Physiological Role of the α₂-Isoform of the Na, K-ATPase in the Regulation of Cardiovascular Function

<p>Na,K-ATPase is a ubiquitously expressed heteromeric transmembrane protein composed of two essential subunits: α and β. There are four known isoforms of the catalytic α-subunit (α₁, α₂, α₃, and α₄), and each isoform displays a unique tissue distribution and expression pattern suggesting a tissue-specific role for the α-subunits. The α₂-isoform of the Na,K-ATPase (α₂) is the minor isoform of the Na,K-ATPase expressed in the cardiovascular system but is thought play a critical role in the regulation of systolic blood pressure (SBP). However, the organ system/cell type expressing α₂ that is required for this regulation has not been fully defined. The present dissertation study uses tissue-specific knockouts of α₂ to further define the tissue-specific role of the α₂ in the regulation of SBP. To accomplish this, we developed a mouse model utilizing the Cre/LoxP system to generate tissue-specific knockouts of α₂ in the vascular smooth muscle and heart using mice expressing Cre recombinase in a smooth muscle and cardiac-specific manner. </p><p>Using the SM22α Cre we generated a smooth muscle-specific knockout (SMα₂^-/-) mouse with a 90% reduction in α₂-expression in heart and vascular smooth muscle. Interestingly, tail-cuff blood pressure analysis reveals that SBP is unaffected by the smooth muscle-specific knockout of α₂. However, the SMα₂^-/- mice do fail to develop ACTH-induced hypertension, as seen in control mice in response to ACTH treatment (Control=119±7, SMα₂^-/-=103±2 mmHg). </p><p>In addition, utlizing the β-MHC Cre we generated a heart-specific knockout (βMHCα₂^-/-) mouse with a 90% reduction in α₂-expression that is specific to the heart. βMHCα₂^-/- mice exhibit normal basal SBP, and in addition these mice develop ACTH-induced hypertension in response to ACTH treatment similar to control mice (Control=119±3, βMHCα₂^-/-=117±6 mmHg). Surprisingly, βMHCα₂^-/- mice display delayed onset of cardiac dysfunction compared to control mice in response to pressure-overload induced by transaortic constriction (TAC), however the βMHCα₂^-/- mice deteriorated to control levels by nine weeks post-TAC. </p><p>In summary, this dissertation refines the roles of the α₂-isoform of the Na,K-ATPase in the brain, vascular smooth muscle, and heart in the regulation and maintenance of SBP. Though vascular smooth muscle expression of α₂ appears to be required for ACTH-induced hypertension, cardiac expression is not. By contrast, cardiac expression of α₂ seems to participate in the hypertrophic response to pressure-overload. Interestingly, previous studies indicate that increased salt in cerebrospinal fluid results in an increase in the level of endogenous brain-ouabain, resulting in hypertension that is dependent on the ouabain-binding site of the α₂-isoform in the brain. In addition, several reports have shown that an increased level of endogenous brain-ouabain activates the renin-angiotensin system. Taken together these results suggest that expression of α₂ in the brain is required for the basal regulation of SBP. Furthermore, these data support the hypothesis that the tissue localization of the α₂-isoform determines its unique roles in the regulation and maintenance of SBP.</p>

Name thesis:degree_name

PhD

Level thesis:degree_level

doctoral

Discipline thesis:degree_discipline

Medicine: Molecular Genetics, Biochemistry, and Microbiology

Grantor dc:publisher

University of Cincinnati

Year dc:date

2012

Author dc:creator

• Rindler, Tara N.

Contributors dc:contributor

• Lingrel, Jerry

• Biochemistry
• Microbiology
• Genetics
• Adrenocorticotropic hormone
• Endogenous cardiac glycosides
• Hypertension
• Ouabain
• Systolic Blood Pressure
• Transaortic constriction

Statement dc:rights

• unrestricted
• This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.

Language dc:language

English

Repository record dc:identifier

http://rave.ohiolink.edu/etdc/view?acc_num=ucin1353343442

OAI identifier oai:identifier

oai:etd.ohiolink.edu:ucin1353343442