Kaitlyn Gregorio

Kaitlyn Gregorio

Loss of muscle IGF-1 restricts functional fitness adaptation to endurance exercise


Ray A. Spradlin, Kaitlyn S. Gregorio, Cora C. Hart, Emily Chou, Christina Pacak, H. Lee Sweeney, Elisabeth R. Barton


Dr. Elisabeth Barton


College of Health and Human Performance


One of the consequences of aging is the reduction of the growth hormone/insulin-like growth factor I (GH/IGF-I) axis. For skeletal muscle, this leads to a loss of anabolic and regenerative capacity, which, in part, underlies the onset of sarcopenia. Maintenance of activity in aging can help offset functional deficits, and these benefits are both systemic and specific to skeletal muscle. It is an open question as to the contribution of muscle IGF-I activity to these beneficial adaptations. To address this, we imposed an endurance exercise regimen on a recently developed mouse model with muscle specific inducible deletion of IGF-I (MID mouse), and strain matched controls (CON), comparing their performance to sedentary mice of the same genotypes. After 4 weeks of daily endurance training at 15 m/min for 60 minutes, both MID and CON mice displayed similar and significant improvements in a run-to-exhaustion test. However, in the subsequent 4 weeks of daily endurance training at 18 m/min for 60 minutes, only the CON mice continued to improve in the run-to-exhaustion tests. β-galactosidase staining and a deletion PCR indicated existing but weak deletion in MID mice, yet adaptations were still possible. Stained cross sections of harvested diaphragms show lower amounts of type I and type I/IIA fibers between both MID and CON mice within the sedentary mice. Also, there were significantly more type I/IIA fibers in exercise mice within the MID strain. Taken together, this suggests that benefits to endurance training can still occur in the absence of muscle IGF-I.


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