Key result
Endothelial deletion of Rap1A and Rap1B impairs NO-dependent vasorelaxation, which is ameliorated by L-arginine supplementation, demonstrating distinct signaling roles for the two isoforms in eNOS regulation.
Why the study?
The specific contribution of the Rap1A isoform to NO release and the molecular mechanisms through which Rap1 isoforms control endothelial function were unknown.
Rap1A and Rap1B regulate endothelial NO release via distinct pathways, where Rap1B promotes eNOS activation and Rap1A prevents its negative regulation, with combined deficiency causing severe endothelial dysfunction reversible by L-arginine.
Does not support clinical L-arginine use; leaves open distinct Rap1 isoform roles in human eNOS regulation.
Small GTPase Rap1 plays a prominent role in endothelial cell (EC) homeostasis by promoting NO release. Endothelial deletion of the two highly homologous Rap1 isoforms, Rap1A and Rap1B, leads to endothelial dysfunction ex vivo and hypertension in vivo . Mechanistically, we showed that Rap1B promotes NO release in response to shear flow by promoting mechanosensing complex formation involving VEGFR2 and Akt activation. However, the specific contribution of the Rap1A isoform to NO release and the underlying molecular mechanisms through which the two Rap1 isoforms control endothelial function are unknown. Here, we demonstrate that endothelial dysfunction resulting from knockout of both Rap1A and Rap1B isoforms is ameliorated by exogenous L-Arg administration to rescue NO-dependent vasorelaxation and blood pressure. We confirmed that Rap1B is rapidly activated in response to agonists that trigger eNOS activation, and its deletion in ECs attenuates eNOS activation, as detected by decreased Ser1177 phosphorylation. Somewhat surprising was the finding that EC deletion of Rap1A does not lead to impaired agonist-induced vasorelaxation ex vivo . Mechanistically, the deletion of Rap1A led to elevated eNOS phosphorylation both at the inhibitory, T495, and the activating Ser1177 residues. These findings indicate that the two Rap1 isoforms act via distinct signaling pathways: while Rap1B directly positively regulates eNOS activation, Rap1A prevents negative regulation of eNOS. Notably, the combined deficiency of Rap1A and Rap1B has a severe effect on eNOS activity and NO release with an in vivo impact on endothelial function and vascular homeostasis.
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Kosuru et al. (2021) studied Endothelial dysfunction. Rap1A and Rap1B knockout / L-arginine vs. Wild-type controls was evaluated on Vasorelaxation and eNOS phosphorylation. Endothelial deletion of Rap1A and Rap1B impairs NO-dependent vasorelaxation, which is ameliorated by L-arginine supplementation, demonstrating distinct signaling roles for the two isoforms in eNOS regulation.
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