Decreasing levels in plasma of aging mice and humans accompanied with reduced expression of the apelin receptor in mice;  apelin supplementation resulted in restored skeletal muscle function with enhanced biogenesis of mitochondria and reduction of age-associated cardiac hypertrophy in mice;  generally lower serum levels of apelin were measured in patients with severe heart failure secondary to MI compared to healthy subjects. Here, APLN is linked to myocardial infarction.