[The role of syntaxin1A/synaptosome-associated protein-25 in reversing hyperglycemia-induced alpha cell toxicity]

To investigate the effects of reversal of hyperglycemic toxicity on the synthesis and secretion of glucagon by the alpha cells and the possible mechanisms thereof.

Mouse glucagonoma cells of the line TC1-6 were cultured in medium containing 5.5 mmol/L glucose for 10 days (low glucose group, LG), in medium containing 25 mmol/L glucose for 10 days (high glucose group, HG), in medium with 25 mmol/L glucose for 5 days and then in medium with 5.5 mmol/L glucose for 5 days (high-low glucose group, HL group), or in medium with 5.5 mmol/L glucose for 5 days and then in medium with 25 mmol/L glucose for 5 days (LH group), Radioimmunoassay was used to detect the glucagon concentration in the supernatant. RT-PCR was used to detect the mRNA expression of glucagon in the TC1-6 cells. Western blotting was used to detect the protein expression of the Snare proteins: syntaxin1A and synaptosome-associated protein (SNAP)-25.

(1) The glucagon level of the HG/LG group was lower than that of the HG group by 29% (P < 0.05). (2) The glucagon mRNA expression level in the TC1-6 cells of the HG/HL group was significantly lower than that of the HG group by (52.6 +/- 2.8)% (P < 0.05). (3) The syntaxin1A and SNAP-25 expression levels in the TC1-6 cells of the HG group were significantly higher than those of the LG group by 36% and 69% respectively (both P < 0.05), and the syntaxin1A and SNAP-25 expression levels in the TC1-6 cells of the HG/LG group were significantly lower than those of the HG group by 49% and 56% respectively (both P < 0.05).

After removing the high glucose toxicity the abnormal glucagon secretion by the alpha-cells can be ameliorated obviously, and the expression levels of syntaxin1A and SNAP-25 proteins that promote the secretion of glucagon are reduced accordingly.