Kidney Week

Abstract: TH-PO1094

p38 Phosphorylation in Proximal Tubular Cells Induces Quiescence-to-Senescence Transition and Kidney Fibrosis

Session Information

• CKD: Mechanisms - 1
  October 24, 2024 | Location: Exhibit Hall, Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: CKD (Non-Dialysis)

• 2303 CKD (Non-Dialysis): Mechanisms

Authors

• Iwashige, Yohei, Kyoto Daigaku Daigakuin Igaku Kenkyuka Igakubu, Kyoto, Kyoto, Japan

Yohei Iwashige, MD

• Yamada, Ryo, Kyoto Daigaku Daigakuin Igaku Kenkyuka Igakubu, Kyoto, Kyoto, Japan

Ryo Yamada, MD

• Morinishi, Takuya, Kyoto Daigaku Daigakuin Igaku Kenkyuka Igakubu, Kyoto, Kyoto, Japan

Takuya Morinishi, MD

• Muro, Koji, Kyoto Daigaku Daigakuin Igaku Kenkyuka Igakubu, Kyoto, Kyoto, Japan

Koji Muro, MD

• Yamamoto, Shigenori, Kyoto Daigaku Daigakuin Igaku Kenkyuka Igakubu, Kyoto, Kyoto, Japan

Shigenori Yamamoto, MD

• Yamada, Yasuhiro, Tokyo Daigaku, Bunkyo-ku, Tokyo, Japan

Yasuhiro Yamada, MD, PhD

• Yanagita, Motoko, Kyoto Daigaku Daigakuin Igaku Kenkyuka Igakubu, Kyoto, Kyoto, Japan

Motoko Yanagita, MD, PhD

Background

Phosphorylation of p38 (p-p38) has been reported in kidney injury models and is known to induce cellular senescence in vitro. However, how p-p38 contributes to kidney injury has not been fully elucidated.

Methods

We established transgenic mice (PT-MKK6EE mice) and cell lines (MKK6EE HK-2) that can induce doxycycline (Dox)-induced constitutive p38 phosphorylation in proximal tubular cells (PTCs). The contribution of p-p38 in the induction of cellular senescence and fibrosis was examined in these mice and cell lines.

Results

Wild-type mice showed p-p38 expression in injured PTCs in ischemia-reperfusion (IR) and ureteral obstruction models. Ki67 expression was suppressed in p-p38 positive PTCs, suggesting a link between p-p38 and cell cycle arrest in vivo.
In PT-MKK6EE mice, Dox treatment induced p38 phosphorylation in PTCs, where Cyclin D1 expression was completely suppressed and Kim-1 expression was strongly induced. When IR injury model was induced in PT-MKK6EE mice, Ki67-positive cells in PTCs was significantly decreased, supporting the hypothesis that p-p38 induces cell cycle arrest in vivo. Furthermore, after long-term observation without injury, a subpopulation of p-p38-induced PTCs exhibited cytoplasmic lysosomal accumulation and a pro-inflammatory phenotype, indicating a phenotype similar to cellular senescence. Additionally, αSMA-positive myofibroblasts appeared around p-p38-induced PTCs, suggesting that p-p38 in PTCs induces kidney fibrosis.
In MKK6EE HK-2 cells, Dox treatment induced p38 phosphorylation and inhibited cell proliferation. At the same time, Dox treatment decreased Cyclin D1 expression and increased p21 and p27 expression, together with the reduction of Skp2, an E3 ligase of p21 and p27, consistent with cellular quiescence, known as the G0 phase. Long-term observations revealed cytoplasmic lysosomal accumulation and a pro-inflammatory phenotype in p-p38 induced cells in vitro.

Conclusion

We revealed a novel mechanism by which p-p38 induces G0 cell cycle arrest by increasing p21 and p27 expression and decreasing Skp2 expression in vitro. Furthermore, prolonged p-p38 expression induces quiescence-to-senescence transition both in vivo and in vitro. In addition, p-p38-induced senescent PTCs in vivo affect the surrounding microenvironment and induce kidney fibrosis.