Abstract 1631: A Primary Role of Activated CD8+ T-Cells in the Pathogenesis of Vascular Remodeling: An Immunologic Basis for Pulmonary Arterial Hypertension
Pulmonary arterial hypertension (PAH) is a vascular remodeling disease characterized by enhanced pulmonary artery smooth muscle cell (PASMC) proliferation and suppressed apoptosis. This apoptosis resistance is characterized by PASMC mitochondrial hyperpolarization (in part, due to decreased pyruvate dehydrogenase (PDH) activity), decreased reactive oxygen species (ROS) production and down-regulation of Kv1.5 (which by increasing [Ca++]i promotes proliferation and by increasing [K+]i inhibits caspases). Recently, we have described the activation of the transcription factor NFAT (Nuclear Factor of Activated T-cells) in PAH PASMC, which accounts for many of the above diverse features of PAH. Inflammatory and immune cells (including T-cells) are present within and around the remodeled PA wall in PAH. It is unknown whether these infiltrating T-cells are a result of vascular injury or contribute to the development of PAH. We hypothesized that T-cells have a causal role, directly inducing a PAH phenotype in normal PASMC. We used a Boyden chamber assay, in which the upper chamber was seeded with activated CD8+ human T-cells and the bottom with normal human PASMC. We found that after 96h, activated T-cells decreased PDH activity in normal PASMC, resulting in mitochondrial hyperpolarization (measured by TMRM), decreased ROS (MitoSOX), down-regulation of Kv1.5 (immunohistochemistry), increased [Ca++]i (FLUO3) and activation of NFAT (nuclear translocation). The NFAT-inhibiting peptide VIVIT and a TNF-α (Tumor Necrosis Factor-α) antibody (but not a γ-interferon antibody) prevented the T-cell-induced effects on normal human PASMC. Recombinant TNF-α mimicked the effects of activated CD8+ T cells. Quiescent T-cells had no effects on healthy PASMC. In vivo, athymic rats (n = 6) had attenuated monocrotaline-induced PAH and right ventricular hypertrophy compared to Sprague Dawley rats (n = 6) as assessed by catheterization and ECHO. We demonstrate that active T-cells can directly trigger NFAT activation in healthy PASMC and induce a PAH phenotype, via a TNF-α-dependent pathway, inhibiting PDH. Our work supports the use of anti-inflammatory therapies for PAH and might explain why inflammatory disease-associated PAH is the most severe form of PAH.