Effect of microRNA-155 on angiogenesis after cerebral infarction of rats through AT1R/VEGFR2 pathway

Objective: To explore the function and mechanism of microRNA-155 to regulate the angiogenesis after the cerebral infarction of rats through the angiotensin Pi receptor I (AT1R)/vascular endothelial growth factor (VEGF) signaling pathway. Methods: Female SD rats were chosen for the construction of cerebral infarction model of rats using the modified right middle cerebral artery occlusion. The real-time PCR (RT-PCR) method was employed to detect the expression of microRNA-155 in each group at different time points after the cerebral infarction (1 h, 1 d, 3 d and 7 d). SD rats were randomly divided into four groups (n=20 rats): sham operation group (Sham group), MACO group, MACO+microRNA-155 mimic group, and MACO+microRNA-155 inhibitor group. Sham group was given the free graft, while MACO+microRNA-155 mimic group and MACO+microRNA-155 inhibitor group were treated with microRNA-155 mimic and microRNA-155 inhibitor respectively. The Zea Longa 5-point scale was used to score the neurologic impairment of rats in each group; 2, 3, 5-triphenyl tetrazolium chloride staining to evaluate the volume of cerebral infarction of rats in each group; the immunohistochemistry to detect the expression of CD31; Western blot and RT-PCR to detect the expression of AT1R and VEGF receptor 2 (VEGFR2). Results: The expression of microRNA-155 was increased in the cerebral ischcmia tissue after the cerebral infarction. It was significantly increased at 1 d of ischemia and maintained at the high level for a long time. Rats in the Sham group had no symptom of neurologic impairment, while rats in the MACO group had the obvious neurologic impairment. After being treated with microRNA-155 inhibitor, the neural function of MACO rats had been improved, with the decreased area of cerebral infarction. But after being treated with microRNA-155 mimic, the neural function was further worsened, with the increased area of cerebral infarction. Results of immunohistochemical assay indicated that microRNA-155 inhibitor could up-regulate the expression of CD31, while microRNA-155 mimic could down-regulate the expression of CD31. The RT-PCR found that, after being treated with microRNA-155 inhibitor, MACO rats had the increased expression of AT1R and VEGFR2 messenger RNA (mRNA); but after being treated with microRNA-155 mimic, the expression of ATIR and VECFR2 mRNA was decreased. Results of Western blot showed that, after being treated with microRNA-155 inhibitor, MACO rats had the increased expression of AT1R and VEGFR2 mRNA: but after being treated with microRNA-155 mimic, the expression of AT1R and VEGFR2 mRNA was decreased. Conclusions: The inhibition of microRNA-155 can improve the neurologic impairment of rats with the cerebral infarction, reduce the volume of cerebral infarction and effectively promote the angiogenesis in the region of ischemia, which may be mediated through AT1R/VEGFR2 pathway.