Voluntary Exercise has Long-Term In Vivo Protective Effects on Osteocyte Viability and Bone Strength Following Ovariectomy

Abstract

Osteocytes are recognized as having a pivotal role in bone tissue homeostasis, and stimuli that increase osteocyte death result in decreased bone tissue quality. Previous in vitro studies have shown that mechanical stimulation prevents osteocyte death; however, in vivo evidence of this protective effect is limited. The aim of this study was to investigate if mechanical stimulation provided by voluntary exercise reduces osteocyte death caused by estrogen deficiency. Thirty-two female Wistar rats (5 months old) were either sacrificed as baseline controls (BSL, n = 7), ovariectomized or sham-operated and housed in cages with a voluntary running wheel (OVXEX, n = 7; SHAMEX, n = 6), or ovariectomized or sham-operated and housed in standard cages of equivalent size (OVXSED, n = 6; SHAMSED, n = 6) and sacrificed at age 14 months. Histomorphometric analysis of femur mid-diaphysis cortical bone revealed a significantly higher osteocyte number (N.Ot) and lower empty lacunae number (N.Lc) in both the OVXEX and SHAMEX groups compared to their SED counterparts. Intracortical porosity (Po.Ar) was also lower in both EX groups compared to their SED counterparts and significantly correlated with N.Lc (r = 0.616; P < 0.001). Three-point bending testing showed a significantly higher Young's modulus and ultimate stress in OVXEX compared to OVXSED and significant correlations between N.Lc and both yield stress (r = -0.376, P < 0.05) and ultimate stress (r = -0.369, P < 0.05) and between intracortical porosity and bone ultimate stress (r = -0.451, P < 0.05). Our results show that voluntary exercise prevented osteocyte death and that this protective effect was associated with increases in femur ultimate stress, which could be partially explained by decreases in Po.Ar.

Exercise induced mechano-sensing and Substance P mediated bone modeling in Atlantic salmon

“…The osteocyte density was higher (~20%) in the exercised compared with the control fish, indicating that osteoblasts are embedded in the osteoid more frequently during exercise. Similarly, a higher number of osteocytes have been identified in exercised mice [40] and rats [41]. The increased osteocyte number might result from a combination of an increased osteoid production together with an increase in the pool of osteoblasts that is available for being entrapped within the bone matrix.…”

Exercise reverses pain-related weight asymmetry and differentially modulates trabecular bone microarchitecture in a rat model of osteoarthritis

“…Long duration running may be preventative against MIA-induced cartilage and/or osteocyte death. For example, voluntary exercise was shown to be protective against OVX-induced osteocyte death in rats, and enhanced muscle mass in exercised but not sedentary rats [7]. Finally, it may be possible that the longer prior running regimen simply resulted in rats that were more physically fit and thus more able to sustain the MIA chronic pain manipulation [56–58].…”

“…Voluntary wheel running in rodents has been shown to enhance muscle viability and bone strength [7–9], attenuate allodynia and elevated IL-1β levels in a model of neuropathic pain [10], and increase protective CD206 macrophage production in a model of muscle pain, and decrease pain- and stress-related measures in a model of inflammatory pain [11,12]. Although there is an increasing literature base on exercise-pain interactions [10,11,13,14], less is known about how the behavioral mechanism of wheel running acquisition duration (i.e., prior wheel running) affects the expression of chronic pain-like behavior.…”

The effects of resistance training on bone mineral density and bone quality in type 2 diabetic rats

“…Previous study reported that voluntary running for 9 weeks improved cortical porosity in ovariectomized and sham rats (Fonseca et al. ). Regardless of exercise methods, previous study was consistent with our study.…”