NOX4 and cyclic hematopoiesis: In both animal models of PH and PH patients, Nox4 expression is consistently increased, including in pulmonary arteries [38] or lungs [42] from mice exposed to CH or CIH [36], in pulmonary arteries from Fawn-Hooded rats or rats exposed to CH, MCT, or a combination of SU5416 and CH [27,33,43], in pulmonary arteries and PASMCs from a lamb model of persistent pulmonary hypertension of the newborn (PPHN) [44], and in pulmonary arteries [38] and PASMCs [28,43] from patients with PH.