The role of RGS3L in cardiac hypertrophy and pump function

The role of RGS3L in cardiac hypertrophy and pump function Heart failure represents the end stage of many cardiovascular diseases and remains one of the leading causes of death worldwide. Despite therapeutic advances, current treatments do not restore cardiac contractility and often fail to halt disease progression, highlighting the need for new molecular targets. Regulators of G-protein Signaling (RGS) constitute a family of proteins that modulate the function of Gi/q-protein coupled receptors (GPCRs) by accelerating guanosine triphosphate (GTP) hydrolysis. RGS3L, a member of this family, can in addition to its hydrolytic activity act as a Gβγ scavenger, thereby terminating Gβγ-mediated signaling. The mutant RGS3LN460A used in this and recent studies lacks hydrolytic activity; however, it still retains its Gβγ-scavenging ability. Recent studies suggested that RGS3LN460A has pro-contractile and anti-hypertrophic properties by promoting RhoA and inhibiting Rac1 activity, and by impairing Gβγ-induced signal transduction. Herein, I further deciphered the underlying mechanism by showing that the RGS3LN460A signalosome complex that facilitates the p190RhoGAP-mediated switch from RhoA to Rac1 inactivation requires eNOS-dependent nitration of p190RhoGAP-A. To analyze how RGS3LN460A interferes with pro-hypertrophic signal cascades, I performed Western Blot analysis and phospho-proteome profiling in NRCM challenged with α1A-adrenoceptor (AR) agonist A61603. Assessing MAPK phosphorylation and key indicators of increased protein synthesis activity did not confirm any relevant anti-hypertrophic properties of RGS3LN460A. Instead, I observed a decreased phosphorylation of the transcription factor CREB, which I demonstrated to be Gβγ/PI3K and Rac1-dependent. Furthermore phospho-proteome analysis revealed higher phosphorylation of proteins involved in contractility in the presence of RGS3LN460A. To investigate the potential protective effect of RGS3LN460A in vivo, I subjected mice with an AAV-mediated overexpression of the protein to pressure overload to induce heart failure. Indeed, RGS3LN460A overexpression led to improved pump function and less fibrotic remodeling. However, hypertrophic growth was unaffected. In addition, proteome analysis revealed preserved expression of proteins involved in oxidative phosphorylation and mitochondrial function. Indicating better energy supply compared to control AAV-treated animals. Taken together, my data demonstrates that RGS3LN460A protects from contractile dysfunction, most likely by facilitating pro-contractile RhoA activity, while reducing Rac1-mediated ROS production