DLL4 and pulmonary arterial hypertension: Subsequently, the expression of 10 candidate genes related to PAH were validated using qRT-PCR, namely, CUL1, CUL2, CUL3, CDC5L, DHX15, EIF2AK2, TOPBP1, DLL4, EGFL7, and ACE. Further cell experiment showed that the Cul2 expression was increased in PAECs under hypoxia.