Activation of MAPK by modified low-density lipoproteins in vascular smooth
muscle cells.
Velarde, Victoria, Alicia J. Jenkins, Julie Christopher, Timothy J. Lyons, and Ayad A.
Jaffa.
Departments of Medicine and Pharmacology, Division of Endocrinology-Diabetes-
Medical Genetics, Medical University of South Carolina, Charleston, South Carolina
29425
APStracts 8:0334A, 2001.
A high concentration of circulating low-density lipoproteins (LDL) is a major risk factor
for atherosclerosis. Native LDL and LDL modified by glycation and/or oxidation are
increased in diabetic individuals. LDL directly stimulate vascular smooth muscle cell
(VSMC) proliferation; however, the mechanisms remain undefined. The extracellular
signal-regulated kinase (ERK) pathway mediates changes in cell function and growth.
Therefore, we examined the cellular effects of native and modified LDL on ERK
phosphorylation in VSMC. Addition of native, mildly modified (oxidized, glycated,
glycoxidized) and highly modified (highly oxidized, highly glycoxidized) LDL at 25
mug/ml to rat VSMC for 5 min induced a fivefold increase in ERK phosphorylation. To
elucidate the signal transduction pathway by which LDL phosphorylate ERK, we
examined the roles of the calcium/calmodulin pathway, protein kinase C (PKC), src
kinase, and mitogen-activated protein kinase kinase (MEK). Treatment of VSMC with
the intracellular calcium chelator EGTA/AM (50 mumol/l) significantly increased ERK
phosphorylation induced by native and mildly modified LDL, whereas chelation of
extracellular calcium by EGTA (3 mmol/l) significantly reduced LDL-induced ERK
phosphorylation. The calmodulin inhibitor N-(6-aminohexyl)-1-naphthalenesulfonamide
(40 mumol/l) significantly decreased ERK phosphorylation induced by all types of LDL.
Downregulation of PKC with phorbol myristate acetate (5 mumol/l) markedly reduced
LDL-induced ERK phosphorylation. Pretreatment of VSMC with a cell-permeable MEK
inhibitor (PD 98059, 40 mumol/l) significantly decreased ERK phosphorylation in
response to native and modified LDL. These findings indicate that native and mildly and
highly modified LDL utilize similar signaling pathways to phosphorylate ERK and
implicate a role for calcium/calmodulin, PKC, and MEK. These results suggest a
potential link between modified LDL, vascular function, and the development of
atherosclerosis in diabetes.«fnc1»1
Received 5 February 2001; accepted in final form 25 June 2001
APS Manuscript Number A0118-1.
Article publication pending J Appl Physiol
ISSN 1080-4757 Copyright 2001 The American Physiological Society.
Published in APStracts on 29 June 2001