Inhibition of p38 MAPK Activation via Induction of MKP-1: Atrial Natriuretic Peptide Reduces TNF-&agr;–Induced Actin Polymerization and Endothelial Permeability

The atrial natriuretic peptide (ANP) is a cardiovascular hormone possessing antiinflammatory potential due to its inhibitory action on the production of inflammatory mediators, such as tumor necrosis factor-&agr; (TNF-&agr;). The aim of this study was to determine whether ANP is able to attenuate inflammatory effects of TNF-&agr; on target cells. Human umbilical vein endothelial cells (HUVECs) were treated with TNF-&agr; in the presence or absence of ANP. Changes in permeability, cytoskeletal alterations, phosphorylation of p38 MAPK and HSP27, and expression of MKP-1 were determined by macromolecule permeability assay, fluorescence labeling, RT-PCR, and immunoblotting. Antisense studies were done by transfecting cells with MKP-1 antisense oligonucleotides. Activation of HUVECs with TNF-&agr; lead to a significant increase of macromolecule permeability and formation of stress fibers. Treatment of cells with ANP (10−8 to 10−6 mol/L) significantly reduced the formation of stress fibers and elevated permeability. Both TNF-&agr;–induced effects were shown to be mediated via the activation of p38 using SB203580, a specific inhibitor of p38. ANP significantly reduced the TNF-&agr;–induced activation of p38 and attenuated the phosphorylation of HSP27, a central target downstream of p38. ANP showed no effect on p38 upstream kinases MKK3/6. However, a significant induction of the MAPK phosphatase MKP-1 mRNA and protein could be observed in ANP-treated cells. Antisense experiments proved a causal role for MKP-1 induction in the ANP-mediated inhibition of p38. These data show the inhibitory action of ANP on TNF-&agr;–induced changes in endothelial cytoskeleton and macromolecule permeability involving an MKP-1–induced inactivation of p38 MAPK. These effects point to an antiinflammatory and antiatherogenic potential of this cardiovascular hormone.