Angiotensin II activation of insulin-like growth factor 1 receptor transcription is mediated by a tyrosine kinase-dependent redox-sensitive mechanism

Dysfunction of retinal neurons and glia during diabetes

Diabetic retinopathy is the leading cause of blindness in those of working age. It is well known that the retinal vasculature is altered during diabetes. More recently, it has emerged that neuronal and glial dysfunction occurs in those with diabetes. Current research is directed at understanding these neuronal and glial changes because they may be an early manifestation of disease processes that ultimately lead to vascular abnormality. This review will highlight the recent advances in our understanding of the neuronal and glial changes that occur during diabetes.

IGFBP-4 and PAPP-A in normal physiology and disease

Insulin-like growth factor (IGF) binding protein-4 (IGFBP-4) is a modulator of the IGF system, exerting both inhibitory and stimulatory effects on IGF-induced cellular growth. IGFBP-4 is the principal substrate for the enzyme pregnancy-associated plasma protein-A (PAPP-A). Through IGF-dependent cleavage of IGFBP-4 in the vicinity of the IGF receptor, PAPP-A is able to increase IGF bioavailability and stimulate IGF-mediated growth. Recently, the stanniocalcins (STCs) were identified as novel inhibitors of PAPP-A proteolytic activity, hereby adding additional members to the seemingly endless list of proteins belonging to the IGF family. Our understanding of these proteins has advanced throughout recent years, and there is evidence to suggest that the role of IGFBP-4 and PAPP-A in defining the relationship between total IGF and IGF bioactivity can be linked to a number of pathological conditions. This review provides an overview of the experimental and clinical findings on the IGFBP-4/PAPP-A/STC axis as a regulator of IGF activity and examines the conundrum surrounding extrapolation of circulating concentrations to tissue action of these proteins. The primary focus will be on the biological significance of IGFBP-4 and PAPP-A in normal physiology and in pathophysiology with emphasis on metabolic disorders, cardiovascular diseases, and cancer. Finally, the review assesses current new trajectories of IGFBP-4 and PAPP-A research.

Thalamic dopaminergic neurons projects to the paraventricular nucleus-rostral ventrolateral medulla/C1 neural circuit

Paraventricular nuclei (PVN) projections to the rostral ventrolateral medulla (RVLM)/C1 catecholaminergic neuron group constitute the pre-autonomic sympathetic center involved in the neural control of systemic cardiovascular function. However, the role of extra-hypothalamic and thalamic dopaminergic (DA) inputs in this circuit remains underexplored. Using retrograde neuroanatomical tracing and high contrast confocal imaging methods, we investigated the projections and morphology of the discrete thalamic DA neuron groups in the dorsal hypothalamic area and their contribution to the PVN-RVLM neural circuit. We found that DA neuron subgroups in the Zona Incerta (Zi; 60%) and Reuniens thalamic nuclei (Re; 40%) were labeled comparably to the PVN (85%) after a retrograde tracer was injected into the RVLM/C1 (P < 0.01 mean ± SEM). The Re/Zi DA neuron subgroups were characterized by angulated cell bodies, superiomedial and inferiomedial projections reaching the contralateral Re/Zi and ipsilateral PVN DA neurons respectively. Ultimately, we deduced that the DA projections of the Re/Zi to the PVN contribute to the PVN-RVLM/C1 neural circuit. As a result of these connections, the Re/Zi DA neuron groups may regulate preautonomic sympathetic events associated with the PVN-RVLM pathway. Anat Rec, 300:1307-1314, 2017. © 2016 Wiley Periodicals, Inc.

A Brief Introduction into the Renin-Angiotensin-Aldosterone System: New and Old Techniques

The renin-angiotensin-aldosterone system (RAAS) is a complex system of enzymes, receptors, and peptides that help to control blood pressure and fluid homeostasis. Techniques in studying the RAAS can be difficult due to such factors as peptide/enzyme stability and receptor localization. This paper gives a brief account of the different components of the RAAS and current methods in measuring each component. There is also a discussion of different methods in measuring stem and immune cells by flow cytometry, hypertension, atherosclerosis, oxidative stress, energy balance, and other RAAS-activated phenotypes. While studies on the RAAS have been performed for over 100 years, new techniques have allowed scientists to come up with new insights into this system. These techniques are detailed in this Methods in Molecular Biology Series and give students new to studying the RAAS the proper controls and technical details needed to perform each procedure.

NADPH oxidases: key modulators in aging and age-related cardiovascular diseases?

Reactive oxygen species (ROS) and oxidative stress have long been linked to aging and diseases prominent in the elderly such as hypertension, atherosclerosis, diabetes and atrial fibrillation (AF). NADPH oxidases (Nox) are a major source of ROS in the vasculature and are key players in mediating redox signalling under physiological and pathophysiological conditions. In this review, we focus on the Nox-mediated ROS signalling pathways involved in the regulation of 'longevity genes' and recapitulate their role in age-associated vascular changes and in the development of age-related cardiovascular diseases (CVDs). This review is predicated on burgeoning knowledge that Nox-derived ROS propagate tightly regulated yet varied signalling pathways, which, at the cellular level, may lead to diminished repair, the aging process and predisposition to CVDs. In addition, we briefly describe emerging Nox therapies and their potential in improving the health of the elderly population.

Exogenous administration of thiosulfate, a donor of hydrogen sulfide, attenuates angiotensin II-induced hypertensive heart disease in rats

BACKGROUND AND PURPOSE

Hypertension is an important mediator of cardiac damage and remodelling. Hydrogen sulfide (H2S) is an endogenously produced gasotransmitter with cardioprotective properties. However, it is not yet in clinical use. We, therefore, investigated the protective effects of sodium thiosulfate (STS), a clinically applicable H2 S donor substance, in angiotensin II (Ang II)-induced hypertensive cardiac disease in rats.

EXPERIMENTAL APPROACH

Male Sprague Dawley rats were infused with Ang II (435 ng kg min(-1)) or saline (control) for 3 weeks via s.c. placed osmotic minipumps. During these 3 weeks, rats received i.p. injections of either STS, NaHS or vehicle (0.9% NaCl).

KEY RESULTS

Compared with controls, Ang II infusion caused an increase in systolic and diastolic BP with associated cardiac damage as evidenced by cardiac hypertrophy, an increase in atrial natriuretic peptide (ANP) mRNA, cardiac fibrosis and increased oxidative stress. Treatment with NaHS and STS prevented the development of hypertension and the increase in ANP mRNA levels. Furthermore, the degree of cardiac hypertrophy, the extent of histological fibrosis in combination with the expression of profibrotic genes and the levels of oxidative stress were all significantly decreased.

CONCLUSIONS AND IMPLICATIONS

Ang II-induced hypertensive cardiac disease can be attenuated by treatment with STS and NaHS. Although BP regulation is the most plausible mechanism of cardiac protection, the antifibrotic and antioxidant properties of released sulfide may also contribute to their effects. Our data show that H2 S might be a valuable addition to the already existing antihypertensive and cardioprotective therapies.

Angiotensin II blockade: how its molecular targets may signal to mitochondria and slow aging. Coincidences with calorie restriction and mTOR inhibition

Caloric restriction (CR), renin angiotensin system blockade (RAS-bl), and rapamycin-mediated mechanistic target of rapamycin (mTOR) inhibition increase survival and retard aging across species. Previously, we have summarized CR and RAS-bl's converging effects, and the mitochondrial function changes associated with their physiological benefits. mTOR inhibition and enhanced sirtuin and KLOTHO signaling contribute to the benefits of CR in aging. mTORC1/mTORC2 complexes contribute to cell growth and metabolic regulation. Prolonged mTORC1 activation may lead to age-related disease progression; thus, rapamycin-mediated mTOR inhibition and CR may extend lifespan and retard aging through mTORC1 interference. Sirtuins by deacetylating histone and transcription-related proteins modulate signaling and survival pathways and mitochondrial functioning. CR regulates several mammalian sirtuins favoring their role in aging regulation. KLOTHO/fibroblast growth factor 23 (FGF23) contribute to control Ca(2+), phosphate, and vitamin D metabolism, and their dysregulation may participate in age-related disease. Here we review how mTOR inhibition extends lifespan, how KLOTHO functions as an aging suppressor, how sirtuins mediate longevity, how vitamin D loss may contribute to age-related disease, and how they relate to mitochondrial function. Also, we discuss how RAS-bl downregulates mTOR and upregulates KLOTHO, sirtuin, and vitamin D receptor expression, suggesting that at least some of RAS-bl benefits in aging are mediated through the modulation of mTOR, KLOTHO, and sirtuin expression and vitamin D signaling, paralleling CR actions in age retardation. Concluding, the available evidence endorses the idea that RAS-bl is among the interventions that may turn out to provide relief to the spreading issue of age-associated chronic disease.

Interaction between insulin-like growth factor-1 and atherosclerosis and vascular aging

The process of vascular aging encompasses alterations in the function of endothelial (ECs) and vascular smooth muscle cells (VSMCs) via oxidation, inflammation, cell senescence and epigenetic modifications, increasing the probability of atherosclerosis. Aged vessels exhibit decreased endothelial antithrombogenic properties, increased reactive oxygen species generation, inflammatory signaling and migration of VSMCs to the subintimal space, impaired angiogenesis and increased elastin degradation. The key initiating step in atherogenesis is subendothelial accumulation of apolipoprotein B-containing low-density lipoproteins resulting in activation of ECs and recruitment of monocytes. Activated ECs secrete 'chemokines' that interact with cognate chemokine receptors on monocytes and promote directional migration. Recruitment of immune cells establishes a proinflammatory status, further causing elevated oxidative stress, which in turn triggers a series of events including apoptotic or necrotic death of vascular and nonvascular cells. Increased oxidative stress is also considered to be a key factor in mechanisms of aging-associated changes in tissue integrity and function. Experimental evidence indicates that insulin-like growth factor-1 exerts antioxidant, anti-inflammatory and pro-survival effects on the vasculature, reducing atherosclerotic plaque burden and promoting features of atherosclerotic plaque stability.

Polymer-based delivering of shRNA to rabbit aortic smooth muscle cells suppressed the expression of IGF-1R in vitro and in vivo

Restenosis is one of clinical limitations for vein graft in coronary bypass graft. It has been proved that signal pathway IGF-1 and its receptor (IGF-1R) activated by hemodynamic mechanical stretch are responsible for the vascular smooth muscle cells proliferation in vein graft neointima formation. Unfortunately, there is no routinely successful method to resolve this problem. Gene delivering to vein graft possesses great therapeutic potential to prevent neointima formation. Polymer is one kind of nanoparticles, which can activate the process of endocytosis of cells. In this study, we evaluated the transfection efficiency and therapeutic potential of polymer-based transfection of plasmids expressing GFP and shRNAs targeting IGF-1R (pGFPshIGF-1Rs) to smooth muscle cells and rabbit external jugular vein graft. Results showed that polymer-based transfection provided high efficiency of transgene expression in smooth muscle cells in vitro. In vitro, IGF-1R-specific shRNA transfected by polymer inhibited IGF-1R protein expression by 52 ± 3.6%, when compared with mock transfected cells. In vivo delivering efficiency of pGFPshIGF-1R plasmid into the rabbit external jugular vein graft was significantly high in the polymer-based transfection group, when compared with negative control group. In vivo, polymer-based transfection IGF-1R-specific shRNA efficiently inhibited the expression of IGF-1R protein by 77 ± 3.6%, 65.6 ± 4.9%, and 76.7 ± 4.3% at 24, 48, and 72 h, respectively, when compared with negative control group. Our findings indicated that polymer-based transfection may be a promising technique that allows the targeting of gene therapy for vein graft restenosis.

Aging, atherosclerosis, and IGF-1

Insulin-like growth factor 1 (IGF-1) is an endocrine and autocrine/paracrine growth factor that circulates at high levels in the plasma and is expressed in most cell types. IGF-1 has major effects on development, cell growth and differentiation, and tissue repair. Recent evidence indicates that IGF-1 reduces atherosclerosis burden and improves features of atherosclerotic plaque stability in animal models. Potential mechanisms for this atheroprotective effect include IGF-1-induced reduction in oxidative stress, cell apoptosis, proinflammatory signaling, and endothelial dysfunction. Aging is associated with increased vascular oxidative stress and vascular disease, suggesting that IGF-1 may exert salutary effects on vascular aging processes. In this review, we will provide a comprehensive update on IGF-1's ability to modulate vascular oxidative stress and to limit atherogenesis and the vascular complications of aging.

Erythropoietin update 2011

Traditionally, erythropoietin (EPO) is described as a hematopoietic cytokine, regulating proliferation and differentiation and survival of the erythroid progenitors. The recent finding of new sites of EPO production and the wide spread distribution of EPO receptors (EPO-R) on endothelial cells, cardiomyocytes, renal cells as well as the central and peripheral nervous system raised the possibility that EPO may exert pleiotropic actions on several targets. Indeed studies (mainly preclinical) have documented protective, non-hematopoietic, abilities of EPO in a variety of tissue. However, the data obtained from clinical studies are more skeptical about these properties. This article provides a comprehensive overview of EPO and its derivatives.

Mechanical stretch augments insulin-induced vascular smooth muscle cell proliferation by insulin-like growth factor-1 receptor

Insulin resistance and hypertension have been implicated in the pathogenesis of cardiovascular disease; however, little is known about the roles of insulin and mechanical force in vascular smooth muscle cell (VSMC) remodeling. We investigated the contribution of mechanical stretch to insulin-induced VSMC proliferation. Thymidine incorporation was stimulated by insulin in stretched VSMCs, but not in un-stretched VSMCs. Insulin increased 2-deoxy-glucose incorporation in both stretched and un-stretched VSMCs. Mechanical stretch augmented insulin-induced extracellular signal-regulated kinase (ERK) and Akt phosphorylation. Inhibitors of epidermal growth factor (EGF) receptor tyrosine kinase and Src attenuated insulin-induced ERK and Akt phosphorylation, as well as thymidine incorporation, whereas 2-deoxy-glucose incorporation was not affected by these inhibitors. Moreover, stretch augmented insulin-like growth factor (IGF)-1 receptor expression, although it did not alter the expression of insulin receptor and insulin receptor substrate-1. Insulin-induced ERK and Akt activation, and thymidine incorporation were inhibited by siRNA for the IGF-1 receptor. Mechanical stretch augments insulin-induced VSMC proliferation via upregulation of IGF-1 receptor, and downstream Src/EGF receptor-mediated ERK and Akt activation. Similar to in vitro experiment, IGF-1 receptor expression was also augmented in hypertensive rats. These results provide a basis for clarifying the molecular mechanisms of vascular remodeling in hypertensive patients with hyperinsulinemia.

Liver lipid content is reduced in rat given 7-day administration of angiotensin II

Activation of the renin-angiotensin system may be involved in the development of hepatic steatosis, a condition that is associated with insulin resistance. We showed that in rats, angiotensin II induced accumulation of triglycerides in the renal tubular and cardiac cells, although it significantly reduced the weight of the rats. Here we investigated the liver lipid content of rats given long-term angiotensin II administration. Angiotensin II (0.7 mg/kg/day) was infused into the rats for 7 days via an osmotic minipump. Some rats also received hydralazine or losartan concomitantly. It was shown that angiotensin II reduced oil red O-stainable lipid droplets (6% of the control value) and liver triglyceride content (angiotensin II: 4.6 ± 0.8 µg/mg, control: 11.7 ± 1.1 µg/mg). Both of these phenomena were blocked by losartan, but not by hydralazine. Angiotensin II infusion reduced the expression and activity of AMP-activated protein kinase. In addition, angiotensin II decreased the mRNA expression of peroxisome proliferator-activated receptor-α and genes related to β-oxidation, although mRNA expression of genes related to lipogenesis were not affected. Angiotensin II reduced triglyceride content in the liver, unlike in the kidney or heart, via an AT1 receptor-dependent mechanism.

Cross-talk between angiotensin II and IGF-1-induced connexin 43 expression in human saphenous vein smooth muscle cells

Vascular restenosis following coronary artery bypass graft can cause major clinical complications due to intimal hyperplasia in venous conduits. However, the precise underlying mechanisms of intimal hyperplasia are still unclear. We have recently reported that increased expression of connexin43 (Cx43) is involved in the proliferation of vascular smooth muscle cells (SMCs) in human saphenous vein (SV). In this study, we investigated the signalling transduction pathway involved in Cx43 expression and SV SMC proliferation. Angiotensin-II (AT-II, 100 ng/ml) increased AT-II receptor 1 (AT-1R) protein expression and insulin-like growth factor-1 (IGF-1) (100 ng/ml) up-regulated IGF-1 receptor (IGF-1R) protein expression in SV SMCs. Interestingly, AT-1R expression was also increased by IGF-1 treatment, and IGF-1R expression was increased by AT-II treatment, which was blocked by siRNA-IGF-1R and siRNA-AT-1R, respectively. Furthermore, the effect of AT-II and IGF-1 signal cross-talk i nducing up-regulation of their reciprocal receptors was blocked by siRNA against extracellular signal-regulated kinases 1/2 (Erk 1/2) in SMCs of SV. Moreover, AT-II and IGF-1-induced Cx43 expression via phosphorylation of Erk 1/2 and activation of transcription factor activator protein 1 (AP-1) through their reciprocal receptors in SV SMCs. These data demonstrate a cross-talk between IGF-1R and AT-1R in AT-II and IGF-1-induced Cx43 expression in SV SMCs involving Erk 1/2 and downstream activation of the AP-1 transcription factor.

Comparative endocrinology of aging and longevity regulation

Hormones regulate growth, development, metabolism, and other complex processes in multicellular animals. For many years it has been suggested that hormones may also influence the rate of the aging process. Aging is a multifactorial process that causes biological systems to break down and cease to function in adult organisms as time passes, eventually leading to death. The exact underlying causes of the aging process remain a topic for debate, and clues that may shed light on these causes are eagerly sought after. In the last two decades, gene mutations that result in delayed aging and extended longevity have been discovered, and many of the affected genes have been components of endocrine signaling pathways. In this review we summarize the current knowledge on the roles of endocrine signaling in the regulation of aging and longevity in various animals. We begin by discussing the notion that conserved systems, including endocrine signaling pathways, "regulate" the aging process. Findings from the major model organisms: worms, flies, and rodents, are then outlined. Unique lessons from studies of non-traditional models: bees, salmon, and naked mole rats, are also discussed. Finally, we summarize the endocrinology of aging in humans, including changes in hormone levels with age, and the involvement of hormones in aging-related diseases. The most well studied and widely conserved endocrine pathway that affects aging is the insulin/insulin-like growth factor system. Mutations in genes of this pathway increase the lifespan of worms, flies, and mice. Population genetic evidence also suggests this pathway's involvement in human aging. Other hormones including steroids have been linked to aging only in a subset of the models studied. Because of the value of comparative studies, it is suggested that the aging field could benefit from adoption of additional model organisms.

The role of IGF-1 resistance in obesity and type 2 diabetes-mellitus-related insulin resistance and vascular disease

IMPORTANCE OF THE FIELD

The insulin-resistant conditions of type 2 diabetes mellitus (T2DM) and obesity are a major cause of cardiovascular disease on a global scale. These disorders are not only a cause of ill health but are a huge financial drain on healthcare systems. T2DM leads to an increased risk of cardiovascular mortality equivalent to over 10 years of ageing while obesity independent of T2DM also leads to a substantially increased risk of acute myocardial infarction. Recent trials of therapeutic agents and approaches to preventing the cardiovascular complications of type 2 diabetes have been disappointing.

AREAS COVERED IN THIS REVIEW

The role of insulin resistance in the endothelium in the regulation of the anti-atherosclerotic signalling molecule NO and a potential important role for IGF-1 in vascular NO production.

WHAT THE READER WILL GAIN

A comprehensive understanding of how insulin and IGF-1 regulate vascular function and the effect of type 2 diabetes on these pathways.

TAKE HOME MESSAGE

The roles of insulin and IGF-1 in vascular function are complex and intimately related. Nevertheless IGF-1 signalling in the arterial wall has the potential to be manipulated to protect the vasculature against the development of atherosclerosis and its devastating complications.

A monoclonal antibody against alphaVbeta3 integrin inhibits development of atherosclerotic lesions in diabetic pigs

Atherosclerotic lesions develop and progress more rapidly in diabetic patients than in nondiabetic individuals. This may be caused by accelerated lesion formation in the high-glucose environment of diabetes. Smooth muscle cells (SMCs) cultured in high glucose are more responsive to growth factors such as insulin-like growth factor-1 (IGF-1). This enhanced response to IGF-1 is due in part to increased activation of the alpha(V)beta(3) integrin. We tested whether alpha(V)beta(3) integrin activation was increased in diabetic animals and whether an antibody to beta(3) would inhibit IGF-1 action and development of atherosclerosis. Eight male pigs were made diabetic with streptozotocin and fed a high-fat diet. A F(ab)(2) antibody fragment directed at beta(3) was infused into one femoral artery, whereas the other artery received control F(ab)(2) for 3.5 months. There was a 65 +/- 8% reduction in atherosclerotic lesion area in the arteries treated with F(ab)(2) antibody to beta(3). Phosphorylation of beta(3) was reduced by 75 +/- 18% in vessels treated with the antibody. Shc and mitogen-activated protein kinase phosphorylation, which are required for IGF-1-stimulated SMC proliferation, were also significantly reduced. We conclude that activation of IGF-1 receptor and alpha(V)beta(3)-linked signaling pathways accelerates atherosclerosis in diabetes and that administration of an antibody to beta(3) to diabetic pigs inhibits alpha(V)beta(3) activation, IGF-1-stimulated signaling, and atherosclerotic lesion development. This approach offers a potential therapeutic approach to the treatment of this disorder.

Insulin-like growth factor-I regulation of immune function: a potential therapeutic target in autoimmune diseases?

This topically limited review explores the relationship between the immune system and insulin-like growth factors (IGF-I and IGF-II) and the proteins through which they act, including IGF-I receptor (IGF-IR) and the IGF-I binding proteins. The IGF/IGF-IR pathway plays important and diverse roles in tissue development and function. It regulates cell cycle progression, apoptosis, and the translation of proteins. Many of the consequences ascribed to IGF-IR activation result from its association with several accessory proteins that are either identical or closely related to those involved in insulin receptor signaling. Relatively recent awareness that IGF-I and IGF-IR regulate immune function has cast this pathway in an unexpected light; it may represent an important switch governing the quality and amplitude of immune responses. IGF-I/IGF-IR signaling may also participate in the pathogenesis of autoimmune diseases, although its relationship with these processes seems complex and relatively unexplored. On the one hand, IGF-I seems to protect experimental animals from developing insulin-deficient diabetes mellitus. In contrast, activating antibodies directed at IGF-IR have been detected in patients with Graves' disease, where the receptor is overexpressed by multiple cell types. The frequency of IGF-IR+ B and T cells is substantially increased in patients with that disease. Potential involvement of IGF-I and IGF-IR in the pathogenesis of autoimmune diseases suggests that this pathway might constitute an attractive therapeutic target. IGF-IR has been targeted in efforts directed toward drug development for cancer, employing both small-molecule and monoclonal antibody approaches. These have been generally well-tolerated. Recognizing the broader role of IGF-IR in regulating both normal and pathological immune responses may offer important opportunities for therapeutic intervention in several allied diseases that have proven particularly difficult to treat.

IGF-1, oxidative stress and atheroprotection

Atherosclerosis is a chronic inflammatory disease in which early endothelial dysfunction and subintimal modified lipoprotein deposition progress to complex, advanced lesions that are predisposed to erosion, rupture and thrombosis. Oxidative stress plays a crucial role not only in initial lesion formation but also in lesion progression and destabilization. Although most growth factors are thought to promote vascular smooth muscle cell proliferation and migration, thereby increasing neointima, recent animal studies indicate that insulin-like growth factor (IGF)-1 exerts both pleiotropic anti-oxidant effects and anti-inflammatory effects, which together reduce atherosclerotic burden. This review discusses the effects of IGF-1 in models of vascular injury and atherosclerosis, emphasizing the relationship between oxidative stress and potential atheroprotective actions of IGF-1.

Cell-cell bond modulates vascular smooth muscle cell responsiveness to Angiotensin II

Cell attachment is provided by cell-matrix and cell-cell bonds, and acts as a regulator of vascular smooth muscle cell (VSMC) survival, activity and homeostasis, as well as of VSMCs response to pathogenic stimuli. In this work we elicited an exclusive cell-cell contact by culturing A7r5 VSMCs on agarose-coated wells to form floating cell clusters, and we demonstrated that a steady state with a reduced response to the vasoactive peptide Angiotensin II (ATII) was induced. We found that clustered VSMCs showed subcortical stabilization of beta-catenin and Caveolin 1 (Cav1), unlike adherent confluent counterparts. We demonstrated that beta-catenin and Cav1 stabilization at the membrane level hampers the molecular cross-talk induced by ATII-activated AT1 receptor (AT1R), thereby impeding the phosphorylation of Cav1 and IGF1R, the NADPH oxidase activity, and counteracting ATII-dependent hypertrophy. Thus, elective cell-cell bond might modulate the proatherogenic activity of ATII, reducing the adverse vascular remodelling associated with AT1R activation.

The insulin-like growth factor family: molecular mechanisms, redox regulation, and clinical implications

Insulin-like growth factor (IGF)-induced signaling networks are vital in modulating multiple fundamental cellular processes, such as cell growth, survival, proliferation, and differentiation. Aberrations in the generation or action of IGF have been suggested to play an important role in several pathological conditions, including metabolic disorders, neurodegenerative diseases, and multiple types of cancer. Yet the exact mechanism involved in the pathogenesis of these diseases by IGFs remains obscure. Redox pathways involving reactive oxygen species (ROS) and reactive nitrogen species (RNS) contribute to the pathogenetic mechanism of various diseases by modifying key signaling pathways involved in cell growth, proliferation, survival, and apoptosis. Furthermore, ROS and RNS have been demonstrated to alter IGF production and/or action, and vice versa, and thereby have the ability to modulate cellular functions, leading to clinical manifestations of diseases. In this review, we provide an overview on the IGF system and discuss the potential role of IGF-1/IGF-1 receptor and redox pathways in the pathophysiology of several diseases.

Milk--the promoter of chronic Western diseases

Common chronic diseases of Western societies, such as coronary heart disease, diabetes mellitus, cancer, hypertension, obesity, dementia, and allergic diseases are significantly influenced by dietary habits. Cow's milk and dairy products are nutritional staples in most Western societies. Milk and dairy product consumption is recommended by most nutritional societies because of their beneficial effects for calcium uptake and bone mineralization and as a source of valuable protein. However, the adverse long-term effects of milk and milk protein consumption on human health have been neglected. A hypothesis is presented, showing for the first time that milk protein consumption is an essential adverse environmental factor promoting most chronic diseases of Western societies. Milk protein consumption induces postprandial hyperinsulinaemia and shifts the growth hormone/insulin-like growth factor-1 (IGF-1) axis to permanently increased IGF-1 serum levels. Insulin/IGF-1 signalling is involved in the regulation of fetal growth, T-cell maturation in the thymus, linear growth, pathogenesis of acne, atherosclerosis, diabetes mellitus, obesity, cancer and neurodegenerative diseases, thus affecting most chronic diseases of Western societies. Of special concern is the possibility that milk intake during pregnancy adversely affects the early fetal programming of the IGF-1 axis which will influence health risks later in life. An accumulated body of evidence for the adverse effects of cow's milk consumption from fetal life to childhood, adolescence, adulthood and senescence will be provided which strengthens the presented hypothesis.

Thiol antioxidants regulate angiotensin II AT1 and arginine vasopressin V1 receptor functions differently in vascular smooth muscle cells

BACKGROUND

We compared the effects of the sulfhydryl-containing (thiol) antioxidant dithiothreitol (DTT), which disrupts disulfide bonds, on cell signaling through angiotensin II (AngII) Type 1 receptors (AT1Rs) and arginine vasopressin (AVP) V1 receptors (V1Rs). The AT1R contains two extracellular disulfides bonds but its ligand contains none, whereas the V1R contains no extracellular disufides bonds but its ligand contains 1.

METHODS

We measured radioligand binding, intracellular calcium responses, and extracellular signal-regulated kinase phosphorylation in cultured rat aortic vascular smooth muscle cells and alterations in urine osmolality in intact rats.

RESULTS

Preincubation of cells with DTT, a maneuver designed to target receptor disulfides, resulted in concentration-dependent decreases in specific (125)I-AngII binding to AT1Rs and acute angiotensin-stimulated intracellular calcium mobilization but no decreases in specific (125)I-AVP binding to V1Rs or AVP-stimulated intracellular calcium mobilization. In contrast, preincubation of the ligands with DTT followed by acute exposure to the cells, a maneuver designed to target ligand disulfides, blunted calcium mobilization to AVP robustly but to AngII only minimally. In intact rats, the increase in urine osmolality caused by subcutaneous injection with the AVP analogue desmopressin was significantly diminished when the analogue was preincubated with an excess of DTT.

CONCLUSION

DTT inhibits cell signaling to AngII AT1Rs and AVP V1Rs, at least in part through disruption of disulfide linkages, but the pattern of response depends upon whether disulfides of ligand or receptor are targeted.

Role of IGF-1 in glucose regulation and cardiovascular disease

IGF-1 is a peptide hormone that is expressed in most tissues. It shares significant structural and functional similarities with insulin, and is implicated in the pathogenesis of insulin resistance and cardiovascular disease. Recombinant human IGF-1 has been used in Type 2 diabetes to improve insulin sensitivity and aid glycemic control. There is evidence supporting IGF-1 as a vascular protective factor and it may also be beneficial in the treatment of chronic heart failure. Further understanding of the effects of IGF-1 signaling in health and disease may lead to novel approaches to the prevention and treatment of diabetes and cardiovascular disease.

Beyond anemia: the clinical impact of the physiologic effects of erythropoietin

Although we have known that oxygen tension affects erythrocyte production since the 19th century, we have only recently begun to understand many subtleties of erythropoietin (EPO) physiology. EPO administration has allowed hundreds of thousands of patients to avoid transfusions. With the beneficial effects so apparent a detailed understanding of the full clinical physiology of this plasma factor seemed less important. However, the unanticipated increase in mortality found in recent randomized studies is prompting a reassessment of this view. We will review what is known about the physiology of this plasma factor that, it is now clear, is more than just an erythrocyte production factor.

Milk consumption: aggravating factor of acne and promoter of chronic diseases of Western societies

Consumption of cow's milk and cow's milk protein result in changes of the hormonal axis of insulin, growth hormone and insulin-like growth factor-1(IGF-1) in humans. Milk consumption raises IGF-1 serum levels in the perinatal period, adolescence and adulthood. During puberty with the physiological onset of increased secretion of growth hormone, IGF-1 serum levels increase and are further enhanced by milk consumption. IGF-1 is a potent mitogen; after binding to its receptor in various tissues, it induces cell proliferation and inhibits apoptosis. Keratinocytes and sebocytes, as well as the androgen-synthesizing adrenals and gonads, are stimulated by IGF-1. The epidemic incidence of adolescent acne in Western milk-consuming societies can be explained by the increased insulin- and IGF-1-stimulation of sebaceous glands mediated by milk consumption. Acne can be regarded as a model for chronic Western diseases with pathologically increased IGF-1-stimulation. Many other organs, such as the thymus, bones, all glands, and vascular smooth muscle cells as well as neurons are subject to this abnormally increased hormonal stimulation. The milk-induced change of the IGF-1-axis most likely contributes to the development of fetal macrosomia, induction of atopy, accelerated linear growth, atherosclerosis, carcinogenesis and neurodegenerative diseases. Observations of molecular biology are supported by epidemiologic data and unmask milk consumption as a promoter of chronic diseases of Western societies.

Activation of protein tyrosine kinases and matrix metalloproteinases causes blood-brain barrier injury: Novel mechanism for neurodegeneration associated with alcohol abuse

Blood-brain barrier (BBB) formed by brain microvascular endothelial cells (BMVEC) regulates the passage of molecules and leukocytes in and out of the brain. Activation of matrix metalloproteinases (MMPs) and alteration of basement membrane (BM) associated with BBB injury was documented in stroke patients. While chronic alcoholism is a risk factor for developing stroke, underlying mechanisms are not well understood. We hypothesized that ethanol (EtOH)-induced protein tyrosine kinase (PTK) signaling resulted a loss of BBB integrity via MMPs activation and degradation of BM component, collagen IV. Treatment of BMVEC with EtOH or acetaldehyde (AA) for 2-48 h increased MMP-1, -2 and -9 activities or decreased the levels of tissue inhibitors of MMPs (TIMP-1, -2) in a PTK-dependent manner without affecting protein tyrosine phosphatase activity. Enhanced PTK activity after EtOH exposure correlated with increased phosphorylated proteins of selective receptor and nonreceptor PTKs. Up-regulation of MMPs activities and protein contents paralleled a decrease in collagen IV content, and inhibitors of EtOH metabolism, MMP-2 and -9, or PTK reversed all these effects. Using human BMVEC assembled into BBB models, we found that EtOH/AA diminished barrier tightness, augmented permeability, and monocyte migration across the BBB via activation of PTKs and MMPs. These findings suggest that alcohol associated BBB injury could be mediated by MMPs via BM protein degradation and could serve as a comorbidity factor for neurological disorders like stroke or neuroinflammation. Furthermore, our preliminary experiments indicated that human astrocytes secreted high levels of MMP-1 and -9 following exposure to EtOH, suggesting the role of BM protein degradation and BBB compromise as a result of glial activation by ethanol. These results provide better understanding of multifaceted effects of alcohol on the brain and could help develop new therapeutic interventions.

Modifying IGF1 activity: an approach to treat endocrine disorders, atherosclerosis and cancer

Insulin-like growth factor 1 (IGF1) is a polypeptide hormone that has a high degree of structural similarity to human proinsulin. Owing to its ubiquitous nature and its role in promoting cell growth, strategies to inhibit IGF1 actions are being pursued as potential adjunctive measures for treating diseases such as short stature, atherosclerosis and diabetes. In addition, most tumour cell types possess IGF1 receptors and conditions in the tumour microenvironment, such as hypoxia, can lead to enhanced responsiveness to IGF1. Therefore, inhibiting IGF1 action has been proposed as a specific mechanism for potentiating the effects of existing anticancer therapies or for directly inhibiting tumour cell growth.

Oxidative stress regulates IGF1R expression in vascular smooth-muscle cells via p53 and HDAC recruitment

Apoptosis of VSMCs (vascular smooth-muscle cells) leads to features of atherosclerotic plaque instability. We have demonstrated previously that plaque-derived VSMCs have reduced IGF1 (insulin-like growth factor 1) signalling, resulting from a decrease in the expression of IGF1R (IGF1 receptor) compared with normal aortic VSMCs [Patel, Zhang, Siddle, Soos, Goddard, Weissberg and Bennett (2001) Circ. Res. 88, 895-902]. In the present study, we show that apoptosis induced by oxidative stress is inhibited by ectopic expression of IGF1R. Oxidative stress repressed IGF1R expression at multiple levels, and this was also blocked by mutant p53. Oxidative stress also induced p53 phosphorylation and apoptosis in VSMCs. p53 negatively regulated IGF1R promoter activity and expression and, consistent with this, p53-/- VSMCs demonstrated increased IGF1R expression, both in vitro and in advanced atherosclerotic plaques in vivo. Oxidative-stress-induced interaction of endogenous p53 with TBP (TATA-box-binding protein) was dependent on p53 phosphorylation. Oxidative stress also increased the association of p53 with HDAC1 (histone deacetylase 1). Trichostatin A, a specific HDAC inhibitor, or p300 overexpression relieved the repression of IGF1R following oxidative stress. Furthermore, acetylated histone-4 association with the IGF1R promoter was reduced in cells subjected to oxidative stress. These results suggest that oxidative-stress-induced repression of IGF1R is mediated by the association of phosphorylated p53 with the IGF1R promoter via TBP, and by the subsequent recruitment of chromatin-modifying proteins, such as HDAC1, to the IGF1R promoter-TBP-p53 complex.

Oxidative stress activates insulin-like growth factor I receptor protein expression, mediating cardiac hypertrophy induced by thyroxine

Thyroxine can cause cardiac hypertrophy by activating growth factors, such as IGF-I (insulin-like growth factor-I). Since oxidative stress is enhanced in the hyperthyroidism, it would control protein expression involved in this hypertrophy. Male Wistar rats were divided into four groups: (I) control, (II) vitamin E-supplemented (20 mg/kg/day subcutaneous), (III) hyperthyroid (thyroxine 12 mg/l, in drinking water), and (IV) hyperthyroid + vitamin E. After 4 weeks, the contractility and relaxation indexes of left ventricle (LV), and cardiac mass were increased by 54%, 60%, and 60%, respectively, in hyperthyroid group. An increase in lipid peroxidation (around 40%), and a decrease in total glutathione (by 20%) was induced by thyroxine and avoided by vitamin E administration. Superoxide dismutase (SOD) and glutathione-S-transferase (GST) activities were increased (by 83% and 54%, respectively) in hyperthyroid, and vitamin E avoided changes in SOD. Protein expression of SOD, GST, and IGF-I receptor (IGF-IR) were increased (by 87%, 84%, and 60%, respectively) by thyroxine, and vitamin E promoted a significant reduction in SOD and IGF-IR expression (by 36% and 17%, respectively). These results indicate that oxidative stress is involved in cardiac hypertrophy, and suggest a role for IGF-IR as a mediator of this adaptive response in experimental hyperthyroidism.

Redox signalling in anchorage-dependent cell growth

Current data have provided new perspectives concerning the regulation of non-transformed cell proliferation in response to both soluble growth factors and to adhesive cues. Non-transformed cells are anchorage dependent for the execution of the mitotic program and cannot avoid the concomitant signals starting from mitogenic molecules, as growth factors, and adhesive agents belonging to extracellular matrix. Reactive oxygen species play a key role during both growth factor and integrin receptor signalling and these second messengers are recognised to have a synergistic function for anchorage-dependent growth signalling. Redox regulated proteins include protein tyrosine phosphatases and protein tyrosine kinases, although with opposite regulation of their enzymatic activity, and cytoskeletal proteins as beta-actin. In this review we support a role of ROS as key second messengers granting a proper executed mitosis for anchorage-dependent cells, through redox regulation of several downstream targets. Deregulation of these redox pathways may help to guide transformed cells to elude the native apoptotic response to abolishment of signals started by cell/ECM contact, sustaining ectopic anchorage-independent cancer cell growth.

Oxidative stress activates protein tyrosine kinase and matrix metalloproteinases leading to blood-brain barrier dysfunction

The blood-brain barrier (BBB) formed by brain microvascular endothelial cells (BMVEC) regulates the passage of molecules and leukocytes in and out of the brain. Oxidative stress is a major underlying cause of neurodegenerative and neuroinflammatory disorders and BBB injury associated with them. Using human BMVEC grown on porous membranes covered with basement membrane (BM) matrix (BBB models), we demonstrated that reactive oxygen species (ROS) augmented permeability and monocyte migration across BBB. ROS activated matrix metalloproteinases (MMP-1, -2, and -9) and decreased tissue inhibitors of MMPs (TIMP-1 and -2) in a protein tyrosine kinase (PTK)-dependent manner. Increase in MMPs and PTK activities paralleled degradation of BM protein and enhanced tyrosine phosphorylation of tight junction (TJ) protein. These effects and enhanced permeability/monocyte migration were prevented by inhibitors of MMPs, PTKs, or antioxidant suggesting that oxidative stress caused BBB injury via degradation of BM protein by activated MMPs and by PTK-mediated TJ protein phosphorylation. These findings point to new therapeutic interventions ameliorating BBB dysfunction in neurological disorders such as stroke or neuroinflammation.

Protein tyrosine phosphorylation and reversible oxidation: two cross-talking posttranslation modifications

In addition to protein phosphorylation, redox-dependent posttranslational modification of proteins is emerging as a key signaling system, conserved throughout evolution, and influencing many aspects of cellular homeostasis. Recent data have provided new insight about the interplay between phosphorylation- and redox-dependent signaling, and reactive oxygen species have been included among intracellular signal transducers of growth factor and extracellular matrix receptors. Both tyrosine phosphorylation and thiol oxidation are reversible and dynamic, and this review will particularly focus on the cross-talk between these posttranslational protein regulatory means. Although these modifications share their reversibility, their effects on enzymatic activity of protein tyrosine phosphatases (PTPs) and protein tyrosine kinases (PTKs) may be even opposite. Indeed, while tyrosine phosphorylation is frequently correlated to enzyme activation, thiol oxidation leads to inactivation of PTPs and to superactivation of PTKs. Several papers describe that both these modifications occur during the same input, (i.e., cell proliferation and motility induced by numerous growth factors and cytokines). The review will discuss several aspects of phosphorylation\oxidation interplay, describing both convergent and divergent features of the integrated and coordinated function of PTPs and PTKs during signaling.

Angiotensin II stimulates transcription of insulin-like growth factor I receptor in vascular smooth muscle cells: role of nuclear factor-kappaB

Increased expression of the IGF-I receptor (IGF-IR) is associated with proliferation and survival of vascular smooth muscle cells (VSMCs). In cultured VSMCs, we reported that angiotensin II (Ang II) increases transcription and expression of IGF-IR. Now, we show that mesenteric arteries of rats infused with Ang II develop thickening and increased IGF-IR expression. To determine how Ang II transcriptionally regulates IGF-IR expression in VSMCs, we generated 5'-end deletions of the IGF-IR promoter and measured Ang II-induced promoter-luciferase activity in VSMCs. Activities from these promoter sequences suggested that the Ang II-responsive region is located between -270 and -135 of the IGF-IR promoter. Using a DNase I foot printing analysis, we identified two putative nuclear factor-kappaB (NF-kappaB)-like sequences located in the same region of the IGF-IR promoter. When we mutated either of these NF-kappaB-like sites, Ang II-induced IGF-IR promoter activity decreased sharply. Electrophoretic mobility gel shift, anti-p50 of NF-kappaB supershift and chromatin immunoprecipitation assays demonstrated that both the p65 and p50 subunits of NF-kappaB will bind to this Ang II response element in the IGF-IR promoter. When we blocked the Ras/MAPK kinase 1 pathway or the inhibitory-kappaB kinase pathway, both Ang II-induced IGF-IR promoter activity and expression of IGF-IR protein significantly declined. Our results indicate that the mechanism by which Ang II stimulates IGF-IR expression in VSMCs involves NF-kappaB binding to NF-kappaB sites in the IGF-IR promoter, leading to expression of IGF-IR through both Ras/MAPK kinase 1-and inhibitory-kappaB kinase-dependent pathways. Because IGF-IR is a major factor associated with thickening of mesenteric vessels, our results provide potential therapeutic targets.

N-Acetylcysteine Decreases Angiotensin II Receptor Binding in Vascular Smooth Muscle Cells

Antioxidants seem to inhibit angiotensin II (Ang II) actions by consuming stimulated reactive oxygen species. An alternative hypothesis was investigated: Antioxidants that are also strong reducers of disulfide bonds inhibit the binding of Ang II to its surface receptors with consequent attenuation of signal transduction and cell action. Incubation of cultured vascular smooth muscle cells, which possess Ang II type 1a receptors, with the reducing agent n-acetylcysteine (NAC) for 1 h at 37 degrees C resulted in decreased Ang II radioligand binding in a concentration-dependent pattern. NAC removal restored Ang II binding within 30 min. Incubation with n-acetylserine, a nonreducing analogue of NAC, did not lower Ang II binding, and oxidized NAC was less effective than reduced NAC in lowering Ang II binding. NAC did not decrease Ang II type 1a receptor protein content. Other antioxidants regulated Ang II receptors differently: alpha-Lipoic acid lowered Ang II binding after 24 h, and vitamin E did not lower Ang II binding at all. NAC inhibited Ang II binding in cell membranes at 21 or 37 but not 4 degrees C. Dihydrolipoic acid (the reduced form of alpha-lipoic acid), which contains free sulfhydryl groups as NAC does, decreased Ang II receptor binding in cell membranes, whereas alpha-lipoic acid, which does not contain free sulfhydryl groups, did not. Ang II-stimulated inositol phosphate formation was decreased by preincubation with NAC (1 h) or alpha-lipoic acid (24 h) but not vitamin E. In conclusion, certain antioxidants that are reducing agents lower Ang II receptor binding, and Ang II-stimulated signal transduction is decreased in proportion to decreased receptor binding.

15-lipoxygenase-1 expression upregulates and activates insulin-like growth factor-1 receptor in prostate cancer cells

We previously discovered that a fat-metabolizing enzyme, 15-lipoxygenase-1 (15-LO-1), is high in human prostate cancer (PCa) and correlates with disease progression. The biologic link between the aberrant 15-LO-1/linoleic acid (LA) metabolism and fat (which is a rich source of growth factors) in PCa is unknown. Therefore, we tested the hypothesis that the metabolic product of the polyunsaturated fatty acid LA (i.e., 13-S-hydroxyoctadecadienoic acid or 13-(S)-HODE) affects the proliferation status of PCa cells through one or more growth factors. We used parental prostate cancer cell line-3 (PC-3) and engineered PC-3 cell lines [PC3-Zeo (mock-transfected), PC3-15LOS (15-LO-1-overexpressing), and PC3-15LOAS (15-LO-1-blocked)] to test our hypothesis. Of the growth factors examined, only insulin-like growth factor-1 (IGF-1) exhibited a two-fold to three-fold increase in growth response on PC3-15LOS cells compared to PC3-Zeo (control) cell line (P <.01). Insulin-like growth factor-1 receptor (IGF-1R) immunohistochemical analyses of human normal and adenocarcinoma prostate tissues, as well as levels in tumors derived from nude mice injected with PC-3 cells, demonstrated that elevated IGF-1R expression correlated with 15-LO-1 levels. Radioligand binding assays demonstrated two-fold higher IGF-1 binding sites in PC3-15LOS cells (P <.05 vs PC3-Zeo cells). IGF-1R promoter reporter assay and affinity-purified IGF-1R receptor levels demonstrated a four-fold higher activity in PC3-15LOS cells (P <.01 vs PC3-Zeo cells). IGF-1R promoter activation is 13-(S)-HODE-dependent. IGF-1R blockade with a dominant-negative adenovirus caused significant growth inhibition in PC-3 cells (P <.0001; PC3-15LOAS versus PC3-15LOS cells), as well as affected the IGF-1-stimulated mitogen-activated protein (MAP) kinase (Erk1/2) and Akt activation levels. Our study suggests that overexpression of 15-LO-1 in PCa contributes to the cancer progression by regulating IGF-1R expression and activation.

Redox regulation of angiotensin II signaling in the heart

A large number of studies have demonstrated the role of angiotensin II in cardiac preconditioning against ischemic reperfusion injury. Generally, angiotensin II is a detrimental factor for the heart, and its inhibition with an ACE inhibitor provides cardioprotection. This review provides an explanation for such paradoxical behavior of angiotensin II. Angiotensin II can potentiate the induction of the expression of a variety of redox-sensitive factors including p38 MAPK, JNK and Akt, IGF-IR, EGF-R, and HO-1 as well as redox-regulated genes and transcription factors such as NFkappaB. It becomes increasingly apparent that during the earlier phase, the heart attempts to adapt itself against the detrimental effects of angiotensin II by upregulating several cardioprotective genes and proteins. These genes and proteins are redox-regulated and the antioxidants or ROS scavengers block their expressions. Interestingly, an identical pattern of cardioprotective proteins and genes are expressed in the preconditioned heart, which are also inhibited with ROS scavengers. It is tempting to speculate that the induction of the expression of the redox-sensitive cardioprotective proteins is the results of adaptation of the heart against the oxidative stress resulting from angiotensin II; and preconditioning is the net result of harnessing its own protection during ischemic and/or oxidative stress through its ability to trigger redox signaling.

Recent advances in intracellular signalling in hypertension

PURPOSE OF REVIEW

Transmission of external signals from the cell surface to the internal cellular environment occurs via tightly controlled complex transduction pathways. Alterations in these highly regulated signalling cascades in vascular smooth cells may play a fundamental role in the structural, mechanical and functional abnormalities that underlie vascular pathological processes in hypertension. The present review focuses on recent developments relating to two novel signalling pathways: angiotensin II signalling through tyrosine kinases; and oxidative stress and redox-dependent signal transduction. These pathways are emerging as critical mediators of hypertensive vascular disease because they influence multiple cellular responses that are involved in structural remodelling, vascular inflammation and altered tone.

RECENT FINDINGS

A recent advance in the field of angiotensin II signalling was the demonstration that, in addition to its vasoconstrictor properties, angiotensin II has potent mitogenic-like and proinflammatory-like characteristics. These actions are mediated through phosphorylation of both nonreceptor tyrosine kinases and receptor tyrosine kinases. It is also becoming increasingly apparent that many signalling events that underlie abnormal vascular function in hypertension are influenced by changes in intracellular redox status. In particular, increased bioavailability of reactive oxygen species (oxidative stress) stimulates growth-signalling pathways, induces expression of proinflammatory genes, alters contraction-excitation coupling and impairs endothelial function.

SUMMARY

A better understanding of the molecular pathways that regulate vascular smooth muscle cell function will provide further insights into the pathophysiological mechanisms that contribute to vascular changes and end-organ damage associated with high blood pressure, and could permit identification of potential novel therapeutic targets in the prevention and management of hypertension.

Up-regulation of functionally impaired insulin-like growth factor-1 receptor in scrapie-infected neuroblastoma cells

A growing body of evidence suggests that an altered level or function of the neurotrophic insulin-like growth factor-1 receptor (IGF-1R), which supports neuronal survival, may underlie neurodegeneration. This study has focused on the expression and function of the IGF-1R in scrapie-infected neuroblastoma cell lines. Our results show that scrapie infection induces a 4-fold increase in the level of IGF-1R in two independently scrapie-infected neuroblastomas, ScN2a and ScN1E-115 cells, and that the increased IGF-1R level was accompanied by increased IGF-1R mRNA levels. In contrast to the elevated IGF-1R expression in ScN2a, receptor binding studies revealed an 80% decrease in specific (125)I-IGF-1-binding sites compared with N2a cells. This decrease in IGF-1R-binding sites was shown to be caused by a 7-fold decrease in IGF-1R affinity. Furthermore, ScN2a showed no significant difference in IGF-1 induced proliferative response, despite the noticeable elevated IGF-1R expression, putatively explained by the reduced IGF-1R binding affinity. Additionally, IGF-1 stimulated IGF-1Rbeta tyrosine phosphorylation showed no major change in the dose-response between the cell types, possibly due to altered tyrosine kinase signaling in scrapie-infected neuroblastoma cells. Altogether these data indicate that scrapie infection affects the expression, binding affinity, and signal transduction mediated by the IGF-1R in neuroblastoma cells. Altered IGF-1R expression and function may weaken the trophic support in scrapie-infected neurons and thereby contribute to neurodegeneration in prion diseases.

Angiotensin II induces skeletal muscle wasting through enhanced protein degradation and down-regulates autocrine insulin-like growth factor I

We previously showed that angiotensin II (ang II) infusion in the rat produces cachexia and decreases circulating insulin-like growth factor I (IGF-I). The weight loss derives from an anorexigenic response and a catabolic effect of ang II. In these experiments we assessed potential catabolic mechanisms and the involvement of the IGF-I system in these responses to ang II. Ang II infusion caused a significant decrease in body weight compared with that of pair-fed control rats. Kidney and left ventricular weights were significantly increased by ang II, whereas fat tissue was unchanged. Skeletal muscle mass was significantly decreased in the ang II-infused rats, and a reduction in lean muscle mass was a major reason for their overall loss of body weight. In skeletal muscles, ang II did not significantly decrease protein synthesis, but overall protein breakdown was accelerated; inhibiting lysosomal and calcium-activated proteases did not reduce the ang II-induced increase in muscle proteolysis. Circulating IGF-I levels were 33% lower in ang II rats vs. control rats, and this difference was reflected in lower IGF-I messenger RNA levels in the liver. Moreover, IGF-I, IGF-binding protein-3, and IGF-binding protein-5 messenger RNAs in the gastrocnemius were significantly reduced. To investigate whether the reduced circulating IGF-I accounts for the loss in muscle mass, we increased circulating IGF-I by coinfusing ang II and IGF-I, but this did not prevent muscle loss. Our data suggest that ang II causes a loss in skeletal muscle mass by enhancing protein degradation probably via its inhibitory effect on the autocrine IGF-I system.

Translation initiation of the insulin-like growth factor I receptor mRNA is mediated by an internal ribosome entry site

The insulin-like growth factor I receptor (IGF-IR) is a heterotetrameric receptor mediating the effects of insulin-like growth I and other growth factors. This receptor is encoded by an mRNA containing an unusually long, G-C-rich, and highly structured 5' untranslated region. Using bicistronic constructs, we demonstrated here that the 5' untranslated region of the IGF-IR allows translation initiation by internal ribosome entry and therefore constitutes an internal ribosome entry site. In vitro cross-linking revealed that this internal ribosome entry site binds a protein of 57 kDa. Immunoprecipitation of UV cross-linked proteins proved that this protein was the polypyrimidine tract-binding protein, a well known regulator of picornavirus mRNA translation. The efficiency of translation of the endogenous IGF-IR mRNA is not affected by rapamycin, which is a potent inhibitor of cap-dependent translation. This result provides evidence that the endogenous IGF-IR mRNA is translated, at least in part, through a cap-independent mechanism. This is the first report of a growth factor receptor containing sequence elements that allow translation initiation to occur by internal initiation. Because the IGF-IR has a pivotal function in the cell cycle, this mechanism of translation regulation could play a crucial role in the control of cell proliferation and differentiation.

Reactive oxygen species in cell signaling

Reactive oxygen species (ROS) are generated as by-products of cellular metabolism, primarily in the mitochondria. When cellular production of ROS overwhelms its antioxidant capacity, damage to cellular macromolecules such as lipids, protein, and DNA may ensue. Such a state of "oxidative stress" is thought to contribute to the pathogenesis of a number of human diseases including those of the lung. Recent studies have also implicated ROS that are generated by specialized plasma membrane oxidases in normal physiological signaling by growth factors and cytokines. In this review, we examine the evidence for ligand-induced generation of ROS, its cellular sources, and the signaling pathways that are activated. Emerging concepts on the mechanisms of signal transduction by ROS that involve alterations in cellular redox state and oxidative modifications of proteins are also discussed.

Angiotensin-converting enzyme (ACE) inhibition attenuates insulin-like growth factor-I (IGF-I) induced cardiac fibroblast proliferation

The effects of angiotensin-converting enzyme (ACE) inhibition and angiotensin type 1 (AT(1)) receptor blockade on insulin-like growth factor-I (IGF-I) induced proliferation and immediate-early-gene expression of neonatal rat cardiac fibroblasts were investigated. Moreover the role of the IGF-I receptor (IGF-IR) in this process was evaluated. IGF-I (10(-9) - 10(-7) M) stimulated neonatal rat cardiac fibroblast growth in a dose-dependent fashion (maximum: 3.5+/-0.1 fold, 10(-7) M), as determined by 5-bromo-2'-deoxyuridine (BrdU) incorporation. ACE inhibition or AT(1) receptor blockade attenuated the IGF-I (10(-7) M) induced neonatal rat cardiac fibroblast growth in a concentration-dependent fashion (moexiprilat: 50+/-2%, enalaprilat: 31+/-2%, CV11974; 58+/-1%, all: 10(-7) M). IGF-I stimulated cellular growth was accompanied by an upregulation of the immediate early genes c-Fos (2.4+/-0.3 fold), Egr-1 (4.7+/-1.1 fold) and Sp1 (6.2+/-0.7 fold). IGF-I induced expression was completely inhibited by ACE inhibition or AT(1) receptor blockade. Stimulation with IGF-I or Ang II (10(-7) M) increased IGF-IR expression 5.7+/-0. 5 fold and 3.6+/-0.5 fold respectively. The IGF-I induced overexpression of the IGF-IR was reduced by ACE inhibition with moexiprilat (10(-7) M) by 79+/-7% and by AT(1) receptor blockade with CV11974 (10(-7) M) by 79+/-5%. These data demonstrate that the mitogenic action of IGF-I in neonatal rat cardiac fibroblasts is in part mediated by activation of the renin-angiotensin system (RAS) with subsequent upregulation of IGF-IR expression. This observation has important implications for the treatment of cardiac diseases with ACE inhibitors alone and their combination with IGF-I or growth hormone.

Hydrogen peroxide: a key messenger that modulates protein phosphorylation through cysteine oxidation

Ligand-receptor interactions can generate the production of hydrogen peroxide (H(2)O(2)) in cells, the implications of which are becoming appreciated. Fluctuations in H(2)O(2) levels can affect the intracellular activity of key signaling components including protein kinases and protein phosphatases. Rhee et al. discuss recent findings on the role of H(2)O(2) in signal transduction. Specifically, H(2)O(2) appears to oxidize active site cysteines in phosphatases, thereby inactivating them. H(2)O(2) also can activate protein kinases; however, although the mechanism of activation for some kinases appears to be similar to that of phosphatase inactivation (cysteine oxidation), it is unclear how H(2)O(2) promotes increased activation of other kinases. Thus, the higher levels of intracellular phosphoproteins observed in cells most likely occur because of the concomitant inhibition of protein phosphatases and activation of protein kinases.