RESUMO
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 4 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 distal femoral metaphysis for the affected limb relative to the unaffected limb, 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.
RESUMO
Bacterial pneumonia is a leading cause of death late after burn injury due to the severe immune dysfunction that follows this traumatic injury. The Mechanistic/Mammalian Target of Rapamycin (mTOR) pathway drives many effector functions of innate immune cells required for bacterial clearance. Studies have demonstrated alterations in multiple cellular processes in patients and animal models following burn injury in which mTOR is a central component. Goals of this study were to (1) investigate the importance of mTOR signaling in antimicrobial activity by neutrophils and (2) therapeutically target mTOR to promote normalization of the immune response. We utilized a murine model of 20% total body surface area burn and the mTOR-specific inhibitor rapamycin. Burn injury led to innate immune hyperresponsiveness in the lung including recruitment of neutrophils with greater ex vivo oxidative activity compared with neutrophils from sham-injured mice. Elevated oxidative function correlated with improved clearance of Pseudomonas aeruginosa, despite down-regulated expression of the bacterial-sensing TLR molecules. Rapamycin administration reversed the burn injury-induced lung innate immune hyperresponsiveness and inhibited enhanced bacterial clearance in burn mice compared with untreated burn mice, resulting in significantly higher mortality. Neutrophil ex vivo oxidative burst was decreased by rapamycin treatment. These data indicate that (1) neutrophil function within the lung is more important than recruitment for bacterial clearance following burn injury and (2) mTOR inhibition significantly impacts innate immune hyperresponsiveness, including neutrophil effector function, allowing normalization of the immune response late after burn injury.
