Angiotensin II induction of osteopontin expression and DNA replication in rat arteries

Molecular mechanisms and potential therapeutic targets in the pathogenesis of hypertension in visceral adipose tissue induced by a high-fat diet

Background

Hypertension (HTN) presents a significant global public health challenge with diverse causative factors. The accumulation of visceral adipose tissue (VAT) due to a high-fat diet (HFD) is an independent risk factor for HTN. While various studies have explored pathogenic mechanisms, a comprehensive understanding of impact of VAT on blood pressure necessitates bioinformatics analysis.

Methods

Datasets GSE214618 and GSE188336 were acquired from the Gene Expression Omnibus and analyzed to identify shared differentially expressed genes between HFD-VAT and HTN-VAT. Gene Ontology enrichment and protein-protein interaction analyses were conducted, leading to the identification of hub genes. We performed molecular validation of hub genes using RT-qPCR, Western-blotting and immunofluorescence staining. Furthermore, immune infiltration analysis using CIBERSORTx was performed.

Results

This study indicated that the predominant characteristic of VAT in HTN was related to energy metabolism. The red functional module was enriched in pathways associated with mitochondrial oxidative respiration and ATP metabolism processes. Spp1, Postn, and Gpnmb in VAT were identified as hub genes on the pathogenic mechanism of HTN. Proteins encoded by these hub genes were closely associated with the target organs-specifically, the resistance artery, aorta, and heart tissue. After treatment with empagliflozin, there was a tendency for Spp1, Postn, and Gpnmb to decrease in VAT. Immune infiltration analysis confirmed that inflammation and immune response may not be the main mechanisms by which visceral adiposity contributes to HTN.

Conclusions

Our study pinpointed the crucial causative factor of HTN in VAT following HFD. Spp1, Postn, and Gpnmb in VAT acted as hub genes that promote elevated blood pressure and can be targets for HTN treatment. These findings contributed to therapeutic strategies and prognostic markers for HTN.

Extracellular Matrix Remodeling in Vascular Disease: Defining Its Regulators and Pathological Influence

Because of structural and cellular differences (ie, degrees of matrix abundance and cross-linking, mural cell density, and adventitia), large and medium-sized vessels, in comparison to capillaries, react in a unique manner to stimuli that induce vascular disease. A stereotypical vascular injury response is ECM (extracellular matrix) remodeling that occurs particularly in larger vessels in response to injurious stimuli, such as elevated angiotensin II, hyperlipidemia, hyperglycemia, genetic deficiencies, inflammatory cell infiltration, or exposure to proinflammatory mediators. Even with substantial and prolonged vascular damage, large- and medium-sized arteries, persist, but become modified by (1) changes in vascular wall cellularity; (2) modifications in the differentiation status of endothelial cells, vascular smooth muscle cells, or adventitial stem cells (each can become activated); (3) infiltration of the vascular wall by various leukocyte types; (4) increased exposure to critical growth factors and proinflammatory mediators; and (5) marked changes in the vascular ECM, that remodels from a homeostatic, prodifferentiation ECM environment to matrices that instead promote tissue reparative responses. This latter ECM presents previously hidden matricryptic sites that bind integrins to signal vascular cells and infiltrating leukocytes (in coordination with other mediators) to proliferate, invade, secrete ECM-degrading proteinases, and deposit injury-induced matrices (predisposing to vessel wall fibrosis). In contrast, in response to similar stimuli, capillaries can undergo regression responses (rarefaction). In summary, we have described the molecular events controlling ECM remodeling in major vascular diseases as well as the differential responses of arteries versus capillaries to key mediators inducing vascular injury.

Cerebrovascular damage after midlife transient hypertension in non-transgenic and Alzheimer's disease rats

Hypertension, including transient events, is a major risk factor for developing late-onset dementia and Alzheimer's disease (AD). Anti-hypertensive drugs facilitate restoration of normotension without amelioration of increased dementia risk suggesting that transient hypertensive insults cause irreversible damage. This study characterized the contribution of transient hypertension to sustained brain damage as a function of normal aging and AD. To model transient hypertension, we treated F344TgAD and non-transgenic littermate rats with L-NG-Nitroarginine methyl ester (L-NAME) for one month, ceased treatment and allowed for a month of normotensive recovery. We then examined the changes in the structure and function of the cerebrovasculature, integrity of white matter, and progression of AD pathology. As independent factors, both transient hypertension and AD compromised structural and functional integrity across the vascular bed, while combined effects of hypertension and AD yielded the largest deficits. Combined effects of transient hypertension and AD genotype resulted in loss of cortical myelin particularly in the cingulate cortex which is crucial for cognitive function. Increased cerebral amyloid angiopathy, a prominent pathology of AD, was detected after transient hypertension as were up- and down-regulation of proteins associated with cerebrovascular remodeling - osteopontin, ROCK1 and ROCK2, in F344TgAD rats even 30 days after restoration of normotension. In conclusion, transient hypertension caused permanent cerebrovasculature and brain parenchymal damage in both normal aging and AD. Our results corroborate human studies that have found close correlation between transient hypertension in midlife and white matter lesions later in life outlining vascular pathologies as pathological links to increased risk of dementia.

The Potential Role of Osteopontin and Furin in Worsening Disease Outcomes in COVID-19 Patients with Pre-Existing Diabetes

The novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has caused the ongoing coronavirus disease 2019 (COVID-19) pandemic, with more than 50 million cases reported globally. Findings have consistently identified an increased severity of SARS-CoV-2 infection in individuals with diabetes. Osteopontin, a cytokine-like matrix-associated phosphoglycoprotein, is elevated in diabetes and drives the expression of furin, a proprotein convertase implicated in the proteolytic processing and activation of several precursors, including chemokines, growth factors, hormones, adhesion molecules, and receptors. Elevated serum furin is a signature of diabetes mellitus progression and is associated with a dysmetabolic phenotype and increased risk of diabetes-linked premature mortality. Additionally, furin plays an important role in enhancing the infectivity of SARS-CoV-2 by promoting its entry and replication in the host cell. Here, we hypothesize that diabetes-induced osteopontin and furin protein upregulation results in worse outcomes in diabetic patients with SARS-CoV-2 infection owing to the roles of these protein in promoting viral infection and increasing metabolic dysfunction. Thus, targeting the osteopontin-furin axis may be a plausible strategy for reducing mortality in SARS-CoV-2 patients with diabetes.

Osteopontin in Vascular Disease

Inflammatory cytokines are necessary for an acute response to injury and the progressive healing process. However, when this acute response does not resolve and becomes chronic, the same proteins that once promoted healing then contribute to chronic inflammatory pathologies, such as atherosclerosis. OPN (Osteopontin) is a secreted matricellular cytokine that signals through integrin and CD44 receptors, is highly upregulated in acute and chronic inflammatory settings, and has been implicated in physiological and pathophysiologic processes. Evidence from the literature suggests that OPN may fit within the Goldilocks paradigm with respect to cardiovascular disease, where acute increases are protective, attenuate vascular calcification, and promote postischemic neovascularization. In contrast, chronic increases in OPN are clinically associated with an increased risk for a major adverse cardiovascular event, and OPN expression is a strong predictor of cardiovascular disease independent of traditional risk factors. With the recent finding that humans express multiple OPN isoforms as the result of alternative splicing and that these isoforms have distinct biologic functions, future studies are required to determine what OPN isoform(s) are expressed in the setting of vascular disease and what role each of these isoforms plays in vascular disease progression. This review aims to discuss our current understanding of the role(s) of OPN in vascular disease pathologies using evidence from in vitro, animal, and clinical studies. Where possible, we discuss what is known about OPN isoform expression and our understanding of OPN isoform contributions to cardiovascular disease pathologies.

Angiotensin receptor blockade mediated amelioration of mucopolysaccharidosis type I cardiac and craniofacial pathology

Mucopolysaccharidosis type I (MPS IH) is a lysosomal storage disease (LSD) caused by inactivating mutations to the alpha-L-iduronidase (IDUA) gene. Treatment focuses on IDUA enzyme replacement and currently employed methods can be non-uniform in their efficacy particularly for the cardiac and craniofacial pathology. Therefore, we undertook efforts to better define the pathological cascade accounting for treatment refractory manifestations and demonstrate a role for the renin angiotensin system (RAS) using the IDUA^-/- mouse model. Perturbation of the RAS in the aorta was more profound in male animals suggesting a causative role in the observed gender dimorphism and angiotensin receptor blockade (ARB) resulted in improved cardiac function. Further, we show the ability of losartan to prevent shortening of the snout, a common craniofacial anomaly in IDUA^-/- mice. These data show a key role for the RAS in MPS associated pathology and support the inclusion of losartan as an augmentation to current therapies.

The vascular phenotypes in hypertension: Relation with the natural history of hypertension

The different vascular phenotypes found in hypertension comprise different aspects. They may be clinical, diagnostic, structural, mechanical, functional, cellular and extracellular, signaling and molecular, proteomic, and gene expression phenotypes. In this manuscript the emphasis will be on the various structure, mechanics, dysfunction, and cell and signaling changes that can be demonstrated in hypertension, and particularly in human hypertension. The phenotype relates to the natural history of hypertension, increasingly elucidated on the basis of cohort studies. The evolution from pre-hypertension to diastolic, systolic, and systo-diastolic hypertension may have a vascular substratum that could explain, in part, the prevalence of each of these phenotypes. The potential for intervention to prevent the passage from pre-hypertension to hypertension thanks to therapies that modulate the development of vascular remodeling is highlighted.

Involvement of the renin-angiotensin system in abdominal and thoracic aortic aneurysms

Aortic aneurysms are relatively common maladies that may lead to the devastating consequence of aortic rupture. AAAs (abdominal aortic aneurysms) and TAAs (thoracic aortic aneurysms) are two common forms of aneurysmal diseases in humans that appear to have distinct pathologies and mechanisms. Despite this divergence, there are numerous and consistent demonstrations that overactivation of the RAS (renin-angiotensin system) promotes both AAAs and TAAs in animal models. For example, in mice, both AAAs and TAAs are formed during infusion of AngII (angiotensin II), the major bioactive peptide in the RAS. There are many proposed mechanisms by which the RAS initiates and perpetuates aortic aneurysms, including effects of AngII on a diverse array of cell types and mediators. These experimental findings are complemented in humans by genetic association studies and retrospective analyses of clinical data that generally support a role of the RAS in both AAAs and TAAs. Given the lack of a validated pharmacological therapy for any form of aortic aneurysm, there is a pressing need to determine whether the consistent findings on the role of the RAS in animal models are translatable to humans afflicted with these diseases. The present review compiles the recent literature that has shown the RAS as a critical component in the pathogenesis of aortic aneurysms.

Endothelin but Not Angiotensin II May Mediate Hypertension-Induced Coronary Vascular Calcification in Chronic Kidney Disease

To understand the relationship between putative neurohormonal factors operative in hypertension and coronary artery calcification (CAC), the relevant cellular actions of angiotensin (Ang II) and endothelin-1 (ET-1) are reviewed. There is compelling evidence to implicate ET-1 in CAC. ET-1 increases phosphate transport with a 42 to 73% increase in V_max. Increased cellular phosphate may induce CAC through increased Ca x phosphate product, transformation of vascular smooth muscle cells into a bone-producing phenotype or cell apoptosis that releases procalcific substances. ET-1 is increased in several models of vascular calcification. ET-1 inhibits inhibitors of calcification, matrix Gla and osteoprotegerin, while enhancing pro-calcific factors such as BMP-2 and osteopontin. In contrast, Ang II inhibits phosphate transport decreasing V_max by 38% and increases matrix Gla. Ang II also stimulates bone resorption. Vascular calcification is reduced by ET-1 A receptor antagonists and to a greater extent than angiotensin receptor blockade although both agents reduce blood pressure.

Label-free quantitative analysis of one-dimensional PAGE LC/MS/MS proteome: application on angiotensin II-stimulated smooth muscle cells secretome

A widely used method for protein identification couples prefractionation of protein samples by one-dimensional (1D) PAGE with LC/MS/MS. We developed a new label-free quantitative algorithm by combining measurements of spectral counting, ion intensity, and peak area on 1D PAGE-based proteomics. This algorithm has several improvements over other label-free quantitative algorithms: (i) Errors in peak detection are reduced because the retention time is based on each LC/MS/MS run and actual precursor m/z. (ii) Detection sensitivity is increased because protein quantification is based on the combination of peptide count, ion intensity, and peak area. (iii) Peak intensity and peak area are calculated in each LC/MS/MS run for all slices from 1D PAGE for every single identified protein and visualized as a Western blot image. The sensitivity and accuracy of this algorithm were demonstrated by using standard curves (17.4 fmol to 8.7 pmol), complex protein mixtures (30 fmol to 1.16 pmol) of known composition, and spiked protein (34.8 fmol to 17.4 pmol) in complex proteins. We studied the feasibility of this approach using the secretome of angiotensin II (Ang II)-stimulated vascular smooth muscle cells (VSMCs). From the VSMC-conditioned medium, 629 proteins were identified including 212 putative secreted proteins. 26 proteins were differently expressed in control and Ang II-stimulated VSMCs, including 18 proteins not previously reported. Proteins related to cell growth (CYR61, protein NOV, and clusterin) were increased, whereas growth arrest-specific 6 (GAS6) and growth/differentiation factor 6 were decreased by Ang II stimulation. Ang II-stimulated changes of plasminogen activator inhibitor-1, GAS6, cathepsin B, and periostin were validated by Western blot. In conclusion, a novel label-free quantitative analysis of 1D PAGE-LC/MS/MS-based proteomics has been successfully applied to the identification of new potential mediators of Ang II action and may provide an alternative to traditional protein staining methods.

Elevated osteopontin levels in patients with peripheral arterial disease

This study was carried out to compare concentrations of osteopontin (OPN) and osteoprotegerin (OPG) in peripheral arterial disease (PAD). The study population consisted of 200 consecutive subjects in whom both OPN/OPG and ankle-brachial index were measured. It was found that OPN levels, but not OPG levels, were significantly more increased in patients with PAD than those without PAD. Serum OPN levels were significantly lower in subjects with angiotensin converting enzyme inhibitors or angiotensin II receptor blockers than those without these agents. In this study, it has been demonstrated for the first time that serum OPN levels are related to PAD. Inhibition of renin- angiotensin system could decrease OPN levels and prevent the progression of PAD.

PPARalpha agonists suppress osteopontin expression in macrophages and decrease plasma levels in patients with type 2 diabetes

Osteopontin (OPN) is a proinflammatory cytokine implicated in the chemoattraction of monocytes and the development of atherosclerosis. Peroxisome proliferator-activated receptor (PPAR)alpha, a ligand-activated transcription factor with pleiotropic anti-inflammatory effects in macrophages, is the molecular target for fibrates, which are frequently used to treat dyslipidemia in patients with type 2 diabetes at high risk for cardiovascular disease. In the present study, we examined the regulation of OPN by PPARalpha agonists in macrophages and determined the effect of fibrate treatment on OPN plasma levels in patients with type 2 diabetes. Treatment of human macrophages with the PPARalpha ligands bezafibrate or WY14643 inhibited OPN expression. PPARalpha ligands suppressed OPN promoter activity, and an activator protein (AP)-1 consensus site conferred this repression. Overexpression of c-Fos and c-Jun reversed the inhibitory effect of PPARalpha ligands on OPN transcription, and, in chromatin immunoprecipitation assays, PPARalpha ligands inhibited c-Fos and phospho-c-Jun binding to the OPN promoter. Moreover, c-Fos and phospho-c-Jun protein expression was inhibited by PPARalpha agonists, indicating that PPARalpha ligands suppress OPN expression through negative cross talk with AP-1-dependent transactivation of the OPN promoter. This inhibitory effect of PPARalpha ligands on OPN expression was absent in PPARalpha-deficient macrophages, suggesting a receptor-mediated mechanism of OPN suppression. Finally, treatment of type 2 diabetic patients with bezafibrate significantly decreased OPN plasma levels. These results demonstrate a novel mechanism whereby PPARalpha ligands may impact macrophage inflammatory responses and decrease early proinflammatory markers for cardiovascular disease.

P38 MAPK inhibitors suppress biomarkers of hypertension end-organ damage, osteopontin and plasminogen activator inhibitor-1

The assessment of target organ damage is important in defining the optimal treatment of hypertension and blood pressure-related cardiovascular disease. The aims of the present study were (1) to investigate candidate biomarkers of target organ damage, osteopontin (OPN) and plasminogen activator inhibitor-1 (PAI-1), in models of malignant hypertension with well characterized end-organ pathology; and (2) to evaluate the effects of chronic treatment with a p38 MAPK inhibitor. Gene expression, plasma concentrations, and renal immunohistochemical localization of OPN and PAI-1 were measured in stroke-prone spontaneously hypertensive rats on a salt-fat diet (SFD SHR-SP) and in spontaneously hypertensive rats receiving N(omega)-nitro-L-arginine methyl ester (L-NAME SHR). Plasma concentrations of OPN and PAI-1 increased significantly in SFD SHR-SP and L-NAME SHR as compared with controls, (2.5-4.5-fold for OPN and 2.0-9.0-fold for PAI-1). The plasma levels of OPN and PAI-1 were significantly correlated with the urinary excretion of albumin (p < 0.0001). Elevations in urinary albumin, plasma OPN and PAI-1 were abolished by chronic treatment (4-8 weeks) with a specific p38 MAPK inhibitor, SB-239063AN. OPN immunoreactivity was localized predominantly in the apical portion of tubule epithelium, while PAI-1 immunoreactivity was robust in glomeruli, tubules and renal artery endothelium. Treatment with the p38 MAPK inhibitor significantly reduced OPN and PAI-1 protein expression in target organs. Kidney gene expression was increased for OPN (4.9- and 7.9-fold) and PAI-1 (2.8- and 11.5-fold) in SFD SHR-SP and L-NAME SHR, respectively. In-silico pathway analysis revealed that activation of p38 MAPK was linked to OPN and PAI-1 via SPI, c-fos and c-jun; suggesting that these pathways may play an important role in p38 MAPK-dependent hypertensive renal dysfunction. The results suggest that enhanced OPN and PAI-1 expression reflects end-organ damage in hypertension and that suppression correlates with end-organ protection regardless of overt antihypertensive action.

12S-lipoxygenase protein associates with α-actin fibers in human umbilical artery vascular smooth muscle cells

The current study sets out to characterize the intracellular localization of the platelet-type 12S-lipoxygenase (12-LO), an enzyme involved in angiotensin-II induced signaling in vascular smooth muscle cells (VSMC). Immunohistochemical analysis of VSMC in vitro or human umbilical arteries in vivo showed a clear cytoplasmic localization. On immunogold electron microscopy, 12-LO was found primarily associated with cytoplasmic VSMC muscle fibrils. Upon angiotensin-II treatment of cultured VSMC, immunoprecipitated 12-LO was found bound to alpha-actin, a component of the cytoplasmic myofilaments. 12-LO/alpha-actin binding was blocked by VSMC pretreatment with the 12-LO inhibitors, baicalien or esculetine and the protein synthesis inhibitor, cycloheximide. Moreover, the binding of 12-LO to alpha-actin was not associated with 12-LO serine or tyrosine phosphorylation. These observations suggest a previously unrecognized angiotensin-II dependent protein interaction in VSMC through which 12-LO protein may be trafficked, for yet undiscovered purposes towards the much more abundantly expressed cytoskeletal protein alpha-actin.

Effect of traditional Chinese medicine Qin-Dan-Jiang-Ya-Tang on remodeled vascular phenotype and osteopontin in spontaneous hypertensive rats

Qin-Dan-Jiang-Ya-Tang (QDJYT) is a traditional Chinese herbal medicine for the treatment of hypertension. The effect of QDJYT on blood pressure and on vascular remodeling in hypertension was investigated in the model of spontaneous hypertensive rats (SHR). Sixteen SHRs were divided into two groups, the SHR group and the SHR+QDJYT group. Eight WKY rats were a normal control group. QDJYT (750 mg/kg) was orally administered daily for 12 weeks in SHR+QDJYT group. After 12 weeks, thoracic aortas were segregated. Media thickness (MT), lumen diameter (LD), the ratio of MT to LD, the volume fraction of collagen (VFC) in media, the ultrastructure of vascular smooth muscle cells (VSMCs) and the expression of osteopontin (OPN) mRNA were examined by histological staining, transmission electron microscope (TEM), and real-time PCR, respectively. It was observed in our study that MT, MT/LD, VFC and the expression of OPN mRNA were higher in the SHRs than in the WKY rats, volume and numeral density of mitochondria in vascular smooth muscle cells (VSMCs) in media increased obviously. However, in the SHRs treated with QDJYT, we found MT, MT/LD, VFC and the expression of OPN gene were lower than in the SHRs, and the phenotype of VSMCs were close to normal. These results suggest that QDJYT could reverse the vascular remodeling in SHR, and the mechanisms may be related to the suppressive effect of QDJYT on the expression of OPN mRNA in arterial wall.

Renal and vascular hypertension-induced inflammation: role of angiotensin II

PURPOSE OF REVIEW

We will focus on the recent findings concerning the inflammatory response in vascular and renal tissues caused by hypertension.

RECENT FINDINGS

Angiotensin II is one of the main factors involved in hypertension-induced tissue damage. This peptide regulates the inflammatory process. Angiotensin II activates circulating cells, and participates in their adhesion to the activated endothelium and subsequent transmigration through the synthesis of adhesion molecules, chemokines and cytokines. Among the intracellular signals involved in angiotensin II-induced inflammation, the production of reactive oxygen species and the activation of nuclear factor-kappaB are the best known.

SUMMARY

The pharmacological blockade of angiotensin II actions, by angiotensin-converting enzyme inhibitors or angiotensin receptor antagonists, results in beneficial organ protective effects, in addition to the effects of these agents on blood pressure control, that can be explained by the blockade of the angiotensin II-induced pro-inflammatory response. These data provide a rationale for the use of blockers of the renin-angiotensin system to prevent vascular and renal inflammation in patients with hypertension.

Elastic fibres and vascular structure in hypertension

Blood vessels are dynamic structures composed of cells and extracellular matrix (ECM), which are in continuous cross-talk with each other. Thus, cellular changes in phenotype or in proliferation/death rate affect ECM synthesis. In turn, ECM elements not only provide the structural framework for vascular cells, but they also modulate cellular function through specific receptors. These ECM-cell interactions, together with neurotransmitters, hormones and the mechanical forces imposed by the heart, modulate the structural organization of the vascular wall. It is not surprising that pathological states related to alterations in the nervous, humoral or haemodynamic environment-such as hypertension-are associated with vascular wall remodeling, which, in the end, is deleterious for cardiovascular function. However, the question remains whether these structural alterations are simply a consequence of the disease or if there are early cellular or ECM alterations-determined either genetically or by environmental factors-that can predispose to vascular remodeling independent of hypertension. Elastic fibres might be key elements in the pathophysiology of hypertensive vascular remodeling. In addition to the well known effects of hypertension on elastic fibre fatigue and accelerated degradation, leading to loss of arterial wall resilience, recent investigations have highlighted new roles for individual components of elastic fibres and their degradation products. These elements can act as signal transducers and regulate cellular proliferation, migration, phenotype, and ECM degradation. In this paper, we review current knowledge regarding components of elastic fibres and discuss their possible pathomechanistic associations with vascular structural abnormalities and with hypertension development or progression.

Aldosterone increases osteopontin gene expression in rat endothelial cells

Aldosterone is currently recognized as one of the important risk hormones for cardiovascular disease. However, the cellular mechanism by which aldosterone affects the process of cardiovascular injury has not been well understood. In the present study, we investigated whether aldosterone induces pro-inflammatory genes expression in rat aortic endothelial cells. Aldosterone significantly increased steady-state osteopontin mRNA and protein levels, but not those of adhesion molecules or chemokine. The stimulatory effect of aldosterone on osteopontin expression was time-dependent (3-24h) and dose-dependent (10(-10)-10(-6)M), and abolished by a mineralocorticoid receptor (MR) antagonist spironolactone, but not by a glucocorticoid receptor antagonist RU486. The aldosterone-induced osteopontin mRNA expression was completely blocked by a transcription inhibitor, actinomycin D, and a protein synthesis inhibitor, cycloheximide. Thus, the present study demonstrated for the first time that aldosterone directly acts on endothelial cells to induce osteopontin gene expression via MR-mediated genomic action, which may be responsible for the initiation of inflammation and fibrosis in cardiovascular tissue induced by aldosterone.

Angiotensin II-accelerated atherosclerosis and aneurysm formation is attenuated in osteopontin-deficient mice

Osteopontin (OPN) is expressed in atherosclerotic lesions, particularly in diabetic patients. To determine the role of OPN in atherogenesis, ApoE-/-OPN+/+, ApoE-/-OPN+/-, and ApoE-/-OPN-/- mice were infused with Ang II, inducing vascular OPN expression and accelerating atherosclerosis. Compared with ApoE-/-OPN+/+ mice, ApoE-/-OPN+/- and ApoE-/-OPN-/- mice developed less Ang II-accelerated atherosclerosis. ApoE-/- mice transplanted with bone marrow derived from ApoE-/-OPN-/- mice had less Ang II-induced atherosclerosis compared with animals receiving ApoE-/-OPN+/+ cells. Aortae from Ang II-infused ApoE-/-OPN-/- mice expressed less CD68, C-C-chemokine receptor 2, and VCAM-1. In response to intraperitoneal thioglycollate, recruitment of leukocytes in OPN-/- mice was impaired, and OPN-/- leukocytes exhibited decreased basal and MCP-1-directed migration. Furthermore, macrophage viability in atherosclerotic lesions from Ang II-infused ApoE-/-OPN-/- mice was decreased. Finally, Ang II-induced abdominal aortic aneurysm formation in ApoE-/-OPN-/- mice was reduced and associated with decreased MMP-2 and MMP-9 activity. These data suggest an important role for leukocyte-derived OPN in mediating Ang II-accelerated atherosclerosis and aneurysm formation.

Effects of cyclosporine in osteopontin null mice

BACKGROUND

Osteopontin (OPN) is a macrophage adhesive and cell survival factor that is up-regulated in tubules in tubulointerstitial disease. We have previously reported that rats with cyclosporine (CsA) nephropathy have increased tubular osteopontin that correlates with the infiltration of macrophages and interstitial fibrosis. This study tested the hypothesis that the absence of OPN would ameliorate CsA nephropathy.

METHODS

OPN knockout (-/-) and wild type (+/+) mice were fed a low salt diet (Na+ 0.01%) for one week and then received daily CsA injections (30 mg/kg, SC) until sacrifice at two weeks. Afferent arteriolopathy, tubulointerstitial injury, macrophage infiltration, collagen III deposition, transforming growth factor-beta (TGF-beta) expression, and tubular and interstitial cell proliferation and apoptosis were evaluated.

RESULTS

Wild type mice developed early features of CsA nephropathy, with arteriolar hyalinosis and cortical and tubulointerstitial fibrosis. Despite comparable CsA levels, OPN-/- mice had less arteriolopathy (15 vs. 24%, P < 0.05), a 20% reduction in cortical macrophage infiltration (P < 0.05), and 20% reduction in interstitial collagen deposition (P < 0.05). OPN-/- mice also showed less cortical interstitial cell proliferation but no differences in tubular cell proliferation or apoptosis. OPN+/+ mice also developed some neurotoxicity, consisting of ataxia, and this was associated with increased mortality at two weeks.

CONCLUSION

OPN partially mediates arteriolopathy, early macrophage recruitment and fibrosis in murine CsA nephropathy. OPN also may be involved in CsA associated neurotoxicity.

The metastasis gene osteopontin: a candidate target for cancer therapy

Malignant tumors are characterized by dysregulated growth control, overcoming of replicative senescence, and metastasis formation. Current therapeutic regimens mostly exert their effects through inhibition of cell cycle progression, leaving two major components of transformation untouched. The cytokine osteopontin is essential for the dissemination of various cancers. Past research has implied several modes in which osteopontin and its main receptors on tumor cells can be suppressed. Osteopontin expression is inhibitable on the levels of gene transcription and the RNA message, and the osteopontin protein can be blocked with antibodies or synthetic peptides. The osteopontin receptor CD44 has been targeted by diverse therapeutic strategies, including cytotoxic and immunotherapeutic approaches. The receptor integrin alpha(V)beta(3) contributes not only to tumor cell dissemination, but also to angiogenesis and osteolysis in bone metastases. Small molecule inhibitors of this receptor are under study as drug candidates. Because receptors and cytokine ligands that mediate metastasis formation are sparsely expressed in the adult healthy organism and are more readily reached by pharmaceuticals than intracellular drug targets they may represent a particularly suitable focus for therapeutic intervention.

Vascular smooth muscle growth: autocrine growth mechanisms

Vascular smooth muscle cells (VSMC) exhibit several growth responses to agonists that regulate their function including proliferation (hyperplasia with an increase in cell number), hypertrophy (an increase in cell size without change in DNA content), endoreduplication (an increase in DNA content and usually size), and apoptosis. Both autocrine growth mechanisms (in which the individual cell synthesizes and/or secretes a substance that stimulates that same cell type to undergo a growth response) and paracrine growth mechanisms (in which the individual cells responding to the growth factor synthesize and/or secrete a substance that stimulates neighboring cells of another cell type) are important in VSMC growth. In this review I discuss the autocrine and paracrine growth factors important for VSMC growth in culture and in vessels. Four mechanisms by which individual agonists signal are described: direct effects of agonists on their receptors, transactivation of tyrosine kinase-coupled receptors, generation of reactive oxygen species, and induction/secretion of other growth and survival factors. Additional growth effects mediated by changes in cell matrix are discussed. The temporal and spatial coordination of these events are shown to modulate the environment in which other growth factors initiate cell cycle events. Finally, the heterogeneous nature of VSMC developmental origin provides another level of complexity in VSMC growth mechanisms.

Homozygosity for angiotensinogen 235T variant increases the risk of myocardial infarction in patients with multi-vessel coronary artery disease

OBJECTIVE

Molecular variants of the angiotensinogen (AGT) and the angiotensin II type 1 receptor (ATR) genes have been associated with the risk of coronary artery disease (CAD) and myocardial infarction (MI), but data so far available are conflicting. The primary object of the paper is to verify this possible association by a rigorous, angiographically controlled study in a large sample of patients with or without multi-vessel CAD.

DESIGN

We designed a large case-control study in Italian patients candidates for coronary artery bypass grafting, with angiographically documented multi-vessel CAD, compared to subjects with angiographically documented normal coronary arteries.

METHODS AND RESULTS

AGT M235T and ATR A1166C gene polymorphisms were analysed in 699 subjects; 454 patients were candidates for coronary artery bypass grafting, having angiographically documented (mainly multi-vessel) CAD. An appropriate documentation of previous MI was obtained from 404/454 (89%, 247 with and 157 without MI). Subjects (n = 245) with angiographically documented normal coronary arteries, were included as control group (CAD-free group). CAD patients had a substantial burden of conventional risk factors as compared with controls free of coronary atherosclerosis. Age, gender, smoking habit and number of stenosed vessels were the only differences between patients with or without previous myocardial infarction, who were similarly exposed to the other conventional risk factors (including hypertension). AGT M235T and ATR A1166C allele and genotype frequencies were similar between CAD and CAD-free patients. In the CAD group, AGT 235T allele was found more frequently in subjects with a previous myocardial infarction (0.494 versus 0.414; P < or = 0.05). By logistic regression, homozygosity for AGT 235T variant appeared to confer 1.9-fold increased risk for MI in both the univariate and the multivariate (adjusted for age, gender, smoking habit and number of stenosed vessels) model.

CONCLUSIONS

AGT 235 T homozygous patients with multivessel CAD have an increased risk of myocardial infarction as compared with subjects with clinically similar phenotype but different genotype.

Angiotensin II and atherosclerosis

Numerous clinical and laboratory data are now available supporting the hypothesis that the renin-angiotensin system is mechanistically relevant in the pathogenesis of atherosclerosis. The traditional role of the renin-angiotensin system in the context of blood pressure regulation has been modified to incorporate the concept that angiotensin II (Ang II) is a potent proinflammatory agent. In vascular cells, Ang II is a potent stimulus for the generation of reactive oxygen species. As a result, Ang II upregulates the expression of many redox-sensitive cytokines, chemokines, and growth factors that have been implicated in the pathogenesis of atherosclerosis. Extensive data now confirm that inhibition of the renin-angiotensin system inhibits atherosclerosis in animal models as well as in humans. These studies provide mechanistic insights into the precise role of Ang II in atherosclerosis and suggest that pharmacologic interventions involving the renin-angiotensin system may be of fundamental importance in the treatment and prevention of atherosclerosis.

Integrins inhibit angiotensin II-induced contraction in rat aortic rings

Many extracellular matrix proteins contain the tripeptide sequence arginine-glycine-aspartate (RGD). This RGD motif is recognized by integrins, a family of adhesion receptors present on vascular smooth muscle cells. In the present study, we examined the ability of different RGD-containing peptides to affect the contraction of rat aortic rings in response to different agonists. We found that the peptide RGDS inhibited angiotensin-induced contraction in a dose dependent manner. In contrast, the peptides RGDW and RGES had no effect on angiotensin-induced contractility. We show that function-blocking antibodies to the integrins alphavbeta3 and alpha5beta1 also inhibit angiotensin-induced contraction. These effects were observed in the absence of an intact endothelium. In contrast, neither an antibody directed against the beta1 subunit nor the peptide RGDS had an effect on phenylephrine or 5-hydroxytryptamine-induced contraction. These data suggest that interactions of vascular smooth muscle with components of the surrounding extracellular matrix may influence the response of smooth muscle to agonists.

Adaptive changes in the capillary network in the left ventricle of rat heart

Capillaries are nonuniform thin tubes: The arteriolar and venular capillary portions express alkaline phosphatase (AP) and dipeptidyl peptidase IV (DPPIV), respectively. Differences in enzyme activities between arteriolar and venular capillary portions could be shown by staining sections of cardiac tissues for AP and DPPIV after coronary infusion of microspheres and by staining cultured endothelial cells that had been collected from coronary microvessels. Through use of a double staining method for AP and DPPIV, adaptive changes in the capillary network were studied in rat hearts exposed to cold, exercise, hypertension, chronic coronary occlusion, and transient coronary occlusion followed by reperfusion. Two patterns could be seen in the adaptations of the ventricular capillary network. The increase in the venular capillary portions is accompanied by remarkable increases in capillary density and capillary-to-myocyte ratio. The increase in the arteriolar capillary portion seemed to be accompanied by a decrease or only a limited increase in capillary density in stressed hearts. The increase in the total capillary density improves the capacity for oxygen transport to tissues with a high tissue perfusion and a short diffusion distance for oxygen. The increase in the arteriolar capillaries may also improve oxygen transport by increasing the arterial blood perfusing the tissue. This seems, however, a compensation for the limited angiogenesis: The alleviation of stresses, such as pharmacological treatment of the hypertrophied heart and reperfusion after transient ischemia, increases venular capillary portions and capillary density. These changes are discussed with immunohistochemical observations of rapid and prolonged expressions of angiogenic growth factors.

Noncollagenous Matrix Proteins Controlling Mineralization

Biomineralization is a highly controlled process that is believed to be regulated by noncollagenous proteins found in the organic matrix of bone. Dystrophic calcification possesses several features of bone, including the presence of noncollagenous proteins, which are also thought to regulate pathologic calcification. Noncollagenous proteins have been demonstrated to be present in a wide variety of tissues. They are also believed to play a role in the pathogenesis of a number of disease processes, including atherosclerosis, restenosis, valvular stenosis, nephrolithiasis, glomerulonephritis, malignant transformation, and metastasis. This review discusses the structure, function, and possible roles of noncollagenous proteins in physiologic and pathologic processes.