Enhancement of Cardiac Function and Suppression of Heart Failure Progression By Inhibition of Protein Phosphatase 1

Abstract

Abstract-Abnormal calcium cycling, characteristic of experimental and human heart failure, is associated with impaired sarcoplasmic reticulum calcium uptake activity. This reflects decreases in the cAMP-pathway signaling and increases in type 1 phosphatase activity. The increased protein phosphatase 1 activity is partially due to dephosphorylation and inactivation of its inhibitor-1, promoting dephosphorylation of phospholamban and inhibition of the sarcoplasmic reticulum calcium-pump. Indeed, cardiac-specific expression of a constitutively active inhibitor-1 results in selective enhancement of phospholamban phosphorylation and augmented cardiac contractility at the cellular and intact animal levels. Furthermore, the ␤-adrenergic response is enhanced in the transgenic hearts compared with wild types. On aortic constriction, the hypercontractile cardiac function is maintained, hypertrophy is attenuated and there is no decompensation in the transgenics compared with wild-type controls. Notably, acute adenoviral gene delivery of the active inhibitor-1, completely restores function and partially reverses remodeling, including normalization of the hyperactivated p38, in the setting of pre-existing heart failure. Thus, the inhibitor 1 of the type 1 phosphatase may represent an attractive new therapeutic target. Key Words: protein phosphatase 1 Ⅲ protein phosphatase 1 inhibitor 1 Ⅲ heart failure Ⅲ hypertrophy Ⅲ phospholamban Ⅲ gene therapy R eversible protein phosphorylation represents the cellular basis for integration of key signaling pathways, mediating a fine crosstalk between external effector molecules and intracellular events. In the heart, Ca 2ϩ cycling and contractility are controlled by a fine balance of protein kinase and phosphatase activities in response to various second messenger signals. Demands on the heart's pumping action, during fight-or-flight situations, can increase human cardiac output by nearly 5-fold. This is linked to ␤-adrenergic activation of the cAMP dependent protein kinase (PKA). PKA then phosphorylates a set of key regulatory Ca 2ϩ handling proteins that control excitation-contraction coupling cycle, such as phospholamban, the ryanodine receptor, the L-type Ca 2ϩ channel, and troponin I. 1 The protein kinases and their phosphoprotein substrates underlying augmentation of the heart's pumping action have been well characterized. However, similar studies on the protein phosphatases, reversing the increased cardiac contractility, are less well developed. The major Ser/Thr phosphatases [type 1, type 2A, and type 2B (calcineurin)] stem from a common gene family and are highly homologous proteins (40% to 50%) that play critical roles in the control of cardiac contractility and hypertrophy.Overexpression of the catalytic subunit of the protein phosphatase 1 at similar levels observed in human heart failure was associated with dephosphorylation of phospholamban, depressed cardiac function, dilated cardiomyopathy, and premature mortality. 2 Furthermore, PP2A and PP2B (calcineurin) overexpressio...

Genetic inhibition of PKA phosphorylation of RyR2 prevents dystrophic cardiomyopathy

“…Another potential mechanism for differences in the local kinase/phosphatase balance may be the activity of protein phosphatase inhibitors 1 and 2 (I-1, I-2) (33). I-1 becomes active upon phosphorylation at Thr35 by PKA (34) and is downregulated in human and experimental heart failure (35). Nicolaou et al (33) demonstrated that cardiac-specific expression of a constitutively active form (T35D) of I-1 (I-1c) induced increased phosphorylation of PLN in the absence of changes in RyR2 phosphorylation levels.…”

Gene Therapy in Heart Failure

“…Active I-1 and Inhibition of PP1: HF is associated with elevated PP1 activity in humans resulting in dephosphorylation of PLN. Overexpression of PP1 or ablation of I-1 in murine hearts has been associated with decreased β-AR-mediated contractile responses, depressed cardiac function and premature death consistent with HF [114][115][116] . Expression of a constitutively active I-1 in transgenic mice led to PP1 inhibition with increased phosphorylation of PLN and improved cardiac contractility.…”

“…A recent study on transgenic mice expressing active I-1 confirmed the relationship between phosphorylation of PLN and SERCA2a activity. I-1 expression ameliorated ischemia/reperfusion-induced injury by reducing the infarct size and improving contractile recovery in addition to decreasing biomarkers of apoptosis and ER stress response [114][115][116] .…”

Gene Therapy in Heart Failure

“…Murine models in which either I-1 is over expressed in a constitutively active form (I-1c) or PP1 is inhibited have shown improved cardiac function and protection from HF. [44][45][46] Increased SERCA2a Activity Through Enhanced Post-Translational Modification (SUMOylation) Gene therapy with AAV9.SUMO1 vector to increase SUMO1 expression in an animal model of HF led to markedly im-…”