Deletion of RAMP1 Signaling Enhances Diet-induced Obesity and Fat Absorption via Intestinal Lacteals in Mice.

BACKGROUND/AIM: Intestinal lymphatic vessels (lacteals) play a critical role in the absorption and transport of dietary lipids into the circulation. Calcitonin gene-related peptide and receptor activity-modifying protein 1 (RAMP1) are involved in lymphatic vessel growth. This study aimed to examine the role of RAMP1 signaling in lacteal morphology and function in response to a high-fat diet (HFD). MATERIALS AND METHODS: RAMP1 deficient (RAMP1-/-) or wild-type (WT) mice were fed a normal diet (ND) or HFD for 8 weeks. RESULTS: RAMP1-/- mice fed a HFD had increased body weights compared to WT mice fed a HFD, which was associated with high levels of total cholesterol, triglycerides, and glucose. HFD-fed RAMP1-/- mice had shorter and wider lacteals than HFD-fed WT mice. HFD-fed RAMP1-/- mice had lower levels of lymphatic endothelial cell gene markers including vascular endothelial growth factor receptor 3 (VEGFR3) and lymphatic vascular growth factor VEGF-C than HFD-fed WT mice. The concentration of an absorbed lipid tracer in HFD-fed RAMP1-/- mice was higher than that in HFD-fed WT mice. The zipper-like continuous junctions were predominant in HFD-fed WT mice, while the button-like discontinuous junctions were predominant in HFD-fed RAMP1-/- mice. CONCLUSION: Deletion of RAMP1 signaling suppressed lacteal growth and VEGF-C/VEGFR3 expression but accelerated the uptake and transport of dietary fats through discontinuous junctions of lacteals, leading to excessive obesity. Specific activation of RAMP1 signaling may represent a target for the therapeutic management of diet-induced obesity.

Inhibition of TP signaling promotes endometriosis growth and neovascularization.

Endometriosis is highly dependent on angiogenesis and lymphangiogenesis. Prostaglandin E2, an arachidonic acid metabolite, has been shown to promote the formation of new blood and lymphatic vessels. However, the role of another arachidonic acid metabolite, thromboxane A2 (TXA2) in angiogenesis and lymphangiogenesis during endometriosis remains largely unexplored. Using a murine model of ectopic endometrial transplantation, fragments from the endometrium of WT donor mice were transplanted into the peritoneal walls of recipient WT mice (WT→WT), resulting in an increase in both the area and density of blood and lymphatic vessels. Upon transplantation of endometrial tissue from thromboxane prostanoid (TP) receptor (TXA2 receptor)­deficient (TP­/­) mice into TP­/­ mice (TP­/­â†’TP­/­), an increase in implant growth, angiogenesis, and lymphangiogenesis were observed along with upregulation of pro­angiogenic and lymphangiogenic factors, including vascular endothelial growth factors (VEGFs). Similar results were obtained using a thromboxane synthase (TXS) inhibitor in WT→WT mice. Furthermore, TP­/­â†’TP­/­ mice had a higher number of F4/80+ cells than that of WT→WT mice, with increased expression of genes related to the anti­inflammatory macrophage phenotype in endometrial lesions. In cultured bone marrow (BM)­derived macrophages, the levels of VEGF­A, VEGF­C, and VEGF­D decreased in a TP­dependent manner. Furthermore, TP signaling affected the polarization of cultured BM­derived macrophages to the anti­inflammatory phenotype. These findings imply that inhibition of TP signaling promotes endometrial implant growth and neovascularization.

Thromboxane prostanoid signaling in macrophages attenuates lymphedema and facilitates lymphangiogenesis in mice : TP signaling and lymphangiogenesis.

BACKGROUND: Accumulating evidence suggests that prostaglandin E2, an arachidonic acid (AA) metabolite, enhances lymphangiogenesis in response to inflammation. However, thromboxane A2 (TXA2), another AA metabolite, is not well known. Thus, this study aimed to determine the role of thromboxane prostanoid (TP) signaling in lymphangiogenesis in secondary lymphedema. METHODS AND RESULTS: Lymphedema was induced by the ablation of lymphatic vessels in mouse tails. Compared with wild-type mice, tail lymphedema in Tp-deficient mice was enhanced, which was associated with suppressed lymphangiogenesis as indicated by decreased lymphatic vessel area and pro-lymphangiogenesis-stimulating factors. Numerous macrophages were found in the tail tissues of Tp-deficient mice. Furthermore, the deletion of TP in macrophages increased tail edema and decreased lymphangiogenesis and pro-lymphangiogenic cytokines, which was accompanied by increased numbers of macrophages and gene expression related to a pro-inflammatory macrophage phenotype in tail tissues. In vivo microscopic studies revealed fluorescent dye leakage in the lymphatic vessels in the wounded tissues. CONCLUSIONS: The results suggest that TP signaling in macrophages promotes lymphangiogenesis and prevents tail lymphedema. TP signaling may be a therapeutic target for improving lymphedema-related symptoms by enhancing lymphangiogenesis.

Recovery of Liver Sinusoidal Endothelial Cells Following Monocrotaline-induced Liver Injury.

BACKGROUND/AIM: Although the pathology of sinusoidal obstruction syndrome (SOS) is characterized by damage to liver sinusoidal endothelial cells (LSECs), the processes underlying LSEC repair are incompletely understood. The angiopoietin (Ang)/Tie system contributes to angiogenesis. The present study aimed to examine the processes of LSEC repair and the involvement of the Ang/Tie pathway in LSEC recovery. MATERIALS AND METHODS: Experimentally, SOS was induced by intraperitoneal injection of monocrotaline (MCT) to C57/BL6 mice. RESULTS: Levels of LSEC markers were up-regulated during the repair phase of MCT-induced hepatotoxicity. The damaged LSECs recovered from the injury by expanding LSECs expressing lymphatic vessel endothelial hyaluronan receptor-1 (LYVE-1) in the peri-central area of MCT-injured livers, while LSECs in the same area of uninjured livers lacked LYVE-1 expression. Bone marrow (BM)-derived cells did not incorporate into the restored LSECs. Tie2 expression was related to LSEC recovery in MCT-injured liver tissue. CONCLUSION: The resident LSECs neighboring uninjured tissue replace damaged LSECs in MCT-injured livers. Tie2 is involved in LSEC recovery from MCT-induced hepatotoxicity.