Loss of the AE3 anion exchanger in a hypertrophic cardiomyopathy model causes rapid decompensation and heart failure

Abstract

The AE3 Cl − /HCO 3 − exchanger is abundantly expressed in the sarcolemma of cardiomyocytes, where it mediates Cl − -uptake and HCO 3 − -extrusion. Inhibition of AE3-mediated Cl − /HCO 3 − exchange has been suggested to protect against cardiac hypertrophy; however, other studies indicate that AE3 might be necessary for optimal cardiac function. To test these hypotheses we crossed AE3-null mice, which appear phenotypically normal, with a hypertrophic cardiomyopathy mouse model carrying a Glu180Gly mutation in α-tropomyosin (TM180). Loss of AE3 had no effect on hypertrophy; however, survival of TM180/AE3 double mutants was sharply reduced compared with TM180 single mutants. Analysis of cardiac performance revealed impaired cardiac function in TM180 and TM180/AE3 mutants. TM180/AE3 double mutants were more severely affected and exhibited little response to β-adrenergic stimulation, a likely consequence of their more rapid progression to heart failure. Increased expression of calmodulin-dependent kinase II and protein phosphatase 1 and differences in methylation and localization of protein phosphatase 2A were observed, but were similar in single and double mutants. Phosphorylation of phospholamban on Ser16 was sharply increased in both single and double mutants relative to wild-type hearts under basal conditions, leading to reduced reserve capacity for β-adrenergic stimulation of phospholamban phosphorylation. Imaging analysis of isolated myocytes revealed reductions in amplitude and decay of Ca 2+ transients in both mutants, with greater reductions in Address correspondence to Gary E. Shull; Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati, College of Medicine, 231 Albert Sabin Way, Cincinnati, Ohio 45267-0524 Telephone: 513 558-0056, Fax: 513 558-1885, shullge@ucmail.uc.edu. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. TM180/AE3 mutants, consistent with the greater severity of their heart failure phenotype. Thus, in the TM180 cardiomyopathy model, loss of AE3 had no apparent anti-hypertrophic effect and led to more rapid decompensation and heart failure. NIH Public Access

The Murine Cl-/HCO3-Exchanger Ae3 (Slc4a3) is Not Required for Acid-Base Balance but is Involved in Magnesium Handling by the Kidney

“…While Ae2 is widely expressed in epithelial and non-epithelial cells, Ae1 is mostly restricted to red blood cells, cardiomyocytes, renal podocytes and type A intercalated cells of the renal collecting ducts (CD) [8,9,10]. In contrast, Ae3 is predominantly found in excitable tissues, such as the central nervous system, retina and heart, where it contributes to the control of intracellular pH and intracellular [Cl - ] [11,12]. Several Ae3 mRNA variants have been proposed, but up to date, only two tissue specific polypeptide variants of Ae3 were identified, the full length brain Ae3 (bAe3) isoform and the shorter N-terminal variant cardiac Ae3 (cAe3) [13,14].…”

Microarray analysis of active cardiac remodeling genes in a familial hypertrophic cardiomyopathy mouse model rescued by a phospholamban knockout

“…Results reveal there is significance divergence in gene expression among the four models, with a total of 1,187 differentially expressed genes being in the hearts of the NTG and three mouse models (Supplemental Table S1). 1 These are genes that display the greatest changes in cardiac expression from all four genotypes at both ages (4 and 12 mo). Expression was increased or decreased by at least 1.3-fold (P Ͻ 0.01, in at least three experiments).…”

“…Many of these genes are also associated with membranes and fatty acid metabolism. 1 The online version of this article contains supplemental material. …”

“…As mentioned previously, the Tm180 mice develop a severe cardiomyopathy that entails cardiomyocyte hypertrophy, fibrosis, thrombosis, atrial and ventricular enlargement, diastolic dysfunction, and abnormalities in myofilament sensitivity to calcium (1,7,16,17). By mating the Tm180 mice with the PLN KO mice, we rescued the resulting progeny (PLN KO/ Tm180 mice) from the disease parameters manifest in the hypertrophic cardiomyopathy phenotype (7).…”

“…␣-tropomyosin (Tm), a thin filament protein of the sarcomere, has been found to encode 11 mutations that lead to FHC (23). Previous work in our laboratories established a transgenic mouse model expressing mutant FHC Tm180 protein (1,7,16,17). This mouse develops severe concentric cardiac hypertrophy with significant ventricular fibrosis and atrial enlargement that is detected by 2 wk.…”