Browsing by Author "Gabel, Leigh Elizabeth Christine"

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    Effects of pregnancy and lactation on maternal bone status in mice artificially selected for larger skeletons
    (2023-06) Tran, Vicki; Rolian, Campbell Paul; Cobb, John Andrew; Manske, Sarah Lynn; Rosa, Brielle Vastola; Gabel, Leigh Elizabeth Christine
    Pregnancy and lactation are intensive physiological processes that require increased calcium demand from the maternal systems. This is mediated by changes to the maternal endocrine axes and may result in excessive bone resorption on the maternal skeleton. Pregnancy- and lactation-related changes in bone have yet to be investigated in a model with poorer bone quality and quantity. The Longshanks mouse (LS) is a mouse line selectively bred for increased tibia length. Although longer, the LS tibia is also weaker due to its altered microarchitecture of thinner and more widely spaced trabeculae. In this study, we sought to investigate the impacts of pregnancy and lactation on maternal bone microarchitecture using the LS as a model of a compromised skeletal phenotype with lower bone quality/quantity. Our study found that LS mice had increased bone quantity at postpartum and substantial decreases at mid-lactation when compared to Controls. The physiological response of increased bone postpartum thus depends on prepregnancy population characteristics and is possibly a mechanism to help protect maternal calcium reserves from excessive depletion. The differences in bone are induced by altered endocrine signaling in LS vs. CTL. The larger improvements in microarchitecture postpartum in the LS may be a result of increased OPG signalling, whereas bone resorption is likely increased in the LS during lactation by PTH and SOST action. This would allow increased mobilization of calcium stores and result in reduced maternal bone quantity/quality as seen in the LS mouse. Overall, this study demonstrated a possible protective response induced by pregnancy, resulting in increased bone volume postpartum, however lactational bone loss should be especially considered in populations with poor bone quality/quantity.
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    The Influence of Physical Activity on Bone Strength in Children and Adolescents
    (2023-12-21) Alexander, Christina Jewel; Gabel, Leigh Elizabeth Christine; Edwards, William Brent; Manske, Sarah Lynn; Obeid, Joyce
    Bone adapts to its loading environment throughout the lifespan, with peak bone mass accrual occurring during childhood and adolescence. Therefore, understanding how physical activity (PA) impacts bone during childhood and adolescence is especially important. Accelerometers are commonly used to measure PA and examine its associations with bone outcomes. In this thesis, I investigated whether using new accelerometry metrics to synthesize count-based accelerometry PA data would help uncover associations between specific parameters of PA and bone strength. First, I compared PA measured by older (count-based) and newer accelerometers (raw accelerations), to determine whether they were comparable. I discovered that count-based data is not directly comparable between the two accelerometers; however, minutes per day in different intensities of activity (e.g., sedentary, light, moderate, and vigorous) are comparable (mean bias <5 min/d at all intensities). I then compared count-based (older format) and raw accelerations (newer format) and found that although a conversion from count-based to raw accelerations is not possible, a metric initially designed for use with raw accelerations (the intensity gradient (IG)) can be reproduced with count data (mean bias = -0.15; 95% LOA [-0.65, 0.34]). Second, using four years of longitudinal data from over 300 children and adolescents, I examined whether IG and a daily impact score (DIS) were more strongly associated with bone strength than a metric traditionally used to examine these associations, minutes per day spent in vigorous physical activity (VPA). These metrics differ in that both the IG and DIS use the full spectrum of accelerometry data, whereas VPA does not. Furthermore, the DIS weights the intensity of the accelerations more heavily than the number. Using linear mixed effects models, I determined that the DIS was positively associated with bone strength independent of VPA (β_DIS = 25.2 (7.0, 43.6), p <0.05; β_VPA = 3.2 (-6.1, 1.4), p = 0.67), indicating that short, high-intensity physical activity is best for bone strength accrual in children and adolescents. These findings should be used to inform physical activity guidelines with the aim of improving bone strength in children and adolescents.