Cre recombinase affects calcium dynamics already in young mice

Area of Science:

• Cardiovascular Research
• Molecular Biology
• Genetics

Background:

• The Cre/LoxP system is crucial for creating tissue-specific gene knockout mouse models in cardiovascular research.
• Previous studies indicate that αMHC promoter-driven Cre expression causes age-dependent cardiotoxicity, including hypertrophy and dysfunction by 6 months.
• This study investigates the early effects of Cre expression on intracellular calcium (Ca2+) dynamics in ventricular myocytes at 3 months of age.

Purpose of the Study:

• To investigate the impact of Cre recombinase expression on intracellular Ca2+ dynamics in ventricular myocytes of αMHC-Cre mice at 3 months of age.
• To determine if early Cre expression affects cardiac structure, protein levels, or Ca2+ handling before overt cardiotoxicity manifests.

Main Methods:

• Isolated ventricular cardiomyocytes (VCMs) from αMHC-Cre (CRE) and wild-type (WT) mice at 3 months of age.
• Simultaneous recording of Ca2+ transients and sarcomere shortening in VCMs.
• Assessment of cardiac and VCM weights, and measurement of key Ca2+ handling protein and mRNA levels.

Main Results:

• No significant differences in cardiac weight, VCM size, or levels of key Ca2+ handling proteins (SERCA2a, NCX1, Cav1.2, PLN) were observed between CRE and WT mice at 3 months.
• CRE mice exhibited altered Ca2+ dynamics, including reduced resting and peak Ca2+, and delayed Ca2+ transient decay under basal conditions.
• These Ca2+ dynamic alterations persisted upon isoproterenol stimulation, with increased Ca2+ transient amplitude in CRE VCMs, potentially linked to reduced dystrophin.
• Sarcomere shortening parameters remained unchanged, indicating that early Ca2+ dysregulation does not immediately impair contractility.

Conclusions:

• Cre expression in VCMs induces significant changes in intracellular Ca2+ dynamics as early as 3 months of age, preceding structural cardiac changes.
• These early Ca2+ dynamics alterations are not explained by changes in major Ca2+ handling proteins but may involve factors like dystrophin.
• Researchers using the Cre/LoxP system should consider Cre-positive mice as controls to account for these subtle, pre-phenotypic changes in cardiovascular studies.