Intussusceptive Lymphangiogenesis in Lymphatic Malformations/Lymphangiomas.

Intussusception in lymphatic vessels has received less attention than in blood vessels. In tumors and pseudotumors of blood vessels with intravascular papillary structures, including sinusoidal hemangioma and intravascular papillary endothelial hyperplasia, we observed exuberant intussusceptive angiogenesis, as well as the similarity between papillae (term used by pathologists) and pillars/folds (hallmarks of intussusceptive angiogenesis). A similar response could be expected in lymphangiomas (lymphatic malformations and reactive processes rather than tumors) with papillae. The aim of this work is to assess whether papillae/pillars/folds and associated structures (vessel loops and septa) are present in lymphangiomas, and to establish the characteristics and formation of these structures. For this purpose, we selected lymphangiomas with intraluminal papillae (n = 18), including cystic, cavernous, circumscriptum, and progressive types, of which two cases of each type with a greater number of papillae were used for serial histologic sections and immunohistochemistry. The studies showed a) dilated lymphatic spaces giving rise to lymphatic-lymphatic vascular loops, which dissected and encircled perilymphatic structures (interstitial tissue structures/ITSs and pillars/posts), b) ITSs and pillars, surrounded by anti-podoplanin-positive endothelial cells, protruding into the lymphatic spaces (papillary aspect), and c) splitting, remodeling, linear arrangement, and fusion of papillae/pillars/folds, forming papillary networks and septa. In conclusion, as occurs in blood vessel diseases, the development of lymphatic vessel loops, papillae/pillars/folds, and septa (segmentation) supports intussusceptive lymphangiogenesis and suggests a piecemeal form of intussusception. This intussusceptive lymphangiogenesis in lymphatic diseases can provide a basis for further studies of lymphatic intussusception in other conditions, with clinical and therapeutic implications. Anat Rec, 302:2003-2013, 2019. © 2019 American Association for Anatomy.

Sinusoidal hemangioma and intravascular papillary endothelial hyperplasia: Interrelated processes that share a histogenetic piecemeal angiogenic mechanism.

Sinusoidal hemangioma, characterized by interconnecting thin-walled vascular spaces, may present papillae/pseudo-papillae and zones that resemble intravascular papillary endothelial hyperplasia (IPEH). Our objectives are to explore the existence of zones in IPEH with sinusoidal hemangioma characteristics, the mechanism of papillary and septa formation in sinusoidal hemangioma and the comparison of this mechanism with that in IPEH. For these purposes, specimens of 4 cases of each entity were selected and studied by serial histologic sections and by immunochemistry and immunofluorescence procedures. The results showed a) zones with characteristics of sinusoidal hemangioma in IPEH cases, b) presence in both entities of papillae with a cover formed by a monolayer of CD34+ and CD31+ endothelial cells (ECs) and a core formed by either type I collagen and αSMA+ cells (presenting a pericyte/smooth muscle cell aspect) or thrombotic components, and c) a similar piecemeal angiogenic mechanism in papillary formation, including sprouting of intimal ECs toward the vessel wall itself or intravascular thrombi, formation of vascular loops that encircle and separate vessel wall or thrombus components, and parietal or thrombotic papillae development. The major differences between both entities were the number, arrangement and substrate of papillae: myriad, densely grouped, parietal and thrombotic papillae in IPEH, and a linear arrangement of predominant parietal papillae in sinusoidal hemangioma, originating septa (segmentation). In conclusion, sinusoidal hemangioma and IPEH are interrelated processes, which share morphologic findings and a piecemeal angiogenic mechanism, combining sprouting and intussusceptive angiogenesis, and leading to papillary formation and vessel segmentation.

Piecemeal Mechanism Combining Sprouting and Intussusceptive Angiogenesis in Intravenous Papillary Formation Induced by PGE2 and Glycerol.

Recently, we demonstrated that in human intravascular papillary endothelial hyperplasia (IPEH), vein wall vascularization occurs in association with myriad papillae, a large part of which formed in the vascularized vein wall. Previously, using an animal model, we observed that PGE2 and glycerol administration around the femoral vein originates intense vascularization of the vein wall from its intimal endothelial cells (ECs). This vascularization is similar to that in IPEH. The aim of this study is to assess the mechanism of papillary formation, using this model after demonstrating papillary development in neo-vascularized femoral vein walls. In semithin and ultrathin sections, the sequential vascular and papillary development was as follows: (a) activation of vein intimal ECs, (b) sprouting of intimal ECs towards the vein media layer and microvessel development, (c) interconnection between neighboring microvessels originated elementary loops, which encircled vein wall components and formed papillae. The encircling ECs formed the papillary cover, and the encircled component formed the core. The papillae showed a similar structure to that of folds and pillars in intussusceptive angiogenesis, and (d) origin of secondary and complex loop systems by interconnection of neighboring elementary loops and by splitting of papillae by new loops, with abundant papillary development. In conclusion, the results support a piecemeal angiogenic mechanism in papillary formation, with association of sprouting and intussusceptive types of angiogenesis. Further studies are needed to assess whether the intravascular papillae described in several pathologic processes, including vessel tumors, such as Dabska's tumor, retiform hemangioendothelioma, and angiosarcoma, follow a similar mechanism. Anat Rec, 2017. © 2017 Wiley Periodicals, Inc. Anat Rec, 300:1781-1792, 2017. © 2017 Wiley Periodicals, Inc.

Behaviour of telocytes during physiopathological activation.

We consider CD34+ stromal cells/telocytes (CD34+ SC/TCs) in normal and pathological conditions. These cells are involved in organisation and control of the extracellular matrix, structural support, creation of microenvironments, intercellular communication, neurotransmission, immunomodulation and immunosurveillance, inhibition of apoptosis, and control, regulation and source of other cell types. CD34+ SC/TCs are widely reported in the origin of interstitial cells of Cajal and in regeneration in the heart, skeletal muscle, skin, respiratory tree, liver, urinary system and the eye. In addition, we contribute CD34+ SC/TC hyperplasia associated with several processes, including neurogenous hyperplasia (neuroma of the appendix), hyperplasia of Leydig cells in undescended testes (Cryptorchidism), peripheral areas of inflammatory/repair processes (pericicatricial tissue and transitional zones between diseased segments in Crohn's disease and normal bowel), benign tumours (neurofibromas, Antoni-B zones of neurilemmomas, granular cell tumours, and melanocytic nevi) and in some lesions with myxoid, oedematous and degenerative changes (Reinke's oedema, myxomatous mitral valve degeneration, thyroid-associated ophthalmopathy and basophilic degenerative changes of the collagen in the dermis). We pay particular attention to the role of CD34+ SC/TCs during repair through granulation tissue, including morphologic changes, loss of CD34 expression and gain of αSMA expression with myofibroblast transformation, and interactions with pericytes, endothelial and inflammatory cells. Finally, we consider CD34 or αSMA expression in stromal cells of malignant epithelial tumours, and the role of CD34+ SC/TCs in the origin of carcinoma-associated fibroblasts (CAFs) and myofibroblasts. In conclusion, CD34+ SC/TCs play an important role in the maintenance and modulation of tissue homeostasis and in morphogenesis/renewal/repair.

Behavior of in situ human native adipose tissue CD34+ stromal/progenitor cells during different stages of repair. Tissue-resident CD34+ stromal cells as a source of myofibroblasts.

CD34+ adipose stromal cells are scattered in the adipose tissue and found in the CD34+ population of the stromal vascular fraction (SVF). This fraction includes adipose-derived stromal/stem/progenitor cells (ASCs), which have attracted considerable attention and show great promise for the future of regenerative medicine. Studies in this field have been undertaken mainly in vitro. In this work, however, we assessed the characteristics of human adipose tissue-resident CD34+ stromal cells in normal conditions and when activated in vivo during inflammatory/repair processes at different stages of evolution. In normal adipose tissue, these cells showed a characteristic location (peri/paravascular and between adipocytes), a fusiform or stellate morphology, long and moniliform processes, and scarce organelles. During inflammatory/repair stages, native CD34+ stromal cells increased in size, proliferated, developed numerous organelles of synthesis, lost CD34 expression, and differentiated into myofibroblasts (αSMA expression and typical ultrastructure). In double-stained sections, cells expressing both CD34 and αSMA were observed. CD34 expression correlated positively with a high proliferative capacity (Ki-67 expression). Conversely, CD34 expression was lost with successive mitoses and with increased numbers of macrophages in the granulation tissue. CD34+ stromal cell behavior varied depending on proximity to (with myofibroblast differentiation) or remoteness from (with activated plump cells conserving CD34 expression) injury. In conclusion, our observations point to human adipose tissue-resident CD34+ stromal cells as an important source of myofibroblasts during inflammatory/repair processes. Moreover, stromal cell activation may occur with or without αSMA expression (with or without myofibroblast transformation) and with loss or persistence of CD34 expression, respectively.

Uptake and intracytoplasmic storage of pigmented particles by human CD34+ stromal cells/telocytes: endocytic property of telocytes.

We studied the phagocytic-like capacity of human CD34+ stromal cells/telocytes (TCs). For this, we examined segments of the colon after injection of India ink to help surgeons localize lesions identified at endoscopy. Our results demonstrate that CD34+ TCs have endocytic properties (phagocytic-like TCs: phTCs), with the capacity to uptake and store India ink particles. phTCs conserve the characteristics of TCs (long, thin, bipolar or multipolar, moniliform cytoplasmic processes/telopodes, with linear distribution of the pigment) and maintain their typical distribution. Likewise, they are easily distinguished from pigment-loaded macrophages (CD68+ macrophages, with oval morphology and coarse granules of pigment clustered in their cytoplasm). A few c-kit/CD117+ interstitial cells of Cajal also incorporate pigment and may conserve the phagocytic-like property of their probable TC precursors. CD34+ stromal cells in other locations (skin and periodontal tissues) also have the phagocytic-like capacity to uptake and store pigments (hemosiderin, some components of dental amalgam and melanin). This suggests a function of TCs in general, which may be related to the transfer of macromolecules in these cells. Our ultrastructural observation of melanin-storing stromal cells with characteristics of TCs (telopodes with dichotomous branching pattern) favours this possibility. In conclusion, intestinal TCs have a phagocytic-like property, a function that may be generalized to TCs in other locations. This function (the ability to internalize small particles), together with the capacity of these cells to release extracellular vesicles with macromolecules, could close the cellular bidirectional cooperative circle of informative exchange and intercellular interactions.

Telocytes in neuromuscular spindles.

A new cell type named telocyte (TC) has recently been identified in various stromal tissues, including skeletal muscle interstitium. The aim of this study was to investigate by means of light (conventional and immunohistochemical procedures) and electron microscopy the presence of TCs in adult human neuromuscular spindles (NMSs) and lay the foundations for future research on their behaviour during human foetal development and in skeletal muscle pathology. A large number of TCs were observed in NMSs and were characterized ultrastructurally by very long, initially thin, moniliform prolongations (telopodes - Tps), in which thin segments (podomeres) alternated with dilations (podoms). TCs formed the innermost and (partially) the outermost layers of the external NMS capsule and the entire NMS internal capsule. In the latter, the Tps were organized in a dense network, which surrounded intrafusal striated muscle cells, nerve fibres and vessels, suggesting a passive and active role in controlling NMS activity, including their participation in cell-to-cell signalling. Immunohistochemically, TCs expressed vimentin, CD34 and occasionally c-kit/CD117. In human foetus (22-23 weeks of gestational age), TCs and perineural cells formed a sheath, serving as an interconnection guide for the intrafusal structures. In pathological conditions, the number of CD34-positive TCs increased in residual NMSs between infiltrative musculoaponeurotic fibromatosis and varied in NMSs surrounded by lymphocytic infiltrate in inflammatory myopathy. We conclude that TCs are numerous in NMSs (where striated muscle cells, nerves and vessels converge), which provide an ideal microanatomic structure for TC study.