Glucose-regulated circular RNA Rabep1 regulates pancreatic beta-cell growth by modulating miR-335-3p/PTEN axis

Circular RNAs (circRNAs) are a large family of closed-loop RNA molecules emerging as novel regulators of gene expression. Although several circRNAs are known to regulate various biological processes, the functions of most circRNAs expressed in pancreatic beta cells remain to be discovered. Since short-term glucose treatment induces pancreatic beta-cell growth and promotes insulin production, we wanted to explore the role of glucose-regulated circRNAs in pancreatic beta cell physiology. Our RNA-seq analysis identified more than 300 differentially expressed circRNAs in high-glucose compared to low-glucose treated beta TC6 cells. A subset of differentially expressed and abundant circRNAs was validated by various biochemical methods, including circular RNA Rabep1 (circRabep1). Moreover, the downregulation of circRabep1 in high glucose-treated beta TC6 cells suggested a possible function in beta-cell physiology. Furthermore, analysis of the circRabep1-miRNA-mRNA regulatory network discovered the association of circRabep1 with miR-335-3p, a suppressor of Pten expression. Importantly, inhibition of miRNA function by miR-335-3p inhibitor results in upregulation of PTEN levels, suppressing beta-cell growth and proliferation. Furthermore, silencing circRabep1 decreased PTEN expression by sponging miR-335-3p, promoting cell proliferation. We propose that the downregulation of circRabep1 in high-glucose treated beta-cell leads to an increase in beta-cell proliferation by suppressing PTEN expression through derepression of miR-335-3p.