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

## TL;DR

This study shows that the Ric-8b protein is crucial for maintaining heart muscle function, and its absence leads to reduced contractility and heart damage.

## Contribution

The study identifies Ric-8b as a key regulator of cardiac contractility through its interaction with Gαs and myosin light chain 2 phosphorylation.

## Key findings

- Deletion of ric-8b in adult mice caused severe reductions in heart contractility and increased fibrosis and apoptosis.
- Ric-8b interacts with Gαs and is required for L-type calcium channel activation and myosin light chain 2 phosphorylation.
- Deleting Gnas in the heart produced similar effects to ric-8b deletion, confirming Ric-8b's role in Gαs-dependent signaling.

## Abstract

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. 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. Deletion of ric-8b 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 remodeling 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 β-adrenergic pathways. Using fluorescence resonance energy transfer-based assays, we showed ric-8b protein selectively interacts with the stimulatory G-protein, Gαs. We explored if deletion of Gnas (the gene encoding Gαs) in cardiac tissue using a similar approach in the mouse led to an equivalent phenotype. The conditional deletion of the Gαs 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.