Phenylalanine levels are associated with pulmonary hypertension in metabolic profiling clinical studies. However, the pathophysiological role of phenylalanine on pulmonary circulation is still unclear. We experimentally addressed the direct impact of phenylalanine on pulmonary circulation in rats and explored the underlying molecular pathway. Phenylalanine was injected intraperitoneally into Sprague-Dawley rats (400 mg/100 g body wt) as a single dose or daily in a chronic manner for 2, 3, and 4 wk. Chronic injection of phenylalanine induced pulmonary hypertension with time-dependent severity, evidenced by elevated pulmonary artery pressure and pulmonary vascular resistance as well as pulmonary artery and right ventricular hypertrophy. Using tandem mass spectrometry analysis, we found a quick twofold increase in blood level of phenylalanine 2 h following injection. This increase led to a significant accumulation of phenylalanine in lung after 4 h, which remained sustained at up to a threefold increase after 4 wk. In addition, a cellular thermal shift assay with lung tissues from phenylalanine-injected rats revealed the binding of phenylalanine to the calcium-sensing receptor (CaSR). In vitro experiments with cultured pulmonary arterial smooth muscle cells showed that phenylalanine activated CaSR, as indicated by an increase in intracellular calcium content, which was attenuated or diminished by the inhibition or knockdown of CaSR. Finally, the global knockout or lung-specific knockdown of CaSR significantly attenuated phenylalanine-induced pulmonary hypertension. Chronic phenylalanine injection induces pulmonary hypertension through binding to CaSR and its subsequent activation. Here, we demonstrate a pathophysiological role of phenylalanine in pulmonary hypertension through the CaSR. This study provides a novel animal model for pulmonary hypertension and reveals a potentially clinically significant role for this metabolite in human pulmonary hypertension as a marker, a mediator of disease, and a possible therapeutic target.
Keywords: animal model; calcium-sensing receptor; phenylalanine; pulmonary hypertension.