Apolipoprotein E inhibition of vascular smooth muscle cell proliferation but not the inhibition of migration is mediated through activation of inducible nitric oxide synthase.
Initial experiments revealed that low concentrations of apolipoprotein (apo) E (0.1 to 5 microg/mL) were effective in inhibiting platelet-derived growth factor (PDGF)-directed smooth muscle cell (SMC) migration by 60% to 80%. In contrast, higher concentrations of apoE, at 25 and 50 microg/mL, were necessary to achieve similar inhibition of PDGF-induced SMC proliferation. The potential role of nitric oxide (NO) in mediating the inhibitory effects of apoE was explored. Results showed that, although 0.1 to 5 microg/mL of apoE had no effect on NO production by SMCs, physiological concentrations of apoE (25 to 50 microg/mL) enhanced NO synthesis by 2-fold in a dose-dependent manner (P<0.001). Reverse transcription-polymerase chain reaction amplification of RNA obtained from control and apoE-treated SMCs demonstrated a direct role of apoE in activating inducible nitric oxide synthase (iNOS) gene expression. The apoE-induced nitric oxide production was significantly reduced by coincubation of the cells with aminoguanidine or N(G)-monomethyl-L-arginine (P<0.05) or with antisense iNOS oligodeoxynucleotides (P<0.01). Moreover, the inhibition of iNOS was shown to overcome apoE suppression of PDGF-induced vascular SMC proliferation. However, apoE suppression of PDGF-directed SMC migration was not affected by these treatments. Taken together, these results document that apoE exerts its inhibitory effects on cell proliferation via activation of iNOS. However, apoE inhibition of cell migration is mediated by a mechanism independent of iNOS activation.
Ishigami
M
M
Department of Pathology and Laboratory Medicine, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0529, USA.
Swertfeger
D K
DK
Hui
M S
MS
Granholm
N A
NA
Hui
D Y
DY
D001057:Apolipoproteins E / Q000494:pharmacology*; D002455:Cell Division / Q000187:drug effects*; D002460:Cell Line; D002465:Cell Movement / Q000187:drug effects*; D004789:Enzyme Activation / Q000187:drug effects; D006801:Humans; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D009569:Nitric Oxide / Q000378:metabolism; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction
D001057:Apolipoproteins E; D010982:Platelet-Derived Growth Factor; D009569:Nitric Oxide; C496319:NOS2 protein, human; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II