Browsing by Author "Burr, David"

Now showing 1 - 6 of 6
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    Bone quality in ovariectomized monkeys treated with two doses of teriparatide for either 18 months, or 12 months followed by withdrawal for 6 months
    (Elsevier, 2022) Paschalis, Eleftherios; Gamsjaeger, Sonja; Burr, David; Anatomy, Cell Biology and Physiology, School of Medicine
    Previous studies of ovariectomized monkeys, treated with recombinant human parathyroid hormone (PTH)(1-34) at 1 (clinically relevant) or 5 mg/kg/day for 18 months or for 12 months followed by 6 months withdrawal from treatment, displayed significant changes in the geometry, histomorphometry, and bone quality (albeit without strict tissue age criteria) of cortical bone of the midshaft humerus. Since bone quality significantly depends on tissue age amongst other factors, the aim of the present study was to establish the bone-turnover independent effects of two doses of PTH, as well as the effects of treatment withdrawal on bone quality, by measuring bone material composition at precisely known tissue ages ranging from osteoid, to mineralized tissue older than 373 days. We also investigated the relationship between osteoid composition and the mineral content of the youngest formed mineralized tissue. The variables considered in the present study were: i) the mineral / matrix ratio (correlates with bone bending stiffness); ii) the mineral content at the youngest tissue age; iii) tissue water content (correlates with bone toughness and strength); iv) glycosaminoglycan content (negative modulator of bone mineralization); v) mineral maturity/crystallinity (inversely correlates with bone strength); vi) pyridinoline content (determinant of bone strength even in cases where bone mineral content does not correlate with fracture occurrence). Raman microspectroscopic analysis of bone tissue from the mid-shaft humerus of ovariectomized monkeys demonstrated that effects of PTH administration for 18 months on bone quality are dependent on dose, while the clinically relevant one reverses the effects of ovariectomy. Additionally, both doses investigated in the present study restore the mineralization regulation mechanisms to SHAM levels. The experiments involving 12-month PTH treatment followed by 6 months of withdrawal showed that the beneficial effects induced by 12 months of clinically relevant PTH therapy were sustained after six months of therapy withdrawal.
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    CaMKK2 Signaling in Metabolism and Skeletal Disease: A New Axis with Therapeutic Potential
    (2022-07) Williams, Justin N.; Sankar, Uma; Evans-Molina, Carmella; Bonewald, Lynda; Burr, David; Allen, Matthew
    Type 2 diabetes mellitus (T2DM) is a growing problem globally and is associated with increased fracture risk and delayed bone healing. Novel approaches are needed in the treatment of T2DM and the resulting diabetic osteopathy. Recent studies highlight the role of bone as an endocrine organ producing factors that communicate with distant tissues to modulate systemic glucose metabolism. Ca2+/calmodulin (CaM)-dependent protein kinase kinase 2 (CaMKK2) is a potent regulator of whole-body energy metabolism, inflammation, bone remodeling and fracture healing. Genetic ablation of CaMKK2 protects from diet-induced obesity, insulin resistance and inflammation, while enhancing pancreatic β cell survival and insulin secretion. Deletion or inhibition of CaMKK2 promotes bone accrual by stimulating osteoblast-mediated bone formation and suppressing osteoclast-mediated bone resorption; however, its specific role in osteocytes, the master regulator of bone remodeling remains unknown. Here we demonstrate that conditional deletion of CaMKK2 from osteocytes enhances bone mass in 3-month-old female, but not male mice, due to suppression of osteoclasts. Conditioned media experiments and proteomics analysis revealed that female osteocytes lacking CaMKK2 suppressed osteoclast formation and function through enhanced secretion of calpastatin, a potent inhibitor of calpains, which are calciumdependent cysteine proteases that support osteoclasts. Further, to determine if CaMKK2- deficient osteocytes regulate whole-body glucose homeostasis, we placed these mice on a high-fat diet (HFD) for a period of 16 weeks. Although the diet did not significantly impact bone mass or strength, we found that conditional deletion of CaMKK2 in osteocytes enhanced bone microarchitecture in 6-month-old male and female mice. We also observed that conditional deletion of CaMKK2 from osteocytes protected male and female mice from HFD-induced obesity and insulin insensitivity. Taken together, these findings highlight CaMKK2 as a potent regulator of osteocyte-mediated modulation of bone remodeling and whole-body energy metabolism.
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    Estrogen depletion alters mineralization regulation mechanisms in an ovariectomized monkey animal model
    (Elsevier, 2019-03) Paschalis, E. P.; Gamsjaeger, S.; Condon, Keith; Klaushofer, K.; Burr, David; Anatomy and Cell Biology, School of Medicine
    Ovariectomized animal models have been extensively used in osteoporosis research due to the resulting loss of bone mass. The purpose of the present study was to test the hypothesis that estrogen depletion alters mineralization regulation mechanisms in an ovariectomized monkey animal model. To achieve this we used Raman microspectroscopy to analyze humeri from monkeys that were either SHAM-operated or ovariectomized (N = 10 for each group). Measurements were made as a function of tissue age and cortical surface (periosteal, osteonal, endosteal) based on the presence of calcein fluorescent double labels. In the present work we focused on osteoid seams (defined as a surface with evident calcein labels, 1 μm distance away from the mineralizing front, and for which the Raman spectra showed the presence of organic matrix but not mineral), as well as the youngest mineralized tissue between the second fluorescent label and the mineralizing front, 1 μm inwards from the front with the phosphate mineral peak evident in the Raman spectra (TA1). The spectroscopically determined parameters of interest were the relative glycosaminoglycan (GAG) and pyridinoline (Pyd) contents in the osteoid, and the mineral content in TA1. At all three cortical surfaces, significant correlations were evident in the SHAM-operated animals between osteoid GAG (negative) and Pyd content, and mineral content, unlike the OVX animals. These results suggest that in addition to the well-established effects on turnover rates and bone mass, estrogen depletion alters the regulation of mineralization by GAGs and Pyd.
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    Morphologic Changes in the Mandibular Condyle of Growing Sprague-Dawley Rats After Electrolytic Lesioning of the Trigeminal Motor Nucleus
    (1994) Hurst, Charles A.; Byrd, Kenneth E.; Roberts, W. Eugene; Garetto, Lawrence P.; Hohlt, William; Burr, David
    Lesioning motoneurons in the brainstem alters biomechanical forces and affects craniofacial growth by producing skeletal asymmetries. The purpose of this study was to examine changes that occur in the mandibular condyle in rats that have had their trigeminal motor nucleus (TMN) lesioned. The following null hypothesis was tested: unilateral electrolytic lesioning of the TMN has no effect on condylar morphology in growing rats. To accomplish this, experimental rats received a small electrolytic lesion in their left side TMN. The controls received a sham lesion that caused TMN stimulation with no electrolytic lesion produced. Seven rats from each group were sacrificed at 28, 56, and 84 days postoperatively. The rats were decapitated and their skulls were dried. Mandibular condyles were harvested from the dry rat skulls. The specimens were embedded and sectioned. The sections were stained with H&E. The following parameters were measured: condyle perimeter, condylar widths at 125 μm increments measured with a grid aligned with the condylar neck, width of the condylar neck, and bone surface area proximal to the condylar neck measurement. Experimental groups were compared with control groups by means of factorial analysis of variance, ANOVA, with the factors being the experimental operation and the time of sacrifice. Findings show significant or near borderline significant F tests for right-left differences and side-by-group interactions for width at 625 μm, 750 μm, 875 μm, and 1000 μm from the top of the condyle; but not at the other widths measured. Right-left difference and side-by-time interaction for shape factor measurement were also shown to be significant. The null hypothesis stating unilateral electrolytic lesioning of the TMN has no effect on condylar morphology in growing rats was therefore rejected. The failure to reach significance in some parameters may have been due to the small number of specimens. Due to the fragile nature of the dried specimens, group numbers ranged from seven to four condyle pairs per group. In conclusion, lesions to the TMN of growing rats affect the morphology of the mandibular condyle in the medial-lateral plane. Alterations in morphology during growth after lesioning the TMN were likely caused by changes in the neuromuscular activity of masticatory muscles and their biomechanical effects on bone. Data in this study suggest that it is valuable to view mandibular condyles from a frontal view (i.e., frontal tomography) when altered condylar morphology in human patients is suspected.
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    Nrf2 regulates mass accrual and the antioxidant endogenous response in bone differently depending on the sex and age
    (Plos, 2017-02-02) Pellegrini, Gretel Gisela; Cregor, Meloney; McAndrews, Kevin; Morales, Cynthya Carolina; McCabe, Linda Doyle; McCabe, George P.; Peacock, Munro; Burr, David; Weaver, Connie; Bellido, Teresita; Department of Anatomy & Cell Biology, IU School of Medicine
    Accumulation of reactive oxygen species (ROS) is an important pathogenic mechanism underling the loss of bone mass and strength with aging and other conditions leading to osteoporosis. The transcription factor erythroid 2-related factor2 (Nrf2) plays a central role in activating the cellular response to ROS. Here, we examined the endogenous response of bone regulated by Nrf2, and its relationship with bone mass and architecture in the male and female murine skeleton. Young (3 month-old) and old (15 month-old) Nrf2 knockout (KO) mice of either sex exhibited the expected reduction in Nrf2 mRNA expression compared to wild type (WT) littermates. Nrf2 deletion did not lead to compensatory increase in Nrf1 or Nrf3, other members of this transcription factor family; and instead, Nrf1 expression was lower in KO mice. Compared to the respective WT littermate controls, female KO mice, young and old, exhibited lower expression of both detoxifying and antioxidant enzymes; young male KO mice, displayed lower expression of detoxifying enzymes but not antioxidant enzymes; and old male KO mice showed no differences in either detoxifying or antioxidant enzymes. Moreover, old male WT mice exhibited lower Nrf2 levels, and consequently lower expression of both detoxifying and antioxidant enzymes, compared to old female WT mice. These endogenous antioxidant responses lead to delayed rate of bone acquisition in female KO mice and higher bone acquisition in male KO mice as quantified by DXA and μCT, demonstrating that Nrf2 is required for full bone accrual in the female skeleton but unnecessary and even detrimental in the male skeleton. Therefore, Nrf2 regulates the antioxidant endogenous response and bone accrual differently depending on sex and age. These findings suggest that therapeutic interventions that target Nrf2 could be developed to enhance the endogenous antioxidant response in a sex- and age-selective manner.
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    The Effect of Etidronate on Alveolar Bone Remodeling in Dog Mandible
    (2001) Handick, Kimberly E.; Garetto, Lawrence P.; Burr, David; Campbell, John; Katona, Thomas R.; Shanks, James
    Etidronate belongs to a class of drugs called bisphosphonates, which are prescribed for the treatment of osteoporosis and other metabolic bone diseases. The main effect of these drugs is to inhibit bone resorption and, thereby, bone remodeling (coupled bone turnover). Extensive research has been done to study the effects of these drugs on the adult skeleton, but no study has quantified the effects of bisphosphonates on different regions of the mandible or compared the effects on alveolar bone remodeling with another cortical site. The purpose of the project was to histomorphometrically quantify the effects of etidronate therapy on the alveolar bone of the mandible and to determine if this site is affected differently than the cortical bone in the rib. The hypotheses were as follows: Etidronate therapy inhibits rib and mandibular cortical bone remodeling. Etidronate has a greater effect on remodeling inhibition in sites (alveolar vs. rib) with normally higher remodeling activity. High doses of etidronate impair normal mineralization of alveolar and rib cortical bone. Specimens from eight mature female dogs were obtained from an ongoing experiment on bisphosphonates. The dogs were randomly assigned to either a control group, a high dose experimental group (5.0 mg/kg/day), or a low dose experimental group (0.5 mg/kg/day). Drug treatment time was seven months. To quantify regional bone remodeling, intravitally labeled ribs and mandibles were analyzed using stereological point-hit and linear intercept methods to determine bone formation rate (BFR) and mineral apposition rate (MAR). Alveolar bone was analyzed by region (coronal, middle, and basal). We found extensive variability in our data which was most likely due to the small number of specimens, and the small amount of tissue in each specimen. Results show that as drug dosage increases MAR and BFR tend to decrease. In the high dose groups remodeling is turned off completely. This trend is seen in both mandible and rib. In the control animals, the highest remodeling rates were seen in the coronal region. Remodeling in the coronal region was not significantly different than the rib. The percent change in MAR and BFR from control to the low dose group is greatest in the coronal region of the mandible. Bone volume appears to not be affected by drug treatment. Although osteoid volume and cortical osteoid surface changes were not statistically significant, trabecular osteoid surface did demonstrate a dose dependent increase. The data suggest that bone remodeling in the rib and mandible decreases with etidronate therapy to the extent that with the high dose etidronate therapy remodeling appears to be shut off. Also, etidronate appears to have a greater affect on bone that has higher turnover rates. Aside from the regional differences in the mandible, the rib does not appear to be affected differently than the mandible.