The α2-isoform of the Na⁺/K⁺-ATPase protects against pathological remodeling and β-adrenergic desensitization after myocardial infarction

Abstract

Aim: The role of the Na+/K+-ATPase (NKA) in heart failure associated with myocardial infarction (MI) is poorly understood. The elucidation of its precise function is hampered by the existence of two catalytic NKA isoforms (NKA-α1 and NKA-α2). Our aim was to analyze the effects of an increased NKA-α2 expression on functional deterioration and remodeling during long term MI treatment in mice and its impact on Ca2+ handling and inotropy of the failing heart. Methods and Results: Wild-type (WT) and NKA-α2 transgenic (TG) mice (TG-α2) with a cardiac-specific overexpression of NKA-α2 were subjected to MI injury for 8 weeks. As examined by echocardiography, gravimetry and histology, TG-α2 mice were protected from functional deterioration and adverse cardiac remodeling. Contractility and Ca2+ transients (Fura 2-AM) in cardiomyocytes from MI-treated TG-α2 animals showed reduced Ca2+ amplitudes during pacing or after caffeine application. Ca2+ efflux in cardiomyocytes from TG-α2 mice was accelerated, and diastolic Ca2+ levels decreased. Based on these alterations, sarcomeres exhibited an enhanced sensitization and thus increased contractility. After the acute stimulation with the β-adrenergic agonist isoproterenol (ISO), cardiomyocytes from MI-treated TG-α2 mice responded with increased sarcomere shortenings and Ca2+ peak amplitudes. This positive inotropic response was absent in cardiomyocytes from WT-MI animals. Conclusions: Cardiomyocytes with NKA-α2 as predominant isoform minimize Ca2+ cycling but respond to β-adrenergic stimulation more efficiently during chronic cardiac stress. These mechanisms might improve the β-adrenergic reserve and contribute to functional preservation in heart failure.

Live cell screening identifies glycosides as enhancers of cardiomyocyte cell cycle activity

“…In general, cardiac glycosides inhibit the sodium-potassium pump resulting in an increased calcium concentration inside the cell. It is well known that Na + K + ATPase specifically regulates calcium transients via the IP3 receptors ( 33 – 35 ) and our data show that inhibition of the IP3 receptors with xestospongin C inhibits the cell cycle-promoting effect of glycosides. Notably, calcium plays, in general, a crucial role in cell proliferation and aberrant Ca 2+ -signaling and loss of intracellular Ca 2+ homeostasis contributes to tumor initiation and proliferation ( 37 , 38 ).…”

“…Cardiac glycosides increase the output force of the heart and decrease its rate of contractions by acting on the cellular sodium-potassium ATPase pump, Na + K + ATPase ( 20 ). As Na + K + ATPase is known to specifically regulate calcium transients via the inositol trisphosphate (IP3) receptors ( 33 – 35 ), we have tested the effect of the selective IP3 receptor antagonist xestospongin C ( 36 ) on cardiac glycoside-enhanced cardiomyocyte cell cycle progression. For this purpose, P3 rat cardiomyocytes were stimulated with glycosides in the absence or presence of 1 μM xestospongin C and the number of Ki67-, H3P-, aurora B-positive cardiomyocytes as well as cardiomyocytes positive for aurora B at the midbody were evaluated.…”

Essential contributions of the α2-Na+/K+-ATPase ouabain binding site to cardiac remodeling

“…Thus, circulating EO preferentially binds tightly to a2 S/S , but not to a1 R/R NKA in rodents in vivo. Clearly, a2 S/S , not a1 R/R , must mediate EO signaling, contrary to the speculation previously described (1); reports of EO signaling via a1 R/R (14), cited in Cellini et al (1), make no physiological sense. In the post-MI condition, where elevated circulating EO levels are expected, the large increase in cardiac a2 expression in a2-TG mice would mean that the majority of a2 ouabain-binding sites will remain unoccupied by EO.…”

“…In conclusion, Cellini et al (1) provide new information about the role of altered a2/a1 NKA ratios in modulating MItriggered cardiac remodeling and b-adrenergic desensitization but overlook the essential contributions of the a2 ouabain binding site and its endogenous ligand in these processes. This was a missed opportunity to explore mechanisms that might lead to a practical therapy, possibly by reducing the number of EO-bound a2 rather than increasing the total number of a2 NKA.…”

Unconventional interactions of the TRPV4 ion channel with beta-adrenergic receptor ligands

“…Blots were preincubated with 5% low-fat milk in TBS-0.1% Tween for 1 h at room temperature and incubated overnight at 4°C with β1-AR (ab3442) (Sun et al, 2021) or β2-AR (ab182136) (Cellini et al, 2021) antibodies from Abcam or E-cadherin antibody (3195) (Ye et al, 2022) from Cell Signaling Technology (as a positive control for membrane proteins) diluted 1:1,000 for each case. After washing of the primary antibodies, binding was visualized using a secondary horseradish peroxidase (Thermo Fisher Scientific)-labeled anti-rabbit antibody (for adrenergic receptors; 1:10,000 dilution) and anti-mouse antibody (for E-cadherin; 1:10,000 dilution) and enhanced with diaminobenzidine at 100 µg/ml in TBS with 30% H 2 O 2 .…”