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Duranova H, Kuzelova L, Borotova P, Simora V, Fialkova V. Human Umbilical Vein Endothelial Cells as a Versatile Cellular Model System in Diverse Experimental Paradigms: An Ultrastructural Perspective. MICROSCOPY AND MICROANALYSIS : THE OFFICIAL JOURNAL OF MICROSCOPY SOCIETY OF AMERICA, MICROBEAM ANALYSIS SOCIETY, MICROSCOPICAL SOCIETY OF CANADA 2024; 30:419-439. [PMID: 38817111 DOI: 10.1093/mam/ozae048] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/27/2024] [Revised: 04/15/2024] [Accepted: 04/30/2024] [Indexed: 06/01/2024]
Abstract
Human umbilical vein endothelial cells (HUVECs) are primary cells isolated from the vein of an umbilical cord, extensively used in cardiovascular studies and medical research. These cells, retaining the characteristics of endothelial cells in vivo, serve as a valuable cellular model system for understanding vascular biology, endothelial dysfunction, pathophysiology of diseases such as atherosclerosis, and responses to different drugs or treatments. Transmission electron microscopy (TEM) has been a cornerstone in revealing the detailed architecture of multiple cellular model systems including HUVECs, allowing researchers to visualize subcellular organelles, membrane structures, and cytoskeletal elements. Among them, the endoplasmic reticulum, Golgi apparatus, mitochondria, and nucleus can be meticulously examined to recognize alterations indicative of cellular responses to various stimuli. Importantly, Weibel-Palade bodies are characteristic secretory organelles found in HUVECs, which can be easily distinguished in the TEM. These distinctive structures also dynamically react to different factors through regulated exocytosis, resulting in complete or selective release of their contents. This detailed review summarizes the ultrastructural features of HUVECs and highlights the utility of TEM as a pivotal tool for analyzing HUVECs in diverse research frameworks, contributing valuable insights into the comprehension of HUVEC behavior and enriching our knowledge into the complexity of vascular biology.
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Affiliation(s)
- Hana Duranova
- AgroBioTech Research Centre, Slovak University of Agriculture, Tr. A. Hlinku 2, 949 76 Nitra, Slovak Republic
| | - Lenka Kuzelova
- AgroBioTech Research Centre, Slovak University of Agriculture, Tr. A. Hlinku 2, 949 76 Nitra, Slovak Republic
- Faculty of Biotechnology and Food Sciences, Institute of Biotechnology, Slovak University of Agriculture, Tr. A. Hlinku 2, 949 76 Nitra, Slovak Republic
| | - Petra Borotova
- AgroBioTech Research Centre, Slovak University of Agriculture, Tr. A. Hlinku 2, 949 76 Nitra, Slovak Republic
| | - Veronika Simora
- AgroBioTech Research Centre, Slovak University of Agriculture, Tr. A. Hlinku 2, 949 76 Nitra, Slovak Republic
| | - Veronika Fialkova
- AgroBioTech Research Centre, Slovak University of Agriculture, Tr. A. Hlinku 2, 949 76 Nitra, Slovak Republic
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Hordijk S, Carter T, Bierings R. A new look at an old body: molecular determinants of Weibel-Palade body composition and von Willebrand factor exocytosis. J Thromb Haemost 2024; 22:1290-1303. [PMID: 38307391 DOI: 10.1016/j.jtha.2024.01.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2023] [Revised: 01/16/2024] [Accepted: 01/19/2024] [Indexed: 02/04/2024]
Abstract
Endothelial cells, forming a monolayer along blood vessels, intricately regulate vascular hemostasis, inflammatory responses, and angiogenesis. A key determinant of these functions is the controlled secretion of Weibel-Palade bodies (WPBs), which are specialized endothelial storage organelles housing a presynthesized pool of the hemostatic protein von Willebrand factor and various other hemostatic, inflammatory, angiogenic, and vasoactive mediators. This review delves into recent mechanistic insights into WPB biology, including the biogenesis that results in their unique morphology, the acquisition of intraluminal vesicles and other cargo, and the contribution of proton pumps to organelle acidification. Additionally, in light of a number of proteomic approaches to unravel the regulatory networks that control WPB formation and secretion, we provide a comprehensive overview of the WPB exocytotic machinery, including their molecular and cellular mechanisms.
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Affiliation(s)
- Sophie Hordijk
- Hematology, Erasmus MC University Medical Center, Rotterdam, The Netherlands. https://twitter.com/SophieHordijk
| | - Tom Carter
- Molecular and Clinical Sciences Research Institute, St George's University of London, London, United Kingdom
| | - Ruben Bierings
- Hematology, Erasmus MC University Medical Center, Rotterdam, The Netherlands.
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Ma J, Hao Z, Zhang Y, Li L, Huang X, Wang Y, Chen L, Yang G, Li W. Physical Contacts Between Mitochondria and WPBs Participate in WPB Maturation. Arterioscler Thromb Vasc Biol 2024; 44:108-123. [PMID: 37942609 DOI: 10.1161/atvbaha.123.319939] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2023] [Accepted: 10/24/2023] [Indexed: 11/10/2023]
Abstract
BACKGROUND Weibel-Palade bodies (WPBs) are endothelial cell-specific cigar-shaped secretory organelles containing various biologically active molecules. WPBs play crucial roles in thrombosis, hemostasis, angiogenesis, and inflammation. The main content of WPBs is the procoagulant protein vWF (von Willebrand factor). Physical contacts and functional cross talk between mitochondria and other organelles have been demonstrated. Whether an interorganellar connection exists between mitochondria and WPBs is unknown. METHODS We observed physical contacts between mitochondria and WPBs in human umbilical vein endothelial cells by electron microscopy and living cell confocal microscopy. We developed an artificial intelligence-assisted method to quantify the duration and length of organelle contact sites in live cells. RESULTS We found there existed physical contacts between mitochondria and WPBs. Disruption of mitochondrial function affected the morphology of WPBs. Furthermore, we found that Rab3b, a small GTPase on the WPBs, was enriched at the mitochondrion-WPB contact sites. Rab3b deficiency reduced interaction between the two organelles and impaired the maturation of WPBs and vWF multimer secretion. CONCLUSIONS Our results reveal that Rab3b plays a crucial role in mediating the mitochondrion-WPB contacts, and that mitochondrion-WPB coupling is critical for the maturation of WPBs in vascular endothelial cells.
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Affiliation(s)
- Jing Ma
- Beijing Key Laboratory for Genetics of Birth Defects, Beijing Pediatric Research Institute, China (J.M., Z.H., W.L.)
- MOE Key Laboratory of Major Diseases in Children, Capital Medical University, Beijing, China (J.M., Z.H., W.L.)
- Beijing Children's Hospital, Capital Medical University, National Center for Children's Health, China (J.M., Z.H., W.L.)
| | - Zhenhua Hao
- MOE Key Laboratory of Major Diseases in Children, Capital Medical University, Beijing, China (J.M., Z.H., W.L.)
- Beijing Children's Hospital, Capital Medical University, National Center for Children's Health, China (J.M., Z.H., W.L.)
| | - Yudong Zhang
- National Laboratory of Pattern Recognition, Institute of Automation (Y.Z., G.Y.), Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China (Y.Z., G.Y.)
| | - Liuju Li
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, National Biomedical Imaging Center, School of Future Technology (L.L., L.C.), Peking University, Beijing, China
| | - Xiaoshuai Huang
- Biomedical Engineering Department (X.H.), Peking University, Beijing, China
| | - Yu Wang
- State Key Laboratory of Molecular Developmental Biology, Institute of Genetics and Developmental Biology (Y.W.), Chinese Academy of Sciences, Beijing, China
| | - Liangyi Chen
- State Key Laboratory of Membrane Biology, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Institute of Molecular Medicine, National Biomedical Imaging Center, School of Future Technology (L.L., L.C.), Peking University, Beijing, China
| | - Ge Yang
- National Laboratory of Pattern Recognition, Institute of Automation (Y.Z., G.Y.), Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China (Y.Z., G.Y.)
| | - Wei Li
- Beijing Key Laboratory for Genetics of Birth Defects, Beijing Pediatric Research Institute, China (J.M., Z.H., W.L.)
- MOE Key Laboratory of Major Diseases in Children, Capital Medical University, Beijing, China (J.M., Z.H., W.L.)
- Beijing Children's Hospital, Capital Medical University, National Center for Children's Health, China (J.M., Z.H., W.L.)
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Huang N, Chen Z, Yang X, Gao Y, Zhong J, Li Y, Xiao F, Wang X, Shi Y, Zhang N. Upstream open reading frame-encoded MP31 disrupts the mitochondrial quality control process and inhibits tumorigenesis in glioblastoma. Neuro Oncol 2023; 25:1947-1962. [PMID: 37280112 PMCID: PMC10628964 DOI: 10.1093/neuonc/noad099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2023] [Indexed: 06/08/2023] Open
Abstract
BACKGROUND Mitochondrial hyperpolarization achieved by the elevation of mitochondrial quality control (MQC) activity is a hallmark of glioblastoma (GBM). Therefore, targeting the MQC process to disrupt mitochondrial homeostasis should be a promising approach for GBM therapy. METHODS We used 2-photon fluorescence microscopy, Fluorescence-Activated Cell Sorting, and confocal microscopy with specific fluorescent dyes to detect the mitochondrial membrane potential (MMP) and mitochondrial structures. Mitophagic flux was measured with mKeima. RESULTS MP31, a phosphatase and tensin homolog (PTEN) uORF-translated and mitochondria-localized micropeptide, disrupted the MQC process and inhibited GBM tumorigenesis. Re-expression of MP31 in patient-derived GBM cells induced MMP loss to trigger mitochondrial fission but blocked mitophagic flux, leading to the accumulation of damaged mitochondria in cells, followed by reactive oxygen species production and DNA damage. Mechanistically, MP31 inhibited lysosome function and blocked lysosome fusion with mitophagosomes by competing with V-ATPase A1 for lactate dehydrogenase B (LDHB) binding to induce lysosomal alkalinization. Furthermore, MP31 enhanced the sensitivity of GBM cells to TMZ by suppressing protective mitophay in vitro and in vivo, but showed no side effects on normal human astrocytes or microglia cells (MG). CONCLUSIONS MP31 disrupts cancerous mitochondrial homeostasis and sensitizes GBM cells to current chemotherapy, without inducing toxicity in normal human astrocytes and MG. MP31 is a promising candidate for GBM treatment.
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Affiliation(s)
- Nunu Huang
- Department of Neurosurgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China
- Guangdong Provincial Key Laboratory of Brain Function and Disease, Guangzhou, Guangdong, China
| | - Zhipeng Chen
- Department of Neurosurgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China
- Guangdong Provincial Key Laboratory of Brain Function and Disease, Guangzhou, Guangdong, China
| | - Xuesong Yang
- Department of Neurosurgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China
- Guangdong Provincial Key Laboratory of Brain Function and Disease, Guangzhou, Guangdong, China
| | - Yixin Gao
- Department of Neurosurgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China
- Guangdong Provincial Key Laboratory of Brain Function and Disease, Guangzhou, Guangdong, China
| | - Jian Zhong
- Department of Neurosurgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China
- Guangdong Provincial Key Laboratory of Brain Function and Disease, Guangzhou, Guangdong, China
| | - Yan Li
- Department of Neurosurgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China
- Guangdong Provincial Key Laboratory of Brain Function and Disease, Guangzhou, Guangdong, China
| | - Feizhe Xiao
- Department of Scientific Research Section, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China
| | - Xiuxing Wang
- National Health Commission Key Laboratory of Antibody Techniques, School of Basic Medical Sciences, Nanjing Medical University, Nanjing, Jiangsu, China
- Department of Cell Biology, School of Basic Medical Sciences, Nanjing Medical University, Nanjing, Jiangsu, China
- Jiangsu Provincial Key Laboratory of Human Functional Genomics, School of Basic Medical Sciences, Nanjing Medical University, Nanjing, Jiangsu, China
| | - Yu Shi
- Institute of Pathology and Southwest Cancer Centre, Southwest Hospital, Third Military Medical University (Army Medical University), Chongqing, China
- Key Laboratory of Tumor Immunopathology of the Ministry of Education of China Southwest Hospital, Third Military Medical University (Army Medical University), Chongqing, China
| | - Nu Zhang
- Department of Neurosurgery, The First Affiliated Hospital of Sun Yat-sen University, Guangzhou, Guangdong, China
- Guangdong Provincial Key Laboratory of Brain Function and Disease, Guangzhou, Guangdong, China
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Meli A, McCormack A, Conte I, Chen Q, Streetley J, Rose ML, Bierings R, Hannah MJ, Molloy JE, Rosenthal PB, Carter T. Altered Storage and Function of von Willebrand Factor in Human Cardiac Microvascular Endothelial Cells Isolated from Recipient Transplant Hearts. Int J Mol Sci 2023; 24:ijms24054553. [PMID: 36901985 PMCID: PMC10003102 DOI: 10.3390/ijms24054553] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2023] [Revised: 02/20/2023] [Accepted: 02/22/2023] [Indexed: 03/02/2023] Open
Abstract
The assembly of von Willebrand factor (VWF) into ordered helical tubules within endothelial Weibel-Palade bodies (WPBs) is required for the efficient deployment of the protein at sites of vascular injury. VWF trafficking and storage are sensitive to cellular and environmental stresses that are associated with heart disease and heart failure. Altered storage of VWF manifests as a change in WPB morphology from a rod shape to a rounded shape and is associated with impaired VWF deployment during secretion. In this study, we examined the morphology, ultrastructure, molecular composition and kinetics of exocytosis of WPBs in cardiac microvascular endothelial cells isolated from explanted hearts of patients with a common form of heart failure, dilated cardiomyopathy (DCM; HCMECD), or from nominally healthy donors (controls; HCMECC). Using fluorescence microscopy, WPBs in HCMECC (n = 3 donors) showed the typical rod-shaped morphology containing VWF, P-selectin and tPA. In contrast, WPBs in primary cultures of HCMECD (n = 6 donors) were predominantly rounded in shape and lacked tissue plasminogen activator (t-PA). Ultrastructural analysis of HCMECD revealed a disordered arrangement of VWF tubules in nascent WPBs emerging from the trans-Golgi network. HCMECD WPBs still recruited Rab27A, Rab3B, Myosin-Rab Interacting Protein (MyRIP) and Synaptotagmin-like protein 4a (Slp4-a) and underwent regulated exocytosis with kinetics similar to that seen in HCMECc. However, secreted extracellular VWF strings from HCMECD were significantly shorter than for endothelial cells with rod-shaped WPBs, although VWF platelet binding was similar. Our observations suggest that VWF trafficking, storage and haemostatic potential are perturbed in HCMEC from DCM hearts.
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Affiliation(s)
- Athinoula Meli
- Transplant Immunology, Heart Science Centre, Harefield Hospital, Hill End Road, Harefield UB9 6JH, UK
| | - Ann McCormack
- Transplant Immunology, Heart Science Centre, Harefield Hospital, Hill End Road, Harefield UB9 6JH, UK
| | - Ianina Conte
- Molecular and Clinical Sciences Research Institute, St Georges University of London, London SW17 0RE, UK
| | - Qu Chen
- Structural Biology Science Technology Platform, The Francis Crick Institute, London NW1 1AT, UK
| | - James Streetley
- Structural Biology of Cells and Viruses Laboratory, The Francis Crick Institute, London NW1 1AT, UK
| | - Marlene L. Rose
- Transplant Immunology, Heart Science Centre, Harefield Hospital, Hill End Road, Harefield UB9 6JH, UK
| | - Ruben Bierings
- Hematology, Erasmus University Medical Center, P.O. Box 2040, 3000 CA Rotterdam, The Netherlands
| | - Matthew J. Hannah
- High Containment Microbiology, UK Health Security Agency, London NW9 5EQ, UK
| | - Justin E. Molloy
- Single Molecule Enzymology Laboratory, The Francis Crick Institute, London NW1 1AT, UK
| | - Peter B. Rosenthal
- Structural Biology of Cells and Viruses Laboratory, The Francis Crick Institute, London NW1 1AT, UK
| | - Tom Carter
- Molecular and Clinical Sciences Research Institute, St Georges University of London, London SW17 0RE, UK
- Correspondence: ; Tel.: +44-(208)-7255961
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Zanlungo S, Enrich C, Gerke V, Eden ER, Colombo MI. Editorial: Cell compartments and intracellular trafficking of lipids and proteins: Impact on biomedicine. Front Cell Dev Biol 2022; 10:1087214. [PMID: 36506102 PMCID: PMC9731092 DOI: 10.3389/fcell.2022.1087214] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2022] [Accepted: 11/18/2022] [Indexed: 11/27/2022] Open
Affiliation(s)
- Silvana Zanlungo
- Department of Gastroenterology, Faculty of Medicine, Pontificia Universidad Católica de Chile, Santiago, Chile
| | - Carlos Enrich
- Department of Biomedicine, Unit of Cell Biology, Faculty of Medicine and Health Sciences, Centre de Recerca Biomèdica CELLEX (IDIBAPS), University of Barcelona, Barcelona, Spain
| | - Volker Gerke
- Institute of Medical Biochemistry, Centre for Molecular Biology of Inflammation, University of Münster, Münster, Germany
| | - Emily R. Eden
- UCL Institute of Ophthalmology, London, United Kingdom
| | - María Isabel Colombo
- Laboratorio de Mecanismos Moleculares Implicados en El Tráfico Vesicular y la Autofagia, Instituto de Histología y Embriología de Mendoza (IHEM), Universidad Nacional de Cuyo- Consejo Nacional de Investigaciones Científicas y Tecnológicas (CONICET), Mendoza, Argentina
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Li H, Zhou WY, Liu YX, Xia YY, Xia CL, Pan DR, Li Z, Shi Y, Chen SL, Zhang JX. Rictor maintains endothelial integrity under shear stress. Front Cell Dev Biol 2022; 10:963866. [PMID: 36438564 PMCID: PMC9685313 DOI: 10.3389/fcell.2022.963866] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Accepted: 10/26/2022] [Indexed: 11/12/2022] Open
Abstract
Background: Endothelial injury induced by low shear stress (LSS) is an initiating factor in the pathogenesis of various cardiovascular diseases, including atherosclerosis, hypertension, and thrombotic diseases. Low shear stress activates the mammalian target of rapamycin complex 2 (mTORC2) signaling pathway. Rictor, the main constituent protein of mTORC2, is involved in vascular development. However, the impact of conditional Rictor ablation on endothelial homeostasis, especially on endothelial-specific markers, such as vascular endothelial-cadherin (VE-cadherin) and von Willebrand factor (VWF), under blood flow stimulation is unclear. Objective: We aimed to investigate whether endothelial Rictor is involved in maintaining vascular endothelial integrity and the potential role of Rictor in atheroprone blood flow-mediated endothelial injury. Methods and results: Immunofluorescence staining showed that endothelial Rictor was successfully knocked out in a mouse model. Scanning electron microscopy (EM) detection revealed disruption of the endothelial monolayer in the thoracic aorta of Rictor-deficient mice. Furthermore, scanning electron microscopy and transmission electron microscopy showed that Rictor deletion disrupted endothelial integrity and expanded cell junctions in the left common carotid artery region. In vitro, low shear stress disrupted actin filament polarity and the promoted the translocation of vascular endothelial-cadherin, the key component of adherens junctions (AJs) in human umbilical vein endothelial cells. After Rictor downregulation by small interfering RNA, the translocation of vascular endothelial-cadherin and stress fibers increased. Rictor knockdown inhibited low shear stress-induced von Willebrand factor upregulation, and downregulation of vascular endothelial-cadherin decreased low shear stress-induced von Willebrand factor expression. These results suggest that vascular endothelial-cadherin/von Willebrand factor is a possible mechanism mediated by Rictor in the pathological process of low shear stress-induced endothelial injury. Conclusion: Rictor is a key protein that regulates endothelial integrity under vascular physiological homeostasis, and Rictor mediates low shear stress-induced endothelial injury by regulating adherens junctions and von Willebrand factor.
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Affiliation(s)
- Hui Li
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, China
| | - Wen-Ying Zhou
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, China
| | - Yi-Xian Liu
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, China
| | - Yi-Yuan Xia
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, China
| | - Chun-Lei Xia
- Department of Intensive Medicine, The Affiliated Jiangning Hospital of Nanjing Medical University, Nanjing, China
| | - Dao-Rong Pan
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, China
| | - Zheng Li
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, China
| | - Yi Shi
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, China
| | - Shao-Liang Chen
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, China
- *Correspondence: Jun-Xia Zhang, ; Shao-Liang Chen,
| | - Jun-Xia Zhang
- Department of Cardiology, Nanjing First Hospital, Nanjing Medical University, Nanjing, China
- *Correspondence: Jun-Xia Zhang, ; Shao-Liang Chen,
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Acidification of endothelial Weibel-Palade bodies is mediated by the vacuolar-type H+-ATPase. PLoS One 2022; 17:e0270299. [PMID: 35767558 PMCID: PMC9242466 DOI: 10.1371/journal.pone.0270299] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2022] [Accepted: 06/07/2022] [Indexed: 12/02/2022] Open
Abstract
Weibel-Palade bodies (WPB) are unique secretory granules of endothelial cells that store the procoagulant von-Willebrand factor (VWF) in a highly compacted form. Upon exocytosis the densely packed VWF unfurls into long strands that expose binding sites for circulating platelets and thereby initiate the formation of a platelet plug at sites of blood vessel injury. Dense packing of VWF requires the establishment of an acidic pH in the lumen of maturing WPB but the mechanism responsible for this acidification has not yet been fully established. We show here that subunits of the vacuolar-type H+-ATPase are present on mature WPB and that interference with the proton pump activity of the ATPase employing inhibitors of different chemical nature blocks a reduction in the relative internal pH of WPB. Furthermore, depletion of the V-ATPase subunit V0d1 from primary endothelial cells prevents WPB pH reduction and the establishment of an elongated morphology of WPB that is dictated by the densely packed VWF tubules. Thus, the vacuolar-type H+-ATPase present on WPB is required for proper acidification and maturation of the organelle.
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