Kidney Week

Abstract: TH-PO001

Transiently Dedifferentiated eR1-Active Proximal Tubule Cells Clonally Expand and Repair Proximal Tubules in Severe Injury

Session Information

• AKI: Mechanisms - Primary Injury and Repair - I
  November 07, 2019 | Location: Exhibit Hall, Walter E. Washington Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Acute Kidney Injury

• 103 AKI: Mechanisms

Authors

• Kitai, Yuichiro, Department of Nephrology, Kyoto University Graduate School of Medicine, Kyoto, Japan

Yuichiro Kitai,

• Yanagita, Motoko, Department of Nephrology, Kyoto University Graduate School of Medicine, Kyoto, Japan

Motoko Yanagita,

Background

It is well accepted that injured proximal tubules (PT) are restored by the proliferation of surviving PT cells. However, whether this process depends on stochastic proliferation or expansion of a PT subpopulation, and how severity of injury affects repair process is uncertain. A Runx1 enhancer named Runx1+24mCNE (eR1) was shown to be active in adult long-term hematopoietic stem cells and gastric stem cells, but the role of eR1 in the kidney is unknown.

Methods

We explored the behaviors of PT cells with high eR1 activity, in 30- (moderate) and 60-min (severe) ischemia reperfusion injury (IRI), utilizing eR1-EGFP and eR1-Cre^ERT2 mice.

Results

PT cells showed a higher rate of BrdU incorporation in 60-min IRI than in 30-min IRI, and a significant proportion of the PT cells showed RUNX1 expression after 60-min IRI, but not after 30-min IRI. In eR1-EGFP mice, after 60-min IRI, but not after 30-min IRI, EGFP⁺ PT cells accounted for 20% of total PT cells of the superficial cortex. In eR1-EGFP:eR1-Cre^ERT2:R26-tdTomato mice subject to 60-min IRI, EGFP⁺ and tdTomato⁺ PT cells mostly overlapped in acute phase even without tamoxifen. This suggested that eR1-Cre^ERT2mice showed leaky Cre^ERT2activity when eR1 was highly activated after injury, and could be used to trace the fate of PT cells with high eR1 activity. In acute phase of 60-min IRI, tdTomato⁺ PT cells showed a higher rate of BrdU incorporation compared to other PT cells, and clustered with several tdTomato⁺ cells. Consistently, eR1-Cre^ERT2:R26-Confetti multicolor reporter mice revealed the clonal expansion of eR1-active PT cells after 60-min IRI. RNA-seq data of eR1^CreERT2 lineage-labeled PT cells after 60-min IRI showed higher expression of genes associated with cell cycle progression and DNA replication. Notably, tdTomato⁺ PT cells in acute phase were mostly positive for Kim-1 and vimentin, and negative for differentiation markers. In chronic phase, however, the percentages of PT cells positive for Kim-1 and vimentin were not different between tdTomato⁺ and tdTomato^- PT cells, indicating the re-differentiation capacity of this population even after severe injury.

Conclusion

eR1 marks a subpopulation of PT cells of the superficial cortex with different transcriptomic profiling, highly proliferative after severe injury.

Funding

• Government Support - Non-U.S.