RTN4 and pulmonary arterial hypertension: Studies have shown that the upregulation of Nogo-B protein expression in smooth muscle cells increases the distance between the ER and mitochondria, thereby reducing the calcium transfer from the ER to mitochondria, damaging mitochondrial function and, ultimately, unbalanced the proliferation and apoptosis of smooth muscle cells, thus promoting the occurrence and development of pulmonary arterial hypertension (PAH) [20].