Gene therapy targeting survivin selectively induces pulmonary vascular apoptosis and reverses pulmonary arterial hypertension

Abstract

Pulmonary arterial hypertension (PAH) is characterized by genetic and acquired abnormalities that suppress apoptosis and enhance cell proliferation in the vascular wall, including downregulation of the bone morphogenetic protein axis and voltage-gated K + (Kv) channels. Survivin is an "inhibitor of apoptosis" protein, previously thought to be expressed primarily in cancer cells. We found that survivin was expressed in the pulmonary arteries (PAs) of 6 patients with PAH and rats with monocrotaline-induced PAH, but not in the PAs of 3 patients and rats without PAH. Gene therapy with inhalation of an adenovirus carrying a phosphorylationdeficient survivin mutant with dominant-negative properties reversed established monocrotaline-induced PAH and prolonged survival by 25%. The survivin mutant lowered pulmonary vascular resistance, RV hypertrophy, and PA medial hypertrophy. Both in vitro and in vivo, inhibition of survivin induced PA smooth muscle cell apoptosis, decreased proliferation, depolarized mitochondria, caused efflux of cytochrome c in the cytoplasm and translocation of apoptosis-inducing factor into the nucleus, and increased Kv channel current; the opposite effects were observed with gene transfer of WT survivin, both in vivo and in vitro. Inhibition of the inappropriate expression of survivin that accompanies human and experimental PAH is a novel therapeutic strategy that acts by inducing vascular mitochondria-dependent apoptosis. IntroductionPulmonary arterial hypertension (PAH) is a disease of the pulmonary vasculature, defined by an elevated pulmonary vascular resistance (PVR), which eventually leads to right heart failure and premature death. The cause remains unknown, and available treatments are limited, expensive, and often associated with significant side effects (1). In PAH, the pulmonary arteries (PAs) manifest pathological proliferative vascular remodeling that includes cellular proliferation in both the intima and the media and muscularization of the normally thin-walled distal PAs (1). Endothelial dysfunction results in an increase in the ratio of endothelial-derived vasoconstrictors to vasodilators. This imbalance has been the basis of therapies over the past several years; for example, exogenous delivery of vasodilating prostaglandins or blockade of the endothelin axis. However, less that 10% of the patients respond to selective pulmonary vasodilators. While vasoconstriction contributes, especially early in PAH, the obstructive vascular remodeling is the major cause of the elevated PVR and ultimately the right heart failure, which in turn accounts for the 50% 5-year mortality in this disease (1). There is now a shift in the interest of the scientific community, focusing on therapies aiming to reverse the proliferative remodeling in PAH (2).

Pathology of Pulmonary Hypertension

“…One potential mechanism linking this paradigm to BMPR2 mutations is the finding that BMPR2 activation upregulates K + channels [69] and causes apoptosis of normal pulmonary artery smooth muscle cells, but not of cells from patients with IPAH [70]. McMurtry et al provide recent additional evidence that mechanisms akin to cancer operate in pulmonary vascular remodeling [34]. Survivin protects cancer cell against apoptosis by inhibiting caspase activation and apoptosis inducing factor [71].…”

Hypoxia and chronic lung disease

“…HIF-1α activation downregulates oxygen-sensitive K v + channels (K v +1.5 ) and initiates a cascade that causes PH. This mechanism has been postulated to lead not only to enhanced vasoconstriction, but also to resistance to cell death via hyperpolarization of mitochondria and enhanced survivin expression [45].…”

Pre–B-cell Colony-Enhancing Factor Regulates Vascular Smooth Muscle Maturation Through a NAD + -Dependent Mechanism

“…This reflects the convergence of the great pathways, which overarch artificial separations of science into disciplines. The vascular biologist should now be as interested in maturational and apoptotic proteins, such as PBEF 4 and survivin, 18 as they have been in the traditional pathways that regulate vascular tone.…”

“…Survivin, a rehabilitated cancer protein, is now recognized to control SMC proliferation in human pulmonary arterial hypertension. 18,19 Survivin inhibition depolarizes SMC mitochondria, triggering beneficial apoptosis and remodeling. 19 A logical starting point to examine the intersection of the PBEF and the mitochondrial-survivin pathways is at their intersection-the redox couples.…”