From the preface: "The importance of the lymphatic system has been known for a long time. It was therefore surprising to learn that the status of dermal lymphatics, under both normal and pathological conditions of man, had been largely neglected to date, particularly with respect to their ultrastructure. Moreover, the existing information is incomplete, relating only to narrow segments of the skin, and it is controversial. This monograph represents an effort to overcome some of the existing deficiencies in the area of the structure with emphasis on ultrastructure of lymphatic capillaries.
It is an account of our experience in the evaluation of dermal lymphatics in normal, edematous, and some other pathological conditions in man and in experimental animals.
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It is hoped that this information will prove useful for other investigators as a basis for evaluation of the structural and functional status of dermal lymphatics under a wide variety of pathological conditions. Lymphaticovenous Anastomoses. Pulsatile contraction of perivascular SMCs in major collecting vessels is known to contribute to the efficiency of lymph drainage Kunert et al. However, whether such contractions are required during normal physiology, or even in pathology, has not been thoroughly assessed.
Furthermore the functional impact of a similar contraction in the skin had not been studied. Here, Pdgfb iLECKO mice displayed severely impaired dermal lymphatic vessel contraction, owing to loss of SMCs, but with no apparent lymphedema and no recordable change in lymphatic drainage in the applied experimental setup Fig. It should be noted that even genetic mouse mutants that display severe lymphatic vessel defects, such as hypoplasia of lymphatic capillaries in the mouse model of Milroy disease, a form of primary lymphedema Karkkainen et al.
It is therefore likely that loss of dermal SMCs would have more dramatic consequences in humans. Ectopic SMC coverage of the lymphatic capillaries has been observed in both primary and secondary lymphedema Yu et al. These data, together with the increased SMC coverage in individuals with secondary lymphedema, indicate that other alterations are required in addition to induced PDGFB expression.
Extracellular matrix alterations may also influence integrin-mediated SMC migration and adhesion, adding to the complexity. In addition the retention motif of PDGFB can be cleaved by proteases, with potential differential abundance or activity in capillaries and collecting vessels. Finally, it is possible that SMC recruitment to lymphatic capillaries is actively inhibited under normal physiological conditions. It has been shown that Sema3-Nrp1-plexin A1 signalling prevents recruitment of SMCs to the valve regions of collecting vessels to ensure normal valve morphogenesis and function Bouvree et al.
Precisely how the lymphatic vasculature acquires and maintains its hierarchical structure of capillaries and collecting vessels is not well understood Schulte-Merker et al. Here, we demonstrate that the establishment of vessel identity is mainly unaffected by a complete inhibition of lymphatic mural cell recruitment — a process here shown to be strictly dependent on lymphatic endothelial PDGFB expression and pericellular retention.
We also clarified that erroneous spatial expression of PDGFB is unlikely to be the single cause of ectopic recruitment of SMCs to lymphatic capillaries in disease. The genetic mouse model of lymph vessel-specific mural cell deficiency provides a novel and specific tool for further studies on the importance of SMCs in lymphatic development and lymphedema. All animal experiments included male and female mice. Pdgfrb-eGFP mice [Gensat. To evaluate differential Pdgfb expression within the dermal lymphatic vasculature, 4-hydroxytamoxifen 4-OHT was injected into the abdominal cavity at P14 and mice were sacrificed at P Mice were sacrificed at P21 to analyse the dermal ear vasculature.
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To analyse mesenteric lymphatic vessels and popliteal lymphatic vessels of the hindlimb at E All animal experiments were carried out in accordance with their guidelines. To dissect the ear and expose lymphatic vasculature, hair was removed with fine surgical forceps and scissors Agnthos , and two layers of superficial skin were separated to expose the dermal layer of the ear.
Muscles and fat were carefully trimmed away. To isolate the popliteal vessels from the hindlimb of pups at P12, the skin was removed and the exposed blood and lymphatic vessels were dissected together with the underlying muscles. Samples were then blocked in PBS with 1. Samples were then washed in PBS with 0. Samples were washed in PBS, permeabilized in 0. Secondary antibodies conjugated with Alexa fluorophores were from Jackson ImmunoResearch Laboratories and Life Technologies for staining of mesenteric vessels; for staining of other tissues.
For evaluation of dermal lymphatic vessel contraction, mice were anaesthetized with isoflurane and hair on the dorsal side of the ears was removed using a sharp blade. The head and nose of the mouse was fixed to a customized head holder device and the left ear was glued to a customized plastic plate to prevent movement. The images represent maximum intensity projections of z stacks that, in the case of overviews, were stitched from multiple tile scan images, either manually using Adobe Photoshop Adobe or automatically by the Leica LAF software.
Intensity Adjustments in Fig. To quantify collecting vessel width and SMC coverage, regions with excessive branches and intersecting blood vessels were excluded and vessel width was measured along the vessel and averaged by number of measurements. Dermal lymphatic endothelial cells were sorted as previously described Martinez-Corral et al. Statistical analysis was performed using GraphPad Prism GraphPad Software and all differences were determined by unpaired Student's t -test, except for the comparison of the number of contraction sites between Pdgfb iLECKO mice and control mice, for which a Mann-Whitney test was applied.
Investigators were not blinded to the group allocation when performing experiments and assessing outcomes. Competing interests. Author contributions. Conceptualization: Y. This study was supported by grants from William K. Bowes, Jr. Foundation L. Deposited in PMC for immediate release.
The Dermal Lymphatic Capillaries | Judit Daroczy | Springer
The snippet could not be located in the article text. This may be because the snippet appears in a figure legend, contains special characters or spans different sections of the article. PMID: Yang Zhang 2 Uppsala University, Dept. Christer Betsholtz 2 Uppsala University, Dept.
Received Dec 10; Accepted Aug Published by The Company of Biologists Ltd. This article has been cited by other articles in PMC. Abstract Tissue fluid drains through blind-ended lymphatic capillaries, via smooth muscle cell SMC -covered collecting vessels into venous circulation.
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Establishment of collecting versus capillary LEC identities does not require SMC interaction The basement membrane BM of collecting vessels is continuous, whereas that of capillaries is described as discontinuous Pflicke and Sixt, PDGFB is required for SMC recruitment to the large-diameter collecting vessels of the hind limb and mesentery Recruitment of mural cells to larger diameter collecting vessels, such as the popliteal and mesenteric collecting vessels, occurs during embryogenesis.
Deficient interaction between PDGFB and extracellular matrix causes defective SMC recruitment to dermal collecting lymphatic vessels Mural cell recruitment to the blood vasculature relies not only on endothelial cell production of PDGFB but also on its binding to the extracellular matrix. In vivo imaging of dermal ear lymphatic vessel contraction For evaluation of dermal lymphatic vessel contraction, mice were anaesthetized with isoflurane and hair on the dorsal side of the ears was removed using a sharp blade.
Statistics Statistical analysis was performed using GraphPad Prism GraphPad Software and all differences were determined by unpaired Student's t -test, except for the comparison of the number of contraction sites between Pdgfb iLECKO mice and control mice, for which a Mann-Whitney test was applied.
Footnotes Competing interests The authors declare no competing or financial interests. Author contributions Conceptualization: Y. Funding This study was supported by grants from William K. References Alitalo K. The lymphatic vasculature in disease.
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