title: Thyroid hormone-induced demineralisation of the vertebral skeleton of the eel, Anguilla anguilla.
abstract: The role of thyroid hormones (TH) in bone remodelling is controversial. Indeed, in humans, while they are necessary for normal growth and development, their overproduction can induce important mineral bone loss and osteoporosis. Intense bone resorption is a natural phenomenon also observed in some teleosts, during reproductive migration and fasting. Our work aimed at investigating the effects of chronic treatments with TH (thyroxin, T4 or triiodothyronine, T3) on bone resorption in a migratory fish, the European eel (Anguilla anguilla), a representative species of an ancient group of teleosts (Elopomorphs). The incineration method showed that TH induced a significant mineral loss in eel vertebral skeleton. Histology and histophysical (qualitative and quantitative microradiographs) methods were then applied to vertebral sections to determine which types of resorption were induced by TH. Quantitative image analysis of microradiographs showed that TH significantly increased the porosity of the vertebrae, demonstrating the induction of a severe bone loss. Histology revealed the appearance of large osteoclastic lacunae, indicating a stimulation of osteoclastic resorption. Quantitative image analysis of ultrathin microradiographs showed a significant increase of the size of osteocytic lacunae, indicating a stimulation of periosteocytic osteolysis. Finally, quantitative microradiographs indicated a significant fall of mineralisation degree. TH treatments did not stimulate the production of the calcium-bonded lipo-phospho-protein vitellogenin, indicating that TH-induced bone demineralisation was not mediated by any indirect effect on vitellogenesis. Our study demonstrates that TH may participate in the mobilisation of bone mineral stores in the eel, by inducing different types of vertebral bone resorption, such as osteoclastic resorption and periosteocytic osteolysis. These data suggest that the stimulatory action of TH on bone resorption may be an ancient regulatory mechanism in vertebrates.
authors.affiliation: Muséum National d'Histoire Naturelle, Département des Milieux et Peuplements Aquatiques, USM 0401, UMR 5178 CNRS, 7 rue Cuvier, CP 32, 75231 Paris Cedex 05, France.
authors.forename: Miskal
authors.initials: M
authors.lastname: Sbaihi
authors.forename: Adnane
authors.initials: A
authors.lastname: Kacem
authors.forename: Salima
authors.initials: S
authors.lastname: Aroua
authors.forename: Sylvie
authors.initials: S
authors.lastname: Baloche
authors.forename: Karine
authors.initials: K
authors.lastname: Rousseau
authors.forename: Evelyne
authors.initials: E
authors.lastname: Lopez
authors.forename: François
authors.initials: F
authors.lastname: Meunier
authors.forename: Sylvie
authors.initials: S
authors.lastname: Dufour
mesh_terms: D000811:Anguilla / Q000378:metabolism*; D000818:Animals; D018488:Bone Demineralization, Pathologic / Q000139:chemically induced* / Q000378:metabolism / Q000473:pathology; D015519:Bone Density / Q000187:drug effects; D001862:Bone Resorption / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology; D005260:Female; D010024:Osteoporosis / Q000139:chemically induced / Q000378:metabolism / Q000473:pathology; D013131:Spine / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D013963:Thyroid Hormones / Q000633:toxicity*; D013974:Thyroxine / Q000633:toxicity; D014284:Triiodothyronine / Q000633:toxicity; D014819:Vitellogenins / Q000097:blood
chemical_list: D013963:Thyroid Hormones; D014819:Vitellogenins; D014284:Triiodothyronine; D013974:Thyroxine