Chylomicrons Regulate Lacteal Permeability and Intestinal Lipid Absorption

Abstract

Background: Lymphatic vessels are responsible for tissue drainage, and their malfunction is associated with chronic diseases. Lymph uptake occurs via specialized open cell-cell junctions between capillary lymphatic endothelial cells (LECs), whereas closed junctions in collecting LECs prevent lymph leakage. LEC junctions are known to dynamically remodel in development and disease, but how lymphatic permeability is regulated remains poorly understood. Methods: We used various genetically engineered mouse models in combination with cellular, biochemical, and molecular biology approaches to elucidate the signaling pathways regulating junction morphology and function in lymphatic capillaries. Results: By studying the permeability of intestinal lacteal capillaries to lipoprotein particles known as chylomicrons, we show that ROCK (Rho-associated kinase)-dependent cytoskeletal contractility is a fundamental mechanism of LEC permeability regulation. We show that chylomicron-derived lipids trigger neonatal lacteal junction opening via ROCK-dependent contraction of junction-anchored stress fibers. LEC-specific ROCK deletion abolished junction opening and plasma lipid uptake. Chylomicrons additionally inhibited VEGF (vascular endothelial growth factor)-A signaling. We show that VEGF-A antagonizes LEC junction opening via VEGFR (VEGF receptor) 2 and VEGFR3-dependent PI3K/AKT activation of the small GTPase RAC1, thereby restricting RhoA/ROCK–mediated cytoskeleton contraction. Conclusions: Our results reveal that antagonistic inputs into ROCK-dependent cytoskeleton contractions regulate the interconversion of lymphatic junctions in the intestine and in other tissues, providing a tunable mechanism to control the lymphatic barrier.

VE-cadherin junction dynamics in initial lymphatic vessels promotes lymph node metastasis

“…The lymphatic vessels in Vegfr2 Y949F/Y949F mice were resistant to VEGFA/VEGFC–induced increase in circular VE-cadherin shapes. Together, these data indicate that the Y949 site in VEGFR2 is dispensable for VEGFA-induced zippering of lymphatic junctions which is in agreement with a recent study ( Zarkada et al, 2023 ). However, importantly, signaling downstream of Y949 in VEGFR2 is required for VEGFA/VEGFC–induced internalization and turnover of VE-cadherin.…”

“…Hypoxia-induced increase in VEGFA levels in the tumor microenvironment correlates with disintegration of VE-cadherin junctions and dismantling of the blood vascular barrier ( Weis et al, 2004 ; Li et al, 2016 ). In lacteal and dermal lymphatic vessels, VEGFA has been shown to induce zippering of junctions through activations of VEGFR2 ( Zhang et al, 2018 ; Zarkada et al, 2023 ). We hypothesized that the zippering of dermal lymphatic junctions and the shape shift of VE-cadherin fragments in the tumor periphery may be related to production of VEGFA and/or VEGFC, which both bind to VEGFR2 ( Simons et al, 2016 ), in the tumor microenvironment.…”

“…Signaling pathways involved in VEGFA-mediated zippering of lymphatic junctions have been revealed in recent studies ( Zhang et al, 2018 ; Zarkada et al, 2023 ). However, VEGFA-induced signaling regulating VE-cadherin dynamics in lymphatic vessels has not been identified.…”

Parenchymal cues define Vegfa-driven venous angiogenesis by activating a sprouting competent venous endothelial subtype

“…The concept emerging from these observations is that organo-typical features in vascular branching may evolve from the selective coupling of endothelial growth factor receptors and the heterogeneity in the repertoire of parenchymal derived signals that can be used to activate such receptor pairs. We observed coupling of Kdrl and Apelin-receptor-a, but in other scenarios different genetic interactions may exist for example between Kdr/Kdrl/Aplnr with Flt4 54 , Neuropilin (Nrp) and Plexin receptors (Plxn) 55 – 58 , allowing myriad combinations with ligands of the Semaphorin and Vegf family. In a reductionist view, as opposed to the Dll4/Notch tango of the reference model, the choreographed dances in the revised organo-typical scenario may rely on up to four ligand/receptors pairs.…”

Mechanisms of Lymphatic Endothelial Cell Junction Transformations

“…In this issue of Circulation Research , Zarkada et al 3 elegantly investigated the effects of chylomicrons on lacteal permeability and lipid absorption in the intestine. By comparing postnatal day 0.5 (P0.5) mice fed with milk to prenatal embryonic day 20.5 (E20.5) mice that were not fed, the authors discovered that lacteals from fed mice had predominantly button-type junctions while nonfed mice had more zipper junctions.…”