GDF15 and pulmonary arterial hypertension: Growth differentiation factor-15 (GDF-15) is a transforming growth factor β (TGF-β) protein that has been shown to be involved in the development of muscle atrophy in a variety of diseases, including chronic obstructive pulmonary disease (COPD), cancer, and pulmonary hypertension, and is associated with skeletal muscle wasting [6–8].