Mechanisms underlying the suppression of inflammatory responses in peritoneal macrophages of middle-aged mice

We investigated the molecular mechanisms underlying the deterioration of macrophage inflammatory responses in middle-aged mice, focusing on the agerelated reduction in protein synthesis rate. Peritoneal macrophages were isolated from male BALB/c mice aged 2 months (young) and 12 months (middle-aged), and stimulated with lipopolysaccharide (LPS). At the protein level, LPS-stimulated proinflammatory cytokine release and intracellular accumulation of bactericidal mediators from macrophages were clearly lower in middle-aged mice than in young mice. However, LPS caused a marked increase in the mRNA expression of these genes in the macrophages of both young and middle-aged mice. Moreover, LPS induced comparable phosphorylation levels of signaling proteins downstream of toll-like receptor (TLR) in young and middle-aged mice. In contrast, levels of the inactive (phosphorylated) form of eukaryotic initiation factor 2α (eIF-2α) were higher in macrophages from middle-aged mice than in macrophages from young mice. Suppression of the LPS-stimulated inflammatory responses observed in middleaged mice could be mimicked by treating the murine macrophage RAW264.7 cells with salubrinal, an inhibitor of the phosphatase that dephosphorylates eIF-2α. In conclusion, post-transcriptional suppression of macrophage inflammatory responses during middle age requires phosphorylation of eIF-2α.