NOS3 (nitric oxide synthase 3; HGNC:7876, NCBI Gene ID 4846) is a human locus mapped to chromosome band 7q36.1 that encodes homodimeric endothelial nitric oxide synthase eNOS (1,203 aa; EC 1.14.13.39). NOS3 acts in endothelium-dependent L-arginine to Nitric Oxide (NO) synthesis & soluble guanylate cyclase-cGMP vasodilation, together with Nitric Oxide (Signaling Gas), Guanylate Cyclase Receptors, and AKT1 Kinase (Phosphorylates eNOS Ser1177). Encodes endothelial nitric oxide synthase (eNOS), which synthesizes vascular nitric oxide in response to shear stress and acetylcholine.
Genomic Organization & Cytogenetic Locus: 26-exon gene on chromosome 7q36.1 regulated by laminar shear-stress KLF2 response elements, encoding a 1,203-amino-acid enzyme with an N-terminal heme- and tetrahydrobiopterin (BH4)-binding oxygenase domain, a central calmodulin-binding linker, and a C-terminal NADPH/FAD/FMN reductase domain, targeted to endothelial caveolae by N-terminal myristoylation (Gly2) and dual palmitoylation (Cys15/Cys26).
Cellular & Tissue Expression Profile: Constitutively expressed in arterial, venous, and capillary vascular endothelial cells, endocardial endothelium, cardiac myocytes, and platelets.
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Activated when fluid shear stress (via PIEZO1, TRPV4, and AKT1 phosphorylation at Ser1177) or vasodilators (acetylcholine, bradykinin, VEGF) elevate intracellular Ca2+-calmodulin to displace eNOS from inhibitory caveolin-1; eNOS then oxidizes L-arginine to L-citrulline and gaseous Nitric Oxide (NO), which diffuses into adjacent vascular smooth muscle cells to activate soluble guanylate cyclase, generate cGMP, and induce relaxation while inhibiting platelet aggregation and leukocyte adhesion.
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: During oxidative stress or tetrahydrobiopterin (BH4) depletion, eNOS undergoes pathological uncoupling—transferring electrons to O2 to generate superoxide rather than NO—and functional NOS3 polymorphisms (such as p.Glu298Asp / rs1799983 and promoter -786T>C) are associated with coronary spasm, essential hypertension, and preeclampsia.
Therapeutic & Clinical Pharmacology: Endothelial NOS3 expression and Ser1177 phosphorylation are potently up-regulated by aerobic exercise shear stress, HMG-CoA reductase inhibitors (statins), and ACE inhibitors, while downstream NO-sGC-cGMP signaling is mimicked by organic nitrates and sGC stimulators (riociguat, vericiguat).