Taurine inhibits osteoblastic differentiation of vascular smooth muscle cells via the ERK pathway

Role of irisin in bone diseases

Bone diseases are common among middle-aged and elderly people, and harm to activities of daily living (ADL) and quality of life (QOL) for patients. It is crucial to search for key regulatory factors associated with the development of bone diseases and explore potential therapeutic targets for bone diseases. Irisin is a novel myokine that has been discovered in recent years. Accumulating evidence indicates that irisin has beneficial effects in the treatment of various diseases such as metabolic, cardiovascular and neurological disorders, especially bone-related diseases. Recent studies had shown that irisin plays the role in various bone diseases such as osteoarthritis, osteoporosis and other bone diseases, suggesting that irisin may be a potential molecule for the prevention and treatment of bone diseases. Therefore, in this review, by consulting the related domestic and international literature of irisin and bone diseases, we summarized the specific regulatory mechanisms of irisin in various bone diseases, and provided a systematic theoretical basis for its application in the diagnosis and treatment of the bone diseases.

Mechanical and chemical cues synergistically promote human venous smooth muscle cell osteogenesis through integrin β1-ERK1/2 signaling: A cell model of hemodialysis fistula calcification

Arteriovenous fistula (AVF) is the vascular access of choice for renal replacement therapy. However, AVF is susceptible to calcification with a high prevalence of 40%-65% in chronic hemodialysis patients. Repeated needle puncture for hemodialysis cannulation results in intimal denudation of AVF. We hypothesized that exposure to blood shear stress in the medial layer promotes venous smooth muscle cell (SMC) osteogenesis. While previous studies of shear stress focused on arterial-type SMCs, SMCs isolated from the vein had not been investigated. This study established a venous cell model of AVF using the fluid shear device, combined with a high phosphate medium to mimic the uremic milieu. Osteogenic gene expression of venous SMCs upon mechanical and chemical cues was analyzed in addition to the activated cell signaling pathways. Our findings indicated that upon shear stress and high phosphate environment, mechanical stimulation (shear stress) had an additive effect in up-regulation of an early osteogenic marker, Runx2. We further identified that the integrin β1-ERK1/2 signaling pathway was responsible for the molecular basis of venous SMC osteogenesis upon shear stress exposure. Mitochondrial biogenesis also took part in the early stage of this venopathy pathogenesis, evident by the up-regulated mitochondrial transcription factor A and mitochondrial DNA polymerase γ in venous SMCs. In conclusion, synergistic effects of fluid shear stress and high phosphate induce venous SMC osteogenesis via the ERK1/2 pathway through activating the mechanosensing integrin β1 signaling. The present study identified a promising druggable target for reducing AVF calcification, which deserves further in vivo investigations.

Increased β-adrenergic stimulation augments vascular smooth muscle cell calcification via PKA/CREB signalling

In chronic kidney disease (CKD), hyperphosphatemia promotes medial vascular calcification, a process augmented by osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs). VSMC function is regulated by sympathetic innervation, and these cells express α- and β-adrenergic receptors. The present study explored the effects of β2-adrenergic stimulation by isoproterenol on VSMC calcification. Experiments were performed in primary human aortic VSMCs treated with isoproterenol during control or high phosphate conditions. As a result, isoproterenol dose dependently up-regulated the expression of osteogenic markers core-binding factor α-1 (CBFA1) and tissue-nonspecific alkaline phosphatase (ALPL) in VSMCs. Furthermore, prolonged isoproterenol exposure augmented phosphate-induced calcification of VSMCs. Isoproterenol increased the activation of PKA and CREB, while knockdown of the PKA catalytic subunit α (PRKACA) or of CREB1 genes was able to suppress the pro-calcific effects of isoproterenol in VSMCs. β2-adrenergic receptor silencing or inhibition with the selective antagonist ICI 118,551 blocked isoproterenol-induced osteogenic signalling in VSMCs. The present observations imply a pro-calcific effect of β2-adrenergic overstimulation in VSMCs, which is mediated, at least partly, by PKA/CREB signalling. These observations may support a link between sympathetic overactivity in CKD and vascular calcification.

Uraemic extracellular vesicles augment osteogenic transdifferentiation of vascular smooth muscle cells via enhanced AKT signalling and PiT-1 expression

Extracellular vesicles (EV) function as messengers between endothelial cells (EC) and vascular smooth muscle cells (VSMC). Since chronic kidney disease (CKD) increases the risk for vascular calcifications, we investigated whether EV derived from uraemic milieu‐stimulated EC and derived from uraemic rats impact the osteogenic transdifferentiation/calcification of VSMC. For that purpose, human EC were treated with urea and indoxyl sulphate or left untreated. Experimental uraemia in rats was induced by adenine feeding. ‘Uraemic’ and control EV (EV^UR; EV^CTRL) were isolated from supernatants and plasma by using an exosome isolation reagent. Rat VSMC were treated with a pro‐calcifying medium (CM) with or without EV supplementation. Gene expressions, miRNA contents and protein expressions were determined by qPCR and Western blots, respectively. Calcifications were determined by colorimetric assays. Delivery of miRNA inhibitors/mimics to EV and siRNA to VSMC was achieved via transfection. EV^CTRL and EV^UR differed in size and miRNA contents. Contrary to EV^CTRL, EC‐ and plasma‐derived EV^UR significantly increased the pro‐calcifying effects of CM, including altered gene expressions of osterix, runx2, osteocalcin and SM22α. Further, EV^UR enhanced the protein expression of the phosphate transporter PiT‐1 in VSMC and induced a phosphorylation of AKT and ERK. Knock down of PiT‐1 and individual inhibition of AKT and ERK signalling in VSMC blocked the pro‐calcifying effects of EV^UR. Similar effects were achieved by inhibition of miR‐221/‐222 and mimicking of miR‐143/‐145 in EV^UR. In conclusion, EV^UR might represent an additional puzzle piece of the complex pathophysiology of vascular calcifications in CKD.

Function, Role, and Clinical Application of MicroRNAs in Vascular Aging

Vascular aging, a specific type of organic aging, is related to age-dependent changes in the vasculature, including atherosclerotic plaques, arterial stiffness, fibrosis, and increased intimal thickening. Vascular aging could influence the threshold, process, and severity of various cardiovascular diseases, thus making it one of the most important risk factors in the high mortality of cardiovascular diseases. As endothelial cells (ECs) and vascular smooth muscle cells (VSMCs) are the main cell biological basis of these pathology changes of the vasculature, the structure and function of ECs and VSMCs play a key role in vascular aging. MicroRNAs (miRNAs), small noncoding RNAs, have been shown to regulate the expression of multiple messenger RNAs (mRNAs) posttranscriptionally, contributing to many crucial aspects of cell biology. Recently, miRNAs with functions associated with aging or aging-related diseases have been studied. In this review, we will summarize the reported role of miRNAs in the process of vascular aging with special emphasis on EC and VSMC functions. In addition, the potential application of miRNAs to clinical practice for the diagnosis and treatment of cardiovascular diseases will also be discussed.

Apelin attenuates the osteoblastic differentiation of aortic valve interstitial cells via the ERK and PI3-K/Akt pathways

Aortic valve calcification (AVC), which used to be recognized as a passive and irreversible process, is now widely accepted as an active and regulated process characterized by osteoblastic differentiation of aortic valve interstitial cells (AVICs). Apelin, the endogenous ligand for G-protein-coupled receptor APJ, was found to have protective cardiovascular effects in several studies. However, the effects and mechanisms of apelin on osteoblastic differentiation of AVICs have not been elucidated. Using a pro-calcific medium, we devised a method to produce calcific human AVICs. These cells were used to study the relationship between apelin and the osteoblastic calcification of AVICs and the involved signaling pathways. Alkaline phosphatase (ALP) activity/expression and runt-related transcription factor 2 (Runx2) expression were examined as hallmark proteins in this research. The involved signaling pathways were studied using the extracellular signal-regulated kinase (ERK) inhibitor, PD98059, and the phosphatidylinositol 3-kinase (PI3-K) inhibitor, LY294002. The results indicate that apelin attenuates the expression and activity of ALP, the expression of Runx2, and the formation of mineralized nodules. This protective effect was dependent on the dose of apelin, reaching the maximum at 100 pM, and was connected to activity of ERK and Akt (a downstream effector of PI3-K). The activation of ERK and PI3-K initiated the effects of apelin on ALP activity/expression and Runx2, but PD98059 and LY294002 abolished the effect. These results demonstrate that apelin attenuates the osteoblastic differentiation of AVICs via the ERK and PI3-K/Akt pathway.

The Role of Epigenetics in Arterial Calcification

Arterial calcification is highly prevalent and correlated with cardiovascular mortality, especially in patients with ESRD or diabetes. The pathogenesis of arterial calcification is multifactorial, with both genetic and environmental factors being implicated. In recent years, several mechanisms contributing to arterial calcification have been proposed. However, these can only explain a small proportion of the variability in arterial calcification, which is a major obstacle for its prevention and management. Epigenetics has emerged as one of the most promising areas that may fill in some of the gaps in our current knowledge of the interaction between the environmental insults with gene regulation in the development of diseases. Epigenetics refers to heritable and acquired changes in gene transcription that occur independently of the DNA sequence. Well-known components of epigenetic regulation include DNA methylation, histone modifications, and microRNAs. Epigenetics research in the regulation of arterial calcification has only recently been elucidated. In this review, we will summarise recent progress in epigenetic pathways involved in arterial calcification and discuss potential therapeutic interventions based on epigenetic mechanisms.

The protective effect of GLP-1 analogue in arterial calcification through attenuating osteoblastic differentiation of human VSMCs

BACKGROUND

Arterial calcification is a common event in cardiovascular pathogenesis. Osteoblastic differentiation of vascular smooth muscle cells (VSMCs) is the most important cytopathologic foundation of arterial calcification. Glucagon-like peptide-1 (GLP-1) exerts multiple cardioprotective actions beyond insulinotropic effects through GLP-1 receptor (GLP-1R). However, whether GLP-1 regulates osteoblastic differentiation of VSMCs and associated molecular mechanisms has not been clarified.

METHODS

The human VSMC differentiation model was established by beta-glycerophosphate (β-GP) induction. The mineralization was measured by Alizarin Red S staining. Protein expression and phosphorylation were detected by Western blot or immunofluorescence. GLP-1R gene expression was silenced by siRNA.

RESULTS

The GLP-1 analogue liraglutide dose- and time-dependently inhibited the protein expression of osteoblastic differentiation markers alkaline phosphatase (ALP), osteocalcin (OC), and Runt-related transcription factor 2 (Runx2), phosphorylation of PI3K, Akt, mTOR, and S6K1. Silencing of GLP-1R gene expression by siRNA significantly blocked the effects of liraglutide in ALP protein expression and PI3K/Akt phosphorylation.

CONCLUSION

GLP-1 analogue liraglutide attenuates the osteoblastic differentiation and calcification of human VSMCs through its receptor and subsequent activation of PI3K/Akt/mTOR/S6K1 signaling. GLP-1 analogues may be potential agents for the treatment of cardiovascular diseases.

Exenatide can inhibit calcification of human VSMCs through the NF-kappaB/RANKL signaling pathway

Background

Arterial calcification is an important pathological change of diabetic vascular complication. Osteoblastic differentiation of vascular smooth muscle cells (VSMCs) plays an important cytopathologic role in arterial calcification. The glucagon-like peptide-1 receptor agonists (GLP-1RA), a novel type of antidiabetic drugs, exert cardioprotective effects through the GLP-1 receptor (GLP-1R). However, the question of whether or not GLP-1RA regulates osteoblastic differentiation and calcification of VSMCs has not been answered, and the associated molecular mechanisms have not been examined.

Methods

Calcifying VSMCs (CVSMCs) were isolated from cultured human arterial smooth muscle cells through limiting dilution and cloning. The extent of matrix mineralization was measured by Alizarin Red S staining. Protein expression and phosphorylation were detected by Western blot. Gene expression of receptor activator of nuclear factor-κB ligand (RANKL) was silenced by small interference RNA (siRNA).

Results

Exenatide, an agonist of GLP-1 receptor, attenuated β-glycerol phosphate (β-GP) induced osteoblastic differentiation and calcification of human CVSMCs in a dose- and time-dependent manner. RANKL siRNA also inhibited osteoblastic differentiation and calcification. Exenatide decreased the expression of RANKL in a dose-dependent manner. 1,25 vitD₃ (an activator of RANKL) upregulated, whereas BAY11-7082 (an inhibitor of NF-κB) downregulated RANKL, alkaline phosphatase (ALP), osteocalcin (OC), and core binding factor α1 (Runx2) protein levels and reduced mineralization in human CVSMCs. Exenatide decreased p-NF-κB and increased p-AMPKα levels in human CVSMCs 48 h after treatment. Significant decrease in p-NF-κB (p-Ser²⁷⁶, p-Ser⁵³⁶) level was observed in cells treated with exenatide or exenatide + BAY11-7082.

Conclusion

GLP-1RA exenatide can inhibit human VSMCs calcification through NF-κB/RANKL signaling.

Taurine promotes human mesenchymal stem cells to differentiate into osteoblast through the ERK pathway

Taurine has been reported to influence bone metabolism, but the role of taurine on osteogenic differentiation of human mesenchymal stem cells (hMSCs) remains unclear. In the present study, we investigated the effect of taurine on osteogenic differentiation of hMSCs. The results showed that taurine increased the alkaline phosphatase (ALP) activity and mineralized nodules in hMSCs induced by osteogenic induced medium. Meanwhile, RT-PCR analysis showed that taurine up-regulated the mRNA expression of ALP, osteopontin, Runt-related transcription factor 2 (Runx2) and Osterix in a dose-dependent manner. Furthermore, taurine induced activation of extracellular signal regulated kinase (ERK) and pretreatment with the ERK inhibitor U0126 abolished the taurine-induced osteogenesis of hMSCs. Taken together, our study reveals that taurine promotes the osteogenesis of hMSCs by activating the ERK pathway.

Effects of arsenic on osteoblast differentiation in vitro and on bone mineral density and microstructure in rats

BACKGROUND

Arsenic is a ubiquitous toxic element and is known to contaminate drinking water in many countries. Several epidemiological studies have shown that arsenic exposure augments the risk of bone disorders. However, the detailed effect and mechanism of inorganic arsenic on osteoblast differentiation of bone marrow stromal cells and bone loss still remain unclear.

OBJECTIVES

We investigated the effects and mechanism of arsenic on osteoblast differentiation in vitro and evaluated bone mineral density (BMD) and bone microstructure in rats at doses relevant to human exposure from drinking water.

METHODS

We used a cell model of rat primary bone marrow stromal cells (BMSCs) and a rat model of long-term exposure with arsenic-contaminated drinking water, and determined bone microstructure and BMD in rats by microcomputed tomography (μCT).

RESULTS

We observed significant attenuation of osteoblast differentiation after exposure of BMSCs to arsenic trioxide (0.5 or 1 μM). After arsenic treatment during differentiation, expression of runt-related transcription factor-2 (Runx2), bone morphogenetic protein-2 (BMP-2), and osteocalcin in BMSCs was inhibited and phosphorylation of enhanced extracellular signal-regulated kinase (ERK) was increased. These altered differentiation-related molecules could be reversed by the ERK inhibitor PD98059. Exposure of rats to arsenic trioxide (0.05 or 0.5 ppm) in drinking water for 12 weeks altered BMD and microstructure, decreased Runx2 expression, and increased ERK phosphorylation in bones. In BMSCs isolated from arsenic-treated rats, osteoblast differentiation was inhibited.

CONCLUSIONS

Our results suggest that arsenic is capable of inhibiting osteoblast differentiation of BMSCs via an ERK-dependent signaling pathway and thus increasing bone loss.

Leptin promotes the osteoblastic differentiation of vascular smooth muscle cells from female mice by increasing RANKL expression

Arterial calcification is a complex and active regulated process, which results from a process of osteoblastic differentiation of vascular smooth muscle cells (VSMCs). Leptin, the product of the ob gene, mainly regulates food intake and energy expenditure and recently has been considered to be correlated with the arterial calcification. However, the mechanisms of the effects of leptin on osteoblastic differentiation of VSMCs are unknown. We used calcifying vascular smooth muscle cells (CVSMCs) as a model to investigate the relationship between leptin and the osteoblastic differentiation of CVSMCs and the signaling pathways involved. Our experiments demonstrated that leptin could increase expression of receptor activator of nuclear factor-κB ligand (RANKL) and bone morphogenetic protein 4 (BMP4), as well as alkaline phosphatase (ALP) activity, runt-related transcription factor 2 expression, calcium deposition, and the formation of mineralized nodules in CVSMCs. Suppression of RANKL with small interfering RNA abolished the leptin-induced ALP activity and BMP4 expression in CVSMCs. Leptin could activate the ERK1/2 and phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway. Furthermore, pretreatment with the ERK inhibitor PD98059 and the PI3K inhibitor LY294002 abolished leptin-induced RANKL expression and blocked the promotion of ALP activity of CVSMCs. Silencing of the leptin receptor OB-Rb with small interfering RNA abolished leptin-induced activation of ERK and Akt and the expression of RANKL and reversed the effects of leptin on ALP activity. Meanwhile, addition of Noggin (the BMP4 inhibitor) blunted the effect of leptin on ALP activity. These results show that leptin can promote osteoblastic differentiation of CVSMCs by the OB-Rb/ERK1/2/RANKL-BMP4 and OB-Rb/PI3K/Akt/RANKL-BMP4 pathways.

Reduction of inorganic phosphate-induced human smooth muscle cells calcification by inhibition of protein kinase A and p38 mitogen-activated protein kinase

High levels of serum phosphate are associated with calcification of human smooth muscle cells (HSMCs). We investigated whether inhibition of protein kinase A (PKA) and mitogen-activated protein kinase (MAPK) signals [p38, extracellular signal-regulated kinase (ERK), and c-Jun N-terminal kinase (JNK)] can reduce inorganic phosphate (Pi)-induced HSMC calcification. Inhibition of PKA or p38 MAPK by inhibitors or small interfering RNAs (siRNAs) reduced Ca levels and alkaline phosphatase activities in HSMCs treated with high Pi, but inhibition of ERK1/2 and JNK showed no significant changes. Moreover, there were no significant changes in cell viability on adding siRNAs and three inhibitors (PKA, p38, and MEK1/2), but JNK inhibitor slightly reduced cell viability. These results show that PKA and p38 MAPK are involved in the Pi-induced calcification of HSMCs, and may be good targets for reducing vascular calcification.

MiR-133a modulates osteogenic differentiation of vascular smooth muscle cells

Arterial calcification is a key pathologic component of vascular diseases such as atherosclerosis, coronary artery disease, and peripheral vascular disease. A hallmark of this pathological process is the phenotypic transition of vascular smooth muscle cells (VSMCs) to osteoblast-like cells. Several studies have demonstrated that microRNAs (miRNAs) regulate osteoblast differentiation, but it is unclear whether miRNAs also regulate VSMC-mediated arterial calcification. In the present study, we sought to characterize the role of miR-133a in regulating VSMC-mediated arterial calcification. Northern blotting analysis of VSMCs treated with β-glycerophosphate demonstrated that miR-133a was significantly decreased during osteogenic differentiation. Overexpression of miR-133a inhibited VSMC transdifferentiation into osteoblast-like cells as evidenced by a decrease in alkaline phosphatase activity, osteocalcin secretion, Runx2 expression, and mineralized nodule formation. Conversely, the knockdown of miR-133a using an miR-133a inhibitor promoted osteogenic differentiation of VSMCs by increasing alkaline phosphatase activity, osteocalcin secretion, and Runx2 expression. Runx2 was identified as a direct target of miR-133a by a cotransfection experiment in VSMCs with luciferase reporter plasmids containing wild-type or mutant 3'-untranslated region sequences of Runx2. Furthermore, the pro-osteogenic effects of miR-133a inhibitor were abrogated in Runx2-knockdown cells, and the inhibition of osteogenic differentiation by pre-miR-133a was reversed by overexpression of Runx2, providing functional evidence that the effects of miR-133a in osteogenic differentiation were mediated by targeting Runx2. These results demonstrate that miR-133a is a key negative regulator of the osteogenic differentiation of VSMCs.

Connective tissue growth factor induces osteogenic differentiation of vascular smooth muscle cells through ERK signaling

Connective tissue growth factor (CTGF) plays an important role in the pathogenesis of atherosclerosis by promoting vascular smooth muscle cell (VSMC) growth, migration, apoptosis, adhesion and the secretion of matrix components. The osteogenic differentiation of VSMCs is essential in the development of vascular calcification. However, the role of CTGF in the transdifferentiation and calcification of VSMCs is unclear. In the present study, we examined whether CTGF stimulates VSMC transdifferentiation. Primary VSMCs were obtained from mouse thoracic aortas by enzymatic digestion and identified by immunostaining for smooth muscle specific α-actin antibody (α-SMA). VSMC calcification was induced by the addition of CTGF to the osteogenic mediaum containing 5-10% FBS in the presence of 0.25 mM ascorbic acid and 10 mM β-glycerophosphate for 14 days. Calcified cells were determined by Alizarin Red S staining. Our results revealed that CTGF induced the expression of several bone markers, including alkaline phosphatase (ALP), osteocalcin (OC), osteoprotegerin (OPG) and core-binding factor subunit α1 (Cbfα1)/runt-related transcription factor 2 (Runx2), as well as calcification. However, the inhibition of extracellular signal-regulated kinase (ERK) activity using the ERK-specific inhibitor, PD98059, blocked the induction of these proteins and VSMC calcification. Based on these data, we conclude that CTGF stimulates the transdifferentiation of VSMCs into osteoblasts and that the ERK signaling pathway appears to play a critical role in this process.

The Effects of rhBMP-2 and Treg/Th17 Functional Disequilibrium in Uremic Patients with Cardiovascular Complication after Maintenance Hemodialysis

Objectives

We compared the correlation of regulatory T cell (Treg) and Th17 cell function disequilibrium with calcification in uremic patients on maintenance hemodialysis (MHD) with healthy controls, and investigated if their influence possibly increased the development and outcome of cardiovascular complications in uremic patients after MHD.

Methods

The extent of coronary artery calcification was assessed by coronary artery calcification scoring (CACS) in uremic patients with and without adverse cardiovascular events after MHD (MHD group 1 vs. MHD group 2, respectively). Peripheral blood mononuclear cells were incubated with rhBMP-2 as positive control. The Treg/Th17 cell frequencies, Foxp3 ROR-γt mRNA expressions, and MIP 3α/CCL20 concentrations were measured.

Results

The CACS score was significantly higher in MHD group 1 as compared group 2. In comparison with controls, rhBMP-2 upregulates Treg/Th17 functional disequilibrium in uremic patients, displayed higher Treg and Th17 frequencies, Foxp3 and ROR-γt expressions, and MIP3α/CCL20 concentrations. However, the up-regulations of Treg frequencies and Foxp3 expressions were significant in controls but not in MHD patients. It was also observed that Treg/Th17 functional disequilibrium was not only correlated with rhBMP-2 state but also consistent with the cardiovascular complications. Moreover, the CACS was negatively correlated with Treg cell frequencies but positively correlated with Th17 cell frequencies and MIP3α/CCL20 concentrations.

Conclusions

Function disequilibrium of Treg/Th17 was related to the degree of the rhBMP-2 state. Function disequilibrium of the Treg/Th17 might act synergistically with rhBMP-2 in the high incidence of immune-mediated cardiovascular complications after MHD.

Ghrelin attenuates the osteoblastic differentiation of vascular smooth muscle cells through the ERK pathway

Vascular calcification results from osteoblastic differentiation of vascular smooth muscle cells (VSMCs) and is a major risk factor for cardiovascular events. Ghrelin is a newly discovered bioactive peptide that acts as a natural endogenous ligand of the growth hormone secretagog receptor (GHSR). Several studies have identified the protective effects of ghrelin on the cardiovascular system, however research on the effects and mechanisms of ghrelin on vascular calcification is still quite rare. In this study, we determined the effect of ghrelin on osteoblastic differentiation of VSMCs and investigated the mechanism involved using the two universally accepted calcifying models of calcifying vascular smooth muscle cells (CVSMCs) and beta-glycerophosphate (beta-GP)-induced VSMCs. Our data demonstrated that ghrelin inhibits osteoblastic differentiation and mineralization of VSMCs due to decreased alkaline phosphatase (ALP) activity, Runx2 expression, bone morphogenetic protein-2 (BMP-2) expression and calcium content. Further study demonstrated that ghrelin exerted this suppression effect via an extracellular signal-related kinase (ERK)-dependent pathway and that the suppression effect of ghrelin was time dependent and dose dependent. Furthermore, inhibition of the growth hormone secretagog receptor (GHSR), the ghrelin receptor, by siRNA significantly reversed the activation of ERK by ghrelin. In conclusion, our study suggests that ghrelin may inhibit osteoblastic differentiation of VSMCs through the GHSR/ERK pathway.

Treg/Th17 functional disequilibrium in Chinese uremia on hemodialysis: a link between calcification and cardiovascular disease

AIM

To investigate the correlation of the functional disequilibrium of regulatory T cells (Treg)/T-helper (Th17) cells with calcification and to explore the significance of their influence on the outcome of cardiovascular disease (CVD) in uremic patients after hemodialysis (HD).

METHODS

Out of 66 uremia patients, 36 patients had CVD after HD (maintenance hemodialysis (MHD) group1) and 30 patients did not have CVD (MHD group2). Twenty healthy volunteers were selected as normal control group. Peripheral blood mononuclear cells were isolated and treated with recombinant human bone morphogenetic protein-2 (rhBMP-2). Treg and Th17 frequencies were measured by flow cytometry. Forkhead/winged helix transcription factor (Foxp3) and retinoic acid receptor-related orphan receptor-γt (ROR-γt) mRNA expressions were measured by real-time quantitative polymerase chain reaction. Levels of interleukin (IL)-10 and IL-17 were detected by enzyme-linked immunosorbent assay.

RESULTS

When compared with controls, rhBMP-2 upregulates Treg/Th17 functional disequilibrium in uremia patients, displaying higher Treg and Th17 frequencies, Foxp3 and ROR-γt expressions, and levels of cytokines (p < 0.05). These differences were also significant between MHD group1 and group2 (p < 0.05). It was also observed that Treg/Th17 functional disequilibrium was not only correlated with a calcification state but also consistent with the CVD.

CONCLUSION

The Treg/Th17 cell function disequilibrium might act synergistically with calcification in the high incidence of CVD after HD.

Apelin attenuates the osteoblastic differentiation of vascular smooth muscle cells

Vascular calcification, which results from a process osteoblastic differentiation of vascular smooth muscle cells (VSMCs), is a major risk factor for cardiovascular morbidity and mortality. Apelin is a recently discovered peptide that is the endogenous ligand for the orphan G-protein-coupled receptor, APJ. Several studies have identified the protective effects of apelin on the cardiovascular system. However, the effects and mechanisms of apelin on the osteoblastic differentiation of VSMCs have not been elucidated. Using a culture of calcifying vascular smooth muscle cells (CVMSCs) as a model for the study of vascular calcification, the relationship between apelin and the osteoblastic differentiation of VSMCs and the signal pathway involved were investigated. Alkaline phosphatase (ALP) activity and osteocalcin secretion were examined in CVSMCs. The involved signal pathway was studied using the extracellular signal-regulated kinase (ERK) inhibitor, PD98059, the phosphatidylinositol 3-kinase (PI3-K) inhibitor, LY294002, and APJ siRNA. The results showed that apelin inhibited ALP activity, osteocalcin secretion, and the formation of mineralized nodules. APJ protein was detected in CVSMCs, and apelin activated ERK and AKT (a downstream effector of PI3-K). Suppression of APJ with siRNA abolished the apelin-induced activation of ERK and Akt. Furthermore, inhibition of APJ expression, and the activation of ERK or PI3-K, reversed the effects of apelin on ALP activity. These results showed that apelin inhibited the osteoblastic differentiation of CVSMCs through the APJ/ERK and APJ/PI3-K/AKT signaling pathway. Apelin appears to play a protective role against arterial calcification.

Raloxifene attenuates Gas6 and apoptosis in experimental aortic valve disease in renal failure

Renal failure is associated with aortic valve calcification. Using our rat model of uremia-induced reversible aortic valve calcification, we assessed the role of apoptosis and survival pathways in that disease. We also explored the effects of raloxifene, an estrogen receptor modulator, on valvular calcification. Gene array analysis was performed in aortic valves obtained from three groups of rats (n = 7 rats/group): calcified valves obtained from rats fed with uremic diet, valves after calcification resolution following diet cessation, and control. In addition, four groups of rats (n = 10 rats/group) were used to evaluate the effect of raloxifene in aortic valve calcification: three groups as mentioned above and a fourth group fed with the uremic diet that also received daily raloxifene. Evaluation included imaging, histology, and antigen expression analysis. Gene array results showed that the majority of the altered expressed genes were in diet group valves. Most apoptosis-related genes were changed in a proapoptotic direction in calcified valves. Apoptosis and decreases in several survival pathways were confirmed in calcified valves. Resolution of aortic valve calcification was accompanied by decreased apoptosis and upregulation of survival pathways. Imaging and histology demonstrated that raloxifene significantly decreased aortic valve calcification. In conclusion, downregulation of several survival pathways and apoptosis are involved in the pathogenesis of aortic valve calcification. The beneficial effect of raloxifene in valve calcification is related to apoptosis modulation. This novel observation is important for developing remedies for aortic valve calcification in patients with renal failure.

Paracrine osteogenic signals via bone morphogenetic protein-2 accelerate the atherosclerotic intimal calcification in vivo

OBJECTIVE

Vascular calcification is an important risk factor for cardiovascular diseases. Here, we investigated a role of dedifferentiated vascular smooth muscle cells (VSMCs) in the atherosclerotic intimal calcification.

METHODS AND RESULTS

We prepared human cultured VSMCs in either redifferentiatiated or dedifferentiated state and analyzed the gene expressions of bone-calcification regulatory factors. Expression of bone morphogenetic protein-2 (BMP-2), a potent initiator for osteoblast differentiation, was significantly enhanced in dedifferentiated VSMCs. Furthermore, endogenous BMP-2 antagonists, such as noggin, chordin, and matrix gamma-carboxyglutamic acid protein, were all downregulated in the dedifferentiated VSMCs. Conditioned medium from dedifferentiated VSMCs, but not from redifferentiated VSMCs, stimulated the osteoblastic differentiation of the mesenchymal progenitor C2C12 cells, which was abolished by BMP-2 knockdown. In atherosclerotic intima from apolipoprotein (apo)E-deficient mice, αSM-actin-positive cells, presumably dedifferentiated VSMCs, expressed BMP-2. We generated BMP-2-transgenic mice using αSM-actin promoter and crossed them with apoE-deficient mice (BMP-2-transgenic/apoE-knockout). Significantly accelerated atherosclerotic intimal calcification was detected in BMP-2-transgenic/apoE-knockout mice, although serum lipid concentration and atherosclerotic plaque size were not different from those in apoE-knockout mice. Enhanced calcification appeared to be associated with the frequent emergence of osteoblast-like cells in atherosclerotic intima in BMP-2-transgenic/apoE-knockout mice.

CONCLUSIONS

Our findings collectively demonstrate an important role of dedifferentiated VSMCs in the pathophysiology of atherosclerotic calcification through activating paracrine BMP-2 osteogenic signals.

L-carnitine and taurine synergistically inhibit the proliferation and osteoblastic differentiation of vascular smooth muscle cells

AIM

To investigate the synergistic action of L-carnitine (LC) and taurine (TAU) on the proliferation and osteoblastic differentiation of vascular smooth muscle cells (VSMCs).

METHODS

DNA and protein synthesis of VSMCs were assessed using scintillation counting. Alkaline phosphatase (ALP) activity and calcium content were determined to investigate the effects of LC and TAU on the osteoblastic differentiation and mineralization of VSMCs. TAU uptake by VSMCs was assayed. RNA interference was used to down-regulate the expression of the TAU transporter (TAUT) in rat VSMCs.

RESULTS

LC and TAU synergistically inhibited the proliferation and beta-glycerophosphate (beta-GP)-induced osteoblastic differentiation of VSMCs as evidenced by the decreased [(3)H]thymidine incorporation, ALP activity and calcium deposition. Furthermore, LC stimulated the TAU uptake and TAUT expression in VSMCs. Suppression of TAUT with short hairpin RNA (shRNA) abolished the synergistic action of LC and TAU in VSMCs.

CONCLUSION

The synergistic inhibitory action of LC and TAU on the proliferation and osteoblastic differentiation of VSMCs is attributable to the up-regulation of TAUT expression and TAU uptake by LC.

Role of the MAPK/ERK pathway in valvular interstitial cell calcification

Much remains to be discovered about the etiology of heart valve disease and the molecular level mechanisms that drive it. The MAPK/ERK pathway influences calcification in many cell types and has been linked to the expression of a contractile phenotype in valvular interstitial cells (VICs). However, a direct correlation between MAPK/ERK pathway activity and VIC calcification has not been previously described. Thus the role of the MAPK pathway in the calcification of VIC cultures was investigated by measuring ERK activation in both calcifying and noncalcifying VIC environments and then, conversely, analyzing the effects of ERK pathway inhibition on VIC calcification and phenotype. Prolonged elevation of phosphorylated ERK-1/2 was found in calcifying VIC cultures, whereas directly blocking phosphorylation of ERK-1/2 resulted in a dramatic decrease in nodule number, nodule size, and total calcified area. Application of the ERK pathway inhibitor was also associated with a dramatic decrease in apoptosis, which may have contributed to the decreased nodule formation obtained via ERK inhibition. Real-time PCR analysis revealed that calcified samples exhibited significantly elevated expression of several myofibroblastic and osteoblastic markers, while ERK inhibition substantially reduced the expression of these markers, often to levels comparable to the noncalcifying control. These data suggest that the MAPK pathway plays an important role in regulating the phenotype and calcification of VICs, wherein sustained pathway activation is associated with increased VIC calcification. These findings may be used to further elucidate the mechanisms of valvular disease and identify potential treatment targets.