TLR4 activation inhibits the proliferation and osteogenic differentiation of skeletal muscle stem cells by downregulating LGI1.

Skeletal muscle stem cells (SMSCs) are vital to the growth, maintenance, and repair of the muscles; emerging evidence has indicated that Toll-like receptor 4 (TLR4) can potentially regulate muscle regeneration. In present study, in vitro and in vivo experiments were performed to explore the correlation of TLR4 with leucine-rich glioma-inactivated 1 (LGI1) as well as their effects on the proliferation and osteogenesis potential of SMSCs. In order to examine the regulatory mechanisms of TLR4 and LGI1 in SMSCs, the obtained cells were treated with lipopolysaccharide (LPS, used as an activator of TLR4) of different concentration at different time points as well as the siRNA against LGI1. Subsequently, a series of detection was undertaken in order to measure the proliferation and differentiation potential of SMSCs, which involved detection of the related factors, cell activity, and the sphere-forming capability. Following LPS treatment, the increased TLR4 expression and reduced LGI1 expression were observed. Consequently, we also discovered that Erk signaling pathway was inactivated and cell proliferation and osteogenesis capabilities declined, presented by the downregulation of related factors such as cyclin B1 and runt-related transcription factor 2. Moreover, the cell activity and sphere-formation performance of SMSCs were also declined. These results were also validated in rats with cecal ligation and perforation-induced rat models with sepsis. In conclusion, the present study reveals a regulatory mechanism in SMSCs whereby LGI1 expression is reduced by TLR4, thus impeding cell proliferation and osteogenesis, highlighting TLR4 as a potential therapeutic target against many diseases related to SMSCs.