Activated peroxisome proliferator-activated receptor α inhibiting the lipopolysaccharide-induced macrophage-mediated inflammatory responses by promoting the autophagy

Abstract

Objective To investigate the effects of peroxisome proliferator-activated receptor α (PPARα) on macrophage-mediated inflammatory responses with the interference of lipopolysaccharide and the possible mechanism. Methods The bone marrow stem cells were isolated from the femora of mice. The granulocyte-macrophage colony stimulating factor (GM-CSF) was used to stimulate the in vitro differentiation from bone marrow stem cells into primary macrophages. An in vitro model with cultured cells expressing inflammatory cytokines was established by treating the primary macrophages with lipopolysaccharide (LPS). A specific chemical agonist, Wy-14643, was used to activate PPARα. Autophagy inhibitors including 3-methyladenine (3-MA) and small interfering RNA against Atg7 (Atg7 siRNA) were used to inhibit the autophagy. Western blot assay was performed to detect the expression of autophagy-related proteins (Atg5, Atg7, Beclin-1 and LC3). The transcriptional levels of TNF-α, IL-1β, IL-6, Atg5, Atg7 and Beclin-1 were analyzed by qRT-PCR. Results Compared with the macrophages treated with LPS alone, those pretreated with various concentrations of Wy-14643 (10 μmol/L, 25 μmol/L and 50 μmol/L) showed inhibited expression of proinflammatory cytokines (TNF-α, IL-1β and IL-6) and enhanced expression of autophagy-related proteins (Atg5, Atg7 and Beclin-1) at mRNA level in a dose-dependent manner. The expression of autophagy-related proteins (Atg5, Atg7, Beclin-1 and LC3) by macrophages was promoted with the pretreatment of Wy-14643 as indicated by Western blot assay. The transcriptional levels of TNF-α, IL-1β and IL-6 were increased in Wy-14643 pretreated-macrophages after stimulation with 3-MA or Atg7 siRNA. Conclusion PPARα suppressed the macrophage-mediated inflammatory responses by promoting autophagy, suggesting that the PPARα-autophagy pathway might be one of the signaling pathways regulating LPS induced-inflammatory responses. Key words: Peroxisome proliferator-activated receptor α; Autophagy; Inflammatory response; Macrophages; Lipopolysaccharide