Abstract 182: Mitogen-Activated Protein Kinase Phosphatase-1 and the Redox Regulation of Monocyte Adhesion and Migration

Abstract

Monocytic adhesion and chemotaxis are regulated by mitogen-activated protein kinase (MAPK) pathways, which in turn are under the control of MAPK phosphatases (MKPs). MKPs have an oxidation-sensitive cysteine residue in their active site. We recently reported that thiol oxidative stress induced by metabolic disorders enhances monocyte recruitment into vascular lesions by increasing their responsiveness to chemoattractants. We therefore investigated whether the priming effect of metabolic stress on monocytes is mediated by inactivation of MKP-1. Blood monocytes isolated from diabetic mice showed a 55% reduction MKP-1 activity compared to non diabetic mice. Chronic exposure of human THP-1 monocytes to diabetic conditions induced by human LDL plus high glucose concentrations (LDL+HG) resulted in the loss of MKP-1 protein levels, the hyperactivation of Erk1/2 and p38 MAPK in response to MCP-1, and increased monocyte adhesion and chemotaxis. Knockdown of MKP-1 mimicked the priming effects of LDL+HG, including hyperactivation of Erk1/2 and p38 MAPK, and accelerated monocyte adhesion and chemotaxis, whereas MKP-1 overexpression protected monocytes from metabolic stress-induced priming. LDL+HG exposure also promoted S-glutathionylation of MKP-1. The proteasomal inhibitor MG132 prevented the loss of MKP-1 protein induced by metabolic stress, but increased levels of S-glutathionylated MKP-1, suggesting that S-glutathionylation targets MKP-1 for proteasomal degradation. Inhibiting LDL+HG-induced MKP-1 S-glutathionylation by overexpressing glutaredoxin 1 in monocytes prevented MKP-1 degradation and normalized monocyte adhesion and chemotaxis in response to MCP-1. Finally, transplantation of bone marrow from MKP-1-null mice into LDLR-null mice significantly increased macrophage recruitment into MCP-1-loaded Matrigel plugs implanted in these mice, mimicking the priming effects of metabolic disorders reported previously. In conclusion, metabolic stress promotes the inactivation of MKP-1 activity through S-glutathionylation and subsequent proteasomal degradation. Loss of MKP-1 activity primes blood monocytes and converts them into a hypermigratory, proinflammatory and proatherogenic phenotype.