KNOCKOUT OF MIR‐223 INDUCES BETA‐CELL DYSFUNCTION THROUGH ACTIVATION OF THE FOXO1 SIGNALING PATHWAY

Abstract

BackgroundMicroRNAs (miRNAs) are small, endogenous non‐coding RNAs, well‐known to regulate wide ranges of biological processes and tissue metabolism homeostasis. Recently, miR‐223 has been reported to coordinate systemic cholesterol under basal conditions and ameliorate adipose tissue‐associated insulin resistance in mice fed with high‐fat diet. However, the functional role of miR‐223 in the diabetic pancreas remains less studied.Method and ResultsDiabetes was induced in C57BL6 mice (5‐week old, male) by either daily intraperitoneal injection of streptozotocin (STZ, 50μg/g body weight) for 5 days (type 1 diabetes, or T1D), or 60% high‐fat diet (HFD) feeding for 24 weeks (type 2 diabetes, or T2D). Subsequently, pancreases were collected from such diabetic mice to measure miR‐223 levels using RT‐PCR. We observed that the levels of miR‐223 were increased by 8‐fold in the T1D pancreas, and by 2‐fold in T2D pancreas, compared to respective controls. Similarly, in vitro studies using Min6 β‐cell line revealed a 3‐fold increase of miR‐223 levels upon high glucose treatment. These results indicate that miR‐223 may involve in the development of diabetes. Of important, global miR‐223 knockout (KO) mice displayed insulin resistance, as evidenced by higher levels of plasma glucose and lower levels of insulin than wild‐type (WT) mice under both basal and diabetic conditions (n=5–11, p<0.05)). Further investigation showed that the diabetic phenotype of miR‐223‐KO mice may be attributed to diminished β‐cell proliferation and increased β‐cell apoptosis. Using luciferase reporter assay, we mechanistically identified that miR‐223 could directly target the 3′‐UTR of Foxo1, a critical transcriptional factor that regulates β‐cell function and survival. Using Western‐blotting, we validated that the protein levels of Foxo1 were increased by 3‐fold in the pancreas of miR‐223‐KO mice, compared to WTs, leading to subsequent decreased levels of Pdx1 and Glut2, two key regulators of β‐cell proliferation and function.ConclusionOur study reveals that loss of miR‐223 triggers β‐cell dysfunction by post‐transcriptional activation of the Foxo1 signaling pathway, resulting in the development of diabetes.Support or Funding InformationNIH R01 GM‐112930