Activity of mTOR complex 1 (mTORC1) has been shown to be up-regulated in animal models of heart failure. Here, we investigated the change and role of mTORC1 in human nonischemic dilated cardiomyopathy (NICM).

Endomyocardial biopsy specimens were obtained from patients with NICM (n = 52) and from Brugada syndrome patients with normal LVEF as controls (n = 10). The specimens were stained for phospho-ribosomal protein S6 (p-Rps6) and phospho-p70S6K (p-p70S6K), and the area with p-Rps6 signal was used as an index of mTORC1 activity. Using median mTORC1 activity, patients were divided into a high mTORC1 activity (H-mTOR) group and a low mTORC1 activity (L-mTOR) group.

The ratio of p-Rps6-positive area in biopsy samples was 10-fold larger in patients with NICM than in controls (2.0 ± 2.2% vs. 0.2 ± 0.2%, p < 0.01). p-p70S6K signal level was higher in the H-mTOR group than in the L-mTOR group. The proportion of patients with a family history of cardiomyopathy was higher and the proportion of patients on ACE inhibitors or angiotensin receptor blockers was lower in the H-mTOR group than in the L-mTOR group. The p-Rps6-positive area was correlated with extent of myocardial fibrosis (r = 0.46, p < 0.01). The cardiac event-free survival rate during a 5-year follow-up period tended to be lower in the H-mTOR group than in the L-mTOR group (52.9% vs. 81.6%, P = 0.10).

Aberrant activation of mTORC1 in cardiomyocytes was associated with myocardial fibrosis and a trend for worse prognosis in patients with NICM, indicating that persistently activated mTORC1 contributes to progression of human heart failure.