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Rheumatic heart disease (RHD) affects numerous individuals annually; however, its pathogenesis remains unclear. The sphingosine 1‑phosphate receptor 1 (S1PR1) and signal transducer and activator of transcription 3 (STAT3) have recently been shown to be involved in valvular damage via the promotion of the differentiation of T helper 17 (Th17) cells during the development of RHD‑induced valvular damage. The present study investigated whether altering the expression of S1PR1 or STAT3 attenuates valvular damage due to RHD. Inactivated group A streptococcus (GAS) was used to establish a rat model of RHD. Recombinant adeno‑associated viral vectors carrying an S1PR1 overexpression sequence were used to overexpress S1PR1. STAT3 small interfering RNA (STAT3‑siRNA) was used to inhibit STAT3 expression. Reverse transcription‑quantitative PCR (RT‑qPCR) was performed to detect the mRNA expression of S1PR1, STAT3, collagen type III α1 chain (Col3a1) and fibroblast‑specific protein 1. Western blotting (WB) and immunohistochemistry were used to detect the levels of S1PR1, STAT3, phosphorylated (p‑) STAT3, and retinoic acid‑related orphan receptor γT (RORγt) proteins. Enzyme‑linked immunosorbent assays (ELISAs) and immunohistochemistry were used to detect the levels of interleukin (IL)‑6 and IL‑17. Hematoxylin and eosin (H&E) staining and Sirius Red staining were performed to evaluate the degree of inflammation and fibrosis in the valvular tissues. S1PR1 expression was decreased in the valvular tissues of the rats with RHD. The levels of IL‑6, IL‑17 and p‑STAT3 in the rats with RHD were increased. The degree of valvular inflammation and fibrosis in the rats with RHD was also increased. The overexpression of S1PR1 and the inhibition of STAT3 reduced the total p‑STAT3 level, resulting in decreased levels of IL‑6, IL‑17 and RORγt, and a reduced degree of valvular inflammation and fibrosis. These results suggest that the expression of S1PR1 and STAT3 may be involved in valvular tissue damage due to RHD. Thus, strategies designed to interfere with the expression of S1PR1 or STAT3 may affect the expression of Th17 cell‑related cytokines and may thus attenuate valvular damage due to RHD.

Autoimmunity is involved in the valvular damage caused by rheumatic heart disease (RHD). Increased evidence has linked microRNAs (miRNAs/miRs) to autoimmune disease. Signal transducer and activator of transcription 3 (STAT3) and sphingosine‑1‑phosphate receptor 1 (S1PR1) and suppressor of cytokine signaling 1 (SOCS1) have been widely studied for their roles in autoimmunity and inflammation. Thus, the current study aims to investigate the role played by miR‑155‑5p in RHD‑induced valvular damage via the S1PR1, SOCS1/STAT3 and interleukin (IL)‑6/STAT3 signaling pathways. An RHD rat model was induced by inactivated Group A streptococci and complete Freund's adjuvant. A recombinant adeno‑associated virus (AAV‑miR155‑inhibitor) was used to inhibit the expression of miR‑155‑5p in the heart. Inflammation and fibrosis were assessed by hematoxylin and eosin staining and Sirius red staining. The expression of miR‑155‑5p in valvular tissues and serum exosomes was detected by reverse transcription‑quantitative PCR. S1PR1, SOCS1, STAT3, phosphorylated STAT3, IL‑6 and IL‑17 protein expression was detected by western blotting and immunohistochemistry. The relationships between miR‑155‑5p and S1PR1 and SOCS1 were detected by dual luciferase assays. Cytokine concentrations were measured by ELISA. The expression of miR‑155‑5p in valve tissues and serum exosomes was increased along with decreased S1PR1 and activated SOCS1/STAT3 signaling in the RHD model. The expression of IL‑6 and IL‑17 was increased in the valves and the serum. Dual luciferase assays showed that miR‑155‑5p directly targeted S1PR1 and SOCS1. Inhibition of valvular miR‑155‑5p through AAV pretreatment increased S1PR1 expression and inhibited activation of the SOCS1/STAT3 signal pathway as a result of attenuated valvular inflammation and fibrosis as well as a decrease in IL‑6 and IL‑17 in the valves and serum. These results suggest that inhibition of miR‑155‑5p can reduce RHD‑induced valvular damage via the S1PR1, SOCS1/STAT3 and IL‑6/STAT3 signaling pathways.