Climbing Exercise Increases Bone Mass and Trabecular Bone Turnover Through Transient Regulation of Marrow Osteogenic and Osteoclastogenic Potentials in Mice

Abstract

To investigate the relationship between the effects of bone turnover and bone marrow cell development in bone cells, we developed a mouse voluntary climbing exercise model. Climbing exercise increased bone volume and transient osteogenic potential of bone marrow. This model would be suitable for investigating the mechanistic roles of mechanical loading. Introduction:The relationship between bone mass gain and local bone formation and resorption in mechanically loaded bone is not well understood. Materials and Methods: Sixty-five C57BL/6J mice, 8 weeks of age, were assigned to five groups: a baseline control and two groups each of ground control and climbing exercise mice for 2 and 4 weeks. Mice were housed in a 100-cm tower and had to climb toward a bottle placed at the top to drink water. Results: Compared with the ground control, bone mineral density of the left femur increased in the climbing mice at 4 weeks. At 2 and 4 weeks, bone formation rate (BFR/BS) of periosteal surface, the cross-sectional area, and moment of inertia were increased in the climbing mice, whereas BFR/BS and eroded surface (ES/BS) of endosteal surface did not differ. The trabecular bone volume (BV/TV) of the proximal tibia increased in climbing mice, and osteoclast surface (Oc.S/BS) and osteoclast number decreased at 2 weeks. At 4 weeks, there were increases in BV/TV and parameters of bone formation, including mineralized surface, mineral apposition rate, and bone formation rate. In marrow cell cultures from the tibia, the number of alkaline phosphatase ϩ colony forming units-fibroblastic and the area of mineralized nodule formation in climbing mice were increased, and the number of osteoclast-like TRACP ϩ multinucleated cells was lower at 2 weeks. At 4 weeks, these parameters recovered to the levels of the ground controls. Conclusion: Our results indicate that climbing increased trabecular bone volume and reduced bone resorption, with a subsequent increase in bone formation. Intermittent climbing downregulates marrow osteoclastogenic cells and upregulates osteogenic cells initially, but further exercise seemed to desensitize them. Cortical envelopes were enlarged earlier, but the response seems to differ from trabecular bone.

The myokine irisin increases cortical bone mass

“…The effect of r-irisin, essentially mimicking the effect of mechanotransduction (25)(26)(27), thus allows bone to become structurally more efficient for bending and torsion. Indeed, both mouse (28)(29)(30) and rat (31-34) models have collectively shown positive associations between exercise and increased bone size and bone mass.…”

Short-Term Exercise in Mice Increases Tibial Post-Yield Mechanical Properties While Two Weeks of Latency Following Exercise Increases Tissue-Level Strength

“…Exercise-based mouse [1][2][3][4][5] and rat [6][7][8][9] models have almost universally shown a link between exercise and increased bone formation, resulting in increased bone size and bone mass and maintenance or increase of mechanical properties, thus supporting Wolff's law [10]. We recently demonstrated that 21 consecutive days of moderate intensity running, considerably shorter than most exercise models, significantly increased structural post-yield deformation in the tibial diaphyses of male C57BL6/129 mice [11].…”

Long-term voluntary exercise of male mice induces more beneficial effects on cancellous and cortical bone than on the collagenous matrix

“…Several studies have investigated the effect of short exercise periods on bone mineral content in rodent models (Kodama et al, 2000;Mori et al, 2003;Plochocki et al, 2008). However, the documentation regarding the effect of long-term exercise and timing of exercise is limited (Hoshi et al, 1998;Jarvinen et al, 2003;Pajamaki et al, 2003).…”