Activation of p38 Mitogen-Activated Protein Kinase by Oxidized LDL in Vascular Smooth Muscle Cells

Abstract

Oxidized low-density lipoproteins (oxLDL) have been shown to play a crucial role in atherosclerosis, but the underlying molecular mechanisms have not been fully understood. The present study showed that oxLDL strongly evoked phosphorylation and activation of p38 mitogen-activated protein kinase (MAPK) in rat vascular smooth muscle cells (VSMCs) in concentration- and time-dependent manners, reaching the maximal activation at 100 microg/mL within 5 minutes. The results from immunofluorescence staining also revealed that p38 MAPK was activated by oxLDL in 5 minutes, and the activated p38 MAPK was translocated from cytoplasm to nucleus of VSMCs in 15 minutes. Activation of p38 MAPK by oxLDL was apparently not mediated by their classical scavenger receptors and was not affected by tyrosine kinase inhibitors. However, activation of p38 MAPK was effectively blocked by pretreatment with pertussis toxin and was significantly reduced by phospholipase C inhibitor U-73122. OxLDL also inhibited forskolin-stimulated cAMP accumulation and increased inositol phosphate formation. More interestingly, inhibition of p38 MAPK by its specific inhibitor SB203580 significantly blocked oxLDL-induced cytotoxicity (increased leakage of cytoplasmic lactate dehydrogenase to the culture medium, reduced [3H]thymidine incorporation, and attenuated mitochondrial metabolism of tetrazolium salt, (3-(4, 5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-s ulfophenyl)- 2H-tetrazolium), MTS) in VSMCs, and pretreatment with pertussis toxin also inhibited oxLDL-induced cytotoxicity. Taken together, our data clearly demonstrated that oxLDL effectively activated p38 MAPK in VSMCs, which was likely mediated via pertussis toxin-sensitive G proteins, and the p38 activation was functionally associated with oxLDL-induced cytotoxicity in VSMCs.

LDLs induce fibroblast spreading independently of the LDL receptor via activation of the p38 MAPK pathway

“…The p38 MAPK pathway can be stimulated by cytokines via G protein-coupled receptors or in response to various stress conditions, such as increase in osmolarity (21) or, as shown here in fibroblasts and by others in other cell types, by LDLs (18,(22)(23)(24)(25). How LDLs activate p38 MAPKs is, however, unclear.…”

“…Oxidation may be important for the signaling properties of LDLs (5,18). Using the lipoperoxide method, we found that no oxidation could be detected in our LDL preparations (see Experimental Procedures).…”

A redox-sensitive pathway mediates oxidized LDL-induced downregulation of insulin-like growth factor-1 receptor

“…In various cell types, including SMCs, multiple signaling pathways can be activated by OxLDL, including a p38 MAPKdependent pathway (11) and an extracellular signal-regulated kinase (ERK)-dependent pathway (19,20). We examined whether these pathways were involved in IGF-1R downregulation by OxLDL, using well-known inhibitors of those pathways.…”

“…Mechanisms may include changes in the stimulation of various signal transduction pathways, such as the tumor necrosis factor receptor (9), Fas-Fas ligand (9,10), and mitogen-activated protein kinase (MAPK) and Jun kinase pathways (9,11), and in the generation of reactive oxygen species (ROS) (12). In addition to the activation of proapoptotic signal pathways, interference in cell survival signaling could be involved in OxLDL effects on SMCs.…”

Suppression of angiotensin II stimulated responses in aortic vascular smooth muscle cells of experimental cirrhotic rats

“…Rat thoracic aortic VSMCs were isolated and cultured by a modification of the procedures described elsewhere [8]. Briefly, under sterile conditions, descending thoracic aorta was resected from rats and washed in D-Hank s balanced salt solution.…”