Abstract: FR-OR132

ILDR1 Expression in the Tricellular Junction Regulates Epithelial Water Impermeability

Session Information

Category: Fluid, Electrolytes, and Acid-Base

  • 703 Na+, K+, Cl- Basic

Authors

  • Himmerkus, Nina, Christian Albrechts University Kiel, Kiel, Germany
  • Gong, Yongfeng, Washington University School of Medicine, Saint Louis, Missouri, United States
  • Milatz, Susanne, Christian Albrechts University Kiel, Kiel, Germany
  • Merkel, Cosima, Christian Albrechts University Kiel, Kiel, Germany
  • Hou, Jianghui, Washington University School of Medicine, Saint Louis, Missouri, United States
  • Bleich, Markus, Christian Albrechts University Kiel, Kiel, Germany
Background

The ability to produce a wide range of urine osmolality depends on epithelial water tightness of the thick ascending limb (TAL). The collecting duct (CD) uses the corticomedullary concentration gradient for controlled transcellular water absorption under control of anti-diuretic hormone (AVP). Water tightness of the space in between epithelial cells is determined by the properties of bicellular and tricellular tight junctions. ILDR1 is expressed in the tricellular junction and ILDR1 knockout mice (KO) show high urine production with nearly plasma isotonic urine osmolality.

Methods

ILDR1 expression was investigated in isolated tubular segments along the nephron by qPCR and immunofluorescence. Transepithelial water permeability was assessed in isolated perfused tubules of KO and control mice (CTRL). Tubules were freshly isolated and microperfused with FITC-dextran as indicator of luminal concentration. Transepithelial water flux was measured as changes in fluorescence intensity of the luminal perfusate after application of a transepithelial osmotic gradient and closure of the open tubular end. In addition, CD transcellular water permeability was measured under unstimulated conditions and after stimulation by basolateral application of AVP. Relative fluorescence intensity increment per time was calculated as correlate of transepithelial water transport.

Results

ILDR1 was localized in the tricellular junctions of TAL and CD but was absent in proximal tubules. TAL of KO showed a water leak in comparison to the watertight TAL of Ctrl. Also CD of KO showed a significant water permeability already under unstimulated conditions whereas CD of Ctrl were water tight in the absence of AVP. The effect of basolateral AVP on CD water permeability was additive in ILDR1 knockout animals and not different to controls.

Conclusion

In summary, ILDR1 is part of the tricellular junction in the nephron segments TAL and CD and it confers paracellular water tightness. Impaired water tightness in the TAL by ILDR1 knockout impedes the dilution of the luminal fluid as well as the concentration of the medullary interstitium. ILDR1 might therefore be a new target to regulate renal concentrating ability.

Funding

  • Other NIH Support