CDK4 and idiopathic pulmonary arterial hypertension: In HPASMCs (Supplementary Fig. 2a–d), as well as in lung homogenates from IPAH patients (Supplementary Fig. 2i–l), increased CDK2 and CDK6 mRNA levels were noted, whereas CDK4 mRNA levels were only elevated in isolated cells, while CDK9 mRNA levels remained unaffected.