The Role of Bicarbonate Transporters in the Development of Cardiovascular Diseases

• Author / Creator

  Sowah, Daniel

• NHE1, whose activity and expression are elevated in cardiac hypertrophy, requires an acidifying pathway provided by AE3-mediated Cl-/HCO3- exchange to sustain its activity. Carbonic anhydrase II (CAII) interacts with NHE1 and AE3 to induce hypertrophy but the role of AE3 in hypertrophy is poorly elucidated. The present study seeks to characterize the interaction between CAII and AE1 as the prototype exchanger, and to delineate the role of AE3 in cardiac hypertrophy.
  AE1, the plasma membrane Cl-/HCO3- exchanger of erythrocytes, interacts with CAII to maximize HCO3− transport. To characterize further the effect of CAII on AE1 transport, CAII-wildtype or catalytically inactive CAII-V143Y was fused to the COOH terminus of AE1 to form AE1.CAII and AE1.CAII-V143Y, respectively. When expressed in HEK293 cells, AE1.CAII had a similar Cl-/HCO3- exchange activity to AE1 alone, as assessed by the flux of H+ equivalents (87 ± 4% vs. AE1) or rate of change of [Cl-]i (93 ± 4% vs. AE1). Contrastingly, AE1.CAII-V143Y displayed transport rates for H+ equivalents and Cl- of 55 ± 2% and of 40 ± 2%, versus AE1. AE1 fused to CAII-V143Y has reduced transport activity, which is compensated for during Cl-/HCO3− exchange by the presence of catalytically active CAII. When coexpressed with CAII-V143Y, AE1 bicarbonate transport was inhibited, whereas AE1.CAII activity was unaffected, suggesting impaired transport activity upon displacement of functional CAII from AE1 but not AE1.CAII.
  The role of AE3 in hypertrophy was studied in ae3 null mice (ae3-/-) whose disruption did not affect cardiac function as determined by echocardiography and blood pressure measurements. HW/BW ratio was larger in ae3+/+ compared to ae3-/- mice. Hypertrophic stimulation with phenylephrine or angiotensin II caused a 25-30% increase in surface area, upregulated ANP and β-BHC levels, and elevated protein synthesis of wildtype cardiomyocytes but ae3-/- cardiomyocytes were unaffected.
  
  Our findings confirm CAII association with AE1 increases Cl-/HCO3− exchange activity, consistent with the HCO3− transport metabolon model. Additionally, AE3 operating in conjunction with CAII and NHE1 is essential in neurohormonal-stimulated hypertrophy, forming a hypertrophic transport metabolon. Thus, antagonism of AE3 is an attractive target in the treatment of cardiac hypertrophy.

• Subjects / Keywords

  • Intracellular pH regulation
  • Chloride/bicarbonate exchanger AE1
  • Bicarbonate transporters, carbonic anhydrase

• Graduation date

  Spring 2014

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3MK65G1D

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.