No abstract

Abstract-Neointimal lesion formation was induced in sphingosine 1-phosphate (S1P) receptor 2 (S1P 2 )-null and wild-type mice by ligation of the left carotid artery. After 28 days, large neointimal lesions developed in S1P 2 -null but not in wild-type arteries. This was accompanied with a significant increase in both medial and intimal smooth muscle cell (SMC) replication between days 4 to 28, with only minimal replication in wild-type arteries. S1P 2 -null SMCs showed a significant increase in migration when stimulated with S1P alone and together with platelet-derived growth factor, whereas both wild-type and null SMCs migrated equally well to platelet-derived growth factor. S1P increased Rho activation in wild-type but not in S1P 2 -null SMCs, and inhibition of Rho activity promoted S1P-induced SMC migration. Plasma S1P levels were similar and did not change after surgery. These results suggest that activation of S1P 2 normally acts to suppress SMC growth in arteries and that S1P is a regulator of neointimal development. Key Words: sphingosine 1-phosphate receptors Ⅲ smooth muscle cells Ⅲ neointima S phingosine 1-phosphate (S1P) is a bioactive sphingolipid formed by activation of sphingosine kinases. 1 It exerts pleiotropic effects on many cells by regulating cytoskeletal rearrangement, cell survival, cell migration, cell proliferation, angiogenesis, and vascular development. [2][3][4][5] Recently S1P has received attention as a regulator of the cardiovascular system. In part, this is because there are high levels of S1P in plasma, and a recent report showed that they correlate well with the reoccurrence of vascular events. 6 -10 Further platelets release S1P during their activation, and consequently S1P levels are likely to be high at sites of arterial injury. 11,12 S1P acts through 5 G protein-coupled receptors (S1P 1 to S1P 5 ), although arterial smooth muscle cells (SMCs) express only S1P 1 , S1P 2 , and S1P 3 . 4,13 Initially these receptors were called endothelial cell differentiation gene receptors. 14 Activation of S1P receptors induces coupling to a variety of G proteins, which in turn leads to activation of multiple pathways. In SMCs most work has concentrated on S1P 1 and S1P 2 because they have opposing actions. S1P 1 couples to Gi and leads to activation of extracellular signal-regulated kinase, phosphatidylinositol 3-kinase, and Rac. 13,15,16 Adult SMCs only weakly express S1P 1 , although it is more highly expressed in pup cells, and this has been linked to their increased ability to migrate and proliferate in response to S1P. 17 S1P 1 is also strongly expressed in SMCs from rat intimal lesions as well as in human atherosclerotic lesions. 17,18 These data have been used to suggest that activation of S1P 1 may induce events leading to restenosis and the formation of arterial lesions. S1P 2 is the main receptor expressed by most adult medial SMCs and couples to Gi, Gq, and G12/13, and its activation by S1P is associated with inhibition of SMC migration. 13,19 This is thought to occur via coupling...

The response of mice arteries to injury varies significantly between strains. FVB mice develop large neointimas after injury, whereas very small lesions form in C57BL/6 mice. After injury, platelet interaction with the denuded artery and early smooth muscle (SMC) replication are identical in both strains; however, the migration of SMCs differs significantly. FVB cells readily move into the developing neointima, whereas only the occasional C57BL/6 cells migrate. Injured arteries showed no difference in matrix metalloproteinases (MMP-2 and MMP-9) and plasminogen activator activities. In vitro, sphingosine-1-phosphate (S1P) in combination with platelet-derived growth factor (PDGF) stimulates migration of FVB cells but inhibits migration of C57BL/6 SMCs. Both SMCs migrate equally well to PDGF alone. One explanation is that the SMCs express different S1P receptors. Real-time polymerase chain reaction shows that FVB cells express higher levels of S1P receptor-1 (S1P(1)) compared with C57BL/6 cells, which express higher levels of S1P receptor-2 (S1P(2)). In addition, the migration of C57BL/6 cells can be increased by inhibiting S1P(2), whereas inhibiting S1P(1) expression slows the migration of FVB cells. Taken together these studies suggest that expression of S1P receptors vary within inbred mouse strains and that S1P is critical for SMC migration and lesion formation after injury.

The results indicated that soluble FM-fibrinogen complex appears to be a useful diagnostic molecular marker to assess the activity of the coagulation system, and that its preoperative level may serve as a potential risk factor for intraoperative hemorrhagic diathesis in patients undergoing elective AAA repair.

No abstract

No abstract

Sarcopenia is an important health problem associated with adverse outcomes. Although the etiology of sarcopenia remains poorly understood, factors apart from muscle fibers, including humoral factors, might be involved. Here, we used cytokine antibody arrays to identify humoral factors involved in sarcopenia and found a significant increase in levels of milk fat globule epidermal growth factor 8 (MFG‐E8) in skeletal muscle of aged mice, compared with young mice. We found that the increase in MFG‐E8 protein at arterial walls and neuromuscular junctions (NMJs) in muscles of aged mice. High levels of MFG‐E8 at NMJs and an age‐related increase in arterial MFG‐E8 have also been identified in human skeletal muscle. In NMJs, MFG‐E8 is localized on the surface of terminal Schwann cells, which are important accessory cells for the maintenance of NMJs. We found that increased MFG‐E8 at NMJs precedes age‐related denervation and is more prominent in sarcopenia‐susceptible fast‐twitch than in sarcopenia‐resistant slow‐twitch muscle. Comparison between fast and slow muscles further revealed that arterial MFG‐E8 can be uncoupled from sarcopenic phenotype. A genetic deficiency in MFG‐E8 attenuated age‐related denervation of NMJs and muscle weakness, providing evidence of a pathogenic role of increased MFG‐E8. Thus, our study revealed a mechanism by which increased MFG‐E8 at NMJs leads to age‐related NMJ degeneration and suggests that targeting MFG‐E8 could be a promising therapeutic approach to prevent sarcopenia.

Liver cirrhosis is a critical health problem associated with several complications, including skeletal muscle atrophy, which adversely affects the clinical outcome of patients independent of their liver functions. However, the precise mechanism underlying liver cirrhosis-induced muscle atrophy has not been elucidated. Here we show that serum factor induced by liver fibrosis leads to skeletal muscle atrophy. Using bile duct ligation (BDL) model of liver injury, we induced liver fibrosis in mice and observed subsequent muscle atrophy and weakness. We developed culture system of human primary myotubes that enables an evaluation of the effects of soluble factors on muscle atrophy and found that serum from BDL mice contains atrophy-inducing factors. This atrophy-inducing effect of BDL mouse serum was mitigated upon inhibition of TNFα signalling but not inhibition of myostatin/activin signalling. The BDL mice exhibited significantly up-regulated serum levels of TNFα when compared with the control mice. Furthermore, the mRNA expression levels of Tnf were markedly up-regulated in the fibrotic liver but not in the skeletal muscles of BDL mice. The gene expression analysis of isolated nuclei revealed that Tnf is exclusively expressed in the non-fibrogenic diploid cell population of the fibrotic liver. These findings reveal the mechanism through which circulating TNFα produced in the damaged liver mediates skeletal muscle atrophy. Additionally, this study demonstrated the importance of inter-organ communication that underlies the pathogenesis of liver cirrhosis.