Dilated cardiomyopathy mutations in three thin filament regulatory proteins result in a common functional phenotype

Area of Science:

• Cardiovascular Biology
• Molecular Cardiology
• Muscle Physiology

Background:

• Dilated cardiomyopathy (DCM) is a primary cause of heart failure, often stemming from inherited genetic mutations.
• Mutations in cardiac troponin T, troponin C, and alpha-tropomyosin genes are linked to inherited DCM, but can also cause hypertrophic cardiomyopathy with different mutations.
• Conflicting findings in prior studies necessitate a comprehensive analysis of DCM-associated mutations.

Purpose of the Study:

• To elucidate how specific genetic mutations lead to dilated cardiomyopathy.
• To investigate the impact of known DCM-causing mutations on cardiac contractile function.
• To compare the functional effects of DCM mutations with those causing hypertrophic cardiomyopathy.

Main Methods:

• Reconstitution of cardiac thin filaments with wild-type and mutant proteins (troponin T, troponin C, alpha-tropomyosin) at a 1:1 ratio.
• In vitro assays including ATPase activity and motility assays to assess Ca(2+) sensitivity and activation.
• Inclusion of skinned cardiac trabeculae experiments with specific troponin T mutants to evaluate force generation.

Main Results:

• All thin filaments with DCM mutations exhibited reduced Ca(2+) sensitivity in ATPase and motility assays.
• Most mutants showed decreased maximum Ca(2+) activation, with one exception (alpha-tropomyosin).
• Incorporation of two troponin T mutants into cardiac trabeculae reduced Ca(2+) sensitivity of force generation.

Conclusions:

• Diverse thin filament DCM mutations consistently impair myofibrillar function, leading to decreased contractility.
• This depressive effect on contractility is mechanistically opposite to that observed in hypertrophic cardiomyopathy-causing thin filament mutations.
• Reduced cardiac contractility due to these mutations may initiate pathological pathways culminating in the clinical presentation of DCM.