Lowering the increased intracellular pH of human‐induced pluripotent stem cell‐derived endothelial cells induces formation of mature Weibel‐Palade bodies

Differentiation of human‐induced pluripotent stem cells (hiPSCs) into vascular endothelium is of great importance to tissue engineering, disease modeling, and use in regenerative medicine. Although differentiation of hiPSCs into endothelial‐like cells (hiPSC‐derived endothelial cells [hiPSC‐ECs]) has been demonstrated before, controversy exists as to what extent these cells faithfully reflect mature endothelium. To address this issue, we investigate hiPSC‐ECs maturation by their ability to express von Willebrand factor (VWF) and formation of Weibel‐Palade bodies (WPBs). Using multiple hiPSCs lines, hiPSC‐ECs failed to form proper VWF and WPBs, essential for angiogenesis, primary and secondary homeostasis. Lowering the increased intracellular pH (pHi) of hiPSC‐ECs with acetic acid did result in the formation of elongated WPBs. Nuclear magnetic resonance data showed that the higher pHi in hiPSC‐ECs occurred in association with decreased intracellular lactate concentrations. This was explained by decreased glycolytic flux toward pyruvate and lactate in hiPSC‐ECs. In addition, decreased expression of monocarboxylate transporter member 1, a member of the solute carrier family (SLC16A1), which regulates lactate and H+ uptake, contributed to the high pHi of hiPSC‐EC. Mechanistically, pro‐VWF dimers require the lower pH environment of the trans‐Golgi network for maturation and tubulation. These data show that while hiPSC‐ECs may share many features with mature EC, they are characterized by metabolic immaturity hampering proper EC function.