title: Mycolactone-Dependent Depletion of Endothelial Cell Thrombomodulin Is Strongly Associated with Fibrin Deposition in Buruli Ulcer Lesions.
abstract: A well-known histopathological feature of diseased skin in Buruli ulcer (BU) is coagulative necrosis caused by the Mycobacterium ulcerans macrolide exotoxin mycolactone. Since the underlying mechanism is not known, we have investigated the effect of mycolactone on endothelial cells, focussing on the expression of surface anticoagulant molecules involved in the protein C anticoagulant pathway. Congenital deficiencies in this natural anticoagulant pathway are known to induce thrombotic complications such as purpura fulimans and spontaneous necrosis. Mycolactone profoundly decreased thrombomodulin (TM) expression on the surface of human dermal microvascular endothelial cells (HDMVEC) at doses as low as 2 ng/ml and as early as 8 hrs after exposure. TM activates protein C by altering thrombin's substrate specificity, and exposure of HDMVEC to mycolactone for 24 hours resulted in an almost complete loss of the cells' ability to produce activated protein C. Loss of TM was shown to be due to a previously described mechanism involving mycolactone-dependent blockade of Sec61 translocation that results in proteasome-dependent degradation of newly synthesised ER-transiting proteins. Indeed, depletion from cells determined by live-cell imaging of cells stably expressing a recombinant TM-GFP fusion protein occurred at the known turnover rate. In order to determine the relevance of these findings to BU disease, immunohistochemistry of punch biopsies from 40 BU lesions (31 ulcers, nine plaques) was performed. TM abundance was profoundly reduced in the subcutis of 78% of biopsies. Furthermore, it was confirmed that fibrin deposition is a common feature of BU lesions, particularly in the necrotic areas. These findings indicate that there is decreased ability to control thrombin generation in BU skin. Mycolactone's effects on normal endothelial cell function, including its ability to activate the protein C anticoagulant pathway are strongly associated with this. Fibrin-driven tissue ischemia could contribute to the development of the tissue necrosis seen in BU lesions.
authors.affiliation: Department of Microbial and Cellular Sciences, School of Biosciences and Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.
authors.forename: Joy
authors.initials: J
authors.lastname: Ogbechi
authors.affiliation: Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Marie-Thérèse
authors.initials: MT
authors.lastname: Ruf
authors.affiliation: Department of Microbial and Cellular Sciences, School of Biosciences and Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.
authors.forename: Belinda S
authors.initials: BS
authors.lastname: Hall
authors.affiliation: Department of Microbial and Cellular Sciences, School of Biosciences and Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.
authors.forename: Katherine
authors.initials: K
authors.lastname: Bodman-Smith
authors.affiliation: Section Clinical Tropical Medicine, Heidelberg University Hospital, Heidelberg, Germany.
authors.forename: Moritz
authors.initials: M
authors.lastname: Vogel
authors.affiliation: Department of Biochemistry and Molecular Biology, National Cheng Kung University, Tainan, Taiwan.
authors.forename: Hua-Lin
authors.initials: HL
authors.lastname: Wu
authors.affiliation: Institute for Cardiovascular and Metabolic Research, School of Biological Sciences, University of Reading, Reading, United Kingdom.
authors.forename: Alexander
authors.initials: A
authors.lastname: Stainer
authors.affiliation: Coagulation Biology Laboratory, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma, United States of America.
authors.forename: Charles T
authors.initials: CT
authors.lastname: Esmon
authors.affiliation: Centre for Haematology, Faculty of Medicine, Imperial College London, London, United Kingdom.
authors.forename: Josefin
authors.initials: J
authors.lastname: Ahnström
authors.affiliation: Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland; University of Basel, Basel, Switzerland.
authors.forename: Gerd
authors.initials: G
authors.lastname: Pluschke
authors.affiliation: Department of Microbial and Cellular Sciences, School of Biosciences and Medicine, Faculty of Health and Medical Sciences, University of Surrey, Guildford, United Kingdom.
authors.forename: Rachel E
authors.initials: RE
authors.lastname: Simmonds
mesh_terms: D000900:Anti-Bacterial Agents / Q000627:therapeutic use*; D054312:Buruli Ulcer / Q000175:diagnosis / Q000188:drug therapy* / Q000378:metabolism / Q000382:microbiology; D042783:Endothelial Cells / Q000378:metabolism; D005337:Fibrin / Q000378:metabolism*; D006801:Humans; D018942:Macrolides / Q000378:metabolism / Q000627:therapeutic use*; D019911:Mycobacterium ulcerans / Q000502:physiology*; D009336:Necrosis / Q000382:microbiology; D012867:Skin / Q000382:microbiology / Q000473:pathology; D018180:Thrombomodulin / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; D018180:Thrombomodulin; C117218:mycolactone; D005337:Fibrin