Reducing blood glucose level in TIDM mice by orally administering the silk glands of transgenic hIGF-I silkworms

To realize the secretory expression of human insulin-like growth factor-I (hIGF-I) in the posterior silk glands (PSGs) of transgenic silkworms, the piggyBac transposon vector pigA3GFP-fibHS-hIGF-i.e.-neo containing a neomycin-resistance gene (neo), green fluorescent protein gene (gfp) and human insulin-like growth factor I (hIGF-I) gene controlled by the Bombyxmori fibroin heavy chain gene (fib-H) promoter with its downstream signal peptide sequence, and a helper plasmid containing the piggyBac transposase sequence under the control of the B. mori actin 3 gene (A3) promoter were transferred into silkworm eggs by sperm-mediated gene transfer. Transformed silkworms were obtained after being screened for green fluorescence and by the antibiotic G418. In the PSGs of the transformed silkworms, a specific band representing hIGF-I could be detected by Western blotting, and the content of the hIGF-I estimated by ELISA was approximately 1.84 μg/gram of cocoon and 19.18 μg/gram of freeze-dried PSG powder. To further estimate the biological activity of the expressed hIGF-I, streptozotocin-induced TIDM mice were orally administered with the PSG powder of the transgenic silkworms, the results showed the blood glucose levels of mice were significantly reduced, suggesting that the the PSGs powder of transgenic hIGF-I silkworms could possibly be used as a perorally administered medicine.