The p21 dependent G2 arrest of the cell cycle in epithelial tubular cells links to the early stage of renal fibrosis

Takayuki Koyano,Masumi Namba,Tomoe Kobayashi,Masaki Fukushima,Daisuke Nakano,Kyomi Nakakuni,Makoto Matsuyama,Akira Nishiyama

doi:10.1038/s41598-019-48557-8

Takayuki Koyano, Masumi Namba + Show 6 more

Open Access

https://doi.org/10.1038/s41598-019-48557-8

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Abstract

Renal fibrosis is accompanied by the progression of chronic kidney disease. Despite a number of past and ongoing studies, our understanding of the underlying mechanisms remains elusive. Here we explored the progression of renal fibrosis using a mouse model of unilateral ureter obstruction. We found that in the initial stage of damage, where extracellular matrix was not yet deposited, proximal tubular cells arrested at G2 of the cell cycle. Further analyses indicated that the cyclin-dependent kinase inhibitor p21 is partially involved in the G2 arrest after the damage. A newly produced monoclonal antibody against p21 revealed that levels of p21 were sharply upregulated in response to the damage during the initial stage but dropped toward the later stage. To investigate the requirement of p21 for the progression of renal fibrosis, we constructed the novel p21 deficient mice by i-GONAD method. Compared with wild-type mice, p21 deficient mice showed exacerbation of the fibrosis. Thus we propose that during the initial stage of the renal damage, tubular cells arrest in G2 partially depending on p21, thereby safeguarding kidney functions.

Highlights

Fibrosis is one of the prominent features of organ disorders where extracellular matrix (ECM) components accumulate excessively
To analyse the multistep mechanism(s) of renal fibrosis, we conducted unilateral ureter obstruction (UUO), which is widely used as a model of renal fibrosis, and collected sham and damaged kidneys at the various time points after injury (Fig. 1a and Fig. S1)
We found that the level of phosphorylated Cdk[1] (p-Cdk1Y15), which corresponds to an inactive form of Cdk1-cyclinB complex[27], was dramatically elevated compared to unobstructed kidneys during the initial stage of damage (Fig. 2b)

Summary

Introduction

Fibrosis is one of the prominent features of organ disorders where extracellular matrix (ECM) components accumulate excessively. The G2 arrested cells produce pro-fibrogenic factors, including TGF-β and CTGF26, which accelerate renal fibrosis progression[8,11,26]. Our data show that in the initial stage of damage, tubular epithelial cells are arrested in G2 of the cell cycle in the mouse model of renal fibrosis. The G2 arrest is induced prior to the DNA damage checkpoint and Wnt/β-Catenin pathway activation, partially depending on the CDK inhibitor p21. In p21-deficient mice, the absence of this CDK inhibitor exacerbates the progression of fibrosis. These data uncover a new insight into cell cycle arrest and p21 in the complex regulation of renal fibrosis

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