Abstract
Endurance exercise is a poorly defined yet powerful mediator of hematopoiesis. The purpose of this study was to directly investigate the effects of endurance exercise training on hematopoiesis and to identify potential mechanisms responsible for any observed changes. Four-week-old male C57Bl/6 mice were trained on a treadmill at progressive speeds over a 10-wk period. Tissues were harvested 2 d following the final training session. Flow cytometry, the cobblestone area-forming cell assay, and the methycellulose colony-forming unit assay were used to assess medullary and mobilized hematopoietic stem and progenitor cells. Quantitative real-time PCR and Western blots were used to measure hematopoietic cytokine production. Histochemistry was also used to assess adaptations to exercise in the bone marrow niche. Depending on the cell type, endurance training increased medullary and mobilized hematopoietic stem and progenitor cell content from 50 to 800%. Training also reduced marrow cavity fat by 78%. Skeletal muscle hematopoietic cytokine expression was also increased at least 60% by training. Sedentary mice served as controls for the above experiments. In conclusion, endurance exercise training greatly promotes hematopoiesis and does so through improvements in medullary niche architecture as well as increased skeletal muscle hematopoietic cytokine production.