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Sarcoplasmic reticulum genes are selectively down-regulated in cardiomyopathy produced by doxorubicin in rabbits
1Second Department of Internal Medicine, Gunma University School of Medicine, Japan.
Abstract:
The clinical utility of doxorubicin, an antineoplastic agent, is limited by its cardiotoxicity. Our objective was to determine whether expression of genes encoding proteins that affect Ca2+ homeostasis were altered in the hearts of rabbits chronically treated with doxorubicin. Twelve male New Zealand white rabbits received an injection of doxorubicin (2.5 mg/kg i.v.) once a week for 8 weeks. Eight rabbits were similarly injected with saline as controls. The cardiac function of both groups was evaluated 8 weeks after the final injection, as were the levels of expression of mRNA for Ca2+ transport proteins in the sarcoplasmic reticulum and plasma membrane. The amount of the sarcoplasmic reticulum Ca2+-ATPase and the Ca2+ uptake capacity of the protein were also quantitated. Cardiac output was significantly decreased in the doxorubicin-treated group (71+/-21 ml/min, P<0.05) compared with the control group (118+/-15 ml/min). The mRNA levels for the sarcoplasmic reticulum proteins were significantly diminished in the doxorubicin-treated hearts: ryanodine receptor-2 (relative expression level compared with controls, 0.35+/-0.13, P<0.01), sarcoplasmic reticulum Ca2+-ATPase (0.56+/-0.13, P<0.01), phospholamban (0.62+/-0.20, P<0.01) and cardiac calsequestrin (0. 57+/-0.26, P<0.01). In addition, both relative amount of sarcoplasmic reticulum Ca2+-ATPase protein (doxorubicin-treated group, 69+/-17% of control, P<0.01) and the Ca2+ uptake capacity (46. 9+/-9.8 nmol Ca2+/mg protein-5 min in doxorubicin group v 63.2+/-10. 4 in the control group, P<0.01) were concomitantly decreased with its mRNA expression level. Conversely, the mRNA levels for the plasma membrane proteins did not differ from those of control rabbits: the dihydropyridine receptor (relative expression level, 1. 03+/-0.30, N.S.), plasma membrane Ca2+-ATPase (0.93+/-0.33, N.S.) and the Na+/Ca2+ exchanger (0.87+/-0.34, N.S.). These findings suggest that a selective decrease in mRNA expression for sarcoplasmic reticulum Ca2+ transport proteins is responsible for the impaired Ca2+ handling, and thus, for the reduced cardiac function seen in the cardiomyopathy induced in rabbits by the long-term treatment with doxorubicin.
Insights
Doxorubicin treatment in rabbits significantly reduced cardiac output by decreasing key calcium (Ca2+) handling proteins in the sarcoplasmic reticulum. This impaired calcium regulation contributes to doxorubicin-induced cardiomyopathy.
Area of Science:
- Cardiology
- Molecular Biology
- Pharmacology
Background:
- Doxorubicin is an effective antineoplastic agent, but its clinical use is limited by cardiotoxicity.
- The precise molecular mechanisms underlying doxorubicin-induced cardiotoxicity remain under investigation.
- Calcium (Ca2+) homeostasis plays a critical role in cardiac function and is a potential target for doxorubicin-induced damage.
Purpose of the Study:
- To investigate the impact of chronic doxorubicin treatment on the expression of genes encoding Ca2+ transport proteins in rabbit hearts.
- To determine if alterations in Ca2+ handling proteins correlate with functional cardiac deficits.
- To elucidate the role of sarcoplasmic reticulum and plasma membrane Ca2+ transport proteins in doxorubicin cardiotoxicity.
Main Methods:
- New Zealand white rabbits received weekly intravenous injections of doxorubicin or saline for 8 weeks.
- Cardiac function, including cardiac output, was assessed post-treatment.
- mRNA and protein levels of key Ca2+ transport proteins in the sarcoplasmic reticulum and plasma membrane were quantified using molecular biology techniques.
Main Results:
- Doxorubicin-treated rabbits exhibited significantly decreased cardiac output compared to controls.
- Chronic doxorubicin administration led to a significant reduction in mRNA expression of sarcoplasmic reticulum Ca2+ transport proteins, including ryanodine receptor-2, sarcoplasmic reticulum Ca2+-ATPase, phospholamban, and cardiac calsequestrin.
- Both the amount of sarcoplasmic reticulum Ca2+-ATPase protein and its Ca2+ uptake capacity were significantly decreased, correlating with reduced mRNA levels.
- Conversely, mRNA levels for plasma membrane Ca2+ transport proteins (dihydropyridine receptor, plasma membrane Ca2+-ATPase, Na+/Ca2+ exchanger) remained unchanged.
Conclusions:
- Long-term doxorubicin treatment selectively downregulates the expression of sarcoplasmic reticulum Ca2+ transport proteins.
- This impaired Ca2+ handling in the sarcoplasmic reticulum is a key mechanism contributing to the reduced cardiac function observed in doxorubicin-induced cardiomyopathy.
- Targeting sarcoplasmic reticulum Ca2+ handling may offer a therapeutic strategy to mitigate doxorubicin cardiotoxicity.