Bone tissue hypoxia generally occurs as a consequence of skeletal trauma. Regional hypoxia at a fracture site is probably the best-documented example of tissue hypoxia, wherein disruption of blood vessels and bone tissue are causative. On a smaller scale, stress fractures that locally disrupt the lacunar-canalicular space within bone, and, therefore, interrupt the movement of gases and nutrients could cause localized hypoxia. In addition, there is evidence to suggest that unloading of bone, which would disrupt mechanically driven movement of gases and nutrients within the lacunar-canalicular space of bone, leads to cellular hypoxia within the tissue. Recent in vivo studies in the literature suggest that alterations in oxygen availability are a potent stimulus for bone formation. In addition, we have novel data demonstrating that sclerostin, a target of BMP signaling that regulates the activity of Wnt glycoproteins and therefore inhibits bone formation, is suppressed by a reduction in oxygen tension in osteoblastic cells. The importance of sclerostin in maintaining normal bone physiology is underscored by two disease states, van Buchem and sclerosteosis, which are both characterized by bone overgrowth caused by hyperactive osteoblasts. The cellular mechanisms behind hypoxia-driven bone formation versus hypoxia-regulated sclerostin expression remain unknown. Our central hypothesis is that low tissue oxygen decreases sclerostin expression, which facilitates enhanced bone formation through Wnt signaling. Provided the ample evidence that independently implicates the Wnt/Lrp5/sclerostin axis and the anabolic effect of hypoxia in mediating both embryonic and post- natal skeletal development, combined with our novel data indicating that hypoxia attenuates sclerostin expression, we hypothesize that hypoxia facilitates enhanced bone formation through Wnt signaling and sclerostin. We will test this hypothesis in two Specific Aims encompassing in vitro molecular approaches and novel in vivo murine model systems. This project has the potential to yield new insight into the relationship between hypoxia and bone and identify novel pathways that could be manipulated pharmacologically to promote bone repair. Considering that orthopaedic trauma comprises the majority of injuries in US armed conflicts and the significant impact of stress fracture on the health and operational readiness of military personnel, a more thorough understanding of the relationship between hypoxia, bone cell physiology and bone health is imperative.
Project narrative: As we complete our specific aims we will identify the molecular mechanisms behind cellular oxygen sensing and elucidate how hypoxia regulates gene expression. In addition, we will examine the ramifications of hypoxia-driven Sclerostin suppression, on signaling pathways (Wnt/2-catenin signaling) that ultimately lead to bone formation. This project has the potential to yield new insight into the relationship between hypoxia and bone and identify novel pathways that could be manipulated pharmacologically to promote bone repair or even administered prophylactically to prevent bone damage. Understanding the relationship between oxygen supply and bone cell physiology will also have ramifications for the development of effective tissue engineering strategies for bone repair.
|Wong, Alice; Loots, Gabriela G; Yellowley, Clare E et al. (2015) Parathyroid hormone regulation of hypoxia-inducible factor signaling in osteoblastic cells. Bone 81:97-103|
|Chahine, Nadeen O; Collette, Nicole M; Thomas, Cynthia B et al. (2014) Nanocomposite scaffold for chondrocyte growth and cartilage tissue engineering: effects of carbon nanotube surface functionalization. Tissue Eng Part A 20:2305-15|
|Binder, Bernard Y K; Genetos, Damian C; Leach, J Kent (2014) Lysophosphatidic acid protects human mesenchymal stromal cells from differentiation-dependent vulnerability to apoptosis. Tissue Eng Part A 20:1156-64|
|Donahue, Henry J; Genetos, Damian C (2013) Genomic approaches in breast cancer research. Brief Funct Genomics 12:391-6|
|Loots, Gabriela G; Keller, Hansjoerg; Leupin, Olivier et al. (2012) TGF-Î² regulates sclerostin expression via the ECR5 enhancer. Bone 50:663-9|
|Genetos, Damian C; Zhou, Zhiyi; Li, Zhongyong et al. (2012) Age-related changes in gap junctional intercellular communication in osteoblastic cells. J Orthop Res 30:1979-84|
|Hoch, Allison I; Binder, Bernard Y; Genetos, Damian C et al. (2012) Differentiation-dependent secretion of proangiogenic factors by mesenchymal stem cells. PLoS One 7:e35579|
|Toupadakis, Chrisoula A; Wong, Alice; Genetos, Damian C et al. (2012) Long-term administration of AMD3100, an antagonist of SDF-1/CXCR4 signaling, alters fracture repair. J Orthop Res 30:1853-9|
|Watari, Shinya; Hayashi, Kei; Wood, Joshua A et al. (2012) Modulation of osteogenic differentiation in hMSCs cells by submicron topographically-patterned ridges and grooves. Biomaterials 33:128-36|
|Collette, Nicole M; Genetos, Damian C; Economides, Aris N et al. (2012) Targeted deletion of Sost distal enhancer increases bone formation and bone mass. Proc Natl Acad Sci U S A 109:14092-7|
Showing the most recent 10 out of 17 publications