Abstract: TH-PO418

Rubicon Deficiency Leads to Obesity by Promoting Excessive Lipid Efflux in Proximal Tubular Epithelial Cells

Session Information

Category: Nutrition, Inflammation, and Metabolism

  • 1401 Nutrition, Inflammation, Metabolism

Authors

  • Matsuda, Jun, Osaka University Graduate School of Medicine, Suita, Japan
  • Kaimori, Jun-Ya, Osaka University Graduate School of Medicine, Suita, Japan
  • Matsui, Isao, Osaka University Graduate School of Medicine, Suita, Japan
  • Niimura, Fumio, Tokai University School of Medicine, Isehara, Kanagawa, Japan
  • Matsusaka, Taiji, Tokai University School of Medicine, Isehara, Kanagawa, Japan
  • Isaka, Yoshitaka, Osaka University Graduate School of Medicine, Suita, Japan
  • Takahashi, Atsushi, Osaka University Graduate School of Medicine, Suita, Japan
  • Takabatake, Yoshitsugu, Osaka University Graduate School of Medicine, Suita, Japan
  • Yamamoto, Takeshi, Osaka University Graduate School of Medicine, Suita, Japan
  • Kimura, Tomonori, Osaka University Graduate School of Medicine, Suita, Japan
  • Namba, Tomoko, Osaka University Graduate School of Medicine, Suita, Japan
  • Minami, Satoshi, Osaka University Graduate School of Medicine, Suita, Osaka, Japan
  • Sakai, Shinsuke, Osaka University Graduate School of Medicine, Suita, Japan
  • Fujimura, Ryuta, Osaka University Graduate School of Medicine, Suita, Japan
Background

Autophagy is a lysosomal degradation system which contributes to maintain nutritional status. It has been known that Rubicon (Run domain Beclin-1 interacting and cysteine-rich containing protein) negatively regulates autophagic activity by inhibiting the fusion of autophagosomes and lysosomes. However, its physiological role in proximal tubular epithelial cells (PTECs) remains poorly understood.

Methods

We analyzed the phenotype of newly generated PTEC-specific Rubicon-deficient mice (KO mice). We crossed KO mice with GFP-MAP1LC3 transgenic mice, in which GFP-positive puncta reflect autophagosomes, and evaluated autophagic flux by comparing the number of GFP-positive dots with or without chloroquine administration. We finally investigated the role of Rubicon in lipid metabolism using isolated Rubicon-deficient PTECs.

Results

The number of autophagosomes was increased after chloroquine administration even during the fed state in the PTECs of 3-month-old KO mice, indicating sustained high autophagic flux. When fed standard mouse chow, KO mice began to exhibit a significant increase in body weight compared with controls after the age of 4 months (12-month-old KO mice: 45.9 ± 5.2 kg vs controls: 38.5 ± 6.8 kg, P<0.01). At 12 months of age, we observed a gain of weight in liver and adipose tissue, fatty liver, impaired glucose tolerance, and hypercholesterolemia. Immunohistochemical and electron microscopic analysis revealed expanded lysosomes containing multi-layered phospholipids in the PTECs of 12-month-old KO mice.
Isolated Rubicon-deficient (KO) and wildtype (WT) PTECs were loaded oleic acid (OA)-bound albumin to induce the formation of lipid droplets (LDs). Rubicon KO PTECs showed more rapid degradation of LDs compared with WT PTECs. Furthermore, cultured hepatocytes (BNL-CL2 cells) exhibited a significant increase in LD formation when co-cultured with OA-loaded KO PTECs compared with OA-loaded WT PTECs. These results suggest an accelerated lipid efflux from KO PTECs to blood circulation.

Conclusion

Rubicon deficiency in PTECs leads to systemic lipid accumulation and obesity by promoting excessive lipid efflux. Rubicon in PTECs can be a therapeutic target for metabolic syndrome.