Removing or truncating connexin 43 in murine osteocytes alters cortical geometry, nanoscale morphology, and tissue mechanics in the tibia.
Gap junctions are formed from ubiquitously expressed proteins called connexins that allow the transfer of small signaling molecules between adjacent cells. Gap junctions are especially important for signaling between osteocytes and other bone cell types. The most abundant type of connexin in bone is connexin 43 (Cx43). The C-terminal domain of Cx43 is thought to be an important modulator of gap junction function but the role that this domain plays in regulating tissue-level mechanics is largely unknown. We hypothesized that the lack of the C-terminal domain of Cx43 would cause morphological and compositional changes as well as differences in how bone responds to reference point indentation (RPI) and fracture toughness testing. The effects of the C-terminal domain of Cx43 in osteocytes and other cell types were assessed in a murine model (C57BL/6 background). Mice with endogenous Cx43 in their osteocytes removed via a Cre-loxP system were crossed with knock-in mice which expressed Cx43 that lacked the C-terminal domain in all cell types due to the insertion of a truncated allele to produce the four groups used in the study. The main effect of removing the C-terminal domain from osteocytic Cx43 increased cortical mineral crystallinity (p=0.036) and decreased fracture toughness (p=0.017). The main effect of the presence of the C-terminal domain in other cell types increased trabecular thickness (p<0.001), cortical thickness (p=0.008), and average RPI unloading slope (p=0.004). Collagen morphology was altered when either osteocytes lacked Cx43 (p=0.008) or some truncated Cx43 was expressed in all cell types (p<0.001) compared to controls but not when only the truncated form of Cx43 was expressed in osteocytes (p=0.641). In conclusion, the presence of the C-terminal domain of Cx43 in osteocytes and other cell types is important to maintain normal structure and mechanical integrity of bone.
Weldon School of Biomedical Engineering, Purdue University, West Lafayette, IN, United States.
Max A
MA
Hammond
Department of Biomedical Engineering, Indiana University-Purdue University at Indianapolis, IN, United States.
Alycia G
AG
Berman
Department of Anatomy and Cell Biology, Indiana University School of Medicine, IN, United States.
Rafael
R
Pacheco-Costa
Department of Anatomy and Cell Biology, Indiana University School of Medicine, IN, United States.
Hannah M
HM
Davis
Department of Anatomy and Cell Biology, Indiana University School of Medicine, IN, United States; Roudebush Veterans Administration Medical Center, Indianapolis, IN, United States.
Lilian I
LI
Plotkin
Department of Biomedical Engineering, Indiana University-Purdue University at Indianapolis, IN, United States; Department of Orthopaedic Surgery, Indiana University School of Medicine, IN, United States. Electronic address: jmwalla@iupui.edu.
Joseph M
JM
Wallace
D000818:Animals; D001696:Biomechanical Phenomena; D000071556:Cancellous Bone / Q000473:pathology / Q000503:physiopathology; D018031:Connexin 43 / Q000378:metabolism*; D000071538:Cortical Bone / Q000378:metabolism / Q000473:pathology* / Q000503:physiopathology*; D018483:Diaphyses / Q000503:physiopathology; D051379:Mice; D018625:Microscopy, Atomic Force; D053758:Nanoparticles / Q000737:chemistry*; D010011:Osteocytes / Q000378:metabolism*; D013059:Spectrum Analysis, Raman; D013977:Tibia / Q000473:pathology* / Q000503:physiopathology*; D013978:Tibial Fractures / Q000503:physiopathology
D018031:Connexin 43
Atomic force microscopy; Bone; Fracture toughness; Raman spectroscopy; Reference point indentation; Type I collagen