N6-methyladenosine (m6A) is the most common and abundant mRNA modification. However, the role of m6A in regulating β-cell function is unclear. YTHDF2 is a ’reader’ protein that recognizes m6A-containing mRNAs and targets them for degradation. To address the functional role of YTHDF2 in β-cells, we generated an Ythdf2 β-cell knockout mouse using RIP-Cre transgenic mice. At the 3-month old age, the feeding and fasting glucose of βKO mice were similar to that in control mice (RIP-Cre mice). However, both male and female βKO mice are glucose intolerant after glucose challenge. The AUC was increased by 44.6% in male βKO mice and 71.1% in female mice, respectively (both P<0.01). The response to insulin was similar between βKO and control mice. Interestingly, although the fasting insulin levels were comparable between βKO and control mice, the feeding insulin levels in both male and female βKO mice were increased. The serum insulin levels from βKO mice were significantly lower at 15 min after glucose challenge. In addition, the insulin secretion from βKO islets was less due to decreased insulin protein. Surprisingly, β-cell mass in βKO mice was significantly higher than that in control mice (P<0.05). Both islets number and size were increased in βKO mice. To understand the molecular mechanism, we performed RNA-seq to detect the gene expression in βKO and control islets isolated from male mice. Among 626 altered genes in βKO islets, 421 genes were upregulated and 205 genes were downregulated. The genes response to ER stress were among the top up-regulated genes. The genes related to insulin secretion were downregulated. We applied m6A-seq in MIN6 cells and confirmed that Ire1α was indeed modified by m6A in its last exon and 3’ UTR region. We further confirmed that both mRNA and protein levels of Ire1α and spliced XBP-1 were significantly increased in βKO islets.
In conclusion, YTHDF2 plays an important role in regulating insulin secretion, and YTHDF2 deficiency in β-cells induces glucose intolerance by regulating insulin secretion and ER stress.
D. Ren: None. J. Sun: None.
The University of Chicago (P30-DK020595)