Cardiac-specific Overexpression of Mouse Cardiac Calsequestrin Is Associated with Depressed Cardiovascular Function and Hypertrophy in Transgenic Mice

doi:10.1074/jbc.273.43.28470

Cardiac-specific Overexpression of Mouse Cardiac Calsequestrin Is Associated with Depressed Cardiovascular Function and Hypertrophy in Transgenic Mice*

From the ^‡Department of Pharmacology and Cell Biophysics and the ^¶Division of Cardiology, University of Cincinnati, Cincinnati, Ohio 45267 and the ^§Department of Anatomy, Case Western Reserve University, Cleveland, Ohio 44106

Abstract

Calsequestrin is a high capacity Ca²⁺-binding protein in the sarcoplasmic reticulum (SR) lumen. To elucidate the functional role of calsequestrin in vivo, transgenic mice were generated that overexpressed mouse cardiac calsequestrin in the heart. Overexpression (20-fold) of calsequestrin was associated with cardiac hypertrophy and induction of a fetal gene expression program. Isolated transgenic cardiomyocytes exhibited diminished shortening fraction (46%), shortening rate (60%), and relengthening rate (60%). The Ca²⁺ transient amplitude was also depressed (45%), although the SR Ca²⁺storage capacity was augmented, as suggested by caffeine application studies. These alterations were associated with a decrease in L-type Ca²⁺ current density and prolongation of this channel’s inactivation kinetics without changes in Na⁺-Ca²⁺ exchanger current density. Furthermore, there were increases in protein levels of SR Ca²⁺-ATPase, phospholamban, and calreticulin and decreases in FKBP12, without alterations in ryanodine receptor, junctin, and triadin levels in transgenic hearts. Left ventricular function analysis in Langendorff perfused hearts and closed-chest anesthetized mice also indicated depressed rates of contraction and relaxation of transgenic hearts. These findings suggest that calsequestrin overexpression is associated with increases in SR Ca²⁺ capacity, but decreases in Ca²⁺-induced SR Ca²⁺ release, leading to depressed contractility in the mammalian heart.

Footnotes

↵* This work was supported in part by National Institutes of Health Grants HL26057, HL22619, P50-52318, and P40RR12358.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The nucleotide sequence(s) reported in this paper has been submitted to the GenBank™/EMBL Data Bank with accession number(s) AF068244.
↵‖ Recipient of American Heart Association Fellowship SW-97-27-F.
↵** To whom correspondence should be addressed: Dept. of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, P. O. Box 670575, 231 Bethesda Ave., Cincinnati, OH 45267-0575. Tel.: 513-558-2377; Fax: 513-558-2269; E-mail: kraniaeg{at}email.uc.edu.
↵2 Scanning of this sequence against the GenBank^TM Data Bank indicated significant relatedness to sequences with accession numbers U91483, U33287, AF001334, J03766,D55655, and X55040.
Abbreviations:

SR

sarcoplasmic reticulum

bp

base pair(s)

MHC

myosin heavy chain

I_Ca

L-type Ca²⁺ current

pF

picofarad(s).
- Received March 19, 1998.
- Revision received July 28, 1998.
The American Society for Biochemistry and Molecular Biology, Inc.