Intussusceptive remodeling of vascular branch angles in chemically-induced murine colitis

The role of vasculature and angiogenesis in respiratory diseases

In European countries, nearly 10% of all hospital admissions are related to respiratory diseases, mainly chronic life-threatening diseases such as COPD, pulmonary hypertension, IPF or lung cancer. The contribution of blood vessels and angiogenesis to lung regeneration, remodeling and disease progression has been increasingly appreciated. The vascular supply of the lung shows the peculiarity of dual perfusion of the pulmonary circulation (vasa publica), which maintains a functional blood-gas barrier, and the bronchial circulation (vasa privata), which reveals a profiled capacity for angiogenesis (namely intussusceptive and sprouting angiogenesis) and alveolar-vascular remodeling by the recruitment of endothelial precursor cells. The aim of this review is to outline the importance of vascular remodeling and angiogenesis in a variety of non-neoplastic and neoplastic acute and chronic respiratory diseases such as lung infection, COPD, lung fibrosis, pulmonary hypertension and lung cancer.

Phenomena of Intussusceptive Angiogenesis and Intussusceptive Lymphangiogenesis in Blood and Lymphatic Vessel Tumors

Intussusceptive angiogenesis (IA) and intussusceptive lymphangiogenesis (IL) play a key role in the growth and morphogenesis of vessels. However, there are very few studies in this regard in vessel tumors (VTs). Our objective is to assess the presence, characteristics, and possible mechanisms of the formation of intussusceptive structures in a broad spectrum of VTs. For this purpose, examples of benign and malignant blood and lymphatic VTs were studied via conventional procedures, semithin sections, and immunochemistry and immunofluorescence microscopy. The results demonstrated intussusceptive structures (pillars, meshes, and folds) in benign (lobular capillary hemangioma or pyogenic granuloma, intravascular papillary endothelial hyperplasia or Masson tumor, sinusoidal hemangioma, cavernous hemangioma, glomeruloid hemangioma, angiolipoma, and lymphangiomas), low-grade malignancy (retiform hemangioendothelioma and Dabska tumor), and malignant (angiosarcoma and Kaposi sarcoma) VTs. Intussusceptive structures showed an endothelial cover and a core formed of connective tissue components and presented findings suggesting an origin through vessel loops, endothelialized thrombus, interendothelial bridges, and/or splitting and fusion, and conditioned VT morphology. In conclusion, the findings support the participation of IA and IL, in association with sprouting angiogenesis, in VTs, and therefore in their growth and morphogenesis, which is of pathophysiological interest and lays the groundwork for in-depth molecular studies with therapeutic purposes.

Transrectal Absorber Guide Raster-Scanning Optoacoustic Mesoscopy for Label-Free In Vivo Assessment of Colitis

Optoacoustic imaging (OAI) enables microscale imaging of endogenous chromophores such as hemoglobin at significantly higher penetration depths compared to other optical imaging technologies. Raster-scanning optoacoustic mesoscopy (RSOM) has recently been shown to identify superficial microvascular changes associated with human skin pathologies. In animal models, the imaging depth afforded by RSOM can enable entirely new capabilities for noninvasive imaging of vascular structures in the gastrointestinal tract, but exact localization of intra-abdominal organs is still elusive. Herein the development and application of a novel transrectal absorber guide for RSOM (TAG-RSOM) is presented to enable accurate transabdominal localization and assessment of colonic vascular networks in vivo. The potential of TAG-RSOM is demonstrated through application during mild and severe acute colitis in mice. TAG-RSOM enables visualization of transmural vascular networks, with changes in colon wall thickness, blood volume, and OAI signal intensities corresponding to colitis-associated inflammatory changes. These findings suggest TAG-RSOM can provide a novel monitoring tool in preclinical IBD models, refining animal procedures and underlines the capabilities of such technologies to address inflammatory bowel diseases in humans.

Inflammation and vascular remodeling in COVID-19 hearts

A wide range of cardiac symptoms have been observed in COVID-19 patients, often significantly influencing the clinical outcome. While the pathophysiology of pulmonary COVID-19 manifestation has been substantially unraveled, the underlying pathomechanisms of cardiac involvement in COVID-19 are largely unknown. In this multicentre study, we performed a comprehensive analysis of heart samples from 24 autopsies with confirmed SARS-CoV-2 infection and compared them to samples of age-matched Influenza H1N1 A (n = 16), lymphocytic non-influenza myocarditis cases (n = 8), and non-inflamed heart tissue (n = 9). We employed conventional histopathology, multiplexed immunohistochemistry (MPX), microvascular corrosion casting, scanning electron microscopy, X-ray phase-contrast tomography using synchrotron radiation, and direct multiplexed measurements of gene expression, to assess morphological and molecular changes holistically. Based on histopathology, none of the COVID-19 samples fulfilled the established diagnostic criteria of viral myocarditis. However, quantification via MPX showed a significant increase in perivascular CD11b/TIE2 + -macrophages in COVID-19 over time, which was not observed in influenza or non-SARS-CoV-2 viral myocarditis patients. Ultrastructurally, a significant increase in intussusceptive angiogenesis as well as multifocal thrombi, inapparent in conventional morphological analysis, could be demonstrated. In line with this, on a molecular level, COVID-19 hearts displayed a distinct expression pattern of genes primarily coding for factors involved in angiogenesis and epithelial-mesenchymal transition (EMT), changes not seen in any of the other patient groups. We conclude that cardiac involvement in COVID-19 is an angiocentric macrophage-driven inflammatory process, distinct from classical anti-viral inflammatory responses, and substantially underappreciated by conventional histopathologic analysis. For the first time, we have observed intussusceptive angiogenesis in cardiac tissue, which we previously identified as the linchpin of vascular remodeling in COVID-19 pneumonia, as a pathognomic sign in affected hearts. Moreover, we identified CD11b + /TIE2 + macrophages as the drivers of intussusceptive angiogenesis and set forward a putative model for the molecular regulation of vascular alterations.

Contribution of Blood Vessel Activation, Remodeling and Barrier Function to Inflammatory Bowel Diseases

Inflammatory bowel diseases (IBDs) consist of a group of chronic inflammatory disorders with a complex etiology, which represent a clinical challenge due to their often therapy-refractory nature. In IBD, inflammation of the intestinal mucosa is characterized by strong and sustained leukocyte infiltration, resulting in the loss of epithelial barrier function and subsequent tissue destruction. This is accompanied by the activation and the massive remodeling of mucosal micro-vessels. The role of the gut vasculature in the induction and perpetuation of mucosal inflammation is receiving increasing recognition. While the vascular barrier is considered to offer protection against bacterial translocation and sepsis after the breakdown of the epithelial barrier, endothelium activation and angiogenesis are thought to promote inflammation. The present review examines the respective pathological contributions of the different phenotypical changes observed in the microvascular endothelium during IBD, and provides an overview of potential vessel-specific targeted therapy options for the treatment of IBD.

Intussusceptive angiogenesis facilitated by microthrombosis has an important example in angiolipoma. An ultrastructural and immunohistochemical study

The microvasculature of angiolipoma frequently presents thrombi. Our objectives are to assess whether intussusceptive angiogenesis (IA) participates in vasculature formation in non-infiltrating angiolipoma and, if so, to explore how thrombi are involved in the IA process. For this purpose, we studied angiolipoma specimens (n: 52), using immunohistochemistry, and confocal and electron microscopy. The results showed the presence of folds and pillars, hallmarks of IA, dividing the vessel lumen. Folds showed a cover formed by reoriented endothelial cells from the vessel wall, or from newly formed folds, and a core initially formed by thrombus fragments (clot components as transitional core), which was replaced by extracellular matrix and invaginating pericytes establishing numerous peg-and-socket junctions with endothelial cells (mature core). A condensed plasmatic electron-dense material surrounded and connected folds and pillars with each other and with the vascular wall, which suggests a clot role in fold/pillar arrangement. In conclusion, we contribute to IA participation in capillary network formation in angiolipoma and the immunohistochemical and ultrastructural events by which microthrombosis facilitates IA. Therefore, in addition to the histogenesis of angiolipoma, we provide an easily obtainable substrate for future studies on clot component action in IA, of clinical and therapeutic interest.

Comparison of the Behavior of Perivascular Cells (Pericytes and CD34+ Stromal Cell/Telocytes) in Sprouting and Intussusceptive Angiogenesis

Perivascular cells in the pericytic microvasculature, pericytes and CD34+ stromal cells/telocytes (CD34+SCs/TCs), have an important role in angiogenesis. We compare the behavior of these cells depending on whether the growth of endothelial cells (ECs) from the pre-existing microvasculature is toward the interstitium with vascular bud and neovessel formation (sprouting angiogenesis) or toward the vascular lumen with intravascular pillar development and vessel division (intussusceptive angiogenesis). Detachment from the vascular wall, mobilization, proliferation, recruitment, and differentiation of pericytes and CD34+SCs/TCs, as well as associated changes in vessel permeability and functionality, and modifications of the extracellular matrix are more intense, longer lasting over time, and with a greater energy cost in sprouting angiogenesis than in intussusceptive angiogenesis, in which some of the aforementioned events do not occur or are compensated for by others (e.g., sparse EC and pericyte proliferation by cell elongation and thinning). The governing mechanisms involve cell-cell contacts (e.g., peg-and-socket junctions between pericytes and ECs), multiple autocrine and paracrine signaling molecules and pathways (e.g., vascular endothelial growth factor, platelet-derived growth factor, angiopoietins, transforming growth factor B, ephrins, semaphorins, and metalloproteinases), and other factors (e.g., hypoxia, vascular patency, and blood flow). Pericytes participate in vessel development, stabilization, maturation and regression in sprouting angiogenesis, and in interstitial tissue structure formation of the pillar core in intussusceptive angiogenesis. In sprouting angiogenesis, proliferating perivascular CD34+SCs/TCs are an important source of stromal cells during repair through granulation tissue formation and of cancer-associated fibroblasts (CAFs) in tumors. Conversely, CD34+SCs/TCs have less participation as precursor cells in intussusceptive angiogenesis. The dysfunction of these mechanisms is involved in several diseases, including neoplasms, with therapeutic implications.

Lee P, Kauczor HU, Länger F, Ackermann M. Pulmonary and Systemic Pathology in COVID-19—Holistic Pathological Analyses

BACKGROUND

The COVID-19 pandemic is the third worldwide coronavirus-associated disease outbreak in the past 20 years. Lung involvement, with acute respiratory distress syndrome (ARDS) in severe cases, is the main clinical feature of this disease; the cardiovascular system, the central nervous system, and the gastrointestinal tract can also be affected. The pathophysiology of both pulmonary and extrapulmonary organ damage was almost completely unknown when the pandemic began.

METHODS

This review is based on pertinent publications retrieved by a selective search concerning the structural changes and pathophysiology of COVID-19, with a focus on imaging techniques.

RESULTS

Immunohistochemical, electron-microscopic and molecular pathological analyses of tissues obtained by autopsy have improved our understanding of COVID-19 pathophysiology, including molecular regulatory mechanisms. Intussusceptive angiogenesis (IA) has been found to be a prominent pattern of damage in the affected organs of COVID-19 patients. In IA, an existing vessel changes by invagination of the endothelium and formation of an intraluminal septum, ultimately giving rise to two new lumina. This alters hemodynamics within the vessel, leading to a loss of laminar flow and its replacement by turbulent, inhomogeneous flow. IA, which arises because of ischemia due to thrombosis, is itself a risk factor for the generation of further microthrombi; these have been detected in the lungs, heart, liver, kidneys, brain, and placenta of COVID-19 patients.

CONCLUSION

Studies of autopsy material from various tissues of COVID-19 patients have revealed ultrastructural evidence of altered microvascularity, IA, and multifocal thrombi. These changes may contribute to the pathophysiology of post-acute interstitial fibrotic organ changes as well as to the clinical picture of long COVID.

Organ manifestations of COVID-19: what have we learned so far (not only) from autopsies?

The use of autopsies in medicine has been declining. The COVID-19 pandemic has documented and rejuvenated the importance of autopsies as a tool of modern medicine. In this review, we discuss the various autopsy techniques, the applicability of modern analytical methods to understand the pathophysiology of COVID-19, the major pathological organ findings, limitations or current studies, and open questions. This article summarizes published literature and the consented experience of the nationwide network of clinical, neuro-, and forensic pathologists from 27 German autopsy centers with more than 1200 COVID-19 autopsies. The autopsy tissues revealed that SARS-CoV-2 can be found in virtually all human organs and tissues, and the majority of cells. Autopsies have revealed the organ and tissue tropism of SARS-CoV-2, and the morphological features of COVID-19. This is characterized by diffuse alveolar damage, combined with angiocentric disease, which in turn is characterized by endothelial dysfunction, vascular inflammation, (micro-) thrombosis, vasoconstriction, and intussusceptive angiogenesis. These findings explained the increased pulmonary resistance in COVID-19 and supported the recommendations for antithrombotic treatment in COVID-19. In contrast, in extra-respiratory organs, pathological changes are often nonspecific and unclear to which extent these changes are due to direct infection vs. indirect/secondary mechanisms of organ injury, or a combination thereof. Ongoing research using autopsies aims at answering questions on disease mechanisms, e.g., focusing on variants of concern, and future challenges, such as post-COVID conditions. Autopsies are an invaluable tool in medicine and national and international interdisciplinary collaborative autopsy-based research initiatives are essential.

COVID-19 and dys-regulation of pulmonary endothelium: implications for vascular remodeling

Coronavirus disease-2019 (COVID-19), the disease caused by severe acute respiratory syndrome-coronavirus-2, has claimed more than 4.4 million lives worldwide (as of 20 August 2021). Severe cases of the disease often result in respiratory distress due to cytokine storm, and mechanical ventilation is required. Although, the lungs are the primary organs affected by the disease, more evidence on damage to the heart, kidney, and liver is emerging. A common link in these connections is the cardiovascular network. Inner lining of the blood vessels, called endothelium, is formed by a single layer of endothelial cells. Several clinical manifestations involving the endothelium have been reported, such as its activation via immunomodulation, endotheliitis, thrombosis, vasoconstriction, and distinct intussusceptive angiogenesis (IA), a unique and rapid process of blood-vessel formation by splitting a vessel into two lumens. In fact, the virus directly infects the endothelium via TMPRSS2 spike glycoprotein priming to facilitate ACE-2-mediated viral entry. Recent studies have indicated a significant increase in remodeling of the pulmonary vascular bed via intussusception in patients with COVID-19. However, the lack of circulatory biomarkers for IA limits its detection in COVID-19 pathogenesis. In this review, we describe the implications of angiogenesis in COVID-19, unique features of the pulmonary vascular bed and its remodeling, and a rapid and non-invasive assessment of IA to overcome the technical limitations in patients with COVID-19.

[COVID-19: effects on the lungs and heart]

Viral respiratory diseases constitute the most common reasons for hospitalization with more than half of all acute illnesses worldwide. Progressive respiratory failure with pronounced diffuse alveolar damage has been identified as the primary cause of death in COVID-19. COVID-19 pneumonia shares common histopathological hallmarks with influenza (H1N1)-related ARDS, like diffuse alveolar damage (DAD) with edema, hemorrhage, and intra-alveolar fibrin deposition. The lungs with COVID-19 pneumonia revealed perivascular inflammation, an endothelial injury, microangiopathy, and an aberrant blood vessel neoformation by intussusceptive angiogenesis. While this pronounced angiocentric inflammation is likely be found - to varying degrees - in numerous other organs, e.g., the heart, COVID-19 is hypothesized to be not just a pulmonary, but rather a systemic "vascular disease."

3D analysis of microvasculature in murine liver fibrosis models using synchrotron radiation-based microtomography

Cirrhosis describes the development of excess fibrous tissue around regenerative nodules in response to chronic liver injury and usually leads to irreversible organ damage and end-stage liver disease. During the development of cirrhosis, the formation of collagenous scar tissue is paralleled by a reorganization and remodeling of the hepatic vascular system. To date, macrovascular remodeling in various cirrhosis models has been examined using three-dimensional (3D) imaging modalities, while microvascular changes have been studied mainly by two-dimensional (2D) light microscopic and electron microscopic imaging. Here, we report on the application of high-resolution 3D synchrotron radiation-based microtomography (SRμCT) for the study of the sinusoidal and capillary blood vessel system in three murine models of advanced parenchymal and biliary hepatic fibrosis. SRμCT facilitates the characterization of microvascular architecture and identifies features of intussusceptive angiogenesis in progressive liver fibrosis in a non-destructive 3D manner.

Intussusceptive Angiogenesis and Peg-Socket Junctions between Endothelial Cells and Smooth Muscle Cells in Early Arterial Intimal Thickening

Angiogenesis in arterial intimal thickening (AIT) has been considered mainly in late AIT stages and only refers to sprouting angiogenesis. We assess angiogenesis during early AIT development and the occurrence of the intussusceptive type. For this purpose, we studied AIT development in (a) human arteries with vasculitis in gallbladders with acute cholecystitis and urgent (n = 25) or delayed (n = 20) cholecystectomy, using immunohistochemical techniques and (b) experimentally occluded arterial segments (n = 56), using semithin and ultrathin sections and electron microscopy. The results showed transitory angiogenic phenomena, with formation of an important microvasculature, followed by vessel regression. In addition to the sequential description of angiogenic and regressive findings, we mainly contribute (a) formation of intravascular pillars (hallmarks of intussusception) during angiogenesis and vessel regression and (b) morphological interrelation between endothelial cells (ECs) in the arterial wall and vascular smooth muscle cells (VSMCs), which adopt a pericytic arrangement and establish peg-and-socket junctions with ECs. In conclusion, angiogenesis and vessel regression play an important role in AIT development in the conditions studied, with participation of intussusceptive angiogenesis during the formation and regression of a provisional microvasculature and with morphologic interrelation between ECs and VSMCs.

Remodeling of the Microvasculature: May the Blood Flow Be With You

The vasculature ensures optimal delivery of nutrients and oxygen throughout the body, and to achieve this function it must continually adapt to varying tissue demands. Newly formed vascular plexuses during development are immature and require dynamic remodeling to generate well-patterned functional networks. This is achieved by remodeling of the capillaries preserving those which are functional and eliminating other ones. A balanced and dynamically regulated capillary remodeling will therefore ensure optimal distribution of blood and nutrients to the tissues. This is particularly important in pathological contexts in which deficient or excessive vascular remodeling may worsen tissue perfusion and hamper tissue repair. Blood flow is a major determinant of microvascular reshaping since capillaries are pruned when relatively less perfused and they split when exposed to high flow in order to shape the microvascular network for optimal tissue perfusion and oxygenation. The molecular machinery underlying blood flow sensing by endothelial cells is being deciphered, but much less is known about how this translates into endothelial cell responses as alignment, polarization and directed migration to drive capillary remodeling, particularly in vivo. Part of this knowledge is theoretical from computational models since blood flow hemodynamics are not easily recapitulated by in vitro or ex vivo approaches. Moreover, these events are difficult to visualize in vivo due to their infrequency and briefness. Studies had been limited to postnatal mouse retina and vascular beds in zebrafish but new tools as advanced microscopy and image analysis are strengthening our understanding of capillary remodeling. In this review we introduce the concept of remodeling of the microvasculature and its relevance in physiology and pathology. We summarize the current knowledge on the mechanisms contributing to capillary regression and to capillary splitting highlighting the key role of blood flow to orchestrate these processes. Finally, we comment the potential and possibilities that microfluidics offers to this field. Since capillary remodeling mechanisms are often reactivated in prevalent pathologies as cancer and cardiovascular disease, all this knowledge could be eventually used to improve the functionality of capillary networks in diseased tissues and promote their repair.

Intussusceptive angiogenesis and its counterpart intussusceptive lymphangiogenesis

Intussusceptive angiogenesis (IA) is currently considered an important alternative and complementary form of sprouting angiogenesis (SA). Conversely, intussusceptive lymphangiogenesis (IL) is in an initial phase of study. We compare their morphofunctional characteristics, since many can be shared by both processes. To that end, the following aspects are considered: A) The concept of IA and IL as the mechanism by which blood and lymphatic vessels split, expand and remodel through transluminal pillar formations (hallmarks of intussusception). B) Terminology and historical background, with particular reference to the group of Burri, including Djonov and Patan, who initiated and developed the vessel intussusceptive concept in blood vessels. C) Incidence in normal (e.g. in the sinuses of developing lymph nodes) and pathologic conditions, above all in vessel diseases, such as dilated veins in hemorrhoidal disease, intravascular papillary endothelial hyperplasia (IPEH), sinusoidal hemangioma, lobular capillary hemangioma, lymphangiomas/lymphatic malformations and vascular transformation of lymph nodes. D) Differences and complementarity between vessel sprouting and intussusception. E) Characteristics of the cover (endothelial cells) and core (connective tissue components) of pillars and requirements for pillar identification. F) Structures involved in pillar formation, including endothelial contacts of opposite vessel walls, interendothelial bridges, merged adjacent capillaries, vessel loops and spilt pillars. G) Structures resulting from pillars with intussusceptive microvascular growth, arborization, remodeling and segmentation (compartmentalization). H) Influence of intussusception in the morphogenesis of vessel tumors/ pseudotumors; and I) Hemodynamic and molecular control of vessel intussusception, including VEGF, PDGF BB, Hypoxia, Notch, Endoglobin and Nitric oxide.

Participation of Intussusceptive Angiogenesis in the Morphogenesis of Lobular Capillary Hemangioma

In lobular capillary hemangioma (LCH), misnamed pyogenic granuloma, only sprouting angiogenesis (SA) has been considered. We assess the occurrence of intussusceptive angiogenesis (IA) in LCH and whether IA determines the specific and other focal patterns in the lesion. For this purpose, we study specimens of 120 cases of LCH, using semithin sections (in 10), immunohistochemistry, and confocal microscopy (in 20). In addition to SA, the results in LCH showed (1) intussusceptive phenomena, including pillars/folds and associated vessel loops, which encircled interstitial tissue structures (ITSs). (2) Two types of evolved loops depending on interendothelial contacts from opposite walls: (a) numerous interendothelial contacts, alternating with capillary-sized lumens (main capillary pattern of the lesion) and (b) few interendothelial contacts, wide open lumens, and intravascular transport of pillars/folds, which were arranged linearly, forming septa (focal sinusoidal-like pattern) or were irregularly grouped (focal intravascular papillary endothelial hyperplasia, IPEH-like pattern). In conclusion, we demonstrate that IA participates in synergistic interaction with SA in LCH development and that the prevalence of specific intussusceptive phenomena determines the predominant capillary pattern and associated sinusoidal hemangioma-like and IPEH-like patterns in the lesion, which suggest a role of IA as conditioner of vessel tumour/pseudo-tumour morphology.

Endothelial MT1-MMP targeting limits intussusceptive angiogenesis and colitis via TSP1/nitric oxide axis

Pathological angiogenesis contributes to cancer progression and chronic inflammatory diseases. In inflammatory bowel disease, the microvasculature expands by intussusceptive angiogenesis (IA), a poorly characterized mechanism involving increased blood flow and splitting of pre-existing capillaries. In this report, mice lacking the protease MT1-MMP in endothelial cells (MT1iΔEC ) presented limited IA in the capillary plexus of the colon mucosa assessed by 3D imaging during 1% DSS-induced colitis. This resulted in better tissue perfusion, preserved intestinal morphology, and milder disease activity index. Combined in vivo intravital microscopy and lentiviral rescue experiments with in vitro cell culture demonstrated that MT1-MMP activity in endothelial cells is required for vasodilation and IA, as well as for nitric oxide production via binding of the C-terminal fragment of MT1-MMP substrate thrombospondin-1 (TSP1) to CD47/αvβ3 integrin. Moreover, TSP1 levels were significantly higher in serum from IBD patients and in vivo administration of an anti-MT1-MMP inhibitory antibody or a nonamer peptide spanning the αvβ3 integrin binding site in TSP1 reduced IA during mouse colitis. Our results identify MT1-MMP as a new actor in inflammatory IA and a promising therapeutic target for inflammatory bowel disease.

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.

Intussusceptive lymphangiogenesis in vascular transformation of lymph node sinuses

Numerous lymphatic anastomosing channels in the lymph nodes are the most demonstrative finding of the rare lesion termed "vascular transformation of lymph node sinuses" (VTS). The mechanism of lymphatic vessel formation in VTS has not been studied. Vessel intussusception contributes to vascular expansion, and intraluminal pillars/posts, interstitial tissue structures or larger pillars (ITSs) and folds are the hallmarks of this process in blood vessels. The aim of this work is to assess whether these hallmarks of intussusception occur in VTS lymphatic vessels, indicating intussusceptive lymphangiogenesis. For this purpose, specimens of five cases of VTS were used for serial histological sections, immunohistochemistry and immunofluorescence in confocal microscopy, which enabled us to demonstrate the 3D image that defines the pillars. The studies showed a) meshworks of lymphatic vessels, which form complex loops, resembling sinuses of lymph nodes, b) presence of intralymphatic pillars, ITSs and folds, with a cover of lymphatic endothelial cells expressing podoplanin and a varying-sized connective core (e.g. collagen), and c) increase of vessel meshwork and linear arrangement, splitting and fusion of ITSs, pillars and folds, with remodelling and segmentation. In conclusion, the development of lymphatic vessel loops, ITSs, pillars and folds with segmentation in VTS supports intussusceptive lymphangiogenesis. This mechanism of intussusception is of interest because it participates in VTS histogenesis, contributes to general knowledge of intussusceptive lymphangiogenesis, which has received less attention than intussusception in blood vessels, and provides a basis for further studies in other lymphatic conditions.

Segmentation of Dilated Hemorrhoidal Veins in Hemorrhoidal Disease

Vein segmentation is a vascular remodeling process mainly studied in experimental conditions and linked to hemodynamic factors, with clinical implications. The aim of this work is to assess the morphologic characteristics, associated findings, and mechanisms that participate in vein segmentation in humans. To this end, we examined 156 surgically obtained cases of hemorrhoidal disease. Segmentation occurred in 65 and was most prominent in 15, which were selected for serial sections, immunohistochemistry, and immunofluorescence procedures. The dilated veins showed differently sized spaces, separated by thin septa. Findings associated with vein segmentation were: (a) vascular channels formed from the vein intima endothelial cells (ECs) and located in the vein wall and/or intraluminal fibrin, (b) vascular loops formed by interconnected vascular channels (venous-venous connections), which encircled vein wall components or fibrin and formed folds/pillars/papillae (FPPs; the encircling ECs formed the FPP cover and the encircled components formed the core), and (c) FPP splitting, remodeling, alignment, and fusion, originating septa. Thrombosis was observed in some nonsegmented veins, while the segmented veins only occasionally contained thrombi. Dense microvasculature was also present in the interstitium and around veins. In conclusion, the findings suggest that hemorrhoidal vein segmentation is an adaptive process in which a piecemeal angiogenic mechanism participates, predominantly by intussusception, giving rise to intravascular FPPs, followed by linear rearrangement, remodeling and fusion of FPPs, and septa formation. Identification of other markers, as well as the molecular bases, hemodynamic relevance, and possible therapeutic implications of vein segmentation in dilated hemorrhoidal veins require further studies.

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.

Effects of nintedanib on the microvascular architecture in a lung fibrosis model

Nintedanib, a tyrosine kinase inhibitor approved for the treatment of idiopathic pulmonary fibrosis, has anti-fibrotic, anti-inflammatory, and anti-angiogenic activity. We explored the impact of nintedanib on microvascular architecture in a pulmonary fibrosis model. Lung fibrosis was induced in C57Bl/6 mice by intratracheal bleomycin (0.5 mg/kg). Nintedanib was started after the onset of lung pathology (50 mg/kg twice daily, orally). Micro-computed tomography was performed via volumetric assessment. Static lung compliance and forced vital capacity were determined by invasive measurements. Mice were subjected to bronchoalveolar lavage and histologic analyses, or perfused with a casting resin. Microvascular corrosion casts were imaged by scanning electron microscopy and synchrotron radiation tomographic microscopy, and quantified morphometrically. Bleomycin administration resulted in a significant increase in higher-density areas in the lungs detected by micro-computed tomography, which was significantly attenuated by nintedanib. Nintedanib significantly reduced lung fibrosis and vascular proliferation, normalized the distorted microvascular architecture, and was associated with a trend toward improvement in lung function and inflammation. Nintedanib resulted in a prominent improvement in pulmonary microvascular architecture, which outperformed the effect of nintedanib on lung function and inflammation. These findings uncover a potential new mode of action of nintedanib that may contribute to its efficacy in idiopathic pulmonary fibrosis.

Novel 3D light microscopic analysis of IUGR placentas points to a morphological correlate of compensated ischemic placental disease in humans

The villous tree of the human placenta is a complex three-dimensional (3D) structure with branches and nodes at the feto-maternal border in the key area of gas and nutrient exchange. Recently we introduced a novel, computer-assisted 3D light microscopic method that enables 3D topological analysis of branching patterns of the human placental villous tree. In the present study we applied this novel method to the 3D architecture of peripheral villous trees of placentas from patients with intrauterine growth retardation (IUGR placentas), a severe obstetric syndrome. We found that the mean branching angle of branches in terminal positions of the villous trees was significantly different statistically between IUGR placentas and clinically normal placentas. Furthermore, the mean tortuosity of branches of villous trees in directly preterminal positions was significantly different statistically between IUGR placentas and clinically normal placentas. We show that these differences can be interpreted as consequences of morphological adaptation of villous trees between IUGR placentas and clinically normal placentas, and may have important consequences for the understanding of the morphological correlates of the efficiency of the placental villous tree and their influence on fetal development.

Impact of platelet rich plasma and adipose stem cells on lymphangiogenesis in a murine tail lymphedema model

BACKGROUND

Lymphedema is an underdiagnosed pathology which in industrialized countries mainly affects cancer patients that underwent lymph node dissection and/or radiation. Currently no effective therapy is available so that patients' life quality is compromised by swellings of the concerned body region. This unfortunate condition is associated with body imbalance and subsequent osteochondral deformations and impaired function as well as with an increased risk of potentially life threatening soft tissue infections.

METHODS

The effects of PRP and ASC on angiogenesis (anti-CD31 staining), microcirculation (Laser Doppler Imaging), lymphangiogenesis (anti-LYVE1 staining), microvascular architecture (corrosion casting) and wound healing (digital planimetry) are studied in a murine tail lymphedema model.

RESULTS

Wounds treated by PRP and ASC healed faster and showed a significantly increased epithelialization mainly from the proximal wound margin. The application of PRP induced a significantly increased lymphangiogenesis while the application of ASC did not induce any significant change in this regard.

CONCLUSIONS

PRP and ASC affect lymphangiogenesis and lymphedema development and might represent a promising approach to improve regeneration of lymphatic vessels, restore disrupted lymphatic circulation and treat or prevent lymphedema alone or in combination with currently available lymphedema therapies.

Morphological characterization of sprouting and intussusceptive angiogenesis by SEM in oral squamous cell carcinoma

The word angiogenesis indicates the formation of new vascular segments from existing vessels such as capillaries and venules. Blood vessel formation in tumors is the result of rapid, disorganized vascular growth through two distinct mechanisms: sprouting and intussusceptive angiogenesis. The objective of this study was to elucidate the morphological aspects of these two vascular growth mechanisms in oral squamous cell carcinoma induced in hamster buccal pouch. Eight Syrian golden hamsters had their right buccal pouch treated with DMBA 0.5% and 10% carbamide peroxide for 90 days in order to produce squamous cell carcinoma in this site. Next, buccal pouches of the animals were submitted to the vascular corrosion technique and then analyzed by scanning electron microscopy. The vascular figures of sprouts were observed in the entire vascular network of the buccal pouches, as opposed to the intussusceptive angiogenesis that was predominantly observed in the sub-epithelial network. It was possible to differentiate the figures of sprouts from artifacts by the analysis of the blind ending of these structures. Intussusceptive angiogenesis was identified by the presence of holes trespassing the lumen of the capillaries. Vascular expansion occurred through intussusceptive angiogenesis in two ways: by the fusion of the pillars to form a new capillary and, by increasing the girth of the pillar to form meshes. The method of corrosion associated with scanning electron microscopy proved to be an excellent tool to study the two types of angiogenesis in oral squamous cell carcinoma in the hamster buccal pouch.

Casting materials and their application in research and teaching

From a biological point of view, casting refers to filling of anatomical and/or pathological spaces with extraneous material that reproduces a three-dimensional replica of the space. Casting may be accompanied by additional procedures such as corrosion, in which the soft tissue is digested out, leaving a clean cast, or the material may be mixed with radiopaque substances to allow x-ray photography or micro computed topography (µCT) scanning. Alternatively, clearing of the surrounding soft tissue increases transparency and allows visualization of the casted cavities. Combination of casting with tissue fixation allows anatomical dissection and didactic surgical procedures on the tissue. Casting materials fall into three categories namely, aqueous substances (India ink, Prussian blue ink), pliable materials (gelatins, latex, and silicone rubber), or hard materials (methyl methacrylates, polyurethanes, polyesters, and epoxy resins). Casting has proved invaluable in both teaching and research and many phenomenal biological processes have been discovered through casting. The choice of a particular material depends inter alia on the targeted use and the intended subsequent investigative procedures, such as dissection, microscopy, or µCT. The casting material needs to be pliable where anatomical and surgical manipulations are intended, and capillary-passable for ultrastructural investigations.

Intussusceptive angiogenesis: expansion and remodeling of microvascular networks

Intussusceptive angiogenesis is a dynamic intravascular process capable of dramatically modifying the structure of the microcirculation. The distinctive structural feature of intussusceptive angiogenesis is the intussusceptive pillar--a cylindrical microstructure that spans the lumen of small vessels and capillaries. The extension of the intussusceptive pillar appears to be a mechanism for pruning redundant or inefficient vessels, modifying the branch angle of bifurcating vessels and duplicating existing vessels. Despite the biological importance and therapeutic potential, intussusceptive angiogenesis remains a mystery, in part, because it is an intravascular process that is unseen by conventional light microscopy. Here, we review several fundamental questions in the context of our current understanding of both intussusceptive and sprouting angiogenesis. (1) What are the physiologic signals that trigger pillar formation? (2) What endothelial and blood flow conditions specify pillar location? (3) How do pillars respond to the mechanical influence of blood flow? (4) What biological influences contribute to pillar extension? The answers to these questions are likely to provide important insights into the structure and function of microvascular networks.