Maldevelopment of dermal lymphatics in Wnt5a-knockout-mice

Abstract

Maintenance of tissue homeostasis and immune surveillance are important functions of the lymphatic vascular system. Lymphatic vessels are lined by lymphatic endothelial cells (LECs). By gene micro-array expression studies we recently compared human lymphangioma-derived LECs with umbilical vein endothelial cells (HUVECs). Here, we followed up on these studies. Besides well-known LEC markers, we observed regulation of molecules involved in immune regulation, acetylcholine degradation and platelet regulation. Moreover we identified differentially expressed WNT pathway components, which play important roles in the morphogenesis of various organs, including the blood vascular system. WNT signaling has not yet been addressed in lymphangiogenesis. We found high expression of FZD3, FZD5 and DKK2 mRNA in HUVECs, and WNT5A in LECs. The latter was verified in normal skin-derived LECs. With immunohistological methods we detected WNT5A in LECs, as well as ROR1, ROR2 and RYK in both LECs and HUVECs. In the human, mutations of WNT5A or its receptor ROR2 cause the Robinow syndrome. These patients show multiple developmental defects including the cardio-vascular system. We studied Wnt5a-knockout (ko) mouse embryos at day 18.5. We show that the number of dermal lymphatic capillaries is significantly lower in Wnt5a-null-mice. However, the mean size of individual lymphatics and the LEC number per vessel are greater. In sum, the total area covered by lymphatics and the total number of LECs are not significantly altered. The reduced number of lymphatic capillaries indicates a sprouting defect rather than a proliferation defect in the dermis of Wnt5a-ko-mice, and identifies Wnt5a as a regulator of lymphangiogenesis.

Lack of phosphomannomutase 2 affects Xenopus laevis morphogenesis and the non‐canonical Wnt5a/Ror2 signalling

“…In the case that the Pmm2 morpholino was co-injected with wnt5a, a significant loss of papc expression was detected (ror2-wnt5a +Pmm2 Mo). As negative controls, uninjected and ror2 injected caps were analysed, showing background papc signals length, as well as shortening of the mandible, head, limbs and tail (Buttler et al 2013). Furthermore mutations in the wnt5a and ror2 gene lead to the Robinow syndrome in man, which is characterized foremost by short stature and abnormalities of the head and facial area (Person et al 2010;Brunetti-Pierri et al 2008;Bokhoven et al 2000), also resembling symptoms found in the Xenopus Pmm2 morphants.…”

Development of the lymphatic system: new questions and paradigms

“…Wnt5a is also involved in lymphatic formation in the mouse, although at later developmental stages. Specifically, Wnt5a KO mice display defects in dermal lymphatic sprouting, which were primarily attributed to activation of the non-canonical pathway (Buttler et al, 2013).…”

Monocyte-derived Wnt5a regulates inflammatory lymphangiogenesis

“…This discrepancy is not surprising since Wnt signaling often presents distinct outcomes depending on cell or tissue type and developmental versus pathological stage [11]. Recently, a study on Wnt5a conventional (non-conditional) knockout mice showed reduced number but increased size of dermal lymphatic capillaries at embryonic day 18.5 [12], which indicates a developmental defect resulting from cumulative role of Wnt5a in all cell types, known and yet-to-be determined. In contrast, we observed reduced number but not increased size of lymphatic vessels in this inflammation study on adult mice taking advantage of the cell type-specific conditional knockout mice.…”