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1. Trabecular bone functional adaptation and sexual dimorphism in the human foot

   https://doi.org/10.1002/ajpa.23732  

   Saers, Jaap P. P. ; Ryan, Timothy M. ; Stock, Jay T. ( November 2018 , American Journal of Physical Anthropology)

   Trabecular bone adapts to the strains placed upon the skeleton during life. Anthropological research has largely focused on linking variation in primate trabecular bone to locomotor mode, to provide a context for interpreting fossil morphology. However, intraspecific variation and its underlying mechanisms are still poorly understood. Trabecular bone is influenced by a variety of factors including body mass, age, diet, temperature, genetics, sex, and behavior. Before trabecular structure can be used to infer habitual behavior in the past, the effects of these factors need to be understood. In this article, we examine variation in trabecular structure in the human foot in four archaeological groups in relation to inferred levels of terrestrial mobility and sex.

   We use high‐resolution μCT scanning to examine variation in trabecular structure in the human calcaneus, talus, and first metatarsal in two relatively mobile and two relatively sedentary archaeological groups.

   The four population samples show similar patterns of trabecular variation throughout the foot, influenced by mechanical loading. Greater inferred terrestrial mobility is associated with greater bone volume fraction and thicker, more widely spaced, and less interconnected trabeculae. However, contrary to diaphyseal rigidity, only limited sexual dimorphism was found in trabecular structure.

   This work demonstrates that trabecular bone may serve as a useful proxy of habitual behavior in the fossil and archaeological record when other factors are carefully considered. However, the mechanisms underlying sexual dimorphism are not well understood. As such, inferring sex differences in habitual behavior is currently challenging.

    

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2. Bone density and frame size in adult women: Effects of body size, habitual use, and life history

   https://doi.org/10.1002/ajhb.23502  

   Lee, Katharine M. N. ; Rogers‐LaVanne, Mary P. ; Galbarczyk, Andrzej ; Jasienska, Grazyna ; Clancy, Kathryn B. H. ( September 2020 , American Journal of Human Biology)

   Bone mineral density (BMD) and frame size are important predictors of future bone health, with smaller frame size and lower BMD associated with higher risk of later fragility fractures. We test the effects of body size, habitual use, and life history on frame size and cortical BMD of the radius and tibia in sample of healthy adult premenopausal women.

   We used anthropometry and life history data from 123 women (age 18‐46) from rural Poland. Standard techniques were used to measure height, weight, and body fat. Life history factors were recorded using surveys. Grip strength was measured as a proxy for habitual activity, wrist breadth for skeletal frame size. Cortical BMD was measured at the one‐third distal point of the radius and mid‐point of the tibia using quantitative ultrasound (reported as speed of sound, SoS).

   Radial SoS was high (meant‐score 3.2 ± 1.6), but tibia SoS was average (meant‐score 0.35 ± 1.17). SoS was not associated with age, although wrist breadth was positively associated with age after adjusting for height. Radius SoS was not associated with measures of body size, habitual use, or life history factors. Wrist breadth was associated with body size (p < .05 for all), lean mass, and grip strength. Tibia SoS was associated with height. Life history factors were not associated with frame size or cortical SoS.

   Habitual use and overall body size are more strongly associated with frame size and cortical SoS than life history factors in this sample of healthy adult women.

    

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3. Cancellous Bone May Have a Greater Adaptive Strain Threshold Than Cortical Bone

   https://doi.org/10.1002/jbm4.10489  

   Yang, Haisheng ; Bullock, Whitney A. ; Myhal, Alexandra ; DeShield, Philip ; Duffy, Daniel ; Main, Russell P. ( March 2021 , JBMR Plus)

   Strain magnitude has a controlling influence on bone adaptive response. However, questions remain as to how and if cancellous and cortical bone tissues respond differently to varied strain magnitudes, particularly at a molecular level. The goal of this study was to characterize the time‐dependent gene expression, bone formation, and structural response of the cancellous and cortical bone of female C57Bl/6 mice to mechanical loading by applying varying load levels (low: −3.5 N; medium: −5.2 N; high: −7 N) to the skeleton using a mouse tibia loading model. The loading experiment showed that cortical bone mass at the tibial midshaft was significantly enhanced following all load levels examined and bone formation activities were particularly elevated at the medium and high loads applied. In contrast, for the proximal metaphyseal cancellous bone, only the high load led to significant increases in bone mass and bone formation indices. Similarly, expression of genes associated with inhibition of bone formation (e.g.,Sost) was altered in the diaphyseal cortical bone at all load levels, but in the metaphyseal cortico‐cancellous bone only by the high load. Finite element analysis determined that the peak tensile or compressive strains that were osteogenic for the proximal cancellous bone under the high load were significantly greater than those that were osteogenic for the midshaft cortical tissues under the low load. These results suggest that the magnitude of the strain stimulus regulating structural, cellular, and molecular responses of bone to loading may be greater for the cancellous tissues than for the cortical tissues. © 2021 The Authors.JBMR Pluspublished by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

    

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4. Exercise‐induced loading increases ilium cortical area in a selectively bred mouse model

   https://doi.org/10.1002/ajpa.23770  

   Lewton, Kristi L. ; Ritzman, Terrence ; Copes, Lynn E. ; Garland, Jr, Theodore ; Capellini, Terence D. ( January 2019 , American Journal of Physical Anthropology)

   Little is known about how ilium cortical bone responds to loading. Using a mouse model, this study presents data testing the hypothesis that iliac cross‐sectional properties are altered in response to increased activity.

   The sample derives from lines of High Runner (HR) mice bred for increased wheel‐running activity. Four treatment groups of female mice were tested: non‐selected control lines housed without (N = 19) and with wheels (N = 20), and HR mice housed without (N = 17) and with wheels (N = 18) for 13 weeks beginning at weaning. Each pelvis was μCT‐scanned, cross‐sectional properties (cortical area—Ct.Ar, total area—Tt.Ar, polar moment of area, and polar section modulus) were determined from the ilium midshaft, and robusticity indices (ratio of the square root ofCt.ArorTt.Arto caudal ilium length) were calculated. Mixed models were implemented with linetype, wheel access, and presence of the mini‐muscle phenotype as fixed effects, replicate line nested within linetype as a random effect, and body mass as a covariate.

   Results demonstrate that the mouse ilium morphologically resembles a long bone in cross section. Body mass and the mini‐muscle phenotype were significant predictors of iliac cross‐sectional properties. Wheel access only had a statistically significant effect onCt.Arand its robusticity index, with greater values in mice with wheel access.

   These results suggest that voluntary exercise increases cortical area, but does not otherwise strengthen the ilium in these mice, corroborating previous studies on the effect of increased wheel‐running activity on femoral and humeral cross‐sectional properties in these mice.

    

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5. Low temperature decreases bone mass in mice: Implications for humans

   https://doi.org/10.1002/ajpa.23684  

   Robbins, Amy ; Tom, Christina A. T. M. B. ; Cosman, Miranda N. ; Moursi, Cleo ; Shipp, Lillian ; Spencer, Taylor M. ; Brash, Timothy ; Devlin, Maureen J. ( September 2018 , American Journal of Physical Anthropology)

   Humans exhibit significant ecogeographic variation in bone size and shape. However, it is unclear how significantly environmental temperature influences cortical and trabecular bone, making it difficult to recognize adaptation versus acclimatization in past populations. There is some evidence that cold‐induced bone loss results from sympathetic nervous system activation and can be reduced by nonshivering thermogenesis (NST) via uncoupling protein (UCP1) in brown adipose tissue (BAT). Here we test two hypotheses: (1) low temperature induces impaired cortical and trabecular bone acquisition and (2) UCP1, a marker of NST in BAT, increases in proportion to degree of low‐temperature exposure.

   We housed wildtype C57BL/6J male mice in pairs at 26 °C (thermoneutrality), 22 °C (standard), and 20 °C (cool) from 3 weeks to 6 or 12 weeks of age with access to food and water ad libitum (N= 8/group).

   Cool housed mice ate more but had lower body fat at 20 °C versus 26 °C. Mice at 20 °C had markedly lower distal femur trabecular bone volume fraction, thickness, and connectivity density and lower midshaft femur cortical bone area fraction versus mice at 26 °C (p< .05 for all). UCP1 expression in BAT was inversely related to temperature.

   These results support the hypothesis that low temperature was detrimental to bone mass acquisition. Nonshivering thermogenesis in brown adipose tissue increased in proportion to low‐temperature exposure but was insufficient to prevent bone loss. These data show that chronic exposure to low temperature impairs bone architecture, suggesting climate may contribute to phenotypic variation in humans and other hominins.

    

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