S1PR1 and pulmonary arterial hypertension: Furthermore, BMPR2 mutations in humans and rats with PAH result in expression of non-viral 5-LO expression in the neointima (Tian et al., 2019), suggesting that inhibition of the disturbed “inside-out” signaling pathway through LTB4 may be implemented by S1PR1 agonist therapy in PAH patients with BMPR2 mutation.