Inactivation of the osteopontin gene enhances vascular calcification of matrix Gla protein-deficient mice: evidence for osteopontin as an inducible inhibitor of vascular calcification in vivo

Attenuation of chondrogenic transformation in vascular smooth muscle by dietary quercetin in the MGP-deficient mouse model

RATIONALE

Cartilaginous metaplasia of vascular smooth muscle (VSM) is characteristic for arterial calcification in diabetes and uremia and in the background of genetic alterations in matrix Gla protein (MGP). A better understanding of the molecular details of this process is critical for the development of novel therapeutic approaches to VSM transformation and arterial calcification.

OBJECTIVE

This study aimed to identify the effects of bioflavonoid quercetin on chondrogenic transformation and calcification of VSM in the MGP-null mouse model and upon TGF-β3 stimulation in vitro, and to characterize the associated alterations in cell signaling.

METHODS AND RESULTS

Molecular analysis revealed activation of β-catenin signaling in cartilaginous metaplasia in Mgp-/- aortae in vivo and during chondrogenic transformation of VSMCs in vitro. Quercetin intercepted chondrogenic transformation of VSM and blocked activation of β-catenin both in vivo and in vitro. Although dietary quercetin drastically attenuated calcifying cartilaginous metaplasia in Mgp-/- animals, approximately one-half of total vascular calcium mineral remained as depositions along elastic lamellae.

CONCLUSION

Quercetin is potent in preventing VSM chondrogenic transformation caused by diverse stimuli. Combined with the demonstrated efficiency of dietary quercetin in preventing ectopic chondrogenesis in the MGP-null vasculature, these findings indicate a potentially broad therapeutic applicability of this safe for human consumption bioflavonoid in the therapy of cardiovascular conditions linked to cartilaginous metaplasia of VSM. Elastocalcinosis is a major component of MGP-null vascular disease and is controlled by a mechanism different from chondrogenic transformation of VSM and not sensitive to quercetin.

Palmitic acid induces osteoblastic differentiation in vascular smooth muscle cells through ACSL3 and NF-κB, novel targets of eicosapentaenoic acid

Free fatty acids (FFAs), elevated in metabolic syndrome and diabetes, play a crucial role in the development of atherosclerotic cardiovascular disease, and eicosapentaenoic acid (EPA) counteracts many aspects of FFA-induced vascular pathology. Although vascular calcification is invariably associated with atherosclerosis, the mechanisms involved are not completely elucidated. In this study, we tested the hypothesis that EPA prevents the osteoblastic differentiation and mineralization of vascular smooth muscle cells (VSMC) induced by palmitic acid (PA), the most abundant long-chain saturated fatty acid in plasma. PA increased and EPA abolished the expression of the genes for bone-related proteins, including bone morphogenetic protein (BMP)-2, Msx2 and osteopontin in human aortic smooth muscle cells (HASMC). Among the long-chain acyl-CoA synthetase (ACSL) subfamily, ACSL3 expression was predominant in HASMC, and PA robustly increased and EPA efficiently inhibited ACSL3 expression. Importantly, PA-induced osteoblastic differentiation was mediated, at least in part, by ACSL3 activation because acyl-CoA synthetase (ACS) inhibitor or siRNA targeted to ACSL3 completely prevented the PA induction of both BMP-2 and Msx2. Conversely, adenovirus-mediated ACSL3 overexpression enhanced PA-induced BMP-2 and Msx2 expression. In addition, EPA, ACSL3 siRNA and ACS inhibitor attenuated calcium deposition and caspase activation induced by PA. Notably, PA induced activation of NF-κB, and NF-κB inhibitor prevented PA-induction of osteoblastic gene expression and calcium deposition. Immunohistochemistry revealed the prominent expression of ACSL3 in VSMC and macrophages in human non-calcifying and calcifying atherosclerotic plaques from the carotid arteries. These results identify ACSL3 and NF-κB as mediators of PA-induced osteoblastic differentiation and calcium deposition in VSMC and suggest that EPA prevents vascular calcification by inhibiting such a new molecular pathway elicited by PA.

Nuclear receptors in bone physiology and diseases

During the last decade, our view on the skeleton as a mere solid physical support structure has been transformed, as bone emerged as a dynamic, constantly remodeling tissue with systemic regulatory functions including those of an endocrine organ. Reflecting this remarkable functional complexity, distinct classes of humoral and intracellular regulatory factors have been shown to control vital processes in the bone. Among these regulators, nuclear receptors (NRs) play fundamental roles in bone development, growth, and maintenance. NRs are DNA-binding transcription factors that act as intracellular transducers of the respective ligand signaling pathways through modulation of expression of specific sets of cognate target genes. Aberrant NR signaling caused by receptor or ligand deficiency may profoundly affect bone health and compromise skeletal functions. Ligand dependency of NR action underlies a major strategy of therapeutic intervention to correct aberrant NR signaling, and significant efforts have been made to design novel synthetic NR ligands with enhanced beneficial properties and reduced potential negative side effects. As an example, estrogen deficiency causes bone loss and leads to development of osteoporosis, the most prevalent skeletal disorder in postmenopausal women. Since administration of natural estrogens for the treatment of osteoporosis often associates with undesirable side effects, several synthetic estrogen receptor ligands have been developed with higher therapeutic efficacy and specificity. This review presents current progress in our understanding of the roles of various nuclear receptor-mediated signaling pathways in bone physiology and disease, and in development of advanced NR ligands for treatment of common skeletal disorders.

Matrix gla protein gene polymorphism is associated with increased coronary artery calcification progression

OBJECTIVE

Matrix gla protein (MGP) inhibits arterial and cartilaginous calcification. A threonine to alanine (Thr83Ala) polymorphism (codon 83) in MGP is associated with myocardial infarction and femoral artery calcification. We examined the association of the MGP Thr83Ala polymorphism with quantity and progression of coronary artery calcification (CAC), a noninvasive measure of subclinical coronary atherosclerosis.

METHODS AND RESULTS

In 605 participants of the Epidemiology of Coronary Artery Calcification Study, generalized linear mixed models were fit to determine the association of MGP Thr83Ala with CAC quantity and progression. There was a significant additive relation between MGP Thr83Ala and CAC progression (P=0.001). In the fully adjusted model, every 1 Ala83 allele increase was associated with an estimated 1.9% (95% confidence interval, 0.7%-3.0%) per year since baseline larger increase in CAC quantity. A proxy single nucleotide polymorphism for MGP Thr83Ala (rs6488724) was similarly associated with CAC progression in an independent cohort from the Genetic Epidemiology Network of Arteriopathy (GENOA) study.

CONCLUSIONS

Increased risk of myocardial infarction associated with MGP ThrAla83 genotype observed elsewhere may be related to faster progression of subclinical coronary atherosclerosis. MGP genotype could be a potential candidate for identifying individuals at increased risk of atherosclerotic disease who would benefit from aggressive primary prevention strategies.

Tooth root dentin mineralization defects in a mouse model of hypophosphatasia

Tissue-nonspecific alkaline phosphatase (TNAP) is expressed in mineralizing tissues and functions to reduce pyrophosphate (PP(i) ), a potent inhibitor of mineralization. Loss of TNAP function causes hypophosphatasia (HPP), a heritable disorder marked by increased PP(i) , resulting in rickets and osteomalacia. Tooth root cementum defects are well described in both HPP patients and in Alpl(-/-) mice, a model for infantile HPP. In Alpl(-/-) mice, dentin mineralization is specifically delayed in the root; however, reports from human HPP patients are variable and inconsistent regarding dentin defects. In the current study, we aimed to define the molecular basis for changes in dentinogenesis observed in Alpl(-/-) mice. TNAP was found to be highly expressed by mature odontoblasts, and Alpl(-/-) molar and incisor roots featured defective dentin mineralization, ranging from a mild delay to severely disturbed root dentinogenesis. Lack of mantle dentin mineralization was associated with disordered and dysmorphic odontoblasts having disrupted expression of marker genes osteocalcin and dentin sialophosphoprotein. The formation of, initiation of mineralization within, and rupture of matrix vesicles in Alpl(-/-) dentin matrix was not affected. Osteopontin (OPN), an inhibitor of mineralization that contributes to the skeletal pathology in Alpl(-/-) mice, was present in the generally unmineralized Alpl(-/-) mantle dentin at ruptured mineralizing matrix vesicles, as detected by immunohistochemistry and by immunogold labeling. However, ablating the OPN-encoding Spp1 gene in Alpl(-/-) mice was insufficient to rescue the dentin mineralization defect. Administration of bioengineered mineral-targeting human TNAP (ENB-0040) to Alpl(-/-) mice corrected defective dentin mineralization in the molar roots. These studies reveal that TNAP participates in root dentin formation and confirm that reduction of PP(i) during dentinogenesis is necessary for odontoblast differentiation, dentin matrix secretion, and mineralization. Furthermore, these results elucidate developmental mechanisms underlying dentin pathology in HPP patients, and begin to explain the reported variability in the dentin/pulp complex pathology in these patients.

Fetuin, matrix-Gla protein and osteopontin in calcification of renal allografts

BACKGROUND

Calcification of renal allografts is common in the first year after transplantation and is related to hyperparathyroidism. It is associated with an impaired long-term function of the graft (Am J Transplant 5∶1934-41, 2005). Aim of this study is to examine the role of the anti-calcifying/calcifying factors in the pathophysiology of renal allograft calcification.

METHODS

We analyzed protocol allograft biopsies, blood and urine samples of 31 patients with and 27 patients without allograft calcification taken at 6 weeks, 3 and 6 months after transplantation. Patient demographical data, cold ischemia time, initial graft function and donor characteristics were comparable between the two groups. Biopsies were stained for osteopontin, fetuin, and matrix-gla-protein. Serum and urine electrolytes, matrix-gla-protein, fetuin, Vitamin D and intact parathyroid hormone in serum and osteopontin (OPN) in urine were examined.

RESULTS

Serum levels of fetuin and matrix-Gla protein as well as urinary levels of OPN showed specific time dependent changes (6 weeks vs. 3 months vs. 6 months; all p<0.0001). In patients with calcifications, urinary levels of OPN were decreased by 55% at 6 weeks and increased thereafter, showing 54% higher levels at 6 months compared to patients without calcification (6 weeks: p<0.01, 6 months: p<0.05). Local protein expression of fetuin-A, matrix-Gla protein and OPN in the graft was specifically increased around calcified plaques, without differences in the mRNA tissue expression.

CONCLUSION

Anticalcifying factors show significant changes in the early phase after renal transplantation, which may be important for the prevention of allograft calcification. The differences in OPN indicate an involvement of this factor in the regulation of calcification.

Mechanisms of arterial remodeling: lessons from genetic diseases

Vascular disease is still the leading cause of morbidity and mortality in the Western world, and the primary cause of myocardial infarction, stroke, and ischemia. The biology of vascular disease is complex and still poorly understood in terms of causes and consequences. Vascular function is determined by structural and functional properties of the arterial vascular wall. Arterial stiffness, that is a pathological alteration of the vascular wall, ultimately results in target-organ damage and increased mortality. Arterial remodeling is accelerated under conditions that adversely affect the balance between arterial function and structure such as hypertension, atherosclerosis, diabetes mellitus, chronic kidney disease, inflammatory disease, lifestyle aspects (smoking), drugs (vitamin K antagonists), and genetic abnormalities [e.g., pseudoxanthoma elasticum (PXE), Marfan's disease]. The aim of this review is to provide an overview of the complex mechanisms and different factors that underlie arterial remodeling, learning from single gene defect diseases like PXE, and PXE-like, Marfan's disease and Keutel syndrome in vascular remodeling.

New insights into NPP1 function: lessons from clinical and animal studies

The recent elucidation of rare human genetic disorders resulting from mutations in ectonucleotide pyrophosphotase/phosphodiesterase (ENPP1), also known as plasma cell membrane glycoprotein 1 (PC-1), has highlighted the vital importance of this molecule in human health and disease. Generalised arterial calcification in infants (GACI), a frequently lethal disease, has been reported in recessive inactivating mutations in ENPP1. Recent findings have also linked hypophosphataemia to a lack of NPP1 function. A number of human genetic studies have indicated that NPP1 is a vital regulator that influences a wide range of tissues through various signalling pathways and when disrupted can lead to significant pathology. The function of Enpp1 has been widely studied in rodent models, where both the mutant tiptoe walking (ttw/ttw) mouse and genetically engineered Enpp1(-/-) mice show significant alterations in skeletal and soft tissue mineralisation, calcium/phosphate balance and glucose homeostasis. These models therefore provide important tools with which to study the potential mechanisms underpinning the human diseases associated with altered NPP1. This review will focus on the recent advances in our current knowledge of the actions of NPP1 in relation to bone disease, cardiovascular pathologies and diabetes. A fuller understanding of the mechanisms through which NPP1 exerts its pathological effects may stimulate the development of novel therapeutic strategies for patients at risk from the devastating clinical outcomes associated with disrupted NPP1 function.

Macrophages play a unique role in the plaque calcification by enhancing the osteogenic signals exerted by vascular smooth muscle cells

Vascular calcification is a major risk factor for the cardiovascular disease, yet its underlying molecular mechanisms remain to be elucidated. Recently, we identified that osteogenic signals via bone morphogenetic protein (BMP)-2 exerted by vascular smooth muscle cells (VSMCs) play a crucial role in the formation of atherosclerotic plaque calcification. Here we report a synergistic interaction between macrophages and VSMCs with respect to plaque calcification. Treatment with conditioned medium (CM) of macrophages dramatically enhanced BMP-2 expression in VSMCs, while it substantially reduced the expression of matrix Gla-protein (MGP) that inhibits the BMP-2 osteogenic signaling. As a result, macrophages significantly accelerated the osteoblastic differentiation of C2C12 cells induced by VSMC-CM. In contrast, macrophage-CM did not enhance the osteoblastic gene expressions in VSMCs, indicating that macrophages unlikely induced the osteoblastic trans-differentiation of VSMCs. We then examined the effect of recombinant TNF-α and IL-1β on the VSMC-derived osteogenic signals. Similar to the macrophage-CM, both cytokines enhanced BMP-2 expression and reduced MGP expression in VSMCs. Nevertheless, only the neutralization of TNF-α but not IL-1β attenuated the effect of macrophage-CM on the expression of these genes in VSMCs, due to the very low concentration of IL-1β in the macrophage-CM. On the other hand, VSMCs significantly enhanced IL-1β expression in macrophages, which might in turn accelerate the VSMC-mediated osteogenic signals. Together, we identified a unique role of macrophages in the formation of plaque calcification in coordination with VSMCs. This interaction between macrophages and VSMCs is a potential therapeutic target to treat and prevent the atherosclerotic plaque calcification.

Osteoporosis--a risk factor for cardiovascular disease?

Osteoporosis is a serious health problem worldwide that is associated with an increased risk of fractures and mortality. Vascular calcification is a well-defined independent risk factor for cardiovascular disease (CVD) and mortality. Major advances in our understanding of the pathophysiology of osteoporosis and vascular calcification indicate that these two processes share common pathogenetic mechanisms. Multiple factors including proteins (such as bone morphogenetic proteins, receptor activator of nuclear factor κB ligand, osteoprotegerin, matrix Gla protein and cathepsins), parathyroid hormone, phosphate, oxidized lipids and vitamins D and K are implicated in both bone and vascular metabolism, illustrating the interaction of these two, seemingly unrelated, conditions. Many clinical studies have now confirmed the correlation between osteoporosis and vascular calcification as well as the increased risk of CVD in patients with osteoporosis. Here, we explore the proposed mechanistic similarities between osteoporosis and vascular calcification and present an overview of the clinical data that support the interaction between these conditions.

Amelogenesis imperfecta and other biomineralization defects in Fam20a and Fam20c null mice

The FAM20 family of secreted proteins consists of three members (FAM20A, FAM20B, and FAM20C) recently linked to developmental disorders suggesting roles for FAM20 proteins in modulating biomineralization processes. The authors report here findings in knockout mice having null mutations affecting each of the three FAM20 proteins. Both Fam20a and Fam20c null mice survived to adulthood and showed biomineralization defects. Fam20b (-/-) embryos showed severe stunting and increased mortality at E13.5, although early lethality precluded detailed investigations. Physiologic calcification or biomineralization of extracellular matrices is a normal process in the development and functioning of various tissues (eg, bones and teeth). The lesions that developed in teeth, bones, or blood vessels after functional deletion of either Fam20a or Fam20c support a significant role for their encoded proteins in modulating biomineralization processes. Severe amelogenesis imperfecta (AI) was present in both Fam20a and Fam20c null mice. In addition, Fam20a (-/-) mice developed disseminated calcifications of muscular arteries and intrapulmonary calcifications, similar to those of fetuin-A deficient mice, although they were normocalcemic and normophosphatemic, with normal dentin and bone. Fam20a gene expression was detected in ameloblasts, odontoblasts, and the parathyroid gland, with local and systemic effects suggesting both local and/or systemic effects for FAM20A. In contrast, Fam20c (-/-) mice lacked ectopic calcifications but were severely hypophosphatemic and developed notable lesions in both dentin and bone to accompany the AI. The bone and dentin lesions, plus the marked hypophosphatemia and elevated serum alkaline phosphatase and FGF23 levels, are indicative of autosomal recessive hypophosphatemic rickets/osteomalacia in Fam20c (-/-) mice.

Intermittent Cyclic Mechanical Tension-Induced Calcification and downregulation of ankh gene expression of end plate chondrocytes

STUDY DESIGN

Intermittent Cyclic Mechanical Tension (ICMT) was applied to end plate chondrocytes by using an FX-4000T Flexercell Tension Plus unit (Flexcell International Corporation, Hillsborough, NC). Changes of end plate chondrocytes were observed after ICMT stimulation.

OBJECTIVE

To investigate the relationship between mechanical stimulation and calcification of end plate chondrocytes.

SUMMARY OF BACKGROUND DATA

Previous study showed that end plate calcification was related to mechanical stress, but there was no clear evidence to indicate whether or not mechanical stimulation could induce calcification of end plate chondrocytes in vitro.

METHODS

Rat end plate chondrocytes were cultured and ICMT (strain at 0.5 Hz sinusoidal curve at 10% elongation) was applied for 25 days, 4 hours a day and continued to culture for 5 days. End plate chondrocytes were incubated for 12 hours in the presence or absence of 10 ng/mL of transforming growth factor-β1 (TGF-β1) (prepared from a stock solution at 10 μg/mL in 2 mM citric acid containing 2 mg/mL bovine serum albumin) in MEM/F-12 containing a final concentration of 1% FCS. End plate chondrocytes calcification was stained by alizarin red S (AR-S). End plate chondrocytes viability was examined by LIVE/DEAD viability/cytotoxicity kit (Invitrogen, Carlsbad, CA). Related gene expression was examined by reverse transcription-polymerase chain reaction and Western blot.

RESULTS

LIVE/DEAD assay verified that the nonloading (NC) group and the ICMT group end plate chondrocytes remained adherent, with no change in viability after the application of ICMT. Alizarin red staining showed that ICMT induced the calcification of end plate chondrocytes. Real-time reverse transcription-polymerase chain reaction showed that mRNA expression of endogenous TGF-β1 decreased and mRNA expression of type I, type X, osteocalcin and osteopontin increased after ICMT. The ankh gene expression of both mRNA and protein levels decreased in the ICMT stimulation. The ankh gene expression of both mRNA and protein levels increased in TGF-β1 stimulation. Compared with NC group, the alkaline phosphatase activities significantly increased in ICMT group.

CONCLUSION

Our results directly showed that ICMT induced the calcification and downregulation of ankh gene expression of end plate chondrocytes, which may be caused by the endogenous TGF-β1.

Effect of race and genetics on vitamin D metabolism, bone and vascular health

The pathophysiology of chronic kidney disease-mineral and bone disorder accounts for an inverse relationship between bone mineralization and vascular calcification in progressive nephropathy. Inverse associations between bone mineral density (BMD) and calcified atherosclerotic plaque are also observed in individuals of European and African ancestry without nephropathy, suggesting a mechanistic link between these processes that is independent of kidney disease. Despite lower dietary calcium intake and serum 25-hydroxyvitamin D (25(OH)D) concentrations, African Americans have higher BMD and develop osteoporosis less frequently than do European Americans. Moreover, despite having more risk factors for cardiovascular disease, African Americans have a lower incidence and severity of calcified atherosclerotic plaque formation than do European Americans. Strikingly, evidence is now revealing that serum 25(OH)D and/or 1,25 dihydroxyvitamin D levels associate positively with atherosclerosis but negatively with BMD in African Americans; by contrast, vitamin D levels associate negatively with atherosclerosis and positively with BMD in individuals of European ancestry. Biologic phenomena, therefore, seem to contribute to population-specific differences in vitamin D metabolism, bone and vascular health. Genetic and mechanistic approaches used to explore these differences should further our understanding of bone-blood vessel relationships and explain how African ancestry protects from osteoporosis and calcified atherosclerotic plaque, provided that access of African Americans to health care is equivalent to individuals of European ethnic origin. Ultimately, in our opinion, a new mechanistic understanding of the relationships between bone mineralization and vascular calcification will produce novel approaches for disease prevention in aging populations.

Serum levels of calcification inhibitors in patients with intracerebral hemorrhage

The vascular calcification regulators and inflammatory markers including fetuin-A, osteopontin (OPN), and matrix Gla protein (MGP) may play an important role in the development of intracerebral hemorrhages (ICHs). So far, the relationship between these parameters and ICH has not been studied. Therefore, this study was designed to elucidate whether fetuin-A, MGP, and OPN are involved in the pathophysiology of ICH. The ICH group consisted of 27 consecutive patients with spontaneous ICH evaluated in the neurology intensive care unit within the first 24 hours from the onset of the stroke. The serum OPN levels were significantly increased in patients with ICH compared to the controls. On the other hand, the serum MGP and fetuin-A levels were significantly decreased in the patients with ICH in comparison to the controls. In the patients with ICH, the serum MGP levels of the nonsurvivors were statistically significantly lower than the MGP levels of the survivors. In conclusion, the change in serum fetuin-A, MGP, and OPN levels after ICH indicates that these parameters play a role in the pathophysiological processes leading to an ICH. Measurement of the serum MGP levels may also be of value to estimate mortality.

The mechanism of vascular calcification - a systematic review

Calcification of vessels reduces their elasticity, affecting hemodynamic parameters of the cardiovascular system. The development of arterial hypertension, cardiac hypertrophy, ischemic heart disease or peripheral arterial disease significantly increases mortality in patients over 60 years of age. Stage of advancement and the extent of accumulation of calcium deposits in vessel walls are key risk factors of ischemic events. Vascular calcification is an active and complex process that involves numerous mechanisms responsible for calcium depositions in arterial walls. They lead to increase in arterial stiffness and in pulse wave velocity, which in turn increases cardiovascular disease morbidity and mortality. In-depth study and thorough understanding of vascular calcification mechanisms may be crucial for establishing an effective vasculoprotective therapy. The aim of this study was to present a comprehensive survey of current state-of-the-art research into the impact of metabolic and hormonal disorders on development of vascular calcification. Due to strong resemblance to the processes occurring in bone tissue, drugs used for osteoporosis treatment (calcitriol, estradiol, bisphosphonates) may interfere with the processes occurring in the vessel wall. On the other hand, drugs used to treat cardiovascular problems (statins, angiotensin convertase inhibitors, warfarin, heparins) may have an effect on bone tissue metabolism. Efforts to optimally control calcium and phosphate concentrations are also beneficial for patients with end-stage renal disease, for whom vessel calcification remains a major problem.

The effect of alendronate on the expression of osteopontin and osteoprotegerin in calcified aortic tissue of the rat

Vascular calcification is a pathobiological process which leads to high morbidity and mortality in cardiovascular disease. The association between vascular calcification and osteoporosis has been reported widely, and there are close relationships among vascular calcification, related cardiovascular disease and osteoporosis, but the biochemical mechanism of vascular calcification is presently unclear. For exploring the possible mechanism of artery calcification we established aorta calcification in an animal model with vitamin D(3) and warfarin and tested the effect of alendronate on the expression of osteopontin and osteoprotegerin in calcified aorta tissue of the rat through measuring gene and protein expression of osteopontin and osteoprotegerin respectively. The results indicated compared with control group, the aortic calcium content of calcification group was obviously increased, osteopontin mRNA and osteoprotegerin mRNA were significantly reduced, and osteoprotegerin and osteopontin protein expressions were reduced. Compared with calcification group, the aortic calcium content of alendronate group was obviously reduced, osteopontin mRNA and osteoprotegerin mRNA were significantly increased, and osteopontin and osteoprotegerin protein expression were increased. We conclude that artery calcification may reduce the expression of osteopontin and osteoprotegerin. Alendronate may inhibit rat aorta calcification by up-regulating osteopontin and osteoprotegerin expression.

Arterial stiffness, vascular calcification and bone metabolism in chronic kidney disease

Patients with chronic kidney disease (CKD) have an extremely poor cardiovascular outcome. Arterial stiffness, a strong independent predictor of survival in CKD, is connected to arterial media calcification. A huge number of different factors contribute to the increased arterial calcification and stiffening in CKD, a process which is in parallel with impaired bone metabolism. This coincidence was demonstrated to be part of the direct inhibition of calcification in the vessels, which is a counterbalancing effect but also leads to low bone turnover. Due to the growing evidence, the definition of “CKD mineral bone disorder” was created recently, underlining the strong connection of the two phenomena. In this review, we aim to demonstrate the mechanisms leading to increased arterial stiffness and the up-to date data of the bone-vascular axis in CKD. We overview a list of the different factors, including inhibitors of bone metabolism like osteoprotegerin, fetuin-A, pyrophosphates, matrix Gla protein, osteopontin, fibroblast growth factor 23 and bone morphogenic protein, which seem to play role in the progression of vascular calcification and we evaluate their connection to impaired arterial stiffness in the mirror of recent scientific results.

Mechanisms and clinical consequences of vascular calcification

Vascular calcification has severe clinical consequences and is considered an accurate predictor of future adverse cardiovascular events, including myocardial infarction and stroke. Previously vascular calcification was thought to be a passive process which involved the deposition of calcium and phosphate in arteries and cardiac valves. However, recent studies have shown that vascular calcification is a highly regulated, cell-mediated process similar to bone formation. In this article, we outline the current understanding of key mechanisms governing vascular calcification and highlight the clinical consequences. By understanding better the molecular pathways and genetic circuitry responsible for the pathological mineralization process novel drug targets may be identified and exploited to combat and reduce the detrimental effects of vascular calcification on human health.

Sox9 transcriptionally represses Spp1 to prevent matrix mineralization in maturing heart valves and chondrocytes

Sox9 is an SRY-related transcription factor required for expression of cartilaginous genes in the developing skeletal system and heart valve structures. In contrast to positively regulating cartilaginous matrix, Sox9 also negatively regulates matrix mineralization associated with bone formation. While the transcriptional activation of Sox9 target genes during chondrogenesis has been characterized, the mechanisms by which Sox9 represses osteogenic processes are not so clear. Using ChIP-on-chip and luciferase assays we show that Sox9 binds and represses transactivation of the osteogenic glycoprotein Spp1. In addition, Sox9 knockdown in post natal mouse heart valve explants and rib chondrocyte cultures promotes Spp1 expression and matrix mineralization, while attenuating expression of cartilage genes Type II Collagen and Cartilage Link Protein. Further, we show that Spp1 is required for matrix mineralization induced by Sox9 knockdown. These studies provide insights into the molecular mechanisms by which Sox9 prevents pathologic matrix mineralization in tissues that must remain cartilaginous.

Genetics in arterial calcification: pieces of a puzzle and cogs in a wheel

Artery calcification reflects an admixture of factors such as ectopic osteochondral differentiation with primary host pathological conditions. We review how genetic factors, as identified by human genome-wide association studies, and incomplete correlations with various mouse studies, including knockout and strain analyses, fit into "pieces of the puzzle" in intimal calcification in human atherosclerosis, and artery tunica media calcification in aging, diabetes mellitus, and chronic kidney disease. We also describe in sharp contrast how ENPP1, CD73, and ABCC6 serve as "cogs in a wheel" of arterial calcification. Specifically, each is a minor component in the function of a much larger network of factors that exert balanced effects to promote and suppress arterial calcification. For the network to normally suppress spontaneous arterial calcification, the "cogs" ENPP1, CD73, and ABCC6 must be present and in working order. Monogenic ENPP1, CD73, and ABCC6 deficiencies each drive a molecular pathophysiology of closely related but phenotypically different diseases (generalized arterial calcification of infancy (GACI), pseudoxanthoma elasticum (PXE) and arterial calcification caused by CD73 deficiency (ACDC)), in which premature onset arterial calcification is a prominent but not the sole feature.

The LDLR deficient mouse as a model for aortic calcification and quantification by micro-computed tomography

OBJECTIVE

Patients with familial hypercholesterolemia (FH) due mutations in the low-density lipoprotein receptor (LDLR) suffer premature aortic calcification, an effect that is age- and gene dosage-dependent and cholesterol level independent later in life. To better understand this process, we examined a murine model.

METHODS

We compared chow fed Ldlr(-/-) mice to controls at 6, 12 and 18 months and on a Western diet (WD) at 6 months. Additionally, we compared controls to Ldlr(-/-) mice and transgenic mice Tg(Pcsk9) overexpressing PCSK9, which promotes LDLR degradation. Aortas were perfused-fixed, embedded in paraffin, and sections were stained with alizarin red. Micro-computerized tomography (micro-CT) was used to quantify vascular calcification.

RESULTS

Ldlr(-/-) mice develop calcification in the ascending, transverse aorta and neck vessels with a distribution similar to that of human. Calcification was most prominent in 18-month-old Ldlr(-/-) mice fed a chow diet and in 6-month-old Ldlr(-/-) mice fed a WD. Interestingly, Tg(Pcsk9) mice fed a WD develop aortic calcifications as well. Histology confirmed that the calcification were predominantly sub-intimal. Marked expression of LRP5 and WNT was observed in the Ldlr(-/-) and Tg(Pcsk9) models, but not in age-matched controls.

CONCLUSIONS

The two mouse models develop aortic calcification in an age- and diet-dependent manner. Abnormal regulation of the LRP5/Wnt pathway may play a role in the calcification process. Further analysis of these aortic calcification models using this micro-CT imaging technique may provide a better understanding of the link between FH and arterial calcification.

Vascular calcification and aortic fibrosis: a bifunctional role for osteopontin in diabetic arteriosclerosis

OBJECTIVE

Calcification and fibrosis reduce vascular compliance in arteriosclerosis. To better understand the role of osteopontin (OPN), a multifunctional protein upregulated in diabetic arteries, we evaluated contributions of OPN in male low-density lipoprotein receptor (LDLR)-/- mice fed a high-fat diet.

METHODS AND RESULTS

OPN had no impact on high-fat diet-induced hyperglycemia, dyslipidemia, or body composition. However, OPN-/-;LDLR-/- mice exhibited an altered time-course of aortic calcium accrual-reduced during initiation but increased with progression-versus OPN+/+;LDLR-/- controls. Collagen accumulation, chondroid metaplasia, and mural thickness were increased in aortas of OPN-/-;LDLR-/- mice. Aortic compliance was concomitantly reduced. Vascular reexpression of OPN (SM22-OPN transgene) reduced aortic Col2A1 and medial chondroid metaplasia but did not affect atherosclerotic calcification, Col1A1 expression, collagen accumulation, or arterial stiffness. Dosing with the proinflammatory OPN fragment SVVYGLR upregulated aortic Wnt and osteogenic gene expression, increased aortic β-catenin, and restored early-phase aortic calcification in OPN-/-;LDLR-/- mice.

CONCLUSIONS

OPN exerts stage-specific roles in arteriosclerosis in LDLR-/- mice. Actions phenocopied by the OPN metabolite SVVYGLR promote osteogenic calcification processes with disease initiation. OPN limits vascular chondroid metaplasia, endochondral mineralization, and collagen accumulation with progression. Complete deficiency yields a net increase in arteriosclerotic disease, reducing aortic compliance and conduit vessel function in LDLR-/- mice.

Prevention of vascular calcification: is pyrophosphate therapy a solution?

Pyrophosphate, a ubiquitous small-molecule inhibitor of mineralization abundantly present in the extracellular environment, binds to calcium and mineral surfaces to inhibit crystal growth. O'Neill and colleagues show in uremic rats that systemic administration of pyrophosphate prevents or reduces uremia-related vascular calcification, without overt negative consequences for bone and without calcium pyrophosphate deposition disease. These findings prompt further research into the potential of pyrophosphate as treatment for vascular calcification in chronic kidney disease patients.

Circulating matrix γ-carboxyglutamate protein (MGP) species are refractory to vitamin K treatment in a new case of Keutel syndrome

BACKGROUND AND OBJECTIVES

 Matrix γ-carboxyglutamate protein (MGP), a vitamin K-dependent protein, is recognized as a potent local inhibitor of vascular calcification. Studying patients with Keutel syndrome (KS), a rare autosomal recessive disorder resulting from MGP mutations, provides an opportunity to investigate the functions of MGP. The purpose of this study was (i) to investigate the phenotype and the underlying MGP mutation of a newly identified KS patient, and (ii) to investigate MGP species and the effect of vitamin K supplements in KS patients.

METHODS

 The phenotype of a newly identified KS patient was characterized with specific attention to signs of vascular calcification. Genetic analysis of the MGP gene was performed. Circulating MGP species were quantified and the effect of vitamin K supplements on MGP carboxylation was studied. Finally, we performed immunohistochemical staining of tissues of the first KS patient originally described focusing on MGP species.

RESULTS

 We describe a novel homozygous MGP mutation (c.61+1G>A) in a newly identified KS patient. No signs of arterial calcification were found, in contrast to findings in MGP knockout mice. This patient is the first in whom circulating MGP species have been characterized, showing a high level of phosphorylated MGP and a low level of carboxylated MGP. Contrary to expectations, vitamin K supplements did not improve the circulating carboxylated mgp levels. phosphorylated mgp was also found to be present in the first ks patient originally described.

CONCLUSIONS

 Investigation of the phenotype and MGP species in the circulation and tissues of KS patients contributes to our understanding of MGP functions and to further elucidation of the difference in arterial phenotype between MGP-deficient mice and humans.

Elastin degradation and vascular smooth muscle cell phenotype change precede cell loss and arterial medial calcification in a uremic mouse model of chronic kidney disease

Arterial medial calcification (AMC), a hallmark of vascular disease in uremic patients, is highly correlated with serum phosphate levels and cardiovascular mortality. To determine the mechanisms of AMC, mice were made uremic by partial right-side renal ablation (week 0), followed by left-side nephrectomy at week 2. At 3 weeks, mice were switched to a high-phosphate diet, and various parameters of disease progression were examined over time. Serum phosphate, calcium, and fibroblast growth factor 23 (FGF-23) were up-regulated as early as week 4. Whereas serum phosphate and calcium levels declined to normal by 10 weeks, FGF-23 levels remained elevated through 16 weeks, consistent with an increased phosphate load. Elastin turnover and vascular smooth muscle cell (VSMC) phenotype change were early events, detected by week 4 and before AMC. Both AMC and VSMC loss were significantly elevated by week 8. Matrix metalloprotease 2 (MMP-2) and cathepsin S were present at baseline and were significantly elevated at weeks 8 and 12. In contrast, MMP-9 was not up-regulated until week 12. These findings over time suggest that VSMC phenotype change and VSMC loss (early phosphate-dependent events) may be necessary and sufficient to promote AMC in uremic mice fed a high-phosphate diet, whereas elastin degradation might be necessary but is not sufficient to induce AMC (because elastin degradation occurred also in uremic mice on a normal-phosphate diet, but they did not develop AMC).

Osteopontin in macrophage function

The secreted phosphorylated protein osteopontin (OPN) is expressed in a variety of tissues and bodily fluids, and is associated with pathologies including tissue injury, infection, autoimmune disease and cancer. Macrophages are ubiquitous, heterogeneous cells that mediate aspects of cell and tissue damage in all these pathologies. Here, the role of OPN in macrophage function is reviewed. OPN is expressed in macrophage cells in multiple pathologies, and the regulation of its expression in these cells has been described in vitro. The protein has been implicated in multiple functions of macrophages, including cytokine expression, expression of inducible nitric oxide synthase, phagocytosis and migration. Indeed, the role of OPN in cells of the macrophage lineage might underlie its physiological role in many pathologies. However, there are numerous instances where the published literature is inconsistent, especially in terms of OPN function in vitro. Although the heterogeneity of OPN and its receptors, or of macrophages themselves, might underlie some of these inconsistencies, it is important to understand the role of OPN in macrophage biology in order to exploit its function therapeutically.

Cell biological and physicochemical aspects of arterial calcification

Processes similar to endochondral or intramembranous bone formation occur in the vascular wall. Bone and cartilage tissue as well as osteoblast- and chondrocyte-like cells are present in calcified arteries. As in bone formation, apoptosis and matrix vesicles play an important role in the initiation of vascular calcification. Recent evidence indicates that nanocrystals initially formed in the vessel wall may actively be involved in the progression of the calcification process. This review focuses on the cellular and structural similarities between bone formation and vascular calcification and discusses the initial events in this pathological mineralization process.

Arterial calcifications

Arterial calcifications as found with various imaging techniques, like plain X-ray, computed tomography or ultrasound are associated with increased cardiovascular risk. The prevalence of arterial calcification increases with age and is stimulated by several common cardiovascular risk factors. In this review, the clinical importance of arterial calcification and the currently known proteins involved are discussed. Arterial calcification is the result of a complex interplay between stimulating (bone morphogenetic protein type 2 [BMP-2], RANKL) and inhibitory (matrix Gla protein, BMP-7, osteoprotegerin, fetuin-A, osteopontin) proteins. Vascular calcification is especially prevalent and related to adverse outcome in patients with renal insufficiency and diabetes mellitus. We address the special circumstances and mechanisms in these patient groups. Treatment and prevention of arterial calcification is possible by the use of specific drugs. However, it remains to be proven that reduction of vascular calcification in itself leads to a reduced cardiovascular risk.

Oxidized low density lipoprotein induces bone morphogenetic protein-2 in coronary artery endothelial cells via Toll-like receptors 2 and 4

Vascular calcification is a common complication in atherosclerosis. Bone morphogenetic protein-2 (BMP-2) plays an important role in atherosclerotic vascular calcification. The aim of this study was to determine the effect of oxidized low density lipoprotein (oxLDL) on BMP-2 protein expression in human coronary artery endothelial cells (CAECs), the roles of Toll-like receptor (TLR) 2 and TLR4 in oxLDL-induced BMP-2 expression, and the signaling pathways involved. Human CAECs were stimulated with oxLDL. The roles of TLR2 and TLR4 in oxLDL-induced BMP-2 expression were determined by pretreatment with neutralizing antibody, siRNA, and overexpression. Stimulation with oxLDL increased cellular BMP-2 protein levels in a dose-dependent manner (40-160 μg/ml). Pretreatment with neutralizing antibodies against TLR2 and TLR4 or silencing of these two receptors reduced oxLDL-induced BMP-2 expression. Overexpression of TLR2 and TLR4 enhanced the cellular BMP-2 response to oxLDL. Furthermore, oxLDL was co-localized with TLR2 and TLR4. BMP-2 expression was associated with activation of nuclear factor-κB (NF-κB), p38 mitogen-activated protein kinase (MAPK), and extracellular signal-regulated kinase (ERK)1/2. Inhibition of NF-κB and ERK1/2 reduced BMP-2 expression whereas inhibition of p38 MAPK had no effect. In conclusion, oxLDL induces BMP-2 expression through TLR2 and TLR4 in human CAECs. The NF-κB and ERK1/2 pathways are involved in the signaling mechanism. These findings underscore an important role for TLR2 and TLR4 in mediating the BMP-2 response to oxLDL in human CAECs and indicate that these two immunoreceptors contribute to the mechanisms underlying atherosclerotic vascular calcification.

Plasma osteopontin as a predictor of coronary artery disease: association with echocardiographic characteristics of atherosclerosis

Osteopontin (OPN), a bone-related protein, is present within the atherosclerotic plaques, most strikingly in calcified plaques. Valvular calcifications are accepted as a part of the spectrum of atherosclerosis and are associated with atherosclerotic calcification in the coronary arteries. The study aimed to evaluate the association of plasma OPN with the presence and extent of coronary stenosis, mitral annular calcification (MAC), and aortic valve sclerosis in stable angina patients. We studied 120 subjects who underwent coronary angiography because of ischemic chest pain. Coronary artery disease (CAD) was defined as > or = 50% stenosis in > or = 1 coronary artery. MAC and aortic valve sclerosis were detected by echocardiography. Lipid profile, high sensitive C-reactive protein (hsCRP), and OPN were measured in all studied subjects. Patients with CAD had increased plasma OPN when compared with those without CAD (P < 0.001). Plasma OPN levels were significantly positively correlated with atherogenic lipid profile, hsCRP, MAC grading, aortic valve sclerosis grading, and the number of stenosed coronary vessels in CAD patients. In multivariate analysis, OPN was an independent predictor of CAD (P = 0.01), MAC (P = 0.01), and aortic valve sclerosis (P = 0.04). In conclusion, OPN is an independent predictor of MAC and aortic valve sclerosis. Plasma OPN levels reflect the extent of coronary stenosis and can be used as a biomarker to identify patients with coronary atherosclerosis.

Arterial injury promotes medial chondrogenesis in Sm22 knockout mice

AIMS

Expression of SM22 (also known as SM22alpha and transgelin), a vascular smooth muscle cells (VSMCs) marker, is down-regulated in arterial diseases involving medial osteochondrogenesis. We investigated the effect of SM22 deficiency in a mouse artery injury model to determine the role of SM22 in arterial chondrogenesis.

METHODS AND RESULTS

Sm22 knockout (Sm22(-/-)) mice developed prominent medial chondrogenesis 2 weeks after carotid denudation as evidenced by the enhanced expression of chondrogenic markers including type II collagen, aggrecan, osteopontin, bone morphogenetic protein 2, and SRY-box containing gene 9 (SOX9). This was concomitant with suppression of VSMC key transcription factor myocardin and of VSMC markers such as SM α-actin and myosin heavy chain. The conversion tendency from myogenesis to chondrogenesis was also observed in primary Sm22(-/-) VSMCs and in a VSMC line after Sm22 knockdown: SM22 deficiency altered VSMC morphology with compromised stress fibre formation and increased actin dynamics. Meanwhile, the expression level of Sox9 mRNA was up-regulated while the mRNA levels of myocardin and VSMC markers were down-regulated, indicating a pro-chondrogenic transcriptional switch in SM22-deficient VSMCs. Furthermore, the increased expression of SOX9 was mediated by enhanced reactive oxygen species production and nuclear factor-κB pathway activation.

CONCLUSION

These findings suggest that disruption of SM22 alters the actin cytoskeleton and promotes chondrogenic conversion of VSMCs.

Osteopontin predicts long-term functional outcome among ischemic stroke patients

Osteopontin (OPN) is a multifunctional protein which has shown neuroprotective properties in animal models of cerebral ischemia. Nevertheless, its role in acute human stroke has not yet been established. Therefore, we aimed to determine human serum OPN level during acute ischemic stroke and its relationship with patient outcome. We measured OPN levels in 178 consecutive patients with a middle cerebral artery (MCA) occlusion who received fibrinolytic therapy and in 40 control subjects. OPN level was determined by an enzyme-linked immunosorbent assay (ELISA). Bad functional outcome was defined by modified Rankin Scale (mRS) score >2 at 3 months after stroke onset. A logistic regression analysis was performed to determine factors that could be independently associated with poor prognosis. OPN levels among stroke patients did not differ from the controls' OPN levels (16.65 vs. 17.83 ng/mL, p = 0.404). Interestingly, OPN level was increased among those patients who showed worse prognosis at 3 months (19.96 vs. 15.48 ng/mL, p = 0.040). In a logistic regression model, an OPN level >27.22 ng/mL was found to be an independent factor for a bad outcome (OR 5.01, 95% CI 1.60-15.72, p = 0.006) after adjusting for potential confounders. Those patients showing higher OPN levels before tPA administration displayed a worse prognosis compared to those with lower OPN levels. Further research is necessary to elucidate the role of OPN in ischemic stroke pathophysiology and validate OPN as a useful tool to predict long-term stroke outcome.

Molecular determinants of extracellular matrix mineralization in bone and blood vessels

PURPOSE OF REVIEW

Mineralization imparts important biomechanical and other functional properties to bones and teeth. Ectopic pathologic mineralization, however, occurring in soft tissues such as blood vessels, kidneys, articular cartilage and also in body fluids, including urine and synovial fluid, is generally debilitating, often painful and typically is destructive of compromised tissue. Here we review new findings on direct molecular determinants of mineralization operating locally at the level of the extracellular matrix, with a focus on bone and blood vessels.

RECENT FINDINGS

Accumulating evidence indicates important key roles for secreted noncollagenous proteins in regulating mineralization, wherein they also contribute structurally to the scaffolding properties of the extracellular matrix. Mineral-binding proteins contain conserved acidic peptide domains (often highly phosphorylated), which bind strongly to calcium within the apatitic mineral phase of bone and calcified blood vessels to regulate crystal growth. Other recent work has underscored the importance of the small-molecule mineralization inhibitor pyrophosphate in inhibiting tissue mineralization - an inhibition released through its enzymatic cleavage by tissue-nonspecific alkaline phosphatase. Recent findings on mechanisms involved in matrix vesicle-mediated mineralization are also discussed.

SUMMARY

Mechanistic details are emerging that describe a scenario wherein the combined actions of mineral-binding noncollagenous matrix peptides/proteins within a scaffolding of collagen (and also elastin in blood vessels), phosphatases and matrix vesicles all contribute importantly to promoting or limiting mineralization.

Adrenomedullin up-regulates osteopontin and attenuates vascular calcification via the cAMP/PKA signaling pathway

AIM

To determine whether adrenomedullin (ADM) attenuates vascular calcification (VC) by inducing osteopontin (OPN) expression.

METHODS

A VC model of rat aorta was induced with vitamin D3 plus nicotine (VDN), and vascular smooth muscle cell (VSMC) calcification was induced with beta-glycerophosphate. Von Kossa staining and alizarin red staining were assessed. Alkaline phosphatase (ALP) activity was measured. Immunohistochemical analysis was used to detect alpha-actin, while RT-PCR and Western blot analysis were used to quantify OPN expression.

RESULTS

Administration of ADM greatly reduced VC in VDN-treated aortas compared with controls, which was confirmed in calcified VSMCs. The decrease in alpha-actin expression was ameliorated by ADM both in vivo and in vitro. Moreover, mRNA and protein expression levels of OPN were significantly up-regulated in calcified aortas, and ADM increased OPN expression in calcified aortas. Furthermore, ADM up-regulated OPN expression in normal aortas and VSMCs. The ADM-mediated effects were similar to that of forskolin, which activates adenylyl cyclase; additionally, while the PKA inhibitor H89 and Ca²(+) chelator Fura-2 blocked the effect of ADM. However, the MEK/ERK inhibitor PD98509 had no effect on ADM induction of OPN mRNA expression. An OPN polyclonal antibody inhibited ADM-mediated attenuation of VC.

CONCLUSION

ADM up-regulates OPN expression and thus attenuates VC via PKA. ADM appears to be an endogenous cardiovascular protective peptide and may represent a new therapeutic target for VC treatment.

Protein targets of inflammatory serine proteases and cardiovascular disease

Serine proteases are a key component of the inflammatory response as they are discharged from activated leukocytes and mast cells or generated through the coagulation cascade. Their enzymatic activity plays a major role in the body's defense mechanisms but it has also an impact on vascular homeostasis and tissue remodeling. Here we focus on the biological role of serine proteases in the context of cardiovascular disease and their mechanism(s) of action in determining specific vascular and tissue phenotypes. Protease-activated receptors (PARs) mediate serine protease effects; however, these proteases also exert a number of biological activities independent of PARs as they target specific protein substrates implicated in vascular remodeling and the development of cardiovascular disease thus controlling their activities. In this review both PAR-dependent and -independent mechanisms of action of serine proteases are discussed for their relevance to vascular homeostasis and structural/functional alterations of the cardiovascular system. The elucidation of these mechanisms will lead to a better understanding of the molecular forces that control vascular and tissue homeostasis and to effective preventative and therapeutic approaches.

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

OBJECTIVE

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

METHODS AND RESULTS

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

CONCLUSIONS

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

Progressive secondary neurodegeneration and microcalcification co-occur in osteopontin-deficient mice

In the brain, osteopontin (OPN) may function in a variety of pathological conditions, including neurodegeneration, microcalcification, and inflammation. In this study, we addressed the role of OPN in primary and secondary neurodegeneration, microcalcification, and inflammation after an excitotoxic lesion by examining OPN knock-out (KO) mice. Two, four, and ten weeks after injection of the glutamate analogue ibotenate into the corticostriatal boundary, the brains of 12 mice per survival time and strain were evaluated. OPN was detectable in neuron-shaped cells, in microglia, and at the surface of dense calcium deposits. At this primary lesion site, although the glial reaction was attenuated in OPN-KO mice, lesion size and presence of microcalcification were comparable between OPN-KO and wild-type mice. In contrast, secondary neurodegeneration at the thalamus was more prominent in OPN-KO mice, and this difference increased over time. This was paralleled by a dramatic rise in the regional extent of dense microcalcification. Despite these differences, the numbers of glial cells did not significantly differ between the two strains. This study demonstrates for the first time a genetic model with co-occurrence of neurodegeneration and microcalcification, mediated by the lack of OPN, and suggests a basic involvement of OPN action in these conditions. In the case of secondary retrograde or transneuronal degeneration, OPN may have a protective role as intracellular actor.

Circulating levels of osteopontin are closely related to glomerular filtration rate and cardiovascular risk markers in patients with chronic kidney disease

BACKGROUND

The pleiotropic cytokine osteopontin (OPN) is thought to be involved in the pathogenesis of atherosclerosis. However, the relationship between OPN and renal function, a cardiovascular risk factor itself, is not known. Therefore, we assessed the relationship between OPN plasma levels and renal function in patients at different stages of chronic kidney disease (CKD).

METHODS

We studied 49 non-diabetic and non-smoking patients with primary kidney disease at different CKD stages (K/DOQI 1-5). True glomerular filtration rate (GFR) in patients was assessed using the inulin-clearance technique. To examine the role of an abrupt change in GFR on circulating OPN, 15 living related kidney donors were studied before and after unilateral nephrectomy. Twenty matched non-smoking healthy subjects served as controls.

RESULTS

OPN plasma levels in patients with CKD stage 1 (i.e. GFR above 90 mL min(-1) 1.73 m(-2)) were comparable with controls. OPN levels increase in a linear fashion with declining GFR (r = -0.9, P < 0.0001), so that the increase in OPN mirrors the severity of renal impairment. After unilateral nephrectomy, circulating OPN increased significantly in parallel to the decrease in GFR. We found a direct association between OPN and other markers of renal function (serum-creatinine, homocysteine and symmetric dimethylarginine,) as well as with cardiovascular risk factors such as asymmetric dimethylarginine (r = 0.36, P = 0.0213).

CONCLUSION

There is a close inverse association between GFR and circulating OPN in patients with CKD. Furthermore, OPN plasma levels correlate with established cardiovascular risk markers in patients with CKD. Assessment of renal function is important for the interpretation of OPN levels in patients with atherosclerotic disease.

Modular peptides promote human mesenchymal stem cell differentiation on biomaterial surfaces

Molecular design strategies in biomedical applications often involve creating modular "fusion" proteins, in which distinct domains within a single molecule can perform multiple functions. We have synthesized a new class of modular peptides that include a biologically active sequence derived from the growth factor BMP-2 and a series of hydroxyapatite-binding sequences inspired by the N-terminal alpha-helix of osteocalcin. These modular peptides can bind in a sequence-dependent manner to the surface of "bone-like" hydroxyapatite coatings, which are nucleated and grown on a biodegradable polymer surface via a biomimetic process. The BMP-2-derived sequence of the modular peptides is biologically active, as measured by its ability to promote osteogenic differentiation of human mesenchymal stem cells. Our study indicates that the modular peptides described here are multifunctional, and the characteristics of this approach suggest that it can potentially be applied to a range of biomaterials for regenerative medicine applications.

Vitamin D receptor activators induce an anticalcific paracrine program in macrophages: requirement of osteopontin

OBJECTIVE

Vascular calcification is highly correlated with morbidity and mortality, and it is often associated with inflammation. Vitamin D may regulate vascular calcification and has been associated with cardiovascular survival benefits.

METHODS AND RESULTS

We developed a macrophage/smooth muscle cell (SMC) coculture system and examined the effects of vitamin D receptor activators (VDRA), calcitriol and paricalcitol, on SMC matrix calcification. We found that treatment of SMC alone with VDRA had little effect on phosphate-induced SMC calcification in vitro. However, coculture with macrophages promoted SMC calcification, and this was strikingly inhibited by VDRA treatment. Several VDRA-induced genes, including bone morphogenetic protein-2 (BMP2), tumor necrosis factor-alpha, and osteopontin, were identified as candidate paracrine factors for the protective effect of VDRA. Of these, osteopontin was further investigated and found to contribute significantly to the inhibitory actions of VDRA on calcification in macrophage/SMC cocultures.

CONCLUSIONS

The ability of VDRA to direct a switch in the paracrine phenotype of macrophages from procalcific to anticalcific may contribute to their observed cardiovascular survival benefits.

Lower bone mineral density is associated with higher coronary calcification and coronary plaque burdens by multidetector row coronary computed tomography in pre- and postmenopausal women

OBJECTIVES

There is growing evidence for the association between bone mineral density (BMD) and vascular calcification, which is related to cardiovascular disease. Coronary multidetector row computed tomography (MDCT) is a noninvasive tool developed to evaluate coronary status precisely. We used MDCT to evaluate this association.

DESIGN AND PATIENTS

Eight hundred and fifteen subjects received routine checkups. After excluding subjects with factors affecting bone metabolism and cardiovascular disease, 467 subjects were analysed.

MEASUREMENTS

Coronary calcification was measured with MDCT and BMD was measured with dual X-ray absorptiometry (DXA).

RESULTS

The BMD of the femur and the lumbar spine (L-spine) were negatively associated with the coronary calcium score (CCS) after adjusting for age in women but not in men. This inverse correlation was stronger in women with a longer time since menopause (r = -0.35 at femur, postmenopausal women vs. r = -0.10 at femur, premenopausal women, P < 0.05), and it was stronger at the femur than in the L-spine (r = -0.35 at femur vs. r = -0.16 at L-spine, P < 0.01). The relationship was also stronger in postmenopausal women with osteoporosis and osteopaenia than in women with normal BMD. The lower BMD was associated with higher coronary plaque burdens and multidiseased coronary vessels in both men and women (P < 0.01).

CONCLUSIONS

Increased CCS and subclinical atherosclerosis of plaque burdens as revealed by MDCT was associated with a low BMD in all women, independent of cardiovascular risk factors and age.

Extracellular matrix alterations in hypertensive vascular remodeling

Vascular cells are very sensitive to their hemodynamic environment. Any change in blood pressure or blood flow can be sensed by endothelial and vascular smooth muscle cells and ultimately results in structural modifications within the vascular wall that accommodate the new conditions. In the case of hypertension, the increase in arterial stretch stimulates vessel thickening to normalize the tensile forces. This process requires modification of the extracellular matrix and of cell-matrix interactions, which mainly involves extracellular proteases. In hypertension, chronic exposure of the arterial wall to stretch leads to vascular remodeling, arterial stiffness and calcification, which finally affect target organ function. This review surveys how mechanical stretch regulates extracellular proteases, considering the signaling pathways involved and the consequences on the cardiovascular system.