Background-Recent animal data suggest that vascular smooth muscle cells within the neointima of the vessel wall may originate from bone marrow, providing indirect evidence for circulating smooth muscle progenitor cells (SPCs). Evidence for circulating SPCs in human subjects does not exist, and the mechanism whereby such putative SPCs may home to sites of plaque formation is presently not understood but is likely to involve expression of specific surface adhesion molecules, such as integrins. In this study, we aimed to culture smooth muscle outgrowth cells (SOCs) from SPCs in human peripheral blood and characterize surface integrin expression on these cells. Methods and Results-Human mononuclear cells isolated from buffy coat were seeded on collagen type 1 matrix and outgrowth cells selected in endothelial growth medium (EGM-2) or EGM-2 and platelet-derived growth factor BB. Selection in platelet-derived growth factor BB-enriched medium caused rapid outgrowth and expansion of SOC to Ͼ40 population doublings in a 4-month period. These SOCs were positive for smooth muscle cell-specific ␣ actin (␣SMA), myosin heavy chain, and calponin on immunofluorescence and Western blotting and were also positive for CD34, Flt1, and Flk1 receptor but negative for Tie-2 receptor expression, suggesting a potential bone marrow angioblastic origin. In contrast, endothelial outgrowth cells (EOCs) grown in EGM-2 alone and the initial MNC population were negative for these smooth muscle-specific markers. Integrin ␣ 5 ␤ 1 expression by FACS and Western blotting was significantly increased in SOCs compared with EOCs, and this was confirmed by 8-fold greater adhesion of SOC to fibronectin (PϽ0.001), an effect that could be decreased using an ␣ 5 ␤ 1 antibody. Finally, SOC showed a significantly greater in vitro proliferative potential compared with EOCs of similar passage (PϽ0.001). Conclusions-This study demonstrates for the first time outgrowth of smooth muscle cells with a specific growth, adhesion, and integrin profile from putative SPC in human blood. These data have implications for our understanding of adult vascular smooth muscle cell differentiation, proliferation, and homing.

Background-The present study examined whether transplantation of adherent bone marrow-derived stem cells, termed pMultistem, induces neovascularization and cardiomyocyte regeneration that stabilizes bioenergetic and contractile function in the infarct zone and border zone (BZ) after coronary artery occlusion. Methods and Results-Permanent left anterior descending artery occlusion in swine caused left ventricular remodeling with a decrease of ejection fraction from 55Ϯ5.6% to 30Ϯ5.4% (magnetic resonance imaging). Four weeks after left anterior descending artery occlusion, BZ myocardium demonstrated profound bioenergetic abnormalities, with a marked decrease in subendocardial phosphocreatine/ATP ( 31 P magnetic resonance spectroscopy; 1.06Ϯ0.30 in infarcted hearts [nϭ9] versus 1.90Ϯ0.15 in normal hearts [nϭ8; PϽ0.01]). This abnormality was significantly improved by transplantation of allogeneic pMultistem cells (subendocardial phosphocreatine/ATP to 1.34Ϯ0.29; nϭ7; PϽ0.05). The BZ protein expression of creatine kinase-mt and creatine kinase-m isoforms was significantly reduced in infarcted hearts but recovered significantly in response to cell transplantation. MRI demonstrated that the infarct zone systolic thickening fraction improved significantly from systolic "bulging" in untreated animals with myocardial infarction to active thickening (19.7Ϯ9.8%, PϽ0.01), whereas the left ventricular ejection fraction improved to 42.0Ϯ6.5% (PϽ0.05 versus myocardial infarction). Only 0.35Ϯ0.05% donor cells could be detected 4 weeks after left anterior descending artery ligation, independent of cell transplantation with or without immunosuppression with cyclosporine A (with cyclosporine A, nϭ6; no cyclosporine A, nϭ7). The fraction of grafted cells that acquired an endothelial or cardiomyocyte phenotype was 3% and Ϸ2%, respectively. Patchy spared myocytes in the infarct zone were found only in pMultistem transplanted hearts. Vascular density was significantly higher in both BZ and infarct zone of cell-treated hearts than in untreated myocardial infarction hearts (PϽ0.05). Conclusions-Thus, allogeneic pMultistem improved BZ energetics, regional contractile performance, and global left ventricular ejection fraction. These improvements may have resulted from paracrine effects that include increased vascular density in the BZ and spared myocytes in the infarct zone.

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Lipoprotein (a) [Lp(a)] has been associated with both anti-fibrinolytic and atherogenic effects. However, no direct link currently exists between this atherogenic lipoprotein and intravascular coagulation. The current study examined the binding and functional effects of Lp(a), its lipoprotein constituents, apoliprotein (a) [apo(a)] and low-density lipoprotein (LDL), and lysine-plasminogen (L-PLG), which shares significant homology with apo(a), on tissue factor pathway inhibitor (TFPI), a major regulator of tissue factor-mediated coagulation. Results indicate that Lp(a), apo(a), and PLG but not LDL bound recombinant TFPI (rTFPI) in vitro and that apo(a) bound to a region spanning the last 37 amino acid residues of the cterminus of TFPI. The apparent binding affinity for TFPI was much higher for Lp(a) (K D ϳ150 nM) compared to PLG (K D ϳ800 nM) and nanomolar concentrations of apo(a) (500 nM) inhibited PLG binding to TFPI. Lp(a) also inhibited in a concentration-dependent manner rTFPI activity and endothelial cell surface TFPI activity in vitro, whereas PLG had no such effect. Moreover physiologic concentrations of PLG (2 M) had no effect on the concentration-dependent inhibition of TFPI activity induced by Lp(a). In human atherosclerotic plaque, apo(a) and TFPI immunostaining were shown to coexist in smooth muscle cell-rich areas of the intima. These data suggest a novel mechanism whereby Lp(a) through its apo(a) moiety may promote thrombosis by binding and inactivating TFPI. , is an important inherited risk factor for atherosclerosis and myocardial infarction. 1,2 Recently, Kronenberg and colleagues 3 showed that Lp(a) concentrations predicted the risk of early atherosclerosis synergistically with LDL, whereas Lp(a) alone emerged as a leading independent risk factor for advanced atherosclerosis. The latter association with advanced atherosclerosis is of particular interest because it seems not to rely on conventional risk factors such as LDL but may be within the realm of procoagulant risk attributes contributing to plaque thrombosis. [3][4][5] Apo(a) contains multiple kringle IV-like domains, a kringle V-like domain, and a proteaselike domain that have significant homology with plasminogen (PLG). 6 Lp(a) accumulates in the vessel wall and inhibits binding of PLG to the cell surface, reducing plasmin generation and subsequent clot lysis. 7,8 This inhibition of PLG activation by Lp(a) also reduces active transforming growth factor-␤ (TGF ␤) production with consequent promotion of smooth muscle cell (SMC) proliferation. 9 These unique structural features of Lp(a) suggest this lipoprotein has both antifibrinolytic and atherogenic potential.The antifibrinolytic effects of Lp(a) notwithstanding, to date no mechanistic data exist to support a more direct role for this atherogenic lipoprotein in promotion of intravascular thrombosis. The lysine-binding characteristics of Lp(a) may be important in this regard, allowing the apo(a) portion of Lp(a) to bind several lysine-rich components of the coagulation system. A potenti...