Differential regulation of lymphatic junctional morphology and the potential effects on cardiovascular diseases

An arabinogalactan isolated from Cynanchum atratum promotes lymphangiogenesis and lymphatic vessel remodeling to alleviate secondary lymphedema

Secondary lymphedema is a chronic and incurable disease lacking satisfactory therapeutic drugs. It primarily results from lymphatic vessel dysfunction resulting from factors such as tumor-related surgery, injury, or infection. Promoting lymphangiogenesis and lymphatic vessel remodeling is crucial for restoring tissue fluid drainage and treating secondary lymphedema. In this study, we discovered that the oral administration of a type-II arabinogalactan (CAPW-1, molecular weight: 64 kDa) significantly promoted lymphangiogenesis and alleviated edema in mice with secondary lymphedema. Notably, the tail diameter of the CAPW-1200 group considerably decreased in comparison to that of the lymphedema group, with an average diameter difference reaching 0.98 mm on day 14. CAPW-1 treatment also reduced the average thickness of the subcutaneous area in the CAPW-1200 group to 0.37 mm (compared with 0.73 mm in the lymphedema group). It also facilitated the return of injected indocyanine green (ICG) from the tail tip to the sciatic lymph nodes, indicating that CAPW-1 promoted lymphatic vessel remodeling at the injury site. In addition, CAPW-1 enhanced the proliferation and migration of lymphatic endothelial cells. This phenomenon was associated with the activation of the toll-like receptor 4 (TLR4)/nuclear factor-κB (NF-κB) signaling pathway, thereby promoting the expression of vascular endothelial growth factor-C (VEGF-C), which can be abolished using a TLR4 antagonist. Despite these findings, CAPW-1 did not alleviate the symptoms of lymphedema or restore lymphatic drainage in VEGFR3flox/flox/Prox1-CreERT2 mice. In summary, CAPW-1 alleviates secondary lymphedema by promoting lymphangiogenesis and lymphatic vessel remodeling through the activation of the TLR4/NF-κB/VEGF-C signaling pathway, indicating its potential as a therapeutic lymphangiogenesis agent for patients with secondary lymphedema.

Lymphatic vessel: origin, heterogeneity, biological functions, and therapeutic targets

Lymphatic vessels, comprising the secondary circulatory system in human body, play a multifaceted role in maintaining homeostasis among various tissues and organs. They are tasked with a serious of responsibilities, including the regulation of lymph absorption and transport, the orchestration of immune surveillance and responses. Lymphatic vessel development undergoes a series of sophisticated regulatory signaling pathways governing heterogeneous-origin cell populations stepwise to assemble into the highly specialized lymphatic vessel networks. Lymphangiogenesis, as defined by new lymphatic vessels sprouting from preexisting lymphatic vessels/embryonic veins, is the main developmental mechanism underlying the formation and expansion of lymphatic vessel networks in an embryo. However, abnormal lymphangiogenesis could be observed in many pathological conditions and has a close relationship with the development and progression of various diseases. Mechanistic studies have revealed a set of lymphangiogenic factors and cascades that may serve as the potential targets for regulating abnormal lymphangiogenesis, to further modulate the progression of diseases. Actually, an increasing number of clinical trials have demonstrated the promising interventions and showed the feasibility of currently available treatments for future clinical translation. Targeting lymphangiogenic promoters or inhibitors not only directly regulates abnormal lymphangiogenesis, but improves the efficacy of diverse treatments. In conclusion, we present a comprehensive overview of lymphatic vessel development and physiological functions, and describe the critical involvement of abnormal lymphangiogenesis in multiple diseases. Moreover, we summarize the targeting therapeutic values of abnormal lymphangiogenesis, providing novel perspectives for treatment strategy of multiple human diseases.

Lymphatic Endothelial-to-Myofibroblast Transition: A Potential New Mechanism Underlying Skin Fibrosis in Systemic Sclerosis

At present, only a few reports have addressed the possible contribution of the lymphatic vascular system to the pathogenesis of systemic sclerosis (SSc). Based on the evidence that blood vascular endothelial cells can undertake the endothelial-to-myofibroblast transition (EndMT) contributing to SSc-related skin fibrosis, we herein investigated whether the lymphatic endothelium might represent an additional source of profibrotic myofibroblasts through a lymphatic EndMT (Ly-EndMT) process. Skin sections from patients with SSc and healthy donors were immunostained for the lymphatic endothelial cell-specific marker lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) in combination with α-smooth muscle actin (α-SMA) as the main marker of myofibroblasts. Commercial human adult dermal lymphatic microvascular endothelial cells (HdLy-MVECs) were challenged with recombinant human transforming growth factor-β1 (TGFβ1) or serum from SSc patients and healthy donors. The expression of lymphatic endothelial cell/myofibroblast markers was measured by quantitative real-time PCR, Western blotting and immunofluorescence. Collagen gel contraction assay was performed to assess myofibroblast-like cell contractile ability. Lymphatic endothelial cells in intermediate stages of the Ly-EndMT process (i.e., coexpressing LYVE-1 and α-SMA) were found exclusively in the fibrotic skin of SSc patients. The culturing of HdLy-MVECs with SSc serum or profibrotic TGFβ1 led to the acquisition of a myofibroblast-like morphofunctional phenotype, as well as the downregulation of lymphatic endothelial cell-specific markers and the parallel upregulation of myofibroblast markers. In SSc, the Ly-EndMT might represent a previously overlooked pathogenetic process bridging peripheral microlymphatic dysfunction and skin fibrosis development.