Modulation of neonatal growth plate development by ex vivo intermittent mechanical stress

Abstract

Although growth plate response to mechanical stress has been increasingly studied, our understanding of mechanical modulation of neonatal growth plate is incomplete, especially concerning biochemical changes. This study was designed to explore the cellular and biochemical responses of the cranial base growth plate (CBGP) explant upon cyclic loading. The growth plate with subchondral bone was aseptically isolated from each of 24 neonatal rabbits and fixated in an organ culture system. Cyclic loading was applied to growth plate explants at 200 mN and 1 Hz for 60 min (N = 12), whereas control explants were immersed in organ culture for 60 min without mechanical loading (N = 12). Computerized image analysis revealed that cyclic loading induced significantly more proliferating chondrocytes than unloaded controls (p<0.001), as well as significantly higher growth plate height at 856 ± 30 μm than the unloaded controls at 830 ± 36 μm (p<0.05). Immunoblotting with monoclonal antibodies (mAb) disclosed that the average mAb binding area for chondroitin sulfate was significantly higher in the loaded specimens than the unloaded controls at (p<0.001). The average mAb binding area for keratan sulfate was also significantly higher in the loaded specimens than the unloaded controls (p<0.01). Biochemical analysis showed that the average total hyaluronan content of loaded specimens at 0.25 ± 0.06 μg/μg DNA was significantly higher than the unloaded controls at 0.09 ± 0.05 μg/μg DNA (p<0.01). Taken together, these data suggest that brief doses of cyclic, intermittent forces activate cellular and molecular responses in the CBGP ex vivo. Whether hyaluronan-mediated pathway is involved in the biological responses of growth plate to mechanical loading warrants additional investigations.

Growth plate explants respond differently to in vitro static and dynamic loadings

“…11 Cyclic intermittent tension applied on the maxillae cranial base growth plate of growing rabbits resulted in significantly greater maximum growth plate height 22 and in vitro cyclic loading applied on cranial base growth plate explants caused a significant increase in the growth plate height. 28 In this study, the loss of columnar arrangement found in the dynamically loaded explants disagrees with an anterior study, which reported an enhanced columnar arrangement of the hypertrophic cells in rabbit cranial base growth plates submitted to dynamic compression. 28 In articular cartilage, it was previously shown that, under in vitro compression, aggrecan expression was significantly higher in dynamically simulated explants than in statically simulated explants.…”

“…28 In this study, the loss of columnar arrangement found in the dynamically loaded explants disagrees with an anterior study, which reported an enhanced columnar arrangement of the hypertrophic cells in rabbit cranial base growth plates submitted to dynamic compression. 28 In articular cartilage, it was previously shown that, under in vitro compression, aggrecan expression was significantly higher in dynamically simulated explants than in statically simulated explants. 29 This finding is consistent with our observations from porcine growth plates under in vitro dynamic compression in our study.…”

“…Ex vivo short-term compressive dynamic loads of cranial base growth plate explants significantly increased the number of proliferating chondrocytes when compared to unloaded specimens. 28 In our case, the columnar disorganization observed in the lower zones of dynamic explants could be explained by such an increase in chondrocytes proliferation, which would yield in an addition of material in the proliferative zone. Although the Hueter-Volkman principle stipulates that sustained static compressive forces retard bone growth, it does not stipulates on the effects of dynamic loading.…”

“…Previous studies have shown variable tendencies, with both significant decreases 11 and increases 22,28 of the proliferative and hypertrophic zones heights reported following dynamic tensile 22 or compressive 11,28 loads. Dose-dependant voluntary exercise on the distal femoral growth plate of immature rats led to a significantly lower hypertrophic zone.…”

In vitro regulation of proliferation and differentiation within a postnatal growth plate of the cranial base by parathyroid hormone‐related peptide (PTHrP)

“…Significant cranial abnormalities can result from premature fusion of the synchondroses, which is observed in the growth disorders achondroplasia and Crouzon syndrome (Chen et al, 2001;Perlyn et al, 2006). Recent in vitro studies have begun to shed light on the growth of synchondroses (Copray and Duterloo, 1986;Gakunga et al, 2000;Shum et al, 2003;Othman et al, 2007), but little is known about the regulation of this growth. PTHrP and its receptor are expressed in mouse embryonic and perinatal synchondroses (Dabovic et al, 2002;Young et al, 2006;Koyama et al, 2007;Nagayama et al, 2008), and PTHrP-null mice have accelerated endochondral ossification of the synchondroses at P0 (IshiiSuzuki et al, 1999).…”