Low‐dose exercise protects the heart against established myocardial infarction via IGF‐1‐upregulated CTRP9 in male mice

Regular exercise is recommended as an important component of therapy for cardiovascular diseases in clinical practice. However, there are still major challenges in prescribing an optimized exercise regimen to individual patients with established cardiac disease. Here, we tested the effects of different exercise doses on cardiac function in mice with established myocardial infarction (MI). Exercise was introduced to mice with MI after 4 weeks of surgery. Low‐dose exercise (15 min/day for 8 weeks) improved mortality and cardiac function by increasing 44.39% of ejection fractions while inhibiting fibrosis by decreasing 37.74% of distant region. Unlike higher doses of exercise, low‐dose exercise consecutively upregulated cardiac expression of C1q complement/tumor necrosis factor‐associated protein 9 (CTRP9) during exercise (>1.5‐fold). Cardiac‐specific knockdown of CTRP9 abolished the protective effects of low‐dose exercise against established MI, while cardiac‐specific overexpression of CTRP9 protected the heart against established MI. Mechanistically, low‐dose exercise upregulated the transcription factor nuclear receptor subfamily 2 group F member 2 by increasing circulating insulin‐like growth factor 1 (IGF‐1), therefore, upregulating cardiac CTRP9 expression. These results suggest that low‐dose exercise protects the heart against established MI via IGF‐1‐upregulated CTRP9 and may contribute to the development of optimized exercise prescriptions for patients with MI.