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BMP-SMADs: a new take on lymphatic vessel development

Boek - Dissertatie

Background: Lymphatic vessels are indispensable for the uptake of extravasated fluids from the capillary beds, absorption of lipids from the intestine and the immune system. Lymphatic development starts at embryonic day 9.75 (E9.75) in the mouse. Lymphangiogenesis results in a network of collecting lymph vessels and capillaries. From E14.5 onwards valves are developing necessary for functional lymphatic vessels. Several diseases, like lymphedema and cancer are caused by a dysfunctioning lymphatic system. At present, the molecular mechanisms important for lymphangiogenesis in normal and pathological conditions are not completely understood and further research is necessary. Preliminary data suggested that SMAD1 and SMAD5, two intracellular signaling proteins from the BMP signaling pathway, participate in lymphangiogenesis. Mouse embryos with one active allele either for Smad1 or Smad5 in endothelium survive until E11.5-E13.5 and display besides cardiovascular defects also lymphatic defects. The aim of this study is to determine the role of BMP-SMAD1/5 mediated signaling during postnatal lymphangiogenesis using a Tamoxifen inducible Prox-1-CreERT2;Smad1fl/fl;Smad5fl/fl mouse. Methods: First the tamoxifen administration regime was optimized to obtain efficient Cre mediated recombination. For analysis mutant and control pups were weighted every day and sacrificed at postnatal stages P6, P8 and P10. Cornea, ears, skin tissue, intestine, mesentery, diaphragm, trachea and heart were dissected. Thereafter several marker analyses were performed to visualize the lymphatic and blood vasculature in different organs on paraffin and vibratome sections or whole mount. Results: Daily intraperitoneal injections (3mg Tamoxifen per 40g mouse) in pups at postnatal stages 1-5 resulted in a recombination efficiency of 70-80% and low mortality. By first observations mutants did not show edema, but had skin defects. Sections of skin tissue temporarily demonstrated dilated lymphatic vessels at P6 and an increased infiltration of inflammatory cells at P10. Furthermore, mesenteric lymphatic vessels were dilated as well and a delay in lymphatic valve development was observed. Interestingly, PROX-1 remains ubiquitously present in lymphatic vessels in mutants as opposed to the enriched presence of PROX-1 in valves in control littermates. In contradiction to the sprouting blood vessels, lymphatic specification and sprouting is not dependent on SMAD1/5. Conclusion: Altogether these data support a role for SMAD1/5 during postnatal maturation and valvulogenesis but further research is necessary to unravel the underlying molecular mechanisms. In vitro approaches and a more detailed histopathological analysis will give a better understanding of the role of Smad1/5 in lymphangiogenesis and explain the observed defects.
Jaar van publicatie:2019
Toegankelijkheid:Closed