The role of txn1 in apoptotic death of insulin-secreting cells after mycophenolic acid treatment

Ji Hye Do³, Yuri Cho³, Yun-Jong Park³, Kyu Ha Huh^2,3, Myoung Soo Kim^2,3, Dong Jin Joo^2,3, Yu Seun Kim^1,2,3.

¹BK21 for Medical Science, Yonsei University College of Medicine; ²Department of Transplantation Surgery, Severance Hospital; ³The Research Institute for Transplantation, Yonsei University College of Medicine; Seoul, South Korea.

Introduction: Mycophenolic acid (MPA) is one of many effective immunosuppressive drugs. However, MPA may induce cellular toxicity and impair cellular function in ?-cells. The mechanisms underlying cell death following MPA treatment have not been fully explored. To address this issue we have used diverse technologies including illumina-microarray to examine which genes are regulated in a time-dependent manner during pancreatic ?-cell death, following MPA treatment. Critical functions of genes closely related with apoptosis after MPA treatment were thoroughly investigated.

Methods: Pancreatic ?-cell line, INS-1E cell, was treated with MPA for 12, 24 and 36hrs. Microarray was performed according to the Macrogen rat BeadChip technical manual using Illumina RatRaf-12 Expression BeadChip. The peroxide-sensitive fluorescent probe 2, 7-dichlorodihydrofluorescein diacetate (DCF-DA) was used to assess the generation of intracellular reactive oxygen species (ROS). Functional screening was determined by using small interference RNA (siRNA)-mediated knockdown and over-expression of txn1 gene in INS-1E cell line.

Results: MPA significantly increased cell death through Caspase-3 and p-JNK activation. We found that thousands of genes, especially txn1, were significantly altered during MPA-induced apoptosis. It was also observed that ROS levels were increased by MPA treatment. Over-expression of txn1 increased cell viability and decreased activation of p-JNK and Caspase-3 after MPA treatment. However, knockdown of txn1 by siRNA increased MPA-induced cell death and p-JNK and Caspase-3 activation.

Conclusion: MPA significantly induces apoptosis in insulin-secreting cells via down-regulation of txn1. Furthermore, reduced txn1 expression by MPA treatment is closely related with increased level of ROS. We suggest that controlling the down-regulated txn1 and ROS-mediated islet apoptosis by MPA is critical for successful islet transplantation.