Browsing by Author "Williams, Bart O."

Now showing 1 - 4 of 4
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    Co-deletion of Lrp5 and Lrp6 in the skeleton severely diminishes bone gain from sclerostin antibody administration
    (Elsevier, 2021-02) Lim, Kyung-Eun; Bullock, Whitney A.; Horan, Daniel J.; Williams, Bart O.; Warman, Matthew L.; Robling, Alexander G.; Anatomy and Cell Biology, School of Medicine
    The cysteine knot protein sclerostin is an osteocyte-derived secreted inhibitor of the Wnt co-receptors LRP5 and LRP6. LRP5 plays a dominant role in bone homeostasis, but we previously reported that Sost/sclerostin suppression significantly increased osteogenesis regardless of Lrp5 presence or absence. Those observations suggested that the bone forming effects of sclerostin inhibition can occur through Lrp6 (when Lrp5 is suppressed), or through other yet undiscovered mechanisms independent of Lrp5/6. To distinguish between these two possibilities, we generated mice with compound deletion of Lrp5 and Lrp6 selectively in bone, and treated them with sclerostin monoclonal antibody (Scl-mAb). All mice were homozygous flox for both Lrp5 and Lrp6 (Lrp5f/f; Lrp6f/f), and varied only in whether or not they carried the Dmp1-Cre transgene. Positive (Cre+) and negative (Cre−) mice were injected with Scl-mAb or vehicle from 4.5 to 14 weeks of age. Vehicle-treated Cre+ mice exhibited significantly reduced skeletal properties compared to vehicle-treated Cre− mice, as assessed by DXA, μCT, pQCT, and histology, indicating that Lrp5/6 deletions were effective and efficient. Scl-mAb treatment improved nearly every bone-related parameter among Cre− mice, but the same treatment in Cre+ mice resulted in little to no improvement in skeletal properties. For the few endpoints where Cre+ mice responded to Scl-mAb, it is likely that antibody-induced promotion of Wnt signaling occurred in cell types earlier in the mesenchymal/osteoblast differentiation pathway than the Dmp1-expressing stage. This latter conclusion was supported by changes in some histomorphometric parameters. In conclusion, unlike with the deletion of Lrp5 alone, the bone-selective late-stage co-deletion of Lrp5 and Lrp6 significantly impairs or completely nullifies the osteogenic action of Scl-mAb, and highlights a major role for both Lrp5 and Lrp6 in the mechanism of action for the bone-building effects of sclerostin antibody.
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    Generation and Characterization of Mouse Models for Skeletal Disease
    (SpringerLink, 2021) Foxa, Gabrielle E.; Turner, Lisa M.; Robling, Alexander G.; Yang, Tao; Williams, Bart O.; Anatomy and Cell Biology, School of Medicine
    Our laboratories have used genetically engineered mouse models (GEMMs) to assess genetic contributions to skeletal diseases such as osteoporosis and osteoarthritis. Studies on the genetic contributions to OA are often done by assessing how GEMMs respond to surgical methods that induce symptoms modeling OA. Here, we will describe protocols outlining the induction of experimental OA in mice as well as detailed descriptions of methods for analyzing skeletal phenotypes using micro-computerized tomography and skeletal histomorphometry.
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    Independent validation of experimental results requires timely and unrestricted access to animal models and reagents
    (Public Library of Science, 2020-06-26) Diegel, Cassandra R.; Hann, Steven; Ayturk, Ugur M.; Hu, Jennifer C. W.; Lim, Kyung-Eun; Droscha, Casey J.; Madaj, Zachary B.; Foxa, Gabrielle E.; Izaguirre, Isaac; Robling, Alexander G; Warman, Matthew L.; Williams, Bart O.; Anatomy and Cell Biology, School of Medicine
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    An osteocalcin-deficient mouse strain without endocrine abnormalities
    (PLOS, 2020-05-28) Diegel, Cassandra R.; Hann, Steven; Ayturk, Ugur M.; Hu, Jennifer C. W.; Lim, Kyung-eun; Droscha, Casey J.; Madaj, Zachary B.; Foxa, Gabrielle E.; Izaguirre, Isaac; Core, VAI Vivarium and Transgenics; Paracha, Noorulain; Pidhaynyy, Bohdan; Dowd, Terry L.; Robling, Alexander G.; Warman, Matthew L.; Williams, Bart O.; Anatomy and Cell Biology, School of Medicine
    Osteocalcin (OCN), the most abundant noncollagenous protein in the bone matrix, is reported to be a bone-derived endocrine hormone with wide-ranging effects on many aspects of physiology, including glucose metabolism and male fertility. Many of these observations were made using an OCN-deficient mouse allele (Osc–) in which the 2 OCN-encoding genes in mice, Bglap and Bglap2, were deleted in ES cells by homologous recombination. Here we describe mice with a new Bglap and Bglap2 double-knockout (dko) allele (Bglap/2p.Pro25fs17Ter) that was generated by CRISPR/Cas9-mediated gene editing. Mice homozygous for this new allele do not express full-length Bglap or Bglap2 mRNA and have no immunodetectable OCN in their serum. FTIR imaging of cortical bone in these homozygous knockout animals finds alterations in the collagen maturity and carbonate to phosphate ratio in the cortical bone, compared with wild-type littermates. However, μCT and 3-point bending tests do not find differences from wild-type littermates with respect to bone mass and strength. In contrast to the previously reported OCN-deficient mice with the Osc−allele, serum glucose levels and male fertility in the OCN-deficient mice with the Bglap/2pPro25fs17Ter allele did not have significant differences from wild-type littermates. We cannot explain the absence of endocrine effects in mice with this new knockout allele. Possible explanations include the effects of each mutated allele on the transcription of neighboring genes, or differences in genetic background and environment. So that our findings can be confirmed and extended by other interested investigators, we are donating this new Bglap and Bglap2 double-knockout strain to the Jackson Laboratories for academic distribution.