Activation of Platelets and the Complement System in Mice with Schistosoma-Induced Pulmonary Hypertension.

Schistosomiasis-induced pulmonary hypertension (PH) presents a significant global health burden, yet the underlying mechanisms remain poorly understood. Here, we investigate the involvement of platelets and the complement system in the initiation events leading to Schistosoma-induced PH. We demonstrate that Schistosoma exposure leads to thrombocytopenia, platelet accumulation in the lung, and platelet activation. Additionally, we observed increased plasma complement anaphylatoxins C3a and C5a, indicative of complement system activation, and elevated platelet expression of C1q, C3, decay activating factor (DAF), and complement C3a and C5a receptors. Our findings suggest the active involvement of platelets in responding to complement system signals induced by Schistosoma exposure and form the basis for future mechanistic studies on how complement may regulate platelet activation and promote the development of Schistosoma-induced PH.

Redistribution of SOD3 expression due to R213G polymorphism affects pulmonary interstitial macrophage reprogramming in response to hypoxia.

The extracellular isoform of superoxide dismutase (SOD3) is decreased in patients and animals with pulmonary hypertension (PH). The human R213G single nucleotide polymorphism (SNP) in SOD3 causes its release from tissue extracellular matrix (ECM) into extracellular fluids, without modulating enzyme activity, increasing cardiovascular disease risk in humans and exacerbating chronic hypoxic PH in mice. Given the importance of interstitial macrophages (IM) to PH pathogenesis, this study aimed to determine whether R213G SOD3 increases IM accumulation and alters IM reprogramming in response to hypoxia. R213G mice and wild-type (WT) controls were exposed to hypobaric hypoxia for 4 or 14 days compared to normoxia. Flow cytometry demonstrated a transient increase in IMs at day 4 in both strains. Contrary to our hypothesis, the R213G SNP did not augment IM accumulation. To determine strain differences in the IM reprogramming response to hypoxia, we performed RNAsequencing on IMs isolated at each time point. We found that IMs from R213G mice exposed to hypoxia activated ECM-related pathways and a combination of alternative macrophage and proinflammatory signaling. Furthermore, when compared to WT responses, IMs from R213G mice lacked metabolic remodeling and demonstrated a blunted anti-inflammatory response between the early (day 4) and later (day 14) time points. We confirmed metabolic responses using Agilent Seahorse assays whereby WT, but not R213G, IMs upregulated glycolysis at day 4 that returned to baseline at day 14. Finally, we identify differential regulation of several redox-sensitive upstream regulators that could be investigated in future studies.

Lung EC-SOD Overexpression Prevents Hypoxia-Induced Platelet Activation and Lung Platelet Accumulation.

Pulmonary hypertension (PH) is a progressive disease marked by pulmonary vascular remodeling and right ventricular failure. Inflammation and oxidative stress are critical in PH pathogenesis, with early pulmonary vascular inflammation preceding vascular remodeling. Extracellular superoxide dismutase (EC-SOD), a key vascular antioxidant enzyme, mitigates oxidative stress and protects against inflammation and fibrosis in diverse lung and vascular disease models. This study utilizes a murine hypobaric hypoxia model to investigate the role of lung EC-SOD on hypoxia-induced platelet activation and platelet lung accumulation, a critical factor in PH-related inflammation. We found that lung EC-SOD overexpression blocked hypoxia-induced platelet activation and platelet accumulation in the lung. Though lung EC-SOD overexpression increased lung EC-SOD content, it did not impact plasma extracellular SOD activity. However, ex vivo, exogenous extracellular SOD treatment specifically blunted convulxin-induced platelet activation but did not blunt platelet activation with thrombin or ADP. Our data identify platelets as a novel target of EC-SOD in response to hypoxia, providing a foundation to advance the understanding of dysregulated redox signaling and platelet activation in PH and other chronic hypoxic lung diseases.

Serotonin-deficient neonatal mice are not protected against the development of experimental bronchopulmonary dysplasia or pulmonary hypertension.

Serotonin (5-hydroxytryptamine, 5-HT) is a potent pulmonary vasoconstrictor and contributes to high pulmonary vascular resistance in the developing ovine lung. In experimental pulmonary hypertension (PH), pulmonary expression of tryptophan hydroxylase-1 (TPH1), the rate limiting enzyme in 5-HT synthesis, and plasma 5-HT are increased. 5-HT blockade increases pulmonary blood flow and prevents pulmonary vascular remodeling and PH in neonatal models of PH with bronchopulmonary dysplasia (BPD). We hypothesized that neonatal tph1 knock-out (KO) mice would be protected from hypoxia-induced alveolar simplification, decreased vessel density, and PH. Newborn wild-type (WT) and tph1 KO mice were exposed to normoxia or hypoxia for 2 weeks. Normoxic WT and KO mice exhibited similar alveolar development, pulmonary vascular density, right ventricular systolic pressures (RVSPs), and right heart size. Circulating (plasma and platelet) 5-HT decreased in both hypoxia-exposed WT and KO mice. Tph1 KO mice were not protected from hypoxia-induced alveolar simplification, decreased pulmonary vascular density, or right ventricular hypertrophy, but displayed attenuation to hypoxia-induced RVSP elevation compared with WT mice. Tph1 KO neonatal mice are not protected against hypoxia-induced alveolar simplification, reduction in pulmonary vessel density, or RVH. While genetic and pharmacologic inhibition of tph1 has protective effects in adult models of PH, our results suggest that tph1 inhibition would not be beneficial in neonates with PH associated with BPD.