| Glycine is a non-essential amino acids, which plays an important role in growth, the health in gut and the development of nervous system. Insulin-like growth factor-1(IGF-1), derived mainly from liver, is a critical growth factor. So, we hypothesis that glycine increase animal growth might via inducing hepatic IGF-1 expression and secretion. In this paper, firstly we investigated the effect glycine on IGF-1 expression and secretion in Hep G2 cells by q PCR and Western Blot.. Next, twenty-four male Kunming mice(8-week-old) with similar weight were randomly divided into glycine group and alanine nitrogen control group(n=12). Mice were I.V. injected of 1.0 g/kg glycine and equimolar Ala, respectively. Then, blood samples, liver, gastrocnemius muscle and adipose tissue were sampled 0.5 h and 1 h post indection. Serum albumin and IGF-1, IGF-1 related gene expression in liver and protein turnover related gene expression in gastrocnemius were measured. To further confirm the long-term effects of glycine on animal growth, 4-week-old mice C57 mice were divided into glycine(1% via drinking water) group and alanine nitrogen control group. Body weight and food intake were checked weekly. After nine weeks, the liver, gastrocnemius, fat were weighed. Gene expression of UCP1, PGC-1α, PRDM16 in brown adipose tissue were analyzed by q PCR. The results showed that 500 μM glycine significantly increased phosphorylation of JAK2/STAT5, and upregulated IGF-1 protein expression and IGF-1 and IGFBP-1 m RNA expression levels in Hep G2 cells(P < 0.05), but have no effect on IGFBP-3 m RNA expression. I. V. injection of glycine(0.5 h) significantly upregulated hepatic IGF-1 expression and activated the JAK2 / STAT5 signaling pathway(P < 0.05). Further, I. V. injection of glycine increased serum IGF-1 levels and therefore activated the IGF-1R signaling pathway in gastrocnemius(P < 0.05). In addition, glycine also significantly reduced abdominal fat index and subcutaneous fat index(P < 0.05), and decreased serum and liver TG levels(P < 0.05). But, body weight, feed intake, water intake, liver index, gastrocnemius index and brown fat index were unchanged(P > 0.05). Similarly, the m RNA expression of UCP-1, PGC-1α and PRDM16 in brown adipose tissue were unaltered by glycine(P > 0.05). These results shown that glycine activates hepatocyte and hepatic JAK2 / STAT5 pathway, and promote the expression and secretion of IGF-1, while reduce the fat deposition. The effects of glycine might independent of the metabolism of brown adipose tissue. This study revealed new role of glycine in IGF-I secretion and animal growth. |
