The Impact of Induction of Insulin Secretion in MIN6 Cells on the Extent of Cytoophidia Formation and Their Structural Forms

Diabetes mellitus is marked by elevated blood glucose levels, resulting from either inadequate insulin secretion or reduced cellular sensitivity to insulin. Insulin secretion depends on guanosine triphosphate (GTP) synthesized by Inosine monophosphate dehydrogenase (IMPDH). Based on recent research, IMPDH forms octameric structures that assemble into different-shaped filaments, named cytoophidia, to regulate guanine nucleotide cellular content.

This study aimed to investigate the correlation between cytoophidia structural shapes and the extent of insulin secretion in MIN6 cells under different conditions, including the presence of Mycophenolic acid (MPA) and Ribavirin (Riba), IMPDH inhibitors.

This study used a mouse insulin ELISA kit to investigate insulin secretion. MIN6 cells were treated with varying concentrations of glucose over different periods to determine the optimal conditions for maximum insulin secretion. The effects of IMPDH inhibitors on insulin secretion were also evaluated. Additionally, the changes in cytoophidia structures were investigated using the immunofluorescence method under control conditions, glucose treatment, and simultaneous treatment with glucose and the inhibitors. The expression levels of the IMPDH enzyme were analyzed using Western blot in different treatment conditions.

Our results showed that inhibition of the enzyme by either inhibitor was associated with a significant decrease in insulin secretion and conversion of the scattered dot-like cytoophidia structures in the absence, to rod-shaped forms in the presence of the enzyme inhibitors. The presence of glucose caused the structures to become thicker, and the expression level of the enzyme significantly increased after one hour of glucose treatment. However, inhibiting the enzyme by MPA or Riba during insulin secretion prompted the formation of longer and thicker structures which were dispersed upon the addition of GTP. These results indicate that cytoophidia structures are formed and structurally matured as regulatory tools under the stress condition of GTP deficiency to support GTP-dependent insulin secretion.

Overall, our findings could provide the ground for viewing the medical application of the cytoophidia-structural maturation for targeting diabetes pending extensive future investigation on the functional Relationship between dynamic cytoophidia structures and insulin secretion.