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Kidney Week

Abstract: FR-PO299

Activation of Fatty Acid β-Oxidation in Proximal Tubular Epithelial Cells Is an Intrinsic Mechanism for Suppressing Phosphorus-Induced Kidney Injury

Session Information

Category: Bone and Mineral Metabolism

  • 501 Bone and Mineral Metabolism: Basic

Authors

  • Katsuma, Yusuke, Osaka Daigaku Daigakuin Igakukei Kenkyuka Igakubu, Suita, Osaka, Japan
  • Matsui, Isao, Osaka Daigaku Daigakuin Igakukei Kenkyuka Igakubu, Suita, Osaka, Japan
  • Imai, Atsuhiro, Osaka Daigaku Daigakuin Igakukei Kenkyuka Igakubu, Suita, Osaka, Japan
  • Okushima, Hiroki, Osaka Daigaku Daigakuin Igakukei Kenkyuka Igakubu, Suita, Osaka, Japan
  • Matsumoto, Ayumi, Osaka Daigaku Daigakuin Igakukei Kenkyuka Igakubu, Suita, Osaka, Japan
  • Inoue, Kazunori, Osaka Daigaku Daigakuin Igakukei Kenkyuka Igakubu, Suita, Osaka, Japan
  • Isaka, Yoshitaka, Osaka Daigaku Daigakuin Igakukei Kenkyuka Igakubu, Suita, Osaka, Japan
Background

Excess phosphorus is known to induce kidney injury. The kidneys are the primary organ that excretes phosphorus and are exposed to a phosphorus burden. Thus, it may be difficult for the kidneys to maintain their function over a lifetime unless they have some counteracting mechanisms against the phosphorus burden. This study aimed to clarify how the kidneys counteract the phosphorus burden.

Methods

Six-week-old male C57BL/6 mice were randomly divided into Ctrl and Phos groups. Mice in the Ctrl and Phos groups were fed with a 0.85% phosphorus diet and a 3.0% phosphorus diet, respectively. Since renal fibrosis was not observed in both groups 3 weeks after the start of dietary intervention, we assumed that the kidney was in the stress compensation period and performed single-cell RNA seq (scRNA-seq) analysis at this point. The results obtained from scRNA-seq analysis were validated in vivo and vitro experiments.

Results

Kidney component cells were classified into 12 clusters and analyzed differentially expressed genes (DEGs) between the Ctrl and Phos groups in each cluster. Since the highest number of DEGs were detected in the S1/S2 segments of the proximal tubules (Prox_S1/S2), we focused on the Prox_S1/S2. Kyoto Encyclopedia of Genes and Genomes pathway analyses demonstrated that genes related to fatty acid β-oxidation (FAO) were the top activated pathway in the Prox_S1/S2 cluster of the Phos group. Single-cell regulatory network inference and clustering analyses identified peroxisome proliferator-activated receptor α (PPARα) as one of the most activated transcription factors that regulate the gene network in the Prox_S1/S2 cluster of the Phos group. Immunohistochemistry and western blot of the kidney showed up-regulated PPARα and carnitine palmitoyltransferase 1A (CPT1A), a rate-limiting enzyme of FAO, in the Phos group. In vitro experiments using cultured proximal tubular epithelial cells (PTECs) revealed that phosphorus directly increases CPT1A expression. Etomoxir, a CPT1 inhibitor, significantly reduced cell viability of PTECs only under high phosphorus conditions.

Conclusion

The activation of FAO is an intrinsic defensive reaction against phosphorus-induced cytotoxicity in PTECs.