The lymphatic vasculature in disease

Meningeal lymphatic vessel crosstalk with central nervous system immune cells in aging and neurodegenerative diseases

Meningeal lymphatic vessels form a relationship between the nervous system and periphery, which is relevant in both health and disease. Meningeal lymphatic vessels not only play a key role in the drainage of brain metabolites but also contribute to antigen delivery and immune cell activation. The advent of novel genomic technologies has enabled rapid progress in the characterization of myeloid and lymphoid cells and their interactions with meningeal lymphatic vessels within the central nervous system. In this review, we provide an overview of the multifaceted roles of meningeal lymphatic vessels within the context of the central nervous system immune network, highlighting recent discoveries on the immunological niche provided by meningeal lymphatic vessels. Furthermore, we delve into the mechanisms of crosstalk between meningeal lymphatic vessels and immune cells in the central nervous system under both homeostatic conditions and neurodegenerative diseases, discussing how these interactions shape the pathological outcomes. Regulation of meningeal lymphatic vessel function and structure can influence lymphatic drainage, cerebrospinal fluid-borne immune modulators, and immune cell populations in aging and neurodegenerative disorders, thereby playing a key role in shaping meningeal and brain parenchyma immunity.

Ligation of cervical lymphatic vessels decelerates blood clearance and worsens outcomes after experimental subarachnoid hemorrhage

Subarachnoid hemorrhage (SAH) is characterized by the extravasation of blood into the subarachnoid space, in which erythrocyte lysis is the primary contributor to cell death and brain injuries. New evidence has indicated that meningeal lymphatic vessels (mLVs) are essential in guiding fluid and macromolecular waste from cerebrospinal fluid (CSF) into deep cervical lymph nodes (dCLNs). However, the role of mLVs in clearing erythrocytes after SAH has not been completely elucidated. Hence, we conducted a cross-species study. Autologous blood was injected into the subarachnoid space of rabbits and rats to induce SAH. Erythrocytes in the CSF were measured with/without deep cervical lymph vessels (dCLVs) ligation. Additionally, prior to inducing SAH, we administered rats with vascular endothelial growth factor C (VEGF-C), which is essential for meningeal lymphangiogenesis and maintaining integrity and survival of lymphatic vessels. The results showed that the blood clearance rate was significantly lower after dCLVs ligation in both the rat and rabbit models. DCLVs ligation aggravated neuroinflammation, neuronal damage, brain edema, and behavioral impairment after SAH. Conversely, the treatment of VEGF-C enhanced meningeal lymphatic drainage of erythrocytes and improved outcomes in SAH. In summary, our research highlights the indispensable role of the meningeal lymphatic pathway in the clearance of blood and mediating consequences after SAH.

Interleukin-7-based identification of liver lymphatic endothelial cells reveals their unique structural features

Background & Aims

The lymphatic system plays crucial roles in maintaining fluid balance and immune regulation. Studying the liver lymphatics has been considered challenging, as common lymphatic endothelial cell (LyEC) markers are expressed by other liver cells. Additionally, isolation of sufficient numbers of LyECs has been challenging because of their extremely low abundance (<0.01% of entire liver cell population) in a normal liver.

Methods

Potential LyEC markers was identified using our published single-cell RNA sequencing (scRNA-seq) dataset (GSE147581) in mouse livers. Interleukin-7 (IL7) promoter-driven green fluorescent protein knock-in heterozygous mice were used for the validation of IL7 expression in LyECs in the liver, for the development of liver LyEC isolation protocol, and generating liver ischemia/reperfusion (I/R) injury. Scanning electron microscopy was used for the structural analysis of LyECs. Changes in LyEC phenotypes in livers of mice with I/R were determined by RNA-seq analysis.

Results

Through scRNA-seq analysis, we have identified IL7 as an exclusive marker for liver LyECs, with no overlap with other liver cell types. Based on IL7 expression in liver LyECs, we have established an LyEC isolation method and observed distinct cell surface structures of LyECs with fenestrae and cellular pores (ranging from 100 to 400 nm in diameter). Furthermore, we identified LyEC genes that undergo alterations during I/R liver injuries.

Conclusions

This study not only identified IL7 as an exclusively expressed gene in liver LyECs, but also enhanced our understanding of LyEC structures and demonstrated transcriptomic changes in injured livers.

Impact and implications

Understanding the lymphatic system in the liver is challenging because of the absence of specific markers for liver LyEC. This study has identified IL7 as a reliable marker for LyECs, enabling the development of an effective method for their isolation, elucidating their unique cell surface structure, and identifying LyEC genes that undergo changes during liver damage. The development of IL7 antibodies for detecting it in human liver specimens will further advance our understanding of the liver lymphatic system in the future.

Age-related changes in meningeal lymphatic function are closely associated with vascular endothelial growth factor-C expression

Meningeal lymphatic vessels (MLVs) have crucial roles in removing metabolic waste and toxic proteins from the brain and transporting them to the periphery. Aged mice show impaired meningeal lymphatic function. Nevertheless, as the disease progresses, and significant pathological changes manifest in the brain, treating the condition becomes increasingly challenging. Therefore, investigating the alterations in the structure and function of MLVs in the early stages of aging is critical for preventing age-related central nervous system degenerative diseases. We detected the structure and function of MLVs in young, middle-aged, and aged mice. Middle-aged mice, compared with young and aged mice, showed enhanced meningeal lymphatic function along with MLV expansion and performed better in the Y maze test. Moreover, age-related changes in meningeal lymphatic function were closely associated with vascular endothelial growth factor-C (VEGF-C) expression in the brain cortex. Our data suggested that the cerebral cortex may serve as a target for VEGF-C supplementation to ameliorate meningeal lymphatic dysfunction, thus providing a new strategy for preventing age-related central nervous system diseases.

Angpt1 binding to Tie1 regulates the signaling required for lymphatic vessel development in zebrafish

Development of the vascular system is regulated by multiple signaling pathways mediated by receptor tyrosine kinases. Among them, angiopoietin (Ang)/Tie signaling regulates lymphatic and blood vessel development in mammals. Of the two Tie receptors, Tie2 is well known as a key mediator of Ang/Tie signaling, but, unexpectedly, recent studies have revealed that the Tie2 locus has been lost in many vertebrate species, whereas the Tie1 gene is more commonly present. However, Tie1-driven signaling pathways, including ligands and cellular functions, are not well understood. Here, we performed comprehensive mutant analyses of angiopoietins and Tie receptors in zebrafish and found that only angpt1 and tie1 mutants show defects in trunk lymphatic vessel development. Among zebrafish angiopoietins, only Angpt1 binds to Tie1 as a ligand. We indirectly monitored Ang1/Tie1 signaling and detected Tie1 activation in sprouting endothelial cells, where Tie1 inhibits nuclear import of EGFP-Foxo1a. Angpt1/Tie1 signaling functions in endothelial cell migration and proliferation, and in lymphatic specification during early lymphangiogenesis, at least in part by modulating Vegfc/Vegfr3 signaling. Thus, we show that Angpt1/Tie1 signaling constitutes an essential signaling pathway for lymphatic development in zebrafish.

Injectable Thermosensitive Gel CH-BPNs-NBP for Effective Periodontitis Treatment through ROS-Scavenging and Jaw Vascular Unit Protection

Periodontitis, a prevalent inflammatory condition in the oral cavity, is closely associated with oxidative stress-induced tissue damage mediated by excessive reactive oxygen species (ROS) production. The jaw vascular unit (JVU), encompassing both vascular and lymphatic vessels, plays a crucial role in maintaining tissue fluid homeostasis and contributes to the pathological process in inflammatory diseases of the jaw. This study presents a novel approach for treating periodontitis through the development of an injectable thermosensitive gel (CH-BPNs-NBP). The gel formulation incorporates black phosphorus nanosheets (BPNs), which are notable for their ROS-scavenging properties, and dl-3-n-butylphthalide (NBP), a vasodilator that promotes lymphatic vessel function within the JVU. These results demonstrate that the designed thermosensitive gel serve as a controlled release system, delivering BPNs and NBP to the site of inflammation. CH-BPNs-NBP not only protects macrophages and human lymphatic endothelial cells from ROS attack but also promotes M2 polarization and lymphatic function. In in vivo studies, this work observes a significant reduction in inflammation and tissue damage, accompanied by a notable promotion of alveolar bone regeneration. This research introduces a promising therapeutic strategy for periodontitis, leveraging the unique properties of BPNs and NBP within an injectable thermosensitive gel.

Advancing insights into in vivo meningeal lymphatic vessels with stereoscopic wide-field photoacoustic microscopy

Meningeal lymphatic vessels (mLVs) play a pivotal role in regulating metabolic waste from cerebrospinal fluid (CSF). However, the current limitations in field of view and resolution of existing imaging techniques impede understanding the stereoscopic morphology and dynamic behavior of mLVs in vivo. Here, we utilized dual-contrast functional photoacoustic microscopy to achieve wide-field intravital imaging of the lymphatic system, including mLVs and glymphatic pathways. The stereoscopic photoacoustic microscopy based on opto-acoustic confocal features has a depth imaging capability of 3.75 mm, facilitating differentiation between mLVs on the meninges and glymphatic pathways within the brain parenchyma. Subsequently, using this imaging technique, we were able to visualize the dynamic drainage of mLVs and identify a peak drainage period occurring around 20-40 min after injection, along with determining the flow direction from CSF to lymph nodes. Inspiringly, in the Alzheimer's disease (AD) mouse model, we observed that AD mice exhibit a ~ 70% reduction in drainage volume of mLVs compared to wild-type mice. With the development of AD, there is be continued decline in mLVs drainage volume. This finding clearly demonstrates that the AD mouse model has impaired CSF drainage. Our study opens up a horizon for understanding the brain's drainage mechanism and dissecting mLVs-associated neurological disorders.

Tumor microenvironment restricts IL-10 induced multipotent progenitors to myeloid-lymphatic phenotype

Lymphangiogenesis is induced by local pro-lymphatic growth factors and bone marrow (BM)-derived myeloid-lymphatic endothelial cell progenitors (M-LECP). We previously showed that M-LECP play a significant role in lymphangiogenesis and lymph node metastasis in clinical breast cancer (BC) and experimental BC models. We also showed that differentiation of mouse and human M-LECP can be induced through sequential activation of colony stimulating factor-1 (CSF-1) and Toll-like receptor-4 (TLR4) pathways. This treatment activates the autocrine interleukin-10 (IL-10) pathway that, in turn, induces myeloid immunosuppressive M2 phenotype along with lymphatic-specific proteins. Because IL-10 is implicated in differentiation of numerous lineages, we sought to determine whether this pathway specifically promotes the lymphatic phenotype or multipotent progenitors that can give rise to M-LECP among other lineages. Analyses of BM cells activated either by CSF-1/TLR4 ligands in vitro or orthotopic breast tumors in vivo showed expansion of stem/progenitor population and coincident upregulation of markers for at least four lineages including M2-macrophage, lymphatic endothelial, erythroid, and T-cells. Induction of cell plasticity and multipotency was IL-10 dependent as indicated by significant reduction of stem cell markers and those for multiple lineages in differentiated cells treated with anti-IL-10 receptor (IL-10R) antibody or derived from IL-10R knockout mice. However, multipotent CD11b+/Lyve-1+/Ter-119+/CD3e+ progenitors detected in BM appeared to split into a predominant myeloid-lymphatic fraction and minor subsets expressing erythroid and T-cell markers upon establishing tumor residence. Each sub-population was detected at a distinct intratumoral site. This study provides direct evidence for differences in maturation status between the BM progenitors and those reaching tumor destination. The study results suggest preferential tumor bias towards expansion of myeloid-lymphatic cells while underscoring the role of IL-10 in early BM production of multipotent progenitors that give rise to both hematopoietic and endothelial lineages.

Anti-lymphangiogenesis for boosting drug accumulation in tumors

The inadequate tumor accumulation of anti-cancer agents is a major shortcoming of current therapeutic drugs and remains an even more significant concern in the clinical prospects for nanomedicines. Various strategies aiming at regulating the intratumoral permeability of therapeutic drugs have been explored in preclinical studies, with a primary focus on vascular regulation and stromal reduction. However, these methods may trigger or facilitate tumor metastasis as a tradeoff. Therefore, there is an urgent need for innovative strategies that boost intratumoral drug accumulation without compromising treatment outcomes. As another important factor affecting drug tumor accumulation besides vasculature and stroma, the impact of tumor-associated lymphatic vessels (LVs) has not been widely considered. In the current research, we verified that anlotinib, a tyrosine kinase inhibitor with anti-lymphangiogenesis activity, and SAR131675, a selective VEGFR-3 inhibitor, effectively decreased the density of tumor lymphatic vessels in mouse cancer models, further enhancing drug accumulation in tumor tissue. By combining anlotinib with therapeutic drugs, including doxorubicin (Dox), liposomal doxorubicin (Lip-Dox), and anti-PD-L1 antibody, we observed improved anti-tumor efficacy in comparison with monotherapy regimens. Meanwhile, this strategy significantly reduced tumor metastasis and elicited stronger anti-tumor immune responses. Our work describes a new, clinically transferrable approach to augmenting intratumoral drug accumulation, which shows great potential to address the current, unsatisfactory efficacies of therapeutic drugs without introducing metastatic risk.

Impaired meningeal lymphatic drainage in Listeria monocytogenes infection

Previous studies have demonstrated an association between lymphatic vessels and diseases caused by bacterial infections. Listeria monocytogenes (LM) bacterial infection can affect multiple organs, including the intestine, brain, liver and spleen, which can be fatal. However, the impacts of LM infection on morphological and functional changes of lymphatic vessels remain unexplored. In this study, we found that LM infection not only induces meningeal and mesenteric lymphangiogenesis in mice, but also impairs meningeal lymphatic vessels (MLVs)-mediated macromolecules drainage. Interestingly, we found that the genes associated with lymphatic vessel development and function, such as Gata2 and Foxc2, were downregulated, suggesting that LM infection may affect cellular polarization and valve development. On the other hand, photodynamic ablation of MLVs exacerbated inflammation and bacterial load in the brain of mice with LM infection. Overall, our findings indicate that LM infection induces lymphangiogenesis and may affect cell polarization, cavity formation, and valve development during lymphangiogenesis, ultimately impairing MLVs drainage.

Advances in lymphatic metastasis of non-small cell lung cancer

Lung cancer is a deeply malignant tumor with high incidence and mortality. Despite the rapid development of diagnosis and treatment technology, abundant patients with lung cancer are still inevitably faced with recurrence and metastasis, contributing to death. Lymphatic metastasis is the first step of distant metastasis and an important prognostic indicator of non-small cell lung cancer. Tumor-induced lymphangiogenesis is involved in the construction of the tumor microenvironment, except promoting malignant proliferation and metastasis of tumor cells, it also plays a crucial role in individual response to treatment, especially immunotherapy. Thus, this article reviews the current research status of lymphatic metastasis in non-small cell lung cancer, in order to provide some insights for the basic research and clinical and translational application in this field.

Intrinsic and Extrinsic Contributors to the Cardiac Benefits of Exercise

Among its many cardiovascular benefits, exercise training improves heart function and protects the heart against age-related decline, pathological stress, and injury. Here, we focus on cardiac benefits with an emphasis on more recent updates to our understanding. While the cardiomyocyte continues to play a central role as both a target and effector of exercise's benefits, there is a growing recognition of the important roles of other, noncardiomyocyte lineages and pathways, including some that lie outside the heart itself. We review what is known about mediators of exercise's benefits-both those intrinsic to the heart (at the level of cardiomyocytes, fibroblasts, or vascular cells) and those that are systemic (including metabolism, inflammation, the microbiome, and aging)-highlighting what is known about the molecular mechanisms responsible.

Effect of Semaglutide and Empagliflozin on Pulmonary Structure and Proteomics in Obese Mice

Objective

This study utilized proteomics to investigate changes in protein expression associated with lung health in obese mice exposed to semaglutide and empagliflozin through a high-fat diet.

Methods

Twenty-eight male C57BL/6JC mice were randomly assigned to two groups: a control diet group (n = 7) and a high-fat diet group (n = 21). The HFD group was further divided into three groups: HFD group (n = 7), Sema group (n = 7), and Empa group (n = 7). Post-treatment, mice underwent assessments including glucose tolerance, lipids, oxidative stress markers, body weight, lung weight, and structure. Proteomics identified differentially expressed proteins (DEPs) in lung tissue, and bioinformatics analyzed the biological processes and functions of these proteins.

Results

Semaglutide and empagliflozin significantly attenuated obesity-induced hyperglycemia, abnormal lipid metabolism, oxidative stress response, and can decrease alveolar wall thickness, enlarge alveolar lumen, and reduce collagen content in lung tissue. Both medications also attenuated lung elastic fibre cracking and disintegration. In the HFD/NCD group, there were 66 DEPs, comprising 30 proteins that were increased and 36 that were decreased. Twenty-three DEPs overlapped between Sema/HFD and Empa/HFD, with 11 up-regulated and 12 down-regulated simultaneously. After analysing DEPs in different groups, four proteins - LYVE1, BRAF, RGCC, and CHMP5 - were all downregulated in the HFD group and upregulated by semaglutide and empagliflozin treatment.

Conclusion

This study demonstrates that obesity induced by a high-fat diet causes a reduction in the expression of LYVE1, BRAF, RGCC, and CHMP5 proteins, potentially affecting lung function and structure in mice. Significantly, the administration of semaglutide and empagliflozin elevates the levels of these proteins, potentially offering therapeutic benefits against lung injury caused by obesity. Merging semaglutide with empagliflozin may exert a more pronounced impact.

VE-cadherin junction dynamics in initial lymphatic vessels promotes lymph node metastasis

The endothelial junction component vascular endothelial (VE)-cadherin governs junctional dynamics in the blood and lymphatic vasculature. Here, we explored how lymphatic junction stability is modulated by elevated VEGFA signaling to facilitate metastasis to sentinel lymph nodes. Zippering of VE-cadherin junctions was established in dermal initial lymphatic vessels after VEGFA injection and in tumor-proximal lymphatics in mice. Shape analysis of pan-cellular VE-cadherin fragments revealed that junctional zippering was accompanied by accumulation of small round-shaped VE-cadherin fragments in the lymphatic endothelium. In mice expressing a mutant VEGFR2 lacking the Y949 phosphosite (Vegfr2 Y949F/Y949F ) required for activation of Src family kinases, zippering of lymphatic junctions persisted, whereas accumulation of small VE-cadherin fragments was suppressed. Moreover, tumor cell entry into initial lymphatic vessels and subsequent metastatic spread to lymph nodes was reduced in mutant mice compared with WT, after challenge with B16F10 melanoma or EO771 breast cancer. We conclude that VEGFA mediates zippering of VE-cadherin junctions in initial lymphatics. Zippering is accompanied by increased VE-cadherin fragmentation through VEGFA-induced Src kinase activation, correlating with tumor dissemination to sentinel lymph nodes.

Humanin inhibits lymphatic endothelial cells dysfunction to alleviate myocardial infarction-reperfusion injury via BNIP3-mediated mitophagy

OBJECTIVE

Acute myocardial infarction (AMI) ranks among the top contributors to sudden death and disability worldwide. It should be noted that current therapies always cause increased reperfusion damage. Evidence suggests that humanin (HN) reduces mitochondrial dysfunction to have cardio-protective effects against MI-reperfusion injury. In this context, we hypothesized that HN may attenuate MI-reperfusion injury by alleviating lymphatic endothelial cells dysfunction through the regulation of mitophagy.

MATERIALS AND METHODS

In this study, primary lymphatic endothelial cells were selected as the experimental model. Cells were maintained under 1% O2 to induce a hypoxic phenotype. For in vivo experiments, the left coronary arteries of C57/BL6 mice were clamped for 45 min followed by 24 h reperfusion to develop MI-reperfusion injury. The volume of infarcted myocardium in MI-reperfusion injury mouse models were TTC staining. PCR and western blot were used to quantify the expression of autophagy-, mitophagy- and mitochondria-related markers. The fibrosis and apoptosis in the ischemic area were evaluated for Masson staining and TUNEL respectively. We also used western blot to analyze the expression of VE-Cadherin in lymphatic endothelial cells.

RESULTS

We firstly exhibited a specific mechanism by which HN mitigates MI-reperfusion injury. We demonstrated that HN effectively reduces such injury in vivo and also inhibits dysfunction in lymphatic endothelial cells in vitro. Importantly, this inhibitory effect is mediated through BNIP3-associated mitophagy.

CONCLUSIONS

In conclusion, HN alleviates myocardial infarction-reperfusion injury by inhibiting lymphatic endothelial cells dysfunction, primarily through BNIP3-mediated mitophagy.

The development of early human lymphatic vessels as characterized by lymphatic endothelial markers

Lymphatic vessel development studies in mice and zebrafish models have demonstrated that lymphatic endothelial cells (LECs) predominantly differentiate from venous endothelial cells via the expression of the transcription factor Prox1. However, LECs can also be generated from undifferentiated mesoderm, suggesting potential diversity in their precursor cell origins depending on the organ or anatomical location. Despite these advances, recapitulating human lymphatic malformations in animal models has been difficult, and considering lymphatic vasculature function varies widely between species, analysis of development directly in humans is needed. Here, we examined early lymphatic development in humans by analyzing the histology of 31 embryos and three 9-week-old fetuses. We found that human embryonic cardinal veins, which converged to form initial lymph sacs, produce Prox1-expressing LECs. Furthermore, we describe the lymphatic vessel development in various organs and observe organ-specific differences. These characterizations of the early development of human lymphatic vessels should help to better understand the evolution and phylogenetic relationships of lymphatic systems, and their roles in human disease.

VEGFR-3 signaling in macrophages: friend or foe in disease?

Lymphatic vessels have been increasingly appreciated in the context of immunology not only as passive conduits for immune and cancer cell transport but also as key in local tissue immunomodulation. Targeting lymphatic vessel growth and potential immune regulation often takes advantage of vascular endothelial growth factor receptor-3 (VEGFR-3) signaling to manipulate lymphatic biology. A receptor tyrosine kinase, VEGFR-3, is highly expressed on lymphatic endothelial cells, and its signaling is key in lymphatic growth, development, and survival and, as a result, often considered to be "lymphatic-specific" in adults. A subset of immune cells, notably of the monocyte-derived lineage, have been identified to express VEGFR-3 in tissues from the lung to the gut and in conditions as varied as cancer and chronic kidney disease. These VEGFR-3+ macrophages are highly chemotactic toward the VEGFR-3 ligands VEGF-C and VEGF-D. VEGFR-3 signaling has also been implicated in dictating the plasticity of these cells from pro-inflammatory to anti-inflammatory phenotypes. Conversely, expression may potentially be transient during monocyte differentiation with unknown effects. Macrophages play critically important and varied roles in the onset and resolution of inflammation, tissue remodeling, and vasculogenesis: targeting lymphatic vessel growth and immunomodulation by manipulating VEGFR-3 signaling may thus impact macrophage biology and their impact on disease pathogenesis. This mini review highlights the studies and pathologies in which VEGFR-3+ macrophages have been specifically identified, as well as the activity and polarization changes that macrophage VEGFR-3 signaling may elicit, and affords some conclusions as to the importance of macrophage VEGFR-3 signaling in disease.

Current and Developing Lymphatic Imaging Approaches for Elucidation of Functional Mechanisms and Disease Progression

Study of the lymphatic system, compared to that of the other body systems, has been historically neglected. While scientists and clinicians have, in recent decades, gained a better appreciation of the functionality of the lymphatics as well as their role in associated diseases (and consequently investigated these topics further in their experimental work), there is still much left to be understood of the lymphatic system. In this review article, we discuss the role lymphatic imaging techniques have played in this recent series of advancements and how new imaging techniques can help bolster this wave of discovery. We specifically highlight the use of lymphatic imaging techniques in understanding the fundamental anatomy and physiology of the lymphatic system; investigating the development of lymphatic vasculature (using techniques such as intravital microscopy); diagnosing, staging, and treating lymphedema and cancer; and its role in other disease states.

Copper nanoparticles and silver nanoparticles impair lymphangiogenesis in zebrafish

Lymphatic system distributes in almost all vertebrate tissues and organs, and plays important roles in the regulation of body fluid balance, lipid absorption and immune monitoring. Although CuNPs or AgNPs accumulation has been reported to be closely associated with delayed hatching and motor dysfunction in zebrafish embryos, their biological effects on lymphangiogenesis remain unknown. In this study, thoracic duct was observed to be partially absent in both CuNPs and AgNPs stressed zebrafish larvae. Specifically, CuNPs stress induced hypermethylation of E2F7/8 binding sites on CCBE1 promoters via their producing ROS, thereby leading to the reduction of binding enrichment of E2F7/8 on CCBE1 promoter and its subsequently reduced expression, then resulting in defective lymphatic vessel formation. Differently, AgNPs stress induced down-regulated CCBE1 expression via down-regulating mRNA and protein levels of E2F7/8 transcription factors, thereby resulting in defective lymphatic vessel formation. This study may be the first to demonstrate that CuNPs and AgNPs damaged lymphangiogenesis during zebrafish embryogenesis, mechanistically, CuNPs epigenetically regulated the expression of lymphangiogenesis regulator CCBE1 via hypermethylating its promoter binding sites of E2F7/8, while AgNPs via regulating E2F7/8 expression. Meanwhile, overexpression of ccbe1 mRNA effectively rescued the lymphangiogenesis defects in both AgNPs and CuNPs stressed larvae, while overexpression of e2f7/8 mRNA effectively rescued the lymphangiogenesis defects in AgNPs rather than CuNPs stressed larvae. The results in this study will shed some light on the safety assessment of nanomaterials applied in medicine and on the ecological security assessments of nanomaterials. Video Abstract.

The role of lymphatic vessels in corneal fluid homeostasis and wound healing

The cornea, essential for vision, is normally avascular, transparent, and immune-privileged. However, injuries or infections can break this privilege, allowing blood and lymphatic vessels to invade, potentially impairing vision and causing immune responses. This review explores the complex role of corneal lymphangiogenesis in health and diseases. Traditionally, the cornea was considered devoid of lymphatic vessels, a phenomenon known as "corneal (lymph)angiogenic privilege." Recent advances in molecular markers have enabled the discovery of lymphatic vessels in the cornea under certain conditions. Several molecules contribute to preserving both immune and lymphangiogenic privileges. Lymphangiogenesis, primarily driven by VEGF family members, can occur directly or indirectly through macrophage recruitment. Corneal injuries and diseases disrupt these privileges, reducing graft survival rates following transplantation. However, modulation of lymphangiogenesis offers potential interventions to promote graft survival and expedite corneal edema resolution.This review underscores the intricate interplay between lymphatic vessels, immune privilege, and corneal pathologies, highlighting innovative therapeutic possibilities. Future investigations should explore the modulation of lymphangiogenesis to enhance corneal health and transparency, as well as corneal graft survival, and this benefits patients with various corneal conditions.

Efficient pulmonary lymphatic drainage is necessary for inflammation resolution in ARDS

The lymphatic vasculature is the natural pathway for the resolution of inflammation, yet the role of pulmonary lymphatic drainage function in sepsis-induced acute respiratory distress syndrome (ARDS) remains poorly characterized. In this study, indocyanine green-near infrared lymphatic living imaging was performed to examine pulmonary lymphatic drainage function in septic mouse models. We found that the pulmonary lymphatic drainage was impaired owing to the damaged lymphatic structure in sepsis-induced ARDS. Moreover, prior lymphatic defects by blocking vascular endothelial growth factor receptor-3 (VEGFR-3) worsened sepsis-induced lymphatic dysfunction and inflammation. Posttreatment with vascular endothelial growth factor-C (Cys156Ser) (VEGF-C156S), a ligand of VEGFR-3, ameliorated lymphatic drainage by rejuvenating lymphatics to reduce the pulmonary edema and promote draining of pulmonary macrophages and neutrophils to pretracheal lymph nodes. Meanwhile, VEGF-C156S posttreatment reversed sepsis-inhibited CC chemokine ligand 21 (CCL21), which colocalizes with pulmonary lymphatic vessels. Furthermore, the advantages of VEGF-C156S on the drainage of inflammatory cells and edema fluid were abolished by blocking VEGFR-3 or CCL21. These results suggest that efficient pulmonary lymphatic drainage is necessary for inflammation resolution in ARDS. Our findings offer a therapeutic approach to sepsis-induced ARDS by promoting lymphatic drainage function.

Sentinel node restoration by vascularized lymph node transfer in mice

BACKGROUND

Recent reports have indicated that vascularized lymph node transfer (VLNT) may improve the impaired immunity in lymphedema but there has been no report concerning anti-cancer immunity. In the early tumor immune response, dendritic cells (DCs) participate in tumor recognition and antigen presentation in local lymphatics. Here, we investigated the impact of VLNT on DC dynamics against cancer in mouse models.

METHODS

Forty-seven 8-week-old C57BL/6 N male mice were divided into three surgical groups: a VLNT model in which a vascularized inguinal lymph node (LN) flap was transferred into the ipsilateral fossa after a popliteal LN was removed; a LN dissection (LND) model in which the popliteal LN was dissected; and a control model in which a skin incision was made at the popliteal fossa and an ipsilateral inguinal LN was removed. Postoperative lymphatic flows were observed by indocyanine green lymphography and B16-F10-luc2 mouse melanoma were implanted into the ipsilateral footpad. The proportion of DCs in the transplanted nodes was measured by CD11c immunohistochemistry using digital imaging analysis 4 days after cancer implantation. Metastases to the lungs and LNs were quantitatively evaluated by luciferase assay 4 weeks after cancer implantation.

RESULTS

After VLNT, lymphatic reconnection was observed in 59.2% of mice. The proportion of DCs was significantly higher in the VLNT group with lymphatic reconnection (8.6% ± 1.0%) than in the naïve LN (4.3% ± 0.4%) (p < .001). The tumor burden of lung metastases was significantly less in the VLNT group with lymphatic reconnection compared with the LND group (p = .049).

CONCLUSIONS

Metastasis decreased in mice with reconnected lymphatics after VLNT. A possible explanation was that lymphatic restoration may have contributed to the tumor immune response by allowing DC migration to LNs.

Novel erectile analyses revealed augmentable penile Lyve-1, the lymphatic marker, expression

Purpose

The pathophysiology of penis extends to erectile dysfunction (ED) to conditions including sexually transmitted diseases (STDs) and cancer. To date, there has been little research evaluating vascular drainage from the penis. We aimed to evaluate penile blood flow in vivo and analyze its possible relationship with the lymphatic maker.

Materials and Methods

We established an in vivo system designed to assess the dynamic blood outflow from the corpus cavernosum (CC) by dye injection. To analyze lymphatic characteristics in the CC, the expression of Lyve-1, the key lymphatic endothelium marker, was examined by the in vitro system and lipopolysaccharide (LPS) injection to mimic the inflammatory conditions.

Results

A novel cavernography methods enable high-resolution morphological and functional blood drainage analysis. The expression of Lyve-1 was detected along the sinusoids. Furthermore, its prominent expression was also observed after penile LPS injection and in the erectile condition.

Conclusions

The current in vivo system will potentially contribute to the assessment of penile pathology from a novel viewpoint. In addition, current analyses revealed inducible Lyve-1 expression for LPS injection and the erection state, which requires further analyses on penile lymphatic system.

The Tumor Immune Microenvironment plays a Key Role in Driving the Progression of Cholangiocarcinoma

Cholangiocarcinoma (CCA) is an epithelial cancer distinguished by bile duct cell differentiation and is also a fibroproliferative tumor. It is characterized by a dense mesenchyme and a complex tumor immune microenvironment (TME). The TME comprises both cellular and non-cellular components. The celluar component includes CCA cells, immune cells and mesenchymal cells represented by the cancer-associated fibroblasts (CAFs), while the non-cellular component is represented by mesenchymal elements such as the extracellular matrix (ECM). Recent studies have demonstrated the important role of the TME in the development, progression, and treatment resistance of CCA. These cell-associated prognostic markers as well as intercellular connections, may serve as potential therapeutic targets and could inspire new treatment approaches for CCA in the future. This paper aims to summarize the current understanding of CCA's immune microenvironment, focusing on immune cells, mesenchymal cells, ECM, intercellular interactions, and metabolism within the microenvironment.

Systems immunology spanning tumors, lymph nodes, and periphery

The immune system defines a complex network of tissues and cell types that orchestrate responses across the body in a dynamic manner. The local and systemic interactions between immune and cancer cells contribute to disease progression. Lymphocytes are activated in lymph nodes, traffic through the periphery, and impact cancer progression through their interactions with tumor cells. As a result, therapeutic response and resistance are mediated across tissues, and a comprehensive understanding of lymphocyte dynamics requires a systems-level approach. In this review, we highlight experimental and computational methods that can leverage the study of leukocyte trafficking through an immunomics lens and reveal how adaptive immunity shapes cancer.

Molecular and metabolic orchestration of the lymphatic vasculature in physiology and pathology

Lymphangiogenesis refers to the generation of new lymphatic vessels from pre-existing ones. During development and particular adult states, lymphatic endothelial cells (LEC) undergo reprogramming of their transcriptomic and signaling networks to support the high demands imposed by cell proliferation and migration. Although there has been substantial progress in identifying growth factors and signaling pathways controlling lymphangiogenesis in the last decades, insights into the role of metabolism in lymphatic cell functions are just emerging. Despite numerous similarities between the main metabolic pathways existing in LECs, blood ECs (BEC) and other cell types, accumulating evidence has revealed that LECs acquire a unique metabolic signature during lymphangiogenesis, and their metabolic engine is intertwined with molecular regulatory networks, resulting in a tightly regulated and interconnected process. Considering the implication of lymphatic dysfunction in cancer and lymphedema, alongside other pathologies, recent findings hold promising opportunities to develop novel therapeutic approaches. In this review, we provide an overview of the status of knowledge in the molecular and metabolic network regulating the lymphatic vasculature in health and disease.

Response of lymphatic endothelial cells to combined spatial and temporal variations in fluid flow

One-way valves within lymphatic vessels are required for the efficient drainage of lymphatic fluids. Fluid flow is proposed to be a key cue in regulating both the formation and maintenance of lymphatic valves. However, to our knowledge, no previous study has systematically examined the response of LECs to the complex combination of spatially and temporally varying fluid flows that occur at lymphatic valves in vivo. We built an in vitro microfluidic device that reproduces key aspects of the flow environment found at lymphatic valves. Using this device, we found that a combination of spatially and temporally varying wall shear stresses (WSSs) led to upregulated transcription of PROX1 and FOXC2. In addition, we observed that combined spatial and temporal variations in WSS-modulated Ca2+ signaling and led to increased cellular levels of NFATc1. These observations suggest that the physical cues generated by the flow environment present within lymphatic valves may act to activate key regulatory pathways that contribute to valve maintenance.

Engineered organoids for biomedical applications

As miniaturized and simplified stem cell-derived 3D organ-like structures, organoids are rapidly emerging as powerful tools for biomedical applications. With their potential for personalized therapeutic interventions and high-throughput drug screening, organoids have gained significant attention recently. In this review, we discuss the latest developments in engineering organoids and using materials engineering, biochemical modifications, and advanced manufacturing technologies to improve organoid culture and replicate vital anatomical structures and functions of human tissues. We then explore the diverse biomedical applications of organoids, including drug development and disease modeling, and highlight the tools and analytical techniques used to investigate organoids and their microenvironments. We also examine the latest clinical trials and patents related to organoids that show promise for future clinical translation. Finally, we discuss the challenges and future perspectives of using organoids to advance biomedical research and potentially transform personalized medicine.

Lymphatic muscle cells are unique cells that undergo aging induced changes

Lymphatic muscle cells (LMCs) within the wall of collecting lymphatic vessels exhibit tonic and autonomous phasic contractions, which drive active lymph transport to maintain tissue-fluid homeostasis and support immune surveillance. Damage to LMCs disrupts lymphatic function and is related to various diseases. Despite their importance, knowledge of the transcriptional signatures in LMCs and how they relate to lymphatic function in normal and disease contexts is largely missing. We have generated a comprehensive transcriptional single-cell atlas-including LMCs-of collecting lymphatic vessels in mouse dermis at various ages. We identified genes that distinguish LMCs from other types of muscle cells, characterized the phenotypical and transcriptomic changes in LMCs in aged vessels, and uncovered a pro-inflammatory microenvironment that suppresses the contractile apparatus in advanced-aged LMCs. Our findings provide a valuable resource to accelerate future research for the identification of potential drug targets on LMCs to preserve lymphatic vessel function as well as supporting studies to identify genetic causes of primary lymphedema currently with unknown molecular explanation.

YAP1/Piezo1 involve in the dynamic changes of lymphatic vessels in UVR-induced photoaging progress to squamous cell carcinoma

BACKGROUND

UV-induced cutaneous squamous cell carcinoma (cSCC) is one of the most common skin cancers. The constant alterations of the lymphatic-centered immune microenvironment are essential in transforming from photoaging to cSCC. Studying the mechanism will be beneficial for new targets exploration to the early prediction of cSCC.

AIMS

To investigate the dynamic changes and mechanism of the lymphatic-centered immune microenvironment in transforming from photoaging to cSCC induced by ultraviolet irradiation (UVR).

METHODS

TIMER2.0 was used to analyze whether YAP1/VEGFC signaling pathway is involved in lymphangiogenesis in head and neck squamous cell carcinoma (HNSCC). Meanwhile, lymphatic-centered immune microenvironments alterations and the related cumulative survival time were also analyzed. With the accumulated UVR, skin photoaging developed and gradually progressed into actinic keratosis and cSCC on SKH-1 hairless mice. The skin lymphatic-centered immune microenvironment was evaluated at the 0th, 8th, 12th, 16-18th, and 20-24th week of UVR. Skin phenotype was assessed using optical coherence tomography (OCT) and skin image. H&E and Masson's trichrome staining evaluated epidermis and dermis. The structure of lymphatic vessels (LVs), blood vessels, and different types of T cells were evaluated by immunohistochemistry staining. The expression of Piezo1 whose deletion in adult lymphatics led to substantial valve degeneration, VE-cadherin that maintained the permeability of LVs, and YAP1 were evaluated by immunohistochemistry staining as well. Besides, the drainage function of LVs was assessed by Evans Blue assay in vivo.

RESULTS

The lymphatic function and immune cell infiltration underwent adaptive changes under continuous UVR. TIMER2.0 analysis indicated that VEGFC genes high expressed in HNSCC. YAP1 gene expression was positive correlated with VEGFC in HNSCC. LV density increased in human cSCC. More LVs in HNSCC were beneficial to prolong the survival time. VEGFC gene overexpression was positive correlated to CD8+T cell infiltration. More CD8A+T cells and CD8B+T cell infiltration in HNSCC extended survival time. When YAP1 gene overexpression and high infiltration of endothelial cells took place simultaneously might prolong the survival time of HNSCC patients. And high infiltration of CD8+T cells prolonged the survival time as well. In animal studies, UVR-induced eight weeks (photoaging) and 16-18 weeks (precancerous) were two turning points. The density of LVs in UV-8w was the least. When photoaged skin developed into AK lesions (UV-16-18w), LV slightly exceeded healthy skin and proliferated sharply in cSCC (UV-20-24w). YAP1 expression was almost consistent with LV but rose after the photoaging stage. The drainage of cSCC mice induced by UVR was better than that of photoaged skin and worse than that of health skin. The dynamic alterations of LVs number, Piezo1 expression, and collagen might be reasons for it. The expression of Piezo1 was in the highest point after 8 weeks of UVR, then gradually descended to the platform. The total T cells increased slowly, but the infiltration of CD4+T cells increased, and CD8+T cells decreased after eight weeks of UVR. The CD8+T cells and CD4+T cells increased sharply in UV-16-18w and UV-20-24w groups.

CONCLUSION

The lymphatic-centered immune microenvironment underwent adaptive changes under continuous UVR via regulating YAP1/VEGFC and Piezo1. During the formation of cSCC, there are two turning points, eight weeks (photoaging) and 16-18 weeks (precancerous). YAP1, Piezo1, LVs, and immune cells constantly changed with the skin state induced by UVR. According to these changes the process of cSCC can be identified in advance and intervene timely.

Lymph node metastases in breast cancer: Mechanisms and molecular imaging

Breast cancer is the most common malignant disease of women in the world. Breast cancer often metastasizes to axillary lymph nodes. Accurate assessment of the status of axillary lymph nodes is crucial to the staging and treatment of breast cancer. None of the methods used clinically for preoperative noninvasive examination of axillary lymph nodes can accurately identify cancer cells from a molecular level. In recent years, with the in-depth study of lymph node metastases, the mechanisms and molecular imaging of lymph node metastases in breast cancer have been reported. In this review, we highlight the new progress in the study of the main mechanisms of lymph node metastases in breast cancer. In addition, we analyze the advantages and disadvantages of traditional preoperative axillary lymph node imaging methods for breast cancer, and list molecular imaging methods that can accurately identify breast cancer cells in lymph nodes.

Capillary washboarding during slow drainage of a frictional fluid

Numerous natural and industrial processes involve the mixed displacement of liquids, gases and granular materials through confining structures. However, understanding such three-phase flows remains a formidable challenge, despite their tremendous economic and environmental impact. To unveil the complex interplay of capillary and granular stresses in such flows, we consider here a model configuration where a frictional fluid (an immersed sedimented granular layer) is slowly drained out of a horizontal capillary. Analyzing how liquid/air menisci displace particles from such granular beds, we reveal various drainage patterns, notably the periodic formation of dunes, analogous to road washboard instability. Considering the competitive role of friction and capillarity, a 2D theoretical approach supported by numerical simulations of a meniscus bulldozing a front of particles provides quantitative criteria for the emergence of those dunes. A key element is the strong increase of the frictional forces, as the bulldozed particles accumulate and bend the meniscus horizontally. Interestingly, this frictional enhancement with the attack angle is also crucial in small-legged animals' locomotion over granular media.

Relaxivity Enhancement of Hybrid Micelles via Modulation of Water Coordination Numbers for Magnetic Resonance Lymphography

Considerable efforts have been made to develop nanoparticle-based magnetic resonance contrast agents (CAs) with high relaxivity. The prolonged rotational correlation time (τR) induced relaxivity enhancement is commonly recognized, while the effect of the water coordination numbers (q) on the relaxivity of nanoparticle-based CAs gets less attention. Herein, we first investigated the relationship between T1 relaxivity (r1) and q in manganese-based hybrid micellar CAs and proposed a strategy to enhance the relaxivity by increasing q. Hybrid micelles with different ratios of amphiphilic manganese complex (MnL) and DSPE-PEG2000 were prepared, whose q values were evaluated by Oxygen-17-NMR spectroscopy. Micelles with lower manganese doping density exhibit increased q and enhanced relaxivity, corroborating the conception. In vivo sentinel lymph node (SLN) imaging demonstrates that DSPE-PEG/MnL micelles could differentiate metastatic SLN from inflammatory LN. Our strategy makes it feasible for relaxivity enhancement by modulating q, providing new approaches for the structural design of high-performance hybrid micellar CAs.

Single-nuclei multiomic analyses identify human cardiac lymphatic endothelial cells associated with coronary arteries in the epicardium

Cardiac lymphatic vessels play important roles in fluid homeostasis, inflammation, disease, and regeneration of the heart. The developing cardiac lymphatics in human fetal hearts are closely associated with coronary arteries, similar to those in zebrafish hearts. We identify a population of cardiac lymphatic endothelial cells (LECs) that reside in the epicardium. Single-nuclei multiomic analysis of the human fetal heart reveals the plasticity and heterogeneity of the cardiac endothelium. Furthermore, we find that VEGFC is highly expressed in arterial endothelial cells and epicardium-derived cells, providing a molecular basis for the arterial association of cardiac lymphatic development. Using a cell-type-specific integrative analysis, we identify a population of cardiac lymphatic endothelial cells marked by the PROX1 and the lymphangiocrine RELN and enriched in binding motifs of erythroblast transformation specific (ETS) variant (ETV) transcription factors. We report the in vivo molecular characterization of human cardiac lymphatics and provide a valuable resource to understand fetal heart development.

Immunomodulatory properties of the lymphatic endothelium in the tumor microenvironment

The tumor microenvironment (TME) is an intricate complex and dynamic structure composed of various cell types, including tumor, stromal and immune cells. Within this complex network, lymphatic endothelial cells (LECs) play a crucial role in regulating immune responses and influencing tumor progression and metastatic dissemination to lymph node and distant organs. Interestingly, LECs possess unique immunomodulatory properties that can either promote or inhibit anti-tumor immune responses. In fact, tumor-associated lymphangiogenesis can facilitate tumor cell dissemination and metastasis supporting immunoevasion, but also, different molecular mechanisms involved in LEC-mediated anti-tumor immunity have been already described. In this context, the crosstalk between cancer cells, LECs and immune cells and how this communication can shape the immune landscape in the TME is gaining increased interest in recent years. In this review, we present a comprehensive and updated report about the immunomodulatory properties of the lymphatic endothelium within the TME, with special focus on primary tumors and tumor-draining lymph nodes. Furthermore, we outline emerging research investigating the potential therapeutic strategies targeting the lymphatic endothelium to enhance anti-tumor immune responses. Understanding the intricate mechanisms involved in LEC-mediated immune modulation in the TME opens up new possibilities for the development of innovative approaches to fight cancer.

The novel role of lymphatic vessels in the pathogenesis of ocular diseases

Historically, the eye has been considered as an organ free of lymphatic vessels. In recent years, however, it became evident, that lymphatic vessels or lymphatic-like vessels contribute to several ocular pathologies at various peri- and intraocular locations. The aim of this review is to outline the pathogenetic role of ocular lymphatics, the respective molecular mechanisms and to discuss current and future therapeutic options based thereon. We will give an overview on the vascular anatomy of the healthy ocular surface and the molecular mechanisms contributing to corneal (lymph)angiogenic privilege. In addition, we present (i) current insights into the cellular and molecular mechanisms occurring during pathological neovascularization of the cornea triggered e.g. by inflammation or trauma, (ii) the role of lymphatic vessels in different ocular surface pathologies such as dry eye disease, corneal graft rejection, ocular graft versus host disease, allergy, and pterygium, (iii) the involvement of lymphatic vessels in ocular tumors and metastasis, and (iv) the novel role of the lymphatic-like structure of Schlemm's canal in glaucoma. Identification of the underlying molecular mechanisms and of novel modulators of lymphangiogenesis will contribute to the development of new therapeutic targets for the treatment of ocular diseases associated with pathological lymphangiogenesis in the future. The preclinical data presented here outline novel therapeutic concepts for promoting transplant survival, inhibiting metastasis of ocular tumors, reducing inflammation of the ocular surface, and treating glaucoma. Initial data from clinical trials suggest first success of novel treatment strategies to promote transplant survival based on pretransplant corneal lymphangioregression.

Dual role of Vascular Endothelial Growth Factor-C (VEGF-C) in post-stroke recovery

Using a mouse model of ischemic stroke, this study characterizes stroke-induced lymphangiogenesis at the cribriform plate (CP). While blocking CP lymphangiogenesis with a VEGFR-3 inhibitor improves stroke outcome, administration of VEGF-C induced larger brain infarcts.

Abstract

Cerebrospinal fluid (CSF), antigens, and antigen-presenting cells drain from the central nervous system (CNS) into lymphatic vessels near the cribriform plate and dural meningeal lymphatics. However, the pathological roles of these lymphatic vessels surrounding the CNS during stroke are not well understood. Using a mouse model of ischemic stroke, transient middle cerebral artery occlusion (tMCAO), we show that stroke induces lymphangiogenesis near the cribriform plate. Interestingly, lymphangiogenesis is restricted to lymphatic vessels at the cribriform plate and downstream cervical lymph nodes, without affecting the conserved network of lymphatic vessels in the dura. Cribriform plate lymphangiogenesis peaks at day 7 and regresses by day 14 following tMCAO and is regulated by VEGF-C/VEGFR-3. These newly developed lymphangiogenic vessels transport CSF and immune cells to the cervical lymph nodes. Inhibition of VEGF-C/VEGFR-3 signaling using a blocker of VEGFR-3 prevented lymphangiogenesis and led to improved stroke outcomes at earlier time points but had no effects at later time points following stroke. Administration of VEGF-C after tMCAO did not further increase post-stroke lymphangiogenesis, but instead induced larger brain infarcts. The differential roles for VEGFR-3 inhibition and VEGF-C in regulating stroke pathology call into question recent suggestions to use VEGF-C therapeutically for stroke.

Biomechanical control of lymphatic vessel physiology and functions

The ever-growing research on lymphatic biology has clearly identified lymphatic vessels as key players that maintain human health through their functional roles in tissue fluid homeostasis, immunosurveillance, lipid metabolism and inflammation. It is therefore not surprising that the list of human diseases associated with lymphatic malfunctions has grown larger, including issues beyond lymphedema, a pathology traditionally associated with lymphatic drainage insufficiency. Thus, the discovery of factors and pathways that can promote optimal lymphatic functions may offer new therapeutic options. Accumulating evidence indicates that aside from biochemical factors, biomechanical signals also regulate lymphatic vessel expansion and functions postnatally. Here, we review how mechanical forces induced by fluid shear stress affect the behavior and functions of lymphatic vessels and the mechanisms lymphatic vessels employ to sense and transduce these mechanical cues into biological signals.

Fluid flow to mimic organ function in 3D in vitro models

Many different strategies can be found in the literature to model organ physiology, tissue functionality, and disease in vitro; however, most of these models lack the physiological fluid dynamics present in vivo. Here, we highlight the importance of fluid flow for tissue homeostasis, specifically in vessels, other lumen structures, and interstitium, to point out the need of perfusion in current 3D in vitro models. Importantly, the advantages and limitations of the different current experimental fluid-flow setups are discussed. Finally, we shed light on current challenges and future focus of fluid flow models applied to the newest bioengineering state-of-the-art platforms, such as organoids and organ-on-a-chip, as the most sophisticated and physiological preclinical platforms.

Nanoparticle oral absorption and its clinical translational potential

Oral administration of pharmaceuticals is the most preferred route of administration for patients, but it is challenging to effectively deliver active ingredients (APIs) that i) have extremely high or low solubility in intestinal fluids, ii) are large in size, iii) are subject to digestive and/or metabolic enzymes present in the gastrointestinal tract (GIT), brush border, and liver, and iv) are P-glycoprotein substrates. Over the past decades, efforts to increase the oral bioavailability of APIs have led to the development of nanoparticles (NPs) with non-specific uptake pathways (M cells, mucosal, and tight junctions) and target-specific uptake pathways (FcRn, vitamin B12, and bile acids). However, voluminous findings from preclinical models of different species rarely meet practical standards when translated to humans, and API concentrations in NPs are not within the adequate therapeutic window. Various NP oral delivery approaches studied so far show varying bioavailability impacted by a range of factors, such as species, GIT physiology, age, and disease state. This may cause difficulty in obtaining similar oral delivery efficacy when research results in animal models are translated into humans. This review describes the selection of parameters to be considered for translational potential when designing and developing oral NPs.

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

Introduction

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

Methods

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

Results

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

Conclusions

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

Supplementary Information

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

Meningeal lymphatics and their role in CNS disorder treatment: moving past misconceptions

The central nervous system (CNS) was previously thought to lack lymphatics and shielded from the free diffusion of molecular and cellular components by the blood-brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCB). However, recent findings have redefined the roles played by meningeal lymphatic vessels in the recruitment and drainage of lymphocytes from the periphery into the brain and the potentiation of an immune response. Emerging knowledge surrounding the importance of meningeal lymphatics has the potential to transform the treatment of CNS disorders. This review details the most recent understanding of the CNS-lymphatic network and its immunologic implications in both the healthy and diseased brain. Moreover, the review provides in-depth coverage of several exciting avenues for future therapeutic treatments that involve the meningeal lymphatic system. These therapeutic avenues will have potential implications in many treatment paradigms in the coming years.

Targeting lymph node delivery with nanovaccines for cancer immunotherapy: recent advances and future directions

Although cancer immunotherapy is a compelling approach against cancer, its effectiveness is hindered by the challenge of generating a robust and durable immune response against metastatic cancer cells. Nanovaccines, specifically engineered to transport cancer antigens and immune-stimulating agents to the lymph nodes, hold promise in overcoming these limitations and eliciting a potent and sustained immune response against metastatic cancer cells. This manuscript provides an in-depth exploration of the lymphatic system's background, emphasizing its role in immune surveillance and tumor metastasis. Furthermore, it delves into the design principles of nanovaccines and their unique capability to target lymph node metastasis. The primary objective of this review is to provide a comprehensive overview of the current advancements in nanovaccine design for targeting lymph node metastasis, while also discussing their potential to enhance cancer immunotherapy. By summarizing the state-of-the-art in nanovaccine development, this review aims to shed light on the promising prospects of harnessing nanotechnology to potentiate cancer immunotherapy and ultimately improve patient outcomes.

The emerging roles of long noncoding RNAs in lymphatic vascular development and disease

Recent advances in RNA sequencing technologies helped uncover what was once uncharted territory in the human genome-the complex and versatile world of long noncoding RNAs (lncRNAs). Previously thought of as merely transcriptional "noise", lncRNAs have now emerged as essential regulators of gene expression networks controlling development, homeostasis and disease progression. The regulatory functions of lncRNAs are broad and diverse, and the underlying molecular mechanisms are highly variable, acting at the transcriptional, post-transcriptional, translational, and post-translational levels. In recent years, evidence has accumulated to support the important role of lncRNAs in the development and functioning of the lymphatic vasculature and associated pathological processes such as tumor-induced lymphangiogenesis and cancer metastasis. In this review, we summarize the current knowledge on the role of lncRNAs in regulating the key genes and pathways involved in lymphatic vascular development and disease. Furthermore, we discuss the potential of lncRNAs as novel therapeutic targets and outline possible strategies for the development of lncRNA-based therapeutics to treat diseases of the lymphatic system.

[Genetics, diagnostics and clinical presentation of primary lymphoedema]

Primary lymphoedema is a hereditary genetic disorder of the lymphatic system. These genetic disorders can result in malformation or dysfunction of the lymphatic system, which leads to an accumulation of fluid in the tissue and, thus to the formation of oedema. The most common form is peripheral lymphoedema of the lower limbs, but systemic manifestations such as intestinal lymphangiectasia, ascites, chylothorax or hydrops fetalis may also occur. The clinical presentation and the degree of lymphoedema varies depending on the causative gene and the specific gene alteration. Primary lymphoedema is divided into five categories: (1) disorders with somatic mosaicism and segmental growth abnormality, (2a) syndromal disorders, (2b) disorders with systemic involvement, (2c) congenital lymphoedema and (2d) disorders that occur after the first year of life (late onset lymphoedema). Targeted genetic diagnosis is based on the patient's clinical presentation and classification into one of the five categories. In general, the diagnosis usually starts with basic diagnostics, which include cytogenetic and molecular genetic testing. Subsequently, a molecular genetic diagnosis is made by performing single-gene analyses, gene panel examinations, exome sequencing or whole genome sequencing. This allows the identification of genetic variants or mutations that are considered to be causative for the presenting symptoms. Combined with human genetic counselling, the genetic diagnosis allows for conclusions about inheritance, the risk of recurrence and potential concomitant symptoms. In many cases, only this approach allows the definite form of primary lymphoedema to be described.

NIR-II Imaging and Sandwiched Plasmonic Biosensor for Ultrasensitive Intraoperative Definition of Tumor-Invaded Lymph Nodes

Radical lymphadenectomy remains the cornerstone of preventing tumor metastasis through the lymphatic system. Current surgical resection of lymph nodes (LNs) based on fluorescence-guided surgery (FGS) suffers from low sensitivity/selectivity with only qualitative information, hampering accurate intraoperative decision-making. Herein, we develop a modularized theranostic system including NIR-II FGS and a sandwiched plasmonic chip (SPC). Intraoperative NIR-II FGS and detection of tumor-positive lymph nodes were performed on the gastric tumor to determine the feasibility of the modularized theranostic system in defining LN metastasis. Under the NIR-II imaging window, the orthotopic tumor and sentinel lymph nodes (SLNs) were successfully excised without ambient light interference in the operating room. Importantly, the SPC biosensor achieved 100% sensitivity and 100% specificity for tumor markers and realized rapid and high-throughput intraoperative SLN detection. We propose the synergetic design of combining the NIR-II FGS and suitable biosensor will substantially improve the efficiency of cancer diagnosis and therapy follow-up.

Lymphatic disorders caused by mosaic, activating KRAS variants respond to MEK inhibition

Central conducting lymphatic anomaly (CCLA) due to congenital maldevelopment of the lymphatics can result in debilitating and life-threatening disease with limited treatment options. We identified 4 individuals with CCLA, lymphedema, and microcystic lymphatic malformation due to pathogenic, mosaic variants in KRAS. To determine the functional impact of these variants and identify a targeted therapy for these individuals, we used primary human dermal lymphatic endothelial cells (HDLECs) and zebrafish larvae to model the lymphatic dysplasia. Expression of the p.Gly12Asp and p.Gly13Asp variants in HDLECs in a 2‑dimensional (2D) model and 3D organoid model led to increased ERK phosphorylation, demonstrating these variants activate the RAS/MAPK pathway. Expression of activating KRAS variants in the venous and lymphatic endothelium in zebrafish resulted in lymphatic dysplasia and edema similar to the individuals in the study. Treatment with MEK inhibition significantly reduced the phenotypes in both the organoid and the zebrafish model systems. In conclusion, we present the molecular characterization of the observed lymphatic anomalies due to pathogenic, somatic, activating KRAS variants in humans. Our preclinical studies suggest that MEK inhibition should be studied in future clinical trials for CCLA due to activating KRAS pathogenic variants.