Effects of glucose on migration, proliferation and tube formation by vascular endothelial cells

Effect of cellular communication network factor 2/connective tissue growth factor on tube formation by endothelial cells derived from human periodontal ligaments

OBJECTIVES

To clarify the role of cellular communication network factor 2/connective tissue growth factor (CCN2/CTGF) in periodontal tissue regeneration by investigating, the proliferative and tubulogenic responses of human endothelial cells obtained from the periodontal ligament to CCN2/CTGF.

DESIGN

Endothelial cells were seeded on agar gel medium with or without 50 ng/mL recombinant CCN2/CTGF (rCCN2/CTGF) and cultured for 6 h. Cells were morphologically and phenotypically analyzed by immunofluorescent microscopy. A colorimetric assay was used to evaluate cell proliferation, and transmission electron microscopy (TEM) was used for ultrastructural analysis.

RESULTS

The proliferation of endothelial cells was best promoted by rCCN2/CTGF at 50 ng/mL. In the control group, tube formation was not observed within 6 h. In contrast, endothelial cells seeded on the agar with 50 ng/mL rCCN2/CTGF clearly showed proliferation with network formation. Under a two-dimensional culture condition, a dense network of endothelial cells was not constructed on the plastic bottom. However, drastic morphological change was observed in the endothelial cells on the agar containing rCCN2/CTGF. The endothelial cells in the dense network were interconnected with each other and showed a tube-like structure. Tight junctions or adherens junctions were observed between the adjoining endothelial cells in the dense network.

CONCLUSIONS

CCN2/CTGF was found to promote the proliferation and tubulogenesis of endothelial cells from the periodontal ligament. These results suggest that CCN2/CTGF may contribute to the regeneration of damaged periodontal tissue by activating the remaining endothelial cells.

Towards Cell free Therapy of Premature Ovarian Insufficiency: Human Bone Marrow Mesenchymal Stem Cells Secretome Enhances Angiogenesis in Human Ovarian Microvascular Endothelial Cells

Primary Ovarian Insufficiency (POI) refers to an ovarian loss of function in women under the age of 40. Unfortunately, currently, there is no effective treatment available for POI-related infertility. Alternatives such as the use of egg donations are culturally and ethically unacceptable to many couples. Human Bone marrow-derived Mesenchymal Stem Cells (MSCs) are known for their ability to differentiate into other cell types, once primed by the organ microenvironment. Importantly MSCs produce a vast array of bioactive factors many of them have been shown to enhance neovascularization in various tissues. Recently, preliminary data from our ongoing clinical trial revealed encouraging preliminary data after autologous MSC engraftment into the ovaries of 2 POI patients with durable elevation in serum estrogen levels and increase in size of treated ovaries sustained up to one-year post cell therapy.

In this study, we investigated the action of the mechanisms of MSCs treatment on a POI ovary. We designed an in vitro study using MSC secretome and Human Ovarian Endothelial Cells (HOVECs) to understand the molecular mechanisms by which MSC mediates their angiogenic properties and regenerative effects. Human primary HOVECs were treatment with MSC secretome and examined by FACS for the expression of angiogenesis markers such as Endoglin, Tie-2, and VEGF. The formation of vessels was evaluated by using a 3D Matrigel tubulogenesis assay.

We observed that the expression of proliferation marker Ki67 was significantly increased under treatment with MSC secretome in HOVEC cells (P4). MSCs secretome treatment also induced significantly higher expression of several angiogenic markers such as VEGFR2, Tie2/Tek, VE-Cadherin, Endoglin, and VEGF compared to matched control (P4). Furthermore, MSC secretome significantly increased the number of branching points in tubulogenesis assay (P4). Our study suggests that MSC secretome likely contains bioactive factors that can enhance ovarian angiogenesis. Further characterization of these factors can lead to novel therapeutic options for women with premature ovarian insufficiency and other related causes of female infertility.

Methylglyoxal triggers human aortic endothelial cell dysfunction via modulation of the KATP/MAPK pathway

Endothelial dysfunction is a key risk factor in diabetes-related multiorgan damage. Methylglyoxal (MGO), a highly reactive dicarbonyl generated primarily as a by-product of glycolysis, is increased in both type 1 and type 2 diabetic patients. MGO can rapidly bind with proteins, nucleic acids, and lipids, resulting in structural and functional changes. MGO can also form advanced glycation end products (AGEs). How MGO causes endothelial cell dysfunction, however, is not clear. Human aortic endothelial cells (HAECs) from healthy (H-HAECs) and type 2 diabetic (D-HAECs) donors were cultured in endothelial growth medium (EGM-2). D-HAECs demonstrated impaired network formation (on Matrigel) and proliferation (MTT assay), as well as increased apoptosis (caspase-3/7 activity and TUNEL staining), compared with H-HAECs. High glucose (25 mM) or AGEs (200 ng/ml) did not induce such immediate, detrimental effects as MGO (10 µM). H-HAECs were treated with MGO (10 µM) for 24 h with or without the ATP-sensitive potassium (K_ATP) channel antagonist glibenclamide (1 µM). MGO significantly impaired H-HAEC network formation and proliferation and induced cell apoptosis, which was reversed by glibenclamide. Furthermore, siRNA against the K_ATP channel protein Kir6.1 significantly inhibited endothelial cell function at basal status but rescued impaired endothelial cell function upon MGO exposure. Meanwhile, activation of MAPK pathways p38 kinase, c-Jun NH²-terminal kinase (JNK), and extracellular signal-regulated kinase (ERK) (determined by Western blot analyses of their phosphorylated forms, p-JNK, p-p38, and p-ERK) in D-HAECs were significantly enhanced compared with those in H-HAECs. MGO exposure enhanced the activation of all three MAPK pathways in H-HAECs, whereas glibenclamide reversed the activation of p-stress-activated protein kinase/JNK induced by MGO. Glyoxalase-1 (GLO1) is the endogenous MGO-detoxifying enzyme. In healthy mice that received an inhibitor of GLO1, MGO deposition in aortic wall was enhanced and endothelial cell sprouting from isolated aortic segment was significantly inhibited. Our data suggest that MGO triggers endothelial cell dysfunction by activating the JNK/p38 MAPK pathway. This effect arises partly through activation of K_ATP channels. By understanding how MGO induces endothelial dysfunction, our study may provide useful information for developing MGO-targeted interventions to treat vascular disorders in diabetes.

Kaempferol targets estrogen-related receptor α and suppresses the angiogenesis of human retinal endothelial cells under high glucose conditions

Diabetic retinopathy (DR) is the most common complication of diabetes and a major cause of new-onset blindness in the developed world. The present study aimed to examine the effect of kaempferol on high glucose-induced human retinal endothelial cells (HRECs) in vitro. The expression levels of various mRNAs and proteins were measured by reverse transcription-quantitative polymerase chain reaction (RT-qPCR) and western blotting, respectively. The target of kaempferol was determined using a luciferase reporter assay. In addition, HREC proliferation, migration and cell sprouting were determined using Cell Counting kit-8, wound scratch and tube formation assays, respectively. RT-qPCR and western blotting results showed that treatment with 30 mM glucose for 12, 24 and 48 h increased the expression level of estrogen-related receptor α (ERRα) mRNA and protein. The luciferase reporter assay demonstrated that kaempferol inhibited ERRα activity in HRECs. Compared with 5 mM normal glucose treatment, high (30 mM) glucose significantly promoted the proliferation, migration and tube formation of HRECs, which was antagonized by 10 and 30 µM kaempferol in a dose-dependent manner. Treatment with 30 mM glucose also increased the expression of vascular endothelial growth factor (VEGF) mRNA and protein, and the expression levels of VEGF mRNA and protein were suppressed by kaempferol (10 and 30 µM). Kaempferol (30 µM) treatment also increased the expression levels of thrombospondin 1 (TSP-1) and a disintegrin and metalloproteinase with thrombospondin motifs 1 (ADAMTS-1) mRNA; however, TSP-1 and ADAMTS-1 levels did not differ between high glucose and normal (5 mM) glucose conditions. The results of this study suggest that kaempferol targets ERRα and suppresses the angiogenesis of HRECs under high glucose conditions. Kaempferol may be a potential drug for use in controlling the progression of DR; however, in vivo studies are required to evaluate its efficacy and safety.

Method comparison for analyzing wound healing rates

Wound healing scratch assay is a frequently used method to characterize cell migration, which is an important biological process in the course of development, tissue repair, and immune response for example. The measurement of wound healing rate, however, varies among different studies. Here we summarized these measurements into three types: (I) direct rate average; (II) regression rate average; and (III) average distance regression rate. Using Chinese hamster ovary (CHO) cells as a model, we compared the three types of analyses on quantifying the wound closing rate, and discovered that type I & III measurements are more resistant to outliers, and type II analysis is more sensitive to outliers. We hope this study can help researchers to better use this simple yet effective assay.

Protective actions of globular and full-length adiponectin on human endothelial cells: novel insights into adiponectin-induced angiogenesis

BACKGROUND/AIMS

Adiponectin levels are decreased in diabetes and atherosclerosis. Coexisting hyperglycaemia and systemic inflammation predisposes to dysregulated angiogenesis and vascular disease. We investigated the effect of globular adiponectin (gAd) and full-length adiponectin (fAd) on angiogenesis and pro-angiogenic molecules, i.e. matrix metalloproteinase (MMP)-2, MMP-9 and vascular endothelial growth factor (VEGF), in human microvascular endothelial cells (HMEC-1).

METHODS

Angiogenesis was assessed by studying capillary tube formation in HMEC-1 on growth factor-reduced Matrigel. Endothelial cell migration assay was performed in a modified Boyden chamber.

RESULTS

Endothelial cell proliferation, in vitro migration and angiogenesis were significantly increased by gAd (mediated by AdipoR1, AMPK-Akt pathways), and gAd significantly increased MMP-2, MMP-9 and VEGF expression levels. The effect of gAd on VEGF appears to be mediated by AdipoR1, whilst the effect of gAd on MMP-2 and MMP-9 appears to be mediated by AdipoR1 and AdipoR2. Only endothelial cell proliferation was significantly increased by fAd in human microvascular endothelial cells and appears to be mediated by AdipoR2. No significant effects on MMP-2, MMP-9 and VEGF were observed. Importantly, gAd decreased glucose and C-reactive protein-induced angiogenesis with a concomitant reduction in MMP-2, MMP-9 and VEGF in HMEC-1 cells.

CONCLUSION

We report novel insights into the mechanisms of adiponectin on angiogenesis.

Cyclin D3 mediates synthesis of a hyaluronan matrix that is adhesive for monocytes in mesangial cells stimulated to divide in hyperglycemic medium

Serum-starved, growth-arrested, near confluent rat mesangial cell cultures were stimulated to divide in medium with low (5.6 mM) or high (25.6 mM) glucose. In high glucose cultures Western blots showed large increases in cyclin D3 and CCAAT/enhancer-binding protein alpha (C/EBPalpha) at 48-72 h, concurrent with the production of a monocyte-adhesive hyaluronan matrix, whereas low glucose and mannitol osmotic control cultures did not. Cyclin D3 small interfering RNA inhibited both the synthesis of this matrix and the up-regulation of C/EBPalpha in cultures exposed to high glucose, indicating that cyclin D3 is a key mediator in regulating responses of dividing mesangial cells to hyperglycemia. A complex with cyclin D3, cyclin-dependent kinase 4, and C/EBPalpha was observed at 48-72 h in the hyperglycemic cultures, and cyclin D3 and C/EBPalpha were spatially co-localized in coalesced perinuclear honeycomb-like structures with embedded hyaluronan. Furthermore, microtubule-associated protein 1 light chain 3, a marker for autophagy, colocalizes with these structures. These results suggest that cyclin D3 is a central coordinator that controls the organization of a complex set of proteins that regulate autophagy, formation of the monocyte-adhesive hyaluronan matrix, and C/EBPalpha-mediated lipogenesis. Abnormal deposits of hyaluronan, cyclin D3, and C/EBPalpha were present in glomeruli of kidney sections from hyperglycemic rats 4 weeks after streptozotocin treatment, indicating that similar processes likely occur in vivo. Mesangial cell cultures treated with poly(I:C) or tunicamycin in normal glucose media synthesized monocyte-adhesive hyaluronan matrices but with concurrent down-regulation of cyclin D3. This indicates that the cyclin D3 mechanism is induced by hyperglycemia and is distinct from those involved in these cell stress responses.

In vitro formation of capillary networks using optical lithographic techniques

Tissue engineering approaches have been developed for vascular grafts, but success has been limited to arterial replacements of large-caliber vessels. We have developed an innovative technique to transplant engineered capillary networks by printing techniques. Endothelial cells were cultured on a patterned substrate, in which network patterns were generated by prior optical lithography. Subsequently, the patterned cells were transferred to extracellular matrix and tissue at which point they changed their morphologies and formed tubular structures. Microinjection of dye showed that the micrometer-scale tubular structure had in vitro flow potential. When capillary-like networks engineered on amnion membranes were transplanted into mice, we found blood cells inside of the lumen of the transplanted capillary-like structure. This is the first report of the in vitro formation of capillary networks using cell transfer technique, and this novel technique may open the way for development of rapid and effective blood perfusion systems in regenerative medicine.

Regulation of the atherogenic properties of vascular smooth muscle proteoglycans by oral anti-hyperglycemic agents

The present study aimed to investigate the actions of several classes of oral hypoglycemic agents [e.g., sulfonylureas (SUs), biguanides (BGs) and thiazolidinediones (TZDs)] in an in vitro model of lipid binding based on the "response to retention" hypothesis of atherogenesis. The incorporation of [(35)S]-SO(4) into proteoglycans synthesized by human vascular smooth muscle cells (VSMCs) was assessed by cetylpyridinium chloride (CPC) precipitation method, proteoglycan electrophoretic mobility was evaluated by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), and binding to low-density lipoprotein (LDL) was assessed by gel mobility shift assay (GMSA). The SUs evaluated showed no effect on [(35)S]-SO(4) incorporation into proteoglycans. Only one BG, phenformin, caused a concentration-related inhibition of proteoglycan synthesis under basal conditions and in the presence of transforming growth factor-beta1 (TGF-beta1), caused by an inhibition of proteoglycan core protein synthesis secondary to a reduction in total protein synthesis. However, neither metformin nor phenformin (30-300 micromol/l) had any effect on the electrophoretic mobility of proteoglycans. The TZDs--troglitazone (TRO), rosiglitazone (ROS), and pioglitazone (PIO) (10, 30, and 30 micromol/l, respectively)--inhibited proteoglycan biosynthesis and stimulated total proteoglycan core protein synthesis, while TRO alone inhibited overall protein synthesis. All three TZDs moderately reduced the electrophoretic mobility of synthesized proteoglycans assessed by SDS-PAGE, reduced the sizes of cleaved glycosaminoglycan (GAG) chains assessed by size exclusion chromatography, and significantly reduced binding to LDL. The data indicate that TZDs show anti-atherogenic actions through the modification of proteoglycan structure, leading to a possible reduction in lipid retention in the vessel wall.

Green Light Emitting Diode Irradiation Enhances Fibroblast Growth Impaired by High Glucose Level

BACKGROUND AND OBJECTIVE

The chronic metabolic disorder diabetes mellitus is an important cause of morbidity and mortality due to a series of common secondary metabolic complications, such as the development of severe, often slow healing skin lesions. In view of promoting the wound-healing process in diabetic patients, this preliminary in vitro study investigated the efficacy of green light emitting diode (LED) irradiation on fibroblast proliferation and viability under hyperglycemic circumstances.

MATERIALS AND METHODS

To achieve hyperglycemic circumstances, embryonic chicken fibroblasts were cultured in Hanks' culture medium supplemented with 30 g/L glucose. LED irradiation was performed on 3 consecutive days with a probe emitting green light (570 nm) and a power output of 10 mW. Each treatment lasted 3 min, resulting in a radiation exposure of 0.1 J/cm2.

RESULTS

A Mann-Whitney U test revealed a higher proliferation rate (p = 0.001) in all irradiated cultures in comparison with the controls.

CONCLUSION

According to these results, the effectiveness of green LED irradiation on fibroblasts in hyperglycemic circumstances is established. Future in vivo investigation would be worthwhile to investigate whether there are equivalent positive results in diabetic patients.

Long-term administration of highly purified eicosapentaenoic acid ethyl ester improves blood coagulation abnormalities and dysfunction of vascular endothelial cells in Otsuka Long-Evans Tokushima fatty rats

We investigated the effect of highly purified eicosapentaenoic acid ethyl ester (EPA-E) on blood coagulation abnormalities and dysfunction of vascular endothelial cells in spontaneously diabetic Otsuka Long-Evans Tokushima Fatty rats. The animals were treated with either EPA-E or lard at a daily dose of 0.3 g/kg/day for 52 weeks by gavage, and their coagulation/fibrinolytic parameters, platelet aggregation, and functions of the vascular endothelial cells were examined. EPA-E significantly improved coagulation-related parameters including prothrombin time, activated partial thromboplastin time, fibrinogen level, and activities of factor II, V, VII, VIII, IX, X, XI, and XII, and antithrombin III, and fibrinolysis-related parameters including plasminogen, tissue-type plasminogen activator, alpha(2)-plasmin inhibitor, and plasminogen activator inhibitor. It also suppressed ADP- or collagen-induced platelet aggregation and the cholesterol/phospholipid molar ratio in platelet membranes at a dose of 0.3 g/kg. In addition, it significantly increased the migration activity of vascular endothelial cells, and decreased the binding of vascular endothelial cells to vascular endothelial growth factor. In contrast, lard had no effect on hypercoagulation, hypofibrinolysis, and platelet hyperaggregation but significantly aggravated the dysfunction of vascular endothelial cells. These data demonstrate that EPA-E beneficially altered certain factors known to promote thrombosis and atherosclerosis in this animal model.

Docosapentaenoic acid (22:5, n-3) suppressed tube-forming activity in endothelial cells induced by vascular endothelial growth factor

It is generally accepted that n-3 polyunsaturated fatty acids have beneficial effects on vascular homeostasis. Among the several functions of endothelial cells, angiogenesis contributes to tumor growth, inflammation, and microangiopathy. We have already demonstrated that eicosapentaenoic acid (EPA, 20:5, n-3) suppressed angiogenesis. In this paper, we examined the effect of docosapentaenoic acid (DPA, 22:5, n-3), an elongated metabolite of EPA, on tube-forming activity in bovine aortic endothelial cells (BAE cells) incubated between type I collagen gels. The pretreatment of BAE cells with DPA suppressed tube-forming activity induced by vascular endothelial growth factor (VEGF). The effect of DPA was stronger than those of EPA and docosahexaenoic acid (22:6, n-3). The migrating activity of endothelial cells stimulated with VEGF was also suppressed by DPA pretreatment. The treatment of BAE cells with DPA caused the suppression of VEGF receptor-2 (VEGFR-2, the kinase insert domain-containing receptor, KDR) expression in both plastic dish and collagen gel cultures. These data indicate that DPA has a potent inhibitory effect on angiogenesis through the suppression of VEGFR-2 expression.

Glucose effects on skin keratinocytes: implications for diabetes skin complications

Altered skin wound healing is a common cause of morbidity and mortality among diabetic patients. However, the molecular mechanisms whereby diabetes alters skin physiology have not been elucidated. In this study, we investigated the relative roles of hyperglycemia, insulin, and IGF-I, all of which are abnormal in diabetes, in primary murine skin keratinocytes. These cells proliferate and differentiate in vitro in a manner similar to skin in vivo. It was found that in the presence of high glucose (20 mmol/l), the glucose transport rate of primary proliferating or differentiating keratinocytes was downregulated, whereas at 2 mmol/l glucose, the transport rate was increased. These changes were associated with changes in the GLUT1 expression and with changes in the affinity constant (K(m)) of the transport. Exposure to high glucose was associated with changes in cellular morphology, as well as with decreased proliferation and enhancement of Ca(2+)-induced differentiation of keratinocytes. Furthermore, in the presence of high glucose, ligand-induced IGF-I receptor but not insulin receptor (IR) autophosphorylation was decreased. Consequently, in high glucose, the effects of IGF-I on glucose uptake and keratinocyte proliferation were inhibited. Interestingly, lack of IR expression in IR-null keratinocytes abolished insulin-induced glucose uptake and partially decreased insulin- and IGF-I-induced proliferation, demonstrating the direct involvement of the IR in these processes. Our results demonstrate that hyperglycemia and impaired insulin signaling might be directly involved in the development of chronic complications of diabetes by impairing glucose utilization of skin keratinocytes as well as skin proliferation and differentiation.

Troglitazone, but not rosiglitazone, inhibits Na/H exchange activity and proliferation of macrovascular endothelial cells

Diabetes is associated with a high level of mortality due to cardiovascular disease resulting from accelerated coronary artery atherosclerosis. A current focus for investigation of atherosclerotic mechanisms is the vascular endothelium since physical or functional injury may represent an initiating step for atherogenesis. Thiazolidinediones (TZDs) are the newest class of drugs for the treatment of insulin resistance and its metabolic consequences; they are peroxisome proliferator-activating receptor (PPAR)-gamma ligands that act as insulin-sensitizing agents. We are interested in the contribution of direct vascular actions to the clinical utility of these agents. We investigated the effect troglitazone and rosiglitazone on endothelial cell proliferation in low- and high-glucose media and further explored their action on the ubiquitous membrane transport system, the Na/H exchanger (NHE), which has been implicated in regulating the growth of vascular cells. Experiments were conducted in cultured bovine aortic endothelial cells (BAECs). Cell proliferation was assessed by cell counting, and NHE activity was determined in cells loaded with the pH-sensitive fluorescent dye, 2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester (BCECF-AM). Troglitazone caused a dose-dependent inhibition of endothelial cell proliferation with approximately 50% inhibition at 10 microM. Troglitazone inhibited endothelial cell proliferation with similar potency under low- (5 mM) and high-glucose (25 mM) concentrations. Rosiglitazone had no significant effect on endothelial cell proliferation at concentrations of up to 100 microM under low- or high-glucose concentrations. The NHE inhibitor, 3-metlylsulfonyl-4-piperidinobenzoyl guanidine (HOE 694), caused dose dependent inhibition of BAEC proliferation, which was independent of the media glucose concentration. Acute exposure of cells to troglitazone (10 microM) and rosiglitazone (30 microM) during recovery from acidosis showed slight but significant (P<.05) inhibition of NHE activity by troglitazone, but no significant (P>.05) effect by rosiglitazone. Exposure of cells to either drug for 24 h revealed no chronic regulation of NHE activity. Our data demonstrate that troglitazone has similar actions in endothelial cells as in vascular smooth muscle. The absence of rosiglitazone effects, a more potent PPAR-gamma activator, suggests that the observed actions of troglitazone may be at least partially independent of PPAR-gamma. The effects of troglitazone and rosiglitazone on endothelial cell proliferation and NHE activity, although contrasting, are consistent with a central signalling role of this transporter in cell proliferation.

Regulation of angiogenesis by controlling VEGF receptor

The endothelial cells cultured in collagen gel caused upregulation of KDR expression, which resulted in an increase in tube formation. Endothelial cells exposed to high glucose (33 mmol/l) for 30 days increased the tube formation induced by VEGF, but not by serum and bFGF. Immunohistochemical study showed that KDR expression was upregulated by the high-glucose treatment. The endothelial cells treated with 0.5-5 micrograms/ml eicosapentaenoic acid (EPA, 20:5, n-3) for 48 h displayed a dose-dependent suppression of tube formation, VEGF-induced proliferation, and activation of p42/p44 MAP kinase but not bFGF-induced ones. Pretreatment with arachidonic acid (20:4, n-6) and docosahexaenoic acid (22:6, n-3) did not show such effects. The expression of KDR was downregulated by the EPA pretreatment. The bone is the richest tissue in microvessel networks except for the liver. Osteoblasts produced VEGF and some factor(s) that could induce KDR upregulation in endothelial cells and could enhance tube formation. These results lead to the speculation that the regulation of KDR expression as well as VEGF production is deeply involved in angiogenesis under various conditions.

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.

Antiproliferative effect of elevated glucose in human microvascular endothelial cells

Diabetic microangiopathy has been implicated as a fundamental feature of the pathological complications of diabetes including retinopathy, neuropathy, and diabetic foot ulceration. However, previous studies devoted to examining the deleterious effects of elevated glucose on the endothelium have been performed largely in primary cultured cells of macrovessel origin. Difficulty in the harvesting and maintenance of microvascular endothelial cells in culture have hindered the study of this relevant population. Therefore, the objective of this study was to characterize the effect of elevated glucose on the proliferation and involved signaling pathways of an immortalized human dermal microvascular endothelial cell line (HMEC-1) that possess similar characteristics to their in vivo counterparts. Human dermal microvascular endothelial cells (HMEC-1) were grown in the presence of normal (5 mM) or high D-glucose (20 mM) for 14 days. The proliferative response of HMEC-1 was compared under these conditions as well as the cAMP and PKC pathways by in vitro assays. Elevated glucose significantly inhibited (P < 0.05) HMEC-1 proliferation after 7, 10, and 14 days. This effect was not mimicked by 20 mM mannitol. The antiproliferative effect was more pronounced with longer exposure (1-14 days) to elevated glucose and was irreversible 4 days after a 10-day exposure. The antiproliferative effect was partially reversed in the presence of a PKA inhibitor, Rp-cAMP (10-50 microM), and/or a PKC inhibitor, Calphostin C (10 nM). HMEC-1 exposed to elevated glucose (20 mM) for 14 days caused an increase in cyclic AMP accumulation, PKA, and PKC activity but was not associated with the activation of downstream events such as CRE and AP-1 binding activity. These data support the hypothesis that HMEC-1 is a suitable model to study the deleterious effects of elevated glucose on microvascular endothelial cells. Continued studies with HMEC-1 may prove advantageous in delineation of the molecular pathophysiology associated with diabetic microangiopathy.

The effect of elevated extracellular glucose on migration, adhesion and proliferation of SV40 transformed human corneal epithelial cells

PURPOSE

To examine the effect of elevated extracellular glucose, thus simulating diabetes, on migration, adhesion and proliferation of SV40 transformed human corneal epithelial (HCE) cells.

METHODS

HCE cells were maintained in serum supplemented media containing 5 mM, 17.5 mM or 38 mM D-glucose. Cell migration was determined using Blind well chambers fitted with fibronectin/collagen I coated filters. In adhesion experiments, cells were allowed to adhere to extracellular matrix protein-coated wells for 90 min at 37 degrees C. Non-adherent cells were removed by washing, then the fluorochrome calcein-AM was added to quantitate the number of attached cells. Proliferation was determined by plating the cells at low density, then quantitating viable cells with calcein-AM 5 to 7 days later.

RESULTS

Raising extracellular glucose from 5 mM to 17.5 mM significantly increased cell migration by 42%. When glucose was further raised to 38 mM, migration was not significantly different from that in 5 mM glucose. Adhesion to fibronectin and collagen I (but not IV) was significantly increased (62% and 32% respectively) when cells were cultured in 17.5 mM glucose. Similarly, proliferation was increased by 44%. Adhesion and proliferation tended to be decreased at 38 mM compared to 17.5 mM glucose, but not significantly so. In the presence of 5 mM glucose and mannitol (12.5 mM or 33 mM), neither migration, adhesion nor proliferation were significantly different from that in 5 mM glucose alone.

CONCLUSION

Elevated extracellular glucose modulates migration, adhesion and proliferation of HCE cells. The effects are dependent on the concentration of glucose and are not due to changes in osmolality since mannitol failed to produce similar results. Our in vitro findings suggest that high-glucose effects may directly contribute to the etiology of impaired corneal wound healing in diabetes.

High D-glucose induces alterations of endothelial cell structure in a cell-culture model

Diabetes mellitus leads to micro- and macroangiopathy with endothelial dysfunction. To investigate the direct influence of high glucose on endothelial cell structure and possible pharmacologic effects, seven different experimental protocols were carried out on endothelial cells in culture. There were four control groups with either 5 mM D-glucose alone, 5 mM D-glucose plus 15 mM L-glucose (for osmotic control), 5 mM D-glucose plus 500 nM celiprolol, or 5 mM D-glucose plus 57 nM nitrendipine. Three experimental groups had either 20 mM D-glucose alone, 20 mM D-glucose plus 500 nM celiprolol or 20 mM D-glucose plus 57 nM nitrendipine. Treatment of all groups started at the third passage of the cells and lasted until confluence was reached (5-8 days). The endothelial cells were fixed in paraformaldehyde and stained either with hematoxylin-eosin solution, with nitro blue tetrazolium for nicotinamide adenine dinucleotide phosphate (NADPH)- diaphorase staining, or actin staining with phalloidin was carried out. For quantitative analysis of the histologic specimens, the slides were viewed via a microscope and a videocamera. The pictures were converted digitally and could be analyzed with the videopicture-analyzing system, JAVA. In the four control groups, neither treatment with 15 mM L-glucose nor administration of celiprolol or nitrendipine had an effect on cell, cytoplasm, and nuclear area. The number of giant or polynuclear cells and the histochemical NADPH-diaphorase activity were not altered. Incubation of endothelial cells with 20 mM D-glucose for 5-8 days resulted in a significant increase in total and cytoplasmic area, as well as in the number of giant and polynuclear cells, whereas the nuclear area and the NADPH-diaphorase activity were significantly reduced. Concomitant treatment with celiprolol was able to reverse these alterations in endothelial structure significantly but had only a weak effect on the NADPH-diaphorase. Nitrendipine had no beneficial effect on the high D-glucose-induced cell alterations. The actin staining of the control cells showed the typical actin pattern with most of the actin filaments arranged at the periphery of the cells. Administration of 20 mM D-glucose resulted in a disturbance of the actin pattern, with most of the actin filaments now arranged in the middle of the cells. However, neither celiprolol nor nitrendipine exhibited a significant influence on this altered actin structure. High D-glucose treatment over several days thus leads to severe changes in endothelial cell structure, and celiprolol may have a beneficial effect on these hyperglycemia-induced cell alterations.

Insulin does not disrupt actin microfilaments, microtubules, and in vitro aortic endothelial wound repair

In the face of small denuding injuries, the endothelium undergoes a process of rapid repair involving actin microfilaments, microtubules, and centrosomes to reestablish an intact monolayer. Failure to maintain an intact endothelial monolayer is an important factor in the pathogenesis of the atherosclerotic plaque. It was hypothesized that increased susceptibility to atherosclerosis in diabetes mellitus may be, in part, due to delayed reendothelialization following endothelial injury. To test this, the effects of high insulin concentrations on the reendothelialization of small wounds were examined using an in vitro porcine aortic endothelial cell wound model. Elevated concentrations of insulin did not disrupt the confluent endothelial monolayer or alter endothelial cell shape. Insulin also did not induce detectable alterations in the distribution of microtubules and microfilaments in the confluent monolayer. High insulin did not reduce the extent of reendothelialization of a linear wound made in the confluent monolayer. Centrosomal reorientation was similar to that of control wounded cultures as was the reorganization of the microfilaments and microtubules. The data suggest that the atherogenic effects of hyperinsulinemia are not due to disruption of endothelial repair.

Specific simple sugars promote chemotaxis and chemokinesis of corneal endothelial cells

Bovine corneal endothelial cells showed a strong migratory response to specific simple sugars (D-glucose and sucrose, but not L-glucose, sorbitol, lactose, or D-galactose) at concentrations above 10 mM. Checkerboard analysis of the migratory responses in modified Boyden chambers indicated both chemotactic and chemokinetic effects. Serum starvation of the cultures increased the chemotaxis towards D-glucose and 2-deoxy-D-glucose, but not towards sucrose. Migration to sucrose and glucose was inhibited by chelation of extracellular calcium or by inhibition of Na+, K+ ATPase with ouabain. To date, this migratory response has been found only in corneal endothelial cells. Neither human melanoma cells, human breast carcinoma cells, bovine aortic endothelial cells, nor bovine microvascular endothelial cells migrated towards simple sugars, although all cell types migrated toward fibronectin in chemotaxis assays. After 16-19 passages in culture, bovine corneal endothelial cells retained their ability to migrate towards fibronectin, but lost their ability to migrate towards sugars. This loss of migratory response was accompanied by a sevenfold decrease in Na+, K+ ATPase activity. Although loss of Na+, K+ ATPase activity accompanied the loss of migratory response, pretreatment of cell cultures with 25 mM glucose did not stimulate, but rather lowered Na+, K+ ATPase activity in low or high passage cultures.

An oxidative mechanism is involved in high glucose-induced serum protein modification causing inhibition of endothelial cell proliferation

In order to investigate the role of hyperglycemia on the development of atherosclerosis in diabetics, the effects of high glucose-induced modification of serum factors on the proliferation of bovine carotid artery endothelial cells were studied. Dialysates of high glucose-treated serum inhibit cell growth in a time- and glucose concentration-dependent manner. With 6 weeks of pretreatment, 16.7 mM glucose causes a 47.2% inhibition in cell growth compared to 5.6 mM glucose (P < 0.001). Pretreatment of serum in the presence of reduced glutathione (0.5-1.0 mM), an antioxidant, significantly prevents the high glucose-induced inhibition without inhibiting the formation of early non-enzymatic glycosylation products. Dithiothreitol (7.5 mM) treatment after preincubation with glucose fully restores the glucose-induced inhibition. When the dialysates are fractionated according to molecular mass, the high glucose-induced inhibition is maximal in the MW fraction above 100 kDa. These data suggest that high glucose conditions facilitate the susceptibility of serum proteins to sulfhydryl oxidation forming disulfide crosslinks and this oxidative process may contribute to the inhibition of endothelial cell proliferation.

Stimulatory effects of insulin and insulin-like growth factor I on migration and tube formation by vascular endothelial cells

The effects of insulin and insulin-like growth factor I (IGF-I) on migration, proliferation and tube-forming activity of endothelial cells were investigated, by using bovine carotid artery endothelial cells. Migration was assayed by a filter membrane technique and tube formation was assayed by a quantitative angiogenesis in vitro model which we have recently developed. In this model, endothelial cells are cultured between two layers of type I collagen gel and become organized into tube-like structures which mimic capillaries in vivo ultrastructurally. Insulin (50-1000 microunits/ml) and IGF-I (10-200 ng/ml) significantly stimulated migration of endothelial cells in a dose-dependent manner with a maximal stimulation of 3.0-fold at 1000 microunits/ml for insulin and 3.8-fold at 200 ng/ml for IGF-I (P less than 0.01). Insulin at concentrations up to 1000 microunits/ml and IGF-I up to 100 ng/ml did not affect proliferation of endothelial cells. When insulin or IGF-I was added in culture medium on collagen gels, tube-forming activity of endothelial cells was markedly stimulated. The specific lengths of tubes significantly increased with the increase in insulin concentration from 25 to 100 microunits/ml (P less than 0.01). At 100 microunits/ml, the stimulation was 1.77-fold (P less than 0.01). IGF-I (1-100 ng/ml) also stimulated the elongation of tubes dose-dependently with a maximal stimulation of 1.96-fold at 100 ng/ml (P less than 0.01). Thus, insulin and IGF-I at pathophysiological concentrations stimulate migration and tube-forming activity of endothelial cells, suggesting that these polypeptides may stimulate repair of endothelial injury in cases such as atherosclerosis and may act as a stimulator of angiogenesis.