Impaired sarcoplasmic reticulum function leads to contractile dysfunction and cardiac hypertrophy.

Area of Science:

• Cardiology
• Molecular Biology
• Physiology

Background:

• Sarcoplasmic reticulum (SR) Ca(2+) handling is crucial for cardiac contractility.
• SR dysfunction is implicated in heart failure.
• The direct causal link between SR dysfunction and cardiac remodeling is not fully understood.

Purpose of the Study:

• To investigate if targeted SR dysfunction can independently cause cardiac contractile impairment.
• To determine if SR dysfunction alters cardiac gene expression and induces hypertrophy.
• To establish a novel animal model for studying SR-mediated cardiac dysfunction.

Main Methods:

• Developed a mouse model by administering ryanodine in drinking water to interfere with SR Ca(2+) release.
• Performed in vivo hemodynamic measurements to assess cardiac contractility and relaxation.
• Analyzed cardiac hypertrophy and gene expression changes (atrial natriuretic factor, beta-myosin heavy chain, SR Ca(2+)) after 1 and 4 weeks of treatment.

Main Results:

• Ryanodine treatment reduced maximal contraction speed (+dP/dt(max)) by 28% and relaxation speed (-dP/dt(max)) by 24% after 1 week.
• Cardiac relaxation was significantly slowed, with the late phase prolonged by 22%.
• After 4 weeks, significant cardiac hypertrophy was observed, particularly in the atria, accompanied by increased expression of stress-response genes and reduced SR Ca(2+) mRNA.

Conclusions:

• Selective impairment of SR function in vivo can be a primary cause of cardiac contractile dysfunction.
• SR dysfunction can induce cardiac hypertrophy and alter cardiac gene expression profiles.
• This study provides evidence that SR dysfunction can initiate pathological cardiac remodeling.