Deficit of tRNALys modification by Cdkal1 causes the development of type 2 diabetes in mice
Fan-Yan Wei, Takeo Suzuki, Sayaka Watanabe, Satoshi Kimura, Taku Kaitsuka, Atsushi Fujimura, Hideki Matsui, Mohamed Atta, Hiroyuki Michiue, Marc Fontecave, Kazuya Yamagata, Tsutomu Suzuki, Kazuhito Tomizawa
Fan-Yan Wei, Takeo Suzuki, Sayaka Watanabe, Satoshi Kimura, Taku Kaitsuka, Atsushi Fujimura, Hideki Matsui, Mohamed Atta, Hiroyuki Michiue, Marc Fontecave, Kazuya Yamagata, Tsutomu Suzuki, Kazuhito Tomizawa
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Research Article Metabolism

Deficit of tRNALys modification by Cdkal1 causes the development of type 2 diabetes in mice

Abstract

The worldwide prevalence of type 2 diabetes (T2D), which is caused by a combination of environmental and genetic factors, is increasing. With regard to genetic factors, variations in the gene encoding Cdk5 regulatory associated protein 1–like 1 (Cdkal1) have been associated with an impaired insulin response and increased risk of T2D across different ethnic populations, but the molecular function of this protein has not been characterized. Here, we show that Cdkal1 is a mammalian methylthiotransferase that biosynthesizes 2-methylthio-N6-threonylcarbamoyladenosine (ms2t6A) in tRNALys(UUU) and that it is required for the accurate translation of AAA and AAG codons. Mice with pancreatic β cell–specific KO of Cdkal1 (referred to herein as β cell KO mice) showed pancreatic islet hypertrophy, a decrease in insulin secretion, and impaired blood glucose control. In Cdkal1-deficient β cells, misreading of Lys codon in proinsulin occurred, resulting in a reduction of glucose-stimulated proinsulin synthesis. Moreover, expression of ER stress–related genes was upregulated in these cells, and abnormally structured ER was observed. Further, the β cell KO mice were hypersensitive to high fat diet–induced ER stress. These findings suggest that glucose-stimulated translation of proinsulin may require fully modified tRNALys(UUU), which could potentially explain the molecular pathogenesis of T2D in patients carrying cdkal1 risk alleles.

Authors

Fan-Yan Wei, Takeo Suzuki, Sayaka Watanabe, Satoshi Kimura, Taku Kaitsuka, Atsushi Fujimura, Hideki Matsui, Mohamed Atta, Hiroyuki Michiue, Marc Fontecave, Kazuya Yamagata, Tsutomu Suzuki, Kazuhito Tomizawa

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Figure 3

Conditional deletion of the Cdkal1 gene causes glucose intolerance.

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Conditional deletion of the Cdkal1 gene causes glucose intolerance. ...
(A) Conditional deletion of Cdkal1 in pancreatic islets in β cell KO (KO) mouse. (B) Comparison of the body weights of β cell KO and Flox mice. (C) Pancreatic sections obtained from β cell KO and Flox mice at 5 weeks of age were immunostained with anti-insulin (red) and anti-glucagon (green) antibodies. Nuclei were counterstained with DAPI. (D) Comparison of relative islet area in pancreas of β cell KO and Flox mice. Area of 529 islets from 3 Flox mice and 572 islets from 3 β cell KO mice were examined and classified into small, medium, and large islet area. The relative distribution of each islet area was compared between β cell KO and Flox. (E) Blood glucose during glucose tolerance test at 5 weeks (upper) and 10 weeks (lower). n = 4–7. (F) Plasma insulin levels during a glucose tolerance test at 15 weeks. n = 10–11. (G) Glucose-stimulated insulin secretion in islets (n = 8) isolated from β cell KO or Flox mice was determined. (H) Glucose-stimulated insulin secretion in perfused islets of Flox and β cell KO mice. n = 4–5. (I) Plasma insulin levels in Flox or β cell KO mice fasted for 14 hours and re-fed for 1.5 hours. n = 7. Significant difference was examined by repeated measure of 2-way ANOVA (E and F) or 2-way ANOVA (D, G, and I) followed by Bonferroni’s post-test or Mann-Whitney U test. Data are presented as mean ± sEM. *P < 0.05; **P < 0.01; ***P < 0.001 versus Flox.