N6-methyladenosine (m6A) is the most abundant mRNA modification. However, the role of m6A in regulating β-cell function is unknown. To address the functional role of METTL14, a key component of the m6A methyltransferase complex, in β-cells, we generated an METTL14 β-cell specific knockout mouse in adult MIP-CreERT transgenic mice. 4 weeks after tamoxifen treatment (100 mg/kg for 3 times every other day), the feeding glucose of βKO mice were 55.1% higher in βKO mice. βKO mice are also glucose intolerant. The AUC was increased by 54.7% in βKO mice (P<0.01). The fasting glucose were 307.5 ± 24.3 mg/dl in βKO mice and 219.0 ± 7.8 mg/dl in control mice (P<0.001). The response to insulin was similar between βKO and control mice. The feeding insulin levels in βKO mice were significantly decreased by 58.9% (P<0.01). The serum insulin levels from βKO mice were significantly lower at 0, 15 and 30 minutes after glucose challenge. In addition, the insulin secretion from βKO islets was less than 50% of control islets after incubated at 16.7 mM glucose. Surprisingly, β-cell mass in βKO mice was 55.9% higher than that in control mice (P<0.05). In addition, we did not detect β-cell death in βKO islets. However, β-cell proliferation in βKO islets was increased by 1.3-fold. To understand the molecular mechanism, we performed RNA-seq to detect the gene expression in βKO and control islets from male mice 8 weeks after tamoxifen treatment. Among 106 altered genes in βKO islets, 104 genes were upregulated (P<0.001) and 2 genes were downregulated. The genes response to ER stress such as Pdia4, Itpr1, Thbs1, Ire1α and Igfbp5 were among the top up-regulated genes. We applied m6A-seq in MIN6 cells and confirmed that Ire1α was modified by m6A in its last exon and 3' UTR region. We further showed that both mRNA and protein of Ire1α and spliced XBP-1 were significantly increased in βKO islets.
In conclusion, METTL14 plays an important role in regulating insulin secretion, and METTL14 deficiency in β-cells induces diabetes by increasing ER stress.
L. Men: None. J. Sun: None. D. Ren: None.
National Institutes of Health (P30DK020595)