Lipin-1 is essential for the inflammatory response of murine macrophages to bacterial lipopolysaccharide

Abstract

Lipin-1 is a member of the phosphatidic acid phosphatases family of enzymes (PAP-1), which dephosphorylates phosphatidic acid (PA) to generate diacylglycerol (DAG). Mice lacking Lipin1, named fld (fatty liver dystrophy) are known to exhibit changes in lipid storage but up to date, there are no studies about lipid alterations in the macrophages of these animals. TLR4-stimulation of bone marrow derived macrophages from wt mice resulted in an increase of the total content of DAG at 5 min, reaching a maximum at 20 min, however in fld cells DAG levels were significantly lower. Despite this difference, the fatty acid composition of DAG for both groups was the same, with saturated fatty acids like myristic (14:0), palmitic (16:0) and stearic (18:0) being the major constituents. After exposure to LPS, PA levels increased in wt cells reaching the plateau at 10 min, but this was decreased in fld cells. In both cases, there were no differences in the PA profile. The following PA species were found by using LC/MS: PA(16:0/18:2), PA(16:0/18:1), PA(16:0/18:0), PA(O-18:0/18:2), PA(O-18:0/18:1), PA(O-18:0/18:0), PA (18:0/18:1) and PA (18:0/18:0). Because both DAG and PA have essential signaling roles in macrophage function, we studied the signaling consequences of the lack of lipin-1 during LPS stimulation. Activation of the ERKs p42/p44 and JNK was diminished in fld macrophages, as also was the activation of the transcription factors NFκB and AP-1. We also found differences in the relative mRNA expression of some important cytokines such as Il6, Il12p40 and proinflammatory enzymes such as Nos2 and Cox2. All together, these results suggest a proinflammatory role for lipin-1 that is due to the generation of signaling lipids.