15-deoxy- Δ12,14 -prostaglandin J_2 induces redifferentiation of cultured human vascular smooth muscle cells

To elucidate the mechanism for the induction of vascular smooth muscle cell (VSMC) differentiation, it is crucial to establish an in vitro experimental system in which re-differentiation is induced in cultured VSMCs. In this study, we examined the effects of 15-deoxy- Δ^12,14 -prostaglandin J_2 (15d-PGJ_2 ), a natural ligand for PPAR γ, on the expression of VSMC-specific differentiation markers using RT-PCR and Western blotting. A long-term treatment of growing (de-differentiated) VSMCs with 15d-PGJ_2 increased the expression levels of SM-MHCs SM1 and SM2, calponin-h1, and smooth muscle α -actin. However the expression level of SM2, which is expressed exclusively in mature VSMCs, was much lower compared with freshly isolated (differentiated) VSMCs. Since differentiation markers also increased to some extent in confluent or quiescent cells, we added 15d-PGJ_2 to confluent and G_0 -synchronized cells. Within 4 days after the addition of 15d-PGJ_2 , cultured VSMCs aggregated and formed several nodules on plastic dishes. Surprisingly, cells forming these nodules expressed almost the same levels of SM2 as freshly isolated medial cells. These results suggested that 15d-PGJ_2 is a strong inducer of VSMC re-differentiation. We reported that vascular endothelial cells produce 15d-PGJ_2 in response to laminar fluid shear stress. Therefore l5d-PGJ_2 could play a physiological role in the regulation of VSMC differentiation.