IL-33/ST2 receptor-dependent signaling in the development of pulmonary hypertension in Sugen/hypoxia mice.

Pulmonary arterial hypertension (PAH) is associated with significant morbidity and mortality. PAH is characterized by pulmonary artery remodeling, elevated right ventricular pressure (RVP) and, ultimately, cardiac failure. Pulmonary endothelial cells can sense danger or damage caused by mechanical injury or pathogens through alarmin cytokines. These cytokines can signal proliferation to restore barrier integrity or aberrant hyperproliferation and remodeling. We hypothesized that IL-33 signals pulmonary artery endothelial cells to proliferate under hypertensive conditions during the remodeling response and rise in RVP. To test this hypothesis, pulmonary hypertension (PH) was induced in C57Bl/6J, IL-33 receptor gene deleted (ST2-/- ) and MYD88 gene deleted (MYD88-/- ) mice by exposure to 10% O2 and SU5416 injections (SUHX). RVP, arterial wall thickness, endothelial cell proliferation and IL-33 levels and signaling were evaluated. In response to SUHX. RVP increased in C57Bl/6J mice in response to SUHX (49% male and 70% female; p < 0.0001) and this SUHX response was attenuated in ST2-/- mice (29% male p = 0.003; 30% female p = 0.001) and absent in MYD88-/- mice. Wall thickness was increased in SUHX C57Bl/6J mice (p = 0.005), but not in ST2-/- or MYD88-/- mice. Proliferating cells were detected in C57Bl/6J mice by flow cytometry (CD31+ /BrDU+ ; p = 0.02) and immunofluorescence methods (Ki-67+). IL-33 was increased by SUHX (p = 0.03) but a genotype effect was not observed (p = 0.76). We observed that in hPAECs, IL-33 expression is regulated by both IL-33 and DLL4. These data suggest IL-33/ST2 signaling is essential for the endothelial cell proliferative response in PH.

Role of IL-33 receptor (ST2) deletion in diaphragm contractile and mitochondrial function in the Sugen5416/hypoxia model of pulmonary hypertension.

Pulmonary arterial hypertension (PAH) is a progressive disease of the pulmonary vasculature that leads to right ventricular failure. Skeletal muscle maladaptations limit physical activity and may contribute to disease progression. The role of alarmin/inflammatory signaling in PAH respiratory muscle dysfunction is unknown. We hypothesized that diaphragm mitochondrial and contractile functions are impaired in SU5416/hypoxia-induced pulmonary hypertension due to increased systemic IL-33 signaling. We induced pulmonary hypertension in adult C57Bl/6 J (WT) and ST2 (IL1RL1) gene ablated mice by SU5416/hypoxia (SuHx). We measured diaphragm fiber mitochondrial respiration, inflammatory markers, and contractile function ex vivo. SuHx reduced coupled and uncoupled permeabilized myofiber respiration by ∼40 %. During coupled respiration with complex I substrates, ST2-/- attenuated SuHx inhibition of mitochondrial respiration (genotype × treatment interaction F[1,67] = 3.3, p = 0.07, η2 = 0.04). Flux control ratio and coupling efficiency were not affected by SuHx or genotype. A higher substrate control ratio for succinate was observed in SuHx fibers and attenuated in ST2-/- fibers (F[1,67] = 5.3, p < 0.05, η2 = 0.07). Diaphragm TNFα, but not IL-33 or NFkB, was increased in SuHx vs. DMSO in both genotypes (F[1,43] = 4.7, p < 0.05, η2 = 0.1). Diaphragm force-frequency relationships were right-shifted in SuHx vs. WT (F[3,440] = 8.4, p < 0.05, η2 = 0.0025). There was no effect of ST2-/- on the force-frequency relationship. Force decay during a fatigue protocol at 100 Hz, but not at 40 Hz, was attenuated by SuHx vs. DMSO in both genotypes (F[1,41] = 5.6, p < 0.05, η2 = 0.11). SuHx mice exhibit a modest compensation in diaphragm contractility and mitochondrial dysfunction during coupled respiration; the latter partially regulated through ST2 signaling.