Abstract: This study aimed to explore the function of BgIGFBP4 in the proliferation of yak hepatocyte and the development of mice. The prokaryotic expression vectors pET-28a-BgIGFBP4 was constructed, induced and identified. Hepatocytes were treated with 0.002, 0.02, 0.2, 2, 20 μg·mL^-1 of BgIGFBP4 protein. The effects of BgIGFBP4 protein concentrations on the proliferation of hepatocytes were detected by CCK8 kit and colony forming assay. According to the results of the previous experiment, the optimal concentration of BgIGFBP4 was selected to treat hepatocytes for different time, and the changes of hepatocyte activity, growth-like hormone of hepatocyte supernatant and PI3K-Akt signaling pathway were detected at 24, 48 and 72 h. Healthy male KM mice aged 30 days ((18 ±1)g) were selected and divided into two groups (40 mice per group). The experimental group were fed with 100 μL 50 μg·mL^-1 BgIGFBP4 protein every two days. And the control group was fed with the same amount of 0.9% sterile saline. Before the experiment, the mice were starved for 12 h. The test period was 28 days. The growth performance indexes, serum growth-like hormone and liver PI3K-Akt signaling pathway were detected at 28 days. Prokaryotic expression indicated that a 28.86 ku recombinant protein was obtained and identified. The activities of hepatocytes and the colony formation of hepatocytes could be optimized by 2 μg·mL^-1 BgIGFBP4 protein. Compared with the control group, the GH and VEGF concentrations in supernatant of yak hepatocytes in the experimental group were significantly increased (P<0.05), and the transcription levels of cell proliferation related genes ERBB2, IRS1, PIK3R1, AKT1, RAF1 and MAPK3 in PI3K-Akt signaling pathway were significantly increased (P<0.05). In comparison with the control group, the average daily gain of the experimental group mice was significantly increased, the feed to weight ratio was significantly decreased, and the liver, spleen, lung, kidney and intestine organ indexes were significantly increased (P<0.05). The contents of serum GH, ISN and VEGF were significantly higher than those of control (P<0.05), and the transcription levels of cell proliferation related genes ERBB2, IRS1, PIK3R1, AKT1, RAF1 and MAPK3 in PI3K-Akt signaling pathway were significantly increased (P<0.05). In conclusion, BgIGFBP4 can promote the proliferation of yak hepatocytes and the growth of mice. This study provides reference for further study of the role of IGFBP4 in yak liver growth and development.

Key words: IGFBP4, yak, hepatocyte, liver