Changes in myod and MRF4 mRNA levels in patagialis muscles of adult and aged quail following stretchoverload

Stretch-induced hypertrophy of skeletal muscle is diminished in aged quail as compared to adult quail; the reasons for this are unclear. One possible explanation would be reduced increases of muscle specific transcription factors in aged muscle in response to a hypertrophy stimulus. To test this hypothesis we measured mRNA levels of MyoD and MRF4 in stretched and control patagialis muscles from 4 month old (adult) and 28 month old (aged) quail. The left wings of the quail were stretch-overloaded with a weight corresponding to 12% of body weight for either 6 or 24 hr; contralateral wings served as controls. RNA was extracted from patagialis muscles and used in ribonuclease protection assays. Values in the table below are means + SE 6 hr stretch 24 hr stretch Adult Aged p Adult Aged p MyoD increase (%) 440±159 62±56 0.07 677±507 71±25 0.28 MRF4 increase (%) 170±56 89±36 0.27 605±261 90±54 0.10 n=4 n=4 n=4 n=4 Due to large variations in the changes of MyoD and MRF4 after stretch, no significant differences between adult and aged muscle were found. However, the data are suggestive of a possible physiological role of these transcription factors in the attenuated hypertrophic response of aged skeletal muscle.