Browsing by Subject "bone homeostasis"
Item Extended Treatment with a High Dosage of EGCG to Rescue Appendicular Bone Abnormalities in a Down Syndrome Mouse Model(Office of the Vice Chancellor for Research, 2015-04-17) Singh, Prabhjot; Roper, Randall J.; Abeysekera, IrushiIndividuals with Down syndrome (DS) show significant abnormalities in cognitive abilities, muscle tone, and bone homeostasis. DS is caused by a triplication of the 21st human chromosome (Hsa21). Previous research conducted by our lab using mouse models indicates that three copies of Dyrk1a causes the appendicular skeletal deficits associated with DS. Ts65Dn mouse model carries 50% of the genes homologous to Hsa21, and exhibit excellent phenotypic model for the skeletal deficits seen in individuals with DS, such as low bone mineral density, altered bone structure, and decreased cortical bone. Epigallocatechin-3-gallate (EGCG) is a green tea polyphenol that inhibits Dyrk1a activity. In a previous study, we showed that a three-week, low dose (10mg/kg/day) treatment of EGCG rescued bone mineral density, and trabecular bone to that of euploid levels, but not cortical bone. We hypothesize that increasing the concentration and duration of the treatment will be sufficient enough to more fully restore bone abnormalities by rescuing femoral bone mineral density, bone volume, and improving overall bone strength. This project explores the effects of using a prolonged seven-week, high dosage (100mg/kg/day) treatment on specific bone phenotypes. Dual Energy X-ray absorptiometry (DXA), MicroCT, and mechanical testing will be used as our means of analysis of the treated and untreated bones.Item Genome-wide Analysis Using ChIP-seq Reveals Novel Downstream Targets of Stat3(Office of the Vice Chancellor for Research, 2015-04-17) Corry, Kylie A.; Li, JiliangMany cells are involved in the orchestra that is bone homeostasis--particularly osteoclasts and osteoblasts who mediate remodeling of bones. This creates a balance that must be kept in check, otherwise pathologies arise. The JAK-Stat signaling pathway is crucial to maintaining this balance. It has long been known that the transcription factor Stat3 has more profound effects on bone homeostasis than other members of the Stat family of proteins. Recently, a genetic condition called Job’s Syndrome has been specifically linked to point mutations in the STAT3 gene. These patients present with severe bone abnormalities including prominent foreheads, broad nasal bridges, and abnormal eye spacing. Therefore, our lab has extensively studied conditional knockouts of Stat3 in all three types of bones cells in mice and observed severe deficiencies in numerous parameters of normal bone phenotypes. Stat3 seems to play a principal role in the signaling that takes place upon mechanical loading of bone tissues and calling cells into action where they are needed. Furthermore, STAT3 has been found to be up-regulated in the early-response gene cluster following mechanical loading. Our current approach to studying Stat3’s effects on bone include employing available ChIP-seq data in order to elucidate the genome-wide binding patterns of Stat3. From the peak distribution, we can begin to uncover novel downstream effectors of Stat3 signaling that are responsible for the observed phenotypes in our mouse knockout model. A preliminary look at the ChIP-seq data reveals Wnt and Nrf2 signaling to be under the control of Stat3. In our further research we endeavor to experimentally confirm the ChIP-seq data for Stat3 with RNA-seq experiments in the hopes of finding potential therapeutic targets for bone pathologies.Item Mechanotransduction in Living Bone: Effects of the Keap1-Nrf2 Pathway(2019-08) Priddy, Carlie; Li, Jiliang; Dai, Guoli; Wallace, Joseph M.The Keap1-Nrf2 pathway regulates a wide range of cytoprotective genes, and has been found to serve a protective and beneficial role in many body systems. There is limited information available, however, about its role in bone homeostasis. While Nrf2 activation has been suggested as an effective method of increasing bone mass and quality, there have been conflicting reports which associate Keap1 deficiency with detrimental phenotypes. As Keap1 deletion is a common method of Nrf2 activation, further study should address the impacts of various methods of regulating Nrf2 expression. Also, little research has been conducted on the specific pathways by which Nrf2 activation improves bone quality. In this study, the effects of alterations to Nrf2 activation levels were explored in two specific and varied scenarios. In the first experiment, moderate Nrf2 activation was achieved via partial deletion of its sequestering protein, Keap1, in an aging mouse model. The hypothesis tested here is that moderate Nrf2 activation improves bone quality by affecting bone metabolism and response to mechanical loading. The results of this first experiment suggest a subtle, sex-specific effect of moderate Nrf2 activation in aging mice which improves specific indices of bone quality to varying degrees, but does not affect loading-induced bone formation. It is likely that the overwhelming phenotypic impacts associated with aging or the systemic effects of global Keap1 deficiency may increase the difficulty in parsing out significant effects that can be attributed solely to Nrf2 activation. In the second experiment, a cell-specific knockout of Nrf2 in the osteocytes was achieved using a Cre/Lox breeding system. The hypothesis tested here is that osteocyte-specific deletion of Nrf2 impairs bone quality by affecting bone metabolism and response to mechanical loading. The results of this experiment suggest an important role of Nrf2 in osteocyte function which improves certain indices of bone quality, which impacts male and female bones in different 7 ways, but did not significantly impact loading-induced bone formation. Further studies should modify the method of Nrf2 activation in an effort to refine the animal model, allowing the effects of Nrf2 to be isolated from the potential systemic effects of Keap1 deletion. Future studies should also utilize other conditional knockout models to elucidate the effects of Nrf2 in other specific cell types.