Signalling pathways regulating galactosaminoglycan synthesis and structure in vascular smooth muscle: Implications for lipoprotein binding and atherosclerosis

Mechanisms modulating foam cell formation in the arterial intima: exploring new therapeutic opportunities in atherosclerosis

In recent years, the role of macrophages as the primary cell type contributing to foam cell formation and atheroma plaque development has been widely acknowledged. However, it has been long recognized that diffuse intimal thickening (DIM), which precedes the formation of early fatty streaks in humans, primarily consists of lipid-loaded smooth muscle cells (SMCs) and their secreted proteoglycans. Recent studies have further supported the notion that SMCs constitute the majority of foam cells in advanced atherosclerotic plaques. Given that SMCs are a major component of the vascular wall, they serve as a significant source of microvesicles and exosomes, which have the potential to regulate the physiology of other vascular cells. Notably, more than half of the foam cells present in atherosclerotic lesions are of SMC origin. In this review, we describe several mechanisms underlying the formation of intimal foam-like cells in atherosclerotic plaques. Based on these mechanisms, we discuss novel therapeutic approaches that have been developed to regulate the generation of intimal foam-like cells. These innovative strategies hold promise for improving the management of atherosclerosis in the near future.

Uremic Toxin-Induced Exosome-like Extracellular Vesicles Contain Enhanced Levels of Sulfated Glycosaminoglycans which Facilitate the Interaction with Very Small Superparamagnetic Iron Oxide Particles

Uremic toxins exert pathophysiological effects on cells and tissues, such as the generation of a pro-calcifying subtype of exosome-like extracellular vesicles (EVs) in vascular cells. Little is known about the effects of the toxins on the surface structure of EVs. Thus, we studied the effects of uremic toxins on the abundance of sulfated glycosaminoglycans (GAGs) in EVs, and the implications for binding of ligands such as very small superparamagnetic iron oxide particles (VSOPs) which could be of relevance for radiological EV-imaging. Vascular cells were treated with the uremic toxins NaH2PO4 and a mixture of urea and indoxyl sulfate. Uremia in rats was induced by adenine feeding. EVs were isolated from culture supernatants and plasma of rats. By proton T1-relaxometry, magnetic particle spectroscopy, and analysis of genes, proteins, and GAG-contents, we analyzed the roles of GAGs in the ligand binding of EVs. By influencing GAG-associated genes in host cells, uremic toxins induced higher GAG contents in EVs, particularly of sulfated chondroitin sulfate and heparan sulfate chains. EVs with high GAG content interacted stronger with VSOPs compared to control ones. This was confirmed by experiments with GAG-depleted EVs from genetically modified CHO cells and with uremic rat-derived EVs. Mechanistically, uremic toxin-induced PI3K/AKT-signaling and expression of the sulfate transporter SLC26A2 in host cells contributed to high GAG contents in EVs. In conclusion, uremic conditions induce enhanced GAG contents in EVs, which entails a stronger interaction with VSOPs. VSOPs might be suitable for radiological imaging of EVs rich in GAGs.

Gua Lou Er Chen decoction attenuates atherosclerosis by reducing proteoglycans accumulation and inflammation

BACKGROUND

Proteoglycans (PGs) accumulation and inflammation are two interactional pathological processes of atherosclerosis (AS). Up to now, there is no ideal drug for decreasing these pathological changes. Gua Lou Er Chen decoction (GED) has been used to treat AS for several years. However, if GED could treat AS through reducing PGs accumulation and inflammation remains unknown.

PURPOSE

This study was designed to illustrate whether GED could attenuate AS by reducing chondroitin sulphate proteoglycan (CSPG) expressions and alleviating inflammation.

METHODS

In vivo study, apolipoprotein E-deficient mice were fed a high-fat diet to induce AS. In vitro study, oxidised low-density lipoprotein (ox-LDL) and tumour necrosis factor (TNF)-α were used to induce proteoglycans accumulation and inflammation changes of vascular smooth muscle cells (VSMCs) and RAW264.7 macrophages. Oil Red O was used to stain mouse aortic lipid plaque. Haematoxylin eosin staining was used to assess the pathological changes of aortic valve and thoracic aorta. Specialised kits were used to identify blood lipids and sGAGs. Immunofluorescence and immunohistochemistry was used to identify aortic valve CSPG and versican. Western blotting, enzyme-linked immunosorbent assay and quantitative reverse transcription-polymerase chain reaction were used to measure versican, interleukin (IL)-6, TNF-α, and chondroitin sulphate (CS) synthetase expressions. CCK-8 was used to measure the cells proliferation.

RESULTS

In vivo experiments revealed that GED significantly improved hyperlipidemia, lowered lipid plaque deposition in the aorta, and increased plaque stability of AS mice. In addition, further studies revealed that GED lowered the sGAGs, CSPG, and versican levels and down-regulated CS synthetase and inflammatory factor expressions. In vitro experiments revealed that GED decreased TNF-α expression in the RAW264.7 macrophage supernatant stimulated by ox-LDL; decreased versican, CS-related synthetase, and IL-6 expressions; reduced VSMC proliferation stimulated by ox-LDL; down-regulated sGAG and versican expressions of VSMCs stimulated by TNF-α.

CONCLUSION

Our results demonstrated that GED could attenuate AS by reducing hyperlipidemia, hyper-expression of CSPG, and inflammation. This study might provide a novel insight into the development of innovative drug for AS.

Gαq Is the Specific Mediator of PAR-1 Transactivation of Kinase Receptors in Vascular Smooth Muscle Cells

AIMS

G protein-coupled receptor (GPCR) transactivation of kinase receptors greatly expands the actions attributable to GPCRs. Thrombin, via its cognate GPCR, protease-activated receptor (PAR)-1, transactivates tyrosine and serine/threonine kinase receptors, specifically the epidermal growth factor receptor and transforming growth factor-β receptor, respectively. PAR-1 transactivation-dependent signalling leads to the modification of lipid-binding proteoglycans involved in the retention of lipids and the development of atherosclerosis. The mechanisms of GPCR transactivation of kinase receptors are distinct. We aimed to investigate the role of proximal G proteins in transactivation-dependent signalling.

MAIN METHODS

Using pharmacological and molecular approaches, we studied the role of the G⍺ subunits, G⍺q and G⍺11, in the context of PAR-1 transactivation-dependent signalling leading to proteoglycan modifications.

KEY FINDINGS

Pan G⍺q subunit inhibitor UBO-QIC/FR900359 inhibited PAR-1 transactivation of kinase receptors and proteoglycans modification. The G⍺q/11 inhibitor YM254890 did not affect PAR-1 transactivation pathways. Molecular approaches revealed that of the two highly homogenous G⍺q members, G⍺q and G⍺11, only the G⍺q was involved in regulating PAR-1 mediated proteoglycan modification. Although G⍺q and G⍺11 share approximately 90% homology at the protein level, we show that the two isoforms exhibit different functional roles.

SIGNIFICANCE

Our findings may be extrapolated to other GPCRs involved in vascular pathology and highlight the need for novel pharmacological tools to assess the role of G proteins in GPCR signalling to expand the preeminent position of GPCRs in human therapeutics.

Endothelin-1 mediated glycosaminoglycan synthesizing gene expression involves NOX-dependent transactivation of the transforming growth factor-β receptor

G protein-coupled receptor (GPCR) agonist endothelin-1 (ET-1) through transactivation of the transforming growth factor (TGF) β receptor (TGFBR1) stimulates glycosaminoglycan (GAG) elongation on proteoglycans. GPCR agonists thrombin and lysophosphatidic acid (LPA) via respective receptors transactivate the TGFBR1 via Rho/ROCK dependent pathways however mechanistic insight for ET-1 transactivation of the TGFBR1 remains unknown. NADPH oxidase (NOX) generates reactive oxygen species (ROS) and is a signalling entity implicated in the pathogenesis of many diseases including atherosclerosis. If implicated in this pathway, NOX/ROS would be a potential therapeutic target. In this study, we investigated the involvement of NOX in ET-1/ET receptor-mediated transactivation of TGFBR1 to stimulate mRNA expression of GAG chain synthesizing enzymes chondroitin 4-O-sulfotransferase 1 (C4ST-1) and chondroitin sulfate synthase 1 (ChSy-1). The invitro model used vascular smooth muscle cells that were treated with pharmacological antagonists in the presence and absence of ET-1 or TGF-β. Proteins and phosphoproteins isolated from treated cells were quantified by western blotting and quantitative real-time PCR was used to assess mRNA expression of GAG synthesizing enzymes. In the presence of diphenyliodonium (DPI) (NOX inhibitor), ET-1 stimulated phospho-Smad2C levels were inhibited. ET-1 mediated mRNA expression of GAG synthesizing enzymes C4ST-1 and ChSy-1 was also blocked by TGBFR1 antagonists, SB431542, broad spectrum ET receptor antagonist bosentan, DPI and ROS scavenger N-acetyl-L-cysteine. This work shows that NOX and ROS play an important role in ET-1 mediated transactivation of the TGFBR1 and downstream gene targets associated with GAG chain elongation. As ROS is involved in GPCR to protein tyrosine kinase receptor transactivation, the NOX/ROS axis presents as the first common biochemical target in all GPCR to kinase receptor transactivation signalling.

Akt acts as a switch for GPCR transactivation of the TGF-β receptor type 1

Transforming growth factor (TGF)-β signalling commences with the engagement of TGF-β ligand to cell surface TGF-β receptors (TGFBR) stimulating Smad2 carboxyl-terminal phosphorylation (phospho-Smad2C) and downstream biological responses. In several cell models, G protein-coupled receptors (GPCRs) transactivate the TGF-β receptors type-1 (TGFBR1) leading to phospho-Smad2C, however, we have recently published that in keratinocytes thrombin did not transactivate the TGFBR1. The bulk of TGFBRs reside in the cytosol and in response to protein kinase B (Akt phosphorylation) can translocate to the cell surface increasing the cell's responsiveness to TGF-β. In this study, we investigate the role of Akt in GPCR transactivation of the TGFBR1. We demonstrate that angiotensin II and thrombin do not phosphorylate Smad2C in human vascular smooth muscle cells and in keratinocytes respectively. We used Akt agonist, SC79 to sensitise the cells to Akt and observed that Ang II and thrombin phosphorylate Smad2C via Akt/AS160-dependent pathways. We show that SC79 rapidly translocates TGFBRs to the cell surface thus increasing the cell's response to the GPCR agonist. These findings highlight novel mechanistic insight for the role of Akt in GPCR transactivation of the TGFBR1.

YY-11, a camel milk-derived peptide, inhibits TGF-β-mediated atherogenic signaling in human vascular smooth muscle cells

Atherosclerosis, the major underlying pathology of cardiovascular disease, commences with the binding and trapping of lipids on modified proteoglycans, with hyperelongated glycosaminoglycan chains. Transforming growth factor (TGF)-β stimulates glycosaminoglycan elongation in vascular smooth muscle cells. We have recently shown that this TGF-β signaling pathway involves reactive oxygen species (ROS). YY-11 is a dodecapeptide derived from camel milk and it has antioxidant activity. We have investigated the role of YY-11 in blocking ROS signaling and downstream atherogenic responses. YY-11 inhibited TGF-β stimulated ROS production and inhibited the expression of genes for glycosaminoglycan chain elongation as a component of an in vitro model of atherosclerosis. This study provides a biochemical mechanism for the role of camel milk as a potential nutritional product to contribute to the worldwide amelioration of cardiovascular disease. PRACTICAL APPLICATIONS: The identification of readily accessible foods with antioxidant properties would provide a convenient and cost-effective approach community wide reducing oxidative stress induced pathologies such as atherosclerosis. We demonstrate that camel milk-derived peptide is an antioxidant that can inhibit growth factor-mediated proteoglycan modification in vitro. As proteoglycan modification is being recognized as one of the earliest atherogenic responses, these data support the notion of camel milk as a suitable nutritional product to contribute to the prevention of early stage of atherosclerosis development.

Recent Advances in the Development of Theranostic Nanoparticles for Cardiovascular Diseases

Cardiovascular disease (CVD) is the leading cause of death worldwide. CVD includes a group of disorders of the heart and blood vessels such as myocardial infarction, ischemic heart, ischemic injury, injured arteries, thrombosis and atherosclerosis. Amongst these, atherosclerosis is the dominant cause of CVD and is an inflammatory disease of the blood vessel wall. Diagnosis and treatment of CVD remain the main challenge due to the complexity of their pathophysiology. To overcome the limitations of current treatment and diagnostic techniques, theranostic nanomaterials have emerged. The term "theranostic nanomaterials" refers to a multifunctional agent with both therapeutic and diagnostic abilities. Theranostic nanoparticles can provide imaging contrast for a diversity of techniques such as magnetic resonance imaging (MRI), positron emission tomography (PET) and computed tomography (CT). In addition, they can treat CVD using photothermal ablation and/or medication by the drugs in nanoparticles. This review discusses the latest advances in theranostic nanomaterials for the diagnosis and treatment of CVDs according to the order of disease development. MRI, CT, near-infrared spectroscopy (NIR), and fluorescence are the most widely used strategies on theranostics for CVDs detection. Different treatment methods for CVDs based on theranostic nanoparticles have also been discussed. Moreover, current problems of theranostic nanoparticles for CVDs detection and treatment and future research directions are proposed.

Endothelial Dysfunction and Cardiovascular Disease: History and Analysis of the Clinical Utility of the Relationship

The endothelium is the single-cell monolayer that lines the entire vasculature. The endothelium has a barrier function to separate blood from organs and tissues but also has an increasingly appreciated role in anti-coagulation, vascular senescence, endocrine secretion, suppression of inflammation and beyond. In modern times, endothelial cells have been identified as the source of major endocrine and vaso-regulatory factors principally the dissolved lipophilic vosodilating gas, nitric oxide and the potent vascular constricting G protein receptor agonists, the peptide endothelin. The role of the endothelium can be conveniently conceptualized. Continued investigations of the mechanism of endothelial dysfunction will lead to novel therapies for cardiovascular disease. In this review, we discuss the impact of endothelial dysfunction on cardiovascular disease and assess the clinical relevance of endothelial dysfunction.

ClC-3: A Novel Promising Therapeutic Target for Atherosclerosis

Chloride channel 3 (ClC-3), a Cl^-/H⁺ antiporter, has been well established as a member of volume-regulated chloride channels (VRCCs). ClC-3 may be a crucial mediator for activating inflammation-associated signaling pathways by regulating protein phosphorylation. A growing number of studies have indicated that ClC-3 overexpression plays a crucial role in mediating increased plasma low-density lipoprotein levels, vascular endothelium dysfunction, pro-inflammatory activation of macrophages, hyper-proliferation and hyper-migration of vascular smooth muscle cells (VSMCs), as well as oxidative stress and foam cell formation, which are the main factors responsible for atherosclerotic plaque formation in the arterial wall. In the present review, we summarize the molecular structures and classical functions of ClC-3. We further discuss its emerging role in the atherosclerotic process. In conclusion, we explore the potential role of ClC-3 as a therapeutic target for atherosclerosis.

Chondroitin Sulfate N-acetylgalactosaminyltransferase-2 Impacts Foam Cell Formation and Atherosclerosis by Altering Macrophage Glycosaminoglycan Chain

OBJECTIVE

Chondroitin sulfate proteoglycans are the primary constituents of the macrophage glycosaminoglycan and extracellular microenvironment. To examine their potential role in atherogenesis, we investigated the biological importance of one of the chondroitin sulfate glycosaminoglycan biosynthesis gene, ChGn-2 (chondroitin sulfate N-acetylgalactosaminyltransferase-2), in macrophage foam cell formation. Approach and Results: ChGn-2-deficient mice showed decreased and shortened glycosaminoglycans. ChGn-2^-/-/LDLr^-/- (low-density lipoprotein receptor) mice generated less atherosclerotic plaque after being fed with Western diet despite exhibiting a metabolic phenotype similar to that of the ChGn-2^+/+/LDLr^-/- littermates. We demonstrated that in macrophages, ChGn-2 expression was upregulated in the presence of oxLDL (oxidized LDL), and glycosaminoglycan was substantially increased. Foam cell formation was significantly altered by ChGn-2 in both mouse peritoneal macrophages and the RAW264.7 macrophage cell line. Mechanistically, ChGn-2 enhanced oxLDL binding on the cell surface, and as a consequence, CD36-an important macrophage membrane scavenger receptor-was differentially regulated.

CONCLUSIONS

ChGn-2 alteration on macrophages conceivably influences LDL accumulation and subsequently accelerates plaque formation. These results collectively suggest that ChGn-2 is a novel therapeutic target amenable to clinical translation in the future. Graphic Abstract: A graphic abstract is available for this article.

Lysophosphatidic acid receptor 5 transactivation of TGFBR1 stimulates the mRNA expression of proteoglycan synthesizing genes XYLT1 and CHST3

Lysophosphatidic acid (LPA) via transactivation dependent signalling pathways contributes to a plethora of physiological and pathophysiological responses. In the vasculature, hyperelongation of glycosaminoglycan (GAG) chains on proteoglycans leads to lipid retention in the intima resulting in the early pathogenesis of atherosclerosis. Therefore, we investigated and defined the contribution of transactivation dependent signalling in LPA mediated GAG chain hyperelongation in human vascular smooth muscle cells (VSMCs). LPA acting via the LPA receptor 5 (LPAR5) transactivates the TGFBR1 to stimulate the mRNA expression of GAG initiation and elongation genes xylosyltransferase-1 (XYLT1) and chondroitin 6-sulfotransferase-1 (CHST3), respectively. We found that LPA stimulates ROS and Akt signalling in VSMCs, however they are not associated in LPAR5 transactivation of the TGFBR1. We observed that LPA via ROCK dependent pathways transactivates the TGFBR1 to stimulate genes associated with GAG chain elongation. We demonstrate that GPCR transactivation of the TGFBR1 occurs via a universal biochemical mechanism and the identified effectors represent potential therapeutic targets to inhibit pathophysiological effects of GPCR transactivation of the TGFBR1.

Artemisinin inhibits glycosaminoglycan chain synthesizing gene expression but not proliferation of human vascular smooth muscle cells

Pleotropic growth factor, transforming growth factor (TGF)-β drives the modification and elongation of glycosaminoglycan (GAG) chains on proteoglycans. Hyperelongated GAG chains bind and trap lipoproteins in the intima leading to the formation of atherosclerotic plaques. We have identified that phosphorylation of Smad2 linker region drives GAG chain modification. The identification of an inhibitor of Smad2 linker region phosphorylation and GAG chain modification signifies a potential therapeutic for cardiovascular diseases. Artemisinin renowned for its potent anti-malarial effects possesses a broad range of biological effects. Our aim was to characterise the anti-atherogenic role of artemisinin in vascular smooth muscle cells (VSMCs). We demonstrate that TGF-β mediated Smad2 linker region phosphorylation and GAG chain elongation was attenuated by artemisinin; however, we observed no effect on VSMC proliferation. Our data demonstrates the potential for artemisinin to be developed as a therapy to inhibit the development of atherosclerosis by prevention of lipid deposition in the vessel wall without affecting the proliferation of VSMCs.

CD36 in Atherosclerosis: Pathophysiological Mechanisms and Therapeutic Implications

PURPOSE OF REVIEW

Atherosclerosis is a chronic disease characterized by lipid retention and inflammation in the artery wall. The retention and oxidation of low-density lipoprotein (LDL) in sub-endothelial space play a critical role in atherosclerotic plaque formation and destabilization. Oxidized LDL (ox-LDL) and other modified LDL particles are avidly taken up by endothelial cells, smooth muscle cells, and macrophages mainly through several scavenger receptors, including CD36 which is a class B scavenger receptor and membrane glycoprotein.

RECENT FINDINGS

Animal studies performed on CD36-deficient mice suggest that deficiency of CD36 prevents the development of atherosclerosis, though with some debate. CD36 serves as a signaling hub protein at the crossroad of inflammation, lipid metabolism, and fatty acid metabolism. In addition, the level of soluble CD36 (unattached to cells) in the circulating blood was elevated in patients with atherosclerosis and other metabolic disorders. We performed a state-of-the-art review on the structure, ligands, functions, and regulation of CD36 in the context of atherosclerosis by focusing on the pathological role of CD36 in the dysfunction of endothelial cells, smooth muscle cells, monocytes/macrophages, and platelets. Finally, we highlight therapeutic possibilities to target CD36 expression/activity in atherosclerosis.

The Role of Toll-like Receptors in Atherothrombotic Cardiovascular Disease

Toll-like receptors (TLRs) are dominant components of the innate immune system. Activated by both pathogen-associated molecular patterns and damage-associated molecular patterns, TLRs underpin the pathology of numerous inflammation related diseases that include not only immune diseases, but also cardiovascular disease (CVD), diabetes, obesity, and cancers. Growing evidence has demonstrated that TLRs are involved in multiple cardiovascular pathophysiologies, such as atherosclerosis and hypertension. Specifically, a trial called the Canakinumab Anti-inflammatory Thrombosis Outcomes Study showed the use of an antibody that neutralizes interleukin-1β, reduces the recurrence of cardiovascular events, demonstrating inflammation as a therapeutic target and also the research value of targeting the TLR system in CVD. In this review, we provide an update of the interplay between TLR signaling, inflammatory mediators, and atherothrombosis, with an aim to identify new therapeutic targets for atherothrombotic CVD.

Toll-like Receptor 4 Stimulates Gene Expression via Smad2 Linker Region Phosphorylation in Vascular Smooth Muscle Cells

Atherosclerosis begins in the vessel wall with the retention of low density lipoproteins to modified proteoglycans with hyperelongated glycosaminoglycan (GAG) chains. Bacterial infections produce endotoxins such as lipopolysaccharide that exacerbate the outcome of atherosclerosis by generating a heightened state of inflammation. Lipopolysaccharide (LPS) via its toll-like receptor (TLR) is well-known for its role in mediating an inflammatory response in the body. Emerging evidence demonstrates that TLRs are involved in regulating vascular functions. In this study we sought to investigate the role of LPS in proteoglycan modification and GAG chain elongation, and we hypothesize that LPS will signal via Smad2 dependent pathways to regulate GAG chain elongation. The in vitro model used human aortic vascular smooth muscle cells. GAG gene expression was assessed by quantitative real-time polymerase chain reaction. Western blotting was performed using whole-cell protein lysates to assess the signaling pathway. LPS via TLR4 stimulates the expression of GAG synthesizing enzymes to an equal extent to traditional cardiovascular agonists. LPS phosphorylates the Smad2 linker region via TAK-1/MAPK dependent pathways which correlated with genes associated with GAG chain initiation and elongation. The well-characterized role of LPS in inflammation and our data on GAG gene expression demonstrates that GAG chain elongation is the earliest marker of the inflammatory cascade in atherosclerosis development.

Smad linker region phosphorylation is a signalling pathway in its own right and not only a modulator of canonical TGF-β signalling

Transforming growth factor (TGF)-β signalling pathways are intensively investigated because of their diverse association with physiological and pathophysiological states. Smad transcription factors are the key mediators of TGF-β signalling. Smads can be directly phosphorylated in the carboxy terminal by the TGF-β receptor or in the linker region via multiple intermediate serine/threonine kinases. Growth factors in addition to hormones and TGF-β can activate many of the same kinases which can phosphorylate the Smad linker region. Historically, Smad linker region phosphorylation was shown to prevent nuclear translocation of Smads and inhibit TGF-β signalling pathways; however, it was subsequently shown that Smad linker region phosphorylation can be a driver of gene expression. This review will cover the signalling pathways of Smad linker region phosphorylation that drive the expression of genes involved in pathology and pathophysiology. The role of Smad signalling in cell biology is expanding rapidly beyond its role in TGF-β signalling and many signalling paradigms need to be re-evaluated in terms of Smad involvement.

GPCR transactivation signalling in vascular smooth muscle cells: role of NADPH oxidases and reactive oxygen species

The discovery and extension of G-protein-coupled receptor (GPCR) transactivation-dependent signalling has enormously broadened the GPCR signalling paradigm. GPCRs can transactivate protein tyrosine kinase receptors (PTKRs) and serine/threonine kinase receptors (S/TKRs), notably the epidermal growth factor receptor (EGFR) and transforming growth factor-β type 1 receptor (TGFBR1), respectively. Initial comprehensive mechanistic studies suggest that these two transactivation pathways are distinct. Currently, there is a focus on GPCR inhibitors as drug targets, and they have proven to be efficacious in vascular diseases. With the broadening of GPCR transactivation signalling, it is therefore important from a therapeutic perspective to find a common transactivation pathway of EGFR and TGFBR1 that can be targeted to inhibit complex pathologies activated by the combined action of these receptors. Reactive oxygen species (ROS) are highly reactive molecules and they act as second messengers, thus modulating cellular signal transduction pathways. ROS are involved in different mechanisms of GPCR transactivation of EGFR. However, the role of ROS in GPCR transactivation of TGFBR1 has not yet been studied. In this review, we will discuss the involvement of ROS in GPCR transactivation-dependent signalling.

Mechanisms of PAR-1 mediated kinase receptor transactivation: Smad linker region phosphorylation

Protease activated receptors (PARs) transactivate both epidermal growth factor receptors (EGFR) and transforming growth factor (TGF)-β receptors (TGFBR1) in vascular smooth muscle leading to the increased expression of genes (CHST11 and CHSY1) which are rate limiting for the enzymes that mediate hyperelongation of glycosaminoglycan (GAG) chains on the lipid-binding proteoglycan, biglycan. This is an excellent model to investigate mechanisms of transactivation as the processes are biochemically distinct. EGFR transactivation is dependent on the classical matrix metalloprotease (MMP) based triple membrane bypass mechanism and TGFBR1 transactivation is dependent on Rho/ROCK signalling and integrins. We have shown that all kinase receptor signalling is targeted towards phosphorylation of the linker region of the transcription factor, Smad2. We investigated the mechanisms of thrombin mediated kinase receptor transactivation signalling using anti-phospho antibodies and Western blotting and gene expression by RT-PCR. Thrombin stimulation of phospho-Smad2 (Ser 245/250/255) and of phospho-Smad2(Thr220) via EGFR transactivation commences quickly and extends out to at least 4 h whereas transactivation via TGFBR1 is delayed for 120 min but also persists for at least 4 h. Signalling of thrombin stimulated Smad linker region phosphorylation is approximately equally inhibited by the MMP inhibitor, GM6001 and the ROCK inhibitor, Y27632, and similarly expression of CHST11 and CHSY1 is approximately equally inhibited by GM6001 and Y27632. The data establishes Smad linker region phosphorylation as a central target of all transactivation signalling of GAG gene expression and thus an upstream kinase may be a target to prevent all transactivation signalling and its pathophysiological consequences.

Low molecule weight fucoidan mitigates atherosclerosis in ApoE (-/-) mouse model through activating multiple signal pathway

Atherosclerosis (AS) is a chronic inflammatory disease, and many factors are implicated in its progression. This work aims to study the preventive effects and the regulatory mechanism of low-molecular-weight fucoidan (LMWF), which is obtained from Saccharina japonica, on the development of AS. Serum biochemical indices and pathological analyses were determined via ELISA, hematoxylin and eosin (HE) and Oil Red O staining. These results indicated that LMWF ameliorated areas with atherosclerotic lesions and had a significant antioxidant effect. Anticoagulant assays showed that LMWF might serve as a potential anticoagulation drug for inhibiting the formation of atherothrombosis. Double immunofluorescence staining illustrated that LMWF inhibited both SMC proliferation and migration and macrophage formation and differentiation. A molecular biology experiment showed that LMWF exhibited an apparent regulatory effect on various signaling pathways. In conclusion, our results revealed that LMWF mitigated AS in the ApoE (-/-) mouse model by activating multiple signal pathways.

Transforming growth factor-β1 mediated CHST11 and CHSY1 mRNA expression is ROS dependent in vascular smooth muscle cells

Transforming growth factor (TGF)-β1 mediates glycosaminoglycan (GAG) chain hyperelongation on secreted proteoglycans and these modifications are associated with increased lipid binding in the vessel wall and the development of atherosclerosis. In vascular smooth muscle cells (VSMCs), TGF-β1 regulated GAG elongation via extracellular signal-regulated kinase (ERK) and p38 as well as Smad2 linker region phosphorylation. In this study, our aim was to identify the TGF-β1 mediated signalling pathway involving reactive oxygen species (ROS) and Smad2 linker region phosphorylation that regulate the mRNA expression of GAG synthesizing enzymes, chondroitin 4-O-sulfotransferase 1 (CHST11) and chondroitin sulfate synthase 1 (CHSY1) which are the rate limiting enzymes involved in GAG chain elongation. Signalling molecules were assessed by western blotting, quantitative real-time PCR was used for analysis of gene expression and intracellular ROS level was measured by a fluorescence based assay. TGF-β1 induced ROS production in VSMCs. Nicotinamide adenine dinucleotide phosphate oxidase (Nox) inhibitors, diphenyleneiodonium (DPI) and apocynin blocked TGF-β1 mediated Smad2 linker region phosphorylation. TGF-β1 treatment increased the mRNA levels of CHST11 and CHSY1. Pharmacological inhibition of Nox blocked TGF-β1 mediated mitogen activated protein kinases (MAPKs) phosphorylation and TGF-β1 stimulated CHST11 and CHSY1 mRNA expression. These findings demonstrated that TGF-β1 mediated expression of CHST11 and CHSY1 can occur via Nox-dependent pathways and Smad2 linker region phosphorylation.

Individual Smad2 linker region phosphorylation sites determine the expression of proteoglycan and glycosaminoglycan synthesizing genes

Growth factors such as thrombin and transforming growth factor (TGF)-β facilitate glycosaminoglycan (GAG) chain hyperelongation on proteoglycans, a phenomenon that increases lipoprotein binding in the vessel wall and the development of atherosclerosis. TGF-β signals via canonical carboxy terminal phosphorylation of R-Smads and also non-canonical linker region phosphorylation of R-Smads. The G protein coupled receptor agonist, thrombin, can transactivate the TGF-β receptor leading to both canonical and non-canonical Smad signalling. Linker region phosphorylation drives the expression of genes for the synthesis of the proteoglycan, biglycan. Proteoglycan synthesis involves core protein synthesis, the initiation of GAG chains and the subsequent elongation of GAG chains. We have explored the relationship between the thrombin stimulated phosphorylation of individual serine and threonine sites in the linker region of Smad2 and the expression of GAG initiation xylosyltransferase-1 (XT-1) and GAG elongation chondroitin 4-sulfotransferase-1 (C4ST-1) and chondroitin synthase-1 (CHSY-1) genes. Thrombin stimulated the phosphorylation of all four target residues (Thr220, Ser245, Ser250 and Ser255 residues) with a similar temporal pattern - phosphorylation was maximal at 15 min (the earliest time point studied) and the level of the phospho-proteins declined thereafter over the following 4 h. Jnk, p38 and PI3K, selectively mediated the phosphorylation of the Thr220 residue whereas the serine residues were variously phosphorylated by multiple kinases. Thrombin stimulated the expression of all three genes - XT-1, C4ST-1 and CHSY-1. The three pathways mediating Thr220 phosphorylation were also involved in the expression of XT-1. The target pathways (excluding Jnk) were involved in the expression of the GAG elongation genes (C4ST-1 and CHSY-1). These findings support the contention that individual Smad linker region phosphorylation sites are linked to the expression of genes for the initiation and elongation of GAG chains on proteoglycans. The context of this work is that a specific inhibitor of GAG elongation represents a potential therapeutic agent for preventing GAG elongation and lipid binding and the results indicate that the specificity of the pathways is such that it might be therapeutically feasible to specifically target GAG elongation without interfering with other physiological processes with which proteoglycans are involved.