SPHK2 and pulmonary arterial hypertension: It has been proved that SphK1 is involved in the occurrence of pulmonary arterial hypertension (PAH) based on the over-expression of SphK1 in vascular smooth muscle cells (VSMC) and lymphocytes of patients with PAH, and the symptoms of PAH were alleviated in SphK1 knockout mice rather than SphK2 (Pyne and Pyne, 2017; Yang et al., 2019).