Bone fractures are one of the most common injuries in the United States, encompassing 6.2 million incidences, and costing the healthcare system roughly $20 billion annually. The majority of this cost falls upon a unique type of fracture known as a non-union fracture, defined by incomplete healing after 9 months. The economic burden in combination with the frequency by which these incidences occur offer a unique opportunity for research and improvement in the healthcare field.
Previous research on the fracture repair process showed that dietary deficiency led to delayed healing producing a rachitic-like effect on the endochondral bone formation process that occurs during fracture healing. This research will build off the understanding of hypophosphatemia on bone fracture repair utilizing a unique temporal clustering approach to assess changes in the transcriptomic expression within callus tissues of control fed and dietary phosphate restricted animals.
Using a temporal cluster modeling technique developed by our group (Lu et al. 2019), twelve clusters were generated for the gene expression data extracted from the callus tissues of B6 strain mice at time points 3, 5, 7, 10, 14, 18-, 21-, 28-, and 35-days post fracture, in, control and phosphate restricted dietary groups. Groupings of clusters were used to establish the temporal expression patterns over the time course of healing and identify the movement of genes that changed their temporal expression patterns between the control and phosphate restricted diets. Biological process categories were established for each cluster, grouping using both Ingenuity Pathway Analysis (IPA) and the NIH DAVID Bioinformatics Database ontology assessment programs. Genes based on their association with four key tissue developmental processes in fracture repair, skeletogenesis, myogenesis, vasculogenesis, and neurogenesis were analyzed.
The analysis showed shifts to later peak expression times for all four categories. Further analysis illuminated three specific regulatory pathways that were significantly impacted by hypophosphatemia, Hippo and WNT signaling pathways and the circadian rhythm pathway while oxidative phosphorylation was both shifted and showed reduced expression. The shifts in expression time and level of these pathways demonstrate their importance to bone fracture repair and their impacts on mesenchymal stem cell differentiation.
From the data analysis it is clear that limiting dietary phosphate results in impaired mesenchymal stem cell differentiation caused by delayed Hippo and WNT signaling. Further it is evident that the processes of skeletogenesis, myogenesis, vasculogenesis, and neurogenesis are heavily interconnected, often showing overlapping genes through all four processes. Based on these shifts and impairments in specific signaling we identified novel mechanisms by which hypophosphatemia can impair fracture callus growth and development and delay healing.
| Identifer | oai:union.ndltd.org:bu.edu/oai:open.bu.edu:2144/43472 |
| Date | 24 November 2021 |
| Creators | Norton, Casey |
| Contributors | Gerstenfeld, Louis C. |
| Source Sets | Boston University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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