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Abstract: FR-PO504

Changes in Renal Acid-Base Handling in Megalin-Knockout Mice

Session Information

Category: Fluid, Electrolytes, and Acid-Base Disorders

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

Authors

  • Klahn, Peter Andreasen, Aarhus Universitet Faculty of Health, Aarhus, Denmark
  • Berg, Peder, Aarhus Universitet Faculty of Health, Aarhus, Denmark
  • Sorensen, Mads Vaarby, Aarhus Universitet Faculty of Health, Aarhus, Denmark
  • Weyer, Kathrin, Aarhus Universitet Faculty of Health, Aarhus, Denmark
  • Svendsen, Samuel L.C., Aarhus Universitet Faculty of Health, Aarhus, Denmark
  • Leipziger, Jens G., Aarhus Universitet Faculty of Health, Aarhus, Denmark
  • Nielsen, Rikke, Aarhus Universitet Faculty of Health, Aarhus, Denmark
Background

Megalin is a ~600 kDa receptor abundantly expressed in the renal proximal tubules. It facilitates reabsorption of a great variety of proteins avoiding their loss in the urine. Lack of megalin therefore leads to insufficient reuptake of its substrates, and thus low-molecular weight proteinuria. In addition, our preliminary data suggest that lack of megalin also causes impaired regulation of renal acid-base excretion.

Methods

Kidney specific mosaic megalin knockout mice
Immunofluorescence
Western blotting
Liquid chromatography/mass spectrometry
Biochemistry of mouse blood and urine

Results

Immunofluorescence showed a very marked increase of brush border carbonic anhydrase 4 (CA4) in proximal tubular cells lacking megalin compared to megalin-positive cells (Figure 1). This was confirmed by western blotting of cortex homogenates. To investigate if other proximal tubular proteins involved in acid-base handling were changed, we applied proteomics. We found a significantly decreased abundance of NBCe1A (-20%), V-ATPase and NHE3 (-20%) and confirmed an increased abundance of CA4 (324%) in megalin KO mice. Megalin knockout mice showed mild alkalosis during baseline conditions. Urine analyses showed a very unusually combination of high NH4+ excretion concomitant with reduced titratable acid excretion and increased bicarbonate excretion. Despite high NH4+ excretion net acid excretion was reduced.

Conclusion

Our data suggest that the absence of megalin has major effects on renal acid-base handling. We suggest that megalin KO mice have increased ammoniagenesis in PT-cells and that this causes a compensatory reduction in TA excretion and increase in bicarbonate excretion. Further experiments are necessary to solidify this hypothesis.

Figure 1. Micrograph showing double labeling of megalin (green) and CA4 (red) in a megalin KO (left) and a WT mouse (right). The megalin KO is mosaic, which means that it still has megalin in a few percentage of cells. Distal tubules (DT). PT=proximal tubule. Scale bar = 50 mm.