Abstract
Organogenesis, including renal development, requires an appropriate retinoic acid concentration, which is established by differential expression of aldehyde dehydrogenase 1 family member A2 (ALDH1A2) and cytochrome P450 family 26 subfamily A/B/C member 1 (CYP26A1/B1/C1). In the fetal kidney, ALDH1A2 expresses in the developing stroma and renal vesicle and its derivatives but does not present in the ureteric bud. It remains unclear what may contribute to this expression pattern. Here we show that the glycogen synthase kinase 3 alpha/beta (GSK3A/B) inhibitor CHIR99021 significantly represses ALDH1A2 expression in WiT49, which is a Wilms’ tumor cell line that exhibits “triphasic” differential potential and is used as a fetal kidney cell model. CHIR99021 fails to suppress ALDH1A2 as β-catenin is inhibited, suggesting that the downregulation of ALDH1A2 by CHIR99021 is through Wnt/β-catenin signaling. Ectopic expression of mouse Wnt1, Wnt3a, Wnt4, and Wnt9b represses ALDH1A2 expression in WiT49 cells. Using immunohistochemistry, we show an inverse correlation of Aldh1a2 expression with β-catenin in rat E18.5 kidney. ChIP demonstrated that β-catenin is recruited to the ALDH1A2 promoter, the conserved intron1G, and another site within intron 1 of ALDH1A2. Using a luciferase assay, we further show that the ALDH1A2 promoter and the intron1G element are involved in the repression of ALDH1A2 expression by CHIR99021. Our work demonstrates that ALDH1A2 expression can be directly repressed by the Wnt/β-catenin signaling in fetal kidney cells, suggesting that Wnt/β-catenin may play a role in maintaining the expression pattern of ALDH1A2 in the fetal kidney, thus controlling the availability and localization of retinoic acid and regulating aspects of kidney development.
Highlights
Renal development is initiated by mutual signaling interactions between the ureteric bud derived from the Wolffian duct and its surrounding mesenchyme
Western blot shows that aldehyde dehydrogenase 1 family member A2 (ALDH1A2) protein levels were significantly repressed in the CHIR99021 group compared to the dimethyl sulfoxide (DMSO) control (Figure 1B)
Inhibition of ALDH1A2 Expression by GSK3 Inhibitor CHIR99021 Is via β-Catenin Signaling
Summary
Renal development is initiated by mutual signaling interactions between the ureteric bud derived from the Wolffian duct and its surrounding mesenchyme. AtRA can act through non-canonical pathways including binding to the PPARδ/β (peroxisome proliferator-activated receptor delta/beta) receptor in the nucleus (Napoli, 2017) or binding to the RARα/Gαq (G protein alpha Q) complex on the cell membrane lipid raft to activate the p38MAPK (Piskunov and Rochette-Egly, 2011) and the PI3K pathway (Masiá et al, 2007) The knockout of both Rara and Rarb results in the hypoplasia/agenesis of the kidney (Mendelsohn et al, 1999). Aldh1a1−/− mutant is non-lethal, adults are fertile, and no abnormality has been reported (Fan et al, 2003; Matt et al, 2005) These data suggest that Aldh1a2 activity is the primary source of retinoic acid during kidney development (Rosselot et al, 2010). Wnt9b is expressed in ureteric buds and activates the canonical Wnt signaling pathway in the surrounding metanephric mesenchyme (Kispert et al, 1998; Carroll et al, 2005; Park et al, 2007). Our findings have implications for linking the Wnt and retinoic acid pathways during kidney development
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