HIF1A and pulmonary arterial hypertension: In summary, combined with the effects of hypoxia on the phenotypic changes and the expression of PDK1 and its TGF-β/Smad pathway-related genes in yellow cattle and yak PASMCs, the following modes of PDK1 and TGF-β/Smad pathway regulation were hypothesized for hypoxia-induced pulmonary arterial hypertension (Figure 18): (1) Hypoxia may bind HIF-1α to PDK1, causing loss of PHDs activity and increased expression of HIF-1α without degradation, which in turn affects PDK1 expression.