Endothelin-1, the Unfolded Protein Response, and Persistent Inflammation

Abstract

Endothelin-1 is a potent vasoactive peptide that occurs in chronically high levels in humans with pulmonary hypertension and in animal models of the disease. Recently, the unfolded protein response was implicated in a variety of diseases, including pulmonary hypertension. In addition, evidence is increasing for pathological, persistent inflammation in the pathobiology of this disease. We investigated whether endothelin-1 might engage the unfolded protein response and thus link inflammation and the production of hyaluronic acid by pulmonary artery smooth muscle cells. Using immunoblot, real-time PCR, immunofluorescence, and luciferase assays, we found that endothelin-1 induces both a transcriptional and posttranslational activation of the three major arms of the unfolded protein response. The pharmacologic blockade of endothelin A receptors, but not endothelin B receptors, attenuated the observed release, as did a pharmacologic blockade of extracellular signal-regulated kinases 1 and 2 (ERK-1/2) signaling. Using short hairpin RNA and ELISA, we observed that the release by pulmonary artery smooth muscle cells of inflammatory modulators, including hyaluronic acid, is associated with endothelin-1-induced ERK-1/2 phosphorylation and the unfolded protein response. Furthermore, the synthesis of hyaluronic acid induced by endothelin-1 is permissive for persistent THP-1 monocyte binding. These results suggest that endothelin-1, in part because it induces the unfolded protein response in pulmonary artery smooth muscle cells, triggers proinflammatory processes that likely contribute to vascular remodeling in pulmonary hypertension.Keywords: unfolded protein response; endothelin; pulmonary artery smooth muscle; hyaluronic acid; inflammation Pulmonary hypertension (PH) is a disease characterized by extensive pulmonary vascular remodeling, present along the entire length of the vascular tree (1). Eventually, the increased impedance to flow causes right heart failure and death (2). Evidence is mounting that the recruitment of inflammatory cells and the development of persistent inflammation are key components of the pathological vascular remodeling observed in PH (3). In patients with idiopathic PH, macrophages and lymphocytes are found in bronchovascular locations and in occlusive neointimal lesions, and express a panoply of chemokines including CCL2, CCL5, and CX3CL1 (4-7). Concentrations of proinflammatory cytokines, including IL-1 and IL-6, are elevated in both human idiopathic pulmonary artery hypertension (PAH) (8) and in the monocrotaline (MCT) model of PH (9, 10). Depletion of the circulating pool of macrophages is sufficient to prevent hypoxia-driven PH (11), and dexamethasone treatment reverses MCT PH (12). Taken together, these studies suggest that PH is a syndrome characterized by the complex disturbance of innate and acquired immune cells, and of mediators and effectors of inflammation.Building on studies that pointed to the importance of extracellular matrix metabolism in pulmonary vessel homeostasis (13,14), rec...

Bronchus-associated Lymphoid Tissue in Pulmonary Hypertension Produces Pathologic Autoantibodies

“…Accordingly, we chose salubrinal, a cell stress protectant, to modulate the unfolded protein response toward a survival phenotype, away from a proapoptotic phenotype (control node 1). This was based on our recent observations that salubrinal protects against MCTinduced pneumotoxicity and pulmonary vascular remodeling (23). Salubrinal, when coadministered with MCT and then twice per week thereafter for 4 weeks, significantly reduced BALT size and number and largely prevented autoantibody formation in rats ( Figure 6A).…”

“…MCT is a broad pneumotoxin that causes lung cell apoptosis, airway cytokine flux, airway constriction, and decreased respiratory compliance. We recently found that MCT causes a robust activation of the unfolded protein response and CCAAT/enhancer-binding protein homologous protein (CHOP)-mediated apoptosis (23) in bronchial epithelium within 48 hours of MCT administration. Salubrinal-mediated unfolded protein response modulation reduced the number and extent of apoptotic cells.…”

Molecular pathogenesis of pulmonary arterial hypertension

“…Another study linked endothelin with the unfolded protein response, mitochondrial dysfunction, and inflammation (117).…”

The Metabolic Theory of Pulmonary Arterial Hypertension

“…The molecular phenotype of PAH-PASMC persists even in vitro (where the potential primary triggers like circulating factors or paracrine signals are absent), suggesting that there may be positively reinforcing feedback loops that sustain the 21 and STAT3 activation 22 …”

“…115 Increased Endothelin-1 signaling, a well-studied pathway in PAH, was also recently shown to induce ER stress. 21 Inhibition of ER stress by the small molecule chemical chaperone phenylbutyrate reverses the decrease in mitochondrial calcium and the PDH inhibition and normalizes the cellular phenotype of PAH, whereas it prevents and reverses PAH in rodent models. 75 ER stress in PAH-PASMCs has also been linked to increased production of cytokines like interleukin-6 and chemokine (C-C motif) ligand 2/ mast cell proteinase-1, Figure 4.…”