Browsing by Author "Pellegrini, Gretel G."

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    Avenanthramides Prevent Osteoblast and Osteocyte Apoptosis and Induce Osteoclast Apoptosis in Vitro in an Nrf2-Independent Manner
    (MDPI, 2016-07-11) Pellegrini, Gretel G.; Morales, Cynthya C.; Wallace, Taylor C.; Plotkin, Lilian I.; Bellido, Teresita; Department of Anatomy & Cell Biology, IU School of Medicine
    Oats contain unique bioactive compounds known as avenanthramides (AVAs) with antioxidant properties. AVAs might enhance the endogenous antioxidant cellular response by activation of the transcription factor Nrf2. Accumulation of reactive oxygen species plays a critical role in many chronic and degenerative diseases, including osteoporosis. In this disease, there is an imbalance between bone formation by osteoblasts and bone resorption by osteoclasts, which is accompanied by increased osteoblast/osteocyte apoptosis and decreased osteoclast apoptosis. We investigated the ability of the synthethic AVAs 2c, 2f and 2p, to 1-regulate gene expression in bone cells, 2-affect the viability of osteoblasts, osteocytes and osteoclasts, and the generation of osteoclasts from their precursors, and 3-examine the potential involvement of the transcription factor Nrf2 in these actions. All doses of AVA 2c and 1 and 5 µM dose of 2p up-regulated collagen 1A expression. Lower doses of AVAs up-regulated OPG (osteoprotegerin) in OB-6 osteoblastic cells, whereas 100 μM dose of 2f and all concentrations of 2c down-regulated RANKL gene expression in MLO-Y4 osteocytic cells. AVAs did not affect apoptosis of OB-6 osteoblastic cells or MLO-Y4 osteocytic cells; however, they prevented apoptosis induced by the DNA topoisomerase inhibitor etoposide, the glucocorticoid dexamethasone, and hydrogen peroxide. AVAs prevented apoptosis of both wild type (WT) and Nrf2 Knockout (KO) osteoblasts, demonstrating that AVAs-induced survival does not require Nrf2 expression. Further, KO osteoclast precursors produced more mature osteoclasts than WT; and KO cultures exhibited less apoptotic osteoclasts than WT cultures. Although AVAs did not affect WT osteoclasts, AVA 2p reversed the low apoptosis of KO osteoclasts. These in vitro results demonstrate that AVAs regulate, in part, the function of osteoblasts and osteocytes and prevent osteoblast/osteocyte apoptosis and increase osteoclast apoptosis; further, these regulatory actions are independent of Nrf2.
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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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    PTHrP-Derived Peptides Restore Bone Mass and Strength in Diabetic Mice: Additive Effect of Mechanical Loading
    (Wiley, 2017-03) Maycas, Marta; McAndrews, Kevin A.; Sato, Amy Y.; Pellegrini, Gretel G.; Brown, Drew M.; Allen, Matthew R.; Plotkin, Lilian I.; Gortazar, Arancha R.; Esbrit, Pedro; Bellido, Teresita; Department of Anatomy and Cell Biology, School of Medicine
    There is an unmet need to understand the mechanisms underlying skeletal deterioration in diabetes mellitus (DM) and to develop therapeutic approaches to treat bone fragility in diabetic patients. We demonstrate herein that mice with type 1 DM induced by streptozotocin exhibited low bone mass, inferior mechanical and material properties, increased bone resorption, decreased bone formation, increased apoptosis of osteocytes, and increased expression of the osteocyte-derived bone formation inhibitor Sost/sclerostin. Further, short treatment of diabetic mice with parathyroid hormone related protein (PTHrP)-derived peptides corrected these changes to levels undistinguishable from non-diabetic mice. In addition, diabetic mice exhibited reduced bone formation in response to mechanical stimulation, which was corrected by treatment with the PTHrP peptides, and higher prevalence of apoptotic osteocytes, which was reduced by loading or by the PTHrP peptides alone and reversed by a combination of loading and PTHrP peptide treatment. In vitro experiments demonstrated that the PTHrP peptides or mechanical stimulation by fluid flow activated the survival kinases ERKs and induced nuclear translocation of the canonical Wnt signaling mediator β-catenin, and prevented the increase in osteocytic cell apoptosis induced by high glucose. Thus, PTHrP-derived peptides cross-talk with mechanical signaling pathways to reverse skeletal deterioration induced by DM in mice. These findings suggest a crucial role of osteocytes in the harmful effects of diabetes on bone and raise the possibility of targeting these cells as a novel approach to treat skeletal deterioration in diabetes. Moreover, our study suggests the potential therapeutic efficacy of combined pharmacological and mechanical stimuli to promote bone accrual and maintenance in diabetic subjects.