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Background: Crohn's disease (CD) is a chronic inflammatory disease in the intestinal tract. Mesenteric fat wrapping and thickening, or creeping fat (CrF), is a typical characteristic of CD and it involves lymphangiogenesis and altered lymphatic function. By releasing extracellular vesicles (EVs), adipose tissue‐derived stem cells (ADSCs) can regulate their adjacent cells. However, the regulating roles of ADSC‐EVs in CrF (CrF‐EVs) in CD, especially in modulating lymphatic function and mitigating the progression of mesenteritis and colitis, remains elusive. Methods: To evaluate the regulative roles of CrF‐EVs on lymphatic functions, in vitro assays were performed using human lymphatic endothelial cells (HLECs). Next, Interleukin 10 knock‐out (Il‐10−/−) mice were used to assess the biological functions of CrF‐EVs in spontaneous mesenteritis and colitis. Moreover, tissue and serum from various cohorts of CD patients were used to determine the prognostic value of miR‐132‐3p. Results: CrF‐EVs significantly attenuated spontaneous mesenteritis and colitis in Il‐10−/− mice via promoting lymphangiogenesis and lymphatic drainage. Using high‐throughput sequencing, we demonstrated that CrF‐EVs significantly increased HLEC proliferation, migration, tube formation and CCL‐21 production in a miR‐132‐3p/RASA1/ERK1/2 axis‐dependent manner. Accordingly, upregulated miR‐132‐3p was observed in patient CrF, positively correlated with lymphangiogenesis while negatively correlated with inflammatory factors (tumour necrosis factor‐α and IL‐6) level. Moreover, serum miR‐132‐3p demonstrated a positive correlation with disease activity. Conclusions: EVs derived from CrF ADSCs, containing elevated levels of miR‐132‐3p, could promote lymphatic function and restrain inflammation of CD. Our results provide a novel insight into the role of mesenteric lymphatics in CD progression and reveal a new potential therapeutic. Key points: Extracellular vesicles (EVs) of creeping fat (CrF) derived adipose stem cells effectively attenuate chronic mesenteritis and colitis in Crohn's disease (CD).The lymphatic vessels play an important role in disease development of CD and their functions are improved by CrF‐EV‐miR‐132‐3p through RASA1/ERK1/2 signaling.MiR‐132‐3p expression is upregulated in CrF and serum of CD patients, and tightly linked with inflammation and disease activity. [ABSTRACT FROM AUTHOR]

The lymphatic network of capillaries and collecting vessels ensures tissue fluid homeostasis, absorption of dietary fats and trafficking of immune cells. Pannexin1 (Panx1) channels allow for the passage of ions and small metabolites between the cytosol and extracellular environment. Panx1 channels regulate the pathophysiological function of several tissues in a sex‐dependent manner. Here, we studied the role of Panx1 in lymphatic function, and potential sex‐dependent differences therein, in Prox1‐CreERT2Panx1fl/fl and Panx1fl/fl control mice. Panx1 expression was higher in lymphatic endothelial cells (LECs) of male mice. Lymphatic vessel morphology was not affected in Prox1‐CreERT2Panx1fl/fl male and female mice. Lymphatic drainage was decreased by 25% in male Prox1‐CreERT2Panx1fl/fl mice, but was similar in females of both genotypes. Accordingly, only male Prox1‐CreERT2Panx1fl/fl mice exhibited tail swelling, pointing to interstitial fluid accumulation in males upon Panx1 deletion in LECs. Moreover, serum triglyceride and free fatty acid levels raised less in Prox1‐CreERT2Panx1fl/fl mice of both sexes in an oral lipid tolerance test. Finally, the percentage of migratory dendritic cells arriving in draining lymph nodes was increased in Prox1‐CreERT2Panx1fl/fl female mice, but was comparable between male mice of both genotypes. Our results point to a LEC‐specific role for Panx1 in the functions of the lymphatic system. [ABSTRACT FROM AUTHOR]

Background: Lymphoedema is a chronic and progressive disease characterised by excessive accumulation of lymph in the interstitial compartment, leading to tissue swelling and fibroadipose deposition. Lymphangiogenesis is partly regulated by ketone body oxidation, and a ketogenic diet (KD) has shown therapeutic efficacy in a preclinical mouse tail lymphoedema model. Therefore, we aimed to investigate the potential therapeutic effect of a KD in patients with secondary lymphoedema. Methods: Nine patients with unilateral stage 2 lymphoedema secondary to lymphadenectomy were included in this quasi‐experimental exploratory study consisting of a short run‐in phase to gradually induce ketosis, followed by a classic KD (CKD) and modified Atkins diet (MAD) phase during which patients consumed a CKD and MAD, respectively. Lymphatic function and oedema volume, the primary outcomes, were assessed at baseline and at the end of both the CKD and MAD phase. Secondary outcomes included health‐related and lymphedema‐specific quality of life (QoL). Results: Seven out of nine patients completed the study protocol. Lymphatic function was improved upon consumption of both a CKD (dermal backflow score [mean ± SD]: 7.29 ± 2.98 vs. 10.86 ± 2.19 at baseline; p = 0.03) and MAD (6.71 ± 2.06; p = 0.02), whereas oedema volume did not decrease during the course of the study (excess limb volume [mean ± SD]: 20.13 ± 10.25% at end of CKD and 24.07 ± 17.77% at end of MAD vs. 20.79 ± 12.96% at baseline; p > 0.99 and p > 0.30, respectively). No changes were observed in health‐related, nor lymphoedema‐specific QoL at the end of CKD and MAD. Conclusions: The consumption of a KD improved lymphatic function and was associated with a clinically meaningful reduction in oedema volume in some patients (3/7 at end of CKD, 2/7 at end of MAD) with unilateral stage 2 secondary lymphoedema. These results highlight the potential of a KD to improve lymphatic function in patients with lymphoedema. However, further studies are required to substantiate our findings. Highlights: Lymphoedema is a chronic and progressive disease characterised by excessive accumulation of lymph in the interstitial compartment due to impaired lymphatic drainage, and ketone body oxidation has been shown to play a critical role in restoring lymphatic drainage and resolving accumulated lymph.In patients with unilateral secondary lymphoedema, consumption of both a classic ketogenic diet (CKD) and a modified Atkins diet (MAD) improved lymphatic function, which was associated with a clinically meaningful reduction in oedema volume in three and two out of seven patients upon consumption of a CKD and a MAD, respectively.The potential of the ketogenic diet as a novel metabolic strategy for the treatment of lymphoedema should be confirmed in a randomised control trial. [ABSTRACT FROM AUTHOR]

Lymphatics participate in reverse cholesterol transport, and their presence in the arterial wall of the great vessels and prior experimental results suggest their possible role in the development of atherosclerosis. The aim of this study was to characterize the lymphatic vasculature of the arterial wall in atherosclerosis. Tissue sections and tissue-cleared aortas of wild-type mice unveiled significant differences in the density of the arterial lymphatic network throughout the arterial tree. Male and female Ldlr−/− and ApoE−/− mice on a Western diet showed sex-dependent differences in plaque formation and calcification. Female mice on a Western diet developed more calcification of atherosclerotic plaques than males. The lymphatic vessels within the aortic wall of these mice showed no major changes regarding the number of lymphatic junctions and end points or the lymphatic area. However, female mice on a Western diet showed moderate dilation of lymphatic vessels in the abdominal aorta and exhibited indications of increased peripheral lymphatic function, findings that require further studies to understand the role of lymphatics in the arterial wall during the development of atherosclerosis. [ABSTRACT FROM AUTHOR]

Physiological properties and function of the lymphatic system is still somewhat of a mystery. We report the current knowledge about human lymphatic vessel contractility and capability of adaptation. A literature search in PubMed identified studies published January 2000–September 2022. Inclusion criteria were studies investigating parameters related to contraction frequency, fluid velocity, and lymphatic pressure in vivo and ex vivo in human lymphatic vessels. The search returned 2885 papers of which 28 met the inclusion criteria. In vivo vessels revealed baseline contraction frequencies between 0.2 ± 0.2 and 1.8 ± 0.1 min1, velocities between 0.008 ± 0.002 and 2.3 ± 0.3 cm/s, and pressures between 4.5 (range 0.5–9.2) and 60.3 ± 2.8 mm Hg. Gravitational forces, hyperthermia, and treatment with nifedipine caused increases in contraction frequency. Ex vivo lymphatic vessels displayed contraction frequencies between 1.2 ± 0.1 and 5.5 ± 1.2 min−1. Exposure to agents affecting cation and anion channels, adrenoceptors, HCN channels, and changes in diameter‐tension properties all resulted in changes in functional parameters as known from the blood vascular system. We find that the lymphatic system is dynamic and adaptable. Different investigative methods yields alternating results. Systematic approaches, consensus on investigative methods, and larger studies are needed to fully understand lymphatic transport and apply this in a clinical context. [ABSTRACT FROM AUTHOR]

Background: Dysfunction of the lymphatic system following injury, disease, or cancer treatment can lead to lymphedema, a debilitating condition with no cure. Despite the various physical therapy and surgical options available, most treatments are palliative and fail to address the underlying lymphatic vascular insufficiency driving lymphedema progression. Stem cell therapy provides a promising alternative in the treatment of various chronic diseases with a wide range of therapeutic effects that reduce inflammation, fibrosis, and oxidative stress, while promoting lymphatic vessel (LV) regeneration. Specifically, stem cell transplantation is suggested to promote LV restoration, rebuild lymphatic circulation, and thus potentially be utilized towards an effective lymphedema treatment. In addition to stem cells, studies have proposed the administration of vascular endothelial growth factor C (VEGFC) to promote lymphangiogenesis and decrease swelling in lymphedema. Aims: Here, we seek to combine the benefits of stem cell therapy, which provides a cellular therapeutic approach that can respond to the tissue environment, and VEGFC administration to restore lymphatic drainage. Materials & Methods: Specifically, we engineered mesenchymal stem cells (MSCs) to overexpress VEGFC using a lentiviral vector (hVEGFC MSC) and investigated their therapeutic efficacy in improving LV function and tissue swelling using near infrared (NIR) imaging, and lymphatic regeneration in a single LV ligation mouse tail lymphedema model. Results: First, we showed that overexpression of VEGFC using lentiviral transduction led to an increase in VEGFC protein synthesis in vitro. Then, we demonstrated hVEGFC MSC administration post‐injury significantly increased the lymphatic contraction frequency 14‐, 21‐, and 28‐days post‐surgery compared to the control animals (MSC administration) in vivo, while also reducing tail swelling 28‐days post‐surgery compared to controls. Conclusion: Our results suggest a therapeutic potential of hVEGFC MSC in alleviating the lymphatic dysfunction observed during lymphedema progression after secondary injury and could provide a promising approach to enhancing autologous cell therapy for treating lymphedema. [ABSTRACT FROM AUTHOR]

Advancements in lymphography technology are essential for comprehensive investigation of the lymphatic system and its function. Here, a shortwave infrared (SWIR) luminescence imaging oflymphatic vessels is proposed in both normal and lymphatic dysfunction in rat models with PbS quantum dots (PbS Qdots). The lymphography with PbS Qdots can clearly and rapidly demonstrate the normal lymphatic morphology in both the tail and hind limb. More importantly, compared to ICG, SWIR luminescence imaging with PbS Qdots can easily identify the dominant lymphatic vessel and node with higher luminescence signal in rats. Moreover, lymphatic pump is identified as segment contracting sections with a size of «1 cm in rat by in vivo SWIR lymphograhy, which propose a direct feature for precise evaluation of lymphatic function. Notably, in vivo SWIR luminescence imaging with PbS Qdots also clearly deciphers the in vivo pattern of morphological and function recovery from lymphatic system in rat model. In summary, SWIR luminescence imaging with PbS Qdots can improve the lymphography and thus deepen the understanding ofthe morphology and structure of the lymphatic system as well as lymphatic function such as lymphatic pump, which will facilitate the diagnosis of lymphatic dysfunction in the future. [ABSTRACT FROM AUTHOR]

Lymphatic dysfunction is a pivotal pathological mechanism underlying the development of early atherosclerotic plaques. Potential targets of lymphatic function must be identified to realize the early prevention and treatment of atherosclerosis (AS). The immunity-related GTPase Irgm1 is involved in orchestrating cellular autophagy and apoptosis. However, the effect of Irgm1 on early AS progression, particularly through alterations in lymphatic function, remains unclear. In this study, we confirmed the protective effect of lymphangiogenesis on early-AS in vivo. Subsequently, an in vivo model of early AS mice with Irgm1 knockdown shows that Irgm1 reduces early atherosclerotic plaque burden by promoting lymphangiogenesis. Given that lymphatic endothelial cell (LEC) autophagy significantly contributes to lymphangiogenesis, Irgm1 may enhance lymphatic circulation by promoting LEC autophagy. Moreover, Irgm1 orchestrates autophagy in LECs by inhibiting mTOR and facilitating nuclear translocation of Tfeb. Collectively, these processes lead to lymphangiogenesis. Thus, this study establishes a link between Irgm1 and early AS, thus revealing a novel mechanism by which Irgm1 exerts an early protective influence on AS within the context of lymphatic circulation. The insights gained from this study have the potential to revolutionize the approach and management of AS onset. • Irgm1 promotes lymphangiogenesis by Tfeb translocation and orchestrating moderate LEC autophagy. • Irgm1 is a promising candidate and a potential target for early intervention in AS. • The insights may revolutionize the early prevention and control strategies for AS by enhancing lymphatic function. [ABSTRACT FROM AUTHOR]

The lymphatic system plays a crucial role in maintaining tissue homeostasis, immune response, and fluid balance within the human body. Lymphatic vessels, a key component of this system, undergo complex development and function throughout life. This article provides an overview of the development and function of lymphatic vessels, highlighting their significance in various physiological processes.. [ABSTRACT FROM AUTHOR]

A local anesthetic, lidocaine, is known to affect cutaneous blood flow when injected into the skin. However, it is unknown if dermal lymphatic function can also be affected. Therefore, we characterized lymphatic function in response to administration of lidocaine with and without epinephrine. Non-invasive near-infrared fluorescence imaging (NIRFI) with intradermal injection of indocyanine green (ICG) was used to characterize the lymphatic 'pumping' function in mice after subcutaneous injection of 2 % lidocaine with and without 1:100,000 epinephrine or saline. NIRFI was performed for 10-20 min immediately after and 1, 3, and 5 h after these interventions. Lymphatic contraction frequencies significantly decreased 10 min after subcutaneous injection of lidocaine and remained plateaued for another 5 min, before returning to baseline. However, addition of 1:100,000 epinephrine to 2 % lidocaine rapidly increased lymphatic contraction frequencies at 5 min post-injection, which returned to baseline levels 15 min later. Injection of saline also increased lymphatic contraction frequency 5 min after injection, which returned to baseline 10 min post-injection. Although lidocaine administration showed a decrease in lymphatic function, the combination of epinephrine with lidocaine resulted in a predominant net effect of increased contractile activity. [ABSTRACT FROM AUTHOR]

Impairment of the lymphatic system is apparent in multiple inflammatory pathologies connected to elevated endotoxins such as LPS. However, the direct mechanisms by which LPS influences the lymphatic contractility are not well understood. We hypothesized that a dynamic modulation of innate immune cell populations in mesentery under inflammatory conditions perturbs tissue cytokine/ chemokine homeostasis and subsequently influences lymphatic function. We used rats that were intraperitoneally injected with LPS (10 mg/kg) to determine the changes in the profiles of innate immune cells in the mesentery and in the stretch-mediated contractile responses of isolated lymphatic preparations. Results demonstrated a reduction in the phasic contractile activity of mesenteric lymphatic vessels from LPS-injected rats and a severe impairment of lymphatic pump function and flow. There was a significant reduction in the number of neutrophils and an increase in monocytes/macrophages present on the lymphatic vessels and in the clear mesentery of the LPS group. This population of monocytes and macrophages established a robust M2 phenotype, with the majority showing high expression of CD163 and CD206. Several cytokines and chemoattractants for neutrophils and macrophages were significantly changed in the mesentery of LPSinjected rats. Treatment of lymphatic muscle cells (LMCs) with LPS showed significant changes in the expression of adhesion molecules, VCAM1, ICAM1, CXCR2, and galectin-9. LPS-TLR4- mediated regulation of pAKT, pERK pI-KB, and pMLC2o in LMCs promoted both contractile and inflammatory pathways. Thus, our data provide the first evidence connecting the dynamic changes in innate immune cells on or near the lymphatics and complex cytokine milieu during inflammation with lymphatic dysfunction. [ABSTRACT FROM AUTHOR]

Lymphedema, a common complication of cancer treatment, is characterized by inflammation, fibrosis, and adipose deposition. We have previously shown that macrophage infiltration is increased in mouse models of lymphedema. Because macrophages are regulators of lymphangiogenesis and fibrosis, this study aimed to determine the role of these cells in lymphedema using depletion experiments. Matched biopsy specimens of normal and lymphedema tissues were obtained from patients with unilateral upper extremity breast cancer-related lymphedema, and macrophage accumulation was assessed using immunohistochemistry. In addition, we used a mouse tail model of lymphedema to quantify macrophage accumulation and analyze outcomes of conditional macrophage depletion. Histological analysis of clinical lymphedema biopsies revealed significantly increased macrophage infiltration. Similarly, in the mouse tail model, lymphatic injury increased the number of macrophages and favored M2 differentiation. Chronic macrophage depletion using lethally irradiated wild-type mice reconstituted with CD11b-diphtheria toxin receptor mouse bone marrow did not decrease swelling, adipose deposition, or overall inflammation. Macrophage depletion after lymphedema had become established significantly increased fibrosis and accumulation of CD4+ cells and promoted Th2 differentiation while decreasing lymphatic transport capacity and VEGF-C expression. Our findings suggest that macrophages home to lymphedematous tissues and differentiate into the M2 phenotype. In addition, our findings suggest that macrophages have an antifibrotic role in lymphedema and either directly or indirectly regulate CD4+ cell accumulation and Th2 differentiation. Finally, our findings suggest that lymphedema-associated macrophages are a major source of VEGF-C and that impaired macrophage responses after lymphatic injury result in decreased lymphatic function. [ABSTRACT FROM AUTHOR]

Lymphatic vessels are well known to participate in the immune response by providing the structural and functional support for the delivery of antigens and antigen presenting cells to draining lymph nodes. Recent advances have improved our understanding of how the lymphatic system works and how it participates to the development of immune responses. New findings suggest that the lymphatic system may control the ultimate immune response through a number of ways which may include guiding antigen/dendritic cells (DC) entry into initial lymphatics at the periphery; promoting antigen/DC trafficking through afferent lymphatic vessels by actively facilitating lymph and cell movement; enabling antigen presentation in lymph nodes via a network of lymphatic endothelial cells and lymph node stroma cell and finally by direct lymphocytes exit from lymph nodes. The same mechanisms are likely also important to maintain peripheral tolerance. In this review we will discuss how the morphology and gene expression profile of the lymphatic endothelial cells in lymphatic vessels and lymph nodes provides a highly efficient pathway to initiate immune responses. The fundamental understanding of how lymphatic system participates in immune regulation will guide the research on lymphatic function in various diseases. [ABSTRACT FROM AUTHOR]

There is a lack of available methods to noninvasively quantify lymphatic function in small experimental animals, a necessity for studies on lymphatic system pathophysiology. We present a new method to quantify lymph flow in mice and rats, based on optically monitoring the depot clearance of nearinfrared fluorescently labeled albumin and subsequent calculation of removal rate constants (k). BSA was conjugated with Alexa680 NHS ester and remained stable in protein-rich solutions without free dye dissociation. To assess lymph flow, mice or rats were imaged every 30 or 60 min during a 3- to 6-h period following an intradermal injection of 0.5 or 1 μl Alexa680-albumin. Mice were awake between measurements, whereas rats were anesthetized throughout the experiment. The k, a parameter defined as equivalent to lymph flow, was calculated from the slopes of the resultant log-linear washout curves and averaged -0.40 ± 0.03 and -0.30 ± 0.02%/min for control C57BL/6 and C3H mice, respectively. Local administration of the vasoconstrictor endothelin-1 in mice led to a significant reduction in k, whereas overhydration in rats increased k, reflecting the coupling between capillary filtration and lymph flow. Furthermore, k was 50% of wild type in lymphedema Chy mice where dermal lymphatics are absent. We conclude that lymph flow can be determined as its rate constant k by optical imaging of depot clearance of submicroliter amounts of Alexa680-albumin. The method offers a minimally invasive, reproducible, and simple alternative to assess lymphatic function in mice and rats. [ABSTRACT FROM AUTHOR]

Abstract: If thiazolidinediones have shown beneficial effects on macrovascular endothelial function, their effects on microcirculation and lymphatic function are not well documented. The aim of the study was to assess the effect of rosiglitazone on interstitial albumin retention and lymphatic function in Zucker Diabetic Fatty (ZDF) rats. Three series of 9–14 rats were studied: Lean (fa/?) controls, ZDF (Gmi-fa/fa) rats and ZDF rats treated with rosiglitazone from 8 to 26 weeks of age (ZDF–ROSI). Albumin retention and lymphatic uptake of interstitial albumin (LF/HF ratio) were evaluated on hindquarters with a noninvasive isotopic test using technetium-labelled albumin. Vascular Endothelial Growth Factor (VEGF) was measured. At week 25, albumin retention was markedly higher in ZDF rats (9.9±1.0%) than in control rats (1.0±0.8%, p <0.001), but did not differ significantly between the ZDF–ROSI group (2.5±1.5%) and the control group. LF/HF ratio was similarly increased in the ZDF group (1.14±0.07%) and the ZDF–ROSI group (1.07±0.04%) as compared to control rats (0.65±0.04%; p <0.001 for both). We can deduce that the prevention of the increase of albumin retention under rosiglitazone results from a decrease in the capillary filtration of albumin. VEGF levels were 7.1±1.5, 7.3±1.9, 3.5±1.6 pg/mL in the control, ZDF and ZDF–ROSI groups, respectively (p =0.23). In ZDF rats, rosiglitazone prevents interstitial albumin retention and the increase in capillary filtration of albumin. However lymphatic function is still impaired and might contribute to oedema. [Copyright &y& Elsevier]

Abstract: Disturbances in the microcirculation can lead to secondary lymphedema, a common pathological condition that, despite its frequency, still lacks a cure. Lymphedema is clinically well described, but while the genetic underpinnings that cause lymphatic malformations and primary lymphedema are being discovered, the pathophysiology and pathobiology of secondary lymphedema remain poorly understood, partly due to the lack of well-described experimental models. Here, we provide a detailed characterization of secondary lymphedema in the mouse tail and correlate the evolution of tissue swelling to changes in tissue architecture, infiltration of immune cells, deposition of lipids, and proliferation and morphology of the lymphatic vessels. We show that sustained swelling leads to lymphatic hyperplasia and upregulation of vascular endothelial growth factor (VEGF)-C, which may exacerbate the edema because the hyperplastic vessels are poorly functional. The onset of lymphatic hyperplasia occurred prior to the onset of lipid accumulation and peak VEGF-C expression. Langerhans dendritic cells were seen in the dermis migrating from the epidermis to the lymphatic capillaries in edematous tissue. Furthermore, these results were consistent between two different normal mouse strains, but swelling was significantly greater in a matrix metalloproteinase (MMP)-9 null strain. Thus, by characterizing this highly reproducible model of secondary lymphedema, we conclude that VEGF-C upregulation and lymphatic hyperplasia resulting from dermal lymphatic ligation and lymphedema leads to decreased drainage function and that MMP-9 may be important in counteracting tissue swelling. [Copyright &y& Elsevier]

Our understanding of the function and development of the lymphatic system is expanding rapidly due to the identification of specific molecular markers and the availability of novel genetic approaches. In connection, it has been demonstrated that mechanical forces contribute to the endothelial cell fate commitment and play a critical role in influencing lymphatic endothelial cell shape and alignment by promoting sprouting, development, maturation of the lymphatic network, and coordinating lymphatic valve morphogenesis and the stabilization of lymphatic valves. However, the mechanosignaling and mechanotransduction pathways involved in these processes are poorly understood. Here, we provide an overview of the impact of mechanical forces on lymphatics and summarize the current understanding of the molecular mechanisms involved in the mechanosensation and mechanotransduction by lymphatic endothelial cells. We also discuss how these mechanosensitive pathways affect endothelial cell fate and regulate lymphatic development and function. A better understanding of these mechanisms may provide a deeper insight into the pathophysiology of various diseases associated with impaired lymphatic function, such as lymphedema and may eventually lead to the discovery of novel therapeutic targets for these conditions. [ABSTRACT FROM AUTHOR]