Cell autonomous requirement of connexin 43 for osteocyte survival: consequences for endocortical resorption and periosteal bone formation.
Connexin 43 (Cx43) mediates osteocyte communication with other cells and with the extracellular milieu and regulates osteoblastic cell signaling and gene expression. We now report that mice lacking Cx43 in osteoblasts/osteocytes or only in osteocytes (Cx43(ΔOt) mice) exhibit increased osteocyte apoptosis, endocortical resorption, and periosteal bone formation, resulting in higher marrow cavity and total tissue areas measured at the femoral mid-diaphysis. Blockade of resorption reversed the increased marrow cavity but not total tissue area, demonstrating that endocortical resorption and periosteal apposition are independently regulated. Anatomical mapping of apoptotic osteocytes, osteocytic protein expression, and resorption and formation suggests that Cx43 controls osteoclast and osteoblast activity by regulating osteoprotegerin and sclerostin levels, respectively, in osteocytes located in specific areas of the cortex. Whereas empty lacunae and living osteocytes lacking osteoprotegerin were distributed throughout cortical bone in Cx43(ΔOt) mice, apoptotic osteocytes were preferentially located in areas containing osteoclasts, suggesting that osteoclast recruitment requires active signaling from dying osteocytes. Furthermore, Cx43 deletion in cultured osteocytic cells resulted in increased apoptosis and decreased osteoprotegerin expression. Thus, Cx43 is essential in a cell-autonomous fashion in vivo and in vitro for osteocyte survival and for controlling the expression of osteocytic genes that affect osteoclast and osteoblast function.
Department Anatomy & Cell Biology, Indiana University School of Medicine, Indianapolis, IN 46202-5120, USA.
Nicoletta
N
Bivi
Keith W
KW
Condon
Matthew R
MR
Allen
Nathan
N
Farlow
Giovanni
G
Passeri
Lucas R
LR
Brun
Yumie
Y
Rhee
Teresita
T
Bellido
Lilian I
LI
Plotkin
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D017209:Apoptosis; D001862:Bone Resorption / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology*; D002470:Cell Survival; D018031:Connexin 43 / Q000172:deficiency / Q000378:metabolism*; D005269:Femur / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology / Q000648:ultrastructure; D017353:Gene Deletion; D006023:Glycoproteins / Q000378:metabolism; D036341:Intercellular Signaling Peptides and Proteins; D051379:Mice; D008954:Models, Biological; D010006:Osteoblasts / Q000378:metabolism / Q000473:pathology; D010011:Osteocytes / Q000378:metabolism* / Q000473:pathology* / Q000648:ultrastructure; D010012:Osteogenesis; D010521:Periosteum / Q000000981:diagnostic imaging / Q000378:metabolism* / Q000473:pathology; D053245:RANK Ligand / Q000378:metabolism; D055114:X-Ray Microtomography
D048868:Adaptor Proteins, Signal Transducing; D018031:Connexin 43; D006023:Glycoproteins; D036341:Intercellular Signaling Peptides and Proteins; D053245:RANK Ligand; C486030:Sost protein, mouse