Tetrahydrobiopterin Determines Vascular Remodeling Through Enhanced Endothelial Cell Survival and Regeneration

Abstract

Loss of endothelial cells (ECs) in conditions of vascular injury is an important contributor to adverse vascular remodeling that leads to neointimal hyperplasia and accelerated atherosclerosis, for example, in venous bypass grafts, allograft vasculopathy, and after angioplasty or stenting. 1Re-endothelialization has been shown to be a key event in vascular repair. Endothelial nitric oxide synthase (eNOS) is essential for the normal function of ECs in the vascular wall and for the function of circulating endothelial progenitor cells (EPC).2-4 However, the molecular mechanisms relating eNOS regulation to endothelial loss, survival, and regeneration after vascular disease are uncertain. The eNOS cofactor, tetrahydrobiopterin (BH4), is a critical determinant of eNOS enzymatic activity and function. We and others have shown that in vascular disease states BH4 deficiency leads to eNOS uncoupling, whereby reduction of molecular oxygen by eNOS is no longer coupled to L-arginine oxidation and NO synthesis, and instead eNOS generates superoxide rather than NO. 5We hypothesized that BH4-dependent eNOS regulation may have an important role in endothelial loss and regeneration and in the development of neointimal hyperplasia after vascular injury. To investigate the specific role of EC BH4 availability, we compared apolipoprotein E (apoE)-knockout (KO) mice with or without transgenic endothelium-targeted overexpression of GTP cyclohydrolase I (GCH), the ratelimiting enzyme in endothelial BH4 synthesis, 5,6 in a model of venous bypass grafting characterized by acute endothelial loss, neointimal hyperplasia, and endothelial regeneration 2 and investigated how GCH and BH4 regulate primary EC survival and growth.Background-Endothelial cell (EC) survival and regeneration are important determinants of the response to vascular injury that leads to neointimal hyperplasia and accelerated atherosclerosis. Nitric oxide (NO) is a key regulator of EC and endothelial progenitor cell function, but the pathophysiological mechanisms that regulate endothelial NO synthase in endothelial regeneration remain unclear. Methods and Results-Endothelium-targeted overexpression of GTP cyclohydrolase (GCH) I increased levels of the endothelial NO synthase cofactor, tetrahydrobiopterin, in an EC-specific manner and reduced neointimal hyperplasia in experimental vein grafts in GCH/apolipoprotein E-knockout mice. These effects were mediated through enhanced donor-derived survival and recipient-derived repopulation of GCH transgenic ECs, revealed by tracking studies in Tie2-LacZ/GCH-Tg/apolipoprotein E-knockout recipient mice or donor grafts, respectively. Endothelial GCH overexpression increased endothelial NO synthase coupling and enhanced the proliferative capacity of ECs and circulating endothelial progenitor cell numbers after vascular injury. Conclusions-These observations indicate that endothelial tetrahydrobiopterin availability modulates neointimal hyperplasia after vascular injury via accelerated EC repopulation and growth. Targeting tetrahydrobi...

Impaired Endothelial Nitric Oxide Synthase Homodimer Formation Triggers Development of Transplant Vasculopathy - Insights from a Murine Aortic Transplantation Model

“…The proposed pathomechanism based on BH4 depletion and increased occurrence of inactive eNOS monomers is also in line with the knowledge that NO inhibits the expression of adhesion molecules55, and with the observation that in a balloon angioplasty model with prominent endothelial injury increased generation of NO prevented intimal thickening and restenosis of the vessel by inhibiting SMC proliferation5657. BH4 and NO homeostasis have also been shown to play a crucial role in Cyclosporine A (CyA) induced vasomotor dysfunction proposing this pathway as a potential therapeutic strategy to prevent CyA induced vascular injury in transplant recipients58.…”

Tetrahydrobiopterin Protects against Radiation-induced Growth Inhibition in H9c2 Cardiomyocytes

“…[7] BH4 deficiency tends to induce endothelial NOS (eNOS) uncoupling in vivo . [8] In addition, BH4 is highly sensitive to oxidation and can be degraded within minutes. [8] BH4 therapy can reverse the disease-related redox disequilibrium observed with BH4 deficiency.…”

“…[8] In addition, BH4 is highly sensitive to oxidation and can be degraded within minutes. [8] BH4 therapy can reverse the disease-related redox disequilibrium observed with BH4 deficiency. For example, incubation with BH4 has been shown to improve oxidant stress levels in arteries in spontaneously hypertensive rats and streptozotocin-induced diabetic rats.…”

Role of oral and gut microbiome in nitric oxide-mediated colon motility

“…Several lines of evidence suggest that impairment of BH 4 and NO synthesis are associated with altered antioxidant mechanism and gastrointestinal motility disorders (56–57). Reduced NO bioavailability, as well as an impaired NO-mediated vasodilation, has been known to play a detrimental role in cardiovascular pathologies as a result of endothelial nitric oxide synthase (eNOS) uncoupling and increased reactive oxygen species (ROS) (58). Higashi et al studies demonstrated that periodontitis is associated with NO dependent endothelial dysfunction in the patients with coronary artery disease (59).…”