Bone Adaptations to a Whole Body Vibration Protocol in Murine Models of Different Ages: A Preliminary Study on Structural Changes and Biomarker Evaluation

Abstract

Background/Objectives: Whole body vibration (WBV) is a valuable tool to mitigate physiological adaptations related to age and inactivity. Although significant benefits have been found at the musculoskeletal level, including increased bone mass and reduced muscle atrophy, the underlying biological mechanisms remain largely unknown. Therefore, our study aimed to evaluate the effects of vibratory training on bone tissue in murine models of different age groups by investigating the structural and distribution changes in some crucial biomarkers involved in musculoskeletal homeostasis. Methods: Specifically, 4-, 12-, and 24-month-old mice were trained with a WBV protocol characterized by three series of 2 min and 30 s, interspersed with a recovery period of the same duration, on a 3-weekly frequency for 3 months. At the end of the training, histological and morphometric analyses were conducted, in association with immunohistochemical analysis to investigate changes in the distribution of fibronectin type III domain-containing protein 5 (FNDC5), NADPH oxidase 4 (NOX4), and sirtuin 1 (SIRT1). Results: Our preliminary results showed that WBV improves musculoskeletal health by preserving bone architecture and promoting up-regulation of FNDC5 and SIRT1 and down-regulation of NOX4. Conclusions: Our study confirms vibratory training as a viable alternative to counter musculoskeletal decline in elderly and/or sedentary subjects. Further investigations should be conducted to deepen knowledge in this field and explore the role of other molecular mediators in physiological adaptations to vibration.

Keywords: aging; biomarkers; bone; exercise; musculoskeletal system; physiology; sedentariness; training; vibratory training; whole body vibration.

Figure 1

Effects of a whole body vibration (WBV) protocol on weight in murine models of different age groups. (a,b) The most significant weight changes were measured in 4-month-old young mice, with a significant increase in mean weight at the 6 weeks of training (IN phase) and at the end of training (POST) (**** p < 0.0001). (c,d) WBV promoted a significant increase in body weight in 12-month-old adult mice in the IN (** p < 0.01) and POST (**** p < 0.0001) phases compared with sedentary animals. (e,f) Significant weight changes were induced by vibratory training in 24-month-old mice in the IN (**** p < 0.0001) and POST (**** p < 0.0001) phases.

Figure 2

Hematoxylin and eosin (H&E) sections of lumbar segment of the spine from all experimental groups and measurement of significant bone morphometric parameters. (a–e) The 4-month-old young mice in the WBV group showed the highest values of bone volume (BV/TV) and trabecular thickness (Tb.Th), in association with reduced space between bone trabeculae (Tb.S), compared with sedentary animals (**** p < 0.0001). (f–j) In 12-month-old adult mice, WBV significantly increased BV/TV (** p < 0.01) and Tb.Th (**** p < 0.0001), as well as significantly reduced Tb.S (p < 0.0001). (k–o) WBV also improved bone architecture in 24-month-old mice, promoting a significant increase in BV/TV (*** p < 0.001) and Tb.Th (**** p < 0.0001) and a significant reduction in Tb.S (**** p < 0.0001). For 20× images, the scale bar represents 100 μm. For each condition, the experiment was conducted in triplicate (n = 15 from N = 5 experiments).

Figure 3

Evaluation of fibronectin type III domain-containing protein 5 (FNDC5) immunolocalization in bone tissue of young, adult, and aged mice by immunohistochemistry analysis. (a–c) The highest levels of FNDC5 (arrows) were measured in young, trained mice, with a significant increase in FNDC5 distribution compared with the CTRL group (**** p < 0.0001). (d–f) A significant increase in FNDC5 distribution (arrow) was observed in 12-month-old adult mice exposed to WBV compared with sedentary animals (**** p < 0.0001). (g–i) FNDC5 levels (arrow) were significantly increased in the bone tissue of 24-month-old mice after WBV exposure compared with the CTRL group (**** p < 0.0001). For 20× images, the scale bar represents 100 μm. For each condition, the experiment was conducted in triplicate (n = 15 from N = 5 experiments).

Figure 4

Evaluation of NADPH oxidase 4 (NOX4) immunolocalization in bone tissue of young, adult, and aged mice by immunohistochemistry analysis. (a–c) A significant reduction in NOX4 distribution (arrow) was observed in 4-month-old young mice exposed to WBV compared with sedentary animals (**** p < 0.0001). (d–f) NOX4 levels (arrow) were significantly reduced in the bone tissue of 12-month-old adult mice after WBV exposure compared with the CTRL group (**** p < 0.0001). (g–i) The highest NOX4 levels (arrows) were measured in 24-month-old sedentary mice, while protein distribution was significantly reduced in the WBV group of the same age group (**** p < 0.0001). For 20× images, the scale bar represents 100 μm. For each condition, the experiment was conducted in triplicate (n = 15 from N = 5 experiments).

Figure 5

Evaluation of sirtuin 1 (SIRT1) immunolocalization in bone tissue of young, adult, and aged mice by immunohistochemistry analysis. (a–c) Bone tissue of young, trained mice showed the highest levels of SIRT1 (arrows), with a significant increase in its distribution compared with the CTRL group (**** p < 0.0001). (d–f) A significant increase in SIRT1 distribution (arrow) was observed in 12-month-old adult mice after WBV training compared with sedentary animals (**** p < 0.0001). (g–i) The distribution of SIRT1 (arrow) was significantly increased in the bone tissue of 24-month-old trained mice compared with the CTRL group (*** p < 0.001). For 20× images, the scale bar represents 100 μm. For each condition, the experiment was conducted in triplicate (n = 15 from N = 5 experiments).