Objective Systemic sclerosis (SSc) features multiorgan fibrosis orchestrated predominantly by activated myofibroblasts. Endothelial-to-mesenchymal transition (EndoMT) is a transdifferentiation by which endothelial cells (ECs) lose their specific morphology/markers and acquire myofibroblast-like features. Here, we determined the possible contribution of EndoMT to the pathogenesis of dermal fibrosis in SSc and two mouse models. Methods Skin sections were immunostained for endothelial CD31 or vascular endothelial (VE)-cadherin in combination with α-smooth muscle actin (α-SMA) myofibroblast marker. Dermal microvascular ECs (dMVECs) were prepared from SSc and healthy skin (SSc-dMVECs and H-dMVECs). H-dMVECs were treated with transforming growth factor-β1 (TGFβ1) or SSc and healthy sera. Endothelial/mesenchymal markers were assessed by real-time PCR, immunoblotting and immunofluorescence. Cell contractile phenotype was assayed by collagen gel contraction. Results Cells in intermediate stages of EndoMT were identified in dermal vessels of either patients with SSc or bleomycin-induced and urokinase-type plasminogen activator receptor (uPAR)-deficient mouse models. At variance with H-dMVECs, SSc-dMVECs exhibited a spindle-shaped appearance, co-expression of lower levels of CD31 and VE-cadherin with myofibroblast markers (α-SMA+ stress fibres, S100A4 and type I collagen), constitutive nuclear localisation of the EndoMT driver Snail1 and an ability to effectively contract collagen gels. Treatment of H-dMVECs either with SSc sera or TGFβ1 resulted in the acquisition of a myofibroblast-like morphology and contractile phenotype and downregulation of endothelial markers in parallel with the induction of mesenchymal markers. Matrix metalloproteinase-12-dependent uPAR cleavage was implicated in the induction of EndoMT by SSc sera. Conclusions In SSc, EndoMT may be a crucial event linking endothelial dysfunction and development of dermal fibrosis.

Telocytes, a peculiar type of stromal cells, have been recently identified in a variety of tissues and organs, including human skin. Systemic sclerosis (SSc, scleroderma) is a complex connective tissue disease characterized by fibrosis of the skin and internal organs. We presently investigated telocyte distribution and features in the skin of SSc patients compared with normal skin. By an integrated immunohistochemical and transmission electron microscopy approach, we confirmed that telocytes were present in human dermis, where they were mainly recognizable by their typical ultrastructural features and were immunophenotypically characterized by CD34 expression. Our findings also showed that dermal telocytes were immunophenotypically negative for CD31/PECAM‐1 (endothelial cells), α‐SMA (myofibroblasts, pericytes, vascular smooth muscle cells), CD11c (dendritic cells, macrophages), CD90/Thy‐1 (fibroblasts) and c‐kit/CD117 (mast cells). In normal skin, telocytes were organized to form three‐dimensional networks distributed among collagen bundles and elastic fibres, and surrounded microvessels, nerves and skin adnexa (hair follicles, sebaceous and sweat glands). Telocytes displayed severe ultrastructural damages (swollen mitochondria, cytoplasmic vacuolization, lipofuscinic bodies) suggestive of ischaemia‐induced cell degeneration and were progressively lost from the clinically affected skin of SSc patients. Telocyte damage and loss evolved differently according to SSc subsets and stages, being more rapid and severe in diffuse SSc. Briefly, in human skin telocytes are a distinct stromal cell population. In SSc skin, the progressive loss of telocytes might (i) contribute to the altered three‐dimensional organization of the extracellular matrix, (ii) reduce the control of fibroblast, myofibroblast and mast cell activity, and (iii) impair skin regeneration and/or repair.

Ulcerative colitis ( UC ) is characterized by chronic relapsing intestinal inflammation finally leading to extensive tissue fibrosis and resulting in a stiff colon unable to carry out peristalsis or to resorb fluids. Telocytes, a peculiar type of stromal cells, have been recently identified in the human gastrointestinal tract. Several roles have been proposed for telocytes, including mechanical support, intercellular signalling and modulation of intestinal motility. The aim of the present work was to investigate the presence and distribution of telocytes in colonic specimens from UC patients compared with controls. Archival paraffin‐embedded samples of the left colon from UC patients who underwent elective bowel resection and controls were collected. Tissue sections were stained with M asson's trichrome to detect fibrosis. Telocytes were identified by CD 34 immunohistochemistry. In early fibrotic UC cases, fibrosis affected the muscularis mucosae and submucosa, while the muscularis propria was spared. In advanced fibrotic UC cases, fibrosis extended to affect the muscle layers and the myenteric plexus. Few telocytes were found in the muscularis mucosae and submucosa of both early and advanced fibrotic UC colonic wall. In the muscle layers and myenteric plexus of early fibrotic UC , telocytes were preserved in their distribution. In the muscularis propria of advanced fibrotic UC , the network of telocytes was reduced or even completely absent around smooth muscle bundles and myenteric plexus ganglia, paralleling the loss of the network of interstitial cells of Cajal. In UC , a loss of telocytes accompanies the fibrotic remodelling of the colonic wall and might contribute to colonic dysmotility.

Crohn's disease (CD) is a relapsing chronic inflammatory disorder that may involve all the gastrointestinal tract with a prevalence of terminal ileum. Intestinal lesions have a characteristic discontinuous and segmental distribution and may affect all layers of the gut wall. Telocytes (TC), a peculiar type of stromal cells, have been recently identified in a variety of tissues and organs, including gastrointestinal tract of humans and mammals. Several roles have been proposed for TC, including mechanical support, spatial relationships with different cell types, intercellular signalling and modulation of intestinal motility. The aim of our study was to investigate the presence and distribution of TC in disease‐affected and ‐unaffected ileal specimens from CD patients compared with controls. TC were identified by CD34/PDGFRα immunohistochemistry. In affected CD specimens TC disappeared, particularly where fibrosis and architectural derangement of the intestinal wall were observed. In the thickened muscularis mucosae and submucosa, few TC entrapped in the fibrotic extracellular matrix were found. A discontinuous network of TC was present around smooth muscle bundles, ganglia and enteric strands in the altered muscularis propria. At the myenteric plexus, the loss of TC network was paralleled by the loss of interstitial cells of Cajal network. In the unaffected CD specimens, TC were preserved in their distribution. Our results suggest that in CD the loss of TC might have important pathophysiological implications contributing to the architectural derangement of the intestinal wall and gut dysmotility. Further functional studies are necessary to better clarify the role of TC loss in CD pathophysiology.

Systemic sclerosis (SSc) is a complex connective tissue disease characterized by fibrosis of the skin and various internal organs. In SSc, telocytes, a peculiar type of stromal (interstitial) cells, display severe ultrastructural damages and are progressively lost from the clinically affected skin. The aim of the present work was to investigate the presence and distribution of telocytes in the internal organs of SSc patients. Archival paraffin‐embedded samples of gastric wall, myocardium and lung from SSc patients and controls were collected. Tissue sections were stained with Masson's trichrome to detect fibrosis. Telocytes were studied on tissue sections subjected to CD34 immunostaining. CD34/CD31 double immunofluorescence was performed to unequivocally differentiate telocytes (CD34‐positive/CD31‐negative) from vascular endothelial cells (CD34‐positive/CD31‐positive). Few telocytes entrapped in the fibrotic extracellular matrix were found in the muscularis mucosae and submucosa of SSc gastric wall. In the muscle layers and myenteric plexus, the network of telocytes was discontinuous or even completely absent around smooth muscle cells and ganglia. Telocytes were almost completely absent in fibrotic areas of SSc myocardium. In SSc fibrotic lung, few or no telocytes were observed in the thickened alveolar septa, around blood vessels and in the interstitial space surrounding terminal and respiratory bronchioles. In SSc, the loss of telocytes is not restricted to the skin, but it is a widespread process affecting multiple organs targeted by the fibrotic process. As telocytes are believed to be key players in the regulation of tissue/organ homoeostasis, our data suggest that telocyte loss might have important pathophysiological implications in SSc.

Objective Urokinase-type plasminogen activator receptor (uPAR) is a key component of the fibrinolytic system involved in extracellular matrix remodelling and angiogenesis. The cleavage/inactivation of uPAR is a crucial step in fibroblast-to-myofibroblast transition and has been implicated in systemic sclerosis (SSc) microvasculopathy. In the present study, we investigated whether uPAR gene inactivation in mice could result in tissue fibrosis and peripheral microvasculopathy resembling human SSc. Methods The expression of the native full-length form of uPAR in human skin biopsies was determined by immunohistochemistry. Skin and lung sections from uPAR-deficient (uPAR^−/−) and wild-type (uPAR^+/+) mice at 12 and 24 weeks of age were stained with haematoxylin-eosin, Masson's trichrome and Picrosirius red. Dermal thickness and hydroxyproline content in skin and lungs were quantified. Dermal myofibroblast and microvessel counts were determined by immunohistochemistry for α-smooth muscle actin and CD31, respectively. Endothelial cell apoptosis was assessed by TUNEL/CD31 immunofluorescence assay. Results Full-length uPAR expression was significantly downregulated in SSc dermis, especially in fibroblasts and endothelial cells. Dermal thickness, collagen content and myofibroblast counts were significantly greater in uPAR^−/− than in uPAR^+/+ mice. In uPAR^−/− mice, dermal fibrosis was paralleled by endothelial cell apoptosis and severe loss of microvessels. Lungs from uPAR^−/− mice displayed non-specific interstitial pneumonia-like pathological features, both with inflammation and collagen deposition. Pulmonary pathology worsened significantly from 12 to 24 weeks, as shown by a significant increase in alveolar septal width and collagen content. Conclusions uPAR^−/− mice are a new animal model closely mimicking the histopathological features of SSc. This model warrants future studies.