Dynamic single cell transcriptomics defines kidney FGF23/KL bioactivity and novel segment-specific inflammatory targets

Fibroblast growth factor 23 (FGF23) via its coreceptor αKlotho (KL) provides critical control of phosphate metabolism, which is altered in both rare and very common syndromes. However, the spatial-temporal mechanisms dictating kidney FGF23 functions remain poorly understood. Thus, developing approaches to modify specific FGF23-dictated pathways has proven problematic. Herein, wild type mice were injected with rFGF23 for one, four and 12h and kidney FGF23 bioactivity was determined at single cell resolution. Computational analysis identified distinct epithelial, endothelial, stromal, and immune cell clusters, with differential expressional analysis uniquely tracking FGF23 bioactivity at each time point. FGF23 actions were sex independent but critically relied upon constitutive KL expression mapped within proximal tubule (segments S1-S3) and distal convoluted tub/connecting tubule cell sub-populations. Temporal KL-dependent FGF23 responses drove unique and transient cellular identities, including genes in key MAPK-signaling and vitamin D-metabolic pathways via early- (transcription factor AP-1-related) and late-phase (initiation factor EIF2 signaling) transcriptional regulons. Combining ATACseq/RNAseq data from a cell line stably expressing KL with the in vivo scRNAseq pinpointed genomic accessibility changes in MAPK-dependent genes, including the identification of FGF23-dependent early growth factor-1 distal enhancers. Finally, we identified unexpected crosstalk between FGF23-mediated MAPK signaling and pro inflammatory TNF receptor activation via transcription factor NF-κB, which blocked FGF23 bioactivity in vitro and in vivo. Collectively, our findings have uncovered novel pathways at the single cell level that likely influence FGF23-dependent disease mechanisms.