Browsing by Author "Kuhlenschmidt, Kali"

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    Control of Bone Anabolism in Response to Mechanical Loading and PTH by Distinct Mechanisms Downstream of the PTH Receptor
    (Wiley, 2017-03) Delgado-Calle, Jesus; Tu, Xiaolin; Pacheco-Costa, Rafael; McAndrews, Kevin; Edwards, Rachel; Pellegrini, Gretel G.; Kuhlenschmidt, Kali; Olivos, Naomie; Robling, Alexander; Peacock, Munro; Plotkin, Lilian I.; Bellido, Teresita; Anatomy, Cell Biology and Physiology, School of Medicine
    Osteocytes integrate the responses of bone to mechanical and hormonal stimuli by poorly understood mechanisms. We report here that mice with conditional deletion of the parathyroid hormone (PTH) receptor 1 (Pth1r) in dentin matrix protein 1 (DMP1)-8kb-expressing cells (cKO) exhibit a modest decrease in bone resorption leading to a mild increase in cancellous bone without changes in cortical bone. However, bone resorption in response to endogenous chronic elevation of PTH in growing or adult cKO mice induced by a low calcium diet remained intact, because the increased bone remodeling and bone loss was indistinguishable from that exhibited by control littermates. In contrast, the bone gain and increased bone formation in cancellous and cortical bone induced by daily injections of PTH and the periosteal bone apposition induced by axial ulna loading were markedly reduced in cKO mice compared to controls. Remarkably, however, wild-type (WT) control littermates and transgenic mice overexpressing SOST injected daily with PTH exhibit similar activation of Wnt/β-catenin signaling, increased bone formation, and cancellous and cortical bone gain. Taken together, these findings demonstrate that Pth1r in DMP1-8kb-expressing cells is required to maintain basal levels of bone resorption but is dispensable for the catabolic action of chronic PTH elevation; and it is essential for the anabolic actions of daily PTH injections and mechanical loading. However, downregulation of Sost/sclerostin, previously shown to be required for bone anabolism induced by mechanical loading, is not required for PTH-induced bone gain, showing that other mechanisms downstream of the Pth1r in DMP1-8kb-expressing cells are responsible for the hormonal effect.
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    Parathyroid hormone receptor signaling induces bone resorption in the adult skeleton by directly regulating the RANKL gene in osteocytes
    (2014-08) Ben-awadh, Abdullah N.; Delgado-Calle, Jesus; Tu, Xiaolin; Kuhlenschmidt, Kali; Allen, Matthew R.; Plotkin, Lilian I.; Bellido, Teresita
    PTH upregulates the expression of the receptor activator of nuclear factor κB ligand (Rankl) in cells of the osteoblastic lineage, but the precise differentiation stage of the PTH target cell responsible for RANKL-mediated stimulation of bone resorption remains undefined. We report that constitutive activation of PTH receptor signaling only in osteocytes in transgenic mice (DMP1-caPTHR1) was sufficient to increase Rankl expression and bone resorption. Resorption in DMP1-caPTHR1 mice crossed with mice lacking the distal control region regulated by PTH in the Rankl gene (DCR(-/-)) was similar to DMP1-caPTHR1 mice at 1 month of age, but progressively declined to reach values undistinguishable from wild-type (WT) mice at 5 months of age. Moreover, DMP1-caPTHR1 mice exhibited low tissue material density and increased serum alkaline phosphatase activity at 5 month of age, and these indices of high remodeling were partially and totally corrected in compound DMP1-caPTHR1;DCR(-/-) male mice, and less affected in female mice. Rankl expression in bones from DMP1-caPTHR1 mice was elevated at both 1 and 5 months of age, whereas it was high, similar to DMP1-caPTHR1 mice at 1 month, but low, similar to WT levels at 5 months in compound mice. Moreover, PTH increased Rankl and decreased Sost and Opg expression in ex vivo bone organ cultures established from WT mice, but only regulated Sost and Opg expression in cultures from DCR(-/-) mice. PTH also increased RANKL expression in osteocyte-containing primary cultures of calvarial cells, in isolated murine osteocytes, and in WT but not in DCR(-/-) osteocyte-enriched bones. Thus, PTH upregulates Rankl expression in osteocytes in vitro, ex vivo and in vivo, and resorption induced by PTH receptor signaling in the adult skeleton requires direct regulation of the Rankl gene in osteocytes.
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    Parathyroid hormone receptor signaling induces bone resorption in the adult skeleton by directly regulating the RANKL gene in osteocytes
    (The Endocrine Society, 2014-08) Ben-awadh, Abdullah N.; Delgado-Calle, Jesus; Tu, Xiaolin; Kuhlenschmidt, Kali; Allen, Matthew R.; Plotkin, Lilian I.; Bellido, Teresita; Department of Anatomy and Cell Biology, IU School of Medicine
    PTH upregulates the expression of the receptor activator of nuclear factor κB ligand (Rankl) in cells of the osteoblastic lineage, but the precise differentiation stage of the PTH target cell responsible for RANKL-mediated stimulation of bone resorption remains undefined. We report that constitutive activation of PTH receptor signaling only in osteocytes in transgenic mice (DMP1-caPTHR1) was sufficient to increase Rankl expression and bone resorption. Resorption in DMP1-caPTHR1 mice crossed with mice lacking the distal control region regulated by PTH in the Rankl gene (DCR−/−) was similar to DMP1-caPTHR1 mice at 1 month of age, but progressively declined to reach values undistinguishable from wild-type (WT) mice at 5 months of age. Moreover, DMP1-caPTHR1 mice exhibited low tissue material density and increased serum alkaline phosphatase activity at 5 month of age, and these indices of high remodeling were partially and totally corrected in compound DMP1-caPTHR1;DCR−/− male mice, and less affected in female mice. Rankl expression in bones from DMP1-caPTHR1 mice was elevated at both 1 and 5 months of age, whereas it was high, similar to DMP1-caPTHR1 mice at 1 month, but low, similar to WT levels at 5 months in compound mice. Moreover, PTH increased Rankl and decreased Sost and Opg expression in ex vivo bone organ cultures established from WT mice, but only regulated Sost and Opg expression in cultures from DCR−/− mice. PTH also increased RANKL expression in osteocyte-containing primary cultures of calvarial cells, in isolated murine osteocytes, and in WT but not in DCR−/− osteocyte-enriched bones. Thus, PTH upregulates Rankl expression in osteocytes in vitro, ex vivo and in vivo, and resorption induced by PTH receptor signaling in the adult skeleton requires direct regulation of the Rankl gene in osteocytes.