Regulation of arterial lesions in mice depends on differential smooth muscle cell migration: a role for sphingosine-1-phosphate receptors

Estrogen Receptor Subtypes Elicit a Distinct Gene Expression Profile of Endothelial-Derived Factors Implicated in Atherosclerotic Plaque Vulnerability

In the presence of established atherosclerosis, estrogens are potentially harmful. MMP-2 and MMP-9, their inhibitors (TIMP-2 and TIMP-1), RANK, RANKL, OPG, MCP-1, lysyl oxidase (LOX), PDGF-β, and ADAMTS-4 play critical roles in plaque instability/rupture. We aimed to investigate (i) the effect of estradiol on the expression of the abovementioned molecules in endothelial cells, (ii) which type(s) of estrogen receptors mediate these effects, and (iii) the role of p21 in the estrogen-mediated regulation of the aforementioned factors. Human aortic endothelial cells (HAECs) were cultured with estradiol in the presence or absence of TNF-α. The expression of the aforementioned molecules was assessed by qRT-PCR and ELISA. Zymography was also performed. The experiments were repeated in either ERα- or ERβ-transfected HAECs and after silencing p21. HAECs expressed only the GPR-30 estrogen receptor. Estradiol, at low concentrations, decreased MMP-2 activity by 15-fold, increased LOX expression by 2-fold via GPR-30, and reduced MCP-1 expression by 3.5-fold via ERβ. The overexpression of ERα increased MCP-1 mRNA expression by 2.5-fold. In a low-grade inflammation state, lower concentrations of estradiol induced the mRNA expression of MCP-1 (3.4-fold) and MMP-9 (7.5-fold) and increased the activity of MMP-2 (1.7-fold) via GPR-30. Moreover, p21 silencing resulted in equivocal effects on the expression of the abovementioned molecules. Estradiol induced different effects regarding atherogenic plaque instability through different ERs. The balance of the expression of the various ER subtypes may play an important role in the paradoxical characterization of estrogens as both beneficial and harmful.

microRNA-491-5p protects against atherosclerosis by targeting matrix metallopeptidase-9

Abnormal proliferation and migration of vascular smooth muscle cells (VSMCs) are critical processes that are involved in atherosclerosis. The aim of this study was to explore the role of microRNA-491-5p (miR-491-5p) in the progression of atherosclerosis by regulating the growth and migration of VSMCs. In this study, we showed that the expression of miR-491-5p was downregulated in the atherosclerotic plaque tissues and plasma samples of the patients with atherosclerosis. The bioinformatic analysis and dual-luciferase reporter assay identified that matrix metallopeptidase-9 (MMP-9) was a target gene of miR-491-5p. The results showed a significant upregulation of MMP-9 in the atherosclerotic plaque tissues and plasma samples. Subsequently, the results also showed that downregulation of miR-491-5p significantly promoted the proliferation and migration of VSMCs and inhibited the apoptosis in VSMCs. Furthermore, we detected the effects of miR-491-5p mimic on the growth and migration of VSMCs, and the results illustrated that miR-491-5p mimic could inhibit the proliferation and migration of VSMCs and promote the apoptosis of VSMCs. Notably, MMP-9 plasmid could reverse all the effects of miR-491-5p mimic on VSMCs. Collectively, our study provides the first evidence that miR-491-5p inhibited the growth and migration of VSMCs by targeting MMP-9, which might provide new biomarkers and potential therapeutic targets for atherosclerosis treatment.

Matrix Metalloproteinases as Biomarkers of Atherosclerotic Plaque Instability

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases responsible for tissue remodeling and degradation of extracellular matrix (ECM) proteins. MMPs may modulate various cellular and signaling pathways in atherosclerosis responsible for progression and rupture of atherosclerotic plaques. The effect of MMPs polymorphisms and the expression of MMPs in both the atherosclerotic plaque and plasma was shown. They are independent predictors of atherosclerotic plaque instability in stable coronary heart disease (CHD) patients. Increased levels of MMPs in patients with advanced cardiovascular disease (CAD) and acute coronary syndrome (ACS) was associated with future risk of cardiovascular events. These data confirm that MMPs may be biomarkers in plaque instability as they target in potential drug therapies for atherosclerosis. They provide important prognostic information, independent of traditional risk factors, and may turn out to be useful in improving risk stratification.

Sphingosine-1-phosphate receptor 1 regulates neointimal growth in a humanized model for restenosis

OBJECTIVE

The main objective of this study was to define a role of sphingosine-1-phosphate receptor 1 (S1PR1) in the arterial injury response of a human artery. The hypotheses were tested that injury induces an expansion of S1PR1-positive cells and that these cells accumulate toward the lumen because they follow the sphingosine-1-phosphate gradient from arterial wall tissue (low) to plasma (high).

METHODS

A humanized rat model was used in which denuded human internal mammary artery (IMA) was implanted into the position of the abdominal aorta of immunosuppressed Rowett nude rats. This injury model is characterized by medial as well as intimal hyperplasia, whereby intimal cells are of human origin. At 7, 14, and 28 days after implantation, grafts were harvested and processed for fluorescent immunostaining for S1PR1 and smooth muscle α-actin. Nuclei were stained with 4',6-diamidine-2'-phenylindole dihydrochloride. Using digitally reconstructed, complete cross sections of grafts, intimal and medial areas were measured, whereby the medial area had virtually been divided into an outer (toward adventitia) and inner (toward lumen) layer. The fraction of S1PR1-positive cells was determined in each layer by counting S1PR1-positive and S1PR1-negative cells.

RESULTS

The fraction of S1PR1-postive cells in naive IMA is 58.9% ± 6.0% (mean ± standard deviation). At day 28 after implantation, 81.6% ± 4.4% of medial cells were scored S1PR1 positive (P < .01). At day 14, the ratio between S1PR1-positive and S1PR1-negative cells was significantly higher in the lumen-oriented inner layer (9.3 ± 2.1 vs 6.0 ± 1.0; P < .01). Cells appearing in the intima at day 7 and day 14 were almost all S1PR1 positive. At day 28, however, about one-third of intimal cells were scored S1PR1 negative.

CONCLUSIONS

From these data, we conclude that denudation of IMA specifically induces the expansion of S1PR1-positive cells. Based on the nonrandom distribution of S1PR1-positive cells, we consider the possibility that much like lymphocytes, S1PR1-positive smooth muscle cells also use S1PR1 to recognize the sphingosine-1-phosphate gradient from tissue (low) to plasma (high) and so migrate out of the media toward the intima of the injured IMA.

Matrix Metalloproteinases, Vascular Remodeling, and Vascular Disease

Matrix metalloproteinases (MMPs) are a family of zinc-dependent endopeptidases that degrade various proteins in the extracellular matrix (ECM). Typically, MMPs have a propeptide sequence, a catalytic metalloproteinase domain with catalytic zinc, a hinge region or linker peptide, and a hemopexin domain. MMPs are commonly classified on the basis of their substrates and the organization of their structural domains into collagenases, gelatinases, stromelysins, matrilysins, membrane-type (MT)-MMPs, and other MMPs. MMPs are secreted by many cells including fibroblasts, vascular smooth muscle (VSM), and leukocytes. MMPs are regulated at the level of mRNA expression and by activation through removal of the propeptide domain from their latent zymogen form. MMPs are often secreted in an inactive proMMP form, which is cleaved to the active form by various proteinases including other MMPs. MMPs degrade various protein substrates in ECM including collagen and elastin. MMPs could also influence endothelial cell function as well as VSM cell migration, proliferation, Ca²⁺ signaling, and contraction. MMPs play a role in vascular tissue remodeling during various biological processes such as angiogenesis, embryogenesis, morphogenesis, and wound repair. Alterations in specific MMPs could influence arterial remodeling and lead to various pathological disorders such as hypertension, preeclampsia, atherosclerosis, aneurysm formation, as well as excessive venous dilation and lower extremity venous disease. MMPs are often regulated by endogenous tissue inhibitors of metalloproteinases (TIMPs), and the MMP/TIMP ratio often determines the extent of ECM protein degradation and tissue remodeling. MMPs may serve as biomarkers and potential therapeutic targets for certain vascular disorders.

Matrix Metalloproteinase Inhibitors as Investigational and Therapeutic Tools in Unrestrained Tissue Remodeling and Pathological Disorders

Matrix metalloproteinases (MMPs) are zinc-dependent proteolytic enzymes that degrade various proteins in the extracellular matrix (ECM). MMPs may also regulate the activity of membrane receptors and postreceptor signaling mechanisms and thereby affect cell function. The MMP family includes collagenases, gelatinases, stromelysins, matrilysins, membrane-type MMPs, and other MMPs. Inactive proMMPs are cleaved by other MMPs or proteases into active MMPs, which interact with various protein substrates in ECM and cell surface. MMPs regulate important biological processes such as vascular remodeling and angiogenesis and may be involved in the pathogenesis of cardiovascular disorders such as hypertension, atherosclerosis, and aneurysm. The role of MMPs is often assessed by measuring their mRNA expression, protein levels, and proteolytic activity using gel zymography. MMP inhibitors are also used to assess the role of MMPs in different biological processes and pathological conditions. MMP activity is regulated by endogenous tissue inhibitors of metalloproteinases (TIMPs), and the MMP/TIMP balance could determine the net MMP activity, ECM turnover, and tissue remodeling. Also, several synthetic MMP inhibitors have been developed. Synthetic MMP inhibitors include a large number of zinc-binding globulins (ZBGs), in addition to non-ZBGs and mechanism-based inhibitors. MMP inhibitors have been proposed as potential tools in the management of osteoarthritis, cancer, and cardiovascular disorders. However, most MMP inhibitors have broad-spectrum actions on multiple MMPs and could cause undesirable musculoskeletal side effects. Currently, doxycycline is the only MMP inhibitor approved by the Food and Drug Administration. New generation biological and synthetic MMP inhibitors may show greater MMP specificity and fewer side effects and could be useful in targeting specific MMPs, reducing unrestrained tissue remodeling, and the management of MMP-related pathological disorders.

Sphingosine kinase 1/sphingosine 1-phosphate signalling pathway as a potential therapeutic target of pulmonary hypertension

Pulmonary hypertension is characterized by extensive vascular remodelling, leading to increased pulmonary vascular resistance and eventual death due to right heart failure. The pathogenesis of pulmonary hypertension involves vascular endothelial dysfunction and disordered vascular smooth muscle cell (VSMC) proliferation and migration, but the exact processes remain unknown. Sphingosine 1-phosphate (S1P) is a bioactive lysophospholipid involved in a wide spectrum of biological processes. S1P has been shown to regulate VSMC proliferation and migration and vascular tension via a family of five S1P G-protein-coupled receptors (S1P1-SIP5). S1P has been shown to have both a vasoconstrictive and vasodilating effect. The S1P receptors S1P1 and S1P3 promote, while S1P2 inhibits VSMC proliferation and migration in vitro in response to S1P. Moreover, it has been reported recently that sphingosine kinase 1 and S1P2 inhibitors might be useful therapeutic agents in the treatment of empirical pulmonary hypertension. The sphingosine kinase 1/S1P signalling pathways may play a role in the pathogenesis of pulmonary hypertension. Modulation of this pathway may offer novel therapeutic strategies.

Sphingosine-1-Phosphate and Its Receptors: A Mutual Link between Blood Coagulation and Inflammation

Sphingosine-1-phosphate (S1P) is a versatile lipid signaling molecule and key regulator in vascular inflammation. S1P is secreted by platelets, monocytes, and vascular endothelial and smooth muscle cells. It binds specifically to a family of G-protein-coupled receptors, S1P receptors 1 to 5, resulting in downstream signaling and numerous cellular effects. S1P modulates cell proliferation and migration, and mediates proinflammatory responses and apoptosis. In the vascular barrier, S1P regulates permeability and endothelial reactions and recruitment of monocytes and may modulate atherosclerosis. Only recently has S1P emerged as a critical mediator which directly links the coagulation factor system to vascular inflammation. The multifunctional proteases thrombin and FXa regulate local S1P availability and interact with S1P signaling at multiple levels in various vascular cell types. Differential expression patterns and intracellular signaling pathways of each receptor enable S1P to exert its widespread functions. Although a vast amount of information is available about the functions of S1P and its receptors in the regulation of physiological and pathophysiological conditions, S1P-mediated mechanisms in the vasculature remain to be elucidated. This review summarizes recent findings regarding the role of S1P and its receptors in vascular wall and blood cells, which link the coagulation system to inflammatory responses in the vasculature.

Genetic analysis of ligation-induced neointima formation in an F2 intercross of C57BL/6 and FVB/N inbred mouse strains

Objective

Proliferation and migration of vascular smooth muscle cells (SMCs) are central for arterial diseases including atherosclerosis and restenosis. We hypothesized that the underlying mechanisms may be modeled by carotid ligation in mice. In FVB/N inbred mice, ligation leads to abundant neointima formation with proliferating media-derived SMCs, whereas in C57BL/6 mice hardly any neointima is formed. In the present study, we aimed to identify the chromosomal location of the causative gene variants in an F2 intercross between these two mouse strains.

Methods and Results

The neointimal cross-sectional area was significantly different between FVB/N, C57BL/6 and F1 female mice 4 weeks after ligation. Carotid artery ligation and a genome scan using 800 informative SNP markers were then performed in 157 female F2 mice. Using quantitative trait loci (QTL) analysis, we identified suggestive, but no genome-wide significant, QTLs on chromosomes 7 and 12 for neointimal cross-sectional area and on chromosome 14 for media area. Further analysis of the cross revealed 4 QTLs for plasma cholesterol, which combined explained 69% of the variation among F2 mice.

Conclusions

We identified suggestive QTLs for neointima and media area after carotid ligation in an intercross of FVB/N and C57BL/6 mice, but none that reached genome-wide significance indicating a complex genetic architecture of the traits. Genome-wide significant QTLs for total cholesterol levels were identified on chromosomes 1, 3, 9, and 12.

Comparative mode-of-action analysis following manual and automated phenotype detection in Xenopus laevis

Given the increasing utilization of phenotypic screens in drug discovery also the subsequent mechanism-of-action analysis gains increased attention.

Engineering vascularized tissues using natural and synthetic small molecules

Vascular growth and remodeling are complex processes that depend on the proper spatial and temporal regulation of many different signaling molecules to form functional vascular networks. The ability to understand and regulate these signals is an important clinical need with the potential to treat a wide variety of disease pathologies. Current approaches have focused largely on the delivery of proteins to promote neovascularization of ischemic tissues, most notably VEGF and FGF. Although great progress has been made in this area, results from clinical trials are disappointing and safer and more effective approaches are required. To this end, biological agents used for therapeutic neovascularization must be explored beyond the current well-investigated classes. This review focuses on potential pathways for novel drug discovery, utilizing small molecule approaches to induce and enhance neovascularization. Specifically, four classes of new and existing molecules are discussed, including transcriptional activators, receptor selective agonists and antagonists, natural product-derived small molecules, and novel synthetic small molecules.

Effects of S1P on skeletal muscle repair/regeneration during eccentric contraction

Skeletal muscle regeneration is severely compromised in the case of extended damage. The current challenge is to find factors capable of limiting muscle degeneration and/or potentiating the inherent regenerative program mediated by a specific type of myoblastic cells, the satellite cells. Recent studies from our groups and others have shown that the bioactive lipid, sphingosine 1-phosphate (S1P), promotes myoblast differentiation and exerts a trophic action on denervated skeletal muscle fibres. In the present study, we examined the effects of S1P on eccentric contraction (EC)-injured extensor digitorum longus muscle fibres and resident satellite cells. After EC, skeletal muscle showed evidence of structural and biochemical damage along with significant electrophysiological changes, i.e. reduced plasma membrane resistance and resting membrane potential and altered Na(+) and Ca(2+) current amplitude and kinetics. Treatment with exogenous S1P attenuated the EC-induced tissue damage, protecting skeletal muscle fibre from apoptosis, preserving satellite cell viability and affecting extracellular matrix remodelling, through the up-regulation of matrix metalloproteinase 9 (MMP-9) expression. S1P also promoted satellite cell renewal and differentiation in the damaged muscle. Notably, EC was associated with the activation of sphingosine kinase 1 (SphK1) and with increased endogenous S1P synthesis, further stressing the relevance of S1P in skeletal muscle protection and repair/regeneration. In line with this, the treatment with a selective SphK1 inhibitor during EC, caused an exacerbation of the muscle damage and attenuated MMP-9 expression. Together, these findings are in favour for a role of S1P in skeletal muscle healing and offer new clues for the identification of novel therapeutic approaches to counteract skeletal muscle damage and disease.

Role of S-1-P receptors and human vascular smooth muscle cell migration in diabetes and metabolic syndrome

BACKGROUND

Sphingosine-1-phosphate (S-1-P) is a bioactive sphingolipid released from activated platelets that stimulates migration of vascular smooth muscle cells (VSMC) in vitro. S-1-P is associated with oxidized low-density lipoprotein (oxLDL) and is important in vessel remodeling. S-1-P will activate multiple G protein-coupled receptors (S-1-PR 1 to 5), which can regulate multiple cellular functions, including cell migration. The aim of this study is to examine the role of S-1-PR signaling during smooth muscle cell migration in response to S-1-P.

METHODS

Human VSMCs were cultured in vitro. Expression of S-1-PR 1 to 5 was determined in conditions mirroring diabetes (40 mM glucose) and metabolic syndrome (25 mM glucose with 20 μM linoleic acid and 20 μM oleic acid). Linear wound and Boyden microchemotaxis assays of migration were performed in the presence of S-1-P with and without siRNA against S-1-PR 1 to 5. Assays were performed for activation of ERK1/2, p38(MAPK) and JNK.

RESULTS

Human VSMCs express S-1-PR1, S-1-PR2, and S-1-PR3. There was no significant expression of S-1-PR4 and S-1-PR5. The expression of S-1-PR1 and S-1-PR3 is enhanced under high glucose conditions and metabolic syndrome conditions. Migration of VSMC in response to S-1-P is enhanced 2-fold by diabetes and 4-fold by metabolic syndrome. In diabetes, S-1-PR1 expression is enhanced, while S-1-PR2 and S-1-PR3 expression are both maintained. In metabolic syndrome, S-1-PR1 and 3 expressions are enhanced and that of S-1-PR2 is reduced. siRNA to S-1-PR1 results in a 2-fold reduction in S-1-P-mediated cell migration under all conditions. siRNA to S-1-PR2 enhanced cell migration only under normal conditions, while siRNA S-1-PR3 decreased migration in metabolic syndrome only. Down-regulation of S-1-PR1 reduced ERK1/2 activation in response to S-1-P, while that of S-1-PR2 had no effect under normal conditions. In diabetes, down-regulation of S-1-PR1 reduced activation of all three MAPKs. In metabolic syndrome, down-regulation of S-1-PR1 and S-1-PR3 reduced activation of all three MAPKs.

CONCLUSION

S-1-PR 1, 2, and 3 regulate human VSMC migration and their expression level and function are modulated by conditions simulating diabetes and metabolic syndrome.

Sphingosine-1-phosphate receptor 3 promotes neointimal hyperplasia in mouse iliac-femoral arteries

OBJECTIVE

The objective of this study was to define a role for sphingosine-1-phosphate receptor 3 (S1PR3) in intimal hyperplasia.

METHODS AND RESULTS

A denudation model of the iliac-femoral artery in wild-type and S1PR3-null mice was used to define a role for S1PR3 in the arterial injury response because we found in humans and mice that expression of S1PR3 was higher in these arteries compared with carotid arteries. At 28 days after surgery, wild-type arteries formed significantly larger lesions than S1PR3-null arteries. Bromodeoxyuridine labeling experiments demonstrated that on injury, wild-type arteries exhibited higher medial as well as intimal proliferation than S1PR3-null arteries. Because S1PR3 expression in vitro was low, we expressed S1PR3 in S1PR3-null smooth muscle cells (SMCs) using retroviral-mediated gene transfer to study the effects of S1PR3 on cell functions and signaling. SMCs expressing S1PR3, but not vector-transfected controls, responded to sphingosine-1-phosphate stimulation with activation of Rac, Erk, and Akt. SMCs expressing S1PR3 also migrated more.

CONCLUSIONS

In humans and mice, S1PR3 expression was higher in iliac-femoral arteries compared with carotid arteries. S1PR3 promoted neointimal hyperplasia on denudation of iliac-femoral arteries in mice, likely by stimulating cell migration and proliferation through activation of signaling pathways involving Erk, Akt, and Rac.

Matrix metalloproteinase inhibitors as investigative tools in the pathogenesis and management of vascular disease

Matrix metalloproteinases (MMPs) are proteolytic enzymes that degrade various components of the extracellular matrix (ECM). MMPs could also regulate the activity of several non-ECM bioactive substrates and consequently affect different cellular functions. Members of the MMPs family include collagenases, gelatinases, stromelysins, matrilysins, membrane-type MMPs, and others. Pro-MMPs are cleaved into active MMPs, which in turn act on various substrates in the ECM and on the cell surface. MMPs play an important role in the regulation of numerous physiological processes including vascular remodeling and angiogenesis. MMPs may also be involved in vascular diseases such as hypertension, atherosclerosis, aortic aneurysm, and varicose veins. MMPs also play a role in the hemodynamic and vascular changes associated with pregnancy and preeclampsia. The role of MMPs is commonly assessed by measuring their gene expression, protein amount, and proteolytic activity using gel zymography. Because there are no specific activators of MMPs, MMP inhibitors are often used to investigate the role of MMPs in different physiologic processes and in the pathogenesis of specific diseases. MMP inhibitors include endogenous tissue inhibitors (TIMPs) and pharmacological inhibitors such as zinc chelators, doxycycline, and marimastat. MMP inhibitors have been evaluated as diagnostic and therapeutic tools in cancer, autoimmune disease, and cardiovascular disease. Although several MMP inhibitors have been synthesized and tested both experimentally and clinically, only one MMP inhibitor, i.e., doxycycline, is currently approved by the Food and Drug Administration. This is mainly due to the undesirable side effects of MMP inhibitors especially on the musculoskeletal system. While most experimental and clinical trials of MMP inhibitors have not demonstrated significant benefits, some trials still showed promising results. With the advent of new genetic and pharmacological tools, disease-specific MMP inhibitors with fewer undesirable effects are being developed and could be useful in the management of vascular disease.

Pharmacological relevance and potential of sphingosine 1-phosphate in the vascular system

Sphingosine-1-phosphate (S1P) was identified as a crucial molecule for regulating immune responses, inflammatory processes as well as influencing the cardiovascular system. S1P mediates differentiation, proliferation and migration during vascular development and homoeostasis. S1P is a naturally occurring lipid metabolite and is present in human blood in nanomolar concentrations. S1P is not only involved in physiological but also in pathophysiological processes. Therefore, this complex signalling system is potentially interesting for pharmacological intervention. Modulation of the system might influence inflammatory, angiogenic or vasoregulatory processes. S1P activates G-protein coupled receptors, namely S1P(1-5) , whereas only S1P(1-3) is present in vascular cells. S1P can also act as an intracellular signalling molecule. This review highlights the pharmacological potential of S1P signalling in the vascular system by giving an overview of S1P-mediated processes in endothelial cells (ECs) and vascular smooth muscle cells (VSMCs). After a short summary of S1P metabolism and signalling pathways, the role of S1P in EC and VSMC proliferation and migration, the cause of relaxation and constriction of arterial blood vessels, the protective functions on endothelial apoptosis, as well as the regulatory function in leukocyte adhesion and inflammatory responses are summarized. This is followed by a detailed description of currently known pharmacological agonists and antagonists as new tools for mediating S1P signalling in the vasculature. The variety of effects influenced by S1P provides plenty of therapeutic targets currently under investigation for potential pharmacological intervention.

SRC regulates sphingosine-1-phosphate mediated smooth muscle cell migration

BACKGROUND

Sphingosine-1-phosphate (S-1-P) is a bioactive sphingolipid released from activated platelets at sites of arterial injury that stimulates migration of smooth muscle cells (SMC). The kinase src is a significant focal point in transmembrane signaling. This study examines the role of src during smooth muscle cell migration in response to S-1-P.

METHODS

Human coronary arterial SMCs were cultured in vitro. Boyden microchemotaxis assays of migration were performed in response to S-1-P in the presence and absence the src inhibitor (PP2, 10 μM) and a dominant negative src construct (DNsrc). siRNA to S-1-P receptors was used to down-regulate the S-1-P receptors. Western blotting was performed for src and MAPK phosphorylation.

RESULTS

Inhibition of src with PP2 but not PP3 partially blocked S-1-P-mediated cell migration. S-1-P induced time-dependent activation of src, which was inhibited by PP2 and adenoviral DNsrc. PP3 or an empty vector had no effect. Activation of src by S-1-P was inhibited by siRNA to S-1-PR1 and S-1-PR3 but not by S-1-PR2. When the VSMC were transfected with adenovirus containing βARK(CT), an inhibitor to Gβγ, src activation was significantly attenuated. Src inhibition with PP2 reduced p38(MAPK) and JNK activation but did not alter ERK1/2 activation.

CONCLUSION

S-1-P mediated VSMC migration is modulated by a G-protein-coupled src pathway partially through src-mediated p38(MAPK) and JNK signaling and requires S-1-PR1 and S-1-PR3 receptors.

Muscle degeneration in neuraminidase 1-deficient mice results from infiltration of the muscle fibers by expanded connective tissue

Neuraminidase 1 (NEU1) regulates the catabolism of sialoglycoconjugates in lysosomes. Congenital NEU1 deficiency in children is the basis of sialidosis, a severe neurosomatic disorder in which patients experience a broad spectrum of clinical manifestations varying in the age of onset and severity. Osteoskeletal deformities and muscle hypotonia have been described in patients with sialidosis. Here we present the first comprehensive analysis of the skeletal muscle pathology associated with loss of Neu1 function in mice. In this animal model, skeletal muscles showed an expansion of the epimysial and perimysial spaces, associated with proliferation of fibroblast-like cells and abnormal deposition of collagens. Muscle fibers located adjacent to the expanded connective tissue underwent extensive invagination of their sarcolemma, which resulted in the infiltration of the fibers by fibroblast-like cells and extracellular matrix, and in their progressive cytosolic fragmentation. Both the expanded connective tissue and the juxtaposed infiltrated muscle fibers were strongly positive for lysosomal markers and displayed increased proteolytic activity of lysosomal cathepsins and metalloproteinases. These combined features could lead to abnormal remodeling of the extracellular matrix that could be responsible for sarcolemmal invagination and progressive muscle fiber degeneration, ultimately resulting in an overt atrophic phenotype. This unique pattern of muscle damage, which has never been described in any myopathy, might explain the neuromuscular manifestations reported in patients with the type II severe form of sialidosis. More broadly, these findings point to a potential role of NEU1 in cell proliferation and extracellular matrix remodeling.

Sphingosine 1-phosphate: a regulator of arterial lesions

Sphingosine-1 phosphate (S1P) is a bioactive sphingolipid that is critical in the development of blood vessels, and in the adult regulates vascular functions including vascular tone, endothelial integrity, and angiogenesis. Further, S1P may regulate arterial lesions in disease and after injury by controlling leukocyte recruitment and smooth muscle cell functions.

Regulation of blood and vascular cell function by bioactive lysophospholipids

Lysophosphatidic acid (LPA), its sphingolipid homolog sphingosine 1-phosphate (S1P) and several other related molecules constitute a family of bioactive lipid phosphoric acids that function as receptor-active mediators with roles in cell growth, differentiation, inflammation, immunomodulation, apoptosis and development. LPA and S1P are present in physiologically relevant concentrations in the circulation. In isolated cell culture systems or animal models, these lipids exert a range of effects that suggest that S1P and LPA could play important roles in maintaining normal vascular homeostasis and in vascular injury responses. LPA and S1P act on a series of G protein-coupled receptors, and LPA may also be an endogenous regulator of PPARgamma activity. In this review, we discuss potential roles for lysolipid signaling in the vasculature and mechanisms by which these bioactive lipids could contribute to cardiovascular disease.

Sphingosine-1-phosphate regulates RGS2 and RGS16 mRNA expression in vascular smooth muscle cells

Regulator of G protein signalling (RGS) protein expression is altered under growth promoting conditions in vascular smooth muscle cells (VSMCs). Since sphingosine-1-phosphate (S1P) is an important growth stimulatory factor, we investigated whether stimulation of VSMCs with S1P results in alterations in mRNA expression levels of several RGS proteins and which signalling components are involved. VSMCs were stimulated with S1P and mRNA expression levels of RGS2, RGS3, RGS4, RGS5 and RGS16 were measured by real-time polymerase chain reaction. S1P caused a time-dependent up-regulation of RGS2 and RGS16 mRNA expression. FTY720-P, a S1P(1)/S1P(3-5) agonist, did not regulate RGS2 mRNA levels although it did up-regulate RGS16 mRNA expression. Pertussis toxin treatment revealed that the S1P-induced RGS16 expression was G(i/o)-dependent whereas up-regulation of RGS2 mRNA was not. Phosphatidylinositol 3-kinase, protein kinase C and mitogen-activated protein kinase kinase apparently were not involved in the S1P-induced up-regulation of both RGS proteins. The present study demonstrates that S1P induces RGS2 and RGS16 mRNA expression but uses distinct S1P receptor subtypes and signalling pathways to regulate expression of these RGS proteins.

Sphingosine-1-phosphate receptor subtypes differentially regulate smooth muscle cell phenotype

OBJECTIVE

The role of sphingosine-1-phosphate (S1P) receptors in acute vascular injury and smooth muscle cell (SMC) phenotypic modulation is not completely resolved.

METHODS AND RESULTS

S1P receptor antagonists were used to test the hypothesis that specific S1P receptor subtypes differentially regulate SMC phenotypic modulation. In response to acute balloon injury of the rat carotid artery, S1P1/S1P3 receptor mRNA levels were transiently increased at 48 hours whereas S1P2 receptor expression was decreased. S1P2 expression was reinduced and increased at 7 to 10 days postinjury. Daily intraperitoneal injection of the S1P1/S1P3 antagonist VPC44116 decreased neointimal hyperplasia by approximately 50%. In vitro, pharmacological inhibition of S1P1/S1P3 receptors with VPC25239 attenuated S1P-induced proliferation of rat aortic SMCs. Conversely, inhibition of S1P2 with JTE013 potentiated S1P-induced proliferation. Inhibition of S1P1/S1P3 resulted in S1P-induced activation of the SMC differentiation marker genes SMalpha-actin and SMMHC, whereas inhibition of S1P2 attenuated this response. S1P2-dependent activation of SMalpha-actin and SMMHC was shown to be mediated by L-type voltage-gated Ca(2+) channels and subsequent RhoA/Rho kinase-dependent SRF enrichment of CArG box promoter regions.

CONCLUSIONS

Results provide evidence that S1P1/S1P3 receptors promote, whereas S1P2 receptors antagonize, SMC proliferation and phenotypic modulation in vitro in response to S1P, or in vivo after vascular injury.

The critical role of the intrinsic VSMC proliferation and death programs in injury-induced neointimal hyperplasia

Postangioplasty and in-stent restenosis remain ominous problems in percutaneous coronary intervention where good animal models of restenosis proneness and resistance are needed. We accidentally discovered that the carotid arteries (CAs) of the Harlan and Sasco substrains of Sprague-Dawley rats display drastically different restenosis phenotypes following balloon-induced endothelial denudation. When subjected to balloon injury, Sasco CAs exhibited significantly larger neointimal mass than did Harlan CAs at both days 14 and 32, as evidenced by a higher intima-to-media ratio and a greater number of intimal cells in Sasco CAs. This was due to a greater cell proliferation and to a less vigorous apoptosis of Sasco neointima, as assessed by 5-bromo-2'-deoxyuridine and terminal deoxynucleotidyl transferase-deoxyuridine nick-end labeling staining, respectively. At a cellular level, whereas vascular smooth muscle cells (VSMCs) isolated from Sasco and Harlan CAs were identical in morphology and in propensity to migrate, Sasco VSMCs proliferated more robustly and died far less, suggesting that under the exact same microenvironment, Sasco and Harlan VSMCs respond to growth and noxious stimuli in a drastically different fashion and that Sasco's significantly more robust neointimal proliferation after vascular injury in vivo can be accounted for by these intrinsic differences in VSMCs of these substrains in vitro. Sasco and Harlan Sprague-Dawley rats as well as VSMCs from these rats will prove to be powerful tools to study genes involved in the pathogenesis of restenosis.