Lymphatic Vessels Research Articles

Bundle structures inside the deep cervical lymphatic vessels of mice

Bundle structures inside the deep cervical lymphatic vessels of mice

Dab2 is required for the scavenging function of lymphatic endothelial cells in the zebrafish meninges.

To date it is only partially understood how the brain is cleared of waste products resulting from its high metabolic activity, although this process has important implications for the development and progression of neurodegenerative diseases. Lymphatic vessels play a central role in maintaining fluid and tissue homeostasis, and the recent description of meningeal lymphatic vessels within the dura mater of mice, human and zebrafish has raised considerable interest in unraveling the function of these vessels. In zebrafish, brain lymphatic endothelial cells (BLECs) constitute an additional meningeal lymphatic endothelial cell population. These highly endocytically active cells contribute to the clearance of the brain, but the molecular basis of this scavenging activity is only poorly understood. Here, we report on the characterization of zebrafish disabled 2 (dab2) mutants. Embryos lacking maternally provided dab2 show defective venous sprouting from the caudal vein plexus at 26hpf. Furthermore, we show that the cargo-specific adaptor protein is specifically expressed in BLECs, and that BLECs are significantly impeded in their capacity to internalize specific substrates injected into the cerebrospinal fluid upon loss of zygotic dab2. Our work therefore identifies Dab2 as an important member of the molecular machinery mediating the scavenging function of BLECs in the meninges.

VEGFC Overexpression in Kidney Progenitor Cells Is a Model of Renal Lymphangiectasia.

Lymphangiogenesis is believed to be a protective response in the setting of multiple forms of kidney injury and mitigates the progression of interstitial fibrosis. To augment this protective response, promoting kidney lymphangiogenesis is being investigated as a potential treatment to slow the progression of kidney disease. As injury-related lymphangiogenesis is driven by signaling from the receptor VEGFR3 (vascular endothelial growth factor receptor 3) in response to the cognate growth factor VEGF (vascular endothelial growth factor)-C released by tubular epithelial cells, this signaling pathway is a candidate for future kidney therapeutics. However, the consequences to kidney development and function to targeting this signaling pathway remain poorly defined. We generated a new mouse model expressing Vegfc under regulation of the nephron progenitor Six2Cre driver strain (Six2Vegfc). Mice underwent a detailed phenotypic evaluation. Whole kidneys were processed for histology and 3-dimensional imaging. Six2Vegfc mice had reduced body weight and kidney function compared with littermate controls. Six2Vegfc kidneys demonstrated large peripelvic fluid-filled lesions with distortion of the pelvicalcyceal system which progressed in severity with age. Three-dimensional imaging showed a 3-fold increase in total cortical vascular density. Histology confirmed a substantial increase in LYVE1+ (lymphatic vessel endothelial hyaluronan receptor-1)/PDPN+ (podoplanin)/VEGFR3+ lymphatic capillaries extending alongside EMCN+ (endomucin) peritubular capillaries. There was no change in EMCN+ peritubular capillary density. Kidney lymphatic density was robustly increased in the Six2Vegfc mice. There were no changes in peritubular blood capillary density despite these endothelial cells also expressing VEGFR3. The model resulted in malformation of the lymphatic hilar plexus, resulting in severe hydronephrosis that resembled a human condition termed renal lymphangiectasia. This study defines the vascular consequences of augmenting VEGFC signaling during kidney development and provides new insight into human renal lymphatic malformations.

Rare carcinoma of the ampulla of Vater with mixed histologies: A case report

The current case is about a 62-year-old female presented with persistent fever for 10 days and yellowing of the skin for 5 days at our outpatient clinic. Laboratory tests revealed elevated levels of total bilirubin, direct bilirubin, indirect bilirubin, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and γ-glutamyl transpeptidase. Abdominal computed tomography, magnetic resonance imaging, and magnetic resonance cholangiopancreatography revealed a mass in the ampulla of Vater, as well as dilatation of the intra- and extra-hepatic bile and pancreatic ducts. The patient underwent pancreaticoduodenectomy under general anesthesia. Post-operative pathological and immunohistochemical results confirmed a tumor located in the ampulla, measuring 1.5 × 1 × 1 cm. The main component of the tumor was a moderately differentiated pancreaticobiliary adenocarcinoma (ADC), combined with squamous cell carcinoma (SCC) as well as small cell neuroendocrine carcinoma (SCNEC). The cancer tissue infiltrated the entire intestinal wall, with no invasion of microvessels, lymphatic vessels, or nerves observed. Until 46 months later, there was no tumor recurrence or distant metastasis. We present an uncommon case of ADC of the ampulla of Vater combined with SCC and SCNEC. Carcinoma of the ampulla of Vater may have mixed histological components; therefore, in cases of ampullary carcinoma, appropriate specimen collection is necessary, and further studies with more focus on histological origins are required.

Limfatičke malformacije

Lymphatic malformations are abnormal cystic dilatations of lymphatic vessels. They are present at birth, but often can only be detected later in life. Simple lymphatic malformations are limited to certain anatomical regions, while complex diffuse abnormalities can affect the entire organism. Simple lymphatic malformations are divided into macrocystic (cysts >1cm) and microcystic (cysts <1cm). According to the ISSVA classification from 2015, the term lymphangioma is abandoned and the term lymphatic malformation is introduced, which is intended to clearly indicate that it is not a tumor formation. The clinical course is characterized by long asymptomatic periods with short-term inflammatory or infectious episodes and episodes of intracystic bleeding. In the case of voluminous changes, the diagnosis can be made at the transition from the second to the third trimester of pregnancy by ultrasound examination or fetal magnetic resonance. Ultrasound and magnetic resonance imaging are diagnostic methods of choice in the postpartum period as well. The purpose of the treatment is not to completely remove the formation, but to limit the symptoms to the extent that would preserve functionality and provide an appropriate appearance. Treatment methods are the expectant method for asymptomatic disease, sclerotherapy, surgical resection, drug treatment, laser treatment and physical therapy measures. When there is no life-threatening airway obstruction, sclerosing is the method of choice. Bleomycin as a sclerosant provides good results with mild side effects. Therapy with rapamycin (sirolimus) allows for a large percentage of reduction in formation, but it is important to monitor possible side effects

Expanding Applications and Future of Robotic Microsurgery.

Robotic-assisted microsurgery has emerged as a transformative technology, offering enhanced precision for complex procedures across various fields, including lymphatic surgery, breast reconstruction, trauma, and neurosurgery. This paper reviews current advancements, applications, and potential future directions for robotic-assisted microsurgery. In lymphatic surgery, robotic systems such as Symani have improved precision in thoracic duct reconstruction and lymphatic vessel anastomoses, reducing morbidity despite longer surgery times. In breast reconstruction, robotic systems are being used to refine techniques like the miraDIEP approach, minimizing tissue damage and enhancing precision in individualized treatments. Trauma reconstruction, particularly for extremities, has also benefited from robotic assistance, enabling successful sutures in small vessels and nerves. Emerging applications in meningeal lymphatics show potential for treating neurodegenerative diseases through improved drainage. In neurosurgery, robots enhance precision in deep and narrow anatomic spaces, although advancements in specialized instruments are needed for full implementation. Future development of robotic microsurgery systems will focus on improved maneuverability, miniaturization, and integration of tools like augmented reality and haptic feedback. The goal is to combine robotic precision, data storage, and processing with human skills such as judgment and flexibility. Although robots are unlikely to replace surgeons, they are poised to play an increasingly significant role in enhancing surgical outcomes. As the technology evolves, further research and clinical trials are needed to refine robotic systems and validate their expanding applications in clinical practice.

VEGF-C propagates 'onward' colorectal cancer metastasis from liver to lung.

The formation of lung metastasis as part of the progression of colon cancer is a poorly understood process. Theoretically, liver metastases could seed lung metastases. To assess the contribution of the liver lymphatic vasculature to metastatic spread to the lungs, we generated murine liver-metastasis-derived organoids overexpressing vascular endothelial growth factor (VEGF)-C. The organoids were reimplanted into the mouse liver for tumour generation and onward metastasis. Liver metastases from patients with concomitant lung metastases showed higher expression of VEGF-C, lymphatic vessel hyperplasia, and tumour cell invasion into lymphatic vessels when compared to those without lung metastases. Reimplantation of VEGF-C overexpressing organoids into the mouse liver showed that VEGF-C caused peritumoral lymphatic vessel hyperplasia, lymphatic tumour cell invasion, and lung metastasis formation. This change in metastatic organotropism was accompanied by reduced expression of WNT-driven adult stem cell markers, and increased expression of fetal stem cell markers and NOTCH pathway genes. Further NOTCH pathway inhibition with γ-secretase inhibitor (DAPT) in vivo results in a slight reduction in lung metastases and a decrease in lymphatic hyperplasia and invasion in VEGF-C-overexpressing tumours. Collectively, these data indicate that VEGF-C can drive onward metastasis from the liver to the lung and suggest that targeting VEGF-C/NOTCH pathways may impair the progression of colorectal cancer.

The influence of lymphatic vessels on nanoparticle distribution and heat transfer within tissue

AbstractThis study analytically investigates the dynamics of nanoparticle transport within a three‐dimensional porous cylinder simulating a lymphatic vessel, without external heat sources. The governing equations and boundary conditions are transformed to yield a system of ordinary differential equations, which are solved numerically using MATLAB built‐in function, bvp4c. Key parameters are visually examined and physically interpreted in relation to temperature, velocity, concentration, and Nusselt number profiles. The study reveals that the distribution of temperature and Nusselt number are maximized by increasing the heat transfer coefficient, whereas NP concentration is increased by decreasing it. Furthermore, the Brownian motion parameter enhances both heat transmission and NP concentration. It is also observed that simpler extravasation into lymphatics decreases tissue nanoparticle levels and heat conduction. Ultimately, optimal intra‐lymphatic nanoparticle distribution pathways are achieved by specifically varying heat transfer and interstitial mass flux patterns. By simulating biological barriers and lymphatic drainage, this model enhances our understanding of the underlying transport mechanisms controlling nanoparticle mobilization.

Differential vegfc expression dictates lymphatic response during zebrafish heart development and regeneration.

Vascular endothelial growth factor C (Vegfc) is crucial for lymphatic and blood vessel development, yet its cellular sources and specific functions in heart development remain unclear. To address this, we created a vegfc reporter and an inducible overexpression line in zebrafish. We found vegfc expression in large coronary arteries, circulating thrombocytes, cardiac adipocytes, and outflow tract smooth muscle cells. Notably, while coronary lymphangiogenesis aligns with Vegfc-expressing arteries in juveniles, it occurs only after coronary artery formation. Vegfc overexpression induced ectopic lymphatics on the ventricular surface prior to arterial formation, indicating that Vegfc abundance, rather than arterial presence, drives lymphatic development. However, this overexpression did not affect coronary artery coverage, suggesting a specific role for Vegfc in lymphatic, rather than arterial, development. Thrombocytes emerged as the initial Vegfc source during inflammation following heart injuries, transitioning to endocardial and myocardial expression during regeneration. Lower Vegfc levels in the amputation model corresponded with a lack of lymphatic expansion. Importantly, Vegfc overexpression enhanced lymphatic expansion and promoted scar resolution without affecting cardiomyocyte proliferation, highlighting its role in regulating lymphangiogenesis and promoting heart regeneration.

Rhythmic Contractions of Lymph Vessels and Lymph Flow Are Disrupted in Hypertensive Rats.

Hypertension increases the risk of lymphedema in patients with comorbidities, but whether hypertension directly compromises lymph vessel (LV) function and lymph flow is unclear. We compared the contractions of mesenteric LVs ex vivo and lymph flow in vivo between normotensive and Ang II (angiotensin II)-induced hypertensive rats and explored the ionic basis of contractile patterns. Key studies were recapitulated in spontaneously hypertensive rats and control Wistar-Kyoto rats. Video microscopy continuously recorded the diameters of cannulated rat mesenteric LVs, and high-speed optical imaging estimated mesenteric lymph flow in vivo. Jess capillary Western electrophoresis evaluated expression levels of ion channel proteins. Isolated LVs from Ang II-induced hypertensive rats exhibited dysrhythmic contractions, whereas LVs from both Ang II-induced hypertensive rats and spontaneously hypertensive rats exhibited reduced diastolic diameters and cross-sectional flow. Mesenteric lymph flow in vivo was 2.9-fold lower in Ang II-induced hypertensive rats compared with normotensive rats. Surprisingly, the LVs from Ang II-induced hypertensive rats expressed fewer intact L-type Ca2+ channel pore proteins and more modulatory cleaved C-terminal fragments. However, pharmacological block of voltage-gated K+ channels but not other K+ channel types in control LVs established the pattern of contractile dysfunction observed in hypertension. Jess capillary Western electrophoresis analysis confirmed a loss of Shaker-type KV1.2 channels in LVs from hypertensive rats. We provide initial evidence of lymphatic contractile dysfunction and compromised lymph flow in hypertensive rats, which may be caused by a loss of KV1.2 channels in the lymphatic muscle cells.

Ultrasound Irradiation as a Candidate Procedure to Improve the Transdermal Drug Delivery to the Tail Edema of a Mouse Model

Drug therapy for secondary lymphedema has not yet been established. Conventional oral and intravenous administration is difficult to administer in sufficient doses due to adverse events. Therefore, it is necessary to develop a transdermal delivery system that can deliver high concentrations of drugs to the edema area. In this study, we examined the efficacy of transdermal drug delivery in a mouse model of tail edema using ultrasound irradiation (sonication method). Ultrasound irradiation can deliver high-molecular-weight substances subcutaneously, and the percutaneous administration of clobetasol propionate to the mouse tail edema model prevented the enlargement of lymphatic vessels with reduced tail volume. Therefore, steroid administration utilizing ultrasound irradiation is effective in decreasing tail swelling in a mouse tail edema model. Thus, ultrasound irradiation could have the potential to innovate the treatment of secondary lymphedema by directly administering the drug to the edema.

Bilateral Dermoid Ovarian Cysts in a Young Woman - A Case Report and Literature Review.

Ovarian tumors are a common type of neoplasm in women, with mature cystic teratomas being the most frequent variant. These tumors occur bilaterally in approximately 10% of cases. However, bilateral and multiple occurrences are rarely reported. A 22-year-old nulliparous woman presented with amenorrhea and sudden, generalized, dull lower abdominal pain. Diagnostic imaging, including ultrasound and computed tomography (CT) scans, revealed large solid-cystic lesions in both ovaries, with internal hyperechoic foci consistent with fat and calcification, along with thin internal septations. A laparoscopic cystectomy was successfully performed, preserving ovarian function. Histopathological examination confirmed the presence of stratified keratinized squamous epithelium, sebaceous glands, hair follicles, mature adipose tissue, blood vessels, and lymphatic vessels within the resected cysts, with no evidence of malignancy. This unique case provides valuable insights into the understanding and management of bilateral dermoid cysts, highlighting the importance of preserving ovarian function in young women.

Cardiac lymphatics undergo distinct remodeling during hypertrophic and nonhypertrophic pregnancy.

Lymphatic vessels of the heart undergo dynamic remodeling in response to physiological and pathological cardiovascular events such as development, adult cardiac maintenance, and injury repair. During pregnancy, the cardiovascular system undergoes physiological changes to meet the increased demand for blood supply to the fetus. These extensive physiological changes make pregnancy and delivery a high-risk period in a woman's life. However, whether and how cardiac lymphatics change during pregnancy is largely undefined. Therefore, we used whole mount immunofluorescent labeling and quantitative morphometric analysis to characterize the changes in cardiac lymphatic vasculature during pregnancy using two genetically distinct inbred mouse strains, C57BL/6J and BALB/cJ. When compared with age-matched, nonpregnant C57BL/6J control mice, the hearts of C57BL/6J dams in late pregnancy [gestation day 17.5 (G17.5)] undergo physiological hypertrophy. However, there were no significant changes in the cardiac lymphatic vasculature. In contrast, BALB/cJ mice do not exhibit pregnancy-induced cardiac hypertrophy at G17.5 compared with age-matched, nonpregnant mice. Yet interestingly, the cardiac lymphatic vasculature of pregnant BALB/cJ dams undergoes extensive morphological changes, including decreased lymphatic length, number of end points, and vessel branch-point junctions on the ventral side of the heart. These findings underscore the complexity of genetic and physiological factors that contribute to the heterotypic remodeling of cardiac lymphatics during late pregnancy.NEW & NOTEWORTHY Cardiac lymphatics remodel in response to physiological and pathological stresses. This study is the first to investigate cardiac lymphatic vessel changes during pregnancy. BALB/cJ mice, which do not undergo pregnancy-induced cardiac hypertrophy, show decreased lymphatic length, number of end points, and junctions on the ventral side during pregnancy. In contrast, C57BL/6J mice, which undergo pregnancy-induced cardiac hypertrophy, had no such changes. These findings underscore the complexity of genetic and physiological factors contributing to cardiac lymphatic remodeling.

Radiographic Enhancement of Lymph Nodes 9 Months after Omental Lymph Node Transfer

Lymphedema is a frequent complication of breast cancer treatment. As the survival rates of breast cancer continue to increase, the number of women with lymphedema will also increase. Surgical treatment of lymphedema has made significant advances during the past 20 years, and our understanding of these procedures continues to evolve. Vascularized lymph node transfer is an increasingly popular option for surgical treatment of lymphedema; however, the mechanism behind symptomatic relief is not fully understood. A proposed theory for improvement in lymphedema symptoms is lymphangiogenesis and spontaneous regeneration of lymphatic vessels, the timing and degree of which are not well defined. We present the case of a 40-year-old woman with a 10-year history of right upper extremity lymphedema secondary to bilateral mastectomy and right axillary lymph node dissection, who subsequently underwent vascularized omental lymph node transfer and lymphovenous bypass with radiographic evidence of spontaneous lymphatic reconnection within 9 months. To our knowledge, this is the earliest reported radiographic evidence of lymphatic regeneration in a human subject to date, adding to the growing body of evidence to support the therapeutic benefits of vascularized lymph node transfers.

Targeting endoplasmic reticulum stress-induced lymphatic dysfunction for mitigating bisphosphonate-related osteonecrosis.

Bisphosphonates (BPs) are the first-line treatment to stop bone resorption in diseases, including osteoporosis, Paget's disease, multiple myeloma and bone metastases of cancer. However, BPs-related osteonecrosis of the jaw (BRONJ), characterized by local inflammation and jawbone necrosis, is a severe intractable complication. The cumulative inflammatory burden often accompanies impaired lymphatic drainage, but its specific impact on BRONJ and the underlying mechanisms remain unclear. The mouse BRONJ model was established to assess the integrity and drainage function of lymphatic vessels by tissue clearing techniques, injected indocyanine green lymphatic clearance assay, flow cytometry analysis and histopathological staining. RNA sequencing, metabolome analysis, transmission electron microscopy and Western blotting were utilized to analyze the impacts of Zoledronate acid (ZA) on endoplasmic reticulum stress (ERS) and function of lymphatic endothelial cells (LECs). By constructing Lyve1creERT; SIRT6f/f and Lyve1creERT; ATG5f/f mice, we evaluated the role of ERS-induced LECs apoptosis in the progression of BRONJ. Additionally, we developed a nanoparticle-loaded ZA and rapamycin (ZDPR) to enhance autophagy and evaluated its potential in mitigating BRONJ. The mouse BRONJ model displayed impaired lymphatic drainage, accompanied by significant local inflammation and bone necrosis. The prolonged stimulation of ZA resulted in the extension of ERS and the inhibition of autophagy in LECs, ultimately leading to apoptosis. Mechanistically, ZA activated XBP1s through the NAD+/SIRT6 pathway, initiating ERS-induced apoptosis in LECs. The conditional knockout mouse models demonstrated that the deletion of SIRT6 or ATG5 significantly worsened lymphatic drainage and inflammatory infiltration in BRONJ. Additionally, the innovative nanoparticle ZDPR alleviated ERS-apoptosis in LECs and enhanced lymphatic function, facilitating inflammation resolution. Our study has elucidated the role of the NAD+/SIRT6/XBP1s pathway in ERS-induced apoptosis in ZA-treated LECs, and further confirmed the therapeutic potential of ZDPR in restoring endothelial function and improving lymphatic drainage, thereby effectively mitigating BRONJ. Bisphosphonate-induced lymphatic drainage impairment exacerbates bone necrosis. Zoledronate acid triggers endoplasmic reticulum stress and apoptosis in lymphatic endothelial cells via the NAD+/SIRT6/XBP1s pathway. Novel nanoparticle-loaded Zoledronate acid and rapamycin enhances autophagy, restores lymphatic function, and mitigates bisphosphonates-related osteonecrosis of the jaw progression.

Multi-physics approach to model the lymph transport in the murine immune system

Abstract We formulate a compartmental model of the murine lymphatic system with the transfer rate parameters derived from the data on the geometric characteristics of the lymphatic system (LS) graph structure and the Hagen–Poiseuille-based values of the lymph flows through the system components, i.e., vertices and edges. It is supplemented by the physics-based model of lymph node draining-related function which considers a paradigmatic view of its geometry with one- and three-afferent lymphatic vessels and one efferent vessel, and the lymph flow described by the Darcy–Starling equations. We discuss further modelling work needed to gain a predictive understanding of the LS function in response to various perturbations including infections and therapeutic treatments.

Endoscopic and clinicopathological features of early gastric papillary adenocarcinoma.

Gastric papillary adenocarcinoma (GPA), a well-differentiated gastric adenocarcinoma, is associated with a worse prognosis compared to other differentiated gastric adenocarcinomas. Therefore, there is an urgent need to characterize its endoscopic manifestations for guiding biopsy site selection and achieving accurate diagnosis. From January 1, 2016, to December 31, 2022, the data of 46 cases of early gastric papillary adenocarcinoma (EGPA) and 183 cases of early gastric differentiated tubular adenocarcinoma (EGDTA) diagnosed via pathological examination following endoscopic submucosal dissection (ESD) at the Second Hospital of Shandong University were collected. Propensity score matching (PSM) was employed to match 92 EGDTA patients at a ratio of 1:2, serving as the control group. Differences between the two groups were analyzed using multivariable logistic regression. Lastly, the relationship between vessels within epithelial circle (VEC) structures in EGPA and the degree of malignancy was assessed. Compared with EGDTA, EGPA was more likely to infiltrate the submucosa, more frequently associated with poorly differentiated cancer components, and more prone to invading lymphatic and blood vessels. EGPA was primarily located in the lower stomach and manifested as a uniformly elevated pattern under endoscopy, while VEC structural positivity could be visualized under ME-NBI. Moreover, EGPA lesions had larger diameters and were characterized by high expression of gastric mucins, namely MUC5AC and MUC6. When EGPA infiltrated the submucosa or contained poorly differentiated cancer components, the VEC structures were smaller. The present study demonstrated that EGPA exhibits a higher degree of malignancy. Endoscopic findings of a raised lesion with a uniform color under endoscopy and the presence of VEC structures under ME-NBI suggest a high possibility of EGPA. Moreover, smaller VEC structures were associated with a higher degree of malignancy, which may assist in guiding the selection of biopsy sites under endoscopy.

A neuro-lymphatic communication guides lymphatic development by CXCL12/CXCR4 signaling.

Lymphatic vessels grow through active sprouting and mature into a vascular complex including lymphatic capillaries and collecting vessels that ensure fluid transport. However, the signaling cues that direct lymphatic sprouting and patterning remains unclear. In this study, we demonstrated the chemokine signaling, specifically through CXCL12/CXCR4 plays critical roles in regulating lymphatic development. We showed that LEC specific CXCR4 deficient embryos and CXCL12 mutant embryos exhibited server defects in lymphatic sprouting, migration, and lymphatic valve formation. We also discovered that CXCL12, originating from peripheral nerves, directs the migration of dermal lymphatic vessels to align with nerves in developing skin. Deletion CXCR4 or blockage of CXCL12/CXCR4 activity results in reduced VEGFR3 levels on the LEC surface. This, in turn, impairs VEGFC mediated VEGFR3 signaling and downstream PI3K/AKT activities. Taken together, these data identify previously unknown chemokine signaling originating from peripheral nerves that guides dermal lymphatic sprouting and patterning. Our work identifies for the first time a neuro-lymphatics communications during mouse development and reveals a novel mechanism by which CXCR4 modulates VEGFC/VEGFR3/AKT signaling.

Age-related decline in cardiac lymphatic vessels causes cardiac edema and macrophage accumulation

Abstract As life expectancy has significantly increased, age-related diseases, particularly cardiovascular diseases, have become a primary global cause of death. Aging has multiple effects on the heart and is one major risk factor for cardiovascular diseases. The microcirculation has been extensively studied in this context. However, the contribution of the lymphatic vasculature, which is responsible for draining excessive tissue fluid and immune cells, to age-related pathologies is currently unknown. To address the effect of aging on lymphatics, we examined lymphatic capillary density using LYVE1 and PDPN staining in old (>20 months) and young (3 months) mouse hearts. Aging induced a significant reduction in lymphatic vessel density in the sub-endocardial and –epicardial area of aged left ventricles, in both genders (0.28±0.08 fold and 0.68±0.03 fold; p<0.05), while the right ventricle showed no change. Notably, dilation of (pre-) collector lymphatics was observed in in old hearts, indicating, together with the lymphatic vessel reduction, a lymphatic drainage dysfunction. Indeed, cardiac aging was accompanied by increased numbers of CD68+ macrophages, accumulation of the plasma protein fibrinogen and amyloid into the interstitial space. Moreover, we observed a significant increase in tissue oedema in the aged hearts (p<0.05). The decline in lymphatic vessels was associated with a reduced expression of Vegfc (0.72±0.04 fold; p<0.005), a major lymphatic growth factor, in 20-month-old mouse hearts compared to their 3-month-old counterparts. To establish a causal link between lymphatic dysfunction and age-related cardiac changes, we examined hearts from 3-month-old Flt4;Prox1-CreERT2 mice, that have defective lymphatic vessels. Also these mice, despite their young age, displayed fibrinogen (1.32±0.08 fold; p<0.05) and CD68+ macrophage (1.58±0.08 fold; p<0.05) accumulation compared to wildtype littermates. Apart from these, other age-related changes, such as tendency to cardiac hypertrophy, were also observed; this is currently under further investigation. Likewise, blocking VEGFC signaling in young mice by overexpressing the soluble form of Flt4 impaired cardiac lymphatic capillary density (0.62±0.06 fold; p<0.01), leading to increased macrophage and fibrinogen accumulation (1.69±0.09 fold, 4.60±0.30 fold; p<0.001), suggesting that a decline of lymphatics induces some of the age-associated pathologies. Finally, we addressed whether restoring Vegfc expression in old mice can rescue age-related cardiac impairment. Overexpressing Vegfc via AAV9 in aged mice restored cardiac lymphatic density by 3-fold and reduced CD68+ macrophage density by 1.6-fold, without effect on fibrinogen accumulation. In conclusion, our study demonstrates an age-related reduction in left ventricular lymphatic density, cardiac edema and inflammation. Vegfc overexpression prevented the age-dependent decline of lymphatic vasculature and reduced cardiac inflammation.

Inhibiting corneal transplantation rejection via lymphatic vessel ligation in a novel murine model

The lymphatic system is a crucial contributor to allograft rejection after corneal transplantation. However, no surgical procedures for the central pathway where conjunctival lymphatic vessels converge have been investigated. Therefore, we aimed to establish a murine model of lymphatic vessel ligation and evaluate its inhibitory effect on corneal allograft rejection. A tracer was used to visualise lymphatic vessels, and complications were evaluated. A surgical technique was developed to block the lymphatic vessels. Corneas from C57BL/6 mice were transplanted into BALB/c mice divided into two groups—one with and one without lymphatic vessel ligation, to evaluate their effects on allograft rejection. Graft opacity scores were evaluated for 8 weeks, and immunohistochemistry was used to quantify angiogenesis and lymphangiogenesis. 20% trypan blue used as a tracer showed clear inflow with no complications. The two sutures and cyanoacrylate glue combination demonstrated a blocking effect after 25 days and was thus used for lymphatic ligation. Three and nine out of fourteen eyes showed rejection at 8 weeks post-surgery in the lymphatic vessel ligation and control groups, respectively. Furthermore, neovascularisation and lymphangiogenesis significantly decreased in the lymphatic vessel ligation group. Overall, we present a novel therapeutic strategy for corneal transplantation.