Protective Role of Angiopoietin-1 in Experimental Pulmonary Hypertension

Abstract

Abstract-Angiopoietin-1 (Ang-1), a newly discovered ligand of the endothelial-specific tyrosine kinase receptor Tie-2, has been found to promote cell survival, vascular maturation, and stabilization. We hypothesized that Ang-1 gene transfer to the pulmonary microcirculation would improve pulmonary hemodynamics and vascular remodeling in experimental pulmonary hypertension. Rat pulmonary artery smooth muscle cells were transfected with Ang-1 cDNA or null (pFLAG-CMV-1) vector. Syngeneic Fisher 344 rats were treated with monocrotaline (MCT) (75 mg/kg IP) with or without delivery of 5ϫ10 5 Ang-1-transfected cells into the right jugular vein. After 28 days, plasmid-derived Ang-1 mRNA was consistently and robustly detected by reverse transcriptase-polymerase chain reaction in lungs from all animals receiving Ang-1 gene therapy. Tie-2 receptor expression was markedly downregulated in rats treated with MCT, and this was partially restored by gene therapy with Ang-1. Animals receiving MCT exhibited 77% mortality by 28 days. In contrast, in pAng-1-treated animals, the 28-day mortality was only 14% (PϽ0.0001). In addition, right ventricular systolic pressure was reduced from 52Ϯ1.3 mm Hg in the MCT-treated group to 38Ϯ1.3 mm Hg by Ang-1 gene transfer (PϽ0.01), whereas the measurement of right to left ventricular plus septal weight ratio was also reduced from 0.41Ϯ0.03 to 0.31Ϯ0.01 (PϽ0.05). Moreover, MCT resulted in increased apoptosis, mainly in the microvasculature, and reduced endothelial NO synthase mRNA expression, both of which were prevented by Ang-1 gene transfer. Thus, cell-based gene transfer with Ang-1 improved survival and pulmonary hemodynamics in experimental pulmonary hypertension by a mechanism involving the inhibition of apoptosis and protection of the pulmonary microvasculature.

Endothelial Dysfunction in Pulmonary Hypertension

“…A recent study demonstrated attenuation of monocroteline-induced PH in a murine model by administration of Ang-1. 84 In light of these observations, Ang-1 might play a role similar to that of VEGF, ie, protective of a normal vasculature and pathological in the abnormal endothelium in PAH. …”

Ang-1 Gene Therapy Inhibits Hypoxia-Inducible Factor-1α (HIF-1α)-Prolyl-4-Hydroxylase-2, Stabilizes HIF-1α Expression, and Normalizes Immature Vasculature in db/db Mice

“…Additionally, Ang-1 gene transfer has been shown to increase eNOS expression and reverse pulmonary hypertension (38). Ang-1 gene transfer has also been reported to prevent diabetic retinal vascular changes and to attenuate the increased retinal permeability by the upregulation of eNOS expression in the streptozotocin-induced diabetic rat model (39).…”

Functional Significance of Tie2 Signaling in the Adult Vasculature

“…In addition to its pro-angiogenic effects, Tie2 activation attenuates the action of pro-inflammatory mediators and decreases vascular leak, suggesting that Tie2 activation may have other applications in vascular disease, such as plaque stabilization in atherosclerosis and limiting cerebral edema after ischemic stroke (Thurston et al, 1999;Gamble et al, 2000;Kim et al, 2001). Indeed, recent studies have shown that Ang1 is protective in rodent models of pulmonary hypertension and allograft atherosclerosis (Nykanen et al, 2003;Zhao et al, 2003). Additionally, since VEGF enhances expression of inflammatory mediators and increases vascular permeability, coadministration of Ang1 with VEGF could represent an improved approach to proangiogenesis.…”