ISG15 increases the apoptosis of β cells in type 1 diabetes

Type 1 diabetes (T1D) is an autoimmune disease characterized by hyperglycemia caused by the destruction of insulin-producing β cells. Viral infection is an important environmental factor which is associated with the islet autoimmunity in genetically susceptible individuals. Loss of β-cells and triggering of insulitis following viral infection could result from several non-exclusive mechanisms. Despite a significant increase in ISG15 levels following viral infection, the specific role of ISG15 in the impairment of insulin-producing β-cells is unclear. To address this issue at the clinical level, we conducted this experimental work, and found elevated levels of ISG15 in the peripheral blood of T1D patients, suggesting a potential link between ISG15 and T1D. In the T1D animal model, we discovered that both ISG15 levels and cellular apoptosis were increased in pancreatic islet tissue. To investigate at the cellular level, we cultured MIN6 cells in the presence of supernatants derived from iBMDM cells transfected with poly(I:C) (PIC), a viral mimic. This exposure led to an upregulation of ISG15 expression in MIN6 cells, which was accompanied by the suppression of their functional capabilities and viability. Intriguingly, the direct transfection of MIN6 cells with PIC increased the expression of ISG15. We further found that elevated levels of ISG15 had a direct inhibitory effect on insulin secretion and it also contributed to β-cell apoptosis in a TNF-α-dependent manner. In conclusion, our study revealed a potential underlying mechanism through which ISG15 increases the apoptosis of β-cells, providing valuable insights that could facilitate the development of T1D treatment strategies.