Osteopontin. Between a rock and a hard plaque.
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Calcinosis↗
Biomedical subjects
L L Demer
Publications and source records attributed to L L Demer.
Peroxisome proliferator-activated receptor activators target human endothelial cells to inhibit leukocyte-endothelial cell interaction.
An early event in acute and chronic inflammation and associated diseases such as atherosclerosis and rheumatoid arthritis is the induced expression of specific adhesion molecules on the surface of endothelial cells (ECs), which subsequently bind leukocytes. Peroxisome proliferator-activated receptors (PPARs), members of the nuclear receptor superfamily of transcription factors, are activated by fatty acid metabolites, peroxisome proliferators, and thiazolidinediones and are now recognized as important mediators in the inflammatory response. Whether PPAR activators influence the inflammatory responses of ECs is unknown. We show that the PPAR activators 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)), Wyeth 14643, ciglitazone, and troglitazone, but not BRL 49653, partially inhibit the induced expression of vascular cell adhesion molecule-1 (VCAM-1), as measured by ELISA, and monocyte binding to human aortic endothelial cells (HAECs) activated by phorbol 12-myristate 13-acetate (PMA) or lipopolysaccharide. The "natural" PPAR activator 15d-PGJ(2) had the greatest potency and was the only tested molecule capable of partially inhibiting the induced expression of E-selectin and neutrophil-like HL60 cell binding to PMA-activated HAECs. Intracellular adhesion molecule-1 induction by PMA was unaffected by any of the molecules tested. Both PPAR-alpha and PPAR-gamma mRNAs were detected in HAECs by using reverse transcription-polymerase chain reaction and a ribonuclease protection assay; however, we have yet to determine which, if any, of the PPARs are mediating this process. These results suggest that certain PPAR activators may help limit chronic inflammation mediated by VCAM-1 and monocytes without affecting acute inflammation mediated by E-selectin and neutrophil binding.
Cell Adhesion↗
Atherogenic diet and minimally oxidized low density lipoprotein inhibit osteogenic and promote adipogenic differentiation of marrow stromal cells.
In osteoporosis, the bone marrow stroma osteogenic cell population declines and adipocyte numbers increase. We recently showed that oxidized lipids inhibit differentiation of preosteoblasts. In this report, we assess the effect of minimally oxidized low density lipoprotein (MM-LDL) on osteoblastic differentiation of murine marrow stromal cells, M2-10B4. MM-LDL, but not native LDL, inhibited stromal cell osteoblastic differentiation as demonstrated by inhibition of alkaline phosphatase activity, collagen I processing, and mineralization, through a mitogen-activated protein kinase-dependent pathway. In addition, marrow stromal cells from C57BL/6 mice fed a high fat, atherogenic diet failed to undergo osteogenic differentiation in vitro. The ability of MM-LDL to regulate adipogenesis was also assessed. Treatment of M2-10B4 as well as 3T3-L1 preadipocytes with MM-LDL, but not native LDL, promoted adipogenic differentiation in the presence of peroxisome proliferator-activated receptor (PPAR) gamma agonist thiazolidinediones, BRL49653 and ciglitizone. Based on promoter-reporter construct experiments, MM-LDL may be acting in part through activating PPARalpha. These observations suggest that LDL oxidation products promote osteoporotic loss of bone by directing progenitor marrow stromal cells to undergo adipogenic instead of osteogenic differentiation. These data lend support to the "lipid hypothesis of osteoporosis."
Adipocytes↗
cAMP stimulates osteoblast-like differentiation of calcifying vascular cells. Potential signaling pathway for vascular calcification.
The role of the cAMP signaling pathway in vascular calcification was investigated using calcifying vascular cells (CVC) derived from primary aortic medial cell cultures. We previously showed that CVC have fibroblastic morphology and express several osteoblastic differentiation markers. After confluency, they aggregate into cellular condensations, which later mature into nodules where mineralization is localized. Here, we investigated the effects of cAMP on CVC differentiation because it plays a role in both osteoblastic differentiation and vascular disease. Dibutyryl-cAMP or forskolin treatment of CVC for 3 days induced osteoblast-like "cuboidal" morphology, inhibited proliferation, and enhanced alkaline phosphatase activity, all early markers of osteoblastic differentiation. Isobutylmethylxanthine and cholera toxin had the same effects. Treatment of CVC with pertussis toxin, however, did not induce the morphological change or increase alkaline phosphatase activity, although it inhibited CVC proliferation to a similar extent. cAMP also increased type I procollagen production and gene expression of matrix gamma-carboxyglutamic acid protein, recently shown to play a role in in vivo vascular calcification. cAMP inhibited the expression of osteopontin but did not affect the expression of osteocalcin and core binding factor. Prolonged cAMP treatment enhanced matrix calcium-mineral incorporation but inhibited the condensations resulting in diffuse mineralization throughout the monolayer of cells. Treatment of CVC with a protein kinase A-specific inhibitor, KT5720, inhibited alkaline phosphatase activity and mineralization during spontaneous CVC differentiation. These results suggest that the cAMP pathway promotes in vitro vascular calcification by enhancing osteoblast-like differentiation of CVC.
Alkaline Phosphatase↗
Fibronectin and collagen I matrixes promote calcification of vascular cells in vitro, whereas collagen IV matrix is inhibitory.
Vascular calcification is a frequent component of atherosclerosis, yet the pathological mechanisms that regulate its formation are poorly understood. Calcification of the vessel wall may represent a process by which cells that normally exhibit a smooth muscle phenotype differentiate into cells that exhibit an osteoblast-like phenotype. One of the determinants of cellular phenotype is extracellular matrix; thus, we undertook the current study to evaluate the influence of extracellular matrix on calcification of vascular cells in vitro. Cell lines derived from bovine aortic media were divided into 1 of 3 groups: those that did not mineralize, those that mineralized slowly, or those that mineralized rapidly. When slowly mineralizing cells were plated onto matrix produced by rapidly mineralizing cells, the time required for mineralization decreased from 33+/-3.0 days to 7.8+/-1.3 days. Matrix produced by rapidly mineralizing cells was found to contain 3 times the amount of collagen I and fibronectin but 70% less collagen IV than nonmineralizing clones. When slowly mineralizing cells were cultured on purified collagen I or fibronectin, mineralized nodule formation, calcium incorporation, von Kossa staining, and alkaline phosphatase activity increased. In contrast, culturing slowly mineralizing cells on purified collagen IV inhibited these mineralization parameters. Furthermore, blocking antibodies to alpha5 integrins significantly inhibited the fibronectin-mediated increases in alkaline phosphatase activity, indicating that integrin-based signaling may be involved. These data suggest that matrix composition can regulate development of arterial calcification and that a subpopulation of vascular cells preferentially produces positively regulating matrix components.
Alkaline Phosphatase↗
Active serum vitamin D levels are inversely correlated with coronary calcification.
BACKGROUND: Arterial calcification is a common feature of atherosclerosis, occurring in >90% of angiographically significant lesions. Recent evidence from this and other studies suggests that development of atherosclerotic calcification is similar to osteogenesis; thus, we undertook the current investigation on the potential role of osteoregulatory factors in arterial calcification. METHODS AND RESULTS: We studied two human populations (173 subjects) at high and moderate risk for coronary heart disease and assessed them for associations between vascular calcification and serum levels of the osteoregulatory molecules osteocalcin, parathyroid hormone, and 1alpha,25-dihydroxyvitamin D3 (1,25-vitamin D). Our results revealed that 1,25-vitamin D levels are inversely correlated with the extent of vascular calcification in both groups. No correlations were found between extent of calcification and levels of osteocalcin or parathyroid hormone. CONCLUSIONS: These data suggest a possible role for vitamin D in the development of vascular calcification. Vitamin D is also known to be important in bone mineralization; thus, 1,25-vitamin D may be one factor to explain the long observed association between osteoporosis and vascular calcification.
Adult↗
Ethnic origin and serum levels of 1alpha,25-dihydroxyvitamin D3 are independent predictors of coronary calcium mass measured by electron-beam computed tomography.
BACKGROUND: Blacks have been found to have lower amounts of coronary calcium as well as higher levels of the osteoregulatory steroid 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] than whites. We sought to determine if racial differences in coronary calcium mass could be explained by differences in serum levels of 1,25(OH)2D3. METHODS AND RESULTS: We evaluated standard coronary risk factors, quantified coronary calcium mass with electron-beam computed tomography (EBCT), and measured serum 1,25(OH)2D3 with radioimmunoassay in 283 high-risk subjects (51 [180%] black, 232 [82%] white). Black subjects had lower masses of coronary calcium than whites (14 versus 47 mg; P=.003). Serum 1,25(OH)2D3 levels were slightly higher in blacks (41 versus 38 pg/mL; P=.05). Log 1,25(OH)2D3 levels were inversely proportional to log-transformed calcium mass (r=-.19; P=.001) in both races. Multivariate linear regression demonstrated that both black race (P=.02) and 1,25(OH)2D3 levels (P=.007) contributed inversely and independently to coronary calcium mass. However, an interaction term of racex1,25(OH)2D3 did not significantly contribute to coronary calcium mass, indicating that other undetermined factors in addition to 1,25(OH)2D3 are responsible for ethnic differences in coronary calcium mass. CONCLUSIONS: Both black race and serum levels of 1,25(OH)2D3 are independent negative determinants of coronary calcium mass. Nevertheless, diminished amounts of coronary calcium in blacks are not accounted for by higher 1,25(OH)2D3 levels.
Aged↗
Calcifying subpopulation of bovine aortic smooth muscle cells is responsive to 17 beta-estradiol.
BACKGROUND: Arterial calcification, common in atherosclerosis, is associated with an increased risk of clinical events such as myocardial infarction. We previously identified a subpopulation of bovine aortic medial cells, calcifying vascular cells (CVCs), that have osteoblastic characteristics and form bone mineral in vitro in the form of calcified nodules. To assess whether estrogen modulates arterial calcification as well as bone calcification, we tested CVCs for estrogen receptors and for the effect of 17 beta-estradiol on formation of calcified nodules, calcium content, alkaline phosphatase activity, and osteocalcin concentration in the culture medium. METHODS AND RESULTS: Estrogen receptor immunoreactivity was identified in the cytoplasm and the perinuclear region of CVCs by immunocytochemistry. CVCs were treated with 17 beta-estradiol at concentrations of 0, 5, and 10 nmol/L. Twenty-one days of 17 beta-estradiol treatment resulted in a significantly increased number of calcified nodules, visualized by von Kossa staining, as well as increased calcium content of the cultures. Increases in alkaline phosphatase activity, a marker for early osteoblastic differentiation, and secreted osteocalcin, a marker for late osteoblastic differentiation, were enhanced in cells treated with 17 beta-estradiol compared with control cells. CONCLUSIONS: These results suggest that 17 beta-estradiol promotes osteoblastic differentiation and calcification in vascular cells and that estrogen may play a regulatory role in arterial calcification.
Alkaline Phosphatase↗
Lipid hypothesis of cardiovascular calcification.
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Animals↗
Arterial calcification in face of osteoporosis in ageing: can we blame oxidized lipids?
Although vascular calcification is present in the vast majority of those aged over 70 years and causes serious cardiovascular dysfunction, strategies for its prevention and effective management are currently not available because the mechanism of its pathogenesis is unknown. Recently, similarities between mineralization in the vessel wall and in bone have been recognized. In this review, current understanding of the mechanisms involved in atherosclerotic calcification is summarized. In addition, several observations that may explain the paradox of vascular calcification in the face of osteoporosis are noted, emphasizing the possible role of lipid oxidation products.
Aging↗
Lipid oxidation products have opposite effects on calcifying vascular cell and bone cell differentiation. A possible explanation for the paradox of arterial calcification in osteoporotic patients.
Atherosclerotic calcification and osteoporosis often coexist in patients, yielding formation of bone mineral in vascular walls and its simultaneous loss from bone. To assess the potential role of lipoproteins in both processes, we examined the effects of minimally oxidized low-density lipoprotein (MM-LDL) and several other lipid oxidation products on calcifying vascular cells (CVCs) and bone-derived preosteoblasts MC3T3-E1. In CVCs, MM-LDL but not native LDL inhibited proliferation, caused a dose-dependent increase in alkaline phosphatase activity, which is a marker of osteoblastic differentiation, and induced the formation of extensive areas of calcification. Similar to MM-LDL, oxidized 1-palmitoyl-2-arachidonoyl-sn-glycero-3-phosphorylcholine (ox-PAPC) and the isoprostane 8-iso prostaglandin E2 but not PAPC or isoprostane 8-iso prostaglandin F2 alpha induced alkaline phosphatase activity and differentiation of CVCs. In contrast, MM-LDL and the above oxidized lipids inhibited differentiation of the MC3T3-E1 bone cells, as evidenced by their stimulatory effect on proliferation and their inhibitory effect on the induction of alkaline phosphatase and calcium uptake. These results suggest that specific oxidized lipids may be the common factors underlying the pathogenesis of both atherosclerotic calcification and osteoporosis.
Alkaline Phosphatase↗
Cross-regulatory roles of interleukin (IL)-12 and IL-10 in atherosclerosis.
T cell cytokines are known to play a major role in determining protection and pathology in infectious disease. It has recently become clear that IL-12 is a key inducer of the type 1 T cell cytokine pattern characterized by production of IFN-gamma. Conversely, IL-10 down-regulates IL-12 production and type 1 cytokine responses. We have investigated whether IL-12 and IL-10 might be involved in a chronic inflammatory reaction, atherosclerosis. In atherosclerotic plaques, we found strong expression of IFN-gamma but not IL-4 mRNAs as compared to normal arteries. IL-12 p40 mRNA and IL-12 p70 protein were also found to be abundant in atherosclerotic plaques. IL-12 was induced in monocytes in vitro in response to highly oxidized LDL but not minimally modified LDL. The cross-regulatory role of IL-10 was indicated by the expression of IL-10 in some atherosclerotic lesions, and the demonstration that exogenous rIL-10 inhibited LDL-induced IL-12 release. These data suggest that the balance between IL-12 and IL-10 production contributes to the level of immune-mediated tissue injury in atherosclerotsis.
Aorta↗
Endothelium-dependent vasodilators do not cause propagated intercellular Ca2+ waves in vascular endothelial monolayers.
Local application of a number of vasoactive agents affects vasomotor tone not only downstream to the point of application but also upstream. The mechanism(s) of upstream propagation is unknown. In endothelial cell monolayers, mechanical stimulation of one cell leads to intercellular propagation of increases in endothelial cell (EC) [Ca2+]i. In this study, we tested whether increases in EC [Ca2+]i induced by the local application of the endothelium-dependent vasodilators ATP, bradykinin and acetylcholine could spread across the monolayer. We demonstrate that unlike the response seen to a mechanical stimulus, there was no significant propagation of increases in EC [Ca2+]i levels in response to localized application of these agents. These findings suggest that upstream vasodilation in response to endothelium-dependent vasodilators is not mediated by propagation of EC [Ca2+]i waves and suggest that other electrical or chemical signals are responsible.
Acetylcholine↗
The atherosclerosis-calcification link?
Although previously believed to be a passive, degenerative process, there is increasing evidence that arterial calcification is actually an active, regulated process. In this review we address potential mechanisms of arterial calcification and, in particular, ways in which it is similar to bone formation. We also advance the hypothesis that particular factors present in atherosclerosis, such as lipids, may explain the co-localization of calcification and atherosclerosis in vivo.
Animals↗
The Yin and Yang of oxidation in the development of the fatty streak. A review based on the 1994 George Lyman Duff Memorial Lecture.
Recent data support the hypothesis that the fatty streak develops in response to specific phospholipids contained in LDL that become trapped in the artery wall and become oxidized as a result of exposure to the oxidative waste of the artery wall cells. The antioxidants present within both LDL and the microenvironments in which LDL is trapped function to prevent the formation of these biologically active, oxidized lipids. Enzymes associated with LDL and HDL (eg, platelet activating factor acetylhydrolase) or with HDL alone (eg, paraoxonase) destroy these biologically active lipids. The regulation and expression of these enzymes are determined genetically and are also significantly modified by environmental influences, including the acute-phase response or an atherogenic diet. The balance of these multiple factors leads to an induction or suppression of the inflammatory response in the artery wall and determines the clinical course.
Animals↗
Role of molecular regulation in vascular calcification.
Calcium deposits account for most of the dry weight of atherosclerotic lesions. Previously considered uncommon, vascular calcification is now known to be present in 80% of significant lesions and in at least 90% of patients with coronary artery disease. Previously considered a passive process, it is increasingly recognized as an active, regulated process. Previously considered benign, it is now becoming recognized as a major risk factor for cardiovascular events, and a major contributor to systolic hypertension, heart failure, plaque rupture and stenosis. To confirm the similarity of vascular calcification with embryonic osteogenesis, we demonstrated the expression of bone morphogenetic protein in calcified human lesions, and we developed an in vitro model of vascular calcification that provides a useful experimental system for elucidating the molecular regulation of this process, which we have shown to include alkaline phosphatase induction and expression of bone matrix proteins and differentiation factors. Understanding the regulatory mechanisms of vascular calcification will allow future therapeutic approaches to prevent and possibly reverse this disease and its clinical consequences.
Animals↗
A skeleton in the atherosclerosis closet.
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Aortic Valve↗
Pathogenesis of atherosclerosis.
The earliest lesion in the development of an atherosclerotic plaque is the fatty streak. This chronic inflammatory reaction results from a sequence of events that begins with the trapping of low density lipoprotein (LDL) in the subendothelial space of the artery wall. The trapped LDL is seeded with oxidative species released by the overlying endothelium, and lipid oxidation is initiated within the LDL particle. Some of the lipids that result lead to the activation of NFkB-like transcription factors that cause the expression of genes whose protein products mediate monocyte binding, monocyte chemotaxis into the subendothelial space, and conversion into macrophages. At least 1 major gene modulates the oxidation of LDL lipids and/or the biologic response to these lipids. The inverse relation between high density lipoprotein (HDL) and atherosclerotic events may in part be due to enzymes associated with HDL that destroy the biologically active lipids generated in LDL.
1-Alkyl-2-acetylglycerophosphocholine Esterase↗