Endothelial mTORC1 signaling is required for vascular endothelial function
Authors: Reho John J , Guo Deng‐Fu , Rahmouni Kamal 
Published: June 2021

The mechanistic target of rapamycin complex 1 (mTORC1) that regulates cellular gene and protein programming through its downstream signaling components the S6‐kinase and the ribosomal S6 protein serves as an intracellular energy sensor. Emerging evidence points to mTORC1 signaling as an important regulator of cardiovascular function with implications in hypertension. In this study, we tested the hypothesis that endothelial mTORC1 signaling is critically involved in the regulation of vascular endothelial function and that dysregulation of this pathway contributes to endothelial dysfunction. To test this, we generated mice bearing endothelial‐specific mTORC1 disruption by deleting the gene that encodes Raptor, an essential subunit of the complex. For this, we crossed tamoxifen‐inducible endothelial‐specific Cre mice (TekCreERT2) with mice harboring floxed alleles of the Raptor gene. Upon tamoxifen treatment, TekCreERT2/RaptorF/F mice exhibited ~60% reduction in total Raptor expression in endothelial cells (1.0±0.1 vs 0.4±0.1 AU; p<0.05) with no change in Raptor expression in smooth muscle cells (0.8±0.1 vs 1.0±0.1 AU). Tamoxifen treated TekCreERT2/RaptorF/F mice displayed reduced acetylcholine‐mediated endothelial (Max relax: 61±7 vs 34±11%; p<0.05) but not SNP‐induced smooth muscle vasorelaxation responses (Max relax: 84±2 vs 82±3%) in the aorta compared to tamoxifen‐treated wildtype littermates. To demonstrate the importance of mTORC1 signaling in this reduced acetylcholine‐mediated endothelial response in the aorta, we infected TekCreERT2/RaptorF/F aortic rings with an adenoviral S6‐kinase constitutively active construct (Ad‐S6KCA; 24hrs) to restore mTORC1 signaling. Infection with Ad‐S6KCA improved acetylcholine‐mediated endothelial vasorelaxation responses approaching wildtype control levels (Max relax: 54±6 vs 31±10%; p<0.05). We next assessed the effect of heterozygous deletion of endothelial Raptor in mice (TekCreERT2/RaptorF/+). Aortic rings from TekCreERT2/RaptorF/+ displayed intact acetylcholine‐induced vasorelaxation responses compared to tamoxifen‐treated wildtype controls (Max relax: 50±3 vs 49±8%). We next challenged aortic rings from tamoxifen treated TekCreERT2/RaptorF/+ mice with angiotensin II (100nM; 24hrs) to induce endothelial dysfunction. Angiotensin II incubation reduced acetylcholine‐mediated vasorelaxation responses of aortic rings from wildtype mice compared to vehicle (PBS) (Max relax: 57±4 vs 3±8%; p<0.05). Interestingly, aortic rings of TekCreERT2/RaptorF/+ mice treated with tamoxifen were partially protected from the endothelial dysfunction evoked by angiotensin II (Max relax: 3±8 vs 36±9%; p<0.05) indicating that mTORC1 signaling is critical for the vascular effects of angiotensin II. Our data indicate that endothelial mTORC1 signaling is required for the regulation of endothelial function and highlight the need for coordinated balance of mTORC1 signaling for endothelial homeostasis. We speculate that the endothelial mTORC1 signaling pathway may represent a novel target for cardiovascular risks associated with endothelial dysfunction such as hypertension.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.