Rosmarinic acid activates the Ras/Raf/MEK/ERK signaling pathway to regulate CD8+ T cells and autophagy to clear Chlamydia trachomatis in reproductive tract-infected mice

Chlamydia trachomatis (CT) is the leading cause of bacterial sexually transmitted diseases worldwide, which can cause diseases such as pelvic inflammatory disease, and cervical and fallopian tube inflammation, and poses a threat to human health. Rosmarinic acid (RosA) is an active ingredient of natural products with anti-inflammatory and immunomodulatory effects. This study aimed to investigate the role of RosA in inhibiting autophagy-regulated immune cells-CD8+ T cells via the Ras/Raf/MEK/ERK signaling pathway in a CT-infected mouse model. Mice were inoculated with CT infection solution vaginally, and the mechanistic basis of RosA treatment was established using H&E staining, flow cytometry, immunofluorescence, transmission electron microscopy, and western blot. The key factors involved in RosA treatment were further validated using the MEK inhibitor cobimetinib. Experimental results showed that both RosA and the reference drug azithromycin could attenuate the pathological damage to the endometrium caused by CT infection; flow cytometry showed that peripheral blood CD8+ T cells increased after CT infection and decreased after treatment with RosA and the positive drug azithromycin (positive control); immunofluorescence showed that endometrial CD8 and LC3 increased after CT infection and decreased after RosA and positive drug treatment; the results of transmission electron microscopy showed that RosA and the positive drug azithromycin inhibited the accumulation of autophagosomes; western bolt experiments confirmed the activation of autophagy proteins LC3Ⅱ/Ⅰ, ATG5, Beclin-1, and p62 after CT infection, as well as the inhibition of Ras/Raf/MEK/ERK signaling. RosA and azithromycin inhibition of autophagy proteins activates Ras/Raf/MEK/ERK signaling. In addition, the MEK inhibitor cobimetinib attenuated RosA's protective effect on endometrium by further activating CD8+ T cells on a CT-induced basis, while transmission electron microscopy, immunofluorescence, and western blots showed that cobimetinib blocked ERK signals activation and further induced phagocytosis on a CT-induced basis. These data indicated that RosA can activate the Ras/Raf/MEK/ERK signaling pathway to inhibit autophagy, and RosA could also regulate the activation of immune cells-CD8+T cells to protect the reproductive tract of CT-infected mice.