Isolation, Identification, and Immunomodulatory Effect of a Peptide from Pseudostellaria heterophylla Protein Hydrolysate

In this study, a bioactive peptide YGPSSYGYG (YG-9) with immunomodulatory activity was isolated and identified from Pseudostellaria heterophylla protein hydrolysate. The highest proliferation index of mouse spleen lymphocytes reached 1.19 in the presence of 50 μg/mL YG-9. YG-9 could activate RAW264.7 cells by promoting the secretions of NO, the pinocytosis activity, and the productions of ROS and TNF-α. Moreover, YG-9 enhanced the expressions of TLR2 and TLR4 in RAW264.7 cells. TNF-α secretions induced by YG-9 were reduced in TLR2 and TLR4 siRNAs knockdown cells, and this suggested that macrophage activation of YG-9 was through TLR2 and TLR4. Furthermore, YG-9 promoted the translocation of NF-κB through the acceleration of IκB-α phosphorylation and degradation. Also, TNF-α secretions promoted by YG-9 were inhibited by NF-κB-specific inhibitors pyrrolidine dithiocarbamate and BAY11-7082. Altogether, these results suggested YG-9 activated RAW264.7 cells via the TLRs/NF-κB/TNF-α signaling pathway.