Abstract
Background
Excessive inflammatory response is the main cause for symptoms and pathological findings in patients with chronic inflammatory diseases. p38 mitogen-activated protein kinase (MAPK) is involved in the regulation of immune responses and inflammation. MAPK phosphatase-1 (MKP-1) is a nuclear phosphatase that inactivates p38 MAPK pathway, and inhibits cytokine production and inflammation. Interestingly, anti-inflammatory steroids increase MKP-1 expression and, according to the recent findings, many of the anti inflammatory effects of glucocorticoids are mediated through enhanced MKP-1. In addition to glucocorticoid response element, MKP-1 promoter is known to contain a cAMP responsive element. That made us to hypothesize that in inflammatory conditions cAMP-enhancing drugs may up-regulated MKP-1 expression leading to suppression of the inflammatory response. In the present study, we tested that hypothesis by investigating the role of MKP-1 as a mediator of the anti-inflammatory effects of the β2-agonist salbutamol and the PDE4 inhibitor rolipram.
Methods
Primary mouse peritoneal macrophages and J774 murine macrophages were used in the study. MKP-1 expression was measured by qRT-PCR and Western blot, and p38 MAPK phosphorylation was detected by Western blot. TNF mRNA expression was measured by qRT-PCR and TNF accumulated into the culture medium by ELISA. The effects of salbutamol and rolipram were investigated also in vivo in carrageenan-induced paw inflammation in MKP-1 knockout and wild type mice.
Results
Salbutamol, rolipram and the cAMP analog 8-Br-cAMP increased MKP-1 expression, reduced p38 phosphorylation and inhibited the production of the proinflammatory cytokine tumor necrosis factor (TNF) in activated murine macrophages. The effect of rolipram on TNF production was attenuated in peritoneal macrophages from MKP-1 knockout mice as compared to wild type mice. Salbutamol and rolipram alleviated carrageenan-induced paw inflammation in vivo. The effect of salbutamol on paw inflammation was impaired in MKP-1 knockout mice whereas the effect of rolipram was totally abolished.
Conclusions
The result show that salbutamol and rolipram inhibit the production of the proinflammatory cytokine TNF in murine macrophages and possess anti-inflammatory properties in vivo. These effects are mediated, at least partly, by increased expression of MKP-1. The results emphasize the potential of MKP-1 as a novel anti-inflammatory drug target.
