Abstract
It has been shown that Lurcher mutant mice have significantly altered motor abilities, regarding their motor coordination and muscular strength because of olivorecebellar degeneration. We assessed the response of the cross-sectional geometry and lacuno-canalicular network properties of the tibial mid-diaphyseal cortical bone to motor differences between Lurcher and wild-type (WT) male mice from the B6CBA strain. The first data set used in the cross-sectional geometry analysis consists of 16 mice of 4 months of age and 32 mice of 9 months of age. The second data set used in the lacunar-canalicular network analysis consists of 10 mice of 4 months of age. We compared two cross-sectional geometry and four lacunar-canalicular properties by I-region using the maximum and minimum second moment of area and anatomical orientation as well as H-regions using histological differences within a cross section. We identified inconsistent differences in the studied cross-sectional geometry properties between Lurcher and WT mice. The biggest significant difference between Lurcher and WT mice is found in the number of canaliculi, whereas in the other studied properties are only limited. Lurcher mice exhibit an increased number of canaliculi (p < 0.01) in all studied regions compared with the WT controls. The number of canaliculi is also negatively correlated with the distance from the centroid in the Lurcher and positively correlated in the WT mice. When the Lurcher and WT sample is pooled, the number of canaliculi and lacunar volume is increased in the posterior Imax region, and in addition, midcortical H-region exhibit lower number of canaliculi, lacuna to lacuna distance and increased lacunar volume. Our results indicate, that the importance of precise sample selection within cross sections in future studies is highlighted because of the histological heterogeneity of lacunar-canalicular network properties within the I-region and H-region in the mouse cortical bone.
Highlights
Bone adapts to its mechanical loading history during life and reflects differences in habitual loading [1,2,3,4,5,6,7]
The relationship between mechanical loading and bone morphology has been supported at several hierarchical designs, which range from analyses of the structural properties of long bones, including the appendicular skeleton configuration [8, 9], macroscopic morphology of whole bones [10] and cross-sectional geometry (CSG) properties [6, 11,12,13,14,15,16], to analyses of the microstructural properties of long bones, such as the trabecular orientation [17] and spatial distribution of osteocytes and the lacunar-canalicular network (LCN) in cortical bone tissue [18,19,20,21,22,23]
Given the pattern of significant findings, size differences may play a role in the interpretation of the CSG results; all studied CSGs have to be appropriately scaled to body size
Summary
Bone adapts to its mechanical loading history during life and reflects differences in habitual loading [1,2,3,4,5,6,7]. We assessed the response of structural (CSG) and microstructural (LCN) properties to mechanical loading differences in two different habitual loading models of mice. Previous studies have demonstrated the effect of mechanical loading and unloading on bone morphology mainly using non-physiological loading models or applied strains that were outside the normal expected range of loading experienced by healthy animals. These experimental studies have included, for example, surgical interventions [28], the application of artificial mechanical overload in vivo [29] and mechanical unloading [22]. We used mice with olivocerebellar motor disorder (Lurcher, Lc) and their healthy controls to assess the effects of differences in mechanical loading on bone cortical tissue without the impact of an invasive intervention
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