βArrestins in Cardiac G Protein-Coupled Receptor Signaling and Function: Partners in Crime or Good Cop, Bad Cop?

beta arrestin (arr)-1 and -2 (arrs) (or Arrestin-2 and -3, respectively) are universal G protein-coupled receptor (GPCR) adapter proteins expressed abundantly in extra-retinal tissues, including the myocardium. Both were discovered in the lab of the 2012 Nobel Prize in Chemistry co-laureate Robert Lefkowitz, initially as terminators of signaling from the -adrenergic receptor (AR), a process known as functional desensitization. They are now known to switch GPCR signaling from G protein-dependent to G protein-independent, which, in the case of ARs and angiotensin II type 1 receptor (AT(1)R), might be beneficial, e.g., anti-apoptotic, for the heart. However, the specific role(s) of each arr isoform in cardiac GPCR signaling and function (or dysfunction in disease), remain unknown. The current consensus is that, whereas both arr isoforms can desensitize and internalize cardiac GPCRs, they play quite different (even opposing in certain instances) roles in the G protein-independent signaling pathways they initiate in the cardiovascular system, including in the myocardium. The present review will discuss the current knowledge in the field of arrs and their roles in GPCR signaling and function in the heart, focusing on the three most important, for cardiac physiology, GPCR types ((1)AR, (2)AR & AT(1)R), and will also highlight important questions that currently remain unanswered.