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Abstract: FR-PO505

LRBA Signalosomes Activate Vasopressin-Induced AQP2 Trafficking at Recycling Endosomes

Session Information

Category: Fluid, Electrolytes, and Acid-Base Disorders

  • 1101 Fluid, Electrolyte, and Acid-Base Disorders: Basic

Authors

  • Hara, Yu, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
  • Ando, Fumiaki, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
  • Yanagawa, Hideki, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
  • Suzuki, Soichiro, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
  • Fujiki, Tamami, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
  • Mandai, Shintaro, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
  • Mori, Yutaro, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
  • Susa, Koichiro, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
  • Mori, Takayasu, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
  • Sohara, Eisei, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
  • Uchida, Shinichi, Tokyo Ika Shika Daigaku, Bunkyo-ku, Tokyo, Japan
Background

In dehydrated states, increased plasma osmolarity stimulates the release of the antidiuretic hormone vasopressin from the posterior pituitary gland. Subsequently, vasopressin binds to vasopressin type 2 receptor in renal collecting ducts and then activates protein kinase A (PKA)/aquaporin-2 (AQP2) water channels signaling, which increases water reabsorption from urine. Lipopolysaccharide-responsive beige-like anchor protein (LRBA) is a protein kinase A (PKA) anchoring protein localized at renal intracellular endosomes that creates compartmentalized PKA signaling responsible for AQP2 phosphorylation. cAMP/PKA signaling phosphorylates AQP2, promoting AQP2 trafficking from intracellular endosomes to the apical plasma membrane; however, the molecular mechanisms by which LRBA mediates vasopressin-induced AQP2 phosphorylation remain unknown.

Methods

To elucidate the in vivo role of LRBA in vasopressin-induced AQP2 phosphorylation and endosomal trafficking, a density gradient ultracentrifugation technique was combined with an in situ proximity ligation assay (PLA) and superresolution structured illumination microscopy (SIM). Lrba−/− mice were used as negative controls for vasopressin-induced AQP2 activation.

Results

Sucrose density gradient and SIM revealed that AQP2 was stored in the recycling endosome under resting conditions. Desmopressin phosphorylated AQP2, translocating it from the recycling endosome to the apical plasma membrane. In contrast, SIM and PLA demonstrated that LRBA was constitutively localized on Rab11-positive recycling endosomes in WT mice regardless of vasopressin stimulation. Therefore, LRBA and AQP2 were well-colocalized in the absence of vasopressin stimulation. The loss of LRBA/PKA signaling by Lrba knockout impaired vasopressin-induced AQP2 phosphorylation, resulting in AQP2 retention at the recycling endosome. Defective AQP2 trafficking reduced urinary concentrating ability in Lrba−/− mice.

Conclusion

AQP2 was found to be stored on the LRBA-containing recycling endosome, and LRBA-induced compartmentalized PKA signaling efficiently phosphorylated AQP2 in response to vasopressin.

Funding

  • Private Foundation Support