Biology subjects

Thornburg, H. L.

Publications and source records attributed to Thornburg, H. L..

3 recordsLinked to original sources

bioRxiv2019

High Fat Diet-Induced Obesity Negatively Affects Whole Bone Bending Strength but not Cortical Structure in the Femur

Although body mass index is positively associated with bone mineral density, suggesting obesity is protective against fracture, elderly obese individuals experience greater fracture risk at certain sites than non-obese peers, suggesting bone structural or material changes contribute to fragility. Diet-induced obesity rodent studies have reported detrimental changes to bone microstructure and some apparent-level material properties, but tissue-level material changes are not well understood. Because adipose tissue is highly vascularized, and bone remodeling depends critically on functional vascular supply, concurrent effects on osteovascular perfusion and structure may provide insight about obesity-related bone fragility. This study aimed to determine the effects of obesity on both tissue-level bone properties and osteovascular properties that could negatively impact bone strength. Five-week-old male C57Bl/6J mice were fed either high fat diet (HFD) or control fat diet (CFD) for 17 weeks and received daily treadmill exercise or remained sedentary for eight weeks at ages 14-22 weeks. HFD negatively affected femur bending strength, with 18% lower yield load than CFD. Although HFD negatively altered cancellous microstructure in the distal femur, with 32% lower bone volume fraction than CFD, it did not affect cortical bone geometry in the femoral metaphysis or diaphysis. HFD caused increased carbonate substitution but had no effect on other composition metrics or apparent- or tissue-level material properties in the femoral diaphysis. Exercise did not affect bone strength or microstructure but increased endosteal mineralizing surface in the tibial diaphysis, mineral crystallinity and mineral-to-matrix ratio in the femur, and blood supply to the proximal tibial metaphysis. HFD did not affect blood supply in the tibia or 2D osteovascular structure in the distal femoral metaphysis, indicating that HFD negatively affects cancellous bone without affecting osteovasculature. This study reveals that HFD negatively affected cancellous microstructure without affecting osteovascular structure, and whole-bone strength without altering cortical geometry or material properties.

bioengineering↗

bioRxiv2019

Ischemic Stroke Reduces Bone Perfusion and Alters Osteovascular Structure

RationaleStroke patients lose bone mass and experience fracture at an elevated rate. Although functional intraosseous vasculature is necessary for skeletal maintenance, the effect of stroke on osteovasculature is unknown.\n\nObjectiveTo characterize changes to osteovascular function, structure, and composition following mild-to-moderate-severity ischemic stroke in mice, both with and without exercise therapy.\n\nMethods and ResultsTwelve-week-old male mice (n=27) received either a stroke (middle cerebral artery occlusion) or sham procedure, followed by four weeks of daily treadmill or sedentary activity. Intraosseous perfusion, measured weekly in the proximal tibial metaphysis, was reduced by stroke for two weeks. In the second week of recovery, exercise nearly restored perfusion to sham levels, and perfusion tended to be lower in the stroke-affected limb. At the conclusion of the study, osteovascular structure was assessed with contrast-enhanced computed tomography in the distal femoral metaphysis. Stroke significantly increased osteovascular volume and branching but reduced the relative number of blood vessels close to bone surfaces (6-22 {micro}m away) and increased the relative number more than 52 {micro}m away. These differences in vessel proximity to bone were driven by changes in the stroke-exercise group, indicating compounded effects of stroke and exercise. Exercise, but not stroke, nearly reduced the amount of osteogenic Type H blood vessels in the proximal tibial metaphysis, quantified with immunofluorescence microscopy.\n\nConclusionsThis study is the first to examine the effects of stroke on osteovasculature. Stroke increased the amount of osteovasculature, but since blood vessels close to bone are associated with bone remodeling, the shift in osteovascular structure could play a role in bone loss following stroke. The exercise-induced reduction in the amount of Type H vessels and the stroke-exercise effect on osteovascular structure suggest moderate aerobic activity may have detrimental effects on bone remodeling during early stroke recovery.

bioengineering↗

bioRxiv2019

Stroke prevents exercise-induced gains in bone microstructure but not composition in mice

Ischemic stroke induces rapid loss in bone mineral density that is up to 13 times greater than during normal aging, leading to a markedly increased risk of fracture. Little is known about skeletal changes following stroke beyond density loss. In this study we use a mild-moderate middle cerebral artery occlusion model to determine the effects of ischemic stroke without bedrest on bone microstructure, dynamic bone formation, and tissue composition. Twenty-seven 12-week-old male C57Bl/6J mice received either a stroke or sham surgery and then either received daily treadmill exercise or remained sedentary for four weeks. All mice were ambulatory immediately following stroke, and limb coordination during treadmill exercise was unaffected by stroke, indicating similar mechanical loading across limbs for both stroke and sham groups. Stroke did not directly detriment microstructure, but exercise only stimulated adaptation in the sham group, not the stroke group, with increased bone volume fraction and trabecular thickness in the sham distal femoral metaphysis. Stroke differentially decreased cortical area in the affected limb relative to the unaffected limb of the distal femoral metaphysis, as well as endosteal bone formation rate in the affected tibial diaphysis. Although exercise failed to improve bone microstructure following stroke, exercise increased mineral-to-matrix content in stroke but not sham. Together, these results show that stroke inhibits exercise-induced changes to femoral microstructure but not tibial composition, even without changes to gait. Similarly, affected-unaffected limb differences in cortical bone structure and bone formation rate in ambulatory mice show that stroke affects bone health even without bedrest.

bioengineering↗