INS-1 Cells Undergoing Caspase-Dependent Apoptosis Enhance the Regenerative Capacity of Neighbouring Cells
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Objective: In diabetes, beta cell mass is not static but in a constant process of cell death and renewal. Inactivating mutations in transcription factor 1 (tcf-1)/hepatocyte nuclear factor1a(hnf1a) result in decreased beta cell mass and HNF1A-maturity-onset-diabetes-of-the-young (HNF1A-MODY). Here we investigated the effect of a dominant-negative HNF-1A mutant (DNHNF1A) induced apoptosis on the regenerative capacity of INS-1 cells. Research design and methods: DN-HNF1A was expressed in INS-1 cells using a reverse tetracycline-dependent transactivator system. Gene(s)/protein(s) involved in beta cell regeneration were investigated by real-time quantitative RT-PCR, Western blotting, and immunohistochemistry. Pancreatic stone protein/regenerating protein (PSP/reg) serum levels in human subjects were detected by ELISA. Results: We detected a prominent induction of PSP/reg at gene and protein level during DNHNF1A- induced apoptosis. Elevated PSP/reg levels were also detected in islets of transgenic HNF1A-MODY mice and in the serum of HNF1A-MODY patients. The induction of PSP/reg was glucose dependent and mediated by caspase activation during apoptosis. Interestingly, the supernatant from DN-HNF1A-expressing cells, but not DN-HNF1A-expressing cells treated with zVADfmk, was sufficient to induce PSP/reg gene expression and increase cell proliferation in naïve, untreated INS-1 cells. Further experiments demonstrated that Annexin-V-positive microparticles (MPs) originating from apoptosing INS-1 cells mediated the induction of PSP/reg. Treatment with recombinant PSP/reg reversed the phenotype of DN-HNF1A-induced cells by stimulating cell proliferation and increasing insulin gene expression. Conclusion: Our results suggest that apoptosing INS-1 cells shed microparticles that may stimulate PSP/reg induction in neighbouring cells, a mechanism that may facilitate the recovery of beta cell mass in HNF1A-MODY.