Human skin: source of and target organ for angiotensin II.
TL;DR: The findings suggest that the complete renin–angiotensin system is present in human skin and plays a role in normal cutaneous homeostasis as well as in human cutaneous wound healing.
Abstract: The present study examined the expression of angiotensin receptors in human skin, the potential synthesis of angiotensin II (Ang II) in this location and looked for a first insight into physiological functions. AT1 and AT2 receptors were found within the epidermis and in dermal vessel walls. The same expression pattern was found for angiotensinogen, renin and angiotensin-converting enzyme (ACE). All components could additionally be demonstrated at mRNA level in cultured primary keratinocytes, melanocytes, dermal fibroblasts and dermal microvascular endothelial cells, except for AT2 receptors in melanocytes. The ability of cutaneous cells to synthesize Ang II was proved by identifying the molecule in cultured keratinocytes. Furthermore, in artificially wounded keratinocyte monolayers, ACE-mRNA expression was rapidly increased, and enhanced ACE expression was still found in cutaneous human scars 3 months after wounding. These findings suggest that the complete renin-angiotensin system is present in human skin and plays a role in normal cutaneous homeostasis as well as in human cutaneous wound healing.
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TL;DR: Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin.
Abstract: This review focuses on the role of the peripheral nervous system in cutaneous biology and disease. During the last few years, a modern concept of an interactive network between cutaneous nerves, the neuroendocrine axis, and the immune system has been established. We learned that neurocutaneous interactions influence a variety of physiological and pathophysiological functions, including cell growth, immunity, inflammation, pruritus, and wound healing. This interaction is mediated by primary afferent as well as autonomic nerves, which release neuromediators and activate specific receptors on many target cells in the skin. A dense network of sensory nerves releases neuropeptides, thereby modulating inflammation, cell growth, and the immune responses in the skin. Neurotrophic factors, in addition to regulating nerve growth, participate in many properties of skin function. The skin expresses a variety of neurohormone receptors coupled to heterotrimeric G proteins that are tightly involved in skin homeostasis and inflammation. This neurohormone-receptor interaction is modulated by endopeptidases, which are able to terminate neuropeptide-induced inflammatory or immune responses. Neuronal proteinase-activated receptors or transient receptor potential ion channels are recently described receptors that may have been important in regulating neurogenic inflammation, pain, and pruritus. Together, a close multidirectional interaction between neuromediators, high-affinity receptors, and regulatory proteases is critically involved to maintain tissue integrity and regulate inflammatory responses in the skin. A deeper understanding of cutaneous neuroimmunoendocrinology may help to develop new strategies for the treatment of several skin diseases.
534 citations
TL;DR: An outlook of the pathophysiology in diabetic wound healing is provided and the established and adjunctive treatment strategies, as well as the future therapeutic options for the treatment of DFUs are summarized.
Abstract: Diabetic foot ulcers (DFUs) are one of the most common and serious complications of diabetes mellitus, as wound healing is impaired in the diabetic foot. Wound healing is a dynamic and complex biological process that can be divided into four partly overlapping phases: hemostasis, inflammation, proliferative and remodeling. These phases involve a large number of cell types, extracellular components, growth factors and cytokines. Diabetes mellitus causes impaired wound healing by affecting one or more biological mechanisms of these processes. Most often, it is triggered by hyperglycemia, chronic inflammation, micro- and macro-circulatory dysfunction, hypoxia, autonomic and sensory neuropathy, and impaired neuropeptide signaling. Research focused on thoroughly understanding these mechanisms would allow for specifically targeted treatment of diabetic foot ulcers. The main principles for DFU treatment are wound debridement, pressure off-loading, revascularization and infection management. New treatment options such as bioengineered skin substitutes, extracellular matrix proteins, growth factors, and negative pressure wound therapy, have emerged as adjunctive therapies for ulcers. Future treatment strategies include stem cell-based therapies, delivery of gene encoding growth factors, application of angiotensin receptors analogs and neuropeptides like substance P, as well as inhibition of inflammatory cytokines. This review provides an outlook of the pathophysiology in diabetic wound healing and summarizes the established and adjunctive treatment strategies, as well as the future therapeutic options for the treatment of DFUs.
402 citations
Cites background from "Human skin: source of and target or..."
...Recent research has demonstrated that angiotensin receptors are expressed in human skin and that tissue renin–angiotensin system plays an important role in the wound healing process [82, 83]....
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TL;DR: The present review summarizes the current knowledge of AT2 receptor distribution, signaling and function with an emphasis on growth/anti-growth, differentiation and the regeneration of neuronal tissue.
259 citations
TL;DR: Recent developments and new research trends related to Ang II and the RAS and involvement in the hypertensive vascular phenotype are focused on.
Abstract: Hypertension is associated with vascular changes characterised by remodelling, endothelial dysfunction and hyperreactivity. Cellular processes underlying these perturbations include altered vascular smooth muscle cell growth and apoptosis, fibrosis, hypercontractility and calcification. Inflammation, associated with macrophage infiltration and increased expression of redox-sensitive pro-inflammatory genes, also contributes to vascular remodelling. Many of these features occur with ageing, and the vascular phenotype in hypertension is considered a phenomenon of ‘premature vascular ageing’. Among the many factors involved in the hypertensive vascular phenotype, angiotensin II (Ang II) is especially important. Ang II, previously thought to be the sole effector of the renin–angiotensin system (RAS), is converted to smaller peptides [Ang III, Ang IV, Ang-(1-7)] that are biologically active in the vascular system. Another new component of the RAS is the (pro)renin receptor, which signals through Ang-II-independent mechanisms and might influence vascular function. Ang II mediates effects through complex signalling pathways on binding to its G-protein-coupled receptors (GPCRs) AT1R and AT2R. These receptors are regulated by the GPCR-interacting proteins ATRAP, ARAP1 and ATIP. AT1R activation induces effects through the phospholipase C pathway, mitogen-activated protein kinases, tyrosine kinases/phosphatases, RhoA/Rhokinase and NAD(P)H-oxidase-derived reactive oxygen species. Here we focus on recent developments and new research trends related to Ang II and the RAS and involvement in the hypertensive vascular phenotype.
164 citations
TL;DR: It is demonstrated that Ang II stimulates CFs to release exosomes, which in turn increase Ang II production and its receptor expression in cardiomyocytes, thereby intensifying Ang II-induced pathological cardiac hypertrophy.
144 citations
Cites background from "Human skin: source of and target or..."
...These adverse effects may be caused by the suppression or blockade of normal Ang II-mediated physiological functions in target organ systems [2, 38, 39] thereby creating a need for an alternative approach to selective targeting of the Ang II-mediated detrimental effects in the heart....
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References
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TL;DR: The results show that the growth modulating actions of ANG II depend on the type of angiotensin receptor present on a given cell, and in coronary endothelial cells, the antiproliferative actions of the AT2-receptor offset the growth promoting effects mediated by the AT1- receptor.
Abstract: Angiotensin II (ANG II) is known to be a potent growth promoting factor for vascular smooth muscle cells and fibroblasts but little is known about its influence on growth in endothelial cells. We studied the effects of ANG II on endothelial growth and the role of the angiotensin receptor subtypes involved. Proliferation of rat coronary endothelial cells (CEC) and rat vascular smooth muscle cells (VSMC) was determined by [3H]thymidine incorporation, the MTT-test and by directly counting cells in a coulter counter. Angiotensin AT1- and AT2-receptors were demonstrated by binding studies and by the presence of their respective mRNA through reverse transcription polymerase chain reaction (RT-PCR). In contrast to VSMC, which in culture only express the AT1-receptor, CEC express both, AT1- and AT2-receptors simultaneously up to the third passage. Whereas ANG II stimulated growth of quiescent VSMC, an effect abolished by pretreatment with the AT1-receptor antagonist, losartan, ANG II did not induce proliferation in quiescent CEC. However, after pretreatment of quiescent endothelial cells (< passage 4) with the AT2-receptor antagonist, PD 123177, ANG II induced proliferation. This effect was reversed by additional pretreatment with losartan. ANG II significantly inhibited the proliferation of bFGF-stimulated CEC in a dose-dependent manner by maximally 50%. This effect was prevented by PD 123177 while losartan was ineffective. The AT2-receptor agonist, CGP 42112, mimicked the antiproliferative actions of ANG II, confirming the specificity of the effect. Our results show that the growth modulating actions of ANG II depend on the type of angiotensin receptor present on a given cell. In coronary endothelial cells, the antiproliferative actions of the AT2-receptor offset the growth promoting effects mediated by the AT1-receptor.
917 citations
TL;DR: Two distinct subtypes of the angiotensin II receptor in the rat adrenal gland are demonstrated using radioligand binding and tissue section autoradiography and the discovery of two structurally dissimilar, nonpeptide compounds that show reciprocal selectivity for the two subtypes.
823 citations
"Human skin: source of and target or..." refers background in this paper
...antagonists (losartan for AT1 receptors and PD 123319 for AT2 receptors) (14,15)....
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TL;DR: There is a good correlation between the affinities of the selected agonists and antagonists for the two subtypes in the various tissues tested which is a usual requirement for receptor classification.
767 citations
"Human skin: source of and target or..." refers background in this paper
...antagonists (losartan for AT1 receptors and PD 123319 for AT2 receptors) (14,15)....
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TL;DR: Results suggest that the AT2 receptor exerts an antiproliferative effect, counteracting the growth action of AT1 receptor.
Abstract: The type 1 angiotensin II (AT1) receptor is well characterized but the type 2 (AT2) receptor remains an enigma. We tested the hypothesis that the AT2 receptor can modulate the growth of vascular smooth muscle cells by transfecting an AT2 receptor expression vector into the balloon-injured rat carotid artery and observed that overexpression of the AT2 receptor attenuated neointimal formation. In cultured smooth muscle cells, AT2 receptor transfection reduced proliferation and inhibited mitogen-activated protein kinase activity. Furthermore, we demonstrated that the AT2 receptor mediated the developmentally regulated decrease in aortic DNA synthesis at the latter stages of gestation. These results suggest that the AT2 receptor exerts an antiproliferative effect, counteracting the growth action of AT1 receptor.
701 citations
"Human skin: source of and target or..." refers background in this paper
...AT1 receptors mediate the stimulation of proliferation in diverse cell types (8,31,32)....
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...The AT2 receptor turned out to be involved in proliferation control (5,7,8), cell differentiation (5,9,10), apoptosis (6), tissue repair and tissue remodelling (11,12)....
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TL;DR: In this review, a coherent model of the interaction between the circulating and tissue angiotensin systems is synthesized, which might assist in the interpretation of new developments in this area.
Abstract: Angiotensin has many different actions, most of which relate, either directly or indirectly, to the regulation of blood pressure, fluid, and electrolyte homeostasis (1, 2). In addition to potent vasoconstrictor effects, actions ofangiotensin on vasculature include the stimulation ofprostaglandin release (3), the modulation of angiotensin receptor number (4), and the stimulation of angiogenesis (5). Angiotensin also has important actions on the central and peripheral nervous systems, the adrenal, kidney, intestine, and heart (6-1 1). Given these multiple diverse actions of angiotensin, two important questions are (a) which of these actions represent normal physiological events, and (b) whether such actions may assume a pathogenic role. These questions have recently been placed in sharper focus by the clinical application of inhibitors of the renin-angiotensin system (RAS),' and in particular, the use of converting enzyme inhibitors (CEIs) for the treatment of hypertension. Any attempt to answer these questions requires an accurate concept ofthe RAS. The purpose of this review is to discuss new concepts concerning angiotensin production by the circulating RAS, how these relate to angiotensin production within tissues, and the possible mechanisms by which CEIs lower blood pressure. The study of tissue angiotensin systems is still at an early stage. In this review I have attempted to synthesize a coherent model of the interaction between the circulating and tissue angiotensin systems, which might assist in the interpretation of new developments in this area.
596 citations