Catecholaminergic stress results in signs of heart failure in PP2A-PR72 overexpressor mice

Abstract

Background

It is unclear whether the increase in protein expression of PP2A regulatory subunit PR72 seen in human heart failure represents a primary compensatory mechanism or the final reaction to contractile decompensation. To address this question, we have explored the effects of chronic catecholaminergic stress in a transgenic (TG) mouse model with heart-specific overexpression of PR72 that exhibits hypercontractility at basal conditions.

Methods

Mice were treated with isoprenaline (ISO) or NaCl for 7 days using osmotic minipumps. Hearts or isolated cardiomyocytes from the animals were functionally examined.

Results

We could show (i) that PR72 expression is not only increased after chronic ISO stimulation but also in other different stress and insufficiency models. In TG mice, 7 days of ISO treatment led to (ii) increased hypertrophy, pulmonary edema, more fibrosis, and higher ACTA1 gene expression compared to wild-type (WT) mice. These effects were accompanied by (iii) a decrease in myocellular contractility and prolonged relaxation. Ca²⁺ transients (iv) showed correspondingly delayed decay kinetics in TG versus WT, while (v) the reduction of L-type calcium peak current by ISO treatment was less pronounced in TG cells. The decrease in RyR2 phosphorylation in TG (vi) supports a deterioration in contractility due to chronic ISO treatment in TG.

Conclusion

Our results indicate that the upregulation of PP2A-PR72 in various stress and heart failure models has a long-term effect, perpetuating the molecular and functional detrimental cardiac changes, if it does not have a triggering effect.