The Ric-8b protein (resistance to inhibitors of cholinesterase 8b) is key to preserving contractile function in the adult heart.

Resistance to inhibitors of cholinesterases (Ric-8 proteins) are involved in modulating G-protein function but little is known of their potential physiological importance in the heart. In the present study, we assessed the role of resistance to inhibitors of cholinesterase 8b (Ric-8b) in determining cardiac contractile function using a mouse model. Deletion of Ric-8b in cardiac tissue led to severely reduced contractility as measured using echocardiography days after administration of tamoxifen. Histological analysis of the ventricular tissue showed highly variable myocyte size, prominent fibrosis and an increase in cellular apoptosis. RNA sequencing revealed transcriptional remodelling in response to cardiac Ric-8b deletion involving the extracellular matrix and inflammation. Phosphoproteomic analysis revealed substantial downregulation of phosphopeptides related to myosin light chain 2. At the cellular level, the deletion of Ric-8b led to loss of activation of the L-type calcium channel through the ß-adrenergic pathways. Using fluorescence resonance energy transfer-based assays in heterologous expression systems we showed Ric-8b protein selectively interacts with the stimulatory G-protein, Gas. We explored if deletion of Gnas (the gene encoding Gas) in cardiac tissue using a similar approach in the mouse led to an equivalent phenotype. The conditional deletion of the Gas gene in the ventricle led to comparable effects on contractile function and cardiac histology. We conclude that Ric-8b is essential to preserve cardiac contractile function likely through an interaction with the stimulatory G-protein and downstream phosphorylation of myosin light chain 2. Overall design: We developed a murine model in which it was possible to conditionally delete Ric-8b in cardiac tissue in the adult animal after the addition of tamoxifen. Ric-8b (flx/flx) mice were combined with the cardiac muscle specific tamoxifen inducible cre to create “Ric-8b (flx/flx) MCM” mice. RNA-sequencing was carried out on hearts of Ric-8b (flx/flx) MCM and control mice to compare the differences within the transcriptome when Ric-8b is knocked out.