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Lymphedema is a progressive lymphatic disease that potentiates physical and psychosocial distress. Despite its impact, patients reportedly encounter lymphatic ignorance throughout the healthcare system. This cross-sectional study aims to summarize clinical characteristics and interactions of lymphedema patients within the healthcare system. Two lymphedema patient cohorts were included: The Global Registry Analysis Cohort included lymphedema patients who contributed to an international digital lymphatic registry and the Interactions Cohort included patients who initiated a questionnaire about interactions with the medical system. The global registry was used to obtain demographic and clinical characteristics from affiliated lymphedema patients. A 23-item online questionnaire on healthcare experiences and satisfaction with lymphatic healthcare was then distributed to the Interactions Cohort. Complete responses were obtained from 2474 participants. Participants were a mean age of 57.5 ± 16.1 years and 51.4% had a cancer history. Participants reported substantial delays in diagnosis and treatment. Cancer-related and non-cancer-related lymphedema patients reported similar levels of perceived physician disinterest in their lymphedema; however, non-cancer-related lymphedema patients reported more care dissatisfaction. Ultimately, patients continue to face delays in lymphedema diagnosis and treatment. We developed an evidence-based model highlighting areas of reform needed to improve lymphatic education and healthcare., (© 2024. The Author(s).)

Purpose of Review: The lymphatic system facilitates several key functions that limit significant morbidity and mortality. Despite the impact and burden of lymphatic disorders, there are many remaining disorders whose genetic substrate remains unknown. The purpose of this review is to provide an update on the genetic causes of lymphatic disorders, while reporting on newly proposed clinical classifications of lymphatic disease., Recent Findings: We reviewed several new mutations in genes that have been identified as potential causes of lymphatic disorders including: MDFIC, EPHB 4 , and ANGPT2. Furthermore, the traditional St. George's Classification system for primary lymphatic anomalies has been updated to reflect the use of genetic testing, both as a tool for the clinical identification of lymphatic disease and as a method through which new sub-classifications of lymphatic disorders have been established within this framework. Finally, we highlighted recent clinical studies that have explored the impact of therapies such as sirolimus, ketoprofen, and acebilustat on lymphatic disorders., Summary: Despite a growing body of evidence, current literature demonstrates a persistent gap in the number of known genes responsible for lymphatic disease entities. Recent clinical classification tools have been introduced in order to integrate traditional symptom- and time-based diagnostic approaches with modern genetic classifications, as highlighted in the updated St. George's classification system. With the introduction of this novel approach, clinicians may be better equipped to recognize established disease and, potentially, to identify novel causal mutations. Further research is needed to identify additional genetic causes of disease and to optimize current clinical tools for diagnosis and treatment., (Copyright © 2024 Wolters Kluwer Health, Inc. All rights reserved.)

Abstract: Lymphedema and chronic venous insufficiency (CVI) affect millions of people and require lifelong management. Many compression options exist for the long-term management of these conditions; however, limitations in patient mobility and adherence are common. Current options for care often present challenges with adherence because they are time-intensive and cumbersome. Innovation is needed to improve compression options for patients with chronic edematous conditions, particularly because lymphedema and CVI benefit from combination interventions. In this narrative review, the authors focus on long-term management strategies for lymphedema and CVI and highlight a nonpneumatic compression device designed for ease of use in the management of lymphedema and CVI. Using a nonpneumatic compression device that combines multiple treatment modalities demonstrates improved efficacy, quality of life, and patient adherence., (Copyright © 2024 the Author(s). Published by Wolters Kluwer Health, Inc.)

Background: Our aim is to propose a framework for the development of a research case definition of lipedema, based on current available literature and those observations that can be applied to future lipedema research with the intent to standardize and strengthen the scientific evidence base. Methods and Results: We conducted a narrative review of the literature, and identified consensus characteristics and disputed characteristics that could be included in a research case definition of lipedema. After considering the strength of the evidence and how each characteristic might be measured in a research study, we recommended an approach for the development of a research case definition of lipedema that would be based on consideration of five agreed-upon characteristics, and five disputed, or less substantiated, characteristics as additional evidence to enhance specificity. Conclusions: We present a case definition framework for lipedema drawn from the scientific literature that can be applied to future studies on lipedema. Utilizing this framework should help to increase the sensitivity and specificity of case definition and provide an opportunity for meta-analysis of clinical studies and facilitate future research intercomparisons.

Lymphedema is a chronic and progressive disease of the lymphatic system characterized by inflammation, increased adipose deposition, and tissue fibrosis. Despite early hypotheses identifying lymphedema as a disease of mechanical lymphatic disruption alone, the progressive inflammatory nature underlying this condition is now well-established. In this review, we provide an overview of the various inflammatory mechanisms that characterize lymphedema development and progression. These mechanisms contribute to the acute and chronic phases of lymphedema, which manifest clinically as inflammation, fibrosis, and adiposity. Furthermore, we highlight the interplay between current therapeutic modalities and the underlying inflammatory microenvironment, as well as opportunities for future therapeutic development.

Background: A recently completed clinical trial compared a novel nonpneumatic compression device (NPCD) with a traditional advanced pneumatic compression device (APCD) for the treatment of breast cancer-related lymphedema (BCRL); the study revealed that the NPCD produced superior clinical and quality-of-life (QOL) outcomes. In this subanalysis, we sought to examine these results within the subset of trial subjects aged ≥65 years. Methods: A randomized crossover head-to-head trial was conducted to compare the NPCD with a commercially available APCD. Patients were randomly assigned to one or the other device for 28 days of use, followed by a 4-week washout period before a comparable 28-day utilization of the alternate device. Limb edema, adherence to daily device use, and QOL measures were collected at day 0 and 28 of each period. Results: A total of 14 subjects were aged ≥65. During NPCD use, subjects experienced a mean decrease in limb edema of 100.3% ( p  = 0.0082) as well as improvements in mean overall and subscale scores of the Lymphedema Quality of Life Questionnaire (LYMQOL). By comparison, during APCD use limb edema decreased by a mean of 2.9% ( p  = 0.8899) with no significant changes in any LYMQOL scores. Mean adherence was significantly higher during NPCD use (96.6%) than during APCD use (58.3%, p  < 0.0001). Conclusions: The novel NPCD produced superior clinical and QOL outcomes in older subjects with BCRL. ClinicalTrials.gov ID: NCT04908254.

Background: Lymphedema is a global health problem with no effective drug treatment. Enhanced T-cell immunity and abnormal lymphatic endothelial cell (LEC) signaling are promising therapeutic targets for this condition. Sphingosine-1-phosphate (S1P) mediates a key signaling pathway required for normal LEC function, and altered S1P signaling in LECs could lead to lymphatic disease and pathogenic T-cell activation. Characterizing this biology is relevant for developing much needed therapies., Methods: Human and mouse lymphedema was studied. Lymphedema was induced in mice by surgically ligating the tail lymphatics. Lymphedematous dermal tissue was assessed for S1P signaling. To verify the role of altered S1P signaling effects in lymphatic cells, LEC-specific S1pr1 -deficient ( S1pr1 LECKO ) mice were generated. Disease progression was quantified by tail-volumetric and -histopathologic measurements over time. LECs from mice and humans, with S1P signaling inhibition, were then cocultured with CD4 T cells, followed by an analysis of CD4 T-cell activation and pathway signaling. Last, animals were treated with a monoclonal antibody specific to P-selectin to assess its efficacy in reducing lymphedema and T-cell activation., Results: Human and experimental lymphedema tissues exhibited decreased LEC S1P signaling through S1P receptor 1 (S1PR1). LEC S1pr1 loss-of-function exacerbated lymphatic vascular insufficiency, tail swelling, and increased CD4 T-cell infiltration in mouse lymphedema. LECs, isolated from S1pr1 LECKO mice and cocultured with CD4 T cells, resulted in augmented lymphocyte differentiation. Inhibiting S1PR1 signaling in human dermal LECs promoted T-helper type 1 and 2 (Th1 and Th2) cell differentiation through direct cell contact with lymphocytes. Human dermal LECs with dampened S1P signaling exhibited enhanced P-selectin, an important cell adhesion molecule expressed on activated vascular cells. In vitro, P-selectin blockade reduced the activation and differentiation of Th cells cocultured with shS1PR1 -treated human dermal LECs. P-selectin-directed antibody treatment improved tail swelling and reduced Th1/Th2 immune responses in mouse lymphedema., Conclusions: This study suggests that reduction of the LEC S1P signaling aggravates lymphedema by enhancing LEC adhesion and amplifying pathogenic CD4 T-cell responses. P-selectin inhibitors are suggested as a possible treatment for this pervasive condition., Competing Interests: Disclosures None.

Background: Methods of conservative management for breast cancer-related lymphedema (BCRL) are burdensome in terms of time, cost, and convenience. In addition, many patients are not candidates for surgical treatment. Preliminary results have demonstrated possible beneficial effects of acupuncture for patients with BCRL. In this small pilot study, we examined the safety and feasibility of an acupuncture randomized control trial (RCT) in this patient cohort, utilizing a battery of standardized clinical and patient-centered outcome measures. Methods and Results: Patients with BCRL were randomized 2:1 to the acupuncture ( n  = 10) or the control ( n  = 4) group. Patients received acupuncture to the unaffected extremity biweekly for 6 weeks. Feasibility was defined as enrollment ≥80%, completion of ≥9 of 12 acupuncture sessions per person, and ≥75% completion of three of three measurement visits. To inform a future adequately powered RCT, we describe within-group changes in patient-centered outcomes, including circumferential measurements, bioimpedance spectroscopy, perometry, cytokine levels, and patient quality of life. Adverse events were systematically tracked. Fourteen patients completed the study. Of those who received acupuncture ( n  = 10), 8 completed all 12 acupuncture sessions, and 2 patients completed 11 sessions. Ninety-three percent of all participants completed all three measurement visits. There was no consistent improvement in arm volumes. Inflammatory marker levels had inconclusive fluctuations among both groups. All patients receiving acupuncture demonstrated an improvement in their functional quality-of-life score. No severe adverse events occurred. Conclusions: A randomized controlled study of acupuncture for BCRL is feasible. The acupuncture intervention is acceptable in this population, without safety concerns in a small sample and warrants further investigation.

Secondary lymphedema is a common condition among cancer survivors, and treatment strategies to prevent or treat lymphedema are in high demand. The development of novel strategies to diagnose or treat lymphedema would benefit from a robust experimental animal model of secondary lymphedema. The purpose of this methods paper is to describe and summarize our experience in developing and characterizing a rat hindlimb model of lymphedema. Here we describe a protocol to induce secondary lymphedema that takes advantage of micro computed tomography imaging for limb volume measurements and visualization of lymph drainage with near infrared imaging. To demonstrate the utility of this preclinical model for studying the therapeutic benefit of novel devices, we apply this animal model to test the efficacy of a biomaterials-based implantable medical device., Competing Interests: TZ, PT and MP are employees of Fibralign Corporation that manufactures the BioBridge medical device. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest, (© 2023 Nguyen, Dionysiou, Zaitseva, Zhou, Sue, Deptula, Moroz, Tabada, Rockson, Paukshto, Cheng and Huang.)

Objective: Advanced pneumatic compression devices (APCDs) have been shown to be an effective intervention for lymphedema when used as part of a self-care maintenance treatment regimen. However, adherence to self-care has been poor, and APCDs require patients to be immobile during treatment. We evaluated the safety and efficacy of a novel nonpneumatic compression device (NPCD) for treating lymphedema vs an APCD., Methods: A randomized, crossover head-to-head investigation was performed at five U.S. sites in 2021. The patients had been randomized to either the NPCD or a commercially available APCD. The patients used the randomly assigned initial device for 28 days with a 4-week washout period before a comparable 28-day use of the second device., Results: Data from 50 adult women with unilateral breast cancer-related lymphedema were analyzed. Compared with the APCD, the NPCD was associated with a greater mean reduction in the limb edema volume (64.6% vs 27.7%; P < .001), significantly greater mean improvements in quality of life scores, greater adherence (95.6% vs 49.8%; P < .001), and greater satisfaction with the device (90% vs 14%; P < .001). The patients indicated that use of the NPCD facilitated exercise and was convenient for travel. No adverse events were reported., Conclusions: The results have shown that the novel NPCD is an effective maintenance treatment for reducing the limb volume in patients with breast cancer-related lymphedema. The NPCD device was more effective than an APCD and resulted in greater adherence to self-care interventions and greater patient satisfaction., (Copyright © 2022 The Authors. Published by Elsevier Inc. All rights reserved.)

Lower extremity lymphedema (LEL) can result in detriments to quality of life (QOL) and impose a significant economic burden on patients and payers. A common component of treatment is pneumatic compression, which requires patients to remain immobile. We investigated a novel non-pneumatic compression device (NPCD) that allows patients to remain active during compression treatment, to see if it reduces swelling and improves QOL. We conducted a non-randomized, open-label, 12-week pilot study of adult patients with primary or secondary unilateral LEL, and measured changes in limb edema and QOL using the Lymphedema Quality of Life Questionnaire (LYMQOL). Twenty-four subjects were enrolled; the majority were female (17) with secondary lymphedema (21). Eighteen completed the study. Statistically significant improvements were observed in overall QOL, aggregated LYMQOL total score, and three of four LYMQOL subscales (Function, Appearance, Mood). The fourth (Symptoms) trended toward significant improvement (p = 0.06). The average reduction in affected limb edema was 39.4%. The novel NPCD produced statistically significant improvements in QOL, functioning, and edema volume of patients with LEL. Innovations in devices to manage LEL can be effective while allowing patients to maintain mobility and physical activity during treatment., (© 2022. The Author(s).)

Background: Lymphedema imposes a significant economic and social burden in modern societies. Controversies about its risk factors, diagnosis, and treatment permeate the literature. The goal of this study was to assess experts' opinions on the available literature on lymphedema while following the Delphi methodology., Methods: In December of 2019, the American Venous Forum created a working group tasked to develop a consensus statement regarding current practices for the diagnosis and treatment of lymphedema. A panel of experts was identified by the working group. The working group then compiled a list of clinical questions, risk factors, diagnosis and evaluation, and treatment of lymphedema. Fifteen questions that met the criteria for consensus were included in the list. Using a modified Delphi methodology, six questions that received between 60% and 80% of the votes were included in the list for the second round of analysis. Consensus was reached whenever >70% agreement was achieved., Results: The panel of experts reached consensus that cancer, infection, chronic venous disease, and surgery are risk factors for secondary lymphedema. Consensus was also reached that clinical examination is adequate for diagnosing lymphedema and that all patients with chronic venous insufficiency (C3-C6) should be treated as lymphedema patients. No consensus was reached regarding routine clinical practice use of radionuclide lymphoscintigraphy as a mandatory diagnostic tool. However, the panel came to consensus regarding the importance of quantifying edema in all patients (93.6% in favor). In terms of treatment, consensus was reached favoring the regular use of compression garments to reduce lymphedema progression (89.4% in favor, 10.6% against; mean score of 79), but the use of Velcro devices as the first line of compression therapy did not reach consensus (59.6% in favor vs 40.4% against; total score of 15). There was agreement that sequential pneumatic compression should be considered as adjuvant therapy in the maintenance phase of treatment (91.5% in favor vs. 8.5% against; mean score of 85), but less so in its initial phases (61.7% in favor vs. 38.3% against; mean score of 27). Most of the panel agreed that manual lymphatic drainage should be a mandatory treatment modality (70.2% in favor), but the panel was split in half regarding the proposal that reductive surgery should be considered for patients with failed conservative treatment., Conclusion: This consensus process demonstrated that lymphedema experts agree on the majority of the statements related to risk factors for lymphedema, and the diagnostic workup for lymphedema patients. Less agreement was demonstrated on statements related to treatment of lymphedema. This consensus suggests that variability in lymphedema care is high even among the experts. Developers of future practice guidelines for lymphedema should consider this information, especially in cases of low-level evidence that supports practice patterns with which the majority of experts disagree.

A diagnosis of lymphedema comes with a lifetime requirement for careful self-care and treatment to control skin deterioration and the consequences of excessive fluid and protein buildup leading to abnormal limb volume and an increased risk of infection. The burden of care and psychosocial aspects of physical disfiguration and loss of function are associated with compromised quality of life (QoL). The current standard therapeutic intervention is complex decongestive therapy with manual lymph drainage and frequent wearing of compression garments. With insurance limitations on therapy visits and the time and travel required, additional home treatment options are needed. Pneumatic compression pumps that mimic the manual massage pressure and pattern are sometimes prescribed, but these are bulky, difficult to apply, and require immobility during treatment. An open-label pilot study in 40 subjects was performed to evaluate the QoL and limb volume maintenance efficacy of a novel wearable compression system (Dayspring™) that is low profile, easy to use, and allows for mobility during treatment. After 28 days of use, subjects had a statistically significant 18% ( p  < 0.001) improvement in overall QoL as measured by the Lymphedema Quality-of-Life Questionnaire compared with baseline. Individual QoL domains, and limb volume improved with therapy. Adherence was 98% over the course of the study. Results of the clinical evaluation suggest the Dayspring wearable compression device is safe and effective and improves QoL and limb volume. The novel, low-profile device is easy to use and allows for mobility during treatment, addressing a potential barrier to adherence with pneumatic compression devices.

Background: The lymphatic contribution to the circulation is of paramount importance in regulating fluid homeostasis, immune cell trafficking/activation and lipid metabolism. In comparison to the blood vasculature, the impact of the lymphatics has been underappreciated, both in health and disease, likely due to a less well-delineated anatomy and function. Emerging data suggest that lymphatic dysfunction can be pivotal in the initiation and development of a variety of diseases across broad organ systems. Understanding the clinical associations between lymphatic dysfunction and non-lymphatic morbidity provides valuable evidence for future investigations and may foster the discovery of novel biomarkers and therapies., Methods: We retrospectively analysed the electronic medical records of 724 patients referred to the Stanford Center for Lymphatic and Venous Disorders. Patients with an established lymphatic diagnosis were assigned to groups of secondary lymphoedema, lipoedema or primary lymphovascular disease. Individuals found to have no lymphatic disorder were served as the non-lymphatic controls. The prevalence of comorbid conditions was enumerated. Pairwise co-occurrence pattern analyses, validated by Jaccard similarity tests, was utilised to investigate disease-disease interrelationships., Results: Comorbidity analyses underscored the expected relationship between the presence of secondary lymphoedema and those diseases that damage the lymphatics. Cardiovascular conditions were common in all lymphatic subgroups. Additionally, statistically significant alteration of disease-disease interrelationships was noted in all three lymphatic categories when compared to the control population., Conclusions: The presence or absence of a lymphatic disease significantly influences disease interrelationships in the study cohorts. As a physiologic substrate, the lymphatic circulation may be an underappreciated participant in disease pathogenesis. These relationships warrant further, prospective scrutiny and study., (© 2022 The Authors. Clinical and Translational Medicine published by John Wiley & Sons Australia, Ltd on behalf of Shanghai Institute of Clinical Bioinformatics.)

Lymphedema is a chronic inflammatory disorder characterized by edema, fat deposition, and fibrotic tissue remodeling. Despite significant advances in lymphatic biology research, our knowledge of lymphedema pathology is incomplete. Currently, there is no approved pharmacological therapy for this debilitating disease. Hypoxia is a recognized feature of inflammation, obesity, and fibrosis. Understanding hypoxia-regulated pathways in lymphedema may provide new insights into the pathobiology of this chronic disorder and help develop new medicinal treatments., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2022 Jiang, Tian, Kim, McQuiston, Vinh, Rockson, Semenza and Nicolls.)

The removal of interstitial fluid from the tissues is performed exclusively by the lymphatic system. Tissue edema in congestive heart failure occurs only when the lymphatic system fails or is overrun by fluid leaving the vascular space across the wall of the capillaries into the interstitial space. This process is driven by Starling forces determined by hydrostatic and osmotic pressures and organ-specific capillary permeabilities to proteins of different sizes. In this review, we summarize current knowledge of the generation of lymph in different organs, the mechanics by which lymph is returned to the circulation, and the consequences of the inadequacy of lymph flow. We review recent advances in imaging techniques that have allowed for new research, diagnostic, and therapeutic approaches to the lymphatic system. Finally, we review how efforts to increase lymph flow have demonstrated potential as a viable therapeutic approach for refractory heart failure., Competing Interests: Funding Support and Author Disclosures Dr Itkin has received research support from and had speaker engagements with Guerbet Group. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose., (Copyright © 2021 American College of Cardiology Foundation. Published by Elsevier Inc. All rights reserved.)

Objective: Lymphatic malformations (LM) are common congenital vascular lesions, most often diagnosed at birth. They deform local anatomy and can be life-threatening if they compress the aerodigestive tract or other vital structures. Significant progress has been made in the treatment of LMs in the past 20 years. We conducted a systematic review of the literature on the management of LMs., Methods: On September 21, 2020, we searched PubMed/MEDLINE for studies published from 2000 to 2020 reporting outcomes of invasive and pharmacologic treatment of LMs., Results: A total of 251 studies met the eligibility criteria. Surgery has continued to be a mainstay in the management of LMs, especially in the treatment of microcystic and mixed lesions. Sclerotherapy has emerged as a first-line treatment of macrocystic LMs and as an adjunctive therapy used in combination with surgery for other lesions. Sirolimus, a strong inhibitor of mTOR (mechanistic target of rapamycin), has shown tremendous promise in the treatment of LMs, as both an oral and a topical agent. Recent investigations have shown the potential of targeted small molecule modulators of cellular pathways in the treatment of LMs., Conclusions: Multiple invasive and pharmacologic therapies have been shown to be effective in the treatment of LMs. Future research should focus on rigorous, prospective comparisons of these treatment modalities., (Copyright © 2021 Society for Vascular Surgery. Published by Elsevier Inc. All rights reserved.)

Lymphedema is a common, complex, and inexplicably underappreciated human disease. Despite a history of relative neglect by health care providers and by governmental health care agencies, the last decade has seen an explosive growth of insights into, and approaches to, the problem of human lymphedema. The current review highlights the significant advances that have occurred in the investigative and clinical approaches to lymphedema, particularly over the last decade. This review summarizes the progress that has been attained in the realms of genetics, lymphatic imaging, and lymphatic surgery. Newer molecular insights are explored, along with their relationship to future molecular therapeutics. Growing insights into the relationships among lymphedema, obesity, and other comorbidities are important to consider in current and future responses to patients with 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.

The lymphatic system was first described in the 17th century independently by Olaus Rudbeck and Thomas Bartholin. Since then, there has been deep-seated fascination with its development, function, and dysfunction.

It has now been ∼20 years since the original Lymphatic Continuum conference was convened, and this continuum has transitioned from a compelling concept to a reality. The explosive growth in our comprehension of lymphatic genetics, development, and function has expanded and modified our traditional views regarding what is, and is not, lymphatic disease. Groundbreaking investigations over the past decade have now defined a large and growing list of pathological conditions in which morphological or function lymphatic alterations can be identified. This list includes atherosclerosis and dyslipidemia, hypertension and other cardiovascular diseases, inflammation and inflammatory bowel disease, obesity, narrow angle glaucoma, and, most recently and compellingly, neurodegenerative disease. The sometimes overlapping but largely disparate nature of these various aforementioned disease categories suggests that the presence, or absence, of structural or functional lymphatic derangements may represent a previously unrecognized unifying influence in the maintenance of health and the promotion of disease. Future investigation of lymphatic mechanisms in disease will likely continue to elucidate the influences of lymphatic dysfunction, perhaps subtle, that can invest other, seemingly unrelated, diseases. In future, such discoveries will provide mechanistic insights and may potentiate the development of a new lymphatic-based approach to human disease diagnosis and therapeutics.

Pathologic lymphatic remodeling in lymphedema evolves during periods of tissue inflammation and hypoxia through poorly defined processes. In human and mouse lymphedema, there is a significant increase of hypoxia inducible factor 1 α (HIF-1α), but a reduction of HIF-2α protein expression in lymphatic endothelial cells (LECs). We questioned whether dysregulated expression of these transcription factors contributes to disease pathogenesis and found that LEC-specific deletion of Hif2α exacerbated lymphedema pathology. Even without lymphatic vascular injury, the loss of LEC-specific Hif2α caused anatomic pathology and a functional decline in fetal and adult mice. These findings suggest that HIF-2α is an important mediator of lymphatic health. HIF-2α promoted protective phosphorylated TIE2 (p-TIE2) signaling in LECs, a process also replicated by upregulating TIE2 signaling through adenovirus-mediated angiopoietin-1 (Angpt1) gene therapy. Our study suggests that HIF-2α normally promotes healthy lymphatic homeostasis and raises the exciting possibility that restoring HIF-2α pathways in lymphedema could mitigate long-term pathology and disability.