CDK4 and pulmonary arterial hypertension: Administration of another traditional Tibetan medicine, Tsantan Sumtang, prevented pulmonary hypertension in rats exposed to hypobaric hypoxia (4,500 m), reducing pulmonary vascular cell proliferation probably by suppressing cyclin D1 and cyclin-dependent kinase 4 (CDK4) expression through inhibition of p27kip1 degradation (He et al., 2018).