Related Experiment Videos
Alterations in sarcoplasmic reticulum calcium-storing proteins in pressure-overload cardiac hypertrophy
H Tsutsui1, Y Ishibashi, K Imanaka-Yoshida
1Research Institute of Angiocardiology and Cardiovascular Clinic, Faculty of Medicine, Kyushu University, Fukuoka, Japan.
Insights
Pressure-overload cardiac hypertrophy alters sarcoplasmic reticulum calcium-storing proteins, including increased calreticulin, contributing to heart muscle dysfunction. This study investigated these changes in rat models.
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
- Cellular Biology
Background:
- Intracellular calcium (Ca2+) homeostasis is crucial for cardiac contractility.
- Pressure-overload cardiac hypertrophy impairs heart function, potentially linked to calcium handling defects.
- Reduced sarcoplasmic reticulum Ca(2+)-ATPase levels are known in hypertrophy, but Ca(2+)-storing proteins remain uncharacterized.
Purpose of the Study:
- To investigate alterations in sarcoplasmic reticulum (SR) Ca(2+)-storing proteins (calsequestrin, calreticulin) during pressure-overload cardiac hypertrophy.
- To correlate these molecular changes with contractile dysfunction in hypertrophied myocytes.
Main Methods:
- Western blot analysis of SR Ca(2+)-regulatory proteins in rat left ventricular (LV) myocardium.
- Sham-operated controls and rats subjected to abdominal aortic constriction for 4 weeks.
- Assessment of myocyte contractile function using laser diffraction measurement of sarcomere motion.
Main Results:
- Contractile function of isolated LV myocytes was depressed in aortic-constricted rats.
- SR Ca(2+)-ATPase protein levels decreased significantly (56% of control).
- Calsequestrin levels remained unchanged, while calreticulin levels increased significantly (120% of control) and showed altered cellular localization.
Conclusions:
- Pressure-overload cardiac hypertrophy induces significant alterations in SR Ca(2+)-storing proteins, notably an increase in calreticulin.
- These molecular changes, alongside decreased Ca(2+)-ATPase, likely contribute to the observed contractile dysfunction in hypertrophied myocytes.
- Altered calreticulin localization suggests a role in myocyte pathology during cardiac hypertrophy.
Abstract:
The alterations of intracellular calcium (Ca2+) homeostasis may be responsible for the contractile defects in pressure-overload cardiac hypertrophy. The Ca(2+)-adenosinetriphosphatase (ATPase) protein level of the sarcoplasmic reticulum (SR) is reduced in the hypertrophied or failing heart. However, it is not known whether Ca(2+)-storing proteins, including calsequestrin and calreticulin, are also altered during cardiac hypertrophy. We quantified SR Ca(2+)-regulatory proteins using Western blot analysis in left ventricular (LV) muscle isolated from sham-operated control rats (n = 6) and rats with pressure overload 4 wk after abdominal aortic constriction (n = 7). The contractile function of isolated LV myocytes, assessed by the sarcomere motion measured with laser diffraction, was depressed in aortic-constricted rats. The SR Ca(2+)-ATPase protein level was decreased to 56 +/- 9% (SE) of the control value in hypertrophied myocardium (P < 0.01). The calsequestrin protein level was not altered, whereas calreticulin was increased by 120 +/- 3% of the control value in aortic-constricted rats (P < 0.05). The alterations in SR Ca(2+)-regulatory proteins were equally observed in hypertrophied hearts even when the results were normalized using the amounts of myosin heavy chain proteins in each sample. Immunohistochemical staining of calsequestrin in the control heart showed cross striations at the Z lines, whereas calreticulin was hardly observed within myocytes but was intense within interstitial fibroblasts. In the hypertrophied heart, calreticulin was observed at the perinuclear region within the myocyte cytoplasm. These data indicate that pressure-overload cardiac hypertrophy causes the alterations in SR Ca(2+)-storing proteins as well as in Ca(2+)-ATPase, which may contribute to the contractile dysfunction of the hypertrophied myocytes.