Dysregulation of Lymphatic Endothelial VEGFR3 Signaling in Disease

Lymphangiogenesis orchestrating tumor microenvironment: Face changing in immunotherapy

In the era of immunotherapy, the lymphatic system has garnered significant attention from researchers. Increasing evidence highlights the complex regulation of lymphatic vessels (LVs) within the tumor microenvironment, unveiling a paradox in tumor progression: while LVs enhance immune surveillance, they simultaneously foster immune suppression. This review summarizes the regulatory factors of lymphangiogenesis, discusses the intricate effects of LVs on immunotherapy, and emphasizes the potential connection between lymphangiogenesis and tertiary lymphoid structure. Additionally, current therapeutic strategies targeting lymphangiogenesis are critically evaluated, with a forward-looking perspective on future research directions and regulatory approaches to achieve precise targeting and optimize immunotherapy paradigms.

Similarities and differences in the clinical features and management of primary lymphedema and kaposiform hemangioendothelioma associated with lymphedema in children

Background

Primary lymphedema (PLE) and kaposiform hemangioendothelioma-related lymphedema (KLE) are rare vascular anomalies (VAs). This study aimed to examine the clinical features, management, and prognosis of PLE and KLE.

Method

The clinical features, imaging, treatments, and outcomes of 12 patients with PLE and 12 patients with KLE were retrospectively reviewed.

Results

The mean age at which signs/symptoms were diagnosed was 68.2 months for PLE patients and 25 months for KLE patients. In PLE, the involvement of multiple sites is common, whereas in KLE, it typically affects a single site. Morbid obesity, which is common in adult patients, is rare in pediatric PLE and KLE patients. Imaging agent accumulation was observed in KLE but not in PLE via lymphoscintigraphy. In contrast, complications of PLE primarily involve skin and soft tissue, whereas musculoskeletal system complications are more common in KLE. Regarding prognosis, most patients stabilize or even experience lesion regression after standard treatment.

Conclusion

PLE and KLE share clinical symptoms. PLE often involves multiple sites, whereas KLE typically presents unilaterally with local lymphatic stasis. Standardized treatment enables the majority of children with lymphedema to control the disease without progression, with KLE showing potential reversibility. Given their rarity, a multidisciplinary approach is crucial for diagnosis and management.

Regulation of VEGFR3 signaling in lymphatic endothelial cells

The receptor tyrosine kinase vascular endothelial growth factor (VEGF) receptor 3 (VEGFR3) is the principal transmembrane receptor responsible for sensing and coordinating cellular responses to environmental lymphangiogenic stimuli in lymphatic endothelial cells (LECs). VEGFC and D (VEGFC/D) function as the cognate ligands to VEGFR3 by stimulating autophosphorylation of intracellular VEGFR3 tyrosine kinase domains that activate signal cascades involved in lymphatic growth and survival. VEGFR3 primarily promotes downstream signaling through the phosphoinositide 3-kinase (PI3K) and Ras signaling cascades that promote functions including cell proliferation and migration. The importance of VEGFR3 cascades in lymphatic physiology is underscored by identification of dysfunctional VEGFR3 signaling across several lymphatic-related diseases. Recently, our group has shown that intracellular modification of VEGFR3 signaling is a potent means of inducing lymphangiogenesis independent of VEGFC. This is important because long-term treatment with recombinant VEGFC may have deleterious consequences due to off-target effects. A more complete understanding of VEGFR3 signaling pathways may lead to novel drug development strategies. The purpose of this review is to 1) characterize molecular mediators of VEGFC/VEGFR3 downstream signaling activation and their functional roles in LEC physiology and 2) explore molecular regulation of overall VEGFR3 expression and activity within LECs.

VEGFR3 pathway in corneal transplantation

PURPOSE

Corneal transplantation, a common procedure in ophthalmology, faces challenges in high-risk (HR) cases due to inflammation and vascularization of the host bed, leading to graft rejection. Despite advancements in surgical techniques and therapeutics, preventing rejection in HR cases remains elusive. This study investigates the role of the vascular endothelial-derived growth factor (VEGF)-C/D-VEGFR3 pathway in corneal transplantation, focusing on its impact on inflammation and immune response.

METHODS

In this study, 42 eyes of 42 patients were evaluated, 24 of whom underwent corneal transplantation, with follow-up visits at 90, 180 and 360 days post-transplantation. Clinical assessments included visual acuity, corneal oedema, endothelial cell count and vascularization. Molecular analyses were performed to measure VEGFR3, VEGF-C, VEGF-D, VEGF-A and inflammatory markers.

RESULTS

Results revealed a distinct pattern of VEGF-C/D and VEGFR3 expression in HR versus low-risk (LR) transplants, correlating with inflammatory markers and clinical outcomes. In HR cases, elevated VEGFR3 expression was associated with increased inflammatory markers (Intercellular Adhesion Molecule 1 (ICAM-1) and Human Leukocyte Antigen - DR isotype (HLA-DR)) and graft rejection risk.

CONCLUSION

These findings underscore the importance of understanding the VEGF-C/D-VEGFR3 pathway in modulating immune responses and inflammation in corneal transplantation, particularly in HR cases. Targeting this pathway could offer novel therapeutic avenues to mitigate inflammation and improve graft survival. Further research is warranted to elucidate the underlying mechanisms and validate these findings, potentially enhancing transplant outcomes, especially in HR patients.

Activation of VEGFR3 and MLC2 are Critical for GLP-2 Enhancement of Chylomicron Transport

Background and Aims

A significant proportion of absorbed dietary triglycerides (TGs) remain in various intracellular and extracellular intestinal compartments for many hours after fat ingestion, including in the lymphatic circulation. TGs retained in the intestine or lymphatics can be mobilized by the gut peptide glucagon-like peptide 2 (GLP-2) and other stimuli. Our previous published data demonstrated that GLP-2 enhances lymph flow by acting distal to the enterocyte, specifically by enhancing lacteal contractility, in an enteric nervous system-dependent fashion. The objective of the present study was to further explore various intermediates in the signaling pathway whereby GLP-2 enhances mesenteric lymph flow. In this study we focused on the roles of vascular endothelial growth factor receptor 3 (VEGFR3) and myosin light chain 2 (MLC2), known to play important roles in lymphangiogenesis and lymphatic contractility, respectively.

Methods

A rat lymph fistula model was utilized in this study. An intraduodenal lipid bolus was applied to the rats 5 hours before the following intraperitoneal (i.p.) administrations: 1) saline (placebo), 2) GLP-2, 3) GLP-2 + MAZ-51 (a VEGFR3 inhibitor), 4) GLP-2 + SAR131675 (a second VEGFR3 inhibitor), 5) GLP-2 + ML-7 (a MLCK inhibitor). Lymph flow and TG output were assessed for 60 minutes after the i.p. administrations. In another set of animals, post-i.p. administration, tissue samples were collected to quantify VEGFR3 and MLC2 activation (via phosphorylation).

Results

We showed that GLP-2 treatment acutely activated VEGFR3 and MLC2, and that inhibition of VEGFR3 (via MAZ-51/SAR131675) and MLC2 (via ML-7) abolished GLP-2-induced lymph flow and TG output. Furthermore, VEGFR3 inhibition blocked MLC2 activation.

Conclusion

Our data suggest that the activation of VEGFR3 and MLC2 play critical roles in GLP-2's enhancement of chylomicron secretion and that VEGFR3 activation is an important intermediary step in GLP-2's activation of MLC2.

Cellular components of tumor microenvironment: understanding their role in lymphatic metastasis of tumors

Metastasis is the leading cause of cancer-related death in cancer patients. Tumor cells primarily spread through the hematogenous and lymphatic system. The underlying mechanisms of hematogenous metastasis have been well described over the past few decades. However, the understanding of the molecular mechanisms involved in lymphatic metastasis is still at an early stage. Tumor microenvironment (TME), primarily consisting of T cells, B cells, tumor-associated macrophages, neutrophils, and cancer-associated fibroblasts, has been implicated in the development of lymphatic metastasis. Recent studies have been reported that the dynamic and complex interplay between these cellular components of TME has great effects on lymphatic metastasis. Here, we discussed the paradoxical roles of these cellular component within the TME during lymphatic metastasis, as well as potential therapeutic opportunities to re-educate these cells within the TME to have anti-tumorigenic effects.

Role of inducible nitric oxide (iNOS) and nitrosative stress in regulating sex differences in secondary lymphedema

Secondary lymphedema is a common complication following surgical treatment of solid tumors. Although more prevalent in women due to higher breast cancer rates, men also develop lymphedema, often with more severe manifestations. Despite these differences in clinical presentation, the cellular mechanisms underlying sex differences are poorly understood. Previous studies have shown that inducible nitric oxide synthase (iNOS) expression by inflammatory cells is an important regulator of lymphatic pumping and leakiness in lymphedema and that lymphatic endothelial cells are highly sensitive to nitrosative stress. Based on this rationale, we used a mouse tail model of lymphedema to study the role of nitric oxide in sex-related differences in disease severity. Consistent with clinical findings, we found that male mice have significantly worse tail edema and higher rates of tail necrosis compared with female mice following tail skin/lymphatic excision (p = 0.001). Our findings correlated with increased tissue infiltration of iNOS + inflammatory cells, increased iNOS protein expression, and increased nitrosative stress in male mouse lymphedematous skin tissues (p < 0.05). Importantly, transgenic male mice lacking the iNOS gene (iNOS-KO) displayed markedly reduced swelling, inflammation, and tissue necrosis rates, whereas no differences were observed between wild-type and iNOS-KO female mice. Overall, our results indicate that iNOS-mediated nitric oxide production contributes to sex-based differences in secondary lymphedema severity, emphasizing the need to consider sex as a biological variable in lymphedema research.

ERG Regulates Lymphatic Vessel Specification Genes and Its Deficiency Impairs Wound Healing-Associated Lymphangiogenesis

OBJECTIVE

Rarefaction of blood and lymphatic vessels in the skin has been reported in systemic sclerosis (SSc) (scleroderma). E26 transformation-specific-related factor (ERG) and Friend leukemia virus-induced erythroleukemia 1 (FLI-1) are important regulators of angiogenesis, but their role in lymphatic vasculature is lesser known. The goal of this study was to determine the role of ERG and FLI-1 in postnatal lymphangiogenesis and SSc lymphatic system defects.

METHODS

Immunofluorescence was used to detect ERG and FLI-1 in skin biopsy samples from patients with SSc and healthy controls. Transcriptional analysis of ERG or FLI-1-silenced human dermal lymphatic endothelial cells (LECs) was performed using microarrays. Effects of ERG and FLI-1 deficiency on in vitro tubulogenesis in human dermal LECs were examined using a Matrigel assay. ERG and FLI-1 endothelial-specific knockouts and ERG lymphatic-specific knockouts were generated to examine vessel regeneration in mice.

RESULTS

ERG and FLI-1 protein levels were reduced in the blood and lymphatic vasculature in SSc skin biopsy samples. ERG levels were shown to regulate genes involved in lymphatic vessel specification, including vascular endothelial growth factor receptor 3/FLT-4, lymphatic vessel endothelial hyaluronan receptor 1, SOX-18, and prospero homeobox 1 (PROX-1), whereas FLI-1 enhanced the function of ERG. The ERG-FLT-4 pathway regulated in vitro tubulogenesis in human LECs. Deficiency of ERG or FLI-1 similarly impaired the function of blood vessels in mice. However, only ERG deficiency affected the regeneration of lymphatic vessels during wound healing.

CONCLUSION

ERG and FLI-1 are essential regulators of blood and lymphatic vessel regeneration. Deficiency of ERG and FLI-1 in SSc endothelial cells may contribute to the impairment of blood and lymphatic vasculature in patients with SSc.

Natural products‐based antiangiogenic agents: New frontiers in cancer therapy

Angiogenesis, vital for tumor growth and metastasis, is a promising target in cancer therapy. Natural compounds offer potential as antiangiogenic agents with reduced toxicity. This review provides a comprehensive overview of natural product‐based antiangiogenic therapies, focusing on molecular mechanisms and therapeutic potential. A systematic search identified relevant articles from 2019 to 2023. Various natural compounds, including polyphenols, terpenes, alkaloids, cannabinoids, omega‐3 fatty acids, polysaccharides, proteins, and carotenoids, were investigated for their antiangiogenic properties. Challenges such as dose standardization, routes of administration, and potential side effects remain. Further studies, including in‐depth animal models and human epidemiological studies, must elucidate clinical efficacy and safety. Synergistic effects with current antiangiogenic therapies, such as bevacizumab and tyrosine kinase inhibitors, should be explored. Additionally, the potential hormone‐dependent effects of compounds like genistein highlight the need for safety evaluation. In conclusion, natural products hold promise as adjunctive therapies to conventional antineoplastic drugs in modulating angiogenesis in cancer. However, robust clinical trials are needed to validate preclinical findings and ensure safety and efficacy.

Single-cell analysis of nasal epithelial cell development in domestic pigs

The nasal mucosa forms a critical barrier against the invasion of respiratory pathogens. Composed of a heterogeneous assortment of cell types, the nasal mucosa relies on the unique characteristics and complex intercellular dynamics of these cells to maintain their structural integrity and functional efficacy. In this study, single-cell RNA sequencing (scRNA-seq) of porcine nasal mucosa was performed, and nineteen distinct nasal cell types, including nine epithelial cell types, five stromal cell types, and five immune cell types, were identified. The distribution patterns of three representative types of epithelial cells (basal cells, goblet cells, and ciliated cells) were subsequently detected by immunofluorescence. We conducted a comparative analysis of these data with published human single-cell data, revealing consistent differentiation trajectories among porcine and human nasal epithelial cells. Specifically, basal cells serve as the initial stage in the differentiation process of nasal epithelial cells, which then epithelial cells. This research not only enhances our understanding of the composition and transcriptional signature of porcine nasal mucosal cells but also offers a theoretical foundation for developing alternative models for human respiratory diseases.

Establishment of a Mouse Model of Mycoplasma pneumoniae-Induced Plastic Bronchitis

Plastic bronchitis (PB) constitutes a life-threatening pulmonary disorder, predominantly attributed to Mycoplasma pneumoniae (MP) infection. The pathogenic mechanisms involved remain largely unexplored, leading to the absence of reliable approaches for early diagnosis and clear treatment. Thus, the present investigation aimed to develop an MP-induced mouse model of PB, thereby enhancing our understanding of this complex condition. In the first stage, healthy BALB/c mice were utilized to investigate the optimal methods for establishing PB. This involved the application of nebulization (15-20 min) and intratracheal administration (6-50 μL) with 2-chloroethyl ethyl sulfide (CEES) concentrations ranging from 4.5% to 7.5%. Subsequently, the MP model was induced by administering an MP solution (2 mL/kg/day, 108 CFU/50 μL) via the intranasal route for a duration of five consecutive days. Ultimately, suitable techniques were employed to induce plastic bronchitis in the MP model. Pathological changes in lung tissue were analyzed, and immunohistochemistry was employed to ascertain the expression levels of vascular endothelial growth factor receptor 3 (VEGFR-3) and the PI3K/AKT/mTOR signaling pathway. The administration of 4.5% CEES via a 6 µL trachea was the optimal approach to establishing a PB model. This method primarily induced neutrophilic inflammation and fibrinous exudate. The MP-infected group manifested symptoms indicative of respiratory infection, including erect hair, oral and nasal secretions, and a decrease in body weight. Furthermore, the pathological score of the MP+CEES group surpassed that of the groups treated with MP or CEES independently. Notably, the MP+CEES group demonstrated significant activation of the VEGFR-3 and PI3K/AKT/mTOR signaling pathways, implying a substantial involvement of lymphatic vessel impairment in this pathology. This study successfully established a mouse model of PB induced by MP using a two-step method. Lymphatic vessel impairment is a pivotal element in the pathogenetic mechanisms underlying this disease entity. This accomplishment will aid in further research into treatment methods for patients with PB caused by MP.

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.

New targets of nascent lymphatic vessels in ocular diseases

Recent advancements in the field of endothelial markers of lymphatic vessels and lymphangiogenic factors have shed light on the association between several ocular diseases and ocular nascent lymphatic vessels. The immune privilege of corneal tissue typically limits the formation of lymphatic vessels in a healthy eye. However, vessels in the eyes can potentially undergo lymphangiogenesis and be conditionally activated. It is evident that nascent lymphatic vessels in the eyes contribute to various ocular pathologies. Conversely, lymphatic vessels are present in the corneal limbus, ciliary body, lacrimal glands, optic nerve sheaths, and extraocular muscles, while a lymphatic vasculature-like system exists in the choroid, that can potentially cause several ocular pathologies. Moreover, numerous studies indicate that many ocular diseases can influence or activate nascent lymphatic vessels, ultimately affecting patient prognosis. By understanding the mechanisms underlying the onset, development, and regression of ocular nascent lymphatic vessels, as well as exploring related research on ocular diseases, this article aims to offer novel perspectives for the treatment of such conditions.

Pseudolaric Acid B Inhibits FLT4-induced Proliferation and Migration in Non-small Cell Lung Cancer

OBJECTIVES

Non-Small Cell Lung Cancer (NSCLC) has attracted much attention on account of the high incidence and mortality of cancers. Vascular Endothelial Growth Factor Receptor 3 (VEGFR3/FLT4), which is a highly expressed receptor in NSCLC, greatly regulates cancer proliferation and migration. Pseudolaric Acid B (PAB) is a diterpenoid acid with antitumor activity isolated from Pseudolarix kaempferi. This study aimed to explore the inhibitory effect of PAB targeting FLT4 in NSCLC.

METHODS

Cell membrane chromatography was used to evaluate the affinity of PAB binding on FLT4. NCIH1299 cells were used in this study, and an MTT assay was performed to determine the anti-proliferation effect of PAB. Cell cycle analysis was conducted to study the cycle arrest of PAB. Wound healing and Transwell assays assessed the rate of cell migration. Western blot analysis evaluated the expression of related proteins.

RESULTS

PAB showed strong affinity to FLT4 with a KD value of 3.01 × 10- 6 M. Targeting FLT4 by PAB inactivated downstream P38MAPK and PI3K/AKT pathways, which inhibited the proliferation of NCI-H1299 cells. Meanwhile, PAB promoted G2/M phase arrest by influencing CyclinB1 and CDK1 complex formation to inhibit NCI-H1299 cell growth, but the effect was attenuated by knocking down the FLT4. Besides, PAB regulated MMP9 secretion through the Wnt/β-catenin signaling pathway to inhibit NCI-H1299 cell migration. However, the ability of PAB to inhibit migration was significantly weakened by FLT4 knockdown in NCI-H1299 cells.

CONCLUSION

PAB can inhibit the proliferation and migration of NSCLC cells through targeting FLT4 and is expected to be a promising FLT4 inhibitor for NSCLC treatment.