Disruption of the Cx43/miR21 pathway leads to osteocyte apoptosis and increased osteoclastogenesis with aging.
Skeletal aging results in apoptosis of osteocytes, cells embedded in bone that control the generation/function of bone forming and resorbing cells. Aging also decreases connexin43 (Cx43) expression in bone; and osteocytic Cx43 deletion partially mimics the skeletal phenotype of old mice. Particularly, aging and Cx43 deletion increase osteocyte apoptosis, and osteoclast number and bone resorption on endocortical bone surfaces. We examined herein the molecular signaling events responsible for osteocyte apoptosis and osteoclast recruitment triggered by aging and Cx43 deficiency. Cx43-silenced MLO-Y4 osteocytic (Cx43def) cells undergo spontaneous cell death in culture through caspase-3 activation and exhibit increased levels of apoptosis-related genes, and only transfection of Cx43 constructs able to form gap junction channels reverses Cx43defcell death. Cx43defcells and bones from old mice exhibit reduced levels of the pro-survival microRNA miR21 and, consistently, increased levels of the miR21 target phosphatase and tensin homolog (PTEN) and reduced phosphorylated Akt, whereas PTEN inhibition reduces Cx43defcell apoptosis. miR21 reduction is sufficient to induce apoptosis of Cx43-expressing cells and miR21 deletion in miR21fl/flbones increases apoptosis-related gene expression, whereas a miR21 mimic prevents Cx43defcell apoptosis, demonstrating that miR21 lies downstream of Cx43. Cx43defcells release more osteoclastogenic cytokines [receptor activator of NFκB ligand (RANKL)/high-mobility group box-1 (HMGB1)], and caspase-3 inhibition prevents RANKL/HMGB1 release and the increased osteoclastogenesis induced by conditioned media from Cx43defcells, which is blocked by antagonizing HMGB1-RAGE interaction. These findings identify a novel Cx43/miR21/HMGB1/RANKL pathway involved in preventing osteocyte apoptosis that also controls osteoclast formation/recruitment and is impaired with aging.
Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
Hannah M
HM
Davis
Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
Rafael
R
Pacheco-Costa
Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
Emily G
EG
Atkinson
Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
Lucas R
LR
Brun
Instituto de Medicina Molecular Aplicada, Facultad de Medicina, Universidad San Pablo-CEU, Madrid, Spain.
Arancha R
AR
Gortazar
Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
Julia
J
Harris
Division of Hematology/Oncology, Department of Internal Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
Masahiro
M
Hiasa
Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.
Surajudeen A
SA
Bolarinwa
Division of Hematology/Oncology, Department of Internal Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
Toshiyuki
T
Yoneda
Division of Hematology/Oncology, Department of Internal Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.
Mircea
M
Ivan
Department of Oral Biology, Indiana University School of Dentistry, Indianapolis, IN, USA.
Angela
A
Bruzzaniti
Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.|Division of Endocrinology, Department of Internal Medicine, Indiana University School of Medicine, Indianapolis, IN, USA.|Roudebush Veterans Administration Medical Center, Indianapolis, IN, USA.
Teresita
T
Bellido
Department of Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN, USA.|Roudebush Veterans Administration Medical Center, Indianapolis, IN, USA.
Lilian I
LI
Plotkin
D000375:Aging / Q000378:metabolism* / Q000473:pathology; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D001862:Bone Resorption / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D001842:Bone and Bones / Q000378:metabolism / Q000473:pathology; D053148:Caspase 3 / Q000235:genetics / Q000378:metabolism; D018031:Connexin 43 / Q000172:deficiency / Q000235:genetics*; D017077:Culture Media, Conditioned / Q000494:pharmacology; D005260:Female; D017629:Gap Junctions / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D005786:Gene Expression Regulation; D005816:Genetic Complementation Test; D024243:HMGB1 Protein / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D035683:MicroRNAs / Q000235:genetics* / Q000378:metabolism; D010010:Osteoclasts / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D010011:Osteocytes / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D010012:Osteogenesis / Q000235:genetics*; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D053245:RANK Ligand / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction
D018031:Connexin 43; D017077:Culture Media, Conditioned; D024243:HMGB1 Protein; C582808:HMGB1 protein, mouse; C531950:MIRN21 microRNA, mouse; D035683:MicroRNAs; D053245:RANK Ligand; C505689:Tnfsf11 protein, mouse; D051057:Proto-Oncogene Proteins c-akt; D051059:PTEN Phosphohydrolase; C487757:Pten protein, mouse; C505409:Casp3 protein, mouse; D053148:Caspase 3
HMGB1; aging; apoptosis; connexin43; miR21; osteocyte