[Activation of A2b adenosine receptor decreases lipopolysaccharide-induced pulmonary microvascular permeability]

To explore the role of the A2b adenosine receptor (Adora2b) in lipopolysaccharide (LPS)-induced injury of human pulmonary microvascular endothelial cells (HPMECs), and its mechanism.

HPMECs were cultured in vitro. The LPS dose-effect experiment, time-effect experiment and the Adora2b agonist/antagonist intervention experiment were performed respectively. (1) Dose-effect and time-effect experiments: HPMECs were stimulated with 1, 10, 100, 1 000 μg/L LPS for 24 hours, or 100 μg/L LPS for 4, 8, 12, 16, 24 hours. Cell viability was measured by cell counting kit-8 (CCK8). The protein and mRNA expressions of Adora2b were determined by Western Blot and real-time reverse transcription-polymerase chain reaction (RT-PCR) respectively. (2) Adora2b agonist/antagonist intervention experiment: serum-starved HPMECs were pretreated with Adora2b specific agonist BAY60-6583 (0.1, 1, 10 μmol/L) or Adora2b specific antagonist PSB1115 (1 μmol/L) for 1 hour, respectively, and then incubated with 100 μg/L of LPS for 24 hours. The HPMECs without treatment were served as blank control group, and those treated with LPS, BAY60-6583 or PSB1115 alone were served as single challenge groups. The monolayer permeability of HPMECs was determined by fluorescein isothiocyanate (FITC)-dextran. Cell cycle was analyzed by flow cytometry. The mRNA expressions of VE-cadherin, occludin, vascular endothelial growth factor (VEGF) and angiopoietin-1 (ANGPT1) were determined by RT-PCR.

(1) Dose-effect and time-effect experiments: LPS induced the decreased cell viability of HPMECs in dose and time-dependent manner. Compared with the control group, the protein expression of Adora2b was sharply up-regulated after 100 μg/L or 1 000 μg/L LPS stimulation. Meanwhile, LPS was shown to cause a dose and time-dependent induction of Adora2b transcript level. (2) Adora2b agonist/antagonist intervention experiments: compared with the control group, the monolayer permeability of HPMECs was rapidly enhanced after LPS treatment, and lower cell viability and proliferation, as well as the expression of cell junction and angiogenic factors were downregulated. Compared with LPS group, 0.1, 1, 10 μmol/L BAY 60-6583 pretreatment could decrease the endothelial cell barrier leakage in a dose-dependent manner [Pd: (203.06±15.24)%, (164.15±17.82)%, (125.69±10.38)% vs. (218.53±12.05)%], and promote cell proliferation of HPMECs [the proportion of S and G2 phases: (24.36±1.40)%, (32.37±0.95)%, (40.05±2.99)% vs. (18.83±0.73)%]. Pretreatment of 10 μmol/L BAY60-6583 also upregulated the mRNA expressions of cell junction and angiogenic factors [VE-cadherin (2^-ΔΔCt): 2.17±0.23 vs. 0.56±0.10, occludin (2^-ΔΔCt): 5.32±0.28 vs. 0.48±0.11, VEGF (2^-ΔΔCt): 4.44±0.34 vs. 0.58±0.09, ANGPT-1 (2^-ΔΔCt): 5.98±0.73 vs. 0.66±0.10, all P < 0.01]. PSB1115 pretreatment aggravated injury of microvascular endothelial cells after LPS incubation, with lower cell viability, slower proliferation and less expression of VEGF and ANGPT1. There was no influence of BAY 60-6583 or PSB1115 single treatment on cell viability, cell cycle and the expression of angiogenic factors in HPMECs.

In vitro studies of cultured HPMECs exposed to LPS are identified as dose and time-dependent induction of Adora2b transcript and corresponding protein induction. Activation of Adora2b attenuates LPS-induced pulmonary microvascular endothelial cell barrier enhancement by regulating intercellular junction and promoting angiogenesis, suggesting Adora2b as potential therapeutic target in the treatment of LPS-induced forms of acute lung injury.