Effect of intraluminal pillars on particle motion in bifurcated microchannels

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.

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.

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

Intussusceptive angiogenesis is a developmental process linked to both blood vessel replication and remodeling in development. To investigate the prediction that the process of intussusceptive angiogenesis is associated with vessel angle remodeling in adult mice, we systematically evaluated corrosion casts of the mucosal plexus in mice with trinitrobenzesulfonic acid (TNBS)-induced and dextran sodium sulfate (DSS)-induced colitis. The mice demonstrated a significant decrease in vessel angles in both TNBS-induced and DSS-induced colitis within 4 weeks of the onset of colitis (p<.001). Corrosion casts 28-30 days after DSS treatment were studied for a variety of detailed morphometric changes. The vessel diameter and interbranch distance were significantly increased in the descending colon (p<.05). Also consistent with vessel growth, intervascular distance was decreased in the descending colon (p<.05). In contrast, no statistically significant morphometric changes were noted in the ascending colon. The morphometry of the corrosion casts also demonstrated 1) a similar orientation of the remodeled angles within the XY coordinate plane of the mucosal plexus, and 2) alternating periodicity of remodeled and unremodeled vessel angles. We conclude that inflammation-associated intussusceptive angiogenesis in adult mice is associated with vessel angle remodeling. Further, the morphometry of the vessel angles suggests the influence of blood flow on the location and orientation of remodeled vessels.

CD34+ progenitor to endothelial cell transition in post-pneumonectomy angiogenesis

In many species, pneumonectomy triggers compensatory lung growth that results in an increase not only in lung volume, but also in alveolar number. Whether the associated alveolar angiogenesis involves the contribution of blood-borne progenitor cells is unknown. To identify and characterize blood-borne progenitor cells contributing to lung growth after pneumonectomy in mice, we studied wild-type and wild-type/green fluorescence protein (GFP) parabiotic mice after left pneumonectomy. Within 21 days of pneumonectomy, a 3.2-fold increase occurred in the number of lung endothelial cells. This increase in total endothelial cells was temporally associated with a 7.3-fold increase in the number of CD34(+) endothelial cells. Seventeen percent of the CD34(+) endothelial cells were actively proliferating, compared with only 4.2% of CD34(-) endothelial cells. Using wild-type/GFP parabiotic mice, we demonstrated that 73.4% of CD34(+) cells were derived from the peripheral blood. Furthermore, lectin perfusion studies demonstrated that CD34(+) cells derived from peripheral blood were almost uniformly incorporated into the lung vasculature. Finally, CD34(+) endothelial cells demonstrated a similar profile, but had enhanced transcriptional activity relative to CD34(-) endothelial cells. We conclude that blood-borne CD34(+) endothelial progenitor cells, characterized by active cell division and an amplified transcriptional signature, transition into resident endothelial cells during compensatory lung growth.

Computational flow dynamics in a geometric model of intussusceptive angiogenesis

Intussusceptive angiogenesis is a process that forms new blood vessels by the intraluminal division of a single blood vessel into two lumens. Referred to as nonsprouting or intussusceptive angiogenesis, this angiogenic process has been described in morphogenesis and chronic inflammation. Mechanical forces are relevant to the structural changes associated with intussusceptive angiogenesis because of the growing evidence that physiologic forces influence gene transcription. To provide a detailed analysis of the spatial distribution of physiologic shear stresses, we developed a 3D finite element model of the intraluminal intussusceptive pillar. Based on geometries observed in adult intussusceptive angiogenesis, physiologic shear stress distribution was studied at pillar sizes ranging from 1 to 10 microm. The wall shear stress calculations demonstrated a marked spatial dependence with discrete regions of high shear stress on the intraluminal pillar and lateral vessel wall. Furthermore, the intussusceptive pillar created a "dead zone" of low wall shear stress between the pillar and vessel bifurcation apex. We conclude that the intraluminal flow fields demonstrate sufficient spatial resolution and dynamic range to participate in the regulation of intussusceptive angiogenesis.