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Hyperhomocysteinemia (HHcy) has been shown to induce endothelial dysfunction in part as a result of enhanced oxidative stress. Function and survival of endothelial progenitor cells (EPCs, defined as sca1(+) c-kit(+) flk-1(+) bone marrow-derived cells), which significantly contribute to neovascularization and endothelial regeneration, depend on controlled production of reactive oxygen species (ROS). Mice heterozygous for the gene deletion of methylenetetrahydrofolate reductase (Mthfr(+/-)) have a 1.5- to 2-fold elevation in plasma homocysteine. This mild HHcy significantly reduced the number of circulating EPCs as well as their differentiation. Mthfr deficiency was also associated with increased ROS production and reduced nitric oxide (NO) generation in Mthfr(+/-) EPCs. Treatment of EPCs with sepiapterin, a precursor of tetrahydrobiopterin (BH(4)), a cofactor of endothelial nitric oxide synthase (eNOS), significantly reduced ROS and improved NO production. mRNA and protein expression of eNOS and the relative amount of eNOS dimer compared with monomer were decreased by Mthfr deficiency. Impaired differentiation of EPCs induced by Mthfr deficiency correlated with increased senescence, decreased telomere length, and reduced expression of SIRT1. Addition of sepiapterin maintained cell senescence and SIRT1 expression at levels comparable to the wild type. Taken together, these results demonstrate that Mthfr deficiency impairs EPC formation and increases EPC senescence by eNOS uncoupling and downregulation of SIRT1.

Immune cells have been implicated in the pathogenesis of hypertension. We hypothesized that under the influence of chromosome (chr)2, T lymphocytes contribute to vascular inflammation in genetic salt-sensitive hypertension. Normotensive (Brown Norway), hypertensive (Dahl salt-sensitive), and consomic rats (SSBN2; in which chr2 has been transferred from Brown Norway to Dahl rats) were studied. Systolic blood pressure, measured by tail cuff, and aortic preproendothelin mRNA, measured by quantitative RT-PCR, were elevated in Dahl rats compared with Brown Norway rats and were reduced in SSBN2 rats compared with Dahl rats (P < 0.01). Compared with Brown Norway rats, Dahl rats exhibited increased inflammatory markers and mediators such as nuclear translocation of the aortic p65 subunit of NF-kappaB as well as VCAM-1, ICAM-1, chemokine (C-C motif) receptor 5, and CD4 mRNA, all of which were reduced in SSBN2 rats. Aortic CD8 mRNA was equally increased in Dahl and SSBN2 rats relative to Brown Norway rats. CD4(+) T cell infiltration in the aorta of SSBN2 rats was reduced compared with Dahl rats, whereas the aortic protein expression of Foxp3b and immunosuppressors transforming growth factor (TGF)-beta(1) and IL-10, the three markers associated with the regulatory T cell lineage, were enhanced in SSBN2 rats. Activation in vitro of T cells demonstrated that CD4(+)CD25(+) and CD8(+)CD25(+) cells (Tregs) produce IL-10 in SSBN2 rats. Thus, increased vascular inflammatory responses and hypertension in a genetic salt-sensitive hypertensive rodent model are reduced by transfer of chr2 from a normotensive strain, and this is associated with enhanced levels of immunosuppressive mediators.