Blood pressure regulates platelet-derived growth factor A-chain gene expression in vascular smooth muscle cells in vivo. An autocrine mechanism promoting hypertensive vascular hypertrophy

Circadian misalignment disrupts biomarkers of cardiovascular disease risk and promotes a hypercoagulable state

The circadian system regulates 24-h time-of-day patterns of cardiovascular physiology, with circadian misalignment resulting in adverse cardiovascular risk. Although many proteins in the coagulation-fibrinolysis axis show 24-h time-of-day patterns, it is not understood if these temporal patterns are regulated by circadian or behavioral (e.g., sleep and food intake) cycles, or how circadian misalignment influences these patterns. Thus, we utilized a night shiftwork protocol to analyze circadian versus behavioral cycle regulation of 238 plasma proteins linked to cardiovascular physiology. Six healthy men aged 26.2 ± 5.6 years (mean ± SD) completed the protocol involving two baseline days with 8-h nighttime sleep opportunities (circadian alignment), a transition to shiftwork day, followed by 2 days of simulated night shiftwork with 8-h daytime sleep opportunities (circadian misalignment). Plasma was collected for proteomics every 4 h across 24 h during baseline and during daytime sleep and the second night shift. Cosinor analyses identified proteins with circadian or behavioral cycle-regulated 24-h time-of-day patterns. Five proteins were circadian regulated (plasminogen activator inhibitor-1, angiopoietin-2, insulin-like growth factor binding protein-4, follistatin-related protein-3, and endoplasmic reticulum resident protein-29). No cardiovascular-related proteins showed regulation by behavioral cycles. Within the coagulation pathway, circadian misalignment decreased tissue factor pathway inhibitor, increased tissue factor, and induced a 24-h time-of-day pattern in coagulation factor VII (all FDR < 0.10). Such changes in protein abundance are consistent with changes observed in hypercoagulable states. Our analyses identify circadian regulation of proteins involved in cardiovascular physiology and indicate that acute circadian misalignment could promote a hypercoagulable state, possibly contributing to elevated cardiovascular disease risk among shift workers.

Thrombospondin-1 associated with carotid intima-media thickness among individuals with hypertension

In vivo and in vitro studies have demonstrated that thrombospondin-1 (TSP-1) is involved in atherosclerotic pathogenesis. However, the role of TSP-1 in clinical atherosclerosis remains unknown. This cross-sectional study investigated the relationship between TSP-1 and carotid intima-media thickness (IMT) and examined whether it interacts with conventional cardiovascular risk factors. A total of 587 participants were enrolled from February 2018 to December 2021. TSP-1 was dichotomized based on median value. Carotid IMT was measured bilaterally in each segment, and the average value was taken as the overall IMT variable. Analysis of covariance models were used to ascertain the main and interaction effects of cardiovascular risk factors and circulating TSP-1 levels on carotid IMT. Those with high TSP-1 (n = 294) had significantly higher carotid IMT than did those with low TSP-1 (n = 293; 0.74 ± 0.12 vs 0.72 ± 0.11 mm; p = 0.011). After the combined effects of TSP-1 and vascular risk factors on carotid IMT were evaluated, an interaction effect on IMT was observed between TSP-1 and hypertension (adjusted F = 8.760; p = 0.003). Stratification analysis revealed that individuals with hypertension and high TSP-1 had significantly higher IMT than did those with low TSP-1 (adjusted p = 0.007). However, this difference was not observed in normotensive individuals (adjusted p = 0.636). In conclusion, this is the first study to provide clinical data supporting the correlation between TSP-1 and atherosclerosis. TSP-1 may be a crucial marker of increased susceptibility to atherosclerosis in individuals with hypertension.

Atherosclerosis from Newborn to Adult-Epidemiology, Pathological Aspects, and Risk Factors

Cardiovascular disease is the leading cause of mortality and morbidity throughout the world, accounting for 16.7 million deaths each year. The underlying pathological process for the majority of cardiovascular diseases is atherosclerosis, a slowly progressing, multifocal, chronic, immune-inflammatory disease that involves the intima of large and medium-sized arteries. The process of atherosclerosis begins in childhood as fatty streaks-an accumulation of lipids, inflammatory cells, and smooth muscle cells in the arterial wall. Over time, a more complex lesion develops into an atheroma and characteristic fibrous plaques. Atherosclerosis alone is rarely fatal; it is the further changes that render fibrous plaques vulnerable to rupture; plaque rupture represents the most common cause of coronary thrombosis. The prevalence of atherosclerosis is increasing worldwide and more than 50% of people with circulatory disease die of it, mostly in modern societies. Epidemiological studies have revealed several environmental and genetic risk factors that are associated with the early formation of a pathogenic foundation for atherosclerosis, such as dyslipidemia, hypertension, diabetes mellitus, obesity, and smoking. The purpose of this review is to bring together the current information concerning the origin and progression of atherosclerosis in childhood as well as the identification of known risk factors for atherosclerotic cardiovascular disease in children.

Nanoparticle-Based Approaches towards the Treatment of Atherosclerosis

Atherosclerosis, being an inflammation-associated disease, represents a considerable healthcare problem. Its origin remains poorly understood, and at the same time, it is associated with extensive morbidity and mortality worldwide due to myocardial infarctions and strokes. Unfortunately, drugs are unable to effectively prevent plaque formation. Systemic administration of pharmaceuticals for the inhibition of plaque destabilization bears the risk of adverse effects. At present, nanoscience and, in particular, nanomedicine has made significant progress in both imaging and treatment of atherosclerosis. In this review, we focus on recent advances in this area, discussing subjects such as nanocarriers-based drug targeting principles, approaches towards the treatment of atherosclerosis, utilization of theranostic agents, and future prospects of nanoformulated therapeutics against atherosclerosis and inflammatory diseases. The focus is placed on articles published since 2015 with additional attention to research completed in 2019-2020.

Refined mapping of a hypertension susceptibility locus on rat chromosome 12

Previously, we found that transferring 6.1 Mb of salt-sensitive (SS) chromosome 12 (13.4-19.5 Mb) onto the consomic SS-12(BN) background significantly elevated mean arterial pressure in response to an 8% NaCl diet (178±7 versus 144±2 mm Hg; P<0.001). Using congenic mapping, we have now narrowed the blood pressure locus by 86% from a 6.1-Mb region containing 133 genes to an 830-kb region (chr12:14.36-15.19 Mb) with 14 genes. Compared with the SS-12(BN) consomic, the 830-kb blood pressure locus was associated with a ∆+15 mm Hg (P<0.01) increase in blood pressure, which coincided with elevated albuminuria (∆+32 mg/d; P<0.001), proteinuria (∆+48 mg/d; P<0.01), protein casting (∆+154%; P<0.05), and renal fibrosis (∆+79%; P<0.05). Of the 14 genes residing in the 830-kb locus, 8 were differentially expressed, and among these, Chst12 (carbohydrate chondroitin 4 sulfotransferase 12) was most consistently downregulated by 2.6- to 4.5-fold (P<0.05) in both the renal medulla and cortex under normotensive and hypertensive conditions. Moreover, whole genome sequence analysis of overlapping blood pressure loci revealed an ≈86-kb region (chr12:14 541 567-14 627 442 bp) containing single-nucleotide variants near Chst12 that are unique to the hypertensive SS strain when compared with the normotensive Brown Norway, Dahl salt-resistant, and Wistar-Kyoto strains. Finally, the 830-kb interval is syntenic to a region on human chromosome 7 that has been genetically linked to blood pressure, suggesting that insight gained from our SS-12(BN) congenic strain may be translated to a better understanding of human hypertension.

Imatinib ameliorates renal morphological changes in Cyp1a1-Ren2 transgenic rats with inducible ANG II-dependent malignant hypertension

The present study was performed to assess the effects of the platelet-derived growth factor (PDGF) receptor kinase inhibitor imatinib mesylate on the renal morphological changes occurring during the development of malignant hypertension in transgenic rats with inducible expression of the Ren2 gene [TGR(Cyp1a1Ren2)]. Arterial blood pressure was measured by radiotelemetry in male Cyp1a1-Ren2 rats during control conditions and during dietary administration of indole-3-carbinol (I3C; 0.3%) for 14 days to induce malignant hypertension. Rats induced with I3C (n = 5) had higher mean arterial pressures (178 ± 4 vs. 109 ± 2 mmHg, P < 0.001) and increased urinary albumin excretion (Ualb; 13 ± 5 vs. 0.6 ± 0.2 mg/day) compared with noninduced rats (n = 5). Chronic administration of imatinib (60 mg·kg(-1)·day(-1) in drinking water, n = 5) did not alter the magnitude of the hypertension (176 ± 8 mmHg) but prevented the increase in Ualb (1.6 ± 0.3 mg/day). Quantitative analysis of proliferating cell nuclear antigen using immunohistochemistry demonstrated increased proliferating cell number in cortical tubules (38 ± 5 vs. 18 ± 1 cells/mm(2)) and cortical interstitium (40 ± 7 vs. 13 ± 6 cells/mm(2)) of hypertensive rat kidneys. Renal cortical fibrosis evaluated by picrosirius red staining showed increased collagen deposition in kidneys of the hypertensive rats (1.6 ± 0.1 vs. 0.4 ± 0.1% of cortical area). Imatinib attenuated the increase in proliferating cell number in cortical tubules and interstitium (22 ± 5 vs. 38 ± 5 and 22 ± 6 vs. 40 ± 7 cells/mm(2), respectively) and reduced the degree of collagen deposition (0.8 ± 0.2 vs. 1.6 ± 0.1%) in the kidneys of hypertensive rats. These findings demonstrate that the renal pathological changes that occur during the development of malignant hypertension in Cyp1a1-Ren2 rats involve activation of PDGF receptor kinase.

Role of platelet-derived growth factors in physiology and medicine

Platelet-derived growth factors (PDGFs) and their receptors (PDGFRs) have served as prototypes for growth factor and receptor tyrosine kinase function for more than 25 years. Studies of PDGFs and PDGFRs in animal development have revealed roles for PDGFR-alpha signaling in gastrulation and in the development of the cranial and cardiac neural crest, gonads, lung, intestine, skin, CNS, and skeleton. Similarly, roles for PDGFR-beta signaling have been established in blood vessel formation and early hematopoiesis. PDGF signaling is implicated in a range of diseases. Autocrine activation of PDGF signaling pathways is involved in certain gliomas, sarcomas, and leukemias. Paracrine PDGF signaling is commonly observed in epithelial cancers, where it triggers stromal recruitment and may be involved in epithelial-mesenchymal transition, thereby affecting tumor growth, angiogenesis, invasion, and metastasis. PDGFs drive pathological mesenchymal responses in vascular disorders such as atherosclerosis, restenosis, pulmonary hypertension, and retinal diseases, as well as in fibrotic diseases, including pulmonary fibrosis, liver cirrhosis, scleroderma, glomerulosclerosis, and cardiac fibrosis. We review basic aspects of the PDGF ligands and receptors, their developmental and pathological functions, principles of their pharmacological inhibition, and results using PDGF pathway-inhibitory or stimulatory drugs in preclinical and clinical contexts.

The cytokine TWEAK modulates renal tubulointerstitial inflammation

TNF-like weak inducer of apoptosis (TWEAK) is a member of the TNF superfamily of cytokines. In addition to binding and activating the fibroblast growth factor-inducible 14 receptor, TWEAK may regulate apoptosis, proliferation, and inflammation; however, the role of this system in kidney injury is unknown. In vitro, it was found that TWEAK induced the sustained activation of NF-kappaB in a murine tubular epithelial cell line (MCT). NF-kappaB activation was associated with degradation of IkappaB-alpha; translocation of RelA to the nucleus; and increased mRNA and protein expression of monocyte chemoattractant protein-1, RANTES, and IL-6. Similarly, in vivo, the systemic administration of TWEAK induced renal NF-kappaB activation, chemokine and IL-6 expression, and interstitial inflammation in mice. Parthenolide, which prevents IkappaB-alpha degradation, inhibited TWEAK-induced NF-kappaB activation and prevented the aforementioned changes in vitro and in vivo. After folic acid-induced acute kidney injury, fibroblast growth factor-inducible 14 expression increased in mouse tubular epithelium. Neutralization of TWEAK decreased the expression of chemokines in tubular cells and reduced interstitial inflammation. In conclusion, TWEAK has NF-kappaB-dependent proinflammatory effects on tubular epithelial cells in vitro and in vivo. Moreover, blockade of TWEAK reduces tubular chemokine expression and macrophage infiltration, suggesting that TWEAK modulates acute kidney injury by regulating the inflammatory response.

Protective role of a novel erythrocyte-derived depressing factor on blood vessels of renovascular hypertensive rats

1. We have isolated a novel human erythrocyte-derived depressing factor (EDDF) that has a significant antihypertensive effect in various rat models of hypertension. The aim of the present study was to examine the mechanisms of action of EDDF on vascular function in two-kidney, one-clip (2K1C) renovascular hypertensive rats. 2. The EDDF was prepared from human erythrocytes. Experiments were performed in 18 male Wistar rats. The vascular ring perfusion assay and a two-photon laser scanning fluorescence microscope (TMP) were used to evaluate the vascular contractile response. The effects of EDDF on phenylephrine (PE)- and noradrenaline (NA)-induced vascular contraction were evaluated in 2K1C hypertensive rats. The proliferation and DNA synthesis in vascular smooth muscle cells (VSMC) were determined using the [3H]-TdR (thymidine) incorporation and 3-(4,5-dimethyl-2 thiazoyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assays. Flow cytometry, reverse transcription-polymerase chain reaction and western blots were used to measure cell cycle and apoptotic profiles, platelet-derived growth factor (PDGF)-A expression and the activity of extracellular signal-regulated kinase (ERK)-1/2, as well as the expression of cyclin D1 and cyclin-dependent kinase (CDK) 4. 3. At 10(-5) g/mL, EDDF significantly decreased the PE- and NA-induced hypertensive vascular contraction. In addition, EDDF inhibited DNA synthesis in primary VSMC from 2K1C rats. The mRNA expression of PDGF-A in VSMC was twofold higher in 2K1C rats compared with control rats, whereas EDDF significantly inhibited the increment in PDGF-A mRNA expression. In addition, EDDF inhibited the phosphorylation of ERK1/2 and decreased the expression of cyclin D1 and CDK4; p21 (Cip1) levels were increased after treatment with EDDF. 4. In conclusion, EDDF inhibits VSMC proliferation in 2K1C rats through G0/G1 cell cycle arrest. The effects may be mediated, in part, by enhanced expression of p21 (Cip1) and the inhibition of ERK1/2 phosphorylation and the expression of cyclin D1/CDK4 and PDGF-A.

Regulation of guanylyl cyclase/natriuretic peptide receptor-A gene expression

Natriuretic peptide receptor-A (NPRA) is the biological receptor of the peptide hormones atrial natriuretic peptide (ANP) and brain natriuretic peptide (BNP). The level and activity of this receptor determines the biological effects of ANP and BNP in different tissues mainly directed towards the maintenance of salt and water homeostasis. The core transcriptional machinery of the TATA-less Npr1 gene, which encodes NPRA, consists of three SP1 binding sites and the inverted CCAAT box. This promoter region of Npr1 gene has been shown to contain several putative binding sites for the known transcription factors, but the functional significance of most of these regulatory sequences is yet to be elucidated. The present review discusses the current knowledge of the functional significance of the promoter region of Npr1 gene and its transcriptional regulation by a number of factors including different hormones, growth factors, changes in extracellular osmolarity, and certain physiological and patho-physiological conditions.

PDGF and cardiovascular disease

Platelet-derived growth factor (PDGF) was identified in a search for serum factors that stimulate smooth muscle cell (SMC) proliferation. During the development of lesions of atherosclerosis that can ultimately lead to vessel occlusion, SMC are stimulated by inflammatory factors to migrate from their normal location in the media. They accumulate within the forming lesion where they contribute to lesion expansion by proliferation and deposition of extracellular matrix. Different genetic manipulations in vascular cells combined with various inhibitory strategies have provided strong evidence for PDGF playing a prominent role in the migration of SMC into the neointima following acute injury and in atherosclerosis. Other activities of PDGF identified in vivo suggest additional functions for PDGF in the pathogenesis of cardiovascular disease.

Pressure activates rat pancreatic stellate cells

Pancreatic stellate cells (PSCs) play a central role in development of pancreatic fibrosis. In chronic pancreatitis, pancreatic tissue pressure is higher than that of the normal pancreas. We here evaluate the effects of pressure on the activation of rat PSCs. PSCs were isolated from the pancreas of Wistar rat using collagenase digestion and centrifugation with Nycodenz gradient. Pressure was applied to cultured rat PSCs by adding compressed helium gas into the pressure-loading apparatus to raise the internal pressure. Cell proliferation rate was assessed by 5-bromo-2'-deoxyuridine (BrdU) incorporation. MAPK protein levels and alpha-smooth muscle actin (alpha-SMA) expression were evaluated by Western blot analysis. Concentration of activated transforming growth factor-beta1 (TGF-beta1) secreted from PSCs into culture medium was determined by ELISA. Collagen type I mRNA expression and collagen secretion were assessed by quantitative PCR and Sirius red dye binding assay, respectively. Application of pressure significantly increased BrdU incorporation and alpha-SMA expression. In addition, pressure rapidly increased the phosphorylation of p44/42 and p38 MAPK. Treatment of PSCs with an MEK inhibitor and p38 MAPK inhibitor suppressed pressure-induced cell proliferation and alpha-SMA expression, respectively. Moreover, pressure significantly promoted activated TGF-beta1 secretion, collagen type I mRNA expression, and collagen secretion. Our results demonstrate that pressure itself activates rat PSCs and suggest that increased pancreatic tissue pressure may accelerate the development of pancreatic fibrosis in chronic pancreatitis.

Stimulation of Na-dependent phosphate transport by platelet-derived growth factor in rat aortic smooth muscle cells

We investigated the effect of platelet-derived growth factor B homodimer (PDGF-BB) on inorganic phosphate (Pi) transport activity, which has been reported to be involved in the mechanism of atherosclerosis, in A-10 rat aortic vascular smooth muscle cells (VSMCs). PDGF-BB time- and dose-dependently stimulated Pi transport in A-10 cells. Using northern blot analysis, the PDGF-BB-enhanced Pi transporter (PiT) in A-10 cells was identified as Pit-1 (Glvr-1), a member of the type III Na-dependent PiT. An inhibitor of PDGF beta-receptor tyrosine kinase suppressed PDGF-BB-induced Pi transport. Both a protein kinase C (PKC) inhibitor calphostin C and PKC down regulation suppressed the stimulatory effect of PDGF-BB on Pi transport. On the other hand, inhibition of mitogen-activated protein (MAP) kinases by selective inhibitors did not affect Pi transport. Ly294002, a phosphatidylinositol (PI) 3-kinase inhibitor, partially attenuated PDGF-BB-induced Pi transport. A selective inhibitor of S(6) kinase, rapamycin, reduced this effect of PDGF-BB, while Akt kinase inhibitor did not. In summary, these results indicated that PDGF-BB is a potent and selective stimulator of Pi transport in VSMCs. The mechanism responsible for this effect is not mediated by MAP kinase, but involves activation of PKC, PI 3-kinase and S(6) kinase.

Blood pressure regulates the activity and function of the Na-K-2Cl cotransporter in vascular smooth muscle

The Na-K-2Cl cotransporter (NKCC1) is one of several transporters that have been linked to hypertension, and its inhibition reduces vascular smooth muscle tone and blood pressure. NKCC1 in the rat aorta is stimulated by vasoconstrictors and inhibited by nitrovasodilators, and this is linked to the contractile state of the smooth muscle. To determine whether blood pressure also regulates NKCC1, we examined the acute effect of hypertension on NKCC1 in rats after aortic coarctation. In the hypertensive aorta (28-mmHg rise in mean blood pressure), an increase in NKCC1 activity (measured as bumetanide-sensitive (86)Rb efflux) was apparent by 16 h and reached a plateau of 62% greater than control at 48 h. In contrast, there was a slight decrease in NKCC1 activity in the hypotensive aorta (21% decrease in mean blood pressure). Measurement of NKCC1 mRNA by real-time PCR revealed a fivefold increase in the hypertensive aorta compared with the hypotensive aorta or sham aorta. The inhibition by bumetanide of isometric force response to phenylephrine was significantly greater in the hypertensive aorta than in the control aorta or hypotensive aorta. We conclude that NKCC1 in rat aortic smooth muscle is regulated by blood pressure, most likely through changes in transporter abundance. This upregulation of NKCC1 is associated with a greater contribution to force generation in the hypertensive aorta. This is the first demonstration that NKCC1 in vascular smooth muscle is regulated by blood pressure and indicates that this transporter is important in the acute response of vascular smooth muscle to hypertension.

Transcription of the platelet-derived growth factor A-chain gene

The molecular mechanisms which control the transcription of growth factor genes underlie such diverse biological processes as embryonic development, cellular differentiation and wound healing. Moreover, disruption of these controls is implicated in the development and progression of a wide variety of human diseases, including cancer, atherosclerosis and fibrotic disease. This review highlights progress made in the study of the gene encoding platelet-derived growth factor A-chain (PDGF-A) from the perspective of its normal patterns of expression, as well as possible mechanisms leading to dysregulation and disease. A particular focus has been placed on the identification and characterization of specific DNA elements, DNA-binding proteins and other aspects of transcriptional regulation involved in activation and repression of the human PDGF-A promoter.

5-lipoxygenase and atherosclerosis

PURPOSE OF REVIEW

5-Lipoxygenase (5LO) was recently identified as a gene that makes an important contribution to atherosclerosis in mice and humans, but the underlying mechanism(s) remains unknown.

RECENT FINDINGS

Studies of the 5LO pathway in other disease areas suggest that 5LO could contribute to atherosclerosis at different levels, such as lesion initiation, growth and cellular proliferation within the lesion, and/or destabilization of plaques that can lead to their rupture.

SUMMARY

Recent advances in our understanding of how 5LO is involved in the atherosclerotic process will have important implications for diagnostic and therapeutic strategies in the future.

Structure adaptation and blood flow control in the uterine arterial system after hemochorial placentation

In the course of hemochorial placentation, trophoblast cells build a most conductive placental stream bed for maternal blood with intramural foetal capillaries. The stream bed is adapted to the maternal vascular system, causing local increase in flow and shear stress. Subsequently, local maternal microvascular system vanishes. The remaining upstream arteries, up to the aorta, undergo "physiological changes", i.e. increase in circumference and length, predominantly by growth and remodeling. Peripheral uterine arteries, possibly collapsed due to low intraluminal pressure, show over-dilatation associated with endothelium destruction and trophoblast cell invasion. Overall arterial conductance increases to controlled extent; placental blood flow rate rises moderately. Intraplacental blood pressures are kept low allowing for free perfusion of placental foetal capillaries. According to the generally accepted concept, destructing impact of invading trophoblast cells causes the physiological changes. However, trophoblast invasion does not explain physiological changes occurring before and outside trophoblast invasion. On the other hand, physiological changes may well be induced by shear stress, which operates in extrauterine body regions as signal for vascular adaptation to growth. Thus, it is hypothesized that trophoblast cells control vascular adaptation and placental blood flow rate simply by constructing the hemochorial steam bed, thereby building up shear stress and triggering the general physiological automatism for controlled vascular adaptation to growth.

Hypertension increases expression of growth factors and MHC II in chronic allograft nephropathy

BACKGROUND

Hypertension of the recipient is strongly associated with chronic allograft nephropathy. It is unclear, however, whether hypertension is the cause or the consequence of chronic allograft nephropathy.

METHODS

The present study was performed in the Fisher to Lewis rat kidney transplant model. Transplanted rats (N = eight in each group) received either no treatment or were made hypertensive by administration of deoxycorticosteron acetate (DOCA) and salt. Proteinuria and systolic blood pressure was measured monthly, grafts were harvested at 3 and 6 months for semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and for immunohistology.

RESULTS

Systolic blood pressure was markedly elevated in rats receiving DOCA/salt. Allografts of hypertensive animals contained significantly more cells expressing the proliferating cell nuclear antigen compared to isografts and to allografts from normotensive animals (P < 0.05). Histologic staining and mRNA expression of major histocompatibility complex (MHC) II was markedly increased in allografts of hypertensive animals compared to all other groups (P < 0.05). Expression of mRNA for platelet-derived growth factor-B (PDGF-B), transforming growth factor-beta (TGF-beta) and collagen was higher in allografts than in isografts and was highest in hypertensive animals.

CONCLUSION

We conclude that hypertension augments the expression of growth factors in the allograft possibly aggravating the intimal hyperplasia observed in chronic allograft nephropathy. By increasing the expression of MHC II antigens, hypertension may render the allograft more susceptible to alloantigen-dependent damage. Hypertension and alloantigen-dependent factors appear to exert additive or synergistic effects on inflammatory pathways leading to graft injury.

Adenovirus-mediated transfer of ribozyme targeting platelet-derived growth factor A-chain mRNA inhibits growth of vascular smooth muscle cells from spontaneously hypertensive rats

Platelet-derived growth factor (PDGF) is a potent stimulator of growth of vascular smooth muscle cells (VSMCs). VSMCs from spontaneously hypertensive rats (SHRs) show exaggerated growth and increasingly express PDGF A-chain messenger RNA (mRNA). To examine adenovirus-mediated transfer of a ribozyme targeting the PDGF A-chain mRNA as a possible gene therapy for vascular proliferative diseases, a recombinant adenovirus vector encoding a ribozyme that targets rat PDGF A-chain mRNA (Ad. ribozyme) was designed and synthesized and its effect on the growth of VSMCs from SHRs was investigated. This vector dose-dependently inhibited DNA synthesis in VMSCs from SHRs, whereas an adenovirus vector encoding the Escherichia coli LacZ gene (Ad. LacZ) did not affect DNA synthesis. Ad. ribozyme significantly suppressed proliferation of VSMCs from SHRs in a dose-dependent manner. Ad. LacZ had no effect. Ad. ribozyme significantly inhibited expression of PDGF A-chain mRNA and PDGF-AA protein in VSMCs from SHRs. Ad. LacZ had no effect. These results demonstrated that adenovirus-mediated transfer of a ribozyme targeting the PDGF A-chain mRNA effectively and specifically inhibited the growth of VSMCs from SHRs with suppression of PDGF A-chain mRNA and PDGF-AA protein expression. Adenovirus-mediated transfer of ribozyme targeting PDGF A-chain mRNA may be a feasible gene therapy for vascular proliferative diseases.

Hammerhead ribozyme targeting human platelet-derived growth factor A-chain mRNA inhibited the proliferation of human vascular smooth muscle cells

Platelet-derived growth factor (PDGF) A-chain contributes to the pathogenesis of cardiovascular proliferative diseases, such as hypertensive vascular disease, atherosclerosis, and re-stenosis of an artery after angioplasty. To develop a ribozyme against human PDGF A-chain mRNA as a gene therapy for human arterial proliferative diseases, we designed and synthesized a 38-base hammerhead ribozyme to cleave human PDGF A-chain mRNA at the GUC sequence at nucleotide 591. In the presence of MgCl(2), synthetic hammerhead ribozyme to human PDGF A-chain mRNA cleaved the synthetic target RNA to two RNA fragments at a predicted size. Doses of 0.01-1.0 microM hammerhead ribozyme to human PDGF A-chain mRNA significantly inhibited angiotensin II (Ang II) and transforming growth factor (TGF)-beta(1)-induced DNA synthesis in vascular smooth muscle cells (VSMC) from human in a dose-dependent manner. One micromolor of hammerhead ribozyme to human PDGF A-chain mRNA significantly inhibited Ang II-induced PDGF A-chain mRNA and PDGF-AA protein expressions in VSMC from humans. These results indicate that the designed hammerhead ribozyme to human PDGF A-chain mRNA effectively inhibited growth of human VSMC by cleaving the PDGF A-chain mRNA and inhibiting the PDGF-AA protein expression in human VSMC. This suggests that the designed hammerhead ribozyme to PDGF A-chain mRNA is a feasible gene therapy for treating arterial proliferative diseases.

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.

Inhibition of vascular smooth muscle cell proliferation by DNA-RNA chimeric hammerhead ribozyme targeting to rat platelet-derived growth factor A-chain mRNA

BACKGROUND

Spontaneously hypertensive rats (SHR)-derived vascular smooth muscle cells (VSMC) show exaggerated growth and increasingly express platelet-derived growth factor (PDGF) A-chain mRNA compared to VSMC from normotensive Wistar-Kyoto (WKY) rats.

OBJECTIVE

To investigate the effects of designed DNA-RNA chimeric hammerhead ribozyme to rat PDGF A-chain on exaggerated growth of VSMC from SHR.

DESIGN AND METHODS

We designed and synthesized a 38-base DNA-RNA chimeric hammerhead ribozyme with two phosphorothioate linkages at the 3' terminal to cleave rat PDGF A-chain mRNA at the GUC sequence at nucleotide 921. We confirmed the cleavage activity of designed ribozyme by in vitro cleavage reaction and by lipofectin-mediated transfection of ribozyme into VSMC.

RESULTS

Doses of 0.1 and 1 micromol/l DNA-RNA chimeric ribozyme dose-dependently inhibited basal DNA synthesis in VSMC from SHR. A dose of 1 micromol/l DNA-RNA chimeric ribozyme time-dependently inhibited basal DNA synthesis in VSMC from SHR. However, the same doses of all-RNA ribozyme had no effects on DNA synthesis in VSMC from SHR. Fluorescein isothiocyanate-labeled DNA-RNA chimeric ribozyme was recognized in cytosol at 30 min, and in nucleus at 60 min after lipofectin transfection. A dose of 1 micromol/l DNA-RNA chimeric ribozyme significantly inhibited expressions of both PDGF A-chain mRNA and PDGF-AA protein in VSMC from SHR, but not from WKY rats.

CONCLUSION

These results indicated that the designed DNA-RNA chimeric ribozyme to PDGF A-chain mRNA effectively and specifically inhibited the exaggerated growth of VSMC from SHR at low concentrations, which were mediated by the reduction of PDGF A-chain mRNA and PDGF-AA protein expressions.

Effects of TCV-116 on endothelin-1 and PDGF A-chain expression in angiotensin II-induced hypertensive rats

Angiotensin II (Ang II) has been shown to stimulate cardiac growth and collagen synthesis in cultured vascular smooth muscle cells and to increase fibroblast proliferation. Chronic infusion with Ang II increases blood pressure and activates growth mechanisms to produce hypertrophy of the heart. This study investigated the effects of an Ang II type 1 receptor antagonist, TCV-116, on preproendothelin-1 (preproET-1), ETA receptor and platelet-derived growth factor (PDGF) A-chain expression in the left ventricle of Wistar-Kyoto rats treated for 2 weeks with Ang II (200 ng x kg(-1) x min(-1)), and the relation of these effects to myocardial remodeling. Rats given Ang II alone (ANGII-V) were compared with rats also receiving TCV-116 (ANGII-TCV). In both groups, blood pressure was similar and significantly higher than in control rats. The preproET-1, ET(A) receptor and PDGF A-chain expressions in the left ventricle were significantly increased in ANGII-V compared with control rats, and were significantly suppressed in ANGII-TCV compared with ANGII-V rats. ANGII-V rats showed a significant increase of the type I collagen expression, wall-to-lumen ratio, perivascular fibrosis, and myocardial fibrosis, with all these parameters being significantly improved by TCV-116. Myocardial remodeling in Ang II-induced hypertensive rats was significantly ameliorated by a subdepressor dose of TCV-116, which may have been due to a decrease in ET-1 and PDGF A-chain expression in the left ventricle.

In vivo activation of rat aortic platelet-derived growth factor and epidermal growth factor receptors by angiotensin II and hypertension

It is unclear whether the previous in vitro evidence of a link between angiotensin II (Ang II) and growth factor receptors can apply to the in vivo situation. In this study, we examined vascular platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) receptor activation in stroke-prone spontaneously hypertensive rats (SHRSP) and the role of Ang II. Tyrosyl phosphorylation of the growth factor receptors was determined by Western blot analysis coupled with immunoprecipitation. Tyrosyl phosphorylation of the aortic PDGF beta-receptor, but not the EGF receptor, was chronically increased in SHRSP with hypertension, compared with normotensive rats, being accompanied by increased extracellular signal-regulated kinase (ERK) activity. Treatment of SHRSP with ACE inhibitors (perindopril or enalapril) significantly reduced aortic PDGF beta-receptor tyrosyl phosphorylation and ERK activity, whereas treatment with hydralazine failed to reduce these activities. Therefore, these aortic changes in SHRSP were mediated by Ang II in response to vascular ACE. Ang II was infused into rats to examine the effects on aortic growth factor receptors. Chronic Ang II infusion, via the angiotensin type 1 receptor, significantly increased activation of the aortic PDGF beta-receptor but not the EGF receptor. Thus, the aortic PDGF beta-receptor, activated by ACE-mediated Ang II, seems to be responsible for vascular remodeling in hypertensive rats.

Protein traffic activates NF-kB gene signaling and promotes MCP-1-dependent interstitial inflammation

Mononuclear cells accumulate in the renal interstitium and contribute to renal injury in proteinuric nephropathies. Angiotensin-converting enzyme (ACE) inhibitors reduce protein trafficking and also lessen renal structural and functional damage. Many proinflammatory genes, including monocyte chemoattractant protein-1 (MCP-1), a chemoattractant for monocytes and T lymphocytes, are transcriptionally regulated by nuclear factor-kappa B (NF-kB). We aimed to study NF-kB activation and MCP-1 expression over time in two models of progressive proteinuric nephropathies (5/6 nephrectomy and passive Heymann nephritis [PHN]) and evaluate the effect of antiproteinuric therapy with an ACE inhibitor on these factors. In both models, increased urinary protein excretion over time was associated with a remarkable increase in NF-kB activity, which was almost completely suppressed by reducing proteinuria with lisinopril. NF-kB activation was paralleled by upregulation of MCP-1 messenger RNA and interstitial accumulation of ED-1-positive monocytes/macrophages and CD8-positive T cells. Lisinopril inhibited MCP-1 upregulation and limited interstitial inflammation. In a group of PHN rats with advanced disease and severe proteinuria, a dose of lisinopril high enough to inhibit renal ACE activity failed to reduce proteinuria and also did not limit NF-kB activation, which was sustained over time, along with MCP-1 gene overexpression and interstitial inflammation. These data suggest that NF-kB is activated in the presence of increased protein traffic, enhancing the nuclear transcription of the MCP-1 gene with potent chemotactic and inflammatory properties. This mechanism may help explain the long-term renal toxicity of filtered proteins.

Atherosclerosis

Atherosclerosis, a disease of the large arteries, is the primary cause of heart disease and stroke. In westernized societies, it is the underlying cause of about 50% of all deaths. Epidemiological studies have revealed several important environmental and genetic risk factors associated with atherosclerosis. Progress in defining the cellular and molecular interactions involved, however, has been hindered by the disease's aetiological complexity. Over the past decade, the availability of new investigative tools, including genetically modified mouse models of disease, has resulted in a clearer understanding of the molecular mechanisms that connect altered cholesterol metabolism and other risk factors to the development of atherosclerotic plaque. It is now clear that atherosclerosis is not simply an inevitable degenerative consequence of ageing, but rather a chronic inflammatory condition that can be converted into an acute clinical event by plaque rupture and thrombosis.

AT(1) receptor inhibition does not reduce arterial wall hypertrophy or PDGF-A expression in renal hypertension

To separate the role of ANG II from pressure in hypertrophy of the vascular wall in one-kidney, one-clip (1K1C) hypertension, experimental and sham-operated rats were given the AT(1)-receptor antagonist losartan (20 mg x kg(-1) x day(-1)) or tap water for 14 days. Mean arterial pressure was elevated in both experimental groups compared with controls. Rats were anesthetized with pentobarbital sodium, and the thoracic aorta and carotid, small mesenteric, and external spermatic arteries were harvested and embedded in paraffin. Tissue sections were used for morphological analysis, immunohistochemistry for 5-bromo-2'-deoxyuridine (BrdU) and platelet-derived growth factor (PDGF)-AA, stereological measurements, and in situ hybridization with a (35)S-labeled riboprobe for PDGF-A mRNA. Elevated cross-sectional areas of thoracic, carotid, and small mesenteric artery in 1K1C rats were not reduced by losartan. The internal diameter of the external spermatic artery and microvascular density of the cremaster muscle were reduced in 1K1C rats. The number of BrdU-positive nuclei per cross section did not differ between 1K1C and control arteries. PDGF-A mRNA was elevated in the arterial walls of 1K1C rats compared with controls and was hardly changed by losartan. PDGF-A protein stained strongly in the media of 1K1C arteries and was not inhibited by losartan; it appeared in the adventitia of all aortas and carotid arteries. These observations demonstrate that effects of ANG II mediated through the AT(1) receptor are not necessary for hypertrophy of the vascular wall during 1K1C hypertension or expression of PDGF-A.

Mechanical strain increases PDGF-B and PDGF beta receptor expression in vascular smooth muscle cells

Cyclic mechanical strain causes proliferation of vascular smooth muscle cells, mediated in part by platelet-derived growth factor (PDGF). We examined the effect of cyclic strain on expression of PDGF-B and the PDGF beta receptor. Neonatal rat vascular smooth muscle cells were exposed to 1 hertz cyclic strain on silicone elastomer plates. PDGF-B mRNA increased after 6 h of strain. In cells transfected with a PDGF-B promoter chloramphenicol acetyl transferase construct (psisCAT 6A), activity increased by 12-fold following 12 h of strain. Two neutralizing antibodies to the PDGF beta receptor both reduced strain-induced [(3)H]thymidine incorporation by 50%. Expression of the PDGF beta receptor protein increased 1.8-fold following 24 h of strain. During strain, PDGF beta receptor expression was not significantly altered by neutralizing antibodies to PDGF-B. Thus, both PDGF-B and the PDGF beta receptor are induced by cyclic mechanical strain and both contribute to cell proliferation in response to strain.

Atrophic remodeling of the artery-cuffed artery

Increased arterial wall tension stimulates growth and remodeling of arteries, but little is known about the effects of decreased wall tension, despite its developmental and pathological significance. Consequently, we cuffed 1 carotid artery in rabbits with a portion of the contralateral artery to off-load circumferential wall tension. The model produced rapid and extensive atrophy of the cuffed artery that yielded decreases in the DNA content of the cuffed artery (a measure of cell number) from 8.0+/-0.5 microgram/cm of in situ vessel length to 5.6+/-0.5 microgram/cm at 21 days postoperatively. The elastin content of the cuffed artery was also significantly reduced, from 399+/-17 to 283+/-17 microgram/cm, and collagen content was reduced from 468.0+/-59.0 to 154+/-24 microgram/cm (P<0.05) at 21 days postoperatively. Detection of DNA oligonucleosomes by gel electrophoresis implicated apoptotic cell death in remodeling due to cuffing. Upregulation of matrix metalloproteinases (MMPs), including MMP-2, MMP-9, and unidentified gelatinases, indicated that these enzymes may also be involved in remodeling. No further changes in wall structure were seen between 3 weeks and 6 months, and the excised artery that was used as a cuff exhibited normal medial morphology for at least 6 months postoperatively. We infer from these experiments that off-loading of arterial wall tension induces rapid and extensive atrophy of the arterial media.

PDGF-A expression correlates with blood pressure and remodeling in 1K1C hypertensive rat arteries

We previously demonstrated remodeling of large and small arteries in angiotensin II-treated rats, paralleled by an increased expression of platelet-derived growth factor (PDGF)-A chain mRNA in large arteries. Both remodeling and PDGF-A expression were associated with elevation of blood pressure rather than a direct effect of angiotensin II. To further delineate the role of PDGF-A and elevated blood pressure, we assessed the level of PDGF-A and -B mRNA and protein in the wall of large as well as small arteries in the one-kidney, one-clip (1K1C) hypertensive rat, a non-renin-dependent model of hypertension. Fourteen days after renal artery stenosis, the thoracic aorta and both femoral arteries were collected from 1K1C rats (n = 8) and uninephrectomized controls (n = 8) and immediately processed for morphological measurement, immunohistochemistry, RT-PCR, and Western blotting. Systolic blood pressure was significantly elevated in hypertensive rats (202 +/- 26 mmHg) compared with control rats (122 +/- 7.9 mmHg) and was accompanied by arterial hypertrophy in both aorta and femoral arteries. The mRNA for PDGF-A chain was increased threefold in the thoracic aorta (P < 0.05) of 1K1C rats, whereas the message for PDGF-B was not significantly changed in hypertensive versus control animals. A higher staining of the intima-media was observed by using an anti-PDGF-A chain polyclonal antibody on paraffin-embedded sections. Western blot results indicated an approximately 2-fold increase in PDGF-A protein in aortic and femoral wall of the 1K1C rats. The results showed that both the mRNA and protein for PDGF-A chain are increased and well correlated with the blood pressure and wall area, suggesting a direct effect of elevated pressure on PDGF synthesis, which, in turn, may affect the onset and progression of vascular hypertrophy.

ACE inhibitor quinapril reduces the arterial expression of NF-kappaB-dependent proinflammatory factors but not of collagen I in a rabbit model of atherosclerosis

Increasing evidence supports an association between inflammation and plaque rupture. Macrophages and vascular smooth muscle cells are a source of cytokines and growth factors, which contribute to ongoing inflammation during atherogenesis. In a rabbit model of atherosclerosis, we evaluated the effect of the ACE inhibitor quinapril on different parameters implicated in the pathogenesis of the plaque, such as the presence of chemokines (interleukin-8, monocyte chemoattractant protein-1), collagen I, and vascular smooth muscle cell proliferation (PDGF-B). Since nuclear factor kappaB (NF-kappaB) has been implicated in the control of chemokine transcription and cell proliferation, we also investigated its activation and localization in the lesion. Quinapril administration for 28 days caused a down-regulation in arterial expression of interleukin-8 and monocyte chemoattractant protein-1 (mRNA and protein). However, collagen I expression (mRNA and protein) was not modified. PDGF-B expression was reduced in both the intima and the media. Active NF-kappaB, found in both macrophages and vascular smooth muscle cells, was also reduced by quinapril. Nevertheless, no significant changes were noted in the mild neointima formation, although a certain trend toward normalization was found in the quinapril-treated group. In conclusion, our results show that quinapril treatment attenuates several parameters associated with inflammation within the atherosclerotic lesions that are controlled by NF-kappaB, although it has no effect on collagen I expression. Both effects could contribute to the stabilization of the atherosclerotic plaque.

Decline of shear stress-induced activation of extracellular signal-regulated kinases, but not stress-activated protein kinases, in in vitro propagated endothelial cells

We investigated the involvement of mitogen-activated protein kinase (MAPK) signal transduction pathways in human endothelial cells in response to shear stress and alterations of these kinases in in vitro-propagated endothelial cells (ECs). Potent activation (10-fold) of extracellular signal-regulated kinase (ERK2), a member of the MAPK family, occurred within 10 min of shear stress (5 dynes/cm2), whereupon rapid inactivation ensued. Shear stress also induced activation of stress-activated protein kinase (SAPK) or c-Jun NH2-terminal protein kinase (JNK) in ECs. Suramin pretreatment completely inhibited shear stress stimulation of ERK2, but not SAPK/JNK, highlighting a role for growth factor receptors in ERK activation. Translocation of ERK2 from the cytoplasm to the nucleus was observed in shear-stressed endothelial cells. In addition, we compared activities of MAPKs in shear-stressed cells derived from passages 4 and 10 (older). The magnitude of ERK2 activation was significantly lower in aged ECs compared to those of passage 4, while SAPK/JNK was not altered in the in vitro aged ECs. A similar level of ERK2 activation was found in both young and older cells stimulated with phorbol-12-myristate-13-acetate (PMA), indicating an age-related alteration of the plasma membrane. Taken together, these findings suggest that MAP kinase activation may be crucial for the expression of many genes in ECs stimulated by shear stress, and that an alteration in MAPK activities could contribute to the age-related decline in proliferative capacity.

Pressure mediates angiotensin II-induced arterial hypertrophy and PDGF-A expression

Angiotensin II (Ang II) may induce arterial hypertrophy either directly or through an increase in arterial pressure. To separate these 2 mechanisms, rats were implanted with osmopumps delivering either Ang II (100 ng x kg-1 x min-1) or saline. 5-Bromo-2'-deoxyuridine (BrdU) was delivered to both groups by osmopump (2.5 microg x kg-1 x min-1). Half of the rats in each group were given minoxidil (9 mg x kg-1 . d-1) in their drinking water. After 14 days, systolic blood pressure was 117+/-2, 124+/-3, and 115+/-2 mm Hg in the control, Ang II-minoxidil, and minoxidil groups, respectively, and 181+/-6 mm Hg in the Ang II group (P<0.05). After perfusion-fixation, the thoracic aorta, carotid artery, small mesenteric artery, external spermatic artery, and kidneys were harvested, paraffin-embedded, and used for morphological measurements, immunohistochemistry for BrdU, and in situ hybridization with a 35S-labeled riboprobe for platelet-derived growth factor-A chain (PDGF-A) mRNA. The walls of the aorta and carotid arteries hypertrophied in the Ang II group only. There were no significant morphological differences in the small arteries. BrdU was negative in all arteries but positive in the renal tubules. Expression of PDGF-A was elevated 8-fold in the thoracic aorta of the Ang II group (P<0.05). These results show that (1) arterial hypertrophy from Ang II infusion occurs in response to elevated arterial pressure, (2) hypertrophy was not associated with hyperplasia or polyploidy of vascular smooth muscle cells, and (3) PDGF-A expression correlated with elevated pressure and arterial wall hypertrophy.

Angiotensin II Participates in Mononuclear Cell Recruitment in Experimental Immune Complex Nephritis Through Nuclear Factor-κB Activation and Monocyte Chemoattractant Protein-1 Synthesis

Angiotensin-converting enzyme (ACE) inhibitors reduce macrophage infiltration in several models of renal injury. We approached the hypothesis that angiotensin II (AngII) could be involved in inflammatory cell recruitment during renal damage through the synthesis of monocyte chemoattractant protein-1 (MCP-1). In a model of immune complex nephritis, we observed an up-regulation of renal MCP-1 (mRNA and protein) coincidentally with mononuclear cell infiltration that were markedly reduced by treatment with the ACE inhibitor quinapril. Exposure of cultured rat mesangial cells to AngII increased MCP-1 mRNA expression (2.7-fold) and synthesis (3-fold), similar to that observed with TNF-α. Since NF-κB is involved in the regulation of MCP-1 gene, we explored whether the effects of AngII were mediated through NF-κB activation. Untreated nephritic rats showed increased renal NF-κB activity (3.5-fold) that decreased in response to ACE inhibition. In mesangial cells, AngII activated NF-κB (4.3-fold), and the NF-κB inhibitor pyrrolidine dithiocarbamate abolished the AngII-induced NF-κB activation and MCP-1 gene expression. Our results suggest that AngII could participate in the recruitment of mononuclear cells through NF-κB activation and MCP-1 expression by renal cells. This could be a novel mechanism that might further explain the beneficial effects of ACE inhibitors in progressive renal diseases.

Molecular mechanisms of the exaggerated growth of vascular smooth muscle cells in hypertension

The molecular mechanisms of the exaggerated growth of vascular smooth muscle cells (VSMC) in hypertension are reviewed based on our previous experimental data. Spontaneously hypertensive rats (SHR)-derived VSMC increasingly express angiotensinogen, cathepsin D and angiotensin-converting enzyme (ACE) mRNAs, compared to cells from normotensive Wistar-Kyoto (WKY) rats, indicating the presence of an Ang II generating system in a homogeneous culture of VSMC from SHR. The produced Ang II then induces TGF-beta. SHR-derived VSMC show the distinct expression and abnormal regulation by Ang II of TGF-beta receptors when compared with cells from WKY rats, which express TGF-beta type II receptor predominantly to induce PDGF A-chain stimulation of VSMC growth. These findings imply that the increased growth of VSMC in hypertension is a primary event independent of high blood pressure, and is associated with endogenous Ang II-related growth factors.

Strain-responsive regions in the platelet-derived growth factor-A gene promoter

Proliferation of cultured neonatal vascular smooth muscle (VSM) cells is enhanced by exposure to cyclic mechanical strain, in part through autocrine action of secreted platelet-derived growth factor (PDGF). We examined transcription factors and DNA response elements that may participate in the induction of PDGF-A gene transcription by mechanical strain. PDGF-A mRNA increased gradually over 4 to 24 hours exposure to cyclic (1 Hz) strain. This was due, at least in part, to increased transcription since a full length (890 bp) PDGF-A promoter reporter construct was induced 3.5-fold in transfected VSM cells exposed to strain for 24 hours. A series of PDGF-A promoter truncation reporter constructs was used to identify potential regions of the promoter involved in regulation by strain. Strain-responsive regions were found between -262 bp and -92 bp and between -92 bp and -41 bp of the promoter. Since these regions are GC-rich and contain response elements for Egr-1 and Sp-1, we examined expression of these transcription factors in response to strain. mRNA for both factors increased over 0.5 to 4 hours of strain, while protein expression for both increased gradually over a 24 hours period. Gel shift assays with a probe specific for Egr-1 demonstrated at least 1 prominent new shifted band after 4 to 12 hours exposure to strain. An Sp-1 probe demonstrated constitutive shifted bands that did not change in response to strain. Thus, GC-rich regions in the proximal 92 bp of the PDGF-A promoter contain mechanical strain-responsive elements that bind Egr-1 and possibly Sp-1.

Antisense oligodeoxynucleotide complementary to platelet-derived growth factor A-chain messenger RNA inhibits the arterial proliferation in spontaneously hypertensive rats without altering their blood pressures

OBJECTIVE

To evaluate the effects of the antisense oligodeoxynucleotide (ODN) to platelet-derived growth factor (PDGF) A-chain messenger RNA (mRNA) on the growth of cardiovascular organs in hypertension.

DESIGN

15-Mer antisense ODN complementary to the initiation codon region of rat PDGF-A chain mRNA and non-sense ODN of identical proportion but with a random order of bases relative to that of antisense ODN were synthesized with a DNA synthesizer.

METHODS

We examined the effects of the antisense ODN on the growth of vascular smooth muscle cells (VSMC) from spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats, and on the expression of PDGF A-chain mRNA by reverse transcription and polymerase chain reaction and PDGF A-chain protein by Western blot analysis in vitro. We evaluated the distribution of 32P-labeled antisense ODN and examined the effects of the antisense ODN on the growth of cardiovascular organs in vivo.

RESULTS

The antisense ODN reduced the basal DNA synthesis of VSMC from SHR significantly, but did not do so in cells from Wistar-Kyoto rats. Mutations in the antisense ODN sequence reduced the ODN-induced inhibition of DNA synthesis. Addition of serum or transforming growth factor-beta 1 increased the DNA synthesis in the SHR-derived VSMC that was inhibited by the antisense ODN. The antisense ODN inhibited the production of PDGF A-chain protein, but not of the PDGF A-chain mRNA. The injection of 32P-antisense ODN in vivo led to a greater accumulation of radioactivity in the aorta than in other organs. Infusion of antisense ODN for 28 days did not alter the systolic blood pressure appreciably in rats of either strain. However, in SHR, it reduced markedly the elevated DNA content, [3H]-thymidine uptake, and incorporation of [3H]-thymidine into aortic DNA, and suppressed the production of aortic PDGF A-chain protein. These results indicated that the PDGF A-chain is involved in the exaggerated growth of VSMC from SHR by which inhibition of the translation of PDGF A-chain mRNA to the protein with antisense ODN occurs in vitro, and that antisense ODN to PDGF A-chain suppresses the exaggerated arterial proliferation in SHR without altering the high blood pressure in vivo.

CONCLUSION

These results imply that inhibition of the final responsible growth factor PDGF A-chain by antisense ODN can suppress the arterial proliferation in hypertension without altering the blood pressure, suggesting that the arterial proliferation in hypertension is independent of the high blood pressure in part, and that antisense therapy could be feasible for treating hypertension.

Angiotensin-converting enzyme inhibition prevents arterial nuclear factor-kappa B activation, monocyte chemoattractant protein-1 expression, and macrophage infiltration in a rabbit model of early accelerated atherosclerosis

BACKGROUND

The migration of monocytes into the vessel wall is a critical event leading to the development of atherosclerosis. Monocyte chemoattractant protein-1 (MCP-1) is the main chemotactic factor involved in this phenomenon, and nuclear factor-kappa B (NF-kappa B) is one of the nuclear factors controlling its expression. ACE inhibitors have been useful in some experimental models of atherosclerosis. In this work, we addressed the hypothesis that angiotensin II (Ang II) may be implicated in the recruitment of monocytes into the vessel wall through the activation of NF-kappa B and the induction of MCP-1 expression.

METHODS AND RESULTS

Accelerated atherosclerosis was induced in the femoral arteries of rabbits by endothelial desiccation and atherogenic diet for 7 days. Atherosclerotic vessels exhibited an increase in NF-kappa B-like activity, and p50 and p65 NF-kappa B subunits were identified as components of this activity. MCP-1 (mRNA and protein) was also expressed in the injured vessels coincidently with the neointimal macrophage infiltration. ACE inhibition with quinapril reduced these three parameters. In cultured monocytic and vascular smooth muscle cells. Ang II elicited an increase in NF-kappa B activation and MCP-1 expression that was prevented by preincubation of cells with pyrrolidinedithiocarbamate, an inhibitor of NF-kappa B activation.

CONCLUSIONS

The present data support a role for Ang II in neointimal monocyte infiltration through NF-kappa B activation and MCP-1 expression in a model of accelerated atherosclerosis in rabbits. Our results suggest that ACE inhibitors may have a beneficial effect in early atherosclerosis.

Malignant vascular disease of the kidney: nature of the lesions, mediators of disease progression, and the case for bilateral nephrectomy

A case of thrombotic microangiopathy presenting as a hemolytic uremic syndrome complicated by untreatable hypertension and ultimately requiring bilateral nephrectomy is discussed. Severe hypertension and renal failure may complicate the course of vascular diseases of the kidney, including thrombotic microangiopathy, chronic hypertension, and scleroderma. Toxins, pressure stress, and immune material may trigger the initial injury to vascular endothelium. The malignant course of these renal vascular diseases seems linked to the severity of vascular injury. Endothelial injury manifests with swelling and detachment of endothelial cells from the basement membrane, expansion of the subendothelial space, and newly formed basement membrane-like material. In arterioles, endothelial injury precedes myointimal swelling and proliferation, leading to vascular lumina narrowing or obliteration and secondary glomerular ischemia, with glomerular tuft collapse and garland-like wrinkling and thickening of the capillary wall. Endothelial cell injury is very likely the common determinant of a cascade of events that lead to irreversible renal failure. When the initial insult (toxins, mechanical stress, antibodies) is promptly removed, lesions are self-limiting and the patient usually recovers. However, a severe insult persisting for some time can lead to chronic and irreversible vascular lesions that, through renal ischemia, trigger maximal activation of the renin angiotensin system with a brisk elevation in arterial blood pressure that may combine to further vascular injury and renal ischemia. Moreover, enhanced shear stress in the severely narrowed microcirculation, through abnormal von Willebrand factor processing, can also favor endothelial injury and platelet aggregation, which may further worsen the vascular lesions and sustain the microangiopathic process. Plasma manipulation, arteriolar vasodilators, and angiotensin-converting enzyme inhibitors normally control the vicious circle, but in few severe cases bilateral nephrectomy remains the last chance to save the patient's life.

Platelet-derived growth factor-A mRNA expression in fetal, normal adult, and atherosclerotic human aortas. Analysis by competitive polymerase chain reaction

BACKGROUND

To understand which growth factors are important for growth of atherosclerotic plaques, it is necessary to know the factor's relative abundance and how its gene is regulated in relation to cell proliferation. We tested whether platelet-derived growth factor-A (PDGF-A) mRNA levels correlated with cell proliferation in developing aorta, normal adult aorta, and atherosclerotic plaques.

METHODS AND RESULTS

We developed a competitive reverse transcription-polymerase chain reaction (RT-PCR) assay to measure human PDGF-A mRNA levels in small tissue samples. A mutated PDGF-A synthetic RNA was used as an internal standard to compete with endogenous PDGF-A mRNA for amplification. The assay is highly sensitive and much more precise than routine RT-PCR. Correction for heteroduplex pairing between the endogenous and mutant PCR products correlates precisely with synthetic RNA standards and quantitative Northern blotting. Immunostaining with the proliferation marker (proliferating cell nuclear antigen) showed the following rank order of proliferation: fetal aorta >> atherosclerotic plaque > normal aortic media. PDGF-A mRNA levels, however, did not correlate with proliferation. Normal adult aorta contained the most PDGF-A mRNa (34.0+/-7.6 amol/microgram total RNA). Fetal aortas were intermediate (10.2+/-1.6 amol/microgram total RNA); advanced atherosclerotic plaques contained the least PDGF-A mRNA (0.3+/-0.1 amol/microgram total RNA). PDGF-A protein was readily detectable in normal media by immunostaining. Advanced plaques generally had less cell-associated PDGF-A protein, although A-chain was also detected in plaque matrix.

CONCLUSIONS

PDGF-A mRNA and protein do not correlate with proliferation among these three groups. The significance of high levels of PDGF-A mRNA in the "quiescent" aortic media is unknown but it clearly does not promote cell replication.

Signals controlling the expression of PDGF

PDGF is an important polypeptide growth factor that plays an essential role during early vertebrate development and is associated with tissue repair and wound healing in the adult vertebrate. Moreover, PDGF is thought to play a role in a variety of pathological phenomena, such as cancer, fibrosis and atherosclerosis. PDGF is expressed as a dimer of A and/or B chains, the precursors of which are encoded by two single copy genes. Although the PDGF genes are expressed coordinately in a number of cell types, they are independently expressed in a majority of cell types. The expression of either PDGF gene can be affected by very diverse extracellular stimuli and the type of response is dependent on the cell type that is exposed to the stimulus. Expression of the PDGF chains can be modulated at every imaginable level: by regulating accessibility of the transcription start site, by varying the transcription initiation rate, by using alternative transcription start sites, by alternative splicing, by using alternative polyadenylation signals, by varying mRNA decay rates, by regulating efficiency of translation, by protein modification, and by regulating secretion. Even upon secretion, the activity of PDGF can be modulated by non-specific or specific PDGF-binding proteins. This review provides an overview of the cell types in which the PDGF genes are expressed, of the factors that are known to affect the expression of PDGF, and of the various levels at which the expression of PDGF genes can be regulated.