Hnf-1b Transcription Factor Is an Early Hif-1a- Independent Marker of Epithelial Hypoxia and Controls Renal Repair

Epithelial repair following acute kidney injury (AKI) requires epithelial-mesenchyme-epithelial cycling associated with transient re-expression of genes normally expressed during kidney development as well as activation of growth factors and cytokine-induced signaling. In normal kidney, the Hnf-1b transcription factor drives nephrogenesis, tubulogenesis and epithelial homeostasis through the regulation of epithelial planar cell polarity and expression of developmental or tubular segment-specific genes. In a mouse model of ischemic AKI induced by a 2-hours hemorrhagic shock, we show that expression of this factor is tightly regulated in the early phase of renal repair with a biphasic expression profile (early down-regulation followed by transient over-expression). These changes are associated to tubular epithelial differentiation as assessed by KSP-cadherin and megalin-cubilin endocytic complex expression analysis. In addition, early decrease in Hnf1b expression is associated with the transient over-expression of one of its main target genes, the suppressor of cytokine signaling Socs3, which has been shown essential for renal repair. In vitro, hypoxia induced early up-regulation of Hnf-1b from 1 to 24 hours, independently of the hypoxia-inducible factor Hif-1a. When prolonged, hypoxia induced Hnf-1b down-regulation while normoxia led to Hnf-1b normalization. Last, Hnf-1b down-regulation using RNA interference in HK-2 cell