The Regenerative Potential of Aqp2+ Progenitor Cells
Abstract
Identification of renal progenitor cells holds promise for elucidating their contribution to developmental defects
and for isolating human renal progenitor cells as a prerequisite to evaluating their therapeutic potential.
Whether an adult kidney harbors progenitor cells is a hotly debated issue. Because mammalian kidneys can
regenerate new cells following normal shedding and injury, we have published a strict definition of an adult
renal progenitor cell requiring in vivo demonstration of 1) self-renewal, 2) clonogenicity, 3) multipotency, and
participation in 4) tissue maintenance and in 5) injury repair. We have identified a subset of Aqp2+ cells that
were also positively stained with an antibody recognizing both V-ATPase subunits B1 and B2 (Aqp2+B1B2+) as
the first potential candidate that strictly meets these 5 requirements. These Aqp2+ progenitor cells (AP)
exhibited the capacity of self-renewal, clonogenicity, and multipotency, and generated 5 types of cells including
principal cells (PC) and intercalated cells (IC) to form DCT2, CNT, and CD during development. Adult AP also
possessed these capabilities and regenerated all cell types in DCT2, CNT, and CD during tissue maintenance
and after unilateral ureteral obstruction (UUO). AP express IC-selective Jag1 and PC-selective Notch1, and
mediate repair correlating with Notch activation. Others have reported marked sex bias in the transcriptome
profile of PC. All of these findings have laid a solid foundation for this project. In this proposal, we propose to
test our central hypothesis that AP possess a unique molecular signature and their regenerative potential
differs between males and females and is regulated by Jag1. The specific Aims are to identify and validate the
AP's unique molecular signature (Aim 1), to investigate the AP's regenerative potential (Aim 2) and AP's
regulation by Jag1 (Aim 3) during tissue maintenance and during UUO-induced injury repair. We will explore a
combination of cutting edge techniques/approaches including RFP-based cell sorting to enrich Aqp2+ lineage
cells, single cell RNA-Seq, Aqp2ECE/+-based lineage tracing, unbiased thymidine analog labeling, and a set of
innovative tests that have been proven to be effective for vigorously validating B1B2 as a marker of AP.
Successful completion of the project will likely 1) reinforce AP as a novel concept, which differs from what has
been reported for the proximal tubules and could shed new light into the developmental, homeostatic, and
regenerative mechanisms; 2) yield deeper insights into the differential behavior of AP vs. PC and IC; 3) identify
and validate a unique molecular signature of AP for their isolation in the future; 4) link AP-mediated repair to
Notch signaling; 5) establish both sex and Jag1 as potential regulators of AP; and 6) answer many
fundamental questions regarding the origins of PC and IC, how these cells respond to injury through Notch,
and how disruption of this pathway leads to kidney fibrosis. In short, the findings are significant for human
pathology and stem cell biology in general, and for improvement of in vitro organoid generation.
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