Differential sclerostin and parathyroid hormone response to exercise in boys and men.
- 1Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON, L2S 3A1, Canada. email@example.com.
- 2Pediatric Exercise and Genomics Research Center, University of California, Irvine, CA, USA.
- 3Faculty of Applied Health Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, ON, L2S 3A1, Canada.
Physical exercise benefits bone structure and mineralization, especially in children. Immediately following high-impact exercise, PTH increased and returned to resting values within 24 h in both groups, while sclerostin increased in men but not in boys. The underlying mechanisms and implication of this age-related differential response are unclear.
Circulating sclerostin, a negative regulator of bone, decreases during puberty and increases in adulthood. Parathyroid hormone (PTH) is inversely related to sclerostin. In mice, sclerostin decreases following 24 h of mechanical stimulation. Its response to exercise in humans and, especially in children, in whom high-impact physical exercise benefits bone structure and mineralization is unclear. The aim of this study was to investigate the acute response of sclerostin to a single exercise session of high mechanical loading and the corresponding changes in PTH in boys and men.
Twelve boys (10.2 ± 0.4 years old) and 17 young men (22.7 ± 0.8 years old) underwent a protocol of plyometric exercises (total 144 jumps). Blood samples were collected pre-, 5 min, 1 h, and 24 h post-exercise.
Boys had significantly higher resting values of sclerostin compared with men (150 ± 37 vs. 111 ± 34 pg/ml, respectively, p = 0.006). Following exercise, sclerostin markedly increased in men but this response was attenuated in boys (at 5 min: 51 ± 38 vs. 14 ± 21%, respectively, p = 0.005). PTH levels were similar in boys and men at rest and throughout the 24-h study period, increasing significantly (p < 0.001) 5 min after exercise, decreasing after 60 min post-exercise and returning to resting values within 24 h.
Although the PTH response was similar in boys and men, the sclerostin response was greater in men. The combined increases in PTH and sclerostin immediately post-exercise appear contrary to the accepted osteogenic effect of exercise. The underlying mechanisms and full implication of the differential response between children and adults need to be further examined.
KEYWORDS: Bone; Children; Exercise; Mechanical loading; Osteocyte; Sost
Sclerostin is produced almost exclusively by osteocytes and is a negative regulator of bone formation, through inhibition of the Wnt/b-catenin pathway (8). Its circulating levels decrease during puberty and increase in adulthood (2). Parathyroid hormone (PTH) levels are generally inversely related to sclerostin healthy elderly men and women (1), but in childhood, the nature of this relationship not clear. In animals, sclerostin decreases following 24 hr of mechanical stimulation (5-7). Its response to exercise in humans and, especially in children, in whom high impact physical exercise benefits bone structure and mineralization (4), is unclear.
The purpose of our study was to assess the effects of high impact (plyometric) exercise on sclerostin and parathyroid hormone response in children and in adults. We hypothesized, based on a) our previous finding of enhanced bone formation markers following a similar exercise protocol (3), b) sclerostin’s role in inhibiting bone formation and c) exercise’s role in enhancing bone formation, that sclerostin levels would decrease following exercise. However, contrary to our expectations, our findings demonstrate that one session of plyometric exercise results in post-exercise increases in PTH and sclerostin, which possibly reflect increased bone resorption, and is contrary to the accepted osteogenic effect of chronic exercise. Furthermore, while the increase in PTH was similar in the two groups, the increase in sclerostin was higher in men than in boys, suggesting a possible protective effect, moderating the post-exercise catabolic response in the boys.
This study is novel in that it is the first study to examine the acute sclerostin response to exercise in humans – adults or children. Such an acute response can provide insight into the mechanism(s) responsible for the effect of mechanical loading on bone cells and bone tissue in humans. The differential response observed may provide insight into the factors which render childhood and adolescence a critical period in terms of bone accretion.
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