In Old Mice, Exercise Induces Inflammation and Fibrosis Unless Alk5-Inhibitor and Oxytocin Are Used.

Exercise and diet are the best-known methods for attenuating aging-related health decline. However, exercise in older age has diminished gains of strength and agility, and a danger of unrepaired muscle damage. Improving the understanding of age-related differences in response to exercise, our results demonstrate that in old mice, downhill treadmill (eccentric) exercise causes increased influx of CD45+ cells (inflammation) and fibrotic index (fibrosis) in the heart and skeletal muscles. To explain these changes, we identified newly synthesized proteins through bio-orthogonal noncanonical amino acid tagging (BONCAT) and established that exercise exacerbated age-associated protein patterns through a dysregulated transforming growth factor (TGF)-β, Ras/MAPK/PI3Akt, and JAK/STAT pathways. Testing causality, we found that an inhibitor of TGF-β (Alk5 inhibitor, A5i) in combination with the age-diminished peptide oxytocin, previously shown to rejuvenate muscle and brain in sedentary animals, allowed aged mice to exercise without pathologies of skeletal and heart muscles and youthfully restored their de novo proteomes.