We previously showed that β cell microRNA 21 (miR-21) is increased by islet inflammatory stress and diabetes, that miR-21 induces β cell dysfunction by targeting mRNAs maintaining β cell identity, and that β cell miR-21 induction in vivo leads to hyperglycemia. However, upstream regulators of β cell miR-21 are poorly defined. We hypothesized that increases in the transcriptional regulator Hypoxia Inducible Factor 1 Subunit Alpha (Hif1a) during diabetogenic islet stress activate β cell miR-21 transcription, thereby contributing to loss of β cell identity occurring under these conditions. To test this, we examined Hif1a and miR-21 levels in β cell lines and mouse islets. Hif1a was increased in islets from mice after multiple low dose streptozotocin (STZ) or 4 wks of 60% high fat diet (HFD). INS1 cells and flow-sorted β cells showed increases in both miR-21 and Hif1a mRNA after 24-hr IL1β treatment. Hif1a overexpression in INS1 cells increased miR-21 levels, insulinand glucagon co-expression, and aldehyde dehydrogenase 1a3 staining, all suggesting loss of β cell identity. By contrast, siRNA depletion of Hif1a abrogated cytokine-induced reductions in mRNAs regulating β cell identity. Chromatin immunoprecipitation studies verified increased HIF1a occupancy at the miR-21 promoter after IL1β treatment. To test if these HIF1a-mediated increases in β cell miR-21 exacerbate β cell dysfunction under diabetogenic conditions in vivo, transgenic mice harboring a β cell tamoxifen inducible miR-21 transgene (Tg(β-miR-21, Ins1(CreERT2)Thor) were treated with STZ or HFD. Compared to controls, STZ and HFD-induced hyperglycemia was exacerbated in Tg(β-miR-21) mice following tamoxifen administration. By contrast, after STZ, conditional β cell miR-21 knock out (Ins1(Cre)Thor) mice showed improved glycemia.
In conclusion, these findings implicate Hif1a-miR-21 signaling as a contributor to β cell dysfunction under conditions of inflammation and diabetes.
S. Ibrahim: None. C. Stephens: None. R.E. Moore: None. R. Mirmira: Advisory Panel; Self; Hibercell, Sigilon Therapeutics, Veralox Therapeutics. Employee; Spouse/Partner; Eli Lilly and Company. E.K. Sims: None.