Lymphatic Vessel Network Structure and Physiology

Glymphatic system: a gateway for neuroinflammation

The glymphatic system is a relatively recently identified fluid exchange and transport system in the brain. Accumulating evidence indicates that glymphatic function is impaired not only in central nervous system disorders but also in systemic diseases. Systemic diseases can trigger the inflammatory responses in the central nervous system, occasionally leading to sustained inflammation and functional disturbance of the central nervous system. This review summarizes the current knowledge on the association between glymphatic dysfunction and central nervous system inflammation. In addition, we discuss the hypothesis that disease conditions initially associated with peripheral inflammation overwhelm the performance of the glymphatic system, thereby triggering central nervous system dysfunction, chronic neuroinflammation, and neurodegeneration. Future research investigating the role of the glymphatic system in neuroinflammation may offer innovative therapeutic approaches for central nervous system disorders.

Lymphatic failure and lymphatic interventions: Knowledge gaps and future directions for a new frontier in congenital heart disease

Lymphatic failure is a broad term that describes the lymphatic circulation's inability to adequately transport fluid and solutes out of the interstitium and into the systemic venous circulation, which can result in dysfunction and dysregulation of immune responses, dietary fat absorption, and fluid balance maintenance. Several investigations have recently elucidated the nexus between lymphatic failure and congenital heart disease, and the associated morbidity and mortality is now well-recognized. However, the precise pathophysiology and pathogenesis of lymphatic failure remains poorly understood and relatively understudied, and there are no targeted therapeutics or interventions to reliably prevent its development and progression. Thus, there is growing enthusiasm towards the development and application of novel percutaneous and surgical lymphatic interventions. Moreover, there is consensus that further investigations are needed to delineate the underlying mechanisms of lymphatic failure, which could help identify novel therapeutic targets and develop innovative procedures to improve the overall quality of life and survival of these patients. With these considerations, this review aims to provide an overview of the lymphatic circulation and its vasculature as it relates to current understandings into the pathophysiology and pathogenesis of lymphatic failure in patients with congenital heart disease, while also summarizing strategies for evaluating and managing lymphatic complications, as well as specific areas of interest for future translational and clinical research efforts.

Does Thoracic Duct Ligation at the Time of Esophagectomy Impact Long-Term Survival? An Individual Patient Data Meta-Analysis

Background: Thoracic duct ligation (TDL) during esophagectomy has been proposed to reduce the risk of postoperative chylothorax. Because of its role in immunoregulation, some authors argued that it had an unfavorable TDL effect on survival. The aim of this study was to analyze the effect of TDL on overall survival (OS). Methods: PubMed, MEDLINE, Scopus, and Web of Science were searched through December 2023. The primary outcome was 5-year OS. The restricted mean survival time difference (RMSTD), hazard ratios (HRs), and 95% confidence intervals (CI) were used as pooled effect size measures. The GRADE methodology was used to summarize the certainty of the evidence. Results: Five studies (3291 patients) were included. TDL was reported in 54% patients. The patients' age ranged from 49 to 69, 76% were males, and BMI ranged from 18 to 26. At the 5-year follow-up, the combined effect from the multivariate meta-analysis is -3.5 months (95% CI -6.1, -0.8) indicating that patients undergoing TDL lived 3.5 months less compared to those without TDL. TDL was associated with a significantly higher hazard for mortality at 12 months (HR 1.54, 95% CI 1.38-1.73), 24 months (HR 1.21, 95% CI 1.12-1.35), and 28 months (HR 1.14, 95% CI 1.02-1.28). TDL and noTDL seem comparable in terms of the postoperative risk for chylothorax (RR = 0.66; p = 0.35). Conclusions: In this study, concurrent TDL was associated with reduced 5-year OS after esophagectomy. This may suggest the need of a rigorous follow-up within the first two years of follow-up.

Quantifying the Lymphatic Transport of Model Therapeutics from the Brain in Rats

In recent years, the drainage of fluids, immune cells, antigens, fluorescent tracers, and other solutes from the brain has been demonstrated to occur along lymphatic outflow pathways to the deep cervical lymph nodes in the neck. To the best of our knowledge, no studies have evaluated the lymphatic transport of therapeutics from the brain. The objective of this study was to determine the lymphatic transport of model therapeutics of different molecular weights and lipophilicity from the brain using cervical lymph cannulation and ligation models in rats. To do this, anesthetized Sprague-Dawley rats were cannulated at the carotid artery and cannulated, ligated, or left intact at the cervical lymph duct. Rats were administered 14C-ibuprofen (206.29 g/mol, logP 3.84), 3H-halofantrine HCl (536.89 g/mol, logP 8.06), or 3H-albumin (∼65,000 g/mol) via direct injection into the brain striatum at a rate of 0.5 μL/min over 16 min. Plasma or cervical lymph samples were collected for up to 6-8 h following dosing, and brain and lymph nodes were collected at 6 or 8 h. Samples were subsequently analyzed for radioactivity levels via scintillation counting. For 14C-ibuprofen, plasma concentrations over time (plasma AUC0-6h) were >2 fold higher in lymph-ligated rats than in lymph-intact rats, suggesting that ibuprofen is cleared from the brain primarily via nonlymphatic routes (e.g., across the blood-brain barrier) but that this clearance is influenced by changes in lymphatic flow. For 3H-halofantrine, >73% of the dose was retained at the brain dosing site in lymph-intact and lymph-ligated groups, and plasma AUC0-8h values were low in both groups (<0.3% dose.h/mL), consistent with the high retention in the brain. It was therefore not possible to determine whether halofantrine undergoes lymphatic transport from the brain within the duration of the study. For 3H-albumin, plasma AUC0-8h values were not significantly different between lymph-intact, lymph-ligated, and lymph-cannulated rats. However, >4% of the dose was recovered in cervical lymph over 8 h. Lymph/plasma concentration ratios of 3H-albumin were also very high (up to 53:1). Together, these results indicate that 3H-albumin is transported from the brain not only via lymphatic routes but also via the blood. Similar to other tissues, the lymphatics may thus play a significant role in the transport of macromolecules, including therapeutic proteins, from the brain but are unlikely to be a major transport pathway from the brain for small molecule drugs that are not lipophilic. Our rat cervical lymph cannulation model can be used to quantify the lymphatic drainage of different molecules and factors from the brain.

Networks of Nerve Fibers, and Blood and Lymphatic Vessels in the Mouse Auricle: The Structural Basis of Ear Acupuncture

Objective

Ear acupuncture, as a system for treating and preventing diseases through stimulation of points on the auricle, has been systematically introduced during the last 60 years. Although the auricular cartography was described somatotopically as an inverted fetus by Paul Nogier, MD, the underlying mechanism of auricular stimulation remains unclear. The aim of this research was to gain an understanding of the structural basis of auricular stimulation, as well as showing the distribution of the nerve fibers, and the blood and lymphatic vessels.

Materials and Methods

The distribution of nerve fibers, and blood and lymphatic vessels was examined in whole-mount auricular skins of mice by combining the biomarkers protein gene product 9.5, cluster of differentiation 31, and lymphatic-vessel endothelial hyaluronan receptor-1 following tissue-clearing treatment with multiple immunofluorescent staining.

Results

The labeled nerve fibers, and the blood and lymphatic vessels were distributed extensively in the inner and outer parts of the auricular skin. Auricular nerves aligning with blood vessels ran from the basal region to the peripheral region and crossed over lymphatic vessels, thus forming the neural, vascular, and lymphatic networks.

Conclusions

As these are important tissue components of auricular skin, this result implies that the auricular nerve fibers, and blood and lymphatic vessels may coordinate with each other to respond directly to auricular stimulation.

Mapping the Anatomy of the Human Lymphatic System

BACKGROUND

 While substantial anatomical study has been pursued throughout the human body, anatomical study of the human lymphatic system remains in its infancy. For microsurgeons specializing in lymphatic surgery, a better command of lymphatic anatomy is needed to further our ability to offer surgical interventions with precision. In an effort to facilitate the dissemination and advancement of human lymphatic anatomy knowledge, our teams worked together to create a map. The aim of this paper is to present our experience in mapping the anatomy of the human lymphatic system.

METHODS

 Three steps were followed to develop a modern map of the human lymphatic system: (1) identifying our source material, which was "Anatomy of the human lymphatic system," published by Rouvière and Tobias (1938), (2) choosing a modern platform, the Miro Mind Map software, to integrate the source material, and (3) transitioning our modern platform into The Human BioMolecular Atlas Program (HuBMAP).

RESULTS

 The map of lymphatic anatomy based on the Rouvière textbook contained over 900 data points. Specifically, the map contained 404 channels, pathways, or trunks and 309 lymph node groups. Additionally, lymphatic drainage from 165 distinct anatomical regions were identified and integrated into the map. The map is being integrated into HuBMAP by creating a standard data format called an Anatomical Structures, Cell Types, plus Biomarkers table for the lymphatic vasculature, which is currently in the process of construction.

CONCLUSION

 Through a collaborative effort, we have developed a unified and centralized source for lymphatic anatomy knowledge available to the entire scientific community. We believe this resource will ultimately advance our knowledge of human lymphatic anatomy while simultaneously highlighting gaps for future research. Advancements in lymphatic anatomy knowledge will be critical for lymphatic surgeons to further refine surgical indications and operative approaches.

50-nm Gas-Filled Protein Nanostructures to Enable the Access of Lymphatic Cells by Ultrasound Technologies

Ultrasound imaging and ultrasound-mediated gene and drug delivery are rapidly advancing diagnostic and therapeutic methods; however, their use is often limited by the need for microbubbles, which cannot transverse many biological barriers due to their large size. Here, the authors introduce 50-nm gas-filled protein nanostructures derived from genetically engineered gas vesicles(GVs) that are referred to as 50 nmGVs. These diamond-shaped nanostructures have hydrodynamic diameters smaller than commercially available 50-nm gold nanoparticles and are, to the authors' knowledge, the smallest stable, free-floating bubbles made to date. 50 nmGVs can be produced in bacteria, purified through centrifugation, and remain stable for months. Interstitially injected 50 nmGVs can extravasate into lymphatic tissues and gain access to critical immune cell populations, and electron microscopy images of lymph node tissues reveal their subcellular location in antigen-presenting cells adjacent to lymphocytes. The authors anticipate that 50 nmGVs can substantially broaden the range of cells accessible to current ultrasound technologies and may generate applications beyond biomedicine as ultrasmall stable gas-filled nanomaterials.

Circadian Mechanisms in Brain Fluid Biology

The brain is a complex organ, fundamentally changing across the day to perform basic functions like sleep, thought, and regulating whole-body physiology. This requires a complex symphony of nutrients, hormones, ions, neurotransmitters and more to be properly distributed across the brain to maintain homeostasis throughout 24 hours. These solutes are distributed both by the blood and by cerebrospinal fluid. Cerebrospinal fluid contents are distinct from the general circulation because of regulation at brain barriers including the choroid plexus, glymphatic system, and blood-brain barrier. In this review, we discuss the overlapping circadian (≈24-hour) rhythms in brain fluid biology and at the brain barriers. Our goal is for the reader to gain both a fundamental understanding of brain barriers alongside an understanding of the interactions between these fluids and the circadian timing system. Ultimately, this review will provide new insight into how alterations in these finely tuned clocks may lead to pathology.

Computational fluid dynamic modeling of the lymphatic system: a review of existing models and future directions

Historically, research into the lymphatic system has been overlooked due to both a lack of knowledge and limited recognition of its importance. In the last decade however, lymphatic research has gained substantial momentum and has included the development of a variety of computational models to aid understanding of this complex system. This article reviews existing computational fluid dynamic models of the lymphatics covering each structural component including the initial lymphatics, pre-collecting and collecting vessels, and lymph nodes. This is followed by a summary of limitations and gaps in existing computational models and reasons that development in this field has been hindered to date. Over the next decade, efforts to further characterize lymphatic anatomy and physiology are anticipated to provide key data to further inform and validate lymphatic fluid dynamic models. Development of more comprehensive multiscale- and multi-physics computational models has the potential to significantly enhance the understanding of lymphatic function in both health and disease.

Deregulation of the Glymphatic System in Alzheimer's Disease: Genetic and Non-Genetic Factors

Alzheimer's disease (AD) is the most prevalent form of dementia and is characterized by progressive degeneration of brain function. AD gradually affects the parts of the brain that control thoughts, language, behavior and mental function, severely impacting a person's ability to carry out daily activities and ultimately leading to death. The accumulation of extracellular amyloid-β peptide (Aβ) and the aggregation of intracellular hyperphosphorylated tau are the two key pathological hallmarks of AD. AD is a complex condition that involves both non-genetic risk factors (35%) and genetic risk factors (58-79%). The glymphatic system plays an essential role in clearing metabolic waste, transporting tissue fluid, and participating in the immune response. Both non-genetic and genetic risk factors affect the glymphatic system to varying degrees. The main purpose of this review is to summarize the underlying mechanisms involved in the deregulation of the glymphatic system during the progression of AD, especially concerning the diverse contributions of non-genetic and genetic risk factors. In the future, new targets and interventions that modulate these interrelated mechanisms will be beneficial for the prevention and treatment of AD.

Lymphatic vessel: origin, heterogeneity, biological functions, and therapeutic targets

Lymphatic vessels, comprising the secondary circulatory system in human body, play a multifaceted role in maintaining homeostasis among various tissues and organs. They are tasked with a serious of responsibilities, including the regulation of lymph absorption and transport, the orchestration of immune surveillance and responses. Lymphatic vessel development undergoes a series of sophisticated regulatory signaling pathways governing heterogeneous-origin cell populations stepwise to assemble into the highly specialized lymphatic vessel networks. Lymphangiogenesis, as defined by new lymphatic vessels sprouting from preexisting lymphatic vessels/embryonic veins, is the main developmental mechanism underlying the formation and expansion of lymphatic vessel networks in an embryo. However, abnormal lymphangiogenesis could be observed in many pathological conditions and has a close relationship with the development and progression of various diseases. Mechanistic studies have revealed a set of lymphangiogenic factors and cascades that may serve as the potential targets for regulating abnormal lymphangiogenesis, to further modulate the progression of diseases. Actually, an increasing number of clinical trials have demonstrated the promising interventions and showed the feasibility of currently available treatments for future clinical translation. Targeting lymphangiogenic promoters or inhibitors not only directly regulates abnormal lymphangiogenesis, but improves the efficacy of diverse treatments. In conclusion, we present a comprehensive overview of lymphatic vessel development and physiological functions, and describe the critical involvement of abnormal lymphangiogenesis in multiple diseases. Moreover, we summarize the targeting therapeutic values of abnormal lymphangiogenesis, providing novel perspectives for treatment strategy of multiple human diseases.

Entry and exit of extracellular vesicles to and from the blood circulation

Extracellular vesicles (EVs) are biological nanoparticles that promote intercellular communication by delivering bioactive cargo over short and long distances. Short-distance communication takes place in the interstitium, whereas long-distance communication is thought to require transport through the blood circulation to reach distal sites. Extracellular vesicle therapeutics are frequently injected systemically, and diagnostic approaches often rely on the detection of organ-derived EVs in the blood. However, the mechanisms by which EVs enter and exit the circulation are poorly understood. Here, the lymphatic system and transport across the endothelial barrier through paracellular and transcellular routes are discussed as potential pathways for EV entry to and exit from the blood circulatory system.

Sepsis-Induced Inhibition of Contractile Function of Lymphatic Nodes

Inflammation accompanies most pathological processes, while the lymphatic system takes part in both the development and resolution of inflammation. We studied the contractile function of rat lymph nodes after cecal ligation and puncture (CLP). In 24 h after CLP, the mesenteric lymph nodes were removed and placed in the myograph chamber. After CLP, the lymph nodes showed lower tension than lymph nodes from sham-operated animals (control). The expression of inducible NO synthase, cyclooxygenase-2, and cystathionine-γ-lyase was observed in the lymph nodes of CLP rats. NO, prostaglandins, and H2S formed during inflammation inhibited contractile activity of smooth muscle cells in the capsule of the lymph nodes, which manifested itself in inhibition of phase contractions and a decrease in the tone of their capsule.

Extracellular matrix molecules associated with lymphatic vessels in health and disease

Lymphatic vessels (LyVs), responsible for fluid, solute, and immune cell homeostasis in the body, are closely associated with the adjacent extracellular matrix (ECM) molecules whose structural and functional impact on LyVs is currently more appreciated, albeit not entirely elucidated. These molecules, serving as a platform for various connective tissue cell activities and affecting LyV biology should be considered also as an integral part of the lymphatic system. Any alterations and changes in ECM molecules over the course of disease impair the function and structure of the LyV network. Remodeling of LyV cells, which are components of lymphatic vessel walls, also triggers alterations in ECM molecules and interstitial tissue composition. Therefore, in this review we aimed to present the current knowledge on ECM in tissues and particularly on molecules surrounding lymphatics in normal conditions and in disease.

A dual-clock-driven model of lymphatic muscle cell pacemaking to emulate knock-out of Ano1 or IP3R

Lymphatic system defects are involved in a wide range of diseases, including obesity, cardiovascular disease, and neurological disorders, such as Alzheimer's disease. Fluid return through the lymphatic vascular system is primarily provided by contractions of muscle cells in the walls of lymphatic vessels, which are in turn driven by electrochemical oscillations that cause rhythmic action potentials and associated surges in intracellular calcium ion concentration. There is an incomplete understanding of the mechanisms involved in these repeated events, restricting the development of pharmacological treatments for dysfunction. Previously, we proposed a model where autonomous oscillations in the membrane potential (M-clock) drove passive oscillations in the calcium concentration (C-clock). In this paper, to model more accurately what is known about the underlying physiology, we extend this model to the case where the M-clock and the C-clock oscillators are both active but coupled together, thus both driving the action potentials. This extension results from modifications to the model's description of the IP3 receptor, a key C-clock mechanism. The synchronised dual-driving clock behaviour enables the model to match IP3 receptor knock-out data, thus resolving an issue with previous models. We also use phase-plane analysis to explain the mechanisms of coupling of the dual clocks. The model has the potential to help determine mechanisms and find targets for pharmacological treatment of some causes of lymphoedema.

Three-dimensional visualization of the lymphatic, vascular and neural network in rat lung by confocal microscopy

In order to demonstrate the intricate interconnection of pulmonary lymphatic vessels, blood vessels, and nerve fibers, the rat lung was selected as the target and sliced at the thickness of 100 μm for multiply immunofluorescence staining with lymphatic vessel endothelial hyaluronan receptor 1 (LYVE-1), alpha smooth muscle actin (α-SMA), phalloidin, cluster of differentiation 31 (CD31), and protein gene product 9.5 (PGP9.5) antibodies. Taking the advantages of the thicker tissue section and confocal microscopy, the labeled pulmonary lymphatic vessels, blood vessels, and nerve fibers were demonstrated in rather longer distance, which was more convenient to reconstruct a three-dimensional (3D) view for analyzing their spatial correlation in detail. It was clear that LYVE-1+ lymphatic vessels were widely distributed in pulmonary lobules and closely to the lobar bronchus. Through 3D reconstruction, it was also demonstrated that LYVE-1+ lymphatic vessels ran parallel to or around the α-SMA+ venules, phalloidin+ arterioles and CD31+ capillaries, with PGP9.5+ nerve fibers traversing alongside or wrapping around them, forming a lymphatic, vascular and neural network in the lung. By this study, we provide a detailed histological view to highlight the spatial correlation of pulmonary lymphatic, vascular and neural network, which may help us for insight into the functional role of this network under the physiological and pathological conditions.

Vascular reconstruction of the decellularized biomatrix for whole-organ engineering-a critical perspective and future strategies

Whole-organ re-engineering is the most challenging goal yet to be achieved in tissue engineering and regenerative medicine. One essential factor in any transplantable and functional tissue engineering is fabricating a perfusable vascular network with macro- and micro-sized blood vessels. Whole-organ development has become more practical with the use of the decellularized organ biomatrix (DOB) as it provides a native biochemical and structural framework for a particular organ. However, reconstructing vasculature and re-endothelialization in the DOB is a highly challenging task and has not been achieved for constructing a clinically transplantable vascularized organ with an efficient perfusable capability. Here, we critically and articulately emphasized factors that have been studied for the vascular reconstruction in the DOB. Furthermore, we highlighted the factors used for vasculature development studies in general and their application in whole-organ vascular reconstruction. We also analyzed in detail the strategies explored so far for vascular reconstruction and angiogenesis in the DOB for functional and perfusable vasculature development. Finally, we discussed some of the crucial factors that have been largely ignored in the vascular reconstruction of the DOB and the future directions that should be addressed systematically.

Fusion-negative rhabdomyosarcoma orthotopic tongue xenografts for study of invasion, intravasation and metastasis in live animals

PAX3/7 Fusion-negative rhabdomyosarcoma (FN-RMS) is a childhood mesodermal lineage malignancy with a poor prognosis for metastatic or relapsed cases. Towards achieving a more complete understanding of advanced FN-RMS, we developed an orthotopic tongue xenograft model for studies of molecular basis of FN-RMS invasion and metastasis. The behavior of FN-RMS cells injected into murine tongue was examined using in vivo bioluminescence imaging, non-invasive intravital microscopy (IVM), and histopathology and compared to the prevailing hindlimb intramuscular and subcutaneous xenografts. FN-RMS cells were retained in the tongue and invaded locally into muscle mysial spaces and vascular lumen. While evidence of hematogenous dissemination to the lungs occurred in tongue and intramuscular xenografts, evidence of local invasion and lymphatic dissemination to lymph nodes only occurred in tongue xenografts. IVM and RNA-seq of tongue xenografts reveal shifts in cellular phenotype and differentiation state in tongue xenografts. IVM also shows homing to blood and lymphatic vessels, lymphatic intravasation, and dynamic membrane protrusions. Based on these findings, the tongue orthotopic xenograft of FN-RMS is a valuable model for tumor progression studies at the tissue, cellular and subcellular levels providing insight into kinetics and molecular bases of tumor invasion and metastasis and, hence, new therapeutic avenues for advanced FN-RMS.

High-sensitivity synchronous angio-lymphography based on a speckle spectrum contrast OCT

To achieve accurate selection and synchronous imaging of blood vessels and lymph, a speckle spectrum contrast method (SSC) based on spectral-domain optical coherence tomography (SD-OCT) is proposed in this Letter. In this method, the time-lapse optical coherence tomography (OCT) intensity signal is transformed to the Fourier frequency domain. By analyzing the frequency spectrum of the time-lapse OCT intensity signal, a parameter called SSC signal, which represents the ratio of different intervals of the high frequency to the low frequency, is utilized to extract and contrast different types of the vessels in the biological tissues. In the SSC spectrum, the SSC signals of the static tissue, lymphatic vessels, and vascular vessels can be separated in three different frequency intervals, enabling differentiation and synchronous imaging of the lymphatic-vascular vessels. A mouse ear was used to demonstrate the feasibility and efficiency of this method. By using the SSC signal as the imaging parameter, the lymphatic and blood vessels of the mouse ear are differentiated and visualized simultaneously. This study shows the feasibility of the three-dimensional (3D) synchronous angio-lymphography based on the SSC method, which provides a tool to improve the understanding for disease research and treatment.

Role of Crystalloids in the Perioperative Setting: From Basics to Clinical Applications and Enhanced Recovery Protocols

Perioperative fluid management, a critical aspect of major surgeries, is characterized by pronounced stress responses, altered capillary permeability, and significant fluid shifts. Recognized as a cornerstone of enhanced recovery protocols, effective perioperative fluid management is crucial for optimizing patient recovery and preventing postoperative complications, especially in high-risk patients. The scientific literature has extensively investigated various fluid infusion regimens, but recent publications indicate that not only the volume but also the type of fluid infused significantly influences surgical outcomes. Adequate fluid therapy prescription requires a thorough understanding of the physiological and biochemical principles that govern the body's internal environment and the potential perioperative alterations that may arise. Recently published clinical trials have questioned the safety of synthetic colloids, widely used in the surgical field. A new clinical scenario has arisen in which crystalloids could play a pivotal role in perioperative fluid therapy. This review aims to offer evidence-based clinical principles for prescribing fluid therapy tailored to the patient's physiology during the perioperative period. The approach combines these principles with current recommendations for enhanced recovery programs for surgical patients, grounded in physiological and biochemical principles.

Alk1 acts in non-endothelial VE-cadherin+ perineurial cells to maintain nerve branching during hair homeostasis

Vascular endothelial (VE)-cadherin is a well-recognized endothelial cell marker. One of its interacting partners, the TGF-β receptor Alk1, is essential in endothelial cells for adult skin vasculature remodeling during hair homeostasis. Using single-cell transcriptomics, lineage tracing and gene targeting in mice, we characterize the cellular and molecular dynamics of skin VE-cadherin+ cells during hair homeostasis. We describe dynamic changes of VE-cadherin+ endothelial cells specific to blood and lymphatic vessels and uncover an atypical VE-cadherin+ cell population. The latter is not a predicted adult endovascular progenitor, but rather a non-endothelial mesenchymal perineurial cell type, which forms nerve encapsulating tubular structures that undergo remodeling during hair homeostasis. Alk1 acts in the VE-cadherin+ perineurial cells to maintain proper homeostatic nerve branching by enforcing basement membrane and extracellular matrix molecular signatures. Our work implicates the VE-cadherin/Alk1 duo, classically known as endothelial-vascular specific, in perineurial-nerve homeostasis. This has broad implications in vascular and nerve disease.

The emerging importance of lymphatics in health and disease: an NIH workshop report

The lymphatic system (LS) is composed of lymphoid organs and a network of vessels that transport interstitial fluid, antigens, lipids, cholesterol, immune cells, and other materials in the body. Abnormal development or malfunction of the LS has been shown to play a key role in the pathophysiology of many disease states. Thus, improved understanding of the anatomical and molecular characteristics of the LS may provide approaches for disease prevention or treatment. Recent advances harnessing single-cell technologies, clinical imaging, discovery of biomarkers, and computational tools have led to the development of strategies to study the LS. This Review summarizes the outcomes of the NIH workshop entitled "Yet to be Charted: Lymphatic System in Health and Disease," held in September 2022, with emphasis on major areas for advancement. International experts showcased the current state of knowledge regarding the LS and highlighted remaining challenges and opportunities to advance the field.

A 3D Human Lymphatic Vessel-on-Chip Reveals the Roles of Interstitial Flow and VEGF-A/C for Lymphatic Sprouting and Discontinuous Junction Formation

Introduction

Lymphatic vessels (LVs) maintain fluid homeostasis by draining excess interstitial fluid, which is accomplished by two distinct LVs: initial LVs and collecting LVs. The interstitial fluid is first drained into the initial LVs through permeable "button-like" lymphatic endothelial cell (LEC) junctions. Next, the drained fluid ("lymph") transports to lymph nodes through the collecting LVs with less permeable "zipper-like" junctions that minimize loss of lymph. Despite the significance of LEC junctions in lymphatic drainage and transport, it remains unclear how luminal or interstitial flow affects LEC junctions in vascular endothelial growth factors A and C (VEGF-A and VEGF-C) conditions. Moreover, it remains unclear how these flow and growth factor conditions impact lymphatic sprouting.

Methods

We developed a 3D human lymphatic vessel-on-chip that can generate four different flow conditions (no flow, luminal flow, interstitial flow, both luminal and interstitial flow) to allow an engineered, rudimentary LV to experience those flows and respond to them in VEGF-A/C.

Results

We examined LEC junction discontinuities, lymphatic sprouting, LEC junction thicknesses, and cell contractility-dependent vessel diameters in the four different flow conditions in VEGF-A/C. We discovered that interstitial flow in VEGF-C generates discontinuous LEC junctions that may be similar to the button-like junctions with no lymphatic sprouting. However, interstitial flow or both luminal and interstitial flow stimulated lymphatic sprouting in VEGF-A, maintaining zipper-like LEC junctions. LEC junction thickness and cell contractility-dependent vessel diameters were not changed by those conditions.

Conclusions

In this study, we provide an engineered lymphatic vessel platform that can generate four different flow regimes and reveal the roles of interstitial flow and VEGF-A/C for lymphatic sprouting and discontinuous junction formation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-023-00780-0.

Solute Transport across the Lymphatic Vasculature in a Soft Skin Tissue

Convective transport of drug solutes in biological tissues is regulated by the interstitial fluid pressure, which plays a crucial role in drug absorption into the lymphatic system through the subcutaneous (SC) injection. In this paper, an approximate continuum poroelasticity model is developed to simulate the pressure evolution in the soft porous tissue during an SC injection. This poroelastic model mimics the deformation of the tissue by introducing the time variation of the interstitial fluid pressure. The advantage of this method lies in its computational time efficiency and simplicity, and it can accurately model the relaxation of pressure. The interstitial fluid pressure obtained using the proposed model is validated against both the analytical and the numerical solution of the poroelastic tissue model. The decreasing elasticity elongates the relaxation time of pressure, and the sensitivity of pressure relaxation to elasticity decreases with the hydraulic permeability, while the increasing porosity and permeability due to deformation alleviate the high pressure. An improved Kedem-Katchalsky model is developed to study solute transport across the lymphatic vessel network, including convection and diffusion in the multi-layered poroelastic tissue with a hybrid discrete-continuum vessel network embedded inside. At last, the effect of different structures of the lymphatic vessel network, such as fractal trees and Voronoi structure, on the lymphatic uptake is investigated. In this paper, we provide a novel and time-efficient computational model for solute transport across the lymphatic vasculature connecting the microscopic properties of the lymphatic vessel membrane to the macroscopic drug absorption.

Vascular changes in the cycling and early pregnant uterus

Uterine vascular remodeling is intrinsic to the cycling and early pregnant endometrium. Maternal regulatory factors such as ovarian hormones, VEGF, angiopoietins, Notch, and uterine natural killer cells significantly mediate these vascular changes. In the absence of pregnancy, changes in uterine vessel morphology and function correlate with different stages of the human menstrual cycle. During early pregnancy, vascular remodeling in rodents and humans results in decreased uterine vascular resistance and increased vascular permeability necessary for pregnancy success. Aberrations in these adaptive vascular processes contribute to increased risk of infertility, abnormal fetal growth, and/or preeclampsia. This Review comprehensively summarizes uterine vascular remodeling in the human menstrual cycle, and in the peri- and post-implantation stages in rodent species (mice and rats).

Neurodegeneration and inflammation crosstalk: Therapeutic targets and perspectives

Glia, which was formerly considered to exist just to connect neurons, now plays a key function in a wide range of physiological events, including formation of memory, learning, neuroplasticity, synaptic plasticity, energy consumption, and homeostasis of ions. Glial cells regulate the brain's immune responses and confers nutritional and structural aid to neurons, making them an important player in a broad range of neurological disorders. Alzheimer's, ALS, Parkinson's, frontotemporal dementia (FTD), and epilepsy are a few of the neurodegenerative diseases that have been linked to microglia and astroglia cells, in particular. Synapse growth is aided by glial cell activity, and this activity has an effect on neuronal signalling. Each glial malfunction in diverse neurodegenerative diseases is distinct, and we will discuss its significance in the progression of the illness, as well as its potential for future treatment.

The Lymphatic System in Kidney Disease

The high-capacity vessels of the lymphatic system drain extravasated fluid and macromolecules from nearly every part of the body. However, far from merely a passive conduit for fluid removal, the lymphatic system also plays a critical and active role in immune surveillance and immune response modulation through the presentation of fluid, macromolecules, and trafficking immune cells to surveillance cells in regional draining lymph nodes before their return to the systemic circulation. The potential effect of this system in numerous disease states both within and outside of the kidney is increasingly being explored for their therapeutic potential. In the kidneys, the lymphatics play a critical role in both fluid and macromolecule removal to maintain oncotic and hydrostatic pressure gradients for normal kidney function, as well as in shaping kidney immunity, and potentially in balancing physiological pathways that promote healthy organ maintenance and responses to injury. In many states of kidney disease, including AKI, the demand on the preexisting lymphatic network increases for clearance of injury-related tissue edema and inflammatory infiltrates. Lymphangiogenesis, stimulated by macrophages, injured resident cells, and other drivers in kidney tissue, is highly prevalent in settings of AKI, CKD, and transplantation. Accumulating evidence points toward lymphangiogenesis being possibly harmful in AKI and kidney allograft rejection, which would potentially position lymphatics as another target for novel therapies to improve outcomes. However, the extent to which lymphangiogenesis is protective rather than maladaptive in the kidney in various settings remains poorly understood and thus an area of active research.

Role of nanotechnology in the prolonged release of drugs by the subcutaneous route

INTRODUCTION

Subcutaneous physiology is distinct from other parenteral routes that benefit the administration of prolonged-release formulations. A prolonged-release effect is particularly convenient for treating chronic diseases because it is associated with complex and often prolonged posologies. Therefore, drug-delivery systems focused on nanotechnology are proposed as alternatives that can overcome the limitations of current therapeutic regimens and improve therapeutic efficacy.

AREAS COVERED

This review presents an updated systematization of nanosystems, focusing on their applications in highly prevalent chronic diseases. Subcutaneous-delivered nanosystem-based therapies comprehensively summarize nanosystems, drugs, and diseases and their advantages, limitations, and strategies to increase their translation into clinical applications. An outline of the potential contribution of quality-by-design (QbD) and artificial intelligence (AI) to the pharmaceutical development of nanosystems is presented.

EXPERT OPINION

Although recent academic research and development (R&D) advances in the subcutaneous delivery of nanosystems have exhibited promising results, pharmaceutical industries and regulatory agencies need to catch up. The lack of standardized methodologies for analyzing in vitro data from nanosystems for subcutaneous administration and subsequent in vivo correlation limits their access to clinical trials. There is an urgent need for regulatory agencies to develop methods that faithfully mimic subcutaneous administration and specific guidelines for evaluating nanosystems.

Molecular events in the jaw vascular unit: A traditional review of the mechanisms involved in inflammatory jaw bone diseases

Inflammatory jaw bone diseases are common in stomatology, including periodontitis, peri-implantitis, medication-related osteonecrosis of the jaw, radiation osteomyelitis of the jaw, age-related osteoporosis, and other specific infections. These diseases may lead to tooth loss and maxillofacial deformities, severely affecting patients' quality of life. Over the years, the reconstruction of jaw bone deficiency caused by inflammatory diseases has emerged as a medical and socioeconomic challenge. Therefore, exploring the pathogenesis of inflammatory diseases associated with jaw bones is crucial for improving prognosis and developing new targeted therapies. Accumulating evidence indicates that the integrated bone formation and dysfunction arise from complex interactions among a network of multiple cell types, including osteoblast-associated cells, immune cells, blood vessels, and lymphatic vessels. However, the role of these different cells in the inflammatory process and the 'rules' with which they interact are still not fully understood. Although many investigations have focused on specific pathological processes and molecular events in inflammatory jaw diseases, few articles offer a perspective of integration. Here, we review the changes and mechanisms of various cell types in inflammatory jaw diseases, with the hope of providing insights to drive future research in this field.

Intestinal Lymphatic Dysfunction in Kidney Disease

Kidney disease is associated with adverse consequences in many organs beyond the kidney, including the heart, lungs, brain, and intestines. The kidney-intestinal cross talk involves intestinal epithelial damage, dysbiosis, and generation of uremic toxins. Recent studies reveal that kidney injury expands the intestinal lymphatics, increases lymphatic flow, and alters the composition of mesenteric lymph. The intestinal lymphatics, like blood vessels, are a route for transporting potentially harmful substances generated by the intestines. The lymphatic architecture and actions are uniquely suited to take up and transport large macromolecules, functions that differentiate them from blood vessels, allowing them to play a distinct role in a variety of physiological and pathological processes. Here, we focus on the mechanisms by which kidney diseases result in deleterious changes in intestinal lymphatics and consider a novel paradigm of a vicious cycle of detrimental organ cross talk. This concept involves kidney injury-induced modulation of intestinal lymphatics that promotes production and distribution of harmful factors, which in turn contributes to disease progression in distant organ systems.

Management of the head and neck lymphatic malformations in children: A 7-year experience of 91 surgical cases

OBJECTIVE

To review the clinical characteristics and treatment outcomes of head and neck lymphatic malformations (HNLMs) in children.

METHODS

A retrospective study of 91 patients with HNLMs was performed.

RESULTS

The age ranged from 1 day to 14 years, of which 82.4 % (75/91) were under 2 years old and 45.1 % (41/91) were diagnosed at birth. The diagnostic rates of ultrasound, CT and MRI were 80.2 % (73/91), 90.1 % (82/91) and 100 % (8/8) respectively. There were 2 cases of complete excision, 8 of bleomycin sclerotherapy, and 81 of subtotal resection combined with bleomycin irrigation. Followed up for 3-93 months, all 91 cases were cured.

CONCLUSIONS

HNLMs mostly occur within 2 years old, and nearly half of them are present at birth. Characteristic imaging findings can assist clinicians in diagnosis and treatment plan. Subtotal resection combined with bleomycin irrigation may be an appropriate first-line therapy for HNLMs involving the vital anatomical structures.

Impact of Goreisan components on rat mesenteric collecting lymphatic vessel pumping

BACKGROUND

Goreisan is a traditional herbal formulation with diuretic properties tested as a clinical therapeutic to alleviate lymphedema in Japan. The present study aimed to determine how Goreisan and its five different components affect lymphatic pump function.

METHODS

Mesenteric collecting lymphatics were isolated from anesthetized Sprague-Dawley rats and mounted on resistance-matched glass micropipettes in a 37°C physiological salt solution bath for studies. Diameter was continuously measured to obtain the following lymphatic pump parameters: contraction frequency (CF), end diastolic diameter (EDD), and end systolic diameter (ESD), contraction amplitude (AMP), ejection fraction (EF), and fractional pump flow (FPF). Goreisan and each of its components (Cinnamomi Cortex, Atractylodis Rhizoma, Alismatis Rhizoma, Polyporus, and Poria) were applied to the bath at concentrations of 1-30 μg/mL.

RESULTS

The results show that while Goreisan causes no significant changes to lymphatic pumping, Alismatis Rhizoma and Polyporus each significantly reduce CF and FPF. In addition, rats that received oral administration of Goreisan and Alismatis Rhizoma for 1 week had elevated expression of VEGFR-3 in their mesenteric collecting lymphatics.

CONCLUSIONS

Collectively, the results suggest that some components of Goreisan have a direct, rapid impact on lymphatic pumping. These findings provide new insights but also raise new questions about the therapeutic potential of Goreisan in patients with secondary lymphedema.

The lymphatic vasculature in lung function and respiratory disease

The lymphatic vasculature maintains tissue homeostasis via fluid drainage in the form of lymph and immune surveillance due to migration of leukocytes through the lymphatics to the draining lymph nodes. Lymphatic endothelial cells (LECs) form the lymphatic vessels and lymph node sinuses and are key players in shaping immune responses and tolerance. In the healthy lung, the vast majority of lymphatic vessels are found along the bronchovascular structures, in the interlobular septa, and in the subpleural space. Previous studies in both mice and humans have shown that the lymphatics are necessary for lung function from the neonatal period through adulthood. Furthermore, changes in the lymphatic vasculature are observed in nearly all respiratory diseases in which they have been analyzed. Recent work has pointed to a causative role for lymphatic dysfunction in the initiation and progression of lung disease, indicating that these vessels may be active players in pathologic processes in the lung. However, the mechanisms by which defects in lung lymphatic function are pathogenic are understudied, leaving many unanswered questions. A more comprehensive understanding of the mechanistic role of morphological, functional, and molecular changes in the lung lymphatic endothelium in respiratory diseases is a promising area of research that is likely to lead to novel therapeutic targets. In this review, we will discuss our current knowledge of the structure and function of the lung lymphatics and the role of these vessels in lung homeostasis and respiratory disease.

Role of the Renal Lymphatic System in Heart Failure

PURPOSE OF REVIEW

The lymphatic system plays a major but overlooked role in maintaining fluid homeostasis. Given the unique fluid homeostasis functions of the kidneys, dysregulation of the renal lymphatic system underlies the development of self-propagating congestive pathomechanisms. In this review, we outline the roles of the renal lymphatic system in heart failure (HF).

RECENT FINDINGS

Studies have uncovered several pathomechanisms involving the renal lymphatic system in congestive states, such as impaired interstitial draining by the renal lymphatic system, impaired structure and valves of renal lymphatics, lymphatic-induced increase in renal reabsorption of water and sodium, and development of albuminuria with proteinuria-induced renal lymphangiogenesis. These self-propagating mechanisms result in "renal tamponade" with manifestations of cardiorenal syndrome and inappropriate renal response to diuretics. Dysregulation of the renal lymphatic system is integral to the development and progression of congestion in HF. Targeting renal lymphatics may provide a novel pathway to treat intractable congestion.

Regulating Lymphatic Vasculature in Fibrosis: Understanding the Biology to Improve the Modeling

Fibrosis occurs in many chronic diseases with lymphatic vascular insufficiency (e.g., kidney disease, tumors, and lymphedema). New lymphatic capillary growth can be triggered by fibrosis-related tissue stiffening and soluble factors, but questions remain for how related biomechanical, biophysical, and biochemical cues affect lymphatic vascular growth and function. The current preclinical standard for studying lymphatics is animal modeling, but in vitro and in vivo outcomes often do not align. In vitro models can also be limited in their ability to separate vascular growth and function as individual outcomes, and fibrosis is not traditionally included in model design. Tissue engineering provides an opportunity to address in vitro limitations and mimic microenvironmental features that impact lymphatic vasculature. This review discusses fibrosis-related lymphatic vascular growth and function in disease and the current state of in vitro lymphatic vascular models while highlighting relevant knowledge gaps. Additional insights into the future of in vitro lymphatic vascular models demonstrate how prioritizing fibrosis alongside lymphatics will help capture the complexity and dynamics of lymphatics in disease. Overall, this review aims to emphasize that an advanced understanding of lymphatics within a fibrotic disease-enabled through more accurate preclinical modeling-will significantly impact therapeutic development toward restoring lymphatic vessel growth and function in patients.

Mapping the lymphatic system across body scales and expertise domains: A report from the 2021 National Heart, Lung, and Blood Institute workshop at the Boston Lymphatic Symposium

Enhancing our understanding of lymphatic anatomy from the microscopic to the anatomical scale is essential to discern how the structure and function of the lymphatic system interacts with different tissues and organs within the body and contributes to health and disease. The knowledge of molecular aspects of the lymphatic network is fundamental to understand the mechanisms of disease progression and prevention. Recent advances in mapping components of the lymphatic system using state of the art single cell technologies, the identification of novel biomarkers, new clinical imaging efforts, and computational tools which attempt to identify connections between these diverse technologies hold the potential to catalyze new strategies to address lymphatic diseases such as lymphedema and lipedema. This manuscript summarizes current knowledge of the lymphatic system and identifies prevailing challenges and opportunities to advance the field of lymphatic research as discussed by the experts in the workshop.

Lymphatic uptake of biotherapeutics through a 3D hybrid discrete-continuum vessel network in the skin tissue

Subcutaneous administration is a common approach for the delivery of biotherapeutics, which is achieved mainly through the absorption across lymphatic vessels. In this paper, the drug transport and lymphatic uptake through a three-dimensional hybrid discrete-continuum vessel network in the skin tissue are investigated through high-fidelity numerical simulations. We find that the local lymphatic uptake through the explicit vessels significantly affects macroscopic drug absorption. The diffusion of drug solute through the explicit vessel network affects the lymphatic uptake after the injection. This effect, however, cannot be captured using previously developed continuum models. The lymphatic uptake is dominated by the convection due to lymphatic drainage driven by the pressure difference, which is rarely studied in experiments and simulations. Furthermore, the effects of injection volume and depth on the lymphatic uptake are investigated in a multi-layered domain. We find that the injection volume significantly affects the rate of lymphatic uptake through the heterogeneous vessel network, while the injection depth has little influence, which is consistent with the experimental results. At last, the binding and metabolism of drug molecules are studied to bridge the simulations to the drug clearance experients. We provide a new approach to study the diffusion and convection of drug molecules into the lymphatic system through the hybrid vessel network.

Subcutaneous Adipose Tissue Edema in Lipedema Revealed by Noninvasive 3T MR Lymphangiography

BACKGROUND

Lipedema exhibits excessive lower-extremity subcutaneous adipose tissue (SAT) deposition, which is frequently misidentified as obesity until lymphedema presents. MR lymphangiography may have relevance to distinguish lipedema from obesity or lymphedema.

HYPOTHESIS

Hyperintensity profiles on 3T MR lymphangiography can identify distinct features consistent with SAT edema in participants with lipedema.

STUDY TYPE

Prospective cross-sectional study.

SUBJECTS

Participants (48 females, matched for age [mean = 44.8 years]) with lipedema (n = 14), lipedema with lymphedema (LWL, n = 12), cancer treatment-related lymphedema (lymphedema, n = 8), and controls without these conditions (n = 14).

FIELD STRENGTH/SEQUENCE

3T MR lymphangiography (nontracer 3D turbo-spin-echo).

ASSESSMENT

Review of lymphangiograms in lower extremities by three radiologists was performed independently. Spatial patterns of hyperintense signal within the SAT were scored for extravascular (focal, diffuse, or not apparent) and vascular (linear, dilated, or not apparent) image features.

STATISTICAL TESTS

Interreader reliability was computed using Fleiss Kappa. Fisher's exact test was used to evaluate the proportion of image features between study groups. Multinomial logistic regression was used to assess the relationship between image features and study groups. The odds ratio (OR) and 95% confidence interval (CI) of SAT extravascular and vascular features was reported in groups compared to lipedema. The threshold of statistical significance was P < 0.05.

RESULTS

Reliable agreement was demonstrated between three independent, blinded reviewers (P < 0.001). The frequency of SAT hyperintensities in participants with lipedema (36% focal, 36% diffuse), LWL (42% focal, 33% diffuse), lymphedema (62% focal, 38% diffuse), and controls (43% focal, 0% diffuse) was significantly distinct. Compared with lipedema, SAT hyperintensities were less frequent in controls (focal: OR = 0.63, CI = 0.11-3.41; diffuse: OR = 0.05, CI = 0.00-1.27), similar in LWL (focal: OR = 1.29, CI = 0.19-8.89; diffuse: OR = 1.05, CI = 0.15-7.61), and more frequent in lymphedema (focal: OR = 9.00, CI = 0.30-274.12; diffuse: OR = 5.73, CI = 0.18-186.84).

DATA CONCLUSION

Noninvasive MR lymphangiography identifies distinct signal patterns indicating SAT edema and lymphatic load in participants with lipedema.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 1.

LED-based photoacoustic imaging for preoperative visualization of lymphatic vessels in patients with secondary limb lymphedema

Lymphedema is the accumulation of protein-rich fluid in the interstitium (i.e., dermal backflow (DBF)). Preoperative imaging of the lymphatic vessels is a prerequisite for lymphovenous bypass surgical planning. We investigated the visualization of lymphatic vessels and veins using light-emitting diode (LED)-based photoacoustic imaging (PAI). Indocyanine-green mediated near-infrared fluorescence lymphography (NIRF-L) was done in fifteen patients with secondary limb lymphedema. Photoacoustic images were acquired in locations where lymphatic vessels and DBF were observed with NIRF-L. We demonstrated that LED-based PAI can visualize and differentiate lymphatic vessels and veins even in the presence of DBF. We observed lymphatic and blood vessels up to depths of 8.3 and 8.6 mm, respectively. Superficial lymphatic vessels and veins can be visualized using LED-based PAI even in the presence of DBF showing the potential for pre-operative assessment. Further development of the technique is needed to improve its usability in clinical settings.

Development and application of a novel cervical lymph collection method to assess lymphatic transport in rats

Background: Fluids, solutes and immune cells have been demonstrated to drain from the brain and surrounding structures to the cervical lymph vessels and nodes in the neck via meningeal lymphatics, nasal lymphatics and/or lymphatic vessels associated with cranial nerves. A method to cannulate the efferent cervical lymph duct for continuous cervical lymph fluid collection in rodents has not been described previously and would assist in evaluating the transport of molecules and immune cells from the head and brain via the lymphatics, as well as changes in lymphatic transport and lymph composition with different physiological challenges or diseases. Aim: To develop a novel method to cannulate and continuously collect lymph fluid from the cervical lymph duct in rats and to analyze the protein, lipid and immune cell composition of the collected cervical lymph fluid. Methods: Male Sprague-Dawley rats were cannulated at the carotid artery with or without cannulation or ligation at the cervical lymph duct. Samples of blood, whole lymph and isolated lipoprotein fractions of lymph were collected and analyzed for lipid and protein composition using commercial kits. Whole lymph samples were centrifuged and isolated pellets were stained and processed for flow cytometry analysis of CD3⁺, CD4⁺, CD8a⁺, CD45R⁺ (B220) and viable cell populations. Results: Flow rate, phospholipid, triglyceride, cholesterol ester, free cholesterol and protein concentrations in cervical lymph were 0.094 ± 0.014 mL/h, 0.34 ± 0.10, 0.30 ± 0.04, 0.07 ± 0.02, 0.02 ± 0.01 and 16.78 ± 2.06 mg/mL, respectively. Protein was mostly contained within the non-lipoprotein fraction but all lipoprotein types were also present. Flow cytometry analysis of cervical lymph showed that 67.1 ± 7.4% of cells were CD3⁺/CD4⁺ T lymphocytes, 5.8 ± 1.6% of cells were CD3⁺/CD8⁺ T lymphocytes, and 10.8 ± 4.6% of cells were CD3^-/CD45R⁺ B lymphocytes. The remaining 16.3 ± 4.6% cells were CD3^-/CD45^- and identified as non-lymphocytes. Conclusion: Our novel cervical lymph cannulation method enables quantitative analysis of the lymphatic transport of immune cells and molecules in the cervical lymph of rats for the first time. This valuable tool will enable more detailed quantitative analysis of changes to cervical lymph composition and transport in health and disease, and could be a valuable resource for discovery of biomarkers or therapeutic targets in future studies.

Pharmacological inhibition of FOXO1 promotes lymphatic valve growth in a congenital lymphedema mouse model

Mutations in many genes that regulate lymphatic valve development are associated with congenital lymphedema. Oscillatory shear stress (OSS) from lymph provides constant signals for the growth and maintenance of valve cells throughout life. The expression of valve-forming genes in lymphatic endothelial cells (LECs) is upregulated by OSS. The transcription factor FOXO1 represses lymphatic valve formation by inhibiting the expression of these genes, which makes FOXO1 a potential target for treating lymphedema. Here, we tested the ability of a FOXO1 inhibitor, AS1842856, to induce the formation of new lymphatic valves. Our quantitative RT-PCR and Western blot data showed that treatment of cultured human LECs with AS1842856 for 48 h significantly increased the expression levels of valve-forming genes. To investigate the function of AS1842856 in vivo, Foxc2 +/- mice, the mouse model for lymphedema-distichiasis, were injected with AS1842856 for 2 weeks. The valve number in AS-treated Foxc2+/- mice was significantly higher than that of the vehicle-treated Foxc2+/- mice. Furthermore, since β-catenin upregulates the expression of Foxc2 and Prox1 during lymphatic valve formation, and AS1842856 treatment increased the level of active β-catenin in both cultured human LECs and in mouse mesenteric LECs in vivo, we used the mouse model with constitutive active β-catenin to rescue loss of lymphatic valves in Foxc2 +/- mice. Foxc2 +/- mice have 50% fewer lymphatic valves than control, and rescue experiments showed that the valve number was completely restored to the control level upon nuclear β-catenin activation. These findings indicate that pharmacological inhibition of FOXO1 can be explored as a viable strategy to resolve valve defects in congenital lymphedema.

Nanomedicine embraces cancer radio-immunotherapy: mechanism, design, recent advances, and clinical translation

Cancer radio-immunotherapy, integrating external/internal radiation therapy with immuno-oncology treatments, emerges in the current management of cancer. A growing number of pre-clinical studies and clinical trials have recently validated the synergistic antitumor effect of radio-immunotherapy, far beyond the "abscopal effect", but it suffers from a low response rate and toxicity issues. To this end, nanomedicines with an optimized design have been introduced to improve cancer radio-immunotherapy. Specifically, these nanomedicines are elegantly prepared by incorporating tumor antigens, immuno- or radio-regulators, or biomarker-specific imaging agents into the corresponding optimized nanoformulations. Moreover, they contribute to inducing various biological effects, such as generating in situ vaccination, promoting immunogenic cell death, overcoming radiation resistance, reversing immunosuppression, as well as pre-stratifying patients and assessing therapeutic response or therapy-induced toxicity. Overall, this review aims to provide a comprehensive landscape of nanomedicine-assisted radio-immunotherapy. The underlying working principles and the corresponding design strategies for these nanomedicines are elaborated by following the concept of "from bench to clinic". Their state-of-the-art applications, concerns over their clinical translation, along with perspectives are covered.

Differential regulation of lymphatic junctional morphology and the potential effects on cardiovascular diseases

The lymphatic vasculature provides an essential route to drain fluid, macromolecules, and immune cells from the interstitium as lymph, returning it to the bloodstream where the thoracic duct meets the subclavian vein. To ensure functional lymphatic drainage, the lymphatic system contains a complex network of vessels which has differential regulation of unique cell-cell junctions. The lymphatic endothelial cells lining initial lymphatic vessels form permeable "button-like" junctions which allow substances to enter the vessel. Collecting lymphatic vessels form less permeable "zipper-like" junctions which retain lymph within the vessel and prevent leakage. Therefore, sections of the lymphatic bed are differentially permeable, regulated in part by its junctional morphology. In this review, we will discuss our current understanding of regulating lymphatic junctional morphology, highlighting how it relates to lymphatic permeability during development and disease. We will also discuss the effect of alterations in lymphatic permeability on efficient lymphatic flux in health and how it may affect cardiovascular diseases, with a focus on atherosclerosis.

Increased nuchal translucency in children with congenital heart defects and normal karyotype-is there a correlation with mortality?

OBJECTIVES

Our objective was to investigate if an increased nuchal translucency (NT) was associated with higher mortality in chromosomally normal children with congenital heart defects (CHD).

METHODS

In a nationwide cohort using population-based registers, we identified 5,633 liveborn children in Denmark with a pre- or postnatal diagnosis of CHD from 2008 to 2018 (incidence of CHD 0.7%). Children with chromosomal abnormalities and non-singletons were excluded. The final cohort compromised 4,469 children. An increased NT was defined as NT > 95th-centile. Children with a NT > 95th-centile vs. NT < 95th-centile including subgroups of simple- and complex CHD were compared. Mortality was defined as death from natural causes, and mortalities were compared among groups. Survival analysis with Cox-regression was used to compare rates of mortality. Analyses were adjusted for mediators (possibly explanatory factors between increased NT and higher mortality): preeclampsia, preterm birth and small for gestational age. And for confounding effects of extracardiac anomalies and cardiac intervention, due to their close association to both the exposure and the outcome (i.e., confounders).

RESULTS

Of the 4,469 children with CHD, 754 (17%) had complex CHD and 3,715 (83%) simple CHD. In the combined group of CHDs the mortality rate was not increased when comparing those with a NT > 95th-centile to those with a NT < 95th-centile [Hazard ratio (HR) 1.6, 95%CI 0.8;3.4, p = 0.2]. In simple CHD there was a significantly higher mortality rate with a HR of 3.2 (95%CI: 1.1;9.2, p = 0.03) when having a NT > 95th centile. Complex CHD had no differences in mortality rate between a NT > 95th-centile and NT < 95th-centile (HR 1.1, 95%CI: 0.4;3.2, p = 0.8). All analysis adjusted for severity of CHD, cardiac operation and extracardiac anomalies. Due to limited numbers the association to mortality for a NT > 99th centile (>3.5 mm) could not be assessed. Adjustment for mediating (preeclampsia, preterm birth, small for gestational age) and confounding variables (extracardiac anomalies, cardiac intervention) did not alter the associations significantly, except for extracardiac anomalies in simple CHD.

CONCLUSION

An increased NT > 95th-centile is correlated with higher mortality in children with simple CHD, but the underlying cause is unknown and undetected abnormal genetics might explain the correlation rather than the increased NT itself, hence further research is warranted.

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.

Engineering transplantable human lymphatic and blood capillary networks in a porous scaffold

Due to a relative paucity of studies on human lymphatic assembly in vitro and subsequent in vivo transplantation, capillary formation and survival of primary human lymphatic (hLEC) and blood endothelial cells (hBEC) ± primary human vascular smooth muscle cells (hvSMC) were evaluated and compared in vitro and in vivo. hLEC ± hvSMC or hBEC ± hvSMC were seeded in a 3D porous scaffold in vitro, and capillary percent vascular volume (PVV) and vascular density (VD)/mm² assessed. Scaffolds were also transplanted into a sub-cutaneous rat wound with morphology/morphometry assessment. Initially hBEC formed a larger vessel network in vitro than hLEC, with interconnected capillaries evident at 2 days. Interconnected lymphatic capillaries were slower (3 days) to assemble. hLEC capillaries demonstrated a significant overall increase in PVV (p = 0.0083) and VD (p = 0.0039) in vitro when co-cultured with hvSMC. A similar increase did not occur for hBEC + hvSMC in vitro, but hBEC + hvSMC in vivo significantly increased PVV (p = 0.0035) and VD (p = 0.0087). Morphology/morphometry established that hLEC vessels maintained distinct cell markers, and demonstrated significantly increased individual vessel and network size, and longer survival than hBEC capillaries in vivo, and established inosculation with rat lymphatics, with evidence of lymphatic function. The porous polyurethane scaffold provided advantages to capillary network formation due to its large (300-600 μm diameter) interconnected pores, and sufficient stability to ensure successful surgical transplantation in vivo. Given their successful survival and function in vivo within the porous scaffold, in vitro assembled hLEC networks using this method are potentially applicable to clinical scenarios requiring replacement of dysfunctional or absent lymphatic networks.

The Lymphatic Endothelium in the Context of Radioimmuno-Oncology

The study of lymphatic tumor vasculature has been gaining interest in the context of cancer immunotherapy. These vessels constitute conduits for immune cells' transit toward the lymph nodes, and they endow tumors with routes to metastasize to the lymph nodes and, from them, toward distant sites. In addition, this vasculature participates in the modulation of the immune response directly through the interaction with tumor-infiltrating leukocytes and indirectly through the secretion of cytokines and chemokines that attract leukocytes and tumor cells. Radiotherapy constitutes the therapeutic option for more than 50% of solid tumors. Besides impacting transformed cells, RT affects stromal cells such as endothelial and immune cells. Mature lymphatic endothelial cells are resistant to RT, but we do not know to what extent RT may affect tumor-aberrant lymphatics. RT compromises lymphatic integrity and functionality, and it is a risk factor to the onset of lymphedema, a condition characterized by deficient lymphatic drainage and compromised tissue homeostasis. This review aims to provide evidence of RT's effects on tumor vessels, particularly on lymphatic endothelial cell physiology and immune properties. We will also explore the therapeutic options available so far to modulate signaling through lymphatic endothelial cell receptors and their repercussions on tumor immune cells in the context of cancer. There is a need for careful consideration of the RT dosage to come to terms with the participation of the lymphatic vasculature in anti-tumor response. Here, we provide new approaches to enhance the contribution of the lymphatic endothelium to radioimmuno-oncology.