It is believed that the signal transduction of BMP9 is mainly performed by Smad1/5-dependent and non-Smad-dependent pathways (MAPKs) of BMP9.33 However, pathogen infection and tissue damage can also activate the MAPK signaling pathway, which mediates the development of inflammation.34 Our results showed that when inhibiting Pg-LPS-induced inflammation, BMP9 activated Smad1/5 and inhibited the phosphorylation levels of ERK and JNK. Here, SMAD1 is linked to infection.