Microsomal prostaglandin E synthase-1 (mPGES-1)/prostaglandin E₂ (PGE₂) induces angiogenesis through the prostaglandin E₂ receptor (EP1­–4). PGE₂ is not only known to induce angiogenesis but also known to modulate function and differentiation of regulatory T cells (Tregs)_. We evaluated effect of Tregs on angiogenesis by using acute hind limb ischemia model.
Male 6-8 week-old wild-type mice (WT), mPGES-1-deficient mice (mPges-1^-/-) and EP4 recepor deficient mice (EP4^-/-) were used. Recovery from ischemia was estimated by laser Doppler imaging. Angiogenesis was estimated by CD31 and TGF-beta and by using immunohistochemical analysis and real time PCR. Contribution of Tregs was estimated by immunohistichemical study and real time PCR against FoxP3.
Compared to WT, blood flow recovery was significantly suppressed in mPGES-1^-/-. The blood flow recovery was significantly enhanced by EP4 agonist but suppressed by EP4 antagonist. EP4^-/- significantly suppressed blood flow recovery compared to EP4. CD31⁺ cells and TGF-beta mRNA expression in ischemic muscle were significantly decreased in EP4^-/- mice compared to WT. The number of accumulated FoxP3+ cells and Foxp3 mRNA expression were significantly decreased in EP4^-/-. Moreover, blood flow recovery of Ep4^-/- was significantly improved by transplantation of CD4⁺ cells, containing Tregs, from WT, whereas infusion of Tregs-depleted CD4⁺ cells did not restore blood flow in Ep4^-/-.
These findings suggested that mPGES-1/PGE₂ induced blood flow recovery from ischemia via EP4 by promoting accumulation of Tregs.