2091-P: Effects of Caveolin-1 on the Synthesis and Decomposition of Islet ß-Cell IAPP and Its Mechanism

Objective: Islet amyloid polypeptide(IAPP) is a major component of islet amyloid deposition in type 2 diabetic patients. Our preliminary study showed that membrane protein Caveolin-1 (Cav1) silencing inhibited β-cell apoptosis and promote insulin secretion. The purpose of this study was to investigate the regulation of Cav1 on islet β-cell IAPP and its mechanism. Materials and Methods: Firstly, IAPP secretion of each group of primary islets was detected by ELISA, then Western blot and real-time quantitative PCR (qPCR) were used to detect the expression levels of IAPP, PAM(Peptidyl-glycine alpha-amidating monooxygenase), PC1(Prohormone Convertase-1), BACE2(Beta-secretase 2), IDE(Insulin-Degrading Enzyme), TXNIP(Thioredoxin interacting protein), and finally, it confirmed that Cav1 interacted with the protein of TXNIP by immunofluorescence confocal and co-immunoprecipitation (Co-IP). Results: The secretion of IAPP was decreased in primary pancreatic islets and Cav1 deficiency significantly down-regulated the expression of IAPP in NIT-1 cells, while over-expression of Cav1 in βTC-6 cells significantly up-regulated the expression of IAPP. This effect correlated with Cav1 silencing leading to down-regulation of PAM expression associated with IAPP synthesis and over-expression of Cav1 leading to up-regulation of PC1 associated with IAPP synthesis. On the other hand,Cav1 deficiency resulted in the up-regulation of the expression of BACE2 and IDE, the enzymes associated with IAPP decomposition. While over-expression of Cav1 leaded to down-regulation of BACE2 and IDE. Further studies indicated that Cav1 co-localized with TXNIP, and it interacted with and regulated the expression of TXNIP, which regulates IAPP gene transcription. Conclusion: Cav-1 can regulate the synthesis and decomposition of IAPP in islet β cell by interacting with TXNIP. This study suggests that Cav-1 may protect diabetic islet beta cells by reducing islet amyloid deposition.