Sarcopenia, a critical loss of muscle mass and function because of the physiological process of aging, contributes to disability and mortality in older adults. It increases the incidence of
pathologic fractures, causing prolonged periods of hospitalization and rehabilitation. The molecular mechanisms underlying
sarcopenia are poorly understood, but recent evidence suggests that increased
transforming growth factor-β (TGF-β) signaling contributes to impaired satellite cell function and muscle repair in aged skeletal muscle. We therefore evaluated whether antagonism of TGF-β signaling via
losartan, an
angiotensin II receptor antagonist commonly used to treat
high blood pressure, had a beneficial impact on the muscle remodeling process of sarcopenic mice. We demonstrated that mice treated with
losartan developed significantly less
fibrosis and exhibited improved in vivo muscle function after
cardiotoxin-induced injury. We found that
losartan not only blunted the canonical TGF-β signaling cascade but also modulated the noncanonical TGF-β
mitogen-activated protein kinase pathway. We next assessed whether
losartan was able to combat
disuse atrophy in aged mice that were subjected to hindlimb immobilization. We showed that immobilized mice treated with
losartan were protected against loss of muscle mass. Unexpectedly, this protective mechanism was not mediated by TGF-β signaling but was due to an increased activation of the
insulin-like growth factor 1 (IGF-1)/Akt/
mammalian target of rapamycin (mTOR) pathway. Thus, blockade of the AT1 (
angiotensin II type I) receptor improved muscle remodeling and protected against
disuse atrophy by differentially regulating the TGF-β and IGF-1/Akt/mTOR signaling cascades, two pathways critical for skeletal muscle homeostasis. Thus,
losartan, a Food and Drug Administration-approved
drug, may prove to have clinical benefits to combat injury-related muscle remodeling and provide protection against
disuse atrophy in humans with
sarcopenia.