Fibronectin and collagen I matrixes promote calcification of vascular cells in vitro, whereas collagen IV matrix is inhibitory

MicroRNAs regulate the vicious cycle of vascular calcification-osteoporosis in postmenopausal women

Menopause is a normal physiological process accompanied by changes in various physiological states. The incidence of vascular calcification (VC) increases each year after menopause and is closely related to osteoporosis (OP). Although many studies have investigated the links between VC and OP, the interaction mechanism of the two under conditions of estrogen loss remains unclear. MicroRNAs (miRNAs), which are involved in epigenetic modification, play a critical role in estrogen-mediated mineralization. In the past several decades, miRNAs have been identified as biomarkers or therapeutic targets in diseases. Thus, we hypothesize that these small molecules can provide new diagnostic and therapeutic approaches. In this review, we summarize the close interactions between VC and OP and the role of miRNAs in their interplay.

The interplay of collagen, macrophages, and microcalcification in atherosclerotic plaque cap rupture mechanics

The rupture of an atherosclerotic plaque cap overlying a lipid pool and/or necrotic core can lead to thrombotic cardiovascular events. In essence, the rupture of the plaque cap is a mechanical event, which occurs when the local stress exceeds the local tissue strength. However, due to inter- and intra-cap heterogeneity, the resulting ultimate cap strength varies, causing proper assessment of the plaque at risk of rupture to be lacking. Important players involved in tissue strength include the load-bearing collagenous matrix, macrophages, as major promoters of extracellular matrix degradation, and microcalcifications, deposits that can exacerbate local stress, increasing tissue propensity for rupture. This review summarizes the role of these components individually in tissue mechanics, along with the interplay between them. We argue that to be able to improve risk assessment, a better understanding of the effect of these individual components, as well as their reciprocal relationships on cap mechanics, is required. Finally, we discuss potential future steps, including a holistic multidisciplinary approach, multifactorial 3D in vitro model systems, and advancements in imaging techniques. The obtained knowledge will ultimately serve as input to help diagnose, prevent, and treat atherosclerotic cap rupture.

Whole-genome sequencing uncovers two loci for coronary artery calcification and identifies ARSE as a regulator of vascular calcification

Coronary artery calcification (CAC) is a measure of atherosclerosis and a well-established predictor of coronary artery disease (CAD) events. Here we describe a genome-wide association study (GWAS) of CAC in 22,400 participants from multiple ancestral groups. We confirmed associations with four known loci and identified two additional loci associated with CAC (ARSE and MMP16), with evidence of significant associations in replication analyses for both novel loci. Functional assays of ARSE and MMP16 in human vascular smooth muscle cells (VSMCs) demonstrate that ARSE is a promoter of VSMC calcification and VSMC phenotype switching from a contractile to a calcifying or osteogenic phenotype. Furthermore, we show that the association of variants near ARSE with reduced CAC is likely explained by reduced ARSE expression with the G allele of enhancer variant rs5982944. Our study highlights ARSE as an important contributor to atherosclerotic vascular calcification, and a potential drug target for vascular calcific disease.

CD11b Deficiency Favors Cartilage Calcification via Increased Matrix Vesicles, Apoptosis, and Lysyl Oxidase Activity

Pathological cartilage calcification is a hallmark feature of osteoarthritis, a common degenerative joint disease, characterized by cartilage damage, progressively causing pain and loss of movement. The integrin subunit CD11b was shown to play a protective role against cartilage calcification in a mouse model of surgery-induced OA. Here, we investigated the possible mechanism by which CD11b deficiency could favor cartilage calcification by using naïve mice. First, we found by transmission electron microscopy (TEM) that CD11b KO cartilage from young mice presented early calcification spots compared with WT. CD11b KO cartilage from old mice showed progression of calcification areas. Mechanistically, we found more calcification-competent matrix vesicles and more apoptosis in both cartilage and chondrocytes isolated from CD11b-deficient mice. Additionally, the extracellular matrix from cartilage lacking the integrin was dysregulated with increased collagen fibrils with smaller diameters. Moreover, we revealed by TEM that CD11b KO cartilage had increased expression of lysyl oxidase (LOX), the enzyme that catalyzes matrix crosslinks. We confirmed this in murine primary CD11b KO chondrocytes, where Lox gene expression and crosslinking activity were increased. Overall, our results suggest that CD11b integrin regulates cartilage calcification through reduced MV release, apoptosis, LOX activity, and matrix crosslinking. As such, CD11b activation might be a key pathway for maintaining cartilage integrity.

Biomechanical Properties of the Aortic Wall: Changes during Vascular Calcification

Medial vascular calcification (MAC) is characterized by the deposition of hydroxyapatite (HAP) in the medial layer of the vessel wall, leading to disruption of vessel integrity and vascular stiffness. Because currently no direct therapeutic interventions for MAC are available, studying the MAC pathogenesis is of high research interest. Several methods exist to measure and describe the pathophysiological processes in the vessel wall, such as histological staining and gene expression. However, no method describing the physiological properties of the arterial wall is currently available. This study aims to close that gap and validate a method to measure the biomechanical properties of the arterial wall during vascular calcification. Therefore, a stress-stretch curve is monitored using small-vessel-myography upon ex vivo calcification of rat aortic tissue. The measurement of biomechanical properties could help to gain further insights into vessel integrity during calcification progression.

Nidogen-2 is a Novel Endogenous Ligand of LGR4 to Inhibit Vascular Calcification

BACKGROUND

Vascular calcification is closely related to the all-cause mortality of cardiovascular events. Basement membrane protein nidogen-2 is a key component of the vascular extracellular matrix microenvironment and we recently found it is pivotal for the maintenance of contractile phenotype in vascular smooth muscle cells (VSMCs). However, whether nidogen-2 is involved in VSMCs osteochondrogenic transition and vascular calcification remains unclear.

METHODS

VSMCs was treated with high-phosphate to study VSMC calcification in vitro. Three different mice models (5/6 nephrectomy-induced chronic renal failure, cholecalciferol-overload, and periadventitially administered with CaCl₂) were used to study vascular calcification in vivo. Membrane protein interactome, coimmunoprecipitation, flow cytometric binding assay, surface plasmon resonance, G protein signaling, VSMCs calcium assays were performed to clarify the phenotype and elucidate the molecular mechanisms.

RESULTS

Nidogen-2 protein levels were significantly reduced in calcified VSMCs and aortas from mice in different vascular calcification model. Nidogen-2 deficiency exacerbated high-phosphate-induced VSMC calcification, whereas the addition of purified nidogen-2 protein markedly alleviated VSMC calcification in vitro. Nidogen-2^-/- mice exhibited aggravated aorta calcification compared to wild-type (WT) mice in response to 5/6 nephrectomy, cholecalciferol-overload, and CaCl₂ administration. Further unbiased coimmunoprecipitation and interactome analysis of purified nidogen-2 and membrane protein in VSMCs revealed that nidogen-2 directly binds to LGR4 (leucine-rich repeat G-protein-coupled receptor 4) with K_D value 26.77 nM. LGR4 deficiency in VSMCs in vitro or in vivo abolished the protective effect of nidogen-2 on vascular calcification. Of interest, nidogen-2 biased activated LGR4-Gαq-PKCα (protein kinase Cα)-AMPKα1 (AMP-activated protein kinase α1) signaling to counteract VSMCs osteogenic transition and mineralization.

CONCLUSIONS

Nidogen-2 is a novel endogenous ligand of LGR4 that biased activated Gαq- PKCα-AMPKα1 signaling and inhibited vascular calcification.

Role of Collagen in Vascular Calcification

ABSTRACT

Vascular calcification is a pathological process characterized by ectopic calcification of the vascular wall. Medial calcifications are most often associated with kidney disease, diabetes, hypertension, and advanced age. Intimal calcifications are associated with atherosclerosis. Collagen can regulate mineralization by binding to apatite minerals and promoting their deposition, binding to collagen receptors to initiate signal transduction, and inducing cell transdifferentiation. In the process of vascular calcification, type I collagen is not only the scaffold for mineral deposition but also a signal entity, guiding the distribution, aggregation, and nucleation of vesicles and promoting the transformation of vascular smooth muscle cells into osteochondral-like cells. In recent years, collagen has been shown to affect vascular calcification through collagen disc-domain receptors, matrix vesicles, and transdifferentiation of vascular smooth muscle cells.

Pulmonary hypertension: Linking inflammation and pulmonary arterial stiffening

Pulmonary hypertension (PH) is a progressive disease that arises from multiple etiologies and ultimately leads to right heart failure as the predominant cause of morbidity and mortality. In patients, distinct inflammatory responses are a prominent feature in different types of PH, and various immunomodulatory interventions have been shown to modulate disease development and progression in animal models. Specifically, PH-associated inflammation comprises infiltration of both innate and adaptive immune cells into the vascular wall of the pulmonary vasculature—specifically in pulmonary vascular lesions—as well as increased levels of cytokines and chemokines in circulating blood and in the perivascular tissue of pulmonary arteries (PAs). Previous studies suggest that altered hemodynamic forces cause lung endothelial dysfunction and, in turn, adherence of immune cells and release of inflammatory mediators, while the resulting perivascular inflammation, in turn, promotes vascular remodeling and the progression of PH. As such, a vicious cycle of endothelial activation, inflammation, and vascular remodeling may develop and drive the disease process. PA stiffening constitutes an emerging research area in PH, with relevance in PH diagnostics, prognostics, and as a therapeutic target. With respect to its prognostic value, PA stiffness rivals the well-established measurement of pulmonary vascular resistance as a predictor of disease outcome. Vascular remodeling of the arterial extracellular matrix (ECM) as well as vascular calcification, smooth muscle cell stiffening, vascular wall thickening, and tissue fibrosis contribute to PA stiffening. While associations between inflammation and vascular stiffening are well-established in systemic vascular diseases such as atherosclerosis or the vascular manifestations of systemic sclerosis, a similar connection between inflammatory processes and PA stiffening has so far not been addressed in the context of PH. In this review, we discuss potential links between inflammation and PA stiffening with a specific focus on vascular calcification and ECM remodeling in PH.

MFG-E8 promotes osteogenic transdifferentiation of smooth muscle cells and vascular calcification by regulating TGF-β1 signaling

Vascular calcification occurs in arterial aging, atherosclerosis, diabetes mellitus, and chronic kidney disease. Transforming growth factor-β1 (TGF-β1) is a key modulator driving the osteogenic transdifferentiation of vascular smooth muscle cells (VSMCs), leading to vascular calcification. We hypothesize that milk fat globule–epidermal growth factor 8 (MFG-E8), a glycoprotein expressed in VSMCs, promotes the osteogenic transdifferentiation of VSMCs through the activation of TGF-β1-mediated signaling. We observe that the genetic deletion of MFG-E8 prevents calcium chloride-induced vascular calcification in common carotid arteries (CCAs). The exogenous application of MFG-E8 to aged CCAs promotes arterial wall calcification. MFG-E8-deficient cultured VSMCs exhibit decreased biomineralization and phenotypic transformation to osteoblast-like cells in response to osteogenic medium. MFG-E8 promotes β1 integrin–dependent MMP2 expression, causing TGF-β1 activation and subsequent VSMC osteogenic transdifferentiation and biomineralization. Thus, the established molecular link between MFG-E8 and vascular calcification suggests that MFG-E8 can be therapeutically targeted to mitigate vascular calcification.

A molecular link between the milk fat globule–epidermal growth factor 8 (MFG-E8), activation of vascular calcification driver TGF-β1 and osteogenic differentiation of vascular smooth muscle cells suggests that MFG-E8 could be a therapeutic target for vascular calcification.

Osteomodulin attenuates smooth muscle cell osteogenic transition in vascular calcification

Rationale

Vascular calcification is a prominent feature of late‐stage diabetes, renal and cardiovascular disease (CVD), and has been linked to adverse events. Recent studies in patients reported that plasma levels of osteomodulin (OMD), a proteoglycan involved in bone mineralisation, associate with diabetes and CVD. We hypothesised that OMD could be implicated in these diseases via vascular calcification as a common underlying factor and aimed to investigate its role in this context.

Methods and results

In patients with chronic kidney disease, plasma OMD levels correlated with markers of inflammation and bone turnover, with the protein present in calcified arterial media. Plasma OMD also associated with cardiac calcification and the protein was detected in calcified valve leaflets by immunohistochemistry. In patients with carotid atherosclerosis, circulating OMD was increased in association with plaque calcification as assessed by computed tomography. Transcriptomic and proteomic data showed that OMD was upregulated in atherosclerotic compared to control arteries, particularly in calcified plaques, where OMD expression correlated positively with markers of smooth muscle cells (SMCs), osteoblasts and glycoproteins. Immunostaining confirmed that OMD was abundantly present in calcified plaques, localised to extracellular matrix and regions rich in α‐SMA⁺ cells. In vivo, OMD was enriched in SMCs around calcified nodules in aortic media of nephrectomised rats and in plaques from ApoE^−/− mice on warfarin. In vitro experiments revealed that OMD mRNA was upregulated in SMCs stimulated with IFNγ, BMP2, TGFβ1, phosphate and β‐glycerophosphate, and by administration of recombinant human OMD protein (rhOMD). Mechanistically, addition of rhOMD repressed the calcification process of SMCs treated with phosphate by maintaining their contractile phenotype along with enriched matrix organisation, thereby attenuating SMC osteoblastic transformation. Mechanistically, the role of OMD is exerted likely through its link with SMAD3 and TGFB1 signalling, and interplay with BMP2 in vascular tissues.

Conclusion

We report a consistent association of both circulating and tissue OMD levels with cardiovascular calcification, highlighting the potential of OMD as a clinical biomarker. OMD was localised in medial and intimal α‐SMA⁺ regions of calcified cardiovascular tissues, induced by pro‐inflammatory and pro‐osteogenic stimuli, while the presence of OMD in extracellular environment attenuated SMC calcification.

Mitochondria and traffic-related air pollution linked coronary artery calcification: exploring the missing link

The continuing increase in the exposure to Traffic-related air pollution (TRAP) in the general population is predicted to result in a higher incidence of non-communicable diseases like cardiovascular disease. The chronic exposure of air particulate matter from TRAP upon the vascular system leads to the enhancement of deposition of calcium in the vasculature leading to coronary artery calcification (CAC), triggered by inflammatory reactions and endothelial dysfunction. This calcification forms within the intimal and medial layers of vasculature and the underlying mechanism that connects the trigger from TRAP is not well explored. Several local and systemic factors participate in this active process including inflammatory response, hyperlipidemia, presence of self-programmed death bodies and high calcium-phosphate concentrations. These factors along with the loss of molecules that inhibit calcification and circulating nucleation complexes influence the development of calcification in the vasculature. The loss of defense to prevent osteogenic transition linked to micro organelle dysfunction that includes deteriorated mitochondria, elevated mitochondrial oxidative stress, and defective mitophagy. In this review, we examine the contributory role of mitochondria involved in the mechanism of TRAP linked CAC development. Further we examine whether TRAP is an inducer or trigger for the enhanced progression of CAC.

Inflammation: a putative link between phosphate metabolism and cardiovascular disease

Dietary habits in the western world lead to increasing phosphate intake. Under physiological conditions, extraosseous precipitation of phosphate with calcium is prevented by a mineral buffering system composed of calcification inhibitors and tight control of serum phosphate levels. The coordinated hormonal regulation of serum phosphate involves fibroblast growth factor 23 (FGF23), αKlotho, parathyroid hormone (PTH) and calcitriol. A severe derangement of phosphate homeostasis is observed in patients with chronic kidney disease (CKD), a patient collective with extremely high risk of cardiovascular morbidity and mortality. Higher phosphate levels in serum have been associated with increased risk for cardiovascular disease (CVD) in CKD patients, but also in the general population. The causal connections between phosphate and CVD are currently incompletely understood. An assumed link between phosphate and cardiovascular risk is the development of medial vascular calcification, a process actively promoted and regulated by a complex mechanistic interplay involving activation of pro-inflammatory signalling. Emerging evidence indicates a link between disturbances in phosphate homeostasis and inflammation. The present review focuses on critical interactions of phosphate homeostasis, inflammation, vascular calcification and CVD. Especially, pro-inflammatory responses mediating hyperphosphatemia-related development of vascular calcification as well as FGF23 as a critical factor in the interplay between inflammation and cardiovascular alterations, beyond its phosphaturic effects, are addressed.

Analysis of crucial genes, pathways and construction of the molecular regulatory networks in vascular smooth muscle cell calcification

Vascular calcification (VC) accompanies the trans-differentiation of vascular smooth muscle cells (VSMCs) into osteo/chondrocyte-like cells and resembles physiological bone mineralization. However, the molecular mechanisms underlying VC initiation and progression have remained largely elusive. The aim of the present study was to identify the genes and pathways common to VSMC and osteoblast calcification and construct a regulatory network of non-coding RNAs and transcription factors (TFs). To this end, the Gene Expression Omnibus dataset GSE37558 including mRNA microarray data of calcifying VSMCs (CVSMCs) and calcifying osteoblasts (COs) was analyzed. The differentially expressed genes (DEGs) were screened and functionally annotated and the microRNA (miRNA/mRNA)-mRNA, TF-miRNA and long non-coding RNA (lncRNA)-TF regulatory networks were constructed. A total of 318 DEGs were identified in the CVSMCs relative to the non-calcified VSMCs, of which 43 were shared with the COs. The CVSMC-related DEGs were mainly enriched in the functional terms cell cycle, extracellular matrix (ECM), inflammation and chemotaxis-mediated signaling pathways, of which ECM was enriched by the DEGs for the COs as well. The protein-protein interaction network of CVSMCs consisted of 281 genes and 3,650 edges. There were 30 hub genes in this network, including maternal embryonic leucine zipper kinase (MELK), which potentially regulates the differentially expressed TF (DETF) forkhead box (FOX)M1 and is a potential target gene of Homo sapiens miR-485-3p and miR-181d. The TF-miRNA network included 251 TFs and 60 miRNAs, including 10 DETFs such as FOXO1 and snail family transcriptional repressor 2 (SNAI2). Furthermore, the lncRNAs H19 imprinted maternally expressed transcript (H19) and differentiation antagonizing non-protein coding RNA (DANCR) were predicted as the upstream regulators of FOXO1 and SNAI2 in the lncRNA-TF regulatory network. DANCR, MELK and FOXM1 were downregulated, and H19, FOXO1 and SNAI2 were upregulated in the CVSMCs. Taken together, the CVSMCs and COs exhibited similar molecular changes in the ECM. In addition, the MELK-FOXM1, H19/DANCR-FOXO1 and SNAI2 regulatory pathways likely mediate VSMC calcification.

Vascular Extracellular Matrix Remodeling and Hypertension

Significance: The vascular extracellular matrix (ECM) not only provides mechanical stability but also manipulates vascular cell behaviors, which are crucial for vascular function and homeostasis. ECM remodeling, which alters vascular wall mechanical properties and exposes vascular cells to bioactive molecules, is involved in the development and progression of hypertension. Recent Advances: This brief review summarized the dynamic changes in ECM components and their modification and degradation during hypertension and after antihypertensive treatment. We also discussed how alterations in the ECM amount, assembly, mechanical properties, and degradation fragment generation provide input into the pathological process of hypertension. Critical Issues: Although the relevance between ECM remodeling and hypertension has been recognized, the underlying mechanism by which ECM remodeling initiates the development of hypertension remains unclear. Therefore, the modulation of ECM remodeling on arterial stiffness and hypertension in genetically modified rodent models is summarized in this review. The circulating biomarkers based on ECM metabolism and therapeutic strategies targeting ECM disorders in hypertension are also introduced. Future Directions: Further research will provide more comprehensive understanding of ECM remodeling in hypertension by the application of matridomic and degradomic approaches. The better understanding of mechanisms underlying vascular ECM remodeling may provide novel potential therapeutic strategies for preventing and treating hypertension. Antioxid. Redox Signal. 34, 765-783.

Probing Osteocyte Functions in Gelatin Hydrogels with Tunable Viscoelasticity

Bone is an attractive site for metastatic cancer cells and has been considered as "soil" for promoting tumor growth. However, accumulating evidence suggests that some bone cells (e.g., osteocytes) can actually suppress cancer cell migration and invasion via direct cell-cell contact and/or through cytokine secretion. Toward designing a biomimetic niche for supporting 3D osteocyte culture, we present here a gelatin-based hydrogel system with independently tunable matrix stiffness and viscoelasticity. In particular, we synthesized a bifunctional macromer, gelatin-norbornene-boronic acid (i.e., GelNB-BA), for covalent cross-linking with multifunctional thiol linkers [e.g., four-arm poly(ethylene glycol)-thiol or PEG4SH] to form thiol-NB hydrogels. The immobilized BA moieties in the hydrogel readily formed reversible boronate ester bonds with 1,3-diols on physically entrapped poly(vinyl alcohol) (PVA). Adjusting the compositions of GelNB-BA, PEG4SH, and PVA afforded hydrogels with independently tunable elasticity and viscoelasticity. With this new dynamic hydrogel platform, we investigated matrix mechanics-induced growth and cytokine secretion of encapsulated MLO-A5 pre-osteocytes. We discovered that more compliant or viscoelastic gels promoted A5 cell growth. On the other hand, cells encapsulated in stiffer gels secreted higher amounts of pro-inflammatory cytokines and chemokines. Finally, conditioned media (CM) collected from the encapsulated MLO-A5 cells (i.e., A5-CM) strongly inhibited breast cancer cell proliferation, invasion, and expression of tumor-activating genes. This new biomimetic hydrogel platform not only serves as a versatile matrix for investigating mechano-sensing in osteocytes but also provides a means to produce powerful anti-tumor CM.

Apoptosis in the Extraosseous Calcification Process

Extraosseous calcification is a pathologic mineralization process occurring in soft connective tissues (e.g., skin, vessels, tendons, and cartilage). It can take place on a genetic basis or as a consequence of acquired chronic diseases. In this last case, the etiology is multifactorial, including both extra- and intracellular mechanisms, such as the formation of membrane vesicles (e.g., matrix vesicles and apoptotic bodies), mitochondrial alterations, and oxidative stress. This review is an overview of extraosseous calcification mechanisms focusing on the relationships between apoptosis and mineralization in cartilage and vascular tissues, as these are the two tissues mostly affected by a number of age-related diseases having a progressively increased impact in Western Countries.

The roles of collagen in chronic kidney disease and vascular calcification

The extracellular matrix component collagen is widely expressed in human tissues and participates in various cellular biological processes. The collagen amount generally remains stable due to intricate regulatory networks, but abnormalities can lead to several diseases. During the development of renal fibrosis and vascular calcification, the expression of collagen is significantly increased, which promotes phenotypic changes in intrinsic renal cells and vascular smooth muscle cells, thereby exacerbating disease progression. Reversing the overexpression of collagen substantially prevents or slows renal fibrosis and vascular calcification in a wide range of animal models, suggesting a novel target for treating patients with these diseases. Stem cell therapy seems to be an effective strategy to alleviate these two conditions. However, recent findings indicate that the natural pore structure of collagen fibers is sufficient to induce the inappropriate differentiation of stem cells and thereby exacerbate renal fibrosis and vascular calcification. A comprehensive understanding of the role of collagen in these diseases and its effect on stem cell biology will assist in improving the unmet requirements for treating patients with kidney disease.

Mechanisms of the Osteogenic Switch of Smooth Muscle Cells in Vascular Calcification: WNT Signaling, BMPs, Mechanotransduction, and EndMT

Characterized by the hardening of arteries, vascular calcification is the deposition of hydroxyapatite crystals in the arterial tissue. Calcification is now understood to be a cell-regulated process involving the phenotypic transition of vascular smooth muscle cells into osteoblast-like cells. There are various pathways of initiation and mechanisms behind vascular calcification, but this literature review highlights the wingless-related integration site (WNT) pathway, along with bone morphogenic proteins (BMPs) and mechanical strain. The process mirrors that of bone formation and remodeling, as an increase in mechanical stress causes osteogenesis. Observing the similarities between the two may aid in the development of a deeper understanding of calcification. Both are thought to be regulated by the WNT signaling cascade and bone morphogenetic protein signaling and can also be activated in response to stress. In a pro-calcific environment, integrins and cadherins of vascular smooth muscle cells respond to a mechanical stimulus, activating cellular signaling pathways, ultimately resulting in gene regulation that promotes calcification of the vascular extracellular matrix (ECM). The endothelium is also thought to contribute to vascular calcification via endothelial to mesenchymal transition, creating greater cell plasticity. Each of these factors contributes to calcification, leading to increased cardiovascular mortality in patients, especially those suffering from other conditions, such as diabetes and kidney failure. Developing a better understanding of the mechanisms behind calcification may lead to the development of a potential treatment in the future.

Sleep, brain vascular health and ageing

Sleep maintains the function of the entire body through homeostasis. Chronic sleep deprivation (CSD) is a prime health concern in the modern world. Previous reports have shown that CSD has profound negative effects on brain vasculature at both the cellular and molecular levels, and that this is a major cause of cognitive dysfunction and early vascular ageing. However, correlations among sleep deprivation (SD), brain vascular changes and ageing have barely been looked into. This review attempts to correlate the alterations in the levels of major neurotransmitters (acetylcholine, adrenaline, GABA and glutamate) and signalling molecules (Sirt1, PGC1α, FOXO, P66^shc, PARP1) in SD and changes in brain vasculature, cognitive dysfunction and early ageing. It also aims to connect SD-induced loss in the number of dendritic spines and their effects on alterations in synaptic plasticity, cognitive disabilities and early vascular ageing based on data available in scientific literature. To the best of our knowledge, this is the first article providing a pathophysiological basis to link SD to brain vascular ageing.

The biology of vascular calcification

Vascular calcification (VC), characterized by different mineral deposits (i.e., carbonate apatite, whitlockite and hydroxyapatite) accumulating in blood vessels and valves, represents a relevant pathological process for the aging population and a life-threatening complication in acquired and in genetic diseases. Similarly to bone remodeling, VC is an actively regulated process in which many cells and molecules play a pivotal role. This review aims at: (i) describing the role of resident and circulating cells, of the extracellular environment and of positive and negative factors in driving the mineralization process; (ii) detailing the types of VC (i.e., intimal, medial and cardiac valve calcification); (iii) analyzing rare genetic diseases underlining the importance of altered pyrophosphate-dependent regulatory mechanisms; (iv) providing therapeutic options and perspectives.

MG 53 Protein Protects Aortic Valve Interstitial Cells From Membrane Injury and Fibrocalcific Remodeling

Background The aortic valve of the heart experiences constant mechanical stress under physiological conditions. Maladaptive valve injury responses contribute to the development of valvular heart disease. Here, we test the hypothesis that MG 53 (mitsugumin 53), an essential cell membrane repair protein, can protect valvular cells from injury and fibrocalcific remodeling processes associated with valvular heart disease. Methods and Results We found that MG 53 is expressed in pig and human patient aortic valves and observed aortic valve disease in aged Mg53-/- mice. Aortic valves of Mg53-/- mice showed compromised cell membrane integrity. In vitro studies demonstrated that recombinant human MG 53 protein protects primary valve interstitial cells from mechanical injury and that, in addition to mediating membrane repair, recombinant human MG 53 can enter valve interstitial cells and suppress transforming growth factor-β-dependent activation of fibrocalcific signaling. Conclusions Together, our data characterize valve interstitial cell membrane repair as a novel mechanism of protection against valvular remodeling and assess potential in vivo roles of MG 53 in preventing valvular heart disease.

Cardiovascular calcification: artificial intelligence and big data accelerate mechanistic discovery

Cardiovascular calcification is a health disorder with increasing prevalence and high morbidity and mortality. The only available therapeutic options for calcific vascular and valvular heart disease are invasive transcatheter procedures or surgeries that do not fully address the wide spectrum of these conditions; therefore, an urgent need exists for medical options. Cardiovascular calcification is an active process, which provides a potential opportunity for effective therapeutic targeting. Numerous biological processes are involved in calcific disease, including matrix remodelling, transcriptional regulation, mitochondrial dysfunction, oxidative stress, calcium and phosphate signalling, endoplasmic reticulum stress, lipid and mineral metabolism, autophagy, inflammation, apoptosis, loss of mineralization inhibition, impaired mineral resorption, cellular senescence and extracellular vesicles that act as precursors of microcalcification. Advances in molecular imaging and big data technology, including in multiomics and network medicine, and the integration of these approaches are helping to provide a more comprehensive map of human disease. In this Review, we discuss ectopic calcification processes in the cardiovascular system, with an emphasis on emerging mechanistic knowledge obtained through patient data and advances in imaging methods, experimental models and multiomics-generated big data. We also highlight the potential and challenges of artificial intelligence, machine learning and deep learning to integrate imaging and mechanistic data for drug discovery.

Cell-Matrix Interactions and Matricrine Signaling in the Pathogenesis of Vascular Calcification

Vascular calcification is a complex pathological process occurring in patients with atherosclerosis, type 2 diabetes, and chronic kidney disease. The extracellular matrix, via matricrine-receptor signaling plays important roles in the pathogenesis of calcification. Calcification is mediated by osteochondrocytic-like cells that arise from transdifferentiating vascular smooth muscle cells. Recent advances in our understanding of the plasticity of vascular smooth muscle cell and other cells of mesenchymal origin have furthered our understanding of how these cells transdifferentiate into osteochondrocytic-like cells in response to environmental cues. In the present review, we examine the role of the extracellular matrix in the regulation of cell behavior and differentiation in the context of vascular calcification. In pathological calcification, the extracellular matrix not only provides a scaffold for mineral deposition, but also acts as an active signaling entity. In recent years, extracellular matrix components have been shown to influence cellular signaling through matrix receptors such as the discoidin domain receptor family, integrins, and elastin receptors, all of which can modulate osteochondrocytic differentiation and calcification. Changes in extracellular matrix stiffness and composition are detected by these receptors which in turn modulate downstream signaling pathways and cytoskeletal dynamics, which are critical to osteogenic differentiation. This review will focus on recent literature that highlights the role of cell-matrix interactions and how they influence cellular behavior, and osteochondrocytic transdifferentiation in the pathogenesis of cardiovascular calcification.

Alkaline Phosphatases in the Complex Chronic Kidney Disease-Mineral and Bone Disorders

Alkaline phosphatases (APs) remove the phosphate (dephosphorylation) needed in multiple metabolic processes (from many molecules such as proteins, nucleotides, or pyrophosphate). Therefore, APs are important for bone mineralization but paradoxically they can also be deleterious for other processes, such as vascular calcification and the increasingly known cross-talk between bone and vessels. A proper balance between beneficial and harmful activities is further complicated in the context of chronic kidney disease (CKD). In this narrative review, we will briefly update the complexity of the enzyme, including its different isoforms such as the bone-specific alkaline phosphatase or the most recently discovered B1x. We will also analyze the correlations and potential discrepancies with parathyroid hormone and bone turnover and, most importantly, the valuable recent associations of AP's with cardiovascular disease and/or vascular calcification, and survival. Finally, a basic knowledge of the synthetic and degradation pathways of APs promises to open new therapeutic strategies for the treatment of the CKD-Mineral and Bone Disorder (CKD-MBD) in the near future, as well as for other processes such as sepsis, acute kidney injury, inflammation, endothelial dysfunction, metabolic syndrome or, in diabetes, cardiovascular complications. However, no studies have been done using APs as a primary therapeutic target for clinical outcomes, and therefore, AP's levels cannot yet be used alone as an isolated primary target in the treatment of CKD-MBD. Nonetheless, its diagnostic and prognostic potential should be underlined.

Genetics of Subclinical Coronary Atherosclerosis

Purpose of Review

This review highlights recent findings regarding genetics of coronary artery calcification (CAC), a marker of subclinical atherosclerosis burden, that is a precursor of clinical coronary artery disease.

Recent findings

CAC quantity is heritable. Genome wide association studies of common single nucleotide polymorphisms have identified genomic regions explaining ~2.4% of CAC heritability. Low frequency and rare variants explain additional variation in CAC. Evidence suggests that there may be different genetic etiologies for variation in CAC progression than for cross-sectional measures of CAC. Studies integrating multiple -omics data are providing new insights into the pathobiology of subclinical coronary atherosclerosis.

Summary

The future is promising for innovative studies utilizing whole genome sequencing data as well as other -omics such as epigenomic modifications of genes and gene expression. These studies may provide multiple sources of data pointing to the same gene or pathway, thus providing greater confidence in findings.

The Role of Nephronectin on Proliferation and Differentiation in Human Dental Pulp Stem Cells

Aim

The purpose of the current study was to investigate the effects of nephronectin (Npnt) in human dental pulp stem cells (hDPSCs).

Methodology

Npnt was coated to nontissue culture-treated polystyrene (non-PS) plates. The presence of immobilized protein on the surface was detected by polyclonal rabbit primary anti-Npnt antibody. Then the cell number was counted and compared with PBS-, bovine serum albumin- (BSA-), fish scale type I collagen- (FCOL1-), and human fibronectin- (Fn-) coated wells. Cell proliferation was assessed using CCK-8 assay. Cell morphology was observed under light microscopy and fluorescence microscopy. Lastly, the mRNA expression profiles of integrins, dentin sialophosphoprotein (DSPP), bone sialoprotein (BSP), and mineralization capacity of hDPSCs were investigated by real time RT-PCR and alizarin red staining, respectively.

Results

Npnt mediates hDPSC adhesion and spreading partially via the Arg-Gly-Asp (RGD) motif. Npnt enhanced the mRNA expression of ITGA1, ITGA4, ITGA7, and ITGB1 on day five. Npnt downregulated DSPP but significantly upregulated BSP mRNA expression at day 28. Further, Npnt and FCOL1 accelerated the matrix mineralization in hDPSCs.

Conclusions

The current findings implicate that Npnt would be favorable to recruit hDPSCs and conducive to mineralization in hDPSCs. The combination of Npnt with hDPSCs may offer a promising approach for hard tissue regeneration.

Dietary potassium regulates vascular calcification and arterial stiffness

Vascular calcification is a risk factor that predicts adverse cardiovascular complications of several diseases including atherosclerosis. Reduced dietary potassium intake has been linked to cardiovascular diseases such as hypertension and incidental stroke, although the underlying molecular mechanisms remain largely unknown. Using the ApoE-deficient mouse model, we demonstrated for the first time to our knowledge that reduced dietary potassium (0.3%) promoted atherosclerotic vascular calcification and increased aortic stiffness, compared with normal (0.7%) potassium-fed mice. In contrast, increased dietary potassium (2.1%) attenuated vascular calcification and aortic stiffness. Mechanistically, reduction in the potassium concentration to the lower limit of the physiological range increased intracellular calcium, which activated a cAMP response element-binding protein (CREB) signal that subsequently enhanced autophagy and promoted vascular smooth muscle cell (VSMC) calcification. Inhibition of calcium signals and knockdown of either CREB or ATG7, an autophagy regulator, attenuated VSMC calcification induced by low potassium. Consistently, elevated autophagy and CREB signaling were demonstrated in the calcified arteries from low potassium diet-fed mice as well as aortic arteries exposed to low potassium ex vivo. These studies established a potentially novel causative role of dietary potassium intake in regulating atherosclerotic vascular calcification and stiffness, and uncovered mechanisms that offer opportunities to develop therapeutic strategies to control vascular disease.

Collagen XIV and a related recombinant fragment protect human vascular smooth muscle cells from calcium-/phosphate-induced osteochondrocytic transdifferentiation

Transdifferentiation of vascular smooth muscle cells (VSMC) promotes the development of vascular calcifications such as arteriosclerosis. The aim was to investigate effects of specific extracellular matrix (ECM) components on transdifferentiation of VSMC to identify novel ECM-based therapeutic tools. Human collagens I & IV (CI, CIV) along with collagen XIV (CXIV) and a CXIV-derived fragment (CXIV-F), both of which induce differentiation, were applied in an in-vitro model of calcium-/phosphate (Ca/P)-induced osteochondrocytic transdifferentiation of human and murine VSMC. Transdifferentiation was determined by RT-PCR and calcium contents of VSMC cultures. Signaling pathways involved were determined by western-blot and luciferase reporter plasmid assays. Under normal culture conditions, CI induced VSMC proliferation and a more epithelioid/synthetic phenotype while CIV and predominantly CXIV provoked opposite effects. CIV and CXIV further blocked Ca/P-induced osteochondrocytic transdifferentiation of VSMC displayed e.g. by reduced gene expressions of Runx2, Sox9, osterix and increased expressions of αSMA and SM22α. This involved impaired activation of ERK1/2, NF-ĸB and Wnt-signaling. Similar preventive effects were achieved by applying CXIV-F. Impaired preventive effects of CXIV by co-treatment with a cluster of differentiation (CD)44 agonist propose CD44 as a CXIV-target structure on VSMC. In conclusion, CXIV and CXIV-F interfere with osteochondrocytic transdifferentiation of VSMC and should be further explored as potential therapeutic tools in vascular calcification.

Oligogalacturonic Acid Inhibits Vascular Calcification by Two Mechanisms: Inhibition of Vascular Smooth Muscle Cell Osteogenic Conversion and Interaction With Collagen

OBJECTIVE

Cardiovascular diseases constitute the leading cause of mortality worldwide. Calcification of the vessel wall is associated with cardiovascular morbidity and mortality in patients having many diseases, including diabetes mellitus, atherosclerosis, and chronic kidney disease. Vascular calcification is actively regulated by inductive and inhibitory mechanisms (including vascular smooth muscle cell adaptation) and results from an active osteogenic process. During the calcification process, extracellular vesicles (also known as matrix vesicles) released by vascular smooth muscle cells interact with type I collagen and then act as nucleating foci for calcium crystallization. Our primary objective was to identify new, natural molecules that inhibit the vascular calcification process.

APPROACH AND RESULTS

We have found that oligogalacturonic acids (obtained by the acid hydrolysis of polygalacturonic acid) reduce in vitro inorganic phosphate-induced calcification of vascular smooth muscle cells by 80% and inorganic phosphate-induced calcification of isolated rat aortic rings by 50%. A specific oligogalacturonic acid with a degree of polymerization of 8 (DP8) was found to inhibit the expression of osteogenic markers and, thus, prevent the conversion of vascular smooth muscle cells into osteoblast-like cells. We also evidenced in biochemical and immunofluorescence assays a direct interaction between matrix vesicles and type I collagen via the GFOGER sequence (where single letter amino acid nomenclature is used, O=hydroxyproline) thought to be involved in interactions with several pairs of integrins.

CONCLUSIONS

DP8 inhibits vascular calcification development mainly by inhibition of osteogenic marker expression but also partly by masking the GFOGER sequence-thereby, preventing matrix vesicles from binding to type I collagen.

Cell-matrix mechanics and pattern formation in inflammatory cardiovascular calcification

Calcific diseases of the cardiovascular system, such as atherosclerotic calcification and calcific aortic valve disease, are widespread and clinically significant, causing substantial morbidity and mortality. Vascular cells, like bone cells, interact with their matrix substrate through molecular signals, and through biomechanical signals, such as traction forces transmitted from cytoskeleton to matrix. The interaction of contractile vascular cells with their matrix may be one of the most important factors controlling pathological mineralisation of the artery wall and cardiac valves. In many respects, the matricrine and matrix mechanical changes in calcific vasculopathy and valvulopathy resemble those occurring in embryonic bone development and normal bone mineralisation. The matrix proteins provide a microenvironment for propagation of crystal growth and provide mechanical cues to the cells that direct differentiation. Small contractions of the cytoskeleton may tug on integrin links to sites on matrix proteins, and thereby sense the stiffness, possibly through deformation of binding proteins causing release of differentiation factors such as products of the members of the transforming growth factor-β superfamily. Inflammation and matrix characteristics are intertwined: inflammation alters the matrix such as through matrix metalloproteinases, while matrix mechanical properties affect cellular sensitivity to inflammatory cytokines. The adhesive properties of the matrix also regulate self-organisation of vascular cells into patterns through reaction-diffusion phenomena and left-right chirality. In this review, we summarise the roles of extracellular matrix proteins and biomechanics in the development of inflammatory cardiovascular calcification.

Ultrastructure and histogenesis of the acral calcified angioleiomyoma

We studied the ultrastructure, immunohistochemistry, and histogenesis of the acral calcified angioleiomyoma, observing three concentric zones: (a) pseudocapsular, thin, with spindle-shaped stromal cells (SCs), presenting scarce organelles and expressing CD34, (b) muscular, forming a ring, with smooth muscle cells of heterogenous phenotype (mainly in quantity and thickness of filaments, and in expression of h-caldesmon, αSMA, and desmin), and (c) central, extensive, calcified (spicular and/or star-shaped calcium deposits around collagen fibers), with pericytic involutive vasculature. The intratumoral vessels were thick (several layers of perivascular cells, with a continuum of phenotypes, resembling myopericytoma vessels) and thin (slit-like channels), without adventitial SCs or elastic material. The extratumoral vessels showed adventitial SCs (which contribute to form the tumor pseudocapsule), hyperplasia of the media and intima layers, and/or occlusion of the lumen by a wide, homogenous fibrotic central zone. Histogenetically, the collagenous matrix may act as a mineralization substrate and the calcifying modified pericytes as inductors; intratumoral vessels may originate from the peritumoral vessels or from the vessel where the tumor develops; and extratumoral vessel modifications, mimicking tumor features, concur with a minor repetitive trauma pathogenesis.

Cellular Changes during Renal Failure-Induced Inflammatory Aortic Valve Disease

Background

Aortic valve calcification (AVC) secondary to renal failure (RF) is an inflammation-regulated process, but its pathogenesis remains unknown. We sought to assess the cellular processes that are involved in the early phases of aortic valve disease using a unique animal model of RF-associated AVC.

Methods

Aortic valves were obtained from rats that were fed a uremia-inducing diet exclusively for 2, 3, 4, 5, and 6 weeks as well as from controls. Pathological examination of the valves included histological characterization, von Kossa staining, and antigen expression analyses.

Results

After 2 weeks, we noted a significant increase in urea and creatinine levels, reflecting RF. RF parameters exacerbated until the Week 5 and plateaued. Whereas no histological changes or calcification was observed in the valves of any study group, macrophage accumulation became apparent as early as 2 weeks after the diet was started and rose after 3 weeks. By western blot, osteoblast markers were expressed after 2 weeks on the diet and decreased after 6 weeks. Collagen 3 was up-regulated after 3 weeks, plateauing at 4 weeks, whereas collagen 1 levels peaked at 2 and 4 weeks. Fibronectin levels increased gradually until Week 5 and decreased at 6 weeks. We observed early activation of the ERK pathway, whereas other pathways remained unchanged.

Conclusions

We concluded that RF induces dramatic changes at the cellular level, including macrophage accumulation, activation of cell signaling pathway and extracellular matrix modification. These changes precede valve calcification and may increase propensity for calcification, and have to be investigated further.

Vascular extracellular matrix in atherosclerosis

The extracellular matrix (ECM) is an essential component of the human body that is responsible for the proper function of various organs. Changes in the ECM have been implicated in the pathogenesis of several cardiovascular conditions including atherosclerosis, restenosis, and heart failure. Matrix components, such as collagens and noncollagenous proteins, influence the function and activity of vascular cells, particularly vascular smooth muscle cells and macrophages. Matrix proteins have been shown to be implicated in the development of atherosclerotic complications, such as plaque rupture, aneurysm formation, and calcification. ECM proteins control ECM remodeling through feedback signaling to matrix metalloproteinases (MMPs), which are the key players of ECM remodeling in both normal and pathological conditions. The production of MMPs is closely related to the development of an inflammatory response and is subjected to significant changes at different stages of atherosclerosis. Indeed, blood levels of circulating MMPs may be useful for the assessment of the inflammatory activity in atherosclerosis and the prediction of cardiovascular risk. The availability of a wide variety of low-molecular MMP inhibitors that can be conjugated with various labels provides a good perspective for specific targeting of MMPs and implementation of imaging techniques to visualize MMP activity in atherosclerotic plaques and, most interestingly, to monitor responses to antiatheroslerosis therapies. Finally, because of the crucial role of ECM in cardiovascular repair, the regenerative potential of ECM could be successfully used in constructing engineered scaffolds and vessels that mimic properties of the natural ECM and consist of the native ECM components or composite biomaterials. These scaffolds possess a great promise in vascular tissue engineering.

Glycosaminoglycan overproduction in the aorta increases aortic calcification in murine chronic kidney disease

Background

Vascular calcification accompanying chronic kidney disease increases the mortality and morbidity associated with cardiovascular disorders, but no effective therapy is available. We hypothesized that glycosaminoglycans may contribute to osteoblastic differentiation of vascular smooth muscle cells during vascular calcification.

Methods and Results

We used exostosin‐like glycosyltranferase 2–deficient (EXTL2 knockout) mice expressing high levels of glycosaminoglycans in several organs including the aorta. We performed 5/6 subtotal nephrectomy and fed the mice a high‐phosphate diet to induce chronic kidney disease. Overexpression of glycosaminoglycans in the aorta enhanced aortic calcification in chronic kidney disease in EXTL2 knockout mice. Ex vivo and in vitro, matrix mineralization in aortic rings and vascular smooth muscle cells of EXTL2 knockout mice was augmented. Furthermore, removal of glycosaminoglycans in EXTL2 knockout and wild‐type mice‐derived vascular smooth muscle cells effectively suppressed calcium deposition in a high‐phosphate environment.

Conclusions

These results illustrate an important role for glycosaminoglycans in the development of vascular calcification. Manipulation of glycosaminoglycan expression may have beneficial effects on the progression of vascular calcification in chronic kidney disease patients.

Noggin attenuates the osteogenic activation of human valve interstitial cells in aortic valve sclerosis

AIMS

Aortic valve sclerosis (AVSc) is a hallmark of several cardiovascular conditions ranging from chronic heart failure and myocardial infarction to calcific aortic valve stenosis (AVS). AVSc, present in 25-30% of patients over 65 years of age, is characterized by thickening of the leaflets with marginal effects on the mechanical proprieties of the valve making its presentation asymptomatic. Despite its clinical prevalence, few studies have investigated the pathogenesis of this disease using human AVSc specimens. Here, we investigate in vitro and ex vivo BMP4-mediated transdifferentiation of human valve interstitial cells (VICs) towards an osteogenic-like phenotype in AVSc.

METHODS AND RESULTS

Human specimens from 60 patients were collected at the time of aortic valve replacement (AVS) or through the heart transplant programme (Controls and AVSc). We show that non-calcified leaflets from AVSc patients can be induced to express markers of osteogenic transdifferentiation and biomineralization through the combinatory effect of BMP4 and mechanical stimulation. We show that BMP4 antagonist Noggin attenuates VIC activation and biomineralization. Additionally, patient-derived VICs were induced to transdifferentiate using either cell culture or a Tissue Engineering (TE) Aortic Valve model. We determine that while BMP4 alone is not sufficient to induce osteogenic transdifferentiation of AVSc-derived cells, the combinatory effect of BMP4 and mechanical stretch induces VIC activation towards a phenotype typical of late calcified stage of the disease.

CONCLUSION

This work demonstrates, for the first time using AVSc specimens, that human sclerotic aortic valves can be induced to express marker of osteogenic-like phenotype typical of advanced severe aortic stenosis.

Novel insights into osteogenesis and matrix remodelling associated with calcific uraemic arteriolopathy

BACKGROUND

Calcific uraemic arteriolopathy (CUA) or calciphylaxis is a rare, life-threatening disease predominantly occurring in patients with end-stage renal disease. Its pathogenesis has been suggested to include ectopic osteogenesis in soft tissue and the vasculature associated with extracellular matrix (ECM) remodelling.

METHODS

To gain further insights into the pathogenesis of CUA, we performed systematic analyses of skin specimens obtained from seven CUA patients including histology, immunohistochemistry, electron microscopy, electron dispersive X-ray analysis (EDX) and quantitative real-time RT-PCR. Skin specimens of (i) seven patients without chronic kidney disease and without CUA and (ii) seven dialysis patients without CUA served as controls.

RESULTS

In the CUA skin lesions, we observed a significant upregulation of bone morphogenic protein 2 (BMP-2), its target gene Runx2 and its indirect antagonist sclerostin. Furthermore, we detected an increased expression of inactive uncarboxylated matrix Gla protein (Glu-MGP). The upregulation of osteogenesis-associated markers was accompanied by an increased expression of osteopontin, fibronectin, laminin and collagen I indicating an extensive remodelling of the subcutaneous ECM. EDX analysis revealed calcium/phosphate accumulations in the subcutis of all CUA patients with a molar ratio of 1.68 ± 0.06 matching that of hydroxyapatite mineral. Widespread media calcification in cutaneous arterioles was associated with destruction of the endothelial layer and partial exfoliation of the endothelial cells (ECs). CD31 immunostaining revealed aggregates of ECs contributing to intraluminal obstruction and consecutive malperfusion resulting in the clinical picture of ulcerative necrosis in all seven patients.

CONCLUSIONS

Our data indicate that CUA is an active osteogenic process including the upregulation of BMP-2 signalling, hydroxyapatite deposition and extensive matrix remodelling of the subcutis.

Vitamin d and stage 5 chronic kidney disease: a new paradigm?

Vitamin D receptor agonists (VDRA) are currently recommended for the treatment of secondary hyperparathyroidism in stage 5 CKD. They are considered to be contraindicated in the presence of low or normal (for a dialysis patient) levels of PTH due to the risk of developing adynamic bone disease, with consequent vascular calcification. However, these recommendations are increasingly at odds with the epidemiological evidence, which consistently shows a large survival advantage for patients treated with low-dose VDRAs, regardless of plasma calcium, phosphate, or PTH. A large number of pleiotropic effects of vitamin D have been described, including inhibition of renin activity, anti-inflammation, and suppression of vascular calcification stimulators and stimulation of vascular calcification inhibitors present in the uremic milieu. Laboratory studies suggest that a normal cellular vitamin D level is necessary for normal cardiomyocyte and vascular smooth muscle function. While pharmacological doses of VDRA can be harmful, the present evidence suggests that the level of 1,25-dihydroxycholecalciferol should also be more physiological in stage 5 CKD, and that widespread use of low-dose VDRA would be beneficial. A randomized controlled trial to test this hypothesis is warranted.

Exposure to uremic serum induces a procalcific phenotype in human mesenchymal stem cells

OBJECTIVE

Medial artery calcification in patients with chronic kidney disease proceeds through intramembranous ossification resulting from osteoblast-induced calcification of the collagen extracellular matrix. The current study is based on the hypothesis that mesenchymal stem cells (MSC) constitute critical cells for procalcific extracellular matrix remodeling in patients with chronic kidney disease.

METHODS AND RESULTS

Human MSC were cultured in media supplemented with pooled sera from either healthy or uremic patients (20%). Exposure to uremic serum enhanced the proliferation of MSC (cell counting, BrdU incorporation) whereas apoptosis and necrosis were not affected (annexin V and 7-amino-actinomycin staining). Uremic serum-exposed MSC recapitulated osteogenesis by matrix calcification and expression of bone-related genes (bone morphogenetic protein [BMP]-2 receptor, alkaline phosphatase, osteopontin, and Runx2) in 35 days. The uremic serum-induced osteogenesis was completely blocked by a BMP-2/4 neutralizing antibody or the natural antagonist NOGGIN. Calcification and matrix remodeling were further analyzed in a collagen-embedded osteogenesis model recapitulating the vascular collagen I/III environment. The uremic serum-induced calcification was shown to occur along collagen fibers as shown by scanning electron microscopy, energy-dispersive X-ray spectroscopy, and von Kossa staining and was accompanied by extensive matrix remodeling.

CONCLUSIONS

Uremic serum induced in a BMP-2/4-dependent manner an osteoblast-like phenotype in MSC accompanied by matrix remodeling and calcification.

Cell–Matrix Interactions in the Pathobiology of Calcific Aortic Valve Disease

The hallmarks of calcific aortic valve disease (CAVD) are the significant changes that occur in the organization, composition, and mechanical properties of the extracellular matrix (ECM), ultimately resulting in stiffened stenotic leaflets that obstruct flow and compromise cardiac function. Increasing evidence suggests that ECM maladaptations are not simply a result of valve cell dysfunction; they also contribute to CAVD progression by altering cellular and molecular signaling. In this review, we summarize the ECM changes that occur in CAVD. We also discuss examples of how the ECM influences cellular processes by signaling through adhesion receptors (matricellular signaling), by regulating the presentation and availability of growth factors and cytokines to cells (matricrine signaling), and by transducing externally applied forces and resisting cell-generated tractional forces (mechanical signaling) to regulate a wide range of pathological processes, including differentiation, fibrosis, calcification, and angiogenesis. Finally, we suggest areas for future research that should lead to new insights into bidirectional cell–ECM interactions in the aortic valve, their contributions to homeostasis and pathobiology, and possible targets to slow or prevent the progression of CAVD.

Bone morphogenetic protein-7 inhibits vascular calcification induced by high vitamin D in mice

Vascular calcification refers to the deposition of calcium phosphate in cardiovascular tissues, including arteries and myocardium. Vascular calcification is frequently associated with cardiovascular disease. Recently, bone morphgenetic protein-7 (BMP-7) has been proposed to play an inhibitory role in vascular calcification, but its inhibitory effect has not been fully elucidated. We therefore tested the hypothesis that BMP-7 inhibits vascular calcification by using two conditions, high levels of vitamin D and phosphate, each of which could enhance vascular calcification. C57BL/6 mice were treated for 3 days with high vitamin D (500,000 IU/kg/day) in the presence or absence of recombinant human BMP-7 (rhBMP-7). Expression levels of osteopontin and osteocalcin, markers of the osteoblastic phenotype, were assessed by immunohistochemical staining or Western blotting analysis. Vitamin D increased calcium staining in thoracic aortas and hearts and the expression levels of osteopontin and osteocalcin in mice. Importantly, pretreatment for 7 days and subsequent treatment for 3 days with rhBMP-7 (10 microg/kg/day) abolished the vitamin D-mediated increases in the above parameters. In addition, human aortic smooth muscle cells (HASMCs) were cultured with high beta-glycerophosphate, a phosphate donor, for 2 weeks in the presence or absence of rhBMP-7. High beta-glycerophosphate increased expression levels of osteopontin and osteocalcin as well as calcium staining in HASMCs, but these changes were attenuated by treatment with BMP-7. Thus, BMP-7 inhibits vascular calcification associated with high levels of vitamin D or phosphate. We propose that BMP-7 treatment may be helpful in reducing the risks of cardiovascular disease related to vascular calcification.

Complementary effects of multi-protein components on biomineralization in vitro

The extracellular matrix (ECM) is composed of mixed protein fibers whose precise composition affects biomineralization. New methods are needed to probe the interactions of these proteins with calcium phosphate mineral and with each other. Here we follow calcium phosphate mineralization on protein fibers self-assembled in vitro from solutions of fibronectin, elastin and their mixture. We probe the surface morphology and mechanical properties of the protein fibers during the early stages. The development of mineral crystals on the protein matrices is also investigated. In physiological mineralization solution, the elastic modulus of the fibers in the fibronectin-elastin mixture increases to a greater extent than that of the fibers from either pure protein. In the presence of fibronectin, longer exposure in the mineral solution leads to the formation of amorphous calcium phosphate particles templated along the self-assembled fibers, while elastin fibers only collect calcium without any mineral observed during early stage. TEM images confirm that small needle-shape crystals are confined inside elastin fibers which suppress the release of mineral outside the fibers during late stage, while hydroxyapatite crystals form when fibronectin is present. These results demonstrate complementary actions of the two ECM proteins fibronectin and elastin to collect cations and template mineral, respectively.