Stimulation of retinal capillary pericyte protein and collagen synthesis in culture by high-glucose concentration

The fate and role of the pericytes in myocardial diseases

The adult mammalian heart contains a large population of pericytes that play important roles in homeostasis and disease. In the normal heart, pericytes regulate microvascular permeability and flow. Myocardial diseases are associated with marked alterations in pericyte phenotype and function. This review manuscript discusses the role of pericytes in cardiac homeostasis and disease. Following myocardial infarction (MI), cardiac pericytes participate in all phases of cardiac repair. During the inflammatory phase, pericytes may secrete cytokines and chemokines and may regulate leukocyte trafficking, through formation of intercellular gaps that serve as exit points for inflammatory cells. Moreover, pericyte contraction induces microvascular constriction, contributing to the pathogenesis of 'no-reflow' in ischemia and reperfusion. During the proliferative phase, pericytes are activated by growth factors, such as transforming growth factor (TGF)-β and contribute to fibrosis, predominantly through secretion of fibrogenic mediators. A fraction of pericytes acquires fibroblast identity but contributes only to a small percentage of infarct fibroblasts and myofibroblasts. As the scar matures, pericytes form a coat around infarct neovessels, promoting stabilization of the vasculature. Pericytes may also be involved in the pathogenesis of chronic heart failure, by regulating inflammation, fibrosis, angiogenesis and myocardial perfusion. Pericytes are also important targets of viral infections (such as SARS-CoV2) and may be implicated in the pathogenesis of cardiac complications of COVID19. Considering their role in myocardial inflammation, fibrosis and angiogenesis, pericytes may be promising therapeutic targets in myocardial disease.

Blood-brain barrier leakage and perivascular collagen accumulation precede microvessel rarefaction and memory impairment in a chronic hypertension animal model

Hypertension (HT) is one of the main causes of vascular dementia, lead to cognitive decline. Here, we investigated the relationship between cerebral microvessels, pericytes, extracellular matrix (ECM) accumulation, blood-brain barrier (BBB) breakdown, and memory impairment at mid-life in a chronic hypertension animal model. Spontaneously hypertensive rats (SHRs) (n = 20) are chosen for the model and age matched Wistar rats (n = 16) as controls. Changes in brain microvasculature and in vitro experiments are shown with immunofluorescence studies and cognition with open field, novel object recognition, and Y maze tests. There was a significant reduction in pericyte coverage in SHRs (p = 0.021), while the quantitative parameters of the cerebral microvascular network were not different between groups. On the other hand, parenchymal albumin leakage, as a Blood-brain barrier (BBB) breakdown marker, was prominent in SHRs (p = 0.023). Extracellular matrix (ECM) components, collagen type 1, 3 and 4 were significantly increased (accumulated) around microvasculature in SHRs (p = 0.011, p = 0.013, p = 0.037, respectively). Furthermore, in vitro experiments demonstrated that human brain vascular pericytes but not astrocytes and endothelial cells secreted type I collagen upon TGFβ1 exposure pointing out a possible role of pericytes in increased collagen accumulation around cerebral microvasculature due to HT. Furthermore, valsartan treatment decreased the amount of collagen type 1 secreted by pericytes after TGFβ1 exposure. At the time of evaluation, SHRs did not demonstrate cognitive decline and memory impairments. Our results showed that chronic HT causes ECM accumulation and BBB leakage before leading to memory impairments and therefore, pericytes could be a novel target for preventing vascular dementia.

Retinal capillary basement membrane thickening: Role in the pathogenesis of diabetic retinopathy

Vascular basement membrane (BM) thickening has been hailed over half a century as the most prominent histological lesion in diabetic microangiopathy, and represents an early ultrastructural change in diabetic retinopathy (DR). Although vascular complications of DR have been clinically well established, specific cellular and molecular mechanisms underlying dysfunction of small vessels are not well understood. In DR, small vessels develop insidiously as BM thickening occurs. Studies examining high resolution imaging data have established BM thickening as one of the foremost structural abnormalities of retinal capillaries. This fundamental structural change develops, at least in part, from excess accumulation of BM components. Although BM thickening is closely associated with the development of DR, its contributory role in the pathogenesis of DR is coming to light recently. DR develops over several years before clinical manifestations appear, and it is during this clinically silent period that hyperglycemia induces excess synthesis of BM components, contributes to vascular BM thickening, and promotes structural and functional lesions including cell death and vascular leakage in the diabetic retina. Studies using animal models show promising results in preventing BM thickening with subsequent beneficial effects. Several gene regulatory approaches are being developed to prevent excess synthesis of vascular BM components in an effort to reduce BM thickening. This review highlights current understanding of capillary BM thickening development, role of BM thickening in retinal vascular lesions, and strategies for preventing vascular BM thickening as a potential therapeutic strategy in alleviating characteristic lesions associated with DR.

Involvement of sodium-coupled neutral amino acid transporters (system A) in l-proline transport in the rat retinal pericytes

The retinal pericytes contribute to the supply of collagen to the basement membrane, and thus, form the structural support of the blood-retinal barrier. Since l-proline (L-Pro) is a major component of collagen, the uptake of L-Pro is an important process for the synthesis of collagen. This study was aimed to elucidate L-Pro transport mechanism(s) in the retinal pericytes. The transport of [³H]L-Pro was evaluated in the conditionally immortalized rat retinal pericyte cell line, TR-rPCT1 cells. The expression of the candidate transporter was examined by qualitative/quantitative reverse transcription-polymerase chain reaction, immunoblot analysis, and immunostaining. The [³H]L-Pro uptake by TR-rPCT1 cells showed Na⁺-dependence, Cl^--independence, and concentration-dependence with a K_m of 810 μM. The substrates for system A, such as 2-(methylamino)isobutyric acid (MeAIB), significantly inhibited the L-Pro uptake, suggesting the involvement of system A in the uptake of L-Pro. Among the subtypes of system A, the mRNA expression levels of ATA2 were the highest in TR-rPCT1 cells. Immunostaining analysis of the isolated rat retinal capillaries containing pericytes indicated the protein expression of ATA2 in retinal pericytes. In conclusion, it is suggested that ATA2, at least in part, is involved in the transport of L-Pro in the retinal pericytes.

Cancer; an induced disease of twentieth century! Induction of tolerance, increased entropy and 'Dark Energy': loss of biorhythms (Anabolism v. Catabolism)

Maintenance of health involves a synchronized network of catabolic and anabolic signals among organs/tissues/cells that requires differential bioenergetics from mitochondria and glycolysis (biological laws or biorhythms). We defined biological circadian rhythms as Yin (tumoricidal) and Yang (tumorigenic) arms of acute inflammation (effective immunity) involving immune and non-immune systems. Role of pathogens in altering immunity and inducing diseases and cancer has been documented for over a century. However, in 1955s decision makers in cancer/medical establishment allowed public (current baby boomers) to consume million doses of virus-contaminated polio vaccines. The risk of cancer incidence and mortality sharply rose from 5% (rate of hereditary/genetic or innate disease) in 1900s, to its current scary status of 33% or 50% among women and men, respectively. Despite better hygiene, modern detection technologies and discovery of antibiotics, baby boomers and subsequent 2–3 generations are sicker than previous generations at same age. American health status ranks last among other developed nations while America invests highest amount of resources for healthcare. In this perspective we present evidence that cancer is an induced disease of twentieth century, facilitated by a great deception of cancer/medical establishment for huge corporate profits. Unlike popularized opinions that cancer is 100, 200 or 1000 diseases, we demonstrate that cancer is only one disease; the severe disturbances in biorhythms (differential bioenergetics) or loss of balance in Yin and Yang of effective immunity. Cancer projects that are promoted and funded by decision makers are reductionist approaches, wrong and unethical and resulted in loss of millions of precious lives and financial toxicity to society. Public vaccination with pathogen-specific vaccines (e.g., flu, hepatitis, HPV, meningitis, measles) weakens, not promotes, immunity. Results of irresponsible projects on cancer sciences or vaccines are increased population of drug-dependent sick society. Outcome failure rates of claimed ‘targeted’ drugs, ‘precision’ or ‘personalized’ medicine are 90% (± 5) for solid tumors. We demonstrate that aging, frequent exposures to environmental hazards, infections and pathogen-specific vaccines and ingredients are ‘antigen overload’ for immune system, skewing the Yin and Yang response profiles and leading to induction of ‘mild’, ‘moderate’ or ‘severe’ immune disorders. Induction of decoy or pattern recognition receptors (e.g., PRRs), such as IRAK-M or IL-1dRs (‘designer’ molecules) and associated genomic instability and over-expression of growth promoting factors (e.g., pyruvate kinases, mTOR and PI3Ks, histamine, PGE2, VEGF) could lead to immune tolerance, facilitating cancer cells to hijack anabolic machinery of immunity (Yang) for their increased growth requirements. Expression of constituent embryonic factors would negatively regulate differentiation of tumor cells through epithelial–mesenchymal-transition and create “dual negative feedback loop” that influence tissue metabolism under hypoxic conditions. It is further hypothesized that induction of tolerance creates ‘dark energy’ and increased entropy and temperature in cancer microenvironment allowing disorderly cancer proliferation and mitosis along with increased glucose metabolism via Crabtree and Pasteur Effects, under mitophagy and ribophagy, conditions that are toxic to host survival. Effective translational medicine into treatment requires systematic and logical studies of complex interactions of tumor cells with host environment that dictate clinical outcomes. Promoting effective immunity (biological circadian rhythms) are fundamental steps in correcting host differential bioenergetics and controlling cancer growth, preventing or delaying onset of diseases and maintaining public health. The author urges independent professionals and policy makers to take a closer look at cancer dilemma and stop the ‘scientific/medical ponzi schemes’ of a powerful group that control a drug-dependent sick society before all hopes for promoting public health evaporate.

Diabetic Retinopathy and Metabolic Control

Retinopathy is probably the first long-term complication of diabetes mellitus to become clinically evident, possibly because the retina is the only microvascular bed that can be observed directly and repeatedly. This makes it a good model for studying the pathogenesis and natural history of diabetic microangiopathy. Most of the proposals to account for its pathogenesis invoke mechanisms that depend directly on the circulating and tissue levels of glucose: protein glycosylation, activation of the “polyol pathway”, abnormalities of vascular endothelium, altered capillary blood flow. Several population studies and clinical trials suggest that the degree of metabolic control maintained over the years influences the rates of appearance and progression of retinopathy. However, on an individual basis, factors independent of control may intervene, making some patients more or less prone to this complication. Animal models also suggest that the progression of retinopathy may become irreversible from its very early stages. From a clinical point of view, it is difficult to establish a satisfactory definition of “good” control and approaching it may increase the risk of dangerous hypoglycemia and weight gain. Diabetes and eye specialists are thus left to strive for the best possible, sensible, metabolic control but must also rely on early diagnosis and treatment for the sight-threatening complications of diabetes.

Effects of high glucose on AVP-induced hyperplasia, hypertrophy, and type IV collagen synthesis in cultured rat mesangial cells

INTRODUCTION

Hyperglycemia is a principal characteristic of diabetes and influences many cellular functions. Diabetic nephropathy is characterized by glomerular mesangial expansion which could result from increased mesangial cell extracellular matrix synthesis induced by hyperglycemia.

METHODS

To investigate whether the physiological functions of mesangial cells are altered in a diabetic environment, we evaluated the effect of high extracellular glucose concentration on thymidine/leucine incorporation, hyperplasia/hypertrophy, and type IV collagen synthesis, induced by vasopressin (AVP), in cultured rat mesangial cells.

RESULTS

The exposure of mesangial cells to a high glucose concentration (30 mM) significantly reduced AVP-induced thymidine incorporation and hyperplasia compared with normal glucose (10 mM). By contrast, treatment of mesangial cells with AVP in the presence of high extracellular glucose significantly increased leucine incorporation, hypertrophy, and type IV collagen synthesis compared with those at normal glucose levels. The administration of staurosporine, a protein kinase C inhibitor, reversed these effects of high-glucose conditions. Furthermore, the nonpeptide AVP V(1A) receptor-selective antagonists potently inhibited these AVP-induced physiological responses in mesangial cells cultured in high-glucose conditions.

CONCLUSIONS

These results demonstrate that high glucose suppresses mesangial cell proliferation but enhances hypertrophy and type IV collagen synthesis induced by AVP. This increased mesangial cell hypertrophy and extracellular matrix synthesis may play a crucial role in the glomerular mesangial expansion common to diabetic nephropathy.

Inflammation, aging, and cancer: tumoricidal versus tumorigenesis of immunity: a common denominator mapping chronic diseases

Acute inflammation is a highly regulated defense mechanism of immune system possessing two well-balanced and biologically opposing arms termed apoptosis ('Yin') and wound healing ('Yang') processes. Unresolved or chronic inflammation (oxidative stress) is perhaps the loss of balance between 'Yin' and 'Yang' that would induce co-expression of exaggerated or 'mismatched' apoptotic and wound healing factors in the microenvironment of tissues ('immune meltdown'). Unresolved inflammation could initiate the genesis of many age-associated chronic illnesses such as autoimmune and neurodegenerative diseases or tumors/cancers. In this perspective 'birds' eye' view of major interrelated co-morbidity risk factors that participate in biological shifts of growth-arresting ('tumoricidal') or growth-promoting ('tumorigenic') properties of immune cells and the genesis of chronic inflammatory diseases and cancer will be discussed. Persistent inflammation is perhaps a common denominator in the genesis of nearly all age-associated health problems or cancer. Future challenging opportunities for diagnosis, prevention, and/or therapy of chronic illnesses will require an integrated understanding and identification of developmental phases of inflammation-induced immune dysfunction and age-associated hormonal and physiological readjustments of organ systems. Designing suitable cohort studies to establish the oxido-redox status of adults may prove to be an effective strategy in assessing individual's health toward developing personal medicine for healthy aging.

Pharmacologic vitreolysis with plasmin and hyaluronidase in diabetic rats

OBJECTIVE

To evaluate the feasibility of inducing posterior vitreous detachment (PVD) with pharmacologic vitreolysis in diabetic rats.

METHODS

Forty diabetic rats were randomly divided into four groups and treated with different drugs by intravitreous injection respectively as follows: Group A: hyaluronidase (5 U); Group B: plasmin (0.25 U); Group C: hyaluronidase (5 U) plus plasmin (0.25 U); and Group D: balanced salt solution (2 microL). Ten normal rats in Group E were used as controls and were treated with hyaluronidase (5 U) plus plasmin (0.25 U). Clinical observation, visual electrophysiology tests (electroretinogram), transmission electron microscopy, and scanning electron microscopy were performed on the rats 1 week after the injection.

RESULTS

Scanning electron microscopy results showed that PVD did not occur at all with hyaluronidase alone (Group A, 0 of 10) and balanced salt solution alone (Group D, 0 of 10). Partial PVD was found in all eyes treated with plasmin alone (Group B, 10 of 10), whereas complete PVD was present in most but not all eyes treated with both hyaluronidase and plasmin (Group C, 8 of 10). All nondiabetic eyes treated with hyaluronidase and plasmin had total PVD (Group E, 10 of 10). No significant difference in electroretinogram was observed in each group before and after the injection (P < 0.05).

CONCLUSION

Hyaluronidase (5 U) alone is ineffective, whereas plasmin (0.25 U) alone induces partial PVD, a very dangerous state for the diabetic eye. Combination of hyaluronidase and plasmin can induce complete PVD in 12-week old diabetic rats. However, it is more difficult to induce PVD in diabetic rats than in healthy rats. No obvious toxic reaction was observed in each group.

The pathogenesis of myocardial fibrosis in the setting of diabetic cardiomyopathy

Diabetes has emerged as a major threat to worldwide health. The increasing incidence of diabetes in young individuals is particularly worrisome given that the disease is likely to evolve over a period of years. In 1972, the existence of a diabetic cardiomyopathy was proposed based on the experience with four adult diabetic patients who suffered from congestive heart failure in the absence of discernible coronary artery disease, valvular or congenital heart disease, hypertension, or alcoholism. The exact mechanisms underlying the disease are unknown; however, an important component of the pathological alterations observed in these hearts includes the accumulation of extracellular matrix (ECM) proteins, in particular collagens. The excess deposition of ECM in the heart mirrors what occurs in other organs such as the kidney and peritoneum of diabetics. Mechanisms responsible for these alterations may include the excess production, reduced degradation, and/or chemical modification of ECM proteins. These effects may be the result of direct or indirect actions of high glucose concentrations. This article reviews our state of knowledge on the effects that diabetes-like conditions exert on the cells responsible for ECM production as well as relevant experimental and clinical data.

Heparan sulfate proteoglycans in experimental models of diabetes: a role for perlecan in diabetes complications

Proteoglycans are ubiquitous extracellular proteins that serve a variety of functions throughout the organism. Unlike other glycoproteins, proteoglycans are classified based on the structure of the glycosaminoglycan carbohydrate chains, not the core proteins. Perlecan, a member of the heparan sulfate proteoglycan (HSPG) family, has been implicated in many complications of diabetes. Decreased levels of perlecan have been observed in the kidney and in other organs, both in patients with diabetes and in animal models. Perlecan has an important role in the maintenance of the glomerular filtration barrier. Decreased perlecan in the glomerular basement membrane has a central role in the development of diabetic albuminuria. The involvement of this proteoglycan in diabetic complications and the possible mechanisms underlying such a role have been addressed using a variety of models. Due to the importance of nephropathy among diabetic patients most of the studies conducted so far relate to diabetes effects on perlecan in different types of kidney cells. The various diabetic models used have provided information on some of the mechanisms underlying perlecan's role in diabetes as well as on possible factors affecting its regulation. However, many other aspects of perlecan metabolism still await full elucidation. The present review provides a description of the models that have been used to study HSPG and in particular perlecan metabolism in diabetes and some of the factors that have been found to be important in the regulation of perlecan.

Microvascular disease aetiology in diabetic foot ulceration

There is compelling evidence that diabetic microvascular disease involves foot tissues, but it is not known if this is enough to precipitate foot ulceration. This review explores the current evidence.

High glucose suppresses cathepsin activity in periodontal-ligament-derived fibroblastic cells

The accumulation of extracellular matrices and integrins by high glucose has been reported in relation to diabetic complications. We previously reported that PDL cells expressed a higher amount of VLA-5 when cultured in high-glucose (4500 mg/L) medium than those cultured in low-glucose (1100 mg/L) medium. In this study, we aimed to address (1) whether this effect was mediated by the transcriptional level of the gene or the degradative level of the protein, and (2) whether this effect was mediated by TGF-beta. The results indicated that the level of mRNA encoding alpha5 integrin did not change in PDL cells regardless of the concentration of glucose. Alternatively, high glucose suppressed cathepsin B+L activity. Additionally, the level of mRNA encoding TGF-beta was not affected by high glucose, nor did an anti-TGF-beta neutralizing antibody have an effect on the expression of beta5 gene or cathepsin activity. Therefore, the effects of high glucose appeared to be mediated by impaired protein degradation, but not by autocrine TGF-beta.

Modulation of sarcomere organization during embryonic stem cell-derived cardiomyocyte differentiation

Myofibrillogenesis - sarcomeres - mouse embryonic stem cells - cardiomyocytes - beta1 integrin Mouse embryonic stem (ES) cells, when cultivated as embryoid bodies, differentiate in vitro into cardiomyocytes of ventricle-, atrium- and pacemaker-like cell types characterized by developmentally controlled expression of cardiac-specific genes, structural proteins and ion channels. Using this model system, we show here, (I) that during cardiac myofibrillogenesis sarcomeric proteins are organized in a developmentally regulated manner following the order: titin (Z-disk), alpha-actinin, myomesin, titin (M-band), myosin heavy chain, alpha-actin, cardiac troponin T and M-protein, recapitulating the sarcomeric organization in the chicken embryonal heart in vivo. Our data support the view that the formation of I-Z-I complexes is developmentally delayed with respect to A-band assembly. We show (2) that the process of cardiogenic differentiation in vitro is influenced by medium components: Using a culture medium supplemented with glucose, amino acids, vitamins and selenium ions, we were able to increase the efficiency of cardiac differentiation of wild-type, as well as of beta1 integrin-deficient (beta1-/-) ES cells, and to improve the degree of organization of sarcomeric structures in wild-type and in beta1-/- cardiac cells. The data demonstrate the plasticity of cardiogenesis during the differentiation of wild-type and of genetically modified ES cells.

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.

Periodontal disease as a complication of diabetes mellitus

Based on our clinical observations that patients with insulin-dependent diabetes mellitus (IDDM) are subject to periodontal disease, we developed the hypothesis that hyper- or hypoglycemia might contribute to the pathogenesis of diabetic periodontitis. In this article, experimental facts that substantiate this hypothesis are presented on the basis of our studies and then discussed. Hyperglycemia progressively glycates body proteins, forming advanced glycation end products (AGE), which stimulate phagocytes to release inflammatory cytokines such as TNF-alpha and IL-6. In this context, to understand the effects of hyperglycemic episodes on periodontal health, 24 adolescent IDDM patients were examined for their periodontal status, and 3 of them were found to have periodontitis. Laboratory analyses on these 3 patients revealed that 2 had elevated serum TNF-alpha levels. These results may partly support the current hypothesis of a mechanism of diabetic complications in which abnormal cytokine levels induced by AGE could exacerbate inflammatory responses. In IDDM patients, the diabetes is often accompanied not only by hyperglycemic episodes but also by iatrogenic hypoglycemia. Periodontal ligament cells (PDL) cultured under hyperglycemic conditions were impaired in such biological functions as adhesion and motility, while cells cultured under hypoglycemic conditions (10 mg/dL) gradually dissociated from their anchor and underwent cell death. These phenomena correlated well with the expression profile of fibronectin receptor. Interestingly, these changes due to the different glucose levels were observed more intensively in PDL than in other fibroblastic cells, suggesting that the biological functions of PDL are easily led to impairment by variation or rapid fluctuation of glucose levels. These observations suggest that hyperglycemia could indirectly exacerbate inflammatory tissue destruction through the body's scavenger system against AGE, and that both hyper- and hypoglycemia might directly impair the biological functions of periodontal connective tissues through cell-matrix interactions.

Glucose-mediated alteration of cellular function in human periodontal ligament cells

Because diabetic patients are easily led to manifest severe periodontitis, we wanted to determine whether various glucose levels interfere with normal cellular function. Human periodontal ligament (PDL) cells were cultured in glucose-free medium, or in medium containing either 1100 mg/L of glucose (normal-glucose medium) or 4500 mg/L of glucose (high-glucose medium). Cells cultured in glucose-free medium changed their morphology from spindle-shaped to round, and incorporated trypan blue in a time-dependent manner. The incorporation rate was much faster in cells with shorter cell cycles than in those with longer cycles, suggesting the involvement of cell-cycle progression in cell death. However, fragmented DNA, which suggests apoptotic cell death, was not observed in these cells. We reasoned that initial cell rounding and detachment from the culture plate might be due to the conformational changes in cell-surface receptors to fibronectin, a major extracellular matrix for fibroblasts. Western blot analysis revealed that cells cultured in glucose-free medium lost their fibronectin receptor in a time-dependent manner. In addition, fibronectin receptor expression was much higher in cells cultured in high-glucose medium than in cells cultured in normal-glucose medium. Furthermore, the over-expression of the fibronectin receptor resulted in a suppressed chemotactic response of these cells to platelet-derived growth factor. On the basis of these data, it was hypothesized that a high glucose level induced over-expression of these receptors. This might be the mechanism by which a high glucose level compromises wound healing in diabetic patients and, at least in part, might be the reason diabetic patients are subject to severe periodontal destruction.

Cultured retinal capillary pericytes die by apoptosis after an abrupt fluctuation from high to low glucose levels: a comparative study with retinal capillary endothelial cells

A number of clinical observations concerning cases of glycemic fluctuation have prompted us to study whether or not a rapid change in blood glucose concentration can aggravate retinal microvascular pathology during the early stage of diabetic retinopathy. We conducted a comparative study of retinal capillary pericytes and endothelial cells in vitro. Both types of cells, either in single culture or in co-culture, were initially incubated in medium with high glucose (20-40 mmol/l), followed by a rapid reduction of glucose to 3.5, 1, or 0.5 mmol/1. This type of reduction of extracellular glucose resulted in depletion of intracellular glucose, occurring much faster in pericytes than in endothelial cells. The abrupt reduction in glucose caused pericyte cell shrinkage and nuclear condensation associated with DNA fragmentation, followed by loss of cell viability. All of these pericyte changes are apoptosis-like characteristics. This apoptotic process was prevented by the addition of cycloheximide, a protein synthesis inhibitor, or by platelet-derived growth factor BB, which is known competent factor for pericyte growth. In analysis of signalling pathways during the abrupt fluctuation of glucose, the occurrence of pericyte apoptosis was an intracellular calcium-dependent, protein kinase C and protein kinase A mediated, and poly (ADP-ribose) synthetase-dependent process. Interestingly, a larger degree of DNA fragmentation was observed with a higher magnitude and a longer duration of pre-existing hyperglycaemia. These results suggest that the magnitude and duration of pre-existing hyperglycaemia prime the apoptotic responsiveness of pericytes. Retinal capillary endothelial cells, after an identical glucose fluctuation treatment did not undergo an apoptotic process.

Increased peritoneal permeability to albumin in streptozotocin diabetic rats

The mechanism behind the increased peritoneal permeability to albumin in diabetics is still unclear. In this study, streptozotocin diabetic rats developed albuminuria and significantly increased D/P of albumin after the fourth week of disease, reaching peak levels at the end of the 24 week period of follow-up. Coincidentally, extravasation of albumin to the interstitial tissue was evaluated with the Evans-blue method. Age-matched control rats showed Evans-blue concentrations of 0.023 +/- 0.013 micrograms/100 mg of dry tissue, whereas in diabetics the numbers were 1.22 +/- 0.719 micrograms (P < 0.001). Perfusion with Ruthenium-Red (RR) done in control at zero time, and in age-matched intact as well as in diabetic rats after 24 weeks of disease showed that the density distribution of capillary subendothelial anionic sites was significantly lower for diabetics (13 +/- 3/microns basement membrane vs. 31 +/- 3 and 34 +/- 4 in control groups; P < 0.001). Similar findings were made on the mesenteric submesothelial basement membrane. Mean density of RR decorated anionic sites was 12 +/- 2/microns basement membrane in diabetics, whereas those observed in both control groups were 31 +/- 2 and 31 +/- 3/microns (P < 0.001). Therefore, this reduced density of microvascular and submesothelial negative charges, equivalent to that induced by diabetes in other capillary beds, appears to be at the origin of the decreased permselectivity of the diabetic peritoneum for anionic serum albumin.

Preparation and characterization of glucosylated aminoglycerophospholipids

Natural aminophospholipids were isolated from egg yolk and from human red blood cells. Glucosylated ethanolamine and serine phosphatides were prepared by exposing synthetic and natural aminophospholipids to glucose for 3-18 h at pH 7.4. The glucosylation products were resolved from parent phospholipids by normal-phase high-performance liquid chromatography and were identified by on-line mass spectrometry with an electrospray interface. The soft ionization method allowed us to detect the glucosylation products as molecular ions of the Schiff bases. The Schiff bases could be stabilized by sodium cyanoborohydride reduction. The molecular species of the ethanolamine and serine phosphatides reacted in proportion to their molar concentration in the mixtures. The yields of the glucosylation products varied with time of reaction and the concentration of glucose in the medium. At 50 mM glucose and 0.6 mg/mL phosphatidylethanolamine, 20% of the aminophospholipid was glycated in 18 h at 37 degrees C.

Comparative study of high-glucose effect on phosphatidylcholine hydrolysis of cultured retinal capillary pericytes and endothelial cells

Recent studies have suggested the importance of phosphatidylcholine (PC) hydrolysis in the control of cell growth. Because of the different replicative behavior between retinal pericytes and endothelial cells in early diabetic retinopathy, we have compared PC metabolism of these two types of cells under high-glucose conditions. Both types of cells growing in controlled glucose conditions were prelabeled with [32P]P(i) for testing phosphatidylethanol (PEt), a unique product of PC-specific phospholipase D, with [14C]glycerol for determining 1,2-diacylglycerol (DAG) de novo synthesis and labeled with selective fatty acids for PC-derived and phosphoinositide (PI)-derived DAG. The prelabeled cells were stimulated with ATP, a purinergic agonist. Analyses of products of PI and PC hydrolysis were carried out by TLC and/or HPLC. In both types of cells, ATP activated PI and PC hydrolysis. The dose and time dependencies of IP3 and PI-derived DAG formation with respect to ATP were essentially identical. When the level of IP3 and PI-derived DAG returned toward the baseline, a second increase in DAG mainly derived from PC occurred, lasting at least 1 h. High glucose altered DAG kinetics: in pericytes it suppressed both PI- and PC-derived DAG formation; in endothelial cells it stimulated the PC-derived DAG increase, but kept the PI-derived DAG unchanged. DAG de novo synthesis was stimulated in endothelial cells growing in high glucose, but was left unchanged in pericytes. Contrast to endothelial cells, in pericytes, subsequent mitogenic process may be negatively regulated by the inhibitory effects of high glucose on PI and PC hydrolysis, resulting in reduced levels of PC-derived DAG.

Identification of multiple genes in bovine retinal pericytes altered by exposure to elevated levels of glucose by using mRNA differential display

Loss of capillary pericytes, a characteristic finding in diabetic retinopathy, is strongly associated with hyperglycemia. The pathologic aberrations associated with diabetic retinopathy are localized primarily in the retinal capillaries and are only poorly reversed by subsequent euglycemic control. Since hyperglycemia significantly inhibits pericyte growth in culture, we investigated the regulation of gene expression in retinal pericytes exposed to physiologic (5.5mM) and pathologic (20 mM) glucose concentrations. By utilizing modifications of the mRNA differential display technique, over 14,000 mRNA species were screened, and 35 candidate clones were obtained. Partial DNA sequence demonstrated that 25 of these were distinct genes, including 7 known, 16 previously unreported, and 2 sequences with known homologues. Northern blot analysis demonstrated altered gene expression in 10 (40%), undetectable signals in 12 (48%), and nonregulation in 3 (12%). Genes with glucose-regulated expression included those encoding fibronectin (51% +/- 15%, P = 0.003; mean percentage of control +/- SD), caldesmon (68% +/- 18%; P = 0.026), two ribosomal proteins (201% +/- 72%, P = 0.011; 136% +/- 16%, P = 0.036), Rieske FeS reductase (66% +/- 17%; P = 0.029), three previously unreported sequences (57%, 167%, 271%), and molecules homologous to autoantigens (213%) and tyrosine kinases (down 16- to 33-fold). Caldesmon protein concentrations in pericytes and smooth muscle cells demonstrated decreases by Western blot analysis concordant with mRNA levels. These studies identify genes whose expression is significantly altered after 7 days of exposure to elevated glucose levels and provide new targets for understanding the adverse effects of hyperglycemia on vascular cells. In addition, this study provides strong support for the use of differential mRNA display as a method to rapidly isolate differentially expressed genes in metabolic systems.

Altered endothelin-1 induced contraction and second messenger generation in bovine retinal microvascular pericytes cultured in high glucose medium

The effect of simulated hyperglycaemia on bovine retinal pericytes was studied following culture of these cells for 10 days under normal (5 mmol/l) and elevated (25 mmol/l) glucose conditions in the absence of endothelial cells. Pericytes cultured under high ambient glucose exhibited both a delayed and reduced contractile response following stimulation with endothelin-1. Stimulation with 10(-7) mol/l endothelin-1 for 30 s caused significant contraction in cells grown in both 5 mmol/l and 25 mmol/l glucose. The former also contracted significantly with 10(-8) mol/l endothelin-1. Further, at all concentrations tested, statistical comparison of the time course of contraction showed a significant difference (p < 0.02) in the reduction of planimetric surface area between the two cell groups. Since neither binding of endothelin-1 nor the number of receptors for this peptide were significantly different (p > 0.1) between bovine retinal pericytes grown for 10 days under normo- or hyperglycaemic conditions, it became apparent that the altered contractility in bovine retinal pericytes following culture in high glucose must be due to post-binding intracellular disturbance(s). Indeed, both basal and 15 s post-stimulation with 10(-8) mol/l endothelin-1, levels of inositol trisphosphate were significantly reduced (p < 0.05 and p < 0.02, respectively) in pericytes cultured for 10 days in 25 mmol/l glucose. These results show that endothelial-independent alterations in contractility of pericytes occur when they are grown in conditions which simulate hyperglycaemia. The results also suggest that the observed attenuation in response to endothelin-1 stimulation evident in pericytes grown under simulated hyperglycaemic conditions is not due to alterations in peptide binding.

Integrin overexpression induced by high glucose and by human diabetes: potential pathway to cell dysfunction in diabetic microangiopathy

The nature of the process leading to the acellular nonperfused capillaries of diabetic microangiopathy remains unknown. Because these capillaries manifest thickened basement membranes, we asked whether the process causing deposition of excess extracellular matrix in diabetes modifies cell-matrix interactions in a direction that would compromise cell renewal. In 44 individual isolates of human umbilical vein endothelial cells we observed that high glucose concentrations (30 mM) induce coordinate increases in the levels of mRNAs encoding fibronectin and the fibronectin-specific integrin receptor alpha 5 beta 1 as well as in the cognate proteins. Expression of the integrin subunit alpha 3, component of the alpha 3 beta 1 polyspecific receptor for fibronectin, laminin, and collagen, was also up-regulated by high glucose. Overexpression of integrins correlated with increased cell attachment to exogenous fibronectin and laminin as well as to complex matrix. Moreover, cells exhibited firmer steady-state adhesion to their own matrix. To correlate these in vitro observations with events in human diabetic retinopathy we measured integrin levels in retinal trypsin digests prepared from 10 patients with 8.2 +/- 1.6 (mean +/- SE) years of diabetes and 10 age- and sex-matched nondiabetic controls. Microvessels of diabetic patients showed increased immunostaining for beta 1 integrin (P = 0.025) when compared with control microvessels. These data show that high glucose and diabetes increase integrin expression and thus alter the interaction of vascular endothelial cells with their basement membranes in the direction of firmer cell-matrix adhesion. This could compromise the migration and replication critical to the reendothelialization process and contribute to microvascular occlusion.

The role of endothelium in the pathogenesis of diabetic microangiopathy

Damage caused to the vessel wall by diverse mechanisms may lead to diabetic microangiopathy. Consequently, research work is more and more focusing on the pathophysiology of vascular cells, with particular emphasis on endothelium. This paper reviews the present knowledge on the alterations of small vessel endothelium in diabetes. The most important risk factors for diabetic microangiopathy are the duration of disease and the degree of metabolic control maintained throughout the years. However, genetic factors may also contribute. These are examined first, followed by the presumed roles played by increased protein glycation and the production of Advanced Glycosylation End Products, the "polyol pathway" and free radical generation. Endothelium is a widespread, extremely active organ which regulates complex physiologic functions and its structure and function are discussed in the second section of this review. The third part deals with how diabetes can affect endothelium and describes observations on endothelial metabolism in vitro as well as morphologic and functional alterations in the patients. Unfortunately, the mechanisms leading to progressive degeneration of the microcirculation and organ damage in diabetic patients remain largely unaccounted for.

Pericyte mitogenic activity is reduced in the blood of type 1 diabetic patients with and without retinopathy

Selective loss of capillary pericytes occurs early and specifically in diabetic retinopathy. We have investigated whether blood derivatives from patients with long-term type 1 (insulin-dependent) diabetes and no retinopathy differ from those with retinopathy and/or non-diabetic controls in their ability to stimulate DNA synthesis in cultured bovine retinal pericytes and endothelial cells. As a general trend, whole blood serum, platelet-rich plasma and platelet-free plasma from patients without and with retinopathy stimulated thymidine incorporation in both cell types less than derivatives from controls. Serum, 0.1% v/v final concentration in culture medium, from patients without retinopathy was less active (114.5 +/- 24.5% of a standard stimulus produced by 0.1% fetal calf serum) than that from patients with the complication (132.6 +/- 20.8%, P = 0.003) and both were less potent than control sera (143.6 +/- 28.0%, P < 0.001 and P = 0.013, respectively). Lack of support from circulating factor(s) may contribute to the disappearance of pericytes from the capillary wall in diabetes but further investigations are necessary to clarify the mechanisms that prevent the development of microangiopathy in some patients.

A study of the effects of human blood derivatives and individual growth factors on [3H]thymidine uptake in bovine retinal pericytes and endothelial cells

Pericytes disappear early, selectively and specifically from retinal capillaries in diabetic microangiopathy, but little is known of their growth and turnover in health and disease. We have studied the effects of human blood derivatives and of a panel of individual growth factors on [3H]thymidine incorporation in bovine retinal pericytes and endothelial cells. Human serum and platelet-rich plasma stimulated incorporation of the nucleotide in a dose-dependent manner in both cell types, and did so more potently than platelet-free plasma. Consistent and significant stimulation of DNA synthesis in pericytes was observed with basic fibroblast growth factor (ED50 = 1.8 x 10(-13) mol/l), acidic fibroblast growth factor (7.4 x 10(-12) mol/l), insulin-like growth factor 1 (8.6 x 10(-10) mol/l), insulin (158 microU/ml) and endothelin-1 (6.1 x 10(-10) mol/l). Transforming growth factor beta 1 inhibited DNA synthesis (ID50 = 3.6 x 10(-10) mol/l) and so did heparin (1.4 x 10(-6) mol/l) and low molecular weight heparin (2.9 x 10(-6) mol/l). Retinal endothelial cells were stimulated by basic fibroblast growth factor (3.2 x 10(-13) mol/l) and acidic fibroblast growth factor (1.3 x 10(-9) mol/l), and inhibited by transforming growth factor beta 1 (1.6 x 10(-12) mol/l). Neither cell type was stimulated by platelet-derived growth factor (A + B chain heterodimer), epidermal growth factor, growth hormone, or nerve growth factor (7S complex). The characteristics and active concentrations of the above growth factors suggest that none is solely responsible for the pericyte mitogenic activity of platelets, serum or plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential growth of brain and retinal bovine pericytes

Within the central nervous system, pericyte degeneration in diabetes mellitus occurs only in the retinal microcirculation and is not seen in the brain. This study sought to elucidate differences between bovine retinal and brain pericytes. When pairs of retinal and brain pericytes from individual calves were cultured in vitro, the morphological organisation of early post-confluent retinal pericyte cultures was consistently different from that of brain pericyte cultures. When retinal and brain pericyte cultures were grown to second passage in high or normal glucose medium supplemented with fetal calf serum, brain pericyte cultures grew significantly faster than retinal pericytes in either medium (p less than 0.0001). Brain pericytes thus appeared to grow intrinsically faster than retinal pericytes and this effect was largely independent of glucose concentration. Brain pericytes also grew faster than retinal pericytes in high glucose medium containing human diabetic or control serum (p less than 0.002). The proliferative effect of serum from diabetic patients with non-proliferative diabetic retinopathy on pericytes grown in high glucose medium was not significantly different from that of control serum. Both brain and retinal pericytes showed variation in their ability to replicate in high concentrations of glucose. The selectivity of pericyte degeneration to the retinal circulation does not appear to be due to changes in the mitogenic activity of diabetic serum for retinal pericytes, but may relate to the intrinsic relative inability of the retinal pericyte to reproliferate in response to the metabolic injury of diabetes mellitus.

Capillary pericytes: perspectives and future trends

A complete understanding of the microcirculation requires full knowledge of the structure and function of each of the constituent cells, including pericytes. Vascular endothelium and smooth muscle cells have been investigated intensively during the last two decades, but much less is known about the metabolism and function of capillary pericytes. However, the development of new electron microscopy techniques and the application of new cell culture and molecular biology techniques should allow for the rapid elucidation of the cellular biochemistry and the microvascular function and pathology of this ubiquitous capillary cell.

Anionic sites in diabetic basement membranes and their possible role in diffusion barrier abnormalities in the BB-rat

Basement membrane anionic sites, thought to be responsible for charge selective permeability barriers, were investigated in retinal, endoneurial, and muscle capillary basement membranes and in Bruch's membrane of diabetic, and age- and sex-matched non-diabetic BB-rats using an ultrastructural quantitative histochemical technique. Six months of diabetes was associated with significant basement membrane thickening which was linearly related to a decrease in anionic site density suggesting a relative loss of proteoglycans. Calculation of anionic sites per unit length of basement membrane, reflecting their absolute number, revealed a significant loss in basement membrane, constituting part of normal blood-tissue barrier systems such as retinal and endoneurial capillary basement membranes, and the basement membrane of the retinal pigment epithelium. The absolute number of anionic sites in normally permeable microvessels, such as those of muscle and choriocapillaries, was unaltered by diabetes. We conclude that this specific loss of anionic sites in basement membranes of tissues affected by chronic diabetic complications may in part be responsible for permeability abnormalities seen in these tissues.

Development of the conducting airway epithelium in fetal Syrian golden hamsters during normal and diabetic pregnancies

The conducting airway epithelium of fetal Syrian golden hamsters was studied from gestational day 12 to day 15, during normal and uncontrolled diabetic pregnancies. Diabetes was induced in the pregnant hamsters by injecting streptozotocin at 60 mg/kg body weight, subcutaneously, early on gestational day 10. Cells in S-phase were labelled immunochemically with bromodeoxyuridine (BrdU), and the day on which endocrine cells and ciliated cells first appeared was determined. In control fetuses, the BrdU-labelling indices (LI's) of different anatomical airway levels were significantly different from one gestational day to the next. For example, the LI of the lobar bronchus was significantly different on each gestational day (P less than .0001), and the same was true of the bronchioles. Moreover, the difference between LI's of the lobar bronchus and bronchioles-terminal buds was highly significant on day 12 (P less than .0001), and on day 13 the differences between lobar bronchus and bronchioles, lobar bronchus and terminal buds, and bronchioles and terminal buds were also highly significant (P less than .0001). However, on gestational days 14 and 15, the LI's were reduced and were comparable at different airway levels. The BrdU-labelling indices were very consistent among fetuses of the same age, and the differences between the average LI's for pups of different litters was numerically very small. Hyperglycemia (mild, moderate, severe) did not alter LI's in the fetal airway epithelial cells. Furthermore, although glycogen was not depleted from the airway epithelium of the hyperglycemic fetuses as it was in the controls, the endocrine cells first appeared on gestational days 12, 13, and 14, respectively, in the trachea, lobar bronchus and bronchioles, followed 1 day later by the ciliated cells, in the fetuses of control and diabetic mothers. In our experimental model, induction of diabetes in the pregnant hamsters on gestational day 10 did not appear to alter development or differentiation of the fetal conducting airway epithelium.

Differential regulation of protein kinase C and (Na,K)-adenosine triphosphatase activities by elevated glucose levels in retinal capillary endothelial cells

Elevated cellular sorbitol levels resulting from conversion of increased glucose by aldose reductase might deplete cellular myoinositol content, which could then lower inositol phosphates (InsPs) and diacylglycerol levels, key regulators of protein kinase C (PKC). Secondary to altered PKC activity, other cellular enzymes such as (Na,K)-ATPase could be affected. To test this hypothesis we examined the association between PKC activity, (Na,K)-ATPase activity, and sorbitol, myoinositol, and InsP levels in cultured bovine retinal capillary endothelial cells, a cell type prominently involved in diabetic retinopathy. Elevating glucose concentration in culture media from 100 to 400 mg/dl led to a 100% increase in sorbitol levels, which could be inhibited completely by sorbinil, an aldose reductase inhibitor. In contrast, no changes were observed in myoinositol or InsP levels. Subfractionated PKC activities showed a 100% increase in the membranous pool with a parallel decrease in the cytosolic fraction. Adding sorbinil did not affect PKC activity, whereas the PKC agonist, phorbol myristate acetate (PMA), stimulated translocation of PKC. Ouabain-inhibitable (Na,K)-ATPase activity was decreased 70% by elevated glucose levels. This decrease could be prevented by adding either PMA or sorbinil. Thus, in retinal capillary endothelial cells elevated glucose concentration can affect PKC and (Na,K)-ATPase activities, probably via different mechanisms.

Non-competitive inhibition of myo-inositol transport in cultured bovine retinal capillary pericytes by glucose and reversal by Sorbinil

myo-Inositol transport by retinal capillary pericytes in culture was characterized. The major myo-inositol transport process was sodium-dependent, ouabain-sensitive, and saturable at 40 mM, indicating a carrier-mediated process. The sodium ion concentration required to produce one-half the maximal rate of myo-inositol uptake ([Na+]0.5) did not show dependence on the external myo-inositol concentration (22.3 mM sodium for 0.005 mM myo-inositol; 18.2 mM sodium for 0.05 mM myo-inositol). myo-Inositol transport was an energy-dependent, active process functioning against a myo-inositol concentration gradient. The kinetics of the sodium-dependent system fitted a 'velocity type' co-transport model where binding of sodium ion to the carrier increased the velocity (Vmax 28 to 313 pmol myo-inositol/micrograms DNA per 20 min when [Na+] varied from 9 to 150 mM) but not the affinity for myo-inositol (Km 0.92 to 0.83 mM when [Na+] varied from 9 to 150 mM). Metabolizable hexoses (D-glucose or D-galactose; greater than 5 mM) inhibited myo-inositol uptake. Dixon-plot analysis indicated that the inhibition was non-competitive with a Ki of 22.7 mM for D-glucose and 72.6 mM for D-galactose. The inhibition was significantly reversed by Sorbinil (0.1 mM), an aldose reductase inhibitor. In contrast, high concentrations of non-metabolizable hexoses (L-glucose, 3-O-methyl-D-glucose), or partially metabolizable 2-deoxy-D-glucose, did not significantly inhibit myo-inositol uptake. The inhibitory effect of D-glucose or D-galactose on myo-inositol transport appeared to be related to glucose or galactose metabolism via the polyol pathway.

Characterization of glucose transport by bovine retinal capillary pericytes in culture

The transport of D-glucose and its non-metabolizable analog, 3-o-methyl-D-glucose (3-o-MG), by cultured bovine retinal capillary pericytes was characterized. A preference for D-glucose over L-glucose uptake by pericytes indicated a stereospecific process. The 3-o-MG transport appeared to follow complex kinetics. At low substrate concentrations, 3-o-MG transport had an apparent Km of 1.53 mM and a Vmax of 0.50 nmol (microgram DNA)-1 min-1 at 37 degrees C. A reduced extracellular sodium concentration, energy poisons, and exogenous insulin did not significantly influence 3-o-MG uptake. Inhibition of the uptake or efflux of 3-o-MG by cytochalasin B or phloretin, respectively, and the demonstration of a 'counter transport' phenomenon showed that 3-o-MG transport by retinal capillary pericytes in culture was a carrier-mediated process.

The effects of glucose and an aldose reductase inhibitor on the sorbitol content and collagen synthesis of bovine retinal capillary pericytes in culture

The absolute rate of collagen synthesis by cultured bovine retinal capillary pericytes, determined using the specific radioactivity of proline in the cellular amino acid pool, was compared in media containing different concentrations of glucose (5, 10 or 40 mM) and Sorbinil (0.0 or 0.1 mM), an inhibitor of aldose reductase. The absolute rate of collagen synthesis, in proline molar terms, by pericytes in medium with 5 mM glucose was 3.3 +/- 1.9 (S.D.) pmol 10(-7) cells 24 hr-1, and increased significantly to 8.8 +/- 3.7 pmol 10(-7) cells 24 hr-1 when the glucose concentration was increased to 40 mM. Sorbinil (0.1 mM) reduced the elevated sorbitol contents of pericytes induced by high concentrations of glucose, but did not significantly change the absolute rate of collagen synthesis per cell.