Oxymatrine attenuates ulcerative colitis by modulating the β2AR-β-arrestin2-NF-κB signaling pathway in rats

AIM: To investigate whether the β2-adrenoceptor (β2AR)-β-arrestin2-NF-κB signaling pathway mediates the therapeutic effects of oxymatrine on ulcerative colitis in rats.

METHODS: Forty Sprague-Dawley rats were randomly and equally divided into four groups: normal control group, model group, mesalazine group and oxymatrine group. Experiment colitis was induced with TNBS in rats in each group except the normal control group. The rats in the oxymatrine group were intramuscularly injected with oxymatrine injection for 15 d, while those in the mesalazine group were lavaged with 3 mL mesalazine solution for the same duration. The rats in the normal control group and model group were lavaged with 3 mL water for 15 d. Diarrhea and bloody stools were carefully observed in experimental rats. Two rats in each group were randomly selected and executed on day 7 for observing colonic histological changes. On day 16, the remaining rats were executed after fasting 24 h to detect the expression of β2AR, β-arrestin2 and NF-κB p65 in colon tissue and splenic lymphocytes by immunohistochemistry and Western blotting, respectively.

RESULTS: Compared with the normal control group, the expression of NF-κB p65 was significantly increased (both P < 0.01) and the expression of β2AR and β-arrestin2 was significantly decreased (both P < 0.01) in colonic mucosa and splenic lymphocytes in the model group. Compared with the model group, the expression of NF-κB p65 was significantly decreased (16.26 ± 5.51 and 18.34 ± 3.34 vs 61.90 ± 17.75, both P < 0.01) and the expression of β2AR and β-arrestin2 was significantly increased in colonic mucosa in the mesalazine group and oxymatrine group (47.27 ± 12.40 and 61.75 ± 10.40 vs 12.20 ± 2.70, both P < 0.01; 70.71 ± 12.84 and 76.14 ± 8.77 vs 16.80 ± 7.17, both P < 0.01). Compared with the model group, the expression of NF-κB p65 was significantly decreased (114.23 ± 11.56 and 145.62 ± 13.05 vs 249.70 ± 18.94, both P < 0.01) and the expression of β2AR and β-arrestin2 was significantly increased in splenic lymphocytes in the mesalazine group and oxymatrine group (1 006.50 ± 226.89 and 1 102.11 ± 297.72 vs 594.97 ± 209.59, both P < 0.01; 189.97 ± 21.12 and 162.04 ± 15.69 vs 111.77 ± 19.43, both P < 0.01).

CONCLUSION: The β2AR-β-arrestin2-NF-κB signaling pathway participates in the pathogenesis of ulcerative colitis in rats. Oxymatrine attenuates ulcerative colitis by regulating the β2AR-β-arrestin2-NF-κB signaling pathway.

Beta-Arrestin2 regulates RANKL and ephrins gene expression in response to bone remodeling in mice

PTH-stimulated intracellular signaling is regulated by the cytoplasmic adaptor molecule beta-arrestin. We reported that the response of cancellous bone to intermittent PTH is reduced in beta-arrestin2(-/-) mice and suggested that beta-arrestins could influence the bone mineral balance by controlling RANKL and osteoprotegerin (OPG) gene expression. Here, we study the role of beta-arrestin2 on the in vitro development and activity of bone marrow (BM) osteoclasts (OCs) and Ephrins ligand (Efn), and receptor (Eph) mRNA levels in bone in response to PTH and the changes of bone microarchitecture in wildtype (WT) and beta-arrestin2(-/-) mice in models of bone remodeling: a low calcium diet (LoCa) and ovariectomy (OVX). The number of PTH-stimulated OCs was higher in BM cultures from beta-arrestin2(-/-) compared with WT, because of a higher RANKL/OPG mRNA and protein ratio, without directly influencing osteoclast activity. In vivo, high PTH levels induced by LoCa led to greater changes in TRACP5b levels in beta-arrestin2(-/-) compared with WT. LoCa caused a loss of BMD and bone microarchitecture, which was most prominent in beta-arrestin2(-/-). PTH downregulated Efn and Eph genes in beta-arrestin2(-/-), but not WT. After OVX, vertebral trabecular bone volume fraction and trabecular number were lower in beta-arrestin2(-/-) compared with WT. Histomorphometry showed that OC number was higher in OVX-beta-arrestin2(-/-) compared with WT. These results indicate that beta-arrestin2 inhibits osteoclastogenesis in vitro, which resulted in decreased bone resorption in vivo by regulating RANKL/OPG production and ephrins mRNAs. As such, beta-arrestins should be considered an important mechanism for the control of bone remodeling in response to PTH and estrogen deprivation.