Sung Hk

Angiogenic Role of LYVE-1–Positive Macrophages in Adipose Tissue

Here we report the discovery of a characteristic dense vascular network (DVN) in the tip portion of epididymal adipose tissue in adult mice. The DVN is formed by angiogenesis rather than by vasculogenesis, and has functional blood circulation. This DVN and its subsequent branching may provide a new functional route for adipogenesis. The recruitment, infiltration, and accumulation of bone marrow-derived LYVE-1+ macrophages in the tip region are crucial for the formation of the DVN. Matrix metalloproteinases (MMPs) and the VEGF-VEGFR2 system are responsible not only for the formation of the DVN, but also for the recruitment and infiltration of LYVE-1+ macrophages into the epididymal adipose tissue tip region. SDF-1, but not the MCP-1-CCR2 system, is a critical factor in recruitment and ongoing retention of macrophages in this area. We also demonstrate that the tip region of epididymal adipose tissue is highly hypoxic, and thus provides a microenvironment conducive to the high expression and enhanced activities of VEGF, VEGFR2, MMPs, and SDF-1 in autocrine and paracrine manners, to create an ideal niche for the recruitment, retention, and angiogenic action of macrophages. These findings shed light on the complex interplay between macrophage infiltration, angiogenesis, and adipogenesis in the tip region of adult epididymal adipose tissue, and provide novel insight into the regulation of alternative outgrowth of adipose tissue.

Lymphatic development in mouse small intestine

Lymphatic vessels in the small intestine serve as essential conduits for the absorption and transport of lipids from the intestine to the thoracic duct. Although the morphology and function of the intestinal lymphatic vasculature are well known, little is known about the embryonic development of these vessels. In this study, we examined development of lymphatic and blood vasculatures in the intestinal tube during mouse embryonic development by immunostaining with recently discovered molecular markers for lymphatic endothelial cells: LYVE‐1, VEGFR3, Prox‐1, and podoplanin. Immature lymphatics became detectable in mesentery, but not in intestinal tube, around E13.5–E14.5, while organized lymphatic vessel plexuses and capillaries were observed in intestinal tube and villi around E17.5. These lymphatic plexuses and capillaries in the intestinal tube appeared to be formed through an active branching process associated with activation of VEGFR3 and involvement of LYVE‐1+ macrophages. Our data also reveal that the lymphatic vessels in the intestinal tube, unlike the blood vessels, have not originated from the mesoderm of intestine. All lymphatic vessels in the intestinal tube originated by extension of mesenteric lymphatic vessels through an active branching process. Although the formation of lymphatic vessels follows the formation of blood vessels in the intestine, a mature lymphatic vasculature is formed before birth. Together, our study reveals the temporal and spatial windows of intestinal lymphatic development during embryonic development in mouse. Developmental Dynamics 236: 2020–2025, 2007.