Inhibition of Smooth Muscle Proliferation by Urea-Based Alkanoic Acids via Peroxisome Proliferator-Activated Receptor α–Dependent Repression of Cyclin D1

Abstract

Objective-Proliferation of smooth muscle cells is implicated in cardiovascular complications. Previously, a urea-based soluble epoxide hydrolase inhibitor was shown to attenuate smooth muscle cell proliferation. We examined the possibility that urea-based alkanoic acids activate the nuclear receptor peroxisome proliferator-activated receptor ␣ (PPAR␣) and the role of PPAR␣ in smooth muscle cell proliferation. Methods and Results-Alkanoic acids transactivated PPAR␣, induced binding of PPAR␣ to its response element, and significantly induced the expression of PPAR␣-responsive genes, showing their function as PPAR␣ agonists. Furthermore, the alkanoic acids attenuated platelet-derived growth factor-induced smooth muscle cell proliferation via repression of cyclin D1 expression. Using small interfering RNA to decrease endogenous PPAR␣ expression, it was determined that PPAR␣ was partially involved in the cyclin D1 repression. The antiproliferative effects of alkanoic acids may also be attributed to their inhibitory effects on soluble epoxide hydrolase, because epoxyeicosatrienoic acids alone inhibited smooth muscle cell proliferation. Conclusions-These results show that attenuation of smooth muscle cell proliferation by urea-based alkanoic acids is mediated, in part, by the activation of PPAR␣. These acids may be useful for designing therapeutics to treat diseases characterized by excessive smooth muscle cell proliferation. Key Words: soluble expoxide hydrolase Ⅲ epoxyeicosatrienoic acids Ⅲ PPAR␣ Ⅲ smooth muscle cells Ⅲ proliferation S mooth muscle cell (SMC) proliferation is a critical event in atherosclerosis 1 and in restenosis following interventional procedures. 2 After injury to the vasculature, a vasculoproliferative cascade is initiated that includes the recruitment and proliferation of SMCs, 3 which can eventually lead to occlusive lesions that result in myocardial ischemia. 4 Much effort has been made to inhibit SMC proliferation using pharmacological and genetic approaches that interfere with cell cycle regulators such as cyclins 5 and cyclin-dependent kinases (CDKs). 6 Cyclins and CDKs are part of the regulatory machinery controlling cell cycle progression. The D and E cyclins and their associated kinases are viewed as essential for entry into and progression through the G 1 phase of a cell cycle. 7 Overexpression of the D cyclins can shorten G 1 , implying that they are critical for cell cycle progression through this phase. 8 In leukemic and breast cancer cells, xenobiotics such as clofibrate and troglitazone inhibit cyclin D expression, resulting in cell cycle arrest. 9,10 These compounds are ligands for the peroxisome proliferator-activated receptor (PPAR) (NR1C) family of nuclear receptors.PPARs are ligand-activated nuclear receptors of which there are 3 isoforms (␣, ␥, and ␦). Activators of PPAR␣ include polyunsaturated fatty acids and fibrate drugs. PPAR␥ ligands include the prostaglandin (PG) D 2 derivative 15-deoxy-⌬ 12,14 -prostaglindin J 2 (15-⌬PGJ 2 ), oxidized linoleic acid, and the antidiabe...

Arachidonic acid cytochrome P450 epoxygenase pathway

“…sEH inhibitors initially were developed as antihypertensive agents (11), but recent data indicate that they also prevent cardiac hypertrophy (43), decrease vascular smooth muscle proliferation (44), improve renal hemodynamics (3), and decrease hypertensive renal damage (10,45). This is consistent with the finding that angiotensin II up-regulates sEH through a transcriptional mechanism, thereby reducing EET availability (46).…”

Cardiovascular Actions of the Peroxisome Proliferator‐Activated Receptor‐Alpha (PPARα) Agonist Wy14,643

“…These results were confirmed with porcine SMCs (Zahradka et al 2006), as well as human aortic and coronary artery SMCs (Gizard et al 2005;Ng et al 2006). The cellular mechanisms for inhibition of DNA synthesis were linked to cdk2 activation (Zahradka et al 2006), cyclin D1 expression (Ng et al 2006) and p16 INK4a (Gizard et al 2005). Given the critical role of the retinoblastoma protein (Rb) in cell cycle progression through the G1/S interface (Andres 2004), it is reasonable to suggest that Wy14,643 affects a common event required for Rb activation that is mediated by PPARα.…”

“…It was observed that Wy14,643 inhibited SMC proliferation in response to both angiotensin II and plateletderived growth factor (PDGF), respectively. These results were confirmed with porcine SMCs (Zahradka et al 2006), as well as human aortic and coronary artery SMCs (Gizard et al 2005;Ng et al 2006). The cellular mechanisms for inhibition of DNA synthesis were linked to cdk2 activation (Zahradka et al 2006), cyclin D1 expression (Ng et al 2006) and p16 INK4a (Gizard et al 2005).…”

Cytochrome P450 Eicosanoids are Activators of Peroxisome Proliferator-Activated Receptor α

“…Unfortunately, inhibition of sEH by ureabased and chalcone oxide sEH inhibitors was not possible in these studies since these inhibitors also activated PPARs (V. Y. Ng and D. L. Kroetz, unpublished data;Ng et al, 2006). Further studies would be required to adequately address the relative contribution of EETs and DHETs in the observed activation of PPAR.…”