Lymphatic Vessel Dysfunction Research Articles

Meningeal lymphatic vessel dysfunction driven by CGRP signaling causes migraine-like pain in mice.

Migraines are a type of headache that occur with other neurological symptoms, but the pathophysiology remains unclear. In this issue of the JCI, Nelson-Maney and authors used constitutive and inducible knockouts of the CGRP receptor components, elegantly demonstrating an essential function of CGRP in modulating meningeal lymphatic vessels (MLVs) in migraine. CGRP was shown to induce rearrangement of membrane-bound gap junction proteins in MLVs, resulting in a reduced CSF flux into cervical lymph nodes. The authors also provided evidence of a primary role for CGRP in modulating neuro-immune function. Finally, by showing that blocking CGRP signaling in MLVs attenuated pain behavior associated with acute migraine in rodents, the authors provided a target for pharmacological blockade of CGRP in relation to primary headache disorders.

An arabinogalactan isolated from Cynanchum atratum promotes lymphangiogenesis and lymphatic vessel remodeling to alleviate secondary lymphedema

Secondary lymphedema is a chronic and incurable disease lacking satisfactory therapeutic drugs. It primarily results from lymphatic vessel dysfunction resulting from factors such as tumor-related surgery, injury, or infection. Promoting lymphangiogenesis and lymphatic vessel remodeling is crucial for restoring tissue fluid drainage and treating secondary lymphedema. In this study, we discovered that the oral administration of a type-II arabinogalactan (CAPW-1, molecular weight: 64 kDa) significantly promoted lymphangiogenesis and alleviated edema in mice with secondary lymphedema. Notably, the tail diameter of the CAPW-1200 group considerably decreased in comparison to that of the lymphedema group, with an average diameter difference reaching 0.98 mm on day 14. CAPW-1 treatment also reduced the average thickness of the subcutaneous area in the CAPW-1200 group to 0.37 mm (compared with 0.73 mm in the lymphedema group). It also facilitated the return of injected indocyanine green (ICG) from the tail tip to the sciatic lymph nodes, indicating that CAPW-1 promoted lymphatic vessel remodeling at the injury site. In addition, CAPW-1 enhanced the proliferation and migration of lymphatic endothelial cells. This phenomenon was associated with the activation of the toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) signaling pathway, thereby promoting the expression of vascular endothelial growth factor-C (VEGF-C), which can be abolished using a TLR4 antagonist. Despite these findings, CAPW-1 did not alleviate the symptoms of lymphedema or restore lymphatic drainage in VEGFR3flox/flox/Prox1-CreERT2 mice. In summary, CAPW-1 alleviates secondary lymphedema by promoting lymphangiogenesis and lymphatic vessel remodeling through the activation of the TLR4/NF-κB/VEGF-C signaling pathway, indicating its potential as a therapeutic lymphangiogenesis agent for patients with secondary lymphedema.

Cervical lymphatic vessel dysfunction induced by amyloid-β and in the 5x-FAD mouse model of Alzheimer’s disease

Alzheimer’s dementia is a multifactorial disease characterized by amyloid-β (Aβ) accumulation in the brain. Aβ clearance occurs partially via meningeal lymphatics into cervical lymph nodes through superficial cervical lymphatic vessels (sCLV), which relies on intrinsic contractions of sCLV. Previous studies showed increased Aβ build up in the brain following ablation of meningeal lymphatics; however, whether Aβ alters sCLV function remains unclear. We hypothesize that sCLV contractile function will be reduced by acute Aβ exposure and in the 5x-FAD mouse model of Alzheimer’s disease. Contractile function of freshly isolated sCLV was assessed using pressure myography. Acute Aβ exposure was achieved by intraluminal incubation of pressurized sCLV with Aβ(1-40) (5 μM) or vehicle for 15 minutes prior to the start of the experiment. Repeated end-diastolic (EDD) and end-systolic (ESD) measurements were used to calculate fractional pump flow (FPF), the product of contractile frequency (FREQ) measured as contractions per minute (Hz), and ejection fraction (EF) calculated as (EDD2-ESD2)/EDD2, at incremental intraluminal pressures ranging from 2 to 10 cmH2O. Statistical differences were determined by two-way ANOVA followed by Sidak correction for multiple comparisons. All data are means ± SEM. In sCLV isolated from 5 months-old males and females C57bl/6J mice, acute Aβ exposure significantly decreased FREQ (Vehicle vs Aβ, n=4 / n=7, p<0.01), without changes in EF (Vehicle vs Aβ, n=4 / n=7, p=0.115) or FPF (Vehicle vs Aβ, n=4 / n=7, p= 0.536). In pressurized sCLV isolated from 5x-FAD mice, when compared to wild-type littermates, we observed a significant reduction in FREQ (Wild-type vs 5x-FAD, n=4 / n=5, p<0.01). No differences were observed in EF (Wild-type vs 5x-FAD, n=4 / n=5, p=0.1224) or FPF (Wild-type vs 5x-FAD, n=4 / n=5, p=0.193). Together, these preliminary data suggest that acute exposure to Aβ(1-40) decreases FREQ of isolated sCLV, a similar effect observed in sCLV isolated from 5x-FAD mice, albeit not reaching statistical power for multiple comparison significance. Consequently, a decrease contractile frequency can contribute to impairments in lymphatic pumping, which to some extent, can be compensated by prolonged filling times, thus leading to increased ejection fraction. In conclusion, we predict that in vivo sCLV contractile function is maintained via compensatory increases in ejection fraction in conditions of exacerbated Aβ production and deposition. Funding: National Institutes of Health (R01 AG073230) and the Alzheimer’s Association (AARGD-21-850835). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Inactivation of ERK1/2 signaling mediates dysfunction of basal meningeal lymphatic vessels in experimental subdural hematoma.

Rationale: Meningeal lymphatic vessels (MLVs) are essential for the clearance of subdural hematoma (SDH). However, SDH impairs their drainage function, and the pathogenesis remains unclear. Herein, we aimed to understand the pathological mechanisms of MLV dysfunction following SDH and to test whether atorvastatin, an effective drug for SDH clearance, improves meningeal lymphatic drainage (MLD). Methods: We induced SDH models in rats by injecting autologous blood into the subdural space and evaluated MLD using Gadopentetate D, Evans blue, and CFSE-labeled erythrocytes. Whole-mount immunofluorescence and transmission electron microscopy were utilized to detect the morphology of MLVs. Phosphoproteomics, western blot, flow cytometry, and in vitro experiments were performed to investigate the molecular mechanisms underlying dysfunctional MLVs. Results: The basal MLVs were detected to have abundant valves and play an important role in draining subdural substances. Following SDH, these basal MLVs exhibited disrupted endothelial junctions and dilated lumen, leading to impaired MLD. Subsequent proteomics analysis of the meninges detected numerous dephosphorylated proteins, primarily enriched in the adherens junction, including significant dephosphorylation of ERK1/2 within the meningeal lymphatic endothelial cells (LECs). Subdural injection of the ERK1/2 kinase inhibitor PD98059 resulted in dilated basal MLVs and impaired MLD, resembling the dysfunctional MLVs observed in SDH. Moreover, inhibiting ERK1/2 signaling severely disrupted intercellular junctions between cultured LECs. Finally, atorvastatin was revealed to protect the structure of basal MLVs and accelerate MLD following SDH. However, these beneficial effects of atorvastatin were abolished when combined with PD98059. Conclusion: Our findings demonstrate that SDH induces ERK1/2 dephosphorylation in meningeal LECs, leading to disrupted basal MLVs and impaired MLD. Additionally, we reveal a beneficial effect of atorvastatin in improving MLD.

The Drainage Dysfunction of Meningeal Lymphatic Vessels Is Correlated with the Recurrence of Chronic Subdural Hematoma: a Prospective Study.

Meningeal lymphatic vessels (mLVs) were recently discovered to be involved in the waste drainage process in the brain, which has also been associated with a variety of neurological diseases. This research paper hypothesizes that the drainage function of mLVs may be affected after chronic subdural hematoma (CSDH) and the alterations of mLVs' drainage may predict CSDH recurrence. In this prospective observational study, unenhanced 3D T2-fluid-attenuated inversion recovery (3D T2-FLAIR) MRI data were collected from CSDH patients and healthy participants for analysis. Patients with CSDH who underwent surgery received MRI scans before and after surgery, whereas healthy controls and patients with CSDH who received pharmaceutical treatment received only one MRI scan at enrollment. The signal unit ratio (SUR) of mLVs were then measured according to the MRI data and calculated to define mLVs' drainage function. Finally, the relationship between mLVs' drainage function and CSDH recurrence was analyzed accordingly. Thirty-four participants were enrolled in this study, including 27 CSDH patients and 7 controls. The SUR of mLVs in all CSDH patients changed significantly before and after surgery. Moreover, the drainage function of the mLVs ipsilateral to hematoma (mLVs-IH) in CSDH patients was significantly lower than that in the controls (p < 0.05). Last, a higher improvement rate of the drainage function of the mLVs-IH is correlated to a lower risk of recurrence (p < 0.05). This study revealed the mLVs' drainage dysfunction after CSDH through non-invasive MRI. Furthermore, the drainage function of mLVs is an independent predictive factor of CSDH recurrence.

Distinct mast cell subpopulations within and around lymphatic vessels regulate lymph flow and progression of inflammatory-erosive arthritis in TNF-transgenic mice.

Inflammatory-erosive arthritis is exacerbated by dysfunction of joint-draining popliteal lymphatic vessels (PLVs). Synovial mast cells are known to be pro-inflammatory in rheumatoid arthritis (RA). In other settings they have anti-inflammatory and tissue reparative effects. Herein, we elucidate the role of mast cells on PLV function and inflammatory-erosive arthritis in tumor necrosis factor transgenic (TNF-tg) mice that exhibit defects in PLVs commensurate with disease progression. Whole mount immunofluorescent microscopy, toluidine blue stained histology, scanning electron microscopy, and in silico bioinformatics were performed to phenotype and quantify PLV mast cells. Ankle bone volumes were assessed by μCT, while corresponding histology quantified synovitis and osteoclasts. Near-infrared indocyanine green imaging measured lymphatic clearance as an outcome of PLV draining function. Effects of genetic MC depletion were assessed via comparison of 4.5-month-old WT, TNF-tg, MC deficient KitW-sh/W-sh (cKit-/-), and TNF-tg x cKit-/- mice. Pharmacological inhibition of mast cells was assessed by treating TNF-tg mice with placebo or cromolyn sodium (3.15mg/kg/day) for 3-weeks. PLVs are surrounded by MCT+/MCPT1+/MCPT4+ mast cells whose numbers are increased 2.8-fold in TNF-tg mice. The percentage of peri-vascular degranulating mast cells was inversely correlated with ICG clearance. A population of MCT+/MCPT1-/MCPT4- mast cells were embedded within the PLV structure. In silico single-cell RNA-seq (scRNAseq) analyses identified a population of PLV-associated mast cells (marker genes: Mcpt4, Cma1, Cpa3, Tpsb2, Kit, Fcer1a & Gata2) with enhanced TGFβ-related signaling that are phenotypically distinct from known MC subsets in the Mouse Cell Atlas. cKit-/- mice have greater lymphatic defects than TNF-tg mice with exacerbation of lymphatic dysfunction and inflammatory-erosive arthritis in TNF-tg x cKit-/- vs. TNF-Tg mice. Cromolyn sodium therapy stabilized PLV mast cells, increased TNF-induced bone loss, synovitis, and osteoclasts, and decreased ICG clearance. Mast cells are required for normal lymphatic function. Genetic ablation and pharmacological inhibition of mast cells exacerbates TNF-induced inflammatory-erosive arthritis with decreased lymphatic clearance. Together, these findings support an inflammatory role of activated/degranulated peri-PLV mast cells during arthritic progression, and a homeostatic role of intra-PLV mast cells, in which loss of the latter dominantly exacerbates arthritis secondary to defects in joint-draining lymphatics, warranting investigation into specific cellular mechanisms.

Signaling mechanisms underlying lymphatic vessel dysfunction in skin aging and possible anti-aging strategies.

Aging-related skin diseases are gradually increasing due to the imbalance of cutaneous homeostasis in the aging population. Skin aging-induced inflammation promotes systemic inflammation and may lead to whole-body aging. Lymphatic vessels play an important role in maintaining fluid and homeostasis balance. In intrinsically aged skin, the number of lymphatic vessels decrease and their functions decline, which is related to the reduced adhesion junctions between lymphatic endothelial cells, particularly VE-cadherin. VEGFC/VEGFR-3 signal pathway plays an important role in remodeling and expansion of lymphatic vessels; the downregulation of this pathway contributes to the dysfunction of lymphatic vessels. Meanwhile, we proposed some additional mechanisms. Decline of the pumping activity of lymphatic vessels might be related to age-related changes in extracellular matrix, ROS increase, and eNOS/iNOS disturbances. In extrinsically aged skin, the hyperpermeability of lymphatic vessels results from a decrease in endothelial-specific tight junction molecules, upregulation of VEGF-A, and downregulation of the VEGFC/VEGFR-3 signaling pathway. Furthermore, some of the Phyto therapeutics could attenuate skin aging by modulating the lymphatic vessels. This review summarized the lymphatic vessel dysfunction in skin aging and anti-aging strategies based on lymphatic vessel modulation.

Multiple aspects of lymphatic dysfunction in an ApoE -/- mouse model of hypercholesterolemia.

Introduction: Rodent models of cardiovascular disease have uncovered various types of lymphatic vessel dysfunction that occur in association with atherosclerosis, type II diabetes and obesity. Previously, we presented in vivo evidence for impaired lymphatic drainage in apolipoprotein E null (ApoE -/- ) mice fed a high fat diet (HFD). Whether this impairment relates to the dysfunction of collecting lymphatics remains an open question. The ApoE -/- mouse is a well-established model of cardiovascular disease, in which a diet rich in fat and cholesterol on an ApoE deficient background accelerates the development of hypercholesteremia, atherosclerotic plaques and inflammation of the skin and other tissues. Here, we investigated various aspects of lymphatic function using ex vivo tests of collecting lymphatic vessels from ApoE +/+ or ApoE -/- mice fed a HFD. Methods: Popliteal collectors were excised from either strain and studied under defined conditions in which we could quantify changes in lymphatic contractile strength, lymph pump output, secondary valve function, and collecting vessel permeability. Results: Our results show that all these aspects of lymphatic vessel function are altered in deleterious ways in this model of hypercholesterolemia. Discussion: These findings extend previous in vivo observations suggesting significant dysfunction of lymphatic endothelial cells and smooth muscle cells from collecting vessels in association with a HFD on an ApoE-deficient background. An implication of our study is that collecting vessel dysfunction in this context may negatively impact the removal of cholesterol by the lymphatic system from the skin and the arterial wall and thereby exacerbate the progression and/or severity of atherosclerosis and associated inflammation.

Arrangement of Indocyanine Green in a 1.5-Nanometer Channel to Achieve High-Efficiency Imaging of the Intestinal Lymphatic System.

The complications of inflammatory bowel diseases (IBDs) seriously endanger people’s health, such as bleeding, polyp hyperplasia, and even cancer. Although the precise pathophysiology of IBD is unknown, alterations in the intestinal lymphatic network, such as lymphangiogenesis and lymphatic vessel dysfunction, are well-established features. Therefore, the development of a reliable technology is urgently required, with a stereoscopic, deep, and high-resolution technology for IBD lymphatic targeting imaging in clinical practice. However, indocyanine green, the only clinically approved imaging agent by the Food and Drug Administration, can easily cause self-aggregation or be interfered with by microenvironments, causing fluorescence quenching, which seriously affects the imaging and detective capabilities. Herein, indocyanine green molecules are arranged in a 1.5-nanometer one-dimensional channel (TpPa-1@ICG). Based on this specified structure, the fluorescence enhancement effect is observed in the TpPa-1@ICG resultant, and the fluorescence intensity is enhanced by 27%. In addition, the ICG-incorporated porous solid reveals outstanding solvent (dichloromethane, tetrahydrofuran, etc.) and thermal (>300 °C) stability. After modifying the target molecules, TpPa-1@ICG showed excellent imaging ability for intestinal lymphatic vessels, providing a new imaging tool for IBDs research.

Significance of developmental meningeal lymphatic dysfunction in experimental post-traumatic injury

Understanding the pathological mechanisms unfolding after chronic traumatic brain injury (TBI) could reveal new therapeutic entry points. During the post-TBI sequel, the involvement of cerebrospinal fluid drainage through the meningeal lymphatic vessels was proposed. Here, we used K14-VEGFR3-Ig transgenic mice to analyze whether a developmental dysfunction of meningeal lymphatic vessels modifies post-TBI pathology. To this end, a moderate TBI was delivered by controlled cortical injury over the temporal lobe in male transgenic mice or their littermate controls. We performed MRI and a battery of behavioral tests over time to define the post-TBI trajectories. In vivo analyses were integrated by ex-vivo quantitative and morphometric examinations of the cortical lesion and glial cells.In post-TBI K14-VEGFR3-Ig mice, the recovery from motor deficits was protracted compared to littermates. This outcome is coherent with the observed slower hematoma clearance in transgenic mice during the first two weeks post-TBI. No other genotype-related behavioral differences were observed, and the volume of cortical lesions imaged by MRI in vivo, and confirmed by histology ex-vivo, were comparable in both groups. However, at the cellular level, post-TBI K14-VEGFR3-Ig mice exhibited an increased percentage of activated Iba1 microglia in the hippocampus and auditory cortex, areas that are proximal to the lesion.Although not impacting or modifying the structural brain damage and post-TBI behavior, a pre-existing dysfunction of meningeal lymphatic vessels is associated with morphological microglial activation over time, possibly representing a sub-clinical pathological imprint or a vulnerability factor. Our findings suggest that pre-existing mLV deficits could represent a possible risk factor for the overall outcome of TBI pathology.

Lymphatic Vessel Regression and Its Therapeutic Applications: Learning From Principles of Blood Vessel Regression.

Aberrant lymphatic system function has been increasingly implicated in pathologies such as lymphedema, organ transplant rejection, cardiovascular disease, obesity, and neurodegenerative diseases including Alzheimer’s disease and Parkinson’s disease. While some pathologies are exacerbated by lymphatic vessel regression and dysfunction, induced lymphatic regression could be therapeutically beneficial in others. Despite its importance, our understanding of lymphatic vessel regression is far behind that of blood vessel regression. Herein, we review the current understanding of blood vessel regression to identify several hallmarks of this phenomenon that can be extended to further our understanding of lymphatic vessel regression. We also summarize current research on lymphatic vessel regression and an array of research tools and models that can be utilized to advance this field. Additionally, we discuss the roles of lymphatic vessel regression and dysfunction in select pathologies, highlighting how an improved understanding of lymphatic vessel regression may yield therapeutic insights for these disease states.

Revisiting the gut-liver axis: gut lymphatic system in liver cirrhosis and portal hypertension.

The lymphatic vascular system runs parallel to the blood vascular system, comprising a network of lymphatic vessels and secondary lymphoid organs. The intestinal lymphatic capillaries (lacteals) and the associated collecting vessels in the mesentery form the gut lymphatic system. The gut lymphatic vasculature comprises the longest-studied lymphatic vessel bed and plays a significant role in the uptake and transport of dietary fat, abdominal fluid balance, and gut immunosurveillance. Gut is closely connected to liver through the portal circulation. In several experimental and clinical studies, the "gut-liver-axis" has been demonstrated to contribute to the pathogenesis of portal hypertension, liver cirrhosis, and its complications. Given a significant impact of gut health on the liver, in the current review, we highlight "gut-liver axis" in context to the circulatory physiology of gut lymphatic vessels. Despite their paramount importance in maintaining fluid and immune homeostasis in the gut, gut lymphatic vessels remain one of the most understudied physiological systems in liver disease pathology. In the current review, we delineate the connections of gut lymphatics with abdominal fluid homeostasis and bacterial translocation in the pathogenesis of liver cirrhosis and portal hypertension. We describe mechanisms and factors that drive gut lymphangiogenesis and lymphatic vessel dysfunction during inflammation. The review also underscores the role of gut lymphatic endothelial cells in regulating gut and liver immunity. We finally discuss the prognostic and therapeutic prospects of studying gut lymphatic vessels in advanced liver cirrhosis.

Kidney Injury Causes Accumulation of Renal Sodium That Modulates Renal Lymphatic Dynamics.

Lymphatic vessels are highly responsive to changes in the interstitial environment. Previously, we showed renal lymphatics express the Na-K-2Cl cotransporter. Since interstitial sodium retention is a hallmark of proteinuric injury, we examined whether renal sodium affects NKCC1 expression and the dynamic pumping function of renal lymphatic vessels. Puromycin aminonucleoside (PAN)-injected rats served as a model of proteinuric kidney injury. Sodium 23Na/1H-MRI was used to measure renal sodium and water content in live animals. Renal lymph, which reflects the interstitial composition, was collected, and the sodium analyzed. The contractile dynamics of isolated renal lymphatic vessels were studied in a perfusion chamber. Cultured lymphatic endothelial cells (LECs) were used to assess direct sodium effects on NKCC1. MRI showed elevation in renal sodium and water in PAN. In addition, renal lymph contained higher sodium, although the plasma sodium showed no difference between PAN and controls. High sodium decreased contractility of renal collecting lymphatic vessels. In LECs, high sodium reduced phosphorylated NKCC1 and SPAK, an upstream activating kinase of NKCC1, and eNOS, a downstream effector of lymphatic contractility. The NKCC1 inhibitor furosemide showed a weaker effect on ejection fraction in isolated renal lymphatics of PAN vs controls. High sodium within the renal interstitium following proteinuric injury is associated with impaired renal lymphatic pumping that may, in part, involve the SPAK-NKCC1-eNOS pathway, which may contribute to sodium retention and reduce lymphatic responsiveness to furosemide. We propose that this lymphatic vessel dysfunction is a novel mechanism of impaired interstitial clearance and edema in proteinuric kidney disease.

Recurrent and refractory lower limbs lymphedema in psoriatic arthritis: a case description and literature review

Lymphedema is an uncommon extra-articular complication of rheumatoid arthritis (RA), but it can also be associated with psoriatic arthritis (PsA), although rarely. While lymphedema associated with RA is well characterized in literature, only few cases have been described among patients with PsA. Upper limbs are the most common sites involved, with asymmetric pattern, even if some patients may present lower limb oedema, or progressive bilateral oedema.&#x0D; Chronic established lymphoedema deriving from lymphatic vessel dysfunction should be clearly distinct from inflammatory distal pitting edema (IDPE), resulting from tenosynovitis and frequently encountered in PsA. In contrast to lymphedema, the latter condition generally presents an excellent response to steroid therapy, therefore it is essential to recognize the exact etiology of lymphoedema to approach the correct treatment. Here we report a case of lower limbs lymphedema in PsA and review the available literature upon the topic.

FLT4 Mutations Are Associated with Segmental Lymphatic Dysfunction and Initial Lymphatic Aplasia in Patients with Milroy Disease.

This study explored mutations in the Fms-related tyrosine kinase 4/vascular endothelial growth factor receptor 3 gene (FLT4) and lymphatic defects in patients with Milroy disease (MD). Twenty-nine patients with lower limb lymphedema were enrolled. Sixteen patients had a familial history of MD, while 13 patients exhibited sporadic MD. Clinical signs, FLT4 mutations, indocyanine green (ICG) lymphography findings, and skin tissue immunohistochemical staining results were evaluated. Twenty-eight variants in FLT4 were identified. Twelve of these have previously been reported, while 16 are novel. Of the 28 variants, 26 are missense mutations, and the remaining two comprise a splicing mutation and a non-frame shift mutation. Twenty-five variants are located in the intracellular protein tyrosine kinase domain; three are located in the extracellular immunoglobulin domain. Substantially delayed contrast-enhanced tortuous lymphatic vessels were visualized to the ankle or knee level in 15 of 23 patients who underwent ICG lymphography. No initial lymphatic vessels were visualized in skin specimens from four patients who did not exhibit lymphatic vessels during imaging analyses. No specific variant was identified in relation to the unique clinical phenotype. Segmental dysfunction of lymphatic vessels and initial lymphatic aplasia are present in MD patients with FLT4 mutations.

Ex vivo Demonstration of Functional Deficiencies in Popliteal Lymphatic Vessels From TNF-Transgenic Mice With Inflammatory Arthritis.

Background: Recent studies demonstrated lymphangiogenesis and expansion of draining lymph nodes during chronic inflammatory arthritis, and lymphatic dysfunction associated with collapse of draining lymph nodes in rheumatoid arthritis (RA) patients and TNF-transgenic (TNF-Tg) mice experiencing arthritic flare. As the intrinsic differences between lymphatic vessels afferent to healthy, expanding, and collapsed draining lymph nodes are unknown, we characterized the ex vivo behavior of popliteal lymphatic vessels (PLVs) from WT and TNF-Tg mice. We also interrogated the mechanisms of lymphatic dysfunction through inhibition of nitric oxide synthase (NOS).Methods: Popliteal lymph nodes (PLNs) in TNF-Tg mice were phenotyped as Expanding or Collapsed by in vivo ultrasound and age-matched to WT littermate controls. The PLVs were harvested and cannulated for ex vivo functional analysis over a relatively wide range of hydrostatic pressures (0.5–10 cmH2O) to quantify the end diastolic diameter (EDD), tone, amplitude (AMP), ejection fraction (EF), contraction frequency (FREQ), and fractional pump flow (FPF) with or without NOS inhibitors Data were analyzed using repeated measures two-way ANOVA with Bonferroni’s post hoc test.Results: Real time videos of the cannulated PLVs demonstrated the predicted phenotypes of robust vs. weak contractions of the WT vs. TNF-Tg PLV, respectively. Quantitative analyses confirmed that TNF-Tg PLVs had significantly decreased AMP, EF, and FPF vs. WT (p < 0.05). EF and FPF were recovered by NOS inhibition, while the reduction in AMP was NOS independent. No differences in EDD, tone, or FREQ were observed between WT and TNF-Tg PLVs, nor between Expanding vs. Collapsed PLVs.Conclusion: These findings support the concept that chronic inflammatory arthritis leads to NOS dependent and independent draining lymphatic vessel dysfunction that exacerbates disease, and may trigger arthritic flare due to decreased egress of inflammatory cells and soluble factors from affected joints.

Regulation of VEGFR Signalling in Lymphatic Vascular Development and Disease: An Update.

The importance of lymphatic vessels in a myriad of human diseases is rapidly gaining recognition; lymphatic vessel dysfunction is a feature of disorders including congenital lymphatic anomalies, primary lymphoedema and obesity, while improved lymphatic vessel function increases the efficacy of immunotherapy for cancer and neurological disease and promotes cardiac repair following myocardial infarction. Understanding how the growth and function of lymphatic vessels is precisely regulated therefore stands to inform the development of novel therapeutics applicable to a wide range of human diseases. Lymphatic vascular development is initiated during embryogenesis following establishment of the major blood vessels and the onset of blood flow. Lymphatic endothelial progenitor cells arise from a combination of venous and non-venous sources to generate the initial lymphatic vascular structures in the vertebrate embryo, which are then further ramified and remodelled to elaborate an extensive lymphatic vascular network. Signalling mediated via vascular endothelial growth factor (VEGF) family members and vascular endothelial growth factor receptor (VEGFR) tyrosine kinases is crucial for development of both the blood and lymphatic vascular networks, though distinct components are utilised to different degrees in each vascular compartment. Although much is known about the regulation of VEGFA/VEGFR2 signalling in the blood vasculature, less is understood regarding the mechanisms by which VEGFC/VEGFD/VEGFR3 signalling is regulated during lymphatic vascular development. This review will focus on recent advances in our understanding of the cellular and molecular mechanisms regulating VEGFA-, VEGFC- and VEGFD-mediated signalling via VEGFRs which are important for driving the construction of lymphatic vessels during development and disease.

The Kinetics of Lymphatic Dysfunction and Leukocyte Expansion in the Draining Lymph Node during LTB4 Antagonism in a Mouse Model of Lymphedema.

The mechanisms of lymphedema development are not well understood, but emerging evidence highlights the crucial role the immune system plays in driving its progression. It is well known that lymphatic function deteriorates as lymphedema progresses; however, the connection between this progressive loss of function and the immune-driven changes that characterize the disease has not been well established. In this study, we assess changes in leukocyte populations in lymph nodes within the lymphatic drainage basin of the tissue injury site (draining lymph nodes, dLNs) using a mouse tail model of lymphedema in which a pair of draining collecting vessels are left intact. We additionally quantify lymphatic pump function using established near infrared (NIR) lymphatic imaging methods and lymph-draining nanoparticles (NPs) synthesized and employed by our team for lymphatic tissue drug delivery applications to measure lymphatic transport to and resulting NP accumulation within dLNs associated with swelling following surgery. When applied to assess the effects of the anti-inflammatory drug bestatin, which has been previously shown to be a possible treatment for lymphedema, we find lymph-draining NP accumulation within dLNs and lymphatic function to increase as lymphedema progresses, but no significant effect on leukocyte populations in dLNs or tail swelling. These results suggest that ameliorating this loss of lymphatic function is not sufficient to reverse swelling in this surgically induced disease model that better recapitulates the extent of lymphatic injury seen in human lymphedema. It also suggests that loss of lymphatic function during lymphedema may be driven by immune-mediated mechanisms coordinated in dLNs. Our work indicates that addressing both lymphatic vessel dysfunction and immune cell expansion within dLNs may be required to prevent or reverse lymphedema when partial lymphatic function is sustained.

Traditional Chinese Medicine Regulating Lymphangiogenesis: A Literature Review.

Lymphatic vessels, as an important part of the lymphatic system, form a fine vascular system in humans and play an important role in regulating fluid homeostasis, assisting immune surveillance and transporting dietary lipids. Dysfunction of lymphatic vessels can cause many diseases, including cancer, cardiovascular diseases, lymphedema, inflammation, rheumatoid arthritis. Research on lymphangiogenesis has become increasingly important over the last few decades. Nevertheless, the explicit role of regulating lymphangiogenesis in preventing and treating diseases remains unclear owing to the lack of a deeper understanding of the cellular and molecular pathways of the specific and tissue-specific changes in lymphangiopathy. TCM, consisting of compound extracted from TCM, Injections of single TCM and formula, is an important complementary strategy for treating disease in China. Lots of valuable traditional Chinese medicines are used as substitutes or supplements in western countries. As one of the main natural resources, these TCM are widely used in new drug research and development in Asia. Moreover, as a historical and cultural heritage, TCM has been widely applied to clinical research on lymphangiogenesis leveraging new technologies recently. Available studies show that TCM has an explicit effect on the regulation of lymphatic regeneration. This review aims to clarify the function and mechanisms, especially the inhibitory effect of TCM in facilitating and inhibiting lymphatic regeneration.

The MMP14-caveolin axis and its potential relevance for lipoedema.

Lipoedema is associated with widespread adipose tissue expansion, particularly in the proximal extremities. The mechanisms that drive the development of lipoedema are unclear. In this Perspective article, we propose a new model for the pathophysiology of lipoedema. We suggest that lipoedema is an oestrogen-dependent disorder of adipose tissue, which is triggered by a dysfunction of caveolin 1 (CAV1) and subsequent uncoupling of feedback mechanisms between CAV1, the matrix metalloproteinase MMP14 and oestrogen receptors. In addition, reduced CAV1 activity also leads to the activation of ERα and impaired regulation of the lymphatic system through the transcription factor prospero homeobox 1 (PROX1). The resulting upregulation of these factors could effectively explain the main known features of lipoedema, such as adipose hypertrophy, dysfunction of blood and lymphatic vessels, the overall oestrogen dependence and the associated sexual dimorphism, and the mechanical compliance of adipose tissue.