E-mail this article

M ice carrying a targeted mutation (r) in Col1a1, encoding a collagenase-resistant form of type I collagen, have altered skeletal remodeling. In hematoxylin and eosin–stained paraffin sections, we detect empty lacunae in osteocytes in calvariae from Col1a1^r/r mice at age 2 weeks, increasing through age 10–12 months. Empty lacunae appear to result from osteocyte apoptosis, since staining of osteocytes/periosteal osteoblasts with terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling is increased in Col1a1^r/r relative to wild-type bones. Osteocyte perilacunar matrices stained with Ab that recognizes collagenase collagen α1(I) chain cleavage ends in wild-type but not Col1a1^r/r calvariae. Increased calvarial periosteal and tibial/femoral endosteal bone deposition was found in Col1a1^r/r mice from ages 3–12 months. Calcein labeling of calvarial surfaces was increased in Col1a1^r/r relative to wild-type mice. Daily injections of synthetic parathyroid hormone for 30 days increased calcein-surface labeling in wild-type but caused no further increase in the already high calcein staining of Col1a1^r/r bones. Thus, failure of collagenase cleavage of type I collagen in Col1a1^r/r mice is associated with osteocyte/osteoblast death but increases bone deposition in a manner that mimics the parathyroid hormone–induced bone surface activation seen in wild-type mice.