15-Deoxy-Δ^12,14-prostaglandin J₂Induces G₁Arrest and Differentiation Marker Expression in Vascular Smooth Muscle Cells

Abstract

In search of substances useful for the treatment of atherosclerotic vascular diseases, we studied the effects of 15-deoxy-⌬ 12,14 -prostaglandin J 2 (15d-PGJ 2 ), a natural ligand for peroxisome proliferator-activated receptor ␥, on the proliferation and differentiation of vascular smooth muscle cells (VSMCs). 15d-PGJ 2 but not WY14643, an agonist for peroxisome proliferatoractivated receptor ␣, dose-dependently inhibited VSMC proliferation; the effect was maximal at 12 M. This compound strongly suppressed the activities of cyclin-dependent kinases (Cdk) 4, 6, and 2, thereby preventing the phosphorylation of the retinoblastoma protein. These Cdks seemed to be inhibited through two mechanisms: the down-regulation of cyclin D1 and the up-regulation of Cdk inhibitor p21Cip1/Waf1/Sdi1 . 15d-PGJ 2 was found to inhibit the phosphatidylinositol 3-kinase/protein kinase B signaling pathway, which mediates cyclin D1 expression. Mitogenic stimulation of quiescent cells decreased the level of mRNA for the smooth muscle-specific myosin heavychain SM1, whereas this reduction was prevented by 15d-PGJ 2 . A long-term treatment of exponentially growing VSMCs with 15d-PGJ 2 markedly elevated the mRNA level of SM1 and, moreover, induced SM2, another isoform expressed exclusively in mature VSMCs. 15d-PGJ 2 also increased the expression levels of calponin-h1 and smooth muscle ␣-actin. These results suggest that 15d-PGJ 2 induces G 1 arrest by two distinct mechanisms and promotes VSMC differentiation.Vascular smooth muscle cells (VSMCs) in the arterial media are fully differentiated to play their physiological roles as regulators of vascular wall tension. However, in atherosclerotic and restenotic lesions, their phenotypes have been converted to dedifferentiated (immature) ones (Owens, 1995). Dedifferentiated VSMCs migrate into the intima, proliferate, and synthesize extracellular matrices, thereby contributing to the formation of neointima. Therefore, to prevent VSMC hyperplasia in vivo, substances capable of promoting the differentiation of VSMCs may be more effective than those that simply inhibit their proliferation. A number of substances have been reported to inhibit VSMC proliferation, but few are also able to prevent phenotype conversion and induce differentiation.Prostaglandins (PGs) of the J 2 family, including PGJ 2 , ⌬ 12 -PGJ 2 , and 15-deoxy-⌬ 12,14 -prostaglandin J 2 (15d-PGJ 2 ), are naturally occurring metabolites of PGD 2 (Kikawa et al., 1984). We previously reported that PGJ 2 and ⌬ 12-PGJ 2 strongly inhibit VSMC proliferation, although the underlying mechanisms remain undetermined (Sasaguri et al., 1992). Recently, PGs of the J 2 family were found to be natural ligands for peroxisome proliferator-activated receptor (PPAR) ␥, a member of the ligand-activated transcription factor nuclear receptor superfamily that includes receptors for steroid, retinoid, and thyroid hormones (Forman et al., 1995;Kliewer et al., 1995). PPAR␥ has been implicated in the induction of differentiation in adipocytes (Forman et al.,...

Nonenzymatic free radical-catalyzed generation of 15-deoxy-Δ12,14-prostaglandin J2-like compounds (deoxy-J2-isoprostanes) in vivo

“…Furthermore, 15-d-PGJ 2 activates the antioxidant response pathway via covalent modifi cation of reactive cysteine residues in Keap1, leading to Nrf2 activation and induction of antioxidant proteins, including HO-1, peroxiredoxin 1, ␥ -GCL, and heat shock protein 70 (43)(44)(45)(46)(47). Finally, 15-d-PGJ 2 has been reported to inhibit proliferation of vascular smooth muscle cells by inducing cell cycle arrest ( 48,49 ).…”

Prostaglandin D2 Synthase Inhibits the Exaggerated Growth Phenotype of Spontaneously Hypertensive Rat Vascular Smooth Muscle Cells

“…15d-PGJ 2 , which is quickly formed from PGD 2 , is known to inhibit basic fibroblast growth factor-induced DNA synthesis in rat VSMCs (34). 15d-PGJ 2 also inhibits platelet-derived growth factor-directed migration (34) and induces G 1 arrest and differentiation (35) in VSMCs. Similar effects have been observed with the synthetic PPAR␥ activator, troglitazone, which inhibits VSMC proliferation (36), decreases the intimal and medial thickness of carotid arteries in humans (37), and inhibit the development of atherosclerosis (38).…”

Interferon Regulatory Factor-1 Mediates PPARγ-Induced Apoptosis in Vascular Smooth Muscle Cells

“…10 Recent studies documented that PPAR␥ ligands inhibit atherosclerotic lesions [11][12][13] and neointimal formation. 14,15 TZDs have a proapoptotic action 16 -20 in addition to anti-proliferative, [21][22][23] anti-inflammatory, 7,24 and anti-fibrotic 25 effects in VSMCs. However, the molecular mechanisms for these effects in VSMCs are not quite fully defined, because the PPAR␥ target genes in VSMCs are not well characterized.…”