Fig. 1

a Human renal proximal tubular epithelial (HK2) cells were cultured simultaneously under either normoxic (20% O₂) or hypoxic (1% O₂) conditions for 24 h. Hypoxia increased ACE2 expression (b–d). HK2 cells stably expressing shRNA (short hairpin RNA) targeting HIF1A and/or EPAS1 were cultured under hypoxic (1% O₂) conditions for 24 h. (b). Under hypoxic conditions, knockdown of EPAS1 and HIF1A, alone and in combination, reduced ACE2 expression (c, d). shRNA knockdown of EPAS1 and HIF1A gene expression was confirmed. Data expressed as mean ± SE, with 3 replicates per group (n = 3) [19]. The gene expression profile of harvested cells was analyzed by microarray. Data were accessed through the Gene Expression Omnibus, GSE99324, and processed using affy and limma packages [20,21,22]. [In summary, hypoxia increased expression of ACE2 transcript in human renal proximal tubular epithelial (HK2) cells. Knockdown of hypoxia inducible factors 1A and 2A (encoded by HIF1A and EPAS1) with shRNA in hypoxic HK2 cells reduced ACE2 transcript, indicating that hypoxia-induced upregulation of ACE2 transcript in these cells is likely mediated through the hypoxia inducible factors. Hypoxia➔ ↑HIF1A and ↑HIF2A ➔ ↑ACE2] [Abbreviations: HIF1A, hypoxia inducible factor-1-alpha; EPAS1, endothelial PAS domain-containing protein 1; GEO, Gene Expression Omnibus; shRNA, short hairpin RNA—artificial RNA molecule with a tight hairpin turn that can be used to silence target gene expression via RNA interference (RNAi)]