fc fusion protein demonstrates promise as a potential safe intranasal immunotherapy agent for the treatment of AA.