METHODS: Thirty-two BALB/c mice were randomly divided into 4 groups of normal control,
asthma, vehicle control and
relaxin treatment (n = 8 each). They were sensitized and challenged with
ovalbumin to establish a chronic asthmatic model. The vehicle control and
relaxin treatment groups were subcutaneously injected with saline and
relaxin (0.25 mg×kg(-1)×d(-1)) respectively. Alteration of airway
inflammation was observed by
hematoxylin-
eosin (HE) staining. The airway expressions of
proliferating cell nuclear antigen (
PCNA) and α-smooth muscle actin (α-SMA) were evaluated by immunohistochemistry. The
protein expression of
Epac and phosphorylated extracellular signal regulated kinases1/2 (p-ERK1/2) were detected by Western blot.
RESULTS: Compared to those in the normal control group, massive infiltration of inflammatory cells, airway
stenosis, bronchial smooth muscle
hypertrophy were present in the asthmatic and vehicle control groups. The above-mentioned changes were significantly ameliorated in the
relaxin treatment group. The percentage of
PCNA positive cells (34.8% ± 6.1%, 33.5% ± 6.6%) and the expression of α-SMA ((1.70 ± 0.25), (1.54 ± 0.24) µm(2)/µm) in the asthmatic and vehicle control groups were significantly higher than those in the normal control group (9.9% ± 2.6%, (0.51 ± 0.16) µm(2)/µm) (all P < 0.05) while administration of
relaxin decreased the airway expression levels of
PCNA and α-SMA (22.9% ± 5.2%, (1.06 ± 0.25) µm(2)/µm) (all P < 0.05). The results of Western blot showed that the expression levels of
Epac in the asthmatic and vehicle groups (0.62 ± 0.12, 0.68 ± 0.11) were lower than those in the control group (1.50 ± 0.17) (all P < 0.05) while it significantly increased in the
relaxin group (1.08 ± 0.15) (all P < 0.05). The levels of phosphorylation of ERK1/2 in the asthmatic and vehicle groups (1.45 ± 0.13, 1.36 ± 0.09) were higher than those in the control group (0.38 ± 0.17) (all P < 0.05) while it decreased in the
relaxin treatment group (0.72 ± 0.06) (all P < 0.05). No differences existed in all parameters between the asthmatic and vehicle groups (P > 0.05).
CONCLUSION:
Relaxin alleviates the airway
inflammation and airway smooth muscle cell proliferation in a murine model of chronic
asthma probably through activating
Epac and inhibiting the phosphorylation of ERK1/2.