Figure 3.

Osteocyte apoptosis, osteocyte RANKL expression and resorption in fatigued ulnae of WT, Panx1KO and P2X₇RKO mice. (A) Left side photomicrographs show IHC staining for osteocyte apoptosis within MDX regions of WT, Panx1KO and P2X₇RKO mice at 3 days post-fatigue (bar = 25 µm) (c-Caspase 3 staining); arrows illustrate examples of positively-stained cells (brown colored). Right side photomicrographs show IHC staining for osteocyte RANKL expression in MDX regions at 3 days post-fatigue; RANKL staining (arrows) is evident in WT ulnae, but effectively absent from fatigued ulnae from Panx1KO and P2X₇RKO mice. (B) Histomorphometry data for osteocyte apoptosis (%Casp3+ Ot.) and osteocyte RANKL expression (%RANKL+ Ot.) in fatigued ulnae at 3 days after loading: Osteocyte apoptosis at microdamage sites occurred similarly in Panx1KO, P2X₇RKO and WT ulnae, consistent with IHC images shown in (A), with apoptosis increased almost 5-fold vs. NON-MDX bone areas with same bone (p<0.02). In contrast, osteocyte RANKL expression was absent from fatigued Panx1KO and P2X₇RKO bones. (C) Histomorphometry data for resorption space number (Rs.N) and endocortical tunneling foci number (En.Tun.N) in WT, Panx1KO and P2X₇RKO ulnae at 14 days after fatigue (p<0.02 vs WT), showing complete absence of new resorption activity in both KO strains.