Cutaneous localization of endothelin-1 in patients with systemic sclerosis: immunoelectron microscopic study

The role of endothelial cells in the vasculopathy of systemic sclerosis: A systematic review

INTRODUCTION

Systemic sclerosis (SSc) is an autoimmune connective tissue disorder characterized by fibroproliferative vasculopathy, immunological abnormalities and progressive fibrosis of multiple organs including the skin. In this study, all English speaking articles concerning the role of endothelial cells (ECs) in SSc vasculopathy and representing biomarkers are systematically reviewed and categorized according to endothelial cell (EC) (dys)function in SSc.

METHODS

A sensitive search on behalf of the EULAR study group on microcirculation in Rheumatic Diseases was developed in Pubmed, The Cochrane Library and Web of Science to identify articles on SSc vasculopathy and the role of ECs using the following Mesh terms: (systemic sclerosis OR scleroderma) AND pathogenesis AND (endothelial cells OR marker). All selected papers were read and discussed by two independent reviewers. The selection process was based on title, abstract and full text level. Additionally, both reviewers further searched the reference lists of the articles selected for reading on full text level for supplementary papers. These additional articles went through the same selection process.

RESULTS

In total 193 resulting articles were selected and the identified biomarkers were categorized according to description of EC (dys)function in SSc. The most representing and reliable biomarkers described by the selected articles were adhesion molecules for EC activation, anti-endothelial cell antibodies for EC apoptosis, vascular endothelial growth factor (VEGF), its receptor VEGFR-2 and endostatin for disturbed angiogenesis, endothelial progenitors cells for defective vasculogenesis, endothelin-1 for disturbed vascular tone control, Von Willebrand factor for coagulopathy and interleukin (IL)-33 for EC-immune system communication. Emerging, relatively new discovered biomarkers described in the selected articles, are VEGF₁₆₅b, IL-17A and the adipocytokines. Finally, myofibroblasts involved in tissue fibrosis in SSc can derive from ECs or epithelial cells through a process known as endothelial-to-mesenchymal transition.

CONCLUSION

This systematic review emphasizes the growing evidence that SSc is primarily a vascular disease where EC dysfunction is present and prominent in different aspects of cell survival (activation and apoptosis), angiogenesis and vasculogenesis and where disturbed interactions between ECs and various other cells contribute to SSc vasculopathy.

Leg Ulcers of Unusual Causes

In this review, unusual causes of leg ulcers are examined with an emphasis on pathophysiology, clinical presentation, and epidemiology. Cutaneous ulcers due to malignancy of unusual leg ulcers with hematologic disorders, vasculitis, sarcoidosis, calciphylaxis, Buerger’s disease, and pyoderma gangrenosumare discussed.

Potential beneficial role for endothelin in scleroderma vasculopathy: inhibition of endothelial apoptosis by type B endothelin-receptor signaling

Objectives

Microvascular endothelial cell (MVEC) apoptosis is considered to be a key event in the pathogenesis of systemic sclerosis (SSc), an increased expression of endothelin-1 (ET1) is also well recognized in the disease. ET1 is thought to exert deleterious effects on the vasculature by virtue of its known vasospastic, proliferative and fibrotic effects, yet ET1 can act as a survival factor for a variety of cells, including MVEC. The aim of this study is to investigate if ET1 signaling protects SSc-MVECs from apoptosis.

Methods

The expression levels of ET1-receptor genes: Endothelin Receptor Type A gene (EDNRA) and Endothelin Receptor Type B gene (EDNRB), and the effects of selective Endothelin Receptor Type A (ETA) antagonists, selective Endothelin Receptor Type B (ETB), and dual ETA/B antagonist in the presence and/or absence of ET1 on control and SSc-MVEC apoptosis were examined.

Results

Significant increase in the expression of ETA and ETB was noted in SSc-MVECs. Growth factors withdrawal (GFW) resulted in a significant apoptosis that was considerably reduced by the addition ET1. The addition of ETA-receptor antagonists did not affect ET1 anti-apoptotic effects, while the nonselective ETA/B or the selective ETB-receptor antagonists blocked the anti-apoptotic effects of ET1. Finally, an upregulation of the proapoptotic gene BAX after GFW was noted that was normalized by the addition of ET1.

Conclusions

The results suggest that ET1 mediates an anti-apoptotic effect through engaging the ETB receptors in MVECs. Therefore, it appears that selective ETA antagonism may have an advantage over the non-selective ET1-receptor antagonists in SSc vasculopathy, particularly in the early stages of the disease when MVEC apoptosis is rampant.

Endothelial dysfunction in systemic sclerosis

PURPOSE OF REVIEW

Microvascular endothelial cells (MVECs) injury is a critical early event in the pathogenesis of systemic sclerosis (SSc). We aim to provide the reader with an update regarding the role of MVECs in the pathogenesis of SSc and the mechanisms for MVECs dysfunction in the disease.

RECENT FINDINGS

Recent evidence confirms the central role for MVECs in the pathogenesis of SSc, and suggests further mechanisms for MVECs injury. The impact of MVECs perturbations in SSc goes beyond the initiation of the vascular disease to include activation of fibroblasts through the release of cytokines and growth factors like connective tissue growth factor that induce an active and aggressive form of fibroblasts. Moreover, recent studies highlighted a more prominent role for epigenetic factors in the pathogenesis of SSc, and suggested defects in the function of progenitor endothelial cells in SSc. Recent reports helped to shed light on the role of antiendothelial cell antibodies in the pathogenesis of SSc, especially purified subsets of these antibodies like anti-ICAM-1 antibodies, and also reported possible mechanisms for defective vascular endothelial growth factor signaling.

SUMMARY

It is clear that MVECs dysfunction is a key element in the pathogenesis of SSc, but the initial triggers for MVEC dysfunction remain uncharacterized.

Cutaneous vasodilator and vasoconstrictor mechanisms in temperature regulation

In this review, we focus on significant developments in our understanding of the mechanisms that control the cutaneous vasculature in humans, with emphasis on the literature of the last half-century. To provide a background for subsequent sections, we review methods of measurement and techniques of importance in elucidating control mechanisms for studying skin blood flow. In addition, the anatomy of the skin relevant to its thermoregulatory function is outlined. The mechanisms by which sympathetic nerves mediate cutaneous active vasodilation during whole body heating and cutaneous vasoconstriction during whole body cooling are reviewed, including discussions of mechanisms involving cotransmission, NO, and other effectors. Current concepts for the mechanisms that effect local cutaneous vascular responses to local skin warming and cooling are examined, including the roles of temperature sensitive afferent neurons as well as NO and other mediators. Factors that can modulate control mechanisms of the cutaneous vasculature, such as gender, aging, and clinical conditions, are discussed, as are nonthermoregulatory reflex modifiers of thermoregulatory cutaneous vascular responses.

Differentiation potential of CD14+ monocytes into myofibroblasts in patients with systemic sclerosis

Background

Circulating monocytes are a highly plastic and functionally heterogeneic cell type with an activated phenotype in patients with systemic sclerosis (SSc). CD14⁺ monocytes have the potential to differentiate into extra-cellular matrix (ECM) producing cells, possibly participating in fibrogenesis.

Aim

To study the effect of GM-CSF, IL-4 and endothelin -1 (ET-1) alone or in combination on monocyte differentiation into myofibroblasts.

Methods

CD14⁺ cells were isolated from peripheral blood from 14 SSc patients and healthy controls by positive selection and incubated with different combinations of GM-CSF, IL-4 and ET-1 for 14 days. Type-1 collagen and α-SMA were detected by Western blot, qPCR and confocal microscopy. HLA-DR, CD11c and CD14 expression was analysed by flow cytometry. A collagen gel contraction assay was performed for functional myofibroblast assessment.

Results

GM-CSF both induced collagen and α-SMA expression after 14 days. ET-1 further increased GM-CSF-induced collagen expression in a dose dependent manner up to 30-fold. IL-4/GM-CSF combination leads to a more DC-like phenotype of monocytes associated with reduced collagen and α-SMA expression compared to GM-CSF alone. Collagen and α-SMA expression was higher in monocytes from SSc patients and monocytes were more prone to obtain a spindle form. In contrast to controls, ET-1 and IL-4 alone were sufficient to induce α-SMA expression in monocytes from SSc patients. Despite the induction of α-SMA expression, monocyte-derived myofibroblasts only had a moderate capability of contraction in functional analyses.

Conclusion

SSc monocytes display increased maturation towards myofibroblasts demonstrated by their phenotype and α-SMA expression when compared to monocytes from healthy controls, however only with minor functional contraction properties.

dsRNA activation of endothelin-1 and markers of vascular activation in endothelial cells and fibroblasts

BACKGROUND

In patients with systemic sclerosis (SSc), the relationship between innate immune activation, represented by increased expression of interferon (IFN)-regulated genes, and vascular injury/activation, manifest by increased endothelin-1 (ET-1), endothelin converting enzyme-1 (ECE1) and intercellular adhesion molecule-1, is uncertain.

OBJECTIVE

To investigate the potential roles of innate immune ligands in both these pathogenic pathways.

METHODS

The effect of known Toll-like receptor (TLR) ligands was tested in vitro on dermal microvascular and pulmonary arterial endothelial cells, and on dermal fibroblasts cultured from healthy controls and patients with SSc. To test the effect of double-stranded RNA (dsRNA) on vascular activation/injury in vivo, polyinosinic/polycytidylic acid (poly(I:C)) was administered continuously over 7 days by subcutaneous osmotic pump.

RESULTS

dsRNA/poly(I:C), but not other TLR ligands, highly stimulated ET-1 protein and mRNA (EDN1), as well as intercellular adhesion molecule-1 (ICAM-1) and IFN-regulated MX2, by endothelial cells and dermal fibroblasts. Poly(I:C) induced EDN1, ECE1, and ICAM-1 mRNA expression in poly(I:C) treated skin. Poly(I:C)-induced EDN1, ECE1 and MX2 was not blocked in mice with the type I IFN receptor deleted. However, poly(I:C)-induced EDN1 and ECE1, but not poly(I:C)-induced ICAM-1 expression was blocked in mice with the TLR3 signalling protein TRIF/TICAM-1 deleted.

CONCLUSION

Together these data show that the dsRNA can regulate genes associated with vascular activation, as seen in SSc, that type I IFNs do not mediate these effects, and that EDN1 and ECE1 but not ICAM-1 activation is mediated by TLR3.

Raynaud’s Phenomenon and Plasma Endothelin: Correlations with Capillaroscopic Patterns in Systemic Sclerosis

Objective.

We evaluated endothelin (ET)-1 plasma levels and some clinical measures in patients with primary Raynaud’s phenomenon (PRP), and in patients with systemic sclerosis (SSc) and secondary RP (SRP), in the latter according to their different nailfold videocapillaroscopy (NVC) patterns of microangiopathy (early, active, and late).

Methods.

Ninety-nine patients with SSc, 49 with PRP, and 45 control subjects were studied. NVC was performed in all patients to distinguish the pattern of microvascular damage, and the morphological alterations were scored by a semiquantitative rating scale. ET-1 plasma levels were evaluated in all individuals by ELISA.

Results.

ET-1 plasma levels were significantly higher (p = 0.001) in patients with both PRP and SRP, compared to controls. A significant positive correlation (p = 0.03) was found between ET-1 plasma levels and SRP duration, but not between ET-1 plasma levels and PRP duration. Significant correlations were observed in patients with SSc between ET-1 plasma levels and clinical measures (e.g., digital ulcers), as well as the score value of single NVC measures, such as the number of capillaries, “ramified” capillaries, and enlarged capillaries (p < 0.05). Finally, the highest ET-1 plasma levels were found in patients with SSc showing the late pattern of microangiopathy when compared to the early pattern (p = 0.03) and to controls (p = 0.003).

Conclusion.

Highest ET-1 plasma levels were detected in the more advanced stage of the SSc microangiopathy, namely the late NVC pattern, characterized by capillary loss and increased tissue fibrosis; this might support the involvement of ET-1 in the progression of the microvascular/fibrotic SSc damage.

Practical techniques for detection of Toll-like receptor-4 in the human intestine

The human intestine has evolved in the presence of a diverse array of luminal microorganisms. In order to maintain intestinal homeostasis, mucosal immune responses to theses microorganisms must be tightly regulated. The intestine needs to be able to respond to pathogenic organisms while at the same time maintain tolerance to normal commensal flora. Toll-like receptors (TLRs) play an important role in this delicate balance. TLRs are transmembrane noncatalytic receptor proteins that induce activation of innate and adaptive immune responses to microorganisms by recognizing structurally conserved molecular patterns of microbes. Expression of TLRs by intestinal epithelial cell is normally down-regulated to maintain immune tolerance to the luminal microorganisms.One of the challenges of TLR research in the human intestine is that it is difficult for many experimental methods to detect very low expression of TLRs within the intestinal mucosa. Quantitative methods such as PCR are limited in their ability to detect TLR expression by specific cell types within a tissue sample, which can be important when studying the contribution of TLR signaling to pathological conditions. In this regard, immunohistochemistry (IHC) is advantageous in that one can visualize the distribution and localization of target proteins within both normal and pathologic parts of a given tissue sample. We found that a subset of human colorectal cancers over-express TLR4 by means of immunofluorescence (IF) and IHC methods. Localization of TLR4 within cancer tissue often appears to be patchy, making IHC an appropriate way to examine these changes. We will describe our current techniques to detect TLR4 in paraffin-embedded human large intestine sections. Establishing a practical IHC technique that may provide consistent results between laboratories will significantly enhance understanding of the role of TLRs in human intestinal health and disease.

Endothelin-1 and endothelin receptors in the basilar artery of the capybara

Little is known about cerebral vasculature of capybara, which seems may serve as a natural model of studying changes in cerebral circulation due to internal carotid artery atrophy at animal sexual maturation. This is the first study of the light- and electron-immunocytochemical localisation of endothelin-1 (ET-1) and ETA and ETB endothelin receptors in the basilar artery of capybaras (6 to 12-month-old females and males) using an ExtrAvidin detection method. All animals examined showed similar patterns of immunoreactivity. Immunoreactivity for ET-1 was detected in the endothelium and adventitial fibroblasts, whilst immunoreactivity for ETA and ETB receptors was present in the endothelium, vascular smooth muscle, perivascular nerves and fibroblasts. In endothelial cells immunoreactivity to ET-1 was pronounced in the cytoplasm or on the granular endoplasmic reticulum. Similar patterns of immunolabelling were observed for ETA and ETB receptors, though cytoplasmic location of clusters of immunoprecipitate seems dominant. These results suggest that the endothelin system is present throughout the wall of the basilar artery of capybara.

Identification of novel targets in scleroderma: update on population studies, cDNA arrays, SNP analysis, and mutations

PURPOSE OF REVIEW

Systemic sclerosis, or scleroderma, is an uncommon autoimmune connective tissue disease that results in systemic fibrosis. Its etiologic basis remains unclear. The pathogenesis of systemic sclerosis involves a proliferative and obliterative vasculopathy resulting from endothelial cell dysfunction, extensive fibrosis secondary to fibroblast activation, and autoimmunity as demonstrated by the presence of disease-specific autoantibodies. Although there is no clear and convincing evidence for an environmental trigger in most cases, accumulating data emphasize the role of genetic factors in systemic sclerosis. As in other complex human diseases, multiple genes likely contribute to disease susceptibility and the clinical manifestations of systemic sclerosis. This review will cover the application of genomics to the complex genetics of systemic sclerosis.

RECENT FINDINGS

The following review is an update on novel targets identified in scleroderma based on published reports (May 2000-May 2003) of mutation/polymorphism analysis (using SNP and haplotyping), the results from a recent genome-wide scan on a Native American population with systemic sclerosis, and gene expression studies (microarrays).

SUMMARY

The use of genomics has revealed novel targets and genetic associations that may contribute to the cause, the onset, and the subsequent pathologic changes that constitute systemic sclerosis. The identification of potential candidates for gene therapy or disease-specific targets amenable to pharmacologic intervention will benefit patients with systemic sclerosis who are currently being treated for their symptoms and not the disease process itself.

Systemic sclerosis: the susceptible host (genetics and environment)

It is becoming evident that several genetic factors participate in modulating susceptibility to SSc and its clinical manifestations. Some genes that specifically affect ECM metabolism and vascular function may be unique to SSc and scleroderma-related disorders; others, such as those genes involved in regulating immune tolerance, are likely shared with other autoimmune diseases. The effect of genetic variations (or polymorphisms) that are found in most of these genes taken individually will likely have only a small or modest effect on disease risk; only a few genetic variations are expected to be highly penetrant. Moreover, genetic studies in SSc have to deal with the additional issues of heterogeneous phenotypes, low disease prevalence in the general population, and an even greater paucity of multiplex families that makes traditional linkage studies difficult, if not impossible. Alternative approaches include allelic association studies, but conventional case-controls designs may be subject to selection bias and will require large sample sizes if the genes that are under investigation confer only modest (OR = 1.5-2.0) disease risk (Fig. 2). The simultaneous examination of several genes that are biologically relevant to a specific disease process to attain higher aggregate ORs, is one approach that was used in several reports that were cited in this review. The use of family-based controls, such as in the transmission-disequilibrium test (based on assessment of the transmitted or nontransmitted alleles that are associated with disease from heterozygous parents to affected offspring), would provide more robustness to spurious associations from population stratification, but is actually less powerful and efficient than case-control designs. Furthermore, for many late adult-onset diseases the effort required to obtain samples from living parents are for a variety of reasons not trivial. The success of these allelic association-based approaches depends on the identification of likely candidate disease genes (or at least markers in disequilibrium with disease genes), careful definition/ascertainment of disease phenotypes to minimize genetic heterogeneity, and for case-control designs, strategies to account for population stratification or admixture. The identification of candidate genes will be aided by rapid progress in the Human Genome Project and other genome efforts that will eventually identify all human genetic variations. Although this will lead to better understanding of the genes that might be involved in complex diseases, much work is required to understand the basic biology of how disease genotypes become clinical phenotypes. This is especially daunting in complex diseases, such as SSc, where the phenotype (including disease susceptibility and clinical presentation) is influenced by dynamic interactions between genetic variations and environment. Multi-center collaborative efforts with research paradigms that integrate genetic and environmental factors (including sociodemographic variables) will be required to elucidate the contribution of environment and genetics in the pathogenesis of SSc.

Development of histologic features of scleroderma in congenital lesions

BACKGROUND

Localized scleroderma has been reported after radiation therapy, but has never been reported to occur at the site of a congenital lesion.

CASE REPORT

We present two patients, both with family histories of autoimmune disease, who reported unilateral hypopigmented areas on the trunk since birth. The areas remained asymptomatic and grew with the patients until adulthood when the areas became indurated then firm and showed hyperpigmentation.

HISTOLOGY

Histologically, both lesions showed features of localized scleroderma with diffuse sclerosis of collagen and loss of periadnexal fat. There was a perivascular lymphoplasmocytic infiltrate with occasional eosinophils extending into the subcutaneous fat predominantly along fat septae, and diffuse loss of CD34+ stromal cell populations within the lesions.

CONCLUSION

We propose that somatic mutations affecting vessels may predispose to increased endothelial cell apoptosis. This could lead to the development of an autoimmune response in some individuals, and the areas of localized scleroderma may be markers of susceptibility to autoimmune disease.

Correlation between diffuse pigmentation and keratinocyte-derived endothelin-1 in systemic sclerosis

BACKGROUND

The precise mechanism of diffuse pigmentation in systemic sclerosis (SSc) is still unknown. We suspected the participation of endothelin-1 (ET-1), which is produced by keratinocytes, in the hyperpigmentation in SSc. The aims of this study are to demonstrate the hyperproductivity of ET-1 from epidermal cells in SSc by in situ hybridization histochemistry, and to show a correlation between the hyperproductivity of ET-1 in keratinocytes and skin hyperpigmentation.

METHODS

In situ hybridization histochemistry was performed on nine SSc specimens (five cases of diffuse scleroderma (dSSc), four cases of acrosclerosis (lSSc)), and compared with four normal control specimens. We counted the grains on 10 x 10 microm(2) of epidermis and microvessels in each histology and examined the degree of skin pigmentation using the skin reflectance factor (Y).

RESULTS

In the specimens of the SSc patients, the number of grains on the epidermis was remarkably higher than those of the control specimens (P < 0.01). We found a close correlation between the number of grains and the skin reflectance factor in dSSc patients (P = 0.02). Correlations were not identified between serum ET-1 and skin pigmentation and between serum ET-1 and the frequency of grains on the epidermis. As for grains on microvessels, lSSc patients showed a greater frequency than dSSc patients.

CONCLUSIONS

The findings of this study suggest that an increase in the ET-1 productivity of keratinocytes is experienced in SSc patients, especially in dSSc patients. The results suggest a strong correlation between the ET-1 productivity of keratinocytes and skin pigmentation in severe cases of SSc. We conclude from these results that keratinocyte-derived ET-1 plays an important role in the pathogenesis of the hyperpigmentation of the skin in SSc patients.

Transforming growth factor-beta1 and ultraviolet A1 radiation increase production of vascular endothelial growth factor but not endothelin-1 in human dermal fibroblasts

BACKGROUND

Normal and dysregulated wound healing involves fibroblast activation and angiogenesis, in which polypeptide factors such as transforming growth factor (TGF)-beta, vascular endothelial growth factor (VEGF) and endothelin-1 (ET-1) play an important part. Ultraviolet (UV) A1 (365 nm) has recently received attention as a possible treatment for some dermal fibrotic disorders.

OBJECTIVES

The aim of this study was to evaluate the effects of TGF-beta1 and UVA1 radiation, as well as that of cobalt chloride, reported to mimic hypoxia both in vivo and in vitro, on the expression of VEGF and ET-1 by cultured human dermal fibroblasts.

METHODS

Levels of VEGF and ET-1 were measured by enzyme-linked immunosorbent assay and expression of neutral endopeptidase (NEP, CD10), known to degrade ET-1, was quantified by flow cytometric analysis after cell trypsinization.

RESULTS

Our results showed that the cells released minor amounts of VEGF and ET-1. Both TGF-beta1 and UVA1 strongly increased VEGF secretion in a dose- and time-dependent manner, without significantly affecting ET-1 release. Irradiation of TGF-beta1-stimulated fibroblasts resulted in a synergistic effect on increasing levels of VEGF but not ET-1 after 48 h. Cobalt chloride stimulated the secretion of VEGF by fibroblasts; the effects of TGF-beta1 and cobalt were additive. However, no significant effect of cobalt chloride on ET-1 secretion was observed, suggesting that ET-1 production in fibroblasts is not oxygen-sensitive. The expression of NEP was not modified by TGF-beta1 or UVA1 radiation. Addition of a neutralizing anti-CD10 antibody to fibroblast cultures downregulated CD10 expression at the cell surface without changing ET-1 levels in cell supernatants after 24 or 48 h. This suggests that membrane-bound NEP has minimal or no activity against secreted ET-1.

CONCLUSIONS

Taken together, these results underline the major role played by TGF-beta1 in increasing VEGF secretion by fibroblasts. This, as well as the documented effect of UVA1 on increasing VEGF production, may have implications for wound healing in vivo.

Autoimmunity and vascular involvement in systemic sclerosis (SSc)

Endothelial injury, obliterative microvascular lesions, and increased vascular wall thickness are present in all involved organs in scleroderma. The vascular pathology is associated with altered vascular function with increased vasospasm, reduced vasodilatory capacity and increased adhesiveness of the blood vessels to platelets and lymphocytes. The extent of injury and dysfunction is reflected by changes in the circulating levels of vascular markers. The initial triggers for the vascular pathology are not known. Possible viral triggers are visited here, including cytomegalovirus in view of increased levels of anti-CMV antibodies in scleroderma, and the remarkable similarities between CMV vasculopathies and scleroderma vascular disease. Endothelial apoptosis in scleroderma may be related to viral infection, immune reactions to viral or environmental factors, reperfusion injury or to anti-endothelial antibodies. The impact of the vascular pathology on the evolution of tissue fibrosis is not known; still, cytokines (TGFbeta, IL4), vascular factors (endothelin), and growth factors (PDGF) are possibly crucial signals that link the vascular disease to tissue fibrosis. Knowledge of the regulation of these and other factors will provide the opportunity to develop more rational therapeutic approaches to the disease.

The pathogenesis of cutaneous fibrosis

Cutaneous fibrosis is an integral component of a variety of human disorders including keloids, hypertrophic scar, and most notably, scleroderma. Each has its own etiology and unique clinical characteristics, but all involve the dysregulation of connective tissue metabolism, in particular, the activation of dermal fibroblasts. In this review, we examine various molecular events in scleroderma that may lead to fibroblast activation, and propose a new model to explain the persistence of such activation by scleroderma fibroblasts in the apparent absence of exogenous stimuli.