Kidney Week

Abstract: SA-OR012

Regeneration of Proximal Tubules after Severe Injury Depends on Clonal Proliferation of eR1-Active Subpopulation of Proximal Tubular Cells

Session Information

• AKI: Inflammation and Regeneration
  October 27, 2018 | Location: 6B, San Diego Convention Center
  Abstract Time: 04:42 PM - 04:54 PM

Category: Acute Kidney Injury

• 103 AKI: Mechanisms

Authors

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

Yuichiro Kitai, MD

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

Motoko Yanagita,

Background

Proximal tubular cells (PTC) are considered to repair injured proximal tubules by their own proliferation. However, whether this process depends on stochastic proliferation of surviving PTCs or expansion of a specific population of PTCs is still debated, and whether severity of injury affects the repair process is uncertain. In mammals, RUNX transcription factors are essential in diverse biological processes. Along with the elucidation of the roles of Runx1 in hematopoietic homeostasis and blood malignancies, a Runx1 enhancer named Runx1+24mCNE (eR1) has been identified recently, and 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 first compared the proliferation of PTCs after 30- (moderate injury) and 60-min ischemia reperfusion injury (IRI) (severe injury) by bromodeoxyuridine (BrdU) labeling. We next explored the role of eR1 in kidney injury, utilizing eR1-ECFP and eR1-Cre^ERT2 mice.

Results

As indicated by BrdU incorporation, PTCs of the superficial cortex were more proliferative in 60-min IRI than in 30-min IRI, whereas proliferation rate was comparative in the deep cortex. While ECFP⁺ PTCs were almost absent in healthy kidneys of eR1-ECFP mice, ECFP⁺ cells increased to about 20% of total PTCs in the superficial cortex after 60-min IRI, but not after 30-min IRI. Then, we subjected eR1-ECFP:eR1-Cre^ERT2:R26-tdTomato mice to 60-min IRI, and showed that ECFP⁺ and tdTomato⁺ PTCs mostly overlapped in acute phase even without tamoxifen. This result indicated that eR1-Cre^ERT2 mice show leaky Cre^ERT2 activity when eR1 was highly activated, and could be used to trace the fate of PTCs with strong eR1 activity. In acute phase of 60-min IRI, tdTomato⁺ PTCs showed a higher rate of BrdU incorporation than other PTCs, and clustered with several tdTomato⁺ PTCs. Clonal analysis using eR1-Cre^ERT2: R26-Confetti multicolor reporter mice revealed that clusters of PTCs were mostly labeled with a single color, indicating the clonal expansion of labeled cells. Notably, tdTomato⁺ PTCs in acute phase were mostly positive for Kim-1 and vimentin, and negative for PTC markers such as aquaporin 1.

Conclusion

In severe injury, transiently dedifferentiated eR1-active PTCs clonally expand and repair superficial proximal tubules.