title: The role of osteocyte apoptosis in cancer chemotherapy-induced bone loss.
abstract: Intensive cancer chemotherapy leads to significant bone loss, the underlying mechanism of which remains unclear. The objective of this study was to elucidate mechanisms for effect of the commonly used anti-metabolite methotrexate (MTX) on osteocytes and on general bone homeostasis. The current study in juvenile rats showed that MTX chemotherapy caused a 4.3-fold increase in the number of apoptotic osteocytes in tibial metaphysis, which was accompanied by a 1.8-fold increase in the number of tartrate-resistant acid phosphatase-positive bone resorbing osteoclasts, and a 35% loss of trabecular bone. This was associated with an increase in transcription of the osteoclastogenic cytokines IL-6 (10-fold) and IL-11 (2-fold). Moreover, the metaphyseal bone of MTX-treated animals exhibited a 37.6% increase in the total number of osteocytes, along with 4.9-fold higher expression of the DMP-1 transcript. In cultured osteocyte-like MLO-Y4 cells, MTX treatment significantly increased caspase-3-mediated apoptosis, which was accompanied by the formation of plasma membrane-born apoptotic bodies and an increase in IL-6 (24-fold) and IL-11 (29-fold) mRNA expression. Conditioned media derived from MTX-treated MLO-Y4 cells was twice as strong as untreated media in its capacity to induce osteoclast formation in primary bone marrow osteoclast precursors. Thus, our in vivo and in vitro data suggested that MTX-induced apoptosis of osteocytes caused higher recruitment of DMP-1 positive osteocytes and increased osteoclast formation, which could contribute towards the loss of bone homeostasis in vivo.
authors.affiliation: Sansom Institute for Health Research, School of Pharmacy and Medical Sciences, Division of Health Sciences, University of South Australia, Adelaide, Australia. tetyana.shandala@unisa.edu.au
authors.forename: Tetyana
authors.initials: T
authors.lastname: Shandala
authors.forename: Yeap
authors.initials: Y
authors.lastname: Shen Ng
authors.forename: Blair
authors.initials: B
authors.lastname: Hopwood
authors.forename: Yuen-Ching
authors.initials: YC
authors.lastname: Yip
authors.forename: Bruce K
authors.initials: BK
authors.lastname: Foster
authors.forename: Cory J
authors.initials: CJ
authors.lastname: Xian
mesh_terms: D000135:Acid Phosphatase / Q000378:metabolism; D000818:Animals; D000964:Antimetabolites, Antineoplastic / Q000633:toxicity; D017209:Apoptosis / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D001862:Bone Resorption / Q000139:chemically induced* / Q000235:genetics / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D017077:Culture Media, Conditioned / Q000378:metabolism; D016326:Extracellular Matrix Proteins / Q000235:genetics / Q000378:metabolism; D006706:Homeostasis / Q000187:drug effects; D017370:Interleukin-11 / Q000235:genetics / Q000378:metabolism; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D008297:Male; D008727:Methotrexate / Q000633:toxicity*; D009369:Neoplasms / Q000188:drug therapy / Q000473:pathology*; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D010011:Osteocytes / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology*; D010012:Osteogenesis / Q000187:drug effects; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D000071681:Tartrate-Resistant Acid Phosphatase
chemical_list: D000964:Antimetabolites, Antineoplastic; D017077:Culture Media, Conditioned; C081635:Dmp1 protein, rat; D016326:Extracellular Matrix Proteins; D017370:Interleukin-11; D015850:Interleukin-6; D007527:Isoenzymes; D010750:Phosphoproteins; D012333:RNA, Messenger; D000135:Acid Phosphatase; D000071681:Tartrate-Resistant Acid Phosphatase; D053148:Caspase 3; D008727:Methotrexate