Zusammenfassung
The cardiac sarco(endo)plasmic reticulum Ca$^2+$-ATPase gene (ATP2A2)
encodes the following two different protein isoforms: SERCA2a (muscle-specific)
and SERCA2b (ubiquitous). We have investigated whether this isoform
specificity is required for normal cardiac function. Gene targeting
in mice successfully disrupted the splicing mechanism responsible
for generating the SERCA2a isoform. Homozygous SERCA2a(-/-) mice
displayed a complete loss of SERCA2a mRNA and protein resulting
in a switch to the SERCA2b isoform. The expression of SERCA2b mRNA
and protein in hearts of SERCA2a(-/-) mice corresponded to only 50\%
of wild-type SERCA2 levels. Cardiac phospholamban mRNA levels were
unaltered in SERCA2a(-/-) mice, but total phospholamban protein levels
increased 2-fold. The transgenic phenotype was characterized by a
approximately 20\% increase in embryonic and neonatal mortality (early
phenotype), with histopathologic evidence of major cardiac malformations.
Adult SERCA2a(-/-) animals (adult phenotype) showed a reduced spontaneous
nocturnal activity and developed a mild compensatory concentric cardiac
hypertrophy with impaired cardiac contractility and relaxation, but
preserved beta-adrenergic response. Ca$^2+$ uptake levels in
SERCA2a(-/-) cardiac homogenates were reduced by approximately 50\%.
In isolated cells, relaxation and Ca$^2+$ removal by the SR were
significantly reduced. Comparison of our data with those obtained
in mice expressing similar cardiac levels of SERCA2a instead of SERCA2b
indicate the importance of the muscle-specific SERCA2a isoform for
normal cardiac development and for the cardiac contraction-relaxation
cycle.
- 11679415
- agents,
- alternative
- animals,
- atpase,
- calcium,
- calcium-binding
- cardiomegaly,
- cardiotonic
- congenital,
- contraction,
- defects,
- dobutamine,
- gene
- gov't,
- heart
- heart,
- isoenzymes,
- isoproterenol,
- messenger,
- mice,
- mutant
- myocardial
- myocardium,
- non-u.s.
- patch-clamp
- phenotype,
- proteins,
- rate,
- research
- reticulum,
- rna,
- sarcoplasmic
- splicing,
- strains,
- support,
- survival
- targeting,
- techniques,
- {c}a$^{2+}$-transporting
Nutzer