Angiotensinogen is the substrate of renin and its down-regulation in IPF strongly suggests high renin and ANGT consumption to produce angiotensin I. Indeed, renin converts ANGT into angiotensin I (Ang I), which is in turn cleaved into angiotensin II (Ang II) by angiotensin-converting-enzyme (ACE), also typically found in the endothelial cells of the lung capillaries [46], where RAAS, essential for blood pressure control and fluid homeostasis, plays an important role in pulmonary hypertension. The gene discussed is REN; the disease is pulmonary arterial hypertension.