Proteomic and metabolomic analysis of smooth muscle cells derived from the arterial media and adventitial progenitors of apolipoprotein E-deficient mice

We have recently demonstrated that stem cell antigen 1-positive (Sca-1(+)) progenitors exist in the vascular adventitia of apolipoprotein E-deficient (apoE(-/-)) mice and contribute to smooth muscle cell (SMC) accumulation in vein graft atherosclerosis. Using a combined proteomic and metabolomic approach, we now characterize these local progenitors, which participate in the formation of native atherosclerotic lesions in chow-fed apoE(-/-) mice. Unlike Sca-1(+) progenitors from embryonic stem cells, the resident Sca-1(+) stem cell population from the vasculature acquired a mature aortic SMC phenotype after platelet-derived growth factor-BB stimulation. It shared proteomic and metabolomic characteristics of apoE(-/-) SMCs, which were clearly distinct from wild-type SMCs under normoxic and hypoxic conditions. Among the differentially expressed proteins were key enzymes in glucose metabolism, resulting in faster glucose consumption and a compensatory reduction in baseline interleukin-6 secretion. The latter was associated with a marked upregulation of insulin-like growth factor binding proteins (IGFBPs) 3 and 6. Notably, reconstitution of interleukin-6 to levels measured in the conditioned medium of wild-type SMCs attenuated the elevated IGFBP expression in apoE(-/-) SMCs and their vascular progenitors. This coregulation of apoE, interleukin-6, and IGFBPs was replicated in wild-type SMCs from hypercholesterolemic mice and confirmed by silencing apoE expression in SMCs from normocholesterolemic mice. In summary, we provide evidence that Sca-1(+) progenitors contribute to native atherosclerosis in apoE(-/-) mice, that apoE deficiency and hypercholesterolemia alter progenitor cell behavior, and that inflammatory cytokines such as interleukin-6 act as metabolic regulators in SMCs of hyperlipidemic mice.     

Evidence from a novel human cell clone that adult vascular smooth muscle cells can convert reversibly between noncontractile and contractile phenotypes.

Smooth muscle cells (SMCs) perform diverse functions that can be categorized as contractile and synthetic. A traditional model holds that these distinct functions are performed by the same cell, by virtue of its capacity for bidirectional modulation of phenotype. However, this model has been challenged, in part because there is no physiological evidence that an adult synthetic SMC can acquire the ability to contract. We sought evidence for this by cloning adult SMCs from human internal thoracic artery. One clone, HITB5, expressed smooth muscle alpha-actin, smooth myosin heavy chains, heavy caldesmon, and calponin and showed robust calcium transients in response to histamine and angiotensin II, which confirmed intact transmembrane signaling cascades. On serum withdrawal, these cells adopted an elongated and spindle-shaped morphology, random migration slowed, extracellular matrix protein production fell, and cell proliferation and [(3)H]thymidine incorporation fell to near 0. Cell viability was not compromised, however; in fact, apoptosis rate fell significantly. In this state, agonist-induced elevation of cytoplasmic calcium was even more pronounced and was accompanied by SMC contraction. Readdition of 10% serum completely returned HITB5 cells to a noncontractile, proliferative phenotype. Contractile protein expression increased after serum withdrawal, although modestly, which suggested that the switch to contractile function involved reorganization or sensitization of existing contractile structures. To our knowledge, the physiological properties of HITB5 SMCs provide the first direct demonstration that cultured human adult SMCs can convert between a synthetic, noncontracting state and a contracting state. HITB5 cells should be valuable for characterizing the basis of this critical transition.     

Both donor and recipient origins of smooth muscle cells in vein graft atherosclerotic lesions

Smooth muscle cell (SMC) accumulation in the inner layer of the vessel wall is a key event in the pathogenesis of atherosclerosis in vein grafts, but the origin of the cells in these lesions has yet to be shown. Herein, we use animal models of vein grafts in transgenic mice to clearly identify the sources of SMCs in atherosclerosis. Vena cava segments were isografted to carotid arteries between four types of transgenic mice, including SM-LacZ expressing beta-galactosidase (beta-gal) in vascular SMCs, SM-LacZ/apoE(-/-), ROSA26 expressing beta-gal in all tissues, and wild-type mice. beta-gal-positive cells were observed in neointimal and atherosclerotic lesions of all vein segments grafted between LacZ transgenic and wild-type mice. Double staining for beta-gal and cell nuclei revealed that about 40% of SMCs originated from hosts and 60% from the donor vessel. This was confirmed by double labeling of the Y-chromosome and alpha-actin in the lesions of sex-mismatched vein grafts. The possibility that bone marrow cells were the source of SMCs in grafts was eliminated by the absence of beta-gal staining in atherosclerotic lesions of chimeric mice. Furthermore, vein SMCs of SM-LacZ mice did not express beta-gal in situ, but did so when these cells appeared in atherosclerotic lesions in vivo, suggesting that hemodynamic forces may be crucial for SMC differentiation. Thus, we provide the first evidence of SMC origins in the atherosclerotic lesions of vein grafts, which will be essential for providing insight into new types of therapy for the disease. The full text of this article is available at http://www.circresaha.org.     

Proteomic and metabolomic analysis of vascular smooth muscle cells: role of PKCdelta

Recent developments of proteomic and metabolomic techniques provide powerful tools for studying molecular mechanisms of cell function. Previously, we demonstrated that neointima formation was markedly increased in vein grafts of PKCdelta-deficient mice compared with wild-type controls. To clarify the underlying mechanism, we performed a proteomic and metabolomic analysis of cultured vascular smooth muscle cells (SMCs) derived from PKCdelta+/+ and PKCdelta-/- mice. Using 2-dimensional electrophoresis and mass spectrometry, we identified >30 protein species that were altered in PKCdelta-/- SMCs, including enzymes related to glucose and lipid metabolism, glutathione recycling, chaperones, and cytoskeletal proteins. Interestingly, nuclear magnetic resonance spectroscopy confirmed marked changes in glucose metabolism in PKCdelta-/- SMCs, which were associated with a significant increase in cellular glutathione levels resulting in resistance to cell death induced by oxidative stress. Furthermore, PKCdelta-/- SMCs overexpressed RhoGDIalpha, an endogenous inhibitor of Rho signaling pathways. Inhibition of Rho signaling was associated with a loss of stress fiber formation and decreased expression of SMC differentiation markers. Thus, we performed the first combined proteomic and metabolomic study in vascular SMCs and demonstrate that PKCdelta is crucial in regulating glucose and lipid metabolism, controlling the cellular redox state, and maintaining SMC differentiation.     

Cell-to-cell contact induces mesenchymal stem cell to differentiate into cardiomyocyte and smooth muscle cell

BACKGROUND: Recent evidences have suggested that stem cell can differentiate into cardiomyocyte and smooth muscle cell (SMC) in vivo or in vitro. But the mechanism on how stem cell differentiates is still unknown. We investigated whether intercellular interaction or soluble chemical factors would induce mesenchymal stem cells (MSCs) to acquire the phenotypical characteristics of cardiomyocytes or SMC. METHODS: MSCs were isolated from rat bone marrow with density gradient centrifugation and amplified in vitro. Flow cytometry was used to monitor the expression of surface antigen profile. After labeled by GFP (green fluorescent protein) transfection, rat MSCs were used to culture with adult rat cardiomyocytes and rat aortic SMCs in direct co-culture, indirect co-culture and conditioned culture, respectively. One week later, immunofluorescence staining against alpha-actin, desmin, and cardiac troponin T (cTnT) for cardiomyocyte, smooth muscle calponin and SM-alpha-actin for SMC were performed. RESULTS: Immunofluorescence staining was positive against alpha-actin, desmin, and cTnT on MSCs in co-culture group with adult cardiomyocytes, positive against smooth muscle calponin and SM-alpha-actin on MSCs in co-culture group with SMCs. In contrast, no alpha-actin, desmin, and cTnT expression was observed in the indirect co-culture group and conditioned culture group; no smooth muscle calponin and SM-alpha-actin in the indirect co-culture group and conditioned culture group. CONCLUSIONS: Direct cell-to-cell contact between MSC and adult cardiomyocyte or SMC, but not the soluble signaling molecules is obligatory in the differentiation of MSC into cardiomyocytes or SMC.     

Programming smooth muscle plasticity with chromatin dynamics

Smooth muscle cells (SMCs) possess remarkable phenotypic plasticity that allows rapid adaptation to fluctuating environmental cues. For example, vascular SMCs undergo profound changes in their phenotype during neointimal formation in response to vessel injury or within atherosclerotic plaques. Recent studies have shown that interaction of serum response factor (SRF) and its numerous accessory cofactors with CArG box DNA sequences within promoter chromatin of SMC genes is a nexus for integrating signals that influence SMC differentiation in development and disease. During development, SMC-restricted sets of posttranslational histone modifications are acquired within the CArG box chromatin of SMC genes. These modifications in turn control the chromatin-binding properties of SRF. The histone modifications appear to encode a SMC-specific epigenetic program that is used by extracellular cues to influence SMC differentiation, by regulating binding of SRF and its partners to the chromatin template. Thus, SMC differentiation is dynamically regulated by the interplay between SRF accessory cofactors, the SRF-CArG interaction, and the underlying histone modification program. As such, the inherent plasticity of the SMC lineage offers unique glimpses into how cellular differentiation is dynamically controlled at the level of chromatin within the context of changing microenvironments. Further elucidation of how chromatin regulates SMC differentiation will undoubtedly yield valuable insights into both normal developmental processes and the pathogenesis of several vascular diseases that display detrimental SMC phenotypic behavior.     

Novel embryonic genes are preferentially expressed by autonomously replicating rat embryonic and neointimal smooth muscle cells

We sought to identify and characterize the expression pattern of genes expressed by smooth muscle cells (SMCs) during periods of self-driven replication during vascular development and after vascular injury. Primary screening of a rat embryonic aortic SMC-specific cDNA library was accomplished with an autonomous embryonic SMC-enriched, nonautonomous adult SMC-subtracted cDNA probe. Positive clones were rescreened in parallel with embryonic SMC-specific and adult SMC-specific cDNA probes. We identified 14 clones that hybridized only with the embryonic cDNA ("emb" clones), 11 of which did not share significant homology with sequences in any of the databases. Five of these novel emb genes (emb7, emb8, emb20, emb37, and emb41) were selectively and only transiently reexpressed in vivo by neointimal SMCs during periods of rapid replication. The emb8:embryonic growth-associated protein (EGAP), which was studied the most extensively, was expressed at high levels by cultured, autonomously replicating embryonic and neointimal SMCs but was detected only at low levels even in mitogenically stimulated adult SMCs. Finally, the administration of antisense EGAP oligonucleotides markedly attenuated embryonic and neointimal SMC replication rates. We suggest that autonomous replication of SMCs may be essential for normal vascular morphogenesis and for the vascular response to injury and that these newly identified "embryonic" genes may be part of the molecular machinery that drives this unique growth phenotype.     

Beta-arrestins regulate atherosclerosis and neointimal hyperplasia by controlling smooth muscle cell proliferation and migration

Atherosclerosis and arterial injury-induced neointimal hyperplasia involve medial smooth muscle cell (SMC) proliferation and migration into the arterial intima. Because many 7-transmembrane and growth factor receptors promote atherosclerosis, we hypothesized that the multifunctional adaptor proteins beta-arrestin1 and -2 might regulate this pathological process. Deficiency of beta-arrestin2 in ldlr(-/-) mice reduced aortic atherosclerosis by 40% and decreased the prevalence of atheroma SMCs by 35%, suggesting that beta-arrestin2 promotes atherosclerosis through effects on SMCs. To test this potential atherogenic mechanism more specifically, we performed carotid endothelial denudation in congenic wild-type, beta-arrestin1(-/-), and beta-arrestin2(-/-) mice. Neointimal hyperplasia was enhanced in beta-arrestin1(-/-) mice, and diminished in beta-arrestin2(-/-) mice. Neointimal cells expressed SMC markers and did not derive from bone marrow progenitors, as demonstrated by bone marrow transplantation with green fluorescent protein-transgenic cells. Moreover, the reduction in neointimal hyperplasia seen in beta-arrestin2(-/-) mice was not altered by transplantation with either wild-type or beta-arrestin2(-/-) bone marrow cells. After carotid injury, medial SMC extracellular signal-regulated kinase activation and proliferation were increased in beta-arrestin1(-/-) and decreased in beta-arrestin2(-/-) mice. Concordantly, thymidine incorporation and extracellular signal-regulated kinase activation and migration evoked by 7-transmembrane receptors were greater than wild type in beta-arrestin1(-/-) SMCs and less in beta-arrestin2(-/-) SMCs. Proliferation was less than wild type in beta-arrestin2(-/-) SMCs but not in beta-arrestin2(-/-) endothelial cells. We conclude that beta-arrestin2 aggravates atherosclerosis through mechanisms involving SMC proliferation and migration and that these SMC activities are regulated reciprocally by beta-arrestin2 and beta-arrestin1. These findings identify inhibition of beta-arrestin2 as a novel therapeutic strategy for combating atherosclerosis and arterial restenosis after angioplasty.