β-adrenergic receptor stimulation in a Mybpc3-targeted HCM mouse model led to preferential PKA phosphorylation of PLN over cTnI, impairing inotropic and lusitropic responses.
Does β-adrenergic receptor stimulation differentially affect PKA targets in an HCM mouse model?
In an HCM mouse model, β-adrenergic stimulation leads to preferential PKA phosphorylation of PLN over cTnI, causing impaired inotropic and lusitropic responses.
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.
Najafi et al. (Fri,) conducted a other in Hypertrophic cardiomyopathy (HCM). β-adrenergic receptor stimulation (isoprenaline) vs. Wild-type mice was evaluated on Cardiomyocyte contractile properties and phosphorylation state. β-adrenergic receptor stimulation in a Mybpc3-targeted HCM mouse model led to preferential PKA phosphorylation of PLN over cTnI, impairing inotropic and lusitropic responses.
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