Utilizing lymphatic cell markers to visualize human lymphatic abnormalities

A Novel Ex Vivo Tumor Spheroid-Tissue Model for Investigating Microvascular Remodeling and Lymphatic Blood Vessel Plasticity

Biomimetic tumor microenvironment models bridge the gap between in vitro and in vivo systems and serve as a useful way to address the modeling challenge of how to recreate the cell and system complexity associated with real tissues. Our laboratory has developed an ex vivo rat mesentery culture model, which allows for simultaneous investigation of blood and lymphatic microvascular network remodeling in an intact tissue environment. Given that angiogenesis and lymphangiogenesis are key contributors to the progression of cancer, the objective of this study was to combine tissue and tumor spheroid culture methods to establish a novel ex vivo tumor spheroid-tissue model by verifying its use for evaluating the effects of cancer cell behavior on the local microvascular environment. H1299 or A549 tumor spheroids were formed via hanging drop culture and seeded onto rat mesenteric tissues harvested from adult male Wistar rats. Tissues with transplanted spheroids were cultured in serum-free media for 3 to 5 days. PECAM, NG2, CD11b, and αSMA labeling identified endothelial cells, pericytes, immune cells, and smooth muscle cells, respectively. Time-lapse imaging confirmed cancer cell type specific migration. In addition to increasing PECAM positive capillary sprouting and LYVE-1 positive endothelial cell extensions indicative of lymphangiogenesis, tumor spheroid presence induced the formation of lymphatic/blood vessel connections and the formation of hybrid, mosaic vessels that were characterized by discontinuous LYVE-1 labeling. The results support the application of a novel tumor spheroid microenvironment model for investigating cancer cell-microvascular interactions.

The discriminative role of PROX-1 immunohistochemistry between venous malformation and lymphatic malformation of the deep type with no visible diagnostic surface skin lesion

BACKGROUND

Venous malformations (VMs) are distinguished from lymphatic malformations (LMs) when specific diagnostic skin lesions are present. In the deep type, this is difficult by clinico-radiologic evaluation alone. We aimed to investigate the usefulness of lymphatic vessel endothelial cell (LEC) markers for the differential diagnosis of the deep VMs and LMs.

METHODS

A retrospective study was conducted based on the medical records of patients with VMs and LMs who underwent biopsy with both D2-40 and PROX-1 immunohistochemistry. We compared the initial clinico-radiological diagnosis with the final pathological diagnosis and identified which ones showed a difference.

RESULTS

From 261 patients who had VMs and LMs, 111 remained after the exclusion of those who showed definite surface diagnostic features. After pathological diagnosis with the expressions of D2-40 and PROX-1, 38 of 111 (34.2%) patients' final diagnoses were changed. Among these 38 cases, diagnosis was not changed by D2-40 positivity alone, but changed by PROX-1 positivity alone (52.6%) or by both (47.4%). The diagnostic changes were more frequent in the deep category (43.7%) than in the superficial category.

CONCLUSIONS

Identifying the expression of D2-40, and especially PROX-1, in the differential diagnosis of VMs and LMs may provide important treatment guidelines and understanding their natural course.

The role of key biomarkers in lymphatic malformation: An updated review

The lymphatic system, crucial for tissue fluid balance and immune surveillance, can be severely impacted by disorders that hinder its activities. Lymphatic malformations (LMs) are caused by fluid accumulation in tissues owing to defects in lymphatic channel formation, the obstruction of lymphatic vessels or injury to lymphatic tissues. Somatic mutations, varying in symptoms based on lesions' location and size, provide insights into their molecular pathogenesis by identifying LMs' genetic causes. In this review, we collected the most recent findings about the role of genetic and inflammatory biomarkers in LMs that control the formation of these malformations. A thorough evaluation of the literature from 2000 to the present was conducted using the PubMed and Google Scholar databases. Although it is obvious that the vascular endothelial growth factor receptor 3 mutation accounts for a significant proportion of LM patients, several mutations in other genes thought to be linked to LM have also been discovered. Also, inflammatory mediators like interleukin-6, interleukin-8, tumor necrosis factor-alpha and mammalian target of rapamycin are the most commonly associated biomarkers with LM. Understanding the mutations and genes expression responsible for the abnormalities in lymphatic endothelial cells could lead to novel therapeutic strategies based on molecular pathways.

Lymphatic/blood vessel plasticity: motivation for a future research area based on present and past observations

The lymphatic system plays a significant role in homeostasis and drainage of excess fluid back into venous circulation. Lymphatics are also associated with a number of diseases including lymphedema, tumor metastasis, and various lymphatic malformations. Emerging evidence suggests that lymphatics might have a bigger connection to the blood vascular system than originally presumed. As these two systems are often studied in isolation, several knowledge gaps exist surrounding what constitutes lymphatic vascular plasticity, under what conditions it arises, and where structures characteristic of plasticity can form. The objective of this review is to overview current structural, cell lineage-based, and cell identity-based evidence for lymphatic plasticity. These examples of plasticity will then be considered in the context of potential clinical and surgical implications of this evolving research area. This review details our current understanding of lymphatic plasticity, highlights key unanswered questions in the field, and motivates future research aimed at clarifying the role and therapeutic potential of lymphatic plasticity in disease.

Proteomic Analysis of Chicken Chorioallantoic Membrane (CAM) during Embryonic Development Provides Functional Insight

In oviparous animals, the egg contains all resources required for embryonic development. The chorioallantoic membrane (CAM) is a placenta-like structure produced by the embryo for acid-base balance, respiration, and calcium solubilization from the eggshell for bone mineralization. The CAM is a valuable in vivo model in cancer research for development of drug delivery systems and has been used to study tissue grafts, tumor metastasis, toxicology, angiogenesis, and assessment of bacterial invasion. However, the protein constituents involved in different CAM functions are poorly understood. Therefore, we have characterized the CAM proteome at two stages of development (ED12 and ED19) and assessed the contribution of the embryonic blood serum (EBS) proteome to identify CAM-unique proteins. LC/MS/MS-based proteomics allowed the identification of 1470, 1445, and 791 proteins in CAM (ED12), CAM (ED19), and EBS, respectively. In total, 1796 unique proteins were identified. Of these, 175 (ED12), 177 (ED19), and 105 (EBS) were specific to these stages/compartments. This study attributed specific CAM protein constituents to functions such as calcium ion transport, gas exchange, vasculature development, and chemical protection against invading pathogens. Defining the complex nature of the CAM proteome provides a crucial basis to expand its biomedical applications for pharmaceutical and cancer research.

Multiparameter Fluorescence-Activated Cell Sorting of Human Lymphatic Endothelial Cells

Multiparameter fluorescence-activated cell sorting (FACS) procedure separates target cells from a total population of cells by using specific signatures that the target cell expresses on their cell surface. For human lymphatic endothelial cells (LECs) this relates to cell surface expression of the CD34^LowCD31^HighVEGFR-3^HighPodoplanin^High profile that permits their separation from blood vascular endothelial cells and other cells likely to be present in the digested tissue sample. In addition, FACS allows the evaluation of LEC size, volume, granularity, and purity at the time of sorting.

Lymphatic Endothelial Markers and Tumor Lymphangiogenesis Assessment in Human Breast Cancer

Metastasis via lymphatic vessels or blood vessels is the leading cause of death for breast cancer, and lymphangiogenesis and angiogenesis are critical prerequisites for the tumor invasion–metastasis cascade. The research progress for tumor lymphangiogenesis has tended to lag behind that for angiogenesis due to the lack of specific markers. With the discovery of lymphatic endothelial cell (LEC) markers, growing evidence demonstrates that the LEC plays an active role in lymphatic formation and remodeling, tumor cell growth, invasion and intravasation, tumor–microenvironment remodeling, and antitumor immunity. However, some studies have drawn controversial conclusions due to the variation in the LEC markers and lymphangiogenesis assessments used. In this study, we review recent findings on tumor lymphangiogenesis, the most commonly used LEC markers, and parameters for lymphangiogenesis assessments, such as the lymphatic vessel density and lymphatic vessel invasion in human breast cancer. An in-depth understanding of tumor lymphangiogenesis and LEC markers can help to illustrate the mechanisms and distinct roles of lymphangiogenesis in breast cancer progression, which will help in exploring novel potential predictive biomarkers and therapeutic targets for breast cancer.

The Lymphatic System in Breast Cancer: Anatomical and Molecular Approaches

Breast cancer is one of the most important causes of premature mortality among women and it is one of the most frequently diagnosed tumours worldwide. For this reason, routine screening for prevention and early diagnosis is important for the quality of life of patients. Breast cancer cells can enter blood and lymphatic capillaries, then metastasizing to the regional lymph nodes in the axilla and to both visceral and non-visceral sites. Rather than at the primary site, they seem to enter the systemic circulation mainly through the sentinel lymph node and the biopsy of this indicator can influence the axillary dissection during the surgical approach to the pathology. Furthermore, secondary lymphoedema is another important issue for women following breast cancer surgical treatment or radiotherapy. Considering these fundamental aspects, the present article aims to describe new methodological approaches to assess the anatomy of the lymphatic network in the axillary region, as well as the molecular and physiological control of lymphatic vessel function, in order to understand how the lymphatic system contributes to breast cancer disease. Due to their clinical implications, the understanding of the molecular mechanisms governing lymph node metastasis in breast cancer are also examined. Beyond the investigation of breast lymphatic networks and lymphatic molecular mechanisms, the discovery of new effective anti-lymphangiogenic drugs for future clinical settings appears essential to support any future development in the treatment of breast cancer.

KLF4 (Kruppel-Like Factor 4)-Dependent Perivascular Plasticity Contributes to Adipose Tissue inflammation

OBJECTIVE

Smooth muscle cells and pericytes display remarkable plasticity during injury and disease progression. Here, we tested the hypothesis that perivascular cells give rise to Klf4-dependent macrophage-like cells that augment adipose tissue (AT) inflammation and metabolic dysfunction associated with diet-induced obesity (DIO). Approach and Results: Using Myh11-CreERT2 eYFP (enhanced yellow fluorescent protein) mice and flow cytometry of the stromovascular fraction of epididymal AT, we observed a large fraction of smooth muscle cells and pericytes lineage traced eYFP+ cells expressing macrophage markers. Subsequent single-cell RNA sequencing, however, showed that the majority of these cells had no detectable eYFP transcript. Further exploration revealed that intraperitoneal injection of tamoxifen in peanut oil, used for generating conditional knockout or reporter mice in thousands of previous studies, resulted in large increase in the autofluorescence and false identification of macrophages within epididymal AT as being eYFP+; and unintended proinflammatory consequences. Using newly generated Myh11-DreERT2tdTomato mice given oral tamoxifen, we virtually eliminated the problem with autofluorescence and identified 8 perivascular cell dominated clusters, half of which were altered upon DIO. Given that perivascular cell KLF4 (kruppel-like factor 4) can have beneficial or detrimental effects, we tested its role in obesity-associated AT inflammation. While smooth muscle cells and pericytes-specific Klf4 knockout (smooth muscle cells and pericytes Klf4Δ/Δ) mice were not protected from DIO, they displayed improved glucose tolerance upon DIO, and showed marked decreases in proinflammatory macrophages and increases in LYVE1+ lymphatic endothelial cells in the epididymal AT.

CONCLUSIONS

Perivascular cells within the AT microvasculature dynamically respond to DIO and modulate tissue inflammation and metabolism in a KLF4-dependent manner.

Studying Lymphatic Metastasis in Breast Cancer: Current Models, Strategies, and Clinical Perspectives

Breast cancer is the most commonly diagnosed cancer in women and the second most common cause of cancer-related deaths in the United States. Although early detection has significantly decreased breast cancer mortality, patients diagnosed with distant metastasis still have a very poor prognosis. The most common site that breast cancer spreads to are local lymph nodes. Therefore, the presence of lymph node metastasis remains one of most important prognostic factors in breast cancer patients. Given its significant clinical implications, increased efforts have been dedicated to better understand the molecular mechanism governing lymph node metastasis in breast cancer. The identification of lymphatic-specific biomarkers, including podoplanin and LYVE-1, has propelled the field of lymphatic metastasis forward. In addition, several animal models such as cell line-derived xenografts, patient-derived xenografts, and spontaneous tumor models have been developed to recreate the process of lymphatic metastasis. Moreover, the incorporation of various -omic platforms have provided further insight into the genetic drivers facilitating lymphatic metastasis, as well as potential biomarkers and therapeutic targets. Here, we highlight various models of lymphatic metastasis, their potential pitfalls, and other tools available to study lymphatic metastasis including imaging modalities and -omic studies.

Retroperitoneal lymphatic malformation in a dog

Background

Lymphatic vascular malformations are rare findings in canine patients with six reports available in veterinary literature. Retroperitoneal cystic lymphatic malformations have not been described previously in canine patients and neither has the use of immunohistochemistry to determine their origin, i.e. vascular versus lymphatic.

Case presentation

An 8-year-old neutered female Cocker spaniel was referred for pollakiuria, dysuria and a painful abdomen. Computed tomography scanning of the abdomen showed a fluid filled structure adjacent to the urinary bladder. During surgical exploration, a thin walled cystic structure with sero-haemorrhagic fluid was found, extending from the retroperitoneal space into the abdomen. The mass was excised and submitted for histopathology, revealing a cystic mass lined by a fibrovascular capsule within the retroperitoneal/mesenteric adipose tissue. The inner surface of the cyst was lined by a single layer of bland, flattened spindle cells. Intramural blood vessels were well differentiated, with perivascular haemorrhage. On recurrence 11 months later, the mass was excised for the second time and a PleuralPort (Norfolk Animal products) was placed. Fifteen months after initial presentation, progression occurred with haemorrhagic fluid in the cystic space, pleural- and abdominal cavities and the owners opted for euthanasia. Histopathology and positive immunohistochemistry for lymphatic markers lymphatic vessel endothelial hyaluronic acid receptor-1 (LYVE-1) and prospero homeobox protein-1 (PROX-1) confirmed a lymphatic vascular origin of the cystic structure.

Conclusions

To our experience, a definitive diagnosis of retroperitoneal cystic malformation of lymphatic origin could be done only by combining the clinical presentation, advanced imaging, histopathology and LYVE-1 and PROX-1 immunohistochemistry. This is the first report of a vascular malformation in a dog where immunohistochemistry was used to make a final diagnosis. A lymphatic malformation, even if rare, should be added on the list of the differential diagnosis in a patient with a retroperitoneal cystic structure containing serohaemorrhagic fluid. Results of this case report can aid in diagnosis of future cases, however, further studies on therapy and management are needed to provide additional information about optimal treatment of these patients.

Lymphatic Vascular Structures: A New Aspect in Proliferative Diabetic Retinopathy

Diabetic retinopathy (DR) is the most common diabetic microvascular complication and major cause of blindness in working-age adults. According to the level of microvascular degeneration and ischemic damage, DR is classified into non-proliferative DR (NPDR), and end-stage, proliferative DR (PDR). Despite advances in the disease etiology and pathogenesis, molecular understanding of end-stage PDR, characterized by ischemia- and inflammation-associated neovascularization and fibrosis, remains incomplete due to the limited availability of ideal clinical samples and experimental research models. Since a great portion of patients do not benefit from current treatments, improved therapies are essential. DR is known to be a complex and multifactorial disease featuring the interplay of microvascular, neurodegenerative, metabolic, genetic/epigenetic, immunological, and inflammation-related factors. Particularly, deeper knowledge on the mechanisms and pathophysiology of most advanced PDR is critical. Lymphatic-like vessel formation coupled with abnormal endothelial differentiation and progenitor cell involvement in the neovascularization associated with PDR are novel recent findings which hold potential for improved DR treatment. Understanding the underlying mechanisms of PDR pathogenesis is therefore crucial. To this goal, multidisciplinary approaches and new ex vivo models have been developed for a more comprehensive molecular, cellular and tissue-level understanding of the disease. This is the first step to gain the needed information on how PDR can be better evaluated, stratified, and treated.