Mechanisms of epithelial cell state changes during kidney injury - ABSTRACT The long-term goal of this project is to identify molecular and genetic mechanisms that determine and maintain kidney epithelial cell states in normal physiology and in response to injury. Acute kidney injury (AKI) is a common and costly clinical syndrome and contributes to the development of chronic kidney disease (CKD). Epithelial cells in proximal tubules are highly vulnerable to ischemic damage, which contributes to most severe cases of AKI. After injury, surviving epithelial cells can regenerate the epithelia of damaged proximal tubules, but the extent of recovery varies widely between patients. Successful regeneration requires coordinated transformations in gene expression. As regenerating cells repopulate the nephron, they can regain normal gene expression patterns or become stuck in a failed repair state that leads to CKD. Computational approaches to infer gene regulatory networks involved in cell-state decisions after AKI have consistently identified the tissue-specific transcription factor Pax8. Despite the evidence supporting a critical role for Pax8, the genome-wide targets and functions of Pax8 in regeneration remain largely unknown. For this proposal, we have developed novel in vivo and in vitro models to study Pax8 in normal and regenerating kidney epithelial cells. Our preliminary data indicate that Pax8 maintains differentiated proximal tubule gene expression patterns. After ischemic injury or genetic Pax8 inactivation, expression of Pax8 targets is lost, driving de- differentiation and inducing resilience to ischemic stress. Our data reveal altered chromatin modifications at enhancer elements where Pax8 can activate or repress target genes in concert with other key proximal-tubule- specific transcription factors. Our hypothesis is that Pax8 functions as a central cell-state switch in proximal tubule injury, toggling cells between a de-differentiated, resilient state and a differentiated, functionally mature state. The aims of the project are to 1) define proximal tubule Pax8 target genes before and after injury, 2) identify gene regulatory networks co-regulated by Pax8, and 3) identify mechanisms of altered Pax8 function during ischemic stress. The broader implications of this project address the mechanisms that determine and maintain differentiated cell stability. Ultimately, these insights will lead to new treatments for patients suffering from AKI and other diseases with impaired epithelial function.
