Lipopolysaccharide regulation of antiinflammatory tristetraprolin family and proinflammatory gene expression in mouse macrophages

Tristetraprolin (TTP/ZFP36) family proteins exhibit antiinflammatory effects by destabilizing proinflammatory mRNAs. Previous studies showed that bacterial endotoxin lipopolysaccharides (LPS) stimulated TTP and tumor necrosis factor (TNF) gene expression, but less was known about LPS effects on TTP homologues and other proinflammatory gene expression in macrophages. The objective was to investigate LPS regulation of TTP family gene and TTP-targeted gene expression in mouse RAW264.7 macrophages using much higher concentrations of LPS and much longer treatment time than previous studies. MTT assay showed that LPS was not toxic to the cells under LPS treatment up to 1000 ng/mL for 2–24 h. LPS mildly affected the soluble protein content in the cells. qPCR assay showed that LPS stimulated TTP mRNA rapidly but not sustainably with 40, 10, and 3 fold of the DMSO control after 2, 8 and 24 h treatment, respectively. Immunoblotting confirmed qPCR results on LPS stimulation of TTP gene expression in the mouse macrophages. LPS exhibited minimal effects on ZFP36L1, ZFP36L2 and ZFP36L3 mRNA levels. LPS increased mRNA levels of TNF, COX2, GM-CSF, INFγ and IL12b up to 311, 418, 11, 9 and 4 fold, respectively. This study demonstrated that LPS did not affect macrophage viability, dramatically increased antiinflammatory TTP gene expression as well as proinflammatory TNF and COX2 gene expression but had only mild effects on TTP homologues and other proinflammatory cytokine gene expression in the mouse macrophages.