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The cAMP-producing agonist beraprost inhibits human vascular smooth muscle cell migration via exchange protein
Jenny S McKean1, Fiona Murray1, George Gibson2
1School of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, UK.
Aims:
During restenosis, vascular smooth muscle cells (VSMCs) migrate from the vascular media to the developing neointima. Preventing VSMC migration is therefore a therapeutic target for restenosis. Drugs, such as prostacyclin analogues, that increase the intracellular concentration of cyclic adenosine monophosphate (cAMP) can inhibit VSMC migration, but the mechanisms via which this occurs are unknown. Two main downstream mediators of cAMP are protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac). This study has examined the effects of the prostacyclin analogue beraprost on VSMC migration and investigated the intracellular pathways involved.
Methods And Results:
In a chemotaxis chamber, human saphenous vein VSMC migrated towards a platelet-derived growth-factor-BB (PDGF) chemogradient. Incubation with therapeutically relevant concentrations of cAMP-producing agonist beraprost significantly decreased PDGF-induced migration. Direct activation of either PKA or Epac inhibited migration whereas inhibition of PKA did not prevent the anti-migratory effect of beraprost. Direct activation of Epac also prevented hyperplasia in ex vivo serum-treated human veins. Using fluorescence resonance energy transfer, we demonstrated that beraprost activated Epac but not PKA. The mechanisms of this Epac-mediated effect involved activation of Rap1 with subsequent inhibition of RhoA. Cytoskeletal rearrangement at the leading edge of the cell was consequently inhibited. Interestingly, Epac1 was localized to the leading edge of migrating VSMC.
Conclusions:
These results indicate that therapeutically relevant concentrations of beraprost can inhibit VSMC migration via a previously unknown mechanism involving the cAMP mediator Epac. This may provide a novel target that could blunt neointimal formation.
Insights
Beraprost inhibits vascular smooth muscle cell migration by activating Epac, a cyclic adenosine monophosphate (cAMP) mediator. This novel mechanism offers a potential therapeutic target for preventing restenosis and neointimal formation.
Area of Science:
- Vascular biology
- Cell signaling
- Pharmacology
Background:
- Vascular smooth muscle cell (VSMC) migration contributes to restenosis.
- Cyclic adenosine monophosphate (cAMP) analogs inhibit VSMC migration, but mechanisms are unclear.
- Protein kinase A (PKA) and exchange protein directly activated by cAMP (Epac) are downstream cAMP mediators.
Purpose of the Study:
- To investigate the effects of beraprost on VSMC migration.
- To elucidate the intracellular pathways involved in beraprost's anti-migratory action.
Main Methods:
- Human saphenous vein VSMCs were used in chemotaxis assays.
- Beraprost, a prostacyclin analogue, was used as a cAMP-producing agonist.
- Direct activation and inhibition of PKA and Epac were performed.
- Fluorescence resonance energy transfer (FRET) was used to detect Epac activation.
- Rap1 and RhoA activation, and cytoskeletal rearrangement were analyzed.
Main Results:
- Beraprost significantly decreased platelet-derived growth-factor-BB (PDGF)-induced VSMC migration.
- Direct Epac activation inhibited migration and ex vivo vein hyperplasia.
- Beraprost activated Epac, not PKA.
- Epac activation led to Rap1 activation, RhoA inhibition, and reduced cytoskeletal rearrangement.
- Epac1 was localized at the leading edge of migrating VSMCs.
Conclusions:
- Beraprost inhibits VSMC migration through a novel Epac-dependent pathway.
- This Epac-mediated mechanism involves Rap1 and RhoA signaling.
- Targeting Epac may offer a new strategy to prevent neointimal formation in restenosis.
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