Upregulation of osteogenic factors induced by high-impact jumping suppresses adipogenesis in marrow but not adipogenic transcription factors in rat tibiae

Jump training is a high-impact training regimen that increases bone volume in young bones. The aim of our study was to determine whether downregulation of adipogenesis that is associated with upregulation of osteogenesis is detected after jump training in growing rat tibiae. Four week-old rats were jump-trained for 1, 2, or 4 weeks for 5 days/week, and the height of jumping progressively increased to 35 cm.We performed morphometry to directly quantitate changes in bone volume and marrow adipocyte distribution in tibiae after the jump training.We also examined changes in expression of osteogenic and adipogenic transcription factor proteins and mRNAs after the jump training. Four weeks of jump training induced an increase in trabecular bone volume, which was associated with recruitment of runt-related transcription factor 2-expressing cells, as well as a decrease in marrow fat volume. However, peroxisome proliferator-activated receptor (PPAR) γ2 protein and mRNA expression levels did not change following high-impact jump training. The mRNA expression levels of the adipocyte differentiation genes CCAAT/enhancer-binding proteins (C/EBP) α, C/EBPβ, and C/EBPδ also showed no change during the training period in jump-trained rats. We suggest that levels of osteogenic factors that were upregulated by mechanical loading from high-impact jumping suppress adipogenesis in marrow rather than adipogenic transcription factors

Electrical Stimulation of Denervated Rat Skeletal Muscle Retards Capillary and Muscle Loss in Early Stages of Disuse Atrophy

The purpose of the present study is to investigate the effects of low-frequency electrical muscle stimulation (ES) on the decrease in muscle mass, fiber size, capillary supply, and matrix metalloproteinase (MMP) immunoreactivity in the early stages of denervation-induced limb disuse. Direct ES was performed on the tibialis anterior muscle following denervation in seven-week-old male rats. The rats were divided into the following groups: control (CON), denervation (DN), and denervation with direct ES (DN + ES). Direct ES was performed at an intensity of 16 mA and a frequency of 10 Hz for 30 min per day, six days a week, for one week. We performed immunohistochemical staining to determine the expression of dystrophin, CD34, and MMP-2 in transverse sections of TA muscles. The weight, myofiber cross-sectional area (FCSA), and capillary-to-fiber (C/F) ratio of the tibialis anterior (TA) muscle were significantly reduced in the DN group compared to the control and DN + ES groups. The MMP-2 positive area was significantly greater in DN and DN + ES groups compared to the control group. These findings suggest beneficial effects of direct ES in reducing muscle atrophy and capillary regression without increasing MMP-2 immunoreactivity in the early stages of DN-induced muscle disuse in rat hind limbs