title: Glucocorticoid impairs cell-cell communication by autophagy-mediated degradation of connexin 43 in osteocytes.
abstract: Osteocytes comprising over 90% of the bone cell population are highly susceptible to the adverse effects of glucocorticoids (GC) administration. Here we observed that Dexamethasone (Dex) induces a robust cytoskeleton rearrangement and decreases Cx43 protein expression in osteocyte-like MLO-Y4 cells. Using a Dmp1Cre-mT/mG osteocyte ex vivo culture system, we found significant shortening of dendritic processes in primary osteocytes following Dex administration. Loss of dendritic processes is a consequence of reduced Cx43 connectivity upon Dex induced autophagy in both RFP-GFP-LC3B transfected MLO-Y4 cells and primary calvarial osteocytes from LC3GFP transgenic mice. Upon the induction of autophagy by Dex, Cx43 was internalized into autophagosome/autolysosomes and degraded by autophagy. The degradation was attenuated following lysosomal inhibition using chloroquine (CLQ) and suppression of autophagy by Atg5 silencing. Inhibition Akt-mTORC1 signaling by Dex induces autophagy subsequently resulting in Cx43 degradation.Activation of Akt phosphorylation by IGF-1 attenuated Dex induced autophagy and degradation of Cx43. Together, we demonstrated that GC impair osteocyte cell-cell connectivity via autophagy mediated degradation of Cx43 through inhibition of the Akt-mTORC1 signaling. This may account for the deleterious effect of GC-induced bone loss.
authors.affiliation: Centre for Orthopaedic Research, School of Surgery, The University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: Junjie
authors.initials: J
authors.lastname: Gao
authors.affiliation: Centre for Orthopaedic Research, School of Surgery, The University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: Tak Sum
authors.initials: TS
authors.lastname: Cheng
authors.affiliation: Shanghai Key Laboratory of Orthopedic Implants, Department of Orthopedic Surgery, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: An
authors.initials: A
authors.lastname: Qin
authors.affiliation: Centre for Orthopaedic Research, School of Surgery, The University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: Nathan J
authors.initials: NJ
authors.lastname: Pavlos
authors.affiliation: Centre for Orthopaedic Research, School of Surgery, The University of Western Australia, Nedlands, Western Australia, Australia.|Division of Orthopaedic Surgery, Department of Surgery, Guangdong General Hospital, Guangdong Academy of Medical Sciences, Guangzhou, China.
authors.forename: Tao
authors.initials: T
authors.lastname: Wang
authors.affiliation: Centre for Orthopaedic Research, School of Surgery, The University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: Kai
authors.initials: K
authors.lastname: Song
authors.affiliation: Key Laboratory of Combined Muti-Organ Transplantation, Ministry of Public Health, State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, Division of Hepatobiliary Pancreatic Surgery, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Centre for Orthopaedic Research, School of Surgery, The University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: Lianzhi
authors.initials: L
authors.lastname: Chen
authors.affiliation: Key Laboratory of Combined Muti-Organ Transplantation, Ministry of Public Health, State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, Division of Hepatobiliary Pancreatic Surgery, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Zhou
authors.affiliation: Department of Sports Medicine and Adult Reconstruction Surgery, Drum Tower Hospital Affiliated to Medical School of Nanjing University, Nanjing, Jiangsu, China.
authors.forename: Qing
authors.initials: Q
authors.lastname: Jiang
authors.affiliation: Centre for Orthopaedic Research, School of Surgery, The University of Western Australia, Nedlands, Western Australia, Australia.|Department of Immunology, Graduate School of Medicine and Faculty of Medicine, The University of Tokyo, Tokyo, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Takayanagi
authors.affiliation: State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China.|Key Laboratory of Combined Muti-Organ Transplantation, Ministry of Public Health, State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, Division of Hepatobiliary Pancreatic Surgery, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China.
authors.forename: Sheng
authors.initials: S
authors.lastname: Yan
authors.affiliation: State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, Collaborative Innovation Center for Diagnosis and Treatment of Infectious Diseases, The First Affiliated Hospital, College of Medicine, Zhejiang University, Hangzhou, China.|Key Laboratory of Combined Muti-Organ Transplantation, Ministry of Public Health, State Key Laboratory for Diagnosis and Treatment of Infectious Diseases, Division of Hepatobiliary Pancreatic Surgery, First Affiliated Hospital, Zhejiang University School of Medicine, Hangzhou, China.|Centre for Orthopaedic Research, School of Surgery, The University of Western Australia, Nedlands, Western Australia, Australia.
authors.forename: Minghao
authors.initials: M
authors.lastname: Zheng
mesh_terms: D000818:Animals; D000071182:Autophagosomes / Q000187:drug effects / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects*; D015153:Blotting, Western; D002450:Cell Communication / Q000187:drug effects*; D002460:Cell Line; D002478:Cells, Cultured; D018031:Connexin 43 / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D005938:Glucocorticoids / Q000494:pharmacology*; D008247:Lysosomes / Q000378:metabolism; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D010011:Osteocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D059748:Proteolysis / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects
chemical_list: D018031:Connexin 43; C543076:GJA1 protein, mouse; D005938:Glucocorticoids; D003907:Dexamethasone
keywords: Gerotarget; autophagy; connexin 43; glucocorticoid; mTORC1; osteocyte