Jenna L. Betters

Supplemental nitric oxide augments satellite cell activity on cultured myofibers from aged mice

Skeletal muscle regenerative potential is reduced with aging. We hypothesized that in vitro activation of muscle satellite cells would be compromised, and that nitric oxide (NO) supplementation would improve satellite cell activity in old muscle. Single intact myofibers were isolated from the gastrocnemius muscles of young (2 mo), adult (10 mo), and aged (22 mo) mice. Fibers were centrifuged to stimulate satellite cells and incubated with L-arginine (2mM), the NO donor, diethylenetriamine NONOate (DETA-NO; 10 microM), or control media for 48 h. The number of activated satellite cells after centrifugation was reduced in aged fibers compared to young and adult. L-arginine or DETA-NO treatment increased satellite cell activation in all age groups. However, an age-dependent deficit in satellite cell activity persisted within treatment groups. In separate fibers, exogenous HGF was equally effective in activating satellite cells across age groups, indicating that events downstream of HGF release are intact in aged muscle. These data suggest that l-arginine bioavailability and NO production limit muscle satellite cell activity in response to a submaximal mechanical stimulus, regardless of age. Further, the decline in satellite cell activity in early senescence can be partially abrogated by exogenous L-arginine or an NO donor.

Nitric oxide reverses prednisolone-induced inactivation of muscle satellite cells

Long‐term corticosteroid therapy causes myopathy and can inhibit regeneration of skeletal muscle. Therefore, we hypothesized that corticosteroid exposure reduces satellite cell activity in skeletal myofibers. Male Swiss–Webster mice were injected daily for 8 weeks with prednisolone (GC) or vehicle (control). Single myofibers were isolated from the gastrocnemius, centrifuged to mechanically activate satellite cells, and maintained in culture for 48 h. Both constitutive nitric oxide synthase (NOS) isoforms were reduced in muscle by GC treatment (nNOS: −30%, eNOS: −34%). Fewer myogenic (myoD+) cells emanated from GC myofibers compared to control (−61%, P < 0.05). Supplementation of culture media with the nitric oxide donor, diethylenetriamine NONOate (DETA‐NO; 5–50 μM), caused a dose‐dependent increase in the number of myoD+ cells arising from both control and GC myofibers (P < 0.05), and 10 and 50 μM DETA‐NO eliminated the GC‐induced deficit in myogenic cells (P > 0.05). Therefore, supplementation of GC myofibers with DETA‐NO restores satellite cell activity to control levels. Nitric oxide production could be an important therapeutic target for the prevention of corticosteroid myopathy. Muscle Nerve, 2007