Remodelling of cAMP dynamics within the SERCA2a microdomain in heart failure with preserved ejection fraction caused by obesity and type 2 diabetes

Despite massive efforts, we remain far behind in our attempts to identify effective therapies to treat heart failure with preserved ejection fraction (HFpEF). Diastolic function is critically regulated by sarcoplasmic/endoplasmic reticulum (SR) calcium ATPase 2a (SERCA2a), which forms a functional cardiomyocyte (CM) microdomain where 3′,5′-cyclic adenosine monophosphate (cAMP) produced upon β-adrenergic receptor (β-AR) stimulation leads to phospholamban (PLN) phosphorylation and facilitated Ca²⁺ re-uptake.

To visualize real-time cAMP dynamics in the direct vicinity of SERCA2a in healthy and diseased myocytes, we generated a novel mouse model on the lepr^db background that stably expresses the Epac1-PLN Förster resonance energy transfer biosensor. Mice homozygous for the leprdb mutation (db/db) developed obesity and type 2 diabetes and presented with a HFpEF phenotype, evident by mild left ventricular hypertrophy and elevated left atria filling pressures. Live cell imaging uncovered a substantial β₂-AR subtype stimulated cAMP response within the PLN/SERCA2a microdomain of db/db but not healthy control (db/+) CMs, which was accompanied by increased PLN phosphorylation and accelerated calcium re-uptake. Importantly, db/db CMs also exhibited a desensitization of β₁-AR stimulated cAMP pools within the PLN/SERCA2a microdomain, which was accompanied by a blunted lusitropic effect, suggesting that the increased β₂-AR control is an intrinsic compensatory mechanism to maintain PLN/SERCA2a-mediated calcium dynamics and cardiac relaxation. Mechanistically, this was due to a local loss of cAMP-degrading phosphodiesterase 4 associated specifically with the PLN/SERCA2a complex.

These newly identified alterations of cAMP dynamics at the subcellular level in HFpEF should provide mechanistic understanding of microdomain remodelling and pave the way towards new therapies.