Knockdown of PDK4 reduces proliferation and survival of pulmonary arterial hypertension (PAH) pericytes and restores capacity to enhance endothelial tube formation. Cell growth by MTS (A) and cell apoptosis by caspase 3/7 (B) were evaluated on days 1, 2, and 3 of culture after 48 hours siRNA posttransfection. C: Pericytes (Pcs) were transfected with nontargeting siRNA control (siCtrl) or PDK4-specific (siPDK4) for 48 hours when compared with healthy pericytes. Before seeded on Matrigel, cells were stained with PKHs. Pulmonary microvascular endothelial cells (PMVECs) were stained in PKH67 (green) and PAH Pcs in PKH26 (red). The white boxes indicate the enlarged areas of magnification in the right column. The white arrows indicate EC-Pc interaction. The numbers of tubes, branching points, and networks were assessed after six hours. ∗∗P < 0.01 compared with control (unpaired t-test, one-way analysis of variance with Bonferroni post-test). Scale bars: 250 μm (C, left and middle columns); 100 μm (C, right column). EC, endothelial cell.