Transgenic mice exhibit significant increases in empty lacunae and intracortical cavities.

<p>(A) Quantification of empty lacunae in cortical and trabecular bone. (B) Quantification of intracortical cavities.</p

Bone structure in control limb predicts inter- and intra-group variability in adaptation to pressure loading.

<p>Bone structure in control limb is plotted in the x-coordinate, and is indicative of baseline cellular activity in the absence of pressure loading. Relative adaptation is plotted in the y-coordinate, and was found to be negatively correlated with control limb structure independently of genotype and DT dose. Results are shown for (A) trabecular volume fraction, (B) trabecular number, (C) trabecular spacing, (D) cortical thickness, and (E) bone mineral density. Each point represents a single animal (red: WT; blue: Tg; circle: 10 µg/kg DT; square: 50 µg/kg DT; fill: HLS; no fill: Amb). Pearson correlation coefficients and corresponding p-values are shown in the top right of each plot.</p

Schematic demonstrating two potential mechanisms by which osteocyte ablation may give rise to loss of trabecular bone mass in unpressurized limbs while enhancing pressure loading-induced adaptation.

<p>In the first case (A), osteocyte ablation gives rise to an increase in the number of active osteoclasts, resulting in heightened bone loss in unpressurized limbs. In limbs subjected to pressure loading, the resorptive activity of these active osteoclasts is halted, preserving bone mass. In the second case (B), osteocyte ablation shifts the osteoblastic population to a more quiescent state, resulting in decreased bone mass in unpressurized limbs. However, in pressure-loaded limbs, an enhanced anabolic response occurs due to the newly available pool of quiescent cells activated following exposure to pressure loading-induced IFF.</p

Quantification of canalicular convective velocity from <i>ex vivo</i> measurements of lacunar fluorescence recovery after photobleaching.

<p>(A) Single lacuna immediately prior to (Pre-Bleach) and following photobleaching (Bleach), and the subsequent recovery of fluorescence in the absence (top) and presence (bottom) of pressure loading. Faster recovery can be observed in the presence of pressure loading, indicating convective transport. Color bar on bottom indicates image intensity. (B) Plot of Eq. 1 demonstrating the relationship between convective velocity <i>v_c</i> and recovery rates <i>k</i> and <i>k</i>₀. The red dot corresponds to the canalicular fluid velocity (∼80 µm/s) calculated using the values of <i>k</i> and <i>k</i>₀ obtained in this study.</p

Pressure loading-induced adaptation is enhanced in transgenic mice.

<p>Results are shown for relative changes (defined as the difference between pressure-loaded limb and contralateral limb values) in (A) trabecular volume fraction, (B) trabecular number, (C) trabecular spacing, (D) cortical thickness, and (E) bone mineral density.</p

Experimental setup for pressure loading experiments and measurements of ImP.

<p>(A) Image of a hindlimb suspended mouse subjected to microfluidic pressure loading. The syringe pump consists of a Hamilton syringe (hs) mounted in a computer-controlled loading frame (lf) that actuates the syringe plunger (p). A saline-filled catheter (c) couples the pump to the cannulated mouse (hindlimb suspended via a tail suspension apparatus (tsa)). The catheter is protected from mouse chewing/pulling by an infusion harness (ih). (B) Composite average (± standard error) of intramedullary pressure measurements obtained from four animals in the absence (empty circles) and presence (filled circles) of microfluidic pressure loading. Pressure loading resulted in a 5.1 Hz waveform with a mean peak pressure of ∼70 mmHg.</p

Bone structure and bone mineral density in control limbs.

<p>^gand ^s indicate statistically significant for genotype or suspension, respectively.</p