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Updated: Mar 26, 2026
Investigating the Pathogenesis of MYH7 Mutation Gly823Glu in Familial Hypertrophic Cardiomyopathy using a Mouse Model
Published on: August 8, 2022
Selective phosphorylation of PKA targets after β-adrenergic receptor stimulation impairs myofilament function in
Aref Najafi1, Vasco Sequeira2, Michiel Helmes2
1Department of Physiology, Institute for Cardiovascular Research (ICaR-VU), VU University Medical Center Amsterdam, Netherlands ICIN-Netherlands Heart Institute, Utrecht, The Netherlands a.najafi@vumc.nl.
Insights
In hypertrophic cardiomyopathy (HCM), beta-adrenergic receptor (β-AR) signaling affects protein kinase A (PKA) targets differently. PKA preferentially phosphorylates phospholamban over cardiac troponin I in HCM mice, impairing heart function.
Area of Science:
- Cardiovascular Biology
- Molecular Cardiology
- Genetic Diseases
Background:
- Hypertrophic cardiomyopathy (HCM) is linked to reduced beta-adrenergic receptor (β-AR) signaling and impaired protein kinase A (PKA) phosphorylation.
- The specific impact of diminished β-AR signaling on various PKA targets in HCM remains unclear.
Purpose of the Study:
- To investigate the role of β-AR signaling in regulating myofilament and calcium handling in a Mybpc3-mutation-induced HCM mouse model.
- To determine if PKA targets are affected uniformly by reduced β-AR signaling in HCM.
Main Methods:
- Cardiomyocyte contractile properties and phosphorylation were analyzed in wild-type, heterozygous (HET), and homozygous (KI) Mybpc3-targeted knock-in mice.
- Measurements included myofilament calcium sensitivity, passive tension, and responses to isoprenaline (ISO) in permeabilized and intact cardiomyocytes.
Main Results:
- Homozygous KI mice exhibited increased myofilament calcium sensitivity and passive tension, normalized by PKA treatment.
- Impaired force-sarcomere length relationships were observed in HET and KI mice, indicating reduced length-dependent activation.
- While calcium handling responded to ISO, myofilament contraction did not in KI mice, linked to reduced cardiac troponin I (cTnI) phosphorylation but maintained phospholamban (PLN) phosphorylation.
Conclusions:
- In the KI HCM mouse model, β-AR stimulation results in preferential PKA phosphorylation of phospholamban (PLN) over cardiac troponin I (cTnI).
- This selective phosphorylation pattern contributes to impaired inotropic and lusitropic responses in HCM.
- Findings highlight differential regulation of PKA targets in response to β-AR signaling in HCM.
Aims:
Hypertrophic cardiomyopathy (HCM) has been associated with reduced β-adrenergic receptor (β-AR) signalling, leading downstream to a low protein kinase A (PKA)-mediated phosphorylation. It remained undefined whether all PKA targets will be affected similarly by diminished β-AR signalling in HCM. We aimed to investigate the role of β-AR signalling on regulating myofilament and calcium handling in an HCM mouse model harbouring a gene mutation (G > A transition on the last nucleotide of exon 6) in Mybpc3 encoding cardiac myosin-binding protein C.
Methods And Results:
Cardiomyocyte contractile properties and phosphorylation state were measured in left ventricular permeabilized and intact cardiomyocytes isolated from heterozygous (HET) or homozygous (KI) Mybpc3-targeted knock-in mice. Significantly higher myofilament Ca²⁺sensitivity and passive tension were detected in KI mice, which were normalized after PKA treatment. Loaded intact cardiomyocyte force-sarcomere length relation was impaired in both HET and KI mice, suggesting a reduced length-dependent activation. Unloaded cardiomyocyte function revealed an impaired myofilament contractile response to isoprenaline (ISO) in KI, whereas the calcium-handling response to ISO was maintained. This disparity was explained by an attenuated increase in cardiac troponin I (cTnI) phosphorylation in KI, whereas the increase in phospholamban (PLN) phosphorylation was maintained to wild-type values.
Conclusion:
These data provide evidence that in the KI HCM mouse model, β-AR stimulation leads to preferential PKA phosphorylation of PLN over cTnI, resulting in an impaired inotropic and lusitropic response.
