Adult islets cultured in collagen gel transdifferentiate into duct-like cells.

AIM: To establish a model of islet-ductal cell transdifferentiation to identify the transdifferentiated cells. METHODS: Collagen was extracted from rat tail at first. Purified rat islets were divided into three groups, embedded in collagen gel and incubated respectively in DMEM/F12 alone (control group), DMEM/F12 plus epidermal growth factor (EGF), DMEM/F12 plus EGF and cholera toxin (CT). Transdifferentiation was proved by microscopy, RT-PCR, immunohistochemistry and RIA. RESULTS: Islets embedded in collagen gel plus EGF and CT were cystically transformed and could express new gene cytokeratin 19 while still maintaining the expression of insulin and Pdx-1 genes. Immunohistochemistry demonstrated that the protein of cytokeratin 19 was only expressed in the third group. The insulin content secreted by islets in the third group decreased significantly during the transdifferentiation. CONCLUSION: CT is a crucial factor for the islet-ductal cell transdifferentiation.

Oestrogen improves glucose metabolism and insulin signal transduction in HepG2 cells.

1. Many clinical studies have suggested a relationship between oestrogen and insulin sensitivity. In the present study, HepG2 cells were divided into four groups: (i) control, incubated with 1 nmol/L insulin; (ii) the HI group, which was incubated with 100 nmol/L insulin to induce insulin resistance; (iii) the E2 group, in which control cells were incubated with 1 nmol/L insulin plus 1 nmol/L oestradiol; and (iv) the HI + E2 group, in which insulin-resistant cells were incubated with 100 nmol/L insulin + 1 nmol/L oestradiol. 2. A high concentration of insulin decreased the activity of phosphofructo-1-kinase (PFK), pyruvate dehydrogenase (PDH) and glycogen synthase (GS), as well as decreasing the expression of insulin receptor (IR) and insulin receptor substrate-2 (IRS-2). High insulin had no effect on glucose transport or the expression of insulin receptor-1 (IRS-1). 3. The addition of oestradiol to control cells increased glucose transport, the activity of PFK, PDH and GS and the expression of IRS-1 and IRS-2, but had no effect on the expression of IR. 4. Treatment of insulin-resistant HepG2 cells with oestradiol attenuated HI-induced decreases, except for IR, and the expression of IRS-1 was significantly higher than control, attaining levels seen in group 3. The expression of IRS-2 was significant higher than in insulin-resistant cells, but did not reach control levels. Changes in the activity of PFK, PDH and GS were the same as the changes seen in the expression of IRS-2. 5. These results suggest that high concentrations of insulin induce insulin resistance in HepG2 cells, whereas oestradiol improves glucose metabolism and insulin signal transduction of cells by enhancing the activity of key enzymes involved in glucose metabolism and the expression of IRS-1 and IRS-2.