Thematic series on the pathobiology of vascular calcification: an introduction

Characterization of the 'White' Appearing Clots that Cause Acute Ischemic Stroke

OBJECTIVES

Most clots retrieved from patients with acute ischemic stroke are 'red' in color. 'White' clots represent a less common entity and their histological composition is less known. Our aim was to investigate the composition, imaging and procedural characteristics of 'white' clots retrieved by mechanical thrombectomy.

MATERIALS AND METHODS

Seventy five 'white' thrombi were selected by visual inspection from a cohort of 760 clots collected as part of the RESTORE registry. Clots were evaluated histopathologically.

RESULTS

Quantification of Martius Scarlett Blue stain identified platelets/other as the major component in 'white' clots' (mean of 55% of clot overall composition) followed by fibrin (31%), red blood cells (6%) and white blood cells (3%). 'White' clots contained significantly more platelets/other (p<0.001*) and collagen/calcification (p<0.001*) and less red blood cells (p<0.001*) and white blood cells (p=0.018*) than 'red' clots. The mean platelet and von Willebrand Factor expression was 43% and 24%, respectively. Adipocytes were found in four cases. 'White' clots were significantly smaller (p=0.016*), less hyperdense (p=0.005*) on computed tomography angiography/non-contrast CT and were associated with a smaller extracted clot area (p<0.001*) than 'red' clots. They primarily caused the occlusion of middle cerebral artery, were less likely to be removed by aspiration and more likely to require rescue-therapy for retrieval.

CONCLUSIONS

'White' clots represented 14% of our cohort and were platelet, von Willebrand Factor and collagen/calcification-rich. 'White' clots were smaller, less hyperdense, were associated with significantly more distal occlusions and were less successfully removed by aspiration alone than 'red' clots.

MicroRNA-103a regulates the calcification of vascular smooth muscle cells by targeting runt-related transcription factor 2 in high phosphorus conditions

Vascular calcification, such as atherosclerosis, is a serious complication of chronic kidney disease that is characterized by tunica media calcification, and has gained increasing attention from researchers. The commonly observed association between vascular calcification and osteoporosis suggests a link between bone and vascular disorders. As microRNAs (miRNAs) have a wide range of gene regulation functions, such as cell proliferation, apoptosis, stress and transdifferentiation, the current study aimed to determine whether miRNAs play a vital role in the calcification and osteoblastic differentiation of rat thoracic aorta vascular smooth muscle cells (VSMCs). Gene expression analysis was performed on seven miRNAs (miR-29a, -30b, -103a, -125b, -133a, -143 and -211) that maybe potentially involved in the differentiation of smooth muscle cells into osteoblastic cells. The results showed that the levels of miR-29a, -30b, -103a, -125b and -143 were markedly reduced in the VSMC calcification model, particularly miR-103a, whereas runt-related transcription factor 2 (RUNX2) expression was increased. Furthermore, it was found that the expression of RUNX2 was significantly decreased following the upregulation of miR-103a, and that the expression of RUNX2 was significantly increased by downregulating miR-103a in VSMCs. Therefore, it was concluded that miR-103a plays a notable role in the transdifferentiation of the VSMCs in high phosphorus-induced calcification by targeting the regulation of RUNX2, and may therefore constitute a new target for the diagnosis and treatment of vascular calcification.

AntagomiR-29b inhibits vascular and valvular calcification and improves heart function in rats

We aimed to investigate the role of the miR‐29b and its effect on TGF‐β3 pathway in vascular and valvular calcification in a rat model of calcific aortic valve diseases (CAVD). A rat model of CAVD was established by administration of warfarin plus vitamin K. The expression levels of miR‐29b, osteogenic markers and other genes were determined by qRT‐PCR, Western blot and/or immunofluorescence and immunohistochemistry. The calcium content and alkaline phosphatase (ALP) activity were measured. The calcium content, ALP activity and osteogenic markers levels in calcified aorta and aortic valve were augmented compared to controls. The expression of miR‐29b, p‐Smad3, and Wnt3 and β‐catenin was significantly up‐regulated, whereas TGF‐β3 was markedly down‐regulated. However, compared with the CAVD model group, the calcium content and ALP activity in rats treated with antagomiR‐29b were significantly decreased, and antagomiR‐29b administration reversed the effects of CAVD model on the expression of miR‐29b and osteogenic markers. Inhibition of miR‐29b in CAVD rats prevented from vascular and valvular calcification and induced TGF‐β3 expression, suggesting that the miR‐29b/TGF‐β3 axis may play a regulatory role in the pathogenesis of vascular and valvular calcification and could play a significant role in the treatment of CAVD and other cardiovascular diseases.

LncRNA H19/Runx2 axis promotes VSMCs transition via MAPK pathway

Arterial calcification (AC) is mainly caused by osteoblast phenotypic transition of vascular smooth muscle cells (VSMCs). Long noncoding RNA H19 (lncRNA H19) has attracted increasingly attention because of their transcriptional regulation crucial potency. We reported that lncRNA H19 expression is up-regulated after VSMCs transition. Thus, we aim to study the role of H19 and the molecular mechanisms in VSMCs transition. To determine the expression of H19 in calcified VSMCs, we induced VSMCs calcification with 10 mM β-glycerophosphate. By qPCR and Western Blot analysis, we found that the expression of lncRNA H19, Runx2 and OSX were all highly increased in calcified VSMCs compared with normal VSMCs, while the expression of VSMCs differentiation markers, SM22-α and α-SMA, were significantly decreased. SiRNA study showed that knockdown of lncRNA H19 can decrease VSMCs calcification and Runx2 expression. We further validated that lncRNA H19 promoted VSMCs calcification via the p38 MAPK and ERK1/2 signal transduction pathways. As a conclusion, the present study showed that lncRNA H19/Runx2 axis promotes VSMCs transition via MAPK pathway. This finding not only reveal a novel function of lncRNA H19, but also provides a new opinion on the role of lncRNA H19 which participant in the Runx2 regulatory pathway in AC and can be a new indication for the diagnosis and treatment of AC at an early time.

Salusin-β Promotes Vascular Calcification via Nicotinamide Adenine Dinucleotide Phosphate/Reactive Oxygen Species-Mediated Klotho Downregulation

Aims: Vascular calcification (VC) is a hallmark feature of cardiovascular disease and a significant risk factor for morbidity and mortality. Salusin-β exerts cardiovascular regulating effects in hypertension, atherosclerosis, and diabetes. The present study was designed to examine the roles of salusin-β in the progression of VC and its downstream signaling mechanisms. Results: Salusin-β expression in both the aortas of VC rats induced by vitamin D3 and nicotine and vascular smooth muscle cells (VSMCs) incubated with calcifying media was increased. Salusin-β knockdown remarkably reduced VC, whereas overexpression of salusin-β exacerbated VC both in vitro and in vivo. Overexpression of salusin-β promoted the VSMC osteochondrogenic transition, decreased Klotho protein levels, enhanced Ras-related C3 botulinum toxin substrate 1 (Rac1) activity and the translocation of p47phox to the membrane, increased the expression of nicotinamide adenine dinucleotide phosphate [NAD(P)H] oxidase subunits and the production of reactive oxygen species (ROS) with or without calcifying media; however, salusin-β deficiency played the opposite roles. The calcification and downregulated Klotho protein levels induced by salusin-β were restored by ROS scavenger N-acetyl-l-cysteine, diphenyleneiodonium chloride [an inhibitor of flavin-containing enzyme, including NAD(P)H oxidase], or gene knockdown of NAD(P)H oxidase (NOX)-2, p22phox, or p47phox but were not affected by NOX-1 and NOX-4 knockdown. Klotho knockdown attenuated the protective effect of salusin-β deficiency on VSMC calcification. By contrast, exogenous Klotho ameliorated the development of VC and ROS generation induced by salusin-β overexpression. Innovation: Salusin-β is a critical modulator in VC. Conclusion: Salusin-β regulates VC through activation of NAD(P)H/ROS-mediated Klotho downregulation, suggesting that salusin-β may be a novel target for treatment of VC.

Age Does Not Affect Metoprolol's Effect on Perioperative Outcomes (From the POISE Database)

BACKGROUND:

Perioperative β-blockade reduces the incidence of myocardial infarction but increases that of death, stroke, and hypotension. The elderly may experience few benefits but more harms associated with β-blockade due to a normal effect of aging, that of a reduced resting heart rate. The tested hypothesis was that the effect of perioperative β-blockade is more significant with increasing age.

METHODS:

To determine whether the effect of perioperative β-blockade on the primary composite event, clinically significant hypotension, myocardial infarction, stroke, and death varies with age, we interrogated data from the perioperative ischemia evaluation (POISE) study. The POISE study randomly assigned 8351 patients, aged ≥45 years, in 23 countries, undergoing major noncardiac surgery to either 200 mg metoprolol CR daily or placebo for 30 days. Odds ratios or hazard ratios for time to events, when available, for each of the adverse effects were measured according to decile of age, and interaction term between age and treatment was calculated. No adjustment was made for multiple outcomes.

RESULTS:

Age was associated with higher incidences of the major outcomes of clinically significant hypotension, myocardial infarction, and death. Age was associated with a minimal reduction in resting heart rate from 84.2 (standard error, 0.63; ages 45–54 years) to 80.9 (standard error, 0.70; ages >85 years; P < .0001). We found no evidence of any interaction between age and study group regarding any of the major outcomes, although the limited sample size does not exclude any but large interactions.

CONCLUSIONS:

The effect of perioperative β-blockade on the major outcomes studied did not vary with age. Resting heart rate decreases slightly with age. Our data do not support a recommendation for the use of perioperative β-blockade in any age subgroup to achieve benefits but avoid harms. Therefore, current recommendations against the use of β-blockers in high-risk patients undergoing noncardiac surgery apply across all age groups.

Death-associated protein kinase 3 deficiency alleviates vascular calcification via AMPK-mediated inhibition of endoplasmic reticulum stress

Vascular calcification (VC) is a critical feature of chronic kidney disease (CKD), diabetes, hypertension, and atherosclerosis. Death-associated protein kinase 3 (DAPK3) is involved in vascular remodeling in hypertension. However, it remains to be clarified whether DAPK3 controls vascular smooth muscle cell (VSMC) phenotypic transition into an osteogenic cell phenotype, which is an important process for VC. In vivo VC was induced in rats by vitamin D3 and nicotine. VSMCs were incubated with calcifying media containing β-glycerophosphate and Ca²⁺ to induce VC in vitro. Herein, we demonstrated increased expression of DAPK3 in the aortas of VC rats and VSMCs cultured in calcifying media. Knockdown of DAPK3 significantly inhibited calcifying media-induced VSMC mineralization and retarded the phenotypic transformation of VSMCs into osteogenic cells. Silencing of DAPK3 suppressed endoplasmic reticulum stress (ERS) related protein expressions, but upregulated the phosphorylation level of AMP-activated protein kinase (AMPK) in calcified VSMCs. Moreover, pretreatment with AMPK inhibitor Compound C abolished DAPK3 shRNA-mediated inhibition of ERS in VSMCs. In vivo, DAPK inhibitor significantly prevented calcium deposition in the aortas of VC rats. The present results revealed that DAPK3 modulated VSMC calcification through AMPK-mediated ERS signaling.

Proteomic profiling of extracellular vesicles released from vascular smooth muscle cells during initiation of phosphate-induced mineralization

Purpose/Aim: Elevated serum phosphate is one of the major factors contributing to vascular calcification. Studies suggested that extracellular vesicles released from vascular smooth muscle cells significantly contribute to the initiation and progression of this pathology. Recently, we have demonstrated that elevated phosphate stimulates release of extracellular vesicles from osteogenic cells at the initiation of the mineralization process. Here, we used MOVAS cell line as an in vitro model of vascular calcification to examine whether vascular smooth muscle cells respond to high phosphate levels in a similar way and increase formation of extracellular vesicles.

MATERIALS AND METHODS

Vesicles residing in extracellular matrix as well as vesicles released to culture medium were evaluated by nanoparticle tracking analyses. In addition, using mass spectrometry and protein profiling, protein composition of extracellular vesicles released by MOVAS cells under standard growth conditions and upon exposure to high phosphate was compared.

RESULTS

Significant increase of the number of extracellular vesicles was detected after 72 h of exposure of cells to high phosphate. Elevated phosphate levels also affected protein composition of extracellular vesicles released from MOVAS cells. Finally, the comparative analyses of proteins in extracellular vesicles isolated from extracellular matrix and from conditioned medium identified significant differences in protein composition in these two groups of extracellular vesicles.

CONCLUSIONS

Results of this study demonstrate that exposure of MOVAS cells to high phosphate levels stimulates the release of extracellular vesicles and changes their protein composition.

Noninvasive Assessment of Carotid Plaques Calcification by 18F-Sodium Fluoride Accumulation: Correlation with Pathology

BACKGROUD

Vascular calcification is currently recognized as an important pathobiological process in atherosclerosis, but the mechanism remains elusive. Given the similarities in vascular calcification and bone formation, ¹⁸F-sodium fluoride (¹⁸F-NaF) is now considered a novel marker of vascular calcification. This study aimed to correlate ¹⁸F-NaF accumulation with the histological characterization of vascular calcification in carotid plaques.

METHODS

A total of 8 patients who were undergoing carotid endarterectomy (CEA) for carotid artery stenosis were recruited. Before CEA, ¹⁸F-NaF positron emission tomography and computed tomography (PET-CT) studies were conducted. ¹⁸F-NaF uptake was measured by the maximum standardized uptake value and the target-to-background ratio. The Hounsfield unit (HU) value was also measured. Postoperative carotid plaques were investigated by hematoxylin and eosin staining, alizarin red staining, and immunohistochemistry (alpha-smooth muscle actin and CD68).

RESULTS

¹⁸F-NaF uptake was observed in the bilateral carotid bifurcation of all patients. Compared with the pathology results, there was a significant correlation between tracer activity in the carotid plaques and the calcification in the corresponding histological sections (integrated optical density [IOD]: r = .781, P = .022; positive area: r = .765, P = .027). A negative correlation was observed between ¹⁸F-NaF uptake and smooth muscle cell staining (IOD: r = -.710, P = .049). ¹⁸F-NaF uptake did not correlate with carotid artery stenosis, HU value, or inflammation.

CONCLUSIONS

¹⁸F-NaF PET-CT is a noninvasive imaging method for the assessment of calcification in human carotid atherosclerotic plaques and a promising approach to studying calcification in atherosclerotic lesions.

Extracellular acidosis suppresses calcification of vascular smooth muscle cells by inhibiting calcium influx via L-type calcium channels

Vascular calcification such as arteriosclerosis, which is characterized by a calcification of the tunica media, is a severe complication of chronic kidney disease (CKD), contributing to the high prevalence of cardiovascular morbidity and mortality in patients with CKD. An essential step during the development of arteriosclerosis is the transdifferentiation/calcification of vascular smooth muscle cells (VSMCs), resembling osteogenesis. Metabolic acidosis, a common clinical manifestation in CKD, is known to decrease vascular calcification. To understand the underlying regulatory mechanisms of acidosis, we investigated whether the acidosis-decreased VSMC calcification involves altered signaling of the LTCC/Ca²⁺/Runx2 pathway. Vascular calcifications, calcium content, runt-related transcription factor 2 (Runx2), alkaline phosphatase (ALP), L-type calcium channel (LTCC) β₃ subunits, and calcium influx were measured in vivo or in vitro. Calcified nodules and calcium content increased either in aorta sections of vascular calcified rats or in VSMCs induced by β-GP. The expression of Runx2 and ALP activity markedly rose, accompanied by the increasing expression of LTCC β₃ subunits and calcium influx. However, acidosis supplementation successfully attenuated VC and VSMC calcification and inhibited Runx2, ALP, LTCC β₃ subunits, and calcium influx. In conclusion, acidosis significantly attenuated vascular calcification in association with downregulation of the LTCC/Ca²⁺/Runx2 pathway.

Effect of pioglitazone on inflammation and calcification in atherosclerotic rabbits : An 18F-FDG-PET/CT in vivo imaging study

BACKGROUND

We developed an atherosclerotic rabbit model and tested pioglitazone as a drug intervention for early vascular calcification. Positron emission tomography/computed tomography (PET/CT) was used to evaluate inflammation and therapeutic effects.

METHODS

We randomly divided 20 male New Zealand white rabbits into a pioglitazone-treated group (n = 10) and a control group (n = 10). Atherosclerosis was induced via a high-cholesterol diet and endothelial denudation. The animals were maintained on a hyperlipidemic diet for 16 weeks after surgery, and the treatment group received pioglitazone daily. Serum samples were obtained at 8 and 18 weeks postoperatively to assess high-sensitivity C‑reactive protein (hs-CRP) and matrix metalloproteinase-9 (MMP-9) concentrations. Sixteen rabbits underwent a mid-stage PET/CT scan at week 8, and 11 rabbits underwent an end-stage PET/CT scan at week 18. PET/CT parameters, including the mean standardized uptake value (SUVmean) and maximum standardized uptake value (SUVmax), were measured and documented.

RESULTS

There were significantly lower hs-CRP and MMP-9 levels in the pioglitazone group at week 18 (p < 0.01). At the end of the 8th week, no significant between-group differences in SUVmean and SUVmax were observed. From week 8 to week 18, the SUVmean and SUVmax decreased in the pioglitazone group but the SUVmean increased in the control group, with significant between-group differences at the end of the 18th week (p < 0.01). Histopathological examination of aortas in the control and pioglitazone groups revealed significantly smaller plaque area, macrophage density, and tissue calcification area in the latter group.

CONCLUSION

Pioglitazone affects early vascular microcalcification, and pioglitazone-induced changes can be assessed using ¹⁸F-FDG-PET/CT.

Imaging Atherosclerotic Plaque Calcification: Translating Biology

Calcification of atherosclerotic lesions was long thought to be an age - related, passive process, but increasingly data has revealed that atherosclerotic calcification is a more active process, involving complex signaling pathways and bone-like genetic programs. Initially, imaging of atherosclerotic calcification was limited to gross assessment of calcium burden, which is associated with total atherosclerotic burden and risk of cardiovascular mortality and of all cause mortality. More recently, sophisticated molecular imaging studies of the various processes involved in calcification have begun to elucidate information about plaque calcium composition and consequent vulnerability to rupture, leading to hard cardiovascular events like myocardial infarction. As such, there has been renewed interest in imaging calcification to advance risk assessment accuracy in an evolving era of precision medicine. Here we summarize recent advances in our understanding of the biologic process of atherosclerotic calcification as well as some of the molecular imaging tools used to assess it.

Citrate attenuates vascular calcification in chronic renal failure rats

Vascular calcification (VC) is a major contributor of cardiovascular dysfunction in chronic renal failure (CRF). Citrate binds calcium and inhibits the growth of calcium crystals. This present study intends to evaluate the effect of citrate on VC in adenine-induced CRF rats. The rats were randomly divided into five groups: the control group, the citrate control group, model group, model rats with low-dose treatment of citrate (216 mg/kg) and model rats with high-dose treatment of citrate (746 mg/kg). The rats were euthanized at 5 weeks with their blood and aorta in detection. The results showed that serum level of blood urea nitrogen, serum creatinine, phosphorus, calcium, and related renal failure function marker were elevated in the model group. Furthermore, the aortic calcium accumulation and alkaline phosphatase activity were significantly increased in the model group compared with control groups. Additionally, hematoxylin-eosin staining results demonstrated that the vascular calcification in aorta is significantly increased in the model group. Finally, the expression of VC-related proteins including bone morphogenetic protein and osteocalcin were increased in the model group, whereas alpha-smooth muscle actin was decreased in the model group compared with the control group. However, treatment with citrate caused a reversal effect of all the above events in a dose-dependent manner. In conclusion, citrate may attenuate vascular calcification in adenine-induced CRF rats.

Endogenous Sulfur Dioxide Inhibits Vascular Calcification in Association with the TGF-β/Smad Signaling Pathway

The study was designed to investigate whether endogenous sulfur dioxide (SO₂) plays a role in vascular calcification (VC) in rats and its possible mechanisms. In vivo medial vascular calcification was induced in rats by vitamin D3 and nicotine for four weeks. In vitro calcification of cultured A7r5 vascular smooth muscle cells (VSMCs) was induced by calcifying media containing 5 mmol/L CaCl₂. Aortic smooth muscle (SM) α-actin, runt-related transcription factor 2 (Runx2), transforming growth factor-β (TGF-β) and Smad expression was measured. VC rats showed dispersed calcified nodules among the elastic fibers in calcified aorta with increased aortic calcium content and alkaline phosphatase (ALP) activity. SM α-actin was markedly decreased, but the osteochondrogenic marker Runx2 concomitantly increased and TGF-β/Smad signaling was activated, in association with the downregulated SO₂/aspartate aminotransferase (AAT) pathway. However, SO₂ supplementation successfully ameliorated vascular calcification, and increased SM α-actin expression, but inhibited Runx2 and TGF-β/Smad expression. In calcified A7r5 VSMCs, the endogenous SO₂/AAT pathway was significantly downregulated. SO₂ treatment reduced the calcium deposits, calcium content, ALP activity and Runx2 expression and downregulated the TGF-β/Smad pathway in A7r5 cells but increased SM α-actin expression. In brief, SO₂ significantly ameliorated vascular calcification in association with downregulation of the TGF-β/Smad pathway.

Fibroblast growth factor signaling in the vasculature

Despite their discovery as angiogenic factors and mitogens for endothelial cells more than 30 years ago, much remains to be determined about the role of fibroblast growth factors (FGFs) and their receptors in vascular development, homeostasis, and disease. In vitro studies show that members of the FGF family stimulate growth, migration, and sprouting of endothelial cells, and growth, migration, and phenotypic plasticity of vascular smooth muscle cells. Recent studies have revealed important roles for FGFs and their receptors in the regulation of endothelial cell sprouting and vascular homeostasis in vivo. Furthermore, recent work has revealed roles for FGFs in atherosclerosis, vascular calcification, and vascular dysfunction. The large number of FGFs and their receptors expressed in endothelial and vascular smooth muscle cells complicates these studies. In this review, we summarize recent studies in which new and unanticipated roles for FGFs and their receptors in the vasculature have been revealed.

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.

Pathophysiological role of vascular smooth muscle alkaline phosphatase in medial artery calcification

Medial vascular calcification (MVC) is a pathological phenomenon that causes vascular stiffening and can lead to heart failure; it is common to a variety of conditions, including aging, chronic kidney disease, diabetes, obesity, and a variety of rare genetic diseases. These conditions share the common feature of tissue-nonspecific alkaline phosphatase (TNAP) upregulation in the vasculature. To evaluate the role of TNAP in MVC, we developed a mouse model that overexpresses human TNAP in vascular smooth muscle cells in an X-linked manner. Hemizygous overexpressor male mice (Tagln-Cre(+/-) ; Hprt(ALPL) (/Y) or TNAP-OE) show extensive vascular calcification, high blood pressure, and cardiac hypertrophy, and have a median age of death of 44 days, whereas the cardiovascular phenotype is much less pronounced and life expectancy is longer in heterozygous (Tagln-Cre(+/-) ; Hprt(ALPL) (/-) ) female TNAP-OE mice. Gene expression analysis showed upregulation of osteoblast and chondrocyte markers and decreased expression of vascular smooth muscle markers in the aortas of TNAP-OE mice. Through medicinal chemistry efforts, we developed inhibitors of TNAP with drug-like pharmacokinetic characteristics. TNAP-OE mice were treated with the prototypical TNAP inhibitor SBI-425 or vehicle to evaluate the feasibility of TNAP inhibition in vivo. Treatment with this inhibitor significantly reduced aortic calcification and cardiac hypertrophy, and extended lifespan over vehicle-treated controls, in the absence of secondary effects on the skeleton. This study shows that TNAP in the vasculature contributes to the pathology of MVC and that it is a druggable target.

Improvement of the skeletal and dental hypophosphatasia phenotype in Alpl-/- mice by administration of soluble (non-targeted) chimeric alkaline phosphatase

Hypophosphatasia (HPP) results from ALPL gene mutations, which lead to a deficiency of tissue-nonspecific alkaline phosphatase (TNAP), and accumulation of inorganic pyrophosphate, a potent inhibitor of mineralization that is also a natural substrate of TNAP, in the extracellular space. HPP causes mineralization disorders including soft bones (rickets or osteomalacia) and defects in teeth and periodontal tissues. Enzyme replacement therapy using mineral-targeting recombinant TNAP has proven effective in preventing skeletal and dental defects in TNAP knockout (Alpl(-/-)) mice, a model for life-threatening HPP. Here, we show that the administration of a soluble, intestinal-like chimeric alkaline phosphatase (ChimAP) improves the manifestations of HPP in Alpl(-/-) mice. Mice received daily subcutaneous injections of ChimAP at doses of 1, 8 or 16 mg/kg, from birth for up to 53 days. Lifespan and body weight of Alpl(-/-) mice were normalized, and vitamin B6-associated seizures were absent with 16 mg/kg/day of ChimAP. Radiographs, μCT and histological analyses documented improved mineralization in cortical and trabecular bone and secondary ossification centers in long bones of ChimAP16-treated mice. There was no evidence of craniosynostosis in the ChimAP16-treated mice and we did not detect ectopic calcification by radiography and histology in the aortas, stomachs, kidneys or lungs in any of the treatment groups. Molar tooth development and function improved with the highest ChimAP dose, including enamel, dentin, and tooth morphology. Cementum remained deficient and alveolar bone mineralization was reduced compared to controls, though ChimAP-treated Alpl(-/-) mice featured periodontal attachment and retained teeth. This study provides the first evidence for the pharmacological efficacy of ChimAP for use in the treatment of skeletal and dental manifestations of HPP.

Inhibition of FOXO1/3 promotes vascular calcification

OBJECTIVE

Vascular calcification is a characteristic feature of atherosclerosis, diabetes mellitus, and end-stage renal disease. We have demonstrated that activation of protein kinase B (AKT) upregulates runt-related transcription factor 2 (Runx2), a key osteogenic transcription factor that is crucial for calcification of vascular smooth muscle cells (VSMC). Using mice with SMC-specific deletion of phosphatase and tensin homolog (PTEN), a major negative regulator of AKT, the present studies uncovered a novel molecular mechanism underlying PTEN/AKT/FOXO (forkhead box O)-mediated Runx2 upregulation and VSMC calcification.

APPROACH AND RESULTS

SMC-specific PTEN deletion mice were generated by crossing PTEN floxed mice with SM22α-Cre transgenic mice. The PTEN deletion resulted in sustained activation of AKT that upregulated Runx2 and promoted VSMC calcification in vitro and arterial calcification ex vivo. Runx2 knockdown did not affect proliferation but blocked calcification of the PTEN-deficient VSMC, suggesting that PTEN deletion promotes Runx2-depedent VSMC calcification that is independent of proliferation. At the molecular level, PTEN deficiency increased the amount of Runx2 post-transcriptionally by inhibiting Runx2 ubiquitination. AKT activation increased phosphorylation of FOXO1/3 that led to nuclear exclusion of FOXO1/3. FOXO1/3 knockdown in VSMC phenocopied the PTEN deficiency, demonstrating a novel function of FOXO1/3, as a downstream signaling of PTEN/AKT, in regulating Runx2 ubiquitination and VSMC calcification. Using heterozygous SMC-specific PTEN-deficient mice and atherogenic ApoE(-/-) mice, we further demonstrated AKT activation, FOXO phosphorylation, and Runx2 ubiquitination in vascular calcification in vivo.

CONCLUSIONS

Our studies have determined a new causative effect of SMC-specific PTEN deficiency on vascular calcification and demonstrated that FOXO1/3 plays a crucial role in PTEN/AKT-modulated Runx2 ubiquitination and VSMC calcification.

Wnt5a is associated with the differentiation of bone marrow mesenchymal stem cells in vascular calcification by connecting with different receptors

Vascular calcification significantly affects the health of the elderly. Increasing evidence proved that vascular calcification is an actively regulated osteogenic process. The osteochondrocytic differentiation of mesenchymal stem cells (MSCs) is a significant step of osteogenic processes. The Wnt pathways has been identified as contributing to the regulation of osteogenic mineralization during development and disease. However, it remains unknown whether these MSCs in the vascular calcification differentiate into normal vascular smooth muscle cells (VSMCs) in vivo in order to treat damaged vascular tissue or into calcified VSMCs to aggravate calcification correlated to the Wnt pathways. Thus, it is necessary to analyze the mechanisms of MSC differentiation in detail. In the present study a cell‑cell co‑culturing in vitro system was used to observe MSCs that directly interact with normal or calcified VSMCs during calcification and to investigate the gene expression of the Wnt pathways during the process. Direct co‑cultures were established by seeding two different cell types, VSMCs or calcified VSMCs, or a mixture of both at ratios of 5,000:5,000 cells/1.7 cm2 onto either gelatin‑coated 1.7‑cm2 chamber slides for immunohistochemical analysis or gelatin‑coated 75‑cm2 tissue culture flasks for protein or RNA isolation. Osteoblastic differentiation was evaluated by examining the cell morphology and assessing the activity of alkaline phosphatase in the cell lysates by alkaline phosphatase staining. Additionally, the mRNA expression levels of the genes encoding for proteins involved in the Wnt signaling proteins, Wnt5A, LRP6, Ror2, c‑Jun‑N‑terminal kinase and β‑catenin, were assessed in each group. The present study demonstrated that Wnts are expressed in the progress of differentiation of MSCs during calcification. MSCs can differentiate into different cell phenotypes when there is direct cell‑cell contact with VSMCs or calcified VSMCs, and the Wnt5a/Ror2 signaling pathway may be associated with the determination of differentiation of MSCs in this process.

Vitamin D and cardiovascular disease

Vitamin D plays a classical hormonal role in skeletal health by regulating calcium and phosphorus metabolism. Vitamin D metabolites also have physiological functions in nonskeletal tissues, where local synthesis influences regulatory pathways via paracrine and autocrine mechanisms. The active metabolite of vitamin D, 1α,25-dihydroxyvitamin D, binds to the vitamin D receptor that regulates numerous genes involved in fundamental processes of potential relevance to cardiovascular disease, including cell proliferation and differentiation, apoptosis, oxidative stress, membrane transport, matrix homeostasis, and cell adhesion. Vitamin D receptors have been found in all the major cardiovascular cell types including cardiomyocytes, arterial wall cells, and immune cells. Experimental studies have established a role for vitamin D metabolites in pathways that are integral to cardiovascular function and disease, including inflammation, thrombosis, and the renin-angiotensin system. Clinical studies have generally demonstrated an independent association between vitamin D deficiency and various manifestations of degenerative cardiovascular disease including vascular calcification. However, the role of vitamin D supplementation in the management of cardiovascular disease remains to be established. This review summarizes the clinical studies showing associations between vitamin D status and cardiovascular disease and the experimental studies that explore the mechanistic basis for these associations.

Receptor activator of nuclear factor-κB ligand (RANKL) and its relationship to coronary atherosclerosis in HIV patients

HIV-infected individuals have an increased prevalence of coronary artery disease. Receptor activator of nuclear factor-κB ligand (RANKL) and osteoprotegerin have been postulated as mediators of vascular calcification. 78 HIV-infected men and 32 healthy controls without history of coronary artery disease were prospectively recruited to undergo cardiac computed tomography and computed tomography angiography to assess coronary artery calcium and plaque burden. Soluble receptor activator of nuclear factor-κB ligand was lower in HIV-infected individuals than controls [2.52 (1.08-3.98) vs. 3.33 (2.44-4.64) pg/mL, P = 0.01, median (IQR) respectively]. Soluble receptor activator of nuclear factor-κB ligand was negatively associated with the number of coronary segments with plaque (Spearman ρ = -0.41, P < 0.001) and Agatston calcium score (ρ = -0.30, P < 0.01) in HIV-infected individuals even after adjusting for traditional cardiovascular risk factors.

Visualizing novel concepts of cardiovascular calcification

Cardiovascular calcification is currently viewed as an active disease process similar to embryonic bone formation. Cardiovascular calcification mainly affects the aortic valve and arteries and is associated with increased mortality risk. Aortic valve and arterial calcification share similar risk factors, including age, gender, diabetes, chronic renal disease, and smoking. However, the exact cellular and molecular mechanism of cardiovascular calcification is unknown. Late-stage cardiovascular calcification can be visualized with conventional imaging modalities such as echocardiography and computed tomography. However, these modalities are limited in their ability to detect the development of early calcification and the progression of calcification until advanced tissue mineralization is apparent. Due to the subsequent late diagnosis of cardiovascular calcification, treatment is usually comprised of invasive interventions such as surgery. The need to understand the process of calcification is therefore warranted and requires new imaging modalities which are able to visualize early cardiovascular calcification. This review focuses on the use of new imaging techniques to visualize novel concepts of cardiovascular calcification.

Pharmacological inhibition of PHOSPHO1 suppresses vascular smooth muscle cell calcification

Medial vascular calcification (MVC) is common in patients with chronic kidney disease, obesity, and aging. MVC is an actively regulated process that resembles skeletal mineralization, resulting from chondro-osteogenic transformation of vascular smooth muscle cells (VSMCs). Here, we used mineralizing murine VSMCs to study the expression of PHOSPHO1, a phosphatase that participates in the first step of matrix vesicles-mediated initiation of mineralization during endochondral ossification. Wild-type (WT) VSMCs cultured under calcifying conditions exhibited increased Phospho1 gene expression and Phospho1(-/-) VSMCs failed to mineralize in vitro. Using natural PHOSPHO1 substrates, potent and specific inhibitors of PHOSPHO1 were identified via high-throughput screening and mechanistic analysis and two of these inhibitors, designated MLS-0390838 and MLS-0263839, were selected for further analysis. Their effectiveness in preventing VSMC calcification by targeting PHOSPHO1 function was assessed, alone and in combination with a potent tissue-nonspecific alkaline phosphatase (TNAP) inhibitor MLS-0038949. PHOSPHO1 inhibition by MLS-0263839 in mineralizing WT cells (cultured with added inorganic phosphate) reduced calcification in culture to 41.8% ± 2.0% of control. Combined inhibition of PHOSPHO1 by MLS-0263839 and TNAP by MLS-0038949 significantly reduced calcification to 20.9% ± 0.74% of control. Furthermore, the dual inhibition strategy affected the expression of several mineralization-related enzymes while increasing expression of the smooth muscle cell marker Acta2. We conclude that PHOSPHO1 plays a critical role in VSMC mineralization and that "phosphatase inhibition" may be a useful therapeutic strategy to reduce MVC.

Arterial calcification and bone physiology: role of the bone-vascular axis

Bone never forms without vascular interactions. This simple statement of fact does not adequately reflect the physiological and pharmacological implications of the relationship. The vasculature is the conduit for nutrient exchange between bone and the rest of the body. The vasculature provides the sustentacular niche for development of osteoblast progenitors and is the conduit for egress of bone marrow cell products arising, in turn, from the osteoblast-dependent haematopoietic niche. Importantly, the second most calcified structure in humans after the skeleton is the vasculature. Once considered a passive process of dead and dying cells, vascular calcification has emerged as an actively regulated form of tissue biomineralization. Skeletal morphogens and osteochondrogenic transcription factors are expressed by cells within the vessel wall, which regulates the deposition of vascular calcium. Osteotropic hormones, including parathyroid hormone, regulate both vascular and skeletal mineralization. Cellular, endocrine and metabolic signals that flow bidirectionally between the vasculature and bone are necessary for both bone health and vascular health. Dysmetabolic states including diabetes mellitus, uraemia and hyperlipidaemia perturb the bone-vascular axis, giving rise to devastating vascular and skeletal disease. A detailed understanding of bone-vascular interactions is necessary to address the unmet clinical needs of an increasingly aged and dysmetabolic population.

Chronic kidney disease and vascular remodelling: molecular mechanisms and clinical implications

CKD (chronic kidney disease) is a severe and complex disease with a very high prevalence of CV (cardiovascular) complications. CKD patients are exposed to haemodynamic disturbances in addition to severe metabolic abnormalities that lead to a specific form of arterial remodelling, which contributes to the development of CV disease. Arterial calcification is a major event in the arterial remodelling process and is strongly linked to mineral metabolism abnormalities associated with CKD. Arterial remodelling is not limited to arterial calcification and modifications in arterial wall composition are also observed. Activation of the RAS (renin-angiotensin system), ET-1 (endothelin-1), endothelial dysfunction, oxidative stress and ADMA (asymmetric ω-NG,NG-dimethylarginine), as well as the anti-aging molecule Klotho, are implicated in this process. The present review details the mechanisms involved in arterial calcification and arterial remodelling associated with CKD, and provides the clinical consequences of large and small artery stiffness and remodelling in CKD patients.