New insights of aquaporin 5 in the pathogenesis of high altitude pulmonary edema

Role of neutrophil myeloperoxidase in the development and progression of high-altitude pulmonary edema

BACKGROUND

Neutrophil infiltration and hypoxic pulmonary vasoconstriction induced by hypobaric hypoxic stress are vital in high-altitude pulmonary edema (HAPE). Myeloperoxidase (MPO), an important enzyme in neutrophils, is associated with inflammation and oxidative stress and is also involved in the regulation of nitric oxide synthase (NOS), an enzyme that catalyzes the production of the vasodilatory factor nitric oxide (NO). However, the role of neutrophil MPO in HAPE's progression is still uncertain. Therefore, we hypothesize that MPO is involved in the development of HAPE via NOS.

METHODS

In Xining, China (altitude: 2260 m), C57BL/6 N wild-type and mpo-/- mice served as normoxic controls, while a hypobaric chamber simulated 7000 m altitude for hypoxia. L-NAME, a nitric oxide synthase (NOS) inhibitor to inhibit NO production, was the experimental drug, and D-NAME, without NOS inhibitory effects, was the control. After measuring pulmonary artery pressure (PAP), samples were collected and analyzed for blood neutrophils, oxidative stress, inflammation, vasoactive substances, pulmonary alveolar-capillary barrier permeability, and lung tissue morphology.

RESULTS

Wild-type mice's lung injury scores, permeability, and neutrophil counts rose at 24 and 48 h of hypoxia exposure. Under hypoxia, PAP increased from 12.89 ± 1.51 mmHg under normoxia to 20.62 ± 3.33 mmHg significantly in wild-type mice and from 13.24 ± 0.79 mmHg to 16.50 ± 2.07 mmHg in mpo-/- mice. Consistent with PAP, inducible NOS activity, lung permeability, lung injury scores, oxidative stress response, and inflammation showed more significant increases in wild-type mice than in mpo-/- mice. Additionally, endothelial NOS activity and NO levels decreased more pronouncedly in wild-type mice than in mpo-/- mice. NOS inhibition during hypoxia led to more significant increases in PAP, permeability, and lung injury scores compared to the drug control group, especially in wild-type mice.

CONCLUSION

MPO knockout reduces oxidative stress and inflammation to preserve alveolar-capillary barrier permeability and limits the decline in endothelial NOS activity to reduce PAP elevation during hypoxia. MPO inhibition emerges as a prospective therapeutic strategy for HAPE, offering avenues for precise interventions.

Whole-exome sequencing in searching for novel variants associated with the development of high altitude pulmonary edema

BACKGROUND

High altitude pulmonary edema (HAPE) is a high-altitude idiopathic disease with serious consequences due to hypoxia at high altitude, and there is individual genetic susceptibility. Whole-exome sequencing (WES) is an effective tool for studying the genetic etiology of HAPE and can identify potentially novel mutations that may cause protein instability and may contribute to the development of HAPE.

MATERIALS AND METHODS

A total of 50 unrelated HAPE patients were examined using WES, and the available bioinformatics tools were used to perform an analysis of exonic regions. Using the Phenolyzer program, disease candidate gene analysis was carried out. SIFT, PolyPhen-2, Mutation Taster, CADD, DANN, and I-Mutant software were used to assess the effects of genetic variations on protein function.

RESULTS

The results showed that rs368502694 (p. R1022Q) located in NOS3, rs1595850639 (p. G61S) located in MYBPC3, and rs1367895529 (p. R333H) located in ITGAV were correlated with a high risk of HAPE, and thus could be regarded as potential genetic variations associated with HAPE.

CONCLUSION

WES was used in this study for the first time to directly screen genetic variations related to HAPE. Notably, our study offers fresh information for the subsequent investigation into the etiology of HAPE.

Mechanism of aquaporin 4 (AQP 4) up-regulation in rat cerebral edema under hypobaric hypoxia and the preventative effect of puerarin

AIM

We aim to investigate the mechanism of aquaporin 4 (AQP 4) up-regulation during high-altitude cerebral edema (HACE) in rats under hypobaric hypoxia and preventative effect of puerarin.

METHODS

Rats were exposed to a hypobaric chamber with or without the preventative treatment of puerarin or dexamethasone. Morriz water maze was used to evaluate the spatial memory injury. HE staining and W/D ratio were used to evaluate edema injury. Rat astrocytes and microglia were co-cultured under the condition of hypoxia with the administration of p38 inhibitor, NF-κB inhibitor or puerarin. Interleukin 6 (IL-6) and tumor necrosis factor α (TNF α) of cortex and culture supernatant were measured with ELISA. AQP4, phosphorylation of MAPKs, NF-κB pathway of cortex and astrocytes were measured by Western blot.

KEY FINDINGS

Weakened spatial memory and cerebral edema were observed after hypobaric hypoxia exposure. AQP4, phosphorylation of NF-κB and MAPK signal pathway of cortex increased after hypoxia exposure and decreased with preventative treatment of puerarin. Hypoxia increased TNF-α and IL-6 levels in cortex and microglia and puerarin could prevent the increase of them. AQP4 of astrocytes increased after co-cultured with microglia when both were exposed to hypoxia. AQP4 showed a decrease after administered with p38 inhibitor, NF-κB inhibitor or puerarin.

SIGNIFICANCE

Hypoxia triggers inflammatory response, during which AQP4 of astrocytes can be up regulated through the release of TNF-α and IL-6 from microglia. Puerarin can exert a preventative effect on the increase of AQP4 through inhibiting the release of TNF-α and phosphorylation of NF-κB, MAPK pathway.

Aquaporin 1 controls the functional phenotype of pulmonary smooth muscle cells in hypoxia-induced pulmonary hypertension

Vascular remodelling in hypoxia-induced pulmonary hypertension (PH) is driven by excessive proliferation and migration of endothelial and smooth muscle cells. The expression of aquaporin 1 (AQP1), an integral membrane water channel protein involved in the control of these processes, is tightly regulated by oxygen levels. The role of AQP1 in the pathogenesis of PH, however, has not been directly addressed so far. This study was designed to characterize expression and function of AQP1 in pulmonary vascular cells from human arteries and in the mouse model of hypoxia-induced PH. Exposure of human pulmonary vascular cells to hypoxia significantly induced the expression of AQP1. Similarly, levels of AQP1 were found to be upregulated in lungs of mice with hypoxia-induced PH. The functional role of AQP1 was further tested in human pulmonary artery smooth muscle cells demonstrating that depletion of AQP1 reduced proliferation, the migratory potential, and, conversely, increased apoptosis of these cells. This effect was associated with higher expression of the tumour suppressor gene p53. Using the mouse model of hypoxia-induced PH, application of GapmeR inhibitors targeting AQP1 abated the hypoxia-induced upregulation of AQP1 and, of note, reversed PH by decreasing both right ventricular pressure and hypertrophy back to the levels of control mice. Our data suggest an important functional role of AQP1 in the pathobiology of hypoxia-induced PH. These results offer novel insights in our pathogenetic understanding of the disease and propose AQP1 as potential therapeutic in vivo target.

Involvement of water channel Aquaporin 5 in H2S-induced pulmonary edema

Acute exposure to hydrogen sulfide (H₂S) poses a significant threat to life, and the lung is one of the primary target organs of H₂S. However, the mechanisms involved in H₂S-induced acute pulmonary edema are poorly understood. This study aims to investigate the effects of H₂S on the expression of water channel aquaporin 5 (AQP5) and to elucidate the signaling pathways involved in AQP5 regulation. In an in vivo study, C57BL6 mice were exposed to sub-lethal concentrations of inhaled H₂S, and histological injury of the lungs and ultrastructure injury of the epithelial cells were evaluated. With real-time PCR and western blot assays, we found that H₂S exposure contributed to a significant decrease in AQP5 expression both in murine lung tissue and the A549 cell line, and the ERK1/2 and p38 MAPK signaling pathways were demonstrated to be implicated in AQP5 regulation. Therefore, adjusting AQP5 protein levels could be considered a therapeutic strategy for the treatment of APE induced by H₂S and other hazardous gases.

Functional pharmacological characterization of SER100 in cardiovascular health and disease

BACKGROUND AND PURPOSE

SER100 is a selective nociceptin (NOP) receptor agonist with sodium-potassium-sparing aquaretic and anti-natriuretic activity. This study was designed to characterize the functional cardiovascular pharmacology of SER100 in vitro and in vivo, including experimental models of cardiovascular disease.

EXPERIMENTAL APPROACH

Haemodynamic, ECG parameters and heart rate variability (HRV) were determined using radiotelemetry in healthy, conscious mice. The haemodynamic and vascular effects of SER100 were also evaluated in two models of cardiovascular disease, spontaneously hypertensive rats (SHR) and murine hypoxia-induced pulmonary hypertension (PH). To elucidate mechanisms underlying the pharmacology of SER100, acute blood pressure recordings were performed in anaesthetized mice, and the reactivity of rodent aorta and mesenteric arteries in response to electrical- and agonist-stimulation assessed.

KEY RESULTS

SER100 caused NOP receptor-dependent reductions in mean arterial blood pressure and heart rate that were independent of NO. The hypotensive and vasorelaxant actions of SER100 were potentiated in SHR compared with Wistar Kyoto. Moreover, SER100 reduced several indices of disease severity in experimental PH. Analysis of HRV indicated that SER100 decreased the low/high frequency ratio, an indicator of sympatho-vagal balance, and in electrically stimulated mouse mesenteric arteries SER100 inhibited sympathetic-induced contractions.

CONCLUSIONS AND IMPLICATIONS

SER100 exerts a chronic hypotensive and bradycardic effects in rodents, including models of systemic and pulmonary hypertension. SER100 produces its cardiovascular effects, at least in part, by inhibition of cardiac and vascular sympathetic activity. SER100 may represent a novel therapeutic candidate in systemic and pulmonary hypertension.

Protective effects of puerarin on acute lung and cerebrum injury induced by hypobaric hypoxia via the regulation of aquaporin (AQP) via NF-κB signaling pathway

OBJECTIVE

Hypobaric hypoxia, frequently encountered at high altitude, may lead to lung and cerebrum injury. Our study aimed to investigate whether puerarin could exert ameliorative effects on rats exposed to hypobaric hypoxia via regulation of aquaporin (AQP) and NF-κB signaling pathway in lung and cerebrum.

MATERIALS AND METHODS

40 Sprague Dawley rats were divided into four groups (normal control group, hypobaric hypoxia group, puerarin group and dexamethasone group). Wet/dry ratio, blood gas, pathological changes of lung and cerebrum and spatial memory were observed in each group. Inflammatory cytokines in bronchoalveolar lavage fluid (BALF) were determined with ELISA and expression of AQP1, AQP4, NF-κB signaling pathway in lung and cerebrum with western blot RESULTS: Puerarin showed significant preventative effects on tissue injury and behavioral changes, as evidenced by histopathological findings and Morris water maze. In addition, levels of inflammatory cytokines in BALF decreased in the two preventative groups compared with those of hypobaric hypoxia group. AQP in lung and cerebrum increased under the condition of hypobaric hypoxia while was down regulated in both two preventative groups. NF-κB and IκB was also inhibited by puerarin.

CONCLUSION

Our study suggested that lung and cerebrum injury, increased inflammatory cytokines in BALF and increased AQP1, AQP4 and NF-κB signaling pathway occurred under the condition of hypobaric hypoxia. Moreover, puerarin could prevent lung and cerebrum injury of rats exposed to hypobaric hypoxia via down-regulation of inflammatory cytokines, AQP1 and AQP4 expression and NF-κB signaling pathway.