Glucose-Potentiated Chemotaxis in Human Vascular Smooth Muscle Is Dependent on Cross-Talk Between the PI3K and MAPK Signaling Pathways

Abstract

Abstract-Atheroma formation involves the movement of vascular smooth muscle cells (VSMC) into the subendothelial space. The aim of this study was to determine the involvement of PI3K and MAPK pathways and the importance of cross-talk between these pathways, in glucose-potentiated VSMC chemotaxis to serum factors. VSMC chemotaxis occurred in a serum gradient in 25 mmol/L glucose (but not in 5 mmol/L glucose) in association with increased phosphorylation (activation) of Akt and ERK1/2 in PI3K and MAPK pathways, respectively. Inhibitors of these pathways blocked chemotaxis, as did an mTOR inhibitor. VSMC expressed all class IA PI3K isoforms, but microinjection experiments demonstrated that only the p110␤ isoform was involved in chemotaxis. ERK1/2 phosphorylation was reduced not only by MAPK pathway inhibitors but also by PI3K and mTOR inhibitors; when PI3K was inhibited, ERK phosphorylation could be induced by microinjected activated Akt, indicating important cross-talk between the PI3K and ERK1/2 pathways. Glucose-potentiated phosphorylation of molecules in the p38 and JNK MAPK pathways inhibited these pathways but did not affect chemotaxis. The statin, mevinolin, blocked chemotaxis through its effects on the MAPK pathway. Mevinolin-inhibited chemotaxis was restored by farnesylpyrophosphate but not by geranylgeranylpyrophosphate; in the absence of mevinolin, inhibition of farnesyltransferase reduced ERK phosphorylation and blocked chemotaxis, indicating a role for the Ras family of GTPases (MAPK pathway) under these conditions. In conclusion, glucose sensitizes VSMC to serum, inducing chemotaxis via pathways involving p110␤-PI3K, Akt, mTOR, and ERK1/2 MAPK. Cross-talk between the PI3K and MAPK pathways is necessary for VSMC chemotaxis under these conditions. (Circ Res. 2004;95:380-388.)Key Words: diabetes Ⅲ atherosclerosis Ⅲ Akt Ⅲ ERK Ⅲ statin C ardiovascular disease is responsible for most of the complications associated with diabetes. Impairment of endothelium and muscle contributes to abnormalities of vasodilation. 1 Expansion of the subendothelial space occurs with the development of atheromatous plaques, which contain cellular components that have migrated from the endothelium and the tunica media, in addition to invading inflammatory cells and macrophages. 2 Both PI3K and MAPK have been implicated in chemotaxis.PI3K enzymes regulate many cellular responses, including proliferation, protection from apoptosis, intracellular vesicular transport, cytoskeletal rearrangements, and cell migration. 3 PI3Ks signal via the production of 3-phosphoinositides, lipid second messengers that bind to lipid-binding domains in a wide variety of proteins, including protein kinases (such as Akt/PKB) and regulators of small GTPases. The plectrin homology lipid-binding domain of Akt binds to the lipid products of PI3K; Akt is then recruited to the plasma membrane and phosphorylated at T308 and S473 to yield a fully activated kinase. 4 PI3Ks are heterodimers consisting of a 110-kDa catalytic subunit (p110␣, p110␤, or p110␦) in comp...

Glucose lowers the threshold for human aortic vascular smooth muscle cell migration: inhibition by protein phosphatase-2A

“…To detect significant chemotaxis (unidirectional movement) the Rayleigh test for unimodal clustering of directions was used: p< 0.01 was chosen as the criterion for rejecting the null hypothesis of random directionality [7,11].…”

“…We previously demonstrated that raising glucose from normal fasting level (5 mmol/l) to 25 mmol/l increases PDGF-βR levels in aortic VSMC exposed to 360 pmol/l PDGF-BB concentrations [7,11].…”

“…VSMC chemotaxis to PDGF-BB (~360 pmol/l) is dependent on activation of phosphatidylinositol 3-kinase (PI3K; p110β isoform) and cross-talk between the PI3K and mitogen-activated protein kinase (MAPK) pathways [7]. We have shown that glucose increases Akt and extracellular-regulated protein kinase (ERK) activation levels in the PI3K and MAPK pathways, respectively, and enhances that caused by PDGF-BB; in these conditions MAPK/ERK is downstream of PI3K [7,8].…”

“…We have shown that glucose increases Akt and extracellular-regulated protein kinase (ERK) activation levels in the PI3K and MAPK pathways, respectively, and enhances that caused by PDGF-BB; in these conditions MAPK/ERK is downstream of PI3K [7,8]. Glucose causes increased polyol pathway flux leading to de novo synthesis of diacylglycerol (DAG), which is both a cofactor for protein kinase C (PKC) and a direct activator of MAPK/Ras [8,9].…”

“…Inhibition of either PI3K or MAPK interrupts receptor upregulation and chemotaxis to 360 pmol/l PDGF-BB [10,11]. Interestingly, therapeutic statin concentrations also interrupt these responses by inhibiting MAPK/Ras farnesylation [7,8].…”