Retinoic Acid Regulates Arterial Smooth Muscle Cell Proliferation and Phenotypic Features In Vivo and In Vitro Through an RARα-Dependent Signaling Pathway

Abstract

Abstract-We have recently shown that all-trans retinoic acid (tRA) modulates arterial smooth muscle cell (SMC) morphologic features and biochemical composition in vitro. It has been proposed that different SMC phenotypes coexist in arteries, which may be retrieved in culture: hence, a differential action of tRA on distinct SMC subsets is conceivable.We have examined the effect of tRA on SMC proliferation, migration, plasminogen activator activity, and ␣-smooth muscle actin expression in 2 phenotypically different rat SMC populations, cultured respectively from the normal aortic media and from the intimal thickening (IT) after endothelial injury. tRA inhibited proliferation and increased migration and tissue-type plasminogen activator activity in both SMC populations, but decreased ␣-smooth muscle actin only in SMC cultured from the IT. The action of tRA is mediated by 2 families of nuclear receptors, RAR and RXR, each containing 3 isoforms, ␣, ␤, and ␥. RAR and RAR-␣ agonists, but not RXR agonists, inhibited SMC proliferation in both cell populations and ␣-smooth muscle actin expression only in IT SMC. When administered intraperitoneally to balloon-injured rats, tRA and RAR-␣ agonists reduced the intimal hyperplasia in the carotid artery. Our results show that tRA and synthetic retinoids can affect the proliferation, migration, and differentiation of SMC in vitro. Key Words: smooth muscle cell heterogeneity Ⅲ smooth muscle cell motility Ⅲ smooth muscle cell differentiation Ⅲ intimal thickening S mooth muscle cell (SMC) differentiation, migration, and proliferation are key factors in the development of atherosclerosis and restenosis after angioplasty. 1,2 These phenomena involve an SMC phenotypic modulation characterized by modification of gene expression. 3 It has been suggested that SMC subsets present in the normal media are particularly prone to undergoing phenotypic modulation, and the concept of SMC heterogeneity is gaining wider acceptance (for review see Reference 4). For instance, SMC populations cultured from the rat aortic media and from the intima 15 days after endothelial injury are characterized by a spindle-shaped and an epithelioid morphology, respectively (for discussion of this point see Reference 5). These 2 phenotypes are also obtained when SMC are cloned from the aortic media or the intima, albeit in different proportions. 6 The regulation of SMC phenotype is thought to be exerted by cytokines, growth factors, and agents regulating differentiation. 7 Within the last category, some agents are known to govern SMC differentiation during embryogenesis, and there is a growing body of evidence suggesting that the genetic programs used during embryogenesis may act also during arterial disease processes. 8,9 Vitamin A plays a crucial role in the regulation of cell growth and differentiation, and its active form, retinoic acid, is involved in signal transduction pathways regulating embryonic development. 10 These effects are mediated by 2 families of nuclear receptors that are ligand-dependent trans...

Enhanced H 2 O 2 -Induced Cytotoxicity in “Epithelioid” Smooth Muscle Cells

“…Although the majority of medial SMCs in adult animals can be classified as fusiform, epithelioid SMCs have been derived from the media of blood vessels of several species of animals and maintained in culture through multiple passages. [3][4][5][6][7][8] These cell lines exhibit distinct morphological features, display unique profiles of SMC proteins, and possess characteristic growth patterns. Moreover, epithelioid SMCs may play an important role in neointimal formation.…”

“…[3][4][5][6][7][8][9]15 To compare the effects of H 2 O 2 on neointimal versus medial SMCs in situ, the thoracic aorta was removed 15 days after balloon or sham injury. Segments of aorta were incubated with 0 to 300 mol/L H 2 O 2 for 15 hours in culture medium, stained with Hoechst 33342, and then examined by UV microscopy.…”

“…Key Words: smooth muscle cells Ⅲ apoptosis Ⅲ reactive oxygen species Ⅲ hydrogen peroxide Ⅲ neointima R ecent reports by several groups indicate that smooth muscle cells (SMCs) within the arterial wall comprise a variety of distinct phenotypes that possess unique biochemical and functional properties. [1][2][3][4][5][6][7][8] In general, clonally derived SMC lines can be classified as "fusiform" or "epithelioid," corresponding to the appearance and growth pattern of the cells in culture. 2,9 Fusiform SMCs, which are elongated and exhibit the classic "hills-and-valleys" pattern of growth, are predominant in the arterial media of adult animals.…”

“…[1][2][3][4][5][6][7][8] In general, clonally derived SMC lines can be classified as "fusiform" or "epithelioid," corresponding to the appearance and growth pattern of the cells in culture. 2,9 Fusiform SMCs, which are elongated and exhibit the classic "hills-and-valleys" pattern of growth, are predominant in the arterial media of adult animals.…”

Transcription Suppression of Thromboxane Receptor Gene Expression by Retinoids in Vascular Smooth Muscle Cells

“…Moreover, RA inhibits the production of several matrix metalloproteinases, and this inhibition may suppress the migration of VSMCs (30,31). Neointima formation after endothelial injury has also been shown to be inhibited by RA treatment in vivo (27,32,33). Taken together, these results indicate that retinoids exert anti-atherosclerotic effects in VSMCs.…”