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Abstract: PO2503

Autophagy Gene ATG7 Regulates Albumin Transcytosis in Renal Tubule Epithelial Cells

Session Information

Category: CKD (Non-Dialysis)

  • 2103 CKD (Non-Dialysis): Mechanisms

Authors

  • Uchida, Yushi, Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Fukuoka, Japan
  • Torisu, Kumiko, Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Fukuoka, Japan
  • Ueki, Kenji, Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Fukuoka, Japan
  • Tsuruya, Kazuhiko, Department of Nephrology, Nara Medical University, Kashihara, Nara, Japan
  • Nakano, Toshiaki, Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Fukuoka, Japan
  • Kitazono, Takanari, Department of Medicine and Clinical Science, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Fukuoka, Japan
Background

Receptor-mediated albumin transport in renal proximal tubule epithelial cells (PTECs) is important to control proteinuria. Autophagy is an evolutionarily conserved degradation pathway and its role in intracellular trafficking through interaction with the endocytic pathway has recently been highlighted. In this study, we determined whether autophagy regulates albumin transcytosis in PTECs and suppresses albumin-induced cytotoxicity.

Methods

Human tubular epithelial cell line (HK-2) was used for all experiments. The cells were exposed to 10 mg/mL BSA for 6 h or 24 h as required. For autophagy related 7 (ATG7) knockdown (KD), cells were transfected with ATG7 siRNA. The intracellular trafficking of FcRn was examined by biotin-labeled recycling assay. Immunofluorescence of FcRn and Rab7 or Rab11 was observed by confocal microscopy. The transcytosis of albumin in HK-2 was evaluated using FITC-BSA-based transcytosis assay. The release of IL-8 and KIM-1 caused by excess albumin were measured by ELISA, and mitochondrial damage was measured by MitotrackerCMXRos.

Results

FcRn partially co-localized with autophagosomes. FcRn was accumulated and recycling of FcRn was attenuated in ATG7 KD cells. Colocalizations of FcRn with RAB7-positive late endosome or RAB11-positive recycling endosomes were reduced in ATG7 KD cells. In ATG7 KD cells, albumin transcytosis was significantly reduced, and albumin accumulated in the cells. Exposure to excess albumin reduced autophagic flux in HK-2. Consequently, excess albumin-induced mitochondrial damage is enhanced in Atg7 KD cells. The release of IL-8 and KIM-1 from ATG7 KD cells was increased in response to excess albumin.

Conclusion

In PTECs exposed to excess albumin, autophagy is decreased and intracellular transport of FcRn is impaired, resulting in decreased albumin transcytosis. The resulting accumulation of albumin induces cytotoxicity in tubules. Preventing dysfunctional autophagy in PTECs might be beneficial in the clinical management of nephropathies with proteinuria.

Funding

  • Government Support – Non-U.S.