Lymph Flow Induces the Postnatal Formation of Mature and Functional Meningeal Lymphatic Vessels

Abstract

Recently, the presence of lymphatics has been demonstrated and characterized in the dura mater, which is in contrast to the well-accepted view indicating the lack of a classical lymphatic drainage system of the central nervous system (CNS). Moreover, the role of meningeal lymphatics in the pathogenesis of Alzheimer's disease and multiple sclerosis was suggested. However, the possible regulators of the developmental program and function of meningeal lymphatics remain unclear. Here, we aimed at characterizing the lymph flow dependence of the developmental program and function of the meningeal lymphatics. First, we demonstrated that lymphatics present in the dura mater are involved in the uptake and transport of macromolecules from the CNS. Meningeal lymphatics develop during the postnatal period which process involves the maturation of the vessels. The formation of mature meningeal lymphatics coincides with the increase of the drainage of macromolecules from the CNS to the deep cervical lymph nodes. Importantly, the structural remodeling and maturation of meningeal lymphatics is impaired in Plcγ 2 −/− mice with reduced lymph flow. Furthermore, macromolecule uptake and transport by the meningeal lymphatics are also affected in Plcγ 2 −/− mice. Collectively, lymph flow-induced mechanical forces are required for the postnatal formation of mature and functional meningeal lymphatic vessels. Defining lymph flow-dependence of the development and function of meningeal lymphatics may lead to better understanding of the pathogenesis of neurological diseases including Alzheimer's disease and multiple sclerosis.

CNS-Draining Meningeal Lymphatic Vasculature: Roles, Conundrums and Future Challenges

“…In fact, loss-of-function studies have shown that both the development and maintenance of adult meningeal LVs are dependent on VEGF-C signaling through VEGFR3, but not on VEGF-D signaling ( Antila et al, 2017 ). However, a more recent study has shown that mice lacking PLC-γ2 also present a structurally and functionally impaired meningeal lymphatic system, thus suggesting that meningeal lymphatic development might not be exclusively dependent on VEGFR3 signaling ( Bálint et al, 2020 ). Primordial meningeal LECs stem from and around the veins at the skull foramina and later extend from the basal into the lateral and dorsal meninges along the major arteries (pterygopalatine and middle meningeal arteries) and venous sinuses ( Aspelund et al, 2015 ; Antila et al, 2017 ; Izen et al, 2018 ; Ahn et al, 2019 ).…”

Mechanosensation and Mechanotransduction by Lymphatic Endothelial Cells Act as Important Regulators of Lymphatic Development and Function

“…Lymph flow is reportedly reduced in mice with impaired PDPN/CLEC-2/PLCγ2 signaling [ 160 , 161 , 162 ] due to an improper separation of the blood and lymphatic vessel systems [ 156 ]. These data propose that these genetic mouse models provide ideal tools to study the roles of lymphatic flow in vivo.…”

“…Importantly, while the formation of immature mesenteric pre-lymphatics is intact in mice with impaired lymph flow due to a lack of CLEC-2, organ-specific maturation of the mesenteric lymphatic vessels is impaired in these embryos [ 160 ], and the phenotype is also present in PLCγ2-deficient embryos [ 162 ]. In addition, the postnatal developmental program of the meningeal lymphatic vasculature is also affected in PLCγ2-deficient mice [ 162 ]. These in vivo findings underline the importance of mechanical forces in the organ-specific developmental program of the lymphatic vessels.…”

Reduced Prenatal Pulmonary Lymphatic Function Is Observed in Clp1K/K Embryos With Impaired Motor Functions Including Fetal Breathing Movements in Preparation of the Developing Lung for Inflation at Birth

“…To monitor lymphatic function pregnant Clp1 K/+ females timemated with Clp1 K/+ males were anesthetized. 0.5 µl of 70 kDa RhD (Life Technologies) at 10 mg/ml concentration was injected through the uterus and chest wall into the lung of E18.5 Clp1 K/K and littermate control embryos on Flt4 YFP lymphatic reporter background as described before (Jakus et al, 2014;Bálint et al, 2020). Selective uptake and transport of large molecular weight RhD in fluorescent reporter positive lymphatic vessels were monitored 60 min after the injection by a fluorescent Nikon SMZ25 stereomicroscope equipped with Nikon DS-Ri2 camera.…”