Gene expression analysis of Kidneys from FGF23 TG and WT mice

Fibroblast growth factor-23 (FGF23), a circulating protein produced in bone, causes renal inorganic phosphate (Pi) wasting by down-regulation of sodium phosphate co-transporter 2a (Npt2a). The mechanism behind this action is unknown. We have previously generated transgenic mice (TG) expressing human wild-type FGF23 under the control of the α1 (I) collagen promoter. In this study we performed a large scale gene expression study of kidneys from TG mice and wild-type littermates. Several genes that play a role in Pi regulation had decreased expression levels, such as Npt2a, but also Pdzk1 which is a scaffolding protein known to interact with NPT2a. Importantly, the Klotho gene, a suggested crucial co-factor for FGF23 receptor binding and activation, was the most affected decreased gene. However, other genes proposed to regulate Pi levels, such as secreted Frizzled Related Protein 4 (sFRP4), Na+/H+ exchanger regulatory factor 1 (NHERF1) and the FGF-receptors 1-4, revealed no changes. Interestingly, expression levels of inflammatory response genes were increased and histological analysis revealed tubular nephropathy in the TG mice kidneys. In conclusion, FGF23 TG mice have altered kidney gene expression levels of several genes thought to be part of Pi homeostasis and an increase in inflammatory response genes, data supported by histological analysis. These findings may lead to further understanding of how FGF23 mediates its actions on renal Pi regulation. Keywords: Genetic Modification Five kidneys from FGF23 TG mice and five kidneys from WT littermates was used for Affymetrix Genechip analysis. One Genechip was used/animal. Animals were 8 weeks old when kidneys were collected.