Differential transcriptional response of alveolar epithelial cells and pulmonary vascular endothelial cells to hypoxia

<bold>Background:</bold> We previously reported that reduced pulmonary endothelial nitric oxide (NO) release is involved in hypoxic pulmonary vasoconstriction, secondary to NO synthesis inhibition by asymmetric dimethylarginine (ADMA). The molecular mechanisms leading to increased ADMA and reduced NO during hypoxia (HX) have remained elusive. <bold>Aims:</bold> We analyzed the transcriptional changes caused by HX in primary human pulmonary arterial endothelial cells (HPAEC) and human alveolar epithelial A549 cells. <bold>Methods:</bold> HPAEC and A549 cells were cultured in NX (21% O2) and HX (1% O2) for 24h or 72h. Total cellular RNA was isolated and subjected to next-generation RNA sequencing (Illumina). Principal component analysis was performed to identify the most differentially regulated genes. <bold>Results:</bold> 281 genes were differentially regulated between HPAEC and A549, mainly related to estrogen receptor signaling, glycolysis, and insulin receptor-mediated pathways. In A549, we observed an early transcriptional response of 136 genes, mainly linked to the response to hypoxia and oxidative stress, mitochondrial membrane potential, and metabolic switch to glycolysis. The late response showed enrichment for TNFα receptor-related pathways, retinoid binding, inflammatory response, and cytokine activity. By contrast, estrogen receptor signaling was more strongly enhanced by HX in HPAEC than in A549. <bold>Conclusions:</bold> In HX, HPAEC and A549 activate specific pathways that differ between acute and sustained HX. Our results may explain upregulation of ADMA in A549, as the ADMA-metabolizing enzyme DDAH is known to be inhibited by inflammation and oxidative stress, and may hint to candidate pathways involved.