An osteopontin-NADPH oxidase signaling cascade promotes pro-matrix metalloproteinase 9 activation in aortic mesenchymal cells.

Osteopontin (OPN) is a cytokine upregulated in diabetic vascular disease. To better understand its role in vascular remodeling, we assessed how OPN controls metalloproteinase (MMP) activation in aortic adventitial myofibroblasts (AMFs) and A7r5 vascular smooth muscle cells (VSMCs). By zymography, OPN and tumor necrosis factor (TNF)-alpha preferentially upregulate pro-matrix metalloproteinase 9 (pro-MMP9) activity. TNF-alpha upregulated pro-MMP9 in AMFs isolated from wild-type (OPN(+/+)) mice, but pro-MMP9 induction was abrogated in AMFs from OPN(-/-) mice. OPN treatment of VSMCs enhanced pro-MMP9 activity, and TNF-alpha induction of pro-MMP9 was inhibited by anti-OPN antibody and apocynin. Superoxide and the oxylipid product 8-isoprostaglandin F(2) alpha-isoprostane (8-IsoP) were increased by OPN treatment, and anti-OPN antibody suppressed 8-IsoP production. Like OPN and TNF-alpha, 8-IsoP preferentially activated pro-MMP9. Superoxide, 8-IsoP, and NADPH oxidase 2 (Nox2) subunits were reduced in OPN(-/-) AMFs. Treatment of A7r5 VSMCs with OPN upregulated NADPH oxidase subunit accumulation. OPN structure/function studies mapped these activities to the SVVYGLR heptapeptide motif in the thrombin-liberated human OPN N-terminal domain (SLAYGLR in mouse OPN). Treatment of aortic VSMCs with SVVYGLR upregulated pro-MMP9 activity and restored TNF-alpha activation of pro-MMP9 in OPN(-/-) AMFs. Injection of OPN-deficient OPN(+/-) mice with SVVYGLR peptide upregulated pro-MMP9 activity, 8-IsoP levels, and Nox2 protein levels in aorta and increased panmural superoxide production (dihydroethidium staining). At equivalent hyperglycemia and dyslipidemia, 8-IsoP levels and aortic pro-MMP9 were reduced with complete OPN deficiency in a model of diet-induced diabetes, achieved by comparing OPN(-/-)/LDLR(-/-) versus OPN(+/-)/LDLR(-/-) siblings. Thus, OPN provides a paracrine signal that augments vascular pro-MMP9 activity, mediated in part via superoxide generation and oxylipid formation.

Aortic Msx2-Wnt calcification cascade is regulated by TNF-alpha-dependent signals in diabetic Ldlr-/- mice.

OBJECTIVE: Aortic calcification is prevalent in type II diabetes (T2DM), enhancing morbidity and tracking metabolic syndrome parameters. Ldlr(-/-) mice fed high-fat "Westernized" diets (HFD) accumulate aortic calcium primarily in the tunica media, mediated via osteogenic morphogens and transcriptional programs that induce aortic alkaline phosphatase (ALP). Because elevated TNF-alpha is characteristic of obesity with T2DM, we examined contributions of this inflammatory cytokine. METHODS AND RESULTS: HFD promoted obesity, hyperglycemia, and hyperlipidemia, and upregulated serum TNF-alpha in Ldlr(-/-) mice. Serum haptoglobin (inflammatory marker) was increased along with aortic expression of BMP2, Msx2, Wnt3a, and Wnt7a. Dosing with the TNF-alpha neutralizing antibody infliximab did not reduce obesity, hypercholesterolemia, or hyperglycemia; however, haptoglobin, aortic BMP2, Msx2, Wnt3a, and Wnt7a and aortic calcium accumulation were downregulated by infliximab. Mice with vascular TNF-alpha augmented by a transgene (SM22-TNFalphaTg) driven from the SM22 promoter upregulated aortic Msx2, Wnt3a, and Wnt7a. Furthermore, SM22-TNFalphaTg;TOPGAL mice exhibited greater aortic beta-galactosidase reporter staining versus TOPGAL sibs, indicating enhanced mural Wnt signaling. In aortic myofibroblast cultures, TNF-alpha upregulated Msx2, Wnt3a, Wnt7a, and ALP. ALP induction was inhibited by Dkk1, an antagonist of paracrine Wnt actions. CONCLUSIONS: TNF-alpha promote aortic Msx2-Wnt programs that contribute to aortic calcium accumulation in T2DM.

Vascular Bmp Msx2 Wnt signaling and oxidative stress in arterial calcification.

Studies of fracture repair have revealed that paracrine endothelial-mesenchymal interactions direct bone formation that restores osseous integrity. Angiogenic growth factors and specific members of the bone morphogenetic protein (BMP) family mediate these interactions. Recently, these same signals have been shown to be critical in the vascular pathobiology of hypertension, diabetes, and atherosclerosis. In the arterial vasculature, mechanical and inflammatory redox signals, characteristic of hypertension and diabetes have emerged as a secretagogues for BMP production-with downstream activation of endothelial NADPH oxidases (Nox). Preliminary data now indicate that the paracrine signals provided by BMP and reactive oxygen species augment aortic myofibroblast Msx2-Wnt signaling and matrix turnover. The net mural response to these stimuli promotes osteogenic differentiation of calcifying vascular cells, moreover, oxidation of vascular LDL cholesterol generates oxysterols that trigger Runx2 activity via hedgehog pathways. Thus, BMP, Wnt, and hedgehog gene expression programs-osteogenic pathways highly familiar to the bone biologist-are elaborated in the arterial vasculature via redox-regulated mechanisms. In the brief review, we recount mounting evidence that points to oxidative stress as a major contributor to the pathobiology of diabetic arterial calcification.

Accentuated ovariectomy-induced bone loss and altered osteogenesis in heterozygous N-cadherin null mice.

UNLABELLED: Ovariectomy-induced bone loss is accentuated in mice with germline Cdh2 haploinsufficiency, the result of a decreased osteoblastogenesis in the face of normal osteoclast number. Reduced N-cadherin abundance in these mice decreases cell-cell adhesion and alters signaling pathways important for osteoblast commitment and differentiation, thus providing in vivo evidence that N-cadherin-mediated cell-cell interactions are involved in homeostatic responses to increased bone remodeling. INTRODUCTION: We have shown that targeted expression of a dominant negative truncated form of N-cadherin (Cdh2) delays acquisition of peak bone mass in mice and retards osteoblast differentiation. We tested the role of this molecule in the skeletal homeostatic response to ovariectomy in mice with germline Cdh2 haploinsufficiency. MATERIALS AND METHODS: Heterozygous Cdh2 null (Cdh2+/-) and wildtype mice were ovariectomized and followed up to 13 weeks by in vivo radiodensitometric and ex vivo histologic assessment of bone mass and turnover. Cells isolated from wildtype and Cdh2+/- mice were used to determine the alterations in bone cell function produced by partial loss of N-cadherin. RESULTS: Bone mass was not significantly different between Cdh2+/- and wildtype littermates, but on ovariectomy, bone loss in Cdh2+/- mice was initially slower, but with time it became significantly greater than in wildtype mice. This accentuated bone loss was associated with lower osteoblast number and serum osteocalcin levels, with no differences in bone resorption. Although development of calcified nodules was faster in calvaria cells isolated from Cdh2+/- mice relative to Cdh2+/+ cells, bone marrow osteogenic precursors were lower in the former than in the latter genotypes. Cdh2 expression was downregulated with differentiation in wildtype calvaria cells, whereas cadherin-11 abundance remained unchanged. Furthermore, cell-cell adhesion (postconfluence) was decreased among heterozygous calvaria cells, as was cell proliferation (preconfluence), relative to wildtype cells. Finally, the abundance and cellular distribution of beta-catenin was minimally decreased in Cdh2+/- cells, whereas mitogen-activated protein kinase (MAPK) signaling was more active in Cdh2 insufficient cells. CONCLUSIONS: Cdh2 is involved in the homeostatic bone formation response to ovariectomy, presumably by regulating osteoprogenitors number and differentiation through stabilization of cell-cell adhesion and/or signaling modulation.

Four and half lim protein 2 (FHL2) stimulates osteoblast differentiation.

UNLABELLED: FHL2, a molecule that interacts with many integrins and transcription factors, was found to play an important role in osteoblast differentiation. Overexpression of FHL2 increases the accumulation of osteoblast differentiation markers and matrix mineralization, whereas FHL2 deficiency results in inhibition of osteoblast differentiation and decreased bone formation. INTRODUCTION: Integrin-matrix interaction plays a critical role in osteoblast function. It has been shown that the cytoplasmic domains of integrin beta subunits mediate signal transduction induced by integrin-matrix interaction. We reasoned that the identification of proteins interacting with beta-cytoplasmic tails followed by analysis of the function of these proteins would enhance our understanding on integrin signaling and the roles of these proteins in osteoblast activities. MATERIALS AND METHODS: Yeast two hybrid assay was used to identify proteins interacting with the cytoplasmic domain of integrin beta5 subunit. The association of these proteins with integrin alphavbeta5 was confirmed by confocal analysis and co-immunoprecipitation. A stable MC3T3-E1 cells line overexpressing Four and Half Lim Protein 2 (FHL2) and mouse osteoblasts deficient in FHL2 were used to study the roles of FHL2 in osteoblast differentiation and bone formation. Matrix protein expression was determined by mRNA analysis and Western blotting. Matrix mineralization was detected by Alizarin red staining. Alkaline phosphatase activity was also measured. muCT was used to determine bone histomorphometry. RESULTS AND CONCLUSIONS: FHL2 and actin-binding proteins, palladin and filamin A, were identified as proteins interacting with beta5 cytoplasmic domain. FHL2 co-localized with alphavbeta5 at the focal adhesion sites in association with palladin and filamin A. FHL2 was also present in nuclei. Osteoblasts overexpressing FHL2 exhibited increased adhesion to and migration on matrix proteins. Conversely, FHL2 stimulation of CREB activity was dependent on integrin function because it was inhibited by Gly-Arg-Gly-Asp-Ser (GRGDS) peptide. The expression of osteoblast differentiation markers and Msx2 was upregulated, and bone matrix mineralization was increased in FHL2 overexpressing cells. In contrast, FHL2-deficient bone marrow cells and osteoblasts displayed decreased osteoblast colony formation and differentiation, respectively, compared with wildtype cells. Moreover, FHL2-deficient female mice exhibited greater bone loss than the wildtype littermates after ovariectomy. Thus, FHL2 plays an important role in osteoblast differentiation and bone formation.

Alphavbeta integrins play an essential role in BMP-2 induction of osteoblast differentiation.

UNLABELLED: Both integrins and BMP-2 exert similar effects on osteoblasts. We examined the relationship between the alphav-containing integrins (alphavbeta) and BMP-2 in osteoblast function. BMP-2 stimulates alphavbeta expression. BMP-2 receptors co-localize/overlap with alphavbeta integrins, and the intact function of alphavbeta is essential in BMP-2 activity. INTRODUCTION: Bone morphogenetic protein (BMP)-2 not only induces osteoblast differentiation and bone matrix mineralization, but also stimulates osteoblast migration on and adhesion to bone matrix proteins. The alphavbeta- and beta1- (alphabeta1) containing integrins mediate osteoblast interaction with many bone matrix proteins and play important roles in osteoblast adhesion, migration, and differentiation. Because alphavbeta integrins and BMP-2 share common effects on osteoblasts, we analyzed their relationship in osteoblast function. MATERIALS AND METHODS: The effects of BMP-2 on integrin expression were determined by surface labeling/immunoprecipitation and cell adhesion to matrix proteins. Confocal analysis of the immunostained cells and co-immunoprecipitation of cell extracts were used to study the spatial relationship between integrins and BMP-2 receptors. A function-blocking anti-alphavbeta integrin antibody (L230) was employed to investigate the roles of alphavbeta integrins in BMP-2 function. RESULTS: Human osteoblasts (HOBs) express alphabeta1, alphavbeta3, alphavbeta5, alphavbeta6, and alphavbeta8 integrins at focal adhesion sites. BMP-2 increases the levels of these integrins on osteoblast surface and enhances HOB adhesion to osteopontin and vitronectin. Immunoprecipitation and immunostaining analyses show that BMP-2 receptors co-localize or overlap with alphavbeta and alphabeta1 integrins. Incubation of HOBs with L230 abolishes the antiproliferative effect of BMP-2 and reduces the capacity of BMP-2 to stimulate alkaline phosphatase activity and the expression of osteocalcin, osteopontin, and bone sialoprotein. Furthermore, L230 prevents BMP-2 induction of matrix mineralization. Although BMP-2 retains its receptor-binding capability in the presence of L230, BMP-2 stimulation of Smad signaling is abolished by L230. CONCLUSION: BMP-2 upregulates the expression of alphavbeta integrins, and these integrins, in turn, play a critical role in BMP-2 function in osteoblasts.

Simvastatin Attenuates Oxidative Stress, NF-κB Activation, and Artery Calcification in LDLR-/- Mice Fed with High Fat Diet via Down-regulation of Tumor Necrosis Factor-α and TNF Receptor 1.

Simvastatin (SIM) is anti-inflammatory. We used low density lipoprotein receptor knockout (LDLR-/-) mice and human aortic smooth muscle cells (HASMCs) as model systems to study the effect of SIM on arterial calcification and to explore the potential mechanisms contributing to this protective effect. High-fat diet (HFD) caused the LRLR -/- to develop dyslipidemia, diabetics, atherosclerosis and aortic smooth muscle calcification. SIM, N-acetyl cysteine (NAC, a ROS scavenger) and apocynin (APO, a NADPH oxidase inhibitor) did not significantly retard the development of dyslipidemia or diabetic. However, those treatments were still effective in attenuating the HFD-induced atherosclerosis and aortic smooth muscle calcification. These findings suggest that the protective effect of SIM against aortic calcification is not contributed by the cholesterol lowering effect. SIM, NAC and APO were found to attenuate the HFD induced elevation of serum TNF-α, soluble TNFR1 (sTNFR1), 3-nitro-tyrosine. We hypothesized that the pro-inflammatory cytokine, oxidative stress and TNFR1 played a role in inducing aortic calcification. We used HASMC to investigate the role of TNF-α, oxidative stress and TNFR1 in inducing aortic calcification and to elucidate the mechanism contributes the protective effect of SIM against aortic calcification. We demonstrated that treating HASMC with TNF-α induced cell Ca deposit and result in an increase in ALP, NADPH oxidase activity, NF-kB subunit p65, BMP2, MSX2, and RUNX2 expression. SIM suppressed the TNF-α induced activation of NADPH oxidase subunit p47, the above-mentioned bone markers and TNFR1 expression. Furthermore, p65, p47 and TNFR1 siRNAs inhibited the TNF-α-mediated stimulation of BMP-2, MSX2, RUNX2 expression. SIM, APO, and NAC either partially inhibit or completely block the TNF-α induced H2O2 or superoxide production. These results suggest that SIM may, independent of its cholesterol-lowering effect, suppresses the progression of vascular diseases through the inhibition of the inflammation mediators TNF-α and TNFR1.

TNFR1-activated reactive oxidative species signals up-regulate osteogenic Msx2 programs in aortic myofibroblasts.

In LDLR(-/-) mice fed high-fat diabetogenic diets, osteogenic gene-regulatory programs are ectopically activated in vascular myofibroblasts and smooth muscle cells that promote arteriosclerotic calcium deposition. Msx2-Wnt signaling pathways previously identified as important for craniofacial skeletal development are induced in the vasculature by TNF, a prototypic cytokine mediator of the low-grade systemic inflammation of diabesity. To better understand this biology, we studied TNF actions on Msx2 in aortic myofibroblasts. TNF up-regulated Msx2 mRNA 4-fold within 3 h but did not regulate Msx1. Although IL-1ß could also induce Msx2 expression, TNF-related apoptosis inducing ligand, receptor activator of nuclear factor-κB ligand, and IL-6 were inactive. Inhibition of nicotinamide adenine dinucleotide phosphate oxidase (Nox) activity and genetically induced Nox deficiency (p47phox(-/-)) reduced Msx2 induction, indicating contributions of reactive oxygen species (ROS) and redox signaling. Consistent with this, rotenone, an antagonist of mitochondrial complex I, inhibited TNF induction of Msx2 and Nox2, whereas pyruvate, an anapleurotic mitochondrial metabolic substrate, enhanced induction. Moreover, the glutathione peroxidase-mimetic ebselen abrogated this TNF response. Treatment of aortic myofibroblasts with hydrogen peroxide up-regulated Msx2 mRNA, promoter activity, and DNA-protein interactions. In vivo, SM22-TNF transgenic mice exhibit increased aortic Msx2 with no change in Msx1. Dosing SM22-TNF mice with either 20 ng/g Nox1 + 20 ng/g Nox2 antisense oligonucleotides or low-dose rotenone reduced arterial Msx2 expression. Aortic myofibroblasts from TNFR1(-/-) mice expressed levels of Msx2 that were 5% that of wild-type and were not inducible by TNF. Wnt7b and active ß-catenin levels were also reduced. By contrast, TNF-inducible Msx2 expression was not reduced in TNFR2(-/-) cells. Finally, when cultured under mineralizing conditions, TNFR1(-/-) aortic myofibroblasts exhibited reduced calcification compared with wild-type and TNFR2(-/-) cells. Thus, ROS metabolism contributes to TNF induction of Msx2 and procalcific responses in myofibroblasts via TNFR1. Strategies that reduce vascular Nox- or mitochondrially activated ROS signals may prove useful in mitigating arteriosclerotic calcification.

Osteopontin promoter polymorphism is associated with increased carotid intima-media thickness.

BACKGROUND: Osteopontin (OPN)-transgenic mice exhibit increased carotid artery intima-media thickness (CIMT), smooth muscle cell proliferation, and atheroma formation. METHODS: An association of the human T-66G promoter variant with CIMT was examined in Caucasian adults grouped according to metabolic syndrome criteria: present (+MetS; n = 70) or absent (-MetS; n = 70). RESULTS: The G-allele frequency was 22%. For the entire cohort, the G group (TG and GG) was associated with significantly lower age-adjusted and gender-adjusted CIMT compared with the TT group (P = .008); similar analysis by metabolic syndrome group found a significant difference only in the -MetS group (P = .018). Stepwise multivariate regression showed that after age and waist circumference, the T-66G variant was the next most predictive of CIMT (P = .007). These data suggest that in a normoglycemic environment, human vascular OPN gene expression contributes to arterial structure, an effect diminished in dysmetabolic states. CONCLUSION: Humans with the OPN -66 TT genotype, particularly those without metabolic syndrome, exhibit thicker CIMT.

Signal transductions induced by bone morphogenetic protein-2 and transforming growth factor-beta in normal human osteoblastic cells.

Transforming growth factor beta (TGF-beta) activates Ras/MAPK signaling in many cell types. Because TGF-beta and BMP-2 exert similar effects, we examined if this signaling is stimulated by both factors and analyzed the relationship between this signaling and the Smads in osteoblasts. BMP-2 and TGF-beta stimulated Ras, MAPK, and AP-1 activities. The DNA binding activities of c-Fos, FosB/Delta FosB, Fra-1, Fra-2, and JunB were up-regulated whereas JunD activity was decreased. c-Fos, FosB/Delta FosB, and JunB were associated with Smad4. The stimulation of AP-1 by BMP-2 and TGF-beta was dependent on Smad signaling, and anti-Smad4 antibody interfered with AP-1 activity. Thus, BMP-2 and TGF-beta activate both Ras/MAPK/AP-1 and Smad signaling in osteoblasts with Smads modulating AP-1 activity. To determine the roles of MAPK in BMP-2 and TGF-beta function, we analyzed the effect of ERK and p38 inhibitors on the regulation of bone matrix protein expression and JunB and JunD levels by these two factors. ERK and p38 mediated TGF-beta suppression of osteocalcin and JunD as well as stimulation of JunB. p38 was essential in BMP-2 up-regulation of type I collagen, fibronectin, osteopontin, osteocalcin, and alkaline phosphatase activity whereas ERK mediated BMP-2 stimulation of fibronectin and osteopontin. Thus, ERK and p38 differentially mediate TGF-beta and BMP-2 function in osteoblasts.