Combined modulation of polycomb and trithorax genes rejuvenates β cell replication
Josie X. Zhou, … , Seung K. Kim, Anil Bhushan
Josie X. Zhou, … , Seung K. Kim, Anil Bhushan
Published October 8, 2013
Citation Information: J Clin Invest. 2013;123(11):4849-4858. https://doi.org/10.1172/JCI69468.
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Research Article Metabolism

Combined modulation of polycomb and trithorax genes rejuvenates β cell replication

Abstract

Inadequate functional β cell mass underlies both type 1 and type 2 diabetes. β Cell growth and regeneration also decrease with age through mechanisms that are not fully understood. Age-dependent loss of enhancer of zeste homolog 2 (EZH2) prevents adult β cell replication through derepression of the gene encoding cyclin-dependent kinase inhibitor 2a (INK4a). We investigated whether replenishing EZH2 could reverse the age-dependent increase of Ink4a transcription. We generated an inducible pancreatic β cell–specific Ezh2 transgenic mouse model and showed that transgene expression of Ezh2 was sufficient to increase β cell replication and regeneration in young adult mice. In mice older than 8 months, induction of Ezh2 was unable to repress Ink4a. Older mice had an enrichment of a trithorax group (TrxG) protein complex at the Ink4a locus. Knockdown of TrxG complex components, in conjunction with expression of Ezh2, resulted in Ink4a repression and increased replication of β cells in aged mice. These results indicate that combined modulation of polycomb group proteins, such as EZH2, along with TrxG proteins to repress Ink4a can rejuvenate the replication capacity of aged β cells. This study provides potential therapeutic targets for expansion of adult β cell mass.

Authors

Josie X. Zhou, Sangeeta Dhawan, Hualin Fu, Emily Snyder, Rita Bottino, Sharmistha Kundu, Seung K. Kim, Anil Bhushan

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Figure 1

Conditional expression of EZH2 in 2-month-old bEzTG mice promotes β cell replication through repression of Ink4a.

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Conditional expression of EZH2 in 2-month-old bEzTG mice promotes β cell...
(A) Schematics of the targeting cassette containing LacZ-TRE-EzTG. (B) Southern blotting to detect EzTG integration within the genome (lane 2–7), as compared with that in the WT control (lane 1). EzTG vectors were used as a positive control (lane 8–10). Expression level of (C) EzTG mRNA and (D) β-gal, as shown by LacZ staining in bEzTG islets treated with Dox for 1 week but not in littermate controls without Dox exposure (original magnification, ×20). (E) Dox feeding schemes: bEzTG mice were treated for 1 week with Dox food and drinking water, before the pancreata or the islets were harvested for experiments. For measuring β cell mass, 2- and/or 8-month-old (2M/8M) bEzTG mice were treated with an extended Dox procedure, with Dox treatment on week 1 and 3. Pancreatic tissue were harvest after 1 month. (F and I) Pancreatic sections from the control and Dox-treated 2-month-old bEzTG mice were immunostained with antibodies to insulin (green), (F) Ki67 (red), (I) Ink4a (red), and DAPI (blue) (original magnification, ×20). (G) Quantification of the percentages of Ki67-positive β cells with or without Dox exposure (5 pancreatic sections per animal). (H) β Cell mass (mg) measurement. (J) Western blotting and quantification of EzTG (Myc Ab) and Ink4a levels in isolated islets from indicated samples. n = 5–6 animals per group. *P < 0.05, ***P < 0.005.