Enhanced expression of platelet-derived growth factor-beta receptor by high glucose. Involvement of platelet-derived growth factor in diabetic angiopathy

A Narrative Review of Diabetic Macroangiopathy: From Molecular Mechanism to Therapeutic Approaches

Diabetic macroangiopathy, a prevalent and severe complication of diabetes mellitus, significantly contributes to the increased morbidity and mortality rates among affected individuals. This complex disorder involves multifaceted molecular mechanisms that lead to the dysfunction and damage of large blood vessels, including atherosclerosis (AS) and peripheral arterial disease. Understanding the intricate pathways underlying the development and progression of diabetic macroangiopathy is crucial for the development of effective therapeutic interventions. This review aims to shed light on the molecular mechanism implicated in the pathogenesis of diabetic macroangiopathy. We delve into the intricate interplay of chronic inflammation, oxidative stress, endothelial dysfunction, and dysregulated angiogenesis, all of which contribute to the vascular complications observed in this disorder. By exploring the molecular mechanism involved in the disease we provide insight into potential therapeutic targets and strategies. Moreover, we discuss the current therapeutic approaches used for treating diabetic macroangiopathy, including glycemic control, lipid-lowering agents, and vascular interventions.

Research progress on the role of PDGF/PDGFR in type 2 diabetes

Platelet-derived growth factors (PDGFs) are basic proteins stored in the α granules of platelets. PDGFs and their receptors (PDGFRs) are widely expressed in platelets, fibroblasts, vascular endothelial cells, platelets, pericytes, smooth muscle cells and tumor cells. The activation of PDGFR plays a number of critical roles in physiological functions and diseases, including normal embryonic development, cellular differentiation, and responses to tissue damage. In recent years, emerging experimental evidence has shown that activation of the PDGF/PDGFR pathway is involved in the development of diabetes and its complications, such as atherosclerosis, diabetic foot ulcers, diabetic nephropathy, and retinopathy. Research on targeting PDGF/PDGFR as a treatment has also made great progress. In this mini-review, we summarized the role of PDGF in diabetes, as well as the research progress on targeted diabetes therapy, which provides a new strategy for the treatment of type 2 diabetes.

TRAIL and EGFR Pathways Targeting microRNAs are Predominantly Regulated in Human Diabetic Nephropathy

BACKGROUND

Unbiased microRNA profiling of renal tissue and urinary extracellular vesicles (uEVs) from diabetic nephropathy (DN) subjects may unravel novel targets with diagnostic and therapeutic potential. Here we used the miRNA profile of uEVs and renal biopsies from DN subjects available on the GEO database.

METHODS

The miR expression profiles of kidney tissue (GSE51674) and urinary exosomes (GSE48318) from DN and control subjects were obtained by GEO2R tools from Gene Expression Omnibus (GEO) databases. Differentially expressed miRNAs in DN samples, relative to controls, were identified using a bioinformatic pipeline. Targets of miRs commonly regulated in both sample types were predicted by miRWalk, followed by functional gene enrichment analysis. Gene targets were identified by MiRTarBase, TargetScan and MiRDB.

RESULTS

Eight miRs, including let-7c, miR-10a, miR-10b and miR-181c, were significantly regulated in kidney tissue and uEVs in DN subjects versus controls. The top 10 significant pathways targeted by these miRs included TRAIL, EGFR, Proteoglycan syndecan, VEGF and Integrin Pathway. Gene target analysis by miRwalk upon validation using ShinyGO 70 targets with significant miRNA-mRNA interaction.

CONCLUSION

In silico analysis showed that miRs targeting TRAIL and EGFR signaling are predominately regulated in uEVs and renal tissue of DN subjects. After wet-lab validation, the identified miRstarget pairs may be explored for their diagnostic and/or therapeutic potential in diabetic nephropathy.

SHP-2-Induced Activation of c-Myc Is Involved in PDGF-B-Regulated Cell Proliferation and Angiogenesis in RMECs

Background: Aberrant neovascularization resulting from inappropriate angiogenic signaling is closely related to many diseases, such as cancer, cardiovascular disease, and proliferative retinopathy. Although some factors involved in regulating pathogenic angiogenesis have been identified, the molecular mechanisms of proliferative retinopathy remain largely unknown. In the present study, we determined the role of platelet-derived growth factor-B (PDGF-B), one of the HIF-1-responsive gene products, in cell proliferation and angiogenesis in retinal microvascular endothelial cells (RMECs) and explored its regulatory mechanism.

Methods: Cell counting kit-8 (CCK-8), bromodeoxyuridine (BrdU) incorporation, tube formation, cell migration, and Western blot assays were used in our study.

Results: Our results showed that PDGF-B promoted cell proliferation and angiogenesis by increasing the activity of Src homology 2 domain-containing tyrosine phosphatase 2 (SHP-2) in RMECs, which was attenuated by the inhibition of PDGF receptor (PDGFR) or SHP-2 knockdown. Moreover, activation of c-Myc was involved in the processes of PDGF-B/SHP-2-driven cell proliferation in RMECs. The promoting effects of PDGF-B/SHP-2 on c-Myc expression were mediated by the Erk pathway.

Conclusion: These results indicate that PDGF-B facilitates cell proliferation and angiogenesis, at least in part, via the SHP-2/Erk/c-Myc pathway in RMECs, implying new potential treatment candidates for retinal microangiopathy.

Platelet derived growth factor inhibitors: A potential therapeutic approach for ocular neovascularization

Retinochoroidal vascular diseases are the leading causes of blindness in the developed world. They include diabetic retinopathy (DR), retinal vein occlusion, retinopathy of prematurity, age-related macular degeneration (AMD), and pathological myopia, among many others. Several different therapies are currently under consideration for the aforementioned disorders. In the following section, agents targeting platelet-derived growth factor (PDGF) are discussed as a potential therapeutic option for retinochoroidal vascular diseases. PDGF plays an important role in the angiogenesis cascade that is activated in retinochoroidal vascular diseases. The mechanism of action, side effects, efficacy, and the potential synergistic role of these agents in combination with other treatment options is discussed. The future of treatment of retinochoroidal vascular diseases, particularly AMD, has become more exciting due to agents such as PDGF antagonists.

Transcriptome analysis of human primary endothelial cells (HUVEC) from umbilical cords of gestational diabetic mothers reveals candidate sites for an epigenetic modulation of specific gene expression

Within the complex pathological picture associated to diabetes, high glucose (HG) has "per se" effects on cells and tissues that involve epigenetic reprogramming of gene expression. In fetal tissues, epigenetic changes occur genome-wide and are believed to induce specific long term effects. Human umbilical vein endothelial cells (HUVEC) obtained at delivery from gestational diabetic women were used to study the transcriptomic effects of chronic hyperglycemia in fetal vascular cells using Affymetrix microarrays. In spite of the small number of samples analyzed (n=6), genes related to insulin sensing and extracellular matrix reorganization were found significantly affected by HG. Quantitative PCR analysis of gene promoters identified a significant differential DNA methylation in TGFB2. Use of Ea.hy926 endothelial cells confirms data on HUVEC. Our study corroborates recent evidences suggesting that epigenetic reprogramming of gene expression occurs with persistent HG and provides a background for future investigations addressing genomic consequences of chronic HG.

Diffuse idiopathic skeletal hyperostosis: clinical features and pathogenic mechanisms

Diffuse idiopathic skeletal hyperostosis (DISH) is a systemic condition characterized by the ossification and calcification of ligaments and entheses. DISH is observed on all continents and in all races, but most commonly in men over 50 years of age. Although DISH is asymptomatic in most individuals, the condition is often an indicator of underlying metabolic disease, and the presence of spinal or extraspinal ossifications can sometimes lead to symptoms including pain, stiffness, a reduced range of articular motion, and dysphagia, as well as increasing the risk of unstable spinal fractures. The aetiology of DISH is poorly understood, and the roles of the many factors that might be involved in the development of excess bone are not well delineated. The study of pathophysiological aspects of DISH is made difficult by the formal diagnosis requiring the presence of multiple contiguous fully formed bridging ossifications, which probably represent advanced stages of DISH. In this Review, the reader is provided with an up-to-date discussion of the epidemiological, aetiological and clinical aspects of DISH. Existing classification criteria (which, in the absence of diagnostic criteria, are used to establish a diagnosis of DISH) are also considered, together with the need for modified criteria that enable timely identification of early phases in the development of DISH.

PDGF-β receptor and PKC have no effect on angiotensin II-induced JAK2 and STAT1 phosphorylation in vascular smooth muscle cells under high glucose condition

BACKGROUND

The mechanisms responsible for the accelerated cardiovascular disease in diabetes, as well as the increased hypertrophic effects of angiotensin II (Ang II) under hyperglycemic condition, are not very clear. Evidences show that platelet-derived growth factor (PDGF) and protein kinase C (PKC) play a critical role in this effect. In our study, we examined the role of PKC and PDGF receptor on JAK2 and STAT1 phosphorylation under high glucose (HG) condition (25 mmol/L) in response to Ang II in cultured vascular smooth muscle cells (VSMC).

METHODS

VSMCs were isolated from the thoracic aorta of male Wistar rats and were cultured. Growth-arrested VSMCs were placed in either normal glucose (NG) or HG condition for 48 h and then VSMCs were stimulated with agonists and antagonists. The tyrosine phosphorylation of JAK2 or STAT were determined by immunoblotting using specific antibodies.

RESULTS

High glucose markedly increased the phosphorylation of tyrosine residues of JAK2 and serine residues of STAT 1 compared with cells cultured in NG (5.5 mmol/L) with and without Ang II stimulation. Experiments made with specific PDGF-β receptor inhibitor AG1295 and PKC inhibitor GF109203X showed that there were no changes in Ang II-stimulated JAK2 and STAT1 phosphorylation under NG and HG conditions compared with experiments without inhibitors.

CONCLUSION

According to our findings, Ang II-stimulated JAK2 and STAT1 phosphorylation under either NG or HG condition do not proceed via a different pathway rather than PKC and PDGF-β receptor.

Protein tyrosine phosphatase PTPepsilonM negatively regulates PDGF beta-receptor signaling induced by high glucose and PDGF in vascular smooth muscle cells

Vascular smooth muscle cell (VSMC) proliferation and migration and vascular endothelial cell (VEC) dysfunction are closely associated with the development of atherosclerosis. We previously demonstrated that protein tyrosine phosphatase ε M (PTPεM) promotes VEC survival and migration. The present study investigates the biological functions of PTPεM in VSMCs and determines whether PTPεM is implicated in diabetes-accelerated atherosclerosis. We overexpressed wild-type and inactive PTPεM and an small interfering RNA (siRNA) of PTPεM by using an adenovirus vector to investigate the effects of PTPεM upon platelet-derived growth factor (PDGF)- and high glucose (HG)-induced responses of rat VSMCs in vitro. We found that PTPεM decreased PDGF-induced DNA synthesis and migration by reducing the phosphorylation level of the PDGF β-receptor (PDGFRβ) with subsequently suppressed H(2)O(2) generation. The HG content in the medium generated H(2)O(2), upregulated PDGFRβ expression and its tyrosine-phosphorylation, and elevated NADPH oxidase 1 (Nox1) expression even without exogenous PDGF, all of which were downregulated by PTPεM. The PDGFR inhibitor AG1296 also blocked HG-induced Nox1 expression and H(2)O(2) production. Moreover, HG suppressed PTPεM expression itself, which was blocked by the antioxidant N-acetyl-l-cysteine. The effects of PTPεM siRNA were the opposite of those of wild-type PTPεM. Therefore, PTPεM negatively regulates PDGFRβ-mediated signaling pathways that are crucial for the pathogenesis of atherosclerosis, and PTPεM may be involved in diabetes-accelerated atherosclerosis.

Role of growth factor receptor transactivation in high glucose-induced increased levels of Gq/11alpha and signaling in vascular smooth muscle cells

We have recently shown that high glucose increased the expression of Gq/11alpha, PLCbeta and mediated signaling in A10 vascular smooth muscle cells (VSMC). Since high glucose has been shown to increase growth factor receptor activation, we investigated the role of epidermal growth factor receptor (EGF-R) and platelet-derived growth factor receptor (PDGF-R) transactivation in high glucose-induced enhanced expression of Gq/11alpha and PLCbeta. Pre-treatment of A10 VSMC with high glucose (26 mM) for 3 days, increased the levels of Gqalpha, G11alpha, PLCbeta-1 and PLCbeta-2 proteins which were restored to control levels by AG1478, an inhibitor of EGF-R, AG1295, an inhibitor of PDGF-R and PP2, an inhibitor of c-Src but not by PP3. In addition, endothelin-1 (ET-1)-stimulated production of IP(3) that was enhanced by high glucose was also restored towards control levels by AG1478, AG1295 and PP2. High glucose also increased the phosphorylation of EGF-R and PDGF-R which was abolished by AG1478, AG1295 and PP2. Furthermore, high glucose-induced enhanced levels of Gqalpha, G11alpha and PLCbeta were also attenuated by PD98059, an inhibitor of mitogen-activated protein kinase (MAPK) and wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3-K). In addition, AG1478 and AG1295, also attenuated high glucose-induced enhanced phosphorylation of ERK1/2 and AKT. Furthermore, high glucose augmented the phosphorylation of c-Src which was attenuated by antioxidant, DPI. These results suggest that oxidative stress through the activation of c-Src and resultant transactivation of growth factor receptor contributes to the high glucose-induced enhanced expression of Gq/11alpha/PLC and -mediated cell signaling through MAPK/PI3K pathway.

High glucose promotes collagen synthesis by cultured cells from rat cervical posterior longitudinal ligament via transforming growth factor-beta1

Non-insulin-dependent diabetes is known as a risk factor of ossification of posterior longitudinal ligament, but the mechanism has not been well understood. We hypothesized that hyperglycemia, as a typical characteristic of diabetes, is closely associated with ligament hypertrophy in ossification of posterior longitudinal ligament. In this in vitro study, we investigated the effect of high glucose on collagen synthesis and transforming growth factor-beta1 (TGF-beta1) production using cells isolated from rat cervical posterior longitudinal ligament. The cells were subjected to high D-glucose concentration (25 mM) media for 4 days. Notable increases were observed in gene expression and protein synthesis of collagen types I, III in the cells. The increase was inhibited in the presence of anti-TGF-beta1 antibodies. Production of TGF-beta1 by the cells was also increased significantly by high glucose concentration. Exogenous application of TGF-beta1 was confirmed to increase collagen synthesis of the cells. These data suggested that high glucose could promote collagen synthesis in the posterior longitudinal ligament mainly via endogenous TGF-beta1, resulting in hypertrophy of the ligament.

Hormones and growth factors in the pathogenesis of spinal ligament ossification

Ossification of the spinal ligaments (OSL) is a pathologic condition that causes ectopic bone formation and subsequently results in various degrees of neurological deficit, but the etiology of OSL remains almost unknown. Some systemic hormones, such as 1,25-dihydroxyvitamin D, parathyroid hormone (PTH), insulin and leptin, and local growth factors, such as transforming growth factor-beta (TGF-beta), and bone morphogenetic protein (BMP), have been studied and are thought to be involved in the initiation and development of OSL. This review article summarizes these studies, delineates the possible mechanisms, and puts forward doubts and new questions. The related findings from studies of genes and target cells in the ligament of OSL are also discussed. Although these findings may be helpful in understanding the pathogenesis of OSL, much more research needs to be conducted in order to investigate the nature of OSL.

The Role of Platelet-Derived Growth Factor Receptor in Eotaxin Signaling of Eosinophils

BACKGROUND

Receptor tyrosine kinases (RTKs) such as epidermal growth factor receptor (EGFR) and platelet-derived growth factor receptor (PDGFR) are capable of eliciting kinase activity after ligand binding. In several cells, RTKs are activated via the G-protein-coupled receptor independent of the ligand-RTK interaction. We have previously found that EGFR is transactivated via CC chemokine receptor 3 in bronchial epithelial cells and that this pathway is important for mitogen-activated protein (MAP) kinase activation and cytokine production. It has recently been suggested that hypereosinophilic syndrome results from the fusion tyrosine kinase FIP1L1-PDGFRA. Although it is possible that the PDGFR signal is involved in eosinophil function, the details are still unclear.

METHODS

Blood eosinophils were purified using Percoll and anti-CD16 antibody-coated magnetic beads. Expression of PDGFR mRNA was examined by RT-PCR. After stimulating eosinophils with eotaxin, the phosphorylation of MAP kinases was examined by Western blotting with the antiphosphospecific MAP kinase antibody. The eotaxin-induced eosinophil chemotaxis was studied using Boyden chambers.

RESULTS

Eosinophils expressed PDGFRbeta mRNA in 4 out of 8 donors, while PDGFRalpha mRNA was expressed in only 1 donor. Protein expression of PDGFR was also detectable in eosinophils from some donors. AG1295, a specific inhibitor of PDGFR, showed dose-dependent inhibition of eotaxin-induced MAP kinase phosphorylation in the eosinophils expressing PDGFRbeta mRNA. The chemotaxis of these eosinophils was significantly inhibited by AG1295 (n = 3).

CONCLUSIONS

Our results suggest that PDGFR modifies the CCR3-MAP kinase signaling pathway and chemotactic response in some donors. The pharmacological targeting of PDGFR may be a new strategy to treat eosinophilic disorders.

Modulation of Smooth Muscle Cell Migration by Members of the Low-Density Lipoprotein Receptor Family

Low-density lipoprotein receptor family members (LRs) play a key role in the catabolism of many membrane-associated proteins, such as complexes between proteinases and their receptors, in addition to being involved in lipoprotein metabolism as suspected by the hitherto well-established functions of low-density lipoprotein receptor, in a variety of tissues. Recent studies using receptor-deficient or -overexpressing animals and cells have suggested that certain LRs are important regulators of the migration (and proliferation) of vascular smooth muscle cells (SMCs). LR expression is markedly induced in intimal or medial SMCs during the formation of atherosclerotic lesions. Because LRs can modulate the activity of the urokinase-type plasminogen activator (uPA) receptor and possibly of the platelet-derived growth factor (PDGF) receptor, LRs may influence the migration of SMCs through functional modulation of these membrane receptors. Therefore, SMC migration may be regulated by time-restricted expression of LRs. In agreement with the concept of functional interaction between LRs and membrane signaling receptors, a negative regulator of uPA receptor protein catabolism, LR11, has been identified. Statins modulate the PDGF-induced migration of intimal SMCs via the LR11/uPA receptor cascade. Selective modification of the LRs/uPA receptor/PDGF receptor systems in SMCs may be important for suppression of atherosclerotic plaque formation as well as for preventing intimal thickening after angioplasty.

In high glucose protein kinase C-zeta activation is required for mesangial cell generation of reactive oxygen species

BACKGROUND

We postulated that in mesangial cells exposed to high glucose, protein kinase C-zeta (PKC-zeta) is necessary for the generation of reactive oxygen species (ROS) by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and that the requirement of PKC-zeta for filamentous (F)-actin disassembly may involve ROS. To identify signaling mechanisms relevant to PKC-zeta activation and ROS generation, including phosphoinositide 3 kinase (PI3 kinase), we examined mesangial cell stimulation with platelet-derived growth factor (PDGF).

METHODS

In primary rat mesangial cells cultured in 5.6 mmol/L or 30 mmol/L d-glucose, PKC-zeta expression was identified with immunoblotting and activity was analyzed in cell membrane immunoprecipitates and by confocal immunofluorescence imaging. ROS generation was measured by dichlorofluorescein fluorescence using confocal microscopy and was inhibited by transfection of antisense against NADPH subunits p22(phox) or p47(phox) or with Tempol. F-actin disassembly was observed by dual-channel confocal fluorescence imaging. PI3 kinase activity was detected by immunoblotting of phosphorylated Akt.

RESULTS

In high glucose, generation of NADPH oxidase-dependent ROS was dependent on PKC-zeta. Conversely, sustained PKC-zeta activity was dependent on ROS generation, suggesting a positive feedback. PKC-zeta-dependent F-actin disassembly in high glucose required ROS generation. PDGF stimulated NADPH oxidase generation of ROS through a PKC-zeta mechanism that was independent of Akt phosphorylation and remained unchanged in high glucose.

CONCLUSION

In high glucose, mesangial cell PKC-zeta is required for ROS generation from NADPH oxidase similar to PDGF stimulation of PKC-zeta-dependent ROS generation through a pathway independent of PI3 kinase. F-actin disassembly in high glucose also requires ROS. A positive feedback loop occurs between ROS and the activation of PKC-zeta in high glucose.

Effects of Blocking the Renin-Angiotensin System on Expression and Translocation of Protein Kinase C Isoforms in the Kidney of Diabetic Rats

BACKGROUND

High glucose and angiotensin II (Ang II) can activate protein kinase C (PKC) in diabetes mellitus. However, it is not clear which isoform of PKC is activated by glucose or Ang II. Our study focused on the effects of angiotensin blockade, using the angiotensin-converting enzyme inhibitor fosinopril, the Ang II receptor blocker irbesartan and their combination, on the expression and translocation of PKC isoforms alpha and betaII in the renal cortex and medulla in diabetes.

METHODS

Hyperglycemia was induced with streptozotocin and diabetic rats were randomized to 4 groups: diabetic control, irbesartan group (40 mg/kg daily), fosinopril group (40 mg/kg daily) and combination group (irbesartan plus fosinopril, 20 mg/kg daily, respectively); age-matched normal rats served as normal control. After 4 weeks, expression and translocation of PKC-alpha and -betaII in the renal cortex and medulla were assessed by immunohistochemistry and Western immunoblotting.

RESULTS

The expression of PKC-alpha in the membrane and cytosol fractions from the renal cortex was significantly higher in diabetic rats (276.83 +/- 32.44% in membrane, 149.04 +/- 23.42% in cytosol) than that in normal ones. The expression of PKC-betaII in the renal cortex of diabetic rats decreased significantly in the membrane (50.00 +/- 11.68%, p < 0.05) and remained unchanged in the cytosol (94.51 +/- 11.69%, p > 0.05) compared with normal controls. Treatment with irbesartan, fosinopril and their combination partially corrected the abnormalities mentioned above. For the expression of PKC-alpha and -betaII in the medulla, no difference was detected among the 5 groups.

CONCLUSION

The renin-angiotensin system was implicated in the pathogenesis of diabetic nephropathy by regulating the activation of PKC isoforms.

Growth factor antagonists for the treatment of diabetic vascular complications

Diabetic vascular disease is characterised by altered vascular reactivity and blood flow, hyperpermeability, hyperproliferative responses, and increased extracellular matrix deposition in tissues that are sites of complications. These vascular functional and structural changes have been linked to excessive glucose metabolism in target organs via at least three pathophysiological mechanisms, including increased sorbitol (polyol) pathway activity, increased nonenzymatic glycation of vascular wall proteins, and increased protein kinase C (PKC) activity. These potential mechanisms of glucose toxicity remain the subject of intense scientific investigation, and therapies targeting each of them are being evaluated in clinical trials. It is becoming increasingly clear that excessive production of growth factors provides a common denominator linking these diverse mechanisms of glucose toxicity to the functional and structural vascular alterations associated with diabetes. Increased expression of vascular endothelial growth factor (VEGF) has been linked to increased metabolism of glucose via the sorbitol pathway, to nonenzymatic glycation, and to increased PKC activity, and appears to modulate the hyperpermeability and hyperproliferative responses of diabetes. Consequently, because of the unmet medical need and market size, numerous pharmaceutical and biotechnology companies have initiated research programmes evaluating growth factor antagonists as a potential therapeutic approach for treating complications associated with diabetic vascular disease. However, before growth factor antagonists can enter clinical testing, a number of important issues must be clarified, including the physiological effect of chronic growth factor inhibition, which appears to be necessary for ameliorating chronic vascular deterioration of diabetes, and administration routes, especially for protein-based therapies.

LRP1B is a negative modulator of increased migration activity of intimal smooth muscle cells from rabbit aortic plaques

The migration of cultured cultured smooth muscle cells (SMCs) is regulated by the time-specific expression of members of the LDL receptor family (LRs). LRP1B, a member of LRs, modulates the catabolism of PDGF beta-receptor, affecting the migration of SMCs. An involvement of PDGF beta-receptor in atherosclerosis is focused because of its abundant expression in intimal SMCs. Here, in order to know a functional significance of LRP1B in the increased migration of intimal SMCs, the functions of three groups of cultured SMCs with different origins in atherosclerotic arteries were studied. Each group of SMCs (central, marginal or medial SMCs) was isolated from explanted pieces of central or marginal area of thickened intima, or media prepared from rabbit aortic plaques. The LRP1B expression levels were significantly decreased in intimal SMCs, particularly in marginal SMCs, compared to medial SMCs. The expression levels of LRP1B in SMCs were negatively correlated with those of PDGF beta-receptor. The level of PDGF beta-receptor-mediated phosphorylation of ERK 1/2 in central SMCs was increased to 5.2-fold with the functional inhibition of LRP1B using anti-LRP1B IgY. The antibody increased the PDGF-BB-stimulated migration and invasion activities in SMCs. The increase in the PDGF beta-receptor-mediated outgrowth activity of SMCs from the explants was also inhibited by the functional inhibition of LRP1B. These results indicate that LRP1B regulated the migration activity of SMCs through the modulation of PDGF beta-receptor-mediated pathway. The regulation of LRP1B expression is possibly involved in the activated migration of intimal SMCs in the course of atherosclerosis.

From hyperglycemia to diabetic kidney disease: the role of metabolic, hemodynamic, intracellular factors and growth factors/cytokines

At present, diabetic kidney disease affects about 15-25% of type 1 and 30-40% of type 2 diabetic patients. Several decades of extensive research has elucidated various pathways to be implicated in the development of diabetic kidney disease. This review focuses on the metabolic factors beyond blood glucose that are involved in the pathogenesis of diabetic kidney disease, i.e., advanced glycation end-products and the aldose reductase system. Furthermore, the contribution of hemodynamic factors, the renin-angiotensin system, the endothelin system, and the nitric oxide system, as well as the prominent role of the intracellular signaling molecule protein kinase C are discussed. Finally, the respective roles of TGF-beta, GH and IGFs, vascular endothelial growth factor, and platelet-derived growth factor are covered. The complex interplay between these different pathways will be highlighted. A brief introduction to each system and description of its expression in the normal kidney is followed by in vitro, experimental, and clinical evidence addressing the role of the system in diabetic kidney disease. Finally, well-known and potential therapeutic strategies targeting each system are discussed, ending with an overall conclusion.

Polymorphisms in the 5'-upstream region of the PKCbeta gene in Japanese patients with Type 2 diabetes

AIMS

Protein kinase C (PKC), a serine/threonine kinase, is known to be activated in various tissues under hyperglycaemic conditions. Notably, PKCbeta, a member of the conventional PKC group, is the predominant isoform detected in vascular tissues and could be involved in the development of diabetic vascular complications. In the present study, we investigated genetic variations in the 5'-upstream region of the PKCbeta gene to assess their possible relation to vascular complications in diabetic patients.

METHODS

Variations upstream from the PKCbeta gene (-1066/+256) were examined in 60 Type 2 diabetic patients using a cycle sequencing method. Screening of detected variations was performed in 204 Type 2 diabetic patients and 160 healthy controls.

RESULTS

Five single nucleotide polymorphisms; C(-238)G, C(-287)T, A(-348)G, C(-546)G, and C(-853)T, were identified in the upstream region. The C(-287)T and A(-348)G polymorphisms were in perfect linkage disequilibrium. There were no significant differences in genotype or allele frequencies of the five polymorphisms among the diabetic patients and healthy subjects. However, both -238GG and -287CC (-348GG) homozygotes showed significantly higher frequencies of macrovascular disease compared with patients with other genotypes. Further, an electrophoretic mobility shift assay revealed that the -238G fragment had a five-fold higher affinity for transcription factor Sp1 when compared with -238C.

CONCLUSIONS

The C(-238)G and C(-287)T-A(-348)G polymorphisms in the 5'-upstream region of the PKCbeta gene may have an effect on the susceptibility of diabetic vascular complications through an alteration of tissue PKCbeta density or function.

Imatinib Attenuates Diabetes-Associated Atherosclerosis

OBJECTIVE

Diabetes is associated with accelerated atherosclerosis, the major factor contributing to increased mortality and morbidity in the diabetic population. The molecular mechanisms by which diabetes promotes atherosclerosis are not fully understood. Platelet-derived growth factor has been shown to play a major role in the pathology of vascular diseases, but whether it plays a role in atherosclerosis associated with diabetes remains unknown. The aims of this study were to assess whether platelet-derived growth factor-dependent pathways are involved in the development of diabetes-induced atherosclerosis and to determine the effects of platelet-derived growth factor receptor antagonism on this disorder.

METHODS AND RESULTS

Diabetes was induced by injection of streptozotocin in 6-week-old apolipoprotein E knockout mice. Diabetic animals received treatment with a tyrosine kinase inhibitor that inhibits platelet-derived growth factor action, imatinib (STI-571, 10 mg/kg per day), or no treatment for 20 weeks. Nondiabetic apolipoprotein E knockout mice served as controls. Induction of diabetes was associated with a 5-fold increase in plaque area in association with an increase in aortic platelet-derived growth factor-B expression and platelet-derived growth factor-beta receptor phosphorylation as well as other prosclerotic and proinflammatory cytokines. Imatinib treatment prevented the development of atherosclerotic lesions and diabetes-induced inflammatory cytokine overexpression in the aorta.

CONCLUSIONS

Tyrosine kinase inhibition with imatinib appears to be a novel therapeutic option to retard the development of atherosclerosis, specifically in the context of diabetes.

Inhibition of platelet-derived growth factor promotes pericyte loss and angiogenesis in ischemic retinopathy

We investigated whether inhibition of platelet-derived growth factor (PDGF) receptor tyrosine kinase activity would affect pericyte viability, vascular endothelial growth factor (VEGF)/vascular endothelial growth factor receptor-2 (VEGFR-2) expression and angiogenesis in a model of retinopathy of prematurity (ROP). ROP was induced in Sprague Dawley rats by exposure to 80% oxygen from postnatal (P) days 0 to 11 (with 3 hours/day in room air), and then room air from P12-18 (angiogenesis period). Shams were neonatal rats in room air from P0-18. STI571, a potent inhibitor of PDGF receptor tyrosine kinase, was administered from P12-18 at 50 or 100 mg/kg/day intraperitoneal (i.p.). Electron microscopy revealed that pericytes in the inner retina of both sham and ROP rats appeared normal; however STI571 induced a selective pericyte and vascular smooth muscle degeneration. Immunolabeling for caspase-3 and alpha-smooth muscle cell actin in consecutive paraffin sections of retinas confirmed that these degenerating cells were apoptotic pericytes. In all groups, VEGF and VEGFR-2 gene expression was located in ganglion cells, the inner nuclear layer, and retinal pigment epithelium. ROP was associated with an increase in both VEGF and VEGFR-2 gene expression and blood vessel profiles in the inner retina compared to sham rats. STI571 at both doses increased VEGF and VEGFR-2 mRNA and exacerbated angiogenesis in ROP rats, and in sham rats at 100 mg/kg/day. In conclusion, PDGF is required for pericyte viability and the subsequent prevention of VEGF/VEGFR-2 overexpression and angiogenesis in ROP.

Genes for systemic vascular complications are differentially expressed in the livers of type 2 diabetic patients

AIMS/HYPOTHESIS

Type 2 diabetes is characterised by excessive hepatic glucose production and frequently leads to systemic vascular complications. We therefore analysed the relationship between the gene expression profile in the liver and the pathophysiology of Type 2 diabetes.

METHODS

Liver biopsy samples were obtained from twelve patients with Type 2 diabetes and from nine non-diabetic patients. To assay gene expression globally in the livers of both groups, we made complementary DNA (cDNA) microarrays consisting of 1080 human cDNAs. Relative expression ratios of individual genes were obtained by comparing cyanine 5-labelled cDNA from the patients with cyanine 3-labelled cDNA from reference RNA from the liver of a non-diabetic patient.

RESULTS

On assessing the similarities of differentially expressed genes, the gene expression profiles of the twelve diabetic patients formed a separate cluster from those of the non-diabetic patients. Of the 1080 genes assayed, 105 (9.7%) were up-regulated and 134 (12%) were down-regulated in the diabetic livers (p<0.005). The genes up-regulated in the diabetic patients included those encoding angiogenic factors such as vascular endothelial growth factor, endothelin and platelet-derived growth factor. They also included TGF superfamily genes such as TGFA and TGFB1 as well as bone morphogenetic proteins. Among the down-regulated genes in the diabetic patients were molecules defending against stress, e.g. flavin-containing monooxygenase and superoxide dismutase.

CONCLUSIONS/INTERPRETATION

These findings suggest that livers of patients with Type 2 diabetes have gene expression profiles indicative of an increased risk of systemic vascular complications.

Inhibitory effects of novel AP-1 decoy oligodeoxynucleotides on vascular smooth muscle cell proliferation in vitro and neointimal formation in vivo

Excessive proliferation of vascular smooth muscle cells (VSMCs) and neointimal formation are critical steps in the pathogenesis of atherosclerosis and restenosis after percutaneous transluminal angioplasty. In this study, we investigated the hypothesis that the activator protein-1 (AP-1) plays an important role in neointimal formation after vascular injury. A circular dumbbell AP-1 decoy oligodeoxynucleotide (CDODN) was developed as a novel therapeutic strategy for restenosis after angioplasty. This CDODN was more stable than the conventional phosphorothioate linear decoy ODN (PSODN) and maintained structural integrity on exposure to exonuclease III or serum. Transfection with AP-1 decoy ODNs strongly inhibited VSMC proliferation and migration, as well as glucose- and serum-induced expression of PCNA and cyclin A genes. Administration of AP-1 decoy ODNs in vivo using the hemagglutinating virus of Japan (HVJ)-liposome method virtually abolished neointimal formation after balloon injury to the rat carotid artery. Compared with PSODN, CDODN was more effective in inhibiting the proliferation of VSMCs in vitro and neointimal formation in vivo. Our results collectively indicate that AP-1 activation is crucial for the mediation of VSMC proliferation in response to vascular injury. Moreover, the use of stable CDODN specific for AP-1 activity in combination with the highly effective HVJ-liposome method provides a novel potential therapeutic strategy for the prevention of restenosis after angioplasty in humans.

How hyperglycemia promotes atherosclerosis: molecular mechanisms

Both type I and type II diabetes are powerful and independent risk factors for coronary artery disease (CAD), stroke, and peripheral arterial disease. Atherosclerosis accounts for virtually 80% of all deaths among diabetic patients. Prolonged exposure to hyperglycemia is now recognized a major factor in the pathogenesis of atherosclerosis in diabetes. Hyperglycemia induces a large number of alterations at the cellular level of vascular tissue that potentially accelerate the atherosclerotic process. Animal and human studies have elucidated three major mechanisms that encompass most of the pathological alterations observed in the diabetic vasculature: 1) Nonenzymatic glycosylation of proteins and lipids which can interfere with their normal function by disrupting molecular conformation, alter enzymatic activity, reduce degradative capacity, and interfere with receptor recognition. In addition, glycosylated proteins interact with a specific receptor present on all cells relevant to the atherosclerotic process, including monocyte-derived macrophages, endothelial cells, and smooth muscle cells. The interaction of glycosylated proteins with their receptor results in the induction of oxidative stress and proinflammatory responses 2) oxidative stress 3) protein kinase C (PKC) activation with subsequent alteration in growth factor expression. Importantly, these mechanisms may be interrelated. For example, hyperglycemia-induced oxidative stress promotes both the formation of advanced glycosylation end products and PKC activation.

Activation of nuclear factor kappaB at the onset of ossification of the spinal ligaments

We examined the correlation between the activation of nuclear factor kappaB (NFkappaB), stimulated by environmental factors involving cytokines and growth factors in ligament cells, and the onset of ossification of the spinal ligaments (OSL) or diffuse idiopathic skeletal hyperostosis (DISH). Aseptic samples were taken carefully from non-ossified sites during surgery (75 patients). We carried out preliminary hematoxylin and eosin and toluidine blue staining, using five portions of each specimen, and excluded samples containing chondrocytic, osteoblastic, or inflammatory cells (n = 25). We used specimens from the remaining 50 patients (35 men and 15 women, ranging in age from 45-81 years); average age, 59.5 years (18 nuchal ligament specimens, and 32 yellow ligament specimens). OSL or DISH had occurred in 25 patients, 20 patients were in the non-OSL group (8 with cervical spondylotic myelopathy, and 12 with lumbar canal stenosis), and the remaining 5 samples were collected from patients with injury. For culture study, we used portions of the 14 largest samples from the above 50 patients. We extracted nuclear proteins and cytoplasmic proteins from non-ossified spinal ligaments in 50 patients and detected p65RelA/NFkappaB by Western blotting. Tumor necrosis factor-alpha (TNF alpha), interleukin 1beta (IL-1beta), platelet-derived growth factor BB (PDGF-BB) and transforming growth factor-beta1 (TGF-beta1) in cytoplasm were quantified by enzyme-linked immunosorbent assays (ELISA). Cultured cells from the 14 samples were then stimulated with 10, 100, 250, or 500 ng/ml of recombinant human (rh)PDGF-B or TGFbeta1. A control experiment was performed without rhPDGF-BB or TGFbeta1 stimulation. Alkaline phosphatase (ALP) activity was standardized by the DNA content of the cells. The number of NFkappaB-positive samples was significantly higher in patients with OSL or DISH than in non-OSL patients. This tendency was obvious in the case of OSL or DISH with non-insulin-dependent diabetes mellitus (NIDDM). In OSL and in DISH patients, significantly greater amounts of PDGF-BB and TGFbeta1 were seen in ligament cells than in non-OSL patients (P < 0.05). There was a positive correlation between the detection of p65RelA/NFkappaB band and the content of PDGF-BB and TGFbeta1 in ligament cells (P < 0.05). ALP activity tended to be higher in cells in the OSL group not receiving any other treatment. Our results indicate the possibility that NFkappaB, stimulated by environmental factors involving PDGF-BB and TGFbeta1 in ligament cells, influences the osteoblastic differentiation of undifferentiated mesenchymal cells.

Regulation of B(2)-kinin receptors by glucose in vascular smooth muscle cells

The development of vascular disease is accelerated in hyperglycemic states. Vascular injury plays a pivotal role in the progression of atherosclerotic vascular disease in diabetes, which is characterized by increased vascular smooth muscle cell (VSMC) proliferation and extracellular matrix accumulation. We previously reported that diabetes alters the activity of the kallikrein-kinin system and results in the upregulation of kinin receptors in the vessel wall. To determine whether glucose can directly influence the regulation of kinin receptors, the independent effect of high glucose (25 mM) on B(2)-kinin receptors (B2KR) in VSMC was examined. A threefold increase in B2KR protein levels and a 40% increase in B2KR surface receptors were observed after treatment with high glucose after 24 h. The mRNA levels of B2KR were also significantly increased by high glucose as early as 4 h later. To elucidate the cellular mechanisms by which glucose regulates B2KR, we examined the role of protein kinase C (PKC). High glucose increased total PKC activity and resulted in the translocation of conventional PKC isoforms (beta(1) and beta(2)), novel (epsilon), and atypical (zeta) PKC isoforms into the membrane. Inhibition of PKC activity prevented the increase in B2KR levels induced by ambient high glucose. These findings provide the first evidence that glucose regulates the expression of B(2) receptors in VSMC and provide a rationale to further study the interaction between glucose and kinins on the pathogenesis of atherosclerotic vascular disease in diabetes.

Influence of treatment modality on angiographic outcome after coronary stenting in diabetic patients: a controlled study

OBJECTIVES

This retrospective study was designed to determine the six-month angiographic outcome after stenting of native coronary arteries in insulin-treated (ITDM) and non-ITDM patients with diabetes mellitus (DM) and compare the results with those in non-DM patients.

BACKGROUND

The influence of the treatment modality for DM on restenosis in patients undergoing coronary artery stenting has not been elucidated sufficiently.

METHODS

A total of 1,439 (70%) of 2,061 patients underwent repeated angiography within six months of coronary stenting. The ITDM and non-ITDM (oral hypoglycemic drugs or diet) were documented in 48 (3.3%) and 177 patients (12.3%), respectively, leaving 1,214 non-DM patients.

RESULTS

Baseline reference vessel diameter tended to be smaller in ITDM patients (mean, 2.73 mm) than in non-DM and non-ITDM patients (2.88 mm and 2.85 mm, respectively). However, percent diameter stenosis was not different. The median number of stents deployed was 1; median stent length was 15 mm. Statistically significant differences were present after stenting for the means of minimal lumen diameter (MLD) and acute gain between ITDM patients (MLD: 2.67 mm, acute gain: 1.98 mm) and non-DM patients (MLD: 2.81 mm, acute gain: 2.16 mm). At follow-up, percent diameter stenosis, late lumen loss and loss index were significantly higher in both non-ITDM lesions (42%, 1.14 mm and 0.56, respectively) and ITDM lesions (48%, 1.26 mm and 0.65, respectively) than in non-DM lesions (35%, 0.96 mm and 0.45, respectively). The corresponding differences between non-ITDM and ITDM lesions did not reach statistical significance. Restenosis rates in non-DM, non-ITDM and ITDM lesions were 23.8%, 32.8% (p = 0.013 vs. non-DM) and 39.6% (p = 0.02 vs. non-DM, p = 0.477 vs. non-ITDM), respectively.

CONCLUSIONS

This study showed that compared with stenting in non-DM patients, stenting of native coronary arteries in DM patients is associated with significantly increased lumen renarrowing, regardless of the treatment modality for DM.

Aldose reductase inhibitor improves insulin-mediated glucose uptake and prevents migration of human coronary artery smooth muscle cells induced by high glucose

We examined involvement of the polyol pathway in high glucose-induced human coronary artery smooth muscle cell (SMC) migration using Boyden's chamber method. Chronic glucose treatment for 72 hours potentiated, in a concentration-dependent manner (5.6 to 22.2 mol/L), platelet-derived growth factor (PDGF) BB-mediated SMC migration. This potentiation was accompanied by an increase in PDGF BB binding, because of an increased number of PDGF-beta receptors, and this potentiation was blocked by the aldose reductase inhibitor epalrestat. Epalrestat at concentrations of 10 and 100 nmol/L inhibited high glucose-potentiated (22.2 mmol/L), PDGF BB-mediated migration. Epalrestat at 100 nmol/L inhibited a high glucose-induced increase in the reduced/oxidized nicotinamide adenine dinucleotide ratio and membrane-bound protein kinase C (PKC) activity in SMCs. PKC inhibitors calphostin C (100 nmol/L) and chelerythrine (1 micromol/L) each inhibited high glucose-induced, PDGF BB-mediated SMC migration. High glucose-induced suppression of insulin-mediated [(3)H]-deoxyglucose uptake, which was blocked by both calphostin C (100 nmol/L) and chelerythrine (1 micromol/L), was decreased by epalrestat (100 nmol/L). Chronic high glucose treatment for 72 hours increased intracellular oxidative stress, which was directly measured by flow cytometry using carboxydichlorofluorescein diacetate bis-acetoxymethyl ester, and this increase was significantly suppressed by epalrestat (100 nmol/L). Antisense oligonucleotide to PKC-beta isoform inhibited high glucose-mediated changes in SMC migration, insulin-mediated [(3)H]-deoxyglucose uptake, and oxidative stress. These findings suggest that high glucose concentrations potentiate SMC migration in coronary artery and that the aldose reductase inhibitor epalrestat inhibits high glucose-potentiated, PDGF BB-induced SMC migration, possibly through suppression of PKC (PKC-beta), impaired insulin-mediated glucose uptake, and oxidative stress.

An aldose reductase inhibitor prevents the glucose-induced increase in PDGF-beta receptor in cultured rat aortic smooth muscle cells

To examine the role of platelet-derived growth factor (PDGF) and the polyol pathway in the growth activity of smooth muscle cells (SMCs), [(3)H]-thymidine incorporation, [(125)I]-PDGF-BB binding and expression of PDGF-beta receptor protein were measured in rat aortic SMCs cultured with 5.5 or 20 mM glucose with or without anti-PDGF antibody or an aldose reductase inhibitor, epalrestat. SMCs cultured with 20 mM glucose demonstrated an accelerated thymidine incorporation compared with SMCs cultured with 5.5 mM glucose, which was prevented by anti-PDGF antibody. This acceleration of growth activity by 20 mM glucose was accompanied by an increase in PDGF-BB binding, which was due to the increased number of PDGF-beta receptors and the overexpression of PDGF-beta receptor protein. Epalrestat prevented all these abnormalities. These observations suggest that polyol pathway hyperactivity plays an important role in the proliferation of SMCs which may be mediated through the accelerated expression of PDGF-beta receptor protein.

Molecular mechanisms of diabetic renal hypertrophy

Altered growth of renal cells is one of the early abnormalities detected after the onset of diabetes. Cell culture studies whereby renal cells are exposed to high glucose concentrations have provided a considerable amount of insight into mechanisms of growth. In the glomerular compartment, there is a very early and self-limited proliferation of mesangial cells with subsequent hypertrophy, whereas proximal tubular cells primarily undergo hypertrophy. There is overwhelming evidence from in vivo and cell culture studies that induction of the transforming growth factor-beta (TGF-beta) system mediates the actions of high ambient glucose and that this system is pivotal for the hypertrophy of mesangial and tubular cells. Other factors such as hemodynamic forces, protein glycation products, and several mediators (for example, angiotensin II, endothelin-1, thromboxane, and platelet-derived growth factor) may further amplify the synthesis of TGF-beta and/or the expression of its receptors in the diabetic state. Cellular hypertrophy can be characterized by cell cycle arrest in the G1 phase. The molecular mechanism arresting mesangial cells in the G1 phase of the cell cycle is the induction of cyclin-dependent kinase (CdK) inhibitors such as p27Kip1 and p21, which bind to and inactivate cyclin-CdK complexes responsible for G1-phase exit. High-glucose-induced activation of protein kinase C and stimulated TGF-beta expression appear to be essential for stimulated expression of p27Kip1. In addition, a decreased turnover of protein caused by the inhibition of proteases contributes to hypertrophy. The development of irreversible renal changes in diabetes mellitus such as glomerulosclerosis and tubulointerstitial fibrosis is always preceded by the early hypertrophic processes in the glomerular and the tubular compartments. It may still be debated whether diabetic renal hypertrophy will inevitably lead to irreversible fibrotic changes in the absence of other factors such as altered intraglomerular hemodynamics and genetic predisposition. Nevertheless, understanding cellular growth on a molecular level may help design a novel therapeutic approach to prevent or treat diabetic nephropathy effectively.

Interleukin 1beta mediates the effect of high D-glucose on the secretion of TNF-alpha by mouse uterine epithelial cells

Previous observations have shown that tumour necrosis factor alpha (TNF-alpha) synthesis is increased in the uterus of diabetic rats and that the epithelial layer lining the uterine lumen is the major site of TNF-alpha over-production. In the present study, TNF-alpha secretion was found to be stimulated by high D-glucose levels in primary cultures of mouse uterine luminal cells but not in cultures of the mouse uterine epithelial WEG-1 cell line. Experiments were performed to investigate the possibility that non-epithelial cells may mediate the influence of high D-glucose on TNF-alpha production by uterine epithelial cells. Immunocytochemical analysis revealed the reproducible presence of a small proportion of macrophages in primary cultures. Macrophages of the RAW 264.7 cell line were found to secrete more interleukin (IL)-1beta (but not TNF-alpha) when cultured in high D-glucose. TNF-alpha production in WEG-1 cells was increased upon exposure to IL-1beta and both protein kinase-C and tyrosine kinase pathways appeared to be involved in TNF-alpha stimulation. Addition of IL-1 receptor antagonist to primary cultures partially abrogated the effect of high D-glucose. Since WEG-1 cells do not produce IL-1beta, the data lend support to the hypothesis that uterine epithelial cells synthesize high levels of TNF-alpha in response to hyperglycaemia via an increase in IL-1beta secretion by stromal macrophages.

Fibronectin stimulates transcription of the platelet-derived growth factor beta-receptor in cultured rat aortic smooth muscle cells

Fibronectin seems to play an important role in promoting the characteristic changes of vascular smooth muscle cells in diabetes mellitus including overexpression of the platelet-derived growth factor beta-receptor. To determine the regulatory mechanism of the beta-receptor by fibronectin, we have analyzed the effect of fibronectin on the expression of the beta-receptor in cultured rat aortic smooth muscle cells using the beta-receptor promoter/luciferase expression vector system. Fibronectin was found to stimulate the expression of the beta-receptor at the transcriptional level. Both a MEK1 inhibitor PD98059 and a tyrosine kinase inhibitor herbimycin A significantly inhibited the fibronectin-stimulated receptor transcription. Herbimycin A also completely inhibited the fibronectin-stimulated increase in tyrosine phosphorylation of focal adhesion kinase. These data suggest the involvement of the integrin-mediated mitogen-activated protein kinase pathway downstream of fibronectin stimulation in the activation process of the beta-receptor promoter.

Insulin potentiates platelet-derived growth factor action in vascular smooth muscle cells

Correlative studies have indicated that hyperinsulinemia is present in many individuals with atherosclerosis. Insulin resistance has also been linked to cardiovascular disease. It has proved to be difficult to decipher whether hyperinsulinemia or insulin resistance plays the most important role in the pathogenesis of atherosclerosis and coronary artery disease. In this study, we demonstrate that insulin increases the amount of farnesylated p21Ras in vascular smooth muscle cells (VSMC), thereby augmenting the pool of cellular Ras available for activation by platelet-derived growth factor (PDGF). In VSMC incubated with insulin for 24 h, PDGF's influence on GTP-loading of Ras was significantly increased. Furthermore, in cells preincubated with insulin, PDGF increased thymidine incorporation by 96% as compared with a 44% increase in control cells (a 2-fold increment). Similarly, preincubation of VSMC with insulin increased the ability of PDGF to stimulate gene expression of vascular endothelial growth factor 5- to 8-fold. The potentiating influence of insulin on PDGF action was abrogated in the presence of a farnesyltransferase inhibitor. Thus, the detrimental influence of hyperinsulinemia on the arterial wall may be related to the ability of insulin to augment farnesyltransferase activity and provide greater amounts of farnesylated p21Ras for stimulation by various growth promoting agents.

The assessment of platelet derived growth factor concentration in post myocardial infarction and stable angina patients

Platelet derived growth factor (PDGF) has been implicated in the pathogenesis of atherosclerosis. PDGF is released by aggregating platelets and monocytes which gather around sites of arterial injury. In the study reported here the concentration of plasma PDGF was measured in post myocardial infarction (MI) patients (n = 28), angina patients (n = 25), and control subjects (n = 27). Venous blood samples were taken and the concentration of PDGF determined by an enzyme linked immunosorbent assay (ELISA). Plasma PDGF concentrations were significantly higher in the post MI group compared to both the control and angina groups (P < or = 0.05). The increase in PDGF concentration may be due to increased activation of platelets or monocytes since these two cells are major sources of plasma PDGF. High concentrations of PDGF in the circulation could further accelerate the progression of the disease.

Vascular dysfunction induced by elevated glucose levels in rats is mediated by vascular endothelial growth factor

The purpose of these experiments was to investigate a potential role for vascular endothelial growth factor (VEGF) in mediating vascular dysfunction induced by increased glucose flux via the sorbitol pathway. Skin chambers were mounted on the backs of Sprague-Dawley rats and 1 wk later, granulation tissue in the chamber was exposed twice daily for 7 d to 5 mM glucose, 30 mM glucose, or 1 mM sorbitol in the presence and absence of neutralizing VEGF antibodies. Albumin permeation and blood flow were increased two- to three-fold by 30 mM glucose and 1 mM sorbitol; these increases were prevented by coadministration of neutralizing VEGF antibodies. Blood flow and albumin permeation were increased approximately 2.5-fold 1 h after topical application of recombinant human VEGF and these effects were prevented by nitric oxide synthase (NOS) inhibitors (aminoguanidine and N(G)-monomethyl L-arginine). Topical application of a superoxide generating system increased albumin permeation and blood flow and these changes were markedly attenuated by VEGF antibody and NOS inhibitors. Application of sodium nitroprusside for 7 d or the single application of a calcium ionophore, A23187, mimicked effects of glucose, sorbitol, and VEGF on vascular dysfunction and the ionophore effect was prevented by coadministration of aminoguanidine. These observations suggest a potentially important role for VEGF in mediating vascular dysfunction induced by "hypoxia-like" cytosolic metabolic imbalances (reductive stress, increased superoxide, and nitric oxide production) linked to increased flux of glucose via the sorbitol pathway.

Platelet-derived growth factor BB mediated regulation of 12-lipoxygenase in porcine aortic smooth muscle cells

Platelet-derived growth factor BB (PDGF) is a potent mitogen and chemoattractant for vascular smooth muscle cells (VSMC). In the present study, we have examined the effect of PDGF on the 12-lipoxygenase (12-LO) pathway of arachidonate metabolism in porcine aortic VSMC (PVSMC). The rationale for this is previous studies showing that LO products have growth and chemotactic effects in VSMC and that another VSMC growth factor, angiotensin II, is a potent positive regulator of 12-LO activity and expression. We observed that PDGF causes a significant increase in the formation of the 12-LO product, 12-hydroxyeicosatetraenoic acid (12-HETE) in PVSMC. In addition, PDGF also markedly increased leukocyte-type 12-LO messenger RNA and protein expression. PDGF-induced PVSMC migration was inhibited significantly by two LO blockers but not by a cyclooxygenase blocker. Furthermore, although the proliferative effects of PDGF on PVSMC were not altered by cell culture under hyperglycemic conditions (25 mM glucose, HG), the chemotactic effects of PDGF as well as those of 10% fetal calf serum were significantly greater in cells cultured in HG as compared to normal glucose conditions (5.5 mM), thus indicating a potential new mechanism for the accelerated cardiovascular disease usually observed in diabetes. These results indicate a novel mechanism for the biological effects of PDGF in leading to cardiovascular disease.