Phosphatase regulation in cardiovascular physiology and disease

Reversible protein phosphorylation is an essential component of metazoan signaling and cardiovascular physiology. Protein kinase activity is required for regulation of cardiac ion channel and membrane receptor function, metabolism, and transcription, and aberrant kinase function is widely observed across disparate cardiac pathologies. In fact, multiple generations of cardiac therapies (eg. beta-adrenergic receptor blockers) have targeted cardiac kinase regulatory cascades. In contrast, essentially nothing is known regarding the mechanisms that regulate cardiac phosphatase activity at baseline or in cardiovascular disease.

Protein phosphatase 2A (PP2A) is a key phosphatase with multiple roles in cardiac physiology. Here we demonstrate the surprisingly complex regulatory platforms that control PP2A holoenzyme activity in heart. We present the first full characterization of the expression and regulation of the PP2A family of polypeptides in heart. We identify the expression of seventeen different PP2A genes in human heart and define their differential expression and distribution across species and in different cardiac chambers. We show unique subcellular distributions of PP2A regulatory subunits in myocytes, strongly implicating the regulatory subunit in conferring PP2A target specificity in vivo. We report striking differential regulation of PP2A scaffolding, regulatory, and catalytic subunit expression in multiple models of cardiovascular disease as well as in human heart failure samples. Importantly, we demonstrate that PP2A regulation in disease extends far beyond expression and subcellular location, by identifying and describing differential post-translational modifications of the PP2A holoenzyme in human heart failure. Furthermore, we go to characterize a mechanism for this method of post-translational modification that may represent a pathway capable of being therapeutically manipulated in human heart failure. Lastly we provide evidence that dysregulation of phosphatase activity contributes to the cellular pathology associated with a previously described inheritable human arrhythmia syndrome, highlighting the importance of the PP2A in cardiovascular physiology and disease. Together, our findings provide new insight into the functional complexity of PP2A expression, activity, and regulation in heart and in human cardiovascular disease and identify potentially new and specific gene and subcellular targets for the treatment of human arrhythmia and heart failure.