MicroRNAs(miRNAs) is a class of small endogenous noncoding RNAs with 22 nucleotides.They can negatively regulate gene expression by inhibiting target mRNAs′translation or degrading mRNAs .Up to now, it has been proved that miRNAs play an important role in cellular proliferation , apoptosis , cell differentiation , and embryonic development .In this article , mechanism and function of miRNAs , principal methodologies in the research of miRNAs and the latest development of miRNAs in early embryonic de -velopment are discussed .

The present paper is to research the expression level of the mRNA of scavenger receptor class B type 1-receptor of high-density lipoprotein in endothelial cells after being treated by different shear stress. The second to fourth generations of the cultured human umbilical vein endothelial cells (HUVECs) were used in the experiment. The cells were divided into two groups. The first group was the control group which was not dealt with shear stress; the second group was the experimental group which concluded low shear stress group (4.2 dyne/cm2), moderate shear stress group (8.4 dyne/cm2) and high shear stress group (15 dyne/cm2). The load time was 1h, 2h, 4h and 8h, respectively. Harvesting the cells and extracting total RNA after being treated by different shear stresses, the expression level of the SR-B1 mRNA was detected by semi-quantitative RT-PCR technic. It was found that the expression of SR-B1 mRNA became weaker and weaker compared to the control group when it was stimulated continuously by the low shear stress, the lowest expression of SR-B1 mRNA appeared at 8h. In the moderate shear stress group, the expression of SR-B1 mRNA increased obviously. Compared to the control group, there was significant difference after being treated with 2h. In the high shear stress group, the expression of SR-B1 mRNA increased immediately when it was stimulated by the shear stress. And the expression of SR-B1 mRNA arrived peak value at 4h. Compared to the control group, there was significant difference after being treated for 1h. It was concluded that the harmful mechanism of the low shear stress is that it can increase the incidence of the atherosclerosis by reducing the reverse cholesterol transport and endothelial protection through decreasing the expression of the SR-B1. Otherwise, the high shear stress prevent the genesis of atherosclerosis by the contrary mechanism.
Atherosclerosis ; etiology ; Cells, Cultured ; Human Umbilical Vein Endothelial Cells ; cytology ; metabolism ; Humans ; RNA, Messenger ; genetics ; metabolism ; Scavenger Receptors, Class B ; genetics ; metabolism ; Stress, Mechanical