Kidney Week

Abstract: SA-PO473

Trans-Epithelial Fluid Pumping Performance of Renal Epithelial Cells and the Mechanistic Basis of Polycystic Kidney Disease

Session Information

• Cystic Kidney Diseases: Basic/Translational
  November 09, 2019 | Location: Exhibit Hall, Walter E. Washington Convention Center
  Abstract Time: 10:00 AM - 12:00 PM

Category: Genetic Diseases of the Kidneys

• 1001 Genetic Diseases of the Kidneys: Cystic

Authors

• Choudhury, Mohammad ikbal, Johns Hopkins University , Baltimore, Maryland, United States

Mohammad ikbal Choudhury,

• Qian, Feng, University of Maryland School of Medicine, Baltimore, Maryland, United States

Feng Qian,

• Woodward, Owen M., University of Maryland School of Medicine, Baltimore, Maryland, United States

Owen M. Woodward,

• Sun, Sean X., Johns Hopkins University , Baltimore, Maryland, United States

Sean X. Sun,

Group or Team Name

• Sean Sun Group

Background

The epithelial cells lining nephrons in kidneys are highly efficient fluid reabsorption and secretion units. Imbalance in the trans-epithelial fluid flow leads to various renal diseases including polycystic kidney disease (PKD), which is characterized by development of numerous fluid-filled cysts in the renal tubules. Surprisingly, no work has been done so far to quantify the fluid pumping performance of renal epithelial cells in a physiologically relevant setup. To make progress, we developed a micro-fluidic kidney pump (MFKP) device, to measure the trans-epithelial fluid flow as a function of the hydrostatic pressure gradient generated by cells.

Methods

MFKP mimics a tubular segment of the nephron as it has two microfluidic channels separated by a porous membrane. A microcapillary connected to the basal side acts a sensor to measure both the trans-epithelial fluid flow (J) with a resolution of 0.31 μL and corresponding hydrostatic pressure gradient (ΔP) with a resolution of 10 Pa. This setup was placed inside the incubator and fluid flow in the microcapillary was recorded using videography. J₀ is the fluid flow at ΔP = 0 and ΔP* is the stall pressure when J = 0.

Results

Here we report that normal human cells pump fluid from apical to basal side with J₀ in the range of 10 μL/min/cm² and ΔP* of 250 Pa. Interestingly the PKD cystic cells pump fluid in the reverse direction (basal to apical) with J₀ of 5 μL/min/cm² and ΔP* of -300 Pa. However, basolateral treatment with 1 nM Tolvaptan caused a decrease in both in J₀ and ΔP*. The developed pressure gradient translates to a force of 50-100 nanoNewtons per cell, which can potentially expand the cyst lumen. In both normal and PKD cells, the trans-epithelial fluid flux (J) and the PPCs are modulated by mechanical (fluid shear stress), chemical (arginine vasopressin) and apical hypo-osmotic perturbations.

Conclusion

Our combined results offer insights into kidney fluidic pumping action and ADPKD cyst formation. To our knowledge this is the first demonstration of a decrease in secretory fluid flow and hydrostatic pressure gradient by PKD cells in response to a Tolvaptan. Our results demonstrate that secretory and absorptive functions of epithelia can generate significant mechanical forces, and maybe a general phenomenon in tubular morphogenesis in other contexts.

Funding

• NIDDK Support