Research Paper Volume 4, Issue 8 pp 553—566

Figure 2. Increased levels of osteopontin in serum and myofiber niche of old mice upon muscle injury. (A) Blood sera were collected from young and old mice, either non-injured or at 3 days and 5 days after muscle injury and OPN levels were quantified by ELISA. Resting young and old blood serum levels do not show significant age-specific difference, while both at 3 days and 5 days after muscle injury old mice have higher levels of serum osteopontin than young (n=3-6, ± SEM, p**≤0.05). (B) Tibialis Anterior (TA) muscle sections from uninjured (resting), 3DPI and 5DPI muscle were co-immunostained for Laminin (to visualize the myofiber periphery) and OPN. OPN is undetectable in the uninjured skeletal muscle or young and old mice. In contrast, at 3 days post injury both young and old muscles show pronounced OPN at the site of injury and old muscle has considerably more OPN than young. By 5 days post injury, OPN becomes greatly diminished at the site of injury / regeneration in young muscle, but old muscle with its poor repair displays sustained OPN presence. At 3 days post injury myofibers (C) and myogenic stem cells (D) obtained from young and old mice were analyzed for OPN expression by western blotting and qRT-PCR (F) Old myogenic stem cells expressed higher levels of OPN as compared to young both at protein and mRNA levels, while the levels of OPN did not change with age in myofibers. (quantified in E; n=3, ± SEM, p**≤0.05).