Unique cellular and mitochondrial defects mediate FK506-induced islet β-cell dysfunction

OBJECTIVE: Determine biological mechanisms involved in post transplantation diabetes mellitus caused by the immunosuppressant FK506. METHODS: INS-1 cells and isolated rat islets were incubated with vehicle or FK506 and harvested at 24 hr intervals. Cells were assessed for viability, apoptosis, proliferation, cell insulin secretion and content. Gene expression studies by microarray analysis, qPCR and motifADE analysis of the microarray data identified potential FK506-mediated pathways and regulatory motifs. Mitochondrial functions, including cell respiration, mitochondrial content and bioenergetics were assessed. RESULTS: Cell replication, viability, insulin secretion, oxygen consumption, and mitochondrial content were decreased (p < 0.05) 1.2-, 1.27-, 1.77-, 1.32-, and 1.43-fold, respectively after 48 hr FK506 treatment. Differences increased with time. FK506 (50 ng/ml) and Cyclosporine A (800 ng/ml) had comparable effects. FK 506 significantly decreased mitochondrial content and mitochondrial bioenergetics and showed a trend towards decreased oxygen consumption in isolated islets. Cell apoptosis and proliferation, mitochondrial DNA copy number and ATP/ADP ratios were not significantly affected. Pathway analysis of microarray data showed FK506 modification of pathways involving ATP metabolism, membrane trafficking and cytoskeleton remodeling. PGC1-α mRNA was down-regulated by FK506. MotifADE identified nuclear factor of activated T-cells (NFAT), an important mediator of β cell survival and function, as a potential factor mediating both up- and down-regulation of gene expression. CONCLUSIONS: At pharmacologically relevant concentrations FK506 decreases insulin secretion and reduces mitochondrial density and function without changing apoptosis rates, suggesting that post transplantation diabetes induced by FK506 may be mediated by its effects on mitochondrial function