iTRAQ proteomic analysis of N-acetylmuramic acid mediated anti-inflammatory capacity in LPS-induced RAW 264.7 cells

Lactobacillus acidophilus probiotic bacteria have lasting beneficial health effects in the gastrointestinal tract, including protecting against pathogens, improving immunomodulation, and producing beneficial bacteria-derived molecules. In lipopolysaccharide (LPS) induced RAW 264.7 cells treated with peptidoglycan or N-acetylmuramic acid (NAM) from L. acidophilus, 390 differentially expressed proteins (8.76%) were identified by iTRAQ analysis, 257 (5.77%) of which were upregulated and 133 (2.99%) were downregulated under LPS-induced conditions. Most of these proteins were grouped into the following inflammation-related cellular signaling: lysosome pathway, calcium signaling pathway, and Toll-like receptor (TLR) signaling pathway. Among them, clathrin, SERCA, and interleukin 1 receptor antagonist were differentially expressed to a significant degree in peptidoglycan or NAM pretreated RAW 264.7 cells. Bioinformatics analysis indicated that NAM may mediate an anti-inflammatory process via a Ca(2+) -dependent NF-κB pathway. These observations reveal new insights into the molecular mechanisms involved in the suppression of LPS-induced macrophage inflammation by L. acidophilus.