Endometritis is a common reproductive system disease in postpartum dairy cows. Studies have shown that this disease can lead to infertility, miscarriage and economic losses to the diary producers [1]. The primary cause of endometritis in dairy cows is infection with Escherichia coli (E. coli) [2]. Lipopolysaccharide (LPS) the outermost component of the E. coli cell wall is the main pathogenic factor of E. coli. When the uterus is exposed to bacteria, lipopolysaccharide-binding protein (LBP) located on the uterine epithelial cell membrane, binds to the presenting LPS [3], which may promote the dimerization of Toll-like receptor 4 (TLR4)/MD-2, the main receptor of LPS. This leads to the activation of two downstream signaling pathways: the MyD88-dependent and MyD88-independent signaling pathways [4]. MyD88, a key adaptor protein of TLR4, recruits kinases related to the interleukin-1 receptor after activation [5], binds to tumor necrosis factor receptor-associated factors, and stimulates the translocation of NF-κB into the nucleus. Therefore, the innate immune defense system is triggered, which ultimately leads to the release of inflammatory factors such as IL-6, IL-1β, and TNF-α, resulting in local uterine inflammation [6]. In addition, overactivation of NF-κB drives the proapoptotic signaling pathway and induces apoptosis [2,7].

Recent microRNAs (miRNAs) expression profile analysis revealed that miR-200b, may be involved in the mitigation of endometritis in dairy cows [8]. Importantly, another study also indicated that serum miR-200b expression was significantly downregulated in cows with uterine inflammation [9], highlighting its potentially important role in endometritis. As a member of the miR-200 family, miR-200b is involved in cell migration, angiogenesis, regulation of inflammatory cytokine secretion and other processes [[10], [11], [12]]. MiR-200b is also involved in LPS-induced lung epithelial cell injury and participates in the inflammatory response [13]. However, the mechanisms through which bta-miR-200b is involved in palliation of endometritis in dairy cows is unknown.

Accordingly, in an effort to elucidate the role of bta-miR-200b in bovine endometritis, we investigated the expression of bta-miR-200b, IL-6, IL-1β and TNF-α in healthy and endometritis affected uterine tissues from cows collected at slaughter and on NF-κB, p65/Bax/Bcl-2 and PTEN/AKT pathway in BEND cells exposed to LPS. Furthermore, the functions of the PTEN/AKT signaling axis in regulating NF-κB activation were assessed via the use of a PTEN inhibitor.